Micromirror Devices

Abstract

The micromirror device (1) of the present invention comprises: a reflector portion (12); a first actuator (14) arranged in a ring shape around the reflector portion (12) and causing the reflector portion (12) to reciprocate around a first axis (a1); and a second actuator (16) causing the reflector portion (12) to reciprocate around a second axis (a2) and causing the reflector portion (12) and the first actuator (14) to rotate around the first axis (a1) in opposite phases to achieve a resonance frequency A of a lowest-order resonance mode. , the resonance frequency B of the lowest-order resonance mode in the resonance mode in which the reflector portion (12) and the first actuator (14) vibrate with opposite phases in directions orthogonal to both the first axis (a1) and the second axis (a2), the frequency difference F=A-B between the resonance frequency A and the resonance frequency B, the resonance frequency C which is smaller than the frequency difference F and closest to the frequency difference F, and the resonance frequency D which is larger than the frequency difference F and closest to the frequency difference F satisfy F-C≥20Hz and F-D≤-150Hz.

Description

Technical Field

[0001] The invention relates to a micromirror device. Background Art

[0002] As one of the micro-electromechanical systems (MEMS) devices made using silicon (Si) micromachining technology, a micromirror device is known. The micromirror device is small and has low power consumption, so it is expected to be widely used, for example, laser displays such as head-up displays and retinal displays using lasers, and even optical diagnostic scanners such as optical coherence tomography scanners. The main use of micromirror devices is for scanners such as laser displays and optical diagnostic scanners that perform optical scanning by displacement of the reflector part, so they are also called MEMS scanners.

[0003] There are various driving modes for micromirror devices. The piezoelectric driving mode utilizing the deformation of the piezoelectric element has a higher torque density defined by the magnitude of the torque generated per unit mass of the actuator than other modes. Therefore, the piezoelectric driving mode has the advantages of being small and being able to obtain a relatively large displacement angle as the displacement angle of the reflector portion, and is therefore expected to be used for applications requiring a large displacement angle. In particular, in applications requiring a large displacement angle such as laser displays, a resonant drive that causes the reflector portion to resonate is mainly used. In the case of adopting a resonant drive, the magnitude of the torque of the piezoelectric driving mode will become a greater advantage.

[0004] The general structure of a micromirror device suitable for a laser display comprises: a reflector portion that can rotate freely around two axes, a first axis and a second axis, which are orthogonal to each other; and a piezoelectrically driven actuator that causes the reflector portion to reciprocate around the first axis and the second axis according to a driving voltage of the piezoelectric body (see Japanese Patent Gazette No. 2017-132281).

[0005] As one of the performance indicators of the laser display, resolution can be cited, which is greatly affected by the driving frequency and displacement angle of the reflector part of the micromirror device. For example, in a general raster scanning laser display, two-dimensional optical scanning is performed by reciprocating the reflector part of the micromirror device around the first axis and the second axis at two different driving frequencies. When performing two-dimensional optical scanning, the high-speed side of the two driving frequencies is usually set to above 10kHz, and the low-speed side is set to 10 to 100Hz. Basically, the greater the driving frequency and displacement angle of the rotation on the high-speed side, the higher the resolution of the laser display. From the above viewpoint, the driving frequency of the high-speed side is usually set to a resonant frequency of more than 10kHz, and the reflector part is driven at a larger displacement angle through resonance drive.

[0006] When the reflector portion is driven in a drive mode of a specific resonant frequency in the micromirror device as described above, an unnecessary resonance may sometimes be generated at a frequency different from the resonant frequency of the drive mode, causing normal optical scanning to be hindered by abnormal vibrations accompanied by the unnecessary resonance. Hereinafter, the resonance mode that generates the above-mentioned unnecessary resonance is referred to as an abnormal vibration mode.

[0007] Japanese Patent Publication No. 2013-114015 states that when the difference frequency between the n-times frequency (n is a natural number) of the resonance frequency of the driving mode and the resonance frequency of the abnormal vibration mode is small, the abnormal vibration mode is excited. In Japanese Patent Publication No. 2013-114015, setting the differential frequency to above 500 Hz is considered to be a benchmark for suppressing abnormal vibrations, and as a method for suppressing abnormal vibrations, a method of adding a structure such as limiting displacement in the abnormal vibration mode to the structure of the micromirror device is proposed. Summary of the invention

[0008] Technical issues to be solved by the invention

[0009] However, the addition of unnecessary structures of the structure can reduce manufacturing stability due to the complexity of the structure. In addition, the increase in the mass of the micromirror device can cause the natural vibration frequency to decrease, so that the resonant frequency of the drive mode can significantly decrease. The decrease in the resonant frequency of the drive mode can cause the reduction of the displacement angle of the reflector portion, so it is not preferred.

[0010] Furthermore, according to the research of the present inventors, in a micromirror device having a shape different from that described in Japanese Patent Gazette No. 2013-114015, the abnormal vibration mode may sometimes be excited even when the difference frequency between the resonant frequency of the driving mode, which is n times (here, n is a natural number), and the resonant frequency of the abnormal vibration mode differs by more than 500 Hz.

[0011] The inventors of the present invention have considered a micromirror device comprising: a first actuator having a first piezoelectric element arranged in a ring shape around a reflector portion, connected to the reflector portion and causing the reflector portion to reciprocate around a first axis by periodically deforming the first piezoelectric element; and a second actuator having a second piezoelectric element and causing the reflector portion to reciprocate around a second axis orthogonal to the first axis by periodically deforming the second piezoelectric element.

[0012] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a micromirror device capable of suppressing abnormal vibration in the micromirror device having the above structure.

[0013] Means for solving technical problems

[0014] Specific methods for solving the above problems include the following.

[0015] <1> A micromirror device having a reflector portion, the reflector portion having a reflective surface for reflecting incident light, the micromirror device changing the direction of the reflective surface in two dimensions by reciprocating the reflector portion about two axes, a first axis and a second axis, which intersect each other, and comprising:

[0016] a first actuator having a first piezoelectric element arranged in a ring shape around the mirror portion, connected to the mirror portion, and causing the mirror portion to reciprocate around a first axis by periodically deforming the first piezoelectric element; and

[0017] The second actuator includes a second piezoelectric element and causes the mirror portion to reciprocate around the second axis by periodically deforming the second piezoelectric element.

[0018] The resonance frequency of the lowest-order resonance mode in which the mirror portion and the first actuator reciprocate around the first axis in phases opposite to each other among a plurality of resonance modes having different resonance frequencies is defined as A.

[0019] The resonance frequency of the lowest-order resonance mode in which the mirror portion and the first actuator vibrate in opposite phases in directions orthogonal to both the first axis and the second axis among the plurality of resonance modes is denoted as B.

[0020] The difference AB between the resonant frequency A and the resonant frequency B is defined as the frequency difference F.

[0021] The resonance frequency of the resonance mode having a frequency smaller than the resonance frequency of the frequency difference F and having a resonance frequency closest to the frequency difference F among the plurality of resonance modes is defined as C,

[0022] The resonance frequency of the resonance mode having a frequency greater than the resonance frequency of the frequency difference F and having a resonance frequency closest to the frequency difference F among the plurality of resonance modes is set to D. In this case,

[0023] The difference ΔF1 between the frequency difference F and the resonant frequency C satisfies

[0024] ΔF1=FC≥20Hz,

[0025] and,

[0026] The difference ΔF2 between the frequency difference F and the resonant frequency D satisfies

[0027] ΔF2=FD≤-150Hz.

[0028] <2> The micromirror device according to <1>, wherein:

[0029] The difference ΔF1 and the difference ΔF2 satisfy

[0030] ΔF1 ≥ 100Hz,

[0031] ΔF2≤-400Hz.

[0032] <3> The micromirror device according to <1> or <2>, wherein:

[0033] The mirror portion and the first actuator are connected via a first connection portion extending along the first axis.

