JP2006215478A - Electrostatic driving element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrostatic driving element which detects the deformation of a movable part with high sensitivity and high accuracy. <P>SOLUTION: The electrostatic driving element 200 is composed of a movable electrode unit 200A, a fixed electrode unit 200B and a bump 210 which connects them with a distance between them. The movable electrode unit 200A has a supporting frame 202, a movable plate 203 which serves as a movable electrode itself and a bending spring 204 which supports the movable plate 203 allowing it to move straight. The fixed electrode unit 200B has a supporting substrate 201 and a fixed electrode 205 provided on the supporting substrate 201. The supporting substrate 201 has a decreased thickness portion 207 in a part of the region where the fixed electrode 205 is located, so that a part of the fixed electrode 205 is deformed by electrostatic suction force acting between the fixed electrode 205 and the movable plate 203. Further, the fixed electrode unit 200B has a displaced quantity detection element which detects the displaced quantity of the portion of the fixed electrode 205 which is located at the decreased thickness portion 207. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an electrostatic drive element.

  The electrostatic drive element includes a movable part that can be at least partially elastically deformed, a movable electrode provided in the movable part, and a fixed electrode that is spaced from the movable part. The movable portion is driven by being deformed by an electrostatic attractive force acting between the electrodes. A movable part is comprised from the needle | mover provided with the movable electrode, and the elastic member which supports the needle | mover so that displacement is possible, for example.

  Conventionally, as a method of detecting the deformation of the elastic portion of the electrostatic drive element, for example, the position of the mover, a method of detecting the electrostatic capacitance between the mover and the fixed electrode disposed opposite to the mover, or supporting the mover There is a method of monitoring the deformation amount of the elastic member.

  A method for detecting the position of the mover based on the capacitance between the movable electrode and the fixed electrode is disclosed in, for example, Japanese Patent Application Laid-Open No. 7-141457. FIG. 22 schematically shows a configuration for detecting the position of the mover based on the capacitance between the fixed electrode and the movable electrode by the same method as in Japanese Patent Laid-Open No. 7-141457. In FIG. 22, the electrostatic drive element includes a substrate 101, a movable plate 102 as a mover, an elastic member 103 that supports the movable plate 102 with respect to the substrate 101, a fixed electrode 104 provided on the substrate 101, The movable electrode 102 is provided with a movable electrode 105 provided on the movable plate 102. The fixed electrode 104 and the movable electrode 105 have substantially the same shape, and a capacitance measuring device 106 is connected between the fixed electrode 104 and the movable electrode 105.

ここで、ε。は真空の誘電率、Ｓは固定電極１０４および可動電極１０５の面積である。すなわち、容量測定装置１０６によって測定される電極間の静電容量から、（１）式によって可動板１０２の位置を知ることができる。 In the configuration shown in FIG. 22, the position of the mover is detected as follows. First, when a DC power source 107 is connected between the fixed electrode 104 and the movable electrode 105 and a voltage is applied, an electrostatic attractive force is generated between these electrodes, so that the movable plate 102 is drawn toward the fixed electrode 104. The movable plate 102 stops at a position where the electrostatic attractive force balances with the elastic repulsive force of the elastic member 103. The position of the movable plate 102 in this state, that is, the distance d between the movable plate 102 and the substrate 101 is expressed by the following equation by the capacitance C between the fixed electrode 104 and the movable electrode 105.

Where ε. Is the dielectric constant of vacuum, and S is the area of the fixed electrode 104 and the movable electrode 105. That is, the position of the movable plate 102 can be known from the electrostatic capacitance between the electrodes measured by the capacitance measuring device 106 by the equation (1).

  On the other hand, a configuration for detecting the position of the mover based on the deformation amount of the elastic member is disclosed in, for example, Japanese Patent Application Laid-Open No. 11-242180. Japanese Patent Laid-Open No. 11-242180 relates to an electromagnetically driven element, but the same configuration can be applied to an electrostatically driven element. FIG. 23 schematically shows a configuration for detecting the position of the mover based on the deformation amount of the elastic member by the same method as in Japanese Patent Laid-Open No. 11-242180. FIG. 24 is a plan view of the peripheral portion of the elastic member shown in FIG. In FIG. 22, the electrostatic drive element includes a substrate 151, a movable plate 152 as a mover, an elastic member 153 that supports the movable plate 152, a fixed electrode 154 provided on the substrate 151, and the movable plate 102. The strain gauge 111 is formed on the surface or inside of the elastic member 153.

In the configuration shown in FIGS. 23 and 24, the position of the mover is detected as follows. First, by applying a voltage between the fixed electrode 154 and the movable electrode 155, the movable plate 152 is displaced in the same manner as the electrostatic driving element of FIG. At this time, the strain gauge 111 is also deformed in accordance with the deformation of the elastic member 153. Since the resistance value of the strain gauge 111 changes depending on the amount of deformation, the resistance value of the strain gauge 111 changes according to the position of the movable plate 152. Therefore, by monitoring the resistance value of the strain gauge 111, the position of the movable plate 152 can be known.
JP-A-7-141457 Japanese Patent Laid-Open No. 11-242180

  Generally, an electrostatic drive element often requires a very high drive voltage. However, in the method of detecting the capacitance between electrodes as shown in FIG. 22, the electrodes are applied with a high voltage applied between the electrodes. Therefore, it is difficult to design the circuit of the capacitance measuring device 106. The capacitance between the electrodes is generally very small. Further, as can be seen from the equation (1), the capacitance C is proportional to the electrode area S and inversely proportional to the electrode interval d. Sufficient sensitivity cannot be secured with an element having a large electrode interval, in other words, a large stroke.

  Further, the method of detecting the position of the mover based on the deformation amount of the elastic member has a large error because the distance between the electrodes is not directly detected. Also, the elastic member supporting the mover is generally designed to be very thin in order to ensure the driving efficiency of the element, and it is very difficult to form a strain gauge on the surface or inside of the elastic member. is there.

  The present invention has been made in consideration of such a situation, and an object thereof is to provide an electrostatic driving element capable of detecting deformation of a movable part with high sensitivity and high accuracy. .

