Physical quantity sensor element and physical quantity sensor device

Abstract

The invention relates to a physical quantity sensor element and a physical quantity sensor apparatus. The physical quantity sensor element includes a beam fixing portion, a first electrode fixing portion, and a second electrode fixing portion. A support beam having 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 disposed on both sides of the support beam with the support beam sandwiched therebetween in plan view; a first movable comb electrode connected to the movable body and disposed on one side with the support beam sandwiched therebetween in 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 disposed on the other side with the support beam interposed therebetween in plan view; a second fixed comb electrode connected to the second electrode fixing part and facing the second movable comb electrode; and a self-diagnosis electrode that sandwiches the first movable comb electrode, the first fixed comb electrode, the second movable comb electrode, and the second fixed comb electrode.

Description

Technical Field

[0001] This invention relates to physical quantity sensor elements and physical quantity sensor devices. Background Technology

[0002] Conventionally, capacitive physical quantity sensors that detect capacitance formed by a fixed electrode and a movable electrode based on changes in a physical quantity are known. For example, Patent Document 1 discloses a capacitive physical quantity sensor in which a fixed electrode and a movable electrode are positioned parallel to each other, and the distance between the fixed electrode and the movable electrode varies according to a physical quantity. Furthermore, Patent Document 1 discloses a configuration in which a voltage is applied between the fixed electrode and the movable electrode, causing the movable electrode to vibrate due to a change in the voltage value, thereby performing self-diagnosis.

[0003] Patent Document 1: Japanese Patent Application Publication No. 2003-121457 The aforementioned prior art involves a fixed electrode and a movable electrode forming a parallel plate electrode, with the distance between them varying in a direction perpendicular to the plate depending on the physical quantity. However, in capacitive physical quantity sensors, there are sensors where the movable electrode displaces in a direction parallel to the plate. In such sensors, even if a voltage is applied between the fixed and movable electrodes, it is difficult to cause the movable electrode to displace or vibrate in a direction parallel to the plate through a change in voltage. Therefore, self-diagnosis is difficult in sensors where the movable electrode displaces in a direction parallel to the plate. Summary of the Invention

[0004] One embodiment of a physical quantity sensor element includes: a beam fixing portion, a first electrode fixing portion, and a second electrode fixing portion extending in a direction perpendicular to a support substrate; a support beam, one end of which is connected to the beam fixing portion, extending in a direction parallel to the support substrate; a movable body connected to the other end of the support beam, which, when viewed from above, sandwiches the support beam in the middle and is disposed on both sides; a first movable comb electrode connected to the movable body, which, when viewed from above, sandwiches the support beam in the middle and is disposed on one side; a first fixed comb electrode connected to the first electrode fixing portion and opposite to the first movable comb electrode; a second movable comb electrode connected to the movable body, which, when viewed from above, sandwiches the support beam in the middle and is disposed on the other side; a second fixed comb electrode connected to the second electrode fixing portion and opposite to 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 in the middle. Attached Figure Description

[0005] Figure 1 This is a top view of the physical quantity sensor device of this embodiment.

[0006] Figure 2 This is a top view of the Z-direction acceleration sensor element in this embodiment.

[0007] Figure 3 This is a cross-sectional view of the Z-direction acceleration sensor element.

[0008] Figure 4 This diagram illustrates the operation of the detection section of the Z-direction acceleration sensor element.

[0009] Figure 5 This is an illustration of a circuit used to detect acceleration.

[0010] Figure 6 This is a diagram showing the signal waveform when switching from normal acceleration detection to self-diagnosis.

[0011] Figure 7 This is a magnified image of the signal waveform during acceleration detection.

[0012] Figure 8 This is a graph showing the resonant frequency characteristics of the movable electrode.

[0013] Figure 9 This is an illustration of a circuit used to detect acceleration.

[0014] Figure 10 This is a diagram showing the signal waveform when switching from normal acceleration detection to self-diagnosis.

[0015] Figure 11 It is a graph showing the relationship between voltage and displacement. Detailed Implementation

[0016] The following describes this embodiment. Furthermore, the embodiments described below do not unduly limit the scope of the claims. Also, not all components described in this embodiment are necessarily essential elements.

[0017] (1) Composition of physical quantity sensor equipment: The physical quantity sensor device 100 of this embodiment is housed in a generally rectangular package. Figure 1 This is a top view showing the physical quantity sensor device 100 as viewed in a direction perpendicular to the largest face of the cuboid. The state of each part viewed in this direction is referred to as a top view. The physical quantity sensor device 100 according to this embodiment includes multiple physical quantity sensor elements. Specifically, the physical quantity sensor device 100 includes 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. Furthermore, for ease of explanation, the dimensions of each component and the spacing between components are schematically shown in this specification, and not all constituent elements are shown. For example, electrode wiring and electrode terminals are sometimes omitted from the illustration. In this embodiment, 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 is mainly used as an example for explanation, but the physical quantity is not limited to acceleration, and may also be other physical quantities such as velocity, pressure, displacement, attitude, angular velocity, or gravity. In addition, each physical quantity sensor element may also be an element used as a pressure sensor or a MEMS switch, etc.

[0018] Furthermore, in this specification, mutually orthogonal directions are designated 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, but are not limited thereto. For example, the third direction DR3 corresponding to the Z-axis direction is the direction perpendicular to the largest face of the cuboid formed by the physical quantity sensor device 100, and is a vertical direction. The direction opposite to the third direction DR3 is designated as the fifth direction DR5. Additionally, the first direction DR1 corresponding to the X-axis direction and the second direction DR2 corresponding to the Y-axis direction are orthogonal to the third direction DR3, and serve as the XY plane along the faces of the first direction DR1 and the second direction DR2, for example, along a horizontal plane. The direction opposite to the first direction DR1 is designated as the fourth direction DR4, which is, for example, the -X-axis direction. Furthermore, when there is no need to specifically distinguish between opposite directions, the fourth direction DR4 can also be considered as a direction along the first direction DR1. In addition, "orthogonal" means that in addition to intersecting at 90°, it also includes the case of intersecting at a slightly inclined angle from 90°.

[0019] exist Figure 1 The diagram also shows multiple pads provided by the physical quantity sensor device 100. Pad Pgnd is a pad electrically connected to the ground portion. Pad Pxy is a pad electrically connected to a movable comb 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 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 electrode (not shown) provided by the XY direction acceleration sensor element 101, and is set to a potential opposite in phase to pad Py1 for detecting acceleration in the Y direction.

[0020] Pad Px1 is a pad electrically connected to a fixed comb electrode (not shown) of 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 electrically connected to a fixed comb electrode (not shown) of the XY direction acceleration sensor element 101, and is set to a potential opposite in phase to pad Px1 for detecting acceleration in the X direction.

[0021] Pad Pz is electrically connected to the first movable comb electrode and the second movable comb electrode (described later) of the Z-direction acceleration sensor element 1. Pad Pz1 is electrically connected to the first fixed comb electrode (described later) of the Z-direction acceleration sensor element 1 and is set to a potential for detecting acceleration in the Z-direction. Pad Pz2 is electrically connected to the second fixed comb electrode (described later) of the Z-direction acceleration sensor element 1 and is set to a potential opposite in phase to that of pad Pz1 for detecting acceleration in the Z-direction.

[0022] Figure 2 This is a top view of the Z-axis acceleration sensor element 1. The support substrate 2 is, for example, a silicon substrate made of semiconductor silicon or a glass substrate made of glass materials such as borosilicate glass. However, there is no particular limitation on the material of the support substrate 2, and a quartz substrate or an SOI (Silicon On Insulator) substrate may also be used.

[0023] like Figure 2 As shown, the Z-direction acceleration sensor element 1 of this embodiment includes a beam fixing part 40, a support beam 42, a movable body MB, a first fixed electrode part 10A, and a second fixed electrode part 50A. The movable body MB includes a first connecting part 30, a first base 23A, a first movable electrode part 20A, a second connecting part 70, a second base 63, and a second movable electrode part 60A. The first fixed electrode part 10A has a plurality of first fixed comb-tooth electrodes 11 and 12, and the second fixed electrode part 50A has a plurality of second fixed comb-tooth electrodes 51 and 52. The first movable electrode part 20A has a plurality of first movable comb-tooth electrodes 21 and 22, and the second movable electrode part 60A has a plurality of second movable comb-tooth electrodes 61 and 62.

