Acceleration Sensor Device

Abstract

To provide an acceleration sensor device that can detect an acceleration highly precisely.SOLUTION: The acceleration sensor device includes an acceleration sensor and a processing circuit. The acceleration sensor includes: a pair of first displacement detection electrode parts of which changes of the distance between electrodes are opposite in the sign to a displacement of a mass part in a first direction; and a pair of first servo electrodes of which changes of the distance between electrodes are opposite in the sign to the displacement of the mass part in the first direction. The processing circuit includes: a conveyance wave signal generation circuit for inputting a conveyance wave signal including a direct offset voltage and an alternating reference voltage to the mass part; a first capacitance conversion circuit part for outputting a first voltage signal corresponding to the difference between the change of the capacitance of the pair of first displacement detection electrodes; a first synchronization detection circuit for detecting a first detection signal in synchronization with a reference voltage from the first voltage signal; and a first servo signal generation circuit for inputting a first servo signal to the pair of first servo electrode parts on the basis of the first detection signal. The signs of the first servo signal are opposite between a pair of first fixation servo electrodes.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The technology disclosed in this specification relates to an acceleration sensor device having a MEMS (Micro Electro Mechanical Systems) structure. [Background technology]

[0002] An acceleration sensor device having a MEMS structure is known. This type of acceleration sensor device is equipped with a displacement detection electrode section configured such that the inter-electrode distance varies in response to the displacement of a mass section due to acceleration. Acceleration is detected from the change in capacitance of the displacement detection electrode section.

[0003] When the mass portion is displaced excessively, the electrodes in the acceleration sensor collide with each other, causing the electrodes to stick to each other or to break. In order to improve the effects of such excessive displacement, an acceleration sensor device has been proposed that is configured to suppress the displacement of the mass portion by servo control, and an example of this is disclosed in Non-Patent Document 1. In addition, when free vibration occurs in the mass portion, the responsiveness of the acceleration sensor device deteriorates. In order to improve such deterioration of responsiveness, an acceleration sensor device has been proposed that is configured to suppress the displacement of the mass portion by servo control. In such an acceleration sensor device, a servo signal for suppressing the displacement of the mass portion is output. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] S. Ko, et. al., “An Electrostatic Servo-Accelerometer with mG Resolution,” T.IEE Japan, Vol. 119-E, No. 7, 1999 Summary of the Invention [Problem to be solved by the invention]

[0005] The acceleration sensor device of Non-Patent Document 1 is configured to input a servo signal to a mass portion, and to apply an electrostatic attractive force corresponding to the servo signal between the electrodes of the displacement detection electrode portion, thereby suppressing the displacement of the mass portion. In the technology of Non-Patent Document 1, the displacement detection electrode portion also serves as a servo electrode portion for applying an electrostatic attractive force corresponding to the servo signal. Therefore, the servo signal is also transmitted to the displacement detection electrode portion, and the servo signal becomes a noise component during capacitance conversion. The purpose of this specification is to provide an acceleration sensor device capable of detecting acceleration with high accuracy. [Means for solving the problem]

[0006] An embodiment of an acceleration sensor device disclosed in the present specification may include an acceleration sensor and a processing circuit. The acceleration sensor may include a frame, a mass portion, a pair of first displacement detection electrodes, and a pair of first servo electrodes. The mass portion is configured to be swingable in at least a first direction relative to the frame. Each of the pair of first displacement detection electrodes includes a first movable detection electrode and a first fixed detection electrode. The first movable detection electrode and the first fixed detection electrode face each other in the first direction, the first movable detection electrode is fixed to the mass portion, and the first fixed detection electrode is fixed to the frame. The positive and negative of the change in the inter-electrode distance between the first movable detection electrode and the first fixed detection electrode with respect to the displacement of the mass portion in the first direction is opposite between the pair of displacement detection electrodes. Each of the pair of first servo electrodes includes a first movable servo electrode and a first fixed servo electrode. The first movable servo electrode and the first fixed servo electrode face each other in the first direction, the first movable servo electrode is fixed to the mass portion, and the first fixed servo electrode is fixed to the frame. The positive and negative of the change in the inter-electrode distance between the first movable servo electrode and the first fixed servo electrode with respect to the displacement of the mass portion in the first direction is opposite between the pair of first servo electrode portions. The processing circuit has a carrier signal generating circuit, a first capacitance conversion circuit portion, a first synchronous detection circuit, and a first servo signal generating circuit. The carrier signal generating circuit is a circuit for inputting a carrier signal to the mass portion. The carrier signal includes a DC offset voltage and an AC reference voltage. The first capacitance conversion circuit portion outputs a first voltage signal corresponding to a difference in the capacitance change of each of the pair of first displacement detection electrode portions. The first synchronous detection circuit detects a first detection signal synchronized with the reference voltage from the first voltage signal. The first servo signal generating circuit inputs a first servo signal to the first fixed servo electrodes of the pair of first servo electrode portions based on the first detection signal to suppress displacement of the mass portion in the first direction, and the positive and negative polarities of the first servo signals are opposite between the pair of first fixed servo electrodes.In this acceleration sensor device, the pair of first displacement detection electrodes and the pair of first servo electrodes are separated, so that the first servo signal is prevented from being transmitted to the pair of first displacement detection electrodes, and therefore the acceleration sensor device can detect acceleration with high accuracy.

[0007] In the above acceleration sensor device, the acceleration sensor may further have a cap layer fixed to the frame body so as to cover the mass portion. In this case, the mass portion is disposed in a space defined by the frame body and the cap layer, and the space is a vacuum. Since the mass portion is disposed in a vacuum space, the acceleration sensor device can have a high Q value characteristic. Therefore, the acceleration sensor device reduces mechanical noise. In general, it is known that an acceleration sensor device having a high Q value characteristic increases the response time required for the amplitude of free vibration of the mass portion to attenuate when acceleration is applied, and the responsiveness deteriorates. However, the above acceleration sensor device operates to suppress the displacement of the mass portion by servo control, so that such deterioration in responsiveness is improved. The above acceleration sensor device can achieve both low mechanical noise and high responsiveness.

[0008] In the above acceleration sensor device, the acceleration sensor may further include an anchor portion fixed to the frame body, and a first beam portion connected between the mass portion and the anchor portion and elastically deformable in the first direction. Furthermore, a central opening may be formed in the mass portion, and only one of the anchor portions may be disposed at the symmetric center of the mass portion located within the central opening. In this case, the mass portion may be connected to the anchor portion via the first beam portion so as to be able to swing in the first direction. Since the anchor loss is reduced in this acceleration sensor device, it is possible to have characteristics of a high Q value and low mechanical noise.

[0009] In the above acceleration sensor device, the frame body, the mass portion, and the first beam portion may be formed by a laminated substrate of a lower semiconductor layer, an insulating layer, and an upper semiconductor layer. In this case, the frame body is formed by the lower semiconductor layer, the insulating layer, and the upper semiconductor layer. The mass portion is formed by the lower semiconductor layer, the insulating layer, and the upper semiconductor layer. The first beam portion is formed by the upper semiconductor layer. In this acceleration sensor device, the mass of the mass portion is increased, and mechanical noise is reduced.

[0010] In the acceleration sensor device, the mass portion may have a first divided mass portion and a second divided mass portion. The first divided mass portion and the second divided mass portion are connected in an insulated and separated state. The first movable detection electrode of each of the pair of first displacement detection electrode portions is fixed to the first divided mass portion, and the first movable servo electrode of each of the pair of first servo electrode portions is fixed to the second divided mass portion. The carrier signal generating circuit inputs the reference voltage to the first divided mass portion and the offset voltage to the second divided mass portion. In this acceleration sensor device, the reference voltage is prevented from being transmitted to the pair of first servo electrodes, enabling highly accurate servo control and acceleration detection.

