Micromirror device and optical scanning device

Abstract

The micromirror device includes a mirror portion, a pair of first support portions, a pair of movable frames, a pair of second support portions, a drive portion, a fixed frame, a pair of first connection portions, and a pair of second connection portions. The movable frame is symmetrical with respect to the first axis and has a reinforcing structure not in contact with a boundary portion between the movable frame and the first support portion, and the first connection portion and the second connection portion are each in a shape symmetrical with respect to the first axis and support the first actuator and the second actuator so as to be swingable about the first axis.

Description

Technical Field

[0001] The technology of the present invention relates to a micromirror device and a light scanning device. Background Art

[0002] As one of the MEMS devices made using silicon (Si) microfabrication technology, a micromirror device (also called a microscanner) is known. The micromirror device is small and consumes little power, so it is expected to be widely used in laser displays, laser projectors, optical coherence tomography scanners, etc.

[0003] In recent years, the demand for LiDAR (Light Detection And Ranging) devices that scan light 360 degrees in all directions has been increasing as a self-position detection device for low-speed moving objects such as drones. In addition, LiDAR devices equipped with a light scanning device having a micromirror device capable of spiral scanning have attracted attention.

[0004] There are many ways to drive a micromirror device, but the piezoelectric drive method that uses the deformation of a piezoelectric body generates a larger rotational torque than other methods, so a larger scanning angle can be obtained, and is considered to be very promising. In addition, by resonating the piezoelectric drive micromirror device, an even larger scanning angle can be obtained.

[0005] A common micromirror device includes a reflector portion and a piezoelectrically driven actuator (for example, see Japanese Patent Application Publication No. 2017-132281). The reflector portion is able to swing freely around a first axis and a second axis that are orthogonal to each other. The actuator is a driving portion that swings the reflector portion around the first axis and the second axis according to a driving voltage supplied from the outside. For example, the reflector portion precesses by swinging around the first axis and the second axis. Summary of the invention

[0006] Technical issues to be solved by the invention

[0007] As performance indicators of ranging based on LiDAR devices, detection distance, resolution and detection range can be cited. The diameter, operating frequency and deflection angle of the reflector unit have a great influence on these performance indicators. In the LiDAR device, the scanned light is reflected by the object and the return light is reflected by the reflector unit and guided to the light receiving element. Therefore, the larger the diameter of the reflector unit, the greater the reflection amount of the return light becomes, and the larger the detection distance becomes. In addition, the larger the operating frequency, the greater the resolution becomes. Moreover, the larger the deflection angle of the reflector unit, the larger the scanning angle, and therefore the larger the detection range becomes. In addition, the operating frequency refers to the rotation frequency of the reflector unit that performs precession.

[0008] However, in principle, if the diameter of the reflector is increased, the inertia moment of the reflector increases, so the resonance frequency decreases, resulting in a smaller deflection angle. In other words, in principle, if the diameter of the reflector is increased, the operating frequency and deflection angle decrease, and the resolution and detection range of the LiDAR device decrease.

[0009] Furthermore, in order to perform spiral scanning, the oscillation frequency of the reflector unit around the first axis and the oscillation frequency around the second axis must be roughly consistent. However, the micromirror device supports the reflector unit through a so-called universal joint structure, so the resonance frequency differs when it is around the first axis and when it is around the second axis due to the inertia moment of the universal joint structure. The larger the universal joint structure, the greater the difference becomes. On the other hand, in a thin universal joint structure, when the reflector unit rotates, the universal joint structure itself is greatly deformed, resulting in a significant decrease in the resonance frequency and the deflection angle.

[0010] The technical object of the present invention is to provide a micromirror device and an optical scanning device capable of increasing the diameter, operating frequency and deflection angle of a reflective mirror portion.

[0011] Means for solving technical problems

[0012] In order to achieve the above-mentioned purpose, the micromirror device of the present invention comprises: a reflector part having a reflective surface for reflecting incident light; a pair of first supporting parts connected to the reflector part on a first axis in a plane including the reflective surface when the reflector part is stationary, and supporting the reflector part so as to be able to swing around the first axis; a pair of movable frames connected to the first supporting parts and opposed to each other across the first axis; a pair of second supporting parts connected to the movable frame on a second axis in the plane and orthogonal to the first axis, and supporting the reflector part, the first supporting parts and the movable frame so as to be able to swing around the second axis; a pair of first actuators connected to the first actuators and the second actuators connected to the second actuators. 2 supporting parts are connected and are opposite to each other with a second axis in between; a pair of second actuators are configured to surround the first actuator and are opposite to each other with the first axis in between; a fixed frame is configured to surround the second actuator; a pair of first connecting parts connect the first actuator and the second actuator; and a pair of second connecting parts connect the second actuator and the fixed frame, the movable frame is symmetrical with respect to the first axis and has a reinforcing structure that is not in contact with the boundary part between the movable frame and the first supporting part, the first connecting part and the second connecting part are respectively symmetrical in shape with the first axis and support the first actuator and the second actuator so that they can swing around the first axis.

[0013] It is preferred that the combined thickness of the movable frame and the reinforcement structure be the same as the thickness of the fixed frame.

[0014] Preferably, the reinforcement structure is provided on the back side of the movable frame.

[0015] Preferably, the first actuator and the second actuator each include a piezoelectric element.

[0016] Preferably, the first supporting portion is a shape that is line-symmetrical with the first axis as the center, and has a first swing axis arranged on the first axis, and a pair of first connecting portions arranged at positions opposite to each other across the first axis, one end of the first swing axis is connected to the reflector portion and the other end is connected to the first connecting portion, one end of the first connecting portion is connected to the outer end portion of the first swing axis on the first axis and the other end is connected to the movable frame.

