Micromirror device and optical scanning device

Abstract

To provide a micro-mirror device which can reduce power consumption when two-dimensionally driven, 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 A / L≤2 / 3, 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 disclosed herein relates to a micromirror device and an optical scanning device. [Background technology]

[0002] Micromirror devices (also called microscanners) are known as one of the Micro Electro Mechanical Systems (MEMS) devices fabricated using silicon (Si) microfabrication technology. Because these micromirror devices are small and consume low power, they are expected to be used in a wide range of applications, such as laser displays, laser projectors, and optical coherence tomographs.

[0003] There are various drive methods for micromirror devices, but the piezoelectric drive method, which uses the deformation of a piezoelectric body, is considered promising because it generates a higher torque than other methods and can obtain a wide scan angle. In particular, when a wide scan angle is required, such as in a laser display, a higher scan angle can be obtained by resonantly driving a piezoelectric micromirror device.

[0004] A typical micromirror device used in a laser display includes a mirror portion and a piezoelectric actuator (see, for example, Patent Documents 1 and 2). The mirror portion can freely oscillate around a first axis and a second axis that are perpendicular to each other. The actuator oscillates the mirror portion around the first axis and the second axis in response to a driving voltage supplied from the outside. The above-mentioned scan angle corresponds to the deflection angle of the mirror portion.

[0005] The performance indexes of laser displays include resolution and viewing angle. Resolution and viewing angle are related to the oscillation frequency and deflection angle of the mirror part of the micromirror device. For example, in a laser display using the Lissajous scan method, two-dimensional optical scanning is performed by simultaneously oscillating the mirror part around the first and second axes at two different frequencies. The larger the deflection angle of the mirror part, the larger the optical scanning area becomes, and a larger image can be displayed with a shorter optical path length. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2017-132281 A [Patent Document 2] International Publication No. 2009 / 041342 Summary of the Invention [Problem to be solved by the invention]

[0007] In a typical micromirror device, the actuator acting as the driving section is directly connected to the fixed frame on the second axis. In this case, when the mirror section oscillates around the first axis, the movement of the actuator is significantly restricted, so a large amount of energy is required to drive the actuator. This leads to a decrease in the Q value during driving, resulting in increased power consumption.

[0008] An object of the technique disclosed herein is to provide a micromirror device and an optical scanning apparatus that can reduce power consumption during two-dimensional driving. [Means for solving the problem]

[0009] In order to achieve the above object, the micro-mirror device of the present disclosure includes a mirror section having a reflective surface that reflects incident light, a first support section that is connected to the mirror section on a first axis in a plane including the reflective surface of the mirror section when stationary and supports the mirror section so that it can swing about the first axis, a pair of movable frames that are connected to the first support section and face each other across the first axis, a second support section that is connected to the movable frames on a second axis that is orthogonal to the first axis in a plane including the reflective surface of the mirror section when stationary and supports a movable section including the mirror section, the first support section, and the movable frame so that it can swing about the second axis, and a pair of movable frames that are arranged to surround the movable section. The mirror unit is provided with a drive unit having a gap between it and the second support unit on the second axis, a connecting unit that connects the second support unit and the drive unit, and a fixed frame that is connected to the drive unit and arranged to surround the drive unit, and when the mirror unit rotates around the first axis and the absolute value of the rotation angle becomes greater than 0 degrees, in a plane that is perpendicular to the first axis and includes the second axis, the distance between the intersection of a straight line that is on the surface of the second support unit and includes each end point of the second support unit and the second axis and the end of the second support unit on the mirror unit side when stationary is A and the overall length of the second support unit in the second axial direction is L, the relationship A / L≦2 / 3 is satisfied.

[0010] The drive section preferably includes a piezoelectric element.

[0011] It is preferable that the drive unit comprises a pair of first actuators facing each other across the second axis and having piezoelectric elements, and a pair of second actuators arranged surrounding the first actuators, facing each other across the first axis, and having piezoelectric elements.

[0012] It is preferable that the second actuator oscillates the mirror portion about a first axis, and the first actuator oscillates the movable portion about a second axis.

[0013] It is preferable that the distance A and the total length L satisfy the relationship 19 / 50≦A / L≦2 / 3.

