MEMS mirror, image display device, and ranging device

Abstract

To reduce the influence of the vibration of a driving part in the detection of the inclination of a mirror.SOLUTION: The MEMS mirror includes a mirror, a support supporting the mirror, a frame disposed to surround the support in a plan view, a pair of first beams connecting the support to the frame, a pair of drivers disposed on the pair of first beams, respectively, and configured to deform the pair of first beams, respectively, to incline the support about a rotation axis, at least one second beam connecting the support to the frame and deforming in accordance with inclination of the support, and a sensor disposed on the at least one second beam, and configured to detect deformation of the at least one second beam.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a MEMS mirror, an image display device, and a distance measuring device. [Background technology]

[0002] Patent Document 1 discloses a scanning mirror that includes a mirror portion that reflects laser light, a support structure that rotationally oscillates the mirror portion, and a strain sensor that is provided on the support structure and detects the vibration of the mirror portion. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2013 / 140757

[0004] [overview] In the scanning mirror described in Patent Document 1, the strain sensor is provided in the support structure, and therefore, when detecting vibration of the mirror portion, the strain sensor may be affected by vibration of the support structure.

[0005] A MEMS mirror according to one aspect of the present invention comprises: Miller and a support for supporting the mirror; a frame disposed so as to surround the support body in a plan view; a pair of first beams connecting the support to the frame; a pair of drive units respectively disposed on the pair of first beams and configured to tilt the support body around a rotation axis by deforming the pair of first beams; At least one second beam that connects the support to the frame and deforms in accordance with the tilt of the support; a sensor disposed on the at least one second beam and configured to detect deformation of the at least one second beam; Equipped with. [Brief explanation of the drawings]

[0006] [Figure 1] FIG. 1 is a plan view of a MEMS mirror according to one embodiment of the present disclosure. [Figure 2] FIG. 2 is a cross-sectional view taken along line II-II in FIG. [Figure 3] FIG. 3 is a plan view of a MEMS mirror according to a modified example of an embodiment of the present disclosure.

[0007] [Detailed explanation] Hereinafter, a method for manufacturing a MEMS mirror according to an embodiment of the present disclosure will be described with reference to the accompanying drawings. Note that the following description is essentially merely exemplary and is not intended to limit the present disclosure, its applications, or its uses. Furthermore, the drawings are schematic, and the ratios of dimensions, etc., differ from those of the actual objects.

[0008] In the following description, for convenience, among the directions along each side of the MEMS mirror 1 in the plan view shown in FIG. 1, the left-right direction in FIG. 1 will be referred to as the X direction, the up-down direction in FIG. 1 will be referred to as the Y direction, and the thickness direction of the MEMS mirror 1 in the cross-sectional view shown in FIG. 2 (the up-down direction in FIG. 2) will be referred to as the Z direction. In particular, in FIG. 1, the right side may be referred to as the +X direction, the left side as the -X direction, the upper side as the +Y direction, and the lower side as the -Y direction. In FIG. 2, the upper side may be referred to as the +Z direction and the lower side as the -Z direction. In this embodiment, the X direction, the Y direction, and the Z direction are orthogonal to one another. Furthermore, in the following description, the direction orthogonal to the Z direction may be simply referred to as the lateral direction. The lateral direction includes the X direction, the Y direction, and a direction that intersects the X direction and the Y direction and is orthogonal to the Z direction.

[0009] Referring to FIG. 1 , the MEMS mirror 1 includes a mirror 10, a support 20, a frame 30, a pair of first beams 40A and 40B, a pair of actuators 50A and 50B, a pair of second beams 60A and 60B, and a pair of sensors 70A and 70B. In the following description, when there is no need to particularly distinguish between the pair of first beams 40A and 40B, one of the pair of first beams 40A and 40B may be simply referred to as the first beam 40. Similarly, when there is no need to particularly distinguish between the pair of actuators 50A and 50B, one of the pair of actuators 50A and 50B may be simply referred to as the actuator 50. When there is no need to particularly distinguish between the pair of second beams 60A and 60B, one of the pair of second beams 60A and 60B may be simply referred to as the second beam 60. When there is no need to particularly distinguish between the pair of sensors 70A and 70B, one of the pair of sensors 70A and 70B may be simply referred to as the sensor 70.

