Piezoelectric devices and optical deflector driving systems
By reducing the insulating layer thickness at the edges of piezoelectric films, dielectric breakdown is prevented, improving the durability of piezoelectric devices by minimizing hydrogen concentration.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- STANLEY ELECTRIC CO LTD
- Filing Date
- 2024-11-21
- Publication Date
- 2026-06-02
Smart Images
Figure 2026089777000001_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to a piezoelectric device and an optical deflector driving system.
Background Art
[0002] MEMS (Micro Electro Mechanical Systems) devices are used in printer heads (especially for inkjet printers), digital mirror devices (DMD), pressure sensors, HDD heads, acceleration sensors, DNA chips, gyroscopes, optical switches, and the like. When a piezoelectric film (for example, PZT: lead zirconate titanate) is used as an actuator for MEMS, a lower electrode is disposed on the back surface (substrate side) of the piezoelectric film, and an upper electrode is disposed on the surface side, and a voltage is applied between the upper electrode and the lower electrode to generate stress in the piezoelectric film.
[0003] Regarding MEMS devices having the above-described configuration, for example, Patent Document 1 discloses a device in which a piezoelectric film is divided into a plurality of regions, and the voltage magnitude and timing of each region are changed, and an interlayer insulating film covering the entire upper electrode and the side surface of the piezoelectric film is formed, and wiring for applying a voltage to another region is formed thereon (see FIG. 3 of Patent Document 1). The interlayer insulating film is usually formed using plasma CVD. Plasma CVD is a film-forming method in which silane gas (SiH4) and ammonia gas (NH3) are reacted with plasma energy to generate silicon nitride film (Si3N4) and hydrogen (H2), and deposited on a silicon wafer.
Prior Art Documents
Patent Documents
[0004]
Patent Document 1
Summary of the Invention
Problems to be Solved by the Invention
[0005] However, when the piezoelectric film disclosed in Patent Document 1 is driven, a phenomenon was observed in which dielectric breakdown occurs from its edges. This dielectric breakdown reduces the durability of the MEMS device. When the inventors investigated the dielectric breakdown phenomenon in detail, they found that hydrogen entering the piezoelectric film from the interlayer insulating film (a silicon nitride film containing a large amount of hydrogen) reduces the dielectric strength and causes dielectric breakdown. It was also found that dielectric breakdown occurs particularly in the edge region of the piezoelectric film.
[0006] More specifically, hydrogen that enters the piezoelectric film from the interlayer insulating film is in an H+ (+ charged) state. The piezoelectric film's driving bias is negative at the lower electrode and positive at the upper electrode. As a result, the hydrogen that enters the piezoelectric film is attracted to the lower electrode side, leading to a higher hydrogen concentration in the edge region on the lower electrode side. This high hydrogen concentration in the edge region of the piezoelectric film on the lower electrode side reduces its dielectric strength, leading to dielectric breakdown. Therefore, it was found that reducing the hydrogen concentration in the edge region of the piezoelectric film is necessary to suppress dielectric breakdown. In view of these circumstances, the present invention proposes a technology to suppress dielectric breakdown in piezoelectric films and improve the durability of piezoelectric devices. [Means for solving the problem]
[0007] To solve the above problems, the present invention, as an example, Support and A lower electrode formed on the support, An oxide piezoelectric material formed on the lower electrode, An upper electrode formed on the oxide piezoelectric material, Insulating layer and, It includes a wiring section, The insulating layer is formed on the upper electrode and has an interlayer insulating layer on which the wiring portion is formed. We propose a piezoelectric device in which an electric field is generated by applying a voltage between the upper electrode and the lower electrode, and the thickness of the insulating layer formed on the side of the oxide piezoelectric material in the region where the electric field is generated is less than the thickness of the insulating layer in the position overlapping the wiring portion.
[0008] Further features relating to the present invention will become apparent from the description herein and the accompanying drawings. Furthermore, aspects of the present invention are achieved and realized by elements and various combinations of elements and by the modes of the claims described herein in detail and the accompanying claims. The descriptions herein are merely typical examples and do not limit in any way the claims or applications of the present invention. [Effects of the Invention]
[0009] According to the present invention, it is possible to suppress dielectric breakdown in piezoelectric films and improve the durability of piezoelectric devices. [Brief explanation of the drawing]
[0010] [Figure 1] This figure shows a schematic configuration example of an optical deflector driving system 10 according to an embodiment of the present invention. [Figure 2] This is a perspective view showing a schematic configuration example of a single-axis non-resonant / single-axis resonant type optical deflector 1. [Figure 3] This is an example of the third drive voltage Vx1 and the fourth drive voltage Vx2. [Figure 4] This figure shows an example of the displacement of one of the second piezoelectric actuators 51 of the optical deflector 1. [Figure 5] This diagram illustrates how an image p is drawn onto the screen member 20 by a laser beam Ray scanned (raster scan) by the optical deflector 1. [Figure 6] This diagram shows the relationship between the drive signal applied to the optical deflector 1 (see Figure 6A) and the oscillation angle of the mirror section 2 (see Figure 6B). [Figure 7] This is an example of images p with different vertical dimensions that are drawn on the screen component 20. [Figure 8] An example of images p with different vertical positions (offset amounts) drawn on the screen member 20. [Figure 9] A plan view (FIG. 9A) and a cross-sectional view taken along A-A' (FIG. 9B) showing the laminated structure of the main part of the optical deflector 1 according to the present embodiment. [Figure 10] A diagram showing the state of occurrence of dielectric breakdown when adopting a configuration (conventional configuration) in which an interlayer insulating film 95 is laminated over the entire upper electrode 94 and piezoelectric film 93. [Figure 11] A diagram showing a configuration example of the laminated structure of the main part of the optical deflector 1 in which the interlayer insulating film 95 is provided only directly below the wiring 96. [Figure 12] A diagram showing a configuration example of the laminated structure of the main part of the optical deflector 1 in which the thickness of the interlayer insulating film 95 on the above-mentioned end region of the piezoelectric film 93 is made thinner. [Figure 13] A diagram showing a configuration example of the laminated structure of the main part of the optical deflector 1 in which the interlayer insulating film 95 is not arranged on the side surface of the outer peripheral end of the piezoelectric film 93 (side wall of the piezoelectric film 93). [Figure 14] A diagram showing the laminated structure (Modification 1 and Conventional Example) of the main part of the optical deflector 1 in which the outermost layer is formed. [Figure 15] A diagram showing Another form 1 of Modification 1 of the laminated structure of the main part of the optical deflector 1 in which the outermost layer is formed. [Figure 16] A graph (experimental result) showing the dependence of the high-temperature endurance life of a piezoelectric device on the thickness of an insulator layer.
BEST MODE FOR CARRYING OUT THE INVENTION
[0011] An embodiment of the present invention discloses making the thickness of the insulator layer formed on the side portion of the piezoelectric film less than the thickness of the insulator layer at a position overlapping the wiring portion (including not providing an interlayer insulating film). Thereby, it becomes possible to reduce the hydrogen concentration in the lower electrode (when applying a voltage from the upper electrode to the lower electrode) and prevent (suppress) the occurrence of dielectric breakdown.
