JP2014035429A - Light deflector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light deflector which has a movable plate prevented from undesired displacement and has a high long-term reliability.SOLUTION: A light deflector 100 includes: a movable plate 101 having a reflection film 110; a pair of torsion bars 102 supporting the movable plate 101 so as to allow the movable plate 101 to incline about an axis 111; a pair of fixing parts 104 for supporting the torsion bars 102; and a pair of connection parts 103 interposed between the torsion bars 102 and the fixing parts 104. Each of the connection parts 103 includes: a connection part body 103a extending between the torsion bar 102 and the fixing part 104 and a pair of tension applying parts 103b arranged on both sides of the torsion bar 102. The tension applying parts 103b constitute a tension applying structure to generate tensile stress in the torsion bars 102.

Description

  The present invention relates to an optical deflector.

  An optical deflector is used for a switching element in optical fiber communication or an optical scanner that scans a light beam in an optical device. The optical deflector has, for example, a movable plate that can be tilted around a torsion bar, and deflects a light beam reflected by, for example, the movable plate by changing the tilt angle of the movable plate. Recently, micromirror devices using MEMS technology have been used for optical deflectors.

  Patent Document 1 discloses a technique for generating a tensile stress in a torsion bar as a method for suppressing an undesired displacement other than the inclination of a movable plate with the torsion bar as an axis.

JP 2005-321663 A

  Patent Document 1 is effective for suppressing an undesired displacement of the movable plate, but has long-term reliability.

  Patent Document 1 discloses that a tension is generated in a torsion bar by the stress of a thin film. However, if a torsion bar is formed of a polycrystalline film, breakage or fatigue along the crystal grain boundary is likely to occur. For this reason, the torsion bar is desirably formed of a material such as single crystal silicon that is highly reliable in terms of mechanical strength.

  In addition, although a certain degree of suppression is possible depending on the film forming conditions and the like, in practice, there are many cases where the film stress varies with time. Since fluctuations in the film stress change the mechanical characteristics of the torsion bar, the effects of characteristic fluctuations may not be negligible in applications that require precise angle control. The same applies to the case where a polycrystalline film is formed on a torsion bar made of single crystal silicon to give tension.

  Patent Document 1 also discloses an example in which stress is generated by thermal deformation of silicon. However, it is difficult to control during manufacturing, and it is difficult to obtain stable characteristics practically.

  The present invention has been made in consideration of such a situation, and an object thereof is to provide an optical deflector with high long-term reliability in which an undesired displacement of a movable plate is suppressed.

  An optical deflector according to the present invention includes a movable plate, a pair of torsion bars that support the movable plate in a tiltable manner, a fixed portion for supporting the torsion bar, and a space between the torsion bar and the fixed portion. At least one connecting portion interposed therebetween. At least one of the connecting portions includes a tension applying structure that generates a tensile stress in the torsion bar.

  According to the present invention, an optical deflector with high long-term reliability in which an undesired displacement of a movable plate is suppressed is provided.

It is a top view of the optical deflector of an embodiment. It is sectional drawing along the A-A 'line | wire shown in FIG. It is a perspective view of the principal part of the optical deflector shown in FIG. 1 and FIG. 4 shows a wafer prepared for manufacturing the optical deflector shown in FIGS. 4B shows a wafer in which fixed comb teeth are formed on the wafer shown in FIG. 4A. 4 shows another wafer prepared for manufacturing the optical deflector shown in FIGS. 5B shows a wafer having grooves formed in the wafer shown in FIG. 5A. The wafer which formed the tension | tensile_strength provision part in the wafer shown to FIG. 5A is shown. 5B shows a structure obtained by bonding the wafer shown in FIG. 4B and the wafer shown in FIG. 5C. FIG. 6B shows a structure in which a reflective film is formed on the structure shown in FIG. 6A. 6B shows a structure in which a photoresist mask is formed on the structure shown in FIG. 6B. 6C shows a finished optical deflector in which a movable plate, a torsion bar, a connecting portion, and a fixed portion are formed on the structure shown in FIG. 6C. It is the schematic which showed the force added to the torsion bar at the time of the in-plane rotation of a movable plate in the conventional general optical deflector. It is the schematic which showed the force added to the torsion bar at the time of in-plane rotation of a movable plate in the optical deflector of embodiment. The torsion bar by the modification 1 of embodiment, a connection part, and a fixing | fixed part are shown. The torsion bar by the modification 2 of embodiment, a connection part, and a fixing part are shown. The torsion bar by the modification 3 of embodiment, a connection part, and a fixing | fixed part are shown.