[0010] 1 and 2, mirror 10 has a reflecting surface 11 that reflects incident light. Reflecting surface 11 is disposed on the +Z side surface of mirror 10. Mirror 10 is made of alumina (Al2O3).

[0011] The support 20 supports the mirror 10 from the -Z side. The support 20 is disposed on the -Z side of the mirror 10. In other words, the mirror 10 is stacked on the +Z side of the support 20. The support 20 has a conductive silicon (Si) layer.

[0012] The support body 20 of this embodiment has a rectangular shape in a plan view. Specifically, the support body 20 has four outer surfaces 21A to 21D that form a rectangle in a plan view. In the following description, when there is no need to particularly distinguish between the four outer surfaces 21A to 21D, one of the four outer surfaces 21A to 21D may be simply referred to as the outer surface 21.

[0013] The outer surface 21A is a plane extending in the Y and Z directions, and defines the +X side of the support body 20.

[0014] The outer surface 21B is a plane extending in the X and Z directions, and defines the −Y side of the support 20.

[0015] The outer surface 21C is a plane extending in the Y and Z directions and defines the -X side of the support body 20. The outer surface 21C extends parallel to the outer surface 21A in a plan view. The outer surface 21C, together with the outer surface 21A, constitutes a pair of short sides of the support body 20.

[0016] The outer surface 21D is a plane extending in the X and Z directions, and defines the +Y side of the support body 20. In a plan view, the outer surface 21D extends parallel to the outer surface 21B. The outer surface 21D, together with the outer surface 21B, constitutes a pair of long sides of the support body 20.

[0017] The frame 30 surrounds the support 20 in the X and Y directions. The frame 30 is a rectangular frame in a plan view. The frame 30 has a cavity 30a that is rectangular in a plan view. The mirror 10 and the support 20 are disposed within the cavity 30a of the frame 30. The frame 30 has a conductive silicon (Si) layer.

[0018] The frame 30 has four inner surfaces 31A to 31D that define the cavity 30a. In the following description, when there is no need to particularly distinguish between the four inner surfaces 31A to 31D, one of the four inner surfaces 31A to 31D may be simply referred to as the inner surface 31.

[0019] The inner surface 31A is a plane extending in the Y and Z directions and defines the +X side of the cavity 30a. The inner surface 31A is disposed opposite the outer surface 21A of the support body 20. The inner surface 31A extends parallel to the outer surface 21A of the support body 20 in a plan view.

[0020] The inner surface 31B is a plane extending in the X and Z directions and defines the -Y side of the cavity 30a. The inner surface 31B is disposed opposite the outer surface 21B of the support body 20. The inner surface 31B extends parallel to the outer surface 21B of the support body 20 in a plan view.

[0021] The inner surface 31C is planar and extends in the Y and Z directions, and defines the -X side of the cavity 30a. The inner surface 31C is disposed facing the inner surface 31C. The inner surface 31C extends parallel to the inner surface 31C in a plan view. The inner surface 31C is disposed facing the outer surface 21C of the support body 20. The inner surface 31C extends parallel to the outer surface 21C of the support body 20 in a plan view.

[0022] The inner surface 31D is planar and extends in the X and Z directions, and defines the +Y side of the cavity 30a. The inner surface 31D is disposed facing the inner surface 31D. The inner surface 31D extends parallel to the inner surface 31D in a plan view. The inner surface 31D is disposed facing the outer surface 21D of the support body 20. The inner surface 31D extends parallel to the outer surface 21D of the support body 20 in a plan view.

[0023] The first beam 40 connects the support 20 to the frame 30. The pair of first beams 40A, 40B supports the support 20 from both sides in the X direction and holds the support 20 within the cavity 30a. The first beam 40 has a conductive silicon (Si) layer.

[0024] The first beam 40 extends in a meandering manner along the X direction in plan view. Specifically, the first beam 40 includes a plurality of first portions 41 each having a rectangular shape in plan view and a plurality of second portions 42 each having an arc shape in plan view. The plurality of first portions 41 each extend in the Y direction and are arranged side by side in the X direction. Each of the plurality of second portions 42 connects two of the plurality of first portions 41 that are adjacent in the X direction in a folded manner.

