Mirror device and optical scanning device

Abstract

This mirror device includes: a mirror part; a pair of first support parts; a pair of movable frames (22); a pair of second support parts (23); a drive part having a plurality of piezoelectric actuators (24, 25) facing each other across a first axis or a second axis (a2); a fixed frame (27); a plurality of metal pads (80-84) formed on the fixed frame (27); and a plurality of metal wirings (90-94) electrically connecting the plurality of piezoelectric actuators (24, 25) and the plurality of metal pads (80-84). The plurality of piezoelectric actuators (24, 25) are disposed in a region where the maximum value of the maximum principal stress which is generated when the mirror part is caused to swing about the first axis or the second axis (a2) is 1 / 120 to 1 / 8 of the maximum value of the maximum principal stress which is generated in the entirety of the region.

Description

Mirror device and optical scanning device

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

[0002] Micromirror devices (also called microscanners) are known as one type of microelectromechanical systems (MEMS) device fabricated using silicon (Si) microfabrication technology. Because these micromirror devices are small and consume little power, they are expected to be widely used in laser displays, laser projectors, optical coherence tomography, and other applications.

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

[0004] A typical micromirror device used in a laser display includes a mirror portion and a driving portion having a plurality of piezoelectric actuators (see, for example, International Publication No. 2022 / 025012). The mirror portion is freely oscillating about a first axis and a second axis that are orthogonal to each other. The driving portion oscillates the mirror portion about the first axis and the second axis in response to an externally supplied driving voltage.

[0005] The micromirror device also includes a fixing frame surrounding the mirror section and the driving section, and a plurality of metal pads on the fixing frame, and a plurality of piezoelectric actuators included in the driving section are connected to the metal pads via metal wiring.

[0006] When the mirror part oscillates, stress is generated in each part of the micromirror device in response to the oscillation, and the stress is concentrated in specific areas. As a result, the piezoelectric film included in the piezoelectric actuator may be damaged by the stress generated by the oscillation of the mirror part. In particular, when the micromirror device is resonantly driven to obtain a high scan angle, the stress increases, making the piezoelectric film prone to damage such as cracks.

[0007] Therefore, in order to prevent damage to the piezoelectric film due to the vibration of the mirror, it is preferable to arrange multiple piezoelectric actuators so that the stress applied to the piezoelectric film is small. However, if the stress applied to the piezoelectric film is too small, the work efficiency of the piezoelectric film decreases, resulting in a decrease in torque. For this reason, it is desirable to arrange multiple piezoelectric actuators within an appropriate stress range.

[0008] The technique of the present disclosure aims to provide a mirror device and an optical scanning device in which a plurality of piezoelectric actuators are arranged in an appropriate stress range.

[0009] In order to achieve the above object, the mirror device of the present disclosure includes a mirror unit having a reflective surface that reflects incident light, a pair of first support parts connected to the mirror unit on a first axis in a plane including the reflective surface of the mirror unit when stationary and supporting the mirror unit so that it can swing around the first axis, a pair of movable frames connected to the pair of first support parts and facing each other across the first axis, a pair of second support parts connected to the pair of movable frames on a second axis in the plane and intersecting the first axis and supporting the mirror unit, the pair of first support parts, and the pair of movable frames so that they can swing around the second axis, and a pair of second support parts arranged to surround the pair of movable frames and supporting the mirror unit, the pair of first support parts, and the pair of movable frames so that they can swing around the first axis or the second axis. The mirror element comprises a drive unit having a plurality of piezoelectric actuators facing each other across an axis, a fixed frame arranged to surround the drive unit, a pair of connection parts that are thinner than the fixed frame and extend in the direction of the first axis or the second axis to connect the drive unit and the fixed frame, a plurality of metal pads formed on the fixed frame, and a plurality of metal wirings that electrically connect the plurality of piezoelectric actuators and the plurality of metal pads, and the plurality of piezoelectric actuators are arranged in a region where the maximum value of the maximum principal stress generated when the mirror element is oscillated around the first axis or the second axis is 1 / 120 to 1 / 8 of the maximum value of the maximum principal stress generated overall.

[0010] The plurality of piezoelectric actuators may be arranged in an area where the maximum value of the maximum principal stress generated when the mirror portion is oscillated around the first axis or the second axis is 1 / 40 to 1 / 8 of the maximum value of the maximum principal stress generated overall.

[0011] It is preferable that the drive unit has a first actuator that is arranged around the pair of movable frames and is composed of a pair of piezoelectric actuators that face each other across a second axis, and a second actuator that is arranged around the first actuator and is composed of a pair of piezoelectric actuators that face each other across the first axis.

[0012] It is preferable that the contact areas where the multiple piezoelectric actuators and the multiple metal wirings are in contact are arranged in areas where the maximum value of the maximum principal stress generated when the mirror portion is oscillated around the first axis or the second axis is 1 / 15 or less of the maximum value of the maximum principal stress generated overall.

[0013] Each of the plurality of piezoelectric actuators is preferably composed of an upper electrode, a piezoelectric film, and a lower electrode, and each of the plurality of metal wirings is preferably connected to the upper electrode or the lower electrode.

[0014] At least one of the plurality of metal wirings is preferably formed containing three or more types of metal materials.

[0015] At least one of the plurality of metal wirings is preferably configured by connecting a first wiring formed of Au with a first wiring formed containing Al and Ti.

[0016] The pair of connecting portions are preferably arranged on the second axis.

