Mirror device and optical scanning device

Abstract

This mirror device comprises: a movable part including a mirror part that reflects incident light; a drive part that is connected to the movable part and causes the mirror part to swing around at least one swing axis; an annular part that is connected to the drive part and is disposed so as to surround the drive part; a fix frame that is connected to the annular part and is disposed so as to surround the annular part; and a pair of piezoelectric sensors that are disposed in the annular part and are in a positional relationship that is line-symmetric about the swing axis.

Description

Mirror device and optical scanning device

[0001] The technology disclosed herein relates to a mirror device and an optical scanning device.

[0002] Micromirror devices (also known as microscanners) are a type of micro-electromechanical system (MEMS) device fabricated using silicon (Si) microfabrication technology. Due to their small size and low power consumption, these micromirror devices are expected to have a wide range of applications, including laser displays, laser projectors, and optical coherence tomography (OCT) systems.

[0003] While there are various driving methods for micromirror devices, piezoelectric driving, which utilizes the deformation of a piezoelectric material, is considered promising because it generates higher torque and can achieve higher scan angles compared to other methods. In particular, when high scan angles are required, such as in laser displays, a higher scan angle can be obtained by resonant driving of a piezoelectric-driven micromirror device.

[0004] A typical micromirror device used in laser displays comprises a mirror section and a piezoelectric actuator (see, for example, Japanese Patent Publication No. 2023-142097). The mirror section is pivotable around at least one pivot axis. The actuator pivots the mirror section around the pivot axis in response to a drive voltage supplied from an external source.

[0005] Micromirror devices require angle sensors to detect the angle of the mirror section around each axis in real time during operation. In particular, in micromirror devices using piezoelectric actuators, it is preferable to use piezoelectric sensors as angle sensors. This is because using piezoelectric sensors formed from the same piezoelectric elements as the actuators simplifies the manufacturing process of the micromirror device and allows for miniaturization. Piezoelectric sensors convert the stress generated by the oscillation of the mirror section into a voltage signal and output it.

[0006] In conventional micromirror devices, piezoelectric sensors are placed near support parts (e.g., torsion bars) that support the mirror, where high stress is applied, or near actuators. However, when piezoelectric mirrors are placed in such locations, they can contain a lot of noise due to interference from wiring connected to the actuator, and superposition of signal components from other axes other than the detection target. If the voltage signal contains a lot of noise, the angle detection accuracy of the mirror will decrease.

[0007] The present invention aims to provide a mirror device and an optical scanning device that enable improved angle detection accuracy of the mirror portion.

[0008] To achieve the above objective, the mirror device of this disclosure comprises: a movable part including a mirror portion that reflects incident light; a drive unit connected to the movable part and that causes the mirror portion to swing around at least one pivot axis; an annular portion connected to the drive unit and arranged surrounding the drive unit; a fixed frame connected to the annular portion and arranged surrounding the annular portion; and a pair of piezoelectric sensors arranged in the annular portion and in a positional relationship symmetrical with respect to the pivot axis.

[0009] Each of the pair of piezoelectric sensors consists of an upper electrode, a piezoelectric film, and a lower electrode, and it is preferable that the shape of the pair of upper electrodes is symmetrical with respect to the pivot axis.

[0010] The movable part comprises a pair of first support parts connected to the mirror part and positioned on the first axis, and a pair of movable frames connected to the pair of first support parts and facing each other across the first axis, and the pivot axis is preferably the first axis or a second axis intersecting the first axis.

[0011] The annular portion is preferably connected to the drive unit and the fixed frame on the first or second axis.

[0012] The drive unit comprises a pair of second support parts connected to the movable frame on the second shaft and supporting the movable part, and it is preferable that the pair of second support parts are arranged on the second shaft.

[0013] The drive unit preferably includes a first actuator having a pair of first piezoelectric elements connected to a pair of second support parts and facing each other across a second shaft.

[0014] The drive unit preferably includes a second actuator having a pair of second piezoelectric elements that are arranged around the first actuator and face each other across the first shaft.

[0015] When the mirror part swings, it is preferable that the annular part and the drive part are displaced in opposite phases to each other in the thickness direction of the fixed frame.

[0016] The optical scanning apparatus of the present disclosure comprises the mirror device and a processor that drives a drive unit, wherein the drive unit oscillates the mirror unit in accordance with a drive signal provided by the processor.

[0017] The processor preferably calculates the oscillation angle of the mirror around the pivot axis by subtracting the piezoelectric signal from one of the pair of piezoelectric sensors from the piezoelectric signal from the other.

[0018] The technology disclosed herein provides a mirror device and an optical scanning device that enable improved angle detection accuracy of the mirror portion.

[0019] This is a schematic diagram showing an optical scanning device according to an embodiment. This is a block diagram showing an example of the hardware configuration of the drive control unit. This is an external perspective view of the micromirror device according to an embodiment. This is a plan view of the micromirror device according to an embodiment as seen from the light incident side. This is a cross-sectional view along line A-A in Figure 4. This is a cross-sectional view showing the state in which the mirror part has rotated around the first axis. This is a diagram showing an example of the first drive signal and the second drive signal. This is a cross-sectional view showing a schematic configuration of a piezoelectric sensor. This is a diagram showing an example of the angle detection signal generation process by the CPU. This is a plan view showing the configuration of a micromirror device according to the first comparative example. This is a graph showing the evaluation result of the first angle detection signal. This is a graph showing the evaluation result of the second angle detection signal. This is a contour diagram when the micromirror device according to an embodiment is driven around the first axis. This is a contour diagram when the micromirror device according to an embodiment is driven around the second axis. This is a contour diagram when the micromirror device according to the first comparative example is driven around the first axis. This is a contour diagram when the micromirror device according to the first comparative example is driven around the second axis. This is a plan view showing the configuration of a micromirror device according to the second comparative example. This is a plan view showing the configuration of a micromirror device according to the third comparative example. This figure shows the evaluation results of the first angle detection signal and the second angle detection signal for the embodiment and the first to third comparative examples.

