Piezoelectric devices and ultrasonic devices

Abstract

The present invention provides a piezoelectric device and an ultrasonic device that exhibit large amounts of diaphragm deformation. [Solution] The piezoelectric device comprises a substrate having a vibrating region and a non-vibrating region surrounding the vibrating region; a first electrode provided spanning the vibrating region and the non-vibrating region; a second electrode disposed inside the vibrating region and spaced apart from the first electrode; a piezoelectric body provided spanning the substrate, the first electrode, and the second electrode; and a third electrode on the piezoelectric body that, when viewed from the thickness direction of the substrate, overlaps with at least the first electrode and the second electrode within the vibrating region.

Description

Technical Field

[0001] The present invention relates to a piezoelectric device and an ultrasonic device.

Background Art

[0002] Conventionally, a piezoelectric device is known in which a piezoelectric element is disposed on a diaphragm and the diaphragm is vibrated by applying a voltage to the piezoelectric element (see, for example, Patent Document 1). The piezoelectric device of Patent Document 1 is an ultrasonic device, and includes a silicon substrate having a void portion, a diaphragm provided on the silicon substrate so as to cover the void portion, a first electrode disposed on the diaphragm, a piezoelectric body provided at a position overlapping the void portion when viewed in the thickness direction, and a second electrode provided on the piezoelectric body. In this ultrasonic device, the piezoelectric body is arranged such that 0.65 ≤ Pw / Cw ≤ 0.95, where Cw is the width of the void portion and Pw is the width of the piezoelectric body.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in a conventional piezoelectric device such as that of Patent Document 1, when a voltage is applied to the piezoelectric body, the diaphragm deflects toward the void portion side but does not deflect toward the side opposite to the void portion, so there is a problem that the amount of deformation of the diaphragm is small. Therefore, when the piezoelectric device is used as an ultrasonic device, the amount of deformation of the diaphragm is small, so the sound pressure of the output ultrasonic wave also becomes small.

Means for Solving the Problems

[0005] A piezoelectric device according to a first aspect of the present disclosure comprises: a substrate having a vibrating region and a non-vibrating region surrounding the vibrating region; a first electrode provided spanning the vibrating region and the non-vibrating region; a second electrode disposed inside the vibrating region and spaced apart from the first electrode; a piezoelectric body provided spanning the substrate, the first electrode, and the second electrode; and a third electrode on the piezoelectric body that, when viewed from the thickness direction of the substrate, overlaps with at least the first electrode and the second electrode within the vibrating region.

[0006] An ultrasonic device according to a second aspect of this disclosure comprises the piezoelectric device of the first aspect described above, and transmits ultrasonic waves by driving the piezoelectric device. [Brief explanation of the drawing]

[0007] [Figure 1] A cross-sectional view showing the schematic configuration of the ultrasonic device according to the first embodiment. [Figure 2] A plan view showing the schematic configuration of the ultrasonic device according to the first embodiment. [Figure 3] A diagram showing the displacement of the vibration region when the ultrasonic device of the first embodiment is driven. [Figure 4] This figure shows the drive efficiency when (W1+W2) / Wc is varied in the first embodiment. [Figure 5] This figure shows the drive efficiency when W1 / W2 is varied in the first embodiment. [Figure 6] This figure shows the driving efficiency when the phase difference Δφ between the first driving voltage and the second driving voltage is changed in the first embodiment. [Figure 7] A cross-sectional view showing the schematic configuration of the ultrasonic device according to the second embodiment. [Figure 8] A schematic diagram showing the general configuration of the head of the third embodiment. [Figure 9] A plan view showing the schematic configuration of a piezoelectric device according to modified example 2. [Modes for carrying out the invention]

