Micro-mirror device and optical scanning device

Abstract

To provide a micro-mirror device which allows for suppressing resonance frequency shift due to crosstalk between axes, and to provide an optical scanning device.SOLUTION: A micro-mirror device provided herein comprises a mirror unit, a first support unit for supporting the mirror unit in a manner that allows the mirror unit to swing about a first axis, a pair of movable frames facing each other across the first axis, a second support unit for supporting a movable unit in a manner that allows the movable unit to swing about a second axis, a drive unit provided to surround the movable unit in such a way that an air gap is created between itself and the second support unit along the second axis, a coupling unit for coupling the second support unit to the drive unit, and a fixed frame. When the mirror unit swings about the first axis and reaches an absolute rotation angle exceeding 0 degree, the micro-mirror device satisfies a relationship expressed as 2 / 3<A / L, where A represents, on a plane including the second axis perpendicular to the first axis, a distance between a point of intersection of the second axis and a straight line on a surface of the second support unit including every end point of the second support unit and an end point of the second support unit on the mirror unit side when stationary, and L represents a total length of the second support unit in the second axis direction.SELECTED DRAWING: Figure 8

Description

Technical Field

[0001] The technology of the present disclosure relates to a micromirror device and an optical scanning device.

Background Art

[0002] As one of the microelectromechanical systems (MEMS) devices fabricated using silicon (Si) microfabrication technology, a micromirror device (also referred to as a micro scanner) is known. Since this micromirror device is small and low power consumption, wide applications to a laser display, a laser projector, an optical coherence tomography, etc. are expected.

[0003] Although there are various driving methods for micromirror devices, the piezoelectric driving method that utilizes the deformation of a piezoelectric body is regarded as promising because the torque generated is higher than other methods and a high scan angle can be obtained. In particular, when a high scan angle is required as in the case of a laser display, a higher scan angle can be obtained by resonantly driving a micromirror device with the piezoelectric driving method.

[0004] A general micromirror device used in a laser display includes a mirror part and a piezoelectric actuator (see, for example, Patent Documents 1 and 2). The mirror part is swingable around a first axis and a second axis orthogonal to each other. The actuator swings the mirror part around the first axis and the second axis in response to a driving voltage supplied from the outside. The above-described scan angle corresponds to the deflection angle of the mirror part.

[0005] Resolution and viewing angle are cited as performance indicators of a laser display. The resolution and viewing angle are related to the oscillation frequency and deflection angle of the mirror portion of the micromirror device. For example, in a Lissajous scan type laser display, two-dimensional optical scanning is performed by oscillating the mirror portion simultaneously at two different frequencies around the first axis and the second axis. The larger the deflection angle of the mirror portion, the larger the scanning area of the light, and a larger image can be displayed with a shorter optical path length.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0007] Generally, when a micromirror device is driven in resonance, an inter-axis crosstalk occurs in which the oscillation of the mirror portion around one of the first axis and the second axis affects the oscillation of the mirror portion around the other axis. Specifically, the resonance frequency around the other axis shifts according to the magnitude of the rotation angle around one axis. As a result, the stability of two-dimensional optical scanning is significantly reduced.

[0008] For example, when trying to increase the deflection angle of the mirror portion by sweeping the drive frequency around one axis to bring the drive frequency closer to the resonance frequency, the deflection angle of the mirror portion around the other axis changes greatly due to the shift of the resonance frequency caused by the inter-axis crosstalk. At this time, the change in the deflection angle of the mirror portion around the other axis causes a shift in the resonance frequency around the axis on which the drive frequency is swept. That is, a kind of feedback phenomenon occurs due to the inter-axis crosstalk.

[0009] Thus, when the shift amount of the resonance frequency due to the inter-axis crosstalk is large, even if the drive frequency is swept, the drive frequency cannot be adjusted to the resonance frequency due to the above feedback phenomenon, and there is a problem that the swing angle of the mirror unit cannot be increased.

[0010] An object of the technology of the present disclosure is to provide a micromirror device and an optical scanning device capable of suppressing a shift in the resonance frequency due to inter-axis crosstalk.