[0024] Furthermore, as in Figure 2As shown in the dashed box, the Z-direction acceleration sensor element 1 has a detection unit Z1 and a detection unit Z2, each of which detects physical quantities such as acceleration along the third direction DR3, which is the Z-axis direction. When viewed from above, the detection units Z1 and Z2 are respectively located on the first direction DR1 side and the fourth direction DR4 side of the support beam 42. The detection unit Z1 located on the first direction DR1 side of the support beam 42 includes a first fixed electrode 10A and a first movable electrode 20A. The detection unit Z2 located on the fourth direction DR4 side of the support beam 42 includes a second fixed electrode 50A and a second movable electrode 60A.

[0025] In the above configuration, the beam fixing part 40 is a generally cuboid portion extending from the surface of the support base plate 2 parallel to the first direction DR1 and the second direction DR2 toward the third direction DR3. The beam fixing part 40 is located at the rotation center when the movable body MB swings, and serves as an anchor in this swinging motion. The beam fixing part 40 is connected to one end of the support beam 42. The support beam 42 extends toward the second direction DR2. Therefore, the support beam 42 extends parallel to the surface of the support base plate 2 parallel to the first direction DR1 and the second direction DR2. This state is represented by the support beam 42 extending in a direction parallel to the support base plate 2.

[0026] 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 is present on the first direction DR1 side when viewed from the support beam 42, and the second connecting portion 70 is present 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, when viewed from above, exists on both sides sandwiching the support beam 42. The first connecting portion 30 of the support base plate 2, present on the second direction DR2 side and the side opposite to the second direction DR2, is connected by a third connecting portion 23B extending along the second direction DR2.

[0027] Support beam 42 functions as a torsion spring, providing restoring force during the swinging motion of the movable body MB. For example... Figure 2 As shown, when viewed from above, the support beam 42 is arranged with the second direction DR2 as its long side. Additionally, as... Figure 2 As shown, the thickness of the support beam 42 in the first direction DR1 is thinner than that of the beam fixing portion 40, causing it to flex relative to the swinging motion of the movable body MB. Furthermore, by torsion along the Y-axis in the second direction DR2, a restoring force is generated in the swinging motion of the movable body MB. Thus, in this embodiment, the support beam 42 is a torsion spring that twists about the second direction DR2 as its rotation axis. In this way, the movable body MB can swing about the second direction DR2 as its rotation axis.

[0028] When the movable body MB swings, the first movable electrode portion 20A and the second movable electrode portion 60A of the movable body MB also move in conjunction. In this embodiment, the changes in the capacitance formed by the first movable comb tooth electrodes 21, 22 opposite to the first fixed comb tooth electrodes 11, 12, and the capacitance formed by the second movable comb tooth electrodes 61, 62 opposite to the second fixed comb tooth electrodes 51, 52, according to the swing are detected, thereby performing physical quantity detection.

[0029] 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 23A. The second connecting portion 70 connects this other end of the support beam 42 to the second base 63. The first connecting portion 30 extends towards the first direction DR1 side of the support beam 42 and connects to the first base 23A on the first direction DR1 side of the support beam 42. The second connecting portion 70 extends towards the fourth direction DR4 side of the support beam 42 and connects to the second base 63 on the fourth direction DR4 side of the support beam 42. Thus, the first connecting portion 30 and the second connecting portion 70 connect the first base 23A and the second base 63 respectively at a fixed distance from the support beam 42, which serves as the rotation axis of the movable body MB.

[0030] The first base 23A forms the base of the first movable comb-tooth electrodes 21 and 22 of the first movable electrode portion 20A. That is, as... Figure 2 As shown, when viewed from above, a plurality of first movable comb-tooth electrodes 21, 22 extend from the first base 23A on the first direction DR1 side. Thus, the first movable comb-tooth electrodes 21, 22 are connected to the movable body MB and, when viewed from above, exist on the first direction DR1 side, which serves as a support beam 42. Furthermore, the first base 23A is connected to the support beam 42 via a first connecting portion 30 at a fixed distance from the rotation axis of the movable body MB.

[0031] The second base 63 forms the base of the second movable comb-tooth electrodes 61 and 62 of the second movable electrode section 60A. The second base 63 performs the same function in the detection section Z2 as the first base 23A of the detection section Z1. That is, when viewed from above, the plurality of second movable comb-tooth electrodes 61 and 62 extend from the second base 63 toward the first direction DR1 side and the fourth direction DR side. Thus, the second fixed comb-tooth electrodes 51 and 52 are connected to the movable body MB and, when viewed from above, exist on the fourth direction DR side, which is the other side of the support beam 42. Furthermore, the second base 63 is connected to the support beam 42 via the second connecting portion 70 at a fixed distance from the rotation axis of the movable body MB.

[0032] With this configuration, the first base 23A and the first connecting portion 30 connect the first movable comb electrodes 21 and 22 of the first movable electrode portion 20A at a fixed distance from the rotation axis of the swinging motion of the movable body MB. Furthermore, the second base 63 and the second connecting portion 70 connect the second movable comb electrodes 61 and 62 of the second movable electrode portion 60A at a fixed distance from the rotation axis of the swinging motion. That is, if the first movable electrode portion 20A and the second movable electrode portion 60A are integrated into a single structure including the movable comb electrodes, then when viewed from above, 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 DR4, 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 DR4.

[0033] The first fixed comb-tooth electrodes 11 and 12 of the first fixed electrode section 10A and the first movable comb-tooth electrodes 21 and 22 of the first movable electrode section 20A are probe electrodes of the detection section Z1. The first fixed comb-tooth electrodes 11 and 12 of the first fixed electrode section 10A are probe electrodes fixed to the support substrate 2, and the first movable comb-tooth electrodes 21 and 22 of the first movable electrode section 20A are probe electrodes that can be integrated with the movable body MB for operation. Furthermore, by measuring the change in capacitance formed by the first fixed comb-tooth electrodes 11 and 12 of the first fixed electrode section 10A and the first movable comb-tooth electrodes 21 and 22 of the first movable electrode section 20A, a physical quantity can be detected.

[0034] The first electrode fixing portion 3 is a portion that supports the first fixed electrode portion 10A. The first electrode fixing portion 3 is a generally cuboid portion extending from a surface parallel to the first direction DR1 and the second direction DR2 of the support substrate 2 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 has a first fixed electrode base 13A extending in the second direction DR2, and the first fixed electrode base 13A is connected to the portion extending from the first electrode fixing portion 3 toward the first direction DR1.

[0035] As described above, the first fixed electrode portion 10A is fixed to the support substrate 2 via the first electrode fixing portion 3. Figure 2As shown, the first fixed electrode portion 10A is provided on the first direction DR1 side of the support beam 42. Furthermore, the first fixed electrode portion 10A is provided with comb-shaped first fixed tooth electrodes 11 and 12 extending from the first fixed electrode base 13A toward the first direction DR1 side and the fourth direction DR4 side. That is, the first fixed tooth 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 are opposite to the first movable tooth electrodes 21 and 22.

[0036] The second electrode fixing portions 4 and 5 are portions that support the second fixed electrode portion 50A. The second electrode fixing portions 4 and 5 are generally cuboid portions extending from a surface parallel to the first direction DR1 and the second direction DR2 of the support substrate 2 toward a third direction DR3. The second electrode fixing portions 4 and 5 respectively fix the second fixed electrode portion 50A to the support substrate 2. That is, the second fixed electrode portion 50A has second fixed electrode base portions 53A and 53B extending toward the second direction DR2, and the second fixed electrode base portions 53A and 53B are connected to portions extending from the second electrode fixing portions 4 and 5 toward the fourth direction DR4.

