JP2011514088A - Monolithic capacitive transducer - Google Patents

Monolithic capacitive transducer Download PDF

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JP2011514088A
JP2011514088A JP2010549201A JP2010549201A JP2011514088A JP 2011514088 A JP2011514088 A JP 2011514088A JP 2010549201 A JP2010549201 A JP 2010549201A JP 2010549201 A JP2010549201 A JP 2010549201A JP 2011514088 A JP2011514088 A JP 2011514088A
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series
fingers
body
comb
comb fingers
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JP5258908B2 (en
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ティエンシェン・ジョウ
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ティエンシェン・ジョウ
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    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04RLOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R19/00Electrostatic transducers
    • H04R19/005Electrostatic transducers using semiconductor materials
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04RLOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R19/00Electrostatic transducers
    • H04R19/02Loudspeakers
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04RLOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R19/00Electrostatic transducers
    • H04R19/04Microphones
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04RLOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R7/00Diaphragms for electromechanical transducers; Cones
    • H04R7/16Mounting or tensioning of diaphragms or cones
    • H04R7/18Mounting or tensioning of diaphragms or cones at the periphery

Abstract

The capacitive transducer includes a substrate having a first surface and a second surface. The first surface of the substrate defines a first plane. The substrate has a cavity with an inner peripheral edge. The cavity extends between the first surface and the second surface. A body having an outer peripheral edge is provided. The body is parallel to the first surface and at least partially closes the cavity. The main body is connected to the base body by an elastic hinge, and when the force is applied, the main body moves perpendicularly to the first surface. A first series of comb fingers are attached to the substrate. The first series of fingers is connected to the first electrical connection. A second series of comb fingers are attached to the body and extend beyond the outer peripheral edge of the body. The second series of comb fingers is connected to a second electrical connection that is insulated from the first electrical connection. The first series of comb fingers and the second series of comb fingers interpenetrate to maintain a relative spacing between the first series of comb fingers and the second series of comb fingers as the body moves. . The first series of comb fingers and the second series of comb fingers define a capacitance. The capacitance is related to the relative position of the first series of comb drive fingers and the second series of comb drive fingers.
[Selection] Figure 1

Description

  This patent document relates to monolithic capacitive transducers such as small capacitive transducers.

  Miniature microphones have gained great popularity in various applications. Such micro-microphones are sub-millimeter size, low cost due to mass production, lower power consumption, higher sensitivity and reliability, for example, hearing aids, mobile phones, PDAs, laptop computers, MP3, digital cameras etc. Is widely recognized as a next-generation product that replaces the conventional electret condenser microphone (ECM). Among all micro microphones, capacitive condenser microphones have many advantages over other technical schemes such as piezoelectric or magnet micro microphones due to their smaller size and higher sensitivity and others.

  A micro condenser microphone usually comprises a sound pressure sensing element (generally a variable capacitor) and a preamplifier IC circuit. One prior art example of a condenser microphone having a parallel plate capacitor is disclosed in US Pat. Prior art condenser microphones have some or all of the disadvantages described below due to the structure and sensing behavior of parallel plate variable capacitors.

US Patent Application Publication No. 2006/0093170 (Zhe et al.), Title of invention “Backplateless Silicon Microphone”

  First, residual film stress on the diaphragm reduces microphone sensitivity. Since flexible diaphragms are usually made from thin films of dielectric and conductive materials, there is residual stress even after film formation, so it is very difficult to control and reduce this residual stress. The stress on the diaphragm directly affects the microphone sensitivity. The compressive residual stress results in a defective, buckled diaphragm. Tensile stress severely reduces the sensitivity of the microphone or, in the worst case, completely destroys the diaphragm.

  Second, the adsorption between the flexible diaphragm and the rigid backplate can cause defective devices during microfabrication or malfunction during operation. If the gap between the flexible diaphragm and the backplate is about a few microns, the ratio of surface area to volume increases and the surface forces that cause adsorption increase accordingly, so the diaphragm is fixed with a greater probability Will adhere to the back plate. Adsorption prevents full separation of the flexible diaphragm suspended during the wet process of sacrificial layer etching and can result in permanent attachment to the fixed backplate. During operation, if the microphone is exposed to a moist environment, water vapor can condense and form a film of water on the diaphragm and backplate surface. If the gap between the two surfaces is reduced during operation, the water film on one surface will contact the opposite surface and the two surfaces will adhere.

