MEMS Devices

Abstract

The present invention limits a reduction in the accuracy of detecting a capacitance value.　An inertial sensor 1 comprises: a MEMS substrate 50 including a capacitance portion 110 that has a first movable electrode 111 and a second movable electrode 115 and is configured such that the capacitance changes according to the distance between the first movable electrode 111 and the second movable electrode 115, a retention portion 130 that is configured so as to retain the capacitance portion 110, and a spring portion 150 that connects the capacitance portion 110 and the retention portion 130 and is configured so as to support both the first movable electrode 111 and the second movable electrode 115 such that the electrodes can be displaced with respect to the retention portion 130; and a cover 30 joined to the MEMS substrate 50.

Description

[Technical field]

[0001] The present invention relates to MEMS devices. [Background technology]

[0002] 2. Description of the Related Art Devices manufactured using Micro Electro Mechanical Systems (MEMS) technology have become widespread. These devices are formed, for example, by bonding an upper substrate to a lower substrate having elements thereon.

[0003] For example, Patent Document 1 discloses an acceleration sensor having a movable part that rotates around a rotation axis between a base substrate and a cap substrate, a left capacitor formed by a left upper electrode provided on the cap substrate and a left movable electrode provided on the movable part, and a right capacitor formed by a right upper electrode provided on the cap substrate and a right movable electrode provided on the movable part. In this acceleration sensor, when a vibration acceleration in the vertical direction is input, the left movable electrode and the right movable electrode vibrate in the direction of rotational displacement. Therefore, the capacitance of the capacitor between the left movable electrode and the left upper electrode and the capacitance of the capacitor between the right movable electrode and the right upper electrode vibrate in opposite phases to each other. Then, the acceleration sensor detects the acceleration vibration in the vertical direction based on the output calculated from the capacitance difference between these capacitances, and detects the acceleration. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2017 / 183082 Summary of the Invention [Problem to be solved by the invention]

[0005] In the acceleration sensor of Patent Document 1, an upper left electrode and an upper right electrode are formed on a cap substrate, with the upper left electrode serving as a fixed electrode for the left movable electrode and the upper right electrode serving as a fixed electrode for the right movable electrode.

[0006] On the other hand, the cap substrate may be deformed when, for example, a molding pressure is applied during packaging, or when a pressure caused by a difference in thermal expansion is applied when mounting on a substrate.

[0007] The fixed electrode formed on the cap substrate is easily affected by deformation of the cap substrate, and deformation of the cap substrate can change the capacitance between the fixed electrode and the movable electrode, which can reduce the detection accuracy of the capacitance value.

[0008] The present invention has been made in view of the above circumstances, and has an object to provide a MEMS device capable of suppressing a decrease in the detection accuracy of the capacitance value. [Means for solving the problem]

[0009] A MEMS device according to one aspect of the present invention comprises a first substrate including a capacitance section having a first movable electrode and a second movable electrode, and configured such that the capacitance changes depending on the distance between the first movable electrode and the second movable electrode, a holding section configured to hold the capacitance section, and an elastic section connecting the capacitance section and the holding section, the elastic section configured to support each of the first movable electrode and the second movable electrode so that they can be displaced relative to the holding section, and a second substrate joined to the first substrate. Effect of the Invention

[0010] According to the present invention, it is possible to suppress a decrease in the detection accuracy of the capacitance value. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a perspective view that illustrates a schematic appearance of an inertial sensor according to an embodiment. [Diagram 2] FIG. 2 is an exploded perspective view that illustrates a schematic structure of the resonator device illustrated in FIG. [Diagram 3] FIG. 3 is a plan view that illustrates a schematic structure of the resonator shown in FIG. [Figure 4] FIG. 4 is a cross-sectional view that illustrates an example of the cross-sectional configuration of the inertial sensor shown in FIGS. 1 to 3 taken along line IV-IV. [Diagram 5] FIG. 5 is a cross-sectional view that illustrates roughly another example of the cross-sectional configuration of the inertial sensor taken along line IV-IV illustrated in FIGS. 1 to 3. As illustrated in FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, an embodiment of the present invention will be described. In the following description of the drawings, the same or similar components are represented by the same or similar reference numerals. The drawings are illustrative, and the dimensions and shapes of each part are schematic, and the technical scope of the present invention should not be interpreted as being limited to the embodiment.

[0013] First, a schematic configuration of an inertial sensor according to an embodiment will be described with reference to Fig. 1 and Fig. 2. Fig. 1 is a perspective view that shows a schematic appearance of an inertial sensor 1 according to an embodiment. Fig. 2 is an exploded perspective view that shows a schematic structure of the inertial sensor 1 shown in Fig. 1.

