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, a pair of second support parts, a drive part having a plurality of piezoelectric actuators, a fixed frame, a pair of connection parts which connect the drive part and the fixed frame to one another, and a piezoelectric sensor which generates a signal corresponding to the oscillation of the mirror part around the first axis or the second axis. The piezoelectric sensor is electrically isolated from the plurality of piezoelectric actuators. The plurality of piezoelectric actuators and the piezoelectric sensor each comprise an upper electrode, a piezoelectric film, and a lower electrode. The upper electrodes of the plurality of piezoelectric actuators are connected in common via the first metal wiring. The lower electrode of the piezoelectric sensor is connected to the second metal wiring electrically separated from the first metal wiring.

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] In a two-axis micromirror device, an angle sensor is required to detect the angle of the mirror around each axis in real time during biaxial drive. In a micromirror device that uses a piezoelectric actuator, a piezoelectric sensor is used as the angle sensor.

[0006] The micromirror device also includes a fixing frame that surrounds the mirror and drive units, and multiple metal pads that are connected to the drive units and piezoelectric sensors via metal wiring.

[0007] However, in conventional micromirror devices, the piezoelectric sensor is connected to a common metal wiring for applying ground potential to multiple piezoelectric actuators, so ringing noise generated in the drive unit may be transmitted to the piezoelectric sensor via the metal wiring, which may reduce the angle detection accuracy of the mirror unit.

[0008] The technique of the present disclosure aims to provide a mirror device and an optical scanning device that can improve the angle detection accuracy of a mirror portion.

[0009] In order to achieve the above object, the mirror device of the present disclosure includes a mirror unit that reflects incident light, a pair of first support parts that are connected to the mirror unit on a first axis and support the mirror unit swingably around the first axis, a pair of movable frames that are connected to the pair of first support parts and face each other across the first axis, a pair of second support parts that are connected to the pair of movable frames on a second axis that intersects the first axis and support the mirror unit, the pair of first support parts, and the pair of movable frames swingably around the second axis, a drive unit that is arranged surrounding the pair of movable frames and has a plurality of piezoelectric actuators that face each other across the first axis or the second axis, a fixed frame that is arranged surrounding the drive unit, and a fixed frame. The mirror element is provided with a pair of connecting parts that are thinner than the fixed frame and extend along a first axis or a second axis to connect the drive part and the fixed frame, and a piezoelectric sensor that generates a signal corresponding to the oscillation of the mirror part around the first axis or the second axis, the piezoelectric sensor being electrically isolated from the plurality of piezoelectric actuators, and the plurality of piezoelectric actuators and the piezoelectric sensor each being composed of an upper electrode, a piezoelectric film, and a lower electrode, the upper electrodes of the plurality of piezoelectric actuators being commonly connected via a first metal wiring, and the lower electrode of the piezoelectric sensor being connected to a second metal wiring that is electrically isolated from the first metal wiring.

[0010] The upper electrode of the piezoelectric sensor is preferably connected to a third metal wiring that is electrically isolated from the first metal wiring.

[0011] Preferably, the first metal wiring is connected to a first metal pad for applying a ground potential, and the second metal wiring is connected to a second metal pad for applying a ground potential.

[0012] The pair of connecting portions are preferably arranged on the second axis.

[0013] The optical scanning device disclosed herein is an optical scanning device comprising the above-mentioned mirror device and a processor that drives a drive unit, and the processor oscillates the mirror unit around a first axis and a second axis by applying a drive signal to each lower electrode of a plurality of piezoelectric actuators.

[0014] The drive signal is preferably a positive voltage.

[0015] According to the technique of the present disclosure, it is possible to provide a mirror device and an optical scanning device that can improve the angle detection accuracy of the mirror portion.