  The present invention is directed to an electrostatic drive element. An electrostatic drive element according to the present invention is located at a distance from a movable part that can be elastically deformed at least partially, a support that supports the movable part, a movable electrode provided on the movable part, and the movable part. And a detection means for detecting deformation of the movable part due to electrostatic attraction acting between the fixed electrode and the movable electrode. The detection means is provided on the substrate. It has been.

  ADVANTAGE OF THE INVENTION According to this invention, the electrostatic drive element which can detect the deformation | transformation of a movable part with high sensitivity and high precision is provided.

  As an electrostatic drive element, for example, there is a type in which the movable portion is composed of a movable element provided with a movable electrode and an elastic member that supports the movable element so that the movable element can be displaced. There is a type in which the mover moves linearly and a type in which the mover rotates. As another type, there is a type in which the movable part is formed of an elastic deformation film provided with a movable electrode, and the movable part itself is deformed. Hereinafter, application examples of the present invention to these elements will be described as embodiments.

[First embodiment]
The present embodiment is directed to a direct-acting electrostatic drive element that is a type of electrostatic drive element in which the movable portion includes a mover and an elastic member, and the mover moves linearly. FIG. 1 is a perspective view showing a direct acting electrostatic drive element according to a first embodiment of the present invention. FIG. 2 is a sectional view of the direct acting electrostatic drive element taken along line II-II shown in FIG.

  As shown in FIGS. 1 and 2, the direct acting electrostatic drive element 200 according to the present embodiment includes a movable electrode unit 200A, a fixed electrode unit 200B, and bumps 210 that are coupled to each other with a gap therebetween. It is composed of

  The movable electrode unit 200A has a movable part that can be elastically deformed at least partially, and a support frame 202 that supports the movable part. The movable part includes a movable plate 203 as a mover, and a movable plate 203. And an elastic member that supports the movable plate 203 so that the movable plate 203 can be moved linearly. The movable plate 203, the support frame 202, and the flexible spring 204 are made of silicon. The movable plate 203 itself constitutes a movable electrode.

  The fixed electrode unit 200 </ b> B includes a support substrate 201 and a fixed electrode 205 provided on the support substrate 201. The thickness of the support substrate 201 is reduced to a part of the region where the fixed electrode 205 is positioned so that the part of the fixed electrode 205 is displaced according to the electrostatic attractive force acting between the fixed electrode 205 and the movable plate 203. The reduced thickness portion 207 is provided.

  The support substrate 201 is made of a semiconductor substrate, for example, but not limited to, a single crystal silicon substrate. The thickness reducing unit 207 is formed of a thin film of single crystal silicon, for example. Hereinafter, the thickness reducing portion 207 is also referred to as a silicon film portion.

  FIG. 3 is an enlarged view of the peripheral portion of the thickness reducing portion, that is, the silicon film-like portion shown in FIG. As shown in FIG. 3, a silicon oxide film 235 is provided between the support substrate 201 and the fixed electrode 205 to insulate them.

  The fixed electrode unit 200 </ b> B further includes a displacement amount detection element 231 that detects the displacement amount of the portion of the fixed electrode 205 located in the thickness reduction unit 207. The displacement amount detection element 231 includes a part of the fixed electrode 205, a silicon oxide film 235, a silicon film-like portion 207, and a strain gauge 232. The strain gauge 232 is provided on the fixed electrode 205 via the silicon oxide film 235, and a part of the strain gauge 232 is located in the thickness reducing unit 207. The strain gauge 232 is formed in the support substrate 201 and has a conductivity type different from that of the silicon film portion 207.

  FIG. 4 is a plan view schematically showing the strain gauge shown in FIG. As shown in FIG. 4, the strain gauge 232 has four impurity diffusion layers 211, 212, 213, and 214 having the same shape. The four impurity diffusion layers 211, 212, 213, and 214 are electrically connected via terminals 221, 222, 223, and 224 to form a bridge circuit. In FIG. 4, wiring extending from the fixed electrode 205 and the terminals 221 to 224 is omitted.

  The impurity diffusion layer 211 is partially located in the thickness reduction unit 207, and the other three impurity diffusion layers 212, 213, and 214 are located outside the thickness reduction unit 207. For this reason, only the resistance of the impurity diffusion layer 211 changes when the silicon film-like portion 207 located in the thickness reducing portion 207 is deformed.

  The resistance change of the impurity diffusion layer 211 is detected as follows. First, a voltage generated between the terminal 221 and the terminal 223 in a state where a reverse bias is applied between the impurity diffusion layers 211 to 214 and the support substrate 201 and a DC power source is connected between the terminal 222 and the terminal 224. By measuring the resistance change, it is possible to detect a resistance change due to the deformation of the impurity diffusion layer 211 as a voltage change between the terminal 221 and the terminal 223. The three impurity diffusion layers 212 to 214 do not contribute to the detection of the deformation amount of the silicon film-like portion, but function to cancel the characteristic change of the impurity diffusion layer 211 due to the temperature change.

  As shown in FIG. 2, the support frame 202 and the support substrate 201 are fixed to each other by bumps 210 made of gold, solder, or the like, and the support substrate 201 is located at a distance from the movable plate 203. The support substrate 201 has wiring 208 on the surface, the support frame 202 has wiring 209 on the surface, and the wiring 208 of the support substrate 201 and the wiring 209 of the support frame 202 are electrically connected by bumps 210. The wiring 209 is electrically connected to the movable plate 203, and the wiring 208 is electrically connected to a power source and a driving circuit (not shown). Although not shown in FIG. 2, in addition to the wiring 208, wiring for connecting the fixed electrode 205 and the displacement detection element 231 to a power source and a driving circuit is formed on the surface of the support substrate 201.

  Next, the operation of the direct acting electrostatic drive element 200 will be described.

In FIG. 1 and FIG. 2, when a voltage is applied to the fixed electrode 205 in a state where the movable plate 203 is grounded via the wiring 209, the bump 210, and the wiring 208, electrostatic attraction is generated between the movable plate 203 and the fixed electrode 205. Will occur. Accordingly, the movable plate 203 is attracted toward the fixed electrode 205 and stops at a position where the electrostatic attractive force balances with the elastic repulsive force of the flexible spring 204. At this time, electrostatic attraction also acts on the fixed electrode 205 and the silicon film portion 207. This electrostatic attractive force F is expressed by the following equation.