[0020] An example of an embodiment relating to the technology of this disclosure will be described with reference to the attached drawings.

[0021] [Embodiment] Figure 1 schematically shows an optical scanning device 10 according to an embodiment. The optical scanning device 10 includes a micromirror device (hereinafter referred to as MMD (Micro Mirror Device)) 2, a light source 3, and a drive control unit 4. The optical scanning device 10 optically scans the surface to be scanned 5 by reflecting the light beam LB irradiated from the light source 3 with the MMD 2, according to the control of the drive control unit 4. The surface to be scanned 5 is a screen or the retina of the eye, etc. The MMD 2 is an example of a "mirror device" according to the technology of this disclosure.

[0022] MMD2 is the first axis a １ and the first axis a １ The second axis a is orthogonal to it. ２It is a piezoelectric two-axis drive type micromirror device that enables the mirror unit 20 (see FIG. 3) to swing around. Hereinafter, the first axis a １ The direction parallel to is the X direction, and the second axis a ２ The direction parallel to is the Y direction, and the first axis a １ And the second axis a ２ The direction orthogonal to is referred to as the Z direction. In the present embodiment, an example where the first axis a １ And the second axis a ２ Are orthogonal is shown, but the first axis a １ And the second axis a ２ May intersect at an angle other than 90°. Here, orthogonal means intersecting within a certain angular range including the tolerance around 90°.

[0023] MMD2 is housed in a package such as ceramic not shown. Further, the package housing MMD2 is fixed to a substrate such as a PCB not shown, and the substrate is screwed to a base material not shown.

[0024] The light source 3 is, for example, a laser device that emits laser light as the light beam LB. The light source 3 preferably irradiates the reflection surface 20A (see FIG. 3) provided in the mirror unit 20 with the light beam LB perpendicularly in a state where the mirror unit 20 of the MMD2 is stationary.

[0025] The drive control unit 4 outputs drive signals to the light source 3 and the MMD2 based on the optical scanning information. The light source 3 generates the light beam LB based on the input drive signal and irradiates the MMD2. The MMD2 swings the mirror unit 20 around the first axis a １ And the second axis a ２ . Note that the first axis a １ And the second axis a ２ Are each an example of the "swing axis" according to the technology of the present disclosure.

[0026] Specifically described later, for example, the drive control unit 4 swings the mirror unit 20 around the first axis a １ And the second axis a ２By causing each element to resonate, the light beam LB reflected by the mirror section 20 is scanned on the scanning surface 5 in a manner that traces a Lissajous waveform. This optical scanning method is called the Lissajous scan method.

[0027] The optical scanning device 10 is applicable, for example, to a Lissajous scanning laser display. Specifically, the optical scanning device 10 is applicable to laser scanning displays such as AR (Augmented Reality) glasses or VR (Virtual Reality) glasses.

[0028] Figure 2 shows an example of the hardware configuration of the drive control unit 4. The drive control unit 4 includes a CPU (Central Processing Unit) 40, a ROM (Read Only Memory) 41, a RAM (Random Access Memory) 42, a light source driver 43, and an MMD driver 44. The CPU 40 is an arithmetic unit that realizes the overall function of the drive control unit 4 by reading programs and data from storage devices such as the ROM 41 into the RAM 42 and executing processing. The CPU 40 is an example of a "processor" related to the technology of this disclosure.

[0029] ROM 41 is a non-volatile memory device that stores programs for the CPU 40 to execute processes, as well as data such as the aforementioned optical scanning information. RAM 42 is a volatile memory device that temporarily holds programs and data.

[0030] The light source driver 43 is an electrical circuit that outputs a drive signal to the light source 3 according to the control of the CPU 40. In the light source driver 43, the drive signal is a drive voltage for controlling the irradiation timing and irradiation intensity of the light source 3.

[0031] The MMD driver 44 is an electrical circuit that outputs a drive signal to the MMD 2 according to the control of the CPU 40. In the MMD driver 44, the drive signal is a drive voltage for controlling the timing, period, and swing angle of the oscillating mirror section 20 of the MMD 2.

[0032] 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 optical beam LB scanned on the surface to be scanned 5 and the emission timing of the light source 3.

[0033] Furthermore, the CPU 40, based on the voltage signals output from the multiple piezoelectric sensors provided in the MMD 2 (described later), controls the first axis a of the mirror unit 20. １ and second axis a ２ An angle detection signal representing the angle around the object is generated. The CPU 40 corrects the drive signal based on the generated angle detection signal.

[0034] Next, the configuration of the MMD2 according to the embodiment will be described using Figures 3 to 6. Figure 3 is an external perspective view of the MMD2. Figure 4 is a plan view of the MMD2 as seen from the light incident side. Figure 5 is a cross-sectional view along line A-A in Figure 4. Figure 6 shows the mirror portion 20 along the first axis a １ This is a cross-sectional view showing the state of rotation.

[0035] As shown in Figure 3, the MMD2 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, a pair of third connection sections 26C, a fixed frame 27, and an annular section 60. The MMD2 is a so-called MEMS scanner.

[0036] The mirror portion 20 has a reflective surface 20A that reflects incident light. The reflective surface 20A is formed of a thin metal film, such as gold (Au) or aluminum (Al), provided on one surface of the mirror portion 20. The shape of the reflective surface 20A is, for example, the first axis a １ and the second axis a ２ It is a circular shape centered at the intersection point.

[0037] 1st axis a １ and second axis a ２ For example, when the mirror portion 20 is stationary, it exists within a plane that includes the reflective surface 20A. The planar shape of the MMD2 is rectangular, and the first axis a １ It is symmetric with respect to the second axis a ２It is symmetrical with respect to a line. In this disclosure, “line symmetry” means symmetry that includes manufacturing variations or design-acceptable deviations, and is not necessarily limited to perfect agreement.

[0038] The pair of first support parts 21 are located on the second axis a ２ It is positioned opposite each other with respect to the second axis a ２ The shape is symmetrical with respect to the first axis a. １ The shape is symmetrical with respect to the first axis a. Each of the first support parts 21 is aligned with the first axis a １ It is connected to the mirror section 20 above, and the mirror section 20 is connected to the first axis a １ It is supported in a way that allows it to swing around.

