Physical quantity sensor element and physical quantity sensor device

Abstract

To perform self-diagnosis in a sensor in which a movable electrode is displaced in a direction parallel to a fixed electrode. [Solution] A beam fixing part, a first electrode fixing part and a second electrode fixing part, a support beam with one end connected to the beam fixing part and extending in a direction parallel to the support substrate, a movable body connected to the other end of the support beam and existing on both sides of the support beam in a plan view, a first movable comb electrode connected to the movable body and existing on one side of the support beam in a plan view, a first fixed comb electrode connected to the first electrode fixing part and facing the first movable comb electrode, a second movable comb electrode connected to the movable body and existing on the other side of the support beam in a plan view, a second fixed comb electrode connected to the second electrode fixing part and facing the second movable comb electrode, and the first movable comb electrode, the first fixed comb electrode, the second movable comb electrode, and the second fixed comb electrode are sandwiched by a self-diagnostic electrode.

Description

Technical Field

[0001] The present invention relates to a physical quantity sensor element and a physical quantity sensor device.

Background Art

[0002] Conventionally, a capacitive physical quantity sensor that detects a change in capacitance formed by a fixed electrode and a movable electrode due to a physical quantity is known. For example, Patent Document 1 discloses a capacitive physical quantity sensor in which a fixed electrode and a movable electrode face each other in parallel, and the distance between the fixed electrode and the movable electrode changes according to a physical quantity. Further, Patent Document 1 discloses a configuration in which a voltage is applied between a fixed electrode and a movable electrode, and self-diagnosis is performed by vibrating the movable electrode by changing the voltage value.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the above-mentioned conventional technology, the fixed electrode and the movable electrode constitute parallel plate electrodes, and the distance between the fixed electrode and the movable electrode changes in a direction perpendicular to the plate according to a physical quantity. However, there is a capacitive physical quantity sensor in which the movable electrode is displaced in a direction parallel to the plate. In such a sensor, even if a voltage is applied between the fixed electrode and the movable electrode, it is difficult to displace and vibrate the movable electrode in a direction parallel to the plate by changing the voltage value. Therefore, it has been difficult to perform self-diagnosis in a sensor in which the movable electrode is displaced in a direction parallel to the plate.

Means for Solving the Problems

[0005] In one embodiment, the physical quantity sensor element comprises a beam fixing portion, a first electrode fixing portion, and a second electrode fixing portion extending in a direction perpendicular to the support substrate; a support beam with one end connected to the beam fixing portion and extending in a direction parallel to the support substrate; a movable body connected to the other end of the support beam and existing on both sides of the support beam in a plan view; a first movable comb electrode connected to the movable body and existing on one side of the support beam in a plan view; a first fixed comb electrode connected to the first electrode fixing portion and facing the first movable comb electrode; a second movable comb electrode connected to the movable body and existing on the other side of the support beam in a plan view; a second fixed comb electrode connected to the second electrode fixing portion and facing the second movable comb electrode; and a self-diagnostic electrode sandwiching the first movable comb electrode, the first fixed comb electrode, the second movable comb electrode, and the second fixed comb electrode. [Brief explanation of the drawing]

[0006] [Figure 1] A plan view of the physical quantity sensor device of this embodiment. [Figure 2] A plan view of the Z-direction acceleration sensor element of this embodiment. [Figure 3] Cross-sectional view of the Z-direction acceleration sensor element. [Figure 4] A diagram illustrating the operation of the detection unit of the Z-direction acceleration sensor element. [Figure 5] A diagram illustrating the circuit used to detect acceleration. [Figure 6] This figure shows the signal waveform when switching from normal acceleration detection to self-diagnosis mode. [Figure 7] An enlarged view of the signal waveform during acceleration detection. [Figure 8] A diagram showing the resonant frequency characteristics of the movable electrode. [Figure 9] A diagram illustrating the circuit used to detect acceleration. [Figure 10] This figure shows the signal waveform when switching from normal acceleration detection to self-diagnosis mode. [Figure 11] A diagram showing the relationship between voltage and displacement. [Modes for carrying out the invention]

[0007] The following describes this embodiment. Note that the embodiment described below does not unduly limit the scope of the claims. Furthermore, not all of the configurations described in this embodiment are necessarily essential components.

[0008] (1) Configuration of the physical quantity sensor device: The physical quantity sensor device 100 of this embodiment is housed in a substantially rectangular parallelepiped package. Figure 1 is a plan view showing the physical quantity sensor device 100 as viewed in a direction perpendicular to the largest face of the rectangular parallelepiped. Viewing each part in this direction is called a plan view. The physical quantity sensor device 100 according to this embodiment comprises a plurality of physical quantity sensor elements. Specifically, the physical quantity sensor device 100 comprises a Z-direction acceleration sensor element 1 and an XY-direction acceleration sensor element 101. Each sensor element is a MEMS (Micro Electro Mechanical Systems) device.

[0009] In this specification, for the sake of clarity, the dimensions of each component and the spacing between components are shown schematically, and not all components are shown. For example, electrode wiring, electrode terminals, etc., may be omitted from the illustration. In this embodiment, the explanation mainly takes the case where the physical quantity detected by the Z-direction acceleration sensor element 1 and the XY-direction acceleration sensor element 101 is acceleration as an example, but the physical quantity is not limited to acceleration and may be other physical quantities such as velocity, pressure, displacement, attitude, angular velocity, or gravity. In addition, each physical quantity sensor element may be used as a pressure sensor or a MEMS switch, etc.

[0010] Furthermore, in this specification, mutually orthogonal directions are referred to as the first direction DR1, the second direction DR2, and the third direction DR3. The first direction DR1, the second direction DR2, and the third direction DR3 are, for example, the X-axis direction, the Y-axis direction, and the Z-axis direction, respectively, but are not limited to these. For example, the third direction DR3, which corresponds to the Z-axis direction, is the direction perpendicular to the largest face of the rectangular parallelepiped formed by the physical quantity sensor device 100, and is the vertical direction. The direction opposite to the third direction DR3 is referred to as the fifth direction DR5. The first direction DR1, which corresponds to the X-axis direction, and the second direction DR2, which corresponds to the Y-axis direction, are directions perpendicular to the third direction DR3, and the XY plane, which is the plane along the first direction DR1 and the second direction DR2, is, for example, along the horizontal plane. The direction opposite to the first direction DR1 is referred to as the fourth direction DR4, and the fourth direction DR4 is, for example, the -X-axis direction. Note that if there is no particular need to distinguish the opposite direction, the fourth direction DR4 can also be considered as the direction along the first direction DR1. Furthermore, "orthogonal" includes not only intersections at 90°, but also intersections at angles slightly tilted from 90°.

[0011] Figure 1 also shows the multiple pads provided by the physical quantity sensor device 100. Pad Pgnd is a pad electrically connected to the ground. Pad Pxy is a pad electrically connected to a movable comb-tooth electrode (not shown) provided by the XY direction acceleration sensor element 101, and is set to a common potential in the XY direction. Pad Py1 is a pad electrically connected to a fixed comb-tooth electrode (not shown) provided by the XY direction acceleration sensor element 101, and is set to a potential for detecting acceleration in the Y direction. Pad Py2 is a pad electrically connected to a fixed comb-tooth electrode (not shown) provided by the XY direction acceleration sensor element 101, and is set to a potential opposite in phase to pad Py1 in order to detect acceleration in the Y direction.

[0012] Pad Px1 is a pad that is electrically connected to a fixed comb electrode (not shown) provided in the XY-direction acceleration sensor element 101, and is set to a potential for detecting acceleration in the X direction. Pad Px2 is a pad that is electrically connected to a fixed comb electrode (not shown) provided in the XY-direction acceleration sensor element 101, and is set to a potential with a phase opposite to that of Pad Px1 for detecting acceleration in the X direction.

[0013] Pad Pz is a pad that is electrically connected to a first movable comb electrode and a second movable comb electrode (to be described later) provided in the Z-direction acceleration sensor element 1. Pad Pz1 is a pad that is electrically connected to a first fixed comb electrode (to be described later) provided in the Z-direction acceleration sensor element 1, and is set to a potential for detecting acceleration in the Z direction. Pad Pz2 is a pad that is electrically connected to a second fixed comb electrode (to be described later) provided in the Z-direction acceleration sensor element 1, and is set to a potential with a phase opposite to that of Pad Pz1 for detecting acceleration in the Z direction.

[0014] FIG. 2 is a plan view of the Z-direction acceleration sensor element 1. The support substrate 2 is, for example, a silicon substrate made of semiconductor silicon or a glass substrate made of a glass material such as borosilicate glass. However, the constituent material of the support substrate 2 is not particularly limited, and a quartz substrate or an SOI (Silicon On Insulator) substrate may be used.

[0015] As shown in FIG. 2, the Z-direction acceleration sensor element 1 of the present embodiment includes a beam fixing portion 40, a support beam 42, a movable body MB, a first fixed electrode portion 10A, and a second fixed electrode portion 50A. The movable body MB includes a first connecting portion 30, a first base portion 23A, a first movable electrode portion 20A, a second connecting portion 70, a second base portion 63, and a second movable electrode portion 60A. The first fixed electrode portion 10A has a plurality of first fixed comb electrodes 11, 12, and the second fixed electrode portion 50A has a plurality of second fixed comb electrodes 51, 52. The first movable electrode portion 20A has a plurality of first movable comb electrodes 21, 22, and the second movable electrode portion 60A has a plurality of second movable comb electrodes 61, 62.