  Third, “squeeze membrane” air braking affects the high frequency response and causes noise in the microphone output by generating pressure changes in the microphone structure. For sub-millimeter size capacitive condenser microphones, the air gap needs to be reduced to a few microns to maintain the capacitance value within a range that can effectively drive the input of the buffer amplifier. However, as the air gap narrows, the “squeeze film” braking effect increases rapidly due to the viscous flow of air enclosed between the diaphragm and the backplate. “Squeeze membrane” air braking also affects the sensitivity of the microphone.

  Fourth, the “pull-in” effect of the diaphragm reduces the DC bias voltage, thus reducing the sensitivity of the microphone. The sensitivity increases as the DC bias voltage between the diaphragm and the backplate increases. When the DC bias voltage increases, a large electrostatic attraction is generated between the diaphragm and the back plate. However, in some prior art examples, the gap between the diaphragm and the backplate is narrowed to a few microns, and the diaphragm mechanically is allowed to have some deflection under a certain sound pressure level. Compliance remains fairly low. Greater electrostatic attraction can overcome the mechanical restoring force of the diaphragm, attracting the flexible diaphragm through a small gap and contacting the back plate. This phenomenon is called the “pull-in” effect.

  Fifth, a submillimeter size diaphragm that is fully constrained by the surrounding frame reduces the sensitivity of the microphone. Diaphragm compliance tends to decrease rapidly as the size and thickness of a given diaphragm material decreases. Diaphragm mechanical compliance / stiffness to sound pressure varies with the fourth power of the diaphragm size.

Sixth, the small air gap and flexible diaphragm of the parallel plate capacitive condenser microphone has a large dynamic range because the high sound pressure level drives the flexible diaphragm to contact the back plate over the small air gap. Can not provide.
Seventh, the parasitic capacitance between the flexible diaphragm and the rigid fixed backplate degrades the performance of the microphone. The capacitance between the diaphragm and the back plate has two parts. The first part varies with the acoustic signal and is preferred for the microphone. The second part is a parasitic capacitance that does not change depending on the acoustic signal. Parasitic capacitance degrades performance and must be minimized. However, the parasitic capacitance is related to the configuration of the parallel plate type silicon microphone in the prior art.

  Last but not least, parallel plate capacitive condenser microphones are quite complex to manufacture and costly. At present, the prior art cannot provide an economical manufacturing method for mass production of microphones. Some methods of manufacturing sensing elements disclosed in the prior art are not compatible with standard IC CMOS manufacturing processes, resulting in larger hybrid packages and higher manufacturing costs.

  The capacitive transducer includes a substrate having a first surface and a second surface. The first surface of the substrate defines a first plane. The substrate has a cavity with an inner peripheral edge. The cavity extends between the first surface and the second surface. A body having an outer peripheral edge is provided. The body is parallel to the first surface and at least partially closes the cavity. The main body is connected to the base body by an elastic hinge, and when the force is applied, the main body moves perpendicularly to the first surface. A first series of comb fingers are attached to the substrate. The first series of comb fingers is connected to the first electrical connection. A second series of comb fingers are attached to the body and extend beyond the outer peripheral edge of the body. The second series of comb fingers is connected to a second electrical connection that is separated from the first connection. The first series of comb fingers and the second series of comb fingers interpenetrate as the body moves so that the first series of comb fingers and the second series of comb fingers maintain a relative spacing. The first series of comb fingers and the second series of comb fingers generate a capacitance. The capacitance is related to the relative position of the first series of comb drive fingers and the second series of comb drive fingers.

  These and other features will become more apparent from the following description, made with reference to the accompanying drawings. The drawings are for illustration only and are not intended to be limiting.