[0008] [First Embodiment] A first embodiment of this disclosure will be described. Figure 1 is a cross-sectional view showing the schematic configuration of the ultrasonic device, which is a piezoelectric device in this embodiment, and Figure 2 is a plan view showing the schematic configuration of the ultrasonic device. As shown in Figure 1, the ultrasonic device 10 comprises a substrate 11, a first electrode 12, a second electrode 13, a piezoelectric element 14, a third electrode 15, a vibration suppression unit 16, and a voltage control unit 20. Note that the piezoelectric element 14 and the third electrode 15 are not shown in Figure 2. In this embodiment, a first electrode 12 and a second electrode 13 are laminated on a substrate 11, a piezoelectric body 14 is laminated so as to cover the substrate 11, the first electrode 12, and the second electrode 13, and a third electrode 15 is laminated on the piezoelectric body 14. Hereafter, in the description, the thickness direction of the substrate 11, that is, the lamination direction of the substrate 11, the first electrode 12 (or second electrode 13), the piezoelectric body 14, and the third electrode 15 will be referred to as the Z direction. The plane perpendicular to the Z direction will be referred to as the XY plane, and the two orthogonal axis directions included in the XY plane will be referred to as the X direction and the Y direction, respectively.

[0009] The substrate 11 comprises a base portion 111 and a surface portion 112. The base portion 111 is a flat, plate-shaped substrate made of a semiconductor substrate, and in this embodiment, the semiconductor substrate is made of Si. The surface portion 112 is a surface-processed portion of the base portion 111. For example, in this embodiment, one side of the base portion 111 made of Si is oxidized to form SiO2, and then a ZrO2 layer is laminated by sputtering or the like. In other words, in this embodiment, the surface portion 112 is made of an SiO2 layer and a ZrO2 layer.

[0010] Furthermore, if the -Z side of the substrate 11 (the side where the surface layer 112 is not provided) is defined as the first surface 113, the first surface 113 is formed such that its arithmetic surface roughness is within the range of 0.4 ± 0.5 μm. In other words, in this embodiment, the first surface 113 of the substrate 11 is formed by polishing. This makes it possible to reduce the arithmetic surface roughness compared to the case where the first surface 113 of the substrate 11 is formed by etching or the like.

[0011] As shown in Figures 1 and 2, the substrate 11 includes a vibrating region 11A and a non-vibrating region 11B surrounding the vibrating region 11A. In Figure 2, the dashed line indicates the boundary between the vibration region 11A and the non-vibration region 11B. The area outside the dashed line is the non-vibration region 11B, and the area inside the dashed line is the vibration region 11A. The vibration region 11A is a region in which the piezoelectric body 14 deforms and vibrates when a voltage is applied between the first electrode 12 and the third electrode 15, and between the second electrode 13 and the third electrode 15. The vibration in the vibration region 11A causes ultrasonic waves to be output from the ultrasonic device 10.

[0012] On the other hand, the non-vibration region 11B is a region where vibration is restricted. In this embodiment, vibration suppression is suppressed in the non-vibration region 11B by providing a vibration suppression section 16 on the first surface 113 of the non-vibration region 11B of the substrate 11. The vibration suppression section 16 uses a resin that has a vibration suppression effect. The resin used is not particularly limited, and for example, epoxy resins, acrylic resins, novolac resins, and other resist resins can be used. The vibration suppression section 16 is provided to cover the entire non-vibration region 11B, but not in the vibration region 11A.

[0013] The first electrode 12 is provided on the surface layer 112 of the substrate 11, spanning from the vibrating region 11A to the non-vibrating region 11B in the Z direction. In this embodiment, as shown in Figure 2, the vibration region 11A is circular when viewed from the Z direction, and the first electrode 12 is formed over the circumference of the circle of the vibration region 11A. A notch 121 is provided in a part of the first electrode 12. The notch 121 is the portion to which the second connecting electrode 131, which is connected to the second electrode 13, extends from the vibration region 11A to the non-vibration region 11B. In the example shown in Figure 2, only one notch 121 is provided, but considering the stress balance during vibration of the vibration region 11A, multiple notches 121 may be provided at positions symmetrical with respect to the center of the vibration region 11A. For example, a pair of point-symmetrical notches 121 may be provided with respect to the center of the vibration region 11A, or multiple notches 121 may be provided at positions (equally spaced) that are rotationally symmetrical with respect to the center of the vibration region 11A. Also, in the present embodiment, as described above, the first electrode 12 is formed along the circumferential direction of the vibration region 11A. This means that, in a cross-sectional view (a cross-section excluding the position where the notch 121 is provided) as shown in FIG. 1, the first electrode 12 is arranged with the second electrode 13 interposed therebetween. In addition, a first connection electrode 122 (see FIG. 1) is connected to the first electrode 12, and the first connection electrode 122 is electrically connected to the voltage control unit 20 via a first terminal (not shown in detail) provided in the surface layer portion 112 of the substrate 11.