Here, S is the area of the silicon film portion 207, d is the distance between the fixed electrode 205 and the movable plate 203, and V is the voltage applied to the fixed electrode 205.

The silicon film portion 207 is deformed by the electrostatic attractive force F, and the deformation amount x is proportional to the force F acting on the film. If this is expressed in mathematical formulas,

It is expressed. Here, k is an effective elastic constant in which the silicon film portion 207, the silicon oxide film 235, and the fixed electrode 205 are combined.

The output voltage of the strain gauge 232, that is, the potential difference δH generated between the terminal 221 and the terminal 223 in FIG. 4 is expressed by the following expression.

Here, Vs is the voltage of the DC power supply connected between the terminal 222 and the terminal 224, g is a constant representing the gauge factor, that is, the sensitivity of the strain gauge, and L is the thickness of the impurity diffusion layer 211 constituting the strain gauge. The length of the portion located in the reduction portion 207, β, is a constant representing how much the impurity diffusion layer 211 is deformed with respect to the deformation amount of the silicon film-like portion 207.

Summarizing Formula (2) to Formula (4), the following formula is established.

  That is, by monitoring the change amount δH of the output voltage of the strain gauge and the voltage V applied to the fixed electrode 205, the distance between the fixed electrode 205 and the movable plate 203, in other words, the movable plate, based on the equation (5). The position of 203 is calculated. The position of the movable plate 203 is controlled by feedback control of the voltage applied to the fixed electrode 205 so that the deviation between the position of the movable plate 203 calculated in this way, that is, the value of d and the target value is minimized. It can be controlled accurately.

  In the present embodiment, since the strain gauge is made of Si, which is a substance having a very high gauge factor g, in other words, a strain detection sensitivity is extremely high, a minute deformation of the silicon film portion 207 is detected with high sensitivity. It is possible. Accordingly, the position of the movable plate 203 can be detected with high sensitivity. Further, as shown in the equation (5), since the output voltage of the strain gauge directly reflects the position of the movable plate 203, highly reliable position detection is possible. Further, since the strain gauge is insulated from the fixed electrode 205 by the silicon oxide film 235, the high voltage applied to the fixed electrode 205 does not adversely affect the sensitivity of the displacement amount detection element.

  The above description is based on the premise that the deformation amount of the silicon film portion 207 is negligibly small with respect to the displacement amount of the movable plate 203 when an electrostatic attractive force is applied. The thickness of the portion 207, the silicon oxide film 235, the fixed electrode 205, the area of the silicon film-like portion 207, in other words, the value of the elastic constant k must be designed to be as small as possible within the range in which this precondition is maintained.

  Next, a method for manufacturing the direct acting electrostatic drive element 200 will be described.

  1 and 2, the direct acting electrostatic drive element 200 includes a movable electrode unit 200 </ b> A including a support frame 202, a movable plate 203, a flexible spring 204, a support substrate 201, a fixed electrode 205, and a displacement amount detection element 231. The movable electrode unit 200 </ b> A and the fixed electrode unit 200 </ b> B are connected to each other by the bumps 210.

  Hereinafter, a manufacturing method of the movable electrode unit 200A and the fixed electrode unit 200B will be described.

  The movable electrode unit 200A is manufactured by the method shown in FIGS.

  First, as shown in FIG. 5, a thermal oxide film is formed on the front and back surfaces of an SOI (Silicon on Insulator) substrate 301 composed of an active layer 320, a BOX (Buried Oxide) 321 and a support layer 322. After that, the mask 302 is formed by etching a part of the thermal oxide film. Further, after forming a conductive film such as aluminum, the wiring 303 is formed by etching part of the conductive film.

  Next, as shown in FIG. 6, the active layer 320 and the support layer 322 of the SOI substrate 301 not covered with the mask 302 are removed by etching. Next, as shown in FIG. 7, the exposed portions of the BOX 321 and the mask 302 are removed to form the movable plate 305 and the support frame 340. Although not shown in the drawing, the flexible spring portion is also formed at the same time in the step shown in FIG. In this way, the movable electrode unit 200A is completed.

  On the other hand, the fixed electrode unit 200B is manufactured by the method shown in FIGS.

  First, as shown in FIG. 8, an impurity diffusion layer is formed by diffusing a dopant into a part of the active layer 330 of the SOI substrate 310 composed of the active layer 330, the BOX 331, and the support layer 332 by a method such as ion implantation. 311 is formed. This impurity diffusion layer constitutes a strain gauge.

  Next, as shown in FIG. 9, a thermal oxide film 312 is formed on the surfaces of the active layer 330 and the support layer 332, and then a contact hole 313 is formed in the thermal oxide film 312 formed on the surface of the active layer 330. . Further, after forming a conductive film such as aluminum on the surface of the thermal oxide film 312 formed on the surface of the active layer 330, the wiring 314 and the fixed electrode 315 are formed by etching a part of the conductive film. Here, the wiring 314 is used to connect the strain gauge to a power source or a drive circuit (not shown). Although not shown in FIG. 9, in addition to the wiring 314, a wiring for connecting the fixed electrode 315 to a power source or a drive circuit (not shown) and a wiring corresponding to the wiring 208 in FIG. It is formed at the same time in this step.

  Next, as shown in FIG. 10, a mask 316 is formed by etching a part of the thermal oxide film 312 formed on the surface of the support layer 332. Further, after etching the portion of the support layer 332 that is not covered with the mask 316, the exposed portion of the BOX 331 is removed to form the silicon film portion 318. In this way, the fixed electrode unit 200B is completed.

  Finally, after the fixed electrode unit shown in FIG. 10 and the movable electrode unit shown in FIG. 7 are cut into chips by a method such as dicing, the units are placed so that the movable plate 305 and the fixed electrode 315 face each other. By aligning and bonding with bumps, the direct acting electrostatic drive element 200 shown in FIG. 1 is completed.