  The optical deflector of the embodiment will be described below with reference to the drawings. FIG. 1 is a top view of the optical deflector according to the embodiment, and FIG. 2 is a cross-sectional view taken along the line A-A ′ shown in FIG. 1. FIG. 3 is a perspective view of a main part of the optical deflector shown in FIGS. 1 and 2, and more specifically, a perspective view of a structure inside the region B shown in FIG.

  As shown in FIG. 1, the optical deflector 100 includes a movable plate 101 provided with a reflective film 110, a pair of torsion bars 102 that support the movable plate 101 so as to be tiltable around an axis 111, and a torsion bar 102. And a pair of connecting portions 103 interposed between the torsion bar 102 and the fixing portion 104, respectively. The torsion bar 102 extends from the movable plate 101 to both sides along the shaft 111 and is connected to the connecting portion 103. The shaft 111 extends through the inside of the torsion bar 102 and coincides with the central axis of the torsion bar 102, for example.

  The movable plate 101, the torsion bar 102, the connecting portion 103, and the fixed portion 104 are configured by a mirror layer 201, and the fixed portion 104 is firmly fixed to the support layer 204 through the fixed layer 202 and the insulating layer 203. Therefore, the movable plate 101, the torsion bar 102, and the connecting portion 103 have a beam structure that is supported at both ends by the fixed portion 104.

  As shown in FIG. 2, the optical deflector 100 according to the present embodiment is structurally configured with a four-layer structure including a mirror layer 201, a fixed layer 202, an insulating layer 203, and a support layer 204. The mirror layer 201, the fixed layer 202, and the support layer 204 are made of a conductive silicon material containing impurities such as P, As, and B. The insulating layer 203 is made of an insulating material such as a silicon oxide film.

  As shown in FIG. 1, with respect to one side of the torsion bar 102, the connecting portion 103, and the fixing portion 104, the connecting portions of the connecting portion 103 and the fixing portion 104 are located on both sides of the torsion bar 102. With respect to the direction, that is, the direction parallel to the shaft 111, the movable plate 101 and the connection portion of the torsion bar 102 are located between the connection portion of the torsion bar 102 and the connecting portion 103.

  Each connecting portion 103 includes a connecting portion main body 103 a extending between the torsion bar 102 and the fixing portion 104, and a pair of tension applying portions 103 b disposed on both sides of the torsion bar 102. The tension applying unit 103 b constitutes a tension applying structure that generates a tensile stress in the torsion bar 102. Each tension applying portion 103b presses the peripheral connecting portion main body 103a in the axial direction of the torsion bar 102 in the temperature range of the operating environment.

  Each tension applying portion 103 b extends through the connecting portion 103 in the thickness direction, and is exposed at an end surface facing the torsion bar 102. The tension applying portion 103 b has a structure that is long in a direction parallel to the shaft 113. The linear expansion coefficient of the tension applying part 103b is smaller than the linear expansion coefficient of the connecting part main body 103a. Although not limited thereto, in one example, the movable plate 101, the torsion bar 102, the fixed portion 104, and the connecting portion main body 103a are made of a single crystal silicon material, and the tension applying portion 103b is made of a silicon thermal oxide film. .

  Here, the thickness direction means the stacking direction of the stacked structure constituting the optical deflector 100. The axis 113 means a virtual straight line perpendicular to the axis 111 and perpendicular to the stacking direction.