[0016] 10 is a schematic diagram of an optical scanning device. FIG. 11 is a block diagram showing an example of the hardware configuration of a drive control unit. FIG. 12 is a perspective view of the appearance of a micromirror device. FIG. 13 is a plan view of the micromirror device as viewed from the light incident side. FIG. 14 is a cross-sectional view taken along line A-A in FIG. 4. FIG. 15 is a cross-sectional view showing a state in which the mirror section has rotated around a first axis. FIG. 16 is a diagram showing an example of a first drive signal and a second drive signal. FIG. 17 is a cross-sectional view showing a schematic configuration of a piezoelectric sensor. FIG. 18 is a cross-sectional view showing a schematic configuration of a first actuator and a second actuator. FIG. 19 is a plan view showing an example of the layout of metal pads and metal wiring provided on a micromirror device. FIG. 11 is a diagram schematically showing the connection relationship of the metal wiring shown in FIG. 10. FIG. 19 is a diagram showing an example of signal processing for generating an angle detection signal.

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

[0018] 1 is a schematic diagram of an optical scanning device 10 according to 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 may be a screen, the retina of a human eye, or the like.

[0019] 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.

[0020] The light source 3 is a laser device that emits, for example, laser light as the light beam LB. When the mirror unit 20 of the MMD 2 is stationary, the light source 3 may irradiate the light beam LB perpendicularly to a reflecting surface 20A (see FIG. 3 ) of the mirror unit 20.

[0021] The light source 3 is a laser device that emits, for example, laser light as the light beam LB. The drive control unit 4 outputs drive signals to the light source 3 and the MMD 2 based on the optical scanning information. The light source 3 generates the light beam 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.

[0022] 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.

[0023] 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.

[0024] 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.

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

[0026] The light source driver 43 is an electric circuit that outputs a drive signal to the light source 3 under the control of the CPU 40. In the light source driver 43, the drive signal is a drive voltage for controlling the irradiation timing and irradiation intensity of the light source 3.

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

[0028] The CPU 40 controls the light source driver 43 and the MMD driver 44 based on the optical scanning information. The optical scanning information includes 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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

[0033] 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.

[0034] 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.

[0035] 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 a２ 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.

[0036] 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 50.

[0037] The pair of second support portions 23 are １ and 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 50 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.

[0038] 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 The first actuator 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.

[0039] 3 and 4, the piezoelectric actuator constituting the first actuator 24 is １ 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).

[0040] The pair of second support portions 23 and the first actuator 24 are connected to each other, thereby surrounding the movable portion 50 .

[0041] 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.

[0042] 3 and 4, the piezoelectric actuator constituting the second actuator 25 is ２ It appears to be separated by 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).

[0043] 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.

[0044] 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.

[0045] The second actuator 25 and the pair of second connection portions 26B are connected to each other, thereby surrounding the pair of movable portions 50 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.

[0046] 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 ２ The 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.

[0047] 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.

[0048] 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 along the mirror portion 20. One end of the oscillation shaft 21A is connected to the mirror portion 20, and the other end is connected to the pair of connecting portions 21B.

[0049] 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 １The 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.

[0050] 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 along the axis of the movable frame 22. 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.

[0051] The pair of connecting portions 23B are connected to the second axis a ２ and 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.

[0052] 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.

[0053] 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 １and 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.

[0054] 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.

[0055] 5, the MMD 2 is formed, for example, by etching an SOI (Silicon On Insulator) substrate 30. The SOI substrate 30 is a substrate in which a silicon oxide layer 32 is provided on a silicon support layer 31 made of single crystal silicon, and a silicon active layer 33 made of single crystal silicon is provided on the silicon oxide layer 32.

[0056] 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 a silicon active layer 33 remaining after removing the silicon support layer 31 and the silicon oxide layer 32 from the SOI substrate 30 by etching. The silicon active layer 33 functions as an elastic unit having elasticity. The fixed frame 27 is formed from three layers: the silicon support layer 31, the silicon oxide layer 32, and the silicon active layer 33. That is, 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.