[0017] The optical scanning device of the present disclosure is an optical scanning device comprising the above-mentioned mirror device and a processor, and the processor oscillates the mirror portion around the first axis and the second axis by providing a drive signal to each of the multiple piezoelectric actuators.

[0018] According to the technique of the present disclosure, it is possible to provide a mirror device and an optical scanning device in which a plurality of piezoelectric actuators are arranged in an appropriate stress range.

[0019] 5 is a schematic diagram of an optical scanning device. FIG. 6 is a block diagram showing an example of the hardware configuration of a drive control unit. FIG. 7 is a perspective view of the appearance of a micromirror device. FIG. 8 is a plan view of the micromirror device as viewed from the light incident side. FIG. 9 is a cross-sectional view taken along line A-A in FIG. 4. FIG. 10 is a cross-sectional view showing a state in which the mirror section has rotated around a first axis. FIG. 11 is a diagram showing an example of a first drive signal and a second drive signal. FIG. 12 is a cross-sectional view showing an example of the configuration of a piezoelectric sensor. FIG. 13 is a plan view showing an example of the layout of metal pads and metal wiring provided on the micromirror device. FIG. 14 is a cross-sectional view showing an example of the configuration of metal wiring. FIG. 15 is a diagram showing an example of signal processing for generating an angle detection signal. FIG. 16 is a diagram showing an example of stress distribution when the mirror section is oscillated around a first axis. FIG. 17 is a diagram showing an example of stress distribution when the mirror section is oscillated around a second axis.

[0020] An example of an embodiment of the technology of the present disclosure will be described with reference to the accompanying drawings.

[0021] 1 is a schematic diagram of an optical scanning device 10 according to one embodiment. The optical scanning device 10 includes a micro mirror device (MMD) 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 LB emitted from the light source 3 using the MMD 2 under the control of the drive controller 4. The surface 5 to be scanned is, for example, a screen.

[0022] MMD2 is the first axis a １ and the first axis a １ The second axis a intersects with ２ The micromirror device is a piezoelectric two-axis drive type that can oscillate the mirror portion 20 (see FIG. 3) around the first axis a. １ The direction parallel to this is the X direction, and the second axis a ２ The direction parallel to the axis a is the Y direction. １ and the second axis a ２ The direction perpendicular to the X direction is called the Z direction. In this embodiment, the X direction and the Y direction are perpendicular to each other. The MMD 2 is an example of a "mirror device" according to the technology of the present disclosure.

[0023] The light source 3 is a laser device that emits, for example, laser light as the light beam LB. It is preferable that the light source 3 irradiates the light beam LB perpendicularly to a reflecting surface 20A (see FIG. 3 ) of the mirror portion 20 when the mirror portion 20 of the MMD 2 is stationary.

[0024] 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 LB based on the input drive signal and irradiates the MMD 2 with the light beam LB. The MMD 2 rotates the mirror unit 20 along the first axis a based on the input drive signal. １ and the second axis a ２ Rock it around.

[0025] As will be described in detail later, the drive control unit 4 rotates the mirror unit 20 along the first axis a １ and the second axis a ２ , and the light beam LB reflected by the mirror portion 20 is scanned so as to trace a Lissajous waveform on the surface to be scanned 5. This optical scanning method is called a Lissajous scanning method.

[0026] The optical scanning device 10 is applicable to, for example, a Lissajous scanning laser display. Specifically, the optical scanning device 10 is applicable to a laser scanning display such as an augmented reality (AR) glass or a virtual reality (VR) glass.

[0027] 2 shows an example of the hardware configuration of the drive control unit 4. The drive control unit 4 has a central processing unit (CPU) 40, a read-only memory (ROM) 41, a random access memory (RAM) 42, a light source driver 43, and an MMD driver 44. The CPU 40 is a computing device that realizes the overall function of the drive control unit 4 by reading programs and data from a storage device such as the ROM 41 into the RAM 42 and executing processing. The CPU 40 is an example of a processor according to the technology of the present disclosure.

[0028] 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. The RAM 42 is a volatile storage device that temporarily stores programs and data.

[0029] 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.

[0030] 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 2.

[0031] 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 the scanning pattern of the light beam LB that scans the surface 5 to be scanned and the light emission timing of the light source 3.

[0032] Furthermore, the CPU 40 determines the position of the first axis a of the mirror section 20 based on voltage signals output from four piezoelectric sensors 51 to 54 (described later) provided on the MMD 2. １ and the second axis a ２ The CPU 40 generates an angle detection signal that represents the angle around the target point. The CPU 40 corrects the drive signal based on the generated angle detection signal.

[0033] Next, the configuration of the MMD 2 will be described with reference to Figures 3 to 5. Figure 3 is an external perspective view of the MMD 2. Figure 4 is a plan view of the MMD 2 as seen from the light incident side. Figure 5 is a cross-sectional view taken along line AA in Figure 4.

[0034] 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 first actuator 24, a second actuator 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.

[0035] 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 first axis a １ and the second axis a ２ It is a circle with the intersection point of

[0036] 1st axis a １ and the second axis a ２ For example, when the mirror unit 20 is stationary, the first axis a is present in a plane including the reflecting surface 20A. １ and is symmetrical about the second axis a ２ It is symmetrical about the center.

[0037] The pair of first support portions 21 are ２ and the second axis a ２ Each of the first support portions 21 has a shape that is line-symmetrical about the first axis a. １ Each of the first support portions 21 has a shape that is line-symmetrical about the first axis a １ The mirror section 20 is connected to the first axis a １ It is supported so that it can swing around.

