CA1219056A - Integrated electroacoustic transducer - Google Patents
Integrated electroacoustic transducerInfo
- Publication number
- CA1219056A CA1219056A CA000457580A CA457580A CA1219056A CA 1219056 A CA1219056 A CA 1219056A CA 000457580 A CA000457580 A CA 000457580A CA 457580 A CA457580 A CA 457580A CA 1219056 A CA1219056 A CA 1219056A
- Authority
- CA
- Canada
- Prior art keywords
- diaphragm
- electrodes
- acoustic
- transducer
- array
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
- 239000000758 substrate Substances 0.000 claims abstract description 37
- 230000004044 response Effects 0.000 claims abstract description 29
- 239000004065 semiconductor Substances 0.000 claims abstract description 26
- 239000010410 layer Substances 0.000 claims description 38
- 238000013022 venting Methods 0.000 claims description 12
- 239000012535 impurity Substances 0.000 claims description 9
- 238000005452 bending Methods 0.000 claims description 7
- 238000006243 chemical reaction Methods 0.000 claims description 6
- 238000013016 damping Methods 0.000 claims description 5
- 230000005684 electric field Effects 0.000 claims description 5
- 239000002344 surface layer Substances 0.000 claims description 2
- 239000003990 capacitor Substances 0.000 abstract description 11
- 238000010348 incorporation Methods 0.000 abstract 1
- 230000035945 sensitivity Effects 0.000 description 8
- 239000012528 membrane Substances 0.000 description 6
- 239000000463 material Substances 0.000 description 5
- 229910052710 silicon Inorganic materials 0.000 description 5
- 239000010703 silicon Substances 0.000 description 5
- ZOXJGFHDIHLPTG-UHFFFAOYSA-N Boron Chemical compound [B] ZOXJGFHDIHLPTG-UHFFFAOYSA-N 0.000 description 4
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 4
- 230000008901 benefit Effects 0.000 description 4
- 229910052796 boron Inorganic materials 0.000 description 4
- 230000006870 function Effects 0.000 description 4
- 230000009467 reduction Effects 0.000 description 4
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 3
- 238000013461 design Methods 0.000 description 3
- 239000002184 metal Substances 0.000 description 3
- 229910021420 polycrystalline silicon Inorganic materials 0.000 description 3
- 229910052581 Si3N4 Inorganic materials 0.000 description 2
- 230000008859 change Effects 0.000 description 2
- 238000005229 chemical vapour deposition Methods 0.000 description 2
- 229910052681 coesite Inorganic materials 0.000 description 2
- 229910052906 cristobalite Inorganic materials 0.000 description 2
- 239000013078 crystal Substances 0.000 description 2
- 238000000151 deposition Methods 0.000 description 2
- 230000008021 deposition Effects 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 238000005530 etching Methods 0.000 description 2
- 238000000206 photolithography Methods 0.000 description 2
- 238000012545 processing Methods 0.000 description 2
- 150000003376 silicon Chemical class 0.000 description 2
- 239000000377 silicon dioxide Substances 0.000 description 2
- 235000012239 silicon dioxide Nutrition 0.000 description 2
- 125000006850 spacer group Chemical group 0.000 description 2
- 229910052682 stishovite Inorganic materials 0.000 description 2
- 229910052905 tridymite Inorganic materials 0.000 description 2
- 235000012431 wafers Nutrition 0.000 description 2
- OAICVXFJPJFONN-UHFFFAOYSA-N Phosphorus Chemical compound [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 description 1
- 230000009471 action Effects 0.000 description 1
- 239000000853 adhesive Substances 0.000 description 1
- 230000001070 adhesive effect Effects 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 238000004364 calculation method Methods 0.000 description 1
- 230000006835 compression Effects 0.000 description 1
- 238000007906 compression Methods 0.000 description 1
- 230000008878 coupling Effects 0.000 description 1
- 238000010168 coupling process Methods 0.000 description 1
- 238000005859 coupling reaction Methods 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 238000009795 derivation Methods 0.000 description 1
- 238000011982 device technology Methods 0.000 description 1
- 239000000945 filler Substances 0.000 description 1
- 239000011888 foil Substances 0.000 description 1
- 238000002513 implantation Methods 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 238000000034 method Methods 0.000 description 1
- 229910021421 monocrystalline silicon Inorganic materials 0.000 description 1
- 229910052698 phosphorus Inorganic materials 0.000 description 1
- 239000011574 phosphorus Substances 0.000 description 1
- 238000007493 shaping process Methods 0.000 description 1
- 238000012360 testing method Methods 0.000 description 1
Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
- H04R1/00—Details of transducers, loudspeakers or microphones
- H04R1/06—Arranging circuit leads; Relieving strain on circuit leads
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
- G01L9/00—Measuring steady of quasi-steady pressure of fluid or fluent solid material by electric or magnetic pressure-sensitive elements; Transmitting or indicating the displacement of mechanical pressure-sensitive elements, used to measure the steady or quasi-steady pressure of a fluid or fluent solid material, by electric or magnetic means
- G01L9/0041—Transmitting or indicating the displacement of flexible diaphragms
- G01L9/0072—Transmitting or indicating the displacement of flexible diaphragms using variations in capacitance
- G01L9/0073—Transmitting or indicating the displacement of flexible diaphragms using variations in capacitance using a semiconductive diaphragm
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
- H04R19/00—Electrostatic transducers
- H04R19/005—Electrostatic transducers using semiconductor materials
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
- H04R1/00—Details of transducers, loudspeakers or microphones
- H04R1/20—Arrangements for obtaining desired frequency or directional characteristics
- H04R1/22—Arrangements for obtaining desired frequency or directional characteristics for obtaining desired frequency characteristic only
- H04R1/225—Arrangements for obtaining desired frequency or directional characteristics for obtaining desired frequency characteristic only for telephonic receivers
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T29/00—Metal working
- Y10T29/42—Piezoelectric device making
Landscapes
- Physics & Mathematics (AREA)
- Engineering & Computer Science (AREA)
- Acoustics & Sound (AREA)
- Signal Processing (AREA)
- General Physics & Mathematics (AREA)
- Electrostatic, Electromagnetic, Magneto- Strictive, And Variable-Resistance Transducers (AREA)
Abstract
INTEGRATED ELECTROACOUSTIC TRANSDUCER
Abstract An electroacoustic transducer, primarily in the form of a capacitive microphone, for incorporation into a semiconductor substrate. The vibrating element comprises a largely nontensioned diaphragm, such as an epitaxial layer formed on the semiconductor substrate, so as to greatly reduce its mechanical stiffness. The substrate is etched away in the desired area to define the diaphragm and form an acoustic cavity. A continuous array of microscopic holes is formed in the backplate to cut down the lateral flow of air in the gap between capacitor electrodes.
Narrow gaps made possible by the hole array allow low voltage diaphragm biasing. In at least one embodiment, the acoustic input can be provided through the air hole array.
An acoustic port may be added to alter the frequency response of the device, and a back closure provided to act as a rear acoustic cavity and an EMI shield.
through the air hole array. An acoustic port may be added to alter the frequency response of the device, and a back closure provided to act as a rear acoustic cavity and an EMI shield.
Abstract An electroacoustic transducer, primarily in the form of a capacitive microphone, for incorporation into a semiconductor substrate. The vibrating element comprises a largely nontensioned diaphragm, such as an epitaxial layer formed on the semiconductor substrate, so as to greatly reduce its mechanical stiffness. The substrate is etched away in the desired area to define the diaphragm and form an acoustic cavity. A continuous array of microscopic holes is formed in the backplate to cut down the lateral flow of air in the gap between capacitor electrodes.
Narrow gaps made possible by the hole array allow low voltage diaphragm biasing. In at least one embodiment, the acoustic input can be provided through the air hole array.
An acoustic port may be added to alter the frequency response of the device, and a back closure provided to act as a rear acoustic cavity and an EMI shield.
through the air hole array. An acoustic port may be added to alter the frequency response of the device, and a back closure provided to act as a rear acoustic cavity and an EMI shield.
Description
~Z~9056 INTEG~ATED ELECTROACOUSTIC TRANSDUCER
Backqround of the Invention This invention relates to electroacoustic transducers, such as microphones, and in particular to a structure which is incorporated into a semiconductor substrate.
Demand is growing for electroacoustic transducers which may be formed as part of a semiconductor integrated circuit. These transducers may include, for example, microphones incorporated into the circuitry of telecommunications and audio recording equipment, hearing aid microphones and receivers, or miniature speakers. In the case of microphones, electrostatic device technology presently in widespread use generally takes the form of a metalized polymeric foil (which may be charged) supported over a metalized backplate or stationary structure so as to form a variable capacitor responsive to voiceband frequencies. While adequate, such devices are relatively large, discrete components which cannot be integrated into the semiconductor integrated circuitry with which they are used.
Recently, such an integrated microphone structure and a method of manufacture were proposed. (See the co-pending Canadian Patent Application of I.J. Busch-Vishniac et al, Serial No. 448,021, filed February 22, 1984 and assigned to the present assignee.) Briefly, the microphone included a tensioned membrane formed from a thinned portion of a thicker semiconductor substrate. The membrane had an area and thickness such that it vibrated in response to incident sound waves. A pair of electrodes formed a capacitor, with one of the electrodes vibrating with the membrane to vary the capacitance when a biasing voltage was applied and produce an electrical equivalent to the acoustic signal. It has also been suggested that an integrated capacitive microphone can include an insulating 'J~
layer with fixed charge for providing a built-in diaphragm bias ~or the device.
While such structures offer considerable promise for the replacement of the distinct microphones now in use, several problems and considerations remain in the commercial realization of an integrated microphone.
Foremost, it is desirable to make the area of the vibrating element as small as possible to reduce cost. ~owever, a small area tends to cause a drop in sonic force on the diaphragm element, thereby lowering the sensitivity of the device. Further, smaller area diaphragms produce a smaller device capacitance which in turn tends to increase the noise associated with on-chip circuitry coupled to the device and also tends to further decrease the integrated microphone sensitivity through capacitance divider action.
In order to alleviate such effects of reduced area (i.e., reduce signal-to-noise ratio), it is desirable to reduce the stiffness of the diaphragm.
The above-noted effects of reduced diaphragm area ~0 may also be compensated for by a reduction in the thickness of the air gap between capacitor electrodes. We have found, however, that for air gaps below approximately 1.5 ~m with other dimensions optimized for certain telephone applications, the electrical output frequency response of a microphone with a tensioned diaphragm had a tendency to fall at an unacceptable rate with frequency when utilizing acoustic venting means, common in commercially available devices, comprising 4-20 holes around the periphery of the stationary electrode and backplate. That is, the devices would be overdamped, even at the critical 300-3,500 Hz portion of the audioband which is transmitted in telephone equipment. Specifically, with an air gap of 0.25 ~m which yield the optimum signal-to-noise ratio, the response fell more than 20 dB across the telephone frequency band indicating severe overdamping. Sensitivity levels were also inoperably low. It is, therefore, also desirable to ., ~
.~
~219056 provide some acoustic venting means which will permit reduced area and produce an acceptable output signal at telephone band frequencies or other frequency bands of interest.
