Dynamic quantity sensor and dynamic quantity sensor system

A dynamic quantity sensor includes a force receiving portion, a first movable portion that rotates in a first rotational direction around a first rotational axis according to dynamic quantity in a first direction that the force receiving portion receives, and rotates in the first rotational direction around the first rotational axis according to dynamic quantity in a second direction different from the first direction that the force receiving portion receives; and a second movable portion that rotates in a second rotational direction around a second rotational axis according to the dynamic quantity in the first direction that the force receiving portion receives, and rotates in an opposite direction to the second rotational direction around the second rotational axis according to the dynamic quantity in the second direction that the force receiving portion receives.

INCORPORATION BY REFERENCE

This application is based upon and claims the benefit of priority from Japanese patent application No. 2012-252600, filed on Nov. 16, 2012, and Japanese patent application No. 2013-109119, filed on May 23, 2013, the disclosure of which is incorporated herein in its entirety by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a dynamic quantity sensor and a dynamic quantity sensor system and, in particular, to a dynamic quantity sensor and a dynamic quantity sensor system that are provided with a movable portion that can move according to dynamic quantity.

2. Description of Related Art

Conventionally, a force sensor that detects a force, which is one of dynamic quantity, has been utilized in various systems. For example, advanced processing can be achieved by using a force sensor for a surface of a robot or the like as a tactile sensor. If the force sensor is applied to fingertips of the robot, the robot can perceive a shape of an object, or can grip the object. In addition, the force sensor is applied to a whole body surface of the robot, and the robot perceives by contact a target object and a surrounding situation that cannot be perceived only by visual and auditory senses, whereby it becomes possible for the robot to come in contact with a person, or to autonomously move in a place where various obstacles have been intricately arranged. In order to achieve the above, it is important to be able to accurately measure a state of a contact surface, such as a force of plural axes (multiple axes) or a shear force.

For example, a sensor described in Japanese Unexamined Patent Application Publication No. 2004-61280 has been known as a conventional force sensor.

SUMMARY OF THE INVENTION

Generally, most of conventional force sensors fabricated using a semiconductor micromachining technology take change of physical quantity as change of an electric capacity by a movable electrode (movable portion) that can move according to physical quantity. InFIG. 25, shown is comparison of detection schemes of such conventional electric capacity type force sensors.

A scheme1is the scheme to simply detect capacity change between a movable electrode and a fixed electrode, a scheme2is the scheme to deduct a basic capacity from a capacity of the movable electrode, with a capacity of a reference electrode being set as the basic capacity, and a scheme3is the scheme (differential detection scheme) to calculate a difference of capacities of both sides of the movable electrode. Although structures become simpler as the scheme is the former one, there are such problems that a good temperature characteristic is hard to secure since the structures are subjected to an effect of offset, and that detection accuracy is low since linearity of outputs is hard to keep.

Namely, as shown inFIG. 25, with the scheme without a differential as the scheme1, detection accuracy is the lowest since an offset capacity is large, and linearity of the outputs is poor. With the scheme using a reference electrode as the scheme2, detection accuracy is higher than the scheme1since the offset capacity is small, and linearity of the outputs is better than in the scheme1. With the differential detection scheme as the scheme3, detection accuracy is the highest since the offset capacity is small, a good temperature characteristic can be secured because of a symmetrical structure of electrodes that perform differential as compared with the scheme2, and linearity of the outputs is better than the scheme2. It is to be noted that while two conductor layers are needed in the schemes1and2, three conductor layers are generally needed in the scheme3, the conductor layers serving as electrodes.

There is a problem that since a conventional sensor described in Japanese Unexamined Patent Application Publication No. 2004-61280 can detect forces (Fx, Fy, Fz) in a triaxial direction, but highly accurate detection as differential detection cannot be performed to the force Fz in a Z direction (vertical direction), detection accuracy of a Z axis is low.

Accordingly, there is a problem that it is difficult to accurately detect dynamic quantity by the conventional dynamic quantity sensor.

A first aspect of the present invention is a dynamic quantity sensor including: a force receiving portion; a first movable portion that rotates in a first rotational direction around a first rotational axis according to dynamic quantity in a first direction that the force receiving portion receives, and rotates in the first rotational direction around the first rotational axis according to dynamic quantity in a second direction different from the first direction that the force receiving portion receives; and a second movable portion that rotates in a second rotational direction around a second rotational axis according to the dynamic quantity in the first direction that the force receiving portion receives, and rotates in an opposite direction to the second rotational direction around the second rotational axis according to the dynamic quantity in the second direction that the force receiving portion receives. Further, the dynamic quantity sensor can detect at least the dynamic quantity in the first direction and the dynamic quantity in the second direction.

According to the present invention, can be provided a dynamic quantity sensor and a dynamic quantity sensor system that can accurately detect dynamic quantity.

DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

Hereinafter, embodiments of the present invention will be explained with reference to drawings. Each embodiment explained hereinafter is not individually independent, but can be appropriately combined with one another, and an effect of the combination shall be able to be claimed. The same symbol is given to the same component, and explanation is appropriately omitted.

Hereinafter, an embodiment 1 will be explained with reference to the drawings. The embodiment is an example of a force sensor that detects a force, which is one of dynamic quantity, by triple axes as a multiaxial dynamic quantity sensor. The triaxial force sensor can detect forces in an X direction, a Y direction, and a Z direction.FIG. 1Ais a top view of a force sensor100pertaining to an embodiment of the present invention.FIG. 1Bis a perspective view of a bottom surface of the force sensor100in which a sealing substrate has been omitted.FIG. 1Cis a perspective view of the bottom surface of the force sensor100in which the sealing substrate and a fixed electrode have been omitted.FIG. 1Dis a cross-sectional side view taken along a line A-B of the force sensor100inFIG. 1A.

As shown inFIGS. 1A to 1D, the force sensor100pertaining to the embodiment is provided with a movable support portion10and a sealing portion20, and the movable support portion10and the sealing portion20are sealed and bonded by the bonding portion22. The movable support portion10and the sealing portion20are substantially square shapes in a top view, and have substantially the same size.

The movable support portion10is mainly provided with: seesaw portions (movable portions)30A to30D (any one of them is also referred to as a seesaw portion30); a force receiving portion40; a diaphragm60; and a projection61. The sealing portion20is mainly provided with a sealing substrate21and fixed electrode pairs (opposed electrode pairs)50A to50D (any one of them is also referred to as a fixed electrode pair50).

It is to be noted that a surface direction of the force sensor is a horizontal direction, the X direction (X-axis direction), or the Y direction (Y-axis direction), and that a thickness direction of the force sensor is a vertical direction or the Z direction (Z-axis direction). A surface on a positive side in the Z direction may be referred to as the top surface, a surface on a negative side in the Z direction as the bottom surface, a surface on a side to which a force is applied as a force applying surface, and a surface on a opposite side, which is opposed to the force applying surface, as a force non-applying surface. In the embodiment, the top surface is a force applying surface, and the bottom surface is a force non-applying surface. In addition, in each substrate (each layer) of the movable support portion10and the sealing portion20, a surface on a side where a movable electrode or a fixed electrode is formed is also referred to as a main surface (front surface), and a surface on an opposite side, which is opposed to the main surface, is as a back surface (rear surface). In the movable support portion10and the sealing portion20, a center side is referred to as an inside, and a peripheral end side is as an outside in the top view or the bottom view.

The movable support portion10includes an SOI (Silicon on Insulator) substrate. The SOI substrate is a three-layer-structured substrate, and a first silicon layer11, an SiO2insulator film12, and a second silicon layer13are laminated and formed in order from a top surface side (force applying side).

The first silicon layer11is also a support substrate to support the seesaw portion30. In addition, the first silicon layer11is the silicon layer having conductivity.

The diaphragm60is formed in a center portion of a back surface of the first silicon layer11, and further the projection61is formed in a center portion inside the diaphragm60. The diaphragm60and the projection61have substantially square shapes in the top view similarly to an outline of the first silicon layer11.

The diaphragm60is a thin portion that has a thinner film thickness than a periphery11aof the first silicon layer11, has flexibility, and elastically deforms according to apply of a force to the projection61. The first silicon layer11has a predetermined film thickness, the film thickness of the center portion excluding a portion of the projection61is made thinner from the back surface side by etching, and thereby the diaphragm60is formed.

The projection61is thicker than the diaphragm60and, for example, it has the same thickness as the periphery11aof the first silicon layer11. Since the projection61is thicker than the diaphragm60and projects, a force can be made to be easily received, an applying point of the force can be specified, and thus detection accuracy of the force improves.

The force receiving portion40is formed in a center portion of the second silicon layer13on a main surface side (bottom surface side) of the first silicon layer11, and the four seesaw portions30A to30D are formed around the force receiving portion40. It can be also said that the force receiving portion40is surrounded by the seesaw portions30A to30D. The seesaw portions30A and30C are arranged on both sides in the X direction of the force receiving portion40, and the seesaw portions30B and30D are arranged on both sides in the Y direction of the force receiving portion40. The force receiving portion40and the seesaw portions30A to30D are coupled to one another by hinge beams33A to33D (any one of them is also referred to as a hinge beam33), respectively.

The second silicon layer13has a predetermined film thickness, and the force receiving portion40, the seesaw portions30A to30D, the hinge beams33A to33D, and the like are formed by etching from a main surface side. For this reason, the force receiving portion40, the seesaw portions30A to30D, the hinge beams33A to33D, and the like of the second silicon layer13have substantially the same thickness. The second silicon layer13is the silicon layer having conductivity similarly to the first silicon layer11, the whole force receiving portion40, seesaw portions30A to30D, hinge beams33A to33D, and the like are conducted, and are electrically connected to one another.