[0038] The pair of movable frames 22 are arranged along a first axis a １ and are arranged at positions facing each other across the first axis a １ Each of the movable frames 22 has a shape that is line-symmetrical about the second axis a ２ The movable frames 22 are shaped to be line-symmetrical about the center. Each movable frame 22 is curved along the outer periphery of the mirror section 20. Both ends of each movable frame 22 are connected to a pair of first support sections 21.

[0039] The pair of first support parts 21 and the pair of movable frames 22 are connected to each other to surround the mirror part 20. The mirror part 20, the pair of first support parts 21, and the pair of movable frames 22 constitute the movable part 60.

[0040] The pair of second support portions 23 are １and are arranged at positions facing each other across the first axis a １ Each of the second support portions 23 has a shape that is line-symmetrical about the second axis a. ２ Each of the second support portions 23 has a shape that is line-symmetrical about the second axis a ２ The movable portion 60 having the mirror portion 20 is connected to the movable frame 22 on the second axis a. ２ Both ends of each of the second support portions 23 are connected to a first actuator 24.

[0041] The first actuator 24 is ２ The piezoelectric actuator is configured by a pair of piezoelectric actuators facing each other with the second axis a ２ Each of the first actuators 24 has a shape that is symmetrical about the first axis a. １ The first actuator 24 is disposed along the outer periphery of the pair of movable frames 22 and the pair of first support portions 21.

[0042] 3 and 4, the piezoelectric actuator constituting the first actuator 24 is １ Although it appears to be separated by the first axis a １ The two piezoelectric actuators facing each other with the piezoelectric element sandwiched therebetween are electrically connected by metal wiring (not shown).

[0043] The pair of second support portions 23 and the first actuator 24 are connected to each other, thereby surrounding the movable portion 60 .

[0044] The second actuator 25 is １ The piezoelectric actuator is configured by a pair of piezoelectric actuators facing each other with a first axis a １ The second actuator 25 has a shape that is symmetrical about the second axis a. ２ The second actuator 25 is disposed along the outer periphery of the first actuator 24 and the pair of second support portions 23.

[0045] 3 and 4, the piezoelectric actuator constituting the second actuator 25 is２ Although it appears to be separated near the second axis a ２ The two piezoelectric actuators facing each other with the piezoelectric element sandwiched therebetween are electrically connected by metal wiring (not shown).

[0046] The pair of first connecting portions 26A are connected to the second axis a ２ and the second axis a ２ Each of the first connection portions 26A has a shape that is line-symmetrical about the first axis a. １ Each of the first connection portions 26A has a shape that is line-symmetrical about the first axis a. １ and arranged along a first axis a １ Above, the first actuator 24 and the second actuator 25 are connected.

[0047] The pair of second connection portions 26B are connected to the first axis a １ and are arranged at positions facing each other across the first axis a １ Each of the second connection portions 26B extends in the Y direction and is symmetrical about the second axis a ２ Each of the second connection portions 26B has a shape that is line-symmetrical about the second axis a ２ and arranged along a second axis a ２ The second actuator 25 and the fixed frame 27 are connected to each other via the second connecting portions 26B. The pair of second connecting portions 26B is an example of the "pair of connecting portions" according to the technology of the present disclosure.

[0048] The second actuator 25 and the pair of second connection portions 26B are connected to each other, thereby surrounding the pair of movable portions 60 and the first actuator 24. The first actuator 24 and the second actuator 25 constitute a drive unit arranged to surround the pair of movable frames 22. That is, the drive unit is １ or the second axis a ２ The piezoelectric actuators are arranged opposite each other with the piezoelectric element therebetween.

[0049] The fixed frame 27 is a frame-shaped member having a rectangular outer shape, and has a first axis a １ and the second axis a ２The fixed frame 27 surrounds the outer peripheries of the second actuator 25 and the pair of second connection portions 26B. In other words, the fixed frame 27 is disposed to surround the drive portion.

[0050] The first actuator 24 is connected to the mirror unit 20 and the pair of movable frames 22 by a second axis a ２ By applying a rotational torque around the second axis a ２ The second actuator 25 rotates the mirror unit 20, the pair of movable frames 22, and the first actuator 24 around the first axis a. １ By applying a rotational torque around the first axis a １ Swing it around.

[0051] As shown in Fig. 4, each of the first support parts 21 is composed of a swing shaft 21A and a pair of connecting parts 21B. １ The oscillation shaft 21A is a so-called torsion bar that extends in the direction of the arrow A. One end of the oscillation shaft 21A is connected to the mirror part 20, and the other end is connected to the pair of connecting parts 21B.

[0052] The pair of connecting portions 21B are connected to the first axis a １ and are arranged at positions facing each other across the first axis a １ The connecting portions 21B have a shape that is line-symmetrical about the first axis a. 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. Each connecting portion 21B has a folded structure. Since each connecting portion 21B has elasticity due to the folded structure, the mirror portion 20 can be moved around the first axis a. １ When the swing shaft 21A swings around the shaft 21A, the internal stress acting on the swing shaft 21A is alleviated.

[0053] Each of the second support parts 23 is composed of a swing shaft 23A and a pair of connecting parts 23B. ２ The swing shaft 23A is a so-called torsion bar that extends in the direction of the arrow A. One end of the swing shaft 23A is connected to the movable frame 22, and the other end is connected to the pair of connecting portions 23B.

