An electrostatic clutch

Abstract

The present invention discloses an electrostatic clutch. The electrostatic clutch includes: a plurality of grounded high-impedance node electrode arrays that form a rigid movable body; and a plurality of bias electrode arrays that form another rigid movable body, such that when there is a relative displacement between the plurality of bias electrode arrays and the plurality of high-impedance node electrode arrays, an electrostatic force is generated therebetween. Compared with the prior art, the advantage of the present invention is that it allows the microphone to operate under a wide range of atmospheric pressures that a customer may expect. This is electrostatically achieved in a purely passive manner, which has an advantage over other designs that require complex electronics and active control. Since only the small AC perturbations of the rotor need to be considered without considering the DC variations in the rotor position, the membrane is physically decoupled from the sensing structure, thereby simplifying the design of the sensing structure.

Description

Technical Field

[0001] The present invention relates to the technical field of microphones, and in particular to an electrostatic clutch. Background Art

[0002] Currently, all commercial MEMS microphones have a back cavity behind the diaphragm. This is a semi - sealed air volume that undergoes compression and expansion when there is an input sound wave. For a given package size, this back cavity is necessary to allow the diaphragm to move under an external pressure wave. However, this back cavity is currently the largest source of acoustic noise and thus the largest limiter of the acoustic signal - to - noise ratio (SNR) in the microphone. The smaller the volume behind, the higher the acoustic noise from it. Therefore, it is impossible to achieve a high - SNR microphone with an SNR of about 74 dB or more unless the package size is made very large. If the back cavity is replaced with a vacuum and the sensing part of the MEMS is enclosed inside the vacuum, not only can the back - cavity noise be effectively eliminated, but also the damping noise related to the diaphragm movement (such as back - plate noise) can be eliminated. The only way to achieve a very high SNR in a normal or small - size package is to make the back volume a vacuum.

[0003] There are two major challenges for this type of vacuum - back - cavity microphone: (1) The 1 - atm pressure difference between air and vacuum will cause a normal diaphragm to collapse, so a very stiff diaphragm is required, which results in very low sensitivity; (2) The significant change in ambient pressure leads to a change in the DC offset of the diaphragm displacement, and the traditional rotor - stator design does not work.

[0004] At the same time, existing microphones require a back cavity, which is the largest noise source in the state - of - the - art, commercially available microphones. This limits the SNR unless a very large package size is used, which is not feasible for mobile applications. In a traditional package size, it is impossible to achieve a very high microphone SNR, such as 80 dB, unless a vacuum cavity is used.

[0005] Using a vacuum or low - pressure cavity sealed by a diaphragm facing the atmosphere poses a fundamental measurement challenge. The change in atmospheric pressure depends on the environment where the user and the device are located and is about 100 kPa. In addition to this slow DC pressure change, the device also needs to measure an audio pressure signal on the order of 1 Pa.

[0006] One solution in the prior art is to have a coupling between the membrane facing the atmosphere and the rotor part of the sensing device, which is "open" for alternating current audio signals and "closed" for low-frequency or direct current variations in atmospheric pressure. This clutch-like coupling behavior can be achieved by frequency-dependent electrostatic forces. The electrostatic clutch in the present invention is designed to achieve a coupling force between the rotor and the stator for alternating current sound pressure signals, but not to couple any force for the slow "DC" variations in atmospheric pressure, which typically change the central deformation of the membrane facing the atmosphere in the micrometer range. For the direct current pressure range, the stiffness between the rotor and the stator should be zero or minimal, while the stiffness for alternating current audio pressure should be large. Summary of the Invention

[0007] The object of the present invention is to provide an electrostatic clutch to solve the technical problems in the prior art. The electrostatic clutch includes two mechanical components, between which there is an electrostatic force coupling, such that the movement of any one component generates a force on the other component.

[0008] The present invention provides an electrostatic clutch, comprising:

[0009] An array of multiple grounded high-impedance node electrodes, forming a rigid movable body;

[0010] An array of multiple bias electrodes, forming another rigid movable body, such that when there is a relative displacement between the array of multiple bias electrodes and the array of multiple high-impedance node electrodes, an electrostatic force is generated between them.

