Micromirror device and optical scanning device

Abstract

The micromirror device of the present invention comprises a first supporting portion (21), which is connected to the reflector portion (20) on a first axis (a1) located within a plane including a reflection surface of the reflector portion (20) when the reflector portion (20) is stationary, and supports the reflector portion (20) so as to be able to swing around the first axis (a1). The first supporting portion (21) is composed of a main axis (21A) extending along the first axis (a1) and a plurality of secondary axes (60A, 60B, 60C) symmetrically arranged on both sides of the main axis (21a) across the first axis (a1) and extending along the first axis (a1). The first supporting portion (21) has a folding structure having three or more folding portions (61, 62, 63) connected by the plurality of secondary axes (60A, 60B, 60C). When the curvature radius of the inner side of the folding portion (61, 62, 63) is R1, R2, R3, etc. from the side closest to the first axis (a1), 0.73≤R k+1 / R k ≤0.9, where k=1, 2, ...

Description

Technical Field

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

[0002] Micromirror devices (also known as microscanners) are one type of microelectromechanical systems (MEMS) devices fabricated using silicon (Si) microfabrication technology. Due to their compact size and low power consumption, these devices are expected to find widespread application in laser displays, laser projectors, optical coherence tomography scanners, and other applications.

[0003] There are various methods for driving micromirror devices, but piezoelectric drive, which utilizes the deformation of a piezoelectric element, is considered promising because it generates higher torque and achieves higher scanning angles than other methods. In particular, when a large scanning angle is required, such as in laser displays, resonant drive of piezoelectric micromirror devices can achieve even higher scanning angles.

[0004] Conventional micromirror devices used in laser displays include a reflector and a piezoelectric actuator (for example, see Japanese Patent Application Publication No. 2017-132281). The reflector can swing freely about a first axis and a second axis that are orthogonal to each other. The actuator swings the reflector about the first axis and the second axis based on an externally supplied drive voltage. The above-mentioned scanning angle corresponds to the maximum deflection angle of the reflector (hereinafter referred to as the maximum deflection angle).

[0005] Performance indicators for laser displays include resolution and field of view. Resolution and field of view are related to the oscillation frequency of the micromirror device's reflector and its maximum deflection angle. For example, in a Lissajous scanning laser display, two-dimensional optical scanning is achieved by oscillating the reflector simultaneously around the first and second axes at two different frequencies.

[0006] In the dual-axis drive type micromirror device described above, a universal joint structure is often used. A micromirror device with a universal joint structure, for example, includes a reflector portion, a first support portion, a movable frame, and a second support portion. The first support portion supports the reflector portion so that it can swing about a first axis. The movable frame is connected to the first support portion. The second support portion is connected to the movable frame, supporting the reflector portion and the movable frame so that they can swing about a second axis.

[0007] Here, in order to increase the maximum deflection angle of the reflector portion about the first axis, it is necessary to alleviate the internal stress applied to the first support portion during swinging, and to prevent the internal stress from reaching the limit stress of Si. To alleviate the internal stress applied to the first support portion, a folding structure is known to be provided in the movable frame.

[0008] For example, Japanese Patent Application Laid-Open No. 2016-206235 discloses a method of connecting a connecting portion having a folded structure to an end portion of a torsion beam on the opposite side of the reflector portion corresponding to the first support portion (see Japanese Patent Application Laid-Open No. 2017-132281). Figure 3 The folded structure is formed by forming a first slit and a second slit in the connecting portion. The first slit and the second slit extend linearly in a direction parallel to the reflector plane and perpendicular to the torsion beam. Summary of the Invention

[0009] Technical issues to be solved by the invention

[0010] In the micromirror device described in Japanese Patent Application Laid-Open No. 2016-206235, the lengths of the first and second slits need to be increased to mitigate the stress applied to the torsion beam. The micromirror device described in Japanese Patent Application Laid-Open No. 2016-206235 is a single-axis driven type, so the lengths of the first and second slits do not affect the swing of the reflector portion.

[0011] However, when the micromirror device described in Japanese Patent Application Laid-Open No. 2016-206235 is applied to a dual-axis drive type, increasing the length of the first and second slits increases the moment of inertia around the second axis disposed outside the connecting portion. This increase in the moment of inertia around the second axis reduces the resonant frequency around the second axis. Consequently, the resolution of optical scanning is reduced.

[0012] Furthermore, as a simple method for alleviating the internal stress applied to the first support portion, extending the first support portion can be considered. However, in this case, the moment of inertia about the second axis increases due to the length of the first support portion becoming longer, thereby causing the resonant frequency about the second axis to decrease.

[0013] Thus, in a two-axis drive type micromirror device, it is desired to relax the internal stress applied to the first support portion without lowering the resonance frequency about the second axis, thereby increasing the maximum deflection angle about the first axis.

[0014] The technical object of the present invention is to provide a micromirror device and an optical scanning device that can increase the maximum deflection angle around the first axis without reducing the resonant frequency around the second axis.