[0012] The embodiments and examples of the present invention will be described below with reference to the attached drawings. This embodiment uses an optical deflector driving system as an example, but other systems may also be used. In the attached drawings, functionally identical elements may be indicated by the same number. The attached drawings show specific embodiments and implementation examples in accordance with the principles of the present invention, but these are for the purpose of understanding the present invention and are not to be used in any way to limit the interpretation of the present invention.
[0013] In this embodiment, the description is sufficient for those skilled in the art to carry out the invention. However, it is important to understand that other implementations and forms are possible, and that the configuration and structure can be changed and various elements replaced without departing from the scope and spirit of the technical idea of the invention. Therefore, the following description should not be interpreted as limiting it to this embodiment.
[0014] <Example of a schematic configuration of an optical deflector drive system> Figure 1 shows a schematic example of the configuration of an optical deflector driving system 10 according to an embodiment of the present invention.
[0015] As shown in Figure 1, the optical deflector driving system 10 includes a light source 12, a focusing lens 14 that focuses the light (e.g., laser light) emitted by the light source 12, a correction mirror 18, an optical deflector 1 that scans the laser light Ray, which has been focused by the focusing lens 14 and reflected by the correction mirror 18, in two dimensions (horizontal and vertical directions), a screen member 20 on which an image is drawn by the laser light Ray scanned by the optical deflector 1, and a projection lens 23 that projects the image drawn on the screen member 20. Note that the optical deflector driving system 10 may have any configuration as long as it includes an optical deflector that draws an image by scanning the light emitted by the light source 12.
[0016] The light source 12 is, for example, a laser diode (LD) that emits laser light with an emission wavelength in the blue range. The laser light from the light source 12 is focused (for example, collimated) by the focusing lens 14, reflected by the correction mirror 18, and incident on the optical deflector 1 (mirror section 2). The correction mirror 18 is provided to prevent distortion of the image drawn on the screen member 20. The correction mirror 18 may be omitted.
[0017] The optical deflector 1 scans the laser beam focused by the focusing lens 14 in two dimensions (horizontal and vertical directions). The laser beam scanned by the optical deflector 1 draws an image on the screen member 20. The screen member 20 is, for example, a rectangular plate-shaped phosphor plate. The phosphor plate is a wavelength conversion member that converts at least a portion of the laser beam Ray scanned by the optical deflector 1 into light of a different wavelength (for example, light in the yellow spectrum). The image drawn on the screen member 20 is projected by the projection lens 23.
[0018] The optical deflector 1 is, for example, a MEMS scanner. In this embodiment, a piezoelectric method is used to drive the optical deflector. Piezoelectric methods can be broadly classified into one-axis non-resonant / one-axis resonant type, two-axis non-resonant type, and two-axis resonant type, and any of these methods may be used. Below, as an example, an optical deflector 1 using a piezoelectric method (one-axis non-resonant / one-axis resonant type) will be described.
[0019] <Example of a schematic configuration of optical deflector 1> Figure 2 is a perspective view showing a schematic configuration example of a one-axis non-resonant / one-axis resonant type optical deflector 1. The optical deflector 1 comprises a mirror section 2, a pair of first piezoelectric actuators 31 and 32, a first support section 4, a pair of second piezoelectric actuators 51 and 52, and a second support section 6. The optical converter 1 may be configured in any way as long as an unintended abnormal vibration (abnormal resonance) occurs in the optical converter 1 when the change in offset (or amplitude) is reflected in the drive signal (drive voltage).
[0020] The mirror portion 2 comprises a circular reflective surface 2a that reflects incident light, and a circular reflective surface support 2b that supports the reflective surface 2a.
[0021] The reflective surface support 2b is made of a silicon substrate. A pair of torsion bars 21 and 22 are connected to the reflective surface support 2b, extending outward from both ends thereof.
[0022] The first piezoelectric actuators 31 and 32 are each formed in a semi-circular shape and are arranged with a gap between them so as to surround the mirror portion 2. Furthermore, one end of each of the first piezoelectric actuators 31 and 32 is connected opposite to one torsion bar 21, and the other end of each is connected opposite to the other torsion bar 22.
[0023] The first support portion 4 is formed in the shape of a rectangular frame and is provided to surround the mirror portion 2 and the first piezoelectric actuators 31 and 32. The first support portion 4 is also connected to the outside of the center position of the arc portion of the first piezoelectric actuators 31 and 32 and supports the mirror portion 2 via the first piezoelectric actuators 31 and 32.
[0024] The second piezoelectric actuators 51 and 52 are positioned opposite each other with the first support portion 4 in between. The tips of the second piezoelectric actuators 51 and 52 are connected to a pair of sides of the first support portion 4 in a direction perpendicular to the torsion bars 21 and 22.
[0025] The second support portion 6 is formed in a rectangular frame shape and is provided to surround the first support portion 4 and the second piezoelectric actuators 51 and 52. The other ends of the second piezoelectric actuators 51 and 52, on the sides not connected to the first support portion 4, are connected to the second support portion 6. In this way, the second support portion 6 supports the first support portion 4 via the second piezoelectric actuators 51 and 52.
[0026] The first piezoelectric actuators 31 and 32 each comprise first piezoelectric cantilevers 31A and 32A, respectively, configured to bend and deform by piezoelectric drive. Specifically, one of the first piezoelectric actuators 31 and 32, the first piezoelectric actuator 31, comprises one first piezoelectric cantilever 31A. The other first piezoelectric actuator 32 comprises the other first piezoelectric cantilever 32A. The first piezoelectric actuators 31 and 32, through the bending deformation of the first piezoelectric cantilevers 31A and 32A, enable the mirror portion 2 to swing around a first axis Y relative to the first support portion 4 via torsion bars 21 and 22.
[0027] The second piezoelectric actuators 51 and 52 each comprise a pair of second piezoelectric cantilevers 51A-51D and 52A-52D, respectively, configured to bend and deform by piezoelectric drive. Specifically, one of the pair of second piezoelectric actuators 51 and 52, the second piezoelectric actuator 51, is composed of one second piezoelectric cantilever 51A-51D consisting of four piezoelectric cantilevers. The other second piezoelectric actuator 52, of the pair of second piezoelectric actuators 51 and 52, is composed of the other second piezoelectric cantilever 52A-52D consisting of four piezoelectric cantilevers.
[0028] The second piezoelectric cantilevers 51A to 51D are arranged so that their lengths are the same, with their respective ends adjacent to each other, and the mirror sections 2 are arranged at predetermined intervals so that they can swing around the second axis X (an axis perpendicular to the first axis Y; however, it does not need to be exactly perpendicular). The second piezoelectric cantilevers 51A to 51D are connected so as to fold back with respect to the adjacent piezoelectric cantilever. The second axis X is an example of a swing axis in this embodiment.