[0054] The pair of connecting portions 23B are connected to the second axis a ２and the second axis a ２ The connecting portions 23B have a shape that is line-symmetrical about the second axis a. One end of each connecting portion 23B is connected to the oscillation shaft 23A, and the other end is connected to the first actuator 24. Each connecting portion 23B has a folded structure. Since each connecting portion 23B has elasticity due to the folded structure, the mirror portion 20 can be easily moved around the second axis a. ２ When the swing shaft 23A swings around the shaft 23A, the internal stress acting on the swing shaft 23A is alleviated.

[0055] Furthermore, in the mirror section 20, a plurality of slits 20B and 20C are 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 aligned along the first axis a １ and the second axis a ２ The slits 20B and 20C are arranged at positions that are line-symmetrical with respect to the center of the mirror 20. The slits 20B and 20C have the effect of suppressing distortion that occurs in the reflecting surface 20A when the mirror portion 20 swings.

[0056] Four piezoelectric sensors 51 to 54 are provided near the pair of second connection portions 26B as angle sensors for detecting the angle of the mirror portion 20. The piezoelectric sensors 51 to 54 are formed of piezoelectric elements, similar to the first actuator 24 and the second actuator 25. The piezoelectric sensors 51 to 54 are arranged along the first axis a １ and the second axis a ２ Specifically, the piezoelectric sensors 51 and 52 are arranged near one of the pair of second connection portions 26B, and the positions and shapes of the piezoelectric sensors 51 and 52 are aligned with each other about the second axis a ２ The piezoelectric sensors 53 and 54 are arranged near the other of the pair of second connection portions 26B, and are positioned and shaped such that they are symmetrical about the second axis a ２ The piezoelectric sensors 51 and 52 and the piezoelectric sensors 53 and 54 are in a line-symmetric relationship with respect to the first axis a. １ They are in a line-symmetric relationship with respect to each other.

[0057] 3 and 4 , the metal wiring and metal pads for supplying drive signals to the first actuator 24 and the second actuator 25 are not shown. The metal wiring and metal pads for acquiring voltage signals output from the piezoelectric sensors 51 to 54 are also not shown. A plurality of metal pads are provided on the fixed frame 27. The metal pads are also called electrode pads.

[0058] 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.

[0059] The mirror unit 20, the pair of first support units 21, the pair of movable frames 22, the pair of second support units 23, the first actuators 24, the second actuators 25, the pair of first connecting units 26A, and the pair of second connecting units 26B are formed from 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 unit having elasticity. The fixed frame 27 is formed from three layers: the first silicon active layer 31, the silicon oxide layer 32, and the second silicon active layer 33. In other words, the mirror unit 20, the pair of first support units 21, the pair of movable frames 22, the pair of second support units 23, the first actuators 24, the second actuators 25, the pair of first connecting units 26A, and the pair of second connecting units 26B are each thinner than the fixed frame 27. In this disclosure, thickness refers to the width in the Z direction.

[0060] The piezoelectric actuator constituting the first actuator 24 is composed of a piezoelectric element 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 the same configuration as the first actuator 24.

[0061] The lower electrode and the upper electrode are made of a metal such as gold (Au) or platinum (Pt). The piezoelectric film is made of a piezoelectric material such as PZT (lead zirconate titanate). The lower electrode and the upper electrode are electrically connected to the drive control unit 4 via wiring and electrode pads.

[0062] The lower electrode is connected to the drive control unit 4 via wiring and an electrode pad, and is supplied with a ground potential. A drive voltage is applied from the drive control unit 4 to the upper electrode.

[0063] 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. In other words, the piezoelectric film exhibits the so-called inverse piezoelectric effect. When a drive voltage is applied to the upper electrode from the drive control unit 4, the piezoelectric film exhibits the inverse piezoelectric effect, displacing the first actuator 24 and the second actuator 25.

[0064] FIG. 6 shows a state in which one of a pair of piezoelectric actuators constituting the second actuator 25 is expanded and the other is contracted, whereby the second actuator 25 is caused to move along the first axis a １ In this way, one of the pair of piezoelectric actuators is displaced in the opposite directions, so that the mirror section 20 rotates around the first axis a １ rotates around the

[0065] 6 shows an example in which the second actuator 25 is driven in an anti-phase resonance mode (hereinafter referred to as an anti-phase rotation mode) in which the displacement direction of the pair of piezoelectric actuators 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 piezoelectric actuators and the rotation direction of the mirror section 20 are the same is called an in-phase rotation mode. In this embodiment, the second actuator 25 is driven in the anti-phase rotation mode.

[0066] The first axis a of the mirror section 20 １The deflection angle θ is controlled by a drive signal (hereinafter referred to as a first drive signal) that the drive control unit 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 applied to one of the pair of piezoelectric actuators. 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., a phase difference of 180°).

[0067] The first axis a of the mirror part 20 １ The deflection angle θ corresponds to the angle at which the normal N of the reflecting surface 20A is tilted with respect to the Z direction in the YZ plane.

[0068] The first actuator 24 is driven in an anti-phase resonance mode in the same manner as the second actuator 25. ２ The deflection angle around the piezoelectric actuator 24 is controlled by a drive signal (hereinafter referred to as a second drive signal) that the drive control unit 4 supplies 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., a phase difference of 180°).

[0069] 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.

[0070] Drive voltage waveform V １Ａ (t) and V １Ｂ (t) are expressed as follows: V １Ａ (t) = V ｏｆｆ１ +V １sin(2πf ｄ１ t) V １Ｂ (t) = V ｏｆｆ１ +V １ sin(2πf ｄ１ t + α)

[0071] Here, V １ is the amplitude voltage. V ｏｆｆ１ is the bias voltage. ｄ１ is the drive frequency (hereinafter referred to as the first drive frequency), t is time, and α is the drive voltage waveform V １Ａ (t) and V １Ｂ In this embodiment, for example, α=180°.