[0014] The second electrode 13 is arranged in the vibration region 11A of the substrate 11, separated from the first electrode 12. Preferably, the second electrode 13 is formed in the same shape as the vibration region 11A when viewed from the Z direction. In the present embodiment, as shown in FIG. 2, since the vibration region 11A is circular, the second electrode 13 is also formed in a circular shape, and the vibration region 11A and the second electrode 13 are concentric. In addition, as described above, a second connection electrode 131 is connected to the second electrode 13, and the second connection electrode 131 extends from the vibration region 11A to the non-vibration region 11B through the notch 121 of the first electrode 12. The second connection electrode 131 is electrically connected to the voltage control unit 20 via a second terminal (not shown in detail) provided in the non-vibration region 11B. Incidentally, as described above, when a plurality of notches 121 of the first electrode 12 are provided so as to be symmetric with respect to the center point of the vibration region 11A, it is preferable that the second connection electrode 131 is provided in each of these notches 121. Thereby, the stress balance in the vibration region 11A can be maintained.

[0015] Here, in the XZ cross-section (FIG. 1) passing through the center of the circle of the vibration region 11A, let the widths of the first electrode 12 on the vibration region 11A be W11 and W12, the width of the second electrode 13 be W2, and the width of the vibration region 11A be Wc. In the present embodiment, the vibration region 11A is circular, and the width Wc of the vibration region 11A is the diameter of the circular vibration region 11A. The first electrode 12 is formed with an equal width in the circumferential direction along the outer peripheral edge of the vibration region 11A, and protrudes by the same width along the circumferential direction within the vibration region 11A. Therefore, the widths W11 and W12 of the first electrode 12 on the vibration region 11A are such that W11 = W12. Also, in a cross-sectional view as shown in FIG. 1, let the sum of the widths of the pair of first electrodes 12 arranged with the second electrode 13 interposed therebetween be W1. That is, W1 = W11 + W12, and in the present embodiment, W1 = 2W11. The second electrode 13 is circular and concentric with the vibration region 11A, and the width W2 of the second electrode 13 is the diameter of the second electrode 13.

[0016] In the ultrasonic device 10 of the present embodiment, the sum W1 of the widths of the first electrodes 12, the width W2 of the second electrode 13, and the width Wc of the vibration region 11A satisfy the following relationships. W1 < W2 0.25 ≦ W1 / W2 ≦ 1 0.5 < (W1 + W2) / Wc < 1

[0017] The piezoelectric body 14 is provided on the surface layer portion 112 of the substrate 11, extending from the vibration region 11A to the non-vibration region 11B, and covers the first electrode 12 and the second electrode 13. That is, the piezoelectric body 14 covers the entire vibration region 11A, the first electrode 12, and the second electrode 13. The piezoelectric body 14 may be provided over the entire surface of the substrate 11. The piezoelectric body 14 is composed of, for example, a perovskite-type transition metal oxide containing Pb, and in the present embodiment, it is PZT containing Pb, Zr, and Ti.

[0018] The third electrode 15 is provided on the piezoelectric body 14, extending from the vibration region 11A to the non-vibration region 11B. That is, the third electrode 15 covers the first electrode 12 and the second electrode 13 within the vibration region 11A when viewed from the Z direction. A third connection electrode 151 is connected to the third electrode 15, and the third connection electrode 151 is electrically connected to the voltage control unit 20 via a third terminal (not shown) provided in the non-vibration region 11B.

[0019] Next, the voltage control unit 20 will be described. As described above, the voltage control unit 20 is electrically connected to the first electrode 12, the second electrode 13, and the third electrode 15. The voltage control unit 20 includes a first power supply 21 that applies a voltage to the first electrode 12, a second power supply 22 that applies a voltage to the second electrode 13, and a common potential unit 23 connected to the third electrode 15. The first power supply 21 and the second power supply 22 apply a drive voltage of a predetermined frequency. The common potential section 23, for example, sets the third electrode 15 to a predetermined common potential.

[0020] In this embodiment, when the voltage control unit 20 drives the ultrasonic device 10, it shifts the phase of the first drive voltage applied from the first power supply 21 to the first electrode 12 and the phase of the second drive voltage applied from the second power supply 22 to the second electrode 13 to create a phase difference. Specifically, the phase difference Δφ between the first drive voltage and the second drive voltage is 150° ≤ Δφ ≤ 180°.