Means for Solving the Problems

[0011] To achieve the above object, the micromirror device of the present disclosure includes a mirror unit having a reflective surface for reflecting incident light, a first support portion connected to the mirror unit on a first axis in a plane including the reflective surface of the mirror unit at rest, and supporting the mirror unit so as to be swingable about the first axis, a pair of movable frames connected to the first support portion and facing each other across the first axis, a second support portion connected to the movable frames on a second axis in the plane including the reflective surface of the mirror unit at rest and orthogonal to the first axis, and supporting the movable portion including the mirror unit, the first support portion, and the movable frames so as to be swingable about the second axis, a drive portion disposed surrounding the movable portion and having a gap between the drive portion and the second support portion on the second axis, a connecting portion connecting the second support portion and the drive portion, and a fixed frame connected to the drive portion and disposed surrounding the drive portion. When the mirror unit rotates about the first axis and the absolute value of the rotation angle becomes larger than 0 degree, in a plane orthogonal to the first axis and including the second axis, the distance between the intersection of the straight line including each end point of the second support portion and the second axis on the surface of the second support portion and the end portion on the mirror unit side of the second support portion at rest is defined as A, and the total length of the second support portion in the second axis direction is defined as L, the relationship of 2 / 3 < A / L is satisfied.

[0012] The drive portion preferably has a piezoelectric element.

[0013] The drive unit preferably includes a pair of first actuators that face each other across the second axis and have piezoelectric elements, and a pair of second actuators that are arranged to surround the first actuators, face each other across the first axis, and have piezoelectric elements.

[0014] It is preferable that the second actuator swings the mirror unit around the first axis, and the first actuator swings the movable unit around the second axis.

[0015] Preferably, the distance A and the total length L satisfy the relationship of 2 / 3 < A / L < 6 / 5.

[0016] The optical scanning device of the present disclosure is an optical scanning device including any one of the above micro mirror devices and a processor that drives the drive unit. The processor swings the mirror unit around the first axis and the second axis respectively by applying a drive signal to the drive unit.

Effect of the Invention

[0017] According to the technology of the present disclosure, it is possible to provide a micro mirror device and an optical scanning device capable of suppressing a shift in the resonance frequency due to axial crosstalk.

Brief Description of the Drawings

[0018]

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Figure 20

Mode for Carrying Out the Invention

[0019] An example of an embodiment according to the technology of the present disclosure will be described with reference to the accompanying drawings.

[0020] FIG. 1 schematically shows an optical scanning device 10 according to an 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 optically scans a scanned surface 5 by reflecting a light beam L emitted from the light source 3 with the MMD 2 according to the control of the drive control unit 4. The scanned surface 5 is, for example, a screen.

[0021] The MMD 2 is a piezoelectric two-axis drive type micromirror device capable of swinging a mirror unit 20 (see FIG. 3) around a first axis a1 and a second axis a2 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.

[0022] The light source 3 is, for example, a laser device that emits laser light as the light beam L. The light source 3 preferably irradiates the light beam L perpendicularly to a reflection surface 20A (see FIG. 3) provided in the mirror unit 20 in a state where the mirror unit 20 of the MMD 2 is stationary.

[0023] The drive control unit 4 outputs drive signals to the light source 3 and the MMD 2 based on the optical scanning information. The light source 3 generates the light beam L based on the input drive signal and irradiates the MMD 2. The MMD 2 swings the mirror unit 20 around the first axis a1 and the second axis a2 based on the input drive signal.

[0024] Although details will be described later, the drive control unit 4 resonates the mirror unit 20 around the first axis a1 and the second axis a2, respectively, so that the light beam L reflected by the mirror unit 20 is scanned on the scanned surface 5 so as to draw a Lissajous waveform. This optical scanning method is called a Lissajous scan method.

[0025] The optical scanning device 10 is applied to, for example, a laser display of the Lissajous scan method. Specifically, the optical scanning device 10 can be applied to a laser scan display such as AR (Augmented Reality) glasses or VR (Virtual Reality) glasses.

[0026] FIG. 2 shows an example of the hardware configuration 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 an arithmetic unit that realizes the overall functions of the drive control unit 4 by reading programs and data from a storage device such as the ROM 41 into the RAM 42 and executing processing. The CPU 40 is an example of a processor according to the technology of the present disclosure.

[0027] The ROM 41 is a non-volatile storage device that stores programs for the CPU 40 to execute processing and data such as the aforementioned optical scanning information. The RAM 42 is a volatile storage device that temporarily holds programs and data.

[0028] The light source driver 43 is an electric 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.

[0029] The MMD driver 44 is an electric 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, period, and swing angle for swinging the mirror unit 20 of the MMD driver 44.

[0030] The CPU 40 controls the light source driver 43 and the MMD driver 44 based on the optical scanning information. The optical scanning information is information including the scanning pattern of the light beam L scanned on the scanned surface 5 and the light emission timing of the light source 3.