[0034] <4> The micromirror device according to any one of <1> to <3>, comprising:

[0035] an annular movable frame surrounding the first actuator; and

[0036] a second connection portion connecting the movable frame and the first actuator,

[0037] The second actuator reciprocates the mirror portion around the second axis via the movable frame.

[0038] <5> The micromirror device according to <4>, wherein:

[0039] The second connection portion extends along the first axis.

[0040] <6> The micromirror device according to any one of <1> to <5>, wherein:

[0041] The second actuator includes two or more rectangular plate-shaped portions, the two or more rectangular plate-shaped portions include a meandering structure folded back in a meandering shape via a connecting portion, and the two or more rectangular plate-shaped portions each include a second piezoelectric element.

[0042] <7> The micromirror device according to any one of <1> to <6>, wherein:

[0043] The resonance frequency A is 10 kHz or more.

[0044] Effects of the Invention

[0045] According to the present invention, it is possible to provide a micromirror device capable of suppressing abnormal vibration. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 is a top view of a micromirror device according to an embodiment.

[0047] Figure 2 It is a diagram showing a cross-sectional structure of a part of a micromirror device.

[0048] Figure 3 This is a perspective view of the structure of the micromirror device according to the embodiment as viewed from the upper surface side.

[0049] Figure 4 This is a perspective view of the structure of the micromirror device according to the embodiment as viewed from the bottom surface side.

[0050] Figure 5 This is a diagram for explaining a method of detecting the presence or absence of abnormal vibration.

[0051] Figure 6 is a diagram showing a scan line detected by a photodetector, Figure 6 A represents the scanning line when abnormal vibration occurs. Figure 6 B represents a normal scan line.

[0052] Figure 7 This is a spectrum analysis diagram when abnormal vibration occurs during driving.

[0053] Figure 8 This is a simulation diagram of the shape displacement of the micromirror device in the first resonance mode.

[0054] Fig. 9 This is a simulation diagram of the shape displacement in the second resonance mode of the micromirror device.

[0055] Fig.10 This is a simulation diagram of shape displacement in one of the third resonance modes of the micromirror device ((iii)-1 mode).

[0056] Fig.11 This is a simulation diagram of shape displacement in one of the third resonance modes of the micromirror device ((iii)-2 mode).

[0057] Fig.12 This is a simulation diagram of shape displacement in one of the third resonance modes of the micromirror device ((iii)-3 mode).

[0058] Fig.13 This is a simulation diagram of shape displacement in one of the third resonance modes of the micromirror device ((iii)-4 mode).

[0059] Fig.14 This is a simulation diagram of shape displacement in one of the third resonance modes of the micromirror device ((iii)-5 mode).

[0060] Fig.15 This is a diagram showing changes in the resonance vibration frequency accompanying changes in the size of a part of the elements of the micromirror device.

[0061] Fig.16 It is a figure which shows the dimension of the micromirror device of the test example.

[0062] Fig.17 It is a diagram showing the size change portion of the micromirror device of the test example.

[0063] Fig.18 : is a graph showing the relationship between ΔF1 and the maximum displacement angle related to the test example.

[0064] Fig.19 : is a graph showing the relationship between ΔF2 and the maximum displacement angle related to the test example. DETAILED DESCRIPTION

[0065] Hereinafter, specific embodiments of the present invention will be described with reference to the drawings.

[0066] Figure 1 It is a top view of the micromirror device 1 according to the embodiment. Figure 2 1 is a diagram showing a cross-sectional structure of a part of the micromirror device 1 . Figure 3 This is a perspective view of the micromirror device 1 as viewed from the upper surface side. Figure 4 This is a perspective view of the micromirror device 1 as viewed from the bottom surface side.

[0067] The micromirror device 1 of the present embodiment includes a reflector portion 12, a first actuator 14, a first connecting portion 21, a movable frame 18, a second connecting portion 22, a fixed portion 20, and a second actuator 16. The first actuator 14 is arranged in a ring shape around the reflector portion 12, and has first piezoelectric elements 41 and 42. The first connecting portion 21 connects the reflector portion 12 and the first actuator 14. The movable frame 18 is arranged in a ring shape around the first actuator 14. The second connecting portion 22 connects the first actuator 14 and the movable frame 18. The fixed portion 20 is arranged on the outer periphery of the movable frame 18. The second actuator 16 has second piezoelectric elements 44 and 46, and is arranged between the movable frame 18 and the fixed portion 20. In this example, the second actuator 16 is connected to the first actuator 14 via the movable frame 18 and the second connection portion 22 , and reciprocates the mirror portion 12 and the first actuator 14 around the second axis via the movable frame 18 .

[0068] The first actuator 14 includes a pair of semi-annular actuator parts 14A and 14B, each of which is provided with a first piezoelectric element 41 and 42. In addition, the second actuator 16 includes a pair of meander-type actuator parts 16A and 16B, each of which is provided with a second piezoelectric element 44 and 46. The first piezoelectric element 41 and 42 and the second piezoelectric element 44 and 46 have a stacked structure in which a lower electrode 31, a piezoelectric film 32 and an upper electrode 33 are stacked in this order on a vibration plate 30 (see FIG. 1 ). Figure 2 ). In addition, Figure 2 In order to facilitate visual recognition, the film thickness and the ratio of the film thickness of each layer are shown in a size different from the actual size. Figure 2In the figure, the upper electrode 33 and the lower electrode 31 are arranged opposite to each other with the piezoelectric film 32 sandwiched therebetween, and are arranged at the upper and lower parts of the piezoelectric film 32, respectively. Therefore, for the convenience of explanation, they are expressed as "upper part" and "lower part". However, the "upper part" and "lower part" of the upper electrode 33 and the lower electrode 31 do not necessarily mean the upper part and the lower part in the actual configuration. For example, in the actual configuration, the upper electrode 33 is sometimes located below the lower electrode 31 in the vertical direction. Moreover, in the actual configuration, the upper electrode 33 and the lower electrode 31 are sometimes arranged opposite to each other in the horizontal direction. In this way, the upper part and the lower part are names used for convenience. In the present embodiment, the electrode provided on the vibration plate 30 side of the pair of electrodes sandwiching the piezoelectric film 32 is called the lower electrode 31, and the electrode arranged opposite to the lower electrode 31 with the piezoelectric film 32 sandwiched therebetween is called the upper electrode 33.

[0069] The meander-type actuator section 16A has: a plurality of rectangular plate-like sections 61, each of which has a second piezoelectric element 44; and a connecting section 62, which connects adjacent rectangular plate-like sections 61. In this example, there are six rectangular plate-like sections 61. The six rectangular plate-like sections 61 are arranged side by side with the sides in each length direction parallel to each other, and one end is connected by a connecting section 62. When the six rectangular plate-like sections 61 are observed as a whole, the six rectangular plate-like sections 61 appear to be folded back through the connecting section 62. This shape resembles the shape of a meandering river, so it is called a meandering shape, and a meandering structure is called a meandering structure. In this way, the meander-type actuator section 16A as a whole includes a meandering structure in which six rectangular plate-like sections 61 are folded back into a meandering shape through the connecting section 62. The meander-type actuator section 16B has a plurality of rectangular plate-like sections 61 and a connecting section 62, each of which has a second piezoelectric element 46, and has a structure that is almost the same as that of the meander-type actuator section 16A.

[0070] When a predetermined voltage is applied to each piezoelectric element 41, 42, 44, and 46 of the first actuator 14 and the second actuator 16, the piezoelectric film 32 is deformed. When the piezoelectric film 32 of the first actuator 14 and the second actuator 16 is deformed, it is bent and displaced, and a driving force is generated. That is, the first actuator 14 reciprocates the mirror portion 12 around the first axis a1 by periodically deforming the first piezoelectric elements 41 and 42, respectively. And, the second actuator 16 reciprocates the mirror portion 12 around the second axis a2 by periodically deforming the second piezoelectric elements 44 and 46, respectively.

