Micromirror device and optical scanning apparatus

Abstract

This micromirror device includes a device part and a base part for supporting the device part. The device part includes: a mirror part for reflecting incident light, and an actuator for applying a rotational torque for swinging the mirror part around at least one axis. The base part is made of silicon or glass, is bonded to the device part without using an adhesive, and has a cavity with a depth in the thickness direction of the base part in a region facing at least the mirror part. When the surface of the base part facing the device part is defined as a first surface, and the opposite side of the first surface is defined as a second surface, the planar size on the first surface side of the cavity in a plan view of the base part is greater than that on the second surface side.

Description

Micromirror device and optical scanning device

[0001] The technology of the present disclosure relates to a micromirror 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] In laser projector applications, it is expected that micromirror devices will be used in high-brightness displays for next-generation wearable devices such as AR (Augmented Reality) glasses. For such applications, however, there is a demand for micromirror devices that are even smaller and have a wider scan angle.

[0004] 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.

[0005] A typical micromirror device used in a laser display includes a mirror portion and a piezoelectric actuator (see, for example, Japanese Patent Application Laid-Open Nos. 2022-73956 and 2020-101761). The mirror portion is freely oscillating around a first axis and a second axis that are orthogonal to each other. The actuator oscillates the mirror portion around the first axis and the second axis in response to a drive voltage supplied from an external device. The above-mentioned scan angle corresponds to the deflection angle of the mirror portion.

[0006] Performance indicators of laser displays include resolution and viewing angle. Resolution and viewing angle are related to the oscillation frequency and deflection angle of the mirror part of the micromirror device. For example, in a Lissajous scanning laser display, two-dimensional optical scanning is performed by simultaneously oscillating the mirror part around a first axis and a second axis at two different frequencies. The larger the deflection angle of the mirror part, the larger the optical scanning area becomes, and a larger image can be displayed with a shorter optical path length.

[0007] Such a micromirror device is mounted in a package including a circuit board for use. Japanese Patent Application Laid-Open No. 2022-73956 discloses that a pedestal is provided on the package side to ensure space between the micromirror device and the circuit board in order to suppress physical interference between the mirror portion of the micromirror device and the circuit board. The pedestal has a sidewall member that supports the micromirror device around the mirror portion. The pedestal is formed from a resin material or a metal material. When a resin material is used, the pedestal is produced by a method such as injection molding or using a three-dimensional printer, and when a metal material is used, the pedestal is produced by a method such as forging, cutting, or metal injection molding.

[0008] The micromirror device and the base are fabricated through separate manufacturing processes, and after they are fabricated, they are bonded together with an adhesive. The base, bonded to the micromirror device, is then further bonded to a circuit board with an adhesive.

[0009] In the micromirror device described in JP 2020-101761 A, the support substrate that functions as the base is made of the same silicon as the device portion including the mirror portion.

[0010] Considering applications such as AR glasses and laser projectors, further miniaturization of micromirror devices is required. When miniaturizing a micromirror device, the techniques described in JP 2022-73956 A and JP 2020-101761 A have a problem of insufficient durability.

[0011] The technique of the present disclosure provides a micromirror device and an optical scanning device that can suppress the lack of durability that accompanies miniaturization.

[0012] The micromirror device of the present disclosure comprises a device portion and a base portion that supports the device portion, and the device portion has a mirror portion that reflects incident light and an actuator that applies a rotational torque to oscillate the mirror portion around at least one axis, and the base portion is made of silicon or glass and is bonded to the device portion without using adhesive, and has a cavity that is deep in the thickness direction of the base portion at least in the area facing the mirror portion, and when the surface facing the device portion is defined as the first surface and the side opposite the first surface is defined as the second surface, the planar size of the first surface side of the cavity when the base portion is viewed in a plane is larger than the second surface side.

[0013] The material of the base is preferably single crystal silicon.

[0014] The actuator is arranged around the mirror portion and oscillates when the mirror portion is driven, and it is preferable that the planar size of the cavity is larger than the planar size of the actuator on the first surface side and larger than the planar size of the mirror portion on the second surface side.

[0015] It is preferable that the planar size of the cavity be gradually reduced from the first surface side toward the second surface side.

[0016] The cavity preferably has a first cavity and a second cavity that is disposed closer to the second surface than the first cavity and has a planar size smaller than that of the first cavity.

[0017] It is preferable that the planar size of the cavity continuously decreases from the first surface side toward the second surface side.

[0018] The planar shape of the cavity is preferably rectangular or circular throughout the thickness direction.

[0019] The cavity is preferably closed on the second surface side.

[0020] It is preferable that the mirror portion has a rib protruding toward the base portion on the surface facing the base portion.

[0021] The actuator preferably comprises a piezoelectric element.

[0022] The optical scanning device of the present disclosure is an optical scanning device including any one of the micromirror devices described above and a processor that controls an actuator, and the processor oscillates the mirror portion by providing a drive signal to the actuator.

[0023] According to the technology of the present disclosure, it is possible to suppress the lack of durability that accompanies miniaturization.

[0024] 1. A schematic diagram of an optical scanning device. A block diagram showing an example of the hardware configuration of a drive control unit. A plan view of a micromirror device as viewed from the light incident side. An external perspective view of the micromirror device. A view showing a state in which the mirror section has oscillated around a first axis. A view showing a state in which the mirror section has oscillated around a second axis. An exploded perspective view of the micromirror device. A cross-sectional view taken along line A-A in FIG. 4. A cross-sectional view of a micromirror device of a comparative example. A view showing a micromirror device mounted in a package. A view showing a silicon wafer. A view showing a manufacturing procedure for the micromirror device according to the first embodiment. A view showing a continuation of the manufacturing procedure shown in FIG. 12. A view showing a continuation of the manufacturing procedure shown in FIG. 13. A view showing a micromirror device according to a second embodiment. A view showing a manufacturing procedure for the micromirror device according to the second embodiment. A view showing a continuation of the manufacturing procedure shown in FIG. 16. A view showing a continuation of the manufacturing procedure shown in FIG. 17. A view showing a micromirror device according to a first modification of the first embodiment. A view showing a manufacturing procedure for a micromirror device according to a first modification of the first embodiment. A view showing a continuation of the manufacturing procedure shown in FIG. 20. A view showing a continuation of the manufacturing procedure shown in FIG. 21. A view showing a continuation of the manufacturing procedure shown in FIG. 22. A view showing a micromirror device according to a second modification of the first embodiment. Fig. 25 is an exploded perspective view of the micromirror device shown in Fig. 24. Fig. 26 is a table showing experimental results.