  In this embodiment, since the position of the movable plate is detected from the amount of displacement of the fixed electrode caused by electrostatic attraction acting between the movable plate and the fixed electrode, the movable plate is more accurate and reliable than the conventional method. Can be detected. In addition, since the displacement amount of the fixed electrode is measured using a displacement amount detection film and a strain gauge made of Si having a very high strain detection sensitivity, highly sensitive position detection is possible. Furthermore, since a strain gauge is formed only by impurity diffusion to the Si substrate without forming a new displacement detection film, the displacement detection element, that is, the position detection means of the movable plate can be easily manufactured with a simple configuration. it can. In addition, since the displacement detection element is formed in the fixed electrode portion, there is no restriction on the size or the like in designing the strain gauge, and the degree of freedom is increased as compared with the conventional case formed on the elastic member.

  The present embodiment can be variously modified without departing from the spirit of the invention. First, an example is shown in which a silicon oxide film is used as a film that insulates the fixed electrode and the strain gauge from each other. However, an organic material such as polyimide or silicone resin, or another inorganic material such as a silicon nitride film may be used. . Moreover, although the example which uses aluminum as a material which comprises a fixed electrode and wiring was shown, you may use other conductors, such as titanium, copper, and molybdenum, and semiconductors, such as a polycrystalline silicon. Moreover, although the example which forms a flexible spring by processing a silicon substrate was shown, you may comprise a flexible spring with organic materials, such as a polyimide and a silicone resin, and inorganic materials, such as a silicon nitride and a silicon oxide. However, in this case, it is necessary to form wiring for connecting the movable plate 203 to the power source and the driving circuit on the surface or inside of the flexible spring. Moreover, although the example which uses a silicon | silicone as a material of a board | substrate was shown, you may use other semiconductors, such as a compound semiconductor. In addition, although an example in which the strain gauge is configured by the individual impurity diffusion layers 211 to 214 having the same shape has been shown, the impurity diffusion that is not located in the thickness reduction unit 207 is used in an environment where the temperature does not vary. The layers 212 to 214 may be omitted.

[Second Embodiment]
In the present embodiment, the movable portion is composed of a mover and an elastic member, and is directed to an electrostatic drive element of a type in which the mover rotates. More specifically, the movable element has a reflecting surface and is directed to an optical deflection element that can rotate within a predetermined angular range. FIG. 11 is a perspective view showing an optical deflection element according to the second embodiment of the present invention. FIG. 12 is a cross-sectional view of the light deflection element taken along line XII-XII shown in FIG.

  As shown in FIGS. 11 and 12, the light deflection element 400 according to the present embodiment is composed of a movable electrode unit 400A, a fixed electrode unit 400B, and a bump 412 that couples them with a space therebetween. Yes.

  The movable electrode unit 400A includes a movable part that can be at least partially elastically deformed, and a support frame 402 that supports the movable part. The movable part includes a movable plate 403 as a mover, and a movable plate 403. The elastic member includes a torsion bar 404 that supports the movable plate 403 so as to be rotatable around the rotation shaft 415. The movable plate 403, the support frame 402, and the torsion bar 404 are made of silicon. The movable plate 403 itself constitutes a movable electrode. The movable plate 403 has a reflective surface 407.

  The fixed electrode unit 400B includes a support substrate 401 and two fixed electrodes 405 and 406 provided on the support substrate 401. The support substrate 401 is a region where the fixed electrodes 405 and 406 are respectively positioned so that a part of the fixed electrode 405 is displaced according to the electrostatic attractive force acting between the movable plate 403 and each of the fixed electrodes 405 and 406. Are provided with thickness reduction portions 408 and 409 having a reduced thickness. The fixed electrodes 405 and 406 are provided symmetrically with respect to the rotation axis 415. Similarly, the thickness reducing portions 408 and 409 are also provided symmetrically with respect to the rotating shaft 415.

  The support substrate 401 is manufactured from a semiconductor substrate, for example, but not limited to, a single crystal silicon substrate. The thickness reduction units 408 and 409 are made of a thin film of single crystal silicon, for example. In the following, the thickness reduction portions 408 and 409 are also referred to as silicon film portions. A silicon oxide film 433 is provided between the support substrate 401 and the fixed electrodes 405 and 406 to insulate them.

  The fixed electrode unit 400B further includes displacement amount detection elements 430 and 431 that detect displacement amounts of the portions of the fixed electrodes 405 and 406 located in the thickness reduction units 408 and 409, respectively. The displacement amount detection elements 430 and 431 are each composed of a part of fixed electrodes 405 and 406, a silicon oxide film 433, silicon film-like portions 408 and 409, and strain gauges 410 and 411, respectively. The strain gauges 410 and 411 are provided on the fixed electrodes 405 and 406 via the silicon oxide film 433, respectively, and some of them are located in the thickness reduction portions 408 and 409. The strain gauges 410 and 411 are both formed in the support substrate 401 and have a different conductivity type from the silicon film portions 408 and 409.

  Similar to the first embodiment, the strain gauges 410 and 411 have four impurity diffusion layers having the same shape, and one of the impurity diffusion layers is partially reduced in thickness reduction portions 408 and 409. The other three impurity diffusion layers are located outside the thickness reduction portions 408 and 409. Further, these four impurity diffusion layers constitute a bridge circuit shown in FIG.

  As shown in FIG. 12, the support frame 402 and the support substrate 401 are fixed to each other by bumps 412 made of gold, solder, or the like, and the support substrate 401 is located at a distance from the movable plate 403. The support substrate 401 has wiring 414 on the surface, the support frame 402 has wiring 413 on the surface, and the wiring 414 on the support substrate 401 and the wiring 413 on the support frame 402 are electrically connected by bumps 412. The wiring 413 is electrically connected to the movable plate 403, and the wiring 414 is electrically connected to a power source and a driving circuit (not shown). Although not shown in FIG. 12, in addition to the wiring 414, wiring for connecting the fixed electrodes 405 and 406 and the displacement detection elements 430 and 431 to the power source and the driving circuit is formed on the surface of the support substrate 401. Has been.

  Since the manufacturing method of the light deflection element 400 of this embodiment is the same as that of the direct acting electrostatic drive element 200 of the first embodiment, description thereof is omitted here.

  Next, the operation of the light deflection element 400 will be described.