A reduction in the air gap thickness will also have another beneficial effect, which is to reduce the external dc voltage level needed to bias the diaphragm.
This would provide an alternative to the requirement of a built-in diaphragm bias as suggested in the application of Lindenberger, previously cited.
In addition, a silicon integrated microphone will generally have a nonrising output response as a function of frequency in the audio bandwidth. In some applications, it may be desirable to tailor the response to provide a peak at a certain frequency by means of an appropriately shaped acoustic port and coupling cavity. Further, the microphone chip may, under certain circumstances, be subject to high electromagnetic interference (EMI), and so some shielding means may be needed. In the design of an integrated microphone, therefore, it is desirable to provide these functions with a minimum number of piece parts.
It is therefore an object of the invention to provide an integrated electroacoustic transducer with a small diaphragm area which still provides an acceptable frequency response and signal-to-noise ratio. It is a further object of the invention to provide an electro-acoustic transducer which can be operated at a low dc bias. It is a still ~urther object of the invention to provide acoustical interconnection and tuning means, and EMI shielding means, for an integrated electroacoustic transducer.
Summary of the Invention In accordance with an aspect of the invention there is provided an electroacoustic transducer formed within a semiconductor substrate comprising an essentially ~`
nontensioned dlaphragm having a mechanical bending moment stif~ness such that it vibrates in response to an input signal at audio and/or ultrasonic frequencies; and a pair of electrodes placed with respect to said diaphragm so that the electric field between the electrodes varies in relationship with the vibrating diaphragm to permit conversion between electrical and acoustic signals.
In accordance with a further aspect of the invention, the transducer comprises an air gap formed between the electrodes and acoustic venting means comprisin~ a continuous array of small ho~es extending through one of the electrodes to the air gap, where the array covers essentially the entire area of the electrode co-extensive with the diaphragm.
In accordance with a further aspect of the invention, a front acoustic cavity is defined by a portion of a semiconductor substrate adjacent to the diaphragm, an air gap is formed between the electrodes, and a back acoustic cavity is formed adjacent to one of the electrodes and defined by a member which also shields the transducer from electromagnetic interference. Acoustic venting means is provided by an array of holes connecting the air gap to the back acoustic cavity. An acoustic port is defined by an element adjacent to the front acoustic cavity, with the size of the port being such as to produce a desired frequency response characteristic for the transducer.
Brief Descri~tion of the Drawing These and other features of the invention are delineated in detail in the following description. In the drawing:
FIG. 1 is a cross-sectional view of a microphone in accordance with one embodiment of the invention;
FIG. 2 is a top view of a portion of the device illustrated in FIG. l;
FIG. 3 is an illustration based on computer 12~9056 modeling of typical frequency response curves predicted for microphones fabricated in accordance with the invention as compared with predictions of a prior art type device where the reference level is the 400 Hz response level of curve B;
FIG. 4 is a cross-sectional view of a microphone in accordance with a further embodiment of the invention FIG. 5 is a cross-sectional view of a microphone in accordance with a still further embodiment of the invention; and FI&. 6 is a cross-sectional view of a microphone in accordance with a still further embodiment of the invention.
It will be appreciated that for purposes of illustration, these figures are not necessarily drawn to scale.
Detailed Description Many of the basic features of the invention will be described with reference to the particular embodiment illustrated in FIG. 1. It will be appreciated that the Figure shows only a small portion of a semiconductor substrate which in this example includes a great many other identical, integrated, electronic transducer devices which are separated along saw lines, 40, following batch processing and testing~
The semiconductor substrate, 10, is a standard p-type silicon wafer having a thickness of approximately 300-600 ~m (12-24 mils) and a <100> orientation. It will be appreciated that n-type wafers and other crystal orientations may be employed. A surface layer, 11, of p+ type is formed over at least portions of the substrate, for example, by an implantation of boron impurities to a depth of approximately 0.2 ~Im. The impurity concentration of this region is typically 5 x 10 19/cm3.
Formed over the semiconductor substrate is a monocrystalline silicon epitaxial layer, 12. An 12~9V5~
appropriate area of the semiconductor substrate is etched to form a front acoustic cavity, 13, so that the portion, 14, of the epitaxial layer over the cavity forms the vibrating diaphragm element of the microphone. The characteristics of the diaphragm are discussed in more detail below Formed on the surface of the diaphragm is a metal layer, 15, such as Ti-Au, which comprises one electrode of a capacitor. This layer is typically 0.1-0.5 ~m thick.
Formed over the epitaxial layer is a spacer layer, 16, which is typically polycrystalline silicon and can be formed by chemical vapor deposition. The thickness of the layer in this example is 0.60 ~m and will generally be in the range 0.1 ~m-4.0 ~m. A backplate layer, 17, is formed on the spacer layer with a portion (hereinafter the backplate) over the area of the diaphragm to establish an air gap, 18. The backplate may comprise a layer of SiO2, but could be any insulating layer or layers.
The thickness of the layer is approximately 12 ~m and will generally be in the range 6 ~m-30 ~m. A metal or other conducting layer, 19, is formed on the surface of the backplate facing the air gap and comprises the second electrode of the capacitor. It can be the same material and thickness as the first electrode, 15.
Formed through the backplate and electrode, 19, to the air gap is a continuous array of holes, 20, for acoustic venting. This feature will be discussed in more detail below.
The electronics for driving the device may be fabricated in the adjacent area o the semiconductor substrate designated 21, and electrical contact to the electrodes may be provided through via holes, 22 and 23.
Contact to the outside may be provided through via holes, 23 and 24, and contact pads, 25 and 26, formed on the surface of the backplate layer. If de~ired, additional via holes (not shown) could be provided from the electronics to the outside to establish separate dc supply, 12~9056 signal and ground leads.
In operation, a dc bias is applied to electrodes, 15 and 19, and an acoustic signal is made incident on diaphragm, 14, through the front acoustic cavity. The signal causes the diaphragm to vibratel thus varying the spacing between the electrodes and the capacitance of the capacitor. This change in capacitance can be detected as a change in voltage across some load element, integrated into area, ~1, such as a second capacitance and parallel resistance (not shown), and an electrical equivalent to the acoustic signal is produced.
The array of holes, 20, permits escape of air in the gap, 18, so that air stiffness in the gap is not a significant factor in the diaphragm motion. Desirably, the amplitude of the output signal as a function of frequency will be as shown in curve B in FIG. 3, wherP the signal (at constant sound pressure amplitude) is essentially flat or falls no more than 3 dB over the portion of the audioband transmitted in telephone applications (0.3-3.5 KHz). In accordance with a feature of the invention,the vibrating diaphragm is essentially nontensioned so that the stiffness of the diaphragm is dominated by the mechanical bending moment. This can be contrasted with previous designs for integrated microphones where the diaphragm was a thinned portion of the semiconductor substrate and had a stiffness which was dominated by tensile stress resulting from a heavy boron impurity concentration.
The advantage of using the nontensioned diaphragm results from the fact that the sensitivity (e) of the microphone depends upon the following parameters:
e ~ [km+ka ~ / e (1) where V is the dc bias voltage across the electrodes, A is - 12~90~;6 the area of the diaphragm, km is the effective mechanical lumped parameter (piston-like) stiffness of the diaphragm associated with the diaphragm's linearly averaged deflection~ ka is the stiffness of the rear acoustic cavity (shown, for example, in FIG. 4), and he is the distance between capacitor electrodes, linearly averaged over A, when the bias is applied to the electrodes. Thus, for the same sensitivity, the area, A, of the diaphragm may be~ reduced by decreasing the stiffness km of the diaphragm (ka contributes less than 1/3 of the total stiffness acting on the diaphragm). We have found that when the stiffness is due primarily to tensile stress, a practical lower limit exists for reducing the membrane stiffness. In the present invention, however, km is significantly lowered in order that the diaphragm area may be reduced by allowing the mechanical bending moment of the diaphragm to be the dominant mechanical stiffness component. Further, when the stiffness is due to the mechanical bending moment, the thickness of the diaphragm can be significantly increased over a tensioned membrane and still produce a significantly lower stiffness and diaphragm area.
It will be appreciated that effective stiffness km~ as used in this application, is the stiffness of a piston-like model where the deflection of the piston is equal to the diaphragm deflection averaged over the area of the diaphragm. For a nontensioned diaphragm, this stiffness is given approximately by the relationship:
192~2D
km ~ ~~~~~~~~ (2) where Dp is the flexural rigidity of the diaphragm.
In this example, the diaphragm thickness is 3.0 ~m, the diaphragm is circular with a radius of ',,' 12~9056 g 700 um~ ~ and ka are approximately 625 and 175 N/m respectively. The biasing voltage across the electrodes is 1 . 3 vol ts. The resulting sensitiv ity is approximately -49 dB relative to lV/Pa at 400 Hz (excluding any signal voltage amplifiers that may be integrated on the chip microphone). For most nontensioned diaphragm applications, it is expected that the diaphragm thickness will range from 1 ~m-5 ~m, and area will range from 0.4 mm~-5 mm2 to achieve proper sensitivity.
Stiffness, ~ , of the nontensioned diaphragm is desirably less than 5500 N/m.
While in this example the diaphragm was formed from a single crystal epitaxial layer, 12, other types of nontensioned diaphragms might be employed. However, use of an epitaxial layer provides many advantages in terms of processing. For example, diaphragm thickness can be closely controlled by growing the layer over the boron-doped surface region, 11, and then utilizing an etchant which removes the semiconductor substrate but stops at the region, 11. The portion of region, 11, under the diaphragm can then be removed by applying an appropriate etchant such as KOH and H20 for a predetermined period of time. As shown in FI~. 1, if desired, the etchant may be allowed to penetrate the epitaxial layer-substrate interface to achieve a desired diaphragm thickness less than the original epitaxial layer thickness. Close control of a nontensioned diaphragm's thickness, d, is important since ~ a d 3. This step may also be desirable to remove boron impurities which may have diffused into the epitaxial layer from the substrate and added tension to the layer. A further advantage is the fact that the epitaxial layer can be anisotropically etched to provide via holes (22, 23, 24) or other useful features.
It will be appreciated that, in this example, the epitaxial layer is essentially free of impurities so that there is essentially no tension component contributing to the stiffness of the diaphragm. However, it is ~2~9056 -- 1 o contemplated that layers may be fabricated with some tension component, as alluded ~o above, and still produce advantageous results. The invention is therefore directed to "essentially nontensioned" diaphragms which are intended to include those having a bending stiffness contributing at least 2/3 of the total stiffness of the diaphragm. It is further contemplated that impurities may be intentionally introduced into the epitaxial layer to satisfy certain needs. For example, the introduction of phosphorus impurities into the layer could provide compression in the layer to counteract any tension that might be produced by the presence of boron impurities.