  The movable plate 101 has a plurality of movable comb teeth 106 and 107. The plurality of movable comb teeth 106 and 107 extend from both sides of the movable plate 101 to the outside in a direction parallel to the shaft 113. The movable comb teeth 106 and 107 are arranged at intervals in a direction parallel to the shaft 111. The optical deflector 100 also has a plurality of fixed comb teeth 108 and 109. The fixed comb teeth 108 and 109 extend in a direction parallel to the shaft 113. The fixed comb teeth 108 and 109 are arranged at intervals in a direction parallel to the shaft 111. The movable comb teeth 106 and 107 are arranged with a gap between the fixed comb teeth 108 and 109, respectively, in the projection onto the plane stretched by the shaft 111 and the shaft 113.

  2 and 3, when the movable plate 101 is not inclined, the movable comb teeth 106 are located at positions different from the fixed comb teeth 108 in the thickness direction. Further, as shown in FIG. 2, the movable comb teeth 106 are constituted by a mirror layer 201. The same applies to the movable comb teeth 107. The fixed comb teeth 108 are composed of a fixed layer 202 and are firmly fixed to the support layer 204 through the insulating layer 203. The portion of the fixed layer 202 constituting the fixed comb teeth 108 is electrically independent from the portion of the fixed layer 202 joined to the fixed portion 104. The same applies to the fixed comb teeth 109.

  Here, an example of a manufacturing process of the optical deflector 100 will be described with reference to FIGS. 4A to 4B, 5A to 5C, and 6A to 6D.

  As shown in FIG. 4A, an SOI wafer having a fixed layer 202, an insulating layer 203, and a support layer 204 is prepared. As shown in FIG. 4B, a mask having a shape corresponding to the fixed portion 104 and the fixed comb teeth 108 and 109 is formed on the fixed layer 202 of the SOI wafer, and wet etching using Deep RIE and HF is performed through the mask. As a result, the fixed layer 202 and the insulating layer 203 are selectively removed to form the fixed comb teeth 108 and 109 and the corresponding portion 104 a of the fixed portion 104.

  5A, an SOI wafer having a mirror layer 201, an insulating layer 205, and a support layer 206 is prepared. As shown in FIG. 5B, a silicon nitride film 207 is formed on the mirror layer 201 of the SOI wafer by using CVD, and after patterning the silicon nitride film 207 into a shape corresponding to the tension applying portion 103b, A trench 208 penetrating the silicon nitride film 207 and the mirror layer 201 is formed using RIE or the like. Next, wet thermal oxidation is performed in a furnace at about 1000 ° C., and oxidation is performed until the groove 208 is completely filled, and then the silicon nitride film 207 is removed. As a result, as shown in FIG. 5C, the tension applying portion 103b is formed. The mirror layer 201 is made of silicon, and the tension applying portion 103b is made of a thermal oxide film. The linear expansion coefficient of the thermal oxide film is about 1/10 of the linear expansion coefficient of silicon. For this reason, when the temperature drops to room temperature after oxidation, the shrinkage of silicon is larger than that of the thermal oxide film. For this reason, compressive stress is generated in the thermal oxide film at room temperature.

  As shown in FIG. 6A, the fixed layer 202 and the mirror layer 201 of each wafer are bonded by direct bonding. Next, as shown in FIG. 6B, the support layer 206 and the insulating layer 205 are removed, a metal film is formed, patterned, and etched to form the reflective film 110. Subsequently, as shown in FIG. 6C, a photoresist layer 209 is formed on the mirror layer 201 to have a shape corresponding to the movable plate 101, the movable comb teeth 106 and 107, the torsion bar 102, the connecting portion 103, and the fixed portion 104. The photoresist layer 209 is patterned. Further, as shown in FIG. 6D, after the mirror layer 201 is etched by ICP-RIE using the photoresist layer 209 as a mask, the photoresist layer 209 is removed to complete the optical deflector 100.

  By etching the mirror layer 201 using the photoresist layer 209 as a mask, unnecessary portions of the mirror layer 201 are selectively removed, and each tension applying portion 103b is exposed on the end surface facing the torsion bar 102. As a result, a part of the compressive stress generated in the tension applying portion 103b made of the thermal oxide film is released, and the tension applying portion 103b presses the peripheral connecting portion main body 103a in the axial direction of the torsion bar 102. It will be in the state. Thus, the connecting portion main body 103a is deformed so that the connecting portion between the torsion bar 102 and the connecting portion 103 is moved away from the movable plate 101 along the axis 111, and a tensile stress is generated in the torsion bar 102.