[0017] Preferably, the first connection portion extends from an outer end portion of the first swing shaft on the first axis toward the mirror portion, bends toward the outer circumference in a region adjacent to the mirror portion, and bends again in a region adjacent to the first actuator to be connected to the movable frame.

[0018] Preferably, the second supporting portion is a shape that is line-symmetrical with the second axis as the center, and has a second swing axis arranged on the second axis, and a pair of second connecting portions arranged at positions opposite to each other across the second axis, one end of the second swing axis is connected to the movable frame and the other end is connected to the second connecting portion, the second connecting portion is connected to the outer end portion of the second swing axis on the second axis and the other end is connected to the first actuator.

[0019] Preferably, the second connection portion extends from an outer end portion of the second swing shaft on the second axis toward the mirror portion, bends toward the outer peripheral direction in a region adjacent to the movable frame, and is connected to the first actuator in a region adjacent to the second actuator.

[0020] The optical scanning device of the present invention comprises the above-mentioned micromirror device and a processor for driving the first actuator and the second actuator, wherein the processor swings the reflection mirror part around the first axis and the second axis respectively by giving a driving signal to the first actuator and the second actuator.

[0021] Effects of the Invention

[0022] According to the technology of the present invention, it is possible to provide a micromirror device and an optical scanning device capable of increasing the diameter, operating frequency, and deflection angle of a reflective mirror portion. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is a schematic diagram of a light scanning device.

[0024] Figure 2 This is a block diagram showing an example of the hardware configuration of the drive control unit.

[0025] Figure 3 This is a plan view of the micromirror device according to the first embodiment as viewed from the light incident side.

[0026] Figure 4 This is a perspective view of the micromirror device according to the first embodiment as viewed from the back side.

[0027] Figure 5 is along Figure 3 Sectional view taken along line AA.

[0028] Figure 6 It is a diagram showing an example of the first drive signal and the second drive signal.

[0029] Figure 7 It is a diagram showing a state where the mirror portion is precessing.

[0030] Figure 8 It is a diagram showing parameters related to the dimensions of components of a micromirror device.

[0031] Fig. 9 It is a diagram showing parameters related to the dimensions of components of a micromirror device.

[0032] Fig.10 This is a diagram showing specific setting values ​​of parameters.

[0033] Fig.11 This is a plan view of the micromirror device according to the second embodiment when viewed from the light incident side.

[0034] Fig.12 This is a perspective view of the micromirror device according to the second embodiment when viewed from the back side.

[0035] Fig.13 It is a diagram showing parameters related to the dimensions of components of a micromirror device.

[0036] Fig.14 It is a diagram showing parameters related to the dimensions of components of a micromirror device.

[0037] Fig.15 This is a diagram showing specific setting values ​​of parameters.

[0038] Fig.16 This is a plan view of the micromirror device according to the first comparative example when viewed from the light incident side.

[0039] Fig.17 This is a perspective view of the micromirror device according to the first comparative example as viewed from the back side.

[0040] Fig.18 It is a diagram showing parameters related to the dimensions of components of a micromirror device.

[0041] Fig.19 It is a diagram showing parameters related to the dimensions of components of a micromirror device.

[0042] Fig. 20 This is a diagram showing specific setting values ​​of parameters.

[0043] Fig.21This is a plan view of the micromirror device according to the second comparative example when viewed from the light incident side.

[0044] Fig. 22 This is a perspective view of the micromirror device according to the second comparative example as viewed from the back side.

[0045] Fig.23 It is a diagram showing parameters related to the dimensions of components of a micromirror device.

[0046] Fig.24 It is a diagram showing parameters related to the dimensions of components of a micromirror device.

[0047] Fig.25 This is a diagram showing specific setting values ​​of parameters.

[0048] Fig.26 This is a stress distribution diagram showing the distribution of stress near the boundary portion generated by simulation.

[0049] Fig. 27 It is a figure which shows the experimental results concerning each embodiment and each comparative example mentioned above. DETAILED DESCRIPTION

[0050] An example of an embodiment according to the technology of the present invention will be described with reference to the drawings.

[0051] [First embodiment]

[0052] exist Figure 1 1 schematically shows an optical scanning device 10 according to the first embodiment. The optical scanning device 10 includes a micromirror device (hereinafter referred to as MMD (Micro Mirror Device)) 2, a light source 3, and a drive control unit 4. The optical scanning device 10 is mounted on a LiDAR device, for example.

[0053] The optical scanning device 10 reflects the light beam LB emitted from the light source 3 with the MMD 2 under the control of the drive control unit 4, thereby scanning the light beam LB to draw a spiral track. The spiral track includes a spiral track with a changing radius and a circular track with a constant radius.

[0054] MMD2 is a device capable of making the reflector portion 20 (refer to Figure 3 ) A piezoelectric type biaxial drive micromirror device that swings around a first axis a1 and a second axis a2 that is orthogonal to the first axis a1. Hereinafter, the direction parallel to the first axis a1 is referred to as the X direction, the direction parallel to the second axis a2 is referred to as the Y direction, and the direction orthogonal to the first axis a1 and the second axis a2 is referred to as the Z direction.

[0055] The light source 3 is, for example, a laser device that emits a laser beam as the light beam LB. The light source 3 preferably projects a laser beam toward a reflective surface 20A (see FIG. 2A ) provided on the reflector portion 20 when the reflector portion 20 of the MMD 2 is stationary. Figure 3 )Vertical irradiation beam LB.