[0071] Regarding the size of the micromirror device 1, for example, the length and width are usually about 1 mm to 10 mm, but it can also be a structure larger or smaller than this size without any special restrictions. In addition, the thickness of the actuator is usually about 5 μm to 0.2 mm, as long as it is within the range that can be manufactured, without any special restrictions.

[0072] The first actuator 14 causes a rotation torque about a first axis a1 to act on the reflector portion 12, and the second actuator 16 causes a rotation torque about a second axis a2 orthogonal to the first axis a1 to act on the first actuator 14. Thus, the reflector portion 12 is two-dimensionally rotationally driven about the first axis a1 and the second axis a2. The micromirror device 1 can reflect incident light incident on a reflection surface 12a of the reflector portion 12 to perform two-dimensional scanning by two-dimensionally rotationally driving the reflector portion 12.

[0073] The first axis a1 is located in a plane including the reflection surface 12a of the reflector portion 12 when the reflector portion 12 is stationary. The second axis a2 intersects with the first axis a1 in the plane. In this example, the first axis a1 and the second axis a2 are axes that are orthogonal to each other. In addition, the first axis a1 and the second axis a2 preferably intersect at the center of the reflection surface 12a, but the intersection position may also be offset from the center.

[0074] In the following figures, the normal direction of the reflecting surface 12a of the reflector portion 12 when stationary (i.e., the direction orthogonal to the first axis a1 and the second axis a2) is set as the z-axis direction, the direction parallel to the first axis a1 is set as the x-axis direction, and the direction parallel to the second axis a2 is set as the y-axis direction.

[0075] This micromirror device 1 drives the reflector part 12 around the first axis a1 with a driving frequency on the high speed side, and drives the reflector part 12 around the second axis a2 with a driving frequency on the low speed side. The first actuator 14 is connected to the reflector part 12 through the first connecting portion 21 extending along the first axis a1. The first connecting portion 21 is in an elongated shape extending along the first axis a1, so the moment of inertia around the first axis a1 is relatively small. The structure of transmitting the rotation torque to the reflector part 12 via this first connecting portion 21 is suitable for the high-speed drive of the reflector part 12 around the first axis a1. As the driving frequency around the first axis a1, it is preferably above 10kHz. By setting the driving frequency that makes the reflector part 12 reciprocate around the first axis a1 to above 10kHz, it is possible to display a high-definition image when the micromirror device 1 is applied to a laser display. The serpentine actuator parts 16A and 16B of the second actuator 16 play the function of the long leaf spring connecting the first actuator 14 and the fixed part 20. Therefore, the second actuator 16 has improved flexibility although its responsiveness is reduced, and is therefore suitable for driving the first actuator 14 and the mirror portion 12 at a low speed about the second axis a2. As described above, the resonant frequency is preferably used for the drive about the first axis a1.

[0076] The micromirror device 1 has a resonance mode with a plurality of different resonance frequencies corresponding to a plurality of natural vibration frequencies. Since the driving efficiency is high, the drive around the first axis a1 preferably uses the resonance mode of the lowest order in the plurality of resonance modes in which the reflector portion 12 and the first actuator 14 are reciprocated around the first axis a1 with opposite phases. Hereinafter, the resonance mode of the lowest order in which the reflector portion 12 and the first actuator 14 are reciprocated around the first axis a1 with opposite phases is referred to as a drive mode. By driving the reflector portion 12 with this drive mode, a larger displacement angle can be achieved with a lower drive voltage. In addition, the lowest order indicates that the frequency is the lowest.

[0077] The multiple resonance modes of the present micromirror device 1 satisfy the following relationship.

[0078] The resonance frequency of the driving mode about the first axis a1 is set to A. Furthermore, the resonance frequency of the lowest-order resonance mode in which the mirror portion 12 and the first actuator 14 vibrate in opposite phases in a direction (z-axis direction) orthogonal to both the first axis a1 and the second axis a2 is set to B. Furthermore, the difference AB between the resonance frequency A and the resonance frequency B is set to frequency difference F. Furthermore, the resonance frequency of a resonance mode having a resonance frequency smaller than the frequency difference F and having a resonance frequency closest to the frequency difference F among the plurality of resonance modes is set to C. The resonance frequency of a resonance mode having a resonance frequency larger than the frequency difference F and having a resonance frequency closest to the frequency difference F among the plurality of resonance modes is set to D.

[0079] In this case, the difference ΔF1 between the frequency difference F and the resonance frequency C is

[0080] ΔF1=FC≥20Hz,

[0081] and,

[0082] The difference ΔF2 between the frequency difference F and the resonant frequency D is

[0083] ΔF2=FD≤-150Hz.

[0084] In other words, in the present micromirror device 1 , there is no resonance mode of the micromirror device 1 in the frequency range exceeding F-20 Hz and less than F+150 Hz.

[0085] Furthermore, it is preferred that ΔF1≧100 Hz, and it is preferred that ΔF2≦−400 Hz. That is, it is preferred that there is no resonance mode of the micromirror device 1 in the frequency range exceeding F−100 Hz and less than F+400 Hz.

[0086] In addition, in the micromirror device 1 of this structure, the resonance frequency A is greater than the resonance frequency B.

[0087] According to the research of the present inventors, by making the resonance mode of the micromirror device 1 satisfy the above relationship, when the mirror unit 12 is driven in the driving mode, it is possible to suppress the generation of unnecessary resonance having a frequency different from the resonance frequency A of the driving mode.

[0088] If unnecessary resonance occurs in the micromirror device, the vibration accompanying the unnecessary resonance (hereinafter referred to as abnormal vibration) is superimposed on the reciprocating rotation of the reflector portion 12 around the first axis a1 in the driving mode, and the scanning line will have a large jitter in time relative to the width direction and the length direction due to the abnormal vibration, resulting in an undesirable situation that hinders normal optical scanning. However, by satisfying ΔF1=FC≥20Hz and ΔF2=FD≤-150Hz, the generation of abnormal vibration can be suppressed, so that the reflector portion 12 reciprocates at a sufficient displacement angle without jittering the scanning line. Moreover, by further satisfying ΔF1≥100Hz and ΔF2≤-400Hz, the generation of abnormal vibration can be suppressed until a larger displacement angle. For example, when the micromirror device 1 of this embodiment is applied to a laser display, etc., since there are fewer abnormal vibrations, extremely high-definition images can be displayed.

[0089] According to the research of the present inventors, it has been confirmed that even for a micromirror device having a structure similar to the micromirror device 1, when the multiple resonance modes do not satisfy the above-mentioned relationship, abnormal vibrations will be generated when the reflector portion 12 is driven around the first axis a1, making it impossible to reciprocate at a sufficient displacement angle (refer to the test example described later).

[0090] Whether abnormal vibration of the micromirror device 1 occurs can be confirmed by observing the scanning line. Figure 5 The figure is used to explain the method of detecting the presence or absence of abnormal vibration. When the micromirror device 1 is placed on a horizontal plane and the reflector portion 12 is driven to reciprocate around the first axis a1, the laser beam L 0 The laser beam L is incident on the mirror portion of the micromirror device 1 from the light source 100. The laser beam L reflected by the mirror portion 12 is detected by the two-dimensional photodetector PD, and a scanning line SL of the laser beam scanned along the y-axis direction is observed.

[0091] exist Figure 6 middle, Figure 6 A represents the scanning line SL when abnormal vibration occurs, Figure 6 B represents the scanning line SL in a normal state without abnormal vibration. Figure 6As shown, when abnormal vibration occurs, the width of the scanning line SL in the x-axis direction becomes wider than that of the scanning line SL in the normal state, and the length is greater than the scanning amount in the y-axis direction. In this way, when abnormal vibration occurs, the scanning line SL shakes greatly in both the x-axis direction and the y-axis direction. Therefore, it is possible to determine whether there is shaking of the scanning line SL based on the width of the scanning line SL in the x-axis direction and the length of the scanning line SL in the y-axis direction, and it is possible to determine whether there is abnormal vibration based on whether there is shaking of the scanning line SL. That is, if the scanning line shakes, it is determined that abnormal vibration has occurred, and if the scanning line does not shake, it is determined that no abnormal vibration has occurred.