The force receiving portion40has a force receiving plate41and a stopper42. The force receiving plate41is formed in a substantially square shape in a center of the force receiving portion40. The force receiving plate41(force receiving portion40) is formed at a position corresponding to the projection61. It can be also said that the projection61is formed at a position corresponding to the force receiving plate41(force receiving portion40). The force receiving plate41(force receiving portion40) is formed on the projection61(on the main surface) through the insulator film12, and is fixed and supported by the projection61(first silicon layer11) through the insulator film12. Namely, when a force is applied to the projection61, the applied force is transmitted to the force receiving plate41through the insulator film12.

The stopper42is formed substantially in an L shape at each of corner portions (four corners) around the force receiving plate41so as to extend the force receiving plate41. The stopper42is a contact portion that comes into contact with a sealing portion20side, when a position of the force receiving portion40is inclined and displaced. Etching holes43are formed in the stopper42. The etching hole43is a through hole that penetrates the stopper42, and an opening thereof has a substantially square shape. The etching holes43are arranged in accordance with the shape of the stopper42so as to be able to perform sacrifice layer etching of the insulator film12. The insulator film12is etched through the etching hole43from the main surface side, and thereby the insulator film12under the stopper42is removed. As a result of this, the stopper42is spaced aside from the first silicon layer11, and then a structure supported by the force receiving plate41is obtained.

The stopper42is not formed in a center portion of each side (end) of the force receiving plate41, but the hinge beams33A to33D are combined with the center portion of each side. It can be also said that a concave portion is formed at each side (end) of the force receiving portion41, and that the hinge beams33A to33D are combined with a hollow of the concave portion.

Cross sections of the hinge beams (coupling portions)33A to33D each have a substantially quadrangular shape, the each hinge beam is formed in an elongated beam shape, and is a combination support member having flexibility and twistability (torsionability). The hinge beams33A to33D bend according to displacement of the force receiving portion40, and rotates and displaces the seesaw portions30A to30D.

The seesaw portions30A to30D are each arranged at a place opposed to each side (end) of the force receiving portion40. The seesaw portions30A to30D have the same structure, and have a shape and arrangement of a symmetrical structure centering on the force receiving portion40. The seesaw portions30A to30D have movable electrodes31A to31D (any one of them is also referred to as a movable electrode31), and the movable electrodes31A to31D are supported by torsion beams32A to32D (any one of them is also referred to as a torsion beam32). It can be also said that the seesaw portions30A to30D have the movable electrodes31A to31D and the torsion beams32A to32D.

The movable electrodes31A to31D each has a quadrangular shape in the top view, and each have a concave portion in a center of opposed two sides (ends) of a quadrangle. It can be also said that the movable electrodes31A to31D are each formed substantially in an H shape. The hinge beams33A to33D are combined with hollows of the concave portions of the movable electrodes31A to31D. The movable electrodes31A to31D are combined and supported with/by a fixing portion15by the torsion beams32A to32D in centers of two sides (ends) without the concave portion thereof. Formation points of the torsion beams32A to32D serve as rotational axes35A to35D (any one of them is also referred to as a rotational axis35) that the movable electrodes31A to31D (seesaw portions30A to30D) rotate and move.

An etching hole34is formed in the movable electrodes31A to31D. The etching hole34is formed similarly to the etching hole43of the force receiving portion40. Namely, the etching hole34is a through hole that penetrates the movable electrodes31A to31D, and an opening thereof has a substantially square shape. The etching holes34are arranged in accordance with the shape of the movable electrodes31A to31D so as to be able to perform sacrifice layer etching of the insulator film12. The insulator film12is etched through the etching hole34from the main surface side, and thereby the insulator film12under the movable electrodes31A to31D is removed. As a result of this, the movable electrodes31A to31D are spaced aside from the first silicon layer11, and a structure supported by the fixing portion15is obtained by means of the torsion beams32A to32D.

Cross sections of the torsion beams32A to32D each have a substantially quadrangular shape, the each torsion beam is formed in an elongated beam shape, and is a combination support member having twistability (torsionability). The torsion beams32A to32D support the seesaw portions30A to30D so that they are twisted around the rotational axes35A to35D. Namely, the seesaw portions30A to30D are supported by the fixing portion15through the torsion beams32A to32D so as to be rotatable centering on the rotational axes35A to35D.

The torsion beam32preferably has a shape of a narrow width, a short length, and a thick thickness. Namely, the torsion beam32is narrow so as to be rotatable, and it is short and thick so as to be unable to be displaced in the Z direction. As a result of this, since translation rigidity can be made high, and rotational rigidity can be made low, translation displacement of the seesaw portion30can be suppressed, and only capacity change due to rotation of the seesaw portion30can be detected. A detection principle of the force sensor100will be mentioned later.

In addition, rotational rigidity of the hinge beam33is preferably not more than the rotational rigidity of the torsion beam. Since the seesaw portion30is easy to rotate, and is hard to affect an other axis even though the seesaw portion30is arranged at the triple axes as in the embodiment, a force can be accurately detected.

It is to be noted that in a relationship of spring rigidity in the Z direction of the diaphragm60, the torsion beam32, and the hinge beam33that are elastically displaced, the diaphragm60is preferably higher than the torsion beam32and the hinge beam33(Z rigidity of the diaphragm60>>Z rigidity of the torsion beam32and the hinge beam33). As a result of this, sensor sensitivity can be prescribed by a size of the diaphragm60.

The fixing portion15is formed in an arbitrary shape at a periphery13aof the second silicon layer13. In this example, the fixing portion15is formed continuously from an outer periphery to the vicinity of the seesaw portions30A to30D. The fixing portion15is formed through the insulator film12on the periphery11a(on the main surface) of the first silicon layer11. The fixing portion15is fixed and supported to/by the first silicon layer11through the insulator film12, and thereby supports the seesaw portions30A to30D.

The seesaw portions30A to30D, the hinge beams33A to33D, and the force receiving portion40have the same thickness, and the periphery13amay have the same thickness as the each portion, but may be preferably slightly (several μm) thicker than the each portion. By making the periphery13athick, it is easy to form a gap with the fixed electrode and the like when the periphery13ais sealed by the sealing portion20.

A penetrating electrode14is formed at the periphery13aoutside the seesaw portions30A to30D among the second silicon layers13. The penetrating electrode14penetrates the second silicon layer13and the insulator film12, and electrically connects the first silicon layer11and the second silicon layer13, and the bonding portion22.

In a periphery of the force sensor100, the bonding portion22seals and bonds the second silicon layer13of the movable support portion10and the sealing substrate21of the sealing portion20so as to surround the seesaw portion30and the force receiving portion40. The bonding portion22is a metal diffusion bond member having conductivity, and is, for example, Cu—Sn (copper-tin) alloy or the like.

The sealing substrate21is the substrate that seals the whole movable support portion10including the seesaw portions30A to30D and the force receiving portion40. The sealing substrate21is, for example, a silicon substrate, an LTCC (Low Temperature Co-fired Ceramic) substrate, or an LSI (Large Scale Integration). For example, a via (not shown) through which an electrode potential on the top surface side is pulled out to the bottom surface side is arranged in the sealing substrate21, an external terminal (not shown) connected to this via is arranged at the back surface (bottom surface side) of the sealing substrate21, and an external detection circuit and the like are connected to the external terminal. In addition, if needed, a circuit, such as a detection circuit, and wiring are provided inside the sealing substrate21. The sealing substrate21preferably includes an LSI. As a result of this, since a processing circuit can be arranged at a portion near the sensor structure, it is unlikely to be affected by noise.

Fixed electrode pairs50A to50D are formed on the main surface (top surface side) of the sealing substrate21. The fixed electrode pairs50A to50D include fixed electrodes51A and52A,51B and52B,51C and52C, and51D and52D (any one of them is also referred to as fixed electrodes51and52), respectively. The fixed electrodes51A to51D and52A to52D are conductive films having conductivity, such as metal, and are patterned and formed on the sealing substrate21.

The fixed electrodes51A to51D and52A to52D are arranged at positions corresponding to the movable electrodes31A to31D of the seesaw portions30A to30D, respectively, and are included in a capacitive element together with the movable electrodes31A to31D. The fixed electrodes51A to51D are arranged on the outside of the rotational axes35A to35D of the seesaw portions30A to30D, and the fixed electrodes52A to52D are arranged on the inside thereof. For example, electric capacities of these capacitive elements can be detected by the external detection circuit or the like through the via (not shown) arranged in the sealing substrate21, or by the LSI included in the sealing substrate21.

Next, the operating principle of the force sensor100pertaining to the embodiment will be explained.FIG. 2shows a relationship between displacement operation of the movable electrode and an electric capacity in the force sensor100.

In the movable electrode31of the seesaw portion30, a movable electrode portion311on one end side (outside) with respect to the rotational axis35and the fixed electrode51are opposed to each other, and the movable electrode portion311and the fixed electrode51are included in a first capacitive element511. In the movable electrode31, a movable electrode portion312on the other end side (inside) with respect to the rotational axis35and the fixed electrode52are opposed to each other, and the movable electrode portion312and the fixed electrode52are included in a second capacitive element521. Although in the embodiment, an example of one movable electrode31that continues the whole seesaw portion30is explained, an electrode separately divided into the movable electrode portion311and the movable electrode portion312may be employed. For example, the seesaw portion30has the first movable electrode (movable electrode portion311) and the second movable electrode (movable electrode portion312) sandwiching the rotational axis35therebetween, the first movable electrode and the fixed electrode51may be included in the first capacitive element511, and the second movable electrode and the fixed electrode52may be included in the second capacitive element521.

The movable electrode31rotates and is displaced in an α direction or a β direction centering on the rotational axis35according to an applied force. When a force is applied to the projection61, the force receiving portion40acts, and a force of a positive side or a negative side of the Z axis is applied to an inner end (right side inFIG. 2) of the seesaw portion30through the hinge beam33. As a result of this, the movable electrode31rotates centering on the rotational axis35.