[0014] In the following description, an inertial sensor 1 that includes a bottom cover 20, an element 10 (hereinafter, the bottom cover 20 and the element 10 are collectively referred to as the "MEMS substrate 50"), and an top cover 30 and detects acceleration or angular velocity acting in at least one direction will be described as an example of a MEMS device. However, the embodiment of the present invention is not limited to the inertial sensor 1.

[0015] The inertial sensor 1 includes a bottom cover 20, an element 10, and a top cover 30. That is, the inertial sensor 1 is configured by stacking a MEMS substrate 50, a joint 60, and a top cover 30 in this order. The MEMS substrate 50 corresponds to an example of a "first substrate" in the present invention, and the top cover 30 corresponds to an example of a "second substrate" in the present invention.

[0016] The following describes each component of the inertial sensor 1. In the following description, the side of the inertial sensor 1 on which the upper cover 30 is provided is referred to as the top (or front), and the side on which the lower cover 20 is provided is referred to as the bottom (or back).

[0017] The element 10 is a MEMS element manufactured using MEMS technology, and is, for example, an element for detecting acceleration in the Z-axis direction. The element 10, the lower cover 20, and the upper cover 30 are bonded together so that the element 10 is sealed and a displacement space is formed in which a capacitance section 110 of the element 10, which will be described later, can be displaced. The element 10, the lower cover 20, and the upper cover 30 are each formed using a silicon (Si) substrate (hereinafter referred to as an "Si substrate"), and the Si substrates are bonded together. The element 10, the lower cover 20, and the upper cover 30 may each be formed using a SOI (Silicon On Insulator) substrate in which a silicon layer and a silicon oxide film are stacked. In particular, the element 10 and the lower cover 20 may be integrally formed using a CSOI (Cavity SOI) substrate.

[0018] The bottom cover 20 includes a rectangular flat bottom plate 22 provided along the XY plane, and a side wall 23 extending from the periphery of the bottom plate 22 in the Z-axis direction, i.e., in the stacking direction of the bottom cover 20 and the element 10. The bottom cover 20 has a recess 21 defined by the surface of the bottom plate 22 and the inner surface of the side wall 23 on the surface facing the element 10. The recess 21 forms at least a part of the vibration space of the element 10. The bottom cover 20 may have a flat plate-like configuration without having the recess 21. A getter layer may be formed on the surface of the recess 21 of the bottom cover 20 facing the element 10.

[0019] The upper lid 30 forms a displacement space for the element 10 between itself and the lower lid 20. The upper lid 30 includes a rectangular flat bottom plate 32 provided along the XY plane, and a side wall 33 extending in the Z-axis direction from the peripheral portion of the bottom plate 32. The upper lid 30 has a recess 31 defined by the surface of the bottom plate 32 and the inner surface of the side wall 33 on the surface facing the element 10. The recess 31 forms at least a part of the displacement space for the element 10. The upper lid 30 may have a flat plate-like configuration without the recess 31. A getter layer may be formed on the surface of the recess 31 of the upper lid 30 facing the element 10.

[0020] The displacement space of the element 10 is airtightly sealed and a vacuum state is maintained by joining the upper lid 30, the element 10, and the lower lid 20. This displacement space may be filled with a gas such as an inert gas.

[0021] Next, a schematic configuration of an element according to an embodiment will be described with reference to Fig. 3. Fig. 3 is a plan view that shows a schematic structure of the element 10 shown in Fig. 2.

[0022] As shown in Fig. 3, element 10 is a MEMS element manufactured using MEMS technology. This MEMS element is applied to, for example, a timing device, an RF filter, a duplexer, an ultrasonic transducer, an angular velocity sensor (gyro sensor), an acceleration sensor, etc. It may also be used as a piezoelectric mirror with an actuator function, a piezoelectric gyro, a piezoelectric microphone with a pressure sensor function, an ultrasonic vibration sensor, etc. Furthermore, it may be applied to an electrostatic MEMS element, an electromagnetically driven MEMS element, and a piezo-resistive MEMS element.

[0023] The element 10 includes a capacitance portion 110 , a holding portion 130 , a frame portion 140 , a spring portion 150 , and a groove portion 160 .

[0024] The capacitance section 110 has a first movable electrode 111 and a second movable electrode 115. The first movable electrode 111 and the second movable electrode 115 are arranged to face each other at a predetermined distance in the Z-axis direction. When the main surface of the element 10 is viewed from above in a plan view (hereinafter simply referred to as "plan view"), the first movable electrode 111 and the second movable electrode 115 each have a rectangular or approximately rectangular shape.