[0039] The pair of movable frames 22 are located on the first axis a １ It is positioned opposite each other with respect to the first axis a １ The shape is symmetrical with respect to the second axis a. Each of the movable frames 22 is on the second axis a ２ The shape is symmetrical with respect to the center. In addition, each of the movable frames 22 is curved along the outer circumference of the mirror section 20. Both ends of the movable frames 22 are connected to the first support section 21.

[0040] The pair of first support parts 21 and the pair of movable frames 22 are connected to each other, thereby surrounding 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.

[0041] The pair of second support parts 23 are located on the first axis a １ It is positioned opposite each other with respect to the first axis a １ The shape is symmetrical with respect to the second axis a. Each of the second support parts 23 is aligned with the second axis a ２ The shape is symmetrical with respect to the second axis a. Each of the second support parts 23 is aligned with the second axis a ２ The movable part 50, which is connected to the movable frame 22 above and has a mirror part 20, is on the second axis a ２ It is supported so as to be able to swing around. In addition, each end of the second support part 23 is connected to the first actuator 24.

[0042] The first actuator 24 is located on the second axis a２ It is composed of a pair of first piezoelectric elements 24A facing each other across the second axis a ２ It has a shape that is symmetrical with respect to the first axis a. １ The shape is symmetrical with respect to the center. The first actuator 24 is arranged along the outer circumference of the pair of movable frames 22 and the pair of first support parts 21. The first actuator 24 is a piezoelectric driven actuator.

[0043] In Figures 3 and 4, the first piezoelectric element 24A constituting the first actuator 24 is located on the first axis a １ It appears to be separated by the first axis a １ The two first piezoelectric elements 24A, which are facing each other across the other, are electrically connected by metal wiring (not shown).

[0044] The pair of second support parts 23 and the first actuator 24 are connected to each other, thereby surrounding the movable part 50.

[0045] The second actuator 25 is located on the first axis a １ It is composed of a pair of second piezoelectric elements 25A facing each other across the first axis a １ The shape is symmetrical with respect to the second axis a. ２ The shape is symmetrical with respect to the center. The second actuator 25 is formed along the outer circumference of the first actuator 24 and the pair of second support parts 23. The second actuator 25 is a piezoelectric actuator.

[0046] In Figures 3 and 4, the second piezoelectric element 25A constituting the second actuator 25 is located on the second axis a ２ It appears to be separated by the second axis a ２ The two second piezoelectric elements 25A, which are facing each other across the other, are electrically connected by metal wiring (not shown).

[0047] The pair of first connecting parts 26A are connected to the second shaft a ２ It is positioned opposite each other with respect to the second axis a ２The shape is symmetrical with respect to the first axis a. １ The shape is symmetrical with respect to the first axis a. Each of the first connecting parts 26A is aligned with the first axis a １ It is arranged along the first axis a １ The first actuator 24 and the second actuator 25 are connected above.

[0048] The second actuator 25 surrounds the pair of movable frames 22 and the first actuator 24. The pair of second support parts 23, the first actuator 24, and the second actuator 25 constitute a drive unit arranged to surround the pair of movable frames 22.

[0049] The pair of second connecting parts 26B are connected to the first shaft a １ They are positioned opposite each other, with the second connecting portion 26B in between. ２ The shape is symmetrical with respect to the second axis a. ２ It is arranged along the second axis a ２ Above, the second actuator 25 and the annular portion 60 are connected. The pair of second connecting portions 26B connect the second actuator 25 to the second axis a ２ It is supported in a way that allows it to swing around.

[0050] The annular portion 60 is an annular member arranged around the second actuator 25, and the first axis a １ and second axis a ２ The shapes are symmetrical with respect to each of the two points. In addition, the annular portion 60 has a second axis a ２ A pair of slits 60A are provided on top. The pair of slits 60A are on the first axis a １ They are positioned opposite each other, with the second axis a in between. Each of the slits 60A extends in the X direction and along the second axis a ２ It has a shape that is symmetrical with respect to a central point.

[0051] Furthermore, the annular portion 60 has a first axis a １ A pair of protrusions 60B are provided on top. The pair of protrusions 60B are on the second axis a ２ They are positioned opposite each other, with the first axis a in between. Each of the protrusions 60B extends in the Y direction and along the first axis a１ The shape is symmetrical with respect to the first axis a. Each of the protruding portions 60B is wider than the other parts of the annular portion 60. The pair of protruding portions 60B are along the first axis a １ Moment of inertia of the surroundings and second axis a ２ It is provided to adjust with the surrounding moment of inertia. The amount of protrusion of the pair of protrusions 60B may be changed as appropriate.

[0052] The pair of third connecting parts 26C are connected to the first shaft a １ They are positioned opposite each other, with the second axis a in between. ２ The shape is symmetrical with respect to the center. Each of the third connecting parts 26C is aligned with the second axis a ２ It is arranged along the second axis a ２ Above, the annular portion 60 and the fixed frame 27 are connected. The pair of third connecting portions 26C connect the annular portion 60 to the second axis a ２ It is supported in a way that allows it to swing around.

[0053] Furthermore, the pair of second connecting parts 26B and the pair of third connecting parts 26C are connected to the second shaft a ２ Not limited to the upper axis, the first axis a １ They may be positioned on top. That is, the drive unit, the annular part 60, and the fixed frame 27 are on the second axis a ２ Not limited to the upper axis, the first axis a １ It's okay if it's connected above.

[0054] The fixed frame 27 is a frame-shaped member with a rectangular outer shape, and the first axis a １ and second axis a ２ The shapes are symmetrical with respect to each of the two points. The outer shape of the fixed frame 27 is the first axis a １ Parallel to the second axis a ２ Two opposing sides centered on the second axis a ２ Parallel to the first axis a １ It has two opposing sides centered on a central point. The fixed frame 27 surrounds the outer periphery of the pair of second actuators 25 and the second connecting portion 26B. In other words, the fixed frame 27 is arranged to surround the drive unit.