In accordance with another aspect of the invention, the acoustic venting means comprises a continuous array of small holes, 20, extending through the backplate and electrode, 19, which array extends over essentially the entire area of the backplate and electrode portion co-extensive with the diaphragm. Such an array permits a narrow distance between electrodes, 15 and 19, without overdamping, thereby permitting a reduction in the applied dc bias and in the area of the diaphragm.
FIG. 2 is a top view of some of the holes in the array, which are greatly enlarged for illustrative purposes. It will be appreciated that essentially the entire area of the backplate is covered by these holes and consequently the array is considered to be continuous. The dynamic magnification factor, D, is defined in this application as the amount, in dB, that the fre~uency response rises in traversing the band from 400 Hz to the upper bound frequency of interest. For telephone applications where the upper bound frequency is 3500 Hz, it is desirable that D be greater than -3.0 dB. FIG. 3 shows a generally desirable, calculated, output characteristic (curve B) for telephony, which is achieved in this example in accordance with the invention. Returning to FIG. 2, such a characteristic can be achieved by a radius, r, of - the holes and a center-to-center spacing of the holes, 2~, ~2~9056 which satisfies the relationship:
L [ 1~ 2 L (~ R ~ l where D is the minimum desirable magnification factor, ~ is the highest acoustic input frequency which will be transmitted expressed in radians (here, 2~ x 3.5 KHz), ~n is the natural radian fre~uency of vibration of the diaphragm (/K-M), K is the combined stiffness, km +
kat of the diaphragm and back acoustic cavity, M is the effective lumped parameter mass of the diaphragm compatible with the prior definition of km (which, for a nontensioned diaphragm is approximately 9/5 times the actual mass), Rc is the critical damping level (2M~n), and Ra is the actual acoustic damping level of the air film in the air gap between electrodes. The acoustic damping is determined from the following:
a he
Backqround of the Invention This invention relates to electroacoustic transducers, such as microphones, and in particular to a structure which is incorporated into a semiconductor substrate.
Demand is growing for electroacoustic transducers which may be formed as part of a semiconductor integrated circuit. These transducers may include, for example, microphones incorporated into the circuitry of telecommunications and audio recording equipment, hearing aid microphones and receivers, or miniature speakers. In the case of microphones, electrostatic device technology presently in widespread use generally takes the form of a metalized polymeric foil (which may be charged) supported over a metalized backplate or stationary structure so as to form a variable capacitor responsive to voiceband frequencies. While adequate, such devices are relatively large, discrete components which cannot be integrated into the semiconductor integrated circuitry with which they are used.
Recently, such an integrated microphone structure and a method of manufacture were proposed. (See the co-pending Canadian Patent Application of I.J. Busch-Vishniac et al, Serial No. 448,021, filed February 22, 1984 and assigned to the present assignee.) Briefly, the microphone included a tensioned membrane formed from a thinned portion of a thicker semiconductor substrate. The membrane had an area and thickness such that it vibrated in response to incident sound waves. A pair of electrodes formed a capacitor, with one of the electrodes vibrating with the membrane to vary the capacitance when a biasing voltage was applied and produce an electrical equivalent to the acoustic signal. It has also been suggested that an integrated capacitive microphone can include an insulating 'J~
layer with fixed charge for providing a built-in diaphragm bias ~or the device.
While such structures offer considerable promise for the replacement of the distinct microphones now in use, several problems and considerations remain in the commercial realization of an integrated microphone.
Foremost, it is desirable to make the area of the vibrating element as small as possible to reduce cost. ~owever, a small area tends to cause a drop in sonic force on the diaphragm element, thereby lowering the sensitivity of the device. Further, smaller area diaphragms produce a smaller device capacitance which in turn tends to increase the noise associated with on-chip circuitry coupled to the device and also tends to further decrease the integrated microphone sensitivity through capacitance divider action.
In order to alleviate such effects of reduced area (i.e., reduce signal-to-noise ratio), it is desirable to reduce the stiffness of the diaphragm.
The above-noted effects of reduced diaphragm area ~0 may also be compensated for by a reduction in the thickness of the air gap between capacitor electrodes. We have found, however, that for air gaps below approximately 1.5 ~m with other dimensions optimized for certain telephone applications, the electrical output frequency response of a microphone with a tensioned diaphragm had a tendency to fall at an unacceptable rate with frequency when utilizing acoustic venting means, common in commercially available devices, comprising 4-20 holes around the periphery of the stationary electrode and backplate. That is, the devices would be overdamped, even at the critical 300-3,500 Hz portion of the audioband which is transmitted in telephone equipment. Specifically, with an air gap of 0.25 ~m which yield the optimum signal-to-noise ratio, the response fell more than 20 dB across the telephone frequency band indicating severe overdamping. Sensitivity levels were also inoperably low. It is, therefore, also desirable to ., ~
.~
~219056 provide some acoustic venting means which will permit reduced area and produce an acceptable output signal at telephone band frequencies or other frequency bands of interest.
A reduction in the air gap thickness will also have another beneficial effect, which is to reduce the external dc voltage level needed to bias the diaphragm.
This would provide an alternative to the requirement of a built-in diaphragm bias as suggested in the application of Lindenberger, previously cited.
In addition, a silicon integrated microphone will generally have a nonrising output response as a function of frequency in the audio bandwidth. In some applications, it may be desirable to tailor the response to provide a peak at a certain frequency by means of an appropriately shaped acoustic port and coupling cavity. Further, the microphone chip may, under certain circumstances, be subject to high electromagnetic interference (EMI), and so some shielding means may be needed. In the design of an integrated microphone, therefore, it is desirable to provide these functions with a minimum number of piece parts.
It is therefore an object of the invention to provide an integrated electroacoustic transducer with a small diaphragm area which still provides an acceptable frequency response and signal-to-noise ratio. It is a further object of the invention to provide an electro-acoustic transducer which can be operated at a low dc bias. It is a still ~urther object of the invention to provide acoustical interconnection and tuning means, and EMI shielding means, for an integrated electroacoustic transducer.
Summary of the Invention In accordance with an aspect of the invention there is provided an electroacoustic transducer formed within a semiconductor substrate comprising an essentially ~`
nontensioned dlaphragm having a mechanical bending moment stif~ness such that it vibrates in response to an input signal at audio and/or ultrasonic frequencies; and a pair of electrodes placed with respect to said diaphragm so that the electric field between the electrodes varies in relationship with the vibrating diaphragm to permit conversion between electrical and acoustic signals.
In accordance with a further aspect of the invention, the transducer comprises an air gap formed between the electrodes and acoustic venting means comprisin~ a continuous array of small ho~es extending through one of the electrodes to the air gap, where the array covers essentially the entire area of the electrode co-extensive with the diaphragm.
In accordance with a further aspect of the invention, a front acoustic cavity is defined by a portion of a semiconductor substrate adjacent to the diaphragm, an air gap is formed between the electrodes, and a back acoustic cavity is formed adjacent to one of the electrodes and defined by a member which also shields the transducer from electromagnetic interference. Acoustic venting means is provided by an array of holes connecting the air gap to the back acoustic cavity. An acoustic port is defined by an element adjacent to the front acoustic cavity, with the size of the port being such as to produce a desired frequency response characteristic for the transducer.
Brief Descri~tion of the Drawing These and other features of the invention are delineated in detail in the following description. In the drawing:
FIG. 1 is a cross-sectional view of a microphone in accordance with one embodiment of the invention;
FIG. 2 is a top view of a portion of the device illustrated in FIG. l;
FIG. 3 is an illustration based on computer 12~9056 modeling of typical frequency response curves predicted for microphones fabricated in accordance with the invention as compared with predictions of a prior art type device where the reference level is the 400 Hz response level of curve B;
FIG. 4 is a cross-sectional view of a microphone in accordance with a further embodiment of the invention FIG. 5 is a cross-sectional view of a microphone in accordance with a still further embodiment of the invention; and FI&. 6 is a cross-sectional view of a microphone in accordance with a still further embodiment of the invention.
It will be appreciated that for purposes of illustration, these figures are not necessarily drawn to scale.
Detailed Description Many of the basic features of the invention will be described with reference to the particular embodiment illustrated in FIG. 1. It will be appreciated that the Figure shows only a small portion of a semiconductor substrate which in this example includes a great many other identical, integrated, electronic transducer devices which are separated along saw lines, 40, following batch processing and testing~
The semiconductor substrate, 10, is a standard p-type silicon wafer having a thickness of approximately 300-600 ~m (12-24 mils) and a <100> orientation. It will be appreciated that n-type wafers and other crystal orientations may be employed. A surface layer, 11, of p+ type is formed over at least portions of the substrate, for example, by an implantation of boron impurities to a depth of approximately 0.2 ~Im. The impurity concentration of this region is typically 5 x 10 19/cm3.
Formed over the semiconductor substrate is a monocrystalline silicon epitaxial layer, 12. An 12~9V5~
appropriate area of the semiconductor substrate is etched to form a front acoustic cavity, 13, so that the portion, 14, of the epitaxial layer over the cavity forms the vibrating diaphragm element of the microphone. The characteristics of the diaphragm are discussed in more detail below Formed on the surface of the diaphragm is a metal layer, 15, such as Ti-Au, which comprises one electrode of a capacitor. This layer is typically 0.1-0.5 ~m thick.
Formed over the epitaxial layer is a spacer layer, 16, which is typically polycrystalline silicon and can be formed by chemical vapor deposition. The thickness of the layer in this example is 0.60 ~m and will generally be in the range 0.1 ~m-4.0 ~m. A backplate layer, 17, is formed on the spacer layer with a portion (hereinafter the backplate) over the area of the diaphragm to establish an air gap, 18. The backplate may comprise a layer of SiO2, but could be any insulating layer or layers.
The thickness of the layer is approximately 12 ~m and will generally be in the range 6 ~m-30 ~m. A metal or other conducting layer, 19, is formed on the surface of the backplate facing the air gap and comprises the second electrode of the capacitor. It can be the same material and thickness as the first electrode, 15.
Formed through the backplate and electrode, 19, to the air gap is a continuous array of holes, 20, for acoustic venting. This feature will be discussed in more detail below.
The electronics for driving the device may be fabricated in the adjacent area o the semiconductor substrate designated 21, and electrical contact to the electrodes may be provided through via holes, 22 and 23.
Contact to the outside may be provided through via holes, 23 and 24, and contact pads, 25 and 26, formed on the surface of the backplate layer. If de~ired, additional via holes (not shown) could be provided from the electronics to the outside to establish separate dc supply, 12~9056 signal and ground leads.
In operation, a dc bias is applied to electrodes, 15 and 19, and an acoustic signal is made incident on diaphragm, 14, through the front acoustic cavity. The signal causes the diaphragm to vibratel thus varying the spacing between the electrodes and the capacitance of the capacitor. This change in capacitance can be detected as a change in voltage across some load element, integrated into area, ~1, such as a second capacitance and parallel resistance (not shown), and an electrical equivalent to the acoustic signal is produced.