[0011] In the above acceleration sensor device, the acceleration sensor may further include a pair of second displacement detection electrode units and a pair of second servo electrode units. Each of the pair of second displacement detection electrode units includes a second movable detection electrode and a second fixed detection electrode. The second movable detection electrode and the second fixed detection electrode face each other in a second direction perpendicular to the first direction, the second movable detection electrode is fixed to the mass portion, and the second fixed detection electrode is fixed to the frame body. The positive and negative of the change in the inter-electrode distance between the second movable detection electrode and the second fixed detection electrode with respect to the displacement of the mass portion in the second direction is opposite between the pair of second displacement detection electrode units. Each of the pair of second servo electrodes includes a second movable servo electrode and a second fixed servo electrode. The second movable servo electrode and the second fixed servo electrode face each other in the second direction, the second movable servo electrode is fixed to the mass portion, and the second fixed servo electrode is fixed to the frame body. The positive and negative of the change in the inter-electrode distance between the second movable servo electrode and the second fixed servo electrode with respect to the displacement of the mass portion in the second direction is opposite between the pair of second servo electrode portions. In the above acceleration sensor device, the processing circuit may further include a second capacitance conversion circuit portion, a second synchronous detection circuit, and a second servo signal generation circuit. The second capacitance conversion circuit portion outputs a second voltage signal corresponding to a difference in the capacitance change of each of the pair of second displacement detection electrode portions. The second synchronous detection circuit detects a second detection signal synchronized with the reference voltage from the second voltage signal. The second servo signal generation circuit inputs a second servo signal to the second fixed servo electrode of each of the pair of second servo electrode portions based on the second detection signal in order to suppress the displacement of the mass portion in the second direction. The positive and negative of the second servo signal are opposite between the pair of second fixed servo electrodes. This acceleration sensor device can detect multi-axis acceleration.

[0012] In the above acceleration sensor device for detecting multi-axial acceleration, the acceleration sensor may further include an anchor portion fixed to the frame, a first beam portion connected between the mass portion and the anchor portion and elastically deforming in the first direction, and a second beam portion connected between the mass portion and the anchor portion and elastically deforming in the second direction. Furthermore, a central opening may be formed in the mass portion, and only one of the anchor portions may be disposed at the symmetric center of the mass portion located within the central opening. In this case, the mass portion may be connected to the anchor portion via the first beam portion so as to be swingable in the first direction, and may be connected to the anchor portion via the second beam portion so as to be swingable in the second direction. This acceleration sensor device has a reduced anchor loss, and therefore has a high Q value and low mechanical noise characteristics.

[0013] In the above acceleration sensor device for detecting multi-axial acceleration, the frame body, the mass portion, the first beam portion, and the second beam portion may be formed by a laminated substrate of a lower semiconductor layer, an insulating layer, and an upper semiconductor layer. In this case, the frame body is formed by the lower semiconductor layer, the insulating layer, and the upper semiconductor layer. The mass portion is formed by the lower semiconductor layer, the insulating layer, and the upper semiconductor layer. The first beam portion is formed by the upper semiconductor layer. The second beam portion is formed by the upper semiconductor layer. In this acceleration sensor device, the mass of the mass portion is increased, and mechanical noise is reduced.

[0014] In the acceleration sensor device for detecting multi-axial acceleration, the mass portion may have a first divided mass portion and a second divided mass portion. The first divided mass portion and the second divided mass portion are fixed in an insulated and separated state. The first movable detection electrode of each of the pair of first displacement detection electrode portions and the second movable detection electrode of each of the pair of second displacement detection electrode portions are fixed to the first divided mass portion, and the first movable servo electrode of each of the pair of first servo electrode portions and the second movable servo electrode of each of the pair of second servo electrode portions are fixed to the second divided mass portion. The carrier wave signal generating circuit inputs the reference voltage to the first divided mass portion and inputs an offset voltage to the second divided mass portion. In this acceleration sensor device, the reference voltage is prevented from being transmitted to the pair of first servo electrode portions and the pair of second servo electrode portions, thereby enabling highly accurate servo control and acceleration detection. [Brief description of the drawings]

[0015] [Figure 1] 1 is a diagram illustrating an outline of a configuration of an acceleration sensor included in an acceleration sensor device according to a first embodiment. [Diagram 2] FIG. 1 is a functional block diagram of an acceleration sensor device according to a first embodiment. [Diagram 3] FIG. 13 is a diagram illustrating an outline of the configuration of an acceleration sensor included in an acceleration sensor device according to a second embodiment. [Figure 4] FIG. 11 is a functional block diagram of an acceleration sensor device according to a second embodiment. [Diagram 5] FIG. 2 is a plan view of the acceleration sensor according to the first embodiment, showing a schematic plan view of the sensor with a cap layer removed. [Figure 6] 6 is a cross-sectional view of the acceleration sensor according to the first embodiment, taken along line VI-VI in FIG. 5. [Figure 7] 6 is a cross-sectional view of the acceleration sensor according to a modified example of the first embodiment, taken along line VI-VI in FIG. 5. [Figure 8] FIG. 13 is a plan view of the acceleration sensor according to the second embodiment, showing a schematic plan view of the sensor with a cap layer removed. [Figure 9] FIG. 13 is a plan view of an acceleration sensor according to a modified example of the second embodiment, showing a schematic plan view of the sensor with a cap layer removed. [Figure 10] FIG. 13 is a plan view of the acceleration sensor according to the third embodiment, showing a schematic plan view of the sensor with a cap layer removed. [Figure 11] FIG. 13 is a plan view of the acceleration sensor according to the fourth embodiment, showing a schematic plan view of the sensor with a cap layer removed. [Figure 12] FIG. 13 is a plan view of an acceleration sensor according to a modified example of the fourth embodiment, showing a schematic plan view of the sensor with a cap layer removed. [Figure 13] FIG. 13 is a plan view of the acceleration sensor according to the fifth embodiment, showing a schematic plan view of the sensor with a cap layer removed. [Figure 14] 14 is a cross-sectional view of the acceleration sensor according to the fifth embodiment, showing a schematic cross-sectional view corresponding to line XIV-XIV in FIG. 13. [Figure 15] FIG. 13 is a plan view of the acceleration sensor according to the sixth embodiment, showing a schematic plan view of the sensor with a cap layer removed. [Figure 16] FIG. 13 shows a schematic enlarged plan view of a support having a double folded beam. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] (Acceleration sensor device 1 of the first embodiment) The configuration of the acceleration sensor device 1 will be described with reference to Figures 1 and 2. Figure 1 is a diagram showing an outline of the configuration of an acceleration sensor 100 in the acceleration sensor device 1. Note that Figure 1 also shows a pair of capacitance conversion circuits 212, 214 included in a processing circuit 200 in the acceleration sensor device 1. Figure 2 is a functional block diagram of the acceleration sensor device 1.

[0017] As shown in Fig. 1, the acceleration sensor 100 has a mass portion 112, a pair of x-axis displacement detection electrodes 122, 124, and a pair of x-axis servo electrodes 132, 134. In this example, a plane parallel to the surface of a substrate on which the acceleration sensor 100 is mounted is the xy plane, and a direction perpendicular to the substrate surface is the z-axis. The mass portion 112 is configured to be swingable in the x-axis direction relative to a frame (a portion formed by a part of the substrate) (not shown). A signal voltage application portion 114 is electrically connected to the mass portion 112, and as will be described later, a carrier signal V in is input to the signal voltage application unit 114.

[0018] Each of the pair of x-axis displacement detection electrodes 122, 124 has an x-axis movable detection electrode and an x-axis fixed detection electrode. The x-axis movable detection electrode and the x-axis fixed detection electrode face each other in the x-axis direction, the x-axis movable detection electrode is fixed to the mass portion 112, and the x-axis fixed detection electrode is fixed to the frame. In this example, the mass portion 112 itself is illustrated as operating as the x-axis movable detection electrode. Here, one of the pair of x-axis displacement detection electrodes 122, 124 is the first x-axis displacement detection electrode portion 122, and the other is the second x-axis displacement detection electrode portion 124. In this example, when the mass portion 112 is displaced to the right in the x-axis direction on the paper, the inter-electrode distance between the x-axis movable detection electrode and the x-axis fixed detection electrode of the first x-axis displacement detection electrode portion 122 becomes large, and the inter-electrode distance between the x-axis movable detection electrode and the x-axis fixed detection electrode of the second x-axis displacement detection electrode portion 124 becomes small. In this way, the positive and negative changes in the inter-electrode distance with respect to the displacement of the mass portion 112 in the x-axis direction are opposite between the pair of x-axis displacement detection electrodes 122, 124. When the mass portion 112 is in the initial position, the inter-electrode distances of the pair of x-axis displacement detection electrodes 122, 124 are equal. As will be described later, each of the pair of x-axis displacement detection electrodes 122, 124 may be formed of a comb-tooth electrode portion.