FIG. 2is an example where the movable electrode31has rotated in the α direction from an initial state. In this case, since the movable electrode portion311of the movable electrode31and the fixed electrode51are separated, an electric capacity of the first capacitive element511between the movable electrode portion311and the fixed electrode51decreases (C−ΔC). In addition, since the movable electrode portion312of the movable electrode31and the fixed electrode52get closer to each other, an electric capacity of the second capacitive element521between the movable electrode portion312and the fixed electrode52increases (C+ΔC).

A capacity difference between the first capacitive element511and the second capacitive element521(Cs=(C+ΔC)−(C−ΔC)=2ΔC) is calculated, and thereby a force is detected by the differential detection scheme. While three conductor layers have been needed in a general differential detection scheme as inFIG. 25, the differential detection scheme can be achieved by two conductor layers in a scheme ofFIG. 2. Furthermore, in the embodiment, a difference in a deformation mode of a seesaw structure (rotational direction of the seesaw portion) is utilized using the plurality of seesaw portions30, and a force in a triaxial direction is detected by the differential detection scheme.

FIG. 3shows an arrangement image of the seesaw portion30and the rotational axis35in the force sensor100.FIG. 3is a perspective view when only the movable support portion10is viewed from the main surface side (bottom surface side).

In the seesaw portion30A, the rotational axis35A extends in the Y direction. For this reason, the seesaw portion30A rotates in an αA direction or in a βA direction centering on the rotational axis35A according to forces in the X direction and the Z direction. A capacity outside the rotational axis35A of the seesaw portion30A is set as a capacity A1, and a capacity inside the rotational axis35A is as a capacity A2. When the seesaw portion30A rotates in the αA direction, the capacity A2increases while the capacity A1decreasing, and when the seesaw portion30A rotates in the βA direction, the capacity A2decreases while the capacity A1increasing.

When a force is applied in a negative direction of the Z axis, the seesaw portion30A rotates in the αA direction, and when a force is applied in a positive direction of the Z axis, the seesaw portion30A rotates in the βA direction. When a force is applied in a positive direction of the X axis, the seesaw portion30A rotates in the βA direction, and when a force is applied in a negative direction of the X axis, the seesaw portion30A rotates in the αA direction. The seesaw portion30A is not displaced by a force in the Y direction since the hinge beam33A is twisted around the X axis.

In the seesaw portion30C, the rotational axis35C extends in the Y direction. For this reason, the seesaw portion30C rotates in an αC direction or in a βC direction centering on the rotational axis35C according to forces in the X direction and the Z direction. A capacity outside the rotational axis35C of the seesaw portion30C is set as a capacity C1, and a capacity inside the rotational axis35C is as a capacity C2. When the seesaw portion30C rotates in the αC direction, the capacity C2decreases while the capacity C1increasing, and when the seesaw portion30C rotates in the βC direction, the capacity C2increases while the capacity C1decreasing.

When a force is applied in the negative direction of the Z axis, the seesaw portion30C rotates in the βC direction, and when a force is applied in the positive direction of the Z axis, the seesaw portion30C rotates in the αC direction. When a force is applied in the positive direction of the X axis, the seesaw portion30C rotates in the βC direction, and when a force is applied in the negative direction of the X axis, the seesaw portion30C rotates in the αC direction. The seesaw portion30C is not displaced by the force in the Y direction since the hinge beam33C is twisted around the X axis.

In the seesaw portion30B, the rotational axis35B extends in the X direction. For this reason, the seesaw portion30B rotates in an αB direction or in a βB direction centering on the rotational axis35B according to forces in the Y direction and the Z direction. A capacity outside the rotational axis35B of the seesaw portion30B is set as a capacity B1, and a capacity inside the rotational axis35B is as a capacity B2. When the seesaw portion30B rotates in the αB direction, the capacity B2increases while the capacity B1decreasing, and when the seesaw portion30B rotates in the βB direction, the capacity B2decreases while the capacity B1increasing.

When a force is applied in the negative direction of the Z axis, the seesaw portion30B rotates in the αB direction, and when a force is applied in the positive direction of the Z axis, the seesaw portion30B rotates in the βB direction. When a force is applied in a positive direction of the Y axis, the seesaw portion30B rotates in the βB direction, and when a force is applied in a negative direction of the Y axis, the seesaw portion30B rotates in the αB direction. The seesaw portion30B is not displaced by the force in the X direction since the hinge beam33B is twisted around the Y axis.

In the seesaw portion30D, the rotational axis35D extends in the X direction. For this reason, the seesaw portion30D rotates in an αD direction or in a βD direction centering on the rotational axis35D according to forces in the Y direction and the Z direction. A capacity outside the rotational axis35D of the seesaw portion30D is set as a capacity D1, and a capacity inside the rotational axis35D is as a capacity D2. When the seesaw portion30D rotates in the αD direction, the capacity D2decreases while the capacity D1increasing, and when the seesaw portion30D rotates in the βD direction, the capacity D2increases while the capacity D1decreasing.

When a force is applied in the negative direction of the Z axis, the seesaw portion30D rotates in the βD direction, and when a force is applied in the positive direction of the Z axis, the seesaw portion30D rotates in the αD direction. When a force is applied in the positive direction of the Y axis, the seesaw portion30D rotates in the βD direction, and when a force is applied in the negative direction of the Y axis, the seesaw portion30D rotates in the αD direction. The seesaw portion30D is not displaced by the force in the X direction since the hinge beam33D is twisted around the Y axis.

Next, a specific operation example of the force sensor100pertaining to the embodiment will be explained.FIGS. 4A,4B, and4C show a state of the force sensor100when a force Fz has been applied to the negative direction of the Z axis.FIG. 4Ais a perspective view when only the movable support portion10is viewed from the main surface side (bottom surface side),FIG. 4Bis a cross-sectional side view viewed from the Y direction, andFIG. 4Cis a cross-sectional side view viewed from the X direction. For example, when the force sensor100is arranged at robot skin as a tactile sensor, the force Fz can be detected as a pressure sense force.

As shown inFIGS. 4A to 4C, when the force Fz is applied in the negative direction of the Z axis, the force Fz acts on a top surface of the projection61, and thus the projection61and the force receiving portion40are displaced so as to sink in the negative direction of the Z axis together with the diaphragm60. All the hinge beams33A to33D are displaced in the negative direction of the Z axis, while bending in accordance with displacement of the force receiving portion40.

As a result of it, as shown inFIG. 4B, since the seesaw portion30A is pulled by the hinge beam33A, the inner end of the seesaw portion30A is displaced in the negative direction of the Z axis, and the seesaw portion30A rotates and is displaced in the αA direction centering on the rotational axis35A. For this reason, the capacity A2increases by the inner end of the seesaw portion30A getting closer to the fixed electrode52A, and the capacity A1decreases by the outer end of the seesaw portion30A moving away from the fixed electrode51A. In addition, since the seesaw portion30C is pulled by the hinge beam33C, an inner end of the seesaw portion30C is displaced in the negative direction of the Z axis, and the seesaw portion30C rotates and is displaced in the βC direction centering on the rotational axis35C. For this reason, the capacity C2increases by the inner end of the seesaw portion30C getting closer to the fixed electrode52C, and the capacity C1decreases by the outer end of the seesaw portion30C moving away from the fixed electrode51C.

Furthermore, as shown inFIG. 4C, since the seesaw portion30B is pulled by the hinge beam33B, an inner end of the seesaw portion30B is displaced in the negative direction of the Z axis, and the seesaw portion30B rotates and is displaced in the αB direction centering on the rotational axis35B. For this reason, the capacity B2increases by the inner end of the seesaw portion30B getting closer to the fixed electrode52B, and the capacity B1decreases by the outer end of the seesaw portion30B moving away from the fixed electrode51B. In addition, since the seesaw portion30D is pulled by the hinge beam33D, an inner end of the seesaw portion30D is displaced in the negative direction of the Z axis, and the seesaw portion30D rotates and is displaced in the βD direction centering on the rotational axis35D. For this reason, the capacity D2increases by the inner end of the seesaw portion30D getting closer to the fixed electrode52D, and the capacity D1decreases by the outer end of the seesaw portion30D moving away from the fixed electrode51D.

As described above, when the force Fz is applied in the Z direction (an Fz mode), the seesaw portion30C (first movable portion) rotates in the first direction (for example, βC), and the seesaw portion30A (second movable portion) rotates in the second direction (for example, αA) opposite to the first direction. In addition, the seesaw portion30D rotates in a third direction (for example, βD), and the seesaw portion30B rotates in a fourth direction (for example, αB) opposite to the third direction. Namely, the seesaw portions30A and30C that are opposed to each other in the X direction, and the seesaw portions30B and30D that are opposed to each other in the Y direction respectively rotate in an opposite direction to each other, and result in opposite phase inclination, which is the inclination in the opposite direction. For this reason, the force Fz applied in the Z direction results in a sum of differentials of each seesaw portion30as the following (Expression 1).

FIGS. 5A,5B, and5C show a state of the force sensor100when a force Fx or a force Fy is applied in the positive direction of the X axis or the Y axis.FIG. 5Ais a perspective view when only the movable support portion10at the time of applying the force Fx or the force Fy is viewed from the main surface side (bottom surface side),FIG. 5Bis a cross-sectional side view viewed from the Y direction at the time of applying the force Fx, andFIG. 5Cis a cross-sectional side view viewed from the X direction at the time of applying the force Fy. For example, when the force sensor100is arranged at robot skin as a tactile sensor, the force Fx or the force Fy can be detected as a shear force.

As shown inFIGS. 5A and 5B, when the force Fx is applied in the positive direction of the X axis, moment around the Y axis acts on the projection61according to a height of the projection61and the force Fx, and thus the projection61and the force receiving portion40are displaced so as to incline obliquely viewed from the Y direction. A negative side of the X axis of the force receiving portion40is uplifted to the positive side of the Z axis, and a positive side of the X axis of the force receiving portion40is sunk on the negative side of the Z axis. The hinge beam33A on the X-axis negative side is displaced in the positive direction of the Z axis while bending according to displacement of the force receiving portion40, and the hinge beam33C on the X-axis positive side is displaced in the negative direction of the Z axis while bending.