1 is a cross-sectional perspective view of a microphone according to a first embodiment. It is sectional drawing which shows the structure of the SOI wafer of the transducer by 1st Embodiment. 1 is a cross-sectional view of an SOI wafer after depositing an oxide layer on top and bottom surfaces according to a first embodiment. FIG. 2 is a cross-sectional view of an SOI wafer after anisotropic silicon etching of the backside cavity and oxide etching from the backside of the wafer. FIG. 1 is a perspective view of an SOI wafer after oxide patterning and etching on the front surface of the wafer according to a first embodiment; FIG. FIG. 6 is a perspective view of the SOI wafer in FIG. 5 after pattern formation of a photoresist layer. 6b is an enlarged perspective view of the comb finger and hinge portion C shown in FIG. 6a. FIG. FIG. 7 is a perspective view of the transducer in FIG. 6 after reactive ion etching (RIE) of the oxide layer. FIG. 7b is an enlarged perspective view of the comb finger and hinge portion D shown in FIG. 7a. FIG. 8 is a perspective view of the transducer in FIG. 7 after a first deep reactive ion etch (DRIE) of silicon. FIG. 9 is a perspective view of the transducer in FIG. 8 after removal of the photoresist. FIG. 9b is an enlarged perspective view of the comb finger and hinge portion E shown in FIG. 9a. FIG. 10 is a perspective view of the transducer in FIG. 9 after a second deep reactive ion etch (DRIE) of silicon. 10b is an enlarged perspective view of the comb finger and hinge portion F shown in FIG. 10a. FIG. FIG. 11 is a perspective view of the transducer of FIG. 10 after removing the oxide on the front surface and partially etching the buried oxide layer to release the diaphragm and moveable finger. It is a perspective view of the section of the microphone by a 2nd embodiment. FIG. 13 is a plan view of the microphone shown in FIGS. 1 and 12. FIG. 6 is a perspective view of a cross-section of a microspeaker with a larger back cavity and a higher comb finger according to a third embodiment. FIG. 6 is a perspective view of a cross-section of a microspeaker with a larger back cavity and a higher comb finger according to a fourth embodiment. FIG. 9 is a perspective view of a cross-section of a microspeaker with a larger back cavity and a higher comb finger according to a fifth embodiment. It is a perspective view of the section of the N type substrate of a transducer by a 6th embodiment. FIG. 10 is a perspective view of a cross section of an N-type substrate after epitaxial growth of a silicon layer by P ++ implantation / diffusion or P doping according to a sixth embodiment. FIG. 19 is a cross-sectional perspective view of the substrate shown in FIG. 18 after anisotropic silicon etching of the back cavity according to the sixth embodiment. FIG. 20 is a cross-sectional perspective view of the transducer in FIG. 19 after a deep reactive ion etching (DRIE) treatment of silicon using the self-aligned process disclosed herein.

  The device described below is a sub-millimeter sized micro-capacitance capacitor with higher sensitivity and greater dynamic measurement range that overcomes the shortcomings of the parallel plate capacitor silicon microphone disclosed in the prior art. The microphone sensing element structure reduces or eliminates residual stress effects, adsorption, “squeeze film” air braking and “retraction”. This type of transducer is used in microphones and microspeakers used in hearing aids, cell phones, PDAs, laptop computers, MP3 players, digital cameras and other applications. It may also be used as an accelerometer, pressure sensor, pump actuator, optical switch and optical interferometer. The design and fabrication methods described below are also used for small low voltage electrostatic drive microspeakers, accelerometers and others. In one embodiment, the sensing and operating structure fabrication method is compatible with a standard IC COMS process that forms a monolithically integrated miniature silicon capacitive transducer.

  Vertical comb drive structure that enables sensing or actuation eliminates thin film stress, "pull-in" effect and "squeeze membrane" air braking on diaphragm in parallel plate capacitive sensing and actuation in prior art examples . The working capacitance of the device is obtained by interdigital vertical comb fingers. The vertical comb finger structure eliminates the need for a backplate, with micromachining challenges and performance sacrifices. The discussion here includes sub-millimeter size silicon capacitive microphones with higher sensitivity and wider dynamic range, small electrostatic drive microphone speakers with low power consumption and low drive voltage, and even small capacitance acceleration. Provides design and microfabrication methods for both metering and the like.

  The same structural design principles can be used for either a sensing mode that can be applied to a microphone or accelerometer or the like, or an operating mode that can be applied to a microphone speaker or the like.

