Electrostatic transducer and method for manufacturing the same

Abstract

The present invention provides an electrostatic converter and a method for manufacturing the electrostatic converter. The electrostatic converter can be applied to various sensors, can obtain a high SN ratio, and can increase the degree of freedom in the configuration and structure of the portion for detecting changes in electrostatic capacitance. The displacement plate (12) has a fixed portion (12a) fixed to the support (11) and a variable portion (12b) provided so as to be variable relative to the fixed portion (12a). The detection unit (13) is mounted in such a manner that at least a part thereof can vary together with the variable portion (12b), and is provided in such a manner that it can detect the variation of the variable portion (12b) as a change in electrostatic capacitance. The detection unit (13) is disposed in a vacuum or low-pressure space (19).

Description

Technical Field

[0001] The invention relates to an electrostatic converter and a method for manufacturing the electrostatic converter. Background Art

[0002] The electrostatic transducer is one of the basic components of MEMS. Its basic working principle is to set opposing electrodes with a gap, apply a bias voltage between them, and detect the change in the relative distance between the electrodes as a change in electrostatic capacitance. The electrostatic transducer is also used as an actuator that applies a voltage between two electrodes and drives one or both of these electrodes by electrostatic attraction. If this electrostatic transducer is used, it is possible to detect or control the tiny movements of MEMS.

[0003] On the other hand, since MEMS is very small, the detection limit of the electrostatic transducer is dominated by noise. Among the various noises, there is noise generated by damping caused by the gas (air) existing in the gap between the two electrodes, that is, the electrostatic gap. This is the dominant noise in electrostatic MEMS microphones, for example.

[0004] To eliminate the noise caused by gas damping in the electrostatic gap, the sensor can be vacuum sealed. This method is possible and commonly used in inertial sensors, for example. However, there are also devices such as microphones, ultrasonic sensors, mass sensors, scanning probes, etc. that are difficult to vacuum seal.

[0005] Among these, there is a microphone in which a detection unit for electrostatic capacitance is arranged between two diaphragms, and these diaphragms are connected by pillars so that the closed space between each diaphragm becomes a vacuum (for example, refer to Patent Documents 1 or 2). In this microphone, the pillar synchronizes the movement of the two diaphragms and prevents the closed space between the diaphragms from being destroyed due to the pressure difference between the atmosphere and the vacuum. In this way, the noise caused by gas damping is reduced, the SN ratio is improved, and a higher sound recognition rate is achieved as a microphone.

[0006] In addition, there are other microphones in which the diaphragm and the electrostatic capacitance detection part are separated in the device plane, the latter is arranged in a vacuum space, and the two are connected by a link mechanism (for example, refer to non-patent literature 1 or 2). In this microphone, the diaphragm is connected to one end of the connecting rod, the detection part is connected to the other end, and a hinge as a support part is arranged in the center of the connecting rod. In addition, the electrostatic capacitance detection part is a parallel plate type, and moves like a seesaw using a link mechanism, that is, it moves in the out-of-plane direction.

[0007] In addition, there are also microphones that utilize the piezoelectric effect as MEMS microphones (acoustic transducers). For example, as a piezoelectric MEMS microphone, there is a microphone having the following structure: a plate to which pressure is applied is in the form of four triangular cantilever beams with a piezoelectric layer sandwiched between a pair of electrode layers, and they are arranged in a quadrilateral manner (for example, refer to patent documents 3 to 5 or non-patent document 3). In a piezoelectric MEMS microphone, if the plate to which pressure is applied is made into a diaphragm shape with a fixed periphery, the performance will deteriorate due to the stress of the piezoelectric film, so such a structure is adopted. There is no electrode gap in the piezoelectric transducer, and noise caused by gas damping in the electrode gap is not generated. However, since noise caused by dielectric loss of the piezoelectric film is generated, a high SN ratio like the MEMS microphone described in patent documents 1 or 2 cannot be obtained.

[0008] Prior art literature

[0009] Patent Literature

[0010] Patent Document 1: U.S. Patent No. 9181080

[0011] Patent Document 2: U.S. Patent Application Publication No. 2016 / 0066099

[0012] Patent Document 3: Japanese Patent No. 5936154

[0013] Patent Document 4: U.S. Patent No. 9055372

[0014] Patent Document 5: Japanese Patent Application Publication No. 2011-4129

[0015] Non-patent literature

[0016] Non-patent literature 1: Samer Dagher, Carine Ladner, Stephane Durand and Loic Joet, "NOVEL HINGE MECHANISM FOR VACUUM TRANSDUCTION HIGH PERFORMANCE CAPACITIVE MEMS MICROPHONES," Transducers 2019-EUROSENSORS XXXIII, Berlin, GERMANY, 23-27 June 2019, p. 663-666

[0017] Non-patent document 2: Samer Dagher, Frederic Souchon, Audrey Berthelot, Stephane Durand and Loic Joet, "FIRST MEMS MICROPHONE BASED ON CAPACITIVE TRANSDUCTION IN VACUUM," IEEE MEMS 2020, Vancouver, CANADA, 18-22 January, 2020, p. 838-841