[0029] The other second piezoelectric cantilevers 52A to 52D, like the first second piezoelectric cantilevers 51A to 51D, have their respective ends adjacent to each other so that their lengths are the same, and are arranged at predetermined intervals so that the mirror portion 2 can swing around the second axis X. The other second piezoelectric cantilevers 52A to 52D are connected to the adjacent piezoelectric cantilever in a way that it folds back.
[0030] Thus, one second piezoelectric actuator 51 and the other second piezoelectric actuator 52 have their respective second piezoelectric cantilevers 51A-51D and 52A-52D formed in a so-called meander shape (or bellows shape).
[0031] The cantilevers 51A and 52A of one second piezoelectric cantilever 51A to 51D and the other second piezoelectric cantilever 52A to 52D, which are located on the mirror portion 2 side (first support portion 4 side), have one end (free end) of each that is not connected to the adjacent second piezoelectric cantilever (hereinafter referred to as the "second second piezoelectric cantilever") 51B and 52B connected to the outer circumference of the first support portion 4.
[0032] Similarly, the piezoelectric cantilevers 51D and 52D of one second piezoelectric cantilever 51A to 51D and the other second piezoelectric cantilever 52A to 52D, which are located on the second support portion 6 side (hereinafter referred to as the "fourth second piezoelectric cantilever"), have one end (free end) of each that is not connected to the adjacent second piezoelectric cantilever (hereinafter referred to as the "third second piezoelectric cantilever") 51C, 52C connected to the inner circumference of the second support portion 6.
[0033] As a result, the first support portion 4 is able to swing around the second axis X relative to the second support portion 6 due to the bending deformation of the second piezoelectric cantilevers 51A to 51D and 52A to 52D that constitute the second piezoelectric actuators 51 and 52.
[0034] Hereafter, of the pair of second piezoelectric cantilevers 51A-51D and 52A-52D, the piezoelectric cantilevers that are positioned in odd-numbered positions counting from the mirror section 2 (the first second piezoelectric cantilevers 51A and 52A, and the third second piezoelectric cantilevers 51C and 52C) will be referred to as the odd-numbered second piezoelectric cantilevers 51A, 51C, 52A, and 52C.
[0035] Furthermore, among the odd-numbered second piezoelectric cantilevers 51A, 51C, 52A, and 52C, those included in one of the second piezoelectric cantilevers 51A-51D are referred to as the odd-numbered second piezoelectric cantilevers 51A and 51C of one group, and those included in the other second piezoelectric cantilever 52A-52D are referred to as the odd-numbered second piezoelectric cantilevers 52A and 52C of the other group.
[0036] Similarly, among the pair of second piezoelectric cantilevers 51A-51D and 52A-52D, the piezoelectric cantilevers that are positioned in even-numbered positions counting from the mirror section 2 (the second second piezoelectric cantilevers 51B and 52B and the fourth second piezoelectric cantilevers 51D and 52D) are referred to as the even-numbered second piezoelectric cantilevers 51B, 51D, 52B, and 52D.
[0037] Furthermore, among the even-numbered second piezoelectric cantilevers 51B, 51D, 52B, and 52D, those included in one of the second piezoelectric cantilevers 51A to 51D are referred to as the even-numbered second piezoelectric cantilevers 51B and 51D of that one group. Similarly, those included in the other second piezoelectric cantilever 52A to 52D are referred to as the even-numbered second piezoelectric cantilevers 52B and 52D of that other group.
[0038] <Operation of Optical Deflector 1> (i) When the mirror portion 2 is swung about the first axis Y relative to the first support portion 4 by the first piezoelectric actuators 31 and 32 In the optical deflector 1, drive voltages are applied to the first piezoelectric actuators 31 and 32. In one of the first piezoelectric actuators 31, a first drive voltage Vy1 is applied between one first upper electrode pad 61b and one lower electrode pad 61a to drive one first piezoelectric cantilever 31A. In the other first piezoelectric actuator 32, a second drive voltage Vy2 is applied between the other first upper electrode pad 62b and the other lower electrode pad 62a to drive the other first piezoelectric cantilever 32A. Here, the first drive voltage Vy1 and the second drive voltage Vy2 are AC voltages (e.g., sine waves) that are out of phase or phase-shifted relative to each other.
[0039] At this time, the oscillation voltage components of the first drive voltage Vy1 and the second drive voltage Vy2 are applied such that the angular displacement of one first piezoelectric cantilever 31A and the other first piezoelectric cantilever 32A occurs in opposite directions in the vertical direction (upward U and downward direction in Figure 1) of the first piezoelectric actuators 31 and 32.
[0040] For example, when oscillating around the first axis Y, if one of the first piezoelectric actuators 31 is displaced upward, one of the first piezoelectric cantilevers 31A is displaced upward. To displace one of the first piezoelectric actuators 31 downward, one of the first piezoelectric cantilevers 31A is displaced downward.
[0041] For the other first piezoelectric actuator 32, similar to the first first piezoelectric actuator 31, when displacing the other first piezoelectric actuator 32 upward, the other first piezoelectric cantilever 32A is displacing upward. To displace the other first piezoelectric actuator 32 downward, the other first piezoelectric cantilever 32A is displacing downward.
[0042] In the optical deflector 1, a large deflection angle is obtained when it oscillates around the first axis Y by either "displacing one first piezoelectric actuator 31 upward and displacing the other first piezoelectric actuator 32 downward" or "displacing one first piezoelectric actuator 31 downward and displacing the other first piezoelectric actuator 32 upward". In this way, the mirror section 2 can oscillate around the first axis Y, and optical scanning can be performed at a predetermined first frequency Fy and a predetermined first deflection angle.
[0043] (ii) When the first support portion 4 is swung around the second axis X relative to the second support portion 6 by the second piezoelectric actuators 51 and 52. In the optical deflector 1, drive voltages are applied to the second piezoelectric actuators 51 and 52. One of the second piezoelectric actuators 51 applies a third drive voltage Vx1 between one odd-numbered second upper electrode pad 61c and one lower electrode pad 61a to drive one of the odd-numbered second piezoelectric cantilevers 51A and 51C. At the same time, one of the second piezoelectric actuators 51 applies a fourth drive voltage Vx2 between one even-numbered second upper electrode pad 61d and one lower electrode pad 61a to drive one of the even-numbered second piezoelectric cantilevers 51B and 51D.
[0044] In the other second piezoelectric actuator 52, a third drive voltage Vx1 is applied between the odd-numbered second upper electrode pad 62c and the lower electrode pad 62a of the other actuator to drive the odd-numbered second piezoelectric cantilevers 52A and 52C of the other actuator. Simultaneously, in the other second piezoelectric actuator 52, a fourth drive voltage Vx2 is applied between the even-numbered second upper electrode pad 62d and the lower electrode pad 62a of the other actuator to drive the even-numbered second piezoelectric cantilevers 52B and 52D of the other actuator.