  11 and 12, when the movable plate 403 is grounded via the wiring 413, the bump 412 and the wiring 414, and the fixed electrode 405 is grounded, a voltage is applied to the fixed electrode 405. An electrostatic attractive force is generated during 405. As a result, as shown in FIG. 13, the movable plate 403 rotates around the rotation shaft 415 connecting the two torsion bars 404, and the movable plate 403 is positioned at a position where the electrostatic attractive force balances with the elastic repulsion force of the torsion bar 404. Is stationary. At this time, the reflecting surface 407 formed on the surface of the movable plate 403 also rotates at the same time. The rotation angle of the movable plate 403 depends on the voltage applied to the fixed electrode 405. For this reason, by controlling the voltage applied to the fixed electrode 405, it is possible to reflect the light incident on the reflecting surface 407 in a desired direction.

When rotating the movable plate 403, the fixed electrode 405 and the silicon film portion 408 constituting the displacement amount detection element 430 are deformed by electrostatic attraction as in the first embodiment. By detecting by this, the interval between the silicon film portion 408 and the movable plate 403, in other words, the rotation angle of the movable plate 403 can be known. The rotation angle Θ of the movable plate is expressed by the following expression in the range where the rotation angle of the movable plate 403 is small.

Here, k is an effective elastic constant combining the silicon film portion 408, the silicon oxide film 433, and the fixed electrode 405, and δH is a change in the voltage H generated between the terminal 221 and the terminal 223 in the bridge circuit shown in FIG. 4, V _s is the voltage of the DC power source connected between the terminal 222 and the terminal 224 in the bridge circuit shown in FIG. 4, g is the gauge factor of the strain gauge 410 formed in the silicon film portion 408, L Is the length of the portion of the impurity diffusion layer constituting the strain gauge located at the thickness reducing portion 408, S is the area of the silicon film-like portion 408, and X is a plane passing through the rotation axis of the movable plate 403. A distance from an intersection line 420 perpendicular to 401 to the center of the silicon film portion 408, X ₀ is a distance between the movable plate 403 and the fixed electrode 405 when not driven, and V is applied to the fixed electrode 405. Voltage. Β is a constant representing how much the impurity diffusion layer located in the thickness reducing portion 408 is deformed with respect to the deformation amount of the silicon film-like portion 408.

  That is, by monitoring the change amount δH of the output voltage of the strain gauge and the voltage V applied to the fixed electrode 405, the rotation angle Θ of the movable plate 403 is calculated by Equation (6). By using the value of the rotation angle Θ to feedback control the voltage applied to the fixed electrode 405, the rotation angle of the movable plate 403 can be accurately controlled.

  When rotating the movable plate 403 in the direction opposite to that in FIG. 13, the movable plate 403 is grounded, the fixed electrode 405 is grounded, and a voltage is applied to the fixed electrode 406 to rotate the movable plate 403. The electrostatic attractive force acting between the movable plate 403 and the fixed electrode 406 may be detected by the above-described method using the displacement amount detection element 431.

  Also in this embodiment, since the strain gauge is made of Si, the value of g in the equation (6) becomes a very large value, and minute deformations of the silicon film portions 408 and 409 are detected with high sensitivity. It is possible. Therefore, a slight change in the rotation angle of the movable plate 403 can be detected with high sensitivity. Further, as shown in the equation (6), since the output voltage of the strain gauge directly reflects the rotation angle of the movable plate 403, highly reliable angle detection is possible. Further, since the strain gauge is insulated from the fixed electrodes 405 and 406 by the silicon oxide film 433, the high voltage applied to the fixed electrode does not adversely affect the sensitivity of the displacement amount detection element.

  The above explanation is based on the premise that the deformation amount of the silicon film portions 408 and 409 is negligibly small with respect to the displacement amount of the movable plate 403 when an electrostatic attractive force is applied. The thickness of the portions 408 and 409, the silicon oxide film 433, the fixed electrodes 405 and 406, the area of the silicon film-like portions 408 and 409, in other words, the value of the elastic constant k is as small as possible within the range in which this precondition is maintained. Need to design.

  In the present embodiment, the angle of the movable plate, that is, the position is detected from the displacement amount of the fixed electrode due to the electrostatic attraction acting between the movable plate and the fixed electrode. Therefore, the accuracy and reliability are higher than those of the conventional method. It is possible to detect the position of a movable plate having a gap. In addition, since the displacement amount of the fixed electrode is measured using a displacement amount detection film and a strain gauge made of Si having a very high strain detection sensitivity, highly sensitive position detection is possible. Furthermore, since a strain gauge is formed only by impurity diffusion to the Si substrate without forming a new displacement detection film, the displacement detection element, that is, the position detection means of the movable plate can be easily manufactured with a simple configuration. it can. In addition, since the displacement detection element is formed in the fixed electrode portion, there is no restriction on the size or the like in designing the strain gauge, and the degree of freedom is increased as compared with the conventional case formed on the elastic member.

  The present embodiment can be variously modified without departing from the spirit of the invention. First, an example is shown in which a silicon oxide film is used as a film that insulates the fixed electrode and the strain gauge from each other. However, an organic material such as polyimide or silicone resin, or another inorganic material such as a silicon nitride film may be used. . Moreover, although the example which uses aluminum as a material which comprises a fixed electrode and wiring was shown, you may use other conductors, such as titanium, copper, and molybdenum, and semiconductors, such as a polycrystalline silicon. Moreover, although the example which forms a torsion bar by processing a silicon substrate was shown, you may comprise a torsion bar with organic materials, such as a polyimide and a silicone resin, and inorganic materials, such as a silicon nitride and a silicon oxide. However, in this case, it is necessary to form wiring for connecting the movable plate 403 to the power source and the drive circuit on the surface or inside of the torsion bar. Moreover, although the example which uses a silicon | silicone as a material of a board | substrate was shown, you may use other semiconductors, such as a compound semiconductor. Further, for the sake of simplicity of explanation, the formula (6), which is an approximation formula that can be applied only when the rotation angle of the movable plate is small, has been described as an example of the formula for calculating the rotation angle of the movable plate 403. When the rotation angle of the movable plate is large, the expression (6) may be changed to a more strict expression. In addition, although an example in which the strain gauge is composed of four impurity diffusion layers having the same shape has been shown, impurity diffusion not located in the thickness reduction portions 408 and 409 is used in an environment where the temperature does not vary. The layer may be omitted.