[0031] Next, the configuration of the MMD2 according to the first embodiment will be described with reference to FIGS. 3 to 5. FIG. 3 is an external perspective view of the MMD2. FIG. 4 is a plan view of the MMD2 viewed from the light incident side. FIG. 5 is a cross-sectional view taken along the line A-A of FIG. 4.

[0032] As shown in FIG. 3, the MMD2 includes a mirror unit 20, a pair of first support parts 21, a pair of movable frames 22, a pair of second support parts 23, a pair of first actuators 24, a pair of second actuators 25, a pair of first connection parts 26A, a pair of second connection parts 26B, and a fixed frame 27. The MMD2 is a so-called MEMS scanner.

[0033] The mirror unit 20 has a reflecting surface 20A that reflects incident light. The reflecting surface 20A is formed of a metal thin film such as gold (Au) or aluminum (Al) provided on one surface of the mirror unit 20. The shape of the reflecting surface 20A is, for example, circular with the intersection of the first axis a1 and the second axis a2 as the center.

[0034] The first axis a1 and the second axis a2 exist, for example, in a plane including the reflecting surface 20A when the mirror unit 20 is at rest. The planar shape of the MMD2 is rectangular, line-symmetric with respect to the first axis a1, and line-symmetric with respect to the second axis a2.

[0035] The pair of first support parts 21 are arranged at positions facing each other with the second axis a2 interposed therebetween, and have a shape that is line-symmetric with respect to the second axis a2. Each of the first support parts 21 has a shape that is line-symmetric with respect to the first axis a1. The first support part 21 is connected to the mirror unit 20 on the first axis a1 and supports the mirror unit 20 so as to be swingable around the first axis a1.

[0036] The pair of movable frames 22 are arranged at positions facing each other with the first axis a1 interposed therebetween, and have a shape that is line-symmetric with respect to the first axis a1. Each of the movable frames 22 has a shape that is line-symmetric with respect to the second axis a2. Also, each of the movable frames 22 is curved along the outer periphery of the mirror unit 20. Both ends of the movable frame 22 are respectively connected to the first support part 21.

[0037] The first support portion 21 and the movable frame 22 are connected to each other to surround the mirror portion 20. Note that the mirror portion 20, the first support portion 21, and the movable frame 22 constitute the movable portion 60.

[0038] The pair of second support portions 23 are arranged at positions facing each other with the first axis a1 interposed therebetween, and have a shape that is line-symmetric with respect to the first axis a1. Each of the second support portions 23 has a shape that is line-symmetric with respect to the second axis a2. The second support portion 23 is connected to the movable frame 22 on the second axis a2, and supports the movable portion 60 having the mirror portion 20 so as to be swingable around the second axis a2. Further, both ends of the second support portion 23 are respectively connected to the first actuator 24.

[0039] The pair of first actuators 24 are arranged at positions facing each other with the second axis a2 interposed therebetween, and have a shape that is line-symmetric with respect to the second axis a2. Further, the first actuator 24 has a shape that is line-symmetric with respect to the first axis a1. The first actuator 24 is formed along the outer circumferences of the movable frame 22 and the first support portion 21. The first actuator 24 is an actuator of a piezoelectric drive type including a piezoelectric element.

[0040] In FIGS. 3 and 4, the first actuator 24 appears to be separated near the first axis a1, but the first actuator 24 is electrically connected with the first axis a1 interposed therebetween by wiring (not shown).

[0041] The second support portion 23 and the first actuator 24 are connected to each other to surround the movable portion 60.

[0042] A pair of second actuators 25 are arranged at positions facing each other across the first axis a1 and have a shape that is line-symmetric with respect to the first axis a1. Also, the second actuator 25 has a shape that is line-symmetric with respect to the second axis a2. The second actuator 25 is formed along the outer peripheries of the first actuator 24 and the second support portion 23. The second actuator 25 is a piezoelectric drive type actuator provided with a piezoelectric element.

[0043] In addition, in FIGS. 3 and 4, the second actuator 25 appears to be separated near the second axis a2, but the second actuator 25 is electrically connected across the second axis a2 by wiring (not shown).

[0044] A pair of first connection portions 26A are arranged at positions facing each other across the second axis a2 and have a shape that is line-symmetric with respect to the second axis a2. Also, each of the first connection portions 26A has a shape that is line-symmetric with respect to the first axis a1. The first connection portions 26A are arranged along the first axis a1 and connect the first actuator 24 and the second actuator 25 on the first axis a1.