The array of holes, 20, permits escape of air in the gap, 18, so that air stiffness in the gap is not a significant factor in the diaphragm motion. Desirably, the amplitude of the output signal as a function of frequency will be as shown in curve B in FIG. 3, wherP the signal (at constant sound pressure amplitude) is essentially flat or falls no more than 3 dB over the portion of the audioband transmitted in telephone applications (0.3-3.5 KHz). In accordance with a feature of the invention,the vibrating diaphragm is essentially nontensioned so that the stiffness of the diaphragm is dominated by the mechanical bending moment. This can be contrasted with previous designs for integrated microphones where the diaphragm was a thinned portion of the semiconductor substrate and had a stiffness which was dominated by tensile stress resulting from a heavy boron impurity concentration.
The advantage of using the nontensioned diaphragm results from the fact that the sensitivity (e) of the microphone depends upon the following parameters:
e ~ [km+ka ~ / e (1) where V is the dc bias voltage across the electrodes, A is - 12~90~;6 the area of the diaphragm, km is the effective mechanical lumped parameter (piston-like) stiffness of the diaphragm associated with the diaphragm's linearly averaged deflection~ ka is the stiffness of the rear acoustic cavity (shown, for example, in FIG. 4), and he is the distance between capacitor electrodes, linearly averaged over A, when the bias is applied to the electrodes. Thus, for the same sensitivity, the area, A, of the diaphragm may be~ reduced by decreasing the stiffness km of the diaphragm (ka contributes less than 1/3 of the total stiffness acting on the diaphragm). We have found that when the stiffness is due primarily to tensile stress, a practical lower limit exists for reducing the membrane stiffness. In the present invention, however, km is significantly lowered in order that the diaphragm area may be reduced by allowing the mechanical bending moment of the diaphragm to be the dominant mechanical stiffness component. Further, when the stiffness is due to the mechanical bending moment, the thickness of the diaphragm can be significantly increased over a tensioned membrane and still produce a significantly lower stiffness and diaphragm area.
It will be appreciated that effective stiffness km~ as used in this application, is the stiffness of a piston-like model where the deflection of the piston is equal to the diaphragm deflection averaged over the area of the diaphragm. For a nontensioned diaphragm, this stiffness is given approximately by the relationship:
192~2D
km ~ ~~~~~~~~ (2) where Dp is the flexural rigidity of the diaphragm.
In this example, the diaphragm thickness is 3.0 ~m, the diaphragm is circular with a radius of ',,' 12~9056 g 700 um~ ~ and ka are approximately 625 and 175 N/m respectively. The biasing voltage across the electrodes is 1 . 3 vol ts. The resulting sensitiv ity is approximately -49 dB relative to lV/Pa at 400 Hz (excluding any signal voltage amplifiers that may be integrated on the chip microphone). For most nontensioned diaphragm applications, it is expected that the diaphragm thickness will range from 1 ~m-5 ~m, and area will range from 0.4 mm~-5 mm2 to achieve proper sensitivity.
Stiffness, ~ , of the nontensioned diaphragm is desirably less than 5500 N/m.
While in this example the diaphragm was formed from a single crystal epitaxial layer, 12, other types of nontensioned diaphragms might be employed. However, use of an epitaxial layer provides many advantages in terms of processing. For example, diaphragm thickness can be closely controlled by growing the layer over the boron-doped surface region, 11, and then utilizing an etchant which removes the semiconductor substrate but stops at the region, 11. The portion of region, 11, under the diaphragm can then be removed by applying an appropriate etchant such as KOH and H20 for a predetermined period of time. As shown in FI~. 1, if desired, the etchant may be allowed to penetrate the epitaxial layer-substrate interface to achieve a desired diaphragm thickness less than the original epitaxial layer thickness. Close control of a nontensioned diaphragm's thickness, d, is important since ~ a d 3. This step may also be desirable to remove boron impurities which may have diffused into the epitaxial layer from the substrate and added tension to the layer. A further advantage is the fact that the epitaxial layer can be anisotropically etched to provide via holes (22, 23, 24) or other useful features.
It will be appreciated that, in this example, the epitaxial layer is essentially free of impurities so that there is essentially no tension component contributing to the stiffness of the diaphragm. However, it is ~2~9056 -- 1 o contemplated that layers may be fabricated with some tension component, as alluded ~o above, and still produce advantageous results. The invention is therefore directed to "essentially nontensioned" diaphragms which are intended to include those having a bending stiffness contributing at least 2/3 of the total stiffness of the diaphragm. It is further contemplated that impurities may be intentionally introduced into the epitaxial layer to satisfy certain needs. For example, the introduction of phosphorus impurities into the layer could provide compression in the layer to counteract any tension that might be produced by the presence of boron impurities.
In accordance with another aspect of the invention, the acoustic venting means comprises a continuous array of small holes, 20, extending through the backplate and electrode, 19, which array extends over essentially the entire area of the backplate and electrode portion co-extensive with the diaphragm. Such an array permits a narrow distance between electrodes, 15 and 19, without overdamping, thereby permitting a reduction in the applied dc bias and in the area of the diaphragm.
FIG. 2 is a top view of some of the holes in the array, which are greatly enlarged for illustrative purposes. It will be appreciated that essentially the entire area of the backplate is covered by these holes and consequently the array is considered to be continuous. The dynamic magnification factor, D, is defined in this application as the amount, in dB, that the fre~uency response rises in traversing the band from 400 Hz to the upper bound frequency of interest. For telephone applications where the upper bound frequency is 3500 Hz, it is desirable that D be greater than -3.0 dB. FIG. 3 shows a generally desirable, calculated, output characteristic (curve B) for telephony, which is achieved in this example in accordance with the invention. Returning to FIG. 2, such a characteristic can be achieved by a radius, r, of - the holes and a center-to-center spacing of the holes, 2~, ~2~9056 which satisfies the relationship:
L [ 1~ 2 L (~ R ~ l where D is the minimum desirable magnification factor, ~ is the highest acoustic input frequency which will be transmitted expressed in radians (here, 2~ x 3.5 KHz), ~n is the natural radian fre~uency of vibration of the diaphragm (/K-M), K is the combined stiffness, km +
kat of the diaphragm and back acoustic cavity, M is the effective lumped parameter mass of the diaphragm compatible with the prior definition of km (which, for a nontensioned diaphragm is approximately 9/5 times the actual mass), Rc is the critical damping level (2M~n), and Ra is the actual acoustic damping level of the air film in the air gap between electrodes. The acoustic damping is determined from the following:
a he
2~
where N is the number of holes, X is the local "radius-of-action" associated with each hole (i.e., the radius of the approximate circular area of air which will be vented through each hole (see FIG. 2), ~ is the coefficient of dynamic viscosity of air, and he was defined following equation (1). B is given by the equation:
B = 1 L~n) X ~ _3 + 1 (r) -8 (X) It will be further appreciated that the geometry of the array yields the following relationships:
12~gOS6 X = ~ (6) = _A_ '7) v = 1 N~r2 (8) where ~ is determined by the hole configuration, A is the area of the backplate and electrode portion co-extensive with the diaphragm area, N is the total number of holes, and v is the fraction of the backplate or electrode, 19, which is not consumed by the holes. For the pattern in this example, where the center of each hole lies at the corner of an equilateral triangle, ~ = 1.05. For other patterns of holes, the backplate area (A) can easily be expressed as a unique function of ~ times N, thus determining X and ~ from equations 6 and 7 above. For a square array of holes, for example, ~ is 1.13. Also, if noncircular holes are used, the above relationships may still be used for first order calculations if the radius, r, i5 equated to ~ where Ah is the area of the hole.
Thus, given the desired magnification factor D, the area, A, and mass of the diaphragm, M, the average distance between the electrodes when the bias is supplied, he~ and the combined stiffness of the diaphragm and back acoustic cavity, K, the above e~uations can be solved to give combinations of hole radius and center-to-center spacing (r, 2~) or hole radius and number (r, N) which can be utilized for acoustic venting in accordance with the invention. The preferred combination is that which consumes the minimum amount of electrode area. (For a detailed discussion of the derivation of relationships governing acoustic impedance of the air gap in 12~905~
electrostatic transducers due to holes in one of the electrodes, see Skvor, "On the Acoustical Resistance due to Viscous Losses in the Air Gap of ~lectrostatic Transducers," Acustica, Vol. 19, pp. 259-299 (1967-68).
In this example, D is -0.8 dB, he is 0.56 ~m, N
is approximately 2000, r is 9.8 ~m and 2~ is 29.8 ~m for a diaphragm with area of 1.54 x 10 6m2, and effective mass of 1.93 x 10 8kgm. This leaves a total area not consumed by holes of 61%(v) of the backplate or electrode area. The capacitance is still sufficient, however, to produce a sufficiently high output signal as specified by the sensitivity previously given.
Of course, the above parameters may be varied according to specific needs. It is recommended, however, that there be a minimum of at least 50 holes per square millimeter to avoid overdamping in the output signal and that each hole have a diameter of less than 100 ~m to allow sufficient diaphragm capacitance (at least 1 pF) for operation of the transducer. For the sake of comparison, curve A of FIG. 3 shows the calculated frequency response for a hypothetical microphone having the same dimensions as described in the example shown by curve B, but not including the venting means of the invention. As compared with the microphone of curve B which includes 2000 holes (1300 holes/mm ) each having a diameter of 19.6 ~m, the microphone of curve A includes only 20 holes (13 holes/mm ) each having a diameter of 196 ~m. Both designs have the same electrode area not consumed by holes (61~) so that the capacitances are equal and at least the potential signal-to-noise ratio is the same for both.
Nevertheless, curve A shows a severely overdamped frequency response.
It should be appreciated that the average spacing between electrodes (h~) when a bias is supplied should not vary too much from the air gap (h) with no bias '''` 3~
~Zl9~)5~
applied if the system is to remain stable. It is recommended, therefore, that he be 4-10% less than h. In this example, he = 0.94h.
AS noted previously, a reduced air gap, which is possible with the venting means of the invention, should also permit a reduction in the external dc bias needed for operation. For a gap, h, between electrodes of less than
where N is the number of holes, X is the local "radius-of-action" associated with each hole (i.e., the radius of the approximate circular area of air which will be vented through each hole (see FIG. 2), ~ is the coefficient of dynamic viscosity of air, and he was defined following equation (1). B is given by the equation:
B = 1 L~n) X ~ _3 + 1 (r) -8 (X) It will be further appreciated that the geometry of the array yields the following relationships:
12~gOS6 X = ~ (6) = _A_ '7) v = 1 N~r2 (8) where ~ is determined by the hole configuration, A is the area of the backplate and electrode portion co-extensive with the diaphragm area, N is the total number of holes, and v is the fraction of the backplate or electrode, 19, which is not consumed by the holes. For the pattern in this example, where the center of each hole lies at the corner of an equilateral triangle, ~ = 1.05. For other patterns of holes, the backplate area (A) can easily be expressed as a unique function of ~ times N, thus determining X and ~ from equations 6 and 7 above. For a square array of holes, for example, ~ is 1.13. Also, if noncircular holes are used, the above relationships may still be used for first order calculations if the radius, r, i5 equated to ~ where Ah is the area of the hole.