[0092] Here, a micromirror device 1A (reference numeral 1A) of a test example described later having a shape similar to that of the micromirror device 1 of the above-described embodiment is described. Fig.16 ) is used to illustrate an example of an unnecessary resonance mode generated when abnormal vibration occurs.

[0093] Figure 7 The micromirror device 1A (reference number 140) of the experimental example described below is a device for driving the reflector portion 12 at the resonance frequency of the driving mode to generate abnormal vibration. Fig.16 ) measures the sensor signal of the micromirror device 1A (specifically, Test Example 9) and performs FFT (Fast Fourier Transform) analysis on the micromirror device 1A to obtain a frequency spectrum. Specifically, the frequency spectrum is obtained as follows. For the micromirror device 1A, a driving signal of a resonant frequency A, i.e., 42 kHz, of a driving mode (the first resonance mode (i) in the figure) in which the reflector portion 12 reciprocates around the first axis a1 is input to the first piezoelectric element 41, 42 of the first actuator 14. Furthermore, the vibration generated in the micromirror device 1A when the reflector portion 12 is driven at the resonance frequency A is obtained as a sensor signal of a piezoelectric sensor (not shown) assembled in the micromirror device 1A, and an FFT analysis is performed.

[0094] according to Figure 7 It can be seen from the spectrum shown that, although driven by the driving mode near 42kHz of the first resonance mode (i), other resonance modes near about 26kHz and about 16kHz are still generated. Hereinafter, the resonance mode generated at about 26kHz is referred to as the second resonance mode (ii), and the resonance mode generated at about 16kHz is referred to as the third resonance mode (iii). In addition, in Japanese Patent Gazette No. 2013-114015 recorded as a prior art, when there is a resonance mode within a range of 500Hz different from the resonance frequency of the driving mode and its n times frequency, it is described as abnormal vibration being excited. However, in the micromirror device 1A, as Figure 7As shown, although the resonance frequencies of the unnecessary second resonance mode (ii) and the third resonance mode (iii) differ from the resonance frequency of the first resonance mode (i) as the driving mode and the frequency of the 2nd wave component of the first resonance mode by more than 10kHz, they are still excited, thus failing to comply with the rule for generating abnormal vibrations described in Japanese Patent Gazette No. 2013-114015.

[0095] The exact resonance frequency and vibration shape of the above-mentioned drive mode (first resonance mode (i)) and resonance modes other than the doubled wave thereof (second resonance mode (ii) and third resonance mode (iii)) were examined as follows.

[0096] To obtain the above Figure 7 In the micromirror device 1A of the test example 9 of the spectrum, a chirp signal with a voltage amplitude of 2V and an instantaneous frequency of 0 to 100kHz is input to the first piezoelectric element 41, 42 of the first actuator 14, and the displacement caused by the vibration of the mirror portion 12 and the first actuator 14 generated by the chirp signal is measured using a laser Doppler vibrometer. The measurement method and the method for determining the resonance mode will be described in detail in the test example described later. The resonance frequency and vibration shape of the above-mentioned second resonance mode (ii) and third resonance mode (iii) are determined based on the displacement of the mirror portion 12 and the first actuator 14 measured by the laser Doppler vibrometer.

[0097] Furthermore, a resonance mode analysis simulation was performed on the micromirror device 1A of Test Example 9 using commercially available finite element analysis software, and the resonance frequency and vibration shape of the resonance mode generated between 0 and 100 Hz were obtained.

[0098] By comparing the resonance frequency and vibration shape obtained using the chirp signal and the resonance frequency and vibration shape of the resonance mode obtained by simulation, it was determined that Figure 7 The frequencies of the second resonance mode (ii) and the third resonance mode (iii) and the vibration shapes of the resonance modes (that is, what kind of vibration the resonance is accompanied by).

[0099] The resonance frequency obtained using the chirp signal is Figure 7 The resonant frequencies shown in the spectrum are roughly consistent, so it can be determined Figure 7The peaks in the resonance mode vibrate in which vibration shape. On the other hand, the acquired resonance frequency includes the n-fold wave (n≥2) of the resonance mode, and it is impossible to determine whether the resonance frequency is the resonance frequency of the resonance mode of the 1-fold wave or the resonance frequency of the resonance mode of the n-fold wave. Although the resonance frequency of the resonance mode acquired by simulation is not completely consistent with the resonance frequency obtained by measuring the actual device, the resonance frequency generated by the n-fold wave can be excluded. Therefore, by comparing the resonance frequency acquired using the chirp signal and the resonance frequency of the resonance mode acquired by simulation, the resonance frequency and its vibration shape that are not the n-fold wave of the micromirror device 1A can be determined.

[0100] Here, use Figure 8 to Figure 14 The vibration shapes of the first resonance mode (i), the second resonance mode (ii), and the third resonance mode (iii) obtained as described above, which are drive modes, are described below. Figure 7 The third resonance mode (iii) in the spectrum of appears to be a resonance mode corresponding to a resonance frequency, but in fact, it includes Figure 10 to Figure 14 The multiple third resonance modes (iii)-1 to third resonance modes (iii)-5 are shown. Figure 10 to Figure 14 The plurality of resonance modes shown (third resonance mode (iii)-1 to third resonance mode (iii)-5) respectively correspond to different resonance frequencies. Figure 8 to Figure 14 is a simulation diagram showing the shape of the maximum displacement state of each resonance mode. Figure 8 to Figure 14 In the figure, the displacement is shown by light and dark. In the figure, 0 shown on the displacement scale represents the position of the static state. Relative to the static state, the darker the color (the closer to black), the greater the displacement in the -z axis direction, and the lighter the color (the closer to white), the greater the displacement in the +z axis direction.

[0101] Figure 8 1 is a simulation diagram showing a maximum displacement state when the mirror portion 12 and the first actuator 14 rotate in opposite phases to each other around the first axis a1 (x-axis) in the driving mode. Figure 8 : The following state is shown: the reflector portion 12 is displaced obliquely in the +z-axis direction at one end y1 in the y-axis direction, and is displaced obliquely in the -z-axis direction at the other end y2 in the y-axis direction, with the first axis a1 as the center. Furthermore, although the displacement amount is extremely small, the first actuator 14 displaces the portion of the semi-annular actuator portion 14A that is opposite to the one end y1 of the reflector portion 12 in the -z-axis direction, and displaces the portion of the semi-annular actuator portion 14B that is opposite to the other end y2 of the reflector portion 12 in the +z-axis direction, with the first axis a1 as the center.

[0102] The second resonance mode (ii) is a resonance mode in which the mirror portion 12 and the first actuator 14 rotate in opposite phases in the z-axis direction orthogonal to a plane including the first axis a1 (x-axis) and the second axis a2 (y-axis). Fig. 9 This is a simulation diagram of the second resonance mode (ii). Fig. 9 As shown, the second resonance mode (ii) is a vibration mode in which the first actuator 14 is displaced in the −z-axis direction when the mirror portion 12 is displaced in the +z-axis direction.

[0103] Fig.10 The third resonance mode (iii)-1 shown is a mode in which the mirror portion 12 and the first actuator 14 rotate around the second axis a2 in the same phase.

[0104] Fig.11 The third resonance mode (iii)-2 shown is a mode in which the mirror portion 12 and the first actuator 14 rotate around the first axis a1 in the same phase.

