Piezoelectric actuator and optical scanning device

Abstract

The present invention provides a piezoelectric actuator and an optical scanning device, which reduce the driving voltage of the piezoelectric actuator. The piezoelectric actuator comprises a substrate and a driving source formed on the substrate, wherein the driving source comprises a piezoelectric film with an average particle size of 1 μm or less.

Description

Technical Field

[0001] The present invention relates to a piezoelectric actuator and an optical scanning device. Background Art

[0002] In an optical scanning device that rotates a mirror portion to scan light, a piezoelectric actuator having a piezoelectric film is sometimes used as a driving source for driving the mirror portion. It is preferred that the driving voltage of the piezoelectric actuator is low, and therefore, for example, research is being conducted to increase the piezoelectric constant and reduce the driving voltage of the piezoelectric actuator by using a PZT-based material as the material of the piezoelectric film.

[0003] Specifically, for example, an optical scanning device is proposed, wherein the piezoelectric film of the piezoelectric actuator is composed of a Pb-containing A site of the perovskite ferroelectric and a Mn-containing B acceptor element. A , containing Nb as donor element B D It is composed of PZT materials composed of Pb(Mn,Nb)O3.

[0004] In this optical scanning device, the film thickness of the piezoelectric film is about 2 μm to 10 μm, and the particle size of the piezoelectric film is about 1 μm. In addition, the mirror portion is driven by resonance, and the driving voltage of the piezoelectric actuator is about several tens of V (for example, see Patent Document 1).

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent Application Publication No. 2015-115355 Summary of the invention

[0008] Problems to be solved by the invention

[0009] However, conventionally, it has not been possible to sufficiently reduce the driving voltage of the piezoelectric actuator, and further reduction of the driving voltage of the piezoelectric actuator has been desired.

[0010] The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to reduce the driving voltage of a piezoelectric actuator.

[0011] Methods for solving problems

[0012] The piezoelectric actuator (300) comprises a substrate (310) and a driving source (320) formed on the substrate (310), wherein the driving source (320) comprises a piezoelectric film (340, 360) having an average particle size of less than 1 μm.

[0013] The reference symbols in the above brackets are provided for easy understanding and are only examples and are not intended to limit the illustration.

[0014] Effects of the Invention

[0015] According to the disclosed technology, it is possible to reduce the driving voltage of the piezoelectric actuator. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a cross-sectional view (part 1) illustrating a piezoelectric actuator according to a first embodiment.

[0017] Figure 2 This is a cross-sectional view (part 2) illustrating the piezoelectric actuator according to the first embodiment.

[0018] Figure 3 This is a plan view illustrating an optical scanning device according to the second embodiment.

[0019] Figure 4 This is a diagram illustrating the relationship between the average particle size of the piezoelectric film and the driving voltage.

[0020] Figure 5 This is a cross-sectional photograph of the piezoelectric film 340 on the lower electrode 330 (part 1).

[0021] Figure 6 This is a diagram illustrating the relationship between the average grain size of the piezoelectric thin film and the average grain size of the underlying layer.

[0022] Figure 7 This is a diagram for explaining the reduction in driving voltage.

[0023] Figure 8 This is a cross-sectional photograph of the piezoelectric film 340 on the lower electrode 330 (part 2).

[0024] Fig. 9 FIG. 3 is a cross-sectional photograph of the piezoelectric film 340 on the lower electrode 330 (part 3).

[0025] Explanation of symbols

[0026] 1: optical scanning device, 10: mirror reflection surface, 20: stress relaxation area, 30: slit, 40: mirror portion, 50: torsion bar, 50a: base end portion, 51: piezoelectric sensor, 60, 100: connecting portion, 70: horizontal driving portion, 71: horizontal driving beam, 72: driving source, 80: movable frame, 90: vertical driving beam, 91: driving source, 92: piezoelectric sensor, 110: vertical driving portion, 12 0: fixed frame, 130: terminal, 140: wiring, 140a: substrate contact part, 300, 300A: piezoelectric actuator, 310: substrate, 320: driving source, 330: lower electrode, 331, 351, 371: first layer, 332, 352, 372: second layer, 333, 353: third layer, 340, 360: piezoelectric film, 350: intermediate electrode, 370: upper electrode. DETAILED DESCRIPTION

[0027] Hereinafter, the mode for carrying out the invention will be described with reference to the drawings. In each of the drawings, the same components are denoted by the same reference numerals, and duplicate description may be omitted.