Thus, given the desired magnification factor D, the area, A, and mass of the diaphragm, M, the average distance between the electrodes when the bias is supplied, he~ and the combined stiffness of the diaphragm and back acoustic cavity, K, the above e~uations can be solved to give combinations of hole radius and center-to-center spacing (r, 2~) or hole radius and number (r, N) which can be utilized for acoustic venting in accordance with the invention. The preferred combination is that which consumes the minimum amount of electrode area. (For a detailed discussion of the derivation of relationships governing acoustic impedance of the air gap in 12~905~
electrostatic transducers due to holes in one of the electrodes, see Skvor, "On the Acoustical Resistance due to Viscous Losses in the Air Gap of ~lectrostatic Transducers," Acustica, Vol. 19, pp. 259-299 (1967-68).
In this example, D is -0.8 dB, he is 0.56 ~m, N
is approximately 2000, r is 9.8 ~m and 2~ is 29.8 ~m for a diaphragm with area of 1.54 x 10 6m2, and effective mass of 1.93 x 10 8kgm. This leaves a total area not consumed by holes of 61%(v) of the backplate or electrode area. The capacitance is still sufficient, however, to produce a sufficiently high output signal as specified by the sensitivity previously given.
Of course, the above parameters may be varied according to specific needs. It is recommended, however, that there be a minimum of at least 50 holes per square millimeter to avoid overdamping in the output signal and that each hole have a diameter of less than 100 ~m to allow sufficient diaphragm capacitance (at least 1 pF) for operation of the transducer. For the sake of comparison, curve A of FIG. 3 shows the calculated frequency response for a hypothetical microphone having the same dimensions as described in the example shown by curve B, but not including the venting means of the invention. As compared with the microphone of curve B which includes 2000 holes (1300 holes/mm ) each having a diameter of 19.6 ~m, the microphone of curve A includes only 20 holes (13 holes/mm ) each having a diameter of 196 ~m. Both designs have the same electrode area not consumed by holes (61~) so that the capacitances are equal and at least the potential signal-to-noise ratio is the same for both.
Nevertheless, curve A shows a severely overdamped frequency response.
It should be appreciated that the average spacing between electrodes (h~) when a bias is supplied should not vary too much from the air gap (h) with no bias '''` 3~
~Zl9~)5~
applied if the system is to remain stable. It is recommended, therefore, that he be 4-10% less than h. In this example, he = 0.94h.
AS noted previously, a reduced air gap, which is possible with the venting means of the invention, should also permit a reduction in the external dc bias needed for operation. For a gap, h, between electrodes of less than
3.0 ~m, it is expected that the microphone can be operated at less than 5 volts supplied to the capacitor electrodes.
It should also be appreciated that, although the air hole array is described with use of a nontensioned diaphragm, the hole array as described heretofore may also be used with tensioned diaphragms such as that shown in application of Busch-Vishniac, cited previously. In such cases, the area of the diaphragm may be larger than that for the nontensioned diaphragm, but would still be, advantageously, less than 8 mm2.
It should be further appreciated that while the above relations allow one to specify a uniform air hole array (that is, a constant hole size and pattern), a somewhat nonuniform pattern that might possibly be desired may be designed by applying equation (4) piecewise across the backplate and electrode, and summing over N (holes).
The air gap, 18, electrode, 19, backplate layer, 17, and the air hole array, 20, may be conveniently formed by known deposition and photolithography steps. For example, layer 16, which may comprise polycrystalline silicon, can be deposited by chemical vapor deposition and the area which will comprise the air gap is then defined by selectively etching the layer. An etch-stop material, 27, such as BN or Si3N4 can be formed around the walls of the hole. The hole is then filled with a material such as polycrystalline silicon or SiO2 and planarized. The electrode, 19, may then be formed by a selective deposition leaving the desired hole array therein. The backplate layer, 17, which may comprise BN or ~2~9056 Si3N4 or a combination of like materials, is then deposited and the corresponding hole array formed therein by standard photolithography. The filler material can then be removed from the air cavity by applying another etchant through the hole array. Of course, during these various etching operations, the via holes, 22, 23 and 24, needed for interconnection can also be formed.
It will be appreciated that while the above example employed a circular diaphragm and backplate, the principles of the invention may be applied to any shaped diaphragm and backplate.
In accordance with a further aspect of the invention, various acoustical interconnection means and EMI shielding means may be incorporated into the basic microphone structure previously described. For example, FIG. 4 illustrates the formation of a back acoustic cavity, 30, adjacent to the air hole array, 20. This cavity is formed within a carrier substrate, 31, against which the silicon microphone structure is placed. This substrate can be a printed wiring board or other carrier substrate to which electronic components are usually attached.
Coupled to the front cavity, 13, is an acoustic port, 32, which is formed from an element, 33, which is typically a plastic closure. The acoustic port adds a degree-of-freedom to the microphone system and adds a peak to the frequency response of the device to serve various needs. Thus, in the present example, the response shown as curve C in FIG. 3, where the peak is placed near the upper end of the telephone band, is obtained from the microphone characterized by curve B simply by adding an acoustic port having a diameter of 150 ~m and a length of 1600 ~m. In this example, the cavity, 13, has a volume of 0.94 mm3. Long holes with narrow diameters yielding high acoustic mass are generally needed in this silicon microphone application due to the large stiffness of the small, front acoustic cavity. In general, diameters of 100-180 llm and lengths of 600-2000 ~m are expected to be useful for producing peaks where desired. For telephone applications, it is desirable to form the peak within the frequency range 2.8-4.5 KHz. Although not illustrated in these figures, all members forming acoustic ports or cavities are acoustically sealed by standard means such as with adhesives or by clamping.
If shaping of the fre~uency response, as shown in curve C, is not needed, the embodiment shown in FIG. 5 might be utilized. Here, the cavity, 30, formed in carrier substrate, 31, acts as an extension of front cavity, 13, and the acoustic signal is made incident on the diaphragm through the hole array, 20. In this embodiment, in fact, the cavity extension, 30, may be eliminated so that the acoustic cavity is formed entirely within the semiconductor substrate. In any event, no extra parts are needed to form the acoustic interconnections. A further advantage is that electrical contact can be made to the microphone by wire bonds, 34 and 35, from the carrier substrate, 31, to the top of the backplate layer.
In the embodiment illustrated in FIG. 6, sound is again incident on the diaphragm through an acoustic port, 32, coupled to the front cavity, 13. Here, however, the sound port is formed in the carrier substrate, 31, so 2S that the microphone is again mounted with the backplate side-up permitting wire bonding. Additionally, an enclosure member, 36, is provided surrounding the entire semiconductor microphone. This member can be made of conductive or conductively plated plastic or metal so as to provide a shield for the device against electromagnetic interference. At the same time, the member forms a back acoustic cavity, 30, for the microphone. The member can be ; grounded, for example, by bonding to grounded pad, 37, formed on the carrier substrate. Thus, EMI shielding is provided with a minimum of piece-parts.
It should be appreciated that although the acoustical interconnection means and EMI shielding means ,,, ~ , , lZ~9056 are described with use of a nontensioned diaphragm, such may also be used with tensioned membranes as for example shown in application of Busch-Vishniac, cited previously.
It will be appreciated that the inventive features discussed herein could also apply to a pressure gradient type microphone where sound is allowed to strike both sides of the diaphragm, thus effecting a noise-canceling and directional response. To produce such a device in FIGS. 4 and 5, a secondary sound port would simply be placed in the carrier substrate, 31, while in the embodiment illustrated in FIG. 6 a small secondary port would be placed through enclosure member, 36. In any case, the second side of the diaphragm is accessed.
It will also be appreciated that although the above discussion has focused on a microphone, the principles of the invention may also be applicable to other types of electroacoustic transducers utilizing a capacitor whose capacitance varies in accordance with a vibrating diaphragm, whether an acoustic signal is converted to an electrical signal or vice-versa. For example, a loudspeaker or hearing aid receiver might be fabricated by applying a varying electrical signal to the capacitor electrodes (15 and 19) which causes vibration of the diaphragm (14) due to the varying deflection of the electrode (15) attached thereto. An acoustic output signal would therefore be produced. Thus, whichever way the energy conversion is taking place, the electric field between the electrodes varies in relationship with the vibrating diaphragm to permit conversion between electrical and acoustic signals.
It will also be realized that the invention is not limited to telephone band frequencies (0.3-3.5 KHz) but can be used in the full audio bandwidth (0.02-20 KHz). In factl this silicon transducer invention can find application in the ultrasonic band (20-1000 KHz).
It should also be appreciated that, although the air hole array is described with use of a nontensioned diaphragm, the hole array as described heretofore may also be used with tensioned diaphragms such as that shown in application of Busch-Vishniac, cited previously. In such cases, the area of the diaphragm may be larger than that for the nontensioned diaphragm, but would still be, advantageously, less than 8 mm2.
It should be further appreciated that while the above relations allow one to specify a uniform air hole array (that is, a constant hole size and pattern), a somewhat nonuniform pattern that might possibly be desired may be designed by applying equation (4) piecewise across the backplate and electrode, and summing over N (holes).
The air gap, 18, electrode, 19, backplate layer, 17, and the air hole array, 20, may be conveniently formed by known deposition and photolithography steps. For example, layer 16, which may comprise polycrystalline silicon, can be deposited by chemical vapor deposition and the area which will comprise the air gap is then defined by selectively etching the layer. An etch-stop material, 27, such as BN or Si3N4 can be formed around the walls of the hole. The hole is then filled with a material such as polycrystalline silicon or SiO2 and planarized. The electrode, 19, may then be formed by a selective deposition leaving the desired hole array therein. The backplate layer, 17, which may comprise BN or ~2~9056 Si3N4 or a combination of like materials, is then deposited and the corresponding hole array formed therein by standard photolithography. The filler material can then be removed from the air cavity by applying another etchant through the hole array. Of course, during these various etching operations, the via holes, 22, 23 and 24, needed for interconnection can also be formed.
It will be appreciated that while the above example employed a circular diaphragm and backplate, the principles of the invention may be applied to any shaped diaphragm and backplate.
In accordance with a further aspect of the invention, various acoustical interconnection means and EMI shielding means may be incorporated into the basic microphone structure previously described. For example, FIG. 4 illustrates the formation of a back acoustic cavity, 30, adjacent to the air hole array, 20. This cavity is formed within a carrier substrate, 31, against which the silicon microphone structure is placed. This substrate can be a printed wiring board or other carrier substrate to which electronic components are usually attached.