Detection Mode FIGS. 1, 11 and 12 show suitable examples of device structures and designs used for detection that are useful, for example, as microphones or accelerometers. In this embodiment, the device is formed using an SOI (Silicon on Insulator) substrate. The capacitive transducer is made from conductive bulk silicon deposited on a substrate, also referred to below as carrier wafer 12. The diaphragm 32 is supported by four hinges 29a, 29b, 29c and 29d connected to the corners of the rectangular diaphragm 32. The diaphragm 32 is an object that moves when a force is applied, and is connected to fixed anchors 37a, 37b, 37c, and 37d mounted on the base body by meandering silicon hinges 29a, 29b, 29c, and 29d, respectively. Anchors 37a, 37b, 37c and 37d are located on dielectric material layer 11, such as oxide. The sensing element comprises a vertical comb drive structure including a first series of fixed comb fingers 35 and a lower second series of movable comb fingers 36.

  All of the movable comb fingers 36 are formed on the outer edge of the diaphragm 32. It will be appreciated that the comb fingers 35 and 36 need not be disposed on all sides of the diaphragm 32 as shown. For example, the fingers may be disposed on two parallel edges of the diaphragm 32. A fixed comb finger structure 35 is formed around the diaphragm 32 and is fixed on the dielectric material 11 by anchors 38a, 38b, 38c and 38d. Diaphragm 32, hinges 29a, 29b, 29c and 29d, anchors 37a, 37b, 37c, 37d, 38a, 38b, 38c and 38d, vertical comb fingers 35 and 36, and electrical interconnection structures 39a, 39b and 39c are identical. Made of a layer of conductive material. This conductive material is, for example, conductive single crystal silicon 10 present on the top surface of the layer of dielectric material 11 that separates the silicon layer 10 from the base substrate 12 in the SOI structure.

  Electrical interconnect structures 39a, 39b and 39c are electrically connected to all four fixed comb finger structures 35 present around diaphragm 32. On the other hand, the movable comb finger structure 36 is electrically connected by the diaphragm 32. Thus, any anchors 37a, 37b, 37c and 37d can be used as electrical connection points, and any anchors 38a, 38b, 38c and 38d can be integrated on-chip IC circuits if a hybrid package is required for the transducer. Or as a separate electrical connection point for wire bonding pads.

  As apparent from FIG. 1, the outer peripheral edge of the diaphragm 32 partially overlaps the inner peripheral edge of the cavity 40. When used as a microphone, this overlapping portion of the diaphragm 32 and the carrier wafer 12 forms a long air flow path 33 between the diaphragm 32 having the movable finger 36 and the carrier wafer 12, thereby leaking around the diaphragm 32. Is needed to reduce. This creates a much higher fluid resistance and improves the low frequency response of the transducer. Another way to reduce leakage is to use a lightweight material such as a polymer (not shown) to reduce the gap between the diagram 32 with the movable fingers 36 and the carrier wafer 12, and the diaphragm 32 on the cavity 40 side. Is to coat. This may be performed, for example, by sputtering or other deposition techniques. During deposition, material may also be deposited on the sides of the cavity. However, this is not undesirable because it also reduces the gap.

  The capacitance increases with the number of comb fingers. For sub-millimeter sized diaphragms, it is possible to obtain a picofarad working capacitance equivalent to that achieved by the prior art parallel plate structure by forming a sufficient number of movable comb fingers 36. It is. When the diaphragm 32 receives a pressure wave such as sound pressure or acceleration / deceleration, the diaphragm 32 moves up and down by piston movement. The serpentine shape of the springs 29a, 29b, 29c and 29d helps to generate a generally linear motion throughout. The movement of the diaphragm 32 can be detected by monitoring the change in capacitance between the movable comb finger 36 and the fixed comb finger 35. In addition, the change in capacitance between the movable comb finger 36 and the fixed carrier wafer 12 may be measured, and this measurement method may include, for example, sensor sensitivity by measuring the difference in change in capacitance. Can be increased. In addition, because of the use of vertical comb finger structure and flexible hinges, the capacitance change is more sensitive to sound pressure 34 or acceleration / deceleration due to the fringing effect of the small comb fingers, resulting in a transducer The sensitivity becomes higher. The flexible hinge helps the diaphragm 32 maintain piston motion instead of the parabolic deformation of the diaphragm in the prior art.

  The etching holes 20a, 20b, 20c and 20d on the diaphragm 32 are for reducing the mass of the diaphragm 32 in order to obtain a better high frequency response. The transducer does not require a backplate because the transducer diaphragm 32 is supported in a suspended state on the cavity 40 of the carrier wafer 12. Release of atmospheric pressure is not necessary with this microphone.