[0014] The optical scanning device disclosed herein is an optical scanning device comprising any one of the micromirror devices described above and a processor that drives a drive unit, and the processor provides a drive signal to the drive unit to cause the mirror unit to oscillate around a first axis and a second axis, respectively. Effect of the Invention

[0015] According to the technique of the present disclosure, it is possible to provide a micromirror device and an optical scanning apparatus that can reduce power consumption during two-dimensional driving. [Brief description of the drawings]

[0016] [Figure 1] FIG. 2 is a schematic diagram of an optical scanning device. [Diagram 2] 2 is a block diagram showing an example of a hardware configuration of a drive control unit. FIG. [Diagram 3] FIG. 1 is a perspective view of the appearance of a micromirror device. [Figure 4] FIG. 2 is a plan view of the micromirror device as viewed from the light incident side. [Diagram 5] FIG. 5 is a cross-sectional view taken along line AA in FIG. [Figure 6] 4 is a cross-sectional view showing a state in which the mirror portion has rotated around a first axis. FIG. [Figure 7] 5A and 5B are diagrams illustrating an example of a first drive signal and a second drive signal. [Figure 8] 6A and 6B are diagrams illustrating schematic displacement of a second support portion when the mirror portion rotates around a first axis. [Figure 9] FIG. 2 is a diagram showing dimensional parameters of components of a micromirror device. [Figure 10] FIG. 2 is a diagram showing dimensional parameters of components of a micromirror device. [Figure 11] FIG. 11 is a diagram showing specific setting values ​​of parameters. [Figure 12] FIG. 13 is a plan view of a micromirror device according to a modified example. [Figure 13]13 is a diagram showing parameters relating to dimensions of components of a micromirror device according to a modified example. [Figure 14] 13 is a diagram showing parameters relating to dimensions of components of a micromirror device according to a modified example. [Figure 15] 13 is a diagram showing parameters relating to dimensions of components of a micromirror device according to a modified example. [Figure 16] FIG. 11 is a diagram showing specific setting values ​​of parameters. [Figure 17] FIG. 13 is a diagram showing experimental results for each sample. [Figure 18] 13 is a graph showing the dependence of power consumption on the ratio A / Lb1. [Figure 19] 13 is a graph showing the dependency of the amount of shift of the resonance frequency on the ratio A / Lb1. [Figure 20] FIG. 13 is a diagram showing a simulation result. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] An example of an embodiment of the technology of the present disclosure will be described with reference to the accompanying drawings.

[0018] 1 is a schematic diagram of an optical scanning device 10 according to an embodiment. The optical scanning device 10 includes a micro mirror device (hereinafter referred to as MMD (Micro Mirror Device)) 2, a light source 3, and a drive controller 4. The optical scanning device 10 optically scans a surface 5 to be scanned by reflecting a light beam L irradiated from the light source 3 by the MMD 2 under the control of the drive controller 4. The surface 5 to be scanned is, for example, a screen.

[0019] The MMD2 is a piezoelectric two-axis drive micromirror device that can oscillate a mirror section 20 (see FIG. 3) around a first axis a1 and a second axis a2 perpendicular 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 as the Y direction, and the direction perpendicular to the first axis a1 and the second axis a2 as the Z direction.

[0020] The light source 3 is a laser device that emits, for example, laser light as the light beam L. It is preferable that the light source 3 irradiates the light beam L perpendicularly to a reflecting surface 20A (see FIG. 3) of the mirror section 20 of the MMD 2 when the mirror section 20 is stationary.

[0021] 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 a light beam L based on the input drive signal and irradiates the MMD 2 with the light beam L. The MMD 2 swings the mirror unit 20 around the first axis a1 and the second axis a2 based on the input drive signal.

[0022] Although the details will be described later, the drive control unit 4 causes the mirror unit 20 to resonate around the first axis a1 and the second axis a2, respectively, so that the light beam L reflected by the mirror unit 20 scans the scanned surface 5 so as to draw a Lissajous waveform. This light scanning method is called a Lissajous scan method.

[0023] The optical scanning device 10 is applied to, for example, a Lissajous scan type laser display. Specifically, the optical scanning device 10 is applicable to a laser scan display such as AR (Augmented Reality) glasses or VR (Virtual Reality) glasses.