Coupled to the front cavity, 13, is an acoustic port, 32, which is formed from an element, 33, which is typically a plastic closure. The acoustic port adds a degree-of-freedom to the microphone system and adds a peak to the frequency response of the device to serve various needs. Thus, in the present example, the response shown as curve C in FIG. 3, where the peak is placed near the upper end of the telephone band, is obtained from the microphone characterized by curve B simply by adding an acoustic port having a diameter of 150 ~m and a length of 1600 ~m. In this example, the cavity, 13, has a volume of 0.94 mm3. Long holes with narrow diameters yielding high acoustic mass are generally needed in this silicon microphone application due to the large stiffness of the small, front acoustic cavity. In general, diameters of 100-180 llm and lengths of 600-2000 ~m are expected to be useful for producing peaks where desired. For telephone applications, it is desirable to form the peak within the frequency range 2.8-4.5 KHz. Although not illustrated in these figures, all members forming acoustic ports or cavities are acoustically sealed by standard means such as with adhesives or by clamping.
If shaping of the fre~uency response, as shown in curve C, is not needed, the embodiment shown in FIG. 5 might be utilized. Here, the cavity, 30, formed in carrier substrate, 31, acts as an extension of front cavity, 13, and the acoustic signal is made incident on the diaphragm through the hole array, 20. In this embodiment, in fact, the cavity extension, 30, may be eliminated so that the acoustic cavity is formed entirely within the semiconductor substrate. In any event, no extra parts are needed to form the acoustic interconnections. A further advantage is that electrical contact can be made to the microphone by wire bonds, 34 and 35, from the carrier substrate, 31, to the top of the backplate layer.
In the embodiment illustrated in FIG. 6, sound is again incident on the diaphragm through an acoustic port, 32, coupled to the front cavity, 13. Here, however, the sound port is formed in the carrier substrate, 31, so 2S that the microphone is again mounted with the backplate side-up permitting wire bonding. Additionally, an enclosure member, 36, is provided surrounding the entire semiconductor microphone. This member can be made of conductive or conductively plated plastic or metal so as to provide a shield for the device against electromagnetic interference. At the same time, the member forms a back acoustic cavity, 30, for the microphone. The member can be ; grounded, for example, by bonding to grounded pad, 37, formed on the carrier substrate. Thus, EMI shielding is provided with a minimum of piece-parts.
It should be appreciated that although the acoustical interconnection means and EMI shielding means ,,, ~ , , lZ~9056 are described with use of a nontensioned diaphragm, such may also be used with tensioned membranes as for example shown in application of Busch-Vishniac, cited previously.
It will be appreciated that the inventive features discussed herein could also apply to a pressure gradient type microphone where sound is allowed to strike both sides of the diaphragm, thus effecting a noise-canceling and directional response. To produce such a device in FIGS. 4 and 5, a secondary sound port would simply be placed in the carrier substrate, 31, while in the embodiment illustrated in FIG. 6 a small secondary port would be placed through enclosure member, 36. In any case, the second side of the diaphragm is accessed.
It will also be appreciated that although the above discussion has focused on a microphone, the principles of the invention may also be applicable to other types of electroacoustic transducers utilizing a capacitor whose capacitance varies in accordance with a vibrating diaphragm, whether an acoustic signal is converted to an electrical signal or vice-versa. For example, a loudspeaker or hearing aid receiver might be fabricated by applying a varying electrical signal to the capacitor electrodes (15 and 19) which causes vibration of the diaphragm (14) due to the varying deflection of the electrode (15) attached thereto. An acoustic output signal would therefore be produced. Thus, whichever way the energy conversion is taking place, the electric field between the electrodes varies in relationship with the vibrating diaphragm to permit conversion between electrical and acoustic signals.
It will also be realized that the invention is not limited to telephone band frequencies (0.3-3.5 KHz) but can be used in the full audio bandwidth (0.02-20 KHz). In factl this silicon transducer invention can find application in the ultrasonic band (20-1000 KHz).
Claims (26)
1. An electroacoustic transducer formed within a semiconductor substrate comprising an essentially nontensioned diaphragm having a mechanical bending moment stiffness such that it vibrates in response to an input signal at audio and/or ultrasonic frequencies, and a pair of electrodes placed with respect to said diaphragm so that the electric field between the electrodes varies in relationship with the vibrating diaphragm to permit conversion between electrical and acoustic signals.
2. The device according to claim 1 wherein the transducer is a microphone and one of the electrodes is formed to vibrate with the diaphragm such that the capacitance varies in response to an acoustic signal incident on said diaphragm.
3. The device according to claim 2 wherein the diaphragm is a single crystalline epitaxial layer formed over the surface of a semiconductor substrate.
4. The device according to claim 3 wherein the thickness of the epitaxial layer is in the range 1-5 µm.
5. The device according to claim 2 wherein the area of the diaphragm is less than 5 mm2.
6. The device according to claim 1 wherein the total effective lumped parameter stiffness of the diaphragm due to mechanical bending moment and tension, associated with a linearly average deflection, is less than 5500 N/m.
7. The device according to claim 3 wherein the epitaxial layer is formed over a surface layer in the substrate which has a higher impurity concentration than the bulk of the substrate.
8. The device according to claim 2 wherein an air gap is formed between the two electrodes and the device further comprises a continuous array of small holes extending through one of the electrodes to the air gap, said array covering essentially the entire area of that portion of the electrode which is co-extensive with the diaphragm.
9. The device according to claim 2 wherein the transducer is adapted for operation with a dc bias across the electrodes of less than 5 volts.
10. The device according to claim 1 wherein an air gap is formed between the electrodes and the device further comprises:
a front acoustic cavity defined by a portion of the semiconductor substrate adjacent to the diaphragm;
a rear acoustic cavity adjacent to one of the electrodes and defined by a member which also shields the transducer from electromagnetic interference;
acoustic venting means comprising an array of holes connecting the air gap to the back acoustic cavity;
and an acoustic port defined by an element adjacent to the front acoustic cavity, the size of the port being such as to produce a desired frequency characteristic for the transducer.
a front acoustic cavity defined by a portion of the semiconductor substrate adjacent to the diaphragm;
a rear acoustic cavity adjacent to one of the electrodes and defined by a member which also shields the transducer from electromagnetic interference;
acoustic venting means comprising an array of holes connecting the air gap to the back acoustic cavity;
and an acoustic port defined by an element adjacent to the front acoustic cavity, the size of the port being such as to produce a desired frequency characteristic for the transducer.
11. An elecroacoustic transducer formed within a semiconductor substrate comprising:
a diaphragm which vibrates in response to an input signal at audio and/or ultrasonic frequencies;
a pair of electrodes placed with respect to said diaphragm so that the electric field between the electrodes varies in relation to the vibrating diaphragm to permit conversion between electrical and acoustic signals, the electrodes defining an air gap therebetween; and acoustic venting means comprising a continuous array of small holes extending through one of the electrodes to the air gap, said array covering essentially the entire area of that electrode which is co-extensive with the diaphragm.
a diaphragm which vibrates in response to an input signal at audio and/or ultrasonic frequencies;
a pair of electrodes placed with respect to said diaphragm so that the electric field between the electrodes varies in relation to the vibrating diaphragm to permit conversion between electrical and acoustic signals, the electrodes defining an air gap therebetween; and acoustic venting means comprising a continuous array of small holes extending through one of the electrodes to the air gap, said array covering essentially the entire area of that electrode which is co-extensive with the diaphragm.
12. The device according to claim 11 wherein the transducer is a microphone and one of the electrodes is formed to vibrate with the diaphragm such that the capacitance varies in response to an acoustic signal incident on said diaphragm.
13. The device according to claim 11 wherein a backplate layer is included adjacent to said one of the electrodes and said array of holes is included through the layer.
14. The device according to claim 11 wherein the spacing between electrodes is less than 3.0 µm when no dc bias is supplied to the electrodes.
15. The device according to claim 11 wherein the area of the diaphragm is less than 8 mm2.
16. The device according to claim 11 wherein the density of the holes in the array is at least 50 per mm2 and the diameter of the holes is less than 100 µm.
17. The device according to claim 11 wherein the transducer is adapted to operate with a dc bias across the electrodes of less than 5 volts.
18. The device according to claim 11 wherein the dynamic magnification factor of the output response of the transducer is greater than or equal to -3.0 dB.
19. The device according to claim 11 where the radius, r, center-to-center spacing, 2.epsilon., and number, N, of holes in the array satisfies the relationships:
where D is the minimum desirable dynamic magnification factor, .omega. is the highest radian frequency of input signal to be transmitted, .omega.n is the natural radian frequency of vibration of the diaphragm, Ra is the damping level of the air in the gap, RC is the critical damping level, X
is the local radius-of-action associated with each hole, he is the average distance between the electrodes when the desired dc bias is supplied thereto, .lambda., is a factor relating X and .epsilon. for the geometry of the hole array, A is the area of the diaphragm, and n is the coefficient of dynamic viscosity of air.
where D is the minimum desirable dynamic magnification factor, .omega. is the highest radian frequency of input signal to be transmitted, .omega.n is the natural radian frequency of vibration of the diaphragm, Ra is the damping level of the air in the gap, RC is the critical damping level, X
is the local radius-of-action associated with each hole, he is the average distance between the electrodes when the desired dc bias is supplied thereto, .lambda., is a factor relating X and .epsilon. for the geometry of the hole array, A is the area of the diaphragm, and n is the coefficient of dynamic viscosity of air.
20. The device according to claim 11 further comprising:
a front acoustic cavity defined by a portion of a semiconductor substrate adjacent to the diaphragm;
a back acoustic cavity adjacent to the air hole array and defined by a member which also shields the transducer from electromagnetic interference; and an acoustic port defined by an element adjacent to the front acoustic cavity, the size of the port being such as to produce a desired frequency response characteristic for the transducer.
a front acoustic cavity defined by a portion of a semiconductor substrate adjacent to the diaphragm;
a back acoustic cavity adjacent to the air hole array and defined by a member which also shields the transducer from electromagnetic interference; and an acoustic port defined by an element adjacent to the front acoustic cavity, the size of the port being such as to produce a desired frequency response characteristic for the transducer.
21. The device according to claim 12 wherein the microphone is adapted to receive the acoustic signal through the hole array.
22. An electroacoustic transducer formed within a semiconductor substrate comprising:
a diaphragm which vibrates in response to an input signal at audio and/or ultrasonic frequencies;
a front acoustic cavity defined by a portion of the semiconductor substrate adjacent to the diaphragm:
a pair of electrodes placed with respect to said diaphragm so that the electric field between the electrodes varies in relation with the vibrating diaphragm to permit conversion between electrical and acoustic signals and so that an air gap is formed between the electrodes;
a back acoustic cavity adjacent to one of the electrodes and defined by a member which also shields the transducer from electromagnetic interference;
acoustic venting means comprising an array of holes connecting the air gap to the back acoustic cavity;
and an acoustic port defined by an element adjacent to the front acoustic cavity, the size of the port being such as to produce a desired frequency response characteristic for the transducer.
a diaphragm which vibrates in response to an input signal at audio and/or ultrasonic frequencies;
a front acoustic cavity defined by a portion of the semiconductor substrate adjacent to the diaphragm:
a pair of electrodes placed with respect to said diaphragm so that the electric field between the electrodes varies in relation with the vibrating diaphragm to permit conversion between electrical and acoustic signals and so that an air gap is formed between the electrodes;
a back acoustic cavity adjacent to one of the electrodes and defined by a member which also shields the transducer from electromagnetic interference;
acoustic venting means comprising an array of holes connecting the air gap to the back acoustic cavity;
and an acoustic port defined by an element adjacent to the front acoustic cavity, the size of the port being such as to produce a desired frequency response characteristic for the transducer.