[0015] Means for solving technical problems

[0016] In order to achieve the above-mentioned object, the micromirror device of the present invention comprises: a reflector portion having a reflective surface for reflecting incident light; a first support portion connected to the reflector portion on a first axis located in a plane including the reflective surface when the reflector portion is stationary, and supporting the reflector portion so as to be able to swing around the first axis; a pair of movable frames connected to the first support portion and opposed to each other with the first axis therebetween; a second support portion connected to the movable frame on a second axis located in a plane including the reflective surface when the reflector portion is stationary and orthogonal to the first axis, and supporting the reflector portion, the first support portion and the movable frame so as to be able to swing around the second axis; and a pair of first actuators connected to the second support portion and opposed to each other with the second axis therebetween, the first actuator having a piezoelectric element, in the micromirror device,

[0017] The first supporting portion is composed of a main axis extending along the first axis and a plurality of secondary axes symmetrically arranged on both sides of the main axis and extending along the first axis. The first supporting portion has a folding structure having three or more folding portions connected by the plurality of secondary axes. When the curvature radius of the inner side of the folding portion is R1, R2, R3, etc. from the side closest to the first axis,

[0018] Satisfying 0.73≤R k+1 / R k ≤0.9(k=1, 2, ...).

[0019] It is preferable that the thicknesses of the major axis and the plurality of minor axes are uniform.

[0020] Preferably, in the first actuator, at least a portion of the width in a direction perpendicular to the extending direction is larger than the width of the main axis in a direction along the second axis.

[0021] Preferably, the movable frame and the first actuator are each U-shaped.

[0022] Preferably, the first actuator causes the mirror portion to swing about the second axis by applying a torque about the second axis to the mirror portion and the movable frame.

[0023] Preferably, the device comprises: a fixed frame configured to surround a first actuator; a connecting portion connecting the first actuator and the fixed frame; and a second actuator connected to the connecting portion and arranged on the inner side of the fixed frame, wherein the second actuator has a piezoelectric element and causes the mirror portion to swing around the first axis by applying a torque around the first axis to the mirror portion, the movable frame, and the first actuator.

[0024] The connecting portion is preferably arranged along the first axis.

[0025] An optical scanning device comprises: the above-mentioned micromirror device; and a processor that drives a first actuator and a second actuator. In the optical scanning device, the processor applies a driving signal to the first actuator and the second actuator to cause the reflective mirror to resonate around a first axis and a second axis, respectively.

[0026] Effects of the Invention

[0027] According to the technology of the present invention, it is possible to provide a micromirror device and an optical scanning device that can increase the maximum deflection angle around the first axis without lowering the resonant frequency around the second axis. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is a schematic diagram of an optical scanning device.

[0029] Figure 2 This is a block diagram showing an example of the hardware configuration of the drive control unit.

[0030] Figure 3 This is a three-dimensional diagram of the appearance of a micromirror device.

[0031] Figure 4 This is a top view of the micromirror device as viewed from the light incident side.

[0032] Figure 5 It is along Figure 4 Cross-sectional view of the AA line cutting.

[0033] Figure 6 It is along Figure 4 Cross-sectional view of BB line cutting.

[0034] Figure 7 It is a diagram showing an example of driving the second actuator.

[0035] Figure 8 It is a diagram showing an example of driving the first actuator.

[0036] Figure 9 : is a diagram showing an example of the first drive signal and the second drive signal.

[0037] Figure 10 It is a diagram showing the structure of the first support portion 21 and the second support portion 23 .

[0038] Figure 11 This is a diagram showing parameters related to the dimensions of components of a micromirror device.

[0039] Figure 12 This is a diagram showing parameters related to the dimensions of components of a micromirror device.

[0040] Figure 13 This is a diagram showing parameters related to the dimensions of components of a micromirror device.

[0041] Figure 14 This is a diagram showing parameters related to the dimensions of components of a micromirror device.

[0042] Figure 15This is a diagram showing the setting values ​​of various parameters used in the simulation experiment.

[0043] Figure 16 It is a graph showing the results of simulation experiments on multiple models.

[0044] Figure 17 It is a graph showing the relationship between Mises stress and the first resonance frequency.

[0045] Figure 18 It is a graph showing the relationship between Mises stress and the second resonance frequency. DETAILED DESCRIPTION

[0046] An example of an embodiment according to the technology of the present invention will be described with reference to the drawings.

[0047] Figure 1 The following diagram schematically illustrates an optical scanning device 10 according to one embodiment. The optical scanning device 10 includes a micromirror device (hereinafter referred to as an MMD) 2, a light source 3, and a drive control unit 4. Under control of the drive control unit 4, the optical scanning device 10 reflects a light beam L emitted from the light source 3 via the MMD 2, thereby optically scanning a scanned surface 5. The scanned surface 5 is, for example, a screen.

[0048] MMD2 is a device that can make the reflector portion 20 (refer to Figure 3 ) A piezoelectric two-axis driven micromirror device that oscillates about 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 is referred to as the Y direction, and the direction perpendicular to the first axis a1 and the second axis a2 is referred to as the Z direction.

[0049] The light source 3 is a laser device that emits a laser beam as a light beam L. The light source 3 preferably emits a light beam to the reflective surface 20A (refer to FIG. 2 ) of the reflective mirror 20 when the reflective mirror 20 of the MMD 2 is stationary. Figure 3 )Vertical irradiation beam L.

[0050] The drive control unit 4 outputs a drive signal to the light source 3 and the MMD 2 based on the light scanning information. The light source 3 generates a light beam L based on the input drive signal and irradiates the light beam L to 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.

[0051] Although details will be described later, the drive control unit 4 causes the mirror unit 20 to resonate about the first axis a1 and the second axis a2, respectively, so that the light beam L reflected by the mirror unit 20 is scanned so as to draw a Lissajous waveform on the scanned surface 5. This optical scanning method is called a Lissajous scanning method.