[0037] As described above, the second fixed electrode portion 50A is fixed to the support substrate 2 via the second electrode fixing portions 4 and 5. Figure 2 As shown, the second fixed electrode portion 50A is provided on the fourth direction DR side of the support beam 42. Furthermore, the second fixed electrode portion 50A includes a comb-shaped second fixed tooth electrode 51 extending from the second fixed electrode base 53A towards the fourth direction DR4 and a comb-shaped second fixed tooth electrode 52 extending from the second fixed electrode base 53B towards the first direction DR1. That is, the second fixed tooth electrodes 51 and 52 are connected to the second electrode fixing portions 4 and 5, extend in a direction parallel to the support substrate 2, and are opposite to the second movable tooth electrodes 61 and 62.

[0038] Furthermore, the first electrode fixing part 3, the second electrode fixing parts 4, and 5 are cuboid portions extending from the support substrate 2. Figure 2 The part colored black is the part that extends from the support substrate 2, but the first electrode fixing part 3, the second electrode fixing parts 4 and 5 can also be connected to the support substrate 2 through a part with a larger area.

[0039] Furthermore, the first electrode fixing part 3 is positioned closer to the beam fixing part 40 than the first fixed electrode part 10A on the first direction DR1 of the support beam 42, and the second electrode fixing parts 4 and 5 are positioned closer to the beam fixing part 40 than the second fixed electrode part 50A on the fourth direction DR4 of the support beam 42. Therefore, even if the support substrate 2 warps, it is less affected by it, and the output variation of the Z-direction acceleration sensor element 1 caused by external stress or heat can be suppressed, enabling high-precision detection of physical quantities.

[0040] Figure 3 This is a diagram that simply shows a cross-sectional view of the Z-direction acceleration sensor element 1. Figure 3 The cut position in the cross-sectional view shown is Figure 2 The position of line AA in the diagram mainly indicates that... Figure 2 The diagram shows the structure of the second fixed comb electrode 51 and the second movable comb electrode 61 located in the second fixed electrode portion 50A at the lower right. The cross-sectional shape of the second fixed comb electrode 51 and the second movable comb electrode 61 is cuboid, extending with the same cross-sectional shape in the fourth direction DR and the first direction DR1. Therefore, the second fixed comb electrode 51 is the cuboid portion extending from the second fixed electrode base 53A along the fourth direction DR, and the second movable comb electrode 61 is the cuboid portion extending from the second base 63 along the fourth direction DR.

[0041] Although the support substrate 2 is a generally cuboid component, a recess is formed in one surface of the space accommodating the second fixed comb electrode 51, etc. The Z-direction acceleration sensor element 1 can be considered as being composed of multiple layers, which, in the third direction DR3, are sequentially arranged from the support substrate 2 as a first oxide layer Ox1, a sensor structure forming layer M1, and a second oxide layer Ox2. The layer below the second oxide layer Ox2 is a wiring layer, which consists of conductor forming pads Pgnd or other pads and various wirings. After the wiring layer is a glass frit layer Gf, and the layer below it forms a cover Cp. The cover Cp is positioned opposite the support substrate 2. That is, the support substrate 2 and the cover Cp have various structures such as recesses, but the general shape is a cuboid, and the largest surface is arranged to be parallel.

[0042] The sensor structure forming layer Ml is the layer that forms structures such as the second fixed comb electrode 51. In the sensor structure forming layer Ml, a rectangular frame is formed on its outer periphery when viewed from above. The space enclosed by this frame and sandwiched between the support substrate 2 and the cover Cp becomes the receiving space for the structures such as the second fixed comb electrode 51. Furthermore, the receiving space is sealed by contact between the glass flake layer Gf and the cover Cp. In this embodiment, the sensor structure forming layer Ml and the cover Cp are formed of silicon. However, the material of each layer is not limited; it can be made of glass materials such as borosilicate glass, or it can be made of SOI (Silicon On Insulator).

[0043] Figure 4 This diagram illustrates the operation of the detection units Z1 and Z2 of the Z-direction acceleration sensor element 1 in this embodiment. Specifically, it shows the operation of the first movable comb electrode 21 and the second movable comb electrode 61 relative to the direction of acceleration, in a schematic diagram of the cross-section of each electrode when acceleration occurs from the initial state, viewed along the first direction DR1. Here, the initial state refers to a stationary state in which no acceleration occurs except for gravitational acceleration.

[0044] exist Figure 4 In the initial state shown in the left column, the first fixed comb electrode 11 and the first movable comb electrode 21 of the detection unit Z1 are arranged opposite each other along the third direction DR3 with a partial overlap. Specifically, the ends of the first fixed comb electrode 11 and the first movable comb electrode 21 in the fifth direction DR5 are at the same position, but the ends of the first movable comb electrode 21 in the third direction DR3 are positioned further along the third direction DR3 than the ends 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 partial overlap along the third direction DR3. In addition, the second fixed comb electrode 51 and the second movable comb electrode 61 of the detection unit Z2 are also arranged opposite each other along the third direction DR3 with a partial overlap, and the end of the second movable comb electrode 61 in the third direction DR3 is further along the third direction DR3 than the end of the second fixed comb electrode 51.

[0045] In this initial state, the electrostatic capacitance in the initial state can be obtained by the electrostatic capacitance corresponding to the opposing areas of the first fixed comb electrode 11 and the first movable comb electrode 21 in the detection unit Z1, and the electrostatic capacitance corresponding to the opposing areas of the second fixed comb electrode 51 and the second movable comb electrode 61 in the detection unit Z2.

[0046] Next, the explanation is as follows: Figure 4The operation is shown in the central column when a third-direction DR3 acceleration is generated. When a third-direction DR3 acceleration is generated, the second movable comb electrode 61 in the detection unit Z2 receives inertial forces in the direction of the acceleration and the opposite direction. Therefore, the second movable comb electrode 61 of the detection unit Z2 displaces towards the fifth direction DR5, i.e., the -Z direction, while the first movable comb electrode 21 of the detection unit Z1 displaces towards the +Z direction, which is opposite to the second movable comb electrode 61. As a result, the opposing area between the second fixed comb electrode 51 and the second movable comb electrode 61 is maintained in the detection unit Z2, while the opposing area between the first fixed comb electrode 11 and the first movable comb electrode 21 is reduced in the detection unit Z1. Therefore, by detecting the change in electrostatic capacitance caused by the reduction in the opposing area in the detection unit Z1, the third-direction DR3 acceleration can be detected.

[0047] On the other hand, such as Figure 4 As shown in the right column, in the state where acceleration in the fifth direction DR5 is generated 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 in the detection unit Z1 is displaced in the fifth direction DR5, which is its opposite direction. 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 reduced, 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 electrostatic capacitance caused by the reduction in the opposing area of ​​the detection unit Z2, the acceleration in the fifth direction DR5 can be detected.

[0048] Furthermore, in this embodiment, the second movable comb electrode 61 of the detection unit Z2 generates acceleration in the third direction DR3 or the fifth direction DR5, and displacement in the direction opposite to the direction of acceleration. 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.

[0049] In this embodiment, the thickness of the third-direction DR3 of the first movable comb electrodes 21 and 22 of the first movable electrode section 20A is greater than the thickness of the third-direction DR3 of the first fixed comb electrodes 11 and 12 of the first fixed electrode section 10A, and the thickness of the third-direction DR3 of the second movable comb electrodes 61 and 62 of the second movable electrode section 60A is greater than the thickness of the third-direction DR3 of the second fixed comb electrodes 51 and 52 of the second fixed electrode section 50A.

[0050] In this way, when a third-direction DR3 acceleration is generated, the opposing area of ​​the first fixed comb electrodes 11, 12 and the first movable comb electrodes 21, 22 in the detection unit Z1 decreases, while the opposing area of ​​the second fixed comb electrodes 51, 52 and the second movable comb electrodes 61, 62 can be maintained in the detection unit Z2. Therefore, the change in the third-direction DR3 acceleration can be detected. Furthermore, when a fifth-direction DR5 acceleration is generated, the opposing area of ​​the second fixed comb electrodes 51, 52 and the second movable comb electrodes 61, 62 in the detection unit Z2 decreases, while the opposing area of ​​the first fixed comb electrodes 11, 12 and the first movable comb electrodes 21, 22 can be maintained in the detection unit Z1. Therefore, the change in the fifth-direction DR5 acceleration can be detected.