[0045] A pair of second connection portions 26B are arranged at positions facing each other across the first axis a1 and have a shape that is line-symmetric with respect to the first axis a1. Also, each of the second connection portions 26B has a shape that is line-symmetric with respect to the second axis a2. The second connection portions 26B are arranged along the second axis a2 and connect the second actuator 25 and the fixed frame 27 on the second axis a2.

[0046] The second actuator 25 and the second connection portion 26B are connected to each other to surround the movable portion 60 and the first actuator 24. The first actuator 24 and the second actuator 25 constitute a drive portion arranged to surround the movable portion 60.

[0047] The fixed frame 27 is a frame-shaped member with a rectangular outer shape, and is symmetric about each of the first axis a1 and the second axis a2. The fixed frame 27 surrounds the outer circumferences of the second actuator 25 and the second connection portion 26B. That is, the fixed frame 27 is disposed so as to surround the drive unit.

[0048] The first actuator 24 and the second actuator 25 are piezoelectric actuators each having a piezoelectric element. The pair of first actuators 24 swing the movable part 60 around the second axis a2 by applying a rotational torque around the second axis a2 to the mirror part 20 and the movable frame 22. The pair of second actuators 25 swing the mirror part 20 around the first axis a1 by applying a rotational torque around the first axis a1 to the mirror part 20, the movable frame 22, and the first actuator 24.

[0049] As shown in FIG. 4, 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 mirror part 20, and the other end is connected to the connecting portion 21B.

[0050] On the first axis a1, there is a spatial gap (hereinafter referred to as a gap) G1 between the first support portion 21 and the drive unit.

[0051] The pair of connecting portions 21B are disposed at positions facing each other with the first axis a1 interposed therebetween, and have a shape that is symmetric about the first axis a1. One end of the connecting portion 21B is connected to the swing shaft 21A, and the other end is connected to the movable frame 22. The connecting portion 21B has a folded-back structure. Since the connecting portion 21B has elasticity due to the folded-back structure, when the mirror part 20 swings around the first axis a1, the internal stress applied to the swing shaft 21A is relaxed.

[0052] 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 that extends 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.

[0053] On the second axis a2, there is a gap G2 between the second support portion 23 and the drive portion.

[0054] The pair of connecting portions 23B are arranged at positions facing each other with the second axis a2 interposed therebetween, and have a shape that is line-symmetrical with respect to the second axis a2. One end of the connecting portion 23B is connected to the swing shaft 23A, and the other end is connected to the first actuator 24. The connecting portion 23B has a folded-back structure. Since the connecting portion 23B has elasticity due to the folded-back structure, when the mirror portion 20 swings around the second axis a2, the internal stress applied to the swing shaft 23A is relaxed.

[0055] Also, on the mirror portion 20, outside the reflecting surface 20A, a plurality of slits 20B, 20C are formed along the outer periphery of the reflecting surface 20A. The plurality of slits 20B, 20C are arranged at positions that are line-symmetrical with respect to each of the first axis a1 and the second axis a2. The slit 20B has the effect of suppressing the distortion generated on the reflecting surface 20A when the mirror portion 20 swings.

[0056] In FIGS. 3 and 4, the illustration of the wiring and electrode pads for applying drive signals to the first actuator 24 and the second actuator 25 is omitted. A plurality of electrode pads are provided on the fixed frame 27.

[0057] As shown in FIG. 5, the MMD2 is formed, for example, by 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-crystalline silicon, and a second silicon active layer 33 made of single-crystalline silicon is provided on the silicon oxide layer 32.

[0058] The mirror part 20, the first support part 21, the movable frame 22, the second support part 23, the first actuator 24, the second actuator 25, the first connection part 26A, and the second connection part 26B are formed by the second silicon active layer 33 remaining after removing the first silicon active layer 31 and the silicon oxide layer 32 from the SOI substrate 30 by an etching process. The second silicon active layer 33 functions as an elastic part having elasticity. The fixed frame 27 is formed of three layers, namely, the first silicon active layer 31, the silicon oxide layer 32, and the second silicon active layer 33.

[0059] The first actuator 24 includes a piezoelectric element (not shown) 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 sequentially stacked on the second silicon active layer 33. The second actuator 25 has the same configuration as the first actuator 24.

[0060] The upper electrode and the lower electrode are formed of, for example, gold (Au) or platinum (Pt). The piezoelectric film is formed of, for example, PZT (lead zirconate titanate), which is a piezoelectric material. The upper electrode and the lower electrode are electrically connected to the aforementioned drive control unit 4 via wiring and electrode pads.