[0028] <First Embodiment>

[0029] Figure 1 This is a cross-sectional view illustrating a piezoelectric actuator according to the first embodiment. Figure 1 The piezoelectric actuator 300 includes a substrate 310 and a driving source 320 formed on the substrate 310 .

[0030] The driving source 320 has a lower electrode 330 formed on the substrate 310 , a piezoelectric film 340 formed on the lower electrode 330 , an intermediate electrode 350 formed on the piezoelectric film 340 , a piezoelectric film 360 formed on the intermediate electrode 350 , and an upper electrode 370 formed on the piezoelectric film 360 .

[0031] In the piezoelectric actuator 300, for example, the intermediate electrode 350 is grounded, and a driving signal for driving the piezoelectric actuator 300 is supplied to the lower electrode 330 and the upper electrode 370. If the driving signal is supplied to the lower electrode 330 and the upper electrode 370, the piezoelectric actuator 300 is displaced according to the voltage of the driving signal.

[0032] The substrate 310 is, for example, a silicon substrate. A silicon oxide film or the like may be formed on the upper surface of the silicon substrate. As the substrate 310, an SOI (Silicon On Insulator) substrate having a support layer, an embedded (BOX: Buried Oxide) layer, and an active layer may also be used.

[0033] The lower electrode 330 is, for example, a film formed of three layers: a first layer 331 , a second layer 332 , and a third layer 333 .

[0034] It is preferred that the first layer 331 and the third layer 333 are conductive oxide films having a perovskite structure and a (110) orientation, respectively. As conductive oxide films having a perovskite structure and a (110) orientation, for example, LNO (LaNiO3: lanthanum nickelate) thin films, SRO (Sr2RuO4: strontium ruthenate) thin films, BRO (BaRuO3: barium ruthenate) thin films, etc. can be cited. The thickness of each of the first layer 331 and the third layer 333 is, for example, 30 nm.

[0035] The second layer 332 is, for example, a Pt thin film. The second layer 332 may be a platinum group thin film other than Pt, for example, an Ir thin film, an Os thin film, etc. The film thickness of the second layer 332 is, for example, 150 nm.

[0036] The intermediate electrode 350 is, for example, a film formed of three layers: a first layer 351 , a second layer 352 , and a third layer 353 .

[0037] The first layer 351 and the third layer 353 are preferably conductive oxide films having a perovskite structure and a (110) orientation. The specific materials are the same as those exemplified for the first layer 331 and the third layer 333. The thickness of each of the first layer 351 and the third layer 353 is, for example, 80 nm.

[0038] The second layer 352 is, for example, a Pt thin film. The second layer 352 may be a platinum group thin film other than Pt, for example, an Ir thin film, an Os thin film, etc. The film thickness of the second layer 352 is, for example, 150 nm.

[0039] The upper electrode 370 is, for example, a film formed of two layers, a first layer 371 and a second layer 372 .

[0040] The first layer 371 is preferably a conductive oxide film having a perovskite structure and a (110) orientation. The specific material is the same as that exemplified for the first layer 331 and the third layer 333. The film thickness of the first layer 371 is, for example, 80 nm.

[0041] The second layer 372 is, for example, a Pt thin film. The second layer 372 may be a platinum group thin film other than Pt, for example, an Ir thin film, an Os thin film, etc. The film thickness of the second layer 372 is, for example, 100 nm.

[0042] The first layer 351 of the intermediate electrode 350 and the first layer 371 of the upper electrode 370 suppress degradation of the piezoelectric films 340 and 360 located at the respective lower layers.

[0043] The thickness of the first layer 331 and the third layer 333 of the lower electrode 330, the thickness of the first layer 351 and the third layer 353 of the intermediate electrode 350, and the thickness of the first layer 371 of the upper electrode 370 are preferably set to 30 nm or more. By setting the thickness of these layers to 30 nm or more, the LNO thin film can be formed uniformly.

[0044] The average grain size of the third layer 333 of the lower electrode 330 and the average grain size of the third layer 353 of the intermediate electrode 350 are preferably 35 nm or less, and more preferably 25 nm or less.