[0016] Then, as shown by the dashed-line frame in FIG. 2, the Z-axis acceleration sensor element 1 has a detection unit Z1 and a detection unit Z2, and each detection unit detects a physical quantity such as acceleration in a direction along the third direction DR3 which is the Z-axis direction. The detection units Z1 and Z2 are provided on the first direction DR1 side and the fourth direction DR4 side of the support beam 42, respectively, in a plan view. The detection unit Z1 provided on the first direction DR1 side of the support beam 42 includes a first fixed electrode portion 10A and a first movable electrode portion 20A. The detection unit Z2 provided on the fourth direction DR4 side of the support beam 42 includes a second fixed electrode portion 50A and a second movable electrode portion 60A.

[0017] In the above configuration, the beam fixing portion 40 is a substantially rectangular parallelepiped portion extending from a plane parallel to the first direction DR1 and the second direction DR2 of the support substrate 2 toward the third direction DR3. The beam fixing portion 40 is located at the rotation center when the movable body MB swings, and plays a role as an anchor in the swinging motion. One end of the support beam 42 is connected to the beam fixing portion 40. The support beam 42 extends toward the second direction DR2. Therefore, the support beam 42 extends parallel to a plane parallel to the first direction DR1 and the second direction DR2 of the support substrate 2. This state is expressed as the support beam 42 extending in a direction parallel to the support substrate 2.

[0018] The other end of the support beam 42 is connected to the first connecting portion 30 and the second connecting portion 70 of the movable body MB. The first connecting portion 30 exists on the first direction DR1 side when viewed from the support beam 42, and the second connecting portion 70 exists on the fourth direction DR4 side when viewed from the support beam 42. Therefore, the movable body MB is connected to the other end of the support beam 42 and exists on both sides sandwiching the support beam 42 in a plan view. The first connecting portion 30 existing on the second direction DR2 side and the reverse direction side of the second direction DR2 of the support substrate 2 is connected by a third connecting portion 23B extending along the second direction DR2.

[0019] The support beam 42 functions as a torsional spring, providing a restoring force during the oscillating motion of the movable body MB. As shown in Figure 2, the support beam 42 is positioned such that the second direction DR2 is the longitudinal direction in a plan view. Also, as shown in Figure 2, the thickness of the support beam 42 in the first direction DR1 is thinner than that of the beam fixing part 40, allowing it to flex in response to the oscillating motion of the movable body MB. By twisting along the Y-axis, which is the second direction DR2, it provides a restoring force during the oscillating motion of the movable body MB. Thus, in this embodiment, the support beam 42 is a torsional spring that twists around the second direction DR2 as the axis of rotation. In this way, the movable body MB can perform an oscillating motion around the second direction DR2 as the axis of rotation.

[0020] When the movable body MB performs an oscillating motion, the first movable electrode section 20A and the second movable electrode section 60A of the movable body MB also move in conjunction with it. In this embodiment, physical quantities are detected by detecting how the capacitance formed by the opposition between the first movable comb electrodes 21, 22 and the first fixed comb electrodes 11, 12, and the capacitance formed by the opposition between the second movable comb electrodes 61, 62 and the second fixed comb electrodes 51, 52 changes in response to the oscillating motion.

[0021] The first connecting portion 30 connects the other end of the support beam 42 that is not connected to the beam fixing portion 40 to the first base portion 23A. The second connecting portion 70 connects the other end of the support beam 42 to the second base portion 63. The first connecting portion 30 extends toward the first direction DR1 of the support beam 42 and is connected to the first base portion 23A on the first direction DR1 side of the support beam 42. The second connecting portion 70 extends toward the fourth direction DR4 of the support beam 42 and is connected to the second base portion 63 on the fourth direction DR4 side of the support beam 42. In this way, the first connecting portion 30 and the second connecting portion 70 connect the first base portion 23A and the second base portion 63, respectively, to a certain distance from the support beam 42, which is the axis of rotation of the movable body MB.

[0022] The first base portion 23A forms the base of the first movable comb electrodes 21 and 22 of the first movable electrode portion 20A. That is, as shown in Figure 2, in a plan view, multiple first movable comb electrodes 21 and 22 extend from the first base portion 23A toward the first direction DR1. In this way, the first movable comb electrodes 21 and 22 are connected to the movable body MB and are located on the first direction DR1 side, which is one side of the support beam 42 in a plan view. The first base portion 23A is connected to the support beam 42 by the first connecting portion 30 so as to be located at a certain distance from the rotation axis of the movable body MB.

[0023] The second base portion 63 forms the base of the second movable comb electrodes 61 and 62 of the second movable electrode portion 60A. In the detection unit Z2, the second base portion 63 plays a similar role to the first base portion 23A in the detection unit Z1. That is, in a plan view, multiple second movable comb electrodes 61 and 62 extend from the second base portion 63 toward the first direction DR1 and the fourth direction DR. Thus, the second fixed comb electrodes 51 and 52 are connected to the movable body MB and are located toward the fourth direction DR, which is the other side of the support beam 42 in a plan view. The second base portion 63 is connected to the support beam 42 by the second connecting portion 70 so as to be located at a certain distance from the rotation axis of the movable body MB.

[0024] With this configuration, the first base 23A, together with the first connecting portion 30, connects the first movable comb electrodes 21 and 22 of the first movable electrode portion 20A so that they are at a constant distance from the axis of rotation in the oscillating motion of the movable body MB. The second base 63, together with the second connecting portion 70, connects the second movable comb electrodes 61 and 62 of the second movable electrode portion 60A so that they are at a constant distance from the axis of rotation in the oscillating motion. In other words, if the first movable electrode portion 20A and the second movable electrode portion 60A are considered as an integrated structure including the movable comb electrodes, then in a plan view, the first movable electrode portion 20A and the second movable electrode portion 60A are positioned symmetrically with respect to the Y-axis including the support beam 42. Furthermore, the first movable comb electrodes 21 and 22 of the first movable electrode section 20A extend in the first direction DR1 and the fourth direction DR, and the second movable comb electrodes 61 and 62 of the second movable electrode section 60A also extend in the first direction DR1 and the fourth direction DR.

[0025] The first fixed comb electrodes 11,12 of the first fixed electrode section 10A and the first movable comb electrodes 21,22 of the first movable electrode section 20A are probe electrodes in the detection section Z1. The first fixed comb electrodes 11,12 of the first fixed electrode section 10A are probe electrodes fixed to the support substrate 2, and the first movable comb electrodes 21,22 of the first movable electrode section 20A are probe electrodes that can move together with the movable body MB. Physical quantities can be detected by the change in capacitance formed by the first fixed comb electrodes 11,12 of the first fixed electrode section 10A and the first movable comb electrodes 21,22 of the first movable electrode section 20A.

[0026] The first electrode fixing portion 3 is the portion that supports the first fixed electrode portion 10A. The first electrode fixing portion 3 is a substantially rectangular parallelepiped portion that extends from the planes of the support substrate 2 parallel to the first direction DR1 and the second direction DR2 toward the third direction DR3. The first electrode fixing portion 3 fixes the first fixed electrode portion 10A to the support substrate 2. That is, the first fixed electrode portion 10A includes a first fixed electrode base portion 13A that extends toward the second direction DR2, and the first fixed electrode base portion 13A is connected to a portion that extends toward the first direction DR1 from the first electrode fixing portion 3.

[0027] As described above, the first fixed electrode portion 10A is fixed to the support substrate 2 via the first electrode fixing portion 3. As shown in Figure 2, the first fixed electrode portion 10A is provided on the first direction DR1 side of the support beam 42. The first fixed electrode portion 10A is provided with comb-shaped first fixed comb electrodes 11 and 12 that extend from the first fixed electrode base portion 13A to the first direction DR1 side and the fourth direction DR4 side. That is, the first fixed comb electrodes 11 and 12 are connected to the first electrode fixing portion 3 and extend in a direction parallel to the support substrate 2, and face the first movable comb electrodes 21 and 22.

[0028] The second electrode fixing portions 4 and 5 are parts that support the second fixed electrode portion 50A. The second electrode fixing portions 4 and 5 are substantially rectangular parallelepiped portions that extend from the planes of the support substrate 2 parallel to the first direction DR1 and the second direction DR2 toward the third direction DR3. Each of the second electrode fixing portions 4 and 5 fixes the second fixed electrode portion 50A to the support substrate 2. That is, the second fixed electrode portion 50A is provided with second fixed electrode base portions 53A and 53B that extend toward the second direction DR2, and the second fixed electrode base portions 53A and 53B are connected to portions that extend toward the fourth direction DR4 from the second electrode fixing portions 4 and 5.

[0029] As described above, the second fixed electrode section 50A is fixed to the support substrate 2 via the second electrode fixing sections 4 and 5. As shown in Figure 2, the second fixed electrode section 50A is provided on the fourth direction DR side of the support beam 42. The second fixed electrode section 50A is provided with a comb-shaped second fixed comb electrode 51 extending from the second fixed electrode base 53A toward the fourth direction DR4, and a comb-shaped second fixed comb electrode 52 extending from the second fixed electrode base 53B toward the first direction DR1. That is, the second fixed comb electrodes 51 and 52 are connected to the second electrode fixing sections 4 and 5, extend in a direction parallel to the support substrate 2, and face the second movable comb electrodes 61 and 62.