[0072] Drive voltage waveform V １Ａ (t) and V １Ｂ When the second actuator 25 is applied with the first drive frequency f ｄ１ The first axis a １ Swinging around.

[0073] Drive voltage waveform V ２Ａ (t) and V ２Ｂ (t) are expressed as follows: V ２Ａ (t) = V ｏｆｆ２ +V ２ sin(2πf ｄ２ t+φ) V ２Ｂ (t) = V ｏｆｆ２ +V ２ sin(2πf ｄ２ t + β + φ)

[0074] Here, V ２ is the amplitude voltage. V ｏｆｆ２ is the bias voltage. 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 is set to 180°. φ is the phase difference of the driving voltage waveform V １Ａ (t) and V １Ｂ (t) and the driving voltage waveform V ２Ａ (t) and V ２Ｂ In this embodiment, for example, Vｏｆｆ１ =V ｏｆｆ２ = 0V.

[0075] Drive voltage waveform V ２Ａ (t) and V ２Ｂ When the first actuator 24 is applied with the second drive frequency f ｄ２ and the second axis a ２ Swinging around.

[0076] First drive frequency f ｄ１ is the first axis a of the mirror part 20 １ The second drive frequency f is set to match the surrounding resonant frequency. ｄ２ is the second axis a of the mirror part 20 ２ In this embodiment, the first driving frequency f is set to match the surrounding resonant frequency. ｄ１ is the second driving frequency f ｄ２ Greater than.

[0077] 8 shows a schematic configuration of the piezoelectric sensor 51. The piezoelectric sensor 51 includes a lower electrode 70, a piezoelectric film 71, and an upper electrode 72. The lower electrode 70, the piezoelectric film 71, and the upper electrode 72 are stacked in this order on the second silicon active layer 33. The lower electrode 70 and the upper electrode 72 are made of a metal such as gold (Au) or platinum (Pt). The piezoelectric film 71 is made of, for example, PZT (lead zirconate titanate), a piezoelectric material.

[0078] The upper electrode 72 is covered with an insulating film 73. An opening 73A is formed in the insulating film 73 to expose a portion of the upper electrode 72. A metal wiring 91 made of metal is provided on the insulating film 73. The metal wiring 91 is connected to the upper electrode 72 through the opening 73A. The lower electrode 70 is connected to a metal wiring 90 formed on the second silicon active layer 33. A ground potential is applied to the metal wiring 90.

[0079] The lower electrode 70 , the piezoelectric film 71 , and the upper electrode 72 are manufactured in the same manufacturing process as the lower electrodes, the piezoelectric film, and the upper electrodes of the piezoelectric actuators that make up the first actuator 24 and the second actuator 25 .

[0080] The piezoelectric film 71 converts stress applied when the mirror section 20 oscillates into a voltage signal by the piezoelectric effect, and as a result, a voltage signal corresponding to the angle of the mirror section 20 is obtained from the upper electrode 72.

[0081] The piezoelectric sensors 52 to 54 have the same configuration as the piezoelectric sensor 51. The piezoelectric actuator also has the same configuration as the piezoelectric sensor 51.

[0082] 9 shows an example of the layout of metal pads and metal wiring provided on the MMD 2. FIG. 9 is a partial enlarged view of a region including the piezoelectric sensors 51 and 52.

[0083] A plurality of metal pads 80 to 84 are formed on the fixed frame 27. The metal pad 80 is an electrode pad for applying a ground potential, and is connected to a metal wiring 90. The metal wiring 90 is connected to the lower electrodes of the piezoelectric actuators that make up the first actuator 24 and the second actuator 25, and the lower electrodes of the piezoelectric sensors 51 to 54.

[0084] The metal pad 81 is an electrode pad for acquiring a voltage signal from the piezoelectric sensor 51, and is connected to the above-mentioned metal wiring 91. Similarly, the metal pad 82 is an electrode pad for acquiring a voltage signal from the piezoelectric sensor 52, and is connected to the metal wiring 92.

[0085] The metal pad 83 is an electrode pad for applying a second drive signal to the first actuator 24, and is connected to a metal wiring 93. The metal wiring 93 is connected to the upper electrode of the piezoelectric actuator that constitutes the first actuator 24. ２ A pair of metal pads 83 are provided at positions facing each other with the pad 83 sandwiched therebetween, and are electrically connected to each other via a metal wiring 93 .

[0086] The metal pad 84 is an electrode pad for applying a first drive signal to the second actuator 25, and is connected to a metal wiring 94. The metal wiring 94 is connected to the upper electrode of the piezoelectric actuator that constitutes the second actuator 25.

[0087] The metal wiring 90, 93, and 94 are routed from above the fixed frame 27 through the second connection portion 26B to the formation region of the second actuator 25. Although not shown in Fig. 9, the metal wiring 90 and 93 are further routed from the second actuator 25 through the first connection portion 26A to the formation region of the first actuator 24.

[0088] Furthermore, metal wirings 95 and 93D are formed on the MMD 2. The metal wirings 95 are included in each of the first actuators 24 and are connected to the second axis a ２ The metal wiring 93D connects the upper electrodes of the two piezoelectric actuators that face each other across the second axis a. ２ The dummy wiring is formed at a position that is line-symmetrical with the metal wiring 93 with respect to the center, and is electrically isolated.