[0051] As described above, in the Z-direction acceleration sensor element 1 according to this embodiment, the first movable comb electrode 21, 22 and the second movable comb electrode 61, 62 swing along the third direction DR3. On the other hand, the first movable comb electrode 21, 22 and the second movable comb electrode 61, 62 are cuboid structures extending from the movable body MB towards the first direction DR1 side and the fourth direction DR4 side, and hardly move in the second direction DR2.

[0052] On the other hand, in the XY direction acceleration sensor element 101, an electrostatic capacitance is formed by opposing a fixed comb electrode and a movable comb electrode. However, in the XY direction acceleration sensor element 101, the distance between the fixed comb electrode and the movable comb electrode is displaced according to the acceleration along the first direction DR1 and the second direction DR2 acting on the XY direction acceleration sensor element 101, thereby changing the electrostatic capacitance. The XY direction acceleration sensor element 101 can detect the change in acceleration along the first direction DR1 and the second direction DR2 based on this change in electrostatic capacitance.

[0053] (2) Detection circuit: Next, using the above configuration, 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, will be described. First, the circuit for detecting changes in acceleration along the first direction DR1 and the second direction DR2 will be described.

[0054] (2-1) XY direction acceleration sensor element: The XY direction acceleration sensor element 101 is connected to a control IC (not shown) and used. The control IC has circuitry for detecting acceleration based on signals output from the XY direction acceleration sensor element 101. Figure 5 This is a diagram used to illustrate the circuit. Figure 5In the diagram, the XY direction acceleration sensor element 101 is shown together with the components or wiring that constitute the circuit.

[0055] However, in Figure 5 The detailed structure of the XY direction acceleration sensor element 101 is omitted. The movable electrodes 101a, 101b, 101c, 101d and the fixed electrodes 102a, 102b, 102c, 102d of the XY direction acceleration sensor element 101 are schematically shown.

[0056] Movable electrodes 101a and 101b and fixed electrodes 102a and 102b constitute a parallel plate capacitor oriented in a direction perpendicular to the first direction DR1. The movable electrodes 101a and 101b are electrodes that are displaced in the first direction DR1 according to acceleration in the X direction, which is the first direction DR1. The fixed electrodes 102a and 102b do not shift. Furthermore, when the movable electrodes 101a and 101b are displaced in the first direction DR1 according to acceleration in the X direction, the electrostatic capacitance formed by the movable electrodes 101a and 102a and the electrostatic capacitance formed by the movable electrodes 101b and 102b change.

[0057] Movable electrodes 101c and 101d and fixed electrodes 102c and 102d constitute a parallel plate capacitor oriented in a direction perpendicular to the second direction DR2. The movable electrodes 101c and 101d are electrodes that are displaced in the second direction DR2 according to acceleration in the Y direction, which is the second direction DR2. The fixed electrodes 102c and 102d do not shift. Furthermore, when the movable electrodes 101c and 101d are displaced in the second direction DR2 according to acceleration in the Y direction, the electrostatic capacitance formed by the movable electrodes 101c and 102c and the electrostatic capacitance formed by the movable electrodes 101d and 102d change.

[0058] Additionally, as in Figure 1 As shown, the XY direction acceleration sensor element 101 has multiple pads, in Figure 5 The diagram shows the connection relationships between pads Pxy, Px1, Px2, Py1, Py2 and circuit components, as well as the connection relationships between movable electrodes 101a, 101b, 101c, 101d and fixed electrodes 102a, 102b, 102c, 102d.

[0059] Here, the configuration used for detecting acceleration in the X direction, which is the first direction DR1, is referred to as the first detection unit, and the configuration used 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 changes in the differential capacitance caused by 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 changes in the differential capacitance caused by the movable electrodes 101c, 101d and the fixed electrodes 102c, 102d.

[0060] Furthermore, in this embodiment, the XY direction acceleration sensor element 101 forms an electrode for detecting acceleration in the first direction DR1 and an electrode for detecting acceleration in the Y direction, which is the second direction DR2, within the same chip, but each electrode may also be configured as a different chip.

[0061] The detection circuits 200 and 300 include CV conversion circuits 210 and 310, switching circuits 220 and 320, signal processing circuits 230 and 330, and control signal generation circuit 600.

[0062] The CV conversion circuits 210 and 310 are circuits that convert the change in differential capacitance of the electrostatic capacitor formed by the movable electrodes 101a to 101d and the fixed electrodes 102a to 102d into voltage. Specifically, the CV conversion circuits 210 and 310 include operational amplifiers 210a and 310a, capacitors 210b and 310b, and switches 210c and 310c.

[0063] The inverting input terminals of operational amplifiers 210a and 310a are electrically connected to each of the movable electrodes 101a, 101b, 101c, and 101d. 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 a signal S1X from the control signal generation circuit 600, and switch 310c is driven by a signal S1Y from the control signal generation circuit 600. Then, either a voltage V1 (i.e., the midpoint voltage, 2.5V in this embodiment) half the voltage applied to the fixed electrodes 102a-102d, or a voltage V2 (4V in this embodiment), different from the midpoint voltage, is input to the non-inverting input terminals of operational amplifiers 210a and 310a via switch circuits 220 and 320.

[0064] Switching circuits 220 and 320 input voltages from various voltage sources (not shown) to the non-inverting input terminals of operational amplifiers 210a and 310a in CV conversion circuits 210 and 310. Specifically, switching circuit 220 includes switches 220a and 220b, and switching circuit 320 includes switches 320a and 320b. Switches 220a and 220b are driven based on a signal S2X from control signal generation circuit 600, and switches 320a and 320b are driven based on a signal S2Y from control signal generation circuit 600; when one is closed, the other is open.

[0065] 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 specified frequency band. The GAIN circuits 230b and 330b amplify the output after passing through the LPF circuits 230a and 330a, outputting it as acceleration signals GoutX and GoutY.

[0066] The control signal generation circuit 600 outputs signals (carriers) P1X, P2X, P1Y, P2Y that indicate the timing of the voltage application to the fixed electrodes 102a to 102d, signals S2X, S2Y that indicate the switching timing of the switches 220 and 320, and signals S1X, S1Y that indicate the switching timing of switches 210c and 310c.

[0067] The various signals generated by the control signal generation circuit 600 change during normal acceleration detection (non-self-diagnosis) and during self-diagnosis. That is, the control signal generation circuit 600 outputs various signals based on the clock signal CLK, but outputs a signal for acceleration detection when the self-diagnosis command signal is low, and outputs a signal for self-diagnosis when the self-diagnosis command signal becomes high.

[0068] Furthermore, the self-diagnosis involves inputting a self-diagnostic signal into the XY direction acceleration sensor element 101, determining that the output is normal if it falls within a predetermined range, and abnormal if it falls outside the range. That is, if the output falls outside the predetermined range, it can be considered that an abnormality has occurred, such as damage to the comb teeth of the XY direction acceleration sensor element 101.

[0069] Reference Figure 6 , Figure 7 The signal waveform diagram shown illustrates the operation of this accelerometer sensor. Furthermore, Figure 6This is a diagram showing the signal waveform when switching from normal acceleration detection to self-diagnosis. Figure 7 This is a magnified image of the signal waveform during acceleration detection.

[0070] First, such as Figure 6 As shown, during normal acceleration detection, the self-diagnostic command signal is set to a low level for acceleration detection. Based on Figure 7 This explains the work at this time. Furthermore, although in Figure 7 Not shown in the figure, but during normal acceleration detection, based on signals S2X and S2Y, switches 220a and 320a are turned off, and switches 220b and 320b are turned closed, and a midpoint voltage V1 (2.5V in this embodiment) is applied to the non-inverting input terminals of operational amplifiers 210a and 310a, and the movable electrodes 101a to 101d are set to the midpoint voltage V1.