[0018] Non-patent document 3: Robert Littrell and Ronald Gagnon, “PIEZOELECTRIC MEMSMICROPHONE NOISE SOURCES,” Solid-State Sensors, Actuators and Microsystems Workshop, 2016, p. 258-261 Summary of the invention

[0019] 1. Technical issues to be resolved

[0020] The MEMS microphones described in Patent Documents 1 and 2 have a very high SN ratio, but since the configuration of the detection unit for detecting changes in electrostatic capacitance is limited to the space between the diaphragms, there is a technical problem that the degree of freedom of the structure is small. Therefore, although this structure is effective in microphones and ultrasonic sensors, there is a technical problem that it cannot be applied to other sensors such as mass sensors and scanning probes. In addition, even when it is used as a microphone, the size of the detection unit is limited to less than the size of the diaphragm, which also has a technical problem that the improvement of sensitivity or SN ratio is limited.

[0021] The size of the diaphragm of the MEMS microphone described in non-patent literature 1 and 2 is independent of the size of the electrostatic capacitance detection unit, and their sizes can be freely designed according to the desired specifications. However, the connecting rod that transmits the movement of the diaphragm to the detection unit is connected from the atmosphere to the vacuum through the diaphragm located at the hinge part, so there is a technical problem that the movement of the connecting rod is hindered by the diaphragm, and the SN ratio is reduced. In addition, if the diaphragm is thinned or enlarged, the rigidity of the diaphragm decreases. In principle, the connecting rod is easy to move, but the diaphragm will deform due to the pressure difference between the atmosphere and the vacuum, which becomes an error of the sensor, and due to the stress of the deformed diaphragm, the connecting rod is ultimately difficult to move, and the SN ratio is reduced.

[0022] The present invention is completed with a focus on such technical problems, and its purpose is to provide an electrostatic transducer and a method for manufacturing an electrostatic transducer, which can be applied to various sensors, can obtain a higher SN ratio, and can improve the configuration and structural freedom of the part that detects changes in electrostatic capacitance.

[0023] (II) Technical solution

[0024] In order to achieve the above-mentioned purpose, the electrostatic converter of the present invention is characterized in that it comprises: a support body; a displacement plate, which has a fixed portion fixed to the support body, and a variable portion arranged in a manner that can be moved relative to the fixed portion; and a detection unit, which is installed in a manner that at least a part can move together with the variable portion, and is arranged in a manner that the change of the variable portion can be detected as a change in electrostatic capacitance, and the detection unit is configured in a vacuum or low-pressure space.

[0025] The electrostatic transducer of the present invention is preferably a MEMS device. Since the detection unit of the electrostatic transducer of the present invention is arranged in a vacuum or low-pressure space so as to detect the change of the change portion of the displacement plate as the change of the electrostatic capacitance, it is not easily affected by damping caused by surrounding fluids such as air or liquid. Therefore, noise can be reduced and a higher SN ratio can be obtained.

[0026] In addition, in order to detect the change of the variable portion, it is sufficient to install at least a part of the detection unit in a manner that can be changed together with the variable portion, and the other part of the detection unit (hereinafter referred to as the "change detection unit") can be arranged at the variable portion or at a stable position outside the variable portion. In addition, by arranging the change detection unit at a position that does not hinder the change of the variable portion, the structure of the change detection unit can be configured relatively freely. In this way, the electrostatic converter of the present invention can increase the degree of freedom of configuration and structure of the detection unit that detects the change of electrostatic capacitance.

[0027] With regard to the electrostatic converter of the present invention, since the change detection unit is arranged at a position other than the change unit, the change unit and the change detection unit can be separated, and thus they can be independently designed according to the required performance, and the degree of freedom of design is high. For example, the following structure can be set: the change unit is reduced to improve the resistance to excessive pressure input and mechanical collision, and the change detection unit is enlarged to improve its sensitivity. In this case, since the change detection unit is arranged in a vacuum or low-pressure space, even if the sensitivity of the change detection unit is increased, the increase in noise can be suppressed.

[0028] In addition, regarding the electrostatic converter of the present invention, since the detection unit is arranged in a vacuum or low-pressure space, there is no need for a structure such as a diaphragm that separates the atmosphere and the vacuum or reduced-pressure space in the middle of the detection unit as described in non-patent documents 1 and 2, and the movement of the detection unit will not be hindered by such a structure. In addition, in non-patent documents 1 and 2, the portion detecting electrostatic capacitance is a parallel plate type that moves in the out-of-plane direction, but the electrostatic converter of the present invention can also be designed to have a structure that can move in any direction of the in-plane direction and the out-of-plane direction, or a structure that can move in both directions.

[0029] In the electrostatic converter of the present invention, as a structure in which the change detection part is arranged at a position other than the change part, for example, the detection unit may also have: an elongated connecting part having one end fixed to the change part and the other end extending toward the fixed part; and a change detection part connected to the other end of the connecting part and arranged in a manner that the change of the other end can be detected as the change of the change part. In this case, the change of the change part can be amplified by the connecting part and transmitted to the change detection part. The change detection part can be arranged at any position as long as it is at a position other than the change part, for example, it can be arranged at the fixed part or the support body.