23. The device according to claim 22 wherein the transducer is a microphone and one of the electrodes is formed to vibrate with the diaphragm such that the capacitance varies in response to an acoustic signal incident on said diaphragm.
24. The device according to claim 22 wherein the acoustic port is defined in a carrier to which the semiconductor substrate is attached.
25. The device according to claim 22 wherein the back acoustic cavity is defined by a conductive member which covers the entire semiconductor substrate in which the integrated microphone is formed.
26. The device according to claim 22 wherein the diameter and length of the acoustic port is such as to produce a peak in the output response in the frequency range 2.8-4.5 KHz.
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US06/511,640 US4533795A (en) | 1983-07-07 | 1983-07-07 | Integrated electroacoustic transducer |
US511,640 | 1991-02-19 |
Publications (1)
Publication Number | Publication Date |
---|---|
CA1219056A true CA1219056A (en) | 1987-03-10 |
Family
ID=24035781
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
CA000457580A Expired CA1219056A (en) | 1983-07-07 | 1984-06-27 | Integrated electroacoustic transducer |
Country Status (9)
Country | Link |
---|---|
US (1) | US4533795A (en) |
EP (1) | EP0148893B1 (en) |
JP (1) | JP2530305B2 (en) |
CA (1) | CA1219056A (en) |
DE (1) | DE3466918D1 (en) |
HK (1) | HK11289A (en) |
IT (1) | IT1176379B (en) |
SG (1) | SG15988G (en) |
WO (1) | WO1985000495A1 (en) |
Families Citing this family (96)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4691363A (en) * | 1985-12-11 | 1987-09-01 | American Telephone & Telegraph Company, At&T Information Systems Inc. | Transducer device |
US4817164A (en) * | 1987-03-20 | 1989-03-28 | Northern Telecom Limited | Electrostatic discharge protector for an electret microphone |
DE3807251A1 (en) * | 1988-03-05 | 1989-09-14 | Sennheiser Electronic | CAPACITIVE SOUND CONVERTER |
FR2695787B1 (en) * | 1992-09-11 | 1994-11-10 | Suisse Electro Microtech Centr | Integrated capacitive transducer. |
US5401914A (en) * | 1993-02-03 | 1995-03-28 | The Curran Company | Vent for shielded enclosures |
US5627901A (en) * | 1993-06-23 | 1997-05-06 | Apple Computer, Inc. | Directional microphone for computer visual display monitor and method for construction |
US5682075A (en) * | 1993-07-14 | 1997-10-28 | The University Of British Columbia | Porous gas reservoir electrostatic transducer |
US5619476A (en) * | 1994-10-21 | 1997-04-08 | The Board Of Trustees Of The Leland Stanford Jr. Univ. | Electrostatic ultrasonic transducer |
US5894452A (en) * | 1994-10-21 | 1999-04-13 | The Board Of Trustees Of The Leland Stanford Junior University | Microfabricated ultrasonic immersion transducer |
US5949895A (en) * | 1995-09-07 | 1999-09-07 | Symphonix Devices, Inc. | Disposable audio processor for use with implanted hearing devices |
US5982905A (en) * | 1996-01-22 | 1999-11-09 | Grodinsky; Robert M. | Distortion reduction in signal processors |
US5970159A (en) * | 1996-11-08 | 1999-10-19 | Telex Communications, Inc. | Video monitor with shielded microphone |
FI970409A (en) | 1997-01-31 | 1998-08-01 | Nokia Mobile Phones Ltd | Method of protecting the microphone from external interference and microphone interference shielding |
US5982709A (en) * | 1998-03-31 | 1999-11-09 | The Board Of Trustees Of The Leland Stanford Junior University | Acoustic transducers and method of microfabrication |
WO2000041432A2 (en) * | 1999-01-07 | 2000-07-13 | Sarnoff Corporation | Hearing aid with large diaphragm microphone element including a printed circuit board |
US7003127B1 (en) * | 1999-01-07 | 2006-02-21 | Sarnoff Corporation | Hearing aid with large diaphragm microphone element including a printed circuit board |
WO2001019134A2 (en) * | 1999-09-06 | 2001-03-15 | Microtronic A/S | Silicon-based sensor system |
US6522762B1 (en) | 1999-09-07 | 2003-02-18 | Microtronic A/S | Silicon-based sensor system |
JP3611779B2 (en) * | 1999-12-09 | 2005-01-19 | シャープ株式会社 | Electrical signal-acoustic signal converter, method for manufacturing the same, and electrical signal-acoustic converter |
US6782109B2 (en) * | 2000-04-04 | 2004-08-24 | University Of Florida | Electromechanical acoustic liner |
US7277166B2 (en) * | 2000-08-02 | 2007-10-02 | Honeywell International Inc. | Cytometer analysis cartridge optical configuration |
US6842964B1 (en) | 2000-09-29 | 2005-01-18 | Tucker Davis Technologies, Inc. | Process of manufacturing of electrostatic speakers |
US7434305B2 (en) * | 2000-11-28 | 2008-10-14 | Knowles Electronics, Llc. | Method of manufacturing a microphone |
US7166910B2 (en) * | 2000-11-28 | 2007-01-23 | Knowles Electronics Llc | Miniature silicon condenser microphone |
US7439616B2 (en) * | 2000-11-28 | 2008-10-21 | Knowles Electronics, Llc | Miniature silicon condenser microphone |
US8623709B1 (en) | 2000-11-28 | 2014-01-07 | Knowles Electronics, Llc | Methods of manufacture of top port surface mount silicon condenser microphone packages |
EP1821570B1 (en) * | 2000-11-28 | 2017-02-08 | Knowles Electronics, LLC | Miniature silicon condenser microphone and method for producing same |
US6847090B2 (en) | 2001-01-24 | 2005-01-25 | Knowles Electronics, Llc | Silicon capacitive microphone |
US6671379B2 (en) | 2001-03-30 | 2003-12-30 | Think-A-Move, Ltd. | Ear microphone apparatus and method |
US6647368B2 (en) | 2001-03-30 | 2003-11-11 | Think-A-Move, Ltd. | Sensor pair for detecting changes within a human ear and producing a signal corresponding to thought, movement, biological function and/or speech |
US7065224B2 (en) * | 2001-09-28 | 2006-06-20 | Sonionmicrotronic Nederland B.V. | Microphone for a hearing aid or listening device with improved internal damping and foreign material protection |
WO2003037212A2 (en) * | 2001-10-30 | 2003-05-08 | Lesinski George S | Implantation method for a hearing aid microactuator implanted into the cochlea |
US6677176B2 (en) * | 2002-01-18 | 2004-01-13 | The Hong Kong University Of Science And Technology | Method of manufacturing an integrated electronic microphone having a floating gate electrode |
US8463334B2 (en) * | 2002-03-13 | 2013-06-11 | Qualcomm Incorporated | Apparatus and system for providing wideband voice quality in a wireless telephone |
AU2003236375A1 (en) * | 2002-04-05 | 2003-10-20 | Matsushita Electric Industrial Co., Ltd. | Capacitor sensor |
US6781231B2 (en) * | 2002-09-10 | 2004-08-24 | Knowles Electronics Llc | Microelectromechanical system package with environmental and interference shield |
KR100556684B1 (en) * | 2004-01-20 | 2006-03-10 | 주식회사 비에스이 | A condenser microphone mountable on main PCB |
US7929714B2 (en) * | 2004-08-11 | 2011-04-19 | Qualcomm Incorporated | Integrated audio codec with silicon audio transducer |
US7415121B2 (en) * | 2004-10-29 | 2008-08-19 | Sonion Nederland B.V. | Microphone with internal damping |
US7795695B2 (en) | 2005-01-27 | 2010-09-14 | Analog Devices, Inc. | Integrated microphone |
DE102005008511B4 (en) | 2005-02-24 | 2019-09-12 | Tdk Corporation | MEMS microphone |
DE102005008512B4 (en) | 2005-02-24 | 2016-06-23 | Epcos Ag | Electrical module with a MEMS microphone |
US20060274476A1 (en) * | 2005-04-13 | 2006-12-07 | Andrew Cervin-Lawry | Low loss thin film capacitor and methods of manufacturing the same |
US7885423B2 (en) * | 2005-04-25 | 2011-02-08 | Analog Devices, Inc. | Support apparatus for microphone diaphragm |
US20070071268A1 (en) * | 2005-08-16 | 2007-03-29 | Analog Devices, Inc. | Packaged microphone with electrically coupled lid |
US7449356B2 (en) * | 2005-04-25 | 2008-11-11 | Analog Devices, Inc. | Process of forming a microphone using support member |
US7825484B2 (en) * | 2005-04-25 | 2010-11-02 | Analog Devices, Inc. | Micromachined microphone and multisensor and method for producing same |
US7317234B2 (en) * | 2005-07-20 | 2008-01-08 | Douglas G Marsh | Means of integrating a microphone in a standard integrated circuit process |
US20070040231A1 (en) * | 2005-08-16 | 2007-02-22 | Harney Kieran P | Partially etched leadframe packages having different top and bottom topologies |
US8477983B2 (en) * | 2005-08-23 | 2013-07-02 | Analog Devices, Inc. | Multi-microphone system |
US8130979B2 (en) * | 2005-08-23 | 2012-03-06 | Analog Devices, Inc. | Noise mitigating microphone system and method |
US8351632B2 (en) * | 2005-08-23 | 2013-01-08 | Analog Devices, Inc. | Noise mitigating microphone system and method |
US7961897B2 (en) * | 2005-08-23 | 2011-06-14 | Analog Devices, Inc. | Microphone with irregular diaphragm |
US20070063777A1 (en) * | 2005-08-26 | 2007-03-22 | Mircea Capanu | Electrostrictive devices |
CN101331080B (en) * | 2005-10-14 | 2012-12-26 | 意法半导体股份有限公司 | Substrate-level assembly for an integrated device, manufacturing process thereof and related integrated device |
US7983433B2 (en) | 2005-11-08 | 2011-07-19 | Think-A-Move, Ltd. | Earset assembly |
DE102005053765B4 (en) | 2005-11-10 | 2016-04-14 | Epcos Ag | MEMS package and method of manufacture |
DE102005053767B4 (en) | 2005-11-10 | 2014-10-30 | Epcos Ag | MEMS microphone, method of manufacture and method of installation |