<Basic operation>
A method for driving the optical deflector 100 will be described below. For example, the fixing unit 104 is connected to a ground potential. As a result, the entire mirror layer 201 including the movable comb teeth 106 and 107 and the portion of the fixed layer 202 excluding the fixed comb teeth 108 and 109 become the ground potential. In order to stabilize the peripheral potential, it is desirable that the support layer 204 is also connected to the ground potential. On the other hand, arbitrary potentials V1 and V2 are applied to the fixed comb teeth 108 and 109, respectively. As a result, electrostatic attractive forces are generated between the movable comb teeth 106 and the fixed comb teeth 108 and between the movable comb teeth 107 and the fixed comb teeth 109, respectively. If the alignment between the electrodes is ideally adjusted and the electrostatic gap between the electrodes is the same, the force acting on the individual comb teeth will be in a direction perpendicular to the plane between the shaft 111 and the shaft 113, resulting in As a result, the movable plate 101 can be tilted about the shaft 111. By adjusting the relative magnitudes of the potentials V1 and V2, the movable plate 101 can be tilted clockwise and counterclockwise about the shaft 111, and the tilt angle of the movable plate 101 can be changed. It is possible to control to an arbitrary angle within a predetermined range. Therefore, the light beam reflected by the reflective film 110 of the movable plate 101 can be deflected one-dimensionally in an arbitrary direction.

<Problems of basic operation>
In an optical deflector using an electrostatic actuator, it is necessary to reduce the torsion spring constant of the torsion bar or increase the torque due to electrostatic attraction in order to achieve a large deflection angle or low power. It becomes. In order to reduce the torsion spring constant of the torsion bar, the length of the torsion bar may be increased, or the width and height may be decreased. In order to increase the torque due to electrostatic attraction, in optical deflectors using comb-type electrostatic actuators, the electrostatic gap between the comb teeth is reduced, the number of comb teeth is increased, or the comb tooth length is increased. Therefore, it is necessary to increase the capacitance by increasing the facing area, or to arrange the comb teeth at a position far from the axis that is the center of the inclination.

  In the following, for the sake of brevity and easy understanding, the terms of the present embodiment (for example, the axes 111 and 113) and the reference signs are also used as appropriate for general optical deflectors different from the present embodiment. This will be explained.

  In the optical deflector, it is ideal that the displacement generated in the movable plate 101 is only the inclination around the axis 111, but other displacements may actually occur. One such displacement is the rotation of the movable plate 101 about the shaft 115. Here, the shaft 115 means a virtual straight line that is perpendicular to both the shaft 111 and the shaft 113 and passes through the center of the movable plate 101. Hereinafter, the rotation of the movable plate 101 around the shaft 115 is referred to as in-plane rotation of the movable plate 101.

  Such in-plane rotation of the movable plate 101 can occur, for example, when vibration or impact is applied to the optical deflector 100. Further, in the optical deflector using the comb-shaped electrostatic actuator, it may be caused by an imbalance due to a slight manufacturing error between the movable comb teeth 106 and 107 and the fixed comb teeth 108 and 109.

  Generation of in-plane rotation of the movable plate 101 is an important problem for an optical deflector using a comb-shaped electrostatic actuator. If the in-plane rotation of the movable plate 101 exceeds a certain angle when the drive voltage is applied, the movable comb teeth 106 and 107 and the fixed comb teeth 108 and 109 are attracted and contacted. When the movable comb teeth 106 and 107 and the fixed comb teeth 108 and 109 come into contact with each other, a large current flows through the contact portion so that the movable comb teeth 106 and 107 and the fixed comb teeth 108 and 109 are fused and cannot be restored. End up. Such contact is promoted as the design is aimed at a large deflection angle and low power. For this reason, in many cases, the maximum deflection angle and the required drive power are defined and limited by the safety against the contact of the comb teeth.