[0019] Each of the pair of x-axis servo electrode parts 132, 134 has an x-axis movable servo electrode and an x-axis fixed servo electrode. The x-axis movable servo electrode and the x-axis fixed servo electrode face each other in the x-axis direction, the x-axis movable servo electrode is fixed to the mass part 112, and the x-axis fixed servo electrode is fixed to the frame. In this example, the mass part 112 itself is illustrated as operating as the x-axis movable servo electrode. One of the pair of x-axis servo electrode parts 132, 134 is the first x-axis servo electrode part 132, and the other is the second x-axis servo electrode part 134. In this example, when the mass part 112 is displaced to the right in the x-axis direction on the paper, the inter-electrode distance between the x-axis movable servo electrode and the x-axis fixed servo electrode of the first x-axis servo electrode part 132 becomes larger, and the inter-electrode distance between the x-axis movable servo electrode and the x-axis fixed servo electrode of the second x-axis servo electrode part 134 becomes smaller. In this way, the positive and negative changes in the inter-electrode distance with respect to the displacement of the mass portion 112 in the x-axis direction are opposite between the pair of x-axis servo electrodes 132, 134. When the mass portion 112 is in the initial position, the inter-electrode distances of the pair of x-axis servo electrodes 132, 134 are equal. As will be described later, each of the pair of x-axis servo electrodes 132, 134 may be formed of a comb-tooth electrode portion.

[0020] Next, the configuration of the processing circuit 200 of the acceleration sensor device 1 will be described with reference to Fig. 2. The processing circuit 200 has an x-axis capacitance conversion circuit section 210, a carrier signal generation circuit 220, an x-axis synchronous detection circuit 230, and an x-axis servo signal generation circuit 240.

[0021] The x-axis capacitance conversion circuit section 210 has a pair of capacitance conversion circuits 212, 214 and a differential circuit 216. The first capacitance conversion circuit 212 of the pair of capacitance conversion circuits 212, 214 converts the capacitance (C+ΔC) between the electrodes of the first x-axis displacement detection electrode section 122 into a voltage (V 1 ) (see FIG. 1). Similarly, the second capacitance conversion circuit 214 of the pair of capacitance conversion circuits 212, 214 converts the capacitance (C-ΔC) between the electrodes of the second x-axis displacement detection electrode unit 124 into a voltage (V 2 ) (see FIG. 1). The differential circuit 216 converts the output voltage V 1and the output voltage V of the second capacitance conversion circuit 214 2 That is, a differential voltage corresponding to the difference between the capacitance changes of the pair of x-axis displacement detection electrodes 122, 124 (2ΔC) is output.

[0022] The carrier signal generating circuit 220 generates a DC offset voltage V o and the AC reference voltage V ref This is a power supply circuit that generates the offset voltage V o is a voltage applied to generate a difference in the electrostatic attractive force acting between the electrodes of the pair of x-axis servo electrode units 132 and 134, as described later. ref is an AC voltage having a frequency higher than the mechanical resonance frequency of the acceleration sensor device 1. The carrier signal generating circuit 220 generates the offset voltage V o and the reference voltage V ref A carrier signal V containing in is input to the signal voltage application unit 114 of the acceleration sensor 100. The carrier signal generation circuit 220 further inputs a reference voltage V ref is also input to the x-axis synchronous detection circuit 230.

[0023] The x-axis synchronous detection circuit 230 detects a reference voltage V ref This detects the detection signal synchronized with the reference voltage V ref A noise component having a frequency different from that of the pair of x-axis displacement detection electrodes 122, 124 is removed, and a detection signal is obtained that corresponds to the difference (2ΔC) in the capacitance change between the pair of x-axis displacement detection electrodes 122, 124. The detection signal is input to the x-axis servo signal generation circuit 240.

[0024] The x-axis servo signal generating circuit 240 has a PID controller 242 and a positive / negative inversion circuit 244. The PID controller 242 is a circuit that generates an x-axis servo signal to be input to each fixed servo electrode of the pair of x-axis servo electrode sections 132, 134 based on the detection signal output from the x-axis synchronous detection circuit 230 in order to suppress the displacement of the mass section 112 in the x-axis direction, i.e., to maintain the mass section 112 at its initial position. That is, the PID controller 242 generates an operation amount (x-axis servo signal) for making the detection signal output from the x-axis synchronous detection circuit 230 "0". In addition, this operation amount (x-axis servo signal) is a sensor output, and corresponds to the acceleration measured by the acceleration sensor device 1. The positive / negative inversion circuit 244 inverts the x-axis servo signal (V out ) is inverted. The first x-axis servo electrode unit 132 receives the x-axis servo signal (V out ) is input as is. The second x-axis servo electrode section 134 receives the x-axis servo signal (V out ) is the inverted x-axis servo signal (-V out In this way, the pair of x-axis servo electrode parts 132 and 134 receive x-axis servo signals (V out ) is entered.

[0025] Next, a description will be given of the operation of the acceleration sensor device 1. First, the outputs of the pair of capacitance conversion circuits 212 and 214 will be described.

[0026] 1, each of the pair of capacitance conversion circuits 212, 214 is connected to the corresponding x-axis displacement detection electrode unit 122, 124 of the pair of x-axis displacement detection electrodes 122, 124. Specifically, each of the pair of capacitance conversion circuits 212, 214 has an operational amplifier, the inverting input terminal (-) of which is connected to the x-axis fixed detection electrode of the corresponding pair of x-axis displacement detection electrodes 122, 124, and a capacitance C f A capacitor with resistance R fThe non-inverting input terminal (+) of the operational amplifier of each of the pair of capacitance conversion circuits 212 and 214 is connected to ground. The output voltage V 1 ,V 2 is generalized to be the output voltage V, and the capacitance between the pair of x-axis displacement detection electrodes 122 and 124 is generalized to be the capacitance C, the output voltage V can be expressed by the following formula. ref is the angular frequency of

number

[0027] Offset voltage V o is a DC voltage, so ω=0. Therefore, V=0, and the DC component does not affect the output. On the other hand, the reference voltage V ref is an AC voltage, and ω is sufficiently larger than 1 / CfRf (ω>>1 / CfRf). Therefore, in each of the pair of capacitance conversion circuits 212 and 214, the reference voltage V ref As a result, the output voltage V of each of the pair of capacitance conversion circuits 212 and 214 can be expressed by the following formula:

number

[0028] In this way, each of the pair of x-axis displacement detection electrodes 122, 124 operates as a so-called high-pass filter. o and the reference voltage V ref The carrier signal V in is input, but the reference voltage V ref Only the offset voltage V o has no effect on CV conversion.