[0056] The drive control unit 4 outputs a drive signal to the light source 3 and the MMD 2. The light source 3 generates a light beam LB according to the input drive signal and irradiates the light beam LB to the MMD 2. The MMD 2 swings the mirror unit 20 around the first axis a1 and the second axis a2 according to the input drive signal.

[0057] The details will be described later, but the drive control unit 4 rotates the mirror unit 20 by causing the mirror unit 20 to resonate around the first axis a1 and the second axis a2. The light beam LB reflected by the mirror unit 20 is scanned in a spiral orbit. This light scanning method is called a spiral scanning method.

[0058] The optical scanning device 10 can be applied to a LiDAR device, for example. The LiDAR device is mounted on a low-speed moving object such as an unmanned aerial vehicle. In the LiDAR device, the scanned light beam LB is reflected by the object, and the return light is reflected by the reflector unit 20 and guided to the light receiving element (not shown). Therefore, the larger the diameter of the reflector unit 20, the greater the reflection amount of the return light becomes, and the greater the detection distance based on the distance measurement of the LiDAR device becomes.

[0059] exist Figure 2 4 shows an example of the hardware structure of the drive control unit 4. The drive control unit 4 includes a CPU (Central Processing Unit) 40, a ROM (Read Only Memory) 41, a RAM (Random Access Memory) 42, a light source driver 43, and an MMD driver 44. The CPU 40 is a computing device that realizes the overall function of the drive control unit 4 by reading programs and data from a storage device such as the ROM 41 to the RAM 42 and executing processing. The CPU 40 is an example of a processor involved in the technology of the present invention.

[0060] The ROM 41 is a nonvolatile storage device and stores data such as programs for the CPU 40 to execute processing. The RAM 42 is a volatile storage device that temporarily stores programs and data.

[0061] The light source driver 43 is a circuit that outputs a drive signal to the light source 3 according to the control of the CPU 40. In the light source driver 43, the drive signal is a drive voltage for controlling the irradiation timing and irradiation intensity of the light source 3.

[0062] The MMD driver 44 is a circuit that outputs a drive signal to the MMD 2 according to the control of the CPU 40. In the MMD driver 44, the drive signal is a drive voltage for controlling the timing, operation frequency, and deflection angle of the MMD driver 44 to oscillate the mirror unit 20.

[0063] Next, use Figure 3 to Figure 5 The structure of the MMD 2 according to the first embodiment will be described. Figure 3 This is a top view of the MMD2 as viewed from the light incident side. Figure 4 This is a perspective view of the MMD2 as viewed from the back side. Figure 5 It is a rough representation of the Figure 3 A cross-sectional view of the section taken along line AA.

[0064] like Figure 3 As shown, MMD2 has a mirror section 20, a pair of first support sections 21, a pair of movable frames 22, a pair of second support sections 23, a pair of first actuators 24, a pair of second actuators 25, a pair of first connecting sections 26A, a pair of second connecting sections 26B, and a fixed frame 27. MMD2 is a so-called MEMS scanner.

[0065] The reflector 20 has a reflective surface 20A for reflecting incident light. The reflective surface 20A is formed of a metal thin film such as gold (Au) or aluminum (Al) provided on one surface of the reflector 20. The reflective surface 20A is, for example, a circle centered at the intersection of the first axis a1 and the second axis a2.

[0066] The first axis a1 and the second axis a2 exist in a plane including the reflecting surface 20A when the mirror unit 20 is stationary, for example. The planar shape of the MMD2 is a rectangle, and is line-symmetrical about the first axis a1 and the second axis a2.

[0067] A pair of first support parts 21 are arranged at positions opposite to each other across the second axis a2, and are in a shape that is line-symmetrical with the second axis a2 as the center. Furthermore, the first support parts 21 are in a shape that is line-symmetrical with the first axis a1 as the center. The first support parts 21 are connected to the reflector part 20 on the first axis a1, and support the reflector part 20 so that it can swing around the first axis a1.

[0068] The pair of movable frames 22 are arranged at positions opposite to each other across the first axis a1 and are symmetrical about the first axis a1. The movable frames 22 are symmetrical about the second axis a2. The movable frames 22 are bent along the outer periphery of the reflector portion 20. Both ends of the movable frames 22 are connected to the first support portion 21.

[0069] The first support portion 21 and the movable frame 22 are connected to each other, and surround the mirror portion 20. The mirror portion 20, the first support portion 21, and the movable frame 22 constitute a movable portion 60.

[0070] A pair of second support parts 23 are arranged at positions opposite to each other across the first axis a1, and are in a shape that is line-symmetrical with the first axis a1 as the center. The second support parts 23 are respectively in a shape that is line-symmetrical with the second axis a2 as the center. The second support parts 23 are connected to the movable frame 22 on the second axis a2, and support the movable part 60 having the reflector part 20 so that it can swing around the second axis a2. In addition, both ends of the second support part 23 are respectively connected to the first actuator 24.

[0071] A pair of first actuators 24 are arranged at positions opposite to each other across the second axis a2, and are in a shape that is line-symmetrical about the second axis a2. Furthermore, the first actuator 24 is in a shape that is line-symmetrical about the first axis a1. The first actuator 24 is formed along the outer periphery of the movable frame 22 and the first support portion 21. The first actuator 24 is a piezoelectric drive type actuator having a piezoelectric element.

[0072] The first actuators 24 are electrically connected via a wiring (not shown) via the first axis a1. The pair of first actuators 24 disposed via the second axis a2 are electrically isolated from each other.

[0073] The second support portion 23 and the first actuator 24 are connected to each other so as to surround the movable portion 60 .