[0024] 2 shows an example of a hardware configuration of the drive control unit 4. The drive control unit 4 has 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 calculation 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 into the RAM 42 and executing processing. The CPU 40 is an example of a processor related to the technology of the present disclosure.

[0025] The ROM 41 is a non-volatile storage device that stores programs for the CPU 40 to execute processes, and data such as the optical scanning information described above, etc. The RAM 42 is a volatile storage device that temporarily holds programs and data.

[0026] The light source driver 43 is an electric circuit that outputs a drive signal to the light source 3 under 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.

[0027] The MMD driver 44 is an electric circuit that outputs a drive signal to the MMD 2 under the control of the CPU 40. In the MMD driver 44, the drive signal is a drive voltage for controlling the timing, period, and deflection angle of the oscillation of the mirror portion 20 of the MMD driver 44.

[0028] The CPU 40 controls the light source driver 43 and the MMD driver 44 based on the optical scanning information. The optical scanning information includes a scanning pattern of the light beam L that scans the surface 5 to be scanned and the light emission timing of the light source 3.

[0029] Next, the configuration of the MMD 2 according to the first embodiment will be described with reference to Fig. 3 to Fig. 5. Fig. 3 is an external perspective view of the MMD 2. Fig. 4 is a plan view of the MMD 2 as viewed from the light incident side. Fig. 5 is a cross-sectional view taken along line AA in Fig. 4.

[0030] 3, the MMD 2 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 connection sections 26A, a pair of second connection sections 26B, and a fixed frame 27. The MMD 2 is a so-called MEMS scanner.

[0031] The mirror section 20 has a reflecting surface 20A that reflects incident light. The reflecting surface 20A is formed of a thin metal film such as gold (Au) or aluminum (Al) provided on one surface of the mirror section 20. The shape of the reflecting surface 20A is, for example, a circular shape centered on the intersection of the first axis a1 and the second axis a2.

[0032] The first axis a1 and the second axis a2 exist, for example, in a plane including the reflecting surface 20A when the mirror section 20 is stationary. The planar shape of the MMD 2 is rectangular and is line-symmetric with respect to the first axis a1 and line-symmetric with respect to the second axis a2.

[0033] The pair of first support parts 21 are disposed at positions facing each other across the second axis a2, and are shaped line-symmetrical about the second axis a2. Each of the first support parts 21 is also shaped line-symmetrical about the first axis a1. The first support parts 21 are connected to the mirror part 20 on the first axis a1, and support the mirror part 20 so as to be swingable about the first axis a1.

[0034] The pair of movable frames 22 are disposed at positions facing each other across the first axis a1, and have shapes that are line-symmetrical with respect to the first axis a1. Each of the movable frames 22 has a shape that is line-symmetrical with respect to the second axis a2. Each of the movable frames 22 is curved along the outer periphery of the mirror section 20. Both ends of the movable frame 22 are connected to the first support section 21.

[0035] The first support section 21 and the movable frame 22 are connected to each other to surround the mirror section 20. The mirror section 20, the first support section 21, and the movable frame 22 configure a movable section 60.

[0036] The pair of second support parts 23 are disposed at positions facing each other across the first axis a1, and are shaped line-symmetrical about the first axis a1. Each of the second support parts 23 is shaped line-symmetrical about the second axis a2. 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 mirror part 20 so that the movable part 60 can swing about the second axis a2. In addition, both ends of the second support parts 23 are connected to the first actuators 24, respectively.

[0037] The pair of first actuators 24 are disposed at positions facing each other across the second axis a2, and are shaped line-symmetrical about the second axis a2. The first actuators 24 are also shaped line-symmetrical about the first axis a1. The first actuators 24 are formed along the outer periphery of the movable frame 22 and the first support part 21. The first actuators 24 are piezoelectric actuators equipped with piezoelectric elements.

[0038] Although the first actuator 24 appears to be separated near the first axis a1 in FIGS. 3 and 4, the first actuator 24 is electrically connected across the first axis a1 by wiring (not shown).

[0039] The second support portion 23 and the first actuator 24 are connected to each other, thereby surrounding the movable portion 60.