[0025] The capacitance unit 110 is configured such that the capacitance changes according to the distance between the first movable electrode 111 and the second movable electrode 115 in the direction along the Z axis. More specifically, the first movable electrode 111 and the second movable electrode 115 form a parallel plate capacitor, and when acceleration in the Z axis direction acts on the capacitance unit 110, at least one of the first movable electrode 111 and the second movable electrode 115 is displaced according to the acceleration, and the capacitance of the capacitor in the capacitance unit 110 changes. In this way, by measuring the capacitance value of the capacitance unit 110 that changes with the change in the distance between the first movable electrode 111 and the second movable electrode 115, it is possible to detect the acceleration in the Z axis direction.

[0026] In addition, when the element 10 is an element for detecting an angular velocity, the first movable electrode 111 and the second movable electrode 115 are, for example, In the X-axis direction In the vibrated state, when an angular velocity of Y-axis rotation about the Y-axis direction acts on the capacitance unit 110, at least one of the first movable electrode 111 and the second movable electrode 115 is displaced in the Z-axis direction by the Coriolis force, and the capacitance of the capacitor of the capacitance unit 110 changes. In this way, by measuring the capacitance value of the capacitance unit 110 that changes with the change in the distance between the first movable electrode 111 and the second movable electrode 115, it is possible to detect the angular velocity of Y-axis rotation.

[0027] The holding section 130 is configured to hold the capacitance section 110. More specifically, the holding section 130 holds the capacitance section 110 so that the capacitance section 110 is displaceable at least in the Z-axis direction. Specifically, the holding section 130 includes a holding body 131A arranged on the Y-axis negative direction side and a holding body 131B arranged on the Y-axis positive direction side, sandwiching the capacitance section 110 therebetween, in a plan view of the element 10.

[0028] The frame portion 140 has a rectangular frame shape in a plan view of the element 10, and is formed along the XY plane so as to surround the outside of the capacitance portion 110 and the holding portion 130. As indicated by the dashed line in FIG. 3, a bonding portion 60, which will be described later, is formed on the frame portion 140.

[0029] The frame portion 140 is not limited to a frame shape as long as it is disposed at least partially around the capacitance portion 110 and the holding portion 130. For example, the frame portion 140 is disposed around the capacitance portion 110 and the holding portion 130 to an extent that the frame portion 140 can be joined to the upper cover 30 and the lower cover 20.

[0030] In this embodiment, the frame portion 140 includes frame bodies 141A to 141D that are integrally formed. As shown in FIG. 3, the frame body 141A faces the upper side of the holding body 131A, and is provided with its longitudinal direction parallel to the X-axis. The frame body 141B faces the lower side of the holding body 131B, and is provided with its longitudinal direction parallel to the X-axis. The frame body 141C faces the left sides of the holding body 131A and the holding body 131B and the left end of the capacitance section 110, and is provided with its longitudinal direction parallel to the Y-axis, and both ends of the frame body 141C are connected to one ends of the frame bodies 141A and 141D, respectively. The frame body 141D faces the right sides of the holding body 131A and the holding body 131B and the right end of the capacitance section 110, and is provided with its longitudinal direction parallel to the Y-axis, and both ends of the frame body 141C are connected to the other ends of the frame bodies 141A and 141B, respectively. The frame body 141A and the frame body 141B face each other in the Y-axis direction, sandwiching the capacitance portion 110 and the holding portion 130. The frame body 141C and the frame body 141D face each other in the X-axis direction, sandwiching the capacitance portion 110 and the holding portion 130.

[0031] The spring portion 150 is disposed inside the frame portion 140, and connects the capacitance portion 110 and the holding portion 130. The spring portion 150 is configured to support the capacitance portion 110 in a displaceable manner. More specifically, the spring portion 150 is configured to support each of the first movable electrode 111 and the second movable electrode 115 in a displaceable manner relative to the holding portion 130. Specifically, the spring portion 150 includes a spring 151A having one end connected to the holding body 131A and the other end connected to the first movable electrode 111, and a spring 151B having one end connected to the holding body 131B and the other end connected to the second movable electrode 115.

[0032] The springs 151A and 151B each have elasticity and have the property of being deformed when a force is applied thereto and returning to their original shape when the force is removed. The springs 151A and 151B each have a meandering (serpentine) shape in a plan view of the element 10 and are folded back at their ends in the X-axis direction. The number of times the spring 151A is folded back is different from the number of times the spring 151B is folded back. Therefore, the springs 151A and 151B have different spring constants.