[0061] A drive voltage is applied to the upper electrode from the drive control unit 4. The lower electrode is connected to the drive control unit 4 via wiring and electrode pads and is given a reference potential (for example, a ground potential).

[0062] When a positive or negative voltage is applied to the piezoelectric film in the polarization direction, a deformation (for example, expansion and contraction) proportional to the applied voltage occurs. That is, the piezoelectric film exhibits a so-called inverse piezoelectric effect. The piezoelectric film exhibits the inverse piezoelectric effect when a drive voltage is applied to the upper electrode from the drive control unit 4, thereby displacing the first actuator 24 and the second actuator 25.

[0063] FIG. 6 shows an example in which a rotational torque about the first axis a1 is generated in the second actuator 25 by expanding one piezoelectric film of the pair of second actuators 25 and contracting the other piezoelectric film. In this way, the mirror unit 20 rotates about the first axis a1 as one and the other of the pair of second actuators 25 are displaced in opposite directions to each other.

[0064] Also, FIG. 6 shows an example in which the second actuator 25 is 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 unit 20 are opposite to each other. On the other hand, a in-phase resonance mode in which the displacement direction of the pair of second actuators 25 and the rotation direction of the mirror unit 20 are the same direction is referred to as an in-phase rotation mode. In the present embodiment, the second actuator 25 is driven in the anti-phase rotation mode.

[0065] The swing angle θ of the mirror unit 20 about the first axis a1 is controlled by a drive signal (hereinafter referred to as a first drive signal) that the drive control unit 4 gives to the second actuator 25. The first drive signal is, for example, an alternating voltage of a sine wave. The first drive signal includes a drive voltage waveform V 1A (t) applied to one of the pair of second actuators 25 and a drive voltage waveform V 1B (t) applied to the other. The drive voltage waveform V 1A (t) and the drive voltage waveform V 1B (t) are in anti-phase (that is, the phase difference is 180°) with each other.

[0066] Note that the swing angle θ of the mirror unit 20 about the first axis a1 corresponds to the angle at which the normal line N of the reflecting surface 20A is inclined with respect to the Z direction in the YZ plane. Hereinafter, the swing angle θ is also referred to as the rotation angle θ.

[0067] The first actuator 24 is driven in a resonance mode with an opposite phase, similar to the second actuator 25. The swing angle around the second axis a2 of the mirror unit 20 is controlled by a drive signal (hereinafter referred to as the second drive signal) that the drive control unit 4 applies to the first actuator 24. The second drive signal is, for example, an alternating voltage of a sine wave. The second drive signal includes a drive voltage waveform V 2A (t) applied to one of the pair of second actuators 25 and a drive voltage waveform V 2B (t) applied to the other. The drive voltage waveform V 2A (t) and the drive voltage waveform V 2B (t) are in opposite phases (i.e., a phase difference of 180°) from each other.

[0068] FIG. 7 shows an example of the first drive signal and the second drive signal. FIG. 7(A) shows the drive voltage waveforms V 1A (t) and V 1B (t) included in the first drive signal. FIG. 7(B) shows the drive voltage waveforms V 2A (t) and V 2B (t) included in the second drive signal.

[0069] The drive voltage waveforms V 1A (t) and V 1B (t) are respectively represented as follows. V 1A (t)=V off1 +V1sin(2πf d1 t) V 1B (t)=V off1 +V1sin(2πf d1 t+α)

[0070] Here, V1 is the amplitude voltage. V off1 is the bias voltage. f d1 is the drive frequency (hereinafter referred to as the first drive frequency). t is time. α is the phase difference between the drive voltage waveforms V 1A (t) and V 1B (t). In this embodiment, for example, α = 180°.

[0071] The drive voltage waveforms V 1A (t) and V1B When (t) is applied to the pair of second actuators 25, the mirror unit 20 oscillates around the first axis a1 at the first driving frequency f d1 .

[0072] The drive voltage waveforms V 2A (t) and V 2B (t) are respectively expressed as follows. V 2A (t)=V off2 +V2sin(2πf d2 t + φ) V 2B (t)=V off2 +V2sin(2πf d2 t + β + φ)

[0073] Here, V2 is the amplitude voltage. V off2 is the bias voltage. f d2 is the driving frequency (hereinafter referred to as the second driving frequency). t is time. β is the phase difference between the drive voltage waveforms V 2A (t) and V 2B (t). In this embodiment, for example, β = 180°. Also, φ is the phase difference between the drive voltage waveforms V 1A (t) and V 1B (t), and the drive voltage waveforms V 2A (t) and V 2B (t). Also, in this embodiment, for example, V off1 =V off2 = 0V.