[0025] The first beam 40A is disposed on the +X side of the support body 20. One end of the first beam 40A is connected to a corner formed by the outer surface 21A and the outer surface 21B of the support body 20. The other end of the first beam 40A is cantilevered on the inner surface 31A of the frame 30, which extends in the Y and Z directions. The first beam 40A protrudes from the inner surface 31A into the cavity 30a on the -X side.

[0026] The first beam 40B is disposed on the -X side of the support body 20. One end of the first beam 40B is connected to a corner formed by the outer side surfaces 21B and 21C of the support body 20. The other end of the first beam 40B is cantilevered on the inner side surface 31C of the frame 30, which extends in the Y and Z directions. The first beam 40B protrudes from the inner side surface 31C into the cavity 30a on the +X side.

[0027] The driving units 50A and 50B are configured to tilt the support 20 around a rotation axis a1 by deforming the corresponding first beams 40A and 40B, respectively. The rotation axis a1 extends in the X direction. The driving units 50 are piezoelectric driving units. In other words, the driving method of the MEMS mirror 1 is piezoelectric. The driving unit 50A is disposed on the first beam 40A, and the driving unit 50B is disposed on the first beam 40B.

[0028] The driving section 50 includes a plurality of piezoelectric elements 51 respectively disposed on the plurality of first portions 41 of the first beam 40. Each of the plurality of piezoelectric elements 51 includes a first electrode layer 51a, a piezoelectric layer 51b, and a second electrode layer 51c.

[0029] The first electrode layer 51a is an electrode layer made of platinum (Pt). The first electrode layer 51a is stacked on the +Z side of the first beam 40. More specifically, the first electrode layer 51a is stacked on the +Z side of the first portion 41 of the first beam 40.

[0030] The piezoelectric layer 51b is made of zinc zirconate titanate (PZT) and is laminated on the +Z side of the first electrode layer 51a.

[0031] The second electrode layer 51c is an electrode layer made of iridium oxide (IrO) and is laminated on the +Z side of the piezoelectric layer 51b.

[0032] When a voltage is applied between the first electrode layer 51a and the second electrode layer 51c, the piezoelectric layer 51b expands and contracts in the Y direction. When the piezoelectric layer 51b expands in the Y direction, the first portion 41 of the first beam 40 deforms so as to curve convexly toward the +Z side. When the piezoelectric layer 51b contracts in the Y direction, the first portion 41 of the first beam 40 deforms so as to curve convexly toward the -Z side.

[0033] The driving unit 50 is configured so that voltages of opposite phases are applied to the two piezoelectric elements 51 arranged in each of the two adjacent first portions 41. As a result, the two adjacent first portions 41 are deformed so as to bend in opposite directions in the Z direction, causing the support body 20 to tilt around the rotation axis a1.

[0034] The second beam 60 connects the support 20 to the frame 30. The second beam 60 has a conductive silicon (Si) layer.

[0035] The second beam 60 extends in a meandering manner along the Y direction in plan view. Specifically, the second beam 60 includes a plurality of first portions 61 each having a rectangular shape in plan view and a plurality of second portions 62 each having an arc shape in plan view. The plurality of first portions 61 each extend in the X direction and are arranged side by side in the Y direction. Each of the plurality of second portions 62 connects two of the plurality of first portions 61 that are adjacent in the Y direction in a folded manner.

[0036] The second beam 60A is disposed in the +Y direction of the support body 20. A first end 60a of the second beam 60A is connected to the outer surface 21D of the support body 20. A second end 60b of the second beam 60A is cantilevered on the inner surface 31D of the frame 30, which extends in the X and Z directions. The second beam 60A protrudes from the inner surface 31D into the cavity 30a on the -Y side.

[0037] The second beam 60B is disposed in the -Y direction of the support body 20. A first end 60a of the second beam 60B is connected to the outer surface 21B of the support body 20. A second end 60b of the second beam 60A is cantilevered on the inner surface 31B of the frame 30, which extends in the X and Z directions. The second beam 60A protrudes from the inner surface 31B into the cavity 30a on the -Y side.