[0071] The signals P1X, P2X and P1Y, P2Y output from the control signal generation circuit 600 become signals with amplitude V (5V in this embodiment) after their voltage levels are inverted, forming a fixed-amplitude rectangular wave signal in which the Hi and Low levels change within four periods t1 to t4. Furthermore, the voltage V is not limited to 5V. For example, the voltage V can also be 3V, and the midpoint voltage V1 can also be 1.5V, etc. Of course, in this case, the voltage V2 also changes, and is set to a value between 3V and 1.5V.

[0072] First, during the first period t1, based on signals P1X, P2X and P1Y, P2Y, the potentials of fixed electrodes 102a and 102c are set to V, and the potentials of fixed electrodes 102b and 102d are set to 0. Furthermore, through signals S1X and S1Y from the control signal generation circuit 600, switches 210c and 310c are closed. Therefore, through the operation of operational amplifiers 210a and 310a, movable electrodes 101a to 101d are biased to a potential of V / 2, and the charge accumulated between the electrodes of capacitors 210b and 310b, which serve as feedback capacitors, is discharged.

[0073] At this time, assuming that 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 are in the relationship of C1 > C2, according to this relationship and the relationship between the potential applied to the fixed electrodes 102a to 102d, the movable electrodes 101a to 101d are in a state with more negative charge.

[0074] Next, during the second period t2, based on signals P1X, P2X and P1Y, P2Y, the potentials of fixed electrodes 102a and 102c are maintained at V, and the potentials of fixed electrodes 102b and 102d are maintained at 0. Switches 210c and 310c are turned off by signals S1X and S1Y from the control signal generation circuit 600. Therefore, charge corresponding to the states of movable electrodes 101a to 101d is accumulated in capacitors 210b and 310b. Then, when the voltage value corresponding to the charge accumulated in capacitors 210b and 310b is output from CV conversion circuits 210 and 310, the outputs GoutX and GoutY are sampled via LPF circuit 230a and GAIN circuit 230b.

[0075] Next, during the third period t3, the potentials are changed based on signals P1X, P2X and P1Y, P2Y so that the potentials of fixed electrodes 102a and 102c become 0 and the potentials of fixed electrodes 102b and 102d become V. And through signals S1X and S1Y from the control signal generation circuit 600, switches 210c and 310c are kept open.

[0076] At this time, the charge state of the movable electrodes 101a to 101d becomes opposite to that of the second period t2 through the inversion of signals P1X, P2X and P1Y, P2Y. That is, when the relationship C1 > C2 is satisfied as described above, by inverting the applied potential to the fixed electrodes 102a to 102d, the movable electrodes 101a to 101d become a state with more positive charge.

[0077] However, at this time, a closed circuit is formed between the movable electrodes 101a-101d and the capacitors 210b and 310b. The charge amount during the first period t1 is stored, so the charge overflowing from the balance of the charge amounts of the movable electrodes 101a-101d moves to the capacitors 210b and 310b and is stored. Then, according to the relationship Q=CV, a voltage value that is 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.

[0078] Furthermore, during the fourth period t4, when the potentials of fixed electrodes 102a and 102c are kept at 0 based on signals P1X, P2X and P1Y, P2Y, and the potentials of fixed electrodes 102b and 102d are kept at V, and the outputs of CV conversion circuits 210 and 310 are sufficiently stable, the values ​​at this time are output to GoutX and GoutY via LPF circuits 230a and 330a and GAIN circuits 230b and 330b.

[0079] Finally, the outputs GoutX and GoutY sampled during the second period t2 and the outputs GoutX and GoutY sampled during the fourth period t4 are differentially calculated. Then, based on this, acceleration detection corresponding to the displacement of the movable electrodes 101a to 101d is performed.

[0080] Next, based on Figure 6 The self-diagnosis process is explained below. During self-diagnosis, the self-diagnosis command signal input to the control signal generation circuit 600 is set to a Hi level, and various self-diagnosis signals 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.

[0081] First, during self-diagnosis of the first detection unit, a potential difference is formed between fixed electrodes 102a, 102c and fixed electrodes 102b, 102d based on signals P1X, P2X and P1Y, P2Y. Furthermore, regarding the first detection unit, based on signal S2X, switch 220a of the switching circuit 220 is set to closed, and switch 220b is set to open. Therefore, a voltage V2 (4V in this embodiment), 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.

[0082] Therefore, the potential difference (4V) between the movable electrode 101b and the fixed electrode 102b is greater than the potential difference (1V) between the movable electrode 101a and the fixed electrode 102a, resulting in an increased electrostatic force. This electrostatic force forces the movable electrodes 101a and 101b to move forcibly from the center point. Next, at time T1, a switching operation based on the switching circuit 220 is performed based on the signal S2X. Similar to normal acceleration detection, the midpoint voltage V1 of the fixed electrodes 102a and 102b is applied to the non-inverting input terminal of the operational amplifier 210a.

[0083] Through the above processing, the movable electrodes 101a and 101b can be displaced by electrostatic force. In this embodiment, the period of the drive signal S2X of the switching circuit 220 is set and the time for generating electrostatic force is controlled so that the displacement can be sufficiently detected. For example, the resonant frequency characteristics of the vibration of the movable electrodes 101a and 101b relative to the input frequency of the voltage supplied to the movable electrodes 101a and 101b are as follows: Figure 8 That's how it's represented. In this embodiment, the frequency of the input signal, i.e. Figure 6 The frequency of the input voltage to the first detection unit is set to the resonant frequency f0. As a result, the vibration in the movable electrodes 101a and 101b is generated at the resonant frequency of the movable electrodes 101a and 101b, that is, at the frequency at which the displacement amplitude is the largest.

[0084] In this embodiment, self-diagnosis related to the second detection unit is not performed during the self-diagnosis of the first detection unit. That is, based on the signal S2Y, switch 320a of the switching circuit 320 is set to open and switch 320b is set to 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 in the same way as during normal acceleration detection, resulting in a state where self-diagnosis is not performed.

[0085] Subsequently, the first detection unit performs the same operation as the usual acceleration detection described above, obtaining an output GoutX corresponding to the displacement of the movable electrodes 101a and 101b. At this time, the displacement of the movable electrodes 101a and 101b caused by the electrostatic force is uniquely determined by the voltage applied to the non-inverting input terminal of the operational amplifier 210a. Therefore, the output corresponding to the displacement of the movable electrodes 101a and 101b is also uniquely determined. The first detection unit performs self-diagnosis by comparing the obtained output with the uniquely determined self-diagnostic quantity (output).

[0086] Next, after a predetermined time has elapsed since the self-diagnosis of the first detection unit ended, a self-diagnosis of the second detection unit is performed. The interval between the self-diagnosis of the first and second detection units is set to the time it takes for the vibration of the movable electrodes 101a and 101b to stop after the forced displacement during the self-diagnosis of the first detection unit. Furthermore, 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 crystal oscillators, often used in gyroscope sensors, is on the order of 30,000, but the Q value of the movable electrodes 101a, 101b, 101c, and 101d, which are configured as silicon MEMS, is around 20. Therefore, the vibration forcibly induced during the self-diagnosis of the first detection unit converges within a very short time.

[0087] During self-diagnosis of the second detection unit, a potential difference is formed between fixed electrodes 102a, 102c and fixed electrodes 102b, 102d based on signals P1X, P2X and P1Y, P2Y. Furthermore, regarding the second detection unit, based on signal S2Y, switch 320a of the switching circuit 320 is set to closed, and switch 320b is set to open. Therefore, a voltage V2 (4V in this embodiment), 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.

[0088] Therefore, the potential difference (4V) between the movable electrode 101d and the fixed electrode 102d is greater than the potential difference (1V) between the movable electrode 101c and the fixed electrode 102c, resulting in an increased electrostatic force. This electrostatic force forces the movable electrodes 101c and 101d to move forcibly from the center point. Next, at time T2, a switching operation based on the switching circuit 320 is performed based on the signal S2Y. Similar to normal acceleration detection, the midpoint voltage V1 of the fixed electrodes 102c and 102d is applied to the non-inverting input terminal of the operational amplifier 310a.