[Third embodiment]
The present embodiment is directed to an electrostatic drive element of a type in which the movable part is made of an elastically deformable film and the movable part itself can be deformed. More specifically, the movable part is directed to a deformable mirror having a reflecting surface and deformable. FIG. 14 is a perspective view showing a deformable mirror according to the third embodiment of the present invention. FIG. 15 is a cross-sectional view of the deformable mirror taken along line XV-XV shown in FIG.

  As shown in FIGS. 14 and 15, the deformable mirror 500 according to the present embodiment includes a mirror unit 500 </ b> A, a fixed electrode unit 500 </ b> B, and a spacer 504 that couples them with a space therebetween. .

  The mirror unit 500A has a movable part that can be elastically deformed at least in part, and a support frame 502 that supports the movable part, and the movable part includes an elastic deformation film 503 provided with a movable electrode. . The movable electrode of the elastic deformation film 503 also serves as a reflection surface. The elastic deformation film 503 is composed of, for example, a laminated film of a resin film such as a polyimide film and a metal film such as aluminum.

  The fixed electrode unit 500 </ b> B includes a support substrate 501 and a plurality of fixed electrodes 505 provided on the support substrate 501. The fixed electrode 505 includes a circular electrode and a ring-shaped electrode positioned at the same center around the circular electrode. The support substrate 501 has a thickness in a part of a region where each fixed electrode 505 is positioned so that a part of the fixed electrode 505 is displaced according to an electrostatic attractive force acting between the fixed electrode 505 and the elastic deformation film 503. Has a reduced thickness reducing portion 506.

  In the support substrate 501, the constituent material of the support substrate 501 is removed in the thickness reduction unit 506. That is, the support substrate 501 has a through hole in the thickness reduction portion 506. In other words, the thickness reducing unit 506 has no thickness and is configured by a through hole formed in the support substrate 501. Hereinafter, the thickness reducing portion 506 is also referred to as a through hole.

  FIG. 16 shows an enlarged view of the thickness reduction portion shown in FIG. 15, that is, the peripheral portion of the through hole. As shown in FIG. 16, the fixed electrode unit 500 </ b> B further includes a displacement amount detection element 530 that detects a displacement amount of a portion of the fixed electrode 505 located in the thickness reduction unit 506. The displacement amount detection element 530 includes a part of the fixed electrode 505, a polyimide film 507 as an insulating film provided on the fixed electrode 505, and a strain gauge 508 provided on the polyimide film 507. That is, the polyimide film 507 and the strain gauge 508 are located on the opposite side of the support substrate 501 with respect to the fixed electrode 505. The strain gauge 508 is produced by patterning a polycrystalline silicon film into a predetermined shape to form a gauge resistor.

  The strain gauge 508 has four gauge resistors having the same shape, and one of the gauge resistors is partially located in the thickness reducing portion 506, and the other three gauge resistors. Is located outside the thickness reducing portion 506. The four gauge resistors are connected to each other by a wiring 509, and constitute a bridge circuit in the same manner as the strain gauge shown in FIG. 4 in the first embodiment and the second embodiment.

  Although not shown in FIG. 16, in addition to the wiring 509, wiring for connecting the fixed electrode 505 and the displacement detection element 530 to a power source and a driving circuit is formed on the surface of the support substrate 501. In addition, wiring for connecting the elastic deformation film 503 to a power source and a driving circuit is formed on the surface of the support frame 502.

  Next, the operation of the deformable mirror 500 will be described.

  14 to 16, when a voltage is applied to the fixed electrode 505 with the movable electrode of the elastic deformation film 503 grounded, an electrostatic attractive force is generated between the elastic deformation film 503 and the fixed electrode 505. Thereby, the elastic deformation film 503 is deformed to a position where the elastic repulsion force is balanced with the electrostatic attractive force. By individually controlling the voltage applied to each of the plurality of fixed electrodes 505, the shape of the elastic deformation film 503 can be changed to various shapes. At this time, since electrostatic attraction also acts on the fixed electrode 505, a portion of the fixed electrode 505 positioned at the thickness reducing portion, that is, the through hole 506 is deformed in the direction of the elastic deformation film 503. By detecting the deformation amount of the fixed electrode 505 by the strain gauge 508, the distance between each fixed electrode 505 and the portion of the elastic deformation film 503 opposite to the fixed electrode 505, in other words, the elastic deformation film 503 is detected as in the first embodiment. Can be monitored in real time. By calculating the difference between the shape of the elastic deformation membrane 503 thus obtained and the desired elastic deformation membrane shape, and changing the voltage applied to each fixed electrode 505 so that the value becomes smaller The shape of the reflecting surface constituted by the elastic deformation film 503 and a part thereof can be accurately controlled.

  Also in this embodiment, as in the first embodiment and the second embodiment, since the output voltage of the strain gauge directly reflects the shape of the elastic deformation film 503, it is possible to detect the shape of the reflecting surface with high reliability. . Further, since the strain gauge is insulated from the fixed electrode 505 by the polyimide film 507, the high voltage applied to the fixed electrode 505 does not adversely affect the sensitivity of the displacement detection element 530. Further, as will be described later, since the support substrate 501 is manufactured from a normal silicon substrate instead of an expensive SOI substrate, the manufacturing cost is reduced.

  The above explanation is based on the premise that the deformation amount of the fixed electrode 505 is negligibly small with respect to the deformation amount of the elastic deformation film 503 when an electrostatic attractive force is applied. The thickness of the polyimide film 507 and the area of the bottom surface of the through hole 506, in other words, the value of the elastic constant k must be designed to be as small as possible within the range in which this precondition is maintained.

  Next, a method for manufacturing the deformable mirror 500 will be described.

  The deformable mirror 500 includes a mirror unit 500A including a support frame 502 and an elastic deformation film 503, a fixed electrode unit including a support substrate 501, a fixed electrode 505, a displacement amount detection element 530, and the like shown in FIGS. After 500B is manufactured separately, the mirror unit 500A and the fixed electrode unit 500B are connected by the spacer 504.

  Hereinafter, a manufacturing method of the mirror unit 500A and the fixed electrode unit 500B will be described.

  The mirror unit 500A is manufactured by the method shown in FIGS.