[0057] The piezoelectric actuator constituting the first actuator 24 is composed of a piezoelectric element formed on a silicon active layer 33. The piezoelectric element has a layered structure in which a lower electrode 70, a piezoelectric film 71, and an upper electrode 72 are layered in this order on the silicon active layer 33 (see FIG. 9). The second actuator 25 has the same configuration as the first actuator 24.

[0058] The lower electrode 70 and the upper electrode 72 are electrically connected to the drive control unit 4 via wiring and electrode pads. As will be described in detail later, a drive signal is applied to the lower electrode 70 from the drive control unit 4. The upper electrode 72 is connected to the drive control unit 4 via wiring and electrode pads, and is supplied with a ground potential.

[0059] When a positive or negative voltage is applied to the piezoelectric film 71 in the polarization direction, the piezoelectric film 71 undergoes deformation (e.g., expansion and contraction) proportional to the applied voltage. That is, the piezoelectric film 71 exhibits the so-called inverse piezoelectric effect. When a drive signal is applied from the drive control unit 4 to the lower electrode 70, the piezoelectric film exhibits the inverse piezoelectric effect, displacing the first actuator 24 and the second actuator 25.

[0060] 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

[0061] 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.

[0062] The first axis a of the mirror section 20 １ The 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°).

[0063] 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.

[0064] The first actuator 24 is driven in an anti-phase resonance mode in the same manner as the second actuator 25. ２The 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°).

[0065] 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.

[0066] Drive voltage waveform V １Ａ (t) and V １Ｂ (t) are expressed as follows: V １Ａ (t) = V ｏｆｆ１ +V １ sin(2πf ｄ１ t) V １Ｂ (t) = V ｏｆｆ１ +V １ sin(2πf ｄ１ t + α)

[0067] 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°.

[0068] 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 １Swinging around.

[0069] 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)

[0070] 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 (t) is the phase difference with respect to (t).

[0071] In this embodiment, V ｏｆｆ１ ≧V １ and V ｏｆｆ２ ≧V ２ That is, the first drive signal and the second drive signal are set to positive voltages.

[0072] 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.

[0073] 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 ２In 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.

[0074] 8 shows a schematic configuration of the piezoelectric sensors 51 and 52. Each of the piezoelectric sensors 51 and 52 includes a lower electrode 60, a piezoelectric film 61, and an upper electrode 62. The lower electrode 60, the piezoelectric film 61, and the upper electrode 62 are stacked in this order on the silicon active layer 33. The lower electrode 60 and the upper electrode 62 are made of a metal such as gold (Au) or platinum (Pt). The piezoelectric film 61 is made of, for example, PZT (lead zirconate titanate), a piezoelectric material.

[0075] The upper electrode 62 is covered with an insulating film 63. An opening 63A is formed in the insulating film 63 to expose a portion of the upper electrode 62. A metal wiring 91 made of metal is provided on the insulating film 63. The metal wiring 91 is connected to the upper electrode 62 via the opening 63A. The lower electrode 60 is connected to a metal wiring 90 formed on the silicon active layer 33. The lower electrode 60 of the piezoelectric sensor 51 and the lower electrode 60 of the piezoelectric sensor 52 are connected via the metal wiring 90. A ground potential is applied to the metal wiring 90.

[0076] The piezoelectric film 61 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 62.

[0077] The piezoelectric sensors 53 and 54 have the same configuration as the piezoelectric sensors 51 and 52 .

[0078] 9 schematically shows the configuration of the first actuator 24 and the second actuator 25. The piezoelectric actuators constituting the first actuator 24 and the second actuator 25 include 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 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.

[0079] 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. Metal wiring 93 made of metal is provided on the insulating film 73. The metal wiring 93 is connected to the upper electrode 72 through the opening 73A. The upper electrode 72 of the piezoelectric actuator that constitutes the first actuator 24 and the upper electrode 72 of the piezoelectric actuator that constitutes the second actuator 25 are connected through the metal wiring 93. A ground potential is applied to the metal wiring 93.