[0105] Fig.12 The third resonance mode (iii)-3 shown is a mode in which the mirror portion 12 and the first actuator 14 are hardly displaced, but the rectangular plate-like portion 61 of the pair of serpentine actuator portions 16A and 16B of the second actuator 16 is deformed in the z-axis direction relative to the first actuator 14. Fig.12 In the third resonance mode (iii)-3 shown in FIG. 1 , a pair of serpentine actuator parts 16A and 16B are displaced in the same phase. Here, the same phase refers to the following state: among the plurality of rectangular plate-like parts 61 respectively included in the serpentine actuator parts 16A and 16B, the rectangular plate-like parts 61 arranged in symmetrical positions with the first axis a1 as the symmetry axis are displaced in the same direction in the z-axis direction. For example, in Fig.12 In the pair of meander-type actuator parts 16A and 16B, the rectangular plate-like parts 61 arranged at the position farthest from the first axis a1 in the y-axis direction are displaced so that the central parts thereof bulge in the same direction in the z-axis direction. Fig.12 In the third resonance mode (iii)-3 shown, the closer the rectangular plate-like portion 61 of a pair of serpentine actuator portions 16A and 16B is to the reflector portion 12, the smaller the deformation in the z-axis direction, and the farther away from the reflector portion 12 in the y-axis direction, the larger the deformation in the z-axis direction.

[0106] Fig.13 The third resonance mode (iii)-4 shown is a mode in which the mirror portion 12 and the first actuator 14 are hardly displaced, but the rectangular plate-like portions of the pair of serpentine actuator portions 16A and 16B of the second actuator 16 are deformed in the z-axis direction with the second axis a2 as the center. Fig.12Similarly, the third resonance mode (iii)-3 shown is a mode in which the deformation of the rectangular plate-shaped portion 61 farthest from the reflector portion 12 in the y-axis direction is the largest. Fig.13 The third resonance mode (iii)-4 shown is Fig.12 The third resonance mode (iii)-3 shown in FIG. 1 is different from the mode in which a pair of serpentine actuator parts 16A and 16B are displaced in opposite phases. Here, the opposite phases refer to the following state: among the plurality of rectangular plate-like parts 61 respectively provided in the serpentine actuator parts 16A and 16B, the rectangular plate-like parts 61 arranged in symmetrical positions with the first axis a1 as the symmetry axis are displaced in opposite directions in the z-axis direction. For example, in Fig.13 In the meander type actuator part 16A, the rectangular plate-like part 61 disposed at the position farthest from the first axis a1 in the y-axis direction is displaced so that the central portion thereof is recessed in the z-axis direction. In contrast, in the meander type actuator part 16B, the rectangular plate-like part 61 disposed at the position farthest from the first axis a1 in the y-axis direction is displaced so that the central portion thereof is raised in the z-axis direction.

[0107] Fig.14 The third resonance mode (iii)-5 shown is a mode in which the mirror portion 12 and the first actuator 14 are hardly displaced, but the rectangular plate-like portions of the pair of serpentine actuator portions 16A and 16B of the second actuator 16 are deformed in the z-axis direction with the second axis a2 as the center. Fig.12 Similar to the third resonance mode (iii)-3 shown in FIG. 1 , a pair of serpentine actuator parts 16A and 16B are displaced in the same phase. Fig.12 The third resonance mode (iii)-3 shown is different in that the deformation of the third rectangular plate-like portion 61 from the first actuator 14 side among the rectangular plate-like portions 61 of the meander-type actuator units 16A and 16B is the largest.

[0108] When driving in the first resonance mode (i), if abnormal vibration modes such as the second resonance mode (ii) and the third resonance mode (iii)-1 to (iii)-5 are generated, unnecessary vibrations, i.e., abnormal vibrations, are superimposed on the reciprocating rotation of the reflector portion 12 around the first axis driven by the first resonance mode (i). As a result, the scanning line will vibrate in the width direction and the length direction, making it impossible to obtain the desired scanning angle.

[0109] On the other hand, according to the micromirror device 1 of the present invention, when driven in the first resonance mode (i), the abnormal vibration mode as described above can be suppressed. As a result, abnormal vibration can be suppressed, thereby suppressing the jitter of the scanning line to achieve high-precision optical scanning.

[0110] The natural vibration frequency of the micromirror device 1 is determined according to the material, shape and size of the elements constituting the micromirror device 1. The natural vibration frequency can be changed by adjusting the size of each element. Therefore, the size of each element can be adjusted so that the resonant frequency of the micromirror device 1 satisfies the above relationship. When manufacturing the micromirror device 1, the reference size of each element is determined according to the desired performance of the micromirror device 1. A simulation is performed to obtain the natural vibration frequency based on these reference sizes, and it is checked whether the natural vibration frequency obtained by the simulation satisfies the above relationship. In the case where the above relationship is not satisfied, the size of a certain element is changed. For example, one or more of the diameter of the reflector portion 12, the length of the first connecting portion 21 along the first axis a1 direction (the length from the outer periphery of the reflector portion 12 to the first actuator 14), the width of the first connecting portion 21 in the second axis a2 direction, the length of each rectangular plate-like portion 61 of the serpentine actuator portion 16A, 16B along the first axis a1 direction and the width in the second axis a2 direction, and the width of the first actuator 14 in the first axis a1 direction and the width in the second axis a2 direction may be changed.

[0111] For example, when the width of the first connection portion 21 is changed within a range of ±10 μm, Fig.15 As shown, the resonant frequency of the first resonance mode (i) of the micromirror device 1 can vary greatly. The larger the width of the first connecting portion 21, the larger the resonant frequency of the first resonance mode (i). On the other hand, the resonant frequency of the second resonance mode (ii) is almost constant. In this way, the resonant frequency of the micromirror device 1 and the relationship between them can be changed by changing the size of a part of the components.

[0112] Hereinafter, the details of each element of the micromirror device 1 will be described.

[0113] The reflector portion 12 has a reflective surface 12a for reflecting incident light. The reflective surface 12a is formed of a metal thin film such as Au (gold) or Al (aluminum) provided on one surface of the reflector portion 12. The material and film thickness of the reflective mirror coating used to form the reflective surface 12a are not particularly limited, and various designs can be made using known reflective mirror materials (high reflectivity materials). Figure 4 As shown, in order to maintain the flatness of the reflecting surface, a circular rib along the outer circumference and three ribs 13 parallel to the second axis a2 are provided on the back surface of the reflector portion 12 .

[0114] exist Figure 1In the embodiment of the present invention, the reflector portion 12 is exemplified as having a substantially circular reflecting surface 12a and having a top view shape similar to the reflecting surface 12a, but the top view shape of the reflector portion 12 may be consistent with or different from the shape of the reflecting surface 12a. The shapes of the reflector portion 12 and the reflecting surface 12a are not particularly limited. They may be various shapes such as an ellipse, a square, a rectangle, and a polygon, and are not limited to the illustrated circular shape.

[0115] The first connecting portion 21 is composed of a pair of rod-shaped members symmetrically extending outward from the outer periphery of the reflector portion 12 along the first axis a1, and connects the reflector portion 12 and the first actuator 14 on the first axis a1, and supports the reflector portion 12 so as to be rotatable around the first axis a1. One end of each of the first connecting portions 21 is connected to the outer periphery of the reflector portion 12, and the other end of each is connected to the first actuator 14.

[0116] The first actuator 14 includes a pair of semi-annular actuator portions 14A and 14B respectively including first piezoelectric elements 41 and 42. The pair of semi-annular actuator portions 14A and 14B are connected on the first axis a1 and are arranged in an annular shape around the mirror portion 12.

[0117] Here, the annular shape may be any shape as long as it surrounds the inner area without interruption, and the shapes of the inner and outer circumferences may not be circular, but are concepts including rectangular, polygonal, and the like.

[0118] By bending the semi-annular actuator portion 14A and the semi-annular actuator portion 14B disposed with the first axis a1 interposed therebetween in opposite directions, a torque around the first axis a1 is generated, thereby rotating the mirror portion 12 around the first axis a1.

[0119] The second connection portion 22 is composed of a pair of rod-shaped members symmetrically extending outward from the outer periphery of the first actuator 14 along the first axis a1 , and connects the first actuator 14 and the movable frame 18 on the first axis a1 .