As a result of it, as shown inFIG. 5B, since the seesaw portion30A is pulled by the hinge beam33A, the inner end of the seesaw portion30A is displaced in the positive direction of the Z axis, and the seesaw portion30A rotates and is displaced in the βA direction centering on the rotational axis35A. For this reason, the capacity A2decreases by the inner end of the seesaw portion30A moving away from the fixed electrode52A, and the capacity A1increases by the outer end of the seesaw portion30A getting closer to the fixed electrode51A. In addition, since the seesaw portion30C is pulled by the hinge beam33C, the inner end of the seesaw portion30C is displaced in the negative direction of the Z axis, and the seesaw portion30C is rotated and displaced in the βC direction centering on the rotational axis35C. For this reason, the capacity C2increases by the inner end of the seesaw portion30C getting closer to the fixed electrode52C, and the capacity C1decreases by the outer end of the seesaw portion30C moving away from the fixed electrode51C.

At this time, the force receiving portion40rotates and is displaced, with the hinge beams33B and33D extending in the Y direction being set as an axis. Since the hinge beams33B and33D can be easily twisted around the Y axis, they do not block rotation of the force receiving portion40. In addition, the seesaw portions30B and30D are not displaced since the hinge beams33B and33D are twisted. As described above, the force Fx in the X-axis direction can be effectively detected, cross talk in the Y-axis direction can be suppressed.

As described above, when the force Fx is applied in the X direction (an Fx mode), the seesaw portion30C (first movable portion) rotates in the first direction (for example, βC), and the seesaw portion30A (second movable portion) rotates in the same direction as the first direction, or in the opposite direction (for example, βA) to the second direction (for example, αA). Namely, the seesaw portions30A and30C that are opposed to each other in the X direction rotate in the same direction, and result in the same phase inclination, which is the inclination in the same direction. In addition, the seesaw portions30B and30D are not displaced. For this reason, the force Fx is calculated by subtraction of differentials in the seesaw portions30A and30C as the following (Expression 2).

As shown inFIGS. 5A and 5C, when the force Fy is applied in the positive direction of the Y axis, moment around the X axis acts on the projection61according to the height of the projection61and the force Fy, and thus the projection61and the force receiving portion40are displaced so as to incline obliquely viewed from the X direction. A negative side of the Y axis of the force receiving portion40is uplifted to the positive side of the Z axis, and a positive side of the Y axis of the force receiving portion40is sunk on the negative side of the Z axis. The hinge beam33B on the Y-axis negative side is displaced in the positive direction of the Z axis while bending according to displacement of the force receiving portion40, and the hinge beam33D on the Y-axis positive side is displaced in the negative direction of the Z axis while bending.

As a result of it, as shown inFIG. 5C, since the seesaw portion30B is pulled by the hinge beam33B, an inner end of the seesaw portion30B is displaced in the positive direction of the Z axis, and the seesaw portion30B rotates and is displaced in the βB direction centering on the rotational axis35B. For this reason, the capacity B2decreases by the inner end of the seesaw portion30B moving away from the fixed electrode52B, and the capacity B1increases by the outer end of the seesaw portion30B getting closer to the fixed electrode51B. In addition, since the seesaw portion30D is pulled by the hinge beam33D, the inner end of the seesaw portion30D is displaced in the negative direction of the Z axis, and the seesaw portion30D rotates and is displaced in the βD direction centering on the rotational axis35D. For this reason, the capacity D2increases by the inner end of the seesaw portion30D getting closer to the fixed electrode52D, and the capacity D1decreases by the outer end of the seesaw portion30D moving away from the fixed electrode51D.

At this time, the force receiving portion40rotates and is displaced, with the hinge beams33A and33C extending in the X direction being set as an axis. Since the hinge beams33A and33C can be easily twisted around the X axis, they do not block rotation of the force receiving portion40. In addition, the seesaw portions30A and30C are not displaced since the hinge beams33A and33C are twisted. As described above, the force Fy in the Y-axis direction can be effectively detected, cross talk in the X-axis direction can be suppressed.

As described above, when the force Fy is applied in the Y direction (an Fy mode), the seesaw portion30D rotates in the third direction (for example, βD), and the seesaw portion30B rotates in the same direction as the third direction, or in the opposite direction (for example, βB) to the fourth direction (for example, αB). Namely, the seesaw portions30B and30D that are opposed to each other in the Y direction rotate in the same direction, and result in the same phase inclination, which is the inclination in the same direction. In addition, the seesaw portions30A and30C are not displaced. For this reason, the force Fy is calculated by subtraction of differentials in the seesaw portions30B and30D as the following (Expression 3).

According to (Expression 1) to (Expression 3), in the embodiment, matrix operation is performed as in the following (Expression 4) to calculate a force in each direction. Matrix operation can be achieved by a hardware including an analog circuit and a digital circuit, a software, or both thereof. For example, an operation circuit that performs matrix operation may be incorporated in the sealing substrate21, or may be achieved by an external microcomputer or the like.

As in (Expression 4), the force in each direction is obtained by multiplying a differential (capacity difference) of each capacity by a transformation matrix. In (Expression 4), a coefficient of each differential is set as 2 in operation of the force Fx and the force Fy, and a coefficient of each differential is set as 1 in operation of the force Fz. This is by the following reason: while the seesaw portions in all the directions can move and differential values of all the capacities change in the case of the force Fz, only two seesaw portions in the X direction or in the Y direction can move, and only two differential values change in the case of the force Fx and the force Fy, so that detection sensitivity of the force Fz becomes twice as large as detection sensitivity of the force Fx and the force Fy. The coefficient of the transformation matrix is set according to sensitivity in a direction of a force to be detected, and thereby a force can be accurately detected.

An effect of the embodiment in the above configuration will be explained. In the conventional technology, although a structure to be able to detect triaxial forces has been developed, there is a problem in accuracy of linearity of output values, an offset, and the like. In addition, a sealing structure for protecting a movable portion from an outside air at the time of use of a sensor is essential in a MEMS sensor having the movable portion. However, in a case where a structure is the one hard to be sealed, when the sensor is attached to a robot and is made to work, foreign matters enter a movable body or an electrode of a sensing portion, and a problem leading to malfunction occurs.

For example, in Japanese Unexamined Patent Application Publication No. 2004-61280, differential detection of the force Fz in the Z direction cannot be performed although the forces of triple axes (Fx, Fy, Fz) can be detected, thus affecting accuracy of the Z axis. In addition, in Japanese Unexamined Patent Application Publication No. 2004-61280, a structure is employed where sealing at the time of implementation is hard to perform since a sensor has a structure where both sides thereof penetrate to each other. Accordingly, when the structure is used for a force sensor that directly comes into contact with an object, there is a possibility that foreign matters enter the movable body.

Consequently, in the embodiment, a movable electrode is set as a seesaw portion having a seesaw structure, the two seesaw portions are arranged in the X direction and the Y direction, respectively, and a fixed electrode is arranged at a position opposed to the seesaw portion. Furthermore, matrix operation of a differential capacity of each seesaw portion is performed, and the differential capacity is resolved into forces in triaxial directions. As a result of this, since using an electric capacity scheme, the triaxial forces in the X direction, the Y direction, and the Z direction can be detected, and differential detection can be performed to all the axes, forces can be accurately detected in all the triple axes.

In addition, since the seesaw structure is employed, the force sensor can be made to have the sealing structure by utilizing a diaphragm. Furthermore, since a microstructure as a comb is not needed, the structure is hard to break. Furthermore, a force receiving portion is provided, thereby a point on which a force acts can be specified, and detection accuracy improves.

Hereinafter, an embodiment 2 will be explained with reference to the drawings. The embodiment is an example where the force sensor includes only a movable support portion with respect to the embodiment 1.FIG. 6Ais a top view of the force sensor100pertaining to the embodiment.FIG. 6Bis a cross-sectional side view taken along the line A-B of the force sensor100inFIG. 6A.

As shown inFIGS. 6A and 6B, the force sensor100according to the embodiment does not have a sealing portion, but is provided with only the movable support portion10. In addition, since a force is applied from a side (main surface side) on which a force receiving portion and a seesaw portion are arranged, a force applying direction (orientation of the Z direction) is opposite as compared with the embodiment 1.

The movable support portion10is mainly provided with the seesaw portions30A to30D, the force receiving portion40, and the fixed electrode pairs50A to50D, and is not provided with a diaphragm and a projection. Similarly to the embodiment 1, the movable support portion10is provided with the first silicon layer11, the insulator film12, and the second silicon layer13. At the second silicon layer13, the force receiving portion40is formed in a center, and the four seesaw portions30A to30D are formed around the force receiving portion40. The force receiving portion40and the seesaw portions30A to30D are coupled to one another by the hinge beams33A to33D, respectively. In this example, the force receiving portion40does not have the stopper42, but includes only the force receiving plate41. Since not bonded to the first silicon layer11, the force receiving portion40has a structure supported by the seesaw portions30A to30D by means of the hinge beams33A to33D.

The movable electrodes31A to31D of the seesaw portions30A to30D are fixed to the fixing portion15by the torsion beams32A to32D. In the embodiment, the fixing portion15is formed for each torsion beam32(for each seesaw portion). The fixing portion15has a quadrangular shape in a top view, and is formed by etching the second silicon layer13.