[0038] The pair of second beams 60A, 60B are arranged symmetrically with respect to the rotation axis a1 in a plan view. The first ends 60a of the pair of second beams 60A, 60B are arranged at the same position as each other in the X direction. The second ends 60b of the pair of second beams 60A, 60B are arranged at the same position as each other in the X direction.

[0039] The first beam 40 and the second beam 60 both have the function of connecting the support body 20 to the frame 30, but have different functions as described below.

[0040] The first beam 40 supports the support 20 so as to hold the support 20 within the cavity 30a, while the second beam 60 is not intended to support the support 20. The support stiffness of the second beam 60 for supporting the support 20 in the Z direction is lower than the support stiffness of the first beam 40 for supporting the support 20 in the Z direction.

[0041] The first beam 40 is deformed by the driving unit 50 to cause the support 20 to tilt about the rotation axis a1, while the second beam 60 is configured to deform in accordance with the tilt caused in the support 20. In other words, the second beam 60 is not provided with an element for deforming the second beam 60, and in this respect, the second beam 60 differs from the first beam 40 that is provided with the driving unit 50 for deforming the first beam 40.

[0042] The second beam 60 is formed with lower rigidity than the first beam 40, and is easily deformed in the Z direction. This reduces the effect of the second beam 60 on the movement of the support 20 compared to when the second beam 60 is formed with higher rigidity than the first beam 40. In this embodiment, the bending rigidity of the second beam 60 is lower than that of the first beam 40. The bending rigidity of the second beam 60 is preferably 20% or less of the bending rigidity of the first beam 40, and more preferably 10% or less of the bending rigidity of the first beam 40. Here, the bending rigidity of the first beam 40 refers to the bending rigidity against a bending moment applied in the Z direction from both ends of the first beam 40 in the X direction. Furthermore, the bending rigidity of the second beam 60 refers to the bending rigidity against a bending moment applied in the Z direction from both ends of the second beam 60 in the Y direction. The thickness of the second beam 60, i.e., the dimension in the Z direction, is thicker than the thickness of the first beam 40.

[0043] The sensor 70 detects the deformation of the second beam 60. Specifically, the sensor 70 is a strain sensor that detects the strain of the second beam 60. The sensor 70 in this embodiment is a strain gauge. Specifically, the sensor 70 is a silicon (Si) layer doped with impurities such as boron (B), phosphorus (P), or arsenic (As). The sensor 70 is stacked on the +Z side of the second beam 60. When the second beam 60 deforms in accordance with the tilt of the support 20 around the rotation axis a1, a resistance change occurs in the sensor 70 corresponding to the strain occurring on the surface of the +Z side of the second beam 60. The resistance value of the sensor 70 is measured as a voltage value via a bridge circuit (not shown).

[0044] The sensor 70A is disposed on the second beam 60A. Specifically, the sensor 70A is disposed at a position on the second beam 60A closer to the second end 60b than to the first end 60a. The sensor 70B is disposed on the second beam 60B. Specifically, the sensor 70B is disposed at a position on the second beam 60B closer to the second end 60b than to the first end 60a.

[0045] The MEMS mirror 1 according to this embodiment has the following advantages.

[0046] (1) MEMS mirror 1 is Mirror 10 and a support 20 for supporting the mirror 10; a frame 30 arranged to surround the support body 20 in a plan view; A pair of first beams 40A, 40B connecting the support 20 to the frame 30; a pair of drive units 50A and 50B disposed on the pair of first beams 40A and 40B, respectively, and configured to tilt the support body about the rotation axis by deforming the pair of first beams 40A and 40B, respectively; The support 20 is connected to the frame 30, and at least one second beam 60 (in this embodiment, a pair of second beams 60A, 60B, a sensor 70 (a pair of sensors 70A and 70B in this embodiment) disposed on at least one second beam 60 and detecting deformation of the at least one second beam 60; Equipped with.

[0047] According to this configuration, the sensor 70 detects the deformation of the second beam 60, thereby making it possible to detect the tilt of the mirror 10. Furthermore, according to this configuration, the sensor 70 that detects the tilt of the mirror 10 is disposed on the second beam 60, rather than on the first beam 40 where the driver 50 for tilting the mirror 10 is disposed. Therefore, compared to when the sensor that detects the tilt of the mirror 10 is disposed on the first beam 40, the influence of vibration of the driver 50 on the detection of the tilt of the mirror 10 can be reduced.