[0045] The third drive voltage Vx1 and the fourth drive voltage Vx2 are AC voltages with opposite phases (e.g., sine wave, sawtooth wave, etc.). Figure 3 shows an example of the third drive voltage Vx1 and the fourth drive voltage Vx2. In Figure 3, the sawtooth wave shown by the solid line is an example of the third drive voltage Vx1. Hereafter, the third drive voltage Vx1 will also be called the first drive signal P. Also in Figure 3, the sawtooth wave shown by the dashed line is an example of the fourth drive voltage Vx2. Hereafter, the fourth drive voltage Vx2 will also be called the second drive signal N. Note that the third drive voltage Vx1 and the fourth drive voltage Vx2 may be AC voltages with different phases (e.g., sine wave, sawtooth wave, etc.). The field of view and deflection direction of the image projected by the optical deflector drive system 10 can be varied by changing the amplitude and offset amount of at least one of the two drive signals (first drive signal P, second drive signal N). This allows for control over the angle of oscillation and the angle of offset.
[0046] The oscillation voltage components of the third drive voltage Vx1 and the fourth drive voltage Vx2 are set such that, in the vertical direction of the second piezoelectric actuators 51 and 52 (upward U in Figure 1 and the opposite downward direction), the angular displacement between the odd-numbered second piezoelectric cantilevers 51A, 51C, 52A, and 52C and the even-numbered second piezoelectric cantilevers 51B, 51D, 52B, and 52D occurs in opposite directions.
[0047] For example, when oscillating around the second axis X, to displace the tips of the second piezoelectric actuators 51 and 52 upward (direction U shown in Figure 1), the odd-numbered second piezoelectric cantilevers 51A, 51C, 52A, and 52C are displaced upward, and the even-numbered second piezoelectric cantilevers 51B, 51D, 52B, and 52D are displaced downward. To displace the tips of the second piezoelectric actuators 51 and 52 downward, the odd-numbered second piezoelectric cantilevers 51A, 51C, 52A, and 52C are displaced downward, and the even-numbered second piezoelectric cantilevers 51B, 51D, 52B, and 52D are displaced upward. As a result, the odd-numbered second piezoelectric cantilevers 51A, 51C, 52A, and 52C and the even-numbered second piezoelectric cantilevers 51B, 51D, 52B, and 52D bend in opposite directions.
[0048] <Example of displacement of the second piezoelectric actuator 51> Figure 4 shows an example of displacement of one of the second piezoelectric actuators 51 of the optical deflector 1. Figure 4A shows the state in which one of the second piezoelectric actuators 51 is not displaced. Figure 4B shows the state in which one of the second piezoelectric actuators 51 is displaced.
[0049] As shown in Figure 4B, the fourth second piezoelectric cantilever 51D experiences a downward angular displacement at its tip, with its base end, which is connected to the second support 6, acting as a fulcrum. The third second piezoelectric cantilever 51C experiences an upward angular displacement at its tip, with its base end, which is connected to the tip of the fourth second piezoelectric cantilever 51D, acting as a fulcrum.
[0050] The second piezoelectric cantilever 51B experiences a downward angular displacement at its tip, with its base end, which is connected to the tip of the third piezoelectric cantilever 51C, acting as a fulcrum. The first piezoelectric cantilever 51A experiences an upward angular displacement at its tip (which is connected to the first support part 4), with its base end, which is connected to the tip of the second piezoelectric cantilever 51B, acting as a fulcrum. As a result, one of the second piezoelectric actuators 51 experiences an angular displacement equal to the sum of the bending deformations of each of the second piezoelectric cantilevers 51A to 51D.
[0051] Therefore, the first support portion 4 can be oscillated around the second axis X, and optical scanning can be performed at a predetermined second frequency Fx and a predetermined second deflection angle. At this time, by applying an AC voltage with a frequency near the mechanical resonance frequency of the first support portion 4, including the second piezoelectric actuators 51 and 52, as the driving voltage to resonant drive these second piezoelectric actuators 51 and 52, optical scanning can be performed at a larger deflection angle.
[0052] When the first support portion 4 is oscillated around the second axis X, it is not necessary to apply an AC voltage as described above; a DC voltage may be applied instead. In this case, the magnitude of the bending deformation generated in the second piezoelectric cantilevers 51A to 51D and 52A to 52D changes linearly according to the magnitude of the DC voltage. Therefore, unlike the case where an AC voltage is applied to resonantly drive the piezoelectric cantilever, any output can be obtained from the second piezoelectric actuators 51 and 52 by controlling the magnitude of the DC voltage.
[0053] Thus, in the optical deflector 1, when it oscillates around the second axis X, the deflection angle can be controlled linearly according to the magnitude of the DC voltage applied as the driving voltage, so any deflection angle can be obtained at any speed.
[0054] The second piezoelectric actuators 51 and 52 are each formed with a meander structure (or bellows structure). This is designed so that the bending deformation of each piezoelectric cantilever accumulates. For this reason, the second piezoelectric actuators 51 and 52 can more easily obtain a larger deflection angle than the first piezoelectric actuators 31 and 32.
[0055] Therefore, when the first piezoelectric actuators 31 and 32 are oscillating, in order to obtain the largest possible deflection angle, the frequency (first frequency Fy) used to change the upward or downward displacement of the first piezoelectric actuators 31 and 32 may be set to a resonant frequency determined by the structure and materials of the optical deflector 1 (especially the piezoelectric cantilever, etc.).
[0056] The second piezoelectric actuators 51 and 52 are formed in a meander structure (or bellows structure) and are more prone to oscillation than the first piezoelectric actuators 31 and 32. Therefore, the second frequency Fx can be set to a sufficiently lower value than the first frequency Fy. For example, the first frequency Fy can be set to 30 kHz and the second frequency Fx to 60 Hz.
[0057] <Example of operation when rendering an image> Figure 5 shows how the image p is drawn on the screen member 20 by the laser beam Ray scanned (raster scan) by the optical deflector 1 (the focusing lens 14, correction mirror 18, and projection lens 23 are omitted).
[0058] As the mirror portion 2 swings about the first axis Y relative to the first support portion 4, the laser beam Ray from the light source 12 incident on the mirror portion 2 is scanned in a first direction (for example, horizontally), as shown in Figure 5.
[0059] Furthermore, as the mirror section 2 pivots around the second axis X relative to the second support section 6, the laser beam Ray from the light source 12 incident on the mirror section 2 is scanned in a second direction (for example, vertically), as shown in Figure 5.
[0060] Figure 6 shows the relationship between the drive signal applied to the optical deflector 1 (see Figure 6A) and the oscillation angle of the mirror section 2 (see Figure 6B).
[0061] In the optical deflector 1, when the displacement amounts of the alternately arranged cantilevers (odd-numbered second piezoelectric cantilevers 51A, 51C, 52A, and 52C and even-numbered second piezoelectric cantilevers 51B, 51D, 52B, and 52D) are the same (when the voltages of the first drive signal P and the second drive signal N are the same), the mirror section 2 is positioned at the reference position (= angle 0°: see Figure 6B). The movement (oscillation) of the mirror section 2 around the second axis X is the same as the differential signal of the two signals (the signal obtained by subtracting the second drive signal N from the first drive signal P) from the perspective of the drive signals. That is, when the differential signal is 0V, the mirror section 2 is positioned at the reference position (= angle 0°: see Figure 6B).