[0030] The first electrode fixing portion 3 and the second electrode fixing portions 4 and 5 are rectangular parallelepiped parts extending from the support substrate 2. In Figure 2, the parts colored black are the parts extending from the support substrate 2. However, the first electrode fixing portion 3 and the second electrode fixing portions 4 and 5 may be connected to the support substrate 2 via parts with a larger surface area.

[0031] Furthermore, the first electrode fixing portion 3 is positioned closer to the beam fixing portion 40 than the first fixed electrode portion 10A in the first direction DR1 of the support beam 42, and the second electrode fixing portions 4 and 5 are positioned closer to the beam fixing portion 40 than the second fixed electrode portion 50A in the fourth direction DR4 of the support beam 42. As a result, even if warping occurs in the support substrate 2, it becomes less susceptible to its effects, and output fluctuations caused by external stress, heat, etc., of the Z-direction acceleration sensor element 1 can be suppressed, enabling highly accurate detection of physical quantities.

[0032] Figure 3 is a simplified cross-sectional view of the Z-direction acceleration sensor element 1. The cutting position of the cross-sectional view shown in Figure 3 is the position of line AA in Figure 2, and it mainly shows the structure of the second fixed comb electrode 51 and the second movable comb electrode 61, which belong to the second fixed electrode section 50A located in the lower right of Figure 2. The cross-sectional shape of the second fixed comb electrode 51 and the second movable comb electrode 61 is a rectangular parallelepiped, and they extend in the fourth direction DR and the first direction DR1 with the same cross-sectional shape. Therefore, the second fixed comb electrode 51 is a rectangular parallelepiped portion extending from the second fixed electrode base 53A along the fourth direction DR, and the second movable comb electrode 61 is a rectangular parallelepiped portion extending from the second base 63 along the fourth direction DR.

[0033] The support substrate 2 is a roughly rectangular parallelepiped, but a recess is formed on one surface on the side where the second fixed comb-tooth electrode 51 and the like are housed. The Z-direction acceleration sensor element 1 can be considered to be composed of multiple layers, and in the third direction DR3, from the support substrate 2 in order, they are the first oxide layer Ox1, the sensor structure forming layer Ml, and the second oxide layer Ox2. The layer following the second oxide layer Ox2 is a wiring layer, in which conductors form pads Pgnd and other pads and various wirings. Following the wiring layer is a glass frit layer Gf, and the next layer is the lid Cp. The lid Cp is positioned opposite the support substrate 2. That is, the support substrate 2 and lid Cp have various structures, such as recesses, but their general shape is a rectangular parallelepiped, and they are arranged so that their widest faces are parallel.

[0034] The sensor structure forming layer Ml is a layer that forms structures such as the second fixed comb-tooth electrode 51. In the sensor structure forming layer Ml, the outer periphery in a plan view forms a rectangular frame, and the space enclosed by this frame and sandwiched between the support substrate 2 and the lid Cp becomes the housing space for structures such as the second fixed comb-tooth electrode 51. Furthermore, the housing space is sealed by the contact of the glass frit layer Gf with the lid Cp. In this embodiment, the sensor structure forming layer Ml and the lid Cp are made of silicon. However, the material of each layer is not limited and may be made of glass material such as borosilicate glass, or it may be made of SOI (Silicon On Insulator), etc.

[0035] Figure 4 illustrates the operation of the detection units Z1 and Z2 of the Z-direction acceleration sensor element 1 of this embodiment. Specifically, it shows a schematic cross-sectional view of each electrode along the first direction DR1, illustrating the movement of the first movable comb electrode 21 and the second movable comb electrode 61 with respect to the direction of acceleration when acceleration occurs from the initial state. Here, the initial state refers to a stationary state in which no acceleration occurs except for gravitational acceleration.

[0036] In the initial state shown in the left column of Figure 4, the first fixed comb electrode 11 and the first movable comb electrode 21 of the detection unit Z1 are positioned opposite each other along the third direction DR3, with a portion of each overlapping. Specifically, the ends of the first fixed comb electrode 11 and the first movable comb electrode 21 coincide in the fifth direction DR5, but in the third direction DR3, the end of the first movable comb electrode 21 is positioned further towards the third direction DR3 than the end of the first fixed comb electrode 11. In the initial state, the first fixed comb electrode 11 and the first movable comb electrode 21 are stationary with a portion of each overlapping along the third direction DR3. Similarly, the second fixed comb electrode 51 and the second movable comb electrode 61 of the detection unit Z2 are also positioned opposite each other along the third direction DR3, with a portion of each overlapping, and in the third direction DR3, the end of the second movable comb electrode 61 is positioned further towards the third direction DR3 than the end of the second fixed comb electrode 51.

[0037] In this initial state, the capacitance in the initial state is obtained from the capacitance corresponding to the opposing area between the first fixed comb electrode 11 and the first movable comb electrode 21 in the detection unit Z1, and the capacitance corresponding to the opposing area between the second fixed comb electrode 51 and the second movable comb electrode 61 in the detection unit Z2.

[0038] Next, we will explain the operation when acceleration occurs in the third direction DR3, as shown in the center column of Figure 4. When acceleration occurs in the third direction DR3, the second movable comb electrode 61 in the detection unit Z2 is subjected to an inertial force opposite to the direction of acceleration. As a result, the second movable comb electrode 61 in the detection unit Z2 is displaced toward the fifth direction DR5, i.e., in the -Z direction, and the first movable comb electrode 21 in the detection unit Z1 is displaced in the +Z direction, opposite to that of the second movable comb electrode 61. As a result, in the detection unit Z2, the opposing area between the second fixed comb electrode 51 and the second movable comb electrode 61 is maintained, while in the detection unit Z1, the opposing area between the first fixed comb electrode 11 and the first movable comb electrode 21 decreases. Therefore, by detecting the change in capacitance due to the decrease in the opposing area in the detection unit Z1, the acceleration in the third direction DR3 can be detected.

[0039] On the other hand, as shown in the right column of Figure 4, when acceleration in the fifth direction DR5 occurs from the initial state, the second movable comb electrode 61 is subjected to an inertial force in the third direction DR3. Therefore, in the detection unit Z2, the second movable comb electrode 61 is displaced in the third direction DR3, and the first movable comb electrode 21 of the detection unit Z1 is displaced in the opposite direction, the fifth direction DR5. As a result, in the detection unit Z2, the opposing area between the second fixed comb electrode 51 and the second movable comb electrode 61 decreases, while in the detection unit Z1, the opposing area between the first fixed comb electrode 11 and the first movable comb electrode 21 is maintained. Therefore, by detecting the change in capacitance due to the decrease in the opposing area of ​​the detection unit Z2, the acceleration in the fifth direction DR5 can be detected.

[0040] In this embodiment, the second movable comb electrode 61 of the detection unit Z2 is displaced in the opposite direction to the acceleration in the third direction DR3 or the fifth direction DR5. This is because the movable body MB provided on the fourth direction DR4 side, i.e., the movable body MB on the detection unit Z2 side, is heavier than the movable body MB provided on the first direction DR1 side, i.e., the movable body MB on the detection unit Z1 side.

[0041] In this embodiment, the thickness of the first movable comb electrodes 21 and 22 of the first movable electrode section 20A in the third direction DR3 is greater than the thickness of the first fixed comb electrodes 11 and 12 of the first fixed electrode section 10A in the third direction DR3, and the thickness of the second movable comb electrodes 61 and 62 of the second movable electrode section 60A in the third direction DR3 is greater than the thickness of the second fixed comb electrodes 51 and 52 of the second fixed electrode section 50A in the third direction DR3.

[0042] In this way, when acceleration in the third direction DR3 occurs, the opposing area between the first fixed comb electrodes 11,12 and the first movable comb electrodes 21,22 decreases in the detection unit Z1, while the opposing area between the second fixed comb electrodes 51,52 and the second movable comb electrodes 61,62 is maintained in the detection unit Z2, thus enabling the detection of a change in acceleration in the third direction DR3. Furthermore, when acceleration in the fifth direction DR5 occurs, the opposing area between the second fixed comb electrodes 51,52 and the second movable comb electrodes 61,62 decreases in the detection unit Z2, while the opposing area between the first fixed comb electrodes 11,12 and the first movable comb electrodes 21,22 is maintained in the detection unit Z1, thus enabling the detection of a change in acceleration in the fifth direction DR5.

[0043] As described above, in the Z-direction acceleration sensor element 1 according to this embodiment, the first movable comb electrodes 21, 22 and the second movable comb electrodes 61, 62 swing along the third direction DR3. On the other hand, the first movable comb electrodes 21, 22 and the second movable comb electrodes 61, 62 have a structure in which a rectangular parallelepiped extends from the movable body MB toward the first direction DR1 and the fourth direction DR4, and hardly moves in the second direction DR2.

[0044] On the other hand, in the XY direction acceleration sensor element 101, capacitance is formed by the opposition of the fixed comb-tooth electrode and the movable comb-tooth electrode. However, in the XY direction acceleration sensor element 101, the capacitance changes as the distance between the fixed comb-tooth electrode and the movable comb-tooth electrode is displaced in accordance with the acceleration in the first direction DR1 and the second direction DR2 acting on the XY direction acceleration sensor element 101. The XY direction acceleration sensor element 101 can detect changes in acceleration in the first direction DR1 and the second direction DR2 based on this change in capacitance.