Mode of Operation FIGS. 14, 15 and 16 show a device designed to be used in the mode of operation, for example for a microspeaker. The same reference numerals are used as in the embodiment described above. The silicon capacitive transducer (microspeaker) includes a diaphragm 32 supported by four hinges 29a, 29b, 29c and 29d. Diaphragm 32 is made from bulk conductive silicon that is connected to a fixed anchor by serpentine-shaped silicon hinges 29a, 29b, 29c and 29d. The four hinges are connected to anchors 37a, 37b, 37c and 37d located on the dielectric material 11. The actuating element is a vertical comb drive structure and includes a plurality of movable comb fingers 36 and a plurality of fixed comb fingers 35. A movable comb finger 36 is formed on the outer edge of the diaphragm 32. Fixed comb fingers 35 are formed around diaphragm 32 and are fixed on dielectric material 11 by anchors 38a, 38b, 38c and 38d.

  Diaphragm 32, hinges 29a, 29b, 29c and 29d, anchors 37a, 37b, 37c, 37d, 38a, 38b, 38c and 38d, vertical comb fingers 35 and 36, and electrical interconnection structures 39a, 39b and 39c Is made from the same layer as the layer of conductive silicon 10 on the top surface of the dielectric material 11. Electrical interconnect structures 39a, 39b and 39c electrically connect all four fixed comb finger structures 35 around diaphragm 32. Anchors 37 and 38 are used as electrical connection points for integrated on-chip IC circuits or for bond pads if the transducer requires a hybrid package. For submillimeter or millimeter sized diaphragms, a sufficient number of movable comb fingers 36 are formed at the diaphragm edges to provide a picofarad equivalent to the capacitance achieved by the prior art parallel plate structure. It is possible to obtain a working capacitance.

  When an actuation voltage is applied between the anchors 37 and 38, a high electric field is formed between the fixed comb finger 35 and the movable finger 36. The resulting electrostatic force drives the diaphragm 32 to generate a sound pressure wave. Resilient hinges 29a, 29b, 29c and 29d maintain the piston motion of diaphragm 32 instead of the parabolic deformation common to many prior art devices. The etching holes 20a, 20b, 20c and 20d on the diaphragm 32 are for reducing the mass of the diaphragm 32 in order to obtain a better high frequency response. The transducer does not have a back plate because the transducer diaphragm 32 is supported in a suspended state on the cavity 40 of the carrier wafer 12.

  By comparing the above operating mode embodiment with the previously described sensing mode embodiment, several differences can be shown. In an operational mode embodiment, the outer peripheral edge is present in the inner peripheral edge of the cavity 12 such that the diaphragm 32 only partially covers the cavity 12. In addition, the fixed comb fingers 35 are higher than in the previously described embodiment. These differences are intended to improve performance in operating modes, as will be described in more detail below.

Manufacturing FIGS. 2-11 illustrate the main process steps used to manufacture either sensing or actuation devices.


The general process for manufacturing a capacitive transducer is firstly on a layer deposited on a substrate to define the position of one of a series of movable fingers and a series of fixed fingers. Applying one etching mask. The location of the body and spring is also defined by the first mask. A second etch mask is then applied to position the series of movable fingers, the series of fixed fingers, the body and the spring, the body connected to the series of movable fingers and the spring, and the series of movable fingers Interpenetrates the fixed fingers. The second etch mask is then used to etch the layer and the first etch mask. The second etch mask is removed and the layer is then etched in such a way that one of the series of movable fingers and the series of fixed fingers is shorter than the other of the series of movable fingers and the series of fixed fingers. Etched using a mask. The body, the spring and the series of movable fingers are separated using etching so that when a force is applied to the body, the body moves in parallel with the substrate. Variations in this process for implementing various embodiments will be apparent from the description below.

  FIG. 2 shows a wafer used for the transducer. The process for making such a wafer is not described here. Layer 10 is preferably a layer of conductive material such as single crystal bulk silicon or low stress polysilicon. Layer 11 is a layer of dielectric material such as oxide or nitride. The material of the carrier wafer 12 is normal silicon or glass. The substrate can also be purchased from any SOI (silicon on insulator) vendor. Although various materials can be used, SOI structured wafers are used to describe the process of the first embodiment.