[0062] As described above, an image p is drawn on the screen member 20 by the laser beam Ray scanned by the optical deflector 1. At that time, by changing the amplitude of at least one of the first drive signal P and the second drive signal N (see Figure 3), the vertical width (see symbols H1 to H3 in Figure 7) of the image p drawn on the screen member 20 by the laser beam Ray scanned by the optical deflector 1 can be changed, as shown in Figure 7. Figure 7 shows examples of images p with different vertical widths drawn on the screen member 20.
[0063] Furthermore, by changing the offset (offset amount) of at least one of the first drive signal P and the second drive signal N (see Figure 3), the vertical position (offset amount) of the image p drawn on the screen member 20 by the laser beam Ray scanned by the optical deflector 1 can be changed, as shown in Figure 8. Figure 8 shows examples of images p drawn on the screen member 20 with different vertical positions (offset amounts).
[0064] <Laminated structure of optical deflector 1> Figure 9 is a plan view (Figure 9A) and a cross-sectional view (Figure 9B) of A-A' (a direction perpendicular to the bending direction of the piezoelectric actuator) showing the stacked structure of the main part of the optical deflector 1 according to this embodiment. The number of cantilevers in the second piezoelectric actuators 51 and 52 is arbitrary (four each in Figure 2), but in Figure 9, for convenience, there are three on each side of the mirror section 2 and the first piezoelectric actuators 31 and 32.
[0065] The first piezoelectric actuators 31 and 32 and the second piezoelectric actuators 51 and 52, as shown in Figure 9B, have a laminated structure (basic structure) comprising a substrate (support) 91, a lower electrode 92 provided on the substrate 91, a piezoelectric film (oxide piezoelectric) 93 provided on the lower electrode 92, an upper electrode 94 provided on the piezoelectric film 93, wiring 96, and an interlayer insulating film 95 provided on the upper electrode 94 and below the wiring 96. However, as shown in Figure 9A, the lower electrode 92 and the upper electrode 94 are not provided to cover the entire area of the cantilevers 51A to 51C and 52A to 52C, but only cover a part of them.
[0066] In particular, the upper electrode 94 does not completely cover the lower electrode 92 and the piezoelectric film (oxide piezoelectric material) 93, but only partially. Therefore, when a voltage is applied to the wiring 96 (a voltage is applied between the upper electrode 94 and the lower electrode 92), an electric field is generated in the region where the lower electrode 92 and the upper electrode 94 are provided, but no electric field is generated in the region where they are not provided. The upper electrode 94 is provided along the stretching direction of the first piezoelectric actuators 31 and 32 and the second piezoelectric actuators 51 and 52. Therefore, bending occurs in the first piezoelectric actuators 31 and 32 and the second piezoelectric actuators 51 and 52 in the stretching direction of the substrate 91 where the upper electrode 94 is provided. Focusing on the end of the piezoelectric film 93 in a direction perpendicular to the bending direction of the piezoelectric actuator, an electric field is applied to the first end region 97 in the stretching direction of the piezoelectric film 93 where the upper electrode 94 is provided, but no electric field is applied to the second end region 98 in the stretching direction of the piezoelectric film 93 where the upper electrode 94 is not provided.
[0067] Therefore, in the conventional technology where an interlayer insulating film was also provided in the first end region 97, hydrogen would penetrate the piezoelectric film, leading to dielectric breakdown. Although the first end region 97 also has a portion where the upper electrode 94 is not provided, its width is less than 10 μm, and the effect of the electric field is sufficiently large.
[0068] In contrast, if the electric field is sufficiently small (for example, less than 1 / 10 of the driving electric field, or less than 1 V / μm), the increase in water concentration and oxygen vacancy concentration on the lower electrode (cathode) 92 side due to the electric field is small, and the effect of the decrease in breakdown breakdown pressure becomes sufficiently small. That is, even if an interlayer insulating film 95 is formed at the edge of the piezoelectric film 93 where the electric field strength is sufficiently small, dielectric breakdown will not occur in this region. As shown in the second region 98 of Figure 9A, an interlayer insulating film 95 can be formed at the edge of the piezoelectric film 93 where the electric field strength is sufficiently small (including the case where no electric field is applied).
[0069] In the basic structure shown in Figure 9 of the present invention, it is important that the interlayer insulating film 95 (which serves to insulate the wiring 96 from the upper electrode 94) does not cover the entire area of the piezoelectric film 93 on which the upper electrode 94 is provided. Here, although there are several possible installation methods for the interlayer insulating film 95, at least the following methods are considered to be effective in suppressing dielectric breakdown.
[0070] (i) A configuration in which the interlayer insulating film 95 is provided from the outer edge of the piezoelectric film 93, avoiding a predetermined range (the end region described above). This configuration is shown in Figure 9B. In this configuration, the interlayer insulating film 95 is provided in a region wider than the region directly beneath the wiring 96. The interlayer insulating film 95 is preferably thicker than 500 nm. However, the interlayer insulating film 95 is not provided in the above-mentioned edge region (a region defined by 5 μm inward from the outer edge of the piezoelectric film 93).
[0071] Here, with reference to Figure 10, the reason why this configuration has the effect of preventing (suppressing) dielectric breakdown will be explained. Figure 10A shows the occurrence of dielectric breakdown when a configuration in which the interlayer insulating film 95 is laminated over the entire upper electrode 94 and piezoelectric film 93 (conventional configuration) is adopted. In the conventional configuration (see Figure 10B), the interlayer insulating film 95 is formed with a thickness of more than 500 nm from the entire upper electrode 94 to the side wall of the piezoelectric film 93.
[0072] As shown in Figure 10A, in the conventional configuration, dielectric breakdown 101 occurs in the outer peripheral edge region (first edge region 97) of the piezoelectric film 93. Here, the outer peripheral edge is the side of the piezoelectric film 93, and the outer peripheral edge region is the surrounding region including the outer peripheral edge. As explained in "Problems to be Solved by the Invention" above, when hydrogen enters the piezoelectric film 93 from the interlayer insulating film (silicon nitride film) 95 which contains a large amount of hydrogen, the dielectric strength deteriorates and dielectric breakdown occurs. Here, the inventors' investigations have shown that the edge region where dielectric breakdown is likely to occur corresponds to the region defined by 5 μm inward from the outer peripheral end of the piezoelectric film 93. Therefore, dielectric breakdown can be reduced by not placing the interlayer insulating film 95 in this edge region. Furthermore, the effect of reducing dielectric breakdown is further enhanced by not placing the interlayer insulating film 95 inward from the outer peripheral end of the piezoelectric film 93, including the edge region.
[0073] By doing so, it is possible to prevent the hydrogen concentration from becoming high in the end region of the piezoelectric film 93, thereby ensuring a predetermined dielectric strength in that region and preventing (or at least suppressing) dielectric breakdown in that region.