[0025] An example of an embodiment of the technology of the present disclosure will be described with reference to the accompanying drawings.

[0026] 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 L emitted from the light source 3 by the MMD 2 under the control of the drive controller 4. The surface 5 to be scanned is, for example, a screen.

[0027] MMD2 is the first axis a １ and the first axis a １ A second axis a perpendicular to 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 arrow is called the Z direction.

[0028] The light source 3 is a laser device that emits, for example, laser light as the light beam L. It is preferable that the light source 3 irradiates the light beam L perpendicularly to a reflecting surface 20A (see FIG. 3 ) of the mirror section 20 when the mirror section 20 of the MMD 2 is stationary.

[0029] The drive control unit 4 outputs drive signals to the light source 3 and the MMD 2 based on the optical scanning information. The light source 3 generates a light beam L based on the input drive signal and irradiates the MMD 2 with the light beam L. The MMD 2 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.

[0030] 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 L reflected by the mirror portion 20 is scanned so as to trace a Lissajous waveform, for example, on the surface to be scanned 5. This optical scanning method is called a Lissajous scanning method.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] The MMD driver 44 is an electric circuit that outputs a drive signal to the MMD 2 under the control of the CPU 40. In the MMD driver 44, the drive signal is a drive voltage for controlling the timing, period, and deflection angle of the oscillation of the mirror portion 20 of the MMD driver 44.

[0036] 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 L that scans the surface 5 to be scanned and the light emission timing of the light source 3.

[0037] Next, an example of the configuration of the MMD 2 will be described with reference to Figures 3 to 8. Figure 3 is a plan view showing an outline of the MMD 2, and Figure 4 is a perspective view showing the appearance of the MMD 2. Figures 5 and 6 are views showing the state in which the mirror section 20 oscillates. Figure 7 is an exploded perspective view of the MMD 2. Figure 8 is a diagram showing a schematic cross section of the MMD 2.

[0038] 3 and 4, the MMD 2 has a mirror portion 20, a first actuator 21, a second actuator 22, a first support portion 24, a second support portion 25, a connection portion 26, and a fixing frame 27. The MMD 2 is manufactured, for example, by etching a silicon substrate made of single crystal silicon. A specific example of a method for manufacturing the MMD 2 will be described later.

[0039] The mirror section 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 section 20. The reflective surface 20A is, for example, circular.

[0040] The first actuator 21 is disposed around the mirror section 20, has a ring-shaped planar shape when viewed in the XY plane, and surrounds the mirror section 20. The second actuator 22 is disposed around the mirror section 20 and the first actuator 21, has a ring-shaped planar shape, and surrounds the mirror section 20 and the first actuator 21. The second actuator 22 has a larger planar size than the first actuator 21.

[0041] The first support portion 24 supports the mirror portion 20 along the first axis a １ and the mirror part 20 is connected to the first axis a １ The first axis a is supported so as to be swingable around the first axis a. １ is in a plane including the reflecting surface 20A when the mirror unit 20 is stationary. For example, the first support unit 24 is １It is a torsion bar extending along the

[0042] The second support portion 25 connects the first actuator 21 and the second actuator 22 to the second axis a ２ The mirror part 20 and the first actuator 21 are connected to each other on the second axis a ２ The second axis a is supported so as to be swingable around the second axis a. ２ is the angle of the first axis a in a plane including the reflecting surface 20A when the mirror unit 20 is stationary. １ and perpendicular to each other.

[0043] The fixed frame 27 has, for example, a rectangular frame shape and surrounds the second actuator 22. The lengths of the fixed frame 27 in the X and Y directions are, for example, about 1 mm to 10 mm, and the thickness of the fixed frame 27 in the Z direction is, for example, about 5 μm to 0.2 mm.

[0044] The first actuator 21 and the second actuator 22 are piezoelectric actuators each having a piezoelectric element 31. The first actuator 21 is attached to the mirror section 20 along a first axis a １ The second actuator 22 applies a rotation torque around the second axis a ２ As a result, the mirror part 20 rotates about the first axis a １ Around and second axis a ２ Swinging around.

[0045] The first actuator 21 is an annular thin plate member that surrounds the mirror section 20, and is composed of a pair of a first movable section 21A and a second movable section 21B. The first movable section 21A and the second movable section 21B are each semi-annular. The first movable section 21A and the second movable section 21B are connected to a first axis a １ The shape is symmetrical with respect to the first axis a １ Connected above.

[0046] The second actuator 22 is an annular thin plate member that surrounds the mirror section 20 and the first actuator 21, and is composed of a pair of a first movable section 22A and a second movable section 22B. The first movable section 22A and the second movable section 22B are each semi-annular. The first movable section 22A and the second movable section 22B are connected to a second axis a ２The shape is symmetrical with respect to the second axis a ２ Connected above.

[0047] In the first actuator 21, a piezoelectric element 31 (see FIG. 8) is provided on each of the first movable portion 21A and the second movable portion 21B. In the second actuator 22, a piezoelectric element 31 (see FIG. 8) is provided on each of the first movable portion 22A and the second movable portion 22B.

[0048] The drive control unit 4 rotates the mirror unit 20 relative to the first actuator 21 along the first axis a １ a drive signal for swinging the mirror unit 20 about the second axis a ２ The drive control unit 4 supplies a drive signal to the mirror unit 20 at a resonance frequency corresponding to a natural frequency determined by the shapes of the mirror unit 20, the first actuator 21, and the second actuator 22, thereby resonatingly driving the mirror unit 20. This makes it possible to increase the deflection angle θ (see FIG. 8 ) at which the mirror unit 20 swings. The larger the maximum value of the deflection angle θ, the larger the scan angle, which is the range that can be scanned by light reflected by the mirror unit 20.

[0049] 5 and 6 specifically show the state in which the mirror section 20 is oscillating. As shown in FIG. 5, the mirror section 20 is oscillated along the first axis a １ 6, the second axis a ２ When driving the mirror section 20, the first actuators 21 and second actuators 22 arranged around the mirror section 20 deform in the same phase or in the opposite phase to the mirror section 20 in accordance with the deformation of the piezoelectric elements 31, and oscillate together with the mirror section 20.