[0080] The lower electrode 70 of the piezoelectric actuator constituting the first actuator 24 is connected to a metal wiring 94 formed on the silicon active layer 33. The lower electrode 70 of the piezoelectric actuator constituting the second actuator 25 is connected to a metal wiring 95 formed on the silicon active layer 33.

[0081] 10 shows an example of the layout of metal pads and metal wiring provided on the MMD 2. FIG. 10 is a partial enlarged view of a region including the piezoelectric sensors 51 and 52.

[0082] A plurality of metal pads 80 to 85 are formed on the fixed frame 27. The metal pad 80 is an electrode pad for applying a ground potential to the piezoelectric sensors 51 and 52, and is connected to a metal wiring 90. As described above, the metal wiring 90 is connected in common to the lower electrode 60 of the piezoelectric sensor 51 and the lower electrode 60 of the piezoelectric sensor 52.

[0083] The metal pad 81 is an electrode pad for acquiring a voltage signal from the piezoelectric sensor 51, and is connected to a metal wiring 91 connected to the upper electrode 62 of the piezoelectric sensor 51. Similarly, the metal pad 82 is an electrode pad for acquiring a voltage signal from the piezoelectric sensor 52, and is connected to a metal wiring 91 connected to the upper electrode 62 of the piezoelectric sensor 52.

[0084] The metal pad 83 is an electrode pad for applying a ground potential to the first actuator 24 and the second actuator 25, and is connected to a metal wiring 93. As described above, the metal wiring 93 is connected in common to the upper electrode 72 of the piezoelectric actuator that constitutes the first actuator 24 and the upper electrode 72 of the piezoelectric actuator that constitutes the second actuator 25.

[0085] The metal pad 84 is an electrode pad for applying a second drive signal to the first actuator 24, and is connected to a metal wiring 94. The metal wiring 94 is connected to the lower electrode 70 of the piezoelectric actuator that constitutes the first actuator 24.

[0086] The metal pad 85 is an electrode pad for applying a first drive signal to the second actuator 25, and is connected to a metal wiring 95. The metal wiring 95 is connected to the lower electrode 70 of the piezoelectric actuator that constitutes the second actuator 25.

[0087] The metal wiring 93 to 95 is 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. 10, the metal wiring 93 and 94 is further routed from the second actuator 25 through the first connection portion 26A to the formation region of the first actuator 24.

[0088] Although not shown, the layout of the plurality of metal pads and the plurality of metal wirings in the region including the piezoelectric sensors 53 and 54 is the same as that shown in FIG. 10. In this embodiment, the plurality of metal pads and the plurality of metal wirings are arranged along the first axis a １ and the second axis a ２ The axial direction of the sine wave is 180° rotationally symmetrical about the intersection of the axial direction and the axial direction.

[0089] Fig. 11 schematically shows the connection relationship of the metal wiring shown in Fig. 10. As shown in Fig. 11, the ground potential is applied to the piezoelectric sensors 51 and 52 from the metal pad 80 via the metal wiring 90, and the ground potential is applied to the first actuator 24 and the second actuator 25 from the metal pad 83 via the metal wiring 93, and the metal wiring 90 and the metal wiring 93 are electrically isolated. Therefore, the piezoelectric sensors 51 and 52 are electrically isolated from the first actuator 24 and the second actuator 25. Similarly, the piezoelectric sensors 53 and 54 are electrically isolated from the first actuator 24 and the second actuator 25.

[0090] The upper electrodes 72 of the piezoelectric actuators constituting the first actuator 24 and the second actuator 25 are commonly connected via metal wiring 93. The metal wiring 93 is an example of a "first metal wiring" according to the technology of the present disclosure. The metal pad 83 is an example of a "first metal pad" according to the technology of the present disclosure.

[0091] The lower electrode 60 of each of the piezoelectric sensors 51 and 52 is connected to a metal wiring 90 that is electrically isolated from the metal wiring 93. The metal wiring 90 is an example of a "second metal wiring" according to the technology of the present disclosure. The metal pad 80 is an example of a "second metal pad" according to the technology of the present disclosure.