  First, as shown in FIG. 17, a thermal oxide film 605 is formed on the front surface and the back surface of the silicon substrate 601, and then a part of the thermal oxide film on the back surface of the silicon substrate 601 is etched to form a mask 602. Form. Further, a polyimide film 603 and an aluminum film 604 are formed on the front surface of the silicon substrate 601. Since the aluminum film 604 is used as a reflective surface in addition to the movable electrode, it is desirable that the aluminum film 604 be formed into a highly reflective film by a technique such as vacuum deposition. Although not shown in FIG. 17, the aluminum film 604 as a movable electrode is connected to a power source or a driving circuit by partially processing the aluminum film 604 or forming the aluminum film 604 through a shadow mask. Wiring for this purpose is formed simultaneously in this step.

  Next, as shown in FIG. 18, a portion of the silicon substrate 601 that is not covered with the mask 602 is etched, and the exposed thermal oxide film 605 and the mask 602 are removed to form a support frame 618. In this way, the mirror unit 500A is completed.

  On the other hand, the fixed electrode unit 500B is produced by the method shown in FIGS.

  First, as shown in FIG. 19, a thermal oxide film 611 is formed on the front surface and the back surface of the silicon substrate 610, and then a part of the thermal oxide film on the back surface of the silicon substrate 610 is etched to thereby mask 612. Form. Further, a conductive film is formed on the thermal oxide film on the front surface of the silicon substrate 610 and patterned to form a fixed electrode 613, and then a polyimide film 614 is formed on the surface thereof.

  Next, as shown in FIG. 20, after a silicon film is formed on the surface of the polyimide film 614 by P-CVD (Plasma Assisted Chemical Vapor Deposition), this is patterned to form a strain gauge 615. Further, a conductive film is formed and patterned to form a wiring 616 for connecting the strain gauges 615 to each other to form a bridge. Although not shown in FIG. 20, in addition to the wiring 616, wiring for connecting the strain gauge 615 and the fixed electrode 613 to a power source and a driving circuit (not shown) is simultaneously formed in this step.

  Next, as shown in FIG. 21, the portion of the silicon substrate 610 that is not covered with the mask 612 is removed by etching, and then the exposed thermal oxide film 611 and the mask 612 are removed, whereby the support substrate 617 is removed. Form. In this way, the fixed electrode unit 500B is completed.

  Finally, after cutting the mirror unit 500A shown in FIG. 18 and the fixed electrode unit 500B shown in FIG. 21 into a chip by a method such as dicing, the units are aligned and bonded with a spacer in between. The deformable mirror 500 shown in FIGS. 14 to 16 is completed.

  In the present embodiment, the shape of the reflecting surface, that is, the position is detected from the displacement amount of the fixed electrode due to the electrostatic attractive force acting between the elastically deformable membrane and the fixed electrode, so that the accuracy and reliability are higher than in the conventional method. It is possible to detect the shape of the elastically deformable membrane. Further, since a strain gauge obtained by patterning a newly formed film on the substrate is used for measuring the displacement amount of the fixed electrode, highly sensitive position detection is possible with a very simple configuration. In addition, since a strain gauge is formed by patterning a newly formed film on the substrate, the degree of freedom regarding the specifications of the substrate is high. Further, since the strain gauge is formed in the fixed electrode portion, there is no restriction on the size or the like in designing the strain gauge, and the degree of freedom is increased as compared with the conventional case formed on the elastic member.

  The present embodiment can be variously modified without departing from the spirit of the invention. First, an example in which a polyimide film is used as a film for insulating a fixed electrode and a strain gauge is shown, but other resins such as a silicone resin may be used, and an inorganic insulating film such as a silicon oxide film or a silicon nitride film may be used. May be used. In addition, an example of using a polycrystalline silicon film as a strain gauge material has been shown. However, if the substance has a resistance value that changes due to deformation, a silicon film of another form such as an amorphous silicon film or a metal film such as titanium may be used. May be used. In addition, an example is shown in which the elastic deformation film is composed of a polyimide film and an aluminum film, but instead of polyimide, other organic materials such as silicone resin, inorganic materials such as silicon oxide and silicon nitride, and semiconductor materials such as silicon In addition, other metal films such as gold and platinum may be used in place of the aluminum film, and the elastic deformation film may be constituted only by these metal films or semiconductor films. Further, after the step shown in FIG. 18, a metal thin film made of aluminum, gold, or the like may be formed as a reflective film on the surface of the polyimide film 603 where the aluminum film 604 is not formed. In this case, since the incident light is directly incident on the reflective film without passing through the polyimide film, the reflectance can be easily improved. Moreover, although the example in which the fixed electrodes are arranged concentrically has been shown, the arrangement is not limited to this, and the fixed electrodes may be arranged in any manner. Moreover, although the displacement amount detection element showed the example comprised from a fixed electrode and the strain gauge formed in the surface through an insulating film, the movable electrode was shown like 1st embodiment and 2nd embodiment. And a silicon film formed thereunder via an insulating film, and a strain gauge formed therein, and conversely, in the first embodiment and the second embodiment, the present embodiment The displacement detection element used in the form may be used. In addition, although an example in which the strain gauge is composed of four gauge resistors having the same shape has been shown, in the case where the strain gauge is used in an environment where the temperature does not vary, the gauge resistor that is not located in the thickness reduction unit 506 is May be omitted.

Moreover, although the example which uses silicon | silicone as a support substrate was shown, you may use the board | substrate comprised from other materials, such as glass and resin.

  The embodiments of the present invention have been described above with reference to the drawings. However, the present invention is not limited to these embodiments, and various modifications and changes can be made without departing from the scope of the present invention. Also good.