[0048] (2) The bending rigidity of at least one second beam 60 is smaller than the bending rigidity of each first beam 40 .

[0049] If the bending rigidity of the second beams 60 is excessively large, the second beams 60 may hinder the movement of the support body 20. In contrast, with this configuration, the bending rigidity of at least one second beam 60 is smaller than the bending rigidity of the first beam 40. Therefore, compared to when the bending rigidity of at least one second beam 60A, 60B is larger than the bending rigidity of the first beam 40, the effect of the second beams 60 on the movement of the support body 20 can be reduced.

[0050] (3) The sensor 70 is a strain gauge.

[0051] Compared to a piezoelectric strain sensor, a strain gauge has a higher linearity of the sensor output with respect to the tilt of the mirror 10. In this embodiment, since the sensor 70 is a strain gauge, the accuracy with which the sensor 70 detects the tilt of the mirror 10 can be improved compared to when a piezoelectric strain sensor is used as the sensor 70.

[0052] (4) At least one second beam 60 has a first end 60a connected to the support 20 and a second end 60b connected to the frame 30, and the sensor 70 is positioned on the at least one second beam 60 closer to the second end 60b than to the first end 60a.

[0053] In the second beam 60, the largest bending moment acts on the portion connected to the frame 30, and therefore the strain is greatest in this portion. In this embodiment, the sensor 70 is disposed at a position of at least one second beam 60 closer to the second end 60b than to the first end 60a, and therefore the output of the sensor 70 can be increased compared to when the sensor 70 is disposed at a position of at least one second beam 60 closer to the first end 60a than to the second end 60b. As a result, the accuracy with which the sensor 70 detects the tilt of the mirror 10 can be improved.

[0054] (5) At least one second beam 60 is a plurality of second beams 60A, 60B that are arranged line-symmetrically with respect to the rotation axis a1 in a plan view.

[0055] When one second beam 60 is connected to the support 20, or when multiple second beams 60 are arranged asymmetrically with respect to the rotation axis a1, a difference may occur between the behavior of the support 20 to one side and the behavior to the other side about the rotation axis a1. In contrast, with this configuration, the multiple second beams 60A, 60B are arranged line-symmetrically with respect to the rotation axis a1, so that it is possible to suppress the occurrence of a difference between the behavior of the support 20 to one side and the behavior to the other side about the rotation axis a1.

[0056] The support body 20 has a plurality of outer surfaces 21A to 21D that form a polygon (a rectangle in this embodiment) when viewed in a plane, and at least one second beam 60 is connected to one of the plurality of outer surfaces 21A to 21D, which is different from the outer surfaces 21A and 21C to which the pair of first beams 40A and 40B are connected.

[0057] With this configuration, the distance between the sensor 70 and the drive unit 50 can be increased compared to when at least one second beam 60 is connected to the outer surfaces 21A, 21C of the multiple outer surfaces 21A to 21D of the support body 20 to which a pair of first beams 40A, 40B are connected, thereby reducing the effect of vibration of the drive unit 50 on the detection of the tilt of the mirror 10 by the sensor 70.

[0058] [Variations] The present disclosure is not limited to the configurations described in the above embodiments, and various modifications are possible.

[0059] The MEMS mirror 1 in the above embodiment is a one-axis driven MEMS mirror that can tilt the mirror 10 around the rotation axis a1, but is not limited to this and may be a two-axis driven MEMS mirror that can tilt the mirror 10 around the rotation axis a2 in addition to the rotation axis a1, as in the modified example shown in Fig. 3. In this case, the tilt of the mirror 10 around the rotation axis a1 may be used for vertical scanning, and the tilt of the mirror 10 around the rotation axis a2 may be used for horizontal scanning.

[0060] The MEMS mirror 1 according to the present disclosure may be used in an image display device such as a head-mounted display or a head-up display, or a distance measuring device such as a Light Detection And Ranging (LiDAR) device.