In addition, in the embodiment, the fixed electrode pairs50A to50D are formed on a main surface of the first silicon layer11. Similarly to the embodiment 1, the fixed electrode pairs50A to50D include the fixed electrodes51A and52A,51B and52B,51C and52C, and51D and52D, respectively, and are arranged at positions corresponding to the movable electrodes31A to31D of the seesaw portions30A to30D. The fixed electrodes51A to51D and52A to52D, for example, each have a substantially rectangular shape in a top view, and are formed by implant or the like. For example, an external connection terminal is fabricated around the second silicon layer13, a TSV (Through Silicon Via) connected to the fixed electrodes51and52is fabricated in a thickness direction of the first silicon layer11, the TSV is connected to an external detection circuit or the like, and thereby electric capacities between the movable electrode31, and the fixed electrodes51and52can be detected.

An operating principle of the embodiment is similar to that of the embodiment 1. For example, in a state where the force Fz is applied in the negative direction of the Z axis, the seesaw portions30A and30C operate asFIG. 7. When the force Fz is applied in the negative direction of the Z axis, the force receiving portion40is displaced so as to sink in the negative direction of the Z axis according to the applied force. The inner ends of the seesaw portions30A to30D are displaced in the negative direction of the Z axis according to displacement of the force receiving portion40, and the outer ends of the seesaw portions30A to30D are displaced in the positive direction of the Z axis. Namely, when the force Fz is applied in the Z direction (an Fz mode), the seesaw portions30A and30C, and the seesaw portions30B and30D mutually rotate in opposite directions.

In addition, also when the force Fx is applied in the X-axis direction, and the force Fy is in the Y-axis direction, similarly to the embodiment 1, the seesaw portions30A and30C, or the seesaw portions30B and30D rotate in the same direction. Accordingly, also in the embodiment, triaxial forces can be detected by the similar principle to the embodiment 1.

As described above, in the embodiment, in a force sensor not having a sealing portion, a movable electrode is set as a seesaw portion having a seesaw structure, the two seesaw portions are arranged in the X direction and the Y direction, respectively, and a fixed electrode pair is arranged at a position opposed to the seesaw portion. In addition, four seesaw portions and the force receiving portions are coupled to one another by the hinge beams. As a result of this, similarly to the embodiment 1, since using the electric capacity scheme, the triaxial forces in the X direction, the Y direction, and the Z direction can be detected, and differential detection can be performed to all the axes, forces can be accurately detected in all the triple axes. In addition, since a microstructure as a comb is not needed, the structure is hard to break. Furthermore, a point on which a force acts can be specified by the force receiving portion, and detection accuracy improves.

In addition, the hinge beam that couples the force receiving portion and the seesaw portion has a structure to be able to bend and is twisted, and it extends vertically to a rotational axis of a torsion beam. As a result of this, displacement of the force receiving portion can be accurately transmitted to the seesaw portion, and destruction of each member due to force application can be prevented.

In addition, the force receiving portion has a centrosymmetry structure by being surrounded by the four seesaw portions, and the seesaw portions are orthogonally arranged. As a result of this, symmetrical deformation can be made according to a force, and the force can be accurately detected.

Hereinafter, an embodiment 3 will be explained with reference to the drawings. The embodiment is an example where the force sensor includes three seesaw portions with respect to the embodiment 2.FIG. 8Ais a top view of the force sensor100pertaining to the embodiment.FIG. 8Bis a cross-sectional side view taken along the line A-B of the force sensor100inFIG. 8A.

As shown inFIGS. 8A and 8B, the force sensor100according to the embodiment is provided with only the movable support portion10similarly to the embodiment 2. The movable support portion10is mainly provided with the seesaw portions30A to30C, the force receiving portion40, and the fixed electrode pairs50A to50C. The movable support portion10is provided with the first silicon layer11, the insulator film12, and the second silicon layer13. At the second silicon layer13, the force receiving portion40is formed in a center, and the three seesaw portions30A to30C are formed around the force receiving portion40. In order to form a symmetrical structure centering on the force receiving portion40, the seesaw portions30A to30C are arranged at an interval of 120 degrees centering on the force receiving portion40.

The force receiving portion40and the seesaw portions30A to30C are coupled to one another by the hinge beams33A to33C, respectively. Similarly to the embodiment 2, the force receiving portion40includes only the force receiving plate41, and is supported by the seesaw portions30A to30C by means of the hinge beams33A to33C. In order to equally transmit a force to the three seesaw portions30A to30C, the force receiving portion40is formed substantially in a triangular shape in a top view, and the hinge beams33A to33C are combined with each top portion of the triangle. The movable electrodes31A to31C of the seesaw portions30A to30C are fixed to the fixing portion15by the torsion beams32. Similarly to the embodiment 2, the fixing portion15is formed for each torsion beam32(for each seesaw portion).

The fixed electrode pairs50A to50C are formed on the main surface of the first silicon layer11. The fixed electrode pairs50A to50C include the fixed electrodes51A and52A,51B and52B, and51C and52C, respectively, and are arranged at positions corresponding to the movable electrodes31A to31C of the seesaw portions30A to30C.

An operating principle of the embodiment is similar to those of the embodiments 1 and 2. For example, when the force Fz is applied in the negative direction of the Z axis, according to displacement of the force receiving portion40, the inner ends of the seesaw portions30A to30C are displaced in the negative direction of the Z axis, and the outer ends of the seesaw portions30A to30C are displaced in the positive direction of the Z axis. In addition, when the force Fx is applied in the positive direction of the X axis, according to displacement of the force receiving portion40, the inner end of the seesaw portion30A is displaced in the positive direction of the Z axis, the inner end of the seesaw portion30C is displaced in the negative direction of the Z axis, and the seesaw portions30B is not displaced. In addition, when the force Fy is applied in the positive direction of the Y axis, according to displacement of the force receiving portion40, the inner ends of the seesaw portions30A and30C are displaced in the positive direction of the Z axis, and the inner end of the seesaw portion30B is displaced in the negative direction of the Z axis.

For this reason, in the embodiment, matrix operation is performed as in the following (Expression 5) to calculate a force in each direction.

As in (Expression 5), forces in the three directions are obtained by multiplying a differential (capacity difference) of three capacities by a transformation matrix. A coefficient used for operation is decided by positions (angles) where the seesaw portions30A to30C are arranged, and operation of the seesaw portions30A to30C according to orientation of an added force.

As described above, even when at least three seesaw portions are provided, similarly to the embodiments 1 and 2, triaxial forces can be detected, and differential detection can be performed to all the axes, and thus the forces can be accurately detected. In addition, since a microstructure as a comb is not needed, the structure is hard to break. Furthermore, a point on which a force acts can be specified by the force receiving portion, and detection accuracy improves.

Hereinafter, an embodiment 4 will be explained with reference to the drawings. The embodiment is an example where a diaphragm has been formed at a support substrate with respect to the force sensor of the embodiment 2.FIG. 9Ais a top view of the force sensor100pertaining to the embodiment.FIG. 9Bis a cross-sectional side view taken along the line A-B of the force sensor100inFIG. 9A.

As shown inFIGS. 9A and 9B, the force sensor100according to the embodiment is provided with only the movable support portion10. In order to apply a force from the first silicon layer side (back surface side), a force applying direction is opposite as compared with the embodiment 2.

The movable support portion10is mainly provided with the seesaw portions30A to30D, the force receiving portion40, the fixed electrode pairs50A to50D, and the diaphragm60. Similarly to the embodiment 1, the diaphragm60is formed in the center of the first silicon layer11. A force is applied to this diaphragm60.

In addition, the force receiving portion40is bonded to the diaphragm60(first silicon layer11) through the insulator film12. As a result of this, the force applied to the diaphragm60is transmitted to the force receiving portion40.

The other operation is similar to the embodiment 2. In addition, in order to apply a force to the diaphragm60, the force receiving portion and the main surface on the seesaw portion side may be sealed by the sealing portion20. An operating principle of the embodiment is similar to those of the embodiments 1 and 2.

As described above, in the embodiment, the diaphragm is formed at the first silicon layer with respect to a configuration of the embodiment 2. As a result of this, force application from a surface opposite to a seesaw portion fabricating surface can be performed in addition to the effect of the embodiment 2. Accordingly, there is no possibility that a force applying object comes into contact with machine structures, such as the seesaw portion, and a force can be transmitted even if the force receiving portion and the main surface on the seesaw portion side are implemented so as to be sealed.

Hereinafter, an embodiment 5 will be explained with reference to the drawings. The embodiment is an example where a projection has been formed with respect to the force sensor of the embodiments 2 and 4.

FIG. 10is one example of a cross-sectional side view of the force sensor100pertaining to the embodiment.FIG. 10is the example where the projection has been added to the force sensor ofFIG. 6Bof the embodiment 2. As shown inFIG. 10, in the embodiment, the projection61is formed on a force applying side (positive side of the Z axis) of the force receiving portion40. The projection61has the same substantially square shape as the force receiving portion40in a top view. A thickness (height) of the projection61is thicker than that of the second silicon layer13, and the projection61projects. Force detection sensitivity can be improved by forming the projection61thicker.

FIG. 11is an other example of a cross-sectional side view of the force sensor100pertaining to the embodiment.FIG. 11is the example where the projection has been added to the force sensor ofFIG. 9Bof the embodiment 4. As shown inFIG. 11, similarly to the embodiment 1, the projection61is formed on a force applying side (negative side of the Z axis) in the center of the diaphragm60. The projection61has the same substantially square shape as the force receiving portion40in a bottom view. A thickness (height) of the projection61is substantially the same as the first silicon layer11. Since the projection61is thicker than the diaphragm60and projects, force detection sensitivity improves. The projection61may be made thicker to further improve the force detection sensitivity.

As described above, in the embodiment, the projection connected to the force receiving portion is formed with respect to the embodiments 2 and 4. As a result of this, since a height of a surface of the force receiving portion can be increased in addition to effects of the embodiments 2 and 4, when the force sensor100receives the forces Fx and Fy, moment becomes larger, inclination of the force receiving portion is expanded, and thereby force sensitivity improves. In addition, since a force applying portion can be limited by the projection, a force can be accurately detected.