[0055] The first actuator 24 has a second axis a on the mirror section 20 and the pair of movable frames 22. ２By applying a rotational torque around it, the movable part 50 is swung around the second axis a ２ The second actuator 25 swings the mirror part 20 around the first axis a by applying a rotational torque around the first axis a to the mirror part 20, the pair of movable frames 22, and the first actuator 24 １ By applying a rotational torque around it, the mirror part 20 is swung around the first axis a １ The annular part 60 is displaceable in the thickness direction (i.e., the Z direction) of the fixed frame 27 in a state where the portions connected to the pair of second connection parts 26B and the pair of third connection parts 26C are fixed. The annular part 60 functions as a vibration damping part that has the effect of canceling the vibration generated when the mirror part 20 swings around the first axis a or the second axis a and suppressing the propagation of the vibration to the outside. That is, the annular part 60 has the effect of confining the vibration within the MMD2

[0056] In FIG. 4, the virtual line L indicates the boundary between the pair of third connection parts 26C and the fixed frame 27 １ or the second axis a ２ As shown in FIG. 4, each of the first support parts 21 is composed of a shaft part 21A and a pair of connecting parts 21B. The shaft part 21A is a so-called torsion bar extending along the first axis a. One end of the shaft part 21A is connected to the mirror part 20, and the other end is connected to the connecting part 21B

[0057] The pair of connecting parts 21B are arranged at positions facing each other across the first axis a and have a shape that is line-symmetric about the first axis a. Each of the connecting parts 21B has one end connected to the shaft part 21A and the other end connected to the movable frame 22. Each of the connecting parts 21B has a folded-back structure. Since each of the connecting parts 21B has elasticity due to the folded-back structure, when the mirror part 20 swings around the first axis a, the internal stress applied to the shaft part 21A is relaxed

[0058] Each of the second support parts 23 is composed of a shaft part 23A and a pair of connecting parts 23B. The shaft part 23A is along the second axis a １ and is a so-called torsion bar extending along the second axis a. One end of the shaft part 23A is connected to the movable part 50, and the other end is connected to the connecting part 23B

[0059] The pair of connecting parts 23B are arranged at positions facing each other across the second axis a and have a shape that is line-symmetric about the second axis a. Each of the connecting parts 23B has one end connected to the shaft part 23A and the other end connected to the movable frame 22. Each of the connecting parts 23B has a folded-back structure. Since each of the connecting parts 23B has elasticity due to the folded-back structure, when the movable part 50 swings around the second axis a, the internal stress applied to the shaft part 23A is relaxed １ across it and is arranged at positions facing each other, and is symmetric with respect to the second axis a １ as the center. Each of the connecting parts 21B has one end connected to the shaft part 21A and the other end connected to the movable frame 22. Each of the connecting parts 21B has a folded-back structure. Since each of the connecting parts 21B has elasticity due to the folded-back structure, when the mirror part 20 swings around the first axis a １ the internal stress applied to the shaft part 21A is relaxed

[0060] Each of the second support parts 23 is composed of a shaft part 23A and a pair of connecting parts 23B. The shaft part 23A is along the second axis a ２It is a so-called torsion bar that extends along [the relevant axis]. One end of the shaft portion 23A is connected to the movable frame 22, and the other end is connected to a pair of connecting portions 23B.

[0061] The pair of connecting portions 23B are arranged at positions facing each other with the second axis a ２ interposed therebetween, and have a shape that is symmetric with respect to the second axis a ２ as the center. Each of the connecting portions 23B has one end connected to the shaft portion 23A and the other end connected to the first actuator 24. Each of the connecting portions 23B has a folded-back structure. Since each of the connecting portions 23B has elasticity due to the folded-back structure, when the mirror portion 20 swings around the second axis a ２ the internal stress applied to the shaft portion 23A is relaxed.

[0062] Further, on the outside of the reflecting surface 20A of the mirror portion 20, a plurality of slits 20B and 20C are formed along the outer periphery of the reflecting surface 20A. The plurality of slits 20B and 20C are arranged at positions that are symmetric with respect to the first axis a １ and the second axis a ２ as the centers respectively. The slits 20B and 20C have the effect of suppressing the distortion generated on the reflecting surface 20A when the mirror portion 20 swings.

[0063] In the annular portion 60, four piezoelectric sensors 71 to 74 are provided as angle sensors for detecting the angle of the mirror portion 20. The piezoelectric sensors 71 to 74 are formed by piezoelectric elements, similar to the first actuator 24 and the second actuator 25. The piezoelectric sensors 71 to 74 have a symmetric positional relationship with respect to the first axis a １ and the second axis a ２ as the centers respectively. The piezoelectric sensors 71 to 74 are arranged at positions away from the first axis a １ and the second axis a ２ .

[0064] Specifically, the piezoelectric sensors 71 and 72 are arranged on one side of the annular portion 60 with the first axis a １ as the center, and the piezoelectric sensors 73 and 74 are arranged on the other side of the annular portion 60 with the first axis a １ as the center. The piezoelectric sensors 71 and 72 have positions and shapes that are symmetric with respect to the second axis a２ They are symmetrical with respect to the second axis a. ２ They are symmetrical with respect to the first axis a. １ They are symmetrical with respect to the first axis a. The piezoelectric sensors 72 and 74 have a position and shape that is symmetrical with respect to the first axis a. １ They are symmetrical with respect to each other with respect to the center.

[0065] The shapes of the piezoelectric sensors 71-74 shown in Figures 3 and 4 are the shapes of the upper electrodes, which will be described later. Therefore, the shape of the upper electrodes of piezoelectric sensors 71 and 72 is the second axis a ２ It is symmetrical with respect to the axis. The shape of the upper electrodes of the piezoelectric sensors 73 and 74 is such that the second axis a ２ It is symmetrical with respect to the first axis. The shape of the upper electrodes of the piezoelectric sensors 71 and 73 is such that the first axis a １ It is symmetrical with respect to the first axis. The shape of the upper electrodes of the piezoelectric sensors 72 and 74 is such that the first axis a １ It is symmetrical with respect to the center.