[0030] In the electrostatic converter of the present invention, the change detection part can be of any structure as long as it can detect the change of the change part as the change of electrostatic capacitance. For example, it can be a structure in which the spacing and overlap of electrodes for detecting electrostatic capacitance change according to the change of the change part, or it can be a differential structure.

[0031] The electrostatic converter of the present invention may also have a reinforcing portion provided in such a manner that the variable portion is uniaxially bent and displaced in the thickness direction of the displacement plate. In this case, the uniaxial bending displacement in the thickness direction of the displacement plate can be captured with high accuracy. In addition, the displacement plate can be prevented from being damaged by being changed or twisted in a direction other than the desired direction.

[0032] In the electrostatic converter of the present invention, the displacement plate may be arranged in a cantilever beam shape, with the fixed portion at one end and the variable portion at the other end. Alternatively, the displacement plate may be arranged in a double cantilever beam shape, with the fixed portion arranged in a manner of clamping the variable portion. Alternatively, the displacement plate may be arranged in a diaphragm shape, with the fixed portion at the periphery and the variable portion at the inner side of the periphery.

[0033] In the electrostatic converter of the present invention, it is also possible that, when the displacement plate is arranged in a cantilever beam shape, the support body has an opening in the center, and the displacement plate is arranged in a manner that the variable portion protrudes toward the opening side and covers or substantially covers the opening. Alternatively, it is also possible that the electrostatic converter of the present invention is composed of a plurality of components, each variable portion is made inside, each variable portion is surrounded by each support body, and each variable portion is arranged in a manner that covers or substantially covers the space surrounded by each support body. In these cases, it can be used as an electrostatic microphone, for example, like a virtual diaphragm. In addition, when the variable portion changes, it is preferred that the gap between the variable portion and the support body or the gap between the variable portions of adjacent displacement plates is less than 10 μm to prevent leakage of fluids such as air and reduce sensitivity.

[0034] The electrostatic transducer of the present invention can be used as various sensors such as microphones, acoustic transducers such as ultrasonic sensors, mass sensors, chemical sensors of mass detection method or frequency detection method, displacement sensors, chemical sensors of displacement detection method, flow sensors, scanning probes, etc. In addition, since the detection unit is arranged in a vacuum or low-pressure space, it can be used not only in gas but also in liquid. It is also possible to use the electrostatic transducer of the present invention as an actuator and drive the displacement plate for transmitting sound waves, etc., instead of using it as a sensor.

[0035] The manufacturing method of the electrostatic transducer of the present invention is used to manufacture the electrostatic transducer of the present invention, and is characterized in that a stacked body in which a first layer, a second layer, and a third layer are stacked in sequence on the surface of a base layer is processed from the surface side opposite to the second layer to form the structure of the detection unit, and one or more first through holes penetrating to the second layer are formed, a fourth layer and a fifth layer are formed in sequence on the surface opposite to the second layer of the processed third layer, one or more second through holes are formed in the fifth layer penetrating to the fourth layer from the surface side opposite to the fourth layer, the third layer constitutes the detection unit and the detection unit is arranged in a vacuum or low-pressure space, after removing a part of the fourth layer and the second layer through the second through hole formed on the fifth layer and the first through hole formed on the third layer, the second through hole formed on the fifth layer is closed, and the base layer corresponding to the position of the variable portion is removed in a manner that the first layer constitutes a displacement plate.

[0036] The method for manufacturing an electrostatic converter of the present invention can appropriately manufacture the electrostatic converter of the present invention. The method for manufacturing an electrostatic converter of the present invention can manufacture the electrostatic converter while forming films on the first to fifth layers respectively, and can also manufacture the electrostatic converter using a commercially available double SOI wafer or SOI wafer. In addition, when stacking the first to fifth layers, the stacking process of at least any one layer can be performed using substrate bonding (wafer bonding). In addition, in the method for manufacturing an electrostatic converter of the present invention, for example, the first layer, the third layer, and the fifth layer may be composed of silicon (Si), and the second layer and the fourth layer may be composed of silicon oxide (SiO 2 )constitute.

[0037] In the method for manufacturing an electrostatic converter of the present invention, the fifth layer is preferably made of silicon, and the second through hole formed on the fifth layer is closed by surface flow of the silicon. In this case, the second through hole can be easily closed only by heat treatment. In addition, it is particularly preferred that the fifth layer is single crystal silicon. Thus, even if heat treatment for surface flow is performed, mechanical properties and the like do not change, and a high-quality electrostatic converter can be manufactured.

[0038] In addition, the method for manufacturing an electrostatic converter of the present invention can also be used for silicon, silicon oxide, silicon nitride (Si x N y ), metal, etc., are formed to seal the second through hole formed on the fifth layer. Alternatively, after forming a silicon film on the second through hole, a heat treatment may be performed to seal the second through hole by the surface flow of the silicon.

[0039] The electrostatic transducer manufacturing method of the present invention may be performed by annealing in a nitrogen atmosphere or other environment with low hydrogen partial pressure after the second through hole is sealed. In this case, hydrogen in the space where the detection unit is arranged can be exhausted by diffusion, and the vacuum degree can be increased.