  In order to suppress this contact while maintaining the torsional rigidity of the torsion bar 102, it is effective to some extent to increase the rigidity around the shaft 115 by increasing the width and thickness of the torsion bar 102. However, in that case, since the rigidity in the thickness direction of the torsion bar 102 becomes small, displacement of the movable plate 101 in the thickness direction due to vibration or the like is likely to occur. When the movable plate 101 is displaced in the thickness direction, the positional relationship between the movable comb teeth 106 and 107 and the fixed comb teeth 108 and 109 changes and appears as fluctuations in the tilt angle of the movable plate 101. It becomes difficult to apply to the required use. The torsional rigidity of the torsion bar 102 must be kept high in all other directions.

<Effects on basic operation issues>
In the optical deflector 100 of this embodiment, the torsion bar 102, the connecting portion 103, and the fixing portion 104 are integrally formed from single crystal silicon. As described above, the tension applying portion 103b is made of a thermal oxide film, and is formed at a high temperature of about 1000 ° C. and then cooled to room temperature. Since the linear expansion coefficient of the thermal oxide film is about 1/10 of the linear expansion coefficient of silicon, the shrinkage at the time of cooling is larger in silicon than in the thermal oxide film. Slightly swollen. The tension applying portion 103b is exposed at the end surface facing the torsion bar 102, and the connecting portion main body 103a is separated by the tension applying portion 103b in the peripheral portion of the tension applying portion 103b. Therefore, the portions of the connecting portion main body 103a on both sides of the tension applying portion 103b receive a force so as to be separated from each other. Since the fixing portion 104 is firmly fixed, the connecting portion main body 103 a is deformed so that the connecting portion between the torsion bar 102 and the connecting portion 103 is away from the movable plate 101. As a result, a tensile stress is generated in the torsion bar 102.

  FIG. 7 is a schematic diagram showing the force applied to the torsion bar when the in-plane rotation of the movable plate occurs in a conventional general optical deflector in which no tensile stress is generated in the torsion bar. When the movable plate 101 rotates in the plane, the torsion bar 102 is deformed including a slight elongation during rotation. Actually, the stress distribution in the torsion bar 102 is complicated due to elongation and bending, but here, for simplicity, an average force applied in the longitudinal direction of the torsion bar 102 is considered. Due to the deformation, a tensile stress F1 proportional to the elongation is generated in the longitudinal direction inside the torsion bar 102 on the average. This tensile stress F1 becomes a restoring force to return the movable plate 101 to its original state, and the amount of rotation of the movable plate 101 is determined by a balance between the tensile stress F1 due to the deformation of the torsion bar 102 and the moment M1 due to the force that generates in-plane rotation.

  FIG. 8 is a schematic view showing the force applied to the torsion bar 102 during the in-plane rotation of the movable plate in the optical deflector 100 of the present embodiment. For comparison, it is assumed that in-plane rotation equivalent to that in FIG. In this case, in a state where the in-plane rotation of the movable plate 101 has not occurred, the torsion bar 102 has already generated a tensile stress F2 resulting from the compressive stress of the tension applying portion 103b. When the movable plate 101 rotates in-plane, the torsion bar 102 has a tensile stress F1 ′ that is the sum of the tensile stress F1 due to elongation and the initial tensile stress F2, and this is a restoring force that returns the movable plate 101 to its original state. Become. Therefore, the in-plane rotation of the movable plate 101 generated with respect to the same external force is smaller in the optical deflector 100 of the present embodiment than in a general optical deflector. That is, in the optical deflector 100 of this embodiment, the movable plate 101 is less likely to rotate in the plane than a general optical deflector. Since this tensile stress F2 does not have a great influence on the torsion of the torsion bar 102, as a result, the undesired displacement of the movable plate 101 other than the inclination around the axis 111 of the movable plate 101 is kept relatively small. It is done.

<The subject of patent document 1 and the effect of this embodiment>
For example, as disclosed in Patent Document 1, in a configuration in which a thin film is formed on a torsion bar to give a tensile stress, the tensile stress is mainly determined between the torsion bar and the thin film generated at the time of film formation. Residual stress and warping of the torsion bar. Usually, since the residual stress between the torsion bar and the thin film is released over time, a minute change in the tensile stress directly causes a long-term change in device characteristics. In particular, when a metal film is used, the tensile stress tends to fluctuate, and the influence is remarkable.