[0052] The optical scanning device 10 is applicable to, for example, a Lissajous scanning laser display. Specifically, the optical scanning device 10 can be applied to a laser scanning display such as AR (Augmented Reality) glasses or VR (Virtual Reality) glasses.

[0053] Figure 2 The figure 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 a computing device that reads programs and data from a storage device such as the ROM 41 into the RAM 42 and executes the data, thereby realizing the overall functions of the drive control unit 4. The CPU 40 is an example of a processor involved in the technology of the present invention.

[0054] The ROM 41 is a nonvolatile storage device and stores programs for the CPU 40 to execute processes and data such as the aforementioned light scanning information. The RAM 42 is a nonvolatile storage device that temporarily stores programs and data.

[0055] The light source driver 43 is a circuit that outputs a drive signal to the light source 3 according to the control of the CPU 40. In the light source driver 43, the drive signal is a drive voltage for controlling the irradiation timing and irradiation intensity of the light source 3.

[0056] The MMD driver 44 is a 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, cycle, and deflection angle of the oscillation of the mirror unit 20 of the MMD 2.

[0057] The CPU 40 controls the light source driver 43 and the MMD driver 44 based on the light scanning information. The light scanning information is information including the scanning pattern of the light beam L for scanning the scanned surface 5 and the emission timing of the light source 3.

[0058] Next, use Figures 3 to 6 An example of MMD2 will be described. Figure 3 This is a three-dimensional image of the appearance of MMD2. Figure 4 This is a top view of the MMD2 as viewed from the light incident side. Figure 5 It is along Figure 4 Cross-sectional view of the AA line cutting. Figure 6 It is along Figure 4 Cross-sectional view of BB line cutting.

[0059] like Figure 3 As shown, the MMD 2 includes a mirror unit 20, a pair of first support units 21, a pair of movable frames 22, a pair of second support units 23, a pair of first actuators 24, a pair of second actuators 25, a pair of connecting units 26, and a fixed frame 27. The MMD 2 is a so-called MEMS scanner.

[0060] The reflector 20 includes a reflective surface 20A that reflects incident light. The reflective surface 20A is provided on one surface of the reflector 20 and is formed, for example, from a metal thin film such as gold (Au) or aluminum (Al). The reflective surface 20A is shaped, for example, in a circular manner centered at the intersection of the first axis a1 and the second axis a2.

[0061] The first axis a1 and the second axis a2 exist in a plane including the reflecting surface 20A when the mirror unit 20 is stationary. The planar shape of the MMD 2 is rectangular and is line-symmetric about the first axis a1 and the second axis a2.

[0062] The pair of first support portions 21 are disposed at opposing positions across the second axis a2 and are line-symmetrical about the second axis a2. Furthermore, each first support portion 21 is line-symmetrical about the first axis a1. The first support portions 21 are connected to the reflector portion 20 along the first axis a1 and support the reflector portion 20 so that it can swing about the first axis a1.

[0063] A pair of movable frames 22 are positioned opposite each other across the first axis a1 and are symmetrical about the first axis a1. Each movable frame 22 is symmetrical about the second axis a2. Furthermore, each movable frame 22 is U-shaped, curved in an arc along the outer circumference of the reflector portion 20. Both ends of the movable frame 22 are connected to the first support portion 21.

[0064] The first support portion 21 and the movable frame 22 are connected to each other, thereby surrounding the mirror portion 20 .

[0065] A pair of second support portions 23 are disposed at opposing positions across the first axis a1 and are symmetrical about the first axis a1. Each second support portion 23 is symmetrical about the second axis a2. The second support portions 23 are connected to the movable frame 22 along the second axis a2 and support the mirror portion 20, the first support portion 21, and the movable frame 22 so that they can swing about the second axis a2. Furthermore, each end of the second support portion 23 is connected to the first actuator 24.

[0066] The pair of first actuators 24 are disposed at opposing positions across the second axis a2 and are symmetrical about the second axis a2. Furthermore, each first actuator 24 is symmetrical about the first axis a1. The first actuator 24 has a U-shape that curves along the outer periphery of the first support portion 21. The first actuator 24 is a piezoelectric actuator comprising a piezoelectric element.

[0067] The second support portion 23 and the first actuator 24 are connected to each other, thereby surrounding the mirror portion 20 , the first support portion 21 , and the movable frame 22 .

[0068] The pair of second actuators 25 are positioned opposite each other across the first axis a1 and are symmetrical about the first axis a1. Furthermore, each second actuator 25 is symmetrical about the second axis a2. Each second actuator 25 has a U-shape that curves along the outer periphery of the first actuator 24 and the second support portion 23. Both ends of the second actuator 25 are connected to the connecting portion 26.

[0069] The pair of connecting portions 26 are positioned opposite each other across the second axis a2 and are symmetrical about the second axis a2. Furthermore, each connecting portion 26 is symmetrical about the first axis a1. The connecting portions 26 are arranged along the first axis a1 and connect the first actuator 24 and the fixed frame 27 along the first axis a1. The second actuator 25 is connected to the center of the connecting portion 26.

[0070] The second actuator 25 and the connection portion 26 are connected to each other, thereby surrounding the mirror portion 20 , the first support portion 21 , the movable frame 22 , and the first actuator 24 .

[0071] The fixed frame 27 is a rectangular frame-shaped member with a line-symmetric shape about the first axis a1 and the second axis a2. The fixed frame 27 surrounds the outer periphery of the second actuator 25 and the connecting portion 26. In other words, the fixed frame 27 is arranged to surround the first actuator 24. The second actuator 25 is arranged inside the fixed frame 27.