[0074] (ii) Configuration in which the interlayer insulating film 95 is provided only directly beneath the wiring 96 The embodiment is shown in Figure 11. If the interlayer insulating film 95 is placed only directly beneath the wiring 96, it can avoid the end region where dielectric breakdown may occur, thereby preventing (or at least suppressing) the occurrence of dielectric breakdown in the end region of the piezoelectric film 93. The interlayer insulating film 95 preferably has a thickness of more than 500 nm.
[0075] (iii) A configuration that reduces the thickness of the interlayer insulating film 95 on the end region of the piezoelectric film 93. In this embodiment, as shown in Figure 12, an interlayer insulating film 95 is provided up to the outer peripheral edge and side (side wall) portion of the piezoelectric film 93, but the thickness of the interlayer insulating film 95 provided in the end region and side portion of the piezoelectric film 93 is made thinner than the thickness of the interlayer insulating film 95 under the wiring 96.
[0076] In order to reliably insulate the upper electrode 94 and the wiring 96 directly beneath the region where the wiring 96 is located, an interlayer insulating film 95 of a predetermined thickness is required. However, in other regions, it is not necessary to provide an interlayer insulating film 95 of the same thickness. The inventor conducted an experiment to measure the high-temperature durability life (time) of a piezoelectric device (optical deflector 1) using an oxide piezoelectric material (piezoelectric layer 93). Figure 16 is a graph (experimental result) showing the dependence of the high-temperature durability life of the piezoelectric device on the thickness of the insulating layer. The insulating layer (corresponding to the interlayer insulating film) used in the experiment was formed to cover the entire oxide piezoelectric layer, including the outer edge. That is, it is the experimental result when only the thickness of the interlayer insulating film was changed in the conventional configuration shown in Figure 10B. Examples of materials for the oxide piezoelectric material include lead zirconate titanate and barium titanate, but other oxide piezoelectric materials that have oxygen as a constituent element may also be used. Examples of materials for the insulating layer (interlayer insulating film) include silicon nitride, silicon oxide, and alumina. However, hydrogen-containing raw material gases or carrier gases are used for film formation, and hydrogen is contained within the film. Other materials and formation methods may be used for insulating materials that contain hydrogen.
[0077] As shown in Figure 16, the high-temperature operating life of the piezoelectric device improved as the thickness of the insulating layer decreased, and no dielectric breakdown was observed even after 4,250 hours when the thickness of the insulating layer was 500 nm or less. Therefore, in improving the durability of oxide piezoelectrics (piezoelectric films), it is preferable that the thickness of the insulating layer (interlayer insulating film) on top of it be as thin as possible, but a sufficiently large effect can be obtained with a thickness of 500 nm or less. On the other hand, the insulating layer between the wiring and the upper electrode needs to be thick enough to sufficiently insulate the potential difference applied between the upper and lower electrodes. For example, when the applied voltage is set to 40V to 50V, a thickness of 300 nm or more is preferable to obtain an insulating effect. However, a thicker layer is preferable when the applied voltage is increased further or to ensure insulation more reliably.
[0078] According to these experimental results, even if the thickness of the interlayer insulating film 95 is set to 1 μm in the region directly beneath the wiring 96, as in the conventional method, it can be concluded that the thickness of the interlayer insulating film 95 in other regions can be set to 500 nm or less. This ensures high insulation directly beneath the wiring 96 with a thick interlayer insulating film 95, while maintaining a certain level of insulation in the edge region 97 with a thin interlayer insulating film 95, thereby suppressing hydrogen from entering the piezoelectric film 93. Furthermore, these experiments suggest that the thickness of the interlayer insulating film 95 may be set to 300 nm or more and 500 nm or less throughout the entire piezoelectric film 93 and upper electrode 94.
[0079] (iv) A configuration in which the interlayer insulating film 95 is not provided on the side surface of the outer edge of the piezoelectric film 93 (side wall of the piezoelectric film 93) As shown in Figure 13, the interlayer insulating film 95 is not provided on the side surface of the piezoelectric film 93. Even with this configuration, it is expected that the effect of preventing and suppressing dielectric breakdown will be greater than in the conventional example (Patent Document 1). As mentioned above, dielectric breakdown occurs from the outer edge of the piezoelectric film 93 and gradually spreads to the interior region, and a certain degree of effect can be expected if the high hydrogen concentration on the side walls of the piezoelectric film 93 can be avoided.
[0080] <Laminated structure of optical deflector 1 with the outermost layer formed: Modified example 1> Figure 14 shows the laminated structure of the main part of the optical deflector (piezoelectric device) 1 with the outermost layer formed. Figure 14A shows the structure according to Modification 1 of this embodiment, and Figure 14B shows the structure according to a comparative example (conventional example) with the outermost layer formed.
[0081] In the modified example 1 of this embodiment, the main part of the optical deflector 1 (first piezoelectric actuators 31 and 32 and second piezoelectric actuators 51 and 52) has a laminated structure as shown in Figure 14A, comprising a substrate (support) 91, a lower electrode 92 provided on the substrate 91, a piezoelectric film (oxide piezoelectric) 93 provided on the lower electrode 92, an upper electrode 94 provided on the piezoelectric film 93, wiring 96, an interlayer insulating film 95 provided on the upper electrode 94 and below the wiring 96, and an outermost layer 121 provided on the wiring 96 and a part of the interlayer insulating film 95. On the other hand, the main part of the optical deflector according to the comparative example (conventional example), as shown in Figure 12B, has a laminated structure comprising a substrate (support) 91, a lower electrode 92 provided on the substrate 91, a piezoelectric film (oxide piezoelectric) 93 provided on the lower electrode 92, an upper electrode 94 provided on the piezoelectric film 93, wiring 96, an interlayer insulating film 95 provided on the upper electrode 94 and below the wiring 96, and an outermost layer 121 provided over the entire area of the wiring 96 and the interlayer insulating film 95.
[0082] In optical deflectors, an outermost layer 121 is usually formed outside (above) the wiring 96 to protect it. The outermost layer 121, like the interlayer insulating film 95, is an insulating layer containing a large amount of hydrogen, such as silicon nitride, silicon oxide, or alumina, and is a factor in the reduction of durability in the edge region of the piezoelectric film (oxide piezoelectric material) 93 (5 μm from the outer edge of the piezoelectric film 93). Therefore, it is thought that the durability will be relatively improved simply by not forming the outermost layer 121 in the edge region of the piezoelectric film (oxide piezoelectric material) 93.
[0083] In the conventional structure (Figure 14B), the interlayer insulating film 95 and the outermost layer 121 are formed with a substantially uniform thickness across the entire surface of the piezoelectric film 93. On the other hand, in the modified example 1 of this embodiment, the total thickness of the interlayer insulating film 95 below the wiring 96 and the outermost layer 121 above the wiring 96 is thinner in the edge region of the piezoelectric film 93 than in the vicinity of the wiring 96.