[0045] If the average grain size of the third layer 333 of the lower electrode 330 is within the above range, the average grain size of the piezoelectric film 340 as the upper layer can be reduced. In addition, if the average grain size of the third layer 353 of the intermediate electrode 350 is within the above range, the average grain size of the piezoelectric film 360 as the upper layer can be reduced. For example, when the piezoelectric actuator 300 is used in an optical scanning device having a mirror portion, the smaller the average grain size of each of the piezoelectric films 340 and 360, the lower the driving voltage (hereinafter simply referred to as the driving voltage of the piezoelectric actuator 300) for driving the mirror portion to the same deflection angle in the piezoelectric actuator 300 can be.

[0046] Here, the average particle size is the average value of the crystal particle size in the horizontal direction in the plane of the film as the object. The average particle size can be calculated by analyzing with an electron beam diffraction device. In addition, the horizontal direction in the plane is the direction horizontal to the upper surface of the lower layer formed with the film as the object.

[0047] The piezoelectric material constituting the piezoelectric films 340 and 360 is preferably a perovskite structure. The piezoelectric films 340 and 360 are, for example, PZT (lead zirconate titanate) which is a perovskite structure. The piezoelectric film 340 can be formed on the lower electrode 330 using a sol-gel method, for example, and the piezoelectric film 360 can be formed on the intermediate electrode 350 using a sol-gel method, for example.

[0048] The piezoelectric material constituting the piezoelectric films 340 and 360 may be any material other than PZT as long as it has a perovskite structure, such as PNZT (lead zirconate titanium niobate), PLZT (lead lanthanum zirconate titanate), PLT (lead lanthanum titanate), PMN (lead magnesium niobate), PMNN (lead manganese niobate), BaTiO3 (barium titanate), etc. By using these piezoelectric materials in the piezoelectric films 340 and 360, the driving force per unit voltage can be increased.

[0049] The average particle diameters of the piezoelectric films 340 and 360 are preferably 1 μm or less, more preferably 600 nm or less, and further preferably 450 nm or less. As described above, the smaller the average particle diameters of the piezoelectric films 340 and 360 are, the lower the driving voltage of the piezoelectric actuator 300 can be.

[0050] The lower electrode 330 and the intermediate electrode 350 can be formed by sputtering in order to crystallize the piezoelectric thin films 340 and 360 formed on their respective upper layers, for example, by setting the temperature of the substrate 310 to 500 degrees or higher and making the crystal orientation of the third layers 333 and 353 in the plane perpendicular direction preferentially oriented to (110). By forming the lower electrode 330 and the intermediate electrode 350 under such conditions, the PZT thin film can be crystallized and good piezoelectric characteristics can be obtained. As a result, the driving voltage of the piezoelectric actuator 300 can be reduced.

[0051] It should be noted that the structure of the piezoelectric actuator 300 is not limited to Figure 1 For example, in the piezoelectric actuator 300, the piezoelectric film can be at least one layer. In this case, a three-layer structure is formed with a lower electrode and an upper electrode formed above and below the piezoelectric film, and the intermediate electrode is no longer required. In addition, more than three layers of piezoelectric films can be provided. In this case, on the lower electrode, the piezoelectric film and the intermediate electrode are alternately stacked in the required number, and finally, the piezoelectric film and the upper electrode are sequentially stacked on the uppermost intermediate electrode.

[0052] By providing n layers of piezoelectric thin films, the driving voltage of the piezoelectric actuator 300 can be reduced to 1 / n of that in the case of one layer.

[0053] In addition, it can also be set as Figure 2 The piezoelectric actuator 300A shown in the figure has a structure in which the end of the lower electrode 330 and the end of the intermediate electrode 350 are exposed from the upper layer. Figure 2 In the embodiment, the end of the piezoelectric film 340 may be formed to extend from the middle electrode 350 side to the lower electrode 330 side. Similarly, the end of the piezoelectric film 360 may be formed to extend from the upper electrode 370 side to the middle electrode 350 side. Figure 2 The stacked structure is omitted in the lower electrode 330, the middle electrode 350 and the upper electrode 370, but the stacked structure is similar to Figure 1 It's the same.

[0054] <Second Embodiment>

[0055] In the second embodiment, an example of an optical scanning device using the piezoelectric actuator according to the first embodiment is described. In the second embodiment, description of components that are the same as those in the previously described embodiment may be omitted.