[0074] A pair of second actuators 25 are arranged at positions opposite to each other across the first axis a1, and are in a shape that is line-symmetrical about the first axis a1. Furthermore, the second actuator 25 is in a shape that is line-symmetrical about the second axis a2. The second actuator 25 is formed along the outer periphery of the first actuator 24 and the second support portion 23. The second actuator 25 is a piezoelectric drive type actuator having a piezoelectric element.

[0075] In addition, the pair of second actuators 25 disposed across the first axis a1 are electrically isolated from each other.

[0076] A pair of first connecting parts 26A are arranged at positions opposite to each other across the second axis a2, and are in a shape that is line-symmetrical about the second axis a2. Furthermore, the first connecting parts 26A extend in the X direction, and are in a shape that is line-symmetrical about the first axis a1. The first connecting parts 26A are arranged along the first axis a1, and connect the first actuator 24 and the second actuator 25 on the first axis a1.

[0077] A pair of second connection parts 26B are arranged at positions opposite to each other across the second axis a2, and are in a shape that is line-symmetrical with the second axis a2 as the center. Furthermore, the second connection parts 26B extend along the X direction, and are in a shape that is line-symmetrical with the first axis a1 as the center. The second connection parts 26B are arranged along the second axis a2, and connect the second actuator 25 and the fixed frame 27 on the first axis a1.

[0078] The second actuator 25 is arranged to surround the first actuator 24. The first actuator 24 and the second actuator 25 constitute a driving unit arranged to surround the movable frame 22. The first connecting portion 26A and the second connecting portion 26B support the first actuator 24 and the second actuator 25 so as to be swingable about the first axis a1.

[0079] The fixed frame 27 is a frame-shaped member having a rectangular outer shape and has a shape that is line-symmetrical about the first axis a1 and the second axis a2 . The fixed frame 27 is disposed so as to surround the second actuator 25 .

[0080] The first actuator 24 and the second actuator 25 are piezoelectric actuators each having a piezoelectric element. The pair of first actuators 24 cause the movable portion 60 to swing around the second axis a2 by causing a rotation torque around the second axis a2 to act on the mirror portion 20 and the movable frame 22. The pair of second actuators 25 cause the mirror portion 20 to swing around the first axis a1 by causing a rotation torque around the first axis a1 to act on the mirror portion 20, the movable frame 22, and the first actuator 24.

[0081] The first support portion 21 is composed of a swing shaft 21A and a pair of connecting portions 21B. The swing shaft 21A is a so-called torsion bar extending along the first axis a1. One end of the swing shaft 21A is connected to the reflector portion 20 and the other end is connected to the connecting portion 21B.

[0082] The pair of connecting parts 21B are arranged at positions opposite to each other across the first axis a1 and are line-symmetrical about the first axis a1. One end of the connecting part 21B is connected to the outer end of the swing shaft 21A on the first axis a1 and the other end is connected to the movable frame 22. The connecting part 21B has a folded structure (so-called meandering structure).

[0083] Specifically, the connecting portion 21B extends from the outer end portion of the swing shaft 21A on the first axis a1 toward the direction toward the reflector portion 20, and is bent in the peripheral direction in the area adjacent to the reflector portion 20. Moreover, the connecting portion 21B extends in the peripheral direction, and is bent in the area adjacent to the first actuator 24. Furthermore, the connecting portion 21B extends in the direction toward the reflector portion 20, and is connected to the movable frame 22. That is, the connecting portion 21B has two bent portions B. In this way, the connecting portion 21B has elasticity due to the folding structure, so when the reflector portion 20 swings around the first axis a1, the internal stress applied to the swing shaft 21A is relieved. In addition, the swing shaft 21A and the connecting portion 21B correspond to the "first swing shaft" and the "first connecting portion" involved in the technology of the present invention, respectively.

[0084] The second support portion 23 is composed of a swing shaft 23A and a pair of connecting portions 23B. The swing shaft 23A is a so-called torsion bar extending along the second axis a2. One end of the swing shaft 23A is connected to the movable frame 22 and the other end is connected to the connecting portion 23B.

[0085] The pair of connecting parts 23B are arranged at positions opposite to each other across the second axis a2 and are line-symmetrical about the second axis a2. One end of the connecting part 23B is connected to the outer end of the swing shaft 23A on the second axis a2 and the other end is connected to the first actuator 24. The connecting part 23B has a folded structure.

[0086] Specifically, the connecting portion 23B extends from the outer end of the swing shaft 23A on the second axis a2 toward the reflector portion 20, and is bent in the peripheral direction in the area adjacent to the movable frame 22. Moreover, the connecting portion 23B extends in the peripheral direction and is connected to the first actuator 24 in the area adjacent to the second actuator 25. That is, the connecting portion 23B has a bent portion B. In this way, the connecting portion 23B has elasticity due to the folding structure, so when the reflector portion 20 swings around the second axis a2, the internal stress applied to the swing shaft 23A is relieved. In addition, the swing shaft 23A and the connecting portion 23B correspond to the "second swing shaft" and the "second connecting portion" involved in the technology of the present invention, respectively.

[0087] As described above, the mirror portion 20 is supported by the gimbal structure including the movable frame 22 so as to be swingable about the first axis a1 and about the second axis a2 .

[0088] exist Figure 3 In the figure, wiring and electrode pads for applying drive signals to the first actuator 24 and the second actuator 25 are omitted from the figure. A plurality of electrode pads are provided on the fixing frame 27.

[0089] like Figure 4As shown, a rib 50 is provided on the back side 20B of the reflector portion 20. The back side 20B is a surface on the side opposite to the reflecting surface 20A. The rib 50 has an annular structure concentric with the reflector portion 20. The rib 50 is mainly provided to make the resonance frequency of the reflector portion 20 around the first axis a1 and the resonance frequency around the second axis a2 close to each other. In the present embodiment, the shape of the rib 50 is substantially circular.