[0040] (III) Beneficial effects

[0041] According to the present invention, an electrostatic transducer and a method for manufacturing the electrostatic transducer can be provided, which can be applied to various sensors, can obtain a high SN ratio, and can increase the degree of freedom in the arrangement and structure of a portion for detecting changes in electrostatic capacitance. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 (a) is a plan view and (b) is a cross-sectional view taken along line AA′ of an electrostatic converter according to an embodiment of the present invention.

[0043] Figure 2 yes Figure 1 A top view of the electrostatic converter is shown with the sealing cap removed.

[0044] Figure 3 (a) to (d) are cross-sectional views showing a method for manufacturing an electrostatic converter according to an embodiment of the present invention.

[0045] Figure 4 A method for manufacturing an electrostatic converter according to an embodiment of the present invention is shown. Figure 3 Subsequent cross-sectional views (a) to (f) of the invention.

[0046] Figure 5 It means using multiple Figure 1 The electrostatic converter shown is a plan view of a modified example in which the variable portion is arranged in a diaphragm shape.

[0047] Figure 6 The present invention is a modified example of an electrostatic converter according to an embodiment of the present invention, in which a fluctuation detecting portion moves in the thickness direction of a displacement plate. (a) It is a cross-sectional view showing a state where the fluctuation portion has not fluctuated, and (b) it is a cross-sectional view showing a state where the fluctuation portion has fluctuated.

[0048] Figure 7 (a) is a plan view and (b) is a cross-sectional view along line BB′ showing a modification example in which a fluctuation detection unit is provided in a fluctuation unit of the electrostatic converter according to the embodiment of the present invention.

[0049] Figure 8 yes Figure 7 A top view of the electrostatic converter is shown with the sealing cap removed. DETAILED DESCRIPTION

[0050] Embodiments of the present invention will be described below based on the drawings.

[0051] Figures 1 to 8 An electrostatic transducer and a method for manufacturing the electrostatic transducer according to an embodiment of the present invention are shown.

[0052] like Figure 1 and Figure 2 As shown, the electrostatic converter 10 is composed of a MEMS device, and includes: a support body 11 , a displacement plate 12 , a detection unit 13 , a sealing frame 14 , a reinforcement portion 15 and a sealing cover 16 .

[0053] The support body 11 has a rectangular plate shape having a predetermined thickness.

[0054] The displacement plate 12 is in the form of a relatively thin plate, and has a fixed portion 12a having a rectangular planar shape at one end, and a triangular variable portion 12b having a long side of the fixed portion 12a as a base at the other end. The displacement plate 12 is fixed by adhering one surface of the fixed portion 12a to one surface of the support body 11 in such a manner that the variable portion 12b protrudes from the support body 11. Thus, the displacement plate 12 is in the form of a cantilever beam in which the variable portion 12b provided by extending the fixed portion 12a can be variable relative to the fixed portion 12a.

[0055] The detection unit 13 is arranged along the surface on the opposite side of the support body 11 of the displacement plate 12 with a gap therebetween. The detection unit 13 has an elongated connection portion 21 and a change detection portion 22. One end of the connection portion 21 is arranged at the vertex of the triangular change portion 12b, and the other end extends to the fixed portion 12a at the center of the bottom side of the change portion 12b. The change detection portion 22 has: a first comb-shaped electrode 23, which is arranged at the fixed portion 12a and connected to the other end of the connection portion 21; and a second comb-shaped electrode 24, which is arranged in a manner meshing with the first comb-shaped electrode 23. The second comb-shaped electrodes 24 are arranged in a row, and two groups are symmetrically arranged on the left and right of the extension line of the connection portion 21. The first comb-shaped electrodes 23 are arranged in a row, and are arranged on the left and right of each second comb-shaped electrode 24, and a total of five are symmetrically arranged with respect to the extension line of the connection portion 21.

[0056] Each of the first comb-tooth-shaped electrodes 23 includes a support portion 23a extending parallel to the longitudinal direction of the connection portion 21, and a plurality of teeth 23b arranged so as to extend from the left and right (three in the middle of each first comb-tooth-shaped electrode 23) of the support portion 23a, or from either the left and right (two at both ends of each first comb-tooth-shaped electrode 23) in a direction perpendicular to the longitudinal direction of the connection portion 21. The second and fourth first comb-tooth-shaped electrodes 23 in each of the first comb-tooth-shaped electrodes 23 include a spring-shaped connection portion 23c extending in a spring-like manner from the end of the support portion 23a on the opposite side of the connection portion 21. Each of the second comb-tooth-shaped electrodes 24 includes a support portion 24a extending parallel to the longitudinal direction of the connection portion 21, and a plurality of teeth 24b arranged so as to extend from the left and right of the support portion 24a in a direction perpendicular to the longitudinal direction of the connection portion 21. The change detection unit 22 is configured so that the teeth 23 b of the adjacent first comb-shaped electrodes 23 mesh with the teeth 24 b of the second comb-shaped electrodes 24 and a change in the interval between the adjacent teeth is detected as a change in electrostatic capacitance.