[0072] The first actuator 24 and the second actuator 25 are piezoelectric actuators each including a piezoelectric element. The pair of first actuators 24 apply a torque about the second axis a2 to the mirror portion 20 and the movable frame 22, thereby causing the mirror portion 20 to oscillate about the second axis a2. The pair of second actuators 25 apply a torque about the first axis a1 to the mirror portion 20, the movable frame 22, and the first actuators 24, thereby causing the mirror portion 20 to oscillate about the first axis a1.

[0073] like Figure 4 As shown, the first support portion 21 is composed of a swing shaft 21A and a pair of connecting portions 21B. The swing shaft 21A is a so-called torsion bar extending along the first axis a1. One end of the swing shaft 21A is connected to the reflector portion 20, and the other end is connected to the connecting portion 21B. The swing shaft 21A is an example of a main shaft involved in the technology of the present invention.

[0074] The pair of connecting portions 21B are arranged at opposing positions across the first axis a1 and are line-symmetrical 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 foldable structure. This foldable structure provides elasticity to the connecting portion 21B, thereby alleviating internal stress applied to the swing shaft 21A when the reflector portion 20 swings about the first axis a1.

[0075] The second support portion 23 is composed of a swing shaft 23A and a pair of connecting portions 23B. The swing shaft 23A is a so-called torsion bar extending along the second axis a2. One end of the swing shaft 23A is connected to the movable frame 22, and the other end is connected to the connecting portion 23B.

[0076] The pair of connecting portions 23B are arranged at opposing positions across the second axis a2 and are line-symmetrical about 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 foldable structure. The foldable structure provides elasticity to the connecting portion 23B, thereby alleviating internal stress applied to the swing shaft 23A when the reflector portion 20 swings about the second axis a2.

[0077] The first actuator 24 is composed of an arcuate portion 24A and a pair of fan-shaped portions 24B. The arcuate portion 24A is line-symmetrical about the first axis a1. Both ends of the arcuate portion 24A are connected to the fan-shaped portions 24B.

[0078] The pair of fan-shaped portions 24 are arranged at opposing positions across the first axis a1 and are line-symmetrical about the first axis a1. One end of the fan-shaped portion 24B is connected to the arc-shaped portion 24A, and the other end is connected to the connecting portion 23B of the second support portion 23. The first actuator 24 has a large fan-shaped portion 24B, so the area of ​​the piezoelectric element is large. As a result, a large driving torque is obtained around the second axis a2 by the first actuator 24.

[0079] Furthermore, the reflector portion 20 has a plurality of slits 20B and 20C formed along the outer periphery of the reflective surface 20A outside the reflective surface 20A. The slits 20B and 20C are arranged at positions that are line-symmetrical about the first axis a1 and the second axis a2. The slits 20B suppress deformation of the reflective surface 20A caused by the oscillation of the reflector portion 20.

[0080] exist Figure 3 and Figure 4 In the figure, wiring and electrode pads for applying drive signals to the first actuator 24 and the second actuator 25 are omitted from the figure. A plurality of electrode pads are provided on the fixing frame 27.

[0081] like Figure 5 and Figure 6As shown, the MMD 2 is formed, for example, by etching an SOI (Silicon On Insulator) substrate 30. The SOI substrate 30 comprises a first silicon active layer 31 made of single crystal silicon, a silicon oxide layer 32 provided on top of the first silicon active layer 31, and a second silicon active layer 33 made of single crystal silicon provided on the silicon oxide layer 32.

[0082] The mirror portion 20, first support portion 21, movable frame 22, second support portion 23, first actuator 24, second actuator 25, and connection portion 26 are formed from the second silicon active layer 33 remaining after etching away the first silicon active layer 31 and silicon oxide layer 32 from the SOI substrate 30. The second silicon active layer 33 functions as a resilient elastic portion. The fixed frame 27 is formed from three layers: the first silicon active layer 31, silicon oxide layer 32, and second silicon active layer 33.

[0083] The second actuator 25 is formed by etching the second silicon active layer 33 so that the thickness of the second silicon active layer 33 is thinner than that of the first actuator 24. That is, the second actuator 25 is thinner than the first actuator 24 in the Z direction.

[0084] The first actuator 24 and the second actuator 25 include a piezoelectric element 28 on the second silicon active layer 33. The piezoelectric element 28 has a stacked structure in which a lower electrode 51, a piezoelectric film 52, and an upper electrode 53 are stacked in this order on the second silicon active layer 33. An insulating film is provided on the upper electrode 53, but this is not shown in the figure.

[0085] The upper electrode 53 and the lower electrode 51 are formed of, for example, gold (Au) or platinum (Pt). The piezoelectric film 52 is formed of, for example, PZT (lead zirconate titanate), a piezoelectric material. The upper electrode 53 and the lower electrode 51 are electrically connected to the aforementioned drive control unit 4 via wiring and electrode pads.

[0086] A driving voltage is applied to the upper electrode 53 from the driving control unit 4. The lower electrode 51 is connected to the driving control unit 4 via wiring and electrode pads, and a reference potential (for example, ground potential) is applied thereto.

[0087] When a positive or negative voltage is applied to the piezoelectric film 52 in its polarization direction, it deforms (e.g., expands and contracts) in proportion to the applied voltage. In other words, the piezoelectric film 52 exhibits the so-called inverse piezoelectric effect. The piezoelectric film 52 exhibits the inverse piezoelectric effect when a drive voltage is applied to the upper electrode 53 by the drive control unit 4, causing the first actuator 24 and the second actuator 25 to displace.