[0084] In the conventional example (configuration shown in Figure 14B), typically, for example, an interlayer insulating film 95 with a thickness of 500 nm and an outermost layer 121 with a thickness of 500 nm (a hydrogen-containing film totaling 1 μm) are provided over the entire surface of the piezoelectric film 93. Referring to Figure 16, it can be seen that in the case of an insulating layer with a thickness of 1 μm, dielectric breakdown occurs in a short time (less than 500 hours) when the optical deflector is activated. Therefore, as shown in Figure 14A, the outermost layer 121 with a thickness of 500 nm is provided only near the wiring 96, avoiding the edge region, and an interlayer insulating film 95 with a thickness of less than 500 nm is provided in the edge region and sides (side walls) of the piezoelectric film 93 (including cases where the interlayer insulating film 95 is not provided in these areas), thereby protecting the wiring 96 and preventing (suppressing) the occurrence of dielectric breakdown.
[0085] Furthermore, as shown in Figure 15, it is even better if the interlayer insulating film 95 and the outermost layer 121 are not provided in the end region of the piezoelectric film 93 (exposing the piezoelectric film 93).
[0086] Alternatively, an interlayer insulating film 95 may not be provided in the end region of the piezoelectric film 93, and a configuration may be adopted in which the outermost layer 121 with a low hydrogen content is formed only in the end region of the piezoelectric film 93.
[0087] <Configuration for countermeasures against high humidity environments: Modified example 2> When the optical deflector (piezoelectric device) 1 is used under high humidity conditions, hydrogen may penetrate the piezoelectric film 93 due to moisture in the ambient atmosphere, potentially reducing the durability of the optical deflector 1. In particular, when platinum is used for the upper electrode 94, the catalytic action of platinum accelerates the decomposition of water, allowing more hydrogen to penetrate the piezoelectric film 93. To prevent this, an interlayer insulating film 95 made of silicon nitride, silicon oxide, alumina, etc., with a low hydrogen concentration in the film may be formed in the end region of the piezoelectric film 93, for example, using sputtering or atomic layer deposition (ALD). In this case, the hydrogen content of the interlayer insulating film 95 in the end region will be lower than that near the wiring 96.
[0088] Furthermore, to prevent moisture from coming into contact with the optical deflector 1, a hermetically sealed package may be applied (the optical deflector 1 is housed in the hermetically sealed package), and parts other than the mirror section 2 may be sealed with metal (SUS: Steel Use Stainless).
[0089] <Summary> (i) The piezoelectric device of the present invention comprises a support, a lower electrode 92 formed on the support, an oxide piezoelectric material 93 formed on the lower electrode 92, an upper electrode 94 formed on the oxide piezoelectric material 93, an interlayer insulating film 95 formed on the upper electrode 94, and a wiring portion 96 formed on the interlayer insulating film 95. The wiring portion 96 may further have an outermost layer 121.
[0090] On the side surface of the oxide piezoelectric material 93, the combined thickness of the interlayer insulating film 95 and the outermost layer 121 is thinner than the combined thickness of the interlayer insulating film 95 formed below the wiring portion 96 and the outermost layer 121 formed above it, i.e., the thickness of the insulator that overlaps with the wiring portion 96. This makes it possible to ensure the insulating properties of the wiring portion 96 while suppressing the intrusion of hydrogen into the oxide piezoelectric material 93.
[0091] On the side surface of the oxide piezoelectric material 93, the interlayer insulating film 95 and the outermost layer 121 may be provided only as the interlayer insulating film 95, or only as the outermost layer 121. Alternatively, neither the interlayer insulating film 95 nor the outermost layer 121 may be provided (total thickness 0). Furthermore, on the side surface of the oxide piezoelectric material 93, the combined thickness of the interlayer insulating film 95 and the outermost layer 121 is preferably 500 nm or less, and more preferably 300 nm or less. This condition for total thickness is also true when only one is formed and the other is not formed (interlayer insulating film 95 = 0 nm or outermost layer 121 = 0 nm).
[0092] In the edge region of the oxide piezoelectric material 93 (within 5 μm from the outer peripheral edge of the piezoelectric film 93), the thickness of the insulating film (the sum of the interlayer insulating film 95 and the outermost layer 121) is preferably thinner than the thickness of the insulator that overlaps with the wiring portion 96. Furthermore, in the area including the edge region, within 10 μm from the outer peripheral edge of the oxide piezoelectric material 93, the sum of the interlayer insulating film 95 and the outermost layer 121 is more preferably thinner than the thickness of the insulator that overlaps with the wiring portion 96.
[0093] In the edge region, the interlayer insulating film 95 and the outermost layer 121 may be provided only as the interlayer insulating film 95, or only as the outermost layer 121. Neither the insulating film 95 nor the outermost layer 121 may be provided in the edge region (total thickness 0).
[0094] In the edge region of the oxide piezoelectric material 93 (within 5 μm from the outer edge of the piezoelectric film 93), the combined thickness of the interlayer insulating film 95 and the outermost layer 121 is preferably 500 nm or less, and more preferably 300 nm or less. The combined thickness includes cases where either thickness is 0 nm (interlayer insulating film 95 = 0 nm or outermost layer 121 = 0 nm).
[0095] (ii) In one embodiment of the present invention, as shown in Figure 9B, the thickness of the interlayer insulating film (insulating layer) 95 formed on at least the side of the piezoelectric film (oxide piezoelectric material) 93 in the region where an electric field is applied (the region where an electric field is generated by applying a voltage between the upper electrode 94 and the lower electrode 92) is less than the thickness of the interlayer insulating film 95 under the wiring (wiring portion) 96 (including the state in which the side is not covered with the interlayer insulating film 95 and the piezoelectric film 93 is exposed on the side). By making the interlayer insulating film 95 on the side of the piezoelectric film 93 thinner than under the wiring 96 (including not providing it), it is possible to prevent the concentration of hydrogen on the side of the piezoelectric film 93 from increasing, and to suppress dielectric breakdown in the piezoelectric film 93.
[0096] In this embodiment, the thickness of the interlayer insulating film 95 in the portion of the piezoelectric film 93 other than the side portion (including the region below the wiring 96) may be set to 300 nm or more and 500 nm or less over the entire surface of that portion.
[0097] (iii) In another embodiment of the present invention, the thickness of the interlayer insulating film 95 formed in an end region defined within a predetermined range from the outer edge of the piezoelectric film 93 in the region where an electric field is generated (for example, a range of 5 μm from the outer edge of the piezoelectric film 93) is less than the thickness under the wiring 96 (including a state in which the sides of the piezoelectric film 93 and the end region are not covered with the interlayer insulating film and the upper electrode 94 is exposed). By making the interlayer insulating film 95 thinner than under the wiring 96 not only on the sides of the piezoelectric film 93 but also in the end region (including not providing it), it is possible to prevent the concentration of hydrogen in the end region of the piezoelectric film 93 from increasing, and to further reduce the possibility of dielectric breakdown occurring in the piezoelectric film 93.