[0033] The groove portion 160 is formed in at least a part of the periphery of the holding portion 130 in a plan view of the element 10. More specifically, the groove portion 160 is disposed inside the frame portion 140, and is formed so as to surround the periphery of the holding portion 130 and the spring portion 150. As will be described in detail later, the groove portion 160 is actually a through hole that penetrates the element 10 from the front surface to the back surface. As a result, the holding portion 130 and the spring portion 150 that are disposed inside the groove portion 160 are isolated from the frame portion 140 that is disposed outside the groove portion 160.

[0034] The connection wirings 75A and 75B are configured to electrically connect the top lid 30 and the element 10. More specifically, the connection wirings 75A and 75B are configured to electrically connect the through electrodes V1 and V2, which will be described later, formed in the top lid 30, and the Si substrate F2 and Si film F3, which will be described later, constituting the element 10. Specifically, the connection wiring 75A is formed on the holder 131A, and the connection wiring 75B is formed on the holder 131B.

[0035] Furthermore, when the upper cover 30 and the MEMS substrate 50 (the lower cover 20 and the element 10) are joined together, a through electrode V1 (described below) formed penetrating the upper cover 30 is disposed at the position indicated by the dashed line in Fig. 3. Thus, the through electrode V1 is electrically connected to the connection wiring 75A formed on the holder 131A by joining.

[0036] Similarly, when the upper cover 30 and the MEMS substrate 50 (the lower cover 20 and the element 10) are joined together, a through electrode V2 (described later) formed penetrating the upper cover 30 is disposed at the position indicated by the dashed line in Fig. 3. Thus, the through electrode V2 is electrically connected to the connection wiring 75B formed on the holder 131B by joining.

[0037] The via electrodes 76A and 76B are electrodes for electrically connecting a Si substrate F2 and a Si film F3, which will be described later, in the element 10. The via electrodes 76A and 76B each extend in the Z-axis direction. The via electrode 76A is formed in the capacitance portion 110, and the via electrode 76 B is provided on holding body 131B of holding portion 130.

[0038] Next, a laminated structure of the inertial sensor 1 according to one embodiment of the present invention will be described with reference to Fig. 4 and Fig. 5. Fig. 4 is a cross-sectional view showing an example of the cross-sectional configuration taken along line IV-IV of the inertial sensor 1 shown in Fig. 1 to Fig. 3. Fig. 5 is a cross-sectional view showing another example of the cross-sectional configuration taken along line IV-IV of the inertial sensor 1 shown in Fig. 1 to Fig. 3.

[0039] As shown in Fig. 4, in the inertial sensor 1, the frame 140 of the element 10 is joined onto the side wall 23 of the bottom lid 20, and the frame 140 of the element 10 is further joined to the side wall 33 of the top lid 30. In this manner, the element 10 is held between the bottom lid 20 and the top lid 30, and a displacement space is formed by the bottom lid 20, the top lid 30, and the frame 140 of the element 10. In addition, terminals T1 and T2 are formed on the upper surface of the top lid 30 (the surface opposite to the surface facing the element 10). The terminals T1 and T2 are electrically connected to the element 10 by the through electrodes V1 and V2, the connection portions 70A and 70B, and the connection wirings 75A and 75B.

[0040] The top cover 30 is formed of a silicon (Si) wafer (hereinafter referred to as "Si wafer") L3 having a predetermined thickness. The top cover 30 is joined to a frame 140 of the element 10 at its peripheral portion (side wall 33) by a joining portion 60 described below. The top cover 30 has a front surface and a back surface facing the element 10 and side surfaces of the through electrodes V1 and V2, which are preferably covered with a silicon oxide film L31. The silicon oxide film L31 is formed on the surface of the Si wafer L3, for example, by oxidizing the surface of the Si wafer L3 or by chemical vapor deposition (CVD).

[0041] In addition, a getter layer 34 is formed on the surface of the recess 31 of the top lid 30 facing the element 10. The getter layer 34 is made of, for example, titanium (Ti) or the like, and adsorbs outgassing generated in the vibration space. In the top lid 30 according to this embodiment, the getter layer 34 is formed on almost the entire surface of the recess 31 facing the element 10, so that a decrease in the degree of vacuum in the displacement space can be suppressed.

[0042] The through electrodes V1 and V2 are formed by filling a conductive material into through holes formed in the upper cover 30. The filled conductive material is, for example, polycrystalline silicon (Poly-Si) doped with impurities, copper (Cu), gold (Au), single crystal silicon doped with impurities, etc. The through electrode V1 serves as a wiring that electrically connects the terminal T1 and the connection portion 70A, and the through electrode V2 serves as a wiring that electrically connects the terminal T2 and the connection portion 70B.