[0088] Figure 7The example shows a method of generating torque about the first axis a1 in the second actuator 25 by expanding the piezoelectric film 52 of one of the pair of second actuators 25 and contracting the piezoelectric film 52 of the other. In this manner, one and the other of the pair of second actuators 25 are displaced in opposite directions relative to each other, causing the mirror portion 20 to rotate about the first axis a1.

[0089] and, Figure 7 This example shows that the second actuators 25 are driven in an anti-phase resonance mode in which the displacement directions of the pair of second actuators 25 and the rotational direction of the mirror unit 20 are opposite to each other. Alternatively, the second actuators 25 may be driven in an in-phase resonance mode in which the displacement directions of the pair of second actuators 25 and the rotational direction of the mirror unit 20 are the same.

[0090] The deflection angle of the reflector portion 20 about the first axis a1 is controlled by a drive signal (hereinafter referred to as a first drive signal) applied to the second actuator 25 by the drive control unit 4. The first drive signal is, for example, a sinusoidal AC voltage. The first drive signal includes a drive voltage waveform V applied to one of the pair of second actuators 25. 1A (t) and the driving voltage waveform V applied to the other 1B (t). Driving voltage waveform V 1A (t) and driving voltage waveform V 1B (t) are in opposite phases (i.e., a phase difference of 180°).

[0091] The term "reflector portion 20" refers to an angle between a deflection angle about the first axis a1 and a normal line of the reflecting surface 20A tilted with respect to the Z direction on the YZ plane.

[0092] Figure 8 The example shows a method of generating torque about the second axis a2 in the first actuator 24 by expanding the piezoelectric film 52 of one of the pair of first actuators 24 and contracting the piezoelectric film 52 of the other. In this manner, one and the other of the pair of first actuators 24 are displaced in opposite directions relative to each other, causing the mirror portion 20 to rotate about the second axis a2.

[0093] and, Figure 8 The example in which the first actuators 24 are driven in an in-phase resonant mode in which the displacement directions of the pair of first actuators 24 and the rotational direction of the mirror unit 20 are in the same direction is shown. Alternatively, the first actuators 24 may be driven in an anti-phase resonant mode in which the displacement directions of the pair of first actuators 24 and the rotational direction of the mirror unit 20 are in opposite directions.

[0094] The deflection angle of the reflector portion 20 about the second axis a2 is controlled by a drive signal (hereinafter referred to as a second drive signal) applied to the first actuator 24 by the drive control unit 4. The second drive signal is, for example, a sinusoidal AC voltage. The second drive signal includes a drive voltage waveform V applied to one of the pair of first actuators 24. 2A (t) and the driving voltage waveform V applied to the other 2B (t). Driving voltage waveform V 2A (t) and driving voltage waveform V 2B (t) are in opposite phases (i.e., a phase difference of 180°).

[0095] The deflection angle of the mirror portion 20 about the second axis a2 refers to an angle at which the normal line to the reflecting surface 20A is tilted with respect to the Z direction on the XZ plane.

[0096] Figure 9 An example of the first drive signal and the second drive signal is shown. Figure 9 (A) shows the driving voltage waveform V included in the first driving signal 1A (t) and V 1B (t). Figure 9 (B) shows the driving voltage waveform V included in the second driving signal 2A (t) and V 2B (t).

[0097] Driving voltage waveform V 1A (t) and V 1B (t) are expressed as follows.

[0098] V 1A (t) = V off1 +V1sin(2πf d1 t)

[0099] V 1B (t) = V off1 +V1sin(2πf d1 t+α)

[0100] Here, V1 is the amplitude voltage. off1 is the bias voltage. d1 is the driving frequency (hereinafter referred to as the first driving frequency). t is the time. α is the driving voltage waveform V 1A (t) and V 1B In this embodiment, for example, α is set to 180°.

[0101] Driving voltage waveform V 1A (t) and V 1B (t) is applied to the pair of second actuators 25, whereby the mirror portion 20 is driven at the first driving frequency fd1 To swing around the first axis a1 (reference Figure 7 ).

[0102] Driving voltage waveform V 2A (t) and V 2B (t) are expressed as follows.

[0103] V 2A (t) = V off2 +V2sin(2πf d2 t+φ)

[0104] V 2B (t) = V off2 +V2sin(2πf d2 t+β+φ)

[0105] Here, V2 is the amplitude voltage. off2 is the bias voltage. d2 is the driving frequency (hereinafter referred to as the second driving frequency). t is the time. β is the driving voltage waveform V 2A (t) and V 2B In this embodiment, for example, β is set to 180°. And φ is the driving voltage waveform V 1A (t) and V 1B (t) and driving voltage waveform V 2A (t) and V 2B (t) phase difference. And, in this embodiment, for example, it is set to V off1 =V off2 =0V.

[0106] Driving voltage waveform V 2A (t) and V 2B (t) is applied to the pair of first actuators 24, whereby the mirror portion 20 is driven at the second driving frequency f d2 To swing around the second axis a2 (refer to Figure 8 ).