[0089] When the MMD2 is driven, placing the piezoelectric actuator in a location where stress is concentrated improves the work efficiency of the piezoelectric film and generates a large rotational torque. However, if too much stress is applied to the piezoelectric film, it can crack or cause other damage, so placing multiple piezoelectric actuators in an appropriate stress range is important for improving the performance of the MMD2.

[0090] As described above, since the MMD 2 is primarily made of single-crystal silicon, in order to prevent damage to the MMD 2 when it is driven, it is preferable to drive the MMD 2 so that the maximum principal stress on the single-crystal silicon is 1.2 GPa or less. Meanwhile, the maximum principal stress that is the fracture limit for PZT used as the piezoelectric film is approximately 150 MPa. Furthermore, considering the work efficiency of the piezoelectric film, it is preferable to set the maximum principal stress on the piezoelectric film when the MMD 2 is driven to a range of 10 MPa or more.

[0091] Therefore, assuming that the MMD2 is driven within the maximum range without breaking, when determining an appropriate stress range for the stress applied to the piezoelectric film, it is preferable that this stress range satisfy the relationship 1 / 120 × B≦A≦1 / 8 × B. Here, A is the maximum value of the maximum principal stress generated in the piezoelectric film. B is the maximum value of the maximum principal stress generated throughout the MMD2. Note that the principal stress refers to the stress in the direction perpendicular to the plane where the shear stress is zero. The principal stress has three types of components (eigenvalues ​​of the stress tensor). The three types of components of the principal stress are called the maximum principal stress, the intermediate principal stress, and the minimum principal stress, in order of decreasing stress value.

[0092] The technique of the present disclosure is such that a plurality of piezoelectric actuators included in the driving unit rotate the mirror unit 20 along the first axis a １ or the second axis a ２ The mirror unit 20 is arranged in a region where the maximum value of the maximum principal stress generated when the mirror unit 20 is swung around the first axis a is 1 / 120 to 1 / 8 of the maximum value of the maximum principal stress generated in the entire MMD 2. From the viewpoint of the work efficiency of the piezoelectric film, the plurality of piezoelectric actuators included in the driving unit are arranged in a region where the maximum value of the maximum principal stress generated when the mirror unit 20 is swung around the first axis a is 1 / 120 to 1 / 8 of the maximum value of the maximum principal stress generated in the entire MMD 2. １ or the second axis a ２ It is more preferable that the maximum value of the maximum principal stress generated when the MMD 2 is swung around the center is in a range of 1 / 40 to 1 / 8 of the maximum value of the maximum principal stress generated in the entire MMD 2.

[0093] In this embodiment, the mirror portion 20 is aligned along the first axis a １ and the second axis a ２ Regardless of the axis around which the swinging motion occurs, the maximum principal stress generated in the pair of first support portions 21, the pair of movable frames 22, the pair of second support portions 23, the pair of first connecting portions 26A, the pair of second connecting portions 26B, etc. becomes maximum.

[0094] Furthermore, in the technique of the present disclosure, the contact area where the plurality of piezoelectric actuators and the plurality of metal wirings come into contact with each other is such that the mirror section 20 is rotated along the first axis a １ or the second axis a ２ The maximum value of the maximum principal stress generated when the MMD 2 is swung around the center is 1 / 15 or less of the maximum value of the maximum principal stress generated in the entire MMD 2.

[0095] 9 indicates a contact region where the metal wiring 90 contacts the lower electrode of the piezoelectric actuator, a contact region where the metal wiring 93 contacts the upper electrode of the piezoelectric actuator, and a contact region where the metal wiring 95 contacts the upper electrode of the piezoelectric actuator. In this embodiment, each of the contact regions CR is located in a region where the maximum value of the maximum principal stress generated when the mirror section 20 is oscillated around the first axis a1 or the second axis a2 is 1 / 15 or less of the maximum value of the maximum principal stress generated in the entire MMD 2. This prevents the contact region CR from being destroyed, thereby preventing a decrease in conductivity in the contact region CR.

[0096] Although not shown in the figure, the contact area where the metal wiring 94 and the upper electrode of the piezoelectric actuator come into contact is also arranged in an area where the maximum value of the maximum principal stress generated when the mirror part 20 is oscillated around the first axis a1 or the second axis a2 is 1 / 15 or less of the maximum value of the maximum principal stress generated in the entire MMD2.

[0097] 10 schematically shows an example of the configuration of the metal wiring 90. The metal wiring 90 is configured by connecting a first wiring 90A and a second wiring 90B. One end of the first wiring 90A is connected to the metal pad 80, and the other end is connected to the second wiring 90B. The first wiring 90A is mainly provided in an area (such as the fixed frame 27) where stress applied when the mirror section 20 oscillates is small. The second wiring 90B is mainly provided in an area (such as the second connection section 26B) where stress applied when the mirror section 20 oscillates is large.

[0098] For example, the first wiring 90A is made of gold (Au), and the second wiring 90B is made of a material containing gold (Al) and titanium (Ti). For example, the second wiring 90B is an amorphous metal containing Al and Ti. That is, the metal wiring 90 is made of three types of metal materials. Note that the metal wiring 90 may be made of three or more types of metal materials.

[0099] The metal wirings 93 and 94 are configured by connecting a first wiring and a second wiring, similar to the metal wiring 90. The metal wirings 93 and 94 may be formed by including three or more types of metal materials.