[0056] Figure 3 This is a plan view illustrating the optical scanning device according to the second embodiment, and is a view of the optical scanning device as viewed from the mirror reflection surface 10 side. Figure 3 In the diagram, the longitudinal direction of the two torsion bars 50 is defined as a vertical direction, and the direction perpendicular to the longitudinal direction of the two torsion bars 50 is defined as a horizontal direction.

[0057] Reference Figure 3 The optical scanning device 1 is a MEMS (Micro Electro Mechanical System) having a mirror portion 40, a torsion bar 50, a connecting portion 60, a horizontal driving portion 70, a movable frame 80, a vertical driving portion 110, a fixed frame 120, a terminal 130 and a wiring 140.

[0058] The mirror portion 40 has a mirror reflection surface 10 and a stress relaxation region 20. The horizontal drive portion 70 has a horizontal drive beam 71 and a drive source 72. The vertical drive portion 110 has a vertical drive beam 90, a drive source 91, and a connection portion 100.

[0059] The mirror portion 40 is clamped from both outer sides in the vertical direction by two torsion bars 50 extending in the vertical direction. The mirror portion 40 has a mirror reflection surface 10 at the center, and a stress relief area 20 is formed between the mirror reflection surface 10 and the torsion bar 50. Two slits 30 are formed in each stress relief area 20. In addition, the base end 50a of the torsion bar 50 is connected to the inner corner of the horizontal driving beam 71 via the connecting portion 60. The surface of the horizontal driving beam 71 has a driving source 72, and the outer side is connected to the movable frame 80. The mirror portion 40 is driven by a piezoelectric actuator.

[0060] In the optical scanning device 1, the piezoelectric actuator 300 described in the first embodiment is used as the horizontal driving beam 71 and the driving source 72. That is, the horizontal driving beam 71 is, for example, a silicon substrate. In addition, the driving source 72 includes piezoelectric films 340 and 360, a lower electrode 330, an intermediate electrode 350, and an upper electrode 370. In the piezoelectric actuator 300, the piezoelectric film can be at least one layer, or can be three or more layers.

[0061] Furthermore, a piezoelectric sensor 51 is provided at the base end 50a of the torsion bar 50. The piezoelectric sensor 51 is a swing angle sensor for detecting the swing angle of the mirror reflection surface 10 in the horizontal direction when the mirror portion 40 swings in the horizontal direction. The piezoelectric sensor 51 uses a piezoelectric element, such as a PIEZO element.

[0062] The movable frame 80 supports the connection portion 60, the torsion bar 50, and the mirror portion 40 via the horizontal driving beam 71, and at the same time, surrounds them. The movable frame 80 is connected to the movable frame 80 of the vertical driving beam 90.

[0063] The vertical driving beams 90 are arranged to sandwich the movable frame 80 on both sides in the horizontal direction of the movable frame 80. A plurality of vertical driving beams 90 are provided in parallel with the torsion bar 50. Two vertical driving beams 90 are arranged adjacent to each other in the horizontal direction on each side of the movable frame 80. Two adjacent vertical driving beams 90 are connected by a connecting portion 100.

[0064] One end of the inner vertical driving beam 90 is connected to the movable frame 80, and the other end is connected to the outer vertical driving beam 90. In addition, one end of the outer vertical driving beam 90 is connected to the fixed frame 120, and the other end is connected to the inner vertical driving beam 90. In addition, the vertical driving beam 90 is provided with a driving source 91.

[0065] In the optical scanning device 1, the piezoelectric actuator 300 described in the first embodiment is used as the vertical driving beam 90 and the driving source 91. That is, the vertical driving beam 90 is, for example, a silicon substrate. In addition, the driving source 91 includes piezoelectric films 340 and 360, a lower electrode 330, an intermediate electrode 350, and an upper electrode 370. In the piezoelectric actuator 300, the piezoelectric film can be at least one layer, or can be three or more layers.

[0066] In addition, a piezoelectric sensor 92 is provided at one end of the outer vertical driving beam 90. The piezoelectric sensor 92 is a swing angle sensor for detecting the swing angle of the mirror reflection surface 10 in the vertical direction when the mirror portion 40 is vertically swung. In the piezoelectric sensor 92, a piezoelectric element is used in the same manner as the piezoelectric sensor 51, for example, a piezoelectric PIEZO element is used.