1 is a perspective view showing a direct acting electrostatic drive element according to a first embodiment of the present invention. FIG. 2 is a cross-sectional view of a direct acting electrostatic drive element taken along line II-II shown in FIG. 1. FIG. 3 shows an enlarged view of the thickness reduction portion shown in FIG. 2, that is, the peripheral portion of the silicon film-like portion. FIG. 4 is a plan view schematically showing the strain gauge shown in FIG. 3. 3 shows a first step in the method of manufacturing the movable electrode unit shown in FIGS. 6 shows a step that follows the step of FIG. 5 in the method for manufacturing the movable electrode unit. The process following the process of FIG. 6 in the manufacturing method of a movable electrode unit is shown. The first process in the manufacturing method of the fixed electrode unit shown in FIGS. 1 to 3 is shown. 9 shows a step that follows the step of FIG. 8 in the method for manufacturing the fixed electrode unit. 10 shows a step that follows the step of FIG. 9 in the method of manufacturing the fixed electrode unit. It is a perspective view which shows the optical deflection | deviation element by 2nd embodiment of this invention. It is sectional drawing of the optical deflection | deviation element along the XII-XII line | wire shown by FIG. FIG. 12 shows a state where the movable plate is rotated by a certain angle. It is a perspective view which shows the deformable mirror by 3rd embodiment of this invention. It is sectional drawing of the deformable mirror along the XV-XV line | wire shown by FIG. The thickness reduction part shown by FIG. 15, ie, the peripheral part of a through-hole, is expanded and shown. FIG. 16 shows a first step in the method of manufacturing the mirror unit shown in FIGS. 14 and 15. 18 shows a step that follows the step of FIG. 17 in the method of manufacturing the mirror unit. FIG. 17 shows a first step in the method of manufacturing the fixed electrode unit shown in FIGS. 20 shows a step that follows the step of FIG. 19 in the method of manufacturing the fixed electrode unit. 21 shows a step that follows the step of FIG. 20 in the method for manufacturing the fixed electrode unit. The structure for detecting the position of a needle | mover based on the electrostatic capacitance between a fixed electrode and a movable electrode is shown typically. The structure for detecting the position of a needle | mover based on the deformation amount of an elastic member is shown typically. It is a top view of the peripheral part of the elastic member shown by FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 200 ... Direct-acting electrostatic drive element, 200A ... Movable electrode unit, 200B ... Fixed electrode unit, 201 ... Support substrate, 202 ... Support frame, 203 ... Movable plate, 204 ... Spring, 205 ... Fixed electrode, 207 ... Thickness Reduction part (or silicon film-like part), 208 ... wiring, 209 ... wiring, 210 ... bump, 211 ... impurity diffusion layer, 212 ... impurity diffusion layer, 213 ... impurity diffusion layer, 214 ... impurity diffusion layer, 221 ... terminal, 222 ... terminal, 223 ... terminal, 224 ... terminal, 231 ... displacement detecting element, 232 ... strain gauge, 235 ... silicon oxide film, 301 ... SOI substrate, 302 ... mask, 303 ... wiring, 305 ... movable plate, 310 ... SOI substrate, 311 ... impurity diffusion layer, 312 ... thermal oxide film, 313 ... contact hole, 314 ... wiring, 315 ... fixed electrode, 316 ... mask, 18 ... Silicone-like part, 320 ... Active layer, 321 ... Support layer, 322 ... Support layer, 330 ... Active layer, 332 ... Support layer, 340 ... Support frame, 400 ... Light deflection element, 400A ... Moving electrode unit, 400B ... fixed electrode unit, 401 ... support substrate, 402 ... support frame, 403 ... movable plate, 404 ... torsion bar, 405 ... fixed electrode, 406 ... fixed electrode, 407 ... reflective surface, 408 ... thickness reduction part (or silicon film) 409 ... thickness reduction part (or silicon film-like part), 410 ... strain gauge, 411 ... strain gauge, 412 ... bump, 413 ... wiring, 414 ... wiring, 415 ... rotating shaft, 420 ... intersection line, 430 ... Displacement detection element, 431 ... Displacement detection element, 433 ... Silicon oxide film, 500 ... Deformable mirror, 500A ... Mirror unit, 500B ... Fixed electrode unit 501 ... Support substrate, 502 ... Support frame, 503 ... Elastic deformation film, 504 ... Spacer, 505 ... Fixed electrode, 506 ... Thickness reducing part (or through hole), 507 ... Polyimide film, 508 ... Strain gauge, 509: Wiring, 530 ... Displacement detection element, 601 ... Silicon substrate, 602 ... Mask, 603 ... Polyimide film, 604 ... Aluminum film, 605 ... Thermal oxide film, 610 ... Silicon substrate, 611 ... Thermal oxide film, 612 ... Mask 613, fixed electrode, 614, polyimide film, 615, strain gauge, 616, wiring, 617, support substrate, 618, support frame.

Claims (10)

A movable part at least partially elastically deformable;
A support that supports the movable part;
A movable electrode provided in the movable part;
A substrate located at a distance from the movable part;
A fixed electrode provided on the substrate;
An electrostatic drive element, comprising: a detecting means for detecting deformation of the movable part due to electrostatic attraction acting between the fixed electrode and the movable electrode, and the detecting means is provided on the substrate.   2. The substrate according to claim 1, wherein the thickness of the substrate is reduced to at least a part of a region where the fixed electrode is positioned so that a part of the fixed electrode is displaced according to an electrostatic attractive force acting between the fixed electrode and the movable electrode. An electrostatic drive element, wherein the detection means is a displacement amount detection element for detecting a displacement amount of a fixed electrode portion located in the thickness reduction portion.   3. The displacement amount detecting element according to claim 2, wherein the displacement amount detecting element includes a part of the fixed electrode and a strain gauge provided on the fixed electrode via an insulating film, and at least a part of the strain gauge is located in the thickness reduction portion of the substrate. An electrostatic drive element.   4. The electrostatic driving element according to claim 3, wherein the substrate is formed of a semiconductor substrate, and the strain gauge is formed in the semiconductor substrate.   5. The electrostatic drive element according to claim 4, wherein the strain gauge is constituted by an impurity diffusion layer formed in the semiconductor substrate.   The electrostatic driving element according to claim 3, wherein the insulating film and the strain gauge are located on the opposite side of the substrate with respect to the fixed electrode, and the substrate is made of the constituent material of the substrate removed in the thickness reduction portion.   4. The electrostatic drive element according to claim 3, wherein the movable portion includes a movable element having a movable electrode and an elastic member that supports the movable element so as to be displaceable.   The electrostatic drive element according to claim 7, wherein the elastic member is configured by a flexible spring that supports the mover so as to be linearly movable.   The electrostatic drive element according to claim 7, wherein the elastic member includes a torsion bar that rotatably supports the mover.   4. The electrostatic drive element according to claim 3, wherein the movable part is formed of an elastically deformable film provided with a movable electrode.

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