[0057] The sealing frame 14 is provided along the surface of the displacement plate 12 on the opposite side of the support body 11 and in contact with the surface. The sealing frame 14 is provided with a gap between the connecting portion 21 and the fluctuation detecting portion 22 so as to surround both sides of the connecting portion 21 and the periphery of the fluctuation detecting portion 22. In addition, the sealing frame 14 is connected to one end of the connecting portion 21. The sealing frame 14 is connected to each spring-shaped connecting portion 23c near two corners of the fixed portion 12a on the opposite side to the fluctuation portion 12b in the portion surrounding the periphery of the fluctuation detecting portion 22.

[0058] The reinforcing parts 15 are composed of a plurality of parts, and are provided to extend outward from the sealing frames 14 provided on both sides of the connecting part 21 at predetermined intervals in a direction perpendicular to the longitudinal direction of the connecting part 21 along the longitudinal direction of the connecting part 21 .

[0059] One end of the connection portion 21 of the detection unit 13 is fixed to the variable portion 12b of the displacement plate 12 via the first spacer 17. In addition, the support portion 24a of the second comb-shaped electrode 24 of the detection unit 13 is fixed to the fixed portion 12a of the displacement plate 12 via the first spacer 17. The sealing frame 14 and the reinforcement portion 15 are fixed to the displacement plate 12 via the first spacer 17. In this way, the electrostatic converter 10 causes the variable portion 12b to be uniaxially bent and displaced in the thickness direction of the displacement plate 12 via the reinforcement portion 15.

[0060] In addition, regarding the electrostatic converter 10, by causing one end of the connecting portion 21 to change together with the variable portion 12b, the connecting portion 21 is bent, and the other end of the connecting portion 21 is stretched along its length direction. In addition, thereby, the interval between the teeth 23b of the adjacent first comb-shaped electrode 23 and the teeth 24b of the second comb-shaped electrode 24 changes, and the electrostatic capacitance thereof changes. In this way, the electrostatic converter 10 can detect the change of the variable portion 12b as a change in electrostatic capacitance. In addition, in Figure 1 and 2 In the specific example shown, the change detection section 22 is configured such that when the connection section 21 is bent and stretched, the interval between the teeth 24b and the teeth 23b of the adjacent first comb-shaped electrode 23 (the interval between the teeth for detecting electrostatic capacitance) of each of the second comb-shaped electrodes 24 on the left and right sides of the extension line of the connection section 21 becomes wider, and the interval becomes narrower in the other two second comb-shaped electrodes 24. Thus, the electrostatic transducer 10 performs differential detection.

[0061] The sealing cover 16 is a relatively thin plate-shaped structure that covers the detection unit 13, and is disposed with a gap between the detection unit 13 and the sealing frame 14 so as to sandwich the detection unit 13 and the sealing frame 14 between the displacement plate 12. The sealing cover 16 is fixed to one end of the connecting portion 21, the supporting portion 24a of the second comb-shaped electrode 24, and the sealing frame 14 via the second spacer 18. A portion of the reinforcing portion 15 is formed of a relatively thin plate that constitutes the sealing cover 16. In this portion, the relatively thin plate that constitutes the sealing cover 16 is fixed to the displacement plate 12 via the second spacer 18.

[0062] The detection unit 13 of the electrostatic converter 10 is sealed with a gap around it by the displacement plate 12, the first spacer 17, the sealing frame 14, the second spacer 18, and the sealing cover 16. In addition, the space 19 around the detection unit 13 of the electrostatic converter 10 is vacuum or low pressure, and the detection unit 13 is arranged in the vacuum or low pressure space 19.

[0063] The electrostatic converter 10 can be appropriately manufactured using the method for manufacturing an electrostatic converter according to an embodiment of the present invention. Figure 3 and Figure 4 As shown, in the method for manufacturing an electrostatic converter according to an embodiment of the present invention, first, a laminated body is prepared in which a first layer 31, a second layer 32, and a third layer 33 are sequentially laminated on a surface of a base layer 30 (see Figure 3 In addition, Figure 3 In the specific example shown in (a), a double SOI wafer is used as a laminate, but the laminate can also be formed by forming each layer into a film. 2 The first layer 31 corresponds to the Si layer (thickness is 0.5 μm), and the second layer 32 corresponds to the SiO 2 The layer (thickness: 0.1 μm) corresponds to the Si layer, and the third layer 33 corresponds to the Si layer (thickness: 0.5 μm).

[0064] Next, the third layer 33 is patterned from the surface side opposite to the second layer 32 to form the structures of the detection unit 13, the sealing frame 14 and the reinforcing portion 15, and one or more first through holes 41 penetrating to the second layer 32 are formed (see Figure 3 (b) and Figure 1 ). Next, a fourth layer 34 and a fifth layer 35 are sequentially formed on the surface of the processed third layer 33 opposite to the second layer 32 (refer to Figure 3 (c) and (d)). In addition, Figure 3 In a specific example shown in (c) and (d), the SOI wafer is substrate-bonded on the surface of the third layer 33 (see Figure 3(c)), by removing the handle layer 42 and the BOX layer 43 of the SOI wafer, the fourth layer 34 and the fifth layer 35 are formed (see Figure 3 (d)), and each layer can also be formed by film deposition. In addition, the fourth layer 34 corresponds to a SiO 2 layer (thickness: 0.1 μm), and the fifth layer 35 corresponds to a Si layer (thickness: 0.5 μm).