[0090] Furthermore, a reinforcing structure 51 is provided on the back side of the movable frame 22. The back side of the movable frame 22 is a surface on the same side as the back side 20B of the reflector portion 20. In the present embodiment, two reinforcing structures 51 are provided on the back side of each of the pair of movable frames 22. The four reinforcing structures 51 are line-symmetrical shapes centered on the first axis a1 and the second axis a2, respectively. Each of the reinforcing structures 51 is arranged between the second support portion 23 and the first support portion 21 on the back side of the movable frame 22. However, each of the reinforcing structures 51 does not extend to the boundary portion K between the movable frame 22 and the first support portion 21, and does not contact the boundary portion K.

[0091] like Figure 5 As shown, the MMD 2 is formed by, for example, etching an SOI (Silicon On Insulator) substrate 30. The SOI substrate 30 is a substrate in which a silicon oxide layer 32 is provided on a first silicon active layer 31 made of single crystal silicon, and a second silicon active layer 33 made of single crystal silicon is provided on the silicon oxide layer 32.

[0092] The mirror unit 20, the first support unit 21, the movable frame 22, the second support unit 23, the first actuator 24, the second actuator 25, the first connection unit 26A, and the second connection unit 26B are formed by the second silicon active layer 33 remaining after the first silicon active layer 31 and the silicon oxide layer 32 are removed from the SOI substrate 30 by etching. The second silicon active layer 33 functions as an elastic part having elasticity. The fixed frame 27 is formed by three layers of the first silicon active layer 31, the silicon oxide layer 32, and the second silicon active layer 33. That is, the thickness of the mirror unit 20, the first support unit 21, the movable frame 22, the second support unit 23, the first actuator 24, the second actuator 25, the first connection unit 26A, and the second connection unit 26B is thinner than that of the fixed frame 27. In the present invention, the thickness refers to the width in the Z direction.

[0093] The rib 50 is formed by etching the first silicon active layer 31 and the silicon oxide layer 32. Similarly, the reinforcing structure 51 is formed by etching the first silicon active layer 31 and the silicon oxide layer 32. The thickness of the rib 50 is the same as the thickness of the reinforcing structure 51. Furthermore, the thickness of the movable frame 22 and the reinforcing structure 51 is the same as the thickness of the fixed frame 27.

[0094] The first actuator 24 includes a piezoelectric element formed on the second silicon active layer 33. The piezoelectric element has a stacked structure in which a lower electrode, a piezoelectric film, and an upper electrode are stacked in this order on the second silicon active layer 33. The second actuator 25 has the same structure as the first actuator 24.

[0095] The lower electrode and the upper electrode are formed of metals such as gold (Au) or platinum (Pt). The piezoelectric film is formed of PZT (lead zirconate titanate) as a piezoelectric material. The lower electrode and the upper electrode are electrically connected to the drive control unit 4 via wiring and electrode pads.

[0096] The lower electrode is connected to the drive control unit 4 via wiring and an electrode pad, and a ground potential is applied thereto. A drive voltage is applied from the drive control unit 4 to the upper electrode.

[0097] When a positive or negative voltage is applied in the polarization direction, the piezoelectric film deforms (e.g., expands and contracts) in proportion to the applied voltage. That is, the piezoelectric film exerts the so-called inverse piezoelectric effect. The piezoelectric film exerts the inverse piezoelectric effect by applying a driving voltage from the drive control unit 4 to the upper electrode, so that the first actuator 24 and the second actuator 25 are displaced.

[0098] The second actuator 25 generates a rotation torque about the first axis a1 by extending one piezoelectric film and contracting the other piezoelectric film of the pair of second actuators 25. Thus, one and the other of the pair of second actuators 25 are displaced in opposite directions, and the mirror portion 20 rotates about the first axis a1.

[0099] In the present embodiment, the pair of second actuators 25 are driven in an anti-phase resonance mode (hereinafter referred to as an anti-phase rotation mode) in which the displacement direction of the pair of second actuators 25 and the rotation direction of the mirror portion 20 are opposite to each other.

[0100] The deflection angle of the reflector portion 20 around the first axis a1 is controlled based on a drive signal (hereinafter referred to as a first drive signal) given to the second actuator 25 by the drive control portion 4. The first drive signal is, for example, a sinusoidal AC voltage. The first drive signal includes a drive voltage waveform V applied to one of the pair of second actuators 25. 1A (t) and the driving voltage waveform V applied to the other 1B (t). Driving voltage waveform V 1A (t) and driving voltage waveform V 1B (t) are in anti-phase with each other (ie, out of phase by 180°).

[0101] The first actuator 24 is driven in the reverse phase rotation mode similarly to the second actuator 25. The deflection angle of the reflector portion 20 around the second axis a2 is controlled according to a drive signal (hereinafter referred to as the second drive signal) given to the first actuator 24 by the drive control unit 4. The second drive signal is, for example, a sinusoidal AC voltage. The second drive signal includes a drive voltage waveform V applied to one of the pair of first actuators 24. 2A (t) and the driving voltage waveform V applied to the other 2B (t). Driving voltage waveform V 2A (t) and driving voltage waveform V 2B (t) are in anti-phase with each other (ie, out of phase by 180°).

[0102] exist Figure 6 An example of the first drive signal and the second drive signal is shown in FIG. Figure 6 (A) shows the driving voltage waveform V included in the first driving signal. 1A (t) and V 1B (t). Figure 6 (B) shows the driving voltage waveform V included in the second driving signal. 2A (t) and V 2B (t).