[0066] In Figures 3 and 4, the wiring and electrode pads for supplying drive signals to the first actuator 24 and the second actuator 25 are omitted from the illustration. Similarly, the wiring and electrode pads for acquiring voltage signals output from piezoelectric sensors 71-74 are also omitted from the illustration. Multiple electrode pads are provided on the fixed frame 27.

[0067] As shown in Figure 5, the MMD2 is formed, for example, by etching an SOI (Silicon On Insulator) substrate 30. The SOI substrate 30 is a substrate in which a silicon oxide layer 32 is provided on a 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.

[0068] The mirror portion 20, the pair of first support portions 21, the pair of movable frames 22, the pair of second support portions 23, the first actuator 24, the second actuator 25, the pair of first connecting portions 26A, the pair of second connecting portions 26B, the pair of third connecting portions 26C, and the annular portion 60 are formed by patterning the remaining silicon active layer 33 after removing the silicon support layer 31 and the silicon oxide layer 32 from the SOI substrate 30 by etching.

[0069] The fixed frame 27 is formed of three layers: a silicon support layer 31, a silicon oxide layer 32, and a silicon active layer 33. That is, the mirror portion 20, the pair of first support portions 21, the pair of movable frames 22, the pair of second support portions 23, the first actuator 24, the second actuator 25, the pair of first connecting portions 26A, the pair of second connecting portions 26B, the pair of third connecting portions 26C, and the annular portion 60 are each thinner than the fixed frame 27. In this disclosure, thickness refers to width in the Z direction.

[0070] The first piezoelectric element 24A and the second piezoelectric element 25A described above have a laminated structure in which a lower electrode, a piezoelectric film, and an upper electrode are sequentially stacked on a silicon active layer 33.

[0071] The lower electrode and 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 upper electrode are electrically connected to the drive control unit 4 via wiring and electrode pads.

[0072] The lower electrode is connected to the drive control unit 4 via wiring and electrode pads, and is supplied with ground potential. The upper electrode is supplied with drive voltage from the drive control unit 4.

[0073] When a positive or negative voltage is applied to a piezoelectric film in the polarization direction, deformation (e.g., expansion and contraction) proportional to the applied voltage occurs. In other words, the piezoelectric film exhibits a so-called inverse piezoelectric effect. The piezoelectric film exhibits an inverse piezoelectric effect when a drive voltage is applied to the upper electrode from the drive control unit 4, causing the first actuator 24 and the second actuator 25 to displace.

[0074] Figure 6 shows that by extending one of the pair of second piezoelectric elements 25A that constitute the second actuator 25 and contracting the other, the second actuator 25 moves along the first axis a １ This shows an example of generating rotational torque around the object. In this way, when one of the pair of second piezoelectric elements 25A is displaced in opposite directions, the mirror portion 20 moves along the first axis a １ It rotates around it.

[0075] Figure 6 shows an example in which the second actuator 25 is driven in an out-of-phase resonance mode (hereinafter referred to as the out-of-phase rotation mode) in which the displacement directions of the pair of piezoelectric actuators and the rotation direction of the mirror portion 20 are in opposite directions. In contrast, an in-phase resonance mode in which the displacement directions of the pair of piezoelectric actuators and the rotation direction of the mirror portion 20 are in the same direction is called the in-phase rotation mode. In this embodiment, the second actuator 25 is driven in the out-of-phase rotation mode.

[0076] First axis a of the mirror section 20 １ The surrounding deflection angle θ is controlled by a drive signal (hereinafter referred to as the 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 the drive voltage waveform V applied to one of the pair of piezoelectric actuators. １Ａ (t) and the drive voltage waveform V applied to the other side １Ｂ (t) and the drive voltage waveform V １Ａ (t) and drive voltage waveform V １Ｂ (t) are in opposite phases to each other (i.e., phase difference of 180°).

[0077] Note that the first axis a of the mirror section 20 １ The surrounding deflection angle θ corresponds to the angle at which the normal N of the reflecting surface 20A is inclined with respect to the Z direction in the YZ plane.

[0078] The first actuator 24, like the second actuator 25, is driven in an out-of-phase resonant mode. The second axis a of the mirror section 20 ２The circumference of the actuator is controlled by a drive signal (hereinafter referred to as the second drive signal) that the drive control unit 4 provides to the first actuator 24. The second drive signal is, for example, a sinusoidal AC voltage. The second drive signal is the drive voltage waveform V applied to one of the pair of piezoelectric actuators. ２Ａ (t) and the drive voltage waveform V applied to the other side ２Ｂ (t) and the drive voltage waveform V ２Ａ (t) and drive voltage waveform V ２Ｂ (t) are in opposite phases to each other (i.e., phase difference of 180°).

[0079] Figure 7 shows an example of a first drive signal and a second drive signal. Figure 7(A) shows the drive voltage waveform V included in the first drive signal. １Ａ (t) and V １Ｂ (t) is shown. Figure 7(B) shows the drive voltage waveform V included in the second drive signal. ２Ａ (t) and V ２Ｂ (t) is shown.

[0080] Drive voltage waveform V １Ａ (t) and V １Ｂ (t) can be 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)

[0081] Here, V １ V is the amplitude voltage. ｏｆｆ１ f is the bias voltage. ｄ１ V is the drive frequency (hereinafter referred to as the first drive frequency). t is time. α is the drive voltage waveform V １Ａ (t) and V １Ｂ This is the phase difference of (t). In this embodiment, for example, α = 180°.

[0082] Drive voltage waveform V １Ａ (t) and V １Ｂ When (t) is applied to the second actuator 25, the mirror section 20 operates at the first drive frequency f ｄ１ First axis a １It sways around.