[0050] In this example, the first actuator 21 and the second actuator 22 are configured as separate annular structures, but this is not limiting and they may be configured to coexist within a single structure. For example, a piezoelectric body may be divided and arranged within a single annular structure. By applying a first drive signal and a second drive signal to the two individual piezoelectric body portions thus divided, the first axis a１ Around and second axis a ２ It is possible to realize the surrounding mirror oscillation.

[0051] As shown in Figure 7, the MMD 2 comprises a device section 2A having a mirror section 20, a first actuator 21, a second actuator 22, a first support section 24, and a second support section 25, etc., and a base section 2B that supports the device section 2A and functions as a base for the device section 2A.

[0052] The base portion 2B has a cavity 34 that is deep in the thickness direction of the base portion 2B, at least in the region facing the mirror portion 20. If the surface facing the device portion 2A is defined as a first surface 34S1 and the side opposite the first surface 34S1 is defined as a second surface 34S2, the planar size of the cavity 34 on the first surface 34S1 side when the base portion 2B is viewed from above (i.e., the size in the X-Y plane) is larger than that on the second surface 34S2 side.

[0053] The cross section of the MMD 2 shown in Fig. 8 is taken along line A-A shown in Fig. 4 and Fig. 7. As shown in Fig. 8, the planar size of the cavity 34 decreases stepwise from the first surface 34S1 side toward the second surface 34S2 side.

[0054] Specifically, the cavity 34 has a first cavity 34A and a second cavity 34B. The second cavity 34B is disposed closer to the second surface 34S2 than the first cavity 34A and has a smaller planar size than the first cavity 34A. The planar size of the first cavity 34A is larger than the planar size of the second actuator 22, and the planar size of the second cavity 34B is larger than the planar size of the mirror portion 20.

[0055] In this example, the first cavity 34A and the second cavity 34B are both rectangular in plan view, with a width CL1 corresponding to the length of one side of the first cavity 34A being wider than a width CL2 corresponding to the length of one side of the second cavity 34B. As shown in FIG. 7 , the first cavity 34A and the second cavity 34B are substantially similar in shape, so the width of the first cavity 34A in the depth direction, which is perpendicular to the widths CL1 and CL2, is also wider than the second cavity 34B. Furthermore, the planar shape of the cavity 34A is rectangular throughout the entire thickness direction, although the planar size changes gradually. Furthermore, the second surface 34S2 of the cavity 34 is closed.

[0056] By providing the cavity 34 in the base portion 2B in this manner, physical interference between the mirror portion 20 and the base portion 2B when the mirror portion 20 oscillates can be suppressed. The deflection angle θ of the mirror portion 20 is larger than the deflection angles of the first actuator 21 and the second actuator 22. Therefore, the depth DP2 of the second cavity 34B in the thickness direction of the base portion 2B is made deeper than the depth DP1 of the first cavity 34A. Conversely, because the deflection angles of the first actuator 21 and the second actuator 22 are smaller than those of the mirror portion 20, the depth DP1 of the first cavity 34A can be allowed to be shallower than the depth DP2 of the second cavity 34B. Therefore, even if the planar size of the second cavity 34B is smaller than that of the first cavity 34A, there is no problem in terms of suppressing physical interference between the first actuator 21, the second actuator 22, and the base portion 2B.

[0057] Furthermore, by making the planar size of the second cavity 34B on the second surface 34S2 smaller than that of the first cavity 34A on the first surface 34S1, the rigidity of the base portion 2B is increased in the MMD 2 of the present disclosure. That is, when the cavity 34 is formed in the base portion 2B, a frame-shaped outer edge portion 34C remains around the cavity 34 (see also FIG. 7 ). The larger the planar size of the cavity 34 (represented by widths CL1 and CL2), the wider the widths W1 and W2 (see FIG. 8 ) of the outer edge portion 34C; there is a trade-off between the two. Therefore, by reducing the planar size of the second cavity 34B, the width W2 of the outer edge portion 34C can be increased. Naturally, when the mirror portion 20 or the like oscillates, stress is applied to the outer edge portion 34C. The wider the width W2 of the outer edge portion 34C, the more suppressed deformation of the outer edge portion 34C is, improving rigidity.

[0058] The MMD 200 of the comparative example shown in FIG. 9 is similar to the MMD 2 of the present disclosure, except for the device section 200A, etc., and the base section 200B. In the MMD 200 of the comparative example, the base section 200B also has a cavity 340 to avoid interference with the mirror section 20. However, the planar size of the cavity 340 is the same throughout the thickness direction from the first surface 340S1 to the second surface 340S2. The planar size of the cavity 340 is larger than the planar sizes of the first actuator 21 and the second actuator 22, and is the same as the planar size of the first cavity 34A of the MMD 2 of the present disclosure. Therefore, the width W1 of the outer edge portion 340C of the MMD 200 is the same throughout the thickness direction.

[0059] 8 , the outer edge 34C of the MMD 2 of the present disclosure differs from the outer edge 340C of the MMD 200 of the comparative example in that the width W2 on the second surface 34S2 side is wider than the width W1 on the first surface 34S1 side.

[0060] As shown in FIG. 10 , the MMD 2 is mounted in a package 36 having a circuit board 36B. The package 36 is provided with a window 36A that transmits the light beam L, located opposite the mirror unit 20. In the package 36, the main portion of the housing, excluding the window 36A and other parts, is made of ceramic, for example. The MMD 2 is fixed to the circuit board 36B by bonding the second surface 34S2 of the base unit 2B to the circuit board 36B with an adhesive. The wiring 36C electrically connects the MMD 2 and the circuit board 36B. For example, a thermosetting adhesive is used as the adhesive that bonds the base unit 2B and the circuit board 36B.

[0061] Next, an example of a method for manufacturing an MMD 2 will be described with reference to FIGS. 11 to 14. As shown in FIG. 11, the MMD 2 is manufactured by, for example, using two silicon wafers WF1 and WF2 and processing them by etching or the like. The silicon wafers WF1 and WF2 are, for example, single-crystal silicon. As is well known, a plurality of MMDs 2 are manufactured from the two bonded silicon wafers WF1 and WF2. In FIG. 11, each square indicated by dashed grid lines on the silicon wafers WF1 and WF2 corresponds to the area of ​​an individual MMD 2 chip.