DE102005056759A1 (en) * | 2005-11-29 | 2007-05-31 | Robert Bosch Gmbh | Micromechanical structure for use as e.g. microphone, has counter units forming respective sides of structure, where counter units have respective electrodes, and closed diaphragm is arranged between counter units |
WO2007147049A2 (en) | 2006-06-14 | 2007-12-21 | Think-A-Move, Ltd. | Ear sensor assembly for speech processing |
WO2008003051A2 (en) * | 2006-06-29 | 2008-01-03 | Analog Devices, Inc. | Stress mitigation in packaged microchips |
US8270634B2 (en) * | 2006-07-25 | 2012-09-18 | Analog Devices, Inc. | Multiple microphone system |
US20080042223A1 (en) * | 2006-08-17 | 2008-02-21 | Lu-Lee Liao | Microelectromechanical system package and method for making the same |
US20080075308A1 (en) * | 2006-08-30 | 2008-03-27 | Wen-Chieh Wei | Silicon condenser microphone |
US20080083957A1 (en) * | 2006-10-05 | 2008-04-10 | Wen-Chieh Wei | Micro-electromechanical system package |
US7894622B2 (en) | 2006-10-13 | 2011-02-22 | Merry Electronics Co., Ltd. | Microphone |
WO2008067431A2 (en) * | 2006-11-30 | 2008-06-05 | Analog Devices, Inc. | Microphone system with silicon microphone secured to package lid |
US20080217709A1 (en) * | 2007-03-07 | 2008-09-11 | Knowles Electronics, Llc | Mems package having at least one port and manufacturing method thereof |
US11856375B2 (en) | 2007-05-04 | 2023-12-26 | Staton Techiya Llc | Method and device for in-ear echo suppression |
US11683643B2 (en) | 2007-05-04 | 2023-06-20 | Staton Techiya Llc | Method and device for in ear canal echo suppression |
US8767983B2 (en) * | 2007-06-01 | 2014-07-01 | Infineon Technologies Ag | Module including a micro-electro-mechanical microphone |
US7694610B2 (en) * | 2007-06-27 | 2010-04-13 | Siemens Medical Solutions Usa, Inc. | Photo-multiplier tube removal tool |
SG158758A1 (en) * | 2008-07-14 | 2010-02-26 | Sensfab Pte Ltd | Extended sensor back volume |
TWI404428B (en) * | 2009-11-25 | 2013-08-01 | Ind Tech Res Inst | Acoustics transducer |
CN102104817B (en) * | 2009-12-21 | 2013-10-02 | 财团法人工业技术研究院 | Acoustic sensor |
CN103999484B (en) | 2011-11-04 | 2017-06-30 | 美商楼氏电子有限公司 | As the embedded-type electric medium and manufacture method of the barrier in acoustic equipment |
EP2781107B1 (en) | 2011-11-17 | 2016-11-23 | InvenSense, Inc. | Microphone module with sound pipe |
US9738515B2 (en) | 2012-06-27 | 2017-08-22 | Invensense, Inc. | Transducer with enlarged back volume |
US9078063B2 (en) | 2012-08-10 | 2015-07-07 | Knowles Electronics, Llc | Microphone assembly with barrier to prevent contaminant infiltration |
US8841738B2 (en) | 2012-10-01 | 2014-09-23 | Invensense, Inc. | MEMS microphone system for harsh environments |
US9676614B2 (en) | 2013-02-01 | 2017-06-13 | Analog Devices, Inc. | MEMS device with stress relief structures |
US9809448B2 (en) | 2013-03-13 | 2017-11-07 | Invensense, Inc. | Systems and apparatus having MEMS acoustic sensors and other MEMS sensors and methods of fabrication of the same |
US8692340B1 (en) | 2013-03-13 | 2014-04-08 | Invensense, Inc. | MEMS acoustic sensor with integrated back cavity |
US9338559B2 (en) | 2013-04-16 | 2016-05-10 | Invensense, Inc. | Microphone system with a stop member |
DE102013106353B4 (en) * | 2013-06-18 | 2018-06-28 | Tdk Corporation | Method for applying a structured coating to a component |
US10167189B2 (en) | 2014-09-30 | 2019-01-01 | Analog Devices, Inc. | Stress isolation platform for MEMS devices |
US9794661B2 (en) | 2015-08-07 | 2017-10-17 | Knowles Electronics, Llc | Ingress protection for reducing particle infiltration into acoustic chamber of a MEMS microphone package |
US10131538B2 (en) | 2015-09-14 | 2018-11-20 | Analog Devices, Inc. | Mechanically isolated MEMS device |
US20180160226A1 (en) * | 2016-12-05 | 2018-06-07 | Semiconductor Components Industries, Llc | Reducing or eliminating transducer reverberation |
IT201700103489A1 (en) | 2017-09-15 | 2019-03-15 | St Microelectronics Srl | METHOD OF MANUFACTURE OF A THIN FILTERING MEMBRANE, ACOUSTIC TRANSDUCER INCLUDING THE FILTERING MEMBRANE, ASSEMBLY METHOD OF THE ACOUSTIC TRANSDUCER AND ELECTRONIC SYSTEM |
GB201904005D0 (en) * | 2019-03-22 | 2019-05-08 | Sensibel As | Microphone housing |
US11442155B2 (en) | 2019-10-02 | 2022-09-13 | Semiconductor Components Industries, Llc | Devices, systems and processes for detecting saturation of received echo signals |
US11759822B2 (en) | 2020-01-21 | 2023-09-19 | Semiconductor Components Industries, Llc | Devices, systems and processes for improving frequency measurements during reverberation periods for ultra-sonic transducers |
US11520027B2 (en) | 2020-02-14 | 2022-12-06 | Semiconductor Components Industries, Llc | Devices, systems and processes for ultra-short range detection of obstacles |
US11417611B2 (en) | 2020-02-25 | 2022-08-16 | Analog Devices International Unlimited Company | Devices and methods for reducing stress on circuit components |
CN114374920A (en) * | 2021-12-29 | 2022-04-19 | 瑞声声学科技(深圳)有限公司 | Bone conduction microphone |
Family Cites Families (12)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3118022A (en) * | 1961-08-07 | 1964-01-14 | Bell Telephone Labor Inc | Electroacoustic transducer |
US4016644A (en) * | 1974-03-18 | 1977-04-12 | Kulite Semiconductor Products, Inc. | Methods of fabricating low pressure silicon transducers |
US4203128A (en) * | 1976-11-08 | 1980-05-13 | Wisconsin Alumni Research Foundation | Electrostatically deformable thin silicon membranes |
CA1094229A (en) * | 1976-11-08 | 1981-01-20 | Henry Guckel | Electrostatically deformable thin silicon membranes |
US4225755A (en) * | 1978-05-08 | 1980-09-30 | Barry Block | Capacitive force transducer |
JPS5516228A (en) * | 1978-07-21 | 1980-02-04 | Hitachi Ltd | Capacity type sensor |
GB2044037B (en) * | 1978-12-23 | 1983-03-23 | Tokyo Shibaura Electric Co | Electrostatic microphone |
JPS6234185Y2 (en) * | 1979-10-05 | 1987-09-01 | ||
NL8004351A (en) * | 1980-07-30 | 1982-03-01 | Philips Nv | ELECTRIC CONVERTER. |
US4332000A (en) * | 1980-10-03 | 1982-05-25 | International Business Machines Corporation | Capacitive pressure transducer |
JPS57125600A (en) * | 1981-02-21 | 1982-08-04 | Bulgarsko Radio | Electrostatic acoustic converter |
BG34753A1 (en) * | 1982-01-22 | 1983-11-15 | Knchev | Electrostatic acoustic converter |
-
1983
- 1983-07-07 US US06/511,640 patent/US4533795A/en not_active Expired - Lifetime
-
1984
- 1984-06-25 DE DE8484902570T patent/DE3466918D1/en not_active Expired
- 1984-06-25 JP JP59502526A patent/JP2530305B2/en not_active Expired - Lifetime
- 1984-06-25 EP EP84902570A patent/EP0148893B1/en not_active Expired
- 1984-06-25 WO PCT/US1984/000951 patent/WO1985000495A1/en active IP Right Grant
- 1984-06-27 CA CA000457580A patent/CA1219056A/en not_active Expired
- 1984-07-05 IT IT21761/84A patent/IT1176379B/en active
-
1988
- 1988-03-04 SG SG159/88A patent/SG15988G/en unknown
-
1989
- 1989-02-09 HK HK112/89A patent/HK11289A/en not_active IP Right Cessation
Also Published As
Publication number | Publication date |
---|---|
EP0148893A1 (en) | 1985-07-24 |
JPS60501784A (en) | 1985-10-17 |
EP0148893B1 (en) | 1987-10-21 |
HK11289A (en) | 1989-02-17 |
IT1176379B (en) | 1987-08-18 |
DE3466918D1 (en) | 1987-11-26 |
WO1985000495A1 (en) | 1985-01-31 |
IT8421761A0 (en) | 1984-07-05 |
JP2530305B2 (en) | 1996-09-04 |
US4533795A (en) | 1985-08-06 |
SG15988G (en) | 1988-07-08 |
Similar Documents
Publication | Publication Date | Title |
---|---|---|
CA1219056A (en) | Integrated electroacoustic transducer | |
EP0107843B1 (en) | Acceleration vibration detector | |
EP0782371B1 (en) | Microphone system with reduced in situ acceleration sensitivity | |
US7206428B2 (en) | Acoustic receiver having improved mechanical suspension | |
US7215527B2 (en) | MEMS digital-to-acoustic transducer with error cancellation | |
US8948432B2 (en) | Microphone unit | |
KR20030010560A (en) | A piezoelectric element and an oscillation transducer with a piezoelectric element | |
MXPA97000089A (en) | Systems of acceleration sensitivity microphone in site reduc | |
WO2022223041A1 (en) | Sensing device | |
US4692942A (en) | Electroacoustic transducer with piezoelectric diaphragm | |
CN113316072A (en) | Piezoelectric acoustic transducer with filtering function and manufacturing method thereof | |
US11905164B2 (en) | Micro-electro-mechanical system acoustic sensor, micro-electro-mechanical system package structure and method for manufacturing the same | |
US20130136292A1 (en) | Microphone unit | |
CN109068250B (en) | Microphone and electronic equipment | |
CN207531080U (en) | Mems microphone | |
JPS5979700A (en) | Detector of vibration | |
EP0353092A2 (en) | Apparatus and method for reproducing high fidelity sound | |
JPH08195995A (en) | Detecting element for bone-conduction voice vibration | |
CN105959851B (en) | In-Ear high pitch compensates earphone | |
JP2006311105A (en) | Acoustical sensor | |
KR101738516B1 (en) | Piezoelectric Speaker | |
CN219145557U (en) | Microphone structure and electronic equipment | |
CN217283376U (en) | Packaging part | |
US20230269524A1 (en) | Multi-cavity packaging for microelectromechanical system microphones | |
CN218734951U (en) | Telephone receiver |
Legal Events
Date | Code | Title | Description |
---|---|---|---|
MKEX | Expiry |