[0098] (iv) A piezoelectric device according to yet another embodiment of the present invention comprises an outermost layer 121 on the wiring 96 that functions as a protective film for protecting the wiring 96. The outermost layer 121 may also be provided on the wiring 96, on the interlayer insulating film 95, and on the sides of the piezoelectric film 93. In this case, the thickness of the outermost layer 121 at least on the sides of the piezoelectric film 93 is less than the thickness of the outermost layer 121 formed on the wiring 96 (including not covering the sides with the outermost layer 121). Furthermore, the thickness of the outermost layer 121 formed in an end region defined within a predetermined range from the outer peripheral edge of the piezoelectric film 93 in the electric field generation region (for example, a range of 5 μm from the outer peripheral edge of the piezoelectric film 93) may be less than the thickness of the outermost layer 121 on the wiring 96. The outermost layer 121 contains a large amount of hydrogen because it is formed using the same material and plasma CVD as the interlayer insulating film 95. Therefore, by making the thickness of the outermost layer 121 on the sides and end regions of the piezoelectric film 93 thinner than that on the wiring 96 (including not providing it), dielectric breakdown in the piezoelectric film 93 can be prevented, and the durability of the piezoelectric device can be improved.
[0099] In the configuration in which the outermost layer 121 is provided, the interlayer insulating film 95 may be formed over the entire surface of the piezoelectric film 93 in the electric field generation region. However, in this case, it is preferable that the sum of the thicknesses of the outermost layer 121 and the interlayer insulating film 95 in the end region be less than the sum of the thicknesses of the outermost layer 121 and the interlayer insulating film 95 in the wiring 96.
[0100] (v) A piezoelectric device according to yet another embodiment of the present invention is a form that can be derived from the above experimental results, wherein the thickness of the interlayer insulating film 95 is set to 300 nm or more and 500 nm or less over the entire surface of the piezoelectric device. This makes it possible to sufficiently insulate the potential difference applied between the upper electrode 94 and the lower electrode 92, and to prevent dielectric breakdown for more than 4,250 hours.
[0101] (vi) A piezoelectric device according to yet another embodiment of the present invention may be configured to be housed in a hermetically sealed package (SUS).
[0102] (vii) The processes and techniques described herein are not inherently related to any particular device and can be implemented by combinations of the components. Various types of general-purpose devices can also be added. Dedicated devices may be constructed to perform the functions of this embodiment. Various functions can also be formed by appropriately combining the multiple components disclosed in this embodiment. For example, some components may be removed from all the components shown in the embodiment and each variation, or components from different forms may be appropriately combined.
[0103] In addition, any person with ordinary skill in the art can see from the consideration of this embodiment and each example that other implementations of the present invention may be apparent. The specification and specific examples are typical, and the scope and spirit of the art of the present invention are shown in the subsequent claims. [Explanation of Symbols]
[0104] 1 Optical deflector 2 Mirror section 4 1st support part 6 Second support part 10. Optical deflector driving system 12 light source 14. Focusing lens 18 Correction Mirror 20 Screen components 21, 22 Torsion bars 23 Projection lens 31. First piezoelectric actuator 31A First piezoelectric cantilever 32. First piezoelectric actuator 32A First piezoelectric cantilever 51. Second piezoelectric actuator 51A to 51D Second piezoelectric cantilever 52. Second piezoelectric actuator 52A to 52D Second piezoelectric cantilever 91 Substrate (support) 92 Lower electrode 93 Piezoelectric film (oxide piezoelectric material) 94 Upper electrode 95 Interlayer insulating film 96 Wiring 97 End of piezoelectric film to which an electric field is applied 98 Piezoelectric film end where no electric field is applied 121 Outermost layer
Claims
1. Support and A lower electrode formed on the support, An oxide piezoelectric material formed on the lower electrode, An upper electrode formed on the oxide piezoelectric material, Insulating layer and, It includes a wiring section, The insulating layer is formed on the upper electrode and has an interlayer insulating layer on which the wiring portion is formed. A piezoelectric device wherein an electric field is generated by applying a voltage between the upper electrode and the lower electrode, and the thickness of the insulating layer formed on the side of the oxide piezoelectric material in the region where the electric field is generated is less than the thickness of the insulating layer in the position overlapping the wiring portion.
2. In claim 1, The insulator layer consists only of the interlayer insulating layer, in a piezoelectric device.
3. In claim 1, The insulating layer is composed of the interlayer insulating layer and the outermost layer formed on the wiring portion. A piezoelectric device in which the thickness of the insulating layer at a position overlapping the wiring portion is the sum of the thickness of the interlayer insulating layer below the wiring portion and the thickness of the outermost layer above the wiring layer.
4. In claim 1, A piezoelectric device in which the side portion of the oxide piezoelectric material in the region where the electric field is generated is not covered with the insulating layer.
5. In claim 1, Furthermore, the piezoelectric device wherein the thickness of the insulating layer formed in a region 5 μm from the outer edge of the oxide piezoelectric material in the region where the electric field is generated is less than the thickness of the insulating layer beneath the wiring.
6. In claim 5, Furthermore, the piezoelectric device wherein the thickness of the insulating layer formed in a region of 10 μm from the outer edge of the oxide piezoelectric material is less than the thickness of the insulating layer beneath the wiring.
7. In claim 5, A piezoelectric device in which the oxide piezoelectric material is not covered by the insulating layer in a region of 5 μm from its outer edge.
8. In claim 3, A piezoelectric device in which the thickness of the insulating layer at least on the side is less than the thickness of the outermost layer formed on the wiring portion.
9. In claim 8, Furthermore, the piezoelectric device wherein the thickness of the outermost layer formed in an end region defined within a predetermined range from the outer edge of the oxide piezoelectric material in the region where the electric field is generated is less than the thickness of the outermost layer on the wiring.
10. In claim 9, The end region is defined as a region within a range of 5 μm from the outer edge of the oxide piezoelectric material, in a piezoelectric device.
11. In claim 10, The insulating layer is formed over the entire surface of the oxide piezoelectric material in the region where the electric field is generated. A piezoelectric device in which the sum of the thicknesses of the outermost layer and the insulating layer in the end region is less than the sum of the thicknesses of the outermost layer and the insulating layer in the wiring portion.
12. In claim 1, A piezoelectric device in which the thickness of the insulating layer is 300 nm or more and 500 nm or less.
13. Support and A lower electrode formed on the support, An oxide piezoelectric material formed on the lower electrode, An upper electrode formed on the oxide piezoelectric material, Insulating layer and, It includes a wiring section, The insulating layer is formed on the upper electrode and has an interlayer insulating layer on which the wiring portion is formed. A piezoelectric device in which the thickness of the insulating layer is 300 nm or more and 500 nm or less.
14. In claim 1 or 13, A piezoelectric device housed in a hermetically sealed package.
15. Light source and A focusing lens that collects light from the aforementioned light source, An optical deflector having the piezoelectric device according to claim 1 or 13, which scans the light focused by the focusing lens in two dimensions, A screen section on which an image is drawn by light scanned two-dimensionally by the aforementioned optical deflector, A projection lens for projecting the image drawn on the screen portion, An optical deflector drive system equipped with the above.