[0120] As described above, the second actuator 16 is composed of a pair of serpentine actuator sections 16A and 16B disposed between the first actuator 14 and the fixed section 20. The pair of serpentine actuator sections 16A and 16B are symmetrically disposed with respect to the first axis a1, sandwiching the movable frame 18, the first actuator 14, and the reflector section 12. The connecting section 62 provided at one end of the serpentine actuator sections 16A and 16B is connected to the outer periphery of the first actuator 14, and the connecting section 62 provided at the other end is connected to the fixed section 20.

[0121] The rectangular plate-like portion 61 of each of the meander-type actuator parts 16A and 16B functions as a piezoelectric cantilever. In order to generate torque around the second axis, the adjacent rectangular plate-like portions 61 can be bent in opposite directions to each other. As a result, the tilt angles generated are accumulated at the ends of each rectangular plate-like portion 61, and their sum becomes the inclination of the first actuator 14 (= the inclination of the mirror portion 12). Therefore, voltages are applied to the second piezoelectric elements 44 of the adjacent rectangular plate-like portions 61 and to the second piezoelectric elements 46 in a manner that generates stresses in opposite directions. Specifically, the phases of the voltage waveforms applied thereto can be displaced by 180°. In this way, the second actuator 16 can cause the first actuator 14 and the mirror portion 12 to generate rotational torque.

[0122] In this example, six rectangular plate-like portions 61 are provided in the meander-type actuator portions 16A and 16B, but the number of the rectangular plate-like portions 61 is not limited as long as it is more than one. In the case where there is only one rectangular plate-like portion 61, the connecting portion provided at one end thereof is connected to the outer periphery of the semi-annular actuator portion 14A or 14B, and the connecting portion provided at the other end is connected to the inner periphery of the fixing portion 20, and the whole is formed into a meandering shape through the two connecting portions and the rectangular plate-like portion 61. However, it is preferred that one meander-type actuator portion 16A and 16B includes more than two rectangular plate-like portions 61, and from the viewpoint of suppressing the warping of the micromirror device 1 when it is stationary, the rectangular plate-like portion 61 is preferably an even number.

[0123] In this example, the second actuator 16 is composed of a pair of serpentine actuator portions 16A and 16B. However, the second actuator 16 may have any other shape as long as it can reciprocate the mirror portion 12 and the first actuator 14 integrally around the second axis a2.

[0124] The movable frame 18 has a function of transmitting the rotation torque generated by the second actuator 16 to the first actuator 14 and the mirror unit 12. However, the micromirror device 1 may not include the movable frame 18 and the second connection unit 22, and the second actuator 16 and the first actuator 14 may be directly connected.

[0125] The fixed portion 20 supports the second actuator 16, and supports the movable frame 18, the first actuator 14, and the mirror portion 12 via the second actuator 16. The fixed portion 20 is provided with wiring and electrode terminals, etc., which are not shown. Furthermore, the fixed portion 20 may be further provided with an electronic circuit, which is not shown.

[0126] In this example, the fixing portion 20 is a frame member surrounding the second actuator 16. The fixing portion 20 is not limited to a frame member, and may be composed of two members: a first fixing portion connected to one meander type actuator portion 16A and a second fixing portion connected to the other meander type actuator portion 16B.

[0127] In the micromirror device 1 of this example, the reflector portion 12, the first actuator 14, the movable frame 18, the second actuator 16, the fixed portion 20, the first connecting portion 21 and the second connecting portion 22 are arranged on the first axis a1 with a line-symmetric structure. By this symmetrical structure, the rotational torque can be effectively acted on the central reflector portion 12.

[0128] The micromirror device 1 can be manufactured from a silicon substrate by, for example, processing using semiconductor manufacturing technology into a structure integrally constituted by elements such as the mirror portion 12 , the first actuator 14 , the second actuator 16 , the fixing portion 20 , and the connecting portions 21 , 22 .

[0129] In addition, the fixing portion 20 is thicker than the mirror portion 12, the first actuator 14, the movable frame 18, the second actuator 16, the first connecting portion 21, and the second connecting portion 22 (see FIG. Figure 3 and Figure 4 ). That is, the thickness of the reflector portion 12, the first actuator 14, the movable frame 18, the second actuator 16, the first connecting portion 21 and the second connecting portion 22 is formed to be thinner than the thickness of the fixed portion 20 (thickness in the z-axis direction). As a result, the first actuator 14, the second actuator 16, the first connecting portion 21 and the second connecting portion 22 become a structure that is easy to deform (bending deformation or twisting deformation). The base material portion of the reflector portion 12, the first actuator 14, the second actuator 16 and the fixed portion 20 except the reflecting surface, the piezoelectric film, the electrode and the wiring is called a structure for a micromirror device. And, the portion of the structure except the fixed portion 20 is the main body in the structure. The basic performance of the micromirror device 1 depends on the shape of the main body, not on the shape of the fixed portion 20.

[0130] The upper electrodes 33 of the first piezoelectric elements 41 and 42 provided in the pair of semi-annular actuator portions 14A and 14B of the first actuator 14 may each be composed of a plurality of individual electrode portions.

[0131] The piezoelectric elements 41, 42, 44, and 46 provided in the first actuator 14 and the second actuator 16 will be described. As described above, the piezoelectric elements 41, 42, 44, and 46 have a laminated structure of the lower electrode 31, the piezoelectric film 32, and the upper electrode 33.

[0132] The thickness of the lower electrode and the upper electrode is not particularly limited, and is, for example, about 200 nm. The thickness of the piezoelectric film is not particularly limited as long as it is 10 μm or less, and is usually 1 μm or more, for example, 1 to 5 μm. The film forming method of the lower electrode, the upper electrode, and the piezoelectric film is not particularly limited, but the vapor phase growth method is preferred, and film formation by sputtering is particularly preferred.

[0133] The main component of the lower electrode is not particularly limited, and examples thereof include Au, Pt, Ir, and IrO. 2 、RuO 2 、LaNiO 3 and SrRuO 3 and other metals or metal oxides and combinations thereof.

[0134] The main component of the upper electrode is not particularly limited, and examples thereof include the materials exemplified for the lower electrode, electrode materials generally used in semiconductor processes such as Al, Ti, Ta, Cr, and Cu, and combinations thereof.

[0135] Examples of the piezoelectric film include a piezoelectric film containing one or two or more perovskite-type oxides (P) represented by the following formula.

[0136] General formula ABO 3 (P)

[0137] (Wherein, A: the element at position A, including at least one element of Pb.

[0138] B: The element at the B position is at least one element selected from the group consisting of Ti, Zr, V, Nb, Ta, Sb, Cr, Mo, W, Mn, Sc, Co, Cu, In, Sn, Ga, Zn, Cd, Fe and Ni.

[0139] O: oxygen element.

[0140] The standard molar ratio of the A-site element, the B-site element, and the oxygen element is 1:1:3, but their molar ratios may deviate from the standard molar ratio within the range of the perovskite structure that can be adopted.

[0141] As perovskite-type oxides represented by the above general formula, lead-containing compounds such as lead titanate, lead zirconate titanate (PZT), lead zirconate, lead lanthanum titanate, lead lanthanum zirconate titanate, lead magnesium zirconate titanate, lead zirconate titanate, nickel niobate titanate, and lead zirconate titanate, and their mixed crystal systems; and lead-free compounds such as barium titanate, barium strontium titanate, sodium bismuth titanate, potassium bismuth titanate, sodium niobate, potassium niobate, lithium niobate, and bismuth ferrite, and their mixed crystal systems.

[0142] Furthermore, the piezoelectric film of the present embodiment preferably contains one or two or more perovskite-type oxides (PX) represented by the following formula.

[0143] A a (Zr x 、Ti y 、M b-x-y ) b O c (PX)

[0144] (wherein, A: the element at position A, including at least one element of Pb. M is at least one element selected from the group consisting of V, Nb, Ta and Sb.

[0145] 0<x<b, 0<y<b, 0≤bxy, a:b:c=1:1:3 are the standards, but their molar ratios may deviate from the standard molar ratios within the range that allows the perovskite structure to be adopted.)