[0083] Drive voltage waveform V ２Ａ (t) and V ２Ｂ (t) can be 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)

[0084] Here, V ２ V is the amplitude voltage. ｏｆｆ２ f is the bias voltage. ｄ２ V 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 This is the phase difference of (t). In this embodiment, for example, β = 180°. Also, φ is the drive voltage waveform V １Ａ (t) and V １Ｂ (t) and the drive voltage waveform V ２Ａ (t) and V ２Ｂ This is the phase difference with (t).

[0085] In this embodiment, V ｏｆｆ１ ≧V １ and V ｏｆｆ２ ≧V ２ This means that the first drive signal and the second drive signal are set to positive voltages.

[0086] Drive voltage waveform V ２Ａ (t) and V ２Ｂ When (t) is applied to the first actuator 24, the movable part 50 including the mirror part 20 operates at the second drive frequency f ｄ２ Second axis a ２ It sways around.

[0087] First drive frequency f ｄ１ The first axis a of the mirror section 20 １ It is set to match the surrounding resonant frequency. Second drive frequency f ｄ２ The second axis a of the mirror section 20 ２It is set to match the surrounding resonant frequency. In this embodiment, the first drive frequency f ｄ１ The second drive frequency f ｄ２ Larger.

[0088] The mirror section 20 is on the first axis a １ When it oscillates around, the annular portion 60 and the drive unit are displaced in opposite phases in the thickness direction of the fixed frame 27, thereby canceling out the vibrations. Specifically, the first axis a １ With the center point, the direction of displacement between the annular portion 60 and the drive portion is reversed. In the region where the drive portion is displaced in the +Z direction (positive direction), the annular portion 60 is displaced in the -Z direction (negative direction). Conversely, in the region where the drive portion is displaced in the -Z direction (negative direction), the annular portion 60 is displaced in the +Z direction (positive direction).

[0089] Similarly, the mirror portion 20 is on the second axis a ２ When it oscillates around, the annular portion 60 and the drive unit are displaced in opposite phases in the thickness direction of the fixed frame 27, thereby canceling out the vibrations. Specifically, the second axis a ２ With the center point, the direction of displacement between the annular portion 60 and the drive portion is reversed. In the region where the drive portion is displaced in the +Z direction (positive direction), the annular portion 60 is displaced in the -Z direction (negative direction). Conversely, in the region where the drive portion is displaced in the -Z direction (negative direction), the annular portion 60 is displaced in the +Z direction (positive direction).

[0090] In order to enhance the vibration damping effect of the annular section 60, the first axis a １ Surroundings and second axis a ２ For each oscillation around the ring, it is preferable that the resonant frequency of the mirror portion 20 and the resonant frequency of the annular portion 60 are close.

[0091] Figure 8 schematically shows the configuration of the piezoelectric sensor 71. The piezoelectric sensor 71 is composed of a lower electrode 80, a piezoelectric film 81, and an upper electrode 82. The lower electrode 80, the piezoelectric film 81, and the upper electrode 82 are sequentially laminated on the second silicon active layer 33 that constitutes the annular portion 60. The lower electrode 80 and the upper electrode 82 are made of a metal such as gold (Au) or platinum (Pt). The piezoelectric film 81 is made of a piezoelectric material such as PZT (lead zirconate titanate).

[0092] The upper electrode 72 is covered with an insulating film (not shown), and wiring is connected to the upper electrode 82 through an opening in the insulating film. The lower electrode 80 is supplied with ground potential via wiring (not shown).

[0093] The lower electrode 80, piezoelectric film 81, and upper electrode 82 are manufactured using the same manufacturing process as the lower electrode, piezoelectric film, and upper electrode of the first actuator 24 and the second actuator 25.

[0094] The piezoelectric film 81 converts the stress applied when the mirror portion 20 oscillates into a voltage signal through the piezoelectric effect. As a result, a voltage signal corresponding to the angle of the mirror portion 20 is obtained from the upper electrode 82.

[0095] Piezoelectric sensors 72-74 have the same configuration as piezoelectric sensor 71.

[0096] Figure 9 shows an example of the angle detection signal generation process by the CPU 40. For example, the CPU 40 subtracts the voltage signal V3 obtained from the upper electrode 82 of the piezoelectric sensor 73 from the voltage signal V1 obtained from the upper electrode 82 of the piezoelectric sensor 71, thereby generating the first axis a １ A first angle detection signal S1 representing the angle of the surrounding mirror portion 20 is generated. The CPU 40 also subtracts the voltage signal V2 obtained from the upper electrode 82 of piezoelectric sensor 72 from the voltage signal V1 obtained from the upper electrode 82 of piezoelectric sensor 71, thereby determining the second axis a ２ A second angle detection signal S2 is generated, representing the angle of the surrounding mirror section 20.

[0097] The first axis a included in voltage signal V1 and voltage signal V3 １ The surrounding signal components (the components to be detected) have different phases from each other, and may even be in opposite phases. In contrast, the second axis a contained in voltage signal V1 and voltage signal V3 ２ The surrounding signal components (noise components) are in phase. Therefore, by subtracting voltage signal V3 from voltage signal V1, the component to be detected is amplified, while the noise components, which are signal components around other axes other than the component to be detected, are reduced.

[0098] The second axis a included in voltage signal V1 and voltage signal V2 ２The surrounding signal components (the components to be detected) have different phases from each other, and may even be in opposite phases. In contrast, the first axis a contained in voltage signal V1 and voltage signal V2 １ The surrounding signal components (noise components) are in phase. Therefore, by subtracting voltage signal V2 from voltage signal V1, the component to be detected is amplified, while the noise components, which are signal components around other axes other than the component to be detected, are reduced.

[0099] As described above, in this embodiment, piezoelectric sensors 71 to 74 are provided on the annular portion 60. The wiring connected to the first actuator 24 and the second actuator 25 is connected to the first axis a １ The electrodes are connected to the electrode pads through the second connection part 26B and the third connection part 26C, which are arranged along the ring portion. The piezoelectric sensors 71 to 74 are located on the annular portion 60, away from the wiring connected to the first actuator 24 and the second actuator 25, so interference from the wiring is suppressed. This improves the angle detection accuracy of the mirror portion 20.