[0040] The pair of second actuators 25 are disposed at positions facing each other across the first axis a1, and are shaped line-symmetrical about the first axis a1. The second actuators 25 are also shaped line-symmetrical about the second axis a2. The second actuators 25 are formed along the outer periphery of the first actuator 24 and the second support portion 23. The second actuators 25 are piezoelectric actuators equipped with piezoelectric elements.

[0041] In addition, although the second actuator 25 appears to be separated near the second axis a2 in Figures 3 and 4, the second actuator 25 is electrically connected across the second axis a2 by wiring (not shown).

[0042] The pair of first connection parts 26A are disposed at positions facing each other across the second axis a2, and are shaped line-symmetrical about the second axis a2. Each of the first connection parts 26A is also shaped line-symmetrical about the first axis a1. The first connection parts 26A are disposed along the first axis a1, and connect the first actuator 24 and the second actuator 25 on the first axis a1.

[0043] The pair of second connection parts 26B are disposed at positions facing each other across the first axis a1, and are shaped line-symmetrical with respect to the first axis a1. Also, each of the second connection parts 26B is shaped line-symmetrical with respect to the second axis a2. The second connection parts 26B are disposed along the second axis a2, and connect the second actuator 25 and the fixed frame 27 on the second axis a2.

[0044] The second actuator 25 and the second connection portion 26B are connected to each other, thereby surrounding the movable portion 60 and the first actuator 24. The first actuator 24 and the second actuator 25 configure a drive portion disposed surrounding the movable portion 60.

[0045] The fixed frame 27 is a frame-shaped member having a rectangular outer shape, and is symmetrical with respect to each of the first axis a1 and the second axis a2. The fixed frame 27 surrounds the outer periphery of the second actuator 25 and the second connection portion 26B. In other words, the fixed frame 27 is disposed surrounding the drive portion.

[0046] The first actuator 24 and the second actuator 25 are piezoelectric actuators each having a piezoelectric element. The pair of first actuators 24 apply a rotational torque about the second axis a2 to the mirror section 20 and the movable frame 22, thereby oscillating the movable section 60 about the second axis a2. The pair of second actuators 25 apply a rotational torque about the first axis a1 to the mirror section 20, the movable frame 22, and the first actuators 24, thereby oscillating the mirror section 20 about the first axis a1.

[0047] 4, the first support portion 21 is composed of an oscillation shaft 21A and a pair of connecting portions 21B. The oscillation shaft 21A is a so-called torsion bar that extends along the first axis a1. One end of the oscillation shaft 21A is connected to the mirror portion 20, and the other end is connected to the connecting portions 21B.

[0048] On the first axis a1, a spatial gap (hereinafter, referred to as a gap) G1 exists between the first support portion 21 and the drive portion.

[0049] The pair of connecting portions 21B are disposed at positions facing each other across the first axis a1, and are shaped to be line-symmetrical with respect to the first axis a1. One end of each connecting portion 21B is connected to the oscillation shaft 21A, and the other end is connected to the movable frame 22. The connecting portion 21B has a folded structure. Since the connecting portion 21B has elasticity due to the folded structure, it relieves the internal stress acting on the oscillation shaft 21A when the mirror portion 20 oscillates around the first axis a1.

[0050] 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 portions 23B.

[0051] On the second axis a2, a gap G2 exists between the second support portion 23 and the drive portion.

[0052] The pair of connecting portions 23B are disposed at positions facing each other across the second axis a2, and are shaped to be line-symmetrical with respect to the second axis a2. One end of the connecting portion 23B is connected to the oscillation axis 23A, and the other end is connected to the first actuator 24. The connecting portion 23B has a folded structure. Since the connecting portion 23B has elasticity due to the folded structure, it relieves the internal stress acting on the oscillation axis 23A when the mirror portion 20 oscillates around the second axis a2.

[0053] In addition, the mirror section 20 has a plurality of slits 20B and 20C formed on the outer side of the reflecting surface 20A along the outer periphery of the reflecting surface 20A. The plurality of slits 20B and 20C are arranged at positions that are line-symmetrical with respect to the first axis a1 and the second axis a2, respectively. The slits 20B have the effect of suppressing distortion that occurs in the reflecting surface 20A due to the oscillation of the mirror section 20.