[0074] When the drive voltage waveforms V 2A (t) and V 2B (t) are applied to the pair of first actuators 24, the movable unit 60 including the mirror unit 20 oscillates around the second axis a2 at the second driving frequency f d2 .

[0075] The first driving frequency f d1 is set to match the resonance frequency of the mirror unit 20 around the first axis a1. The second driving frequency f d2is set to match the resonance frequency around the second axis a2 of the mirror unit 20. In the present embodiment, the first driving frequency f d1 is the second driving frequency f d2 and is greater.

[0076] When the MMD2 configured as described above is two-dimensionally driven around the first axis a1 and the second axis a2, the centrifugal force acting when the movable part 60 swings around the second axis a2 helps the mirror unit 20 to swing around the first axis a1. The potential energy due to this centrifugal force affects the total amount of elastic energy and kinetic energy stored when the mirror unit 20 swings. As a result, the spring constant in the swing of the mirror unit 20 changes and crosstalk between the axes occurs, causing the resonance frequency to shift.

[0077] The applicant of the present application has found that when the mirror unit 20 rotates around the first axis a1 and the absolute value of the rotation angle θ becomes greater than 0 degrees, and the displacement of the second support portion 23 satisfies a predetermined condition, the shift of the resonance frequency due to crosstalk between the axes is suppressed.

[0078] When the displacement of the second support portion 23 satisfies a predetermined condition, the displacement amount of the portion other than the mirror unit 20 of the movable part 60 increases. Thereby, the total amount of elastic energy and kinetic energy in the entire MMD2 increases. As a result, the influence of the potential energy due to the centrifugal force on the total energy becomes relatively small, and the shift of the resonance frequency due to crosstalk between the axes is suppressed.

[0079] FIG. 8 schematically shows the displacement of the second support portion 23 when the mirror unit 20 rotates around the first axis a1. FIG. 8(A) shows a state where the mirror unit 20 is stationary and the rotation angle θ is 0 degrees. FIG. 8(B) shows a state where the mirror unit 20 rotates around the first axis a1 and the absolute value of the rotation angle θ is greater than 0 degrees.

[0080] FIG. 8 shows a cross-sectional view of MMD2 cut along a plane orthogonal to the first axis a1 and including the second axis a2. The straight line α and the intersection point C shown in FIG. 8(B) are included in the cross-section of MMD2. Specifically, the straight line α is a straight line on the surface of the second support portion 23 and including each end point of the second support portion 23. The intersection point C is a point where the straight line α intersects the second axis a2.

[0081] Let the total length of the second support portion 23 in the direction of the second axis a2 at rest be Lb1. Also, in the direction of the second axis a2, let the distance from the end of the second support portion 23 on the mirror portion 20 side to the intersection point C at rest be A. The applicant of the present application has found through experiments described later that when the distance A is greater than 2 / 3 times the total length Lb1 (i.e., 2 / 3×Lb1 < A), the shift of the resonance frequency due to the inter-axis crosstalk is suppressed.

[0082] In the experiments described later, the applicant of the present application prepared a plurality of samples of MMD2 with different distances A, and measured the shift amount of the resonance frequency due to the inter-axis crosstalk by driving each sample. Specifically, for each sample, the resonance frequency around the first axis a1 when driven one-dimensionally around the first axis a1 (hereinafter referred to as the first resonance frequency fr1), and the resonance frequency around the first axis a1 when driven two-dimensionally around the first axis a1 and the second axis a2 (hereinafter referred to as the second resonance frequency fr2) were measured. Then, the shift amount Δfr of the resonance frequency due to the inter-axis crosstalk was obtained by calculating the difference between the first resonance frequency fr1 and the second resonance frequency fr2.

[0083] FIGS. 9 and 10 show parameters regarding the width and length of each component of the sample used in the experiment. FIG. 11 shows specific setting values of the parameters.

[0084] Also, the diameter of the mirror portion 20 was 1.5 mm, the thickness of the SOI substrate 30 was 430 μm, the thickness of the second silicon active layer 33 was 60 μm, and the thickness of the silicon oxide layer 32 was 40 μm. Also, the length of one side of the fixed frame 27 was 5.2 mm.

[0085] The applicant of the present application used Xac2 and Yac2 among the parameters shown in FIG. 11 as variables. That is, the applicant prepared a plurality of samples with different distances A by changing the lengths of Xac2 and Yac2 for each sample.