[0045] (2) Detection circuit: Next, we will describe a circuit for detecting changes in acceleration along the first direction DR1 and the second direction DR2, and changes in acceleration along the third direction DR3, using the above configuration. First, we will describe a circuit for detecting changes in acceleration along the first direction DR1 and the second direction DR2.

[0046] (2-1) XY direction acceleration sensor element: The XY directional acceleration sensor element 101 is used in connection with a control IC (not shown). The control IC includes a circuit for detecting acceleration based on the signal output from the XY directional acceleration sensor element 101. Figure 5 is a diagram illustrating this circuit. In Figure 5, the XY directional acceleration sensor element 101 is shown along with the elements and wiring that make up the circuit.

[0047] However, in Figure 5, the structural details of the XY directional acceleration sensor element 101 are omitted, and the movable electrodes 101a, 101b, 101c, and 101d and the fixed electrodes 102a, 102b, 102c, and 102d of the XY directional acceleration sensor element 101 are schematically shown.

[0048] The movable electrodes 101a, 101b and the fixed electrodes 102a, 102b constitute a parallel plate capacitor oriented perpendicular to the first direction DR1. The movable electrodes 101a, 101b are electrodes that are displaced in the first direction DR1 in response to acceleration in the X direction, which is the first direction DR1. The positions of the fixed electrodes 102a, 102b do not change. When the movable electrodes 101a, 101b are displaced in the first direction DR1 in response to acceleration in the X direction, which is the first direction DR1, the capacitance composed of the movable electrode 101a and the fixed electrode 102a, and the capacitance composed of the movable electrode 101b and the fixed electrode 102b, change.

[0049] The movable electrodes 101c, 101d and the fixed electrodes 102c, 102d constitute a parallel plate capacitor oriented perpendicular to the second direction DR2. The movable electrodes 101c, 101d are electrodes that are displaced in the second direction DR2 in response to acceleration in the Y direction, which is the second direction DR2. The positions of the fixed electrodes 102c, 102d do not change. When the movable electrodes 101c, 101d are displaced in the second direction DR2 in response to acceleration in the Y direction, which is the second direction DR2, the capacitance composed of the movable electrode 101c and the fixed electrode 102c, and the capacitance composed of the movable electrode 101d and the fixed electrode 102d, change.

[0050] Furthermore, as shown in Figure 1, the XY directional acceleration sensor element 101 is equipped with multiple pads, and Figure 5 shows the connection relationships between the pads Pxy, Px1, Px2, Py1, Py2 and the circuit components, as well as the connection relationships between the movable electrodes 101a, 101b, 101c, 101d and the fixed electrodes 102a, 102b, 102c, 102d.

[0051] Here, the configuration for detecting acceleration in the X direction, which is the first direction DR1, is referred to as the first detection unit, and the configuration for detecting acceleration in the Y direction, which is the second direction DR2, is referred to as the second detection unit. The first detection unit has a detection circuit 200 that detects acceleration based on the change in differential capacitance between the movable electrodes 101a, 101b and the fixed electrodes 102a, 102b. The second detection unit has a detection circuit 300 that detects acceleration based on the change in differential capacitance between the movable electrodes 101c, 101d and the fixed electrodes 102c, 102d.

[0052] In this embodiment, the XY direction acceleration sensor element 101 has electrodes for detecting acceleration in the first direction DR1 and electrodes for detecting acceleration in the second direction DR2 (Y direction) formed on the same chip; however, each electrode may be configured on a separate chip.

[0053] The detection circuits 200 and 300 are equipped with CV conversion circuits 210 and 310, switch circuits 220 and 320, signal processing circuits 230 and 330, and a control signal generation circuit 600.

[0054] The CV conversion circuits 210 and 310 are circuits that convert the change in differential capacitance formed by the movable electrodes 101a to 101d and the fixed electrodes 102a to 102d into a voltage. Specifically, the CV conversion circuits 210 and 310 include operational amplifiers 210a and 310a, capacitors 210b and 310b, and switches 210c and 310c.

[0055] The inverting input terminals of the operational amplifiers 210a and 310a are electrically connected to the movable electrodes 101a and 101b, 101c and 101d, respectively. Capacitors 210b and 310b and switches 210c and 310c are connected in parallel between the inverting input terminals and the output terminals. Switch 210c is driven by signal S1X from the control signal generation circuit 600, and switch 310c is driven by signal S1Y from the control signal generation circuit 600. The non-inverting input terminals of the operational amplifiers 210a and 310a are input via switch circuits 220 and 320 to either a voltage V1 (i.e., the midpoint voltage, 2.5V in this embodiment) which is half the voltage applied to the fixed electrodes 102a to 102d, or a voltage V2 (4V in this embodiment) which is different from this midpoint voltage.

[0056] Switch circuits 220 and 320 input voltages from respective voltage sources (not shown) to the non-inverting input terminals of the operational amplifiers 210a and 310a in the CV conversion circuits 210 and 310. Specifically, switch circuit 220 includes switches 220a and 220b, and switch circuit 320 includes switches 320a and 320b. Of these, switches 220a and 220b are driven based on the signal S2X from the control signal generation circuit 600, and switches 320a and 320b are driven based on the signal S2Y from the control signal generation circuit 600, so that when one is closed, the other is open.

[0057] The signal processing circuits 230 and 330 include LPF (low-pass filter) circuits 230a and 330a and GAIN circuits 230b and 330b. The LPF circuits 230a and 330a remove high-frequency components from the output of the CV conversion circuits 210 and 310, extracting only components within a predetermined frequency band. The GAIN circuits 230b and 330b amplify the output after passing through the LPF circuits 230a and 330a and output it as acceleration signals GoutX and GoutY.

[0058] The control signal generation circuit 600 outputs signals (carrier waves) P1X, P2X, P1Y, P2Y indicating the timing of voltage application to fixed electrodes 102a to 102d, signals S2X, S2Y indicating the switching timing of switches in switch circuits 220 and 320, and signals S1X, S1Y indicating the switching timing of switches 210c and 310c.

[0059] The various signals generated by this control signal generation circuit 600 change between normal acceleration detection (when not self-diagnostic) and self-diagnostic. Specifically, the control signal generation circuit 600 outputs various signals based on the clock signal CLK, but outputs an acceleration detection signal when the self-diagnostic command signal is at a low level, and outputs a self-diagnostic signal when the self-diagnostic command signal is at a high level.

[0060] The self-diagnosis process involves inputting a self-diagnosis signal to the XY directional acceleration sensor element 101. If the obtained output falls within a predetermined range, it is considered normal; if it falls outside this range, it is considered abnormal. In other words, if the obtained output falls outside the predetermined range, it can be assumed that an abnormality, such as damage to the comb teeth of the XY directional acceleration sensor element 101, has occurred.

[0061] The operation of the acceleration sensor configured in this way will be explained with reference to the signal waveform diagrams shown in Figures 6 and 7. Figure 6 shows the signal waveform when switching from normal acceleration detection to self-diagnosis, and Figure 7 is an enlarged view of the signal waveform during acceleration detection.

[0062] First, as shown in Figure 6, during normal acceleration detection, the self-diagnosis command signal is set to a low level, and acceleration detection is performed. The operation at this time will be explained based on Figure 7. Although not shown in Figure 7, during normal acceleration detection, based on signals S2X and S2Y, switches 220a and 320a are opened, and switches 220b and 320b are closed, and a midpoint voltage V1 (2.5V in this embodiment) is applied to the non-inverting input terminals of the operational amplifiers 210a and 310a, and the movable electrodes 101a to 101d are subjected to the midpoint voltage V1.

[0063] The signals P1X, P2X and P1Y, P2Y output from the control signal generation circuit 600 are signals with amplitudes V (5V in this embodiment) whose voltage levels are inverted from each other, and are constant amplitude rectangular wave signals whose Hi level and Low level change over four periods t1 to t4. Note that the voltage V is not limited to 5V. For example, the voltage V may be 3V, the midpoint voltage V1 may be 1.5V, etc. Of course, in this case, the voltage V2 will also change and will be a value between 3V and 1.5V.

[0064] First, during the first period t1, based on signals P1X, P2X and P1Y, P2Y, the potentials of the fixed electrodes 102a and 102c are set to V, and the potentials of the fixed electrodes 102b and 102d are set to 0. At the same time, the switches 210c and 310c are closed by signals S1X and S1Y from the control signal generation circuit 600. As a result, the operational amplifiers 210a and 310a bias the movable electrodes 101a to 101d to a potential of V / 2, and the charge stored between the electrodes of the feedback capacitors 210b and 310b is discharged.

[0065] In this case, if the capacitance C1 between the movable electrodes 101a, 101c and the fixed electrodes 102a, 102c and the capacitance C2 between the movable electrodes 101b, 101d and the fixed electrodes 102b, 102d satisfy the relationship C1 > C2, then, based on this relationship and the relationship between the potential applied to the fixed electrodes 102a~102d, the movable electrodes 101a~101d will be in a state where they have a large negative charge.