[0107] First driving frequency f d1 The second driving frequency f is set to coincide with the resonance frequency of the mirror portion 20 about the first axis a1 (hereinafter referred to as the first resonance frequency). d2 It is set to coincide with the resonant frequency of the mirror portion 20 about the second axis a2 (hereinafter referred to as the second resonant frequency). In this embodiment, it is set to f d1 >f d2 That is, the oscillation frequency of the mirror portion 20 about the first axis a1 is higher than the oscillation frequency about the second axis a2.

[0108] In the resonance of the mirror portion 20, in addition to the aforementioned phase (in phase or in reverse phase), there are also multiple resonance modes with different orders. For example, the first drive frequency f d1 The first drive frequency f is set to a value that matches the resonant frequency of the resonant mode that obtains the maximum deflection angle from the resonant mode group of opposite phases around the first axis a1. d1 The resonant frequency of the second resonant mode from the lowest order in the resonant mode group with opposite phases coincides with the resonant frequency of the second resonant mode from the lowest order. Hereinafter, the resonant mode around the first axis a1 is referred to as a high-speed scanning mode.

[0109] Furthermore, for example, the second driving frequency f d2 The second drive frequency f is set to a value that matches the resonant frequency of the resonant mode that obtains the maximum deflection angle from the resonant mode group with the same phase around the second axis a2. d2 The resonant frequency of the second resonant mode from the lowest order in the resonant mode group with the same phase coincides with the resonant frequency of the second resonant mode from the lowest order. Hereinafter, the resonant mode around the second axis a2 is referred to as the low-speed scanning mode.

[0110] In addition, the order of the resonance mode that obtains the maximum deflection angle varies depending on the shapes of the first actuator 24 and the second actuator 25. Therefore, the first drive frequency f d1 and the second driving frequency f d2 They are consistent with the frequencies of other orders of resonance modes.

[0111] Figure 10 An example of the structure of the first support portion 21 and the second support portion 23 is shown in detail. The connecting portion 21B included in the first support portion 21 has multiple secondary axes symmetrically arranged on both sides of the first axis a1, which is the main axis, and extending along the first axis a1. The thickness of the main axis and the multiple secondary axes are uniform.

[0112] In this embodiment, the connecting portion 21B has three auxiliary shafts: a first auxiliary shaft 60A, a second auxiliary shaft 60B, and a third auxiliary shaft 60C. The first auxiliary shaft 60A, the second auxiliary shaft 60B, and the third auxiliary shaft 60C are arranged in parallel with the swing shaft 21A in this order from the swing shaft 21A side. The first auxiliary shaft 60A, the second auxiliary shaft 60B, and the third auxiliary shaft 60C have the same width W. b Width W b Smaller than the width W of the swing axis 21A a Width W a shorter than the length L of the swing shaft 21A a .

[0113] The first auxiliary shaft 60A, the second auxiliary shaft 60B, and the third auxiliary shaft 60C are connected to each other to form a first folded portion 61, a second folded portion 62, and a third folded portion 63. The number of folded portions is not limited to three, and three or more may be formed.

[0114] The first folded portion 61 is formed by connecting one end of the first auxiliary shaft 60A and the end of the swing shaft 21A on the opposite side of the mirror portion 20. The first folded portion 61 has a width W r The first folded portion 61 is arranged so that the vertex on the inner circle side of the swing axis 21A contacts the swing axis 21A.

[0115] The second folded portion 62 is formed by connecting the other end of the first auxiliary shaft 60A and one end of the second auxiliary shaft 60B. The second folded portion 62 has a width W r The second folded portion 62 is arranged so that the vertex on the inner circle side of the swing axis 21A contacts the first auxiliary shaft 60A.

[0116] The third folded portion 63 is formed by connecting the other end of the second auxiliary shaft 60B and one end of the third auxiliary shaft 60C. The third folded portion 63 has a width W r The third folded portion 63 is arranged so that the vertex of the inner circle on the swing axis 21A side is in contact with the second auxiliary shaft 60B. The third auxiliary shaft 60C is connected to the inner circle with a width W f The movable frame 22 is connected.

[0117] When the curvature radius inside the first folded portion 61 is R1, the curvature radius inside the second folded portion 62 is R2, and the curvature radius inside the third folded portion 63 is R3, the curvature radii R1, R2, and R3 satisfy the relationship of the following equations (1) and (2).

[0118] 0.73≤R2 / R1≤0.9……(1)

[0119] 0.73≤R3 / R2≤0.9……(2)

[0120] While details will be described later, when the curvature radii R1, R2, and R3 satisfy the aforementioned relationship, the internal stress applied to the swing axis 21A during the swinging of the reflector portion 20 about the first axis a1 is alleviated. This internal stress alleviation increases the maximum deflection angle of the reflector portion 20 about the first axis a1. Furthermore, within the range where the curvature radii R1, R2, and R3 satisfy the aforementioned relationship, the folded structure of the connecting portion 21B does not become excessively large, thereby suppressing an increase in the moment of inertia about the second axis a2. This, in turn, suppresses a decrease in the second resonant frequency.

[0121] When the connection portion 21B has three or more folded portions, the curvature radius of the inner side of the folded portion is sequentially R1, R2, R3, ... from the side closer to the first axis, and the relationship of the following formula (3) may be satisfied.

[0122] 0.73≤R k+1 / R k ≤0.9(k=1,2,…)…(3)

[0123] The connecting portion 23B of the second support portion 23 has a plurality of secondary shafts extending in the direction of the second axis a2. In this embodiment, the connecting portion 23B has two secondary shafts, a first secondary shaft 70A and a second secondary shaft 70B. The first secondary shaft 70A and the second secondary shaft 70B are arranged in parallel with the swing shaft 23A in order from the swing shaft 23A side. The first secondary shaft 70A and the second secondary shaft 70B have the same width W. d Width W d Smaller than the width W of the swing axis 23A c Width W c Smaller than the length L of the swing shaft 23A c .