[0100] Furthermore, as described above, in this embodiment, an angle detection signal is generated by subtracting the piezoelectric signal output from one of the pair of piezoelectric sensors from the piezoelectric signal output from the other (i.e., the deflection angle of the mirror unit 20 is calculated), thus reducing noise components caused by the superposition of signal components around other axes. This further improves the angle detection accuracy of the mirror unit 20.

[0101] In this embodiment, the first angle detection signal S1 is generated by subtracting voltage signal V3 from voltage signal V1, and the second angle detection signal S2 is generated by subtracting voltage signal V2 from voltage signal V1. Alternatively, the first angle detection signal S1 can be generated by adding voltage signal V1 and voltage signal V2, and the second angle detection signal S2 can be generated by subtracting voltage signal V3 from 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 voltage signals V1 to V4.

[0102] [Comparative Example] Next, a comparative example will be described. Figure 10 shows the configuration of MMD2A according to the first comparative example. In Figure 10, the same reference numerals are used for components that perform the same function as MMD2 according to the above embodiment.

[0103] The MMD2A according to the first comparative example differs from the MMD2 according to the embodiment only in that it does not have an annular portion 60 and the piezoelectric sensors 71-74 are provided on the fixed frame 27. In the MMD2A, the pair of second connection portions 26B connect the second actuator 25 and the fixed frame 27. Also, in the MMD2A, the piezoelectric sensors 71-74 are arranged in the vicinity of the pair of second connection portions 26B. The position and shape of the piezoelectric sensors 71-74 are on the first axis a １ and second axis a ２ They are symmetrical with respect to each other with respect to the center.

[0104] Figures 11 and 12 show the evaluation results of the first angle detection signal S1 and the second angle detection signal S2 for MMD2 and MMD2A. Figure 11 shows the first axis a １ The evaluation results of the first angle detection signal S1 with respect to the optical scan angle when the mirror part 20 is oscillated around it are shown. Figure 12 shows the second axis a ２ The evaluation results of the second angle detection signal S2 with respect to the optical scan angle when the mirror unit 20 is oscillated around it are shown. Note that the optical scan angle is the total optical angle, which corresponds to four times the oscillation angle of the mirror unit 20 described above.

[0105] As shown in Figures 11 and 12, the MMD2 according to this embodiment has larger first angle detection signals S1 and second angle detection signals S2 compared to the MMD2A according to the first comparative example. The larger the first angle detection signals S1 and second angle detection signals S2, the greater the noise reduction effect. In this embodiment, the first angle detection signals S1 and second angle detection signals S2 are large because the stress on the annular portion 60 is large when the mirror portion 20 is oscillating.

[0106] Figures 13 and 14 are stress contour diagrams in the MMD2 according to the embodiment. Figure 13 shows the first axis a １ Figure 14 shows the maximum principal stress when the mirror portion 20 is oscillated around it. ２This shows the maximum principal stress when the mirror portion 20 is oscillated around it.

[0107] Figures 15 and 16 are stress contour diagrams in MMD2A according to the first comparative example. Figure 15 shows the first axis a １ Figure 16 shows the maximum principal stress when the mirror portion 20 is oscillated around it. ２ This shows the maximum principal stress when the mirror portion 20 is oscillated around it.

[0108] Figures 13 to 16 show the position SP of one of the piezoelectric sensors 71 to 74, namely piezoelectric sensor 72.

[0109] In the MMD2 according to this embodiment, each of the piezoelectric sensors 71 to 74 is positioned on the annular portion 60 at a location with high stress while avoiding the maximum stress region where cracks are likely to occur. In the MMD2 according to this embodiment, the stress at the positions where the piezoelectric sensors 71 to 74 are positioned is greater than in the MMD2A according to the first comparative example, so the first angle detection signal S1 and the second angle detection signal S2 become larger, and the noise reduction effect is improved.

[0110] Figure 17 shows the configuration of MMD2B according to the second comparative example. In Figure 17, components that perform the same function as MMD2 according to the above embodiment are denoted by the same reference numerals.

[0111] In the MMD2B according to the second comparative example, each of the piezoelectric sensors 71 to 74 is positioned near the second piezoelectric element 25A that constitutes the second actuator 25. The position and shape of the piezoelectric sensors 71 to 74 are aligned with the first axis a １ and second axis a ２ They are symmetrical with respect to the center. The other configurations of MMD2B in the second comparative example are the same as those of MMD2A in the first comparative example.

[0112] In the second comparative example, voltage signals V1 to V4 are output from piezoelectric sensors 71 to 74, respectively. The CPU 40 generates a first angle detection signal S1 by subtracting voltage signal V3 from voltage signal V1, and generates a second angle detection signal S2 by subtracting voltage signal V2 from voltage signal V1.

[0113] Figure 18 shows the configuration of MMD2C according to the third comparative example. In Figure 18, components that perform the same function as MMD2 according to the above embodiment are denoted by the same reference numerals.

[0114] In the MMD2C relating to the third comparative example, the piezoelectric sensors 71 and 72 are located on the fixed frame 27 and on the second axis a ２ It is positioned above. The piezoelectric sensors 71 and 72 are located on the first axis a １ They are symmetrical with respect to the line a. The piezoelectric sensors 73 and 74 are located on a pair of first connection parts 26A and on the first axis a １ It is positioned above. Piezoelectric sensors 73 and 74 are located on the second axis a ２ They are symmetrical with respect to the center. The other configurations of MMD2C in the third comparative example are the same as those of MMD2A in the first comparative example.

[0115] In the third comparative example, voltage signals V1 to V4 are output from piezoelectric sensors 71 to 74, respectively. In the third comparative example, the CPU 40 generates a first angle detection signal S1 by subtracting voltage signal V2 from voltage signal V1, and generates a second angle detection signal S2 by subtracting voltage signal V4 from voltage signal V3.