[0011] An electrostatic clutch as described above, wherein preferably, corresponding through-channels are formed between two arrays of the multiple HIN electrode arrays in a comb structure and the array of multiple bias electrodes, and each array of the multiple bias electrodes moves back and forth in the corresponding through-channel.

[0012] An electrostatic clutch as described above, wherein preferably, the capacitance formed between the resistance part of the high-impedance node electrode array and the adjacent bias electrode array constitutes an RC circuit with a cut-off frequency.

[0013] An electrostatic clutch as described above, wherein preferably, the high-impedance node electrode array includes several high-impedance node electrodes and a grounding piece, an insulating silicon oxide layer is provided between adjacent high-impedance node electrodes, and the grounding piece is electrically connected to several high-impedance node electrodes and then kept grounded.

[0014] An electrostatic clutch as described above, wherein preferably, the high-impedance node electrode includes a first conductive polysilicon layer, a resistance bridge layer, and a second conductive polysilicon layer, and the first conductive polysilicon layer is electrically connected to the second conductive polysilicon layer through the resistance bridge layer; the grounding member is electrically connected to a plurality of the second conductive polysilicon layers and then remains grounded.

[0015] An electrostatic clutch as described above, wherein preferably, within each of the bias electrode arrays, two adjacent ones of the plurality of bias electrodes have opposite polarities and are connected by an insulating mechanical bracket.

[0016] An electrostatic clutch as described above, wherein preferably, each bias electrode array further includes two ground shielding electrodes, which are provided at both ends of each of the plurality of bias electrode arrays.

[0017] An electrostatic clutch as described above, wherein preferably, the high-impedance node electrode array is composed of a composite of a tuned resistance material and a polysilicon conductive material.

[0018] An electrostatic clutch as described above, wherein preferably, the high-impedance node electrode array is formed by an integral block of a tuned resistance material, and the tuned resistance material is connected to a grounded conductive material.

[0019] Compared with the prior art, the advantage of the present invention is that it allows the microphone to operate under a wide range of atmospheric pressures that a customer may expect. This is electrostatically achieved in a purely passive manner, which has an advantage over other designs that require complex electronics and active control. Since only small AC perturbations of the rotor need to be considered without considering the DC variation of the rotor position, the membrane is decoupled from the sensing structure, thus simplifying the design of the sensing structure. Description of the Drawings

[0020] Figure 1 is a schematic structural diagram of an electrostatic clutch composed of a grounded high-impedance node electrode array and a single bias electrode;

[0021] Figure 2 is a schematic structural diagram of a high-impedance node electrode array formed by using a silicon process deposition;

[0022] Figure 3 is a top view of the electrical connection of one layer of the high-impedance node electrode array;

[0023] Figure 4 is a schematic structural diagram of an electrostatic clutch in the case where a plurality of bias electrodes have alternating polarities;

[0024] Figure 5It is a schematic structural diagram of an electrostatic clutch when a ground shielding electrode is arranged at the end of a bias electrode array to enhance stiffness;

[0025] Figure 6a , 6b , 6c and 6d are schematic structural diagrams of the first - structure MEMS capacitive microphone of the present invention, wherein the electrostatic clutch is part of a hinged cantilever transducer having a hinge - cantilever transducer with different combinations of atmospheric pressure and sound pressure;

[0026] Figure 7 It is another schematic structural diagram of the high - impedance node electrode array of the present invention. Detailed implementation manners

[0027] The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and cannot be construed as limiting the present invention.

[0028] To better explain this embodiment, a three - dimensional coordinate system is specifically established, wherein the XY plane is considered parallel to the silicon die surface on which the MEMS layer is deposited, and the Z - axis is considered perpendicular to this surface.