[0089] Through the above processing, the movable electrodes 101c and 101d can be displaced by electrostatic force. In this embodiment, the period of the drive signal S2Y of the switching circuit 320 is set and the time for generating electrostatic force is controlled to ensure sufficient detection of the displacement. In this embodiment, the frequency of the input signal, i.e., Figure 6 The frequency of the input voltage to the second detection unit is set to the resonant frequency f0. As a result, the vibration in the movable electrodes 101c and 101d is generated at the resonant frequency of the movable electrodes 101c and 101d, that is, at the frequency at which the displacement amplitude is the largest.

[0090] During the self-diagnosis of the second detection unit, no self-diagnosis related to the first detection unit is performed. That is, based on the signal S2X, switch 220a of the switching circuit 220 is set to open, and switch 220b is set to closed. Therefore, the midpoint voltage V1 of the fixed electrodes 102a and 102b is applied to the non-inverting input terminal of the operational amplifier 210a in the same way as during normal acceleration detection, resulting in a state where no self-diagnosis is performed.

[0091] Subsequently, the second detection unit performs the same operation as the usual acceleration detection described above, obtaining an output GoutY corresponding to the displacement of the movable electrodes 101c and 101d. At this time, the displacement of the movable electrodes 101c and 101d caused by 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. The second detection unit performs self-diagnosis by comparing the obtained output with the uniquely determined self-diagnostic quantity (output).

[0092] (2-2) Z-direction acceleration sensor element: Z-direction acceleration sensor element 1 is used to connect to a control IC (not shown). The control IC has circuitry for detecting acceleration based on the signal output from Z-direction acceleration sensor element 1. Figure 9 This is a diagram used to illustrate the circuit. Figure 9The diagram shows the components or wiring that make up the circuit, and also shows the Z-direction acceleration sensor component 1.

[0093] However, in Figure 9 The detailed structure of the Z-direction acceleration sensor element 1 is omitted. The diagram schematically shows the first movable comb electrode 21, 22, the second movable comb electrode 61, 62, the first fixed comb electrode 11, 12, and the second fixed comb electrode 51, 52 of the Z-direction acceleration sensor element 1.

[0094] The first movable comb-tooth electrodes 21 and 22 and the first fixed comb-tooth electrodes 11 and 12 constitute a parallel plate capacitor oriented in a direction perpendicular to the second direction DR2. Furthermore, the second movable comb-tooth electrodes 61 and 62 and the second fixed comb-tooth electrodes 51 and 52 constitute a parallel plate capacitor oriented in a direction perpendicular to the second direction DR2. Figure 4 As shown, the first movable comb electrodes 21, 22 and the second movable comb electrodes 61, 62 are electrodes that are displaced in the third direction DR3 and the fifth direction DR5 according to the 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 are not displaced. Furthermore, when 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 according to the acceleration in the Z direction, which is the third direction DR3, the electrostatic capacitance formed by the first movable comb electrodes 21, 22 and the first fixed comb electrodes 11, 12, and the electrostatic capacitance formed by the second movable comb electrodes 61, 62 and the second fixed comb electrodes 51, 52 change.

[0095] In addition, such as Figure 1 As shown, the Z-direction acceleration sensor element 1 has multiple pads, in Figure 9 The diagram 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 and 22, the second movable comb electrodes 61 and 62, and the first fixed comb electrodes 11 and 12, and the second fixed comb electrodes 51 and 52.

[0096] Here, the configuration used for detecting acceleration in the Z direction as a third direction DR3 is referred to as the third detection unit. The third detection unit has a detection circuit 400 that detects acceleration based on the changes in differential capacitance caused by the first movable comb electrode 21, 22 and the first fixed comb electrode 11, 12, and the changes in differential capacitance caused by the second movable comb electrode 61, 62 and the second fixed comb electrode 51, 52.

[0097] The detection circuit 400 includes a CV conversion circuit 410, a switching 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 can also be a different circuit.

[0098] The CV conversion circuit 410 converts the change in differential capacitance of the electrostatic capacitor formed by the first movable comb electrode 21, 22, the second movable comb electrode 61, 62, the first fixed comb electrode 11, 12, and the second fixed comb electrode 51, 52 into a voltage. Specifically, the CV conversion circuit 410 includes an operational amplifier 410a, a capacitor 410b, and a switch 410c.

[0099] The inverting input terminal of operational amplifier 410a is connected to the first movable comb electrodes 21, 22 and the second movable comb electrodes 61, 62. 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. Furthermore, either a voltage V1 (i.e., the midpoint voltage, 2.5V in this embodiment) equal to 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), different from the midpoint voltage, is input to the non-inverting input terminal of operational amplifier 410a via the switching circuit 420.

[0100] Switching circuit 420 inputs voltages from various voltage sources (not shown) to the non-inverting input terminal of operational amplifier 410a in CV conversion circuit 410. Specifically, switching circuit 420 includes switches 420a and 420b. Switches 420a and 420b are driven based on signal S2Z from control signal generation circuit 600, and when one is closed, the other is open.

[0101] 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 specified frequency band. The GAIN circuit 430b amplifies the output after passing through the LPF circuit 430a and outputs it as the acceleration signal GoutZ.

[0102] The control signal generation circuit 600 outputs signals (carriers) P1Z and P2Z that indicate the timing of applying voltages to the first fixed comb electrodes 11, 12 and the second fixed comb electrodes 51, 52, respectively; signal S2Z that indicates the switching timing of the switch of the switch circuit 420; and signal S1Z that indicates the switching timing of the switch 410c.

[0103] The various signals generated by the control signal generation circuit 600 change during normal acceleration detection (non-self-diagnosis) and during self-diagnosis. That is, the control signal generation circuit 600 outputs various signals based on the clock signal CLK, but outputs a signal for acceleration detection when the self-diagnosis command signal is at a low level, and outputs a signal for self-diagnosis when the self-diagnosis command signal becomes a high level.

[0104] Furthermore, the self-diagnosis involves inputting a self-diagnostic signal to the Z-direction acceleration sensor element 1, determining that the output is normal if it falls within a predetermined range, and abnormal if it falls outside the range. That is, if the output falls outside the predetermined range, it can be considered an abnormality such as damage to the comb teeth of the Z-direction acceleration sensor element 1.

[0105] Reference Figure 10 , Figure 7 The signal waveform diagram shown illustrates the operation of this accelerometer sensor. Furthermore, Figure 10 This is a diagram showing the signal waveform when switching from normal acceleration detection to self-diagnosis. Figure 10 The signal waveform shown is because it is related to... Figure 6 The waveform of the signal shown has the same diameter, therefore the amplified waveform of the signal during acceleration detection is used in the attached figure. Figure 7 Please provide an explanation.

[0106] First, such as Figure 10 As shown, during normal acceleration detection, the self-diagnostic command signal is set to a low level for acceleration detection. Based on Figure 7 This explains the work at this time. Furthermore, in Figure 7 Although not illustrated, during normal acceleration detection, based on signal S2Z, switch 420a becomes open and switch 420b becomes closed, and a midpoint voltage V1 (2.5V in this embodiment) is applied to the non-inverting input terminal of operational amplifier 410a. The first movable comb electrode 21, 22 and the second movable comb electrode 61, 62 are set to the midpoint voltage V1.

[0107] During normal operation, not self-diagnostic, the signals P1Z and P2Z output from the control signal generation circuit 600 are signals used to detect capacitance changes. Specifically, signals P1Z and P2Z are signals with amplitude V (5V in this embodiment) that are mutually inverted in voltage level, and are rectangular wave signals with fixed amplitude whose Hi and Low levels change within four periods t1 to t4. Furthermore, the voltage V is not limited to 5V. For example, the voltage V can also be 3V, and the midpoint voltage V1 can also be 1.5V, etc. Of course, in this case, the voltage V2 also changes, and is set to a value between 3V and 1.5V.

[0108] 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. Furthermore, the switch 410c is closed via signal S1Z from the control signal generation circuit 600. Therefore, through the operation of the operational amplifier 410a, the first movable comb electrodes 21 and 22 and the second movable comb electrodes 61 and 62 are biased to a potential of V / 2, and the charge accumulated between the electrodes of the capacitor 410b, which serves as the feedback capacitor, is discharged.