[0029] Next, the pair of x-axis servo electrodes 132 and 134 will be described. The displacement of the mass portion 112 is minute, and the reference voltage V refIn the absence of the above, the electrostatic attractive force F acting on the mass portion 112 by the pair of x-axis servo electrodes 132 and 134 is expressed by the following formula: where ε is the dielectric constant between the electrodes of the pair of x-axis servo electrodes 132 and 134, S is the electrode area, and d 0 is the initial gap between the electrodes. Also, the electrostatic attraction force acting between the electrodes of the first x-axis servo electrode unit 132 is F 1 The electrostatic attraction force acting between the electrodes of the second x-axis servo electrode unit 134 is F 2 Let us assume that.

number

[0030] As described above, the electrostatic attractive force F acting on the mass portion 112 is proportional to the offset voltage V o When is set to a fixed value, the x-axis servo signal (V out Here, in the acceleration sensor 100, the mass portion 112 is supplied with an offset voltage V o and the reference voltage V ref The carrier signal V in Since the reference voltage V is input to each of the x-axis movable servo electrodes of the pair of x-axis servo electrode units 132 and 134, ref is added. The reference voltage V ref Taking this into consideration, the electrostatic attractive force F acting on the mass portion 112 is expressed by the following formula.

number

[0031] The first term on the right side of Equation 4 is the servo generated force. Meanwhile, the second term on the right side of Equation 4 is the unwanted generated force. Here, the reference voltage V ref Let V be the AC voltage with angular frequency ω. ref cosωt and the resonant angular frequency of the acceleration sensor 100 is expressed as ω n Then, the following formula is established regarding vibration due to the unwanted force: m is the mass of the mass portion 112, and x is the vibration amplitude of the mass portion 112 due to the unwanted force.

number

number

[0032] As shown in Equation 6, the vibration amplitude x of the mass portion 112 due to the unwanted force is expressed by the reference voltage V ref The angular frequency ω of the acceleration sensor 100 is expressed as the resonant angular frequency ω n It is possible to make it sufficiently small by making it sufficiently higher than the

[0033] In the acceleration sensor device 1, a pair of x-axis displacement detection electrodes 122, 124 for detecting the displacement of the mass portion 112 in the x-axis direction, and a pair of x-axis servo electrodes 132, 134 for applying an electrostatic force to the mass portion 112 are provided independently. As a result, a reference voltage V ref Even if noise with a frequency close to that of the reference voltage V ref Only the reference voltage V ref Since the influence of unwanted forces due to the vibration can be sufficiently suppressed, highly accurate servo control of the mass portion 112 is possible. In this way, the acceleration sensor device 1 can perform acceleration detection and servo control with high accuracy. In addition, the technology of the acceleration sensor device 1, as will be described later, uses a single reference voltage V ref The present invention can also be suitably used when detecting acceleration along multiple axes. In the examples described later, several acceleration sensors that can be used in the acceleration sensor device 1 of the first embodiment will be exemplified, but the above-mentioned highly accurate acceleration detection and servo control effects can be achieved in the acceleration sensor device 1 using any of the acceleration sensors.

[0034] (Acceleration sensor device 2 of the second embodiment) The configuration of the acceleration sensor device 2 will be described with reference to Figures 3 and 4. Note that components common to the acceleration sensor device 1 shown in Figures 1 and 2 are denoted by the same reference numerals, and description thereof will be omitted.

[0035] The acceleration sensor 100 of the acceleration sensor device 2 is characterized in that the mass portion 112 has a first divided mass portion 112a and a second divided mass portion 112b. The first divided mass portion 112a and the second divided mass portion 112b are connected via a connection portion 113. The first divided mass portion 112a and the connection portion 113 are insulated from each other, and the second divided mass portion 112b and the connection portion 113 are also insulated from each other. Therefore, the first divided mass portion 112a and the second divided mass portion 112b are connected via the connection portion 113 in an insulated and separated state. The first divided mass portion 112a is fixed with each of the x-axis movable detection electrodes of the pair of x-axis displacement detection electrode portions 122, 124. In this example, the first divided mass portion 112a itself is illustrated as operating as the x-axis movable detection electrode. The second divided mass portion 112b is fixed with each of the x-axis movable servo electrodes of the pair of x-axis servo electrode portions 132, 134. In this example, the second divided mass portion 112b itself is illustrated as operating as the x-axis movable servo electrode.

[0036] In the acceleration sensor 100, a reference voltage application section 114a is electrically connected to the first divided mass section 112a, and an offset voltage application section 114b is electrically connected to the second divided mass section 112b. A reference voltage V ref is input, and the offset voltage application unit 114b receives the offset voltage V o is entered.

[0037] In this acceleration sensor 100, the reference voltage V ref The first divided mass section 112a to which the offset voltage V o The second divided mass portion 112b to which the reference voltage V refis prevented from being transmitted to the pair of x-axis servo electrodes 132, 134, the generation of the unnecessary force as shown in Equation 6 is suppressed. This enables highly accurate servo control of the mass portion 112. Similarly to the acceleration sensor device 1, the acceleration sensor device 2 also has a pair of x-axis displacement detection electrodes 122, 124 for detecting the displacement of the mass portion 112 in the x-axis direction, and a pair of x-axis servo electrodes 132, 134 for applying an electrostatic attractive force to the mass portion 112, which are provided independently. For this reason, in addition to the x-axis servo signal Vout, a reference voltage V ref Even if noise with a frequency close to that of the reference voltage V ref Only the reference voltage V ref Since the influence of the unwanted force due to the saturation can be sufficiently suppressed, high-precision servo control of the mass portion 112 is possible. ref Since only the reference voltage V ref The electrostatic attractive force caused by the above can be balanced between the pair of x-axis displacement detection electrodes 122, 124. Therefore, no unnecessary force is applied to the mass portion 112. This also enables highly accurate servo control of the mass portion 112. In the examples described later, several acceleration sensors that can be used in the acceleration sensor device 2 of the second embodiment will be exemplified, but the above-mentioned highly accurate acceleration detection and servo control effects can be achieved in any acceleration sensor used in the acceleration sensor device 2. EXAMPLES

[0038] Hereinafter, examples of acceleration sensors suitable for realizing the acceleration sensor 100 included in the acceleration sensor devices 1 and 2 of the first and second embodiments will be described. Note that components common to the acceleration sensor 100 of the first and second embodiments will be denoted by the same reference numerals.

[0039] (Acceleration sensor 11 of the first embodiment) An acceleration sensor 11 shown in Fig. 5 and Fig. 6 is an example of a realization of the acceleration sensor 100 of the first embodiment described above. The acceleration sensor 11 is formed by processing a laminated substrate of a lower semiconductor layer 20, an insulating layer 30, and an upper semiconductor layer 40. The lower semiconductor layer 20 and the upper semiconductor layer 40 are, for example, semiconductor layers of silicon single crystal. The upper semiconductor layer 40 contains a high concentration of impurities and has electrical conductivity. The insulating layer 30 is, for example, silicon oxide, and electrically insulates the lower semiconductor layer 20 and the upper semiconductor layer 40. The laminated substrate of the lower semiconductor layer 20, the insulating layer 30, and the upper semiconductor layer 40 is a so-called SOI (Silicon on Insulator) substrate.

[0040] The acceleration sensor 11 includes a frame 110 formed to surround the mass portion 112, various support portions, various electrode portions, etc. The frame 110 is formed by a part of a laminated substrate of the lower semiconductor layer 20, the insulating layer 30, and the upper semiconductor layer 40, and can be said to be a part of the laminated substrate excluding the mass portion 112, various support portions, various electrode portions, etc. In this example, the frame 110 also includes the lower semiconductor layer 20 disposed below the mass portion 112. A bonding region 111 for bonding the cap layer 50 is secured on the surface of the upper semiconductor layer 40 of the frame 110. The bonding region 111 is positioned to surround the mass portion 112, various support portions, various electrode portions, etc.

[0041] The mass portion 112 is formed by a part of the upper semiconductor layer 40, and is suspended relative to the frame body 110. The mass portion 112 has a substantially rectangular shape when viewed in a plan view (when observed from the z-axis direction). The mass portion 112 is supported by the frame body 110 via x-axis supports 140 provided in the vicinity of each of the four corners.

[0042] The x-axis support portion 140 is a support structure for allowing the mass portion 112 to be displaced in the x-axis direction relative to the frame body 110, and has an anchor portion 142 and an x-axis beam portion 144. The anchor portion 142 is formed of a laminated substrate of the lower semiconductor layer 20, the insulating layer 30, and the upper semiconductor layer 40, and is a portion fixed to the frame body 110. The x-axis beam portion 144 is formed of a part of the upper semiconductor layer 40. The insulating layer 30 between the x-axis beam portion 144 and the lower semiconductor layer 20 is removed, and the x-axis beam portion 144 is floating with respect to the frame body 110. The x-axis beam portion 144 is configured as a so-called folded beam, with one end connected to the mass portion 112 and the other end connected to the anchor portion 142. The x-axis beam portion 144 is configured so that a beam extending in the y-axis direction is folded back, and has a small spring constant in the x-axis direction and a large spring constant in the y-axis and z-axis directions. For this reason, the x-axis beam portion 144 is easily elastically deformed in the x-axis direction, but is not easily elastically deformed in the y-axis and z-axis directions. As a result, the mass portion 112 supported by the x-axis support portion 140 can be displaced in the x-axis direction relative to the frame body 110 by the x-axis beam portion 144 elastically deforming in the x-axis direction.