[0029] As Figures 1 to 5 shown, an embodiment of the present invention provides an electrostatic clutch 100. The design of the electrostatic clutch 100 is to achieve an alternating - current sound - pressure signal of the coupling force between the rotor and the stator, but not to couple any force of a slow 'direct - current' change in atmospheric pressure, which usually changes the central deformation of the atmospheric surface of the diaphragm 203 within the micron range. For the direct - current voltage range, the stiffness between the rotor and the stator should be zero or minimum. The electrostatic clutch 100 includes:

[0030] A high - impedance node electrode array 101, as the first component of the electrostatic clutch 100, generally acts as a clutch stator. A through - channel is formed between two high - impedance node electrode arrays 101. In this embodiment, the high - impedance node electrode array 101 preferably includes a plurality of high - impedance node electrodes 1011 and a grounding member 1012. The more the high - impedance node electrodes 1011 are, the higher the performance. However, for an embodiment with z - axis rotor displacement, the number of high - impedance node electrodes 1011 is actually limited by process constraints. An insulating silicon oxide layer 1013 is arranged between adjacent high - impedance node electrodes 1011, and the grounding member 1012 is electrically connected to a plurality of high - impedance node electrodes 1011 and then kept grounded.

[0031] The biasing electrode array 102, as the second component of the electrostatic clutch 100, generally acts as the clutch rotor. Of course, those skilled in the art can know that the high-impedance node electrode array 101 can also act as the clutch rotor, while the biasing electrode array 102 acts as the clutch stator, which is not limited herein. One end of the biasing electrode array 102 is connected to the diaphragm 203. As the diaphragm 203 deflects, the other end of the biasing electrode array 102 can reciprocally move within the through-channel, so as to generate an electrostatic force between the biasing electrode array 102 and the high-impedance node electrode array 101.

[0032] The capacitance formed between the resistance portion of the high-impedance node electrode array 101 and the adjacent biasing electrode array 102 constitutes an RC circuit with a cut-off frequency. This cut-off frequency is determined such that above this frequency, the electrostatic clutch 100 transfers a coupling force between the plurality of biasing electrode arrays 102 and the high-impedance node electrode array 101, and below this frequency, the electrostatic coupling force is significantly reduced or negligible.

[0033] The electrostatic clutch 100 effectively "opens" at audio-band frequencies and effectively "closes" at low frequencies. This clutch acts as an RC high-pass filter, which couples the alternating motion of the diaphragm 203 corresponding to the audio signal, but filters the slow motion of the diaphragm 203 caused by the slow change of the atmospheric pressure, usually in the range of 0.5 - 1 atm. For example, such a change may occur with the change of weather, altitude or inside an airliner.

[0034] When the biasing electrode array 102 does not move or moves at a frequency below the cut-off frequency, charges freely flow from or to the surface of the high-impedance node electrode 1011. This means that when the biasing electrode array 102 moves slowly relative to the high-impedance node electrode array 101 and the frequency is below the cut-off value, there is no force coupling or interaction between the clutch stator and the clutch rotor. In this case, the clutch stiffness is approximately zero. However, when the clutch rotor moves at a frequency above the cut-off frequency, the charges induced by the biasing electrode 1021 in the hinge are trapped. Generally, the size of each high-impedance node electrode 1011 will be much smaller than that of the biasing electrode 1021, thus generating a significant restoring force on the alternating displacement of the clutch rotor. This corresponds to a significant coupling stiffness. Therefore, the filter is realized by the frequency-dependent electrostatic stiffness between the diaphragm 203 facing the atmosphere and the rotor part of the capacitive sensing structure 300.

[0035] Refer to Figure 2 and Figure 3As shown, the high-impedance node electrode 1011 includes a first conductive polysilicon layer 1014, a resistive bridge layer 1015, and a second conductive polysilicon layer 1016. The first conductive polysilicon layer 1014 is electrically connected to the second conductive polysilicon layer 1016 through the resistive bridge layer 1015. The grounding member 1012 is electrically connected to a plurality of the second conductive polysilicon layers 1016 and then kept grounded. The material of the resistive bridge layer 1015 connecting each layer to the ground can be doped polysilicon, a material for manufacturing a diode, or a Schottky material. The resistivity of this material and the resistive bridge layer 1015 can be used to adjust the roll-off frequency, which determines the frequency at which the clutch no longer drives the sensing part of the sensor. The roll-off frequency is proportional to 1 / RC, where R is the resistance of the resistive bridge layer 1015 and C is the capacitance between a single high-impedance node electrode 1011 and the bias electrode 1021 facing it.