[0116] [Experimental Results] Figure 19 shows the evaluation results of the first angle detection signal S1 and the second angle detection signal S2 for the embodiment and the first to third comparative examples. The first axis component is the first axis a included in the first angle detection signal S1 or the second angle detection signal S2. １ This is the intensity of the surrounding frequency components. The second axis component is the second axis a included in the first angle detection signal S1 or the second angle detection signal S2. ２ This represents the intensity of the surrounding frequency components. The multi-axis sensitivity in the first angle detection signal S1 is the value obtained by dividing the second axis component by the first axis component. The multi-axis sensitivity in the second angle detection signal S2 is the value obtained by dividing the first axis component by the second axis component.

[0117] According to the evaluation results shown in Figure 19, the MMD2 according to this embodiment shows lower multi-axis sensitivity compared to the first to third comparative examples.

[0118] In the above embodiment, the MMD2 is a two-axis mirror device in which the mirror portion swings around two axes that intersect each other. However, the MMD2 may also be a one-axis mirror device in which the mirror portion swings around a single pivot axis. Furthermore, the MMD2 may be provided with a pair of piezoelectric sensors arranged in the annular portion and in a symmetrical positional relationship with respect to the pivot axis.

[0119] 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 composed of one processor, or it may be composed of a combination of two or more processors of the same or different types. The processor includes a CPU, a programmable logic device (PLD), a dedicated electrical circuit, etc. As is well known, the CPU is a general-purpose processor that executes software (programs) and functions as various processing units. The PLD is a processor such as an FPGA (Field Programmable Gate Array) whose circuit configuration can be changed after manufacturing. The dedicated electrical circuit is a processor such as an ASIC (Application Specific Integrated Circuit) that has a circuit configuration specifically designed to execute a particular process.

[0120] The following technologies can be understood from the above description. [Note 1] A mirror device comprising: a movable part including a mirror part that reflects incident light; a drive part connected to the movable part and that causes the mirror part to swing around at least one pivot axis; an annular part connected to the drive part and arranged surrounding the drive part; a fixed frame connected to the annular part and arranged surrounding the annular part; and a pair of piezoelectric sensors arranged on the annular part and in a positional relationship symmetrical with respect to the pivot axis. [Note 2] The mirror device according to Note 1, wherein each of the pair of piezoelectric sensors is composed of an upper electrode, a piezoelectric film, and a lower electrode, and the shape of the pair of upper electrodes is symmetrical with respect to the pivot axis. [Note 3] The mirror device according to Note 1 or Note 2, wherein the movable part comprises a pair of first support parts connected to the mirror part and arranged on a first axis, and a pair of movable frames connected to the pair of first support parts and facing each other across the first axis, and the oscillating axis is the first axis or a second axis intersecting the first axis. [Note 4] The mirror device according to Note 3, wherein the annular part is connected to the drive unit and the fixed frame on the first axis or the second axis. [Note 5] The mirror device according to Note 4, wherein the drive unit comprises a pair of second support parts connected to the movable frame on the second axis and supporting the movable part, and the pair of second support parts are arranged on the second axis. [Note 6] The mirror device according to Note 5, wherein the drive unit includes a first actuator having a pair of first piezoelectric elements connected to the pair of second support parts and facing each other across the second axis. [Addendum 7] The mirror device according to Addendum 6, wherein the drive unit includes a second actuator having a pair of second piezoelectric elements arranged around the first actuator and facing each other across the first axis. [Addendum 8] The mirror device according to any one of Addendums 1 to 7, wherein when the mirror unit swings, the annular portion and the drive unit are displaced in opposite phases in the thickness direction of the fixed frame.[Appendix 9] An optical scanning device comprising: a mirror device as described in any one of Appendix 1 to Appendix 8; and a processor for driving the drive unit, wherein the drive unit oscillates the mirror unit in accordance with a drive signal provided by the processor. [Appendix 10] The optical scanning device according to Appendix 9, wherein the processor calculates the oscillation angle of the mirror unit around the oscillation axis by subtracting a piezoelectric signal from one of a pair of piezoelectric sensors from a piezoelectric signal from the other.

Claims

1. A mirror device comprising: a movable part including a mirror portion that reflects incident light; a drive unit connected to the movable part and that causes the mirror portion to swing around at least one pivot axis; an annular portion connected to the drive unit and arranged surrounding the drive unit; a fixed frame connected to the annular portion and arranged surrounding the annular portion; and a pair of piezoelectric sensors arranged on the annular portion and in a positional relationship symmetrical with respect to the pivot axis.

2. The mirror device according to claim 1, wherein each of the pair of piezoelectric sensors is composed of an upper electrode, a piezoelectric film, and a lower electrode, and the shapes of the pair of upper electrodes are symmetrical with respect to the pivot axis.

3. The mirror device according to claim 1, wherein the movable part comprises a pair of first support parts connected to the mirror part and arranged on a first axis, and a pair of movable frames connected to the pair of first support parts and facing each other across the first axis, and the pivot axis is the first axis or a second axis intersecting the first axis.

4. The mirror device according to claim 3, wherein the annular portion is connected to the drive unit and the fixed frame on the first axis or the second axis.

5. The mirror device according to claim 4, wherein the drive unit comprises a pair of second support members connected to the movable frame on the second axis and supporting the movable unit, and the pair of second support members are arranged on the second axis.

6. The mirror device according to claim 5, wherein the drive unit includes a first actuator having a pair of first piezoelectric elements connected to a pair of second support units and facing each other across the second axis.

7. The mirror device according to claim 6, wherein the drive unit includes a second actuator having a pair of second piezoelectric elements arranged around the first actuator and facing each other across the first axis.

8. The mirror device according to any one of claims 1 to 7, wherein when the mirror portion swings, the annular portion and the drive portion are displaced in opposite phases to each other in the thickness direction of the fixed frame.

9. An optical scanning apparatus comprising: a mirror device according to claim 1; and a processor for driving the drive unit, wherein the drive unit oscillates the mirror unit in accordance with a drive signal provided by the processor.

10. The optical scanning apparatus according to claim 9, wherein the processor calculates the oscillation angle of the mirror portion around the oscillating axis by subtracting the piezoelectric signal from one of the pair of piezoelectric sensors from the piezoelectric signal from the other.

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