  FIG. 3 shows the SOI wafer after growth of layers of oxides 13 and 16 on the top and bottom surfaces of the wafer. A thermal oxidation process is used to grow the oxide. FIG. 4 shows an anisotropic etching of silicon in KOH (potassium hydroxide) or TMAH (tetramethylammonium hydroxide) followed by protection of the upper surface of the SOI wafer with buffered HF (hydrofluoric acid). Figure 3 shows the substrate after oxide etching in solution. The cavity 14 is formed in the oxide layer 11 and the cavity 40 is formed in the carrier silicon wafer 12. Cavity 40 is also etched using any other anisotropic etching method such as deep reactive ion etching (DRIE) of silicon.

  An important process for forming a vertical comb drive structure is to ensure perfect alignment of the fixed and movable fingers 35 and 36. If both fingers are not aligned, the gap between one movable finger and two adjacent fixed fingers or vice versa (the gap between one fixed finger and two adjacent movable fingers) The air gaps between them are equal, and as a result, different electrostatic forces act on the right and left sides of the fins, causing the lateral movement of the movable fingers 36. This undesirable lateral movement causes malfunction of the comb drive structure.

  The manufacturing process applies a self-alignment process to finely process the vertical comb drive structure. FIG. 5 shows the patterning of the oxide layer on the top surface of the SOI wafer. Oxide patterning is performed using conventional lithography and oxide etching processes such as RIE (Reactive Ion Etching). A pattern of oxide 22 is formed on the movable fingers. Patterns for anchors 37 and 38 are formed in regions 17a, 17b, 17c, 17d, 18a, 18b, 18c and 18d. A pattern for the electrical interconnection structure 39 is formed in the regions 21a, 21b and 21c. In regions 201a, 201b, 201c and 201d, no oxide is present to form silicon holes 20 on diaphragm 32.


FIG. 6a shows the SOI wafer shown in FIG. 5 after formation of the photoresist pattern. This lithography process defines the shape of the movable fingers and hinges and redefines the oxide pattern shown in FIG. In order to accommodate the expected large alignment tolerances during the process, the geometry of the oxide pattern of FIG. 5 is larger than the desired device geometry. An enlarged perspective view of the comb fingers 25 and 27 and the part C of the hinge 26 shown in FIG. 6a is shown in FIG. 6b. The final shapes of movable comb finger 36, fixed comb finger 35, diaphragm 32, and hinges 29a, 29b, 29c and 29d are suitably defined by photoresists 25, 27, 23 and 26, respectively. Excess oxide 24 in oxide layer 13 is removed by a subsequent oxide RIE process. FIG. 7 shows the SOI wafer in FIG. 6 after an oxide RIE etch process. An enlarged perspective view of the comb fingers 25 and 27 and the part D of the hinge 26 shown in FIG. 7a is shown in FIG. 7b.

The patterned photoresist layer is used as an etch mask material for the first silicon DRIE etch. The oxide layer 11 is used as an etch stop layer for the first silicon DRIE. FIG. 8 shows the substrate after the first silicon DRIE.
The photoresist is removed after the first silicon DRIE etch. FIG. 9b is an enlarged perspective view of the comb fingers 28 and 30 and the portion E of the hinge 29a shown in FIG. 9a. Hinge 29a and fixed comb finger 28 do not have oxide on the top surface, but movable finger 30 and diaphragm 32 have oxide on the top surface for subsequent second silicon DRIE etching. The second silicon DRIE etch forms the lower fixed comb fingers, resilient hinges 29a, 29b, 29c and 29d and the holes 20. FIG. 10b shows an enlarged perspective view of the comb fingers 28 and 30 and the portion F of the hinge 29a shown in FIG. 10a.

  After the etching with buffered HF, the diaphragm 32, the hinges 29a, 29b, 29c and 29d and the movable comb finger 36 are in a form in which the oxide layer 11 is removed. The completed transducer is shown in FIGS. The microfabrication process described here does not include a process for integration with a standard IC COMS process. However, it is very easy for those skilled in the art to achieve such integration. FIG. 12 shows a cross-sectional perspective view of a microphone according to the second embodiment having a different comb finger configuration. In FIGS. 1 and 11, the movable finger 35 is higher than the fixed finger 36, whereas in FIG. 12, the movable finger 35 and the fixed finger 36 are offset. A series of fingers may be higher in height than the other series of fingers or may be placed at a higher position. Offset fingers are more difficult to manufacture but have a larger effective range of motion or consume less power in the operating mode.