[0054] 3 and 4, wiring and electrode pads for applying drive signals to the first actuator 24 and the second actuator 25 are omitted. A plurality of electrode pads are provided on the fixed frame 27.

[0055] 5, the MMD 2 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 crystal silicon, and a second silicon active layer 33 made of single crystal silicon is provided on the silicon oxide layer 32.

[0056] The mirror section 20, the first support section 21, the movable frame 22, the second support section 23, the first actuator 24, the second actuator 25, the first connection section 26A, and the second connection section 26B are formed of 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 etching. The second silicon active layer 33 functions as an elastic section having elasticity. The fixed frame 27 is formed of three layers, the first silicon active layer 31, the silicon oxide layer 32, and the second silicon active layer 33.

[0057] The first actuator 24 includes a piezoelectric element (not shown) formed on the second silicon active layer 33. The piezoelectric element has a layered structure in which a lower electrode, a piezoelectric film, and an upper electrode are layered in this order on the second silicon active layer 33. The second actuator 25 has a similar configuration to the first actuator 24.

[0058] 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 drive control unit 4 described above via wiring and electrode pads.

[0059] A driving voltage is applied to the upper electrode from the driving control unit 4. The lower electrode is connected to the driving control unit 4 via wiring and an electrode pad, and is supplied with a reference potential (for example, ground potential).

[0060] When a positive or negative voltage is applied to the piezoelectric film in the polarization direction, the piezoelectric film undergoes deformation (e.g., expansion and contraction) proportional to the applied voltage. That is, the piezoelectric film exhibits a so-called inverse piezoelectric effect. When a drive voltage is applied from the drive control unit 4 to the upper electrode, the piezoelectric film exhibits the inverse piezoelectric effect, displacing the first actuator 24 and the second actuator 25.

[0061] 6 shows an example in which one piezoelectric film of a pair of second actuators 25 is expanded and the other piezoelectric film is contracted, thereby generating a rotational torque around the first axis a1 in the second actuator 25. In this way, one and the other of the pair of second actuators 25 are displaced in the opposite directions, causing the mirror section 20 to rotate around the first axis a1.

[0062] 6 shows an example in which the 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 section 20 are opposite to each other. In contrast, an in-phase resonance mode in which the displacement direction of the pair of second actuators 25 and the rotation direction of the mirror section 20 are the same is referred to as an in-phase rotation mode. In this embodiment, the second actuators 25 are driven in the anti-phase rotation mode.

[0063] The deflection angle θ of the mirror section 20 around the first axis a1 is controlled by a drive signal (hereinafter referred to as a first drive signal) that the drive control section 4 provides to the second actuator 25. The first drive signal is, for example, a sinusoidal AC voltage. The first drive signal is a drive voltage waveform V 1A (t) and the driving voltage waveform V applied to the other 1B (t) and the driving voltage waveform V 1A (t) and the driving voltage waveform V 1B (t) are in opposite phase to each other (i.e., the phase difference is 180°).

[0064] The deflection angle θ of the mirror section 20 about the first axis a1 corresponds to the angle at which the normal N of the reflecting surface 20A is inclined with respect to the Z direction in the YZ plane. Hereinafter, the deflection angle θ will also be referred to as the rotation angle θ.

[0065] The first actuator 24 is driven in an opposite-phase resonant mode, similar to the second actuator 25. The deflection angle of the mirror section 20 about the second axis a2 is controlled by a drive signal (hereinafter referred to as a second drive signal) that the drive control section 4 provides to the first actuator 24. The second drive signal is, for example, a sinusoidal AC voltage. The second drive signal is a drive voltage waveform V 2A (t) and the driving voltage waveform V applied to the other 2B (t) and the driving voltage waveform V 2A (t) and the driving voltage waveform V 2B (t) are in opposite phase to each other (i.e., the phase difference is 180°).

[0066] 7A and 7B show examples of the first and second drive signals. FIG. 7A shows a drive voltage waveform V 1A (t) and V 1B FIG. 7B shows the drive voltage waveform V 2A (t) and V 2B (t) is shown.