[0036] Referring to Figure 7 As shown, the high-impedance node electrode array 101 can also be composed of a composite of a tuning resistor material 1017 and a polysilicon conductive material 1018. The polysilicon conductive material 1018 is grounded, which has the main advantage of avoiding many process layers. For the high-impedance node electrode array 101, in this case, the resistivity of the tuning resistor material 1017 will determine the frequency at which charge is locally trapped when the bias electrode array 102 moves, rather than the resistance of a single resistive bridge layer determining the roll-off frequency. The grounding of this material can be provided by a polysilicon layer or other conductive material with a resistivity less than that of the tuning resistor material 1017. The polysilicon conductive material 1018 has an interface with the tuning resistor material 1017 on the z-axis and has the purpose of achieving zero potential along the z-axis length of the tuning resistor material 1017 on the surface not facing the bias electrode. An insulating layer that eliminates the effect of reducing the z-axis stiffness of the clutch can also be included.

[0037] Referring to Figure 4 、 Figure 5 and Figures 6a - 6dAs shown, the bias electrode array 102 includes a plurality of bias electrodes 1021, and the plurality of bias electrodes 1021 are arranged with alternating polarities. The polarities of adjacent bias electrodes 1021 are opposite and are connected by an insulating mechanical bracket 1022 therebetween. The bias electrode array 102 further includes a power-connected shielding electrode 1023, and the power-connected shielding electrode 1023 is provided at both the head and the tail ends of the bias electrode array 102. Thus, the electric field of the bias electrodes 1021 in the passage leaving between the two high-impedance node electrode arrays 101 is minimized. The stray electric field is the root cause of the non-zero DC force generated between the clutch rotor and the stator within their DC displacement range. When there is no audio signal, a non-zero DC force drives the sensing part of the sensor, which is not required. The power-connected shielding electrode 1023 very effectively reduces the DC force to almost zero within a large distance range of microns required for atmospheric pressure changes.

[0038] Based on the above-described electrostatic clutch 100, this embodiment further provides a MEMS capacitive microphone 200, including a substrate 201, a support portion 202, and a diaphragm 203, wherein: the diaphragm 203 is supported above the substrate 201 through the support portion 202, and the substrate 201, the support portion 202, and the diaphragm 203 enclose a vacuum cavity 204; one side of the diaphragm 203 close to the vacuum cavity 204 is connected to the electrostatic clutch 100 through a connecting rod 205; and the electrostatic clutch 100 is connected to a capacitance sensing structure 300.

[0039] The substrate 201 can be made of single crystal silicon or other materials well-known to those skilled in the art, and the support portion 202 and the diaphragm 203 supported on the substrate 201 through the support portion 202 can be formed by processes such as layer-by-layer deposition, patterning, and sacrificial processes. If necessary, an insulating layer is further provided between the support portion 202 and the substrate 201, which will not be specifically described herein.

[0040] The vacuum cavity 204 can be sealed, for example, by low-pressure plasma-enhanced chemical vapor deposition (PECVD) at 200 - 350 °C. This MEMS process belongs to the common knowledge of those skilled in the art and will not be specifically described herein. Among them, the vacuum cavity 204 is preferably less than 1 kPa, which makes the viscosity of the residual gas in the vacuum cavity 204 much lower than the viscosity of air under standard pressure.

[0041] Since a vacuum chamber 204 with a pressure lower than atmospheric pressure is formed between the diaphragm 203 and the substrate 201, the diaphragm 203 will undergo static deflection under atmospheric pressure and without sound pressure, that is, the diaphragm 203 will undergo static deflection in the direction of the substrate 201, and charges flow freely from or to the surface of the high-impedance node electrode 1011. This means that when the bias electrode array 102 moves slowly relative to the high-impedance node electrode array 101, the frequency is lower than the cut-off value, and there is no force coupling or interaction between the clutch stator and the clutch rotor, and the electrical signal output by the capacitive structure in the capacitive sensing structure 300 remains unchanged. When the diaphragm 203 moves at a frequency higher than the cut-off frequency, the electrostatic clutch 100 generates an electrostatic force to drive the capacitive structure to output a changing electrical signal.

[0042] The present invention provides MEMS capacitive microphones 200 in various structural forms. It can be understood that those skilled in the art can infer more variant embodiments based on the provided microphone structure, which are not limited herein.