  Referring to FIG. 13, the gap 41 between the comb fingers 35 and 36 and the gap 42 between the hinges 29a, 29b, 29c and 29d and the comb fingers 36 are each about 2 μm, thereby reducing the low frequency of the transducer. Provide sufficient resistance to response. If 2 μm can be achieved for the gaps 41 and 42 using current microfabrication technology, the long air flow path 33 shown between the diaphragm 32 and the carrier wafer 12 is not necessary.

  If the device is intended to be used as a microspeaker, it is preferable to generate higher sonic pressure levels from a small silicon microspeaker due to greater translation of diaphragm 32 during operation. Therefore, the thicker silicon layer 10 must be used as shown in FIG. 14 so that the height difference between the fixed finger 35 and the movable finger 36 is greater. In this way, a greater electrostatic force and a corresponding greater actuation translation between the fixed finger 35 and the movable finger 36 is expected. Larger silicon cavities 40 are also formed in the carrier wafer 12, so that the diaphragm 32 gains greater up and down translation without mechanical interference. An embodiment of a small microspeaker is shown in FIG.

  One advantage of silicon microspeakers is that they consume less power due to electrostatic drive. In addition, the same hinge design reduces the overlap area between the fixed and movable comb fingers so that the fixed and movable comb fingers are offset, thereby reducing the drive voltage for the silicon microspeaker. Can be further reduced. This is because the electric field in the overlap region between the fixed comb fingers and the movable comb fingers 35 and 36 prevents the structural movement of the diaphragm 32. One way to reduce the overlap area between the fixed comb finger 35 and the movable comb finger 36 is to etch away the lower portion of the fixed comb finger 35 during manufacture of the designed SOI wafer. . For example, the device layer may be pre-etched before being bonded to the carrier silicon wafer. 15 and 16 show an embodiment in which the lower portion of either the fixed comb finger 35 or the movable finger 36 has been etched away.

  Another alternative embodiment is shown in FIG. 20, which is composed of an N-type substrate and a plurality of P-type structures. The normal N-type silicon wafer 18 in FIG. 17 is the starting material for the transducer. A layer of P ++ silicon 49 is formed on the top surface of N-type silicon 48 by either epitaxial growth or doping / diffusion or implantation / diffusion as shown in FIG. P ++ silicon 49 is used to form the transducer. Referring to FIG. 19, P ++ silicon 49 is used as a silicon etch stop layer to form diaphragm 50 by silicon anisotropic etching with either KOH or TMAH. This silicon anisotropic etching etches the N-type substrate 18 but does not etch the P ++ silicon 49.

  The embodiment shown in FIG. 20 is formed using the self-alignment process method described above with reference to FIGS. The fixed comb finger 35 is electrically insulated from the movable comb finger 36 and the diagram 32 by a PN junction formed between the N-type layer and the P-type layer. Transducers made in accordance with this embodiment reduce wafer costs and increase flexibility for integration with IC CMOS processes.

  In this patent document, the term “comprising” is used in a non-limiting sense and includes items that follow this term, but does not exclude items that are not specifically mentioned. Reference to an element by the indefinite article “a” does not exclude the possibility that more than one element exists unless the context explicitly requires that only one element exist.

  It will be apparent to those skilled in the art that modifications can be made to the embodiments described without departing from the spirit and scope as defined in the claims.

12 Substrate 29a, 29b, 29c, 29d Hinge 32 Diaphragm 35 Fixed comb finger 36 Movable comb finger 40 Cavity

Claims (25)