[0043] Each of the pair of x-axis detection electrodes 122, 124 and the pair of x-axis servo electrodes 132, 134 is configured by a so-called comb-tooth electrode portion. These four electrodes 122, 124, 132, 134 have a common structure. Therefore, only the first x-axis detection electrode portion 122 will be described below. Components with symbols given according to a common rule are components with a common structure and function.

[0044] The first x-axis detection electrode unit 122 has a plurality of x-axis movable detection electrodes 122a and a plurality of x-axis fixed detection electrodes 122b. Each of the plurality of x-axis movable detection electrodes 122a and the plurality of x-axis fixed detection electrodes 122b is formed by a part of the upper semiconductor layer 40. Each of the plurality of x-axis movable detection electrodes 122a is fixed to a side surface of an extension extending from the mass portion 112. This allows the plurality of x-axis movable detection electrodes 122a to be displaced following the displacement of the mass portion 112 in the x-axis direction. Each of the plurality of x-axis fixed detection electrodes 122b is disposed opposite the corresponding x-axis movable detection electrode 122a in the x-axis direction and is fixed to the frame body 110. The plurality of x-axis fixed detection electrodes 122b are electrically connected to a connection electrode 122d formed on the surface of the cap layer 50 via a through silicon via (TSV: Thorough Silicon Via) 122c penetrating the cap layer 50. The silicon through-hole electrode 122c has a through-hole with a side surface covered with SiO 2 The cap layer 50 is insulated with a material such as silicon dioxide, and the through holes are filled with a material such as doped silicon. 2 etc., and the connection electrode 122d and the silicon through electrode 122c are electrically connected to each other. The connection electrode 122d of the first x-axis detection electrode portion 122 is connected to the inverting connection terminal (-) of the first capacitance conversion circuit 212 (see FIG. 1).

[0045] The signal voltage application unit 114 is electrically connected to an upper semiconductor layer 40 arranged around the mass portion 112, various support portions, various electrode portions, etc., via a silicon through electrode (not shown) that penetrates the cap layer 50, and the upper semiconductor layer 40 is connected to the anchor portion 142. As a result, the signal voltage application unit 114 is electrically connected to the movable electrodes 122a, 124a, 132a, 134a of the four electrode portions 122, 124, 132, 134, respectively, via the x-axis support portion 140 and the upper semiconductor layer 40 of the mass portion 112.

[0046] In the acceleration sensor 11, a mass portion 112 is disposed in a space surrounded by a frame 110 and a cap layer 50. For example, a junction region 111 of the semiconductor upper layer 50 and the cap layer 50 may be formed of Si-Si or Si-SiO2 The frame 110 and the cap layer 50 are directly bonded together, and the space surrounded by the frame 110 and the cap layer 50 is a vacuum. That is, the acceleration sensor 11 has a wafer level package (WLP) structure. Therefore, the acceleration sensor 11 can have a high Q value characteristic even in a compact state. The acceleration sensor 11 having a high Q value characteristic has a low mechanical noise (N mech ) is reduced, and acceleration can be detected with high accuracy. B is the Boltzmann constant, T is the absolute temperature, and ω n is the resonance angular frequency of the acceleration sensor 11, m is the mass of the mass portion 112, and Q is the vibration Q value of the acceleration sensor.

number

[0047] It is generally known that an acceleration sensor having a high Q-value characteristic generates free vibration at the resonant frequency in the mass portion when acceleration is applied, and it takes a long time for the amplitude to attenuate. For this reason, it is known that an acceleration sensor having a high Q-value characteristic has poor responsiveness. However, since the acceleration sensor 11 suppresses the displacement of the mass portion 112 by servo control, it is possible to suppress such deterioration in responsiveness. In this way, the acceleration sensor 11 can have high responsiveness while having a high Q-value and low mechanical noise characteristics.

[0048] FIG. 7 shows a modified example of the acceleration sensor 11. In this example, the mass portion 112 is formed by a laminated substrate of the lower semiconductor layer 20, the insulating layer 30, and the upper semiconductor layer 40. In this example, the mass of the mass portion 112 is increased, so that mechanical noise is further reduced. The acceleration sensor 11 of this example also includes a lower cap layer 60 bonded to the rear surface of the lower semiconductor layer 20. The space in which the mass portion 112 exists is maintained as a vacuum by the frame 110, the upper cap layer 50, and the lower cap layer 60. Therefore, the acceleration sensor 11 of this modified example can also have a high Q value and low mechanical noise characteristics. The technology in which the mass portion 112 is formed by a laminated substrate can be applied to other embodiments.

[0049] (Acceleration sensor 12 of the second embodiment) 8 is an example of a realization of the acceleration sensor 100 of the first embodiment described above. This acceleration sensor 12 is characterized in that an x-axis support section 140 that supports a mass section 112 is surrounded by the mass section 112. In other words, the x-axis support section 140 is disposed in a central opening formed in the center of the mass section 112.

[0050] In the x-axis support section 140, only one anchor section 142 is provided for the mass section 112. The mass section 112 is supported by the frame 110 through the single anchor section 142. The anchor section 142 is disposed so as to include a position that is the center of symmetry of the mass section 112, and is located at the center of the acceleration sensor 12, i.e., the center of symmetry of the sensor structure. The anchor section 142 also receives a carrier signal V in A signal voltage application section for inputting a signal voltage is also formed. The x-axis beam section 144 is configured as a so-called straight beam, with one end connected to the mass section 112 and the other end connected to the anchor section 142. The x-axis beam section 144 is composed of multiple beams extending in the y-axis direction, with a small spring constant in the x-axis direction and a large spring constant in the y-axis and z-axis directions. As a result, the mass section 112 supported by the x-axis support section 140 can be displaced in the x-axis direction relative to the frame body 110 by the x-axis beam section 144 elastically deforming in the x-axis direction.

[0051] In this acceleration sensor 12, anchor portion 142 is fixed at one point in the center of mass portion 112, so anchor loss, which is one type of energy loss in vibration, is reduced. As a result, acceleration sensor 12 can have characteristics of a high Q value and low mechanical noise.

[0052] 9, the x-axis beam portion 144 may be configured as a so-called folded beam. Such a folded beam x-axis beam portion 144 has a structure that is not easily affected by residual internal stress. Therefore, the acceleration sensor 12 can have high reliability.

[0053] (Acceleration sensor 13 of the third embodiment) An acceleration sensor 13 shown in Fig. 10 is an example of a realization of the acceleration sensor 100 of the first embodiment described above. In particular, this acceleration sensor 13 is configured to be able to detect acceleration in the y-axis direction as well as acceleration in the x-axis direction. The acceleration sensor 13 can also be said to be a modified example of the acceleration sensor 11 of the first embodiment shown in Figs. 5 and 6.

[0054] The acceleration sensor 13 has a pair of y-axis displacement detection electrodes 322, 324 and a pair of y-axis servo electrodes 332, 334. The pair of y-axis displacement detection electrodes 322, 324 and the pair of y-axis servo electrodes 332, 334 have the same structure as the pair of x-axis displacement detection electrodes 122, 124 and the pair of x-axis servo electrodes 132, 134 except for the orientation, so the description thereof will be omitted. The acceleration sensor 13 further has four y-axis support portions 340 for allowing the mass portion 112 to be displaced in the y-axis direction relative to the frame 110. The y-axis support portions 340 also have the same structure as the x-axis support portions 140 except for the orientation, so the description thereof will be omitted. In the acceleration sensor 13, the pair of x-axis displacement detection electrodes 122, 124 are arranged in a symmetrical positional relationship with respect to the center of the sensor structure. Similarly, a pair of x-axis servo electrode sections 132, 134 are also arranged in a symmetrical positional relationship with respect to the center of the sensor structure, a pair of y-axis displacement detection electrode sections 322, 324 are also arranged in a symmetrical positional relationship with respect to the center of the sensor structure, and a pair of y-axis servo electrode sections 332, 334 are also arranged in a symmetrical positional relationship with respect to the center of the sensor structure.