[0109] At this time, assuming that the capacitance C1 between the first movable comb electrode 21, 22 and the first fixed comb electrode 11, 12 and the capacitance C2 between the second movable comb electrode 61, 62 and the second fixed comb electrode 51, 52 are in the relationship of C1 > C2, according to this relationship and the relationship between the potentials applied to the first fixed comb electrode 11, 12 and the second fixed comb electrode 51, 52, the first movable comb electrode 21, 22 and the second movable comb electrode 61, 62 are in a state with more negative charges.

[0110] Next, during the second period t2, based on signals P1Z and P2Z, the potentials of the first fixed comb electrodes 11 and 12c are maintained at V, and the potentials of the second fixed comb electrodes 51 and 52 are maintained at 0. Furthermore, the switch 410c is turned off by signal S1Z from the control signal generation circuit 600. Therefore, charge corresponding to the states of the first movable comb electrodes 21 and 22 and the second movable comb electrodes 61 and 62 is accumulated in the capacitor 410b. Then, when the voltage value corresponding to the charge accumulated in the capacitor 410b is output from the CV conversion circuit 410, the output GoutZ is sampled via the LPF circuit 430a and the GAIN circuit 430b.

[0111] Next, during the third period t3, the potentials are changed based on signals P1Z and P2Z so that the potentials of the first fixed comb electrodes 11 and 12 become 0 and the potentials of the second fixed comb electrodes 51 and 52 become V. And through the signal S1Z from the control signal generation circuit 600, the switch 410c is kept open.

[0112] At this time, the charge states of the first movable comb electrodes 21, 22 and the second movable comb electrodes 61, 62 are reversed by the inversion of signals P1Z and P2Z, becoming opposite to the second period t2. That is, when the relationship C1 > C2 is satisfied as described above, by reversing the applied potentials 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 become a state with more positive charge.

[0113] However, at this time, a closed circuit is formed between the first movable comb electrode 21, 22 and the second movable comb electrode 61, 62 and the capacitor 410b. The charge amount during the first period t1 is stored, so the charge overflowing from the balance of the charges of the first movable comb electrode 21, 22 and the second movable comb electrode 61, 62 moves to the capacitor 410b and is stored. Then, according to the relationship Q=CV, a voltage value that is 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.

[0114] Furthermore, during the fourth period t4, when the potentials of the first fixed comb electrodes 11 and 12 are kept at 0 based on signals P1Z and P2Z, the potentials of the second fixed comb electrodes 51 and 52 are kept at V, and 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.

[0115] Finally, the output GoutZ sampled in the second period t2 and the output GoutZ sampled in the fourth period t4 are differentially calculated. Then, based on this, acceleration detection corresponding to the displacement of the first movable comb electrode 21, 22 and the second movable comb electrode 61, 62 is performed.

[0116] Next, based on Figure 10 This describes the operation during self-diagnosis. During self-diagnosis, the self-diagnosis command signal input to the control signal generation circuit 600 is set to Hi level, and various signals for self-diagnosis are output from the control signal generation circuit 600.

[0117] During self-diagnosis, signals P1Z and P2Z output from the control signal generation circuit 600 are used to displace the first and second movable comb electrodes for self-diagnosis. Specifically, a potential difference is formed between the first fixed comb electrodes 11 and 12 and the second fixed comb electrodes 51 and 52 based on signals P1Z and P2Z output from the control signal generation circuit 600. Then, based on signal S2Z, switch 420a of the switching circuit 420 is set to closed, and switch 420b is set to open. Therefore, a voltage V2 (4V in this embodiment) different from the midpoint voltage V1 between the first fixed comb electrodes 11 and 12 and the second fixed comb electrodes 51 and 52 is applied to the non-inverting input terminal of the operational amplifier 410a for self-diagnosis.

[0118] Through the above processing, before time T3, the potential difference (4V) between the second movable comb electrode 61, 62 and the second fixed comb electrode 51, 52 is greater than the potential difference (1V) between the first movable comb electrode 21, 22 and the first fixed comb electrode 11, 12. Then, at time T3, a switching operation based on the switching circuit 420 is performed based on the signal S2Z. Similar to normal acceleration detection, the midpoint voltage V1 of the fixed electrodes 102a, 102b is applied to the non-inverting input terminal of the operational amplifier 410a.

[0119] When the above processing is performed, in the XY direction acceleration sensor element 101 described above, the movable electrodes 101a, 101c or movable electrodes 101b, 101d 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 by the voltage applied to the electrostatic capacitor mainly acts in the direction perpendicular to the plates 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 plates constituting the parallel plate capacitor. Therefore, in the XY direction acceleration sensor element 101, by increasing the voltage applied between the electrodes, the force in the direction in which the movable electrodes 101a, 101b, 101c, 101d can be displaced can be increased.

[0120] On the other hand, in the Z-direction acceleration sensor element 1, the direction of displacement of the first movable comb electrode 21, 22 and the second movable comb electrode 61, 62 is as follows: Figure 4 The direction shown is parallel to the plates constituting the parallel plate capacitor. 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.

[0121] Therefore, in the Z-direction acceleration sensor element 1 according to this embodiment, it is configured to change the force in the direction in which the first movable comb electrode 21, 22 and the second movable comb electrode 61, 62 can be displaced. That is, the Z-direction acceleration sensor element 1 has self-diagnostic electrodes E1, E2 that clamp the first movable comb electrode 21, 22, the first fixed comb electrode 11, 12, the second movable comb electrode 61, 62, and the second fixed comb electrode 51, 52.

[0122] Specifically, such as Figure 3As shown, self-diagnostic electrode E1 is formed on cover Cp, and self-diagnostic electrode E2 is formed on support substrate 2. Self-diagnostic electrode E1 is formed on the outer surface of cover Cp, i.e., the plane on the positive side of third direction DR3, and self-diagnostic electrode E2 is formed on the outer surface of support substrate 2, i.e., the plane on the negative side of third direction DR3.

[0123] In this embodiment, the self-diagnostic electrode E1 is formed on approximately the entire outer surface of the cover Cp, and the self-diagnostic electrode E2 is formed on approximately 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 tooth electrodes 21 and 22, the first fixed comb tooth electrodes 11 and 12, the second movable comb tooth electrodes 61 and 62, and the second fixed comb tooth electrodes 51 and 52, which exist inside the space formed by the cover Cp and the support substrate 2.

[0124] Self-diagnostic electrodes E1 and E2 are electrically connected to pads Pz1 and Pz2, respectively. Therefore, each of the signals P1Z and P2Z is ​​applied to each of the self-diagnostic electrodes E1 and E2. Based on the above configuration, the potential difference between the first movable comb electrodes 21 and 22 and the self-diagnostic electrode E1 of the cover 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 of 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, therefore, 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.

[0125] In this embodiment, the period of the drive signal S2Z of the switching circuit 420 is further set so that the displacement of the first movable comb electrode 21, 22 and the second movable comb electrode 61, 62 is sufficiently large. Specifically, the resonant frequency characteristics of the vibration of the first movable comb electrode 21, 22 and the second movable comb electrode 61, 62 relative to the input frequency of the voltage supplied to the first fixed comb electrode 11, 12 and the second fixed comb electrode 51, 52 are as follows: Figure 8 That is how it is represented. Therefore, in this embodiment, the frequency of the input signals (V1, V2) used to displace the first movable comb electrode 21, 22 and the second movable comb electrode 61, 62, i.e. Figure 10 The frequency of the input voltage to the third detection unit is set to the resonant frequency f0. As a result, the vibrations in the first movable comb electrodes 21, 22 and the second movable comb electrodes 61, 62 are generated at the resonant frequency of the first movable comb electrodes 21, 22 and the second movable comb electrodes 61, 62, that is, at the frequency with the largest displacement amplitude.

[0126] Subsequently, the third detection unit performs the same operation as the usual acceleration detection described above, obtaining an output GoutZ corresponding to the displacement of the first movable comb electrodes 21, 22 and the second movable comb electrodes 61, 62. At this time, the displacement of the first movable comb electrodes 21, 22 and the second movable comb electrodes 61, 62 caused by the electrostatic force described above 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. The third detection unit performs self-diagnosis by comparing the obtained output with the uniquely determined self-diagnostic quantity (output).