[0043] Refer to Figure 6a 、 6b As shown in FIGS. 6a, 6b, 6c, and 6d, the first structural form of the MEMS capacitive microphone 200 of the present invention is shown. The electrostatic clutch 100 and the capacitive sensing structure 300 are both disposed in the vacuum chamber 204. The electrostatic clutch 100 further includes a first connection portion and a second connection portion. One end of the first connection portion is connected to the connecting rod 205, and the other end of the first connection portion is connected with a plurality of the bias electrode arrays 102. The plurality of bias electrode arrays 102 constitute the rotor of the electrostatic clutch 100, and the offset of the diaphragm 203 will cause the synchronous displacement of the bias electrode arrays 102.

[0044] There are two second connection portions, and the two second connection portions are symmetrically disposed on opposite sides of the first connection portion. One end of each second connection portion is provided with a plurality of the high-impedance node electrode arrays 101, and the other end of each second connection portion is connected to the capacitive sensing structure 300. The plurality of high-impedance node electrode arrays 101 constitute the stator of the electrostatic clutch 100.

[0045] The plurality of high-impedance node electrode arrays 101 and the plurality of bias electrode arrays 102 are both arranged in a comb shape. The plurality of high-impedance node electrode arrays 101 and the plurality of bias electrode arrays 102 are spatially separated and the high-impedance node electrode arrays 101 and the bias electrode arrays 102 intersect each other. This structure provides a relatively large displacement, reduces acoustic noise, and provides high sensitivity.

[0046] The capacitive sensing structure 300 includes a first lever 301, a first support portion 302, a first sensing moving electrode 303, and a first sensing static electrode 304. The rod body of the first lever 301 is pivotally connected to the first support portion 302. One end of the first lever 301 is connected to the second connection portion, and the other end of the first lever 301 is connected to the first sensing moving electrode 303. The first sensing static electrode 304 is opposite to the first sensing moving electrode 303, and the first sensing static electrode 304 and the first sensing moving electrode 303 form a capacitor structure that can output a varying electrical signal.

[0047] When the diaphragm 203 vibrates, the electrostatic clutch 100 is activated to generate an electrostatic force. The clutch stator is displaced under the AC displacement of the clutch rotor, thereby activating one end of the first lever 301. The first lever 301 increases the mechanical sensitivity by amplifying the displacement of the electrostatic clutch 100. The first sensing moving electrode 303 on the first lever 301 moves synchronously, and the facing area between the first sensing static electrode 304 and the first sensing moving electrode 303 changes, enabling the capacitor structure to output a varying electrical signal. The working principle of the capacitor structure is common knowledge to those skilled in the art.

[0048] Figure 6a , Figure 6b , Figure 6c and Figure 6d The differences between and illustrate the working principle of the present invention. In, there is a relatively high DC atmospheric pressure without an AC sound pressure, resulting in a relatively low position of the electrostatic clutch rotor and no displacement of the first sensing moving electrode 303. For a sound pressure signal having the same atmospheric pressure as in, shows the displacement at the low-pressure portion of the AC sound signal. In this case, the electrostatic clutch is active, causing displacement of the first sensing moving electrode 303 and thus generating a signal. Figure 6a In, there is a relatively high DC atmospheric pressure without an AC sound pressure, resulting in a relatively low position of the electrostatic clutch rotor and no displacement of the first sensing moving electrode 303. For a sound pressure signal having the same atmospheric pressure as in, shows the displacement at the low-pressure portion of the AC sound signal. In this case, the electrostatic clutch is active, causing displacement of the first sensing moving electrode 303 and thus generating a signal. Figure 6a In, there is a relatively high DC atmospheric pressure without an AC sound pressure, resulting in a relatively low position of the electrostatic clutch rotor and no displacement of the first sensing moving electrode 303. For a sound pressure signal having the same atmospheric pressure as in, shows the displacement at the low-pressure portion of the AC sound signal. In this case, the electrostatic clutch is active, causing displacement of the first sensing moving electrode 303 and thus generating a signal. Figure 6b shows the displacement at the low-pressure portion of the AC sound signal. In this case, the electrostatic clutch is active, causing displacement of the first sensing moving electrode 303 and thus generating a signal. Figure 6c shows an alternative situation where a relatively low DC atmospheric pressure results in a relatively high position of the electrostatic clutch rotor. However, since the electrostatic clutch is in an inactive state, the position of the first sensing moving electrode 303 is the same as in. When an AC sound pressure is applied, the movement of the sensing electrode and the generated signal is the same as in. This ability to measure only the AC sound pressure and not the DC atmospheric pressure makes the sensing structure simple and highly sensitive. Figure 6a In, there is a relatively high DC atmospheric pressure without an AC sound pressure, resulting in a relatively low position of the electrostatic clutch rotor and no displacement of the first sensing moving electrode 303. For a sound pressure signal having the same atmospheric pressure as in, shows the displacement at the low-pressure portion of the AC sound signal. In this case, the electrostatic clutch is active, causing displacement of the first sensing moving electrode 303 and thus generating a signal. Figure 6b In, there is a relatively high DC atmospheric pressure without an AC sound pressure, resulting in a relatively low position of the electrostatic clutch rotor and no displacement of the first sensing moving electrode 303. For a sound pressure signal having the same atmospheric pressure as in, shows the displacement at the low-pressure portion of the AC sound signal. In this case, the electrostatic clutch is active, causing displacement of the first sensing moving electrode 303 and thus generating a signal.