[0065] Next, one or more second through-holes 44 are formed on the fifth layer 35, which penetrate from the surface side opposite to the fourth layer 34 to the fourth layer 34 (see Figure 4 (a) and Figure 1 ). Next, with the third layer 33 constituting the detection unit 13, the sealing frame 14, and the reinforcing portion 15, and the detection unit 13 being disposed in a vacuum or low-pressure space 19, and the second layer 32 constituting the first spacer 17, the fourth layer 34 constituting the second spacer 18, and the fifth layer 35 constituting the sealing cover 16, after removing a part of the fourth layer 34 and the second layer 32 by etching through the second through-holes 44 formed on the fifth layer 35 and the first through-holes 41 formed on the third layer 33 (see Figure 4 (b)), the second through-holes 44 formed on the fifth layer 35 are closed (see Figure 4 (c)). In addition, in Figure 4 a specific example shown in (c), since the fifth layer 35 is made of silicon, the second through-holes 44 are closed by the surface flow caused by the heat treatment of the silicon of the fifth layer 35 in hydrogen through so-called silicon migration sealing (SMS). In addition, afterwards, by performing heat treatment in an atmosphere with a sufficiently low hydrogen concentration, hydrogen is discharged from the space 19 in which the detection unit 13 is disposed through the thermal diffusion phenomenon, and the space 19 is made into a vacuum or low pressure.

[0066] Next, the structure of the displacement plate 12 is formed on the first layer 31, and the second layer 32 to the fifth layer 35 are shaped from one side of the fifth layer 35 in such a manner as to form holes 45 for terminals of the first comb-shaped electrodes 23 and the second comb-shaped electrodes 24 of the displacement detection portion 22 of the third layer 33 (see Figure 4 (d)), and metal terminals 46 electrically connected to the teeth of the first comb-shaped electrodes 23 and the teeth of the second comb-shaped electrodes 24 are respectively formed in the formed holes 45 for terminals (see Figure 4 (e)). Next, the base layer 30 corresponding to the position of the moving portion 12b is removed by deep reactive ion etching (DRIE) with the first layer 31 constituting the displacement plate 12 (see Figure 4 (f)). In addition, the base layer 30 constitutes the support 11. In this way, the electrostatic transducer 10 can be manufactured.

[0067] Since the detection unit 13 of the electrostatic converter 10 is arranged in a manner that can detect the change of the change portion 12b of the displacement plate 12 as a change in electrostatic capacitance, it is arranged in a vacuum or low-pressure space 19, and is not easily affected by damping caused by surrounding fluids such as gas such as air and liquid. Therefore, noise can be reduced and a higher SN ratio can be obtained.

[0068] In addition, the change detection part 22 of the electrostatic converter 10 is arranged on the fixed part 12a fixed on the support body 11, and does not hinder the change of the change part 12b, and is very stable. In addition, thereby, the structure of the change detection part 22 can be relatively freely configured, and the configuration and structural freedom of the detection unit 13 that detects the change of electrostatic capacitance can be improved. In addition, since the change part 12b and the change detection part 22 can be separated, they can be independently designed according to the required performance, and the design freedom is high. For example, it can be set as follows: the change part 12b is reduced and the resistance to excessive pressure input and mechanical collision is improved, and the number of teeth of the first comb-shaped electrode 23 and the second comb-shaped electrode 24 of the change detection part 22 is increased to improve the sensitivity. At this time, since the change detection part 22 is arranged in a vacuum or low-pressure space 19, even if the sensitivity of the change detection part 22 is increased, the increase of noise can be suppressed.

[0069] In addition, regarding the electrostatic converter 10, since the change detection part 22 is arranged at a position different from the change part 12b, it is possible to suppress the change part 12b from becoming hard. In addition, the part that changes together with the change part 12b can be reduced, and the resonance frequency of the change part 12b can be increased. The electrostatic converter 10 can suppress the change part 12b from bending in a direction other than the longitudinal direction of the displacement plate 12 by using the reinforcement part 15, so the uniaxial bending displacement of the displacement plate 12 can be captured with high precision. In addition, it is also possible to prevent the displacement plate 12 from changing in a direction other than the desired direction and twisting and being damaged.

[0070] In addition, the electrostatic converter 10 can easily close the second through hole 44 by heat treatment only by utilizing the surface flow of silicon of the fifth layer 35, and can arrange the detection unit 13 in the vacuum or low-pressure space 19. In this case, by forming the fifth layer 35 of single crystal silicon, the mechanical characteristics and the like will not change even if heat treatment for surface flow is performed, and a high-quality electrostatic converter can be obtained. In addition, the plane shape of the variable portion 12b of the electrostatic converter 10 is not limited to a triangular shape, and can be any shape such as a rectangular shape, an elongated rod shape, etc.

[0071] In addition, with respect to the electrostatic converter 10, since the detection unit 13 is arranged in the vacuum or low-pressure space 19, there is no need for a structure such as a diaphragm that separates the atmosphere and the vacuum or reduced-pressure space in the middle of the detection unit as described in non-patent documents 1 and 2, and the operation of the detection unit 13 will not be hindered by such a structure.