[0043] The bottom plate 22 and sidewall 23 of the lower lid 20 are integrally formed from a Si wafer L1. The lower lid 20 is joined to the frame portion 140 of the element 10 by the upper surface of the sidewall 23. The thickness of the lower lid 20 defined in the Z-axis direction is, for example, 150 μm, and the depth of the recess 21 is, for example, 50 μm. The Si wafer L1 is made of non-degenerate silicon, and its resistivity is, for example, 16 mΩ·cm or more.

[0044] In the element 10, the capacitance section 110, the holding section 130, the frame section 140, the spring section 150, and the groove section 160 are integrally formed in the same process. In the element 10, a silicon oxide (e.g., SiO2) layer F21 is formed on a silicon (Si) substrate (hereinafter, referred to as "Si substrate") F2, which is an example of a substrate, and a silicon (Si) film (hereinafter, referred to as "Si film") F3 is further formed on the silicon oxide layer F21. The respective outer shapes of the capacitance section 110, the holding section 130, the spring section 150, and the groove section 160 are formed by removing and patterning a laminate composed of the above-mentioned Si substrate F2, the silicon oxide layer F21, the Si film F3, etc., by dry etching using, for example, irradiating an argon (Ar) ion beam.

[0045] The Si substrate F2 is formed of a degenerate n-type silicon (Si) semiconductor having a thickness of, for example, about 6 μm, and may contain phosphorus (P), arsenic (As), antimony (Sb), or the like as an n-type dopant. The resistance value of the degenerate silicon (Si) used in the Si substrate F2 is, for example, less than 1.6 mΩ·cm, and more preferably 1.2 mΩ·cm or less. In this way, by using degenerate silicon (Si) as the Si substrate F2, the resistance of the Si substrate F2 can be made low. Furthermore, a silicon oxide layer F22 such as SiO2 is formed on the lower surface of the Si substrate F2 as an example of a temperature characteristic correction layer. This makes it possible to improve the temperature characteristics.

[0046] In this embodiment, an example in which a degenerate silicon substrate is used for the Si substrate F2 has been described, but the present invention is not limited to this. For example, the Si substrate F2 may be a single crystal Si substrate. In this manner, by using a single crystal Si substrate as the Si substrate F2 in the element 10, the generation of hillocks due to heat treatment, such as that of aluminum (Al), can be suppressed.

[0047] The material of the Si film F3 is preferably the same as that of the Si substrate F2. The material of the Si film F3 is, for example, the same single crystal silicon (Si) as that of the Si substrate F2. As a result, in the capacitance section 110, the first movable electrode 111 formed of the Si substrate F2 and the second movable electrode 115 formed of the Si film F3 are made of the same material.

[0048] In this way, since the first movable electrode 111 and the second movable electrode 115 are made of the same material, a potential difference corresponding to the work function difference caused by the different materials is less likely to occur between the first movable electrode 111 and the second movable electrode 115.

[0049] The joint 60 is formed in a rectangular ring shape along the XY plane between the MEMS substrate 50 (the element 10 and the bottom lid 20) and the top lid 30. The joint 60 joins the MEMS substrate 50 and the top lid 30 so as to seal the displacement space of the element 10. This hermetically seals the displacement space, and maintains a vacuum state.

[0050] In this embodiment, the joint 60 is formed by laminating an aluminum (Al) layer 61, a germanium (Ge) layer 62, and an aluminum (Al) layer 63 in this order. B and Using the same type of metal can simplify the manufacturing process.

[0051] In the example shown in Fig. 4, the aluminum (Al) layer 61, the germanium (Ge) layer 62, and the aluminum (Al) layer 63 are described as independent layers, but in reality, their interfaces are eutectic bonded. The bonding portion 60 may be formed of a gold (Au) film and a tin (Sn) film, or may be formed of a combination of gold (Au) and silicon (Si), gold (Au) and gold (Au), copper (Cu) and tin (Sn), or the like. In order to improve adhesion, the bonding portion 60 may have a thin layer of titanium (Ti), titanium nitride (TiN), tantalum nitride (TaN), or the like sandwiched between the stacked layers.

[0052] The connection portion 70A is electrically connected to the terminal T1 via the through electrode V1, and is also electrically connected to the connection wiring 75A. Similarly, the connection portion 70B is electrically connected to the terminal T2 via the through electrode V2, and is also electrically connected to the connection wiring 75B. The connection portion 70A and the connection wiring 75B each include a first metal layer and a second metal layer. In the example shown in Fig. 4, the first metal layer and the second metal layer are depicted as independent layers, but in reality, the interface between them is eutectic bonded. That is, the connection portions 70A and 70B are made of a eutectic alloy of the first metal layer and the second metal layer.