[0055] The acceleration sensor 13 further includes four y-axis straight beams 146 , a pair of x-axis frames 148 , four x-axis straight beams 346 , and a pair of y-axis frames 348 .

[0056] Each of the four y-axis straight beams 146 is formed by a part of the upper semiconductor layer 40 and floats with respect to the frame 110. Each of the four y-axis straight beams 146 extends along the x-axis direction, with one end connected to the mass portion 112 and the other end connected to the corresponding x-axis frame 148. Each of the four y-axis straight beams 146 has a small spring constant in the y-axis direction and a large spring constant in the x-axis and z-axis directions. Therefore, each of the four y-axis straight beams 146 is easily elastically deformed in the y-axis direction and is difficult to elastically deform in the x-axis and z-axis directions. Each of the pair of x-axis frames 148 is formed by a part of the upper semiconductor layer 40 and floats with respect to the frame 110. The pair of x-axis frames 148 can be evaluated as a part of the mass portion 112. The first x-axis displacement detection electrode 122, the first x-axis servo electrode 132, and the pair of x-axis support parts 140 are arranged on one of the pair of x-axis frames 148, and the second x-axis displacement detection electrode 124, the second x-axis servo electrode 134, and the pair of x-axis support parts 140 are arranged on the other x-axis frame 148. When the mass part 112 is displaced in the y-axis direction, in addition to the elastic deformation of the four y-axis support parts 340, the four y-axis straight beams 146 also elastically deform, thereby allowing the displacement of the mass part 112 (and the pair of y-axis frames 348) in the y-axis direction. If the four y-axis straight beams 146 were not provided, the displacement of the mass part 112 in the y-axis direction would be prohibited by the four x-axis support parts 140. In the acceleration sensor 13, because four y-axis straight beams 146 are provided, the displacement of the mass portion 112 in the y-axis direction can be tolerated even if four x-axis support portions 140 are provided. Furthermore, when the mass portion 112 is displaced in the y-axis direction, the four y-axis straight beams 146 elastically deform in the y-axis direction, thereby suppressing the displacement of the pair of x-axis frames 148 in the y-axis direction. In this way, in the acceleration sensor 13, the pair of x-axis displacement detection electrodes 122, 124 and the pair of x-axis servo electrodes 132, 134 are independent of the displacement of the mass portion 112 in the y-axis direction.

[0057] Each of the four x-axis straight beams 346 is formed by a part of the upper semiconductor layer 40 and floats with respect to the frame 110. Each of the four x-axis straight beams 346 extends along the y-axis direction, with one end connected to the mass portion 112 and the other end connected to the corresponding y-axis frame 348. Each of the four x-axis straight beams 346 has a small spring constant in the x-axis direction and a large spring constant in the y-axis and z-axis directions. Therefore, each of the four x-axis straight beams 346 is easily elastically deformed in the x-axis direction and is difficult to elastically deform in the y-axis and z-axis directions. Each of the pair of y-axis frames 348 is formed by a part of the upper semiconductor layer 40 and floats with respect to the frame 110. The pair of y-axis frames 348 can be evaluated as a part of the mass portion 112. The first y-axis displacement detection electrode 322, the first y-axis servo electrode 332, and the pair of y-axis support parts 340 are arranged on one y-axis frame 348 of the pair of y-axis frames 348, and the second y-axis displacement detection electrode 324, the second y-axis servo electrode 334, and the pair of y-axis support parts 340 are arranged on the other y-axis frame 348. When the mass part 112 is displaced in the x-axis direction, in addition to the elastic deformation of the four x-axis support parts 140, the four x-axis straight beams 346 also elastically deform, thereby allowing the displacement of the mass part 112 (and the pair of x-axis frames 148) in the x-axis direction. If the four x-axis straight beams 346 were not provided, the displacement of the mass part 112 in the x-axis direction would be prohibited by the four y-axis support parts 340. In the acceleration sensor 13, because four x-axis straight beams 346 are provided, the displacement of the mass portion 112 in the x-axis direction can be tolerated even if four y-axis support portions 340 are provided. Furthermore, when the mass portion 112 is displaced in the x-axis direction, the four x-axis straight beams 346 elastically deform in the x-axis direction, thereby suppressing the displacement of the pair of y-axis frames 348 in the x-axis direction. In this way, in the acceleration sensor 13, the pair of y-axis displacement detection electrodes 322, 324 and the pair of y-axis servo electrodes 332, 334 are independent of the displacement of the mass portion 112 in the x-axis direction.

[0058] In comparison with the processing circuit 200 shown in FIG. 2, the processing circuit connected to the acceleration sensor 13 is configured such that a y-axis capacitance conversion circuit section and a y-axis synchronous detection circuit are added corresponding to a pair of y-axis displacement detection electrodes 322, 324, and a y-axis servo signal generation circuit section is added corresponding to a pair of y-axis servo electrodes 332, 334.

[0059] The acceleration sensor 13 is provided with only one signal voltage application unit 114. In this manner, the acceleration sensor 13 does not need to generate different carrier signals for acceleration detection and servo control in the x-axis direction and the y-axis direction. The acceleration sensor 13 can have a simple configuration.

[0060] As described above, in acceleration sensor 13, the four y-axis straight beams 146 isolate the pair of x-axis displacement detection electrodes 122, 124 and the pair of x-axis servo electrodes 132, 134 from the displacement of mass portion 112 in the y-axis direction, and similarly, the four x-axis straight beams 346 isolate the pair of y-axis displacement detection electrodes 322, 324 and the pair of y-axis servo electrodes 332, 334 from the displacement of mass portion 112 in the x-axis direction. Therefore, in acceleration sensor 13, the influence on other axes is suppressed, and acceleration detection and servo control can be performed with high accuracy in each axial direction.

[0061] (Acceleration sensor 14 of the fourth embodiment) The acceleration sensor 14 shown in FIG. 11 is an example of the acceleration sensor 100 of the first embodiment described above. In particular, the acceleration sensor 14 is configured to be capable of detecting acceleration in the y-axis direction in addition to acceleration in the x-axis direction. Furthermore, the acceleration sensor 14 is characterized in that the anchor portion 118, the pair of x-axis support portions 440, the pair of y-axis support portions 540, the displacement detection electrodes 122, 124, 322, 324, and the servo electrodes 132, 134, 332, 334 are surrounded by the mass portion 112. In other words, these sensor structures are disposed in a central opening formed in the center of the mass portion 112. In the acceleration sensor 14, only one anchor portion 118 is provided for the mass portion 112. The mass portion 112 is supported by the single anchor portion 118 with respect to the frame 110. The anchor portion 118 is disposed so as to include a position that is the symmetric center of the mass portion 112, and is located at the center of the acceleration sensor 14, i.e., the symmetric center of the sensor structure. in In this example, each of the pair of x-axis support parts 440 is configured as a so-called straight beam, and each of the pair of y-axis support parts 540 is also configured as a so-called straight beam.

[0062] Each of the four y-axis straight beams 146 extends along the x-axis direction, with one end connected to the mass portion 112 and the other end connected to the corresponding x-axis frame 148. An x-axis support portion 440 is connected between the x-axis frame 148 and the anchor portion 118. The x-axis support portion 440 has a straight beam extending in the y-axis direction, and is easily elastically deformed in the x-axis direction and is not easily elastically deformed in the y-axis and z-axis directions. The first x-axis displacement detection electrode portion 122, the first x-axis servo electrode portion 132, and the x-axis support portion 440 are arranged on one x-axis frame 148 of the pair of x-axis frames 148, and the second x-axis displacement detection electrode portion 124, the second x-axis servo electrode portion 134, and the x-axis support portion 440 are arranged on the other x-axis frame 148.