[0061] In the above embodiment, the MEMS mirror 1 includes a pair of second beams 60A and 60B, but the MEMS mirror according to the present disclosure may include at least one second beam 60. Furthermore, the MEMS mirror according to the present disclosure may include three or more second beams 60.

[0062] In the above embodiment, the support 20 is rectangular in plan view, but is not limited thereto. The support according to the present disclosure may have other shapes in plan view, including polygonal shapes other than rectangular or circular shapes.

[0063] [Note] The MEMS mirror according to the present disclosure provides the following aspects.

[0064] [Aspect 1] Miller and a support for supporting the mirror; a frame disposed so as to surround the support body in a plan view; a pair of first beams connecting the support to the frame; a pair of drive units respectively disposed on the pair of first beams and configured to tilt the support body around a rotation axis by deforming the pair of first beams; At least one second beam that connects the support to the frame and deforms in accordance with the tilt of the support; a sensor disposed on the at least one second beam and configured to detect deformation of the at least one second beam; A MEMS mirror comprising:

[0065] [Aspect 2] 2. The MEMS mirror of embodiment 1, wherein the bending stiffness of the at least one second beam is less than the bending stiffness of each first beam.

[0066] [Aspect 3] 3. The MEMS mirror of claim 1 or 2, wherein the sensor is a strain gauge.

[0067] [Aspect 4] The at least one second beam is a first end connected to the support; a second end connected to the frame; and 4. The MEMS mirror according to any one of aspects 1 to 3, wherein the sensor is disposed at a position of the at least one second beam closer to the second end than to the first end.

[0068] [Aspect 5] 5. The MEMS mirror according to any one of aspects 1 to 4, wherein the at least one second beam is a plurality of second beams that are arranged line-symmetrically with respect to the rotation axis in a plan view.

[0069] [Aspect 6] the support body has a plurality of outer surfaces that form a polygon in a plan view, 6. The MEMS mirror of any one of aspects 1 to 5, wherein the at least one second beam is connected to one of the plurality of outer surfaces that is different from the outer surfaces to which the pair of first beams are connected.

[0070] [Aspect 7] An image display device comprising the MEMS mirror according to any one of embodiments 1 to 6.

[0071] [Aspect 8] A distance measuring device comprising the MEMS mirror according to any one of embodiments 1 to 6. [Explanation of symbols]

[0072] 1. MEMS mirror 10. Mirror 11 Reflective surface 20 Support 21 External surface 30 frames 30a cavity 31 Inner surface 40 1st beam 41 Part 1 42 Part 2 50 Drive unit 51 Piezoelectric element 51a 1st electrode layer 51b Piezoelectric layer 51c 2nd electrode layer 60 2nd beam 60a 1st end 60b 2nd end 61 Part 1 62 Part 2 70 sensors a1 Rotation axis

Claims

1. Miller and a support for supporting the mirror; a frame disposed so as to surround the support body in a plan view; a pair of first beams connecting the support to the frame; a pair of drive units disposed on the pair of first beams, respectively, and configured to tilt the support body around a rotation axis by deforming the pair of first beams, respectively; at least one second beam that connects the support to the frame and deforms in accordance with the tilt of the support; a sensor disposed on the at least one second beam and configured to detect deformation of the at least one second beam; A MEMS mirror comprising:

2. The MEMS mirror according to claim 1 , wherein the bending stiffness of the at least one second beam is less than the bending stiffness of each first beam.

3. The MEMS mirror of claim 1 , wherein the sensor is a strain gauge.

4. The at least one second beam is a first end connected to the support; a second end connected to the frame; and The MEMS mirror according to claim 3 , wherein the sensor is disposed at a position of the at least one second beam closer to the second end than to the first end.

5. The MEMS mirror according to claim 1 , wherein the at least one second beam comprises a plurality of second beams arranged line-symmetrically with respect to the rotation axis in a plan view.

6. the support body has a plurality of outer surfaces that form a polygon in a plan view, The MEMS mirror according to claim 1 , wherein the at least one second beam is connected to one of the plurality of outer surfaces that is different from the outer surfaces to which the pair of first beams are connected.

7. An image display device comprising the MEMS mirror according to claim 1.

8. A distance measuring device comprising the MEMS mirror according to claim 1.

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