[0127] Specifically, in a state where a portion of the comb teeth constituting the first movable comb tooth electrodes 21, 22 and the second movable comb tooth electrodes 61, 62, the first fixed comb tooth electrodes 11, 12 and the second fixed comb tooth electrodes 51, 52 are damaged, the aforementioned displacement amount is smaller compared to the undamaged state. However, when this displacement amount is small, the change in displacement caused by the damage is small, making it difficult to detect the change in displacement amount.

[0128] However, in this embodiment, the frequency of the input signal (V1, V2) is the frequency at which the first movable comb electrode 21, 22 and the second movable comb electrode 61, 62 resonate. Therefore, the displacement is large, and it becomes easy to detect changes in displacement caused by minor damage to the comb teeth. Figure 11 This is a diagram showing the displacement of the voltage relative to the first fixed comb electrode 11, 12 and the second fixed comb electrode 51, 52. Figure 11 In the figure, 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 (1Hz in the example). Furthermore, the displacement is the value of gravitational acceleration detected by the displacement of the first movable comb electrode 21, 22 and the second movable comb electrode 61, 62.

[0129] like Figure 11 As shown, for example, when the input signal voltage is 3V and the input signal frequency is 1Hz, a displacement equivalent to 2G is generated. On the other hand, if the input signal frequency is the resonant frequency, a displacement exceeding 40G is generated. Therefore, even a tiny break in the comb teeth will produce a difference in the amount of displacement, making it highly likely that anomalies can be accurately detected.

[0130] Furthermore, 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 crystal oscillators, often used in gyroscope sensors, is in the range of 30,000, but the Q values ​​of the first movable comb electrodes 21, 22 and the second movable comb electrodes 61, 62, configured as silicon MEMS, are around 20. Therefore, the vibrations forcibly induced during the self-diagnosis of the third detection unit converge within a very short time.

[0131] (3) Other implementation methods, etc.: The above embodiments are examples of implementing the invention. Therefore, the configuration of each part can be replaced with any configuration that has the same function. In addition, the present invention can also be supplemented with other arbitrary configurations.

[0132] The beam fixing part, the first electrode fixing part, and the second electrode fixing part can all be portions that extend in a direction perpendicular to the support substrate and that support other portions. That is, the support substrate is a substrate that supports other structures, and each part of the physical quantity sensor element is directly or indirectly supported on the support substrate. The beam fixing part, the first electrode fixing part, and the second electrode fixing part are portions that are directly supported on the support substrate.

[0133] A portion that is fixed to the support substrate without relative movement is considered a fixed portion, while a portion that moves relative to the support substrate or the portion fixed to the support substrate is considered a movable portion. The beam fixing portion only needs to support the support beam; the support beam and the portion connected to the support beam can also be movable portions. The first electrode fixing portion and the second electrode fixing portion are the portions that support the first fixed comb electrode and the second fixed comb electrode, respectively. Therefore, the first electrode fixing portion and the second electrode fixing portion are portions that support the fixed portion. The beam fixing portion, the first electrode fixing portion, and the second electrode fixing portion can be configured in various ways, as long as they can connect to and support other portions.

[0134] The support beam is a portion that is connected at one end 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, which extends in a direction perpendicular to the support base plate, and the support beam extends in a direction perpendicular to the beam fixing part, that is, in a direction parallel to the support base plate. Furthermore, it is only necessary to configure it so that the other end of the support beam is connected to a movable body, thereby allowing the movable body to move relative to the support base plate.

[0135] Furthermore, movable bodies exist on both sides of the support beam when viewed from above. That is, as long as the movable bodies exist on both sides of the support beam, allowing them to swing in the rotational direction centered on the support beam, the movable bodies need only displace according to a physical quantity in the direction perpendicular to the support substrate, and the displacements at both sides of the support beam need to be different. Specifically, the displacements of the first movable comb electrode and the second movable comb electrode, corresponding to the physical quantity in the direction perpendicular to the support substrate, need to be different from each other.

[0136] Various configurations can be adopted to ensure that the displacements corresponding to the physical quantities in the direction perpendicular to the support substrate differ in the first and second movable comb electrodes. For example, at least one different configuration in terms of mass, size, and structure can be adopted in the first and second movable comb electrodes.

[0137] The first movable comb electrode and the first fixed comb electrode only need to be opposite each other. Furthermore, it is sufficient that the first fixed comb electrode is fixed relative to the support substrate, while the first movable comb electrode can be displaced relative to the support substrate. That is, the area of ​​the capacitor formed by the first movable comb electrode and the first fixed comb electrode can be displaced by the displacement of the first movable comb electrode.

[0138] The second movable comb electrode and the second fixed comb electrode only need to be opposite each other. Furthermore, it is sufficient that the second fixed comb electrode is fixed relative to the support substrate, while the second movable comb electrode can be displaced relative to the support substrate. That is, it is sufficient that the area of ​​the capacitor formed by the second movable comb electrode and the second fixed comb electrode is displaced by the displacement of the second movable comb electrode.

[0139] Furthermore, the first movable comb electrode and the second movable comb electrode are displaced by a structure in which the movable part is supported by a support beam. Therefore, the first movable comb electrode and the second movable comb electrode are displaced in opposite directions by displacement in the rotational direction centered on the support beam.

[0140] The self-diagnostic electrode only needs to be an electrode that clamps a first movable comb electrode, a first fixed comb electrode, a second movable comb electrode, and a second fixed comb electrode. That is, it only needs to be configured to periodically apply a signal for displacing the first and second movable comb electrodes between the self-diagnostic electrodes. The signal applied to the self-diagnostic electrode only needs to be able to displace the first and second movable comb electrodes. Such an electrode can have various configurations, for example, it can be configured to use a planar electrode parallel to the support substrate to clamp the first movable comb electrode, the first fixed comb electrode, the second movable comb electrode, and the second fixed comb electrode.

Claims

1. A physical quantity sensor element, characterized in that, Include: The beam fixing part, the first electrode fixing part, and the second electrode fixing part extend in a direction perpendicular to the support substrate. A support beam, one end of which is connected to the beam fixing part, extends in a direction parallel to the support base plate; A movable body is connected to the other end of the support beam, which, when viewed from above, sandwiches the support beam in the middle and is positioned on both sides. The first movable comb electrode is connected to the movable body and, when viewed from above, sandwiches the support beam in the middle and is positioned on one side. A first fixed comb tooth electrode is connected to the first electrode fixing part and is opposite to the first movable comb tooth electrode. The second movable comb electrode is connected to the movable body and, when viewed from above, clamps the support beam in the middle and is positioned on the other side. The second fixed comb tooth electrode is connected to the second electrode fixing part and is opposite to the second movable comb tooth electrode. as well as The self-diagnostic electrode has the first movable comb electrode, the first fixed comb electrode, the second movable comb electrode, and the second fixed comb electrode sandwiched in the middle.

2. The physical quantity sensor element according to claim 1, wherein, The physical quantity sensor element includes: The supporting substrate; and The cover is positioned opposite the support substrate. One of the self-diagnostic electrodes is disposed on the support substrate. The other side of the self-diagnostic electrode is disposed on the cover. Within the receiving space sandwiched between the supporting substrate and the cover, It houses the beam fixing part, the first electrode fixing part, the second electrode fixing part, the support beam, the movable body, the first movable comb tooth electrode, the first fixed comb tooth electrode, the second movable comb tooth electrode, and the second fixed comb tooth electrode.

3. A physical quantity sensor device, characterized in that, Include: The physical quantity sensor element according to claim 1 or claim 2; The control signal generation circuit, during normal operation (excluding self-diagnosis), periodically applies signals for detecting capacitance changes to the space 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 used to detect the capacitance change, a signal used to displace the first movable comb electrode and the second movable comb electrode is periodically applied between the self-diagnostic electrodes for the purpose of self-diagnosis. The CV conversion circuit 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 fixed comb electrode; and The signal processing circuit processes the output voltage of the CV conversion circuit and outputs a signal corresponding to the change in the physical quantity.

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

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