Hereinafter, an embodiment 6 will be explained with reference to the drawings. The embodiment is an example where the force sensor ofFIG. 11of the embodiment 5 is further provided with the sealing portion20.FIG. 12Ais a perspective view of a bottom surface of the force sensor100according to the embodiment in which a sealing substrate has been omitted.

FIG. 12Bis a cross-sectional side view taken along the line A-B of the force sensor100inFIG. 12A.

As shown inFIGS. 12A and 12B, the force sensor100according to the embodiment is provided with the movable support portion10and the sealing portion20similarly to the embodiment 1, and the movable support portion10and the sealing portion20are sealed and bonded by the bonding portion22.

The movable support portion10is mainly provided with the seesaw portions30A to30D, the force receiving portion40, the diaphragm60, and the projection61. The sealing portion20is mainly provided with the sealing substrate21and the fixed electrode pairs50A to50D. Similarly to the embodiment 1, the fixed electrode pairs50A to50D including the fixed electrodes51A to51D and52A to52D are formed on the main surface of the sealing substrate21. The fixed electrodes51A to51D and52A to52D each have a substantially rectangular shape in a top view. In addition, similarly to the embodiment 1, the penetrating electrodes14are formed in the periphery13aof the second silicon layer13.

As described above, in the embodiment, the force sensor100is provided with the sealing portion20with respect to the configurations of the embodiments 4 and 5, and the fixed electrode is formed on a sealing portion side. As a result of this, the force sensor can be sealed in addition to the effects of the embodiments 4 and 5, and mixing of dirt in the seesaw portion or the like, and breakage can be prevented. Deformation of the fixed electrode due to deformation of the support substrate can be prevented by fabricating the fixed electrode on the sealing substrate, and a force can be accurately detected. Since the fixed electrode is fabricated on the sealing substrate, the diaphragm on the support substrate side can be widely fabricated.

Hereinafter, an embodiment 7 will be explained with reference to the drawings. The embodiment is an example where a stopper has been formed at a force receiving portion with respect to the force sensor of the embodiment 6.FIG. 13Ais a perspective view of the bottom surface of the force sensor100according to the embodiment in which a sealing substrate has been omitted, andFIG. 13Bis an enlarged view thereof.FIG. 13Cis a cross-sectional side view taken along the line A-B of the force sensor100inFIG. 13A.

As shown inFIGS. 13A to 13C, the force sensor100according to the embodiment is provided with the movable support portion10and the sealing portion20similarly to the embodiment 1, and the movable support portion10and the sealing portion20are sealed and bonded by the bonding portion22. The movable support portion10is mainly provided with the seesaw portions30A to30D, the force receiving portion40, the diaphragm60, and the projection61.

The force receiving portion40has the force receiving plate41and the stopper42similarly to the embodiment 1. The stopper42is formed substantially in an L shape at each of corner portions (four corners) around the force receiving plate41so as to extend the force receiving plate41. It can be also said that the stopper42extends auricularly or pinnately around the force receiving plate41. When a position of the force receiving portion40is inclined and displaced, the stopper42comes into contact with the sealing portion20side, and stops displacement of the seesaw portion30.

In addition, instead ofFIG. 13C, as shown inFIG. 13D, a dummy electrode53may be formed at a position opposed to the force receiving portion40on the main surface of the sealing substrate21. The dummy electrode53has substantially the same size as the force receiving portion40including the stopper42, and is formed as a substantially square shape in a top view. The dummy electrode53has the same potential as the force receiving portion40. A thickness of the dummy electrode53is substantially the same as those of the fixed electrodes51and52.

When the force Fx (or the force Fy) is applied, there is a fear that a tip of the seesaw portion30comes into contact with the fixed electrodes51and52, and electrically shorts out. Consequently, since in the embodiment, the stopper42is formed at the force receiving portion40as shown inFIG. 14, at the time of overload application, the stopper42comes into contact with the sealing substrate21(an insulator) or the dummy electrode53(the same potential electrode), before the tip of the seesaw portion30comes into contact with the fixed electrodes51and52. As a result of this, since the seesaw portion30does not come into contact with the fixed electrodes51and52, electrical short can be prevented. A contact partner on a sealing portion side of the stopper42is desirably the one without a potential difference with the stopper42, or an insulator. As a result of this, short of a stopper portion can also be prevented.

In addition, as shown in the enlarged view ofFIG. 13B, the movable electrode31of the seesaw portion30has a concave portion in which an inner end of the movable electrode31hollows toward the rotational axis35, and the hinge beam33is coupled to a hollow of the concave portion. The movable electrode31has a symmetrical structure centering on the rotational axis35, and has the same concave portion also in the outside thereof. Furthermore, the fixed electrodes51and52also have the same shape as the movable electrode31, and they have a concave portion in the inside and the outside thereof. As a result of this, since capacities of the outer fixed electrode51and the inner fixed electrode52are matched, sensitivity becomes the same, and accuracy of differential detection improves.

As described above, in the embodiment, the stopper is formed at the force receiving portion in addition to the configuration of the embodiment 6. As a result of this, since contact of the seesaw portion and the fixed electrode is suppressed, electrical short can be prevented.

In addition, the movable electrode of the seesaw portion30hollows toward the rotational axis, and the hinge beam is connected to this hollow. Since a rotational angle of the seesaw portion becomes large by connecting the hinge beam near the rotational axis of the seesaw portion, detection sensitivity improves.

In addition, since the hinge beam can be formed to be long, rotational rigidity of the hinge beam becomes low, and the force receiving portion is easy to rotate. As shown inFIG. 5A, since the hinge beam arranged in the X-axis direction is twisted around the X axis at the time of the force sensor100receiving the force Fy, the force receiving portion is easy to rotate, and sensitivity improves. In addition, simultaneously, since the seesaw portion arranged in the X-axis direction is not displaced, cross talk can be suppressed.

In addition, the hinge beam is likely to deform by lengthening the hinge beam. Accordingly, stress concentration at the time of deformation of the hinge beam can be prevented, and destruction of the hinge beam can be prevented.

Hereinafter, an embodiment 8 will be explained with reference to the drawings. The embodiment is an example where a force sensor that detects biaxial forces by two seesaw portions with respect to the embodiment 2. A biaxial force sensor, for example, can detect forces in the X direction and the Z direction.FIG. 15Ais a top view of the force sensor100pertaining to the embodiment.FIG. 15Bis a cross-sectional side view taken along the line A-B of the force sensor100inFIG. 15A.

As shown inFIGS. 15A and 15B, the force sensor100according to the embodiment is provided with only the movable support portion10similarly to the embodiment 2. The movable support portion10is mainly provided with the seesaw portions30A and30B, the force receiving portion40, and the fixed electrode pairs50A and50B. The movable support portion10is provided with the first silicon layer11, the insulator film12, and the second silicon layer13. At the second silicon layer13, the force receiving portion40is formed in a center, and the two seesaw portions30A and30B are formed around the force receiving portion40. In this example, the seesaw portions30A and30B are formed on both sides in the X direction.

The force receiving portion40and the seesaw portions30A and30B are coupled to each other by the hinge beams33A and33B, respectively. Similarly to the embodiment 2, the force receiving portion40includes only the force receiving plate41, and is supported by the seesaw portions30A and30B by means of the hinge beams33A and33B.

The movable electrodes31A and31B of the seesaw portions30A and30B are fixed to the fixing portion15by the torsion beams32A and32B. In the example ofFIG. 15A, the fixing portion15is formed for each torsion beam32(for each seesaw portion). It is to be noted that the fixing portion15may be formed as one continuously from the torsion beams32A to32B as inFIG. 16.

In addition, the fixed electrode pairs50A and50B are formed on the main surface of the first silicon layer11. The fixed electrode pairs50A and50B include the fixed electrodes51A and52A, and51B and52B, respectively, and are arranged at positions corresponding to the movable electrodes31A and31B of the seesaw portions30A and30B.

An operating principle of the embodiment is similar to those of the embodiments 1 and 2. While the triaxial forces are detected in the embodiments 1 and 2, the biaxial forces in the Z direction and the X direction can be detected in the embodiment.

For example, when the force Fz is applied in the negative direction of the Z axis, according to displacement of the force receiving portion40, the inner ends of the seesaw portions30A and30B are displaced in the negative direction of the Z axis, and the outer ends of the seesaw portions30A and30B are displaced in the positive direction of the Z axis. Namely, when the force Fz is applied in the Z direction (an Fz mode), the seesaw portion30A and30B rotate in opposite directions.

In addition, when the force Fx is applied in the positive direction of the X axis, according to displacement of the force receiving portion40, the inner end of the seesaw portion30A is displaced in the positive direction of the Z axis, and the inner end of the seesaw portion30B is displaced in the negative direction of the Z axis. Namely, when the force Fx is applied in the X direction (an Fx mode), the seesaw portion30A and30B rotate in the same direction.

For this reason, in the embodiment, matrix operation is performed as in the following (Expression 6), and a force in each direction is calculated.

As in (Expression 6), forces in the two directions are obtained by multiplying a differential (capacity difference) of two capacities by a transformation matrix. Since the forces Fz and Fx are both detected by two seesaw portions, and thus have the same sensitivity, both forces have the same coefficient.

As described above, even when at least two seesaw portions are provided, biaxial forces can be detected, differential detection can be performed to all the axes, and thus a force can be accurately detected. In addition, since a microstructure as a comb is not needed, the structure is hard to break. Furthermore, a point on which a force acts can be specified by the force receiving portion, and detection accuracy improves.

Hereinafter, an embodiment 9 will be explained with reference to the drawings. The embodiment is an example where displacement of a movable portion is detected by an optical scheme with respect to the embodiment 8.FIG. 17Ais a top view of the force sensor100pertaining to the embodiment.FIG. 17Bis a cross-sectional side view taken along the line A-B of the force sensor100inFIG. 17A.