[0066] Next, during the second period t2, based on signals P1X, P2X and P1Y, P2Y, the potentials of the fixed electrodes 102a and 102c are kept at V, and the potentials of the fixed electrodes 102b and 102d remain at 0. At the same time, the switches 210c and 310c are opened by signals S1X and S1Y from the control signal generation circuit 600. As a result, charges corresponding to the state of the movable electrodes 101a to 101d are stored in the capacitors 210b and 310b. When voltage values ​​corresponding to the charges stored in the capacitors 210b and 310b are output from the CV conversion circuits 210 and 310, the outputs GoutX and GoutY at this time are sampled via the LPF circuit 230a and the GAIN circuit 230b.

[0067] Next, during the third period t3, the potentials of the fixed electrodes 102a and 102c are swapped based on signals P1X, P2X and P1Y, P2Y, so that the potential of the fixed electrodes 102b and 102d becomes V. At the same time, the switches 210c and 310c are kept open by signals S1X and S1Y from the control signal generation circuit 600.

[0068] At this time, the charge state of the movable electrodes 101a to 101d is reversed from that of the second period t2 due to the reversal of signals P1X, P2X and P1Y, P2Y. That is, if the relationship C1 > C2 is satisfied as described above, the movable electrodes 101a to 101d will have a predominantly positive charge due to the reversal of the potential applied to the fixed electrodes 102a to 102d.

[0069] However, at this time, a closed circuit is formed between the movable electrodes 101a to 101d and the capacitors 210b and 310b, and the amount of charge in the first period t1 is conserved. Therefore, the charge that overflows from the balance of charge amounts in the movable electrodes 101a to 101d moves to and is stored in the capacitors 210b and 310b. Then, from the relationship Q=CV, a voltage value proportional to the amount of charge that has moved and inversely proportional to the capacitance C of the capacitors 210b and 310b is output from the CV conversion circuits 210 and 310.

[0070] Furthermore, during the fourth period t4, based on signals P1X, P2X and P1Y, P2Y, the potentials of fixed electrodes 102a and 102c remain at 0, and the potentials of fixed electrodes 102b and 102d remain at V. Once the outputs of the CV conversion circuits 210 and 310 are sufficiently stable, the values ​​at this time are output to GoutX and GoutY via the LPF circuits 230a and 330a and the GAIN circuits 230b and 330b.

[0071] Finally, the outputs GoutX and GoutY sampled in the second period t2 and the outputs GoutX and GoutY sampled in the fourth period t4 are differentially calculated. Based on this, acceleration detection is performed according to the displacement of the movable electrodes 101a to 101d.

[0072] Next, the operation during self-diagnosis will be explained based on Figure 6. During self-diagnosis, the self-diagnosis command signal input to the control signal generation circuit 600 is set to a Hi level, and various signals for self-diagnosis are output from the control signal generation circuit 600. In this embodiment, the diagnosis is performed in the order of self-diagnosis in the first detection unit and self-diagnosis in the second detection unit.

[0073] First, during self-diagnosis of the first detection unit, a potential difference is formed between the fixed electrodes 102a, 102c and the fixed electrodes 102b, 102d based on signals P1X, P2X and P1Y, P2Y. Then, with respect to the first detection unit, based on signal S2X, switch 220a of the switch circuit 220 is closed and switch 220b is opened. For this reason, a voltage V2 (4V in this embodiment), which is different from the midpoint voltage V1 of the fixed electrodes 102a, 102b, is applied to the non-inverting input terminal of the operational amplifier 210a for self-diagnosis.

[0074] As a result, the potential difference between the movable electrode 101b and the fixed electrode 102b (4V) becomes greater than the potential difference between the movable electrode 101a and the fixed electrode 102a (1V), increasing the electrostatic force. This electrostatic force forces the movable electrodes 101a and 101b to move away from the center point. Subsequently, at time T1, the switch circuit 220 switches based on the signal S2X, and the midpoint voltage V1 of the fixed electrodes 102a and 102b is applied to the non-inverting input terminal of the operational amplifier 210a, just as in normal acceleration detection.

[0075] Through the above process, the movable electrodes 101a and 101b can be displaced by electrostatic force. In this embodiment, the period of the drive signal S2X of the switch circuit 220 is set to control the time for generating the electrostatic force so that the amount of displacement can be sufficiently detected. For example, the resonance frequency characteristics of the vibration of the movable electrodes 101a and 101b with respect to the input frequency of the voltage applied to the movable electrodes 101a and 101b are shown in Figure 8. In this embodiment, the frequency of the input signal, that is, the frequency of the input voltage to the first detection unit shown in Figure 6, is set to be the resonance frequency f0. As a result, vibration in the movable electrodes 101a and 101b occurs at the frequency at which the movable electrodes 101a and 101b resonate, that is, at the frequency at which the displacement range is greatest.

[0076] In this embodiment, self-diagnosis of the second detection unit is not performed when self-diagnosis of the first detection unit is performed. That is, based on the signal S2Y, switch 320a of the switch circuit 320 is opened and switch 320b is closed. Therefore, the midpoint voltage V1 of the fixed electrodes 102c and 102d is applied to the non-inverting input terminal of the operational amplifier 310a, just as in normal acceleration detection, and self-diagnosis is not performed.

[0077] Subsequently, the first detection unit operates in the same manner as the conventional acceleration detection described above, and an output GoutX corresponding to the displacement of the movable electrodes 101a and 101b is obtained. At this time, the displacement of the movable electrodes 101a and 101b due to the electrostatic force is uniquely determined by the voltage applied to the non-inverting input terminal of the operational amplifier 210a, and therefore the output corresponding to the displacement of the movable electrodes 101a and 101b is also uniquely determined. Self-diagnosis of the first detection unit is performed by comparing the obtained output with the uniquely determined self-diagnosis amount (output).

[0078] Next, a self-diagnosis of the second detection unit is performed after a predetermined time has elapsed since the completion of the self-diagnosis of the first detection unit. The interval between the self-diagnosis of the first and second detection units is set to a time sufficient for the oscillation of the movable electrodes 101a and 101b, which were forcibly displaced during the self-diagnosis of the first detection unit, to stop. In this embodiment, the movable electrodes 101a, 101b, 101c, and 101d are made of silicon. Therefore, their Q values ​​are low. For example, the Q value of a quartz crystal oscillator, which is often used in gyro sensors, is on the order of 30,000, but the Q value of the movable electrodes 101a, 101b, 101c, and 101d, which are constructed as silicon MEMS, is about 20. As a result, the oscillations forcibly induced during the self-diagnosis of the first detection unit subside in a very short time.

[0079] During self-diagnosis of the second detection unit, a potential difference is formed between the fixed electrodes 102a, 102c and the fixed electrodes 102b, 102d based on signals P1X, P2X and P1Y, P2Y. Then, with respect to the second detection unit, switch 320a of the switch circuit 320 is closed and switch 320b is opened based on signal S2Y. For this reason, a voltage V2 (4V in this embodiment), which is different from the midpoint voltage V1 of the fixed electrodes 102c, 102d, is applied to the non-inverting input terminal of the operational amplifier 310a for self-diagnosis.

[0080] As a result, the potential difference between the movable electrode 101d and the fixed electrode 102d (4V) becomes greater than the potential difference between the movable electrode 101c and the fixed electrode 102c (1V), increasing the electrostatic force. This electrostatic force forces the movable electrodes 101c and 101d to move away from the center point. Subsequently, at time T2, the switch circuit 320 switches based on the signal S2Y, and the midpoint voltage V1 of the fixed electrodes 102c and 102d is applied to the non-inverting input terminal of the operational amplifier 310a, just as in normal acceleration detection.

[0081] Through the above process, the movable electrodes 101c and 101d can be displaced by electrostatic force. In this embodiment, the period of the drive signal S2Y of the switch circuit 320 is set to control the time for generating the electrostatic force so that the amount of displacement can be sufficiently detected. In this embodiment, in the second detection unit as well, the frequency of the input signal, that is, the frequency of the input voltage to the second detection unit shown in Figure 6, is set to be the resonant frequency f0. As a result, vibrations in the movable electrodes 101c and 101d occur at the frequency in which the movable electrodes 101c and 101d resonate, that is, at the frequency in which the displacement range is greatest.

[0082] During the self-diagnosis of the second detection unit, a self-diagnosis of the first detection unit is not performed. That is, based on the signal S2X, switch 220a of the switch circuit 220 is opened and switch 220b is closed. As a result, the midpoint voltage V1 of the fixed electrodes 102a and 102b is applied to the non-inverting input terminal of the operational amplifier 210a, just as during normal acceleration detection, and a self-diagnosis is not performed.

[0083] Subsequently, the second detection unit operates in the same manner as the conventional acceleration detection described above, and an output GoutY is obtained corresponding to the displacement of the movable electrodes 101c and 101d. At this time, the displacement of the movable electrodes 101c and 101d due to the electrostatic force is uniquely determined by the voltage applied to the non-inverting input terminal of the operational amplifier 310a. Therefore, the output corresponding to the displacement of the movable electrodes 101c and 101d is also uniquely determined, and a self-diagnosis of the second detection unit is performed by comparing the obtained output with the uniquely determined self-diagnosis amount (output).

[0084] (2-2) Z-direction acceleration sensor element: The Z-direction acceleration sensor element 1 is used in connection with a control IC (not shown). The control IC includes a circuit for detecting acceleration based on the signal output from the Z-direction acceleration sensor element 1. Figure 9 is a diagram illustrating this circuit. In Figure 9, the Z-direction acceleration sensor element 1 is shown along with the elements and wiring that make up the circuit.