[0103] Driving voltage waveform V 1A (t) and V 1B (t) are expressed as follows.

[0104] V 1A (t) = A1(t)sin(2πf d1 t)

[0105] V 1B (t) = A1(t)sin(2πf d1 t+π)

[0106] Here, t is time. d1 is the driving frequency (hereinafter referred to as the first driving frequency). A1(t) is the amplitude voltage, and changes according to time t. The driving voltage waveform V 1A (t) and driving voltage waveform V 1B The phase difference of (t) is π (ie, 180°).

[0107] By applying the driving voltage waveform V to the pair of second actuators 25 1A (t) and V 1B (t), the mirror portion 20 is rotated at a period T1 (=1 / f d1 ) swings around the first axis a1.

[0108] Driving voltage waveform V 2A(t) and V 2B (t) are expressed as follows.

[0109] V 2A (t) = A2(t)sin(2πf d2 t+φ)

[0110] V 2B (t) = A2(t)sin(2πf d2 t+π+φ)

[0111] Here, f d2 is the driving frequency (hereinafter referred to as the second driving frequency). A2(t) is the amplitude voltage, and changes according to time t. The driving voltage waveform V 2A (t) and driving voltage waveform V 2B The phase difference of (t) is π (i.e., 180°). And φ is the driving voltage waveform V 1A (t) and V 1B (t) and driving voltage waveform V 2A (t) and V 2B In the present embodiment, in order to make the mirror unit 20 precess, φ=π / 2 (that is, 90°) is set.

[0112] First driving frequency f d1 The second driving frequency f is set to coincide with the resonance frequency of the mirror portion 20 about the first axis a1. d2 The first drive frequency f is set to coincide with the resonance frequency of the mirror portion 20 about the second axis a2. d1 and the second driving frequency f d2 Roughly equal.

[0113] By linearly changing the amplitude voltages A1(t) and A2(t) with respect to time t, the trajectory of the light beam LB reflected by the reflector unit 20 becomes a spiral trajectory with a changing radius. By setting the amplitude voltages A1(t) and A2(t) to constant values ​​that are independent of time t, the trajectory of the light beam LB reflected by the reflector unit 20 becomes a circular trajectory with a constant radius.

[0114] exist Figure 7 2 shows the state in which the reflector unit 20 precesses. If the deflection angle of the reflector unit 20 is θ, the scanning angle (full angle) α of the light beam LB is 4 times the deflection angle θ. The deflection angle θ refers to the angle formed by the normal line N of the reflection surface 20A with respect to the Z direction.

[0115] As described above, by providing the reinforcing structure 51 on the movable frame 22, the spring constant (ie, rigidity) of the movable frame 22 constituting the gimbal structure increases, and the mass of the gimbal structure increases. Also, as the mass of the gimbal structure increases, the resonance Q value increases.

[0116] In principle, if the diameter of the reflector unit 20 is increased, the inertia moment of the reflector increases, so the resonance frequency decreases, resulting in a decrease in the deflection angle θ. However, in this embodiment, by providing a reinforcement structure 51 on the movable frame 22, the deformation of the movable frame 22 can be reduced and the decrease in the resonance frequency and the deflection angle θ can be suppressed, so that the diameter of the reflector unit 20 can be increased. That is, according to this embodiment, the diameter, operating frequency and deflection angle θ of the reflector unit 20 can be increased, and the detection distance, resolution and detection range, which are performance indicators of ranging based on the LiDAR device, can be improved.

[0117] Furthermore, although the details will be described later, when the reflector portion 20 precesses, stress is concentrated on the boundary portion K between the movable frame 22 and the first support portion 21. However, in the present embodiment, the reinforcing structure 51 is not connected to the boundary portion K, thereby suppressing stress concentration on the boundary portion K, thereby suppressing structural damage in the boundary portion K.

[0118] In order to verify the above effects, the applicant prepared samples of MMD2 and conducted experiments. Figure 8 and Fig. 9 Parameters related to the width and length of each component of the sample used in the experiment are shown in FIG. Fig.10 The specific setting values ​​of the parameters are shown in .

[0119] The diameter of the reflector 20 is set to 5 mm, the thickness of the SOI substrate 30 is set to 430 μm, and the thickness of the second silicon active layer 33 is set to 80 μm. In addition, the diameter of the reflector 20 is larger than the diameter of the reflector of the MMD used in AR (Augmented Reality) glasses. d1 =1475Hz and f d2 =1445Hz.

[0120] In this experiment, the mirror unit 20 was resonantly driven in the reverse phase rotation mode about the second axis a2 in the atmosphere, and the driving voltage (ie, amplitude voltage) required for α=40° was confirmed. The experimental results showed that the driving voltage required for α=40° was 23V.

[0121] Furthermore, the reflector 20 was precessed in a manner that α=40° described a perfect circle, and the time from the start of the action to the occurrence of a failure in the MMD 2 (hereinafter referred to as the continuous drive time) was confirmed. The results of the experiment showed that even if the MMD 2 was operated for 1000 hours, no damage occurred. In other words, the continuous drive time was more than 1000 hours.

[0122] [Second embodiment]

[0123] Next, a second embodiment will be described. Fig.11 This is a plan view of the MMD 2A according to the second embodiment as viewed from the light incident side. Fig.12 This is a perspective view of the MMD2A according to the second embodiment as viewed from the back side. The MMD2A is different from the MMD2 according to the first embodiment in the structures of the first support portion 21 , the second support portion 23 , and the reinforcing structure 51 .