[0086] [Modification Example] In addition, as a modification example, the applicant prepared a sample for MMD2A in which the shape and the like of each component are different from those of MMD2 according to the above embodiment.

[0087] FIG. 12 shows the configuration of MMD2A according to the modification example. In FIG. 12, the components having the same functions as those of MMD2 according to the above embodiment are denoted by the same reference numerals. In MMD2A, a connecting portion 26 is provided instead of the first connecting portion 26A and the second connecting portion 26B. The connecting portion 26 is provided on the first axis a1, connects the first actuator 24 to the second actuator 25, and connects the second actuator 25 to the fixed frame 27.

[0088] FIGS. 13 to 15 show parameters regarding the width and length of each component of MMD2A. FIG. 16 shows specific set values of the parameters.

[0089] In addition, in the modification example, the diameter of the mirror portion 20 was set to 1.5 mm, the thickness of the SOI substrate 30 was set to 350 μm, the thickness of the second silicon active layer 33 was set to 60 μm, the thickness of the silicon oxide layer 32 was set to 65 μm, and the length of one side of the fixed frame 27 was set to 5.2 mm.

[0090] [Experimental Results] For the above embodiment and the modification example, each sample was driven in a vacuum chamber to measure the first resonance frequency fr1 and the second resonance frequency fr2. Specifically, while irradiating the mirror portion 20 with laser light during driving, the driving frequency was swept, and the driving frequency at which the spread angle of the reflected light became the largest was measured as the resonance frequency. In addition, the deflection angle of the mirror portion 20 was calculated from the spread angle of the reflected light.

[0091] Figure 17 shows the measurement results of the first resonance frequency fr1 and the second resonance frequency fr2 for each sample. Sample number 1 shows a sample fabricated for MMD2A according to the modified example. Sample numbers 2 to 9 show samples fabricated for MMD2 according to the embodiment. For sample numbers 2 to 9, the lengths of Xac2 and Yac2 are different.

[0092] The first resonance frequency fr1 is the resonance frequency during one-dimensional driving when the deflection angle of the mirror unit 20 around the first axis a1 is ±1.25 degrees. The second resonance frequency fr2 is the resonance frequency during two-dimensional driving when the deflection angle of the mirror unit 20 around the first axis a1 is ±1.25 degrees and the deflection angle of the mirror unit 20 around the second axis a2 is ±11.5 degrees. The shift amount Δfr of the resonance frequency is the value obtained by subtracting the first resonance frequency fr1 from the second resonance frequency fr2.

[0093] Also, the distance A was measured for each sample using a laser Doppler vibrometer. Then, using the measured distance A, the ratio A / Lb1 of the distance A to the total length Lb1 of the second support portion 23 was calculated.

[0094] When considering the application to an AR glass laser display, the appropriate values of the deflection angles of the mirror unit 20 around each axis during two-dimensional driving are ±17 degrees around the first axis a1 and ±11.5 degrees around the second axis a2. Therefore, for each sample, it was determined whether two-dimensional driving could be stably performed for 60 seconds or more while maintaining the deflection angle at the appropriate value. "OK" indicates that stable two-dimensional driving for 60 seconds or more was possible. "NG" indicates that stable two-dimensional driving for 60 seconds or more was not possible.

[0095] Also, the power consumption of each sample was measured using a current probe in a state where resonance was achieved by one-dimensional driving around the first axis a1. At this time, the deflection angle of the mirror unit 20 around the first axis a1 was ±17 degrees.

[0096] According to the experimental results shown in FIG. 17, it can be seen that the larger the ratio A / Lb1 is, the smaller the shift amount Δfr of the resonance frequency becomes. Note that the smaller the shift amount Δfr is means that the absolute value of the shift amount Δfr is small. Also, if the ratio A / Lb1 is larger than 2 / 3 (larger than about 0.66), it can be seen that the two-dimensional driving is stabilized and advantages can be obtained from the perspective of application to a laser display for AR glass. FIG. 18 is a graph showing the dependence of the shift amount Δfr of the resonance frequency on the ratio A / Lb1.

[0097] FIG. 19 is a graph showing the dependence of the power consumption on the ratio A / Lb1. In general laser display applications, it is desirable that the power consumption is smaller. As a guideline, if the power consumption during one-dimensional driving is 80 mW or less, it is possible to ensure a certain degree of superiority as a laser display application. Therefore, it can be seen that if the ratio A / Lb1 is 6 / 5 or less (1.2 or less), the power consumption will be 80 mW or less, and a certain degree of superiority can be ensured from the perspective of power consumption.

