JP5287690B2 - Optical deflection device - Google Patents

Description

  The present application relates to an optical deflecting device that changes a reflection direction of a light beam.

There is disclosed an optical deflecting device having a structure in which a pair of support points are formed at positions outside a mirror on a substrate, and two opposite ends of the mirror are supported by torsion beams from each of the support points. The torsion beam acts as a pivot axis. Then, the mirror is rotated by twisting the torsion beam by applying a force such as electrostatic force to the mirror. When the torsional rigidity of the torsion beam is lowered, the mirror can be moved with a small driving force, but sinking is likely to occur and it becomes difficult to obtain a desired tilt angle. Patent Document 1 discloses a technique for increasing the rigidity of the mirror in the sinking direction by generating tension in the torsion beam.

JP 2005-321663 A

  A material having a thermal expansion coefficient smaller than the thermal expansion coefficient of the substrate may be used as the material of the optical deflecting device. When the high-temperature process is completed and the light deflection apparatus contracts, the contraction ratio of the distance between the support points may be larger than the contraction ratio of the mirror and the torsion beam. As a result, tension is not applied to the torsion beam, and conversely a crushing force is applied, which may make it difficult to prevent the mirror from sinking.

  The present application provides a technique capable of generating tension in the torsion beam and preventing sinking regardless of the value of the coefficient of thermal expansion of the material of the optical deflecting device.

  The technology disclosed in this specification relates to an optical deflecting device that changes the reflection direction of a light beam. This optical deflecting device includes a substrate, a movable part, a pair of support parts, and a pair of movable beams. The movable part has a frame shape forming at least one opening. Each support portion is fixed to the substrate and extends upward from the substrate. The pair of support parts are spaced apart from each other and are disposed in the opening. Each movable beam connects the corresponding support portion and the inner peripheral surface of the opening of the movable portion. The pair of movable beams extend on the same straight line parallel to the surface of the substrate, and support the movable part so as to be swingable around the straight line. A low thermal expansion portion formed of a material having a lower thermal expansion coefficient than that of the substrate is present at least in a range extending along the interval in the frame-shaped movable portion.

  Since the support portion is disposed in the opening of the movable portion having a frame shape, the support portion is surrounded by the movable portion. Each of the movable beams extends on the same straight line parallel to the surface of the substrate, and connects the inner peripheral surface of the opening and the support portion. Therefore, the light deflection apparatus has a structure in which two points on the inner peripheral surface of the opening are supported by the movable beam from the inside of the movable part.

  Moreover, since the support part is being fixed to the board | substrate, the thermal expansion coefficient of the space | interval part of a support part becomes the same as the thermal expansion coefficient of a board | substrate. On the other hand, a portion (low thermal expansion portion) formed of a material having a lower thermal expansion coefficient than that of the substrate exists in a range extending along the interval between the support portions in the movable portion. Then, a difference arises between the thermal expansion coefficient of the low thermal expansion part of a movable part, and the thermal expansion coefficient in the space | interval part of a support part.

  Various processes for forming an optical deflector include processes performed at a high temperature of several hundred degrees C., such as a film forming process. Then, when the process in the high temperature state is finished and the temperature is returned from the high temperature state to the room temperature state, the light deflection device contracts. At this time, due to the above-described difference in thermal expansion coefficient, the shrinkage amount of the low thermal expansion portion of the movable portion is smaller than the shrinkage amount of the interval portion of the support portion. That is, the support portion tends to move toward the center of the movable portion by the difference in contraction amount. And since the optical deflection apparatus of this application has a structure which supports a movable part with a movable beam from the inside of a movable part, a movable beam will be pulled by a support part. This makes it possible to apply tension to the movable beam.

  In the above optical deflection device, the entire movable portion and the pair of movable beams may be a low thermal expansion portion. For example, a material having a low thermal expansion coefficient may be formed in a film shape on the entire surface of the movable portion and the pair of movable beams. Thereby, a low thermal expansion part can be easily produced in the range extended along the space | interval of a support part in a movable part.