[0124] In the present embodiment, the first support portion 21 is composed of a swing shaft 21A and a pair of connecting portions 21B. Unlike the first embodiment, the connecting portion 21B does not have a bent portion B. One end of the connecting portion 21B is connected to the outer end of the swing shaft 21A on the first axis a1 and the other end is connected to the movable frame 22. Specifically, the connecting portion 21B extends from the outer end of the swing shaft 21A on the first axis a1 toward the reflector portion 20 and is connected to the movable frame 22 in a region adjacent to the reflector portion 20.

[0125] In this embodiment, the second support portion 23 does not have the connection portion 23B, but is composed only of a swing shaft 23A extending along the second axis a2. One end of the swing shaft 23A is connected to the movable frame 22, and the other end is connected to the first actuator 24 in a region adjacent to the second actuator 25.

[0126] In this embodiment, one reinforcing structure 51 is provided on each of the pair of movable frames 22. Unlike the first embodiment, the reinforcing structure 51 also extends to the region of the movable frame 22 adjacent to the second support portion 23. However, similarly to the first embodiment, the reinforcing structure 51 does not contact the boundary portion K between the movable frame 22 and the first support portion 21.

[0127] The applicant also conducted the same experiment as above on the MMD2A involved in the second embodiment. Fig.13 and Fig.14 Parameters related to the width and length of each component of the sample used in the experiment are shown in FIG. Fig.15 The specific setting values ​​of the parameters are shown in .

[0128] Furthermore, the diameter of the reflector portion 20 is set to 5 mm, the thickness of the SOI substrate 30 is set to 430 μm, and the thickness of the second silicon active layer 33 is set to 80 μm. d1 =1513Hz and f d2 =1483Hz.

[0129] The experimental results show that when the reflector unit 20 is resonantly driven around the second axis a2 in the reverse phase rotation mode in the atmosphere, the driving voltage required for α = 40° is 13 V. In addition, when the reflector unit 20 is precessed in a manner of describing a perfect circle at α = 40°, no failure occurs in the MMD2A within a time of less than 1000 hours. In other words, the continuous driving time is more than 1000 hours.

[0130] [Comparative Example 1]

[0131] Next, a first comparative example will be described. Fig.16 It is a plan view when the MMD 2B according to the first comparative example is viewed from the light incident side. Fig.17 This is a perspective view of the MMD2B according to the first comparative example as seen from the back side. The MMD2B differs from the MMD2 according to the first embodiment in structure only in that the reinforcing structure 51 is not provided on the movable frame 22 .

[0132] The applicant also conducted the same experiment as above on MMD2B involved in the first comparative example. Fig.18 and Fig.19 Parameters related to the width and length of each component of the sample used in the experiment are shown in FIG. Fig. 20 The specific setting values ​​of the parameters are shown in .

[0133] Furthermore, the diameter of the reflector portion 20 is set to 5 mm, the thickness of the SOI substrate 30 is set to 430 μm, and the thickness of the second silicon active layer 33 is set to 80 μm. d1 =1443Hz and f d2 =1446Hz.

[0134] The experimental results showed that when the reflector unit 20 was resonantly driven around the second axis a2 in the reverse phase rotation mode in the atmosphere, the driving voltage required for α = 40° was 38 V. Furthermore, when the reflector unit 20 was precessed in a manner of describing a perfect circle at α = 40°, the piezoelectric film was damaged within less than 200 hours. That is, the continuous driving time was less than 200 hours.

[0135] [Comparative Example 2]

[0136] Next, a second comparative example will be described. Fig.21 It is a plan view when the MMD2C involved in the second comparative example is viewed from the light incident side. Fig. 22 1 is a perspective view of the MMD2C according to the second comparative example as viewed from the back side. The difference between the structure of the MMD2C and the MMD2A according to the second embodiment is that the reinforcing structure 51 provided on the movable frame 22 extends to the boundary K between the movable frame 22 and the first support portion 21 and is in contact with the boundary K. In addition, in the second comparative example, in order to make the resonance frequency around the first axis a1 and the resonance frequency around the second axis a2 close, the rib 50 is set to a stadium shape. The rib 50 is longer in the X direction than in the Y direction.

[0137] The applicant also conducted the same experiment as above on MMD2B involved in the first comparative example. Fig.23 and Fig.24 Parameters related to the width and length of each component of the sample used in the experiment are shown in FIG. Fig.25 The specific setting values ​​of the parameters are shown in .

[0138] Furthermore, the diameter of the reflector portion 20 is set to 5 mm, the thickness of the SOI substrate 30 is set to 430 μm, and the thickness of the second silicon active layer 33 is set to 80 μm. d1 =1487Hz and f d2 =1457Hz.

[0139] The experimental results showed that when the reflector unit 20 was resonantly driven around the second axis a2 in the reverse phase rotation mode in the atmosphere, the driving voltage required for α = 40° was 16 V. Furthermore, when the reflector unit 20 was precessed in a manner of describing a perfect circle at α = 40°, structural damage occurred at the boundary K between the movable frame 22 and the first support unit 21 within a period of less than 20 hours. That is, the continuous driving time was less than 20 hours.

[0140] Fig.26 : is a stress distribution diagram showing the distribution of stress near the boundary portion K generated by simulation. According to the stress distribution diagram, it can be understood that when the reflector portion 20 is precessed, the stress generated by the swing of the reflector portion 20 around the first axis a1 is concentrated on the boundary portion K between the end of the reinforcement structure 51 and the first support portion 21. It is considered that structural damage occurs at the boundary portion K due to the concentration of this stress.