[0063] Each of the four x-axis straight beams 346 extends along the y-axis direction, with one end connected to the mass portion 112 and the other end connected to the corresponding y-axis frame 348. A y-axis support portion 540 is connected between the y-axis frame 348 and the anchor portion 118. The y-axis support portion 540 has a straight beam extending in the x-axis direction, and is easily elastically deformed in the y-axis direction and is not easily elastically deformed in the x-axis and z-axis directions. The first y-axis displacement detection electrode portion 322, the first y-axis servo electrode portion 332, and the y-axis support portion 540 are arranged on one y-axis frame 348 of the pair of y-axis frames 348, and the second y-axis displacement detection electrode portion 324, the second y-axis servo electrode portion 334, and the y-axis support portion 540 are arranged on the other y-axis frame 348.

[0064] When the mass portion 112 is displaced in the y-axis direction, not only the four y-axis support portions 540 but also the four y-axis straight beams 146 are elastically deformed, thereby allowing the mass portion 112 (and the pair of y-axis frames 348) to be displaced in the y-axis direction. When the mass portion 112 is displaced in the y-axis direction, the four y-axis straight beams 146 are elastically deformed in the y-axis direction, thereby suppressing the displacement of the pair of x-axis frames 148 in the y-axis direction. In this way, in the acceleration sensor 14, the pair of x-axis displacement detection electrodes 122, 124 and the pair of x-axis servo electrodes 132, 134 are independent of the displacement of the mass portion 112 in the y-axis direction.

[0065] When the mass portion 112 is displaced in the x-axis direction, not only the four x-axis support portions 440 but also the four x-axis straight beams 346 are elastically deformed, thereby allowing the mass portion 112 (and the pair of x-axis frames 148) to be displaced in the x-axis direction. When the mass portion 112 is displaced in the x-axis direction, the four x-axis straight beams 346 are elastically deformed in the x-axis direction, thereby suppressing the displacement of the pair of y-axis frames 348 in the x-axis direction. In this way, in the acceleration sensor 14, the pair of y-axis displacement detection electrodes 322, 324 and the pair of y-axis servo electrodes 332, 334 are independent of the displacement of the mass portion 112 in the x-axis direction.

[0066] As described above, in the acceleration sensor 14, the pair of x-axis displacement detection electrodes 122, 124 and the pair of x-axis servo electrodes 132, 134 are independent of the displacement of the mass portion 112 in the y-axis direction by the four y-axis straight beams 146, and similarly, the pair of y-axis displacement detection electrodes 322, 324 and the pair of y-axis servo electrodes 332, 334 are independent of the displacement of the mass portion 112 in the x-axis direction by the four x-axis straight beams 346. Therefore, in the acceleration sensor 14, the influence on the other axes is suppressed, so that the acceleration detection and servo control can be performed with high accuracy in each axis direction. Furthermore, in the acceleration sensor device 14, the anchor portion 118 is fixed at one point in the center of the mass portion 112, so that the anchor loss, which is one of the energy losses of vibration, is reduced. Therefore, the acceleration sensor 14 can have a high Q value and low mechanical noise characteristics.

[0067] 12, each of the x-axis support section 440 and the y-axis support section 540 may be configured as a so-called folded beam. Such folded beam x-axis support section 440 and y-axis support section 540 have a structure that is not easily affected by residual internal stress. Therefore, this acceleration sensor 15 can have high reliability.

[0068] (Acceleration sensor 16 of the fifth embodiment) An acceleration sensor 16 shown in Figures 13 and 14 is an example that embodies the acceleration sensor 100 of the second embodiment described above. It can also be said that the acceleration sensor 16 is a modified example of the acceleration sensor 11 of the first example shown in Figures 5 and 6. Note that the technology applied to the acceleration sensor 16 can also be applied to the other examples.

[0069] In this acceleration sensor 16, the mass portion 112 has a first divided mass portion 112a and a second divided mass portion 112b, and the first divided mass portion 112a and the second divided mass portion 112b are connected via a connection portion 113. The connection portion 113 has a structure in which an insulating layer and a silicon layer are laminated, and is joined to the first divided mass portion 112a and the second divided mass portion 112b via the insulating layer. Therefore, the first divided mass portion 112a is insulated from the connection portion 113, and the second divided mass portion 112b is also insulated from the connection portion 113. Therefore, the first divided mass portion 112a and the second divided mass portion 112b are connected via the connection portion 113 in an insulated and separated state. A pair of x-axis displacement detection electrodes 122, 124 is provided in the first divided mass portion 112a. A pair of x-axis servo electrodes 132, 134 is provided in the second divided mass portion 112b.

[0070] The reference voltage application unit 114a is electrically connected to the first divided mass portion 112a, and thereby electrically connected to each of the x-axis movable detection electrodes of the pair of x-axis displacement detection electrode portions 122, 124. The offset voltage application unit 114b is electrically connected to the second divided mass portion 112b, and thereby electrically connected to each of the x-axis movable servo electrodes of the pair of x-axis servo electrode portions 132, 134.

[0071] As described above, in such an acceleration sensor 16, the reference voltage V ref The first divided mass section 112a to which the offset voltage V o The second divided mass portion 112b to which the reference voltage V ref Since the transmission of the reference voltage V to the pair of x-axis servo electrodes 132 and 134 is suppressed, the generation of the unnecessary force as shown in Equation 6 is suppressed. This enables highly accurate servo control of the mass portion 112. In addition, the first divided mass portion 112a is supplied with the reference voltage V ref Since only the reference voltage V refThe electrostatic attractive force caused by the above can be balanced between the pair of x-axis displacement detection electrodes 122, 124. As a result, no unnecessary force is applied to the mass portion 112. This also makes it possible to perform highly accurate servo control of the mass portion 112.

[0072] (Acceleration sensor 17 of the sixth embodiment) An acceleration sensor 17 shown in Fig. 15 is an example of a concrete embodiment of the acceleration sensor 100 of the second embodiment described above. It can also be said that the acceleration sensor 17 is a modified example of the acceleration sensor 13 of the third embodiment shown in Fig. 10. Note that the technology applied to the acceleration sensor 17 can also be applied to the other embodiments.

[0073] In this acceleration sensor 17, the mass portion is divided into four divided mass portions. A reference voltage V ref The pair of divided mass sections to which the offset voltage V is applied is the first divided mass section 112a. o The pair of divided mass portions to which the voltage is applied is the second divided mass portion 112b. These four divided mass portions are fixed together via connecting portion 113 while being insulated and separated from each other. Each of the pair of x-axis frames 148 is also divided into two, and these two divided frames are fixed together via connecting portion 149 while being insulated and separated from each other. Similarly, each of the pair of y-axis frames 348 is also divided into two, and these two divided frames are fixed together via connecting portion 349 while being insulated and separated from each other.

[0074] In this acceleration sensor 17, the reference voltage V ref The first divided mass section 112a to which the offset voltage V o The second divided mass portion 112b to which the reference voltage V ref Since the transmission of the reference voltage V to the pair of x-axis servo electrodes 132, 134 and the pair of y-axis servo electrodes 332, 334 is suppressed, the unnecessary force as shown in Equation 6 is not generated. This enables highly accurate servo control of the mass portion 112. In addition, the reference voltage Vref Since only the reference voltage V ref The electrostatic attractive force generated due to the above can be balanced between the pair of x-axis displacement detection electrodes 122, 124 and between the pair of y-axis displacement detection electrodes 322, 324. Therefore, no unnecessary force is applied to the mass portion 112. This also enables highly accurate servo control of the mass portion 112. With this acceleration sensor 17, acceleration can be detected independently on two axes with high accuracy.

[0075] In the above embodiment, a folded beam is used as an example of the structure of the support part. As shown in FIG. 16, a double folded beam may be used as the structure of the support part. The double folded beam is a structure having multiple folds between the anchor part and the mass part or the frame. The double folded beam can reduce the spring constant without increasing the beam length. Therefore, in an acceleration sensor having a double folded beam, the resonance frequency is reduced and mechanical noise can be further reduced.