[0062] 12 to 14 show a method for manufacturing an individual MMD 2, but in reality, processing is performed on each region of a plurality of MMDs 2 on the silicon wafers WF1 and WF2, and a plurality of MMDs 2 are manufactured collectively. After processing is performed on the silicon wafers WF1 and WF2, the individual MMD 2 regions are divided by dicing.

[0063] In FIGS. 12 to 14, the two substrates bonded to each MMD 2 are called a silicon substrate SB1 corresponding to the silicon wafer WF1 and a silicon substrate SB2 corresponding to the silicon wafer WF2.

[0064] 12, first, in step ST101, one silicon substrate SB2 is prepared. The silicon substrate SB2 is a substrate that mainly constitutes the base portion 2B of the MMD 2 (see also FIG. 10). As described above, the silicon substrate SB2 includes a silicon layer Si made of single crystal silicon, and a silicon oxide film SiO2 formed on one surface of the silicon layer Si.

[0065] In step ST102, oxide film patterning is performed. Specifically, a mask pattern (not shown) corresponding to the planar shape and planar size of the first cavity 34A is formed on the silicon oxide film SiO2, and then the unmasked areas of the silicon oxide film SiO2 are removed by, for example, dry etching to perform patterning.

[0066] Next, in step ST103, a resist mask RM is formed on the surface of the silicon substrate SB2 on which the oxide film patterning has been performed. The resist mask RM has a mask pattern in which an opening having the planar shape and planar size of the second cavity 34B is formed.

[0067] In step ST104, with the resist mask RM still formed, silicon etching is performed on the unmasked region of the silicon substrate SB2. This forms a part of the second cavity 34B. The etching in step ST104 is, for example, wet etching. When the silicon substrate SB2 is to be deeply excavated, as in the case of forming the cavity 34, anisotropic etching is performed, taking into account the crystalline structure of the silicon substrate SB2, so that the etching progresses easily. In step ST105, the resist mask RM is removed.

[0068] As shown in FIG. 13, in step ST106, after the resist mask RM is removed, silicon etching is further performed on the silicon substrate SB2. Like step ST104, the silicon etching in step ST106 is anisotropic etching that takes into account the crystalline structure of the silicon substrate SB2. The silicon oxide film SiO2 remains on the outer edge of the silicon substrate SB2, and the silicon oxide film SiO2 functions as a mask during silicon etching. Therefore, the area inside the silicon oxide film SiO2 corresponding to the planar size of the first cavity 34A is uniformly removed. In step ST104, a portion of the area corresponding to the planar size of the second cavity 34B is removed, making it one step deeper in the thickness direction. Therefore, the second cavity 34B is also removed while maintaining this step, so the area corresponding to the second cavity 34B is deeper in the thickness direction than the first cavity 34A. This results in the formation of the first cavity 34A and the second cavity 34B.

[0069] In step ST107, the silicon substrate SB2 and the silicon substrate SB1 are bonded together. The silicon substrate SB1 is bonded so as to face the processed surface of the silicon substrate SB2 that has been subjected to etching or the like. In the MMD2, the silicon substrate SB1 mainly constitutes the device section 2A. The bonding of the silicon substrate SB1 and the silicon substrate SB2 to each other is performed without using an adhesive. Various methods, such as plasma-assisted bonding and diffusion bonding, can be used to bond silicon substrates together without using an adhesive.

[0070] In step ST108, the silicon substrate SB1 is ground and polished to have the thickness of the device portion 2A.

[0071] In step ST109, a laminated film of the piezoelectric element 31 is formed on the silicon substrate SB1 by sputtering. In the laminated film of the piezoelectric element 31, a lower electrode layer, a piezoelectric layer, and an upper electrode layer are formed in this order from the silicon substrate SB1 side in FIG. 13. The lower electrode and upper electrode layers are made of a conductive metal material, and the piezoelectric layer is made of a piezoelectric material such as lead zirconate titanate (PZT, an acronym for Pb(Zr,Ti)O).

[0072] 14, in step ST110, a resist mask RM is formed on the laminated film of the piezoelectric element 31. Then, in step ST111, the laminated film is etched and the resist mask RM is removed. As a result, the piezoelectric element 31, which is a component of the first actuator 21 and the second actuator 22, is patterned.

[0073] In step ST112, a resist mask RM is formed on the surface on which the piezoelectric element 31 is formed. This resist mask RM is a mask for forming the mirror portion 20, the first actuator 21, and the second actuator 22, and is patterned according to their planar sizes and shapes. In step ST113, silicon etching is performed on the unmasked areas of the resist mask RM, and the resist mask RM is removed. The silicon etching in step ST113 is performed by dry etching, for example. As a result, the mirror portion 20, the first actuator 21, and the second actuator 22 are formed.

[0074] Thereafter, the silicon wafers WF1 and WF2 are diced and separated into individual MMDs 2. As an example, the MMD 2 of the present disclosure is manufactured by the above method. As shown in FIG. 10 , the second surface 34S2 of the MMD 2 is adhered to the package 36 with an adhesive, and wiring 36C is connected.

[0075] As described above, the MMD 2 according to the technology of the present disclosure includes a device portion 2A and a base portion 2B, the base portion 2B is made of silicon and is bonded to the device portion 2A without using adhesive, and has a cavity 34 that is deep in the thickness direction of the base portion 2B at least in the region facing the mirror portion 20. In the base portion 2B, if the surface facing the device portion 2A is defined as a first surface 34S1 and the side opposite to the first surface 34S1 is defined as a second surface 34S2, the planar size of the cavity 34 when the base portion 2B is viewed in plan is larger on the first surface 34S1 side than on the second surface 34S2 side.

[0076] First, in the MMD 2 according to the technology of the present disclosure, the base portion 2B in which the cavity 34 is formed is made of silicon. The device portion 2A, which has the mirror portion 20, the first actuator 21, and the second actuator, is bonded to the base portion 2B without using adhesive. This provides the following advantages compared to the method described in Japanese Patent Application Laid-Open No. 2022-73956, which uses a support substrate that is created using a manufacturing process different from that of the micromirror device made of silicon and is bonded to the micromirror device with adhesive.