  In the optical deflector 100 of this embodiment, a characteristic of the method for generating a tensile stress in the torsion bar 102 is that the tensile stress F2 is mainly determined by a geometric dimension in a plane. In this method, the tensile stress F2 is mainly determined by the distance at which the tension applying portion 103b pushes the peripheral portion of the connecting portion main body 103a parallel to the shaft 111. Since the fixing portion 104 is firmly fixed to the fixing layer 202, the tensile stress F2 hardly changes. Moreover, the tension | tensile_strength provision part 103b can be formed by the silicon etching and thermal oxidation which are generally performed, and the control of the shape is easy.

  Further, as disclosed in Patent Document 1, when a torsion bar is formed using a polycrystalline film, breakage or fatigue along the crystal grain boundary is likely to occur, and a problem in reliability is likely to occur. On the other hand, in this embodiment, the torsion bar can be formed of single crystal silicon that is highly reliable in terms of mechanical strength. The tension applying portion 103b can be formed of a silicon thermal oxide film. The silicon thermal oxide film has high stability and is suitable for a material that generates stress in the torsion bar.

  Therefore, according to this embodiment, it is possible to provide an optical deflector with high long-term reliability in which the undesired displacement of the movable plate 101 is well suppressed. In particular, the occurrence of contact between the movable comb teeth 106 and 107 and the fixed comb teeth 108 and 109 is suitably prevented by suppressing the in-plane rotation of the movable plate 101.

  In the present embodiment, for the purpose of supplying a potential to the movable comb teeth 106 and 107, the tension applying portion 103b is formed in a part of the connecting portion 103 and the silicon connecting portion main body 103a is left. May be configured to completely divide the silicon portion of the fixing portion 104 and the connecting portion main body 103a.

  In the present embodiment, the connecting portion 103 is configured to be connected to the fixing portions 104 on both sides of the torsion bar 102 in consideration of the balance. However, such a configuration is not necessarily required. For example, the fixing portion 104 on one side is not necessarily required. The structure connected only to this may be sufficient.

  In this embodiment, the connecting portion between the connecting portion 103 and the fixed portion 104 is between the connecting portion between the movable plate 101 and the torsion bar 102 and the connecting portion between the torsion bar 102 and the connecting portion 103 in the direction parallel to the shaft 111. For example, if a part of the connecting portion 103 extends toward the movable plate 101, the connecting portion between the torsion bar 102 and the connecting portion 103 is connected to the connecting portion between the movable plate 101 and the torsion bar 102. It may be between the connection part of the connection part 103 and the fixing | fixed part 104. FIG.

  Further, as shown above, silicon and a silicon thermal oxide film are effective as constituent materials for the torsion bar 102 and the tension applying portion 103b, but are not necessarily limited thereto. For example, an oxide film formed by CVD instead of the thermal oxide film may be used as the constituent material of the tension applying unit 103b.

(Modification 1)
The shape of the tension applying unit 103b is not limited to the shape illustrated in FIG. 1 and can be variously changed. A torsion bar 102, a connecting portion 103, and a fixing portion 104 according to this modification are shown in FIG. In this modification, the connecting portion 303 has a connecting portion main body 303 a and a pair of tension applying portions 303 b, and each tension applying portion 303 b meanders in a direction perpendicular to the direction parallel to the torsion bar 102. That is, the tension applying portion 303b has a plurality of portions extending in the axial direction of the torsion bar 102 and a plurality of portions extending in a direction perpendicular to the axial direction of the torsion bar 102, and these portions are continuous with each other. doing. The portion extending in the axial direction of the torsion bar 102 and the portion extending in the direction perpendicular to the axial direction of the torsion bar 102 may each be one. Also in this modified example, the tension applying portion 303b extends through the connecting portion 103 in the thickness direction and is exposed on the end surface facing the torsion bar 102, similarly to the tension applying portion 103b.