[0076] Although specific examples of the present invention have been described above in detail, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and variations of the specific examples exemplified above. The technical elements described in this specification or drawings exhibit technical utility alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. In addition, the technology exemplified in this specification or drawings can achieve multiple objectives simultaneously, and achieving one of these objectives is itself technically useful. [Explanation of symbols]

[0077] 1: acceleration sensor device, 100: acceleration sensor, 114: signal voltage application section, 122: first x-axis detection electrode section, 124: second x-axis displacement detection electrode section, 132: first x-axis servo electrode section, 134: second x-axis servo electrode section, 200: processing circuit, 210: x-axis capacitance conversion circuit section, 212: first capacitance conversion circuit, 214: second capacitance conversion circuit, 216: differential circuit, 220: carrier wave signal generation circuit, 230: x-axis synchronous detection circuit, 240: x-axis servo signal generation circuit, 242: PID controller, 244: positive / negative inversion circuit

Claims

1. An acceleration sensor device including an acceleration sensor and a processing circuit, The acceleration sensor is A frame body, A mass portion configured to be swingable relative to the frame body in at least a first direction; a pair of first displacement detection electrode units, each of the pair of first displacement detection electrode units having a first movable detection electrode and a first fixed detection electrode, the first movable detection electrode and the first fixed detection electrode facing each other in the first direction, the first movable detection electrode being fixed to the mass portion and the first fixed detection electrode being fixed to the frame, and a positive / negative change in an inter-electrode distance between the first movable detection electrode and the first fixed detection electrode in response to a displacement of the mass portion in the first direction is opposite between the pair of first displacement detection electrode units; a pair of first servo electrode portions, each of the pair of first servo electrode portions having a first movable servo electrode and a first fixed servo electrode, the first movable servo electrode and the first fixed servo electrode facing each other in the first direction, the first movable servo electrode being fixed to the mass portion and the first fixed servo electrode being fixed to the frame, and a positive / negative change in an inter-electrode distance between the first movable servo electrode and the first fixed servo electrode in response to a displacement of the mass portion in the first direction is opposite between the pair of first servo electrodes; The processing circuitry includes: a carrier signal generating circuit for inputting a carrier signal to the mass section, the carrier signal including a DC offset voltage and an AC reference voltage; a first capacitance conversion circuit that outputs a first voltage signal corresponding to a difference between capacitance changes of the pair of first displacement detection electrodes; a first synchronous detection circuit that detects a first detection signal synchronized with the reference voltage from the first voltage signal; an acceleration sensor device comprising: a first servo signal generating circuit that inputs a first servo signal to the first fixed servo electrodes of each of the pair of first servo electrode portions based on the first detection signal in order to suppress displacement of the mass portion in the first direction, wherein the positive and negative signs of the first servo signal are opposite between the pair of first fixed servo electrodes.

2. The acceleration sensor further comprises: a cap layer fixed to the frame so as to cover the mass portion, the mass portion is disposed in a space defined by the frame body and the cap layer, 2. The acceleration sensor device according to claim 1, wherein the space is a vacuum.

3. The acceleration sensor further comprises: An anchor portion fixed to the frame body; 3. The acceleration sensor device according to claim 1, further comprising: a first beam portion connected between the mass portion and the anchor portion, the first beam portion being elastically deformable in the first direction.

4. A central opening is formed in the mass portion, Only one of the anchor portions is disposed at a symmetrical center of the mass portion located within the central opening, The acceleration sensor device according to claim 3 , wherein the mass portion is connected to the anchor portion via the first beam portion so as to be swingable in the first direction.

5. the frame body, the mass portion, and the first beam portion are formed by a laminated substrate of a lower semiconductor layer, an insulating layer, and an upper semiconductor layer, the frame body is composed of the lower semiconductor layer, the insulating layer, and the upper semiconductor layer, the mass portion is composed of the lower semiconductor layer, the insulating layer, and the upper semiconductor layer, 5. The acceleration sensor device according to claim 3, wherein the first beam portion is formed of the upper semiconductor layer.

6. The mass portion has a first divided mass portion and a second divided mass portion, the first divided mass portion and the second divided mass portion are connected in an insulated and separated state, the first movable detection electrode of each of the pair of first displacement detection electrode portions is fixed to the first divided mass portion, the first movable servo electrode of each of the pair of first servo electrode portions is fixed to the second divided mass portion, 6. The acceleration sensor device according to claim 1, wherein the carrier signal generating circuit inputs the reference voltage to the first divided mass portion and inputs the offset voltage to the second divided mass portion.

7. The acceleration sensor further comprises: a pair of second displacement detection electrode units, each of the pair of second displacement detection electrode units having a second movable detection electrode and a second fixed detection electrode, the second movable detection electrode and the second fixed detection electrode facing each other in a second direction perpendicular to the first direction, the second movable detection electrode being fixed to the mass portion and the second fixed detection electrode being fixed to the frame, and a positive / negative change in an inter-electrode distance between the second movable detection electrode and the second fixed detection electrode in response to a displacement of the mass portion in the second direction is opposite between the pair of second displacement detection electrode units; the second servo electrode portion further comprises a pair of second servo electrode portions, each of the pair of second servo electrode portions having a second movable servo electrode and a second fixed servo electrode, the second movable servo electrode and the second fixed servo electrode facing each other in the second direction, the second movable servo electrode being fixed to the mass portion, the second fixed servo electrode being fixed to the frame, and a positive / negative change in an inter-electrode distance between the second movable servo electrode and the second fixed servo electrode in response to a displacement of the mass portion in the second direction is opposite between the pair of second servo electrode portions, The processing circuitry further comprises: a second capacitance conversion circuit that outputs a second voltage signal corresponding to a difference between capacitance changes of the pair of second displacement detection electrodes; a second synchronous detection circuit that detects a second detection signal synchronized with the reference voltage from the second voltage signal; 3. The acceleration sensor device of claim 1, further comprising: a second servo signal generating circuit that inputs a second servo signal to the second fixed servo electrodes of each of the pair of second servo electrode portions based on the second detection signal in order to suppress displacement of the mass portion in the second direction, wherein the positive and negative signs of the second servo signal are opposite between the pair of second fixed servo electrodes.

8. The acceleration sensor further comprises: An anchor portion fixed to the frame body; a first beam portion connected between the mass portion and the anchor portion and elastically deformable in the first direction; 8. The acceleration sensor device according to claim 7, further comprising: a second beam portion connected between the mass portion and the anchor portion, the second beam portion being elastically deformable in the second direction.

9. A central opening is formed in the mass portion, Only one of the anchor portions is disposed at a symmetrical center of the mass portion located within the central opening, 9. The acceleration sensor device of claim 8, wherein the mass portion is connected to the anchor portion via the first beam portion so as to be able to swing in the first direction, and is connected to the anchor portion via the second beam portion so as to be able to swing in the second direction.

10. the frame body, the mass portion, the first beam portion, and the second beam portion are formed by a laminated substrate of a lower semiconductor layer, an insulating layer, and an upper semiconductor layer, the frame body is composed of the lower semiconductor layer, the insulating layer, and the upper semiconductor layer, the mass portion is composed of the lower semiconductor layer, the insulating layer, and the upper semiconductor layer, the first beam portion is formed by the upper semiconductor layer, 10. The acceleration sensor device according to claim 8, wherein the second beam portion is formed of the upper semiconductor layer.

11. The mass portion has a first divided mass portion and a second divided mass portion, The first divided mass portion and the second divided mass portion are connected in an insulated and separated state, the first movable detection electrode of each of the pair of first displacement detection electrode portions and the second movable detection electrode of each of the pair of second displacement detection electrode portions are fixed to the first divided mass portion, the first movable servo electrode of each of the pair of first servo electrode portions and the second movable servo electrode of each of the pair of second servo electrode portions are fixed to the second divided mass portion, 11. The acceleration sensor device according to claim 7, wherein the carrier signal generating circuit inputs the reference voltage to the first divided mass portion and inputs an offset voltage to the second divided mass portion.

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