[0021] [Driving efficiency of ultrasonic device 10] Next, we will explain the driving efficiency of the ultrasonic device 10 as described above. Figure 3 shows the displacement of the vibration region 11A when the ultrasonic device 10 is driven. In this embodiment, when a second driving voltage is applied to the second electrode 13, the piezoelectric element 14 between the second electrode 13 and the third electrode 15 deforms so as to become convex to the -Z side, as shown in the upper diagram of Figure 3, and the vibration region 11A is displaced so as to become convex to the -Z side. If the ultrasonic device 10 is provided with only the second electrode 13 and not the first electrode 12, the vibration region 11A will only be displaced by the application of a driving voltage to the second electrode 13, that is, only by the -Z side. In this case, after the vibration region 11A is displaced to the -Z side, the vibration region 11A is displaced to the +Z side by the restoring force of the spring-like properties of the vibration region 11A alone. This restoring force alone is not sufficient to obtain a large displacement. In contrast, in this embodiment, a first drive voltage is applied between the first electrode 12 and the third electrode 15 with a phase difference from the second drive voltage applied to the second electrode 13. In this case, after the vibration region 11A is displaced to the -Z side by the application of the second drive voltage to the second electrode 13, the piezoelectric body 14 between the first electrode 12 and the third electrode 15 deforms so as to bend to the +Z side. Therefore, as shown in the lower part of Figure 3, the vibration region 11A is greatly displaced to the +Z side by the deformation of the piezoelectric body 14 between the first electrode 12 and the third electrode 15 and the restoring force of the spring of the vibration region 11A. In this embodiment, the vibration region 11A alternately deforms between the state shown in the upper and lower diagrams of Figure 3. This allows for a larger vibration amplitude in the vibration region 11A compared to the case where only the second electrode 13 and the third electrode 15 are provided, thereby increasing the sound pressure of the ultrasound output from the ultrasonic device 10.

[0022] Figure 4 shows the driving efficiency when (W1+W2) / Wc is varied. In other words, it shows the driving efficiency corresponding to the sum of the widths of the first electrode 12 W1 and the width of the second electrode 13 W2 with respect to the width Wc of the vibration region 11A. Figure 5 shows the driving efficiency when W1 / W2 is varied. In other words, it shows the driving efficiency corresponding to the sum of the widths of the first electrode 12 and W1 with respect to the width W2 of the second electrode 13. Figure 6 shows the drive efficiency when the phase difference Δφ between the first drive voltage and the second drive voltage is changed.

[0023] In this context, driving efficiency refers to the magnitude of the amplitude when the amplitude is at its maximum when the vibration region 11A is vibrated, with 1 being the value of the amplitude. As shown in Figure 4, a drive efficiency of 0.5 or higher can be obtained in the range where 0.5 < (W1 + W2) / Wc < 1. More preferably, 0.6 < (W1 + W2) / Wc < 0.8, in which case a drive efficiency of 0.9 or higher can be obtained. As shown in Figure 5, a drive efficiency of 0.8 or higher can be obtained in the range where 0.25 ≤ W1 / W2 ≤ 1. As shown in Figure 6, a drive efficiency of 0.9 or higher can be obtained in the range where 150° ≤ Δφ ≤ 210°.

[0024] In this embodiment, as described above, the conditions 0.25 ≤ W1 / W2 ≤ 1 and 0.5 < (W1 + W2) / Wc < 1 are satisfied, and the voltage applied by the voltage control unit 20 to the first electrode 12 and the second electrode 13 satisfies 150° ≤ Δφ ≤ 210°. Therefore, the amplitude of the vibration region 11A can be increased, and the driving efficiency of the ultrasonic device 10 can be dramatically improved.

[0025] [Effects of this embodiment] The ultrasonic device 10 of this embodiment comprises a substrate 11, a first electrode 12, a second electrode 13, a piezoelectric element 14, and a third electrode 15. The substrate 11 comprises a vibration region 11A and a non-vibration region 11B surrounding the vibration region 11A. The first electrode 12 is provided on the +Z side of the substrate 11, straddling the vibration region 11A and the non-vibration region 11B. The second electrode 13 is positioned inside the vibration region 11A and spaced apart from the first electrode 12. The piezoelectric element 14 is provided straddling the substrate 11, the first electrode 12, and the second electrode 13. The third electrode 15 is provided on the piezoelectric element 14 and, when viewed from the Z direction, overlaps with the first electrode 12 and the second electrode 13 within the vibration region 11A.