[0100] In the MMD according to the technology of the present disclosure, at least one of the plurality of metal wirings is configured by connecting a first wiring made of Au to a second wiring made of Al and Ti, and the first wiring is formed integrally with the metal pad using the same metal material as the metal pad.

[0101] 11 shows an example of signal processing for generating an angle detection signal by the CPU 40. For example, the CPU 40 subtracts the voltage signal V3 obtained from the upper electrode 72 of the piezoelectric sensor 53 from the voltage signal V1 obtained from the upper electrode 72 of the piezoelectric sensor 51 to obtain the angle detection signal of the first axis a. １ The CPU 40 generates a first angle detection signal S1 that represents the angle of the mirror unit 20 around the second axis a by subtracting the voltage signal V2 obtained from the upper electrode 72 of the piezoelectric sensor 52 from the voltage signal V1 obtained from the upper electrode 72 of the piezoelectric sensor 51. ２ A second angle detection signal S2 representing the angle of the surrounding mirror portion 20 is generated.

[0102] The first axis a included in the voltage signal V1 and the voltage signal V3 １ The surrounding signal components (detection target components) are in phase with each other. On the other hand, the second axis a included in the voltage signal V1 and the voltage signal V3 ２ The surrounding signal components (noise components) are in phase. Therefore, by subtracting voltage signal V3 from voltage signal V1, the detection target component is amplified and other-axis noise, which is a signal component around an axis other than the detection target, is reduced.

[0103] The second axis a included in the voltage signal V1 and the voltage signal V2 ２ The surrounding signal components (detection target components) are in phase with each other. On the other hand, the first axis a included in the voltage signal V1 and the voltage signal V2 １ The surrounding signal components (noise components) are in phase. Therefore, by subtracting voltage signal V2 from voltage signal V1, the detection target component is amplified and other-axis noise, which is a signal component around an axis other than the detection target, is reduced.

[0104] 12 and 13 show the results of a simulation of the stress generated in the MMD 2. In FIG. １13 shows an example of the stress distribution when the mirror section 20 is swung around the second axis a. ２ 12 shows an example of the stress distribution when the mirror section 20 is swung around the mirror section 20. In FIG. 12, the maximum amplitude of the mirror section 20 is set to 68° in terms of optical full angle. In FIG. 13, the maximum amplitude of the mirror section 20 is set to 46° in terms of optical full angle.

[0105] 12 and 13, stress generated by the oscillation of the mirror section 20 is concentrated in the areas of the movable frame 22, the second connection section 26B, etc. As shown in Fig. 12 and 13, by arranging the contact area CR in an area other than the area where stress is concentrated, it is possible to suppress a decrease in conductivity in the contact area CR.

[0106] The configuration of the MMD 2 according to the above embodiment is an example, and various modifications are possible.

[0107] 11 , the first angle detection signal S1 is generated by subtracting the voltage signal V3 from the voltage signal V1, and the second angle detection signal S2 is generated by subtracting the voltage signal V2 from the voltage signal V1. Alternatively, the first angle detection signal S1 can be generated by adding the voltage signals V1 and V2, and the second angle detection signal S2 can be generated by subtracting the voltage signal V3 from the voltage signal V1. In this way, the first angle detection signal S1 and the second angle detection signal S2 can be generated by adding or subtracting the voltage signals V1 to V4.

[0108] In the above embodiment, the second axis a ２ The lower electrodes of a pair of piezoelectric sensors that are in a line-symmetric relationship with respect to the second axis a are connected via electrode wiring as metal wiring. ２ The upper electrodes of a pair of piezoelectric sensors that are in a line-symmetric relationship with respect to the center may be connected via electrode wiring as metal wiring. In this case, it is possible to generate an angle detection signal using voltage signals obtained from the lower electrodes of the pair of piezoelectric sensors.

[0109] In the above embodiment, four piezoelectric sensors 51 to 54 are provided, but the number of piezoelectric sensors is not limited to four. The shape and arrangement of the piezoelectric sensors can be changed as appropriate. For example, the first axis a １ or the second axis a ２ A piezoelectric sensor may be provided thereon.

[0110] Furthermore, 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 a single processor, or may be configured with a combination of two or more processors of the same or different types. Processors include CPUs, programmable logic devices (PLDs), dedicated electrical circuits, etc. As is well known, a CPU is a general-purpose processor that executes software (programs) to function as various processing units. A PLD is a processor, such as an FPGA (Field Programmable Gate Array), whose circuit configuration can be changed after manufacturing. A dedicated electrical circuit is a processor, such as an ASIC (Application Specific Integrated Circuit), that has a circuit configuration designed specifically to execute specific processing.