[0049] In one embodiment, the high-impedance node electrode array 101 is formed from a monolithic block of tuning resistor material without any insulating spacers; the tuning resistor material is directly connected to a grounded conductive material without a resistor bridge layer 1015.

[0050] The structure, features, and effects of the present invention have been described in detail based on the embodiments shown in the drawings. The above description is only the preferred embodiment of the present invention, but the present invention is not limited to the scope of implementation shown in the drawings. Any changes made according to the concept of the present invention, or equivalent embodiments modified into equivalent changes, should still be within the protection scope of the present invention as long as they do not exceed the spirit covered by the specification and the drawings.

Claims

1. An electrostatic clutch, characterized in that, Comprising: A plurality of grounded high-impedance node electrode arrays, forming a rigid movable body; A plurality of bias electrode arrays, forming another rigid movable body, such that when there is a relative displacement between the plurality of bias electrode arrays and the plurality of high-impedance node electrode arrays, an electrostatic force is generated therebetween; The high-impedance node electrode array includes a plurality of high-impedance node electrodes and a grounding member, an insulating silicon oxide layer is provided between adjacent high-impedance node electrodes, and the grounding member is electrically connected to a plurality of the high-impedance node electrodes and then kept grounded; The high-impedance node electrode includes a first conductive polysilicon layer, a resistance bridge layer, and a second conductive polysilicon layer, the first conductive polysilicon layer is electrically connected to the second conductive polysilicon layer through the resistance bridge layer; the grounding member is electrically connected to a plurality of the second conductive polysilicon layers and then kept grounded.

2. The electrostatic clutch according to claim 1, characterized in that: Corresponding through channels are formed between two arrays of a plurality of HIN electrode arrays in a comb structure and the plurality of bias electrode arrays, wherein each array of the plurality of bias electrode arrays moves back and forth in the corresponding through channel.

3. The electrostatic clutch according to claim 1, characterized in that: The resistance part of the high-impedance node electrode array and the capacitance formed between adjacent bias electrode arrays form an RC circuit having a cut-off frequency.

4. The electrostatic clutch according to claim 1, characterized in that: Within each of the bias electrode arrays, two adjacent ones of the plurality of bias electrodes have opposite polarities and are connected by an insulating mechanical bracket.

5. The electrostatic clutch according to claim 1, characterized in that: Each bias electrode array further includes two grounded shielding electrodes, which are provided at both ends of each array of the plurality of bias electrode arrays.

6. The electrostatic clutch according to claim 1, characterized in that: The high-impedance node electrode array is composed of a composite of a tuned resistance material and a polysilicon conductive material.

7. The electrostatic clutch according to claim 1, characterized in that: The high-impedance node electrode array is formed by an integral block of a tuned resistance material, and the tuned resistance material is connected to a grounded conductive material.

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