  Since the thermal oxide film is formed by the growth and contact of silicon on both sides in the oxidation process, it is not a completely integrated structure. Therefore, the fracture at the interface is likely to occur as compared with the integral structure. By providing a plurality of directions in which the interfaces contact with each other in a meandering shape, it is possible to prevent breakage by providing a contact surface in a plurality of directions with respect to a force from a certain direction.

(Modification 2)
A torsion bar 102, a connecting portion 103, and a fixing portion 104 according to this modification are shown in FIG. In the present modification, the connecting portion 403 includes a connecting portion main body 403 a and a pair of tension applying portions 403 b, and each tension applying portion 403 b is divided into a plurality in the axial direction of the torsion bar 102. In other words, each tension applying unit 403b includes a plurality of elements 403b1, 403b2, 403b3, and 403b4 that are arranged apart from each other in the axial direction of the torsion bar 102. These elements 403b1 to 403b4 extend in a direction perpendicular to the axial direction of the torsion bar 102. Also in this modified example, each element 403b1 to 403b4 of the tension applying portion 403b extends through the connecting portion 103 in the thickness direction and is exposed to the end surface facing the torsion bar 102, like the tension applying portion 103b. Yes.

In the present embodiment, the connecting portion main body 103 a is distorted in order to generate a tensile stress in the torsion bar 102. If the tension applying portion 103b is formed of a thick thermal oxide film in order to increase the tensile stress generated in the torsion bar 102, the connecting portion main body 103a may be damaged due to excessive force applied to a part of the connecting portion main body 103a. There is. In this variation,
In order to increase the tensile stress generated in the torsion bar 102 by distorting a plurality of portions of the connecting portion main body 103a by the elements 403b1 to 403b4 of the tension applying portion 403b, concentration of force on a part of the connecting portion main body 103a is avoided. It is done. In addition, the time for the oxidation process can be shortened by forming a thermal oxide film filling a plurality of narrow through-grooves rather than forming a thermal oxide film filling one wide through-groove.

(Modification 3)
A torsion bar 102, a connecting portion 103, and a fixing portion 104 according to this modification are shown in FIG. In this modified example, the connecting portion 503 has a connecting portion main body 503a and a pair of tension applying portions 503b, and each tension applying portion 503b is a plurality of members arranged with a space in a direction perpendicular to the axial direction of the torsion bar 102. Elements 503b1, 503b2, and 503b3. Each element 503b1 to 503b3 extends through the connecting portion 103 in the thickness direction, and the element 503b1 is exposed at an end surface facing the torsion bar 102. From another viewpoint, the connecting portion main body 503a has through holes 503c1, 503c2, and 503c3 aligned in a direction perpendicular to the axial direction of the torsion bar 102, and one end of the element 503b1 is formed in the through hole 503c1. Both ends of the element 503b2 are exposed in the through holes 503c1 and 503c2, and both ends of the element 503b3 are exposed in the through holes 503c2 and 503c3.

  In this modification, since both end faces of the elements 503b1 to 503b3 in the direction perpendicular to the axial direction of the torsion bar 102 are exposed to the space, the interface between the elements 503b1 to 503b3 of the tension applying part 503b and the connecting part main body 103a. The excess internal stress generated at the time is released, and deformation that does not contribute to the generation of tensile stress in the torsion bar 102 and excessive stress concentration can be suppressed.

  Here, Modification 1 to Modification 3 of the shape of the tension applying portion are shown, but the shape of the tension applying portion is not limited to Modification 1 to Modification 3, and is modified to various other shapes. May be.

  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. The various modifications and changes described here include an implementation in which the above-described embodiments are appropriately combined.

  In the embodiment, the configuration in which the pair of connecting portions 103 are provided and each connecting portion 103 has the tension applying portion 103b is shown, but only one connecting portion 103 has the tension applying portion 103b. It may be. Further, the connecting portion 103 may be interposed only between the one torsion bar 102 and the fixing portion 104, and the other torsion bar 102 may be directly connected to the fixing portion 104. Moreover, although a pair of fixing | fixed part 104 is isolate | separated from each other, the structure which was integrated may be sufficient.