[0067] Drive voltage waveform V 1A (t) and V 1B(t) is expressed as follows, respectively: V 1A (t)=V off1 +V1sin(2πf d1 t) V 1B (t)=V off1 +V1sin(2πf d1 t+α)

[0068] where 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 drive voltage waveform V 1A (t) and V 1B In this embodiment, for example, α=180°.

[0069] Drive voltage waveform V 1A (t) and V 1B When the driving frequency f(t) is applied to the pair of second actuators 25, the mirror section 20 is driven at a first driving frequency f d1 It oscillates around the first axis a1.

[0070] Drive voltage waveform V 2A (t) and V 2B (t) is expressed as follows, respectively: V 2A (t)=V off2 +V2sin(2πf d2 t+φ) V 2B (t)=V off2 +V2sin(2πf d2 t+β+φ)

[0071] where V2 is the amplitude voltage. V off2 is the bias voltage. f d2 is the drive frequency (hereinafter referred to as the second drive frequency). t is time. β is the drive voltage waveform V 2A (t) and V 2B In this embodiment, for example, β=180°. Also, φ is the phase difference of the driving voltage waveform V 1A (t) and V1B (t) and the driving voltage waveform V 2A (t) and V 2B (t). In this embodiment, for example, V off1 =V off2 = 0V.

[0072] Drive voltage waveform V 2A (t) and V 2B When the driving frequency f(t) is applied to the pair of first actuators 24, the movable section 60 including the mirror section 20 is driven at a second driving frequency f d2 It oscillates around the second axis a2.

[0073] First drive 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 is set to coincide with the resonance frequency around the second axis a2 of the mirror portion 20. In this embodiment, the first driving frequency f d1 is the second driving frequency f d2 Greater than.

[0074] The applicant has discovered that in the MMD2 configured as described above, when the mirror portion 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 predetermined conditions, the power consumption is reduced to below a certain value.

[0075] Fig. 8 shows a schematic diagram of the displacement of the second support section 23 when the mirror section 20 rotates around the first axis a1. Fig. 8(A) shows a state in which the mirror section 20 is stationary and the rotation angle θ is 0 degrees. Fig. 8(B) shows a state in which the mirror section 20 rotates around the first axis a1 and the absolute value of the rotation angle θ becomes greater than 0 degrees.

[0076] Fig. 8 shows a cross-sectional view of the MMD2 cut by a plane that is perpendicular to the first axis a1 and includes the second axis a2. The straight line α and intersection point C shown in Fig. 8(B) are included in the cross section of the MMD2. Specifically, the straight line α is a straight line that is on the surface of the second support part 23 and includes each end point of the second support part 23. The intersection point C is the point where the straight line α and the second axis a2 intersect.

[0077] The total length of the second support section 23 in the second axis a2 direction when stationary is defined as Lb1. Also, the distance in the second axis a2 direction from the end of the second support section 23 on the mirror section 20 side when stationary to the intersection C is defined as A. Through an experiment described later, the applicant has found that when the distance A is 2 / 3 times or less the total length Lb1 (i.e., when A≦2 / 3×Lb1), the power consumption is reduced to 50 mW or less.

[0078] In the experiments described below, the applicant created several samples of MMD2 with different distances A, and measured the power consumption of each sample using a current probe while resonating with one-dimensional driving around the first axis a1.

[0079] In addition, when a micromirror device is generally driven resonantly, crosstalk occurs between axes, in which the oscillation of the mirror part around one of the first and second axes affects the oscillation of the mirror part around the other axis. Specifically, the resonance frequency around one axis shifts depending on the magnitude of the rotation angle around the other axis. This significantly reduces the stability of two-dimensional optical scanning.

[0080] For example, when attempting to increase the deflection angle of the mirror by sweeping the drive frequency around one axis to bring the drive frequency closer to the resonant frequency, the deflection angle of the mirror around the other axis changes significantly due to a shift in the resonant frequency caused by inter-axis crosstalk. At this time, the change in the deflection angle of the mirror around the other axis causes a shift in the resonant frequency around the axis on the side where the drive frequency is swept. In other words, a kind of feedback phenomenon occurs due to inter-axis crosstalk.