[0067] The fixed frame 120 supports the vertical drive unit 110 via the outer vertical drive beam 90. That is, the fixed frame 120 supports the mirror portion 40 via the drive unit (the vertical drive unit 110 and the horizontal drive unit 70). It surrounds the vertical drive unit 110 and the movable frame 80 and has a rectangular shape. In this embodiment, the fixed frame 120 has a substantially square shape.

[0068] A plurality of terminals 130 are provided on the surface of the fixing frame 120. A wiring 140 is connected to each terminal 130. The wiring 140 is connected to the driving source 72, 91 and the piezoelectric sensor 51, 92. In addition, the wiring 140 has a substrate contact portion 140a for contacting the wiring 140 with the silicon active layer 303 as a substrate given a ground potential.

[0069] The following is a more detailed description of each part.

[0070] The mirror portion 40 has a substantially circular mirror reflection surface 10 at the center. The mirror reflection surface 10 is formed of a metal film having a high reflectivity, such as silver, copper, or aluminum.

[0071] The stress relief region 20 is provided between the mirror reflecting surface 10 to relieve the torsional stress of the torsion bar 50 and reduce the stress applied to the mirror reflecting surface 10. The stress relief region 20 can disperse the stress generated by the torsional motion of the torsion bar 50 and relieve the stress applied to the mirror reflecting surface 10.

[0072] The slits 30 are holes for dispersing the stress applied to the stress relaxation region 20 , and are provided in the stress relaxation region 20 .

[0073] The torsion bar 50 is a member for supporting the mirror surface 40 from both sides and shaking the mirror surface 40 in the horizontal direction. Here, the horizontal direction is the direction in which the light reflected by the mirror reflection surface 10 is scanned and moved at high speed, which means the lateral direction of the projection surface. That is, the mirror reflection surface 10 is shaken in the lateral direction, which is the direction with the torsion bar 50 as the axis. By twisting the torsion bar 50 alternately left and right, the mirror surface 40 is shaken in the horizontal direction.

[0074] The connection portion 60 is a transmission member for transmitting the horizontal driving force generated in the horizontal driving beam 71 to the torsion bar 50 .

[0075] The horizontal driving beam 71 is a driving member for shaking the mirror portion 40 in the horizontal direction and scanning the light reflected by the mirror reflection surface 10 in the horizontal direction of the projection surface. By alternately applying voltages of different phases to the two driving sources 72, the two horizontal driving beams 71 can be alternately tilted in opposite directions. In this way, a torsion force can be applied to the torsion bar 50, so that the mirror portion 40 shakes around a horizontal rotation axis parallel to the torsion bar 50.

[0076] The drive performed by the horizontal driving beam 71 uses, for example, resonance driving. When the optical scanning device 1 according to the present embodiment is applied to a projector or the like, the mirror portion 40 is driven by, for example, 30 kHz resonance driving.

[0077] Furthermore, the movable frame 80 can be vertically swung by applying voltages of different phases to the adjacent vertical drive beams 90. The mirror portion 40 is supported by the movable frame 80 and thus swung vertically as the movable frame 80 sways.

[0078] It should be noted that the vertical drive unit 110 shakes the movable frame 80 by, for example, non-resonant driving. The vertical drive does not require high-speed driving compared to the horizontal drive, and the driving frequency is, for example, about 60 Hz.

[0079] The optical scanning device 1 having the above-described structure is manufactured using, for example, an SOI wafer.

[0080] Here, the crystal grain size control of the piezoelectric film in the piezoelectric actuator of the optical scanning device 1 is described. In the past, the crystal grain size control of the piezoelectric film was not implemented in the piezoelectric actuator. However, the inventors have found that by controlling the crystal grain size of the piezoelectric film and reducing the average grain size of the piezoelectric film, the driving voltage of the piezoelectric actuator can be reduced.

[0081] Figure 4 This is a diagram illustrating the relationship between the average particle size of the piezoelectric film and the driving voltage. Figure 4In the figure, the “average grain size of the piezoelectric film” on the horizontal axis is the average value of the crystal grain sizes in the horizontal direction within the plane of the piezoelectric films 340 and 360 obtained by analyzing cross-sectional photographs of the piezoelectric films 340 and 360 using an electron beam diffraction device.