[0146] The piezoelectric film composed of the perovskite oxide represented by the above general formula (P) and (PX) has a high piezoelectric strain constant (d 31 Constant), so the actuator having such a piezoelectric film has excellent displacement characteristics. In addition, the piezoelectric constant of the perovskite type oxide represented by the general formula (PX) is higher than the piezoelectric constant of the perovskite type oxide represented by the general formula (P).

[0147] Furthermore, an actuator having a piezoelectric film composed of a perovskite oxide represented by the general formula (P) and (PX) has a voltage-displacement characteristic with excellent linearity within a driving voltage range. These piezoelectric materials exhibit good piezoelectric characteristics when the technology of the present invention is implemented.

[0148] [Test example]

[0149] Hereinafter, the micromirror devices of the embodiments and comparative examples of the technology of the present invention will be described. As the embodiments and comparative examples, the following test examples 1 to 16 were prepared. Test examples 1 to 12 correspond to the embodiments, and test examples 13 to 16 correspond to comparative examples.

[0150] Follow the steps below to create Fig.16 FIG. 1 shows a micromirror device 1A in a top view as Experimental Examples 1 to 16. Figure 1 The micromirror devices 1 shown are identical and identical elements are marked with identical reference numerals. Fig.17 Yes means Fig.16 FIG. 1 is a diagram of the back side of the reflector portion 12 enclosed by the dotted line A in FIG.

[0151] -Manufacturing method-

[0152] (Step 1) As a structural substrate, a back side silicon oxide (SiO 2 The stacked structure of the SOI (Silicon On Insulator) substrate is composed of a 1.5μm Si layer, a 250μm Si processing layer, a 1μm silicon oxide buried layer, a 100μm Si device layer, and a 1μm surface silicon oxide. A 30nm Ti layer and a 150nm Ir layer were formed on the 1μm surface oxide layer of the SOI substrate by sputtering at a substrate temperature of 350°C. The stacked structure of the Ti layer and the Ir layer is equivalent to Figure 2 The lower electrode 31 is provided.

[0153] (Step 2) A 3 μm thick piezoelectric film was formed on the substrate on which the lower electrode (Ti / Ir) was stacked and obtained above using a radio frequency (RF) sputtering device. As a target material for the sputtering of the piezoelectric film, a Pb 1.3 ((Zr 0.52 Ti 0.48 ) 0.88 Nb 0.12 ) 3 The film forming pressure was set to 2.2 mTorr, and the film forming temperature was set to 450° C. The obtained piezoelectric film was a Nb-doped PZT thin film to which 12% of Nb was added in terms of atomic composition ratio.

[0154] (Step 3) An upper electrode having a stacked structure of Au / Ir (150 nm / 50 nm) was patterned on the substrate on which the piezoelectric film obtained above was formed by a lift-off method.

[0155] (Step 4) Then, the piezoelectric film and the lower electrode were pattern-etched by inductively coupled plasma (ICP: inductively coupled plasma) dry etching.

[0156] (Step 5) Then, a 0.6 μm thick Al 2 O 3 After forming the insulating layer, the insulating layer is patterned by ICP dry etching.

[0157] (Step 6) The stacked structure of Au / Ti (300 nm / 50 nm) was patterned by lift-off method to form the reflective surface 12 a of the mirror portion 12 , the electrode terminals, and the wiring layer.

[0158] (Step 7) The device layer is pattern-etched by a silicon dry etching process to form the shapes of the first actuator 14, the second actuator 16, the movable frame 18, the mirror portion 12, the first connection portion 21, the second connection portion 22, and the fixed portion 20.

[0159] (Step 8) Next, the base layer was subjected to reactive ion etching from the back side of the substrate. Basically, the base layer was removed while leaving a portion to be the fixing portion 20.

[0160] (Step 9) Finally, the insulating layer is removed from the back side by dry etching, thereby producing Fig.16 The micromirror device shown.

[0161] In the above-mentioned manufacturing process, the reflecting surface 12a of the reflector portion 12 is formed in step 6, but the reflecting surface 12a can also be formed using a reflecting material different from the material of the electrode terminal and the wiring layer. In this case, for example, the reflecting surface 12a can be formed by a peeling method or the like immediately following step 6.

[0162] The dimensions of the various elements of the micromirror device 1A of this test example are as follows: Fig.16 As shown. The diameter of the reflector portion 12 is set to 1.1 mm, the length of each rectangular plate-like portion 61 of the serpentine actuator portion 16A, 16B along the x-axis direction (the first axis a1 direction) is set to 6.0 mm, the width in the y-axis direction (the second axis a2 direction) is set to 0.49 mm, and the interval between adjacent rectangular plate-like portions 61 is set to 0.04 mm. Regarding the outer shape of the fixing portion 20, the y-axis direction is set to 11.4 mm, and the x-axis direction is set to 8.5 mm. In addition, the thickness of the reflector portion 12, the first actuator 14 and the second actuator 16, and the first connecting portion 21 and the second connecting portion 22 is equal to the thickness of the device layer. However, as Fig.17 As shown, a circular rib along the outer circumference and three parallel ribs 13 are provided on the back surface of the reflector portion 12. The thickness of the rib 13 is set to 250 μm.

[0163] In each of Test Examples 1 to 16, the width Δbar of the first connection portion 21 supporting the reflector portion 12 and the width Δfrm of the rib 13 of the reflector portion 12 were set to the dimensions shown in Table 1, respectively.

[0164] The correlation between the frequency and frequency difference of the resonance mode and the presence or absence of abnormal vibration was examined for the micromirror device of each test example.

[0165] (Frequencies and frequency differences of various resonance modes)

[0166] A laser Doppler vibrometer (MSA-500 MICRO SYSTEM ANALYZER manufactured by Polytec) was used to apply a chirp signal with a voltage amplitude of 2V (instantaneous frequency of 0 to 100 kHz) to the first piezoelectric elements 41 and 42 of the first actuator 14, and the displacements of multiple measurement points on the micromirror device 1A were measured for the micromirror devices of each of Test Examples 1 to 16. Fig.16As shown by the black circles (·), the measuring points are set at multiple positions on the reflector portion 12, the semi-annular actuator portions 14A and 14B of the first actuator 14, the movable frame 18, and the rectangular plate-like portion 61 closest to the movable frame 18 of the serpentine actuator portions 16A and 16B of the second actuator 16. For the displacement at each measuring point obtained by the laser Doppler vibrometer, the spectrum is obtained by FFT processing, and the frequency of vibration is obtained based on the average spectrum of the spectrum at each measuring point. In addition, the vibration shape of each vibration mode is obtained based on the phase relationship between each measuring point. The conditions for FFT processing are set to a sampling frequency of 256 Hz, a sampling time of 1024 ms, and a frequency resolution of 0.9766 Hz. In addition, the frequency of the resonance mode is determined based on the average spectrum of the spectrum at each measuring point.

[0167] Among the multiple resonance modes obtained as described above, the resonance frequency A of the lowest-order first resonance mode (i) in the resonance mode in which the reflector portion 12 and the first actuator 14 reciprocate with opposite phases around the first axis a1 (axis parallel to the x-axis) and the resonance frequency B of the lowest-order second resonance mode (ii) in the resonance mode in which the reflector portion 12 and the first actuator 14 vibrate with opposite phases in a direction (z-axis direction) orthogonal to both the first axis a1 (x-axis) and the second axis a2 (y-axis) are extracted.

[0168] And, calculated

[0169] F=AB.

[0170] Furthermore, among the frequencies of the plurality of resonance modes obtained as described above, the frequencies of the resonance modes having frequencies near F are extracted. Regarding each of the micromirror devices of Experimental Examples 1 to 16, as peripheral modes of F, there are the third resonance mode (iii)-1 to the third resonance mode (iii)-5.