[0141] [Summarize]

[0142] exist Fig. 27The experimental results of the above-mentioned embodiments and comparative examples are shown in FIG. In the application of LiDAR, it is an index to be able to achieve α≥40° in spiral scanning. In addition, it is an index to be able to continuously drive for more than 1000 hours in the application of LiDAR.

[0143] In the first comparative example, the reinforcing structure 51 is not provided on the movable frame 22, so the rigidity of the universal joint structure is low. Therefore, the driving voltage required for α=40° is about 38V. If such a large driving voltage is applied to the driving part, not only the power consumption increases, but also the probability of electrical damage to the piezoelectric film during continuous driving is further increased. In the first comparative example, when the driving voltage is set to 38V and the reflector part 20 is precessed in a manner of describing a perfect circle at α=40°, the piezoelectric film is damaged in less than 200 hours. That is, the continuous driving time is less than 200 hours.

[0144] In the second comparative example, the reinforcing structure 51 is provided on the movable frame 22, so the rigidity of the universal joint structure is high. Therefore, the driving voltage required for α=40° is low, which is 16V. However, in the second comparative example, the reinforcing structure 51 is in contact with the boundary K between the movable frame 22 and the first support portion 21, so when the reflector portion 20 is precessed in a manner that describes a perfect circle at α=40°, structural damage occurs at the boundary K within a time of less than 20 hours. That is, the continuous driving time is less than 20 hours.

[0145] In contrast, in the first and second embodiments, the reinforcing structure 51 is provided on the movable frame 22, and the reinforcing structure 51 is in contact with the boundary portion K. Therefore, in the first and second embodiments, the driving voltage required for α=40° is low, and the continuous driving time when the reflector portion 20 is precessed so as to describe a perfect circle at α=40° is 1000 hours or more.

[0146] In addition, in the above-mentioned embodiment, the hardware structure of the drive control unit 4 can be variously modified. The processing unit of the drive control unit 4 can be composed of one processor, or a combination of two or more processors of the same type or different types. The processor includes a CPU, a programmable logic device (PLD) and a dedicated circuit. As is well known, the CPU is a general-purpose processor that executes software (programs) to function as various processing units. PLD is a processor that can change the circuit structure after manufacturing, such as FPGA (Field Programmable Gate Array). A dedicated circuit is a processor with a circuit structure specially designed to perform specific processing, such as ASIC (Application Specific Integrated Circuit).

[0147] All documents, Japanese patent applications, and technical standards described in this specification are incorporated herein by reference to the same extent as if each document, Japanese patent application, and technical standard were specifically and individually described.

Claims

1. A micromirror device, comprising: a reflector portion having a reflective surface for reflecting incident light; a pair of first support portions connected to the reflector portion on a first axis within a plane including the reflecting surface when the reflector portion is stationary, and supporting the reflector portion so as to be swingable about the first axis; a pair of movable frames connected to the first support portion and opposed to each other across the first axis; a pair of second support portions connected to the movable frame on a second axis that is within the plane and orthogonal to the first axis, and supporting the reflector portion, the first support portion, and the movable frame so as to be able to swing around the second axis; a pair of first actuators connected to the second support portion and opposed to each other across the second shaft; a pair of second actuators arranged to surround the first actuator and to face each other across the first shaft; a fixed frame configured to surround the second actuator; a pair of first connecting parts connecting the first actuator and the second actuator; and a pair of second connecting parts connecting the second actuator and the fixing frame, The movable frame is symmetrical with respect to the first axis and has a reinforcement structure that does not contact a boundary between the movable frame and the first support portion. The first connection portion and the second connection portion each have a shape symmetrical with respect to the first axis, and support the first actuator and the second actuator so as to be able to swing around the first axis.

2. The micromirror device according to claim 1, wherein: The thickness of the movable frame and the reinforcement structure added together is the same as the thickness of the fixed frame.

3. The micromirror device according to claim 2, wherein: The reinforcement structure is disposed on the back side of the movable frame.

4. The micromirror device according to claim 1, wherein: The first actuator and the second actuator each include a piezoelectric element.

5. The micromirror device according to claim 1, wherein: The first support portion is in a line-symmetrical shape with the first axis as the center, and includes a first swing axis disposed on the first axis, and a pair of first connecting portions disposed at positions opposite to each other across the first axis. One end of the first swing shaft is connected to the reflector portion, and the other end is connected to the first connecting portion. One end of the first connecting portion is connected to the outer end portion of the first swing shaft on the first shaft, and the other end is connected to the movable frame.

6. The micromirror device according to claim 5, wherein: The first connection portion extends from an outer end portion of the first swing shaft on the first axis toward the mirror portion, bends toward the outer circumferential direction in a region adjacent to the mirror portion, and bends again in a region adjacent to the first actuator to be connected to the movable frame.

7. The micromirror device according to claim 5, wherein: The second support portion is in a line-symmetrical shape with the second axis as the center, and includes a second swing axis disposed on the second axis, and a pair of second connecting portions disposed at positions opposite to each other across the second axis. One end of the second swing shaft is connected to the movable frame, and the other end is connected to the second connecting portion. The second connection portion is connected to an outer end portion of the second swing shaft on the second shaft, and the other end is connected to the first actuator.

8. The micromirror device according to claim 7, wherein: The second connection portion extends from an outer end portion of the second swing shaft on the second axis toward the mirror portion, is bent in an outer peripheral direction in a region adjacent to the movable frame, and is connected to the first actuator in a region adjacent to the second actuator.

9. An optical scanning device comprising the micromirror device according to claim 1 and a processor for driving the first actuator and the second actuator, wherein: The processor applies a drive signal to the first actuator and the second actuator to thereby swing the mirror portion around the first axis and the second axis, respectively.

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