[0124] One end of the first auxiliary shaft 70A is connected to the end of the swing shaft 23A opposite to the mirror portion 20 , and the other end is connected to one end of the second auxiliary shaft 70B. The other end of the second auxiliary shaft 70B is connected to the fan-shaped portion 24B of the first actuator 24 .

[0125] A slit 71 extending along the second axis a2 is formed between the first secondary shaft 70A and the swing shaft 23A. A slit 72 extending along the second axis a2 is formed between the first secondary shaft 70A and the second secondary shaft 70B. A slit 73 extending along the second axis a2 is formed between the second secondary shaft 70B and the fan-shaped portion 24B. Slits 71, 72, and 73 all have the same width Δ1.

[0126] Furthermore, the connecting portion 23B has an equal interval Δ2 between itself and the movable frame 22 and between itself and the second actuator 25 .

[0127] Furthermore, at least a portion of the width of the first actuator 24 in a direction perpendicular to the extension direction (i.e., the circumferential direction with the center of the mirror portion 20 as the rotation axis) is larger than the width W of the swing shaft 21A in the direction along the second axis a2. a In this embodiment, the width W of the fan-shaped portion 24B is e Greater than the width W of the swing axis 21A a Width W e In this way, in the first actuator 24, by making at least a portion of the width in the direction perpendicular to the extending direction larger than the width W of the swing shaft 21A, a, the area of ​​the first actuator 24 becomes wider, thereby obtaining a large torque.

[0128] Furthermore, in the MMD2, piezoelectric elements are not provided in the first supporting portion 21 and the second supporting portion 23. Instead, piezoelectric first actuators 24 and second actuators 25 are provided separately from the first supporting portion 21 and the second supporting portion 23. Therefore, a large torque can be obtained without increasing the moments of inertia about the first axis a1 and the second axis a2.

[0129] [Example]

[0130] The following describes an embodiment of a micromirror device (MMD) according to the present invention. The present applicant, through vibration analysis simulation using the finite element method, determined the internal stress (maximum value of Si stress) applied to the swing axis 21A of the first support portion 21 when the MMD 2 was simultaneously driven about the first axis a1 and the second axis a2.

[0131] (MMD size)

[0132] First, the parameters related to the dimensions of the components of the MMD2 used in this embodiment are described. Figure 10 shown.

[0133] Figures 11 to 14 Indicates other parameters related to the dimensions of the components of MMD2. Figure 11 In, R m R is the radius of the reflecting surface 20A. S R is the curvature radius of the outer periphery of the slits 20B and 20C. f W is the curvature radius of the outer peripheral portion of the movable frame 22. s θ is the distance between the slit 20B and the slit 20C. s It is the angle formed by the second axis a2 and the line connecting the portion between the slit 20B and the slit 20C and the center of the reflecting surface 20A.

[0134] W h is the width of the outer edge (so-called rim) outside the slits 20B and 20C of the reflector unit 20. R0 is the radius of curvature of the connection between the swing shaft 21A and the reflector unit 20. δ is the interval between the secondary axes included in the connection portion 21B. r1 X is the distance from the center of the circle of the first folded portion 61 to the second axis a2. r2 X is the distance from the center of the circle of the second folded portion 62 to the second axis a2. r3 It is the distance from the center of the circle of the third folded portion 63 to the second axis a2.

[0135] exist Figure 12 In, X ac Y is the distance from the end portion of the second actuator 25 to the second axis a2 in the X direction. ac W is the distance from the end portion of the second actuator 25 to the first axis a1 in the Y direction. ac W is the width of the arc-shaped portion 24A of the first actuator 24. g L is the width of the connecting portion 26. g is the length of the connection portion 26. Δ3 is the length from the end of the connection portion 26 on the first actuator 24 side to the portion connected to the second actuator 25. Δ4 is ​​the distance between the second actuator 25 and the fixed frame 27 in the X direction.

[0136] exist Figure 13 In, L X L is the length of one side of the fixed frame 27 in the X direction. Y is the length of one side of the fixing frame 27 in the Y direction.

[0137] exist Figure 14 In FIG, D1 is the thickness of the fixed frame 27. D2 is the thickness of the second silicon active layer 33 constituting the mirror portion 20, the first support portion 21, the movable frame 22, the second support portion 23, and the first actuator 24. D3 is the thickness of the second silicon active layer 33 constituting the second actuator 25.

[0138] Figure 15 are the set values ​​of various parameters used in this simulation. The applicant has calculated the first resonant frequency f1 in the high-speed scanning mode, the second resonant frequency f2 in the low-speed scanning mode, and the internal stress (maximum value of Si stress) applied to the swing shaft 21A of the first support portion 21 through a resonance mode analysis simulation based on the finite element method. The internal stress is calculated by calculating the Mises stress σ when the reflector portion 20 is driven in the high-speed scanning mode until the maximum deflection angle reaches ±17°. Mises Come and seek out.

[0139] The high-speed scanning mode is the second resonance mode from the lowest order in the aforementioned anti-phase resonance mode group. The low-speed scanning mode is the second resonance mode from the lowest order in the aforementioned in-phase resonance mode group.