  1. A substrate having a first surface and a second surface, wherein the first surface defines a first plane, the substrate having a cavity with an inner peripheral edge, the cavity comprising the first surface and the first surface. A substrate extending between the two surfaces;
    A body having an outer peripheral edge, wherein the body is parallel to the first surface and at least partially closes the cavity, the body applying the force, the body is the first surface; A body connected to the substrate by a resilient hinge so as to move perpendicular to the
    A first series of comb fingers attached to the substrate and connected to a first electrical connector;
    A second series of comb fingers attached to the body and extending beyond an outer peripheral edge of the body, the second series of comb fingers being insulated from the first electrical connection. Connected to a second electrical connection, the first series of comb fingers and the second series of comb fingers when the body moves, the first series of comb fingers and the second series of comb fingers So as to maintain a relative spacing, the first series of comb fingers and the second series of comb fingers defining a capacitance, wherein the capacitance is the first series of comb fingers. A second series of comb fingers related to the relative positions of the comb drive fingers and the second series of comb drive fingers;
    A capacitive transducer comprising:
  2.   The capacitive transducer of claim 1, wherein the force is a pressure wave acting on the body.
  3.   The capacitive transducer according to claim 1, wherein the force is an electrical signal supplied between the first electrical connection body and the second electrical connection body.
  4.   The capacitive transducer of claim 1, wherein the force is an acceleration of the substrate having an element perpendicular to the first surface.
  5.   The capacitive transducer of claim 1, wherein the body is rectangular and the body has a first series of comb drivers on at least two parallel edges of the body.
  6.   The capacitive transducer of claim 5, wherein the body has a spring attached to each corner of the body.
  7.   The capacitive transducer of claim 1, wherein the spring is serpentine.
  8.   The capacitive transducer of claim 1, wherein the spring is attached to the substrate by an anchor, and each of the anchor, the spring, the body, and the second series of comb fingers is conductive.
  9.   One or more first series of comb fingers and one or more second series of comb fingers, each of said first series of comb fingers being electrically connected together, said second series of comb fingers The capacitive transducer of claim 1, wherein each of the comb fingers are electrically connected together.
  10.   The capacitive transducer of claim 1, wherein the first series of comb fingers is higher in height than the second series of comb fingers.
  11.   The capacitive transducer of claim 1, wherein the second series of comb fingers is higher in height than the first series of comb fingers.
  12.   The capacitive transducer of claim 1, wherein the first series of comb fingers are offset from the second series of comb fingers in a direction of movement of the body.
  13.   The capacitive transducer of claim 1, wherein the outer peripheral edge of the body is within the inner peripheral edge of the cavity.
  14.   The capacitive transducer of claim 1, wherein the outer peripheral edge of the body extends beyond the inner peripheral edge of the cavity.
  15.   The capacitive transducer of claim 14, wherein a lightweight material is deposited on a surface of the body facing the cavity to restrict air flow.
  16.   15. The capacitive transducer of claim 14, wherein the first series of comb drive fingers and the second series of comb drive fingers interpenetrate closely enough to limit air flow. .
  17.   The capacitive transducer of claim 1, wherein the capacitance is also related to a relative position of the second series of comb fingers and the first surface of the substrate.
  18.   The base is an n-type material, the first electrical connection body and the second electrical connection body are p-type materials, and the first electrical connection body and the second electrical connection body are directly connected to the base body. The capacitive transducer of claim 1.
  19.   The body, the first series of comb fingers and electrical connections, the second series of comb fingers, the first electrical connections, the second electrical connections, and the spring are made from n-type silicon; The capacitive transducer of claim 1, wherein the substrate is made of n-type silicon.
  20.   The capacitive transducer according to claim 1, wherein a dielectric layer is disposed between the first electrical connection body and the second electrical connection body.
  21. Applying a first etching mask on the layer to define the position of one of the series of movable fingers and the series of fixed fingers, the layer being provided on the substrate;
    Applying a second etching mask to define the series of movable fingers, the series of fixed fingers, a body and a spring, the body connected to the series of movable fingers and the spring; A movable finger interpenetrating with the series of fixed fingers;
    Etching the layer and the first etching mask using the second etching mask;
    Removing the second etching mask;
    Using the etched first etching mask such that one of the series of movable fingers and the series of fixed fingers is shorter than the other of the series of movable fingers and the series of fixed fingers. Etching the layer;
    Separating the body, the spring and the series of movable fingers using etching so that the body moves parallel to the base when a force is applied to the body;
    A method of manufacturing a capacitive transducer comprising:
  22.   The manufacturing method according to claim 21, wherein the etching includes deep reactive ion etching (DRIE).
  23.   The method of claim 21, wherein the layer is a silicon wafer and the silicon wafer is bonded to the substrate using one of fusion, anodic bonding and epoxy resin bonding.
  24.   The method of claim 21, wherein the layer is a layer of p-type material, the substrate is made of n-type material, and the layer is provided on the substrate by one of doping, implantation, and deposition. .
  25.   The method of claim 21, wherein the position of the body and the spring is defined by the first etching mask.
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