  In the above optical deflecting device, the substrate and the low thermal expansion portion may be formed of a laminated material of silicon and silicon oxide. The ratio of silicon oxide to silicon in the low thermal expansion portion may be higher than the ratio of silicon oxide to silicon in the substrate. Thus, the influence of silicon oxide on the thermal expansion coefficient of the low thermal expansion portion is made larger than the influence of silicon oxide on the thermal expansion coefficient of the substrate. The thermal expansion coefficient of silicon oxide is smaller than the thermal expansion coefficient of silicon. Therefore, the thermal expansion coefficient of the low thermal expansion portion can be made smaller than the thermal expansion coefficient of the substrate. Silicon is a broad concept including single crystal silicon and polycrystalline silicon. Silicon oxide includes those formed by various methods such as thermal oxidation and CVD.

  The optical deflecting device of the present application includes a substrate, a movable part, a pair of support parts, and a pair of movable beams. The movable part has a frame shape forming at least one opening. Each support portion is fixed to the substrate and extends upward from the substrate. The pair of support parts are spaced apart from each other and are disposed in the opening. Each movable beam connects the corresponding support portion and the inner peripheral surface of the opening of the movable portion. The pair of movable beams extend on the same straight line parallel to the surface of the substrate, and support the movable part so as to be swingable around the straight line. A tensile stress acts on the pair of movable beams. By applying tension to the movable beam, the rigidity in the vertical direction can be increased compared to the rigidity in the oscillating direction (rotating direction around the movable beam), so the sinking of the movable part can be prevented. It becomes.

  According to the present application, it is possible to provide a technique capable of generating tension in the movable beam and preventing the sinking of the movable part regardless of the value of the thermal expansion coefficient of the material of the optical deflecting device.

It is a perspective view of the optical deflection apparatus of a present Example. It is sectional drawing of the optical deflection | deviation apparatus of a present Example. It is a top view of the light deflection apparatus of the present embodiment. It is a figure which shows the modification of an optical deflection apparatus.

The main features of the embodiment described below are organized.
(Feature 1) The movable portion and the pair of movable beams are formed of polycrystalline silicon, and a thermal oxide film is formed on the surface thereof.

  Embodiments will be described with reference to the drawings. FIG. 1 is a perspective view of the light deflecting device 100. The light deflection apparatus 100 is erected on the substrate 12. The optical deflection apparatus 100 includes a movable portion 42, a pair of support portions 19a and 19b, and a pair of movable beams 41a and 41b. The direction of the line connecting the center of the support portion 19a and the center of the support portion 19b is defined as the x direction. A direction orthogonal to the x direction in a plane parallel to the substrate 12 is defined as a y direction. Further, a direction orthogonal to the xy plane and directed upward of the substrate 12 is defined as a z direction.

  The movable portion 42 has a frame shape by forming the opening 43. Each of the support portions 19 a and 19 b is fixed to the substrate 12 and extends upward from the substrate 12. The pair of support portions 19a and 19b are separated from each other with a gap D1 therebetween. Further, the support portions 19a and 19b are disposed inside the opening 43 when observed from above in the z direction.

  The movable beams 41a and 41b are formed on the same line in the x direction and have a shape extending in parallel with the surface of the substrate 12. One end of the movable beam 41a is fixed to the end on the negative side in the x direction of the support portion 19a, and the other end is connected to the inner peripheral surface of the opening 43 at a point P1a. One end of the movable beam 41b is fixed to the end on the positive side in the x direction of the support portion 19b, and the other end is connected to the inner peripheral surface of the opening 43 at a point P1b. An axis passing through the center line of the movable beams 41a and 41b is defined as a swing axis S1. The movable portion 42 is supported by the movable beams 41a and 41b so as to be swingable around the swing axis S1.

  As described above, the optical deflecting device 100 has a structure in which the points P1a and p1b on the inner peripheral surface of the opening 43 are supported by the movable beams 41a and 41b existing inside the movable portion. Further, the support portions 19a and 19b that support the movable beams 41a and 41b have a structure in which they are separated from each other with a gap D1 therebetween.

  FIG. 2 is a cross-sectional view taken along the line II-II of the optical deflecting device 100 of FIG. The substrate 12 has a structure in which a silicon oxide layer 112 is formed on the surface of the single crystal silicon layer 111. The thickness of the single crystal silicon layer 111 of the substrate 12 in the z direction is 525 (μm), and the thickness of the silicon oxide layer 112 in the z direction is 0.2 (μm).