[0092] The upper electrode 62 of each of the piezoelectric sensors 51 and 52 is connected to a metal wiring 91 that is electrically isolated from the metal wiring 93. The metal wiring 91 is an example of a "third metal wiring" according to the technology of the present disclosure. The same applies to the piezoelectric sensors 53 and 54.

[0093] 12 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 E3 obtained from the upper electrode 62 of the piezoelectric sensor 53 from the voltage signal E1 obtained from the upper electrode 62 of the piezoelectric sensor 51 to obtain the angle detection signal of the first axis a. １The 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 E2 obtained from the upper electrode 62 of the piezoelectric sensor 52 from the voltage signal E1 obtained from the upper electrode 62 of the piezoelectric sensor 51. ２ A second angle detection signal S2 representing the angle of the surrounding mirror portion 20 is generated.

[0094] The first axis a included in the voltage signal E1 and the voltage signal E3 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 E1 and the voltage signal E3 ２ The surrounding signal components (noise components) are in phase. Therefore, by subtracting voltage signal E3 from voltage signal E1, 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.

[0095] The second axis a included in the voltage signal E1 and the voltage signal E2 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 E1 and the voltage signal E2 １ The surrounding signal components (noise components) are in phase. Therefore, by subtracting voltage signal E2 from voltage signal E1, 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.

[0096] As described above, in the MMD according to the technology of the present disclosure, the piezoelectric sensor is electrically isolated from the multiple piezoelectric actuators included in the drive unit, which prevents ringing noise generated in the drive unit from being transmitted to the piezoelectric sensor via the metal wiring, thereby improving the angle detection accuracy of the mirror unit.

[0097] Furthermore, the direction of spontaneous polarization of the piezoelectric film 71 of the piezoelectric actuator is determined by the thin-film formation process, and the spontaneous polarization direction is from the lower electrode 70 to the upper electrode 72. To effectively displace the piezoelectric film 71 using the inverse piezoelectric effect under such spontaneous polarization, a voltage must be applied in the opposite direction to the spontaneous polarization. When applying a ground potential to the lower electrode 70, the drive signal applied to the upper electrode 72 must be a negative voltage. When the drive signal is a negative voltage, there are limited options for circuit elements to generate the negative voltage, and disadvantages include increased power consumption. In contrast, in the MMD according to the technology disclosed herein, a ground potential is applied to the upper electrode 72 and a drive signal is applied to the lower electrode 70, so the drive signal can be a positive voltage. Therefore, the technology disclosed herein broadens the options for circuit elements and enables reduced power consumption.

[0098] The configuration of the MMD 2 according to the above embodiment is an example, and various modifications are possible.

[0099] In the above embodiment, as shown in Fig. 12, the first angle detection signal S1 is generated by subtracting the voltage signal E3 from the voltage signal E1, and the second angle detection signal S2 is generated by subtracting the voltage signal E2 from the voltage signal E1. Alternatively, it is also possible to generate the first angle detection signal S1 by adding the voltage signals E1 and E2, and generate the second angle detection signal S2 by subtracting the voltage signal E3 from the voltage signal E1. 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 E1 to E4.

[0100] Furthermore, in the above embodiment, the lower electrode 60 of the piezoelectric sensor 51 and the lower electrode 60 of the piezoelectric sensor 52 are commonly connected via the metal wiring 90, but the upper electrode 62 of the piezoelectric sensor 51 and the upper electrode 62 of the piezoelectric sensor 52 may also be commonly connected via the metal wiring 90. In this case, a ground potential is applied to the upper electrode 62, and a voltage signal for angle detection is obtained from the lower electrode 60. The same applies to the piezoelectric sensors 53 and 54.

[0101] In the above embodiment, four piezoelectric sensors 51 to 54 are provided, but the number of piezoelectric sensors is not limited to four. １ and the second axis a ２ The shape and the position of the piezoelectric sensor may be changed as appropriate. For example, １ or the second axis a ２ A piezoelectric sensor may be provided thereon.