[0053] The connection parts 70A and 70B are formed by first providing a first metal layer on the upper cover 30 side and providing a second metal layer on the MEMS substrate 50 side. Next, the MEMS substrate 50 and the upper cover 30 are aligned so that the first metal layer and the second metal layer coincide with each other. After alignment, the MEMS substrate 50 and the upper cover 30 are sandwiched by a heater or the like, and a heat treatment for eutectic bonding is performed. The temperature in the heat treatment for eutectic bonding is equal to or higher than the confocal temperature, for example, 424° C. or higher, and the heating time is about 10 minutes to 20 minutes. During heating, the inertial sensor 1 is pressed from the upper cover 30 to the MEMS substrate 50 with a pressure of, for example, about 5 MPa to 25 MPa.

[0054] In this embodiment, the metal of the first metal layer is germanium (Ge), and the metal of the second metal layer is aluminum (Al). Here, a eutectic alloy of germanium (Ge) and aluminum (Al) has a higher tolerance for foreign particles than eutectic alloys of other materials, so that a eutectic reaction is easily realized, and connections 70A and 70B that are good eutectic bonds can be obtained.

[0055] The connection wirings 75A, 75B are electrically connected to the element 10. Specifically, the connection wirings 75A, 75B are electrically connected to the capacitance portion 110 of the element 10 through via electrodes 76A, 76B described below. The connection wirings 75A, 75B are made of a metal such as aluminum (Al), gold (Au), or tin (Sn).

[0056] In this embodiment, the material of the connection wirings 75A and 75B is aluminum (Al), the same as the second metal layer of the connection parts 70A and 70B, which makes it possible to form the connection wirings 75A and 75B simultaneously with the second metal layer of the connection parts 70A and 70B, thereby simplifying the manufacturing process.

[0057] The via electrode 76A electrically connects the Si substrate F2 and the Si film F3 in the capacitance section 110. The via electrode 76B is formed so as to contact the connection wiring 75B, and electrically connects the Si substrate F2 and the Si film F3 in the capacitance section 110. Specifically, a part of the silicon oxide layer F21 and the Si film F3 laminated on the Si substrate F2 are removed so as to expose the Si substrate F2, and a conductive material is filled in the formed through hole, thereby forming the via electrodes 76A and 76B connecting the Si substrate F2 and the Si film F3. The via electrodes 76A and 76B are made of a metal such as aluminum (Al), gold (Au), or tin (Sn).

[0058] The capacitance section 110 is formed by removing a portion of the Si film F3, the silicon oxide layer F21, and the Si substrate F2. Specifically, in the capacitance section 110, a portion of the Si film F3 is removed to form an opening, and the first movable electrode 111 is formed from the portion of the Si film F3 that has not been removed. In addition, in the capacitance section 110, as a result of removing the silicon oxide layer F21 and a portion of the Si substrate F2, the second movable electrode 115 is formed from the portion of the Si substrate F2 that has not been removed.

[0059] The spring portion 150 is formed by removing a part of the Si film F3. One end of the spring 151A is connected to the Si film F3 in the holder 131A, and the other end is connected to the first movable electrode 111 of the capacitance portion 110. As a result, the first movable electrode 111 is supported so as to be displaceable, for example, in the Z-axis direction with respect to the holder 131A of the holder 130. Also, one end of the spring 151B is connected to the Si film F3 in the holder 131B, and the other end is connected to the second movable electrode 115 via the Si film F3 and the silicon oxide layer F21 in the capacitance portion 110. As a result, the second movable electrode 115 is supported so as to be displaceable, for example, in the Z-axis direction with respect to the holder 131B of the holder 130.

[0060] In this way, the spring portion 150 supports the first movable electrode 111 and the second movable electrode 115 so as to be displaceable, and thus the first movable electrode 111 and the second movable electrode 115 are isolated from the holding portion 130 by the spring portion 150. Therefore, even if the upper cover 30 is deformed due to the application of external pressure or a force due to a thermal expansion difference, the force associated with the deformation is less likely to be applied to the first movable electrode 111 and the second movable electrode 115 by the spring portion 150, and it is possible to reduce the change in the inter-electrode distance between the first movable electrode 111 and the second movable electrode 115 due to the deformation of the upper cover 30. Therefore, it is possible to suppress a decrease in the detection accuracy of the capacitance value in the capacitance portion 110.