  The support portion 19a has a structure in which a silicon oxide layer 114a is formed on the surface of the polycrystalline silicon layer 113a. The support portion 19b has a structure in which a silicon oxide layer 114b is formed on the surface of the polycrystalline silicon layer 113b.

  The movable beam 41a has a structure in which a silicon oxide layer 116a is formed on the surface of the polycrystalline silicon layer 115a. The movable beam 41b has a structure in which a silicon oxide layer 116b is formed on the surface of the polycrystalline silicon layer 115b. The movable part 42 has a structure in which a silicon oxide layer 118 is formed on the surface of the polycrystalline silicon layer 117. The thicknesses of the polycrystalline silicon layers 115a, 115b, and 117 in the z direction are 0.3 (μm). The thicknesses of the silicon oxide layers 116a, 116b, and 118 in the z direction are 0.1 (μm). In addition, about the detail of the manufacturing method of the optical deflection | deviation apparatus 100, since a conventionally well-known method can be used, detailed description is abbreviate | omitted here.

  Although not shown, a mirror supported by a support column is formed on the movable part 42. By creating the mirror separately from the movable portion 42, a mirror having a larger area than the movable portion 42 can be formed. The structure of the mirror is not limited to a separate structure from the movable part 42, and a structure in which a reflective film is formed on the upper surface of the movable part 42 may be used. A detailed description of the mirror structure is omitted here.

  Next, a method for driving the optical deflection apparatus 100 will be described. A movable part electrode (not shown) is formed on the lower surface of the movable part 42. The movable part electrode is formed at a symmetrical position around the swing axis S1. A pair of substrate electrodes (not shown) are formed on the surface of the substrate 12 at positions where the movable portion electrodes are opposed to each other.

  For example, when a movable part electrode is grounded and a drive voltage is applied to one of a pair of substrate electrodes using a drive signal generator (not shown), the grounded movable part electrode and the substrate electrode to which the drive voltage is applied Electrostatic attractive force is generated between the movable portion 42 and the movable portion 42 is attracted to the substrate 12 side. Since the movable beams 41a and 41b have low torsional rigidity, the movable portion 42 can be swung around the swing axis S1.

  Next, the action of generating a tensile stress on the movable beams 41a and 41b will be described. First, the thermal expansion coefficient will be described. Here, the coefficient of thermal expansion is the rate at which the length of an object expands with increasing temperature per unit temperature.

The general value of thermal expansion coefficient of silicon oxide is 7.0 × 10 ⁻⁷ (1 / K), and the general value of thermal expansion coefficient of single crystal silicon is 2.5 × 10 ⁻⁶ (1 / K). The general value of the thermal expansion coefficient of polycrystalline silicon is 2.8 × 10 ⁻⁶ (1 / K). The thermal expansion coefficient of single crystal silicon and the thermal expansion coefficient of polycrystalline silicon have the same value. The thermal expansion coefficient of silicon oxide is smaller than the thermal expansion coefficient of single crystal silicon and the thermal expansion coefficient of polycrystalline silicon. This magnitude relationship is established without depending on the silicon oxide formation conditions. In the following description, the thermal expansion coefficient of single crystal silicon and polycrystalline silicon is defined as the silicon thermal expansion coefficient α. In addition, the thermal expansion coefficient of silicon oxide is defined as a silicon oxide thermal expansion coefficient γ.

  As described with reference to FIG. 2, the ratio of the thickness of the silicon oxide layer 112 to the thickness of the single crystal silicon layer 111 in the substrate 12 is sufficiently small. Therefore, the influence of the silicon oxide layer 112 on the thermal expansion coefficient of the substrate 12 can be ignored. Therefore, the thermal expansion coefficient of the portion of the distance D1 in the substrate 12 can be regarded as the silicon thermal expansion coefficient α.

  In the support portion 19a, the ratio of the thickness in the z direction of the silicon oxide layer 114a to the thickness in the z direction of the polycrystalline silicon layer 113a is sufficiently small. Similarly, in the support portion 19b, the ratio of the thickness in the z direction of the silicon oxide layer 114b to the thickness in the z direction of the polycrystalline silicon layer 113b is sufficiently small. Therefore, the influence of the silicon oxide layers 114a and 114b on the thermal expansion coefficient in the x direction of the support portions 19a and 19b can be ignored. Therefore, the thermal expansion coefficients of the support portions 19a and 19b can also be regarded as the silicon thermal expansion coefficient α.