[0072] In addition, if Figure 5 As shown, the electrostatic converter 10 can also be configured to be composed of four parts, with each variable part 12b being the inner side, each variable part 12b being surrounded by each support body 11, and the vertices of each triangular variable part 12b being concentrated at the center of the space surrounded by each support body 11, and each variable part 12b basically covering the space surrounded by each support body 11. Figure 5 In the specific example shown, the vertices of each triangular variable portion 12b are 90°, and each variable portion 12b is configured with a slight gap 12c between the side of the adjacent variable portion 12b. In this case, it can be used as a microphone, for example, like a virtual diaphragm. In addition, when the variable portion 12b changes, it is preferred that the gap 12c between the side edges of adjacent variable portions 12b is less than 10μm to prevent leakage of fluid such as air and reduce sensitivity. The gap 12c can also be eliminated and the space 19 surrounded by each support body 11 can be completely covered. In addition, the electrostatic converter 10 is not limited to four, as long as it is multiple. In addition, the planar shape of the variable portion 12b is not limited to a triangle, and can be any shape as long as it can completely cover or substantially cover the space 19 surrounded by the support body 11.

[0073] In addition, the electrostatic converter 10 may be configured to be composed of a support body 11 having an opening in the center, and the displacement plate 12 may be configured such that the variable portion 12b protrudes toward the opening side and covers or substantially covers the opening. In this case, it can also be used as a microphone, for example, like a virtual diaphragm. In addition, when the variable portion 12b changes, it is preferred that the gap between the variable portion 12b and the support body 11 is less than 10 μm to prevent the leakage of fluid such as air and reduce the sensitivity, and the gap may be eliminated to completely cover the opening of the support body 11. In addition, the plane shape of the variable portion 12b may also be an arbitrary shape corresponding to the shape of the opening of the support body 11. In addition, the displacement plate 12 may be configured in a double cantilever beam shape in a manner covering the opening of the support body 11, and a fixed portion 12a may be provided in a manner clamping the variable portion 12b. In addition, the displacement plate 12 may be configured in a diaphragm shape in a manner covering the opening of the support body 11, and a fixed portion 12a may be provided on the periphery, and a variable portion 12b may be provided on the inner side of the periphery.

[0074] In addition, the first comb-shaped electrode 23 and the second comb-shaped electrode 24 of the electrostatic converter 10 are not limited to Figure 1 and Figure 2 The configuration shown can also be any configuration. Figure 1 and Figure 2 The electrostatic converter 10 shown in the figure is configured such that when the variable portion 12b changes, the connecting portion 21 bends together with the variable portion 12b, and the first comb-shaped electrode 23 of the change detection portion 22 moves in the in-plane direction along the surface of the variable portion 12b. Figure 6 As shown in the figure, when the variable portion 12b changes, the connection portion 21 does not bend, and the change detection portion 22 connected to the other end of the connection portion 21 can move in the out-of-plane direction along the thickness direction of the displacement plate 12. In this case, the change of the variable portion 12b can be detected as a change in the overlap of the first comb-shaped electrode 23 and the second comb-shaped electrode 24 in the thickness direction, or the change of the variable portion 12b can be detected as a change in electrostatic capacitance caused by a change in the interval between the change detection portion 22 and the fixed portion 12a.

[0075] In addition, if Figure 7 and Figure 8 As shown, the electrostatic converter 10 may be configured without the connecting portion 21, and the change detection portion 22 of the detection unit 13 includes a plurality of fixed electrodes 51 and a mesh electrode 52, wherein the fixed electrodes 51 are arranged along the surface of the change portion 12b and fixed to the change portion 12b, the mesh electrode 52 is arranged with a gap between each fixed electrode 51 so as to surround each fixed electrode 51 along the surface of the change portion 12b, and is not fixed to the change portion 12b, and the sealing frame 14 surrounds each fixed electrode 51 and the mesh electrode 52 along the periphery of the change portion 12b. In this case, the change detection portion 22 is provided in the change portion 12b, but since the gap between each fixed electrode 51 and the mesh electrode 52 changes due to the change of the change portion 12b, the electrostatic capacitance thereof changes, and therefore the change of the change portion 12b can be detected as a change in electrostatic capacitance.

[0076] In addition, the method for manufacturing the electrostatic converter according to the embodiment of the present invention is Figure 3 and Figure 4 In the method shown in FIG. 1 , after the third layer 33 is formed, patterning processing or the like may be performed only on the third layer 33 (see FIG. 1 ). Figure 3 (b)), when the fifth layer 35 is formed, a second through hole 44 is formed on the fifth layer 35 (refer to Figure 4 (a)), and the fourth layer 34 and the second layer 32 are etched (refer to Figure 4 (b)), but each time the second layer 32 to the fifth layer 35 are formed, each layer is patterned, and after the second through hole 44 is formed on the fifth layer 35, the fourth layer 34 and the second layer 32 are etched.