As shown inFIGS. 17A and 17B, the force sensor100according to the embodiment is provided with only the movable support portion10similarly to the embodiment 8. The movable support portion10is mainly provided with the seesaw portions30A and30B and the force receiving portion40, and is not provided with a fixed electrode.

In the embodiment, the force sensor100is provided with optical distance measuring devices70ato70dinstead of the fixed electrode. In the example ofFIG. 17B, the optical distance measuring devices70ato70dare arranged above the seesaw portions30A and30B. Two of the optical distance measuring devices70ato70dare arranged for each seesaw portion30similarly to the fixed electrode. The optical distance measuring devices70ato70dare a laser displacement meter, an interference measure, and the like, and they measures a distance L to the seesaw portion30by irradiating light to the seesaw portion30, and receiving reflected light.

In addition, the force sensor100can be configured asFIG. 17Cas an other example where a force is detected by the optical scheme. InFIG. 17C, light emitting diodes71aand71b, and photodiodes72ato72dare arranged on the main surface of the first silicon layer11instead of fixed electrodes. The light emitting diodes71aand71bare arranged at positions opposed to the rotational axes35A and35B of the seesaw portions30A and30B. The photodiodes72ato72dare arranged at positions opposed to both ends of the seesaw portions30A and30B.

Distances L to both ends of the seesaw portion30A are set as A1and A2, and distances L to both ends of the seesaw portion30B as B1and B2. In addition, displacement of a distance sets as ΔL. Outputs of the photodiodes72ato72d(optical distance measuring devices70ato70d) are A1=A2, and B1=B2at the time of ΔL=0. The photodiodes72ato72dare arranged at light reflection positions where the outputs decrease at the time of distance L+ΔL, and where the outputs increase at the time of distance L−ΔL.

The embodiment is an example where a distance is measured instead of an electric capacity, and an operating principle is similar to the other embodiments. Namely, since the seesaw portion30rotates and is displaced by force application, a distance between the seesaw portion30and the optical distance measuring device70(photodiode72) changes.

In the example ofFIG. 17B, since a time until reflected light returns from the seesaw portion30A decreases, the optical distance measuring device70adetects a distance (L−ΔL). Since a time until reflected light returns from the seesaw portion30A increases, the optical distance measuring device70bdetects a distance (L+ΔL). Since a time until reflected light returns from the seesaw portion30B increases, the optical distance measuring device70cdetects a distance (L+ΔL). Since a time until reflected light returns from the seesaw portion30B decreases, the optical distance measuring device70cdetects the distance (L−ΔL).

In addition, in the example ofFIG. 17C, since a reflected light amount from the seesaw portion30A decreases, the photodiode72adetects the distance (L+ΔL). Since a reflected light amount from the seesaw portion30A increases, the photodiode72bdetects the distance (L−ΔL). Since a reflected light amount from the seesaw portion30B increases, the photodiode72cdetects the distance (L−ΔL). Since a reflected light amount from the seesaw portion30B decreases, the photodiode72ddetects the distance (L+ΔL).

For this reason, similarly to an electric capacity, a distance differential 2ΔL=(L+ΔL)−(L−ΔL) is calculated, and a force is detected. Also in the optical scheme, matrix operation of (Expression 6) in the case of the biaxial force sensor is performed, matrix operation of (Expression 4) and (Expression 5) is performed in the case of the triaxial force sensor, and thereby a force of each axis can be detected.

As described above, it is also possible to configure the force sensor100as the force sensor of the optical scheme instead of the electric capacity scheme. Even in the case, differential detection can be performed by plural axes similarly to the embodiments 2, 8, and the like, and thus a force can be accurately detected. In addition, the force sensor100can be made to have a structure hard to break down by the seesaw portions, and detection accuracy can be improved by the force receiving portion. It is to be noted that displacement of the seesaw portion may be detected by a magnetic scheme in addition to the optical scheme.

Hereinafter, an embodiment 10 will be explained with reference to the drawings. The embodiment is an example where a force receiving portion has been arranged in a periphery with respect to the force sensor of the embodiment 2.FIG. 18Ais a top view of the force sensor100pertaining to the embodiment.FIG. 18Bis a cross-sectional side view taken along the line A-B of the force sensor100inFIG. 18A.

As shown inFIGS. 18A and 18B, the force sensor100according to the embodiment is provided with only the movable support portion10. The movable support portion10is mainly provided with the seesaw portions30A to30D, the force receiving portion40, and the fixed electrode pairs50A to50D.

The movable support portion10is provided with the first silicon layer11, the insulator film12, and the second silicon layer13. The four seesaw portions30A to30D are formed at the second silicon layer13similarly to the embodiment 2. The force receiving portion is not formed in a center portion surrounded by the seesaw portions30A to30D.

The movable electrodes31A to31D of the seesaw portions30A to30D are fixed to the fixing portion15by the torsion beams32A to32D. In the embodiment, the fixing portion15is formed so as to be coupled to the two torsion beams32(seesaw portions). The fixing portion15has a substantially square shape in a top view, the torsion beam32is coupled to a center portion of a first side of the square, and an other torsion beam32is coupled to a center portion of a second side in contact with the first side.

The fixed electrode pairs50A to50D are formed on a main surface of the first silicon layer11. The fixed electrode pairs50A to50D include the fixed electrodes51A and52A,51B and52B, and51C and52C,51D and52D, respectively, and are arranged at positions corresponding to the movable electrodes31A to31D of the seesaw portions30A to30D.

In the embodiment, the force receiving portion40is formed in a periphery of the movable support portion10, i.e., outside the seesaw portions30A to30D so as to surround the seesaw portions30A to30D. The force receiving portion40includes the force receiving plate41, and is formed in a quadrangular shape including four side portions. Each side portion of the force receiving portion40and the seesaw portions30A to30D are coupled to one another by the hinge beams33A to33D, respectively. The hinge beams33A to33D are coupled to a substantially center portion of each side portion of the force receiving portion40. Since not bonded to the first silicon layer11, the force receiving portion40is supported by the seesaw portions30A to30D by means of the hinge beams33A to33D.

An operating principle of the embodiment is similar to those of the embodiments 1 and 2. For example, when the force Fz is applied in the negative direction of the Z axis, according to displacement of the force receiving portion40, the outer ends of the seesaw portions30A to30D are displaced in the negative direction of the Z axis, and the inner ends of the seesaw portions30A to30D are displaced in the positive direction of the Z axis. Although rotational directions of the seesaw portions30A to30D are opposite to those in the embodiments 1 and 2, when the force Fz is applied in the Z direction (an Fz mode), the seesaw portions30A and30C, and the seesaw portions30B and30D mutually rotate in opposite directions.

In addition, when the force Fx is applied in the positive direction of the X axis, the hinge beams33D and33B are twisted, and thereby the force receiving portion40effectively rotates and is displaced, with the hinge beams33D and33B being as axes. According to this displacement of the force receiving portion40, the outer end of the seesaw portion30A is displaced in the positive direction of the Z axis, and the outer end of the seesaw portion30C is displaced in the negative direction of the Z axis. In this case, the seesaw portions30B and30D are not displaced similarly to the embodiments 1 and 2. Although rotational directions of the seesaw portions30A and30C are opposite to those in the embodiments 1 and 2, when the force Fx is applied in the X direction (an Fx mode), the seesaw portions30A and30C rotate in the same direction.

Furthermore, when the force Fy is applied in the positive direction of the Y axis, the hinge beams33A and33C are twisted, and thereby the force receiving portion40effectively rotates and is displaced, with the hinge beams33A and33C being as axes. According to this displacement of the force receiving portion40, the outer end of the seesaw portion30B is displaced in the positive direction of the Z axis, and the outer end of the seesaw portion30D is displaced in the negative direction of the Z axis. In this case, the seesaw portions30A and30C are not displaced similarly to the embodiments 1 and 2. Although rotational directions of the seesaw portions30B and30D are opposite to those in the embodiments 1 and 2, when the force Fy is applied in the Y direction (an Fx mode), the seesaw portions30B and30D rotate in the same direction.

In the embodiment, since the rotational direction of the seesaw portion30is opposite to force application as compared with the embodiments 1 and 2, a symbol is changed in the matrix operation of (Expression 1), and thereby a force in each direction can be obtained similarly to the embodiments 1 and 2.

As described above, the force receiving portion is formed in the periphery with respect to the configuration of the embodiment 2. Even in the case, similarly to the embodiment 2, triaxial forces can be detected, differential detection can be performed to all the axes, and thus a force can be accurately detected. In addition, since a microstructure as a comb is not needed, the structure is hard to break.

Hereinafter, an embodiment 11 will be explained with reference to the drawings. The embodiment is an example where the configurations of the embodiments 5 and 6 have been applied to an acceleration sensor that detects an acceleration, which is one of dynamic quantity.

FIG. 19Ais a top view of an acceleration sensor101pertaining to the embodiment.FIG. 19Bis a cross-sectional side view taken along a line A-B of the acceleration sensor101inFIG. 19A.FIG. 19Bis an example where the acceleration sensor101is provided with a mass body62instead of the projection61in the configuration ofFIG. 10of the embodiment 5.

As shown inFIGS. 19A and 19B, the mass body62is formed on a force applying side (positive side of the Z axis) of the force receiving portion40. The mass body62has the same substantially square shape as the force receiving portion40in a top view. A thickness (height) of the mass body62is thicker than that of the second silicon layer13, and the mass body62projects. The mass body62is the member whose mass is heavier than that of the projection and, for example, includes Au or the like.

FIG. 20Ais a top view of the acceleration sensor101pertaining to the embodiment.FIG. 20Bis a cross-sectional side view taken along the line A-B of the acceleration sensor101inFIG. 20A.FIGS. 20A and 20Bare examples where the acceleration sensor101is provided with the mass body62instead of the projection61in the configuration ofFIGS. 12A and 12Bof the embodiment 6.