[0081] In this way, when the amount of shift in the resonant frequency due to inter-axis crosstalk is large, even if the drive frequency is swept, the drive frequency cannot be adjusted to the resonant frequency due to the above-mentioned feedback phenomenon, and the deflection angle of the mirror portion cannot be increased.

[0082] For this reason, the amount of shift in the resonant frequency due to the inter-axis crosstalk was measured by driving each sample prepared for MMD2. Specifically, the resonant frequency around the first axis a1 (hereinafter referred to as the first resonant frequency fr1) when each sample was driven one-dimensionally around the first axis a1, and the resonant frequency around the first axis a1 (hereinafter referred to as the second resonant frequency fr2) when each sample was driven two-dimensionally around the first axis a1 and the second axis a2 were measured. Then, the amount of shift in the resonant frequency Δfr due to the inter-axis crosstalk was obtained by calculating the difference between the first resonant frequency fr1 and the second resonant frequency fr2.

[0083] Figures 9 and 10 show parameters related to the width, length, etc. of each component of the sample used in the experiment, while Figure 11 shows specific setting values ​​of the parameters.

[0084] 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. The length of one side of the fixing frame 27 was 5.2 mm.

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

[0086] [Variations] Moreover, the applicant has produced, as a modified example, a sample of an MMD2A in which the shapes of the components are different from those of the MMD2 according to the above embodiment.

[0087] Fig. 12 shows the configuration of an MMD 2A according to a modified example. In Fig. 12, components having the same functions as those of the MMD 2 according to the above embodiment are given the same reference numerals. Note that in the MMD 2A, a connection portion 26 is provided instead of the first connection portion 26A and the second connection portion 26B. The connection portion 26 is provided on the first axis a1, and connects the first actuator 24 to the second actuator 25, and also connects the second actuator 25 to the fixed frame 27.

[0088] 13 to 15 show parameters relating to the width, length, etc. of each component of the MMD 2A, and Fig. 16 shows specific setting values ​​of the parameters.

[0089] In the modified example, the diameter of the mirror portion 20 is 1.5 mm, the thickness of the SOI substrate 30 is 350 μm, the thickness of the second silicon active layer 33 is 60 μm, and the thickness of the silicon oxide layer 32 is 65 μm. The length of one side of the fixing frame 27 is 5.2 mm.

[0090] [Experimental Results] For the above embodiment and modified 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 was 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] 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 made for the MMD2A according to the modified example. Sample numbers 2 to 7 show samples made for the MMD2 according to the embodiment. Sample numbers 2 to 7 have different lengths of Xac2 and Yac2.

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

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

[0094] When considering application to a laser display for AR glasses, the deflection angle of the mirror section 20 around each axis during two-dimensional driving can be ensured if the deflection angle around the first axis a1 is ±8.5 degrees or more, and the deflection angle around the second axis a2 is ±5.65 degrees or more. Therefore, for each sample, it was judged whether the deflection angle was within the above angle range and whether stable two-dimensional driving was possible for 60 seconds or more. "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] According to FIG. 17, if the ratio A / Lb1 is 19 / 50 or more (0.38 or more), the two-dimensional drive is stabilized, and it is found to be advantageous in terms of application to general laser displays.

[0096] The power consumption was measured using a current probe in a state where the mirror section 20 was resonating by one-dimensional driving about the first axis a1. At this time, the deflection angle of the mirror section 20 about the first axis a1 was ±17 degrees.

[0097] FIG. 18 is a graph showing the dependence of power consumption on the ratio A / Lb1. In general, lower power consumption is desirable for AR glasses laser display applications. As a guideline, if the power consumption during one-dimensional driving is 50mW or less, a significant advantage can be secured for AR glasses laser display applications. According to FIG. 18, if the ratio A / Lb1 is 2 / 3 or less, the power consumption is reduced to 50mW or less, and an advantage can be obtained in terms of application to AR glasses laser displays.

[0098] This reduction in power consumption is also attributable to the fact that the presence of the gap G2 between the second support portion 23 and the drive portion suppresses the decrease in the Q value during drive around the first axis a1.

[0099] Fig. 19 is a graph showing the dependency of the resonant frequency shift amount Δfr on the ratio A / Lb1. It can be seen from Fig. 19 that the larger the ratio A / Lb1, the smaller the resonant frequency shift amount Δfr. Note that a small shift amount Δfr means that the absolute value of the shift amount Δfr is small.