  On the other hand, as described in FIG. 2, in the movable beam 41a, the ratio of the thickness of the silicon oxide layer 116a to the thickness of the polycrystalline silicon layer 115a is large. Therefore, the influence of the silicon oxide layer 116a on the thermal expansion coefficient in the x direction of the movable beam 41a cannot be ignored. Then, the thermal expansion coefficient in the x direction of the movable beam 41a becomes a value smaller than the silicon thermal expansion coefficient α. Similarly, the thermal expansion coefficients in the x direction of the movable beam 41b and the movable portion 42 are also smaller than the silicon thermal expansion coefficient α. Here, the thermal expansion coefficient in the x direction of the movable beams 41a and 41b and the movable portion 42 is defined as a thermal expansion coefficient β. The thermal expansion coefficient β is larger than the silicon oxide thermal expansion coefficient γ and smaller than the silicon thermal expansion coefficient α.

  Next, the action of generating a tensile stress in the movable beams 41a and 41b will be described with reference to FIG. FIG. 3 is a top view of the light deflection apparatus 100. As shown in FIG. 3, a region including the interval D1 and the support portions 19a and 19b is defined as a region R1. The thermal expansion coefficient in the x direction of the region R1 can be regarded as the silicon thermal expansion coefficient α. Further, a range extending along the region R1 in the frame-shaped movable portion 42 is defined as a region R2 (shaded portion in FIG. 3). The region R2 is a region having at least a range extending along the interval D1. The thermal expansion coefficient in the x direction of the region R2 is the thermal expansion coefficient β. Then, there is a difference in the value of the thermal expansion coefficient in the x direction between the region R1 and the region R2. In addition, since there is no difference in the value of a thermal expansion coefficient between parts other than area | region R2 of the movable part 42, and the movable beams 41a and 41b, a thermal stress does not generate | occur | produce. Therefore, in the following, focusing on the regions R1 and R2, the action of generating a tensile stress will be described.

  Various processes for forming the optical deflection apparatus 100 include processes performed at a high temperature of several hundred degrees C., such as a film forming process. In the high temperature state, no stress is generated in the optical deflecting device 100, and the stress is free. When the optical deflecting device 100 is returned from the high temperature state to the room temperature state, the entire optical deflecting device 100 contracts, and thermal stress is generated in the portions having different thermal expansion coefficients.

Here, the temperature difference between the high temperature state and the room temperature state is defined as DT. Further, when the contraction amount of the region R1 is defined as the contraction amount C1, the contraction amount C1 is obtained by the following expression (1).
Shrinkage amount C1 = silicon thermal expansion coefficient α × temperature difference DT × interval D1 Formula (1)
Further, when the contraction amount of the region R2 is defined as the contraction amount C2, the contraction amount C2 is obtained by the following expression (2).
Shrinkage amount C2 = thermal expansion coefficient β × temperature difference DT × interval D1 Formula (2)
Since silicon thermal expansion coefficient α> thermal expansion coefficient β, shrinkage amount C1> shrinkage amount C2. That is, the region R1 contracts more than the region R2. The shrinkage difference DD is obtained by the following equation (3).
Shrinkage difference DD = shrinkage amount C1−shrinkage amount C2 = (silicon thermal expansion coefficient α−thermal expansion coefficient β) × temperature difference DT × interval D1 (3)

  Therefore, the relative position of the support portion 19a with respect to the movable portion 42 moves to the positive side in the x direction (right side in FIG. 3) by a distance that is half the contraction amount difference DD. Since the movable beam 41a connects the support portion 19a and the movable portion 42, it is possible to apply a tension to the movable beam 41a. Similarly, the relative position of the support portion 19b with respect to the movable portion 42 moves to the negative side (left side in FIG. 3) in the x direction by a distance that is half the contraction amount difference DD. Since the movable beam 41b connects the support portion 19b and the movable portion 42, it is possible to apply tension to the movable beam 41b.

  In addition, in order to enlarge the tension | tensile_strength applied to the movable beams 41a and 41b, it turns out that the space | interval D1 should just be enlarged from Formula (3).