[0082] Figure 5 This is a cross-sectional photograph of the piezoelectric film 340 on the lower electrode 330 (part 1), and the portion indicated by the arrow is an example of the crystal grain size in the horizontal direction of the piezoelectric film 340. The position of the arrow is moved in the vertical direction and the horizontal direction to measure the crystal grain size in the horizontal direction of the plane at each position, and the average value obtained is the average value of the crystal grain size in the horizontal direction of the plane (i.e., the average grain size). The cross-sectional photographs of the piezoelectric films 340 and 360 are analyzed in the electron beam diffraction device to obtain the average grain size of the piezoelectric films 340 and 360.

[0083] As an electron beam diffraction apparatus, a crystal orientation analysis system ASTER (manufactured by NanoMEGAS, a registered trademark) based on a TEM (Transmission Electron Microscope) can be used. By using ASTER, a high spatial resolution of about 2 to 5 nm can be achieved.

[0084] Figure 4 In the figure, the "driving voltage" on the vertical axis is the voltage when the deflection angle of the mirror portion 40 is 3.2 degrees, which is formed by grounding the intermediate electrode 350 constituting the driving source 72 and supplying the driving voltage between the upper electrode 370 and the lower electrode 330. The lower the driving voltage value, the higher the deflection angle sensitivity.

[0085] If Figure 4 It can be seen that the smaller the average particle size of the piezoelectric films 340 and 360 is, the lower the driving voltage required for the mirror portion 40 to contact at a certain angle can be. In other words, the smaller the average particle size of the piezoelectric films 340 and 360 is, the higher the deflection angle sensitivity can be.

[0086] For example, by setting the average grain size of the piezoelectric films 340 and 360 to 600 nm to 450 nm, it is possible to reduce the driving voltage required for the mirror portion 40 to contact at a certain angle by about 8%.

[0087] The reason why the deflection angle sensitivity can be improved is that by reducing the average grain size of the piezoelectric films 340 and 360, the gap between the grains can be reduced, and the power loss applied to the piezoelectric films 340 and 360 is reduced. That is, the larger the gap between the grains, the larger the current flowing along the surface. As the gap between the grains decreases, the current flowing along the surface becomes smaller, and more current flows through the inside of the piezoelectric films 340 and 360, so the deflection angle sensitivity can be improved. It should be noted that the current flowing along the surface does not contribute to the deformation of the piezoelectric actuator.

[0088] Furthermore, when the same power is applied, the smaller the crystal grain size, the better the piezoelectric actuator operates, thus increasing the apparent piezoelectric constant. Furthermore, the current flowing along the surface becomes smaller, thus increasing the insulation withstand voltage of the piezoelectric actuator.

[0089] Figure 6 This is a diagram illustrating the relationship between the average grain size of the piezoelectric thin film and the average grain size of the underlying layer. Figure 6 In the figure, the "average grain size of the lower layer" on the vertical axis is the average value of the crystal grain size in the horizontal direction of the third layers 333 and 353, obtained by analyzing the cross-sectional photographs of the third layers 333 and 353 using an electron beam diffraction device. As the electron beam diffraction device, ASTER can be used as in the case of the piezoelectric film. Figure 3 The situation is the same.

[0090] If Figure 6 It can be seen that the smaller the average grain size of the third layers 333 and 353, the smaller the average grain size of the piezoelectric films 340 and 360. To reduce the average grain size of the third layers 333 and 353, the average grain size of the sputtering target used to form the third layers 333 and 353 by sputtering can be reduced.

[0091] That is, Figure 7 As shown, by reducing the average grain size of the sputtering target of the third layer 333, the average grain size of the third layer 333 is reduced, thereby reducing the average grain size of the piezoelectric film 340 formed on the third layer 333. Similarly, by reducing the average grain size of the sputtering target of the third layer 353, the average grain size of the third layer 353 is reduced, thereby reducing the average grain size of the piezoelectric film 360 formed on the third layer 353. Moreover, as a result of reducing the average grain size of the piezoelectric films 340 and 360, the driving voltage can be reduced (the deflection angle sensitivity can be improved).