[0077] First, by forming the base portion 2B from silicon, like the device portion 2A, the device portion 2A and the base portion 2B can be manufactured using the same manufacturing process as shown in Figures 12 to 14. This makes it easier to miniaturize the entire MMD 2, including the device portion 2A, compared to the method described in JP 2020-101761 A, in which the support substrate is manufactured using a separate manufacturing process. In addition, manufacturing costs can be reduced and manufacturing efficiency can be improved.

[0078] Second, because no adhesive is used to bond the device portion 2A and the base portion 2B, distortion caused by the use of adhesive is suppressed. That is, when a thermosetting adhesive is used as the adhesive, distortion occurs in the micromirror device due to the effects of heat applied to harden the adhesive and the shrinkage of the adhesive during thermal hardening. Distortion caused by the use of adhesive can easily cause malfunctions and breakage during long-term operation, resulting in reduced durability. Compared to JP 2020-101761 A, the MMD2 according to the technology disclosed herein can suppress the use of adhesive other than for bonding to the package 36, thereby suppressing distortion caused by adhesive. Furthermore, because the base portion 2B, which is closer to the device portion 2A than the package 36, is bonded without the use of adhesive, the effects of distortion on the device portion 2A, such as a lack of durability, can be further reduced.

[0079] Furthermore, distortion caused by the use of adhesive varies from one MMD to another, resulting in variations in the frequency characteristics of each MMD 2. Such variations in frequency characteristics cause a decrease in yield. By reducing the use of adhesive, the variations in frequency characteristics can be reduced, and as a result, a decrease in yield can be reduced.

[0080] Furthermore, in the MMD 2 according to the technology of the present disclosure, the planar size of the cavity 34 is relatively large on the first surface 34S1 side and relatively small on the second surface 34S2 side. Therefore, compared to the MMD 200 according to the comparative example shown in FIG. 9 , as described in JP 2020-101761 A, the outer edge 34C of the base portion 2B has a wider width W2 on the second surface 34S2 side. As a result, compared to the MMD 200 of the comparative example, the MMD 2 according to the technology of the present disclosure can, even when the overall size is reduced, improve the rigidity of the base portion 2B that supports the device portion 2A while suppressing physical interference with movable parts such as the mirror portion 20 of the device portion 2A, thanks to the ingenious shape of the cavity 34.

[0081] Low rigidity of the base portion 2B naturally leads to a decrease in the durability of the device portion 2A. The decrease in durability due to insufficient rigidity becomes more pronounced as the deflection angle θ of the mirror portion 20 increases. In addition, insufficient rigidity leads to a decrease in energy efficiency, such that the kinetic energy of the mirror portion 20 leaks to the base portion 2B and is wasted. Since the larger the deflection angle θ, the greater the input energy, the more pronounced the decrease in energy efficiency becomes. Furthermore, insufficient rigidity also affects drive stability, such that the mirror portion 20 does not resonate even when a drive signal corresponding to the natural frequency of the mirror portion 20 is input. The decrease in drive stability becomes particularly pronounced when the mirror portion 20 is driven resonantly.

[0082] Furthermore, a lack of rigidity in the base portion 2B manifests itself as variations in the frequency characteristics of the individual MMDs 2. As described above, such variations in frequency characteristics cause a decrease in yield. By increasing the rigidity of the base portion 2B, the variations in frequency characteristics can be suppressed, and as a result, a decrease in yield can also be suppressed.

[0083] In this way, the MMD 2 according to the technology of the present disclosure can suppress the lack of durability that accompanies miniaturization by improving the rigidity of the base portion 2B. Furthermore, improving the rigidity of the base portion 2B can also contribute to improving drive stability and suppressing variations in frequency characteristics.

[0084] Moreover, the material of the base portion 2B of the MMD 2 is, for example, single crystal silicon. Since the silicon wafers WF1 and WF2 are generally made of single crystal silicon, they are easier to manufacture than when, for example, polycrystalline silicon is used.

[0085] In the MMD 2 according to the technology of the present disclosure, the actuators, shown as examples of the first actuator 21 and the second actuator 22, are arranged around the mirror section 20 and oscillate when driving the mirror section 20. The planar size of the cavity 34 is larger than the planar size of the first actuator 21 and the second actuator 22 on the first surface 34S1 side, and larger than the planar size of the mirror section 20 on the second surface 34S2 side. This makes it possible to suppress physical interference with the first actuator 21 and the second actuator 22 in addition to the mirror section 20.

[0086] In the MMD 2 according to the technology of the present disclosure, as an example, the planar size of the cavity 34 decreases stepwise from the first surface 34S1 side to the second surface 34S2 side. By decreasing the planar size stepwise, it is easier to keep the volume of the cavity 34 to the minimum necessary compared to when the volume decreases continuously. This makes it possible to minimize the reduction in rigidity caused by forming the cavity 34.

[0087] Furthermore, in the MMD 2 according to the technology of the present disclosure, as an example, the cavity 34 has a first cavity 34A and a second cavity 34B that is disposed closer to the second surface 34S2 than the first cavity 34A and has a smaller planar size than the first cavity 34. The MMD 2 often has two types of movable parts with different planar sizes, such as the mirror unit 20 and the actuators disposed around it. By providing two cavities, it is possible to realize an appropriate shape for the cavity 34 according to the two movable parts.

[0088] In the MMD 2 according to the technique of the present disclosure, the planar shape of the cavity 34 is, for example, rectangular throughout the thickness direction. By making the shape uniform throughout the thickness direction, manufacturing is easy.

[0089] In the MMD 2 according to the technology of the present disclosure, the cavity 34 is closed on the second surface 34S2 side, for example, which can improve rigidity compared to when the second surface 34S2 of the cavity 34 is open.

[0090] [Second embodiment] In the above-described first embodiment, an example was described in which the second surface 34S2 side of the second cavity 34B of the MMD 2 is closed, but as in the MMD 2 of the second embodiment shown in Figure 15, the second surface 34S2 side of the second cavity 34B may be open.

[0091] Such an MMD 2 of the second embodiment is manufactured, for example, by the method shown in Figures 16 to 18. In the manufacturing method of the MMD 2 of the second embodiment shown in Figures 16 to 18, explanations of the same parts as in the manufacturing method of the MMD 2 of the first embodiment shown in Figures 11 to 14 will be omitted, and the following explanation will focus on the differences.