As shown inFIGS. 20A and 20B, the mass body62is formed on a force applying side (positive side of the Z axis) of the center of the diaphragm60. The mass body62has the same substantially square shape as the force receiving portion40in a top view, and a thickness (height) of the mass body62is substantially the same as the first silicon layer11.

As described above, the mass body (large mass body) is used for a projection of the force sensor, thereby an inertial force can be received by the force receiving portion, and the acceleration sensor that detects an acceleration can be configured. When the acceleration sensor receives an acceleration Az, the mass body translates in the Z direction. When the acceleration sensor receives an acceleration Ax (Ay), a force acts on the mass body by the inertial force, and thus this force is detected by a principle similar to the other embodiments. As a result of this, triaxial acceleration detection can be performed.

Accordingly, similarly to the embodiments 5 and 6, triaxial accelerations can be detected, differential detection can be performed to all the axes, and thus an acceleration can be accurately detected. In addition, since a microstructure as a comb is not needed, the structure is hard to break.

Hereinafter, an embodiment 12 will be explained with reference to the drawings. In the embodiment, an example of a force detection circuit that detects a force using the force sensor of the embodiment 1 will be explained.

FIGS. 21,22A, and22B are one example of connection of the force detection circuit and the force sensor, and are the example using a charge amplifier and a difference circuit (differential circuit). The force detection circuit is connected to the force sensor100of the embodiment 1, and is provided with differential operation circuits201to204, and a matrix operation circuit300. It can be also said that a force sensor system is provided with the force sensor100, the differential operation circuits201to204, and the matrix operation circuit300. In this example, capacity change between electrodes can be taken out as a voltage output, and a force can be detected with high accuracy.

It is to be noted that here, capacities of the seesaw portion30A is set as CA1and CA2, capacities of the seesaw portion30B as CB1and CB2, capacities of the seesaw portion30C as CC1and CC2, and capacities of the seesaw portion30D as CD1and CD2.

The differential operation circuits201to204are provided for each seesaw portion30(fixed electrode pair50). The differential operation circuit201is connected to the capacities CA1and CA2, and outputs a differential voltage VAindicating a capacity difference between the capacities CA1and CA2. The differential operation circuit202is connected to the capacities CB1and CB2, and outputs a differential voltage VBindicating a capacity difference between the capacities CB1and CB2. The differential operation circuit203is connected to the capacities CC1and CC2, and outputs a differential voltage VCindicating a capacity difference between the capacities CC1and CC2. The differential operation circuit204is connected to the capacities CD1and CD2, and outputs a differential voltage VDindicating a capacity difference between the capacities CD1and CD2.

Since the differential operation circuits201to204have the same circuit configuration, only the configuration of the differential operation circuit201will be explained. The differential operation circuit201is provided with charge amplifiers210aand210b, and a differential amplifier220. The charge amplifier210aconverts the capacity of the capacity CA1into a voltage VA1, and outputs it. The charge amplifier210ais provided with an operational amplifier OPAA1, a resistor211a, and a capacitor212a.

An alternating-current power supply230is connected to the movable electrode31A of the seesaw portion30A through metal of the bonding portion22, and the second silicon layer13, and the fixed electrode51A is connected to an inverting input terminal of the operational amplifier OPAA1. Namely, one end of the capacity CA1between the movable electrode31A of the seesaw portion30A and the fixed electrode51A is connected to the alternating-current power supply230, and the other end thereof is connected to the inverting input terminal of the operational amplifier OPAA1. A non-inverting input terminal (+) of the operational amplifier OPAA1is connected to a GND. The resistor211aand the capacitor212aare connected in parallel between the inverting input terminal and an output terminal of the operational amplifier OPAA1.

Given that an input voltage of the operational amplifier OPAA1is V0, and a capacity of the capacitor212ais Cf, an output voltage VA1of the operational amplifier OPAA1is obtained by the following (Expression 7). Namely, the voltage VA1according to the capacity of the capacity CA1is output.

The charge amplifier210bconverts the capacity of the capacity CA2into a voltage VA2, and outputs it. The charge amplifier210bis provided with an operational amplifier OPAA2, a resistor211b, and a capacitor212b.

The alternating-current power supply230is connected to the movable electrode31A of the seesaw portion30A through the metal of the bonding portion22, and the second silicon layer13, and the fixed electrode52A is connected to an inverting input terminal of the operational amplifier OPAA2. Namely, one end of the capacity CA2between the movable electrode31A of the seesaw portion30A and the fixed electrode52A is connected to the alternating-current power supply230, and the other end thereof is connected to the inverting input terminal of the operational amplifier OPAA2. A non-inverting input terminal (+) of the operational amplifier OPAA2is connected to the GND. The resistor211band the capacitor212bare connected in parallel between the inverting input terminal and an output terminal of the operational amplifier OPAA2.

The differential amplifier220outputs the differential voltage VAof the voltages VA1and VA2output from the charge amplifiers210aand210b. The differential amplifier220is provided with an operational amplifier221, and resistors222to225.

The resistor222is connected between the output terminal of the operational amplifier OPAA1and an inverting input terminal of the operational amplifier221. The resistor223is connected between the output terminal of the operational amplifier OPAA2and a non-inverting input terminal of the operational amplifier221. Furthermore, the non-inverting input terminal of the operational amplifier221is connected to the GND through the resistor225. The resistor224is connected between the inverting input terminal and an output terminal of the operational amplifier221.

The output voltage VAof the operational amplifier221is obtained by the following (Expression 8). Namely, according to a ratio of resistors R1and R2, a differential voltage obtained by deducting the voltage VA2from the voltage VA1is output.

The matrix operation circuit300includes a logic circuit and the like, and performs matrix operation using differential voltages VAto VDthat the differential operation circuits201to204have generated. The matrix operation circuit300performs operation of the following (Expression 9). Namely, the differential voltages VAto VDare multiplied by a transformation matrix of (Expression 9), and Fx, Fy, and Fz are calculated.

FIGS. 23,24A, and24B are one examples of connection of a force detection circuit and a force sensor, and are the example employing a switched capacitor scheme. The force detection circuit is connected to the force sensor100of the embodiment 1, and is provided with differential operation circuits401to404, and the matrix operation circuit300. It can be also said that a force sensor system is provided with the force sensor100, the differential operation circuits401to404, and the matrix operation circuit300. This example is adapted for an IC since a detection circuit can be configured with a digital signal processing circuit, and is suitable for a case of being incorporated in an LSI of the sealing substrate21.

The differential operation circuits401to404are provided for each seesaw portion30(fixed electrode pair50). The differential operation circuit401is connected to the capacities CA1and CA2, and outputs the differential voltage VAindicating the capacity difference between the capacities CA1and CA2. The differential operation circuit402is connected to the capacities CB1and CB2, and outputs the differential voltage VBindicating the capacity difference between the capacities CB1and CB2. The differential operation circuit403is connected to the capacities CC1and CC2, and outputs the differential voltage VCindicating the capacity difference between the capacities CC1and CC2. The differential operation circuit404is connected to the capacities CD1and CD2, and outputs the differential voltage VDindicating the capacity difference between the capacities CD1and CD2.

Since the differential operation circuits401to404have the same circuit configuration, only the configuration of the differential operation circuit401will be explained. The differential operation circuit401is provided with a switching circuit410and a charge amplifier420. The switching circuit410switches charge/discharge of the capacities CA1and CA2, and outputs the capacity difference between the capacities CA1and CA2.

The switching circuit410is provided with switches411to416. The switches411and412are connected in series between a power supply Vd and a power supply −Vd, and the switches413and414are also connected in series between the power supply Vd and the power supply −Vd. A GND is connected to the movable electrode31A of the seesaw portion30A through metal of the bonding portion22, and the second silicon layer13, and the fixed electrode51A is connected to a node410abetween the switches411and412. Namely, one of the capacity CA1between the movable electrode31of the seesaw portion30A and the fixed electrode51A is connected to the GND, and the other end thereof is connected to the node410a.

The GND is connected to the movable electrode31A of the seesaw portion30A through metal of the bonding portion22, and the second silicon layer13, and the fixed electrode52A is connected to a node410bbetween the switches413and414. Namely, one of the capacity CA2between the movable electrode31of the seesaw portion30A and the fixed electrode51B is connected to the GND, and the other end thereof is connected to the node410b. Since the first silicon layer11and the second silicon layer13have the same potential, i.e., serve as the GND, the force sensor100is not easily affected by disturbance from outside. For this reason, the force sensor of the embodiment can be configured as the sensor with small noise. The switch415is connected between the node410aand a node410c, and the switch416is connected between the node410band the node410c.

For example, the switch411is turned on, the switch412is turned off, and the power supply Vd is applied to the capacity CA1to be charged. The switch413is turned off, the switch414is turned on, and the power supply −Vd is applied to the capacity CA2to be charged. When the switches415and416are turned on in a state where the capacities CA1and CA2have been charged, a charge corresponding to a capacity obtained by deducting the capacity CA2from the capacity CA1is output to the node410c.

The charge amplifier420inputs a charge according to a capacity difference between the capacities CA1and CA2that the switching circuit410has generated, and outputs the differential voltage VA. The charge amplifier420is provided with an operational amplifier421, a resistor422, a capacitor423, and a switch424. The resistor422is connected to the node410cand an inverting input terminal of the operational amplifier421. The capacitor423and the switch424are connected between the inverting input terminal and an output terminal of the operational amplifier421. A non-inverting input terminal of the operational amplifier421is connected to a GND.

The matrix operation circuit300, similarly toFIG. 21, performs matrix operation by (Expression 9) using the differential voltages VAto VDthat the differential operation circuits401to404have generated, and calculates a force in each direction.

As described above, in the embodiment 1 and the other embodiments, the detection circuit as in the embodiment is used, thereby matrix operation is performed based on a differential detection result of the force sensor, and a force can be accurately detected.

It is to be noted that the present invention is not limited to the above-described embodiments, and that appropriate change can be made without departing from the spirit of the invention.