[0111] The above description allows the understanding of the following technology. [Supplementary Item 1] A mirror section having a reflective surface that reflects incident light; a pair of first support parts connected to the mirror section on a first axis in a plane including the reflective surface when the mirror section is stationary and supporting the mirror section so that it can swing around the first axis; a pair of movable frames connected to the pair of first support parts and facing each other across the first axis; a pair of second support parts connected to the pair of movable frames on a second axis in the plane that intersects the first axis and supporting the mirror section, the pair of first support parts, and the pair of movable frames so that they can swing around the second axis; a drive section arranged to surround the pair of movable frames and having a plurality of piezoelectric actuators facing each other across the first axis or the second axis; a fixed frame arranged to surround the drive section; a pair of connection parts that are thinner than the fixed frame and extend in the direction of the first axis or the second axis to connect the drive section and the fixed frame; and a plurality of metal pads formed on the fixed frame. and a plurality of metal wirings electrically connecting the plurality of piezoelectric actuators and the plurality of metal pads, wherein the plurality of piezoelectric actuators are arranged in a region where a maximum value of a maximum principal stress generated when the mirror section is swung around the first axis or the second axis is 1 / 120 to 1 / 8 of a maximum value of a maximum principal stress generated overall. [Supplementary Item 2] The mirror device according to Supplementary Item 1, wherein the plurality of piezoelectric actuators are arranged in a region where a maximum value of a maximum principal stress generated when the mirror section is swung around the first axis or the second axis is 1 / 40 to 1 / 8 of a maximum value of a maximum principal stress generated overall. [Supplementary Item 3] The mirror device according to Supplementary Item 1 or Supplementary Item 2, wherein the drive unit has: a first actuator arranged to surround the pair of movable frames and consisting of a pair of the piezoelectric actuators facing each other across the second axis; and a second actuator arranged to surround the first actuator and consisting of a pair of the piezoelectric actuators facing each other across the first axis.[Supplementary Item 4] The mirror device according to any one of Supplementary Items 1 to 3, wherein contact regions where the plurality of piezoelectric actuators and the plurality of metal wirings are in contact with each other are arranged in a region where the maximum value of the maximum principal stress generated when the mirror section is swung around the first axis or the second axis is 1 / 15 or less of the maximum value of the maximum principal stress generated overall. [Supplementary Item 5] The mirror device according to any one of Supplementary Items 1 to 4, wherein each of the plurality of piezoelectric actuators is configured by an upper electrode, a piezoelectric film, and a lower electrode, and each of the plurality of metal wirings is connected to the upper electrode or the lower electrode. [Supplementary Item 6] The mirror device according to any one of Supplementary Items 1 to 5, wherein at least one of the plurality of metal wirings is formed containing three or more metal materials. [Supplementary Item 7] The mirror device according to Supplementary Item 6, wherein at least one of the plurality of metal wirings is formed by connecting a first wiring formed of Au and a first wiring formed containing Al and Ti. [Supplementary Item 8] The mirror device according to any one of Supplementary Items 1 to 7, wherein the pair of connecting portions are arranged on the second axis. [Supplementary Item 9] An optical scanning device comprising: the mirror device according to any one of Supplementary Items 1 to 8; and a processor, wherein the processor applies a drive signal to each of the plurality of piezoelectric actuators to cause the mirror portion to oscillate around the first axis and the second axis, respectively.

Claims

1. A mirror portion having a reflective surface that reflects incident light, A pair of first support parts are connected to the mirror part on a first axis that lies in a plane including the reflective surface when the mirror part is stationary, and support the mirror part so that it can swing around the first axis, A pair of movable frames connected to the pair of first support parts and facing each other across the first shaft, A pair of second support parts are connected to a pair of the movable frames on a second axis that intersects the first axis in the aforementioned plane, and support the mirror portion, a pair of the first support parts, and a pair of the movable frames so that they can swing around the second axis. A drive unit having a plurality of piezoelectric actuators arranged around a pair of the aforementioned movable frames and facing each other across the first or second axis, A fixed frame is arranged to surround the aforementioned drive unit, A pair of connecting parts that are thinner than the fixed frame and extend in the direction of the first axis or the second axis to connect the drive unit and the fixed frame, Multiple metal pads formed on the aforementioned fixed frame, Multiple metal wires electrically connect the multiple piezoelectric actuators and the multiple metal pads, Equipped with, The plurality of piezoelectric actuators are arranged in a region where the maximum value of the maximum principal stress generated when the mirror portion is oscillated around the first axis or the second axis is between 1 / 120 and 1 / 8 of the maximum value of the total maximum principal stress. Mirror device.

2. The plurality of piezoelectric actuators are arranged in a region where the maximum value of the maximum principal stress generated when the mirror portion is oscillated around the first axis or the second axis is between 1 / 40 and 1 / 8 of the maximum value of the total maximum principal stress. The mirror device according to claim 1.

3. The aforementioned drive unit is A first actuator is composed of a pair of piezoelectric actuators arranged around the pair of movable frames and facing each other across the second axis, A second actuator is arranged surrounding the first actuator and is composed of a pair of piezoelectric actuators facing each other across the first axis, A mirror device according to claim 1, having the features of claim 1.

4. The contact area where the plurality of piezoelectric actuators and the plurality of metal wirings come into contact is located in a region where the maximum value of the maximum principal stress generated when the mirror portion is oscillated around the first axis or the second axis is 1 / 15 or less of the maximum value of the maximum principal stress generated overall. A mirror device according to any one of claims 1 to 3.

5. Each of the multiple piezoelectric actuators is composed of an upper electrode, a piezoelectric film, and a lower electrode. Each of the multiple metal wirings is connected to the upper electrode or the lower electrode. A mirror device according to any one of claims 1 to 3.

6. At least one of the multiple metal wirings is formed by including three or more types of metal materials. A mirror device according to any one of claims 1 to 3.

7. At least one of the plurality of metal wirings is configured by connecting a first wiring made of Au and a second wiring made of Al and Ti. The mirror device according to claim 6.

8. The pair of connecting parts are arranged on the second axis. A mirror device according to any one of claims 1 to 3.

9. A mirror device according to any one of claims 1 to 3, Processor and An optical scanning device comprising, The processor provides a drive signal to each of the plurality of piezoelectric actuators, thereby causing the mirror portion to swing around the first axis and the second axis, respectively. Optical scanning device.