[0092] 16, first, in step ST201, one silicon substrate SB2 is prepared, and in step ST202, an oxide film is patterned. Steps ST201 and ST202 are similar to steps ST101 and ST102 shown in FIG.

[0093] Next, in step ST203, the surface of the silicon substrate SB2 on which the oxide film patterning has been performed is subjected to silicon etching. The silicon etching in step ST203 is anisotropic etching that takes into account the crystal structure of the silicon substrate SB2, similar to step ST104 in FIG. 12. This forms the first cavity 34A.

[0094] In step ST204, the silicon substrate SB1 is bonded to the silicon substrate SB2 so as to face the first cavity 34A. The bonding method is the same as that in step ST107 of the first embodiment shown in Fig. 13, and is a method that does not use adhesive. In step ST205, the silicon substrate SB1 is ground and polished, similar to that in step ST108 of the first embodiment shown in Fig. 13.

[0095] The method of forming the piezoelectric element 31 from steps ST206 to ST208 shown in FIG. 17 is the same as the method of forming the piezoelectric element 31 from steps ST109 to ST111 of the first embodiment shown in FIGS.

[0096] In step ST209, a resist mask RM is formed on the second surface 34S2 of the silicon substrate SB2. This resist mask RM is a mask for forming the second cavity 34B. As shown in FIG. 18 , in step ST210, silicon etching is performed on the second surface 34S2 of the silicon substrate SB2, and the resist mask RM is removed. This forms the second cavity 34B. Because the silicon substrate SB2 is etched from the second surface 34S2 side, the second surface 34S2 side of the cavity 34 is open. In other words, in the MMD2 of Modification 1, the second surface 34S2 of the cavity 34 is not closed.

[0097] In FIG. 18, steps ST211 and ST212 are the same as steps ST112 and ST113 of the first embodiment shown in FIG.

[0098] In the MMD 2 of the second embodiment, the second surface 34S2 side of the cavity 34 is open and not closed, so the rigidity is reduced compared to when the cavity is closed as in the first embodiment, but other effects are the same as those of the first embodiment. Also, the MMD 2 of the second embodiment has the advantage of being able to reduce the number of steps in the manufacturing process compared to the MMD 2 of the first embodiment shown in Figures 12 to 14.

[0099] [Modification 1 of First Embodiment] Furthermore, as in the MMD2 of Modification 1 of the first embodiment shown in Figure 19, a rib RB that protrudes toward the base portion 2B may be provided on the surface of the mirror portion 20 that faces the base portion 2B. Providing the rib RB can improve the rigidity of the mirror portion 20. In the MMD2 of Modification 1 shown in Figure 19, the second surface 34S2 side of the cavity 34 is closed, similar to the MMD2 shown in Figure 8. An example of a manufacturing method for the MMD2 of Modification 1 shown in Figure 19 is shown in Figures 20 to 23.

[0100] As shown in Fig. 20, steps ST301 to ST305 for processing the silicon substrate SB2 are substantially the same as steps ST101 to ST105 of the first embodiment shown in Fig. 12. However, step ST304 differs in that the depth of the second cavity 34B formed in the silicon substrate SB2 is deeper than step ST104.

[0101] Steps ST306 to ST309 shown in Figure 21 show a processing procedure for a silicon substrate SB1. In the MMD2 in which a rib RB is provided, an SOI (Silicon On Insulator) substrate is used as the silicon substrate SB1. In the SOI substrate, a silicon layer Si is further formed on a silicon oxide film SiO2 that serves as an insulating film. In step ST306, an SOI substrate is prepared as the silicon substrate SB1.

[0102] In step ST307, a resist mask RM is formed on one surface of the silicon substrate SB1. This resist mask RM is used to form the first cavity 34A and the rib RB. In step ST308, silicon etching is performed on the unmasked areas of the silicon substrate SB1. Then, in step ST309, the resist mask RM is removed and oxide film etching is performed. This forms the first cavity 34A and the rib RB.

[0103] 22, in step ST310, the silicon substrate SB2 processed as shown in Fig. 20 is bonded to the silicon substrate SB1 processed as shown in Fig. 21. The bonding direction is such that the first cavity 34A and the second cavity 34B face each other, and the bonding method is a method that does not use an adhesive, as shown in Fig. 13.

[0104] Steps ST311 to ST313 shown in FIG. 22 and steps ST314 to ST316 shown in FIG. 23 are similar to steps ST108 to ST113 of the first embodiment shown in FIGS. 13 and 14, and therefore description thereof will be omitted.

[0105] By the above method, the MMD 2 of Modification 1 provided with the reinforcing ribs RB can be manufactured. The MMD 2 of Modification 1 is similar to the MMD 2 of the first embodiment shown in Figure 8 except for the provision of the ribs RB, and therefore provides the same effects as the first embodiment. Furthermore, by manufacturing the MMD 2 of Modification 1 using the above manufacturing method, the ribs RB can be formed in the same process as the manufacturing process for the device portion 2A, which improves manufacturing efficiency and contributes to reducing manufacturing costs.

[0106] [Modification 2 of First Embodiment] Furthermore, unlike the MMD 2 of the first embodiment having the first cavity 34A and the second cavity 34B described above, the planar size of the cavity 34 may change continuously rather than stepwise. In the MMD 2 of Modification 2 shown in Figures 24 and 25, the wall surfaces of the cavity 34 are inclined, so that the planar size of the cavity 34 continuously decreases from the first surface 34S1 side toward the second surface 34S2 side. In the MMD 2 of Modification 2, too, the planar size of the cavity 34 on the first surface 34S1 side is larger than the sizes of the first actuator 21 and the second actuator 22, and the planar size on the second surface 34S2 side is larger than the planar size of the mirror portion 20.

[0107] The method for forming the cavity 34 in Modification 2 uses anisotropic etching that takes into account the crystalline structure of the silicon substrate. That is, wet etching is performed so that the lines along which the crystalline structure is likely to collapse coincide with the inclined surfaces of the cavity 34. With wet etching that does not take the crystalline structure into account, etching proceeds isotropically, resulting in curved inner wall surfaces of the cavity 34. However, by performing anisotropic etching that takes the crystalline structure into account, it is possible to form linear inner wall surfaces of the cavity 34.