[0171] Furthermore, in the third resonance mode (iii)-1 to the third resonance mode (iii)-5, the resonance frequency that is smaller than F and closest to F is extracted as the resonance frequency C. And, in the third resonance mode (iii)-1 to the third resonance mode (iii)-5, the resonance frequency that is larger than F and closest to F is extracted as the resonance frequency D. Then, the values ​​of

[0172] ΔF1=FC,

[0173] ΔF2=FD.

[0174] (evaluate)

[0175] For the micromirror devices of test examples 11 to 16, a sinusoidal wave signal of the resonance frequency A of the first resonance mode (i) was input to the first actuator 14, and a first axis scanning action was performed to rotate the reflector portion 12 around the first axis. The voltage amplitude was gradually increased, thereby gradually increasing the displacement angle of the reflector portion 12, and the presence or absence of abnormal vibration and the displacement angle of the reflector portion 12 when the abnormal vibration occurred were checked. Specifically, a visible light laser was vertically incident on the reflection surface 12a of the reflector portion 12 of the micromirror device, and the reflected light was detected by a two-dimensional light detector. The presence or absence of abnormal vibration was determined based on the presence or absence of jitter of the scanning line. For the test example in which the reflector portion 12 was destroyed because the Si destruction stress was reached without generating abnormal vibration when the voltage amplitude was gradually increased, 15°, which was the destruction limit angle, was set as the maximum displacement angle. In addition, in the case where abnormal vibration occurred before reaching the destruction limit, the angle at which it occurred was set as the maximum displacement angle. In Table 1, a case where abnormal vibration did not occur up to the destruction limit of mirror portion 12 is indicated as “not occurred”, and a case where abnormal vibration occurred at an angle less than the destruction limit is indicated as “occurred”.

[0176] Furthermore, as an evaluation, the case where no abnormal vibration occurs until the destruction limit is evaluated as A, the case where abnormal vibration occurs, if the maximum displacement angle is 6° or more, it is evaluated as B, and if the maximum displacement angle is less than 6°, it is evaluated as C. When the micromirror device is applied to a laser display, it is considered that at least a displacement angle of ±6° is required. Furthermore, if a displacement angle exceeding ±12° can be obtained, an extremely high-definition image can be achieved.

[0177] Table 1 shows the dimensions of the components of each example, various frequencies, frequency differences, and evaluation results.

[0178]

[0179] As shown in Table 1, Test Examples 1 to 12 evaluated as A or B satisfy ΔF1=FC≥20 Hz and ΔF2=FD≤-150 Hz. On the other hand, Test Examples 13 to 16 evaluated as C have ΔF2 values ​​greater than -150 Hz.

[0180] Fig.18 This is a graph showing the relationship between ΔF1 and the maximum displacement angle for test examples 1 to 16. In the figure, the quadrilateral (□) mark indicates a test example with ΔF2 of -400 Hz or less, and the diamond (◆) mark indicates a test example with ΔF2 greater than -400 Hz. Fig.18It can be seen that in Test Examples 1 to 7 where ΔF2 is below -400 Hz, the closer ΔF1 is to 0, the smaller the abnormal vibration displacement angle generated. In Test Examples 6 and 7 where ΔF1 is below 100 Hz, a maximum displacement angle of ±6° or more can be achieved, but a maximum displacement angle exceeding ±12° cannot be obtained.

[0181] Fig.19 This is a graph showing the relationship between ΔF2 and the maximum displacement angle for test examples 1 to 16. In the figure, the square (□) mark indicates a test example with ΔF1 of 100 Hz or more, and the diamond (◆) mark indicates a test example with ΔF1 of less than 100 Hz. Fig.19 It can be seen that in test examples 1 to 5 and 8 to 16 where ΔF1 is above 100 Hz, the closer ΔF2 is to 0, the smaller the displacement angle of the abnormal vibration generated. As described above, test examples 13 to 16 where ΔF2 is greater than -150 Hz cannot achieve a maximum displacement angle of ±6°, and test examples 8 to 12 where ΔF2 is below -150 Hz but exceeds -400 Hz can achieve a maximum displacement angle of more than ±6°, but cannot achieve a maximum displacement angle of more than ±12°.

[0182] On the other hand, Fig.18 and Fig.19 In Test Examples 1 to 5 where ΔF1 enclosed by a dotted line was 100 Hz or more and ΔF2 was -400 Hz or less, abnormal vibration did not occur until the destruction limit.

[0183] That is, by satisfying ΔF1=FC≥20Hz and ΔF2=FD≤-150Hz, a displacement angle of more than ±6° suitable for laser display applications can be achieved. By satisfying ΔF1=FC≥100Hz and ΔF2=FD≤-400Hz, a displacement angle exceeding ±12° can be achieved. Therefore, it can be said that extremely high-definition optical scanning is possible.

[0184] In addition, when implementing the technology of the present invention, it is not limited to the structure and manufacturing method of this experimental example, and the material of the substrate, electrode material, piezoelectric material, film thickness, film formation conditions, etc. can be appropriately selected according to the purpose.

[0185] The entire contents of Japanese Patent Application No. 2020-076928 filed on April 23, 2020 are incorporated herein by reference.

[0186] All documents, patent applications, and technical standards described in this specification are incorporated herein by reference to the same extent as if each document, patent application, or technical standard was specifically and individually indicated to be incorporated by reference.

Claims

1. A micromirror device, comprising a reflector portion, wherein the reflector portion has a reflective surface for reflecting incident light, wherein the micromirror device reciprocates the reflector portion about a first axis and a second axis intersecting each other to change the direction of the reflective surface in two dimensions, in, The micromirror device has: a first actuator, which is arranged in a ring shape around the reflector portion and has a first piezoelectric element, is connected to the reflector portion and reciprocates the reflector portion around the first axis by periodically deforming the first piezoelectric element; and a second actuator having a second piezoelectric element and causing the mirror portion to reciprocate around the second axis by periodically deforming the second piezoelectric element; The resonance frequency of the lowest-order resonance mode in which the mirror portion and the first actuator reciprocate around the first axis in phases opposite to each other among a plurality of resonance modes having different resonance frequencies is defined as A. The resonance frequency of the lowest-order resonance mode in which the mirror portion and the first actuator vibrate in opposite phases in directions orthogonal to both the first axis and the second axis among the plurality of resonance modes is defined as B, The difference AB between the resonant frequency A and the resonant frequency B is defined as the frequency difference F. The resonance frequency of the resonance mode having a frequency smaller than the resonance frequency of the frequency difference F and closest to the frequency difference F among the plurality of resonance modes is set to C, The resonance frequency of the resonance mode having a frequency greater than the resonance frequency of the frequency difference F and closest to the frequency difference F among the plurality of resonance modes is set to D. In this case, The difference ΔF1 between the frequency difference F and the resonance frequency C satisfies ΔF1=FC≥20Hz, and, The difference ΔF2 between the frequency difference F and the resonance frequency D satisfies ΔF2=FD≤-150Hz.

2. The micromirror device according to claim 1, in, The difference ΔF1 and the difference ΔF2 satisfy ΔF1 ≥ 100Hz, ΔF2≤-400Hz.

3. The micromirror device according to claim 1 or 2, in, The mirror portion and the first actuator are connected via a first connection portion extending along the first axis.

4. The micromirror device according to claim 1 or 2, in, The micromirror device has: an annular movable frame surrounding the first actuator; and a second connection portion connecting the movable frame and the first actuator, The second actuator reciprocates the mirror portion around the second axis via the movable frame.

5. The micromirror device according to claim 4, in, The second connection portion extends along the first axis.

6. The micromirror device according to claim 1 or 2, in, The second actuator includes two or more rectangular plate-shaped portions and has a meandering structure in which the two or more rectangular plate-shaped portions are folded back in a meandering shape via a connecting portion, and each of the two or more rectangular plate-shaped portions includes the second piezoelectric element.

7. The micromirror device according to claim 1 or 2, in, The resonance frequency A is greater than 10 kHz.

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