[0026] In such an ultrasonic device 10, by shifting the phase of the first drive voltage applied between the first electrode 12 and the third electrode 15 and the second drive voltage applied to the second electrode 13 and the third electrode 15, it is possible to generate stress that causes the vibration region 11A to bend in both positive and negative directions (±Z side), thereby increasing the amount of deformation (vibration amplitude) of the vibration region 11A. As a result, the sound pressure of the ultrasound output from the ultrasonic device 10 can also be increased.

[0027] In the ultrasonic device 10 of this embodiment, the first electrode 12 is provided sandwiching the second electrode 13. This makes the stress balance in the vibration region 11A symmetrical, allowing for a larger displacement during vibration.

[0028] In the ultrasonic device 10 of this embodiment, when W1 is the sum of the widths of the portions of the first electrode 12 that are positioned in the vibration region 11A, W2 is the width of the second electrode 13, and Wc is the width of the vibration region 11A, 0.25 <W1 / W2≦1、 0.5 < (W1 + W2) / Wc < 1 It satisfies the condition. This allows for a larger deformation in the vibration region 11A, and enables the driving efficiency of the ultrasonic device 10 to be maintained at a high level.

[0029] The ultrasonic device 10 of this embodiment includes a voltage control unit 20. The voltage control unit 20 includes a first power supply 21 that applies a first drive voltage between the first electrode 12 and the third electrode 15, and a second power supply 22 that applies a second drive voltage between the second electrode 13 and the third electrode 15. The voltage control unit 20 then inputs voltages to the ultrasonic device 10 with the phases of the first drive voltage and the second drive voltage being different. By applying a second drive voltage between the second electrode 13 and the third electrode 15, the vibration region 11A bends to the -Z side due to the deformation of the piezoelectric body 14, and by applying a first drive electrode between the first electrode 12 and the third electrode 15, the vibration region 11A bends to the +Z side due to the deformation of the piezoelectric body 14. By shifting the phase between the first drive voltage and the second drive voltage, the timing of applying stress to bend the vibration region 11A to the +Z side and the timing of applying stress to bend the vibration region 11A to the -Z side are shifted, and the amount of displacement of the vibration region 11A can be increased.

[0030] In this case, if the phase difference between the phase of the first drive voltage and the phase of the second drive voltage is Δφ, then the condition 150°≦Δφ≦210° is satisfied. As a result, after the second drive voltage applies a stress that causes the vibration region 11A to bend to the -Z side, when the vibration region 11A returns to the +Z side due to the spring force of the substrate 11, the first drive voltage can apply a stress that causes the vibration region 11A to bend to the +Z side. Similarly, after the first drive voltage applies a stress that causes the vibration region 11A to bend to the +Z side, when the vibration region 11A returns to the -Z side due to the spring force of the substrate 11, the second drive voltage can apply a stress that causes the vibration region 11A to bend to the -Z side. In other words, in this embodiment, the amount of deformation of the vibration region 11A can be increased by the combined force of the spring force of the substrate 11 and the stress due to the deformation of the piezoelectric element 14.

[0031] [Second Embodiment] In the first embodiment described above, the vibration suppression part 16 is provided on the first surface 113, which is the -Z side surface of the substrate 11. However, the vibration suppression part may also be provided on the +Z side of the substrate 11. Figure 7 shows a schematic configuration of the ultrasonic device 10A according to the second embodiment. In the following description, components that have already been described will be denoted by the same reference numerals, and their descriptions will be omitted.