[0108] Furthermore, the technology of the present disclosure can be applied to various other modified examples. For example, in the above embodiment, the MMD 2 having the mirror unit 20 that oscillates around two axes has been described as an example, but the technology of the present disclosure may also be applied to an MMD having a mirror unit that oscillates around one axis. When the mirror unit 20 oscillates around one axis, only one actuator is required.

[0109] Although the cavity 34 has been described as having a rectangular planar shape, it may have a circular shape. Here, the circular shape includes not only a perfect circular shape but also an elliptical shape and an oval shape.

[0110] Furthermore, the actuator that drives the mirror section 20 has been described as a piezoelectric actuator using the piezoelectric element 31, but it may be an actuator other than a piezoelectric actuator, for example, an electrostatic actuator.

[0111] Although the example in which the mirror unit 20 is resonantly driven has been described, it is not necessary to resonantly drive the mirror unit 20. However, resonant driving increases the deflection angle θ of the mirror unit 20. Since a larger deflection angle θ requires higher rigidity, the technology of the present disclosure is particularly effective when resonantly driving the mirror unit 20.

[0112] Furthermore, in the above embodiment, the base portion 2B is made of silicon, but glass may be used instead of silicon. Even when glass is used as the base portion 2B, etching to form the cavity 34 can be performed in a manner similar to that used for silicon. Furthermore, bonding to the device portion 2A can be performed without using adhesive, as with silicon. Therefore, even when glass is used as the base portion 2B material instead of silicon, the same effects as those described above can be obtained.

[0113] [Experimental Results] Fig. 26 shows the results of an experiment on the variations in durability and frequency characteristics of three aspects: the MMD 2 of the first embodiment shown in Fig. 8, the MMD 2 of the second embodiment shown in Fig. 15, and a comparative example. The comparative example is a modified example of the MMD 200 shown in Fig. 9, in which the second surface 340S2 side of the cavity 340 is open.

[0114] As shown in FIGS. 8 and 15 , the planar size of the cavity 34 varies in the thickness direction in the MMDs 2 of the first and second embodiments, being smaller on the second surface side than on the first surface 34S1 side. As a result, the width W2 of the outer edge 34C on the second surface 34S2 side is wider than the width W1 on the first surface 34S1 side. In contrast, as shown in FIG. 9 , the planar size of the cavity 34 does not vary in the thickness direction in the comparative example. As a result, the width W1 of the outer edge 34C does not change from the first surface 340S1 side to the second surface 340S2 side. The planar size of the first surface 34S1 side in the first and second embodiments is the same as the planar size of the first surface 340S1 side in the comparative example. Therefore, the width W2 of the outer edge 34C on the second surface 34S2 side in the first and second embodiments is wider than the width of the outer edge 34C in the comparative example. Therefore, the first and second embodiments have higher rigidity than the comparative example.

[0115] In the first embodiment, as shown in Fig. 8, the second surface 34S2 side of the cavity 34 is closed, whereas in the second embodiment, as shown in Fig. 15, the cavity 34 is not closed and the second surface 34S2 side is open. As described above, the comparative example is a modified example of the MMD 200 shown in Fig. 9, and similar to the second embodiment shown in Fig. 15, the cavity 340 is not closed and the second surface 340S2 side is open.

[0116] The experiment was conducted on a plurality of MMDs 2 according to the first and second embodiments and a plurality of MMDs 200 according to the comparative example. The measurement time ranges for the plurality of MMDs 2 and MMDs 200 are shown for durability, with longer times indicating higher evaluations. The variation in frequency characteristics was measured by measuring the MMDs 2 and MMDs 200 along the first axis a. １ and the second axis a ２ When the first axis a is driven to resonate, the maximum and minimum variations in the individual differences in the measured resonant frequency values ​​are shown, and the smaller the ± error, the higher the evaluation. １ and the second axis a ２ The variation in each resonance frequency was calculated individually, and the value with the larger variation was recorded.

[0117] In the durability test, the mirror part 20 was swung around two axes in two preset modes, a first mode and a second mode, and the time until the mirror part 20 was broken was measured. １ The scan angle around the axis is 55°, and the second axis a ２ The second mode is a two-axis small scan angle mode in which the scan angle around the first axis is 37°. １ The scan angle around the axis is 68°, and the second axis a ２ This is a two-axis large scan angle mode in which the scan angle is relatively large, with the scan angle around 37°. Here, the scan angle is the full range of angles that can be scanned by the light reflected by the mirror unit 20 while the mirror unit 20 is oscillated when incident light L is perpendicular to the mirror unit 20, and is expressed as a full angle. In order to match the target scan angle, the first axis a １ and the second axis a ２Two drive voltage signals of different frequencies, which correspond to the respective resonance frequencies around the two axes, were simultaneously applied to the actuator, and the scan angle was adjusted by the voltage amplitude. The scan angle was measured by irradiating laser light from vertically above the mirror section 20, projecting the trajectory of the light reflected by the mirror section 20 onto a screen plate, and measuring the length of the trajectory of the light on the screen plate using a camera or the like. The resonance frequency was determined as the frequency at which the scan angle was largest when the drive frequency was changed.

[0118] In the first mode, in which the scan angle θ is relatively small, the time until the mirror section 20 is destroyed is 3000 hours or more in both the first and second embodiments, while it is 100 to 200 hours in the comparative example. In the second mode, in which the scan angle θ is relatively large, the time until the mirror section 20 is destroyed is 3000 hours or more in the first embodiment, while it is 1000 to 1200 hours or more in the second embodiment. In the comparative example, it is 2 to 20 hours.

[0119] The variation in frequency characteristics was ±2% in the first embodiment and ±7% in the second embodiment, while it was ±15% in the comparative example.

[0120] From the above, in the experimental results shown in Figure 26, the first embodiment exhibits the best results in both durability and frequency characteristic variation. Even when comparing the second embodiment, in which the second surface 34S2 side of the cavity 34 is not closed, with the comparative example, the second embodiment exhibits better results in both durability and frequency characteristic variation. The structural difference between the second embodiment and the comparative example is that the planar size of the second surface 34S2 side of the cavity 34 is smaller, and the width W2 of the outer edge portion 34C is correspondingly wider. This shows that the configuration of the cavity 34 of the MMD 2 according to the technology disclosed herein exhibits superior results in terms of durability and frequency characteristic compared to the comparative example.