[0092] Figure 8 is a cross-sectional photograph of the piezoelectric film 340 on the lower electrode 330 (part 2), Figure 8 (b) Figure 8 (a) is an enlarged view of the vicinity of the lower electrode 330.

[0093] Figure 8 The average particle size of the third layer 333 constituting the lower electrode 330 is about 30 nm, and the average particle size of the piezoelectric film 340 is about 579 nm. In this example, the driving voltage when the deflection angle of the mirror portion 40 is 3.2 degrees is about 1.85 to 1.95 V (similar to Figure 4 compared to).

[0094] Fig. 9is a cross-sectional photograph of the piezoelectric film 340 on the lower electrode 330 (part 3), Fig. 9 (b) Fig. 9 (a) is an enlarged view of the vicinity of the lower electrode 330.

[0095] Fig. 9 The average particle size of the third layer 333 constituting the lower electrode 330 is about 20 nm, and the average particle size of the piezoelectric film 340 is about 449 nm. In this example, the driving voltage when the deflection angle of the mirror portion 40 is 3.2 degrees is about 1.7 to 1.8 V (similar to Figure 4 compared to).

[0096] In this way, by reducing the average particle size of the piezoelectric film, the driving voltage of the piezoelectric actuator can be reduced. Considering the driving voltage in actual use, the average particle size of the piezoelectric film is preferably set to 1 μm or less, more preferably to 600 nm or less, and further preferably to 450 nm or less. By setting the average particle size of the piezoelectric film to 600 nm or less, the driving voltage of the piezoelectric actuator can be made less than 2 V.

[0097] The optical scanning device 1 according to the above-described embodiment can be applied to a two-dimensional scanning type optical scanning device such as goggles or a projector.

[0098] In addition, in the above embodiment, as the optical scanning device, an optical scanning device using a torsion bar is cited as an example for description, but the present invention is also applicable to an optical scanning device that does not use a torsion bar. In addition, in the above embodiment, a two-dimensional scanning type optical scanning device is cited as an example for description, but it is not limited to the two-dimensional scanning type, and it can also be a one-dimensional scanning type optical scanning device that causes the mirror portion to swing in one direction.

[0099] Furthermore, the piezoelectric actuator 300 according to the above embodiment may be used in devices other than the optical scanning device, for example, in an inkjet head.

[0100] The preferred embodiments have been described above, but the present invention is not limited to the above embodiments, and various modifications and substitutions may be made to the above embodiments without departing from the scope described in the claims.

Claims

1. A piezoelectric actuator, A substrate and a driving source formed on the substrate, The driving source has a piezoelectric film with an average particle size of less than 1 μm. The piezoelectric film is formed on a conductive oxide film of a perovskite structure. The conductive oxide film has an average particle size of 35 nm or less.

2. A piezoelectric actuator, A piezoelectric film having a substrate and an average grain size of 1 μm or less formed on the substrate, The piezoelectric film is formed on a conductive oxide film of a perovskite structure. The conductive oxide film has an average particle size of 35 nm or less.

3. A piezoelectric actuator, A substrate and a driving source formed on the substrate, The driving source has multiple layers of piezoelectric films with an average particle size of less than 1 μm. Each layer of the piezoelectric film is formed on a conductive oxide film of a perovskite structure. The conductive oxide film has an average particle size of 35 nm or less.

4. The piezoelectric actuator according to claim 1 or 3, wherein: The driving source has a piezoelectric film with an average grain size of 600 nm or less.

5. The piezoelectric actuator according to claim 1 or 3, wherein: The driving source has a piezoelectric film with an average grain size of 450 nm or less.

6. The piezoelectric actuator according to claim 1, 2 or 3, wherein: The piezoelectric film has a perovskite structure.

7. The piezoelectric actuator according to claim 1, 2 or 3, wherein: The piezoelectric material constituting the piezoelectric film is lead zirconate titanate, lead zirconate titanate niobate, lead lanthanum zirconate titanate, lead lanthanum titanate, lead magnesium niobate or lead manganese niobate.

8. The piezoelectric actuator according to claim 1, 2 or 3, wherein: The conductive oxide film is a lanthanum nickelate film, a strontium ruthenate film or a barium ruthenate film.

9. An optical scanning device comprising a mirror portion driven by the piezoelectric actuator according to claim 1, 2 or 3.

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