[0061] The capacitance section 110 includes a cavity 121 having a predetermined depth. The cavity 121 forms a space with a gap corresponding to a predetermined depth between the first movable electrode 111 and the second movable electrode 115 in the Z-axis direction. The cavity 121 is formed, for example, by removing a part of the Si substrate F2 in the capacitance section 110 by dry etching or the like through an opening formed in the Si film F3. The cavity 121 may be formed by thinning a part of the Si film F3 instead of removing a part of the Si substrate F2 or in addition to removing a part of the Si substrate F2. As shown in FIG. 4, the cavity 121 may be in communication with a displacement space formed by the upper cover 30 and the element 10. The cavity 121 may also be in communication with a displacement space formed by the lower cover 20 and the element 10.

[0062] In this way, since the capacitance section 110 has a cavity 121 that forms a space between the first movable electrode 111 and the second movable electrode 115, the initial capacitance value of the capacitance section 110 when no force is acting can be easily adjusted by changing the depth of the cavity 121.

[0063] Moreover, one or more bumps 125 are formed on the bottom surface of the cavity 121, that is, on the upper surface of the second movable electrode 115. The bumps 125 have a shape that protrudes into the space formed by the cavity 121. This makes it possible to suppress sticking between the electrodes when the first movable electrode 111 and the second movable electrode 115 come into contact with each other due to displacement of at least one of the first movable electrode 111 and the second movable electrode 115.

[0064] The material of the bump 125 is, for example, amorphous silicon (also called "amorphous silicon") that does not have a crystal structure. Examples of the amorphous silicon include polycrystalline silicon (Poly-Si), evaporated silicon, and sputtered silicon. In addition, the amorphous silicon of the bump 125 is preferably doped with an impurity (dopant). The impurity added or injected into the amorphous silicon by doping can include, for example, phosphorus (P), boron (B), arsenic (As), and the like.

[0065] In this way, since the material of the bump 125 is amorphous silicon doped with impurities, the conductivity of the bump 125 can be adjusted by the impurities, which can prevent failure of the capacitance section 110 due to a short circuit when the first movable electrode 111 and the second movable electrode 115 come into contact, and can also suppress the accumulation of electric charge in the bump 125 and the resulting electrification.

[0066] In the present embodiment, an example in which the bump 125 is formed on the upper surface of the second movable electrode 115 has been described, but the present invention is not limited to this. For example, the bump 125 may be formed on the upper surface of the cavity 121, i.e., the lower surface of the first movable electrode 111, instead of the upper surface of the second movable electrode 115 or together with the upper surface of the second movable electrode 115.

[0067] The groove 160 is disposed between the holding portion 130 and the frame portion 140, and is formed in at least a part of the periphery of the holding portion 130. The groove 160 penetrates from the Si film F3 to the silicon oxide layer F22 of the element 10. As shown in the example of FIG. 4, a recess may be formed in the lower cover 20 at a position corresponding to the groove 160 of the element 10. Similarly, a recess may be formed in the upper cover 30 at a position corresponding to the groove 160 of the element 10.

[0068] In this way, by including groove portion 160 formed around at least a portion of the periphery of holding portion 130, groove portion 160 isolates holding portion 130 from the outer end of inertial sensor 1. Therefore, even if deformation occurs in upper cover 30 due to external pressure or force caused by thermal expansion difference, groove portion 160 makes it even more difficult for the force associated with the deformation to be applied to first movable electrode 111 and second movable electrode 115.

[0069] In the present embodiment, the springs 151A and 151B of the spring portion 150 are formed using a part of the Si film F3 of the element 10 by way of an example, but the present invention is not limited to this.

[0070] As shown in Fig. 5, the spring portion 150 may be formed by removing a part of the Si film F3 and a part of the Si substrate F2. That is, similar to the example shown in Fig. 4, one end of the spring 151A is connected to the Si film F3 of the holder 131A, and the other end is connected to the first movable electrode 111 of the capacitance portion 110. On the other hand, unlike the example shown in Fig. 4, the spring 151B may be connected to the Si substrate F2 of the holder 131B, and the other end is directly connected to the second movable electrode 115 of the capacitance portion 110.

[0071] The spring portion 150 is not limited to including two springs 151A, 151B, and may include one spring or three or more springs. The shape, arrangement, number of folds, etc. of the springs 151A, 151B in a plan view of the element 10 are not limited to the example shown in Fig. 4. Furthermore, as long as the spring portion 150 supports each of the first movable electrode 111 and the second movable electrode 115 so as to be displaceable relative to the holding portion 130, the holding portion 130 and the spring portion 150 may be in a form different from the example shown in Fig. 4.