[0085] However, in Figure 9, the details of the structure of the Z-direction acceleration sensor element 1 are omitted, and the first movable comb electrodes 21, 22, the second movable comb electrodes 61, 62, the first fixed comb electrodes 11, 12, and the second fixed comb electrodes 51, 52 of the Z-direction acceleration sensor element 1 are schematically shown.

[0086] The first movable comb electrodes 21, 22 and the first fixed comb electrodes 11, 12 constitute a parallel plate capacitor oriented perpendicular to the second direction DR2. The second movable comb electrodes 61, 62 and the second fixed comb electrodes 51, 52 also constitute a parallel plate capacitor oriented perpendicular to the second direction DR2. As shown in Figure 4, the first movable comb electrodes 21, 22 and the second movable comb electrodes 61, 62 are electrodes that displace in the third direction DR3 and the fifth direction DR5 in response to acceleration in the Z direction, which is the third direction DR3. The positions of the first fixed comb electrodes 11, 12 and the second fixed comb electrodes 51, 52 do not displace. Then, as the first movable comb electrodes 21, 22 and the second movable comb electrodes 61, 62 are displaced in the third direction DR3 and the fifth direction DR5 in response to acceleration in the Z direction, which is the third direction DR3, the capacitance composed of the first movable comb electrodes 21, 22 and the first fixed comb electrodes 11, 12, and the capacitance composed of the second movable comb electrodes 61, 62 and the second fixed comb electrodes 51, 52 change.

[0087] Furthermore, as shown in Figure 1, the Z-direction acceleration sensor element 1 is equipped with multiple pads, and Figure 9 shows the connection relationships between pads Pz, Pz1, and Pz2 and circuit components, as well as the connection relationships between the first movable comb electrodes 21, 22, the second movable comb electrodes 61, 62, the first fixed comb electrodes 11, 12, and the second fixed comb electrodes 51, 52.

[0088] Here, the configuration for detecting acceleration in the Z direction, which is the third direction DR3, is referred to as the third detection unit. The third detection unit includes a detection circuit 400 that detects acceleration based on changes in differential capacitance due to the first movable comb electrodes 21, 22 and the first fixed comb electrodes 11, 12, and changes in differential capacitance due to the second movable comb electrodes 61, 62 and the second fixed comb electrodes 51, 52.

[0089] The detection circuit 400 includes a CV conversion circuit 410, a switch circuit 420, a signal processing circuit 430, and a control signal generation circuit 600. In this embodiment, the control signal generation circuit 600 is shared with the first detection unit and the second detection unit, but it may be a different circuit.

[0090] The CV conversion circuit 410 is a circuit that converts the change in the differential capacitance of the capacitance formed by the first movable comb electrodes 21, 22, the second movable comb electrodes 61, 62, the first fixed comb electrodes 11, 12, and the second fixed comb electrodes 51, 52 into a voltage. Specifically, the CV conversion circuit 410 includes an operational amplifier 410a, a capacitor 410b, and a switch 410c.

[0091] The inverting input terminal of the operational amplifier 410a is connected to the first movable comb electrodes 21, 22 and the second movable comb electrodes 61, 62, and a capacitor 410b and a switch 410c are connected in parallel between the inverting input terminal and the output terminal. The switch 410c is driven by a signal S1Z from the control signal generation circuit 600. The non-inverting input terminal of the operational amplifier 410a is input via the switch circuit 420 to either a voltage V1 (i.e., the midpoint voltage, 2.5V in this embodiment) which is half the potential difference between the first fixed comb electrodes 11, 12 and the second fixed comb electrodes 51, 52, or a voltage V2 (4V in this embodiment) which is different from this midpoint voltage.

[0092] The switch circuit 420 inputs voltages from various voltage sources (not shown) to the non-inverting input terminal of the operational amplifier 410a in the CV conversion circuit 410. Specifically, the switch circuit 420 includes switches 420a and 420b. Switches 420a and 420b are driven based on the signal S2Z from the control signal generation circuit 600, and when one is closed, the other is open.

[0093] The signal processing circuit 430 includes an LPF (low-pass filter) circuit 430a and a GAIN circuit 430b. The LPF circuit 430a removes high-frequency components from the output of the CV conversion circuit 410, extracting only components within a predetermined frequency band. The GAIN circuit 430b amplifies the output after passing through the LPF circuit 430a and outputs it as an acceleration signal GoutZ.

[0094] The control signal generation circuit 600 outputs signals (carrier waves) P1Z and P2Z indicating the voltage application timing to the first fixed comb electrodes 11 and 12 and the second fixed comb electrodes 51 and 52, respectively, as well as a signal S2Z indicating the switching timing of the switch in the switch circuit 420 and a signal S1Z indicating the switching timing of switch 410c.

[0095] The various signals generated by this control signal generation circuit 600 change between normal acceleration detection (when not self-diagnostic) and self-diagnostic. Specifically, the control signal generation circuit 600 outputs various signals based on the clock signal CLK, but outputs an acceleration detection signal when the self-diagnostic command signal is at a low level, and outputs a self-diagnostic signal when the self-diagnostic command signal is at a high level.

[0096] The self-diagnosis process involves inputting a self-diagnosis signal to the Z-direction acceleration sensor element 1. If the obtained output falls within a predetermined range, it is considered normal; if it falls outside this range, it is considered abnormal. In other words, if the obtained output falls outside the predetermined range, it can be assumed that an abnormality, such as damage to the comb teeth of the Z-direction acceleration sensor element 1, has occurred.

[0097] The operation of the acceleration sensor configured in this way will be explained with reference to the signal waveform diagrams shown in Figures 10 and 7. Figure 10 shows the signal waveform when switching from normal acceleration detection to self-diagnosis. The signal waveform shown in Figure 10 is similar to the waveform shown in Figure 6, so Figure 7, which is an enlarged view of the signal waveform during acceleration detection, will be explained using the same diagram.

[0098] First, as shown in Figure 10, during normal acceleration detection, the self-diagnosis command signal is set to a low level, and acceleration detection is performed. The operation at this time will be explained based on Figure 7. Although not shown in Figure 7, during normal acceleration detection, based on the signal S2Z, switch 420a is opened and switch 420b is closed, and a midpoint voltage V1 (2.5V in this embodiment) is applied to the non-inverting input terminal of the operational amplifier 410a, and the first movable comb electrodes 21, 22 and the second movable comb electrodes 61, 62 are set to the midpoint voltage V1.

[0099] The signals P1Z and P2Z output from the control signal generation circuit 600 during normal operation (not self-diagnosis) are signals for detecting capacitance changes. Specifically, signals P1Z and P2Z are signals with amplitude V (5V in this embodiment) whose voltage levels are inverted from each other, and are constant amplitude rectangular wave signals whose Hi level and Low level change over four periods t1 to t4. Note that the voltage V is not limited to 5V. For example, the voltage V may be 3V and the midpoint voltage may be 1.5V. Of course, in this case, the voltage V2 will also change and will be a value between 3V and 1.5V.

[0100] First, during the first period t1, based on signals P1Z and P2Z, the potentials of the first fixed comb electrodes 11 and 12 are set to V, and the potentials of the second fixed comb electrodes 51 and 52 are set to 0. At the same time, the switch 410c is closed by the signal S1Z from the control signal generation circuit 600. As a result, the operational amplifier 410a biases the first movable comb electrodes 21 and 22 and the second movable comb electrodes 61 and 62 to a potential of V / 2, and the charge stored between the electrodes of the capacitor 410b, which acts as a feedback capacitance, is discharged.

[0101] In this case, if the capacitance C1 between the first movable comb electrodes 21, 22 and the first fixed comb electrodes 11, 12 and the capacitance C2 between the second movable comb electrodes 61, 62 and the second fixed comb electrodes 51, 52 satisfy the relationship C1 > C2, then, based on this relationship and the relationship between the potentials applied to the first fixed comb electrodes 11, 12 and the second fixed comb electrodes 51, 52, the first movable comb electrodes 21, 22 and the second movable comb electrodes 61, 62 will be in a state where they have a large negative charge.

[0102] Next, during the second period t2, based on signals P1Z and P2Z, the potentials of the first fixed comb electrodes 11 and 12c are kept at V, and the potentials of the second fixed comb electrodes 51 and 52 remain at 0. At the same time, the switch 410c is opened by the signal S1Z from the control signal generation circuit 600. As a result, charge corresponding to the state of the first movable comb electrodes 21 and 22 and the second movable comb electrodes 61 and 62 is stored in the capacitor 410b. When a voltage value corresponding to the charge stored in the capacitor 410b is output from the CV conversion circuit 410, the output GoutZ at this time is sampled via the LPF circuit 430a and the GAIN circuit 430b.

[0103] Next, during the third period t3, the potentials of the first fixed comb electrodes 11 and 12 are swapped based on signals P1Z and P2Z, and the potentials of the second fixed comb electrodes 51 and 52 are swapped so that they become 0, while the switch 410c is kept open by the signal S1Z from the control signal generation circuit 600.

[0104] At this time, the charge state of the first movable comb electrodes 21, 22 and the second movable comb electrodes 61, 62 is reversed from that of the second period t2 due to the reversal of signals P1Z and P2Z. That is, if the relationship C1 > C2 is satisfied as described above, the reversal of the applied potential to the first fixed comb electrodes 11, 12 and the second fixed comb electrodes 51, 52 results in the first movable comb electrodes 21, 22 and the second movable comb electrodes 61, 62 having a large positive charge.