[0077] Moreover, in Figure 3 and Figure 4 In the method shown in FIG. 1 , after forming the first layer 31, the second layer 32 and the third layer 33 on the base layer 30 (see FIG. 1 ), Figure 3 (a)), etching processing is performed, but the connecting portion 21, the second comb-tooth electrode 24, and the spring-shaped connecting portion 23c and the displacement plate 12 can also be connected using the material of the third layer 33 as the first spacer 17. In this case, the second layer 32 can be partially etched and then the third layer 33 is formed. The same process can be performed on the fourth and fifth layers. The connecting rod 21, the second comb-tooth electrode 24, and the spring-shaped connecting portion 23c and the sealing cover 16 can also be connected using the material of the fifth layer 35 as the second spacer 18. In this case, the fourth layer 34 can be partially etched and then the fifth layer 35 is formed. Figure 4 In the sacrificial layer etching of (b), the etching is controlled so as to leave the first spacer 17 and the second spacer 18. This becomes easy if this method is used.

[0078] Description of Reference Numerals

[0079] 10-electrostatic converter; 11-support body; 12-displacement plate; 12a-fixed part; 12b-variable part; 13-detection unit; 21-connecting part; 22-variable detection part; 23-first comb-tooth electrode; 23a-support part; 23b-teeth; 23c-spring-shaped connecting part; 24-second comb-tooth electrode; 24a-support part; 24b-teeth; 14-sealing frame; 15-reinforcement part; 16-sealing cover; 17-first spacer; 18-second spacer; 19-space; 30-base layer; 31-first layer; 32-second layer; 33-third layer; 34-fourth layer; 35-fifth layer; 41-first through hole; 42-processing layer; 43-BOX layer; 44-second through hole; 45-hole; 46-metal terminal; 51-fixed electrode; 52-mesh electrode.

Claims

1. An electrostatic converter, characterized in that, it has: a support; a displacement plate having a fixed portion fixed to the support and a variable portion arranged to be variable relative to the fixed portion; and a detection unit installed in such a manner that at least a part thereof can vary together with the variable portion and arranged to be able to detect the variation of the variable portion as a change in capacitance. The detection unit has: an elongated connection portion with one end fixed to the variable portion and the other end extending toward the fixed portion side; and a variation detection portion connected to the other end of the connection portion and arranged to be able to detect the variation of the other end as the variation of the variable portion, the detection unit is arranged in a vacuum or low-pressure space.

2. The electrostatic converter according to claim 1, characterized in that, the variation detection portion is arranged on the fixed portion or the support.

3. The electrostatic converter according to claim 1, characterized in that, the detection unit is installed on the variable portion.

4. The electrostatic converter according to claim 1, characterized in that, the variable portion has a reinforcing portion arranged to be uniaxially bent and displaced in the thickness direction of the displacement plate.

5. The electrostatic converter according to any one of claims 1 to 4, characterized in that, the displacement plate is arranged in a cantilever beam shape, having the fixed portion on one end side and the variable portion on the other end side.

6. The electrostatic converter according to any one of claims 1 to 4, characterized in that, the displacement plate is arranged in a double cantilever beam shape, and the fixed portion is arranged to clamp the variable portion.

7. The electrostatic converter according to any one of claims 1 to 4, characterized in that, the displacement plate is arranged in a diaphragm shape, having the fixed portion at the periphery and the variable portion inside the periphery.

8. The electrostatic converter according to claim 5, characterized in that, the support has an opening in the center, the displacement plate is arranged such that the variable portion protrudes toward the opening side and covers or substantially covers the opening.

9. The electrostatic converter according to claim 5, characterized in that, it is composed of multiple ones, with each variable portion being the inner side respectively, each support surrounding the periphery of each variable portion, and arranged in such a way that each variable portion covers or substantially covers the space surrounded by each support.

10. The electrostatic converter according to claim 8 or 9, characterized in that, the gap between the variable portion and the support or the gap between the variable portions of adjacent displacement plates is 10 μm or less.

11. The electrostatic converter according to any one of claims 1 to 4, characterized in that, the electrostatic converter is a MEMS device.

12. A manufacturing method of an electrostatic converter for manufacturing the electrostatic converter according to any one of claims 1 to 11, characterized in that, A structure in which a detection unit is formed by processing a third layer of a laminate in which a first layer, a second layer, and a third layer are sequentially stacked on the surface of a base layer from the surface side opposite to the second layer, and one or more first through-holes penetrating to the second layer are formed. A fourth layer and a fifth layer are sequentially formed on the surface of the processed third layer opposite to the second layer. One or more second through-holes penetrating from the surface side opposite to the fourth layer to the fourth layer are formed in the fifth layer. In such a manner that the third layer constitutes the detection unit and the detection unit is disposed in a vacuum or low-pressure space, after removing a part of the fourth layer and the second layer through the second through-holes formed in the fifth layer and the first through-holes formed in the third layer, the second through-holes formed in the fifth layer are closed. The base layer corresponding to the position of the variable portion is removed in such a manner that the first layer constitutes a displacement plate.

13. The method of manufacturing an electrostatic converter according to claim 12, characterized in that, the fifth layer is made of silicon, the second through-holes formed in the fifth layer are closed by flowing on the surface of the silicon.

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