[0072] An exemplary embodiment of the present invention has been described above. In an inertial sensor according to one embodiment, the spring portion supports the first movable electrode and the second movable electrode so that they can be displaced. As a result, the first movable electrode and the second movable electrode are isolated from the holding portion by the spring portion, so that even if the upper cover is deformed due to external pressure or a force caused by a thermal expansion difference, the force associated with the deformation is less likely to be applied to the first movable electrode and the second movable electrode by the spring portion, and the change in the interelectrode distance between the first movable electrode and the second movable electrode due to the deformation of the upper cover can be reduced. Therefore, it is possible to suppress a decrease in the detection accuracy of the capacitance value in the capacitance unit.

[0073] In the inertial sensor described above, the capacitance section further has a cavity that forms a space between the first movable electrode and the second movable electrode, whereby the initial capacitance value of the capacitance section when no force is applied can be easily adjusted by changing the depth of the cavity.

[0074] Moreover, in the above-described inertial sensor, the capacitance section further has a bump on at least one of the first movable electrode and the second movable electrode that protrudes into the space formed by the cavity 121. This makes it possible to suppress sticking between the electrodes when the first movable electrode and the second movable electrode come into contact with each other due to the displacement of at least one of the first movable electrode and the second movable electrode.

[0075] In the inertial sensor described above, the material of the bump is amorphous silicon doped with impurities. This allows the conductivity of the bump to be adjusted by the impurities, thereby preventing a short circuit that may cause a defect in the capacitance section when the first movable electrode and the second movable electrode come into contact with each other, and suppressing the bump from being charged with electricity.

[0076] The inertial sensor further includes a groove formed in at least a part of the periphery of the holding part in a plan view of the element. As a result, the holding part is isolated from the outer end of the inertial sensor by the groove, so that even if the upper cover is deformed due to the application of external pressure or a force due to a thermal expansion difference, the force associated with the deformation is further prevented from being applied to the first movable electrode and the second movable electrode by the groove.

[0077] In the inertial sensor described above, the first movable electrode and the second movable electrode are made of the same material, which makes it difficult for a potential difference caused by a work function difference between the first movable electrode and the second movable electrode due to the different materials to occur between them.

[0078] The above-described embodiments are provided to facilitate understanding of the present invention, and are not intended to limit the present invention. The present invention may be modified / improved without departing from the spirit thereof, and equivalents are also included in the present invention. In other words, the embodiment and / or modification may be modified by a person skilled in the art as long as it has the characteristics of the present invention. For example, the elements and their arrangements, materials, conditions, shapes, sizes, etc. of the embodiment and / or modification are not limited to those shown as examples, and may be modified as appropriate. In addition, the embodiment and modification are illustrative, and it goes without saying that partial replacement or combination of the configurations shown in different embodiments and / or modifications is possible, and these are also included in the scope of the present invention as long as they include the characteristics of the present invention. [Explanation of symbols]

[0079] 1...inertial sensor, 10...element, 20...lower cover, 21...recess, 22...bottom plate, 23...side wall, 30...upper cover, 31...recess, 32...bottom plate, 33...side wall, 34...getter layer, 50...MEMS substrate, 60...junction, 61...aluminum layer, 62...germanium layer, 63...aluminum layer, 70A, 70B...connection, 75A, 75B...connection wiring, 76A, 76B...via electrodes, 110...capacitance portion, 111...first movable electrode, 1 15...second movable electrode, 121...cavity, 125...bump, 130...holding portion, 131A, 131B...holding body, 140...frame portion, 141A, 141B, 141C, 141D...frame body, 150...spring portion, 151A, 151B...spring, 160...groove portion, F2...Si substrate, F3...Si film, F21, F22...silicon oxide layer, L1, L3...Si wafer, L31...silicon oxide film, T1, T2...terminal, V1, V2...through electrode.

Claims

1. A MEMS device comprising a first substrate and a second substrate joined opposite to the first substrate, the first substrate includes a first movable electrode and a second movable electrode arranged to face each other in a stacking direction of the first substrate and the second substrate, a capacitance section configured to change capacitance depending on a distance between the first movable electrode and the second movable electrode, a holding section configured to hold the capacitance section, and an elastic section connecting the capacitance section and the holding section, the elastic section configured to support each of the first movable electrode and the second movable electrode so as to be displaceable relative to the holding section; MEMS device.

2. the capacitance portion further includes a cavity that forms a space between the first movable electrode and the second movable electrode. The MEMS device of claim 1 .

3. the capacitance unit further includes a bump protruding into the space on at least one of the first movable electrode and the second movable electrode; The MEMS device of claim 2 .

4. The material of the bump is amorphous silicon doped with impurities. The MEMS device of claim 3 .

5. The first substrate further includes a groove portion formed in at least a part of a periphery of the holding portion in a plan view. A MEMS device according to any one of claims 1 to 4.

6. The first movable electrode and the second movable electrode are made of the same material. A MEMS device according to any one of claims 1 to 5.

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