  The effect of the optical deflection apparatus 100 according to the present embodiment will be described. In the optical deflecting device 100 of the present embodiment, first, a pair of support portions 19a and 19b are structured to be separated from each other with a gap D1 therebetween. Thereby, a difference can be caused in the value of the thermal expansion coefficient between the region R1 and the region R2. Therefore, thermal stress can be generated so that the support parts 19a and 19b move to the center side of the movable part 42. Secondly, the optical deflecting device 100 according to the present embodiment has a structure in which the movable beams 41 a and 41 b exist inside the movable portion 42. Thereby, it can be set as the form by which the movable beams 41a and 41b are pulled by the support parts 19a and 19b. That is, the generation direction of the thermal stress can be matched with the tension direction of the movable beams 41a and 41b. As described above, tension can be applied to the movable beams 41a and 41b regardless of the value of the thermal expansion coefficient of the material constituting the optical deflecting device 100. Therefore, since the rigidity in the vertical direction can be increased as compared with the rigidity in the swing direction (the rotation direction around the movable beam), it is possible to prevent the movable part from sinking.

  Note that the number of openings is not limited to one, and a plurality of openings may be provided. There may be a plurality of openings 43a and 43b as in the optical deflecting device 100a shown in FIG. In this case, tension is applied to the movable beams 41a and 41b due to the difference in the value of the thermal expansion coefficient in the x direction between the region R1a and the region R2a.

  In the optical deflecting device of this embodiment, the case where the overall thermal expansion coefficient of the movable portion 42 and the movable beams 41a and 41b is lower than the silicon thermal expansion coefficient α has been described. However, the present invention is not limited to this configuration. . In FIG. 3, the thermal expansion coefficient of only the region R2 may be lower than the silicon thermal expansion coefficient α. In addition, as a method of reducing the thermal expansion coefficient of the region R2, a method of forming a material having a low thermal expansion coefficient in the region R2 in a film shape can be given.

  Moreover, it cannot be overemphasized that it is not specifically limited about the structure of the movable part 42 and the movable beams 41a and 41b.

  As mentioned above, although the specific example of this application was demonstrated in detail, these are only illustrations and do not limit a claim. The technology described in the claims includes various modifications and changes of the specific examples illustrated above. The technical elements described in this specification or the drawings exhibit technical usefulness alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. In addition, the technology illustrated in the present specification or the drawings achieves a plurality of objects at the same time, and has technical utility by achieving one of the objects.

12 Substrate 19a, 19b Support part 41a, 41b Movable beam 42 Movable part 100 Optical deflecting device D1 Spacing R1, R2 region

Claims (4)

An optical deflecting device that changes the reflection direction of light,
A substrate, a movable part, a pair of support parts, and a pair of movable beams;
The movable part has a frame shape that forms at least one opening,
Each support portion is fixed to the substrate and extends upward from the substrate.
The pair of support portions are spaced apart from each other with an interval between them and disposed in the opening,
Each movable beam connects the corresponding support part and the inner peripheral surface of the opening of the movable part,
The pair of movable beams extend on the same straight line parallel to the surface of the substrate, and support the movable part so as to be swingable around the straight line.
The light deflection apparatus characterized in that a low thermal expansion portion made of a material having a lower thermal expansion coefficient than the substrate exists in at least a range extending along the interval in the frame-shaped movable portion. The optical deflection apparatus according to claim 1, wherein the entire movable portion and the pair of movable beams are the low thermal expansion portion. The substrate and the low thermal expansion part are made of a laminated material of silicon and silicon oxide,
3. The optical deflection apparatus according to claim 1, wherein a ratio of silicon oxide to silicon in the low thermal expansion portion is higher than a ratio of silicon oxide to silicon in the substrate. . An optical deflecting device that changes the reflection direction of light,
A substrate, a movable part, a pair of support parts, and a pair of movable beams;
The movable part has a frame shape that forms at least one opening,
Each support portion is fixed to the substrate and extends upward from the substrate.
The pair of support portions are spaced apart from each other with an interval between them and disposed in the opening,
Each movable beam connects the corresponding support part and the inner peripheral surface of the opening of the movable part,
The pair of movable beams extend on the same straight line parallel to the surface of the substrate, and support the movable part so as to be swingable around the straight line.
An optical deflecting device, wherein a tensile stress acts on the pair of movable beams.

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