[0121] Furthermore, from the above description, the techniques described in the following supplementary paragraphs can be understood.

[0122] [Supplementary Item 1] A micromirror device comprising a device portion and a base portion supporting the device portion, wherein the device portion has a mirror portion that reflects incident light, and an actuator that applies rotational torque to oscillate the mirror portion around at least one axis, wherein the base portion is made of silicon or glass and is bonded to the device without using an adhesive, and wherein at least a region facing the mirror portion has a cavity that is deep in the thickness direction of the base portion, wherein when the surface facing the device portion is defined as a first surface and the side opposite the first surface is defined as a second surface, the planar size of the first surface side of the cavity in a plan view of the base portion is larger than that of the second surface side. [Supplementary Item 2] The micromirror device according to Supplementary Item 1, wherein the material of the base portion is single crystal silicon. [Supplementary Item 3] The micromirror device according to Supplementary Item 1 or Supplementary Item 2, wherein the actuators are arranged around the mirror section and oscillate when the mirror section is driven, and the planar size of the cavity is larger than the planar size of the actuators on the first surface side and larger than the planar size of the mirror section on the second surface side. [Supplementary Item 4] The micromirror device according to any one of Supplementary Item 1 to Supplementary Item 3, wherein the planar size of the cavity decreases stepwise from the first surface side toward the second surface side. [Supplementary Item 5] The micromirror device according to any one of Supplementary Item 1 to Supplementary Item 3, wherein the cavity has a first cavity and a second cavity that is arranged closer to the second surface side than the first cavity and is smaller in planar size than the first cavity. [Supplementary Item 6] The micromirror device according to any one of Supplementary Item 1 to Supplementary Item 3, wherein the planar size of the cavity continuously decreases from the first surface side toward the second surface side. [Supplementary Item 7] The micromirror device according to any one of Supplementary Items 1 to 6, wherein the planar shape of the cavity is rectangular or circular throughout the thickness direction. [Supplementary Item 8] The micromirror device according to any one of Supplementary Items 1 to 7, wherein the cavity is closed on the second surface side.[Supplementary Item 9] The micromirror device according to any one of Supplementary Items 1 to 8, wherein the mirror portion has a rib on a surface facing the base portion that protrudes toward the base portion. [Supplementary Item 10] The micromirror device according to any one of Supplementary Items 1 to 9, wherein the actuator has a piezoelectric element. [Supplementary Item 11] The micromirror device according to any one of Supplementary Items 1 to 10, wherein the actuator oscillates the mirror portion by resonant driving. [Supplementary Item 12] An optical scanning device comprising: the micromirror device according to any one of Supplementary Items 1 to 11; and a processor that controls the actuator, wherein the processor oscillates the mirror portion by providing a drive signal to the actuator.

[0123] 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.

[0124] The above-described description and illustrations are a detailed explanation of the parts related to the technology of the present disclosure and are merely an example of the technology of the present disclosure. For example, the above description of the configuration, functions, actions, and effects is an explanation of an example of the configuration, functions, actions, and effects of the parts related to the technology of the present disclosure. Therefore, it goes without saying that unnecessary parts may be deleted, new elements may be added, or elements may be replaced in the above-described description and illustrations, as long as they do not deviate from the gist of the technology of the present disclosure. Furthermore, to avoid confusion and facilitate understanding of the parts related to the technology of the present disclosure, the above-described description and illustrations omit explanations of common technical knowledge that do not require particular explanation to enable the implementation of the technology of the present disclosure.

[0125] In this specification, "A and / or B" is synonymous with "at least one of A and B." In other words, "A and / or B" means that it may be only A, only B, or a combination of A and B. Furthermore, in this specification, the same concept as "A and / or B" is also applied when three or more things are expressed by connecting them with "and / or."

[0126] The disclosure of Japanese Patent Application No. 2023-101251, filed on June 20, 2023, is incorporated herein by reference in its entirety. In addition, all documents, patent applications, and technical standards described herein are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard was specifically and individually indicated to be incorporated by reference.

Claims

1. A micromirror device comprising a device portion and a base portion supporting the device portion, the device portion having a mirror portion that reflects incident light, and an actuator that applies a rotational torque to cause the mirror portion to oscillate around at least one axis, the base portion being made of a material such as silicon or glass and being joined to the device portion without the use of adhesive, the base portion having a cavity with a depth in the thickness direction of the base portion at least in a region facing the mirror portion, and when a surface facing the device portion is defined as a first surface and an opposite surface to the first surface is defined as a second surface, the planar size of the first surface side of the cavity when the base portion is viewed in a plane is larger than that of the second surface side.

2. The micromirror device according to claim 1, wherein the material of the base portion is single crystal silicon.

3. The micromirror device of claim 1, wherein the actuator is disposed around the mirror portion and oscillates when the mirror portion is driven, and the planar size of the cavity is larger than the planar size of the actuator on the first surface side and larger than the planar size of the mirror portion on the second surface side.

4. The micromirror device according to claim 1, wherein the cavity has a planar size which decreases stepwise from the first surface side toward the second surface side.

5. The micromirror device according to claim 1, wherein the cavity comprises a first cavity and a second cavity that is disposed closer to the second surface than the first cavity and has a planar size smaller than that of the first cavity.

6. The micromirror device according to claim 1, wherein the cavity has a planar size that continuously decreases from the first surface side toward the second surface side.

7. The micromirror device according to claim 1, wherein the planar shape of the cavity is rectangular or circular over the entire area in the thickness direction.

8. The micromirror device according to claim 1, wherein the cavity is closed on the second surface side.

9. The micromirror device according to claim 1, wherein the mirror section has a surface facing the base section, the surface being provided with a rib protruding toward the base section.

10. The micromirror device of claim 1, wherein the actuator comprises a piezoelectric element.

11. The micromirror device according to claim 1, wherein the actuator oscillates the mirror portion by resonant driving.

12. An optical scanning device comprising: the micromirror device according to claim 1; and a processor that controls the actuator, wherein the processor oscillates the mirror portion by applying a drive signal to the actuator.