[0105] However, at this time, a closed circuit is formed between the first movable comb electrodes 21, 22 and the second movable comb electrodes 61, 62 and the capacitor 410b, and the amount of charge during the first period t1 is conserved. Therefore, the charge that overflows from the balance of the charge amounts of the first movable comb electrodes 21, 22 and the second movable comb electrodes 61, 62 moves to the capacitor 410b and is stored there. Then, from the relationship Q=CV, a voltage value proportional to the amount of charge that has moved and inversely proportional to the capacitance C of the capacitor 410b is output from the CV conversion circuit 410.

[0106] Furthermore, during the fourth period t4, based on signals P1Z and P2Z, the potentials of the first fixed comb electrodes 11 and 12 remain at 0, and the potentials of the second fixed comb electrodes 51 and 52 remain at V. Once the output of the CV conversion circuit 410 is sufficiently stable, the value at this time is output to GoutZ via the LPF circuit 430a and the GAIN circuit 430b.

[0107] Finally, the output GoutZ sampled in the second period t2 and the output GoutZ sampled in the fourth period t4 are differentially calculated. Based on this, acceleration detection is performed according to the displacement of the first movable comb electrodes 21, 22 and the second movable comb electrodes 61, 62.

[0108] Next, the operation during self-diagnosis will be explained based on Figure 10. During self-diagnosis, the self-diagnosis command signal input to the control signal generation circuit 600 is set to a high level, and various signals for self-diagnosis are output from the control signal generation circuit 600.

[0109] The signals P1Z and P2Z output from the control signal generation circuit 600 during self-diagnosis are signals to displace the first movable comb electrode and the second movable comb electrode in order to perform self-diagnosis. Specifically, a potential difference is formed between the first fixed comb electrodes 11, 12 and the second fixed comb electrodes 51, 52 based on the signals P1Z and P2Z output from the control signal generation circuit 600. Then, based on the signal S2Z, switch 420a of the switch circuit 420 is closed and switch 420b is opened. For this reason, a voltage V2 (4V in this embodiment) different from the midpoint voltage V1 between the first fixed comb electrodes 11, 12 and the second fixed comb electrodes 51, 52 is applied to the non-inverting input terminal of the operational amplifier 410a for self-diagnosis.

[0110] As a result of the above processing, before time T3, the potential difference (4V) between the second movable comb electrodes 61, 62 and the second fixed comb electrodes 51, 52 becomes greater than the potential difference (1V) between the first movable comb electrodes 21, 22 and the first fixed comb electrodes 11, 12. Subsequently, at time T3, the switch circuit 420 switches based on the signal S2Z, and the midpoint voltage V1 of the fixed electrodes 102a and 102b is applied to the non-inverting input terminal of the operational amplifier 410a, similar to normal acceleration detection.

[0111] When the above processing is performed, the movable electrodes 101a, 101c or 101b, 101d in the XY direction acceleration sensor element 101 can be displaced significantly. On the other hand, in the Z direction acceleration sensor element 1, it is difficult to displace the first movable comb electrodes 21, 22 and the second movable comb electrodes 61, 62 significantly. Specifically, the force acting on the electrodes due to the voltage applied to the capacitance acts mainly in a direction perpendicular to the plane of the parallel plate capacitor. In the XY direction acceleration sensor element 101, the direction in which the movable electrodes 101a, 101c and movable electrodes 101b, 101d are displaced is perpendicular to the plane that constitutes the parallel plate capacitor. Therefore, in the XY direction acceleration sensor element 101, the force in the direction in which the movable electrodes 101a, 101b, 101c, 101d can be displaced can be increased by increasing the voltage applied between the electrodes.

[0112] On the other hand, in the Z-direction acceleration sensor element 1, the direction in which the first movable comb electrodes 21, 22 and the second movable comb electrodes 61, 62 are displaced is parallel to the planes constituting the parallel plane capacitor, as shown in Figure 4. Therefore, in the Z-direction acceleration sensor element 1, even if the voltage applied between the electrodes is increased, it is difficult to increase the force in the direction in which the first movable comb electrodes 21, 22 and the second movable comb electrodes 61, 62 can be displaced.

[0113] Therefore, the Z-direction acceleration sensor element 1 according to this embodiment is configured to allow the force in the displaceable direction of the first movable comb electrodes 21, 22 and the second movable comb electrodes 61, 62 to be changed. That is, the Z-direction acceleration sensor element 1 has self-diagnostic electrodes E1, E2 sandwiching the first movable comb electrodes 21, 22, the first fixed comb electrodes 11, 12, the second movable comb electrodes 61, 62, and the second fixed comb electrodes 51, 52.

[0114] Specifically, as shown in Figure 3, the self-diagnostic electrode E1 is formed on the lid Cp, and the self-diagnostic electrode E2 is formed on the support substrate 2. The self-diagnostic electrode E1 is formed on the outer surface of the lid Cp, i.e., on the plane on the positive side of the third direction DR3, and the self-diagnostic electrode E2 is formed on the outer surface of the support substrate 2, i.e., on the plane on the negative side of the third direction DR3.

[0115] In this embodiment, the self-diagnostic electrode E1 is formed on substantially the entire outer surface of the lid Cp, and the self-diagnostic electrode E2 is formed on substantially the entire outer surface of the support substrate 2. Therefore, the self-diagnostic electrodes E1 and E2 sandwich the beam fixing part 40, the first electrode fixing part 3, the second electrode fixing parts 4 and 5, the support beam 42, the movable body MB, the first movable comb electrodes 21 and 22, the first fixed comb electrodes 11 and 12, the second movable comb electrodes 61 and 62, and the second fixed comb electrodes 51 and 52, which are located inside the space formed by the lid Cp and the support substrate 2.

[0116] Each of the self-diagnostic electrodes E1 and E2 is electrically connected to the pads Pz1 and Pz2, respectively. Therefore, signals P1Z and P2Z are applied to each of the self-diagnostic electrodes E1 and E2, respectively. With the above configuration, the potential difference between the first movable comb electrodes 21 and 22 and the self-diagnostic electrode E1 on the lid Cp can be set to, for example, 1V, and the potential difference between the second movable comb electrodes 61 and 62 and the self-diagnostic electrode E2 on the support substrate 2 can be set to, for example, 4V. The main direction of the electric field generated by this potential difference is along the third direction DR3, so the first movable comb electrodes 21 and 22 and the second movable comb electrodes 61 and 62 can be forcibly displaced significantly by electrostatic force.

[0117] In this embodiment, the period of the drive signal S2Z of the switch circuit 420 is set so that the displacement of the first movable comb electrodes 21, 22 and the second movable comb electrodes 61, 62 is sufficiently large. Specifically, the resonance frequency characteristics of the vibration of the first movable comb electrodes 21, 22 and the second movable comb electrodes 61, 62 with respect to the input frequency of the voltage applied to the first fixed comb electrodes 11, 12 and the second fixed comb electrodes 51, 52 are shown in Figure 8. Therefore, in this embodiment, the frequencies of the input signals (V1, V2) for displacing the first movable comb electrodes 21, 22 and the second movable comb electrodes 61, 62, that is, the frequencies of the input voltage to the third detection unit shown in Figure 10, are set to be the resonance frequency f0. As a result, vibrations in the first movable comb electrodes 21, 22 and the second movable comb electrodes 61, 62 occur at the frequency in which the first movable comb electrodes 21, 22 and the second movable comb electrodes 61, 62 resonate, that is, at the frequency in which the displacement is greatest.

[0118] Subsequently, the third detection unit operates in the same manner as the conventional acceleration detection described above, and an output GoutZ corresponding to the displacement of the first movable comb electrodes 21, 22 and the second movable comb electrodes 61, 62 is obtained. At this time, the displacement of the first movable comb electrodes 21, 22 and the second movable comb electrodes 61, 62 due to the electrostatic force is uniquely determined by the voltage applied to the non-inverting input terminal of the operational amplifier 410a. Therefore, the output corresponding to the displacement of the first movable comb electrodes 21, 22 and the second movable comb electrodes 61, 62 is also uniquely determined, and a self-diagnosis of the third detection unit is performed by comparing the obtained output with the uniquely determined self-diagnosis amount (output).

[0119] Specifically, when some of the comb teeth constituting the first movable comb electrodes 21, 22 and the second movable comb electrodes 61, 62, the first fixed comb electrodes 11, 12 and the second fixed comb electrodes 51, 52 are damaged, the amount of displacement described above becomes smaller compared to the undamaged state. However, if the amount of displacement is not large, the change in displacement due to the damage will be small, making it difficult to detect the change in displacement.

[0120] However, in this embodiment, since the frequency of the input signals (V1, V2) is the resonant frequency of the first movable comb electrodes 21, 22 and the second movable comb electrodes 61, 62, the displacement is large, making it easy to detect changes in the displacement due to slight damage to the comb teeth. Figure 11 shows the displacement with respect to voltage between the first fixed comb electrodes 11, 12 and the second fixed comb electrodes 51, 52. In Figure 11, the solid line shows an example where the voltage frequency is the resonant frequency, and the dashed line shows an example where the voltage frequency is not the resonant frequency (1 Hz in the example shown). The displacement is the value of the gravitational acceleration detected by the displacement of the first movable comb electrodes 21, 22 and the second movable comb electrodes 61, 62.