[0140] And, as Figure 16 As shown, the applicant prepared 12 models with different curvature radii R1, R2, and R3, and obtained the first resonance frequency f1, the second resonance frequency f2, and the Mises stress σ for each model. Mises .

[0141] Typically, the Mises stress σ Mises The larger the value, the higher the risk of Si fracture. According to experience, the Mises stress σ above 2.26 GPaMises Therefore, the applicant will become σ Mises Models with ≥2.26GPa are judged as unqualified (F) and will become σ Mises Models with a value less than 2.26 GPa are considered qualified (P). Figure 16 As shown, model numbers 1 to 5 are all judged to be unqualified, and model numbers 6 to 12 are all judged to be qualified.

[0142] For model numbers 1 to 5, at least one of the ratios R2 / R1 and R3 / R2 is greater than 0.9. On the other hand, for model numbers 6 to 12, both the ratios R2 / R1 and R3 / R2 are less than 0.9. Therefore, when the relationship of the following formula (4) is satisfied, σ Mises <2.26GPa.

[0143] R k+1 / R k ≤0.9(k=1,2,…)…(4)

[0144] That is, model numbers 6 to 12 are examples of the technology of the present invention, and model numbers 1 to 5 are comparative examples.

[0145] Figure 17 represents the Mises stress σ Mises The relationship between the first resonant frequency f1. Figure 17 As shown, in the models (model numbers 6 to 12) belonging to the embodiment, a high first resonance frequency f1 is obtained.

[0146] Figure 18 represents the Mises stress σ Mises The relationship between and the second resonant frequency f2. Figure 18 , we can see that regarding the second resonant frequency f2, when R k+1 / R k When the value of is small, the second resonant frequency f2 decreases. The reason is that if R k+1 / R k If the value of is too small, the structure of the connection part 21B is too large, thereby increasing the moment of inertia. The applicant has determined 0.73 as the limit at which the auxiliary shafts included in the connection part 21B do not contact each other. k+1 / R k The lower limit value of .

[0147] The structure of the MMD 2 shown in the above embodiment is an example and can be modified as appropriate. For example, in the above embodiment, the connecting portion 23B of the second support portion 23 has a folding structure, but this folding structure is not essential and can be omitted.

[0148] Furthermore, the hardware structure of the drive control unit 4 can be modified in various ways. The processing unit of the drive control unit 4 can be composed of one processor, or can be composed of a combination of two or more processors of the same type or different types. The processor includes a CPU, a programmable logic device (PLD), and a dedicated circuit. As is well known, a CPU is a general-purpose processor that executes software (programs) and functions as a variety of processing units. PLD is a processor such as FPGA (Field Programmable Gate Array) that can change its circuit structure after manufacture. A dedicated circuit is a processor such as ASIC (Application Specific Integrated Circuit) that has a circuit structure specially designed to perform specific processing.

[0149] All documents, patent applications, and technical standards cited in this specification are incorporated herein by reference to the same extent as if each document, patent application, and technical standard were specifically and individually indicated to be incorporated by reference.

Claims

1. A micromirror device comprising: a reflector portion having a reflective surface for reflecting incident light; a first support portion connected to the reflector portion on a first axis located within a plane including the reflecting surface when the reflector portion is stationary, and supporting the reflector portion so as to be swingable about the first axis; a pair of movable frames connected to the first support portion and opposed to each other across the first shaft; a second support portion connected to the movable frame on a second axis that is located in a plane including the reflecting surface when the reflector portion is stationary and is orthogonal to the first axis, and supports the reflector portion, the first support portion, and the movable frame so as to be swingable about the second axis; and a pair of first actuators connected to the second support portion and facing each other across the second shaft, the first actuators including piezoelectric elements; In the micromirror device, The first support portion is composed of a main shaft extending along the first axis and a plurality of sub-shafts symmetrically arranged on both sides of the main shaft with the first axis interposed therebetween and extending along the first axis. The first support portion has a folding structure having three or more folding portions connected by the plurality of auxiliary shafts. When the curvature radius of the inner side of the folded portion is R1, R2, R3, ... from the side closest to the first axis, 0.73≤R k+1 / R k ≤0.9, where k=1, 2, ...

2. The micromirror device according to claim 1, wherein: The thicknesses of the main shaft and the plurality of secondary shafts are uniform.

3. The micromirror device according to claim 1, wherein: In the first actuator, at least a portion of the width in a direction perpendicular to the extending direction is larger than the width of the main shaft in a direction along the second axis.

4. The micromirror device according to claim 1, wherein: The movable frame and the first actuator are each U-shaped.

5. The micromirror device according to claim 1, wherein The first actuator causes the mirror portion to swing about the second axis by applying a torque about the second axis to the mirror portion and the movable frame.

6. The micromirror device according to claim 5, comprising: a fixed frame configured to surround the first actuator; a connecting portion connecting the first actuator and the fixing frame; and a second actuator connected to the connection portion and disposed inside the fixed frame, the second actuator including a piezoelectric element; The second actuator causes the mirror portion to swing about the first axis by applying a torque about the first axis to the mirror portion, the movable frame, and the first actuator.

7. The micromirror device according to claim 6, wherein: The connecting portion is arranged along the first axis.

8. An optical scanning device comprising: The micromirror device according to claim 6 or 7; and a processor that drives the first actuator and the second actuator, In the optical scanning device, The processor applies drive signals to the first actuator and the second actuator to cause the mirror portion to resonate around the first axis and the second axis, respectively.

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