[0098] That is, it is preferable that the ratio A / Lb1 satisfies the relationship 2 / 3 < A / Lb1. Furthermore, it is preferable that the ratio A / Lb1 satisfies the relationship 2 / 3 < A / Lb1 < 6 / 5.

[0099] FIG. 20 shows the simulation results. In FIGS. 20(A) to (C), the lengths of Xac2 and Yac2 are different. The intersection point C corresponds to the point where the displacement of the second support portion 23 is zero. It can be seen that the position of the intersection point C changes (that is, the distance A changes) according to the lengths of Xac2 and Yac2. Also, in the simulation, it was confirmed that the larger the ratio A / Lb1 is, the smaller the shift amount Δfr of the resonance frequency becomes.

[0100] In the above embodiment, the hardware configuration of the drive control unit 4 can be variously modified. The processing unit of the drive control unit 4 may be constituted by one processor, or may be constituted by a combination of two or more processors of the same type or different types. The processor includes a CPU, a programmable logic device (PLD), an application specific electric circuit, etc. The CPU is a general-purpose processor that executes software (program) and functions as various processing units as is well known. The PLD is a processor such as an FPGA (Field Programmable Gate Array) whose circuit configuration can be changed after manufacture. The application specific electric circuit is a processor having a circuit configuration specifically designed to execute specific processing such as an ASIC (Application Specific Integrated Circuit).

[0101] All documents, patent applications, and technical standards described in this specification are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard was specifically and individually indicated to be incorporated by reference.

Explanation of Signs

[0102] 2,2A micromirror device 3 light source 4 drive control unit 5 scanned surface 10 optical scanning device 20 mirror unit 20A reflecting surface 20B,20C slit 21 first support portion 21A rocking axis 21B connecting portion 22 movable frame 23 second support portion 23A rocking axis 23B connecting portion 24 first actuator 25 second actuator 26 connecting portion 26A first connecting portion 26B Second Connection Part 27 Fixed Frame 30 SOI Substrate 31 First Silicon Active Layer 32 Silicon Oxide Layer 33 Second Silicon Active Layer 40 CPU 41 ROM 42 RAM 43 Light Source Driver 44 Driver 60 Movable Part Δfr Shift Amount α Straight Line θ Rotation Angle A Distance C Intersection Point G1, G2 Clearance L Light Beam N Normal a1 First Axis a2 Second Axis

Claims

1. A mirror part having a reflecting surface for reflecting incident light; A first support part connected to the mirror part on a first axis within a plane including the reflecting surface of the mirror part at rest, and supporting the mirror part so as to be swingable around the first axis; A pair of movable frames connected to the first support part and facing each other with the first axis interposed therebetween; Connected to the movable frames on both sides facing in the first axis direction with the second axis interposed therebetween at an end portion on the mirror part side on a second axis orthogonal to the first axis within a plane including the reflecting surface of the mirror part at rest, and a second support part for supporting a movable part including the mirror part, the first support part, and the movable frames so as to be swingable around the second axis; A drive part disposed to surround the movable part and having a gap between the drive part and the second support part on the second axis; A connecting part connecting the second support part and the drive part; A fixed frame connected to the drive part and disposed to surround the drive part; comprising In a state where the mirror part rotates around the first axis and the absolute value of the rotation angle becomes larger than 0 degree, In a plane orthogonal to the first axis and including the second axis, at the intersection of a straight line including each end point of the second support part on the surface of the second support part and the second axis and the second axis, and the distance between the end portion on the mirror part side of the second support part at rest is defined as A, and the total length of the second support part in the second axis direction is defined as L, when 2 / 3 < A / L is satisfied, A micromirror device.

2. The drive part has a piezoelectric element. The micromirror device according to Claim 1.

3. The drive part A pair of first actuators facing each other with the second axis interposed therebetween and having piezoelectric elements; A pair of second actuators disposed to surround the first actuators, facing each other with the first axis interposed therebetween, and having piezoelectric elements; The micromirror device according to claim 1, comprising

4. The second actuator swings the mirror part around the first axis, The first actuator swings the movable part around the second axis. The micromirror device according to claim 3.

5. The distance A and the total length L satisfy the relationship of 2 / 3 < A / L < 6 / 5, The micromirror device according to any one of claims 1 to 4.

6. The micromirror device according to any one of claims 1 to 4, and A processor for driving the driving unit, An optical scanning device comprising The processor swings the mirror part around the first axis and the second axis respectively by applying a driving signal to the driving unit. Optical scanning device.

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