[0121] As shown in Figure 11, for example, if the input signal voltage is 3V, a displacement equivalent to a 2G displacement will occur if the input signal frequency is 1Hz. On the other hand, if the input signal frequency is the resonant frequency, a displacement exceeding that of 40G will occur. Therefore, even slight damage to the comb teeth will result in a difference in the amount of displacement, making it highly likely that the abnormality can be accurately detected.

[0122] In this embodiment, the first movable comb electrodes 21, 22 and the second movable comb electrodes 61, 62 are made of silicon. Therefore, their Q values ​​are low. For example, the Q value of a quartz crystal oscillator, which is often used in gyro sensors, is on the order of 30,000, but the Q values ​​of the first movable comb electrodes 21, 22 and the second movable comb electrodes 61, 62, which are constructed as silicon MEMS, are about 20. As a result, the vibrations forcibly induced during the self-diagnosis of the third detection unit subside in a very short time.

[0123] (3) Other embodiments, etc.: The above embodiments are examples of carrying out the invention. Therefore, the configuration of each part can be replaced with any configuration having a similar function. In addition, any other arbitrary components may be added to the present invention.

[0124] The beam fixing portion, the first electrode fixing portion, and the second electrode fixing portion are parts that extend perpendicular to the support substrate and can be any part that supports other parts. That is, the support substrate is a substrate that supports other structures, and each part of the physical quantity sensor element is supported directly or indirectly by the support substrate. The beam fixing portion, the first electrode fixing portion, and the second electrode fixing portion are parts that are directly supported by the support substrate.

[0125] A part that is considered to be fixed and does not move relative to the support substrate is considered a fixed part, and a part that moves relative to the support substrate or a part fixed to the support substrate is considered a movable part. The beam fixing part only needs to be able to support the support beam, and the support beam and the part connected to the support beam may be movable parts. The first electrode fixing part and the second electrode fixing part are parts that support the first fixed comb electrode and the second fixed comb electrode, respectively. Therefore, the first electrode fixing part and the second electrode fixing part are parts that support the fixed part. The beam fixing part, the first electrode fixing part and the second electrode fixing part only need to be able to connect to other parts and support other parts, and their shape, size and position on the support substrate may be in various forms.

[0126] The support beam is the part that has one end connected to the beam fixing part and extends in a direction parallel to the support base plate. That is, one end of the support beam is connected to the beam fixing part that extends in a direction perpendicular to the support base plate, and the support beam extends in a direction perpendicular to the beam fixing part, i.e., in a direction parallel to the support base plate. The other end of the support beam is connected to the movable body, so that the movable body can be displaced relative to the support base plate.

[0127] Furthermore, the movable bodies are located on both sides of the support beam in a plan view. That is, the presence of movable bodies on both sides of the support beam is sufficient to allow the movable bodies to swing in a rotational direction around the support beam. The movable bodies should be displaced according to a physical quantity perpendicular to the support substrate, and the displacements on both sides of the support beam should be different. That is, the displacements of the first movable comb electrode and the second movable comb electrode corresponding to a physical quantity perpendicular to the support substrate should be different from each other.

[0128] Various configurations can be employed to ensure that the displacement of the first and second movable comb electrodes differs in accordance with a physical quantity perpendicular to the support substrate. For example, the first and second movable comb electrodes can be configured to differ in at least one of their mass, size, or structure.

[0129] The first movable comb electrode and the first fixed comb electrode only need to face each other. Furthermore, the first fixed comb electrode should be fixed relative to the support substrate, and the first movable comb electrode should be configured to be displaceable relative to the support substrate. In other words, the displacement of the first movable comb electrode should cause a displacement in the area of ​​the capacitor formed by the first movable comb electrode and the first fixed comb electrode.

[0130] The second movable comb electrode and the second fixed comb electrode only need to face each other. Furthermore, the second fixed comb electrode should be fixed relative to the support substrate, and the second movable comb electrode should be configured to be displaceable relative to the support substrate. In other words, the displacement of the second movable comb electrode should cause a displacement in the area of ​​the capacitor formed by the second movable comb electrode and the second fixed comb electrode.

[0131] Furthermore, the first and second movable comb electrodes are displaced because their movable parts are supported by a support beam. Consequently, the first and second movable comb electrodes are displaced in opposite directions due to rotational displacement around the support beam.

[0132] The self-diagnostic electrode can be any electrode that sandwiches the first movable comb electrode, the first fixed comb electrode, the second movable comb electrode, and the second fixed comb electrode. In other words, it just needs to be configured so that a signal to displace the first and second movable comb electrodes can be periodically applied between the self-diagnostic electrode. The signal applied to the self-diagnostic electrode only needs to be able to displace the first and second movable comb electrodes. Various configurations can be used for such electrodes, but for example, a configuration in which the first movable comb electrode, the first fixed comb electrode, the second movable comb electrode, and the second fixed comb electrode are sandwiched between planar electrodes parallel to the support substrate can be used. [Explanation of Symbols]

[0133] 1...Z-direction acceleration sensor element, 2...Support substrate, 3...First electrode fixing part, 4...Second electrode fixing part, 5...Second electrode fixing part, 10A...First fixed electrode part, 11...First fixed comb electrode, 12...First fixed comb electrode, 12c...First fixed comb electrode, 13A...First fixed electrode base, 20A...First movable electrode part, 21...First movable comb electrode, 22...First movable comb electrode, 23A...First base, 30...First connecting part, 40...Beam fixing part, 42...Support beam, 50A...Second fixed electrode Electrode part, 51...Second fixed comb electrode, 52...Second fixed comb electrode, 53A...Second fixed electrode base, 53B...Second fixed electrode base, 60A...Second movable electrode part, 61...Second movable comb electrode, 62...Second movable comb electrode, 63...Second base, 70...Second connecting part, 100...Physical quantity sensor device, 101...XY direction acceleration sensor element, 101a...Movable electrode, 101b...Movable electrode, 101c...Movable electrode, 101d...Movable electrode, 102a...Fixed electrode, 102 b...fixed electrode, 102c...fixed electrode, 102d...fixed electrode, 200...detection circuit, 210...conversion circuit, 210a...operational amplifier, 210b...capacitor, 210c...switch, 220...switch circuit, 220a...switch, 220b...switch, 230...signal processing circuit, 230a...LPF circuit, 230b...GAIN circuit, 300...detection circuit, 310...conversion circuit, 310a...operational amplifier, 310b...capacitor, 310c...switch 320…Switch circuit, 320a…Switch, 320b…Switch, 330…Signal processing circuit, 330a…LPF circuit, 330b…Circuit, 400…Detection circuit, 410…CV conversion circuit, 410a…Operational amplifier, 410b…Capacitor, 410c…Switch, 420…Switch circuit, 420a…Switch, 420b…Switch, 430…Signal processing circuit, 430a…LPF circuit, 430b…GAIN circuit, 600…Control signal generation circuit

Claims

1. A beam fixing portion, a first electrode fixing portion, and a second electrode fixing portion extending perpendicular to the support substrate, A support beam having one end connected to the beam fixing portion and extending in a direction parallel to the support base plate, A movable body connected to the other end of the support beam and located on both sides of the support beam in a plan view, A first movable comb-tooth electrode is connected to the movable body and is located on one side of the support beam in a plan view, A first fixed comb electrode is connected to the first electrode fixing portion and faces the first movable comb electrode, A second movable comb-tooth electrode is connected to the movable body and is located on the other side of the support beam in a plan view, A second fixed comb electrode is connected to the second electrode fixing portion and faces the second movable comb electrode, A self-diagnostic electrode sandwiching the first movable comb electrode, the first fixed comb electrode, the second movable comb electrode, and the second fixed comb electrode, A physical quantity sensor element equipped with the following features.

2. The support substrate and, It comprises a lid positioned opposite the support substrate, One of the self-diagnostic electrodes is formed on the support substrate, and the other is formed on the lid. Inside the space formed by the support substrate and the lid, The beam fixing portion, the first electrode fixing portion, the second electrode fixing portion, the support beam, the movable body, the first movable comb electrode, the first fixed comb electrode, the second movable comb electrode, and the second fixed comb electrode are housed in the above. A physical quantity sensor element according to claim 1.

3. A physical quantity sensor element according to claim 1 or claim 2, During normal operation, which is not self-diagnostic, a signal for detecting capacitance changes is periodically applied between the first movable comb electrode and the first fixed comb electrode, and between the second movable comb electrode and the second fixed comb electrode. During self-diagnosis, instead of the signal for detecting capacitance changes, a signal for displacing the first movable comb electrode and the second movable comb electrode for self-diagnosis is periodically applied between the self-diagnostic electrodes. A C-V conversion circuit that outputs a voltage corresponding to the change in capacitance between the first movable comb electrode and the first fixed comb electrode and the change in capacitance between the second movable comb electrode and the second movable comb electrode, The system includes a signal processing circuit that processes the output voltage of the C-V conversion circuit and outputs a signal corresponding to the change in a physical quantity. Physical quantity sensor device.

4. The frequency of the signal applied periodically between the self-diagnostic electrodes to displace the first movable comb electrode and the second movable comb electrode coincides with the resonant frequency of the first movable comb electrode and the second movable comb electrode. The physical quantity sensor device according to claim 3.

Images