[0100] That is, from the viewpoint of power consumption, it is preferable that the ratio A / Lb1 satisfies the relationship of A / Lb1≦2 / 3. Furthermore, from the viewpoint of power consumption and stability of two-dimensional driving, it is preferable that the ratio A / Lb1 satisfies the relationship of 19 / 50≦A / Lb1≦2 / 3.

[0101] Fig. 20 shows the simulation results. In Fig. 20(A) to (C), the lengths of Xac2 and Yac2 are different. The intersection 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 C (i.e., the distance A changes) according to the lengths of Xac2 and Yac2. Also, in the simulation, it was confirmed that the smaller the ratio A / Lb1, the smaller the power consumption.

[0102] In the above embodiment, the hardware configuration of the drive control unit 4 can be modified in various ways. The processing unit of the drive control unit 4 may be configured with one processor, or may be configured with a combination of two or more processors of the same type or different types. The processor includes a CPU, a programmable logic device (PLD), a dedicated electric circuit, and the like. As is well known, a CPU is a general-purpose processor that executes software (programs) and functions as various processing units. A PLD is a processor such as an FPGA (Field Programmable Gate Array) whose circuit configuration can be changed after manufacture. A dedicated electric circuit is a processor having a circuit configuration designed specifically to execute a specific process such as an ASIC (Application Specific Integrated Circuit).

[0103] All publications, patent applications, and standards mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication, patent application, and standard was specifically and individually indicated to be incorporated by reference. [Explanation of symbols]

[0104] 2,2A Micromirror Device 3 light source 4 Drive control section 5. Surface to be scanned 10 Optical scanning device 20 Mirror section 20A reflective surface 20B, 20C Slit 21 1st support part 21A Swing shaft 21B Connection part 22 Movable frame 23 Second support part 23A Swing shaft 23B Connection part 24 First Actuator 25 Second Actuator 26 Connection 26A 1st Connection 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 Moving parts Δfr shift amount α straight line θ Rotation angle A Distance C intersection G1,G2 void L Light beam N Normal a1 First axis a2 2nd axis

Claims

1. a mirror portion having a reflecting surface that reflects incident light; a first support portion connected to the mirror portion on a first axis in a plane including the reflecting surface of the mirror portion when the mirror portion is stationary and supporting the mirror portion so as to be swingable around 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 that has, on a second axis that is orthogonal to the first axis and is in a plane that includes the reflective surface of the mirror portion when the mirror portion is stationary, an end point that is connected to the movable frame and an end point that is opposite to the movable frame, and that supports a movable portion including the mirror portion, the first support portion, and the movable frame so that the movable portion can swing around the second axis; a drive unit disposed around the movable unit, the drive unit having a gap between the drive unit and the second support unit on the second axis; a connecting portion that connects the second support portion and the driving portion; a fixed frame connected to the driving unit and arranged to surround the driving unit; Equipped with When the mirror portion rotates around the first axis and the absolute value of the rotation angle becomes greater than 0 degrees, in a plane perpendicular to the first axis and including the second axis, a distance between an intersection point of a straight line on a surface of the second support portion and the second axis and an end portion of the second support portion on the mirror unit side when stationary is defined as A, and a total length of the second support portion in the second axial direction is defined as L, satisfying a relationship of A / L≦2 / 3. Micromirror device.

2. The driving unit has a piezoelectric element. The micromirror device of claim 1 .

3. The drive unit is a pair of first actuators facing each other across the second axis and each having a piezoelectric element; a pair of second actuators, the second actuators being disposed around the first actuator, facing each other across the first axis, and each having a piezoelectric element; The micromirror device of claim 1 .

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

5. The distance A and the total length L satisfy the relationship of 19 / 50≦A / L≦2 / 3. The micromirror device according to claim 1 .

6. A micromirror device according to any one of claims 1 to 4; A processor that drives the drive unit; An optical scanning device comprising: the processor supplies a drive signal to the drive unit to cause the mirror unit to oscillate around the first axis and the second axis, respectively; Optical scanning device.

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