[0102] 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.

[0103] The above explanation allows one to understand the following techniques. [Supplementary Item 1] A mirror section that reflects incident light; a pair of first support sections connected to the mirror section on a first axis 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 sections and facing each other across the first axis; a pair of second support sections connected to the pair of movable frames on a second axis intersecting the first axis and supporting the mirror section, the pair of first support sections, and the pair of movable frames so that they can swing around the second axis; a drive section that is arranged to surround the pair of movable frames and has a plurality of piezoelectric actuators that face each other across the first axis or the second axis; a fixed frame that is arranged to surround the drive section; a pair of connection sections that are thinner than the fixed frame and extend along the first axis or the second axis to connect the drive section and the fixed frame; and a piezoelectric sensor that generates a signal according to the swing of the mirror section around the first axis or the second axis, A mirror device, wherein the plurality of piezoelectric actuators and the piezoelectric sensor are each composed of an upper electrode, a piezoelectric film, and a lower electrode, the upper electrodes of the plurality of piezoelectric actuators are commonly connected via first metal wiring, and the lower electrodes of the piezoelectric sensors are connected to second metal wiring electrically isolated from the first metal wiring. [Supplementary Item 2] The mirror device according to Supplementary Item 1, wherein the upper electrodes of the piezoelectric sensors are connected to third metal wiring electrically isolated from the first metal wiring. [Supplementary Item 3] The mirror device according to Supplementary Item 1 or Supplementary Item 2, wherein the first metal wiring is connected to a first metal pad for applying a ground potential, and the second metal wiring is connected to a second metal pad for applying a ground potential. [Supplementary Item 4] The mirror device according to any one of Supplementary Items 1 to 3, wherein a pair of the connecting portions are arranged on the second axis.[Supplementary Item 5] An optical scanning device comprising: the mirror device according to any one of Supplementary Items 1 to 4; and a processor that drives the drive section, wherein the processor applies a drive signal to the lower electrode of each of the plurality of piezoelectric actuators to cause the mirror section to oscillate around the first axis and the second axis, respectively. [Supplementary Item 6] The optical scanning device according to Supplementary Item 5, wherein the drive signal is a positive voltage.

Claims

a pair of first support parts connected to the mirror part on a first axis and supporting the mirror part so as to be swingable 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 intersecting the first axis and supporting the mirror part, the pair of first support parts and the pair of movable frames so as to be swingable around the second axis; a drive part arranged surrounding 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 surrounding the drive part; a pair of connection parts thinner than the fixed frame and extending along the first axis or the second axis to connect the drive part and the fixed frame; and a piezoelectric sensor that generates a signal corresponding to the swing of the mirror part around the first axis or the second axis, wherein the piezoelectric sensor is electrically isolated from the plurality of piezoelectric actuators, A mirror device, wherein the plurality of piezoelectric actuators and the piezoelectric sensor are each composed of an upper electrode, a piezoelectric film, and a lower electrode, the upper electrodes of the plurality of piezoelectric actuators are commonly connected via a first metal wiring, and the lower electrode of the piezoelectric sensor is connected to a second metal wiring electrically isolated from the first metal wiring.

2. The mirror device according to claim 1, wherein the upper electrode of the piezoelectric sensor is connected to a third metal wiring that is electrically isolated from the first metal wiring.

3. The mirror device according to claim 1, wherein the first metal wiring is connected to a first metal pad for applying a ground potential, and the second metal wiring is connected to a second metal pad for applying a ground potential.

4. The mirror device according to claim 1, wherein the pair of connecting portions are disposed on the second axis.

5. An optical scanning device comprising: a mirror device according to claim 1; and a processor for driving said drive section, wherein said processor applies a drive signal to the lower electrode of each of a plurality of said piezoelectric actuators, thereby causing said mirror section to oscillate around said first axis and said second axis, respectively.

6. The optical scanning device according to claim 5, wherein the drive signal is a positive voltage.

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