  Further, in the embodiment, the optical deflector using the comb-shaped electrostatic actuator that strongly suppresses the in-plane rotation of the movable plate is taken as an example, but the technical idea of the present embodiment uses the electrostatic actuator. The present invention may be applied to an optical deflector and further to an optical deflector of another driving method. Both optical deflectors are useful because the displacement of the movable plate in the direction perpendicular to the axial direction of the torsion bar is suppressed in addition to the in-plane rotation of the movable plate.

DESCRIPTION OF SYMBOLS 100 ... Optical deflector, 101 ... Movable plate, 102 ... Torsion bar, 103 ... Connection part, 103a ... Connection part main body, 103b ... Tension applying part, 104 ... Fixed part, 104a ... Corresponding part, 106, 107 ... Movable comb tooth 108, 109 ... fixed comb teeth, 110 ... reflective film, 111, 113, 115 ... shaft, 201 ... mirror layer, 202 ... fixed layer, 203 ... insulating layer, 204 ... support layer, 205 ... insulating layer, 206 ... support 207 ... silicon nitride film, 208 ... groove, 209 ... photoresist layer, 303b ... tension applying part, 403b ... tension applying part, 403b1 to 403b4 ... element, 503b ... tension applying part, 503b1 to 503b3 ... element, 503c1 503c3: through hole, F1, F1 ', F2 ... tensile stress, M1 ... moment, V1, V2 ... potential.

Claims (10)

A movable plate,
A pair of torsion bars supporting the movable plate in a tiltable manner;
A fixing part for supporting the torsion bar;
Comprising at least one connecting portion interposed between the torsion bar and the fixed portion;
At least one of the connecting portions is an optical deflector provided with a tension applying structure that generates a tensile stress in the torsion bar. The movable plate, the torsion bar, and the connecting portion have a beam structure that is supported at both ends by the fixed portion,
The connecting portion includes a connecting portion main body and the tension applying structure, and the tension applying structure includes at least one tension applying portion, and the tension applying portion is a portion of the surrounding connecting portion main body. The optical deflector according to claim 1, wherein the optical deflector is pressed in an axial direction of the torsion bar. The connecting part between the connecting part and the fixed part is located on both sides of the torsion bar to which the connecting part is connected, and the torsion bar and the movable plate to which the connecting part is connected in the axial direction of the torsion bar. Between the connecting portion, the torsion bar to which the connecting portion is connected, and the connecting portion of the connecting portion,
The tension applying structure includes a pair of tension applying portions arranged on both sides of a torsion bar to which the connecting portion is connected, and each tension applying portion has a portion of the connecting portion main body around the torsion bar. The optical deflector according to claim 2, wherein the optical deflector is pressed in the axial direction.   Each tension applying portion extends through the connecting portion in the thickness direction, and is exposed at an end surface facing the torsion bar. The linear expansion coefficient of the tension applying portion is greater than the linear expansion coefficient of the connecting portion main body. The optical deflector according to claim 3, which is also small.   The optical deflector according to claim 4, wherein the movable plate, the torsion bar, and the connecting portion main body are made of a single crystal silicon material, and the tension applying portion is made of a silicon thermal oxide film.   5. Each tension applying portion has at least one portion extending in an axial direction of the torsion bar and at least one portion extending in a direction perpendicular to the axial direction of the torsion bar. The optical deflector as described.   5. The optical deflector according to claim 4, wherein each tension applying unit includes a plurality of elements arranged apart from each other in the axial direction of the torsion bar.   5. The optical deflector according to claim 4, wherein each tension applying unit includes a plurality of elements arranged with a space in a direction perpendicular to an axial direction of the torsion bar.   A pair of connecting portions respectively interposed between the torsion bar and the fixing portion are provided, and one connecting portion has a tension applying structure for applying a tensile stress to the torsion bar. Item 9. The optical deflector according to any one of Items 8.   The pair of connecting portions respectively interposed between the torsion bar and the fixed portion, and each connecting portion includes a tension applying structure that applies a tensile stress to the torsion bar. The optical deflector as described in any one of the above.

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