[0032] As shown in Figure 7, the ultrasonic device 10A of the second embodiment comprises a substrate 11, a first electrode 12, a second electrode 13, a piezoelectric element 14, a third electrode 15, a support substrate 17, and a voltage control unit 20. The ultrasonic device 10A of this embodiment is provided with a support substrate 17 positioned on the +Z side of the substrate 11 and facing the third electrode 15. This support substrate 17 is provided, for example, to reinforce a substrate 11 with a small thickness, and is joined to at least one of the substrate 11, the piezoelectric element 14, and the third electrode 15 via support legs 171. The support legs 171 can be made of a resist resin such as epoxy resin, acrylic resin, or novolac resin, similar to the vibration suppression unit 16 of the first embodiment, and suppress vibrations in the non-vibration region 11B. In the example shown in Figure 7, the support legs 171 are joined to the entire non-vibration region 11B. As a result, the support legs 171 function similarly to the vibration suppression unit 16 of the first embodiment.

[0033] Furthermore, the support substrate 17 may be provided with a through hole 172 that penetrates the support substrate 17 in the Z direction, at a position that overlaps with the vibration region 11A when viewed from the Z direction. By providing such through-holes 172, it becomes possible to output the ultrasonic waves generated by the vibration region 11A to both the ±Z sides.

[0034] In the example shown in Figure 7, the piezoelectric element 14 and the third electrode 15 cover the entire non-vibrating region 11B. However, the third electrode 15 may cover only a portion of the non-vibrating region 11B, with the edge of the third electrode 15 positioned on the piezoelectric element 14. In this case, the support legs 171 cover both the edge of the third electrode 15 and the piezoelectric element 14, thereby suppressing the occurrence of cracks and burnout at the boundary between the edge of the third electrode 15 and the piezoelectric element 14. Alternatively, the piezoelectric element 14 and the third electrode 15 may be configured to cover only a portion of the non-vibrating region 11B. In this case, the support legs 171 are joined to the edge of the third electrode 15, the edge of the piezoelectric element 14, and the surface layer 112 of the substrate 11 where the piezoelectric element 14 and the third electrode 15 are not provided.

[0035] The ultrasonic device 10A of the second embodiment described above can also achieve the same effects and advantages as the ultrasonic device 10 of the first embodiment. In addition, the ultrasonic device 10A of this embodiment includes a support substrate 17 positioned on the +Z side of the substrate 11, facing the third electrode 15. The support substrate 17 is joined to at least one of the substrate 11, the piezoelectric element 14, and the third electrode 15 by support legs 171 in the non-vibration region 11B. In other words, in this embodiment, the support legs 171 are joined to the non-vibration region 11B, thereby suppressing vibration in the non-vibration region 11B and enabling vibration in the vibration region 11A. In this configuration, the support substrate 17 can reinforce the substrate 11, thereby suppressing damage to the substrate 11. Furthermore, by joining the support legs 171 to the non-vibration region 11B, it is not necessary to provide the vibration suppression portion 16 on the -Z side of the substrate 11.

[0036] Furthermore, in the ultrasonic device 10A of this embodiment, the support substrate 17 may be configured to have through holes 172 in the portion that overlaps with the vibration region 11A when viewed from the Z direction. This allows the ultrasonic waves generated by the vibration in the vibration region 11A to be output to both the ±Z sides of the substrate 11.

[0037] [Third Embodiment] In the first embodiment described above, an ultrasonic device 10 that outputs ultrasonic waves was exemplified as the piezoelectric device, but the invention is not limited thereto. For example, the piezoelectric device of this disclosure can be applied to a piezoelectric device that applies pressure to an object, and may be applied to a piezoelectric device provided in the head of an inkjet printer, for example. Figure 8 shows a schematic configuration of a head equipped with a piezoelectric device 10B. In Figure 8, the head 30 is a device installed in an inkjet printer (not shown) that ejects ink onto a printing medium. The print head 30 is provided in the inkjet printer so as to be movable along a predetermined scanning direction by a moving mechanism 31. The print head 30 also includes an ink chamber 32 where ink is stored, and a supply pipe 33 for supplying ink, a circulation pipe 34 for circulating the ink, and the like are connected to the ink chamber 32. The ink chamber 32 is also equipped with a nozzle 35 that faces the printing medium and a piezoelectric device 10B that applies pressure to the ink in the ink chamber 32.

[0038] In such a head 30, the head 30 is moved to a predetermined position on the printing medium by the control of a controller (not shown), and then the piezoelectric device 10B is driven by the control of the controller, causing ink to be ejected from the ink chamber 32 to the printing medium via the nozzle 35. In this case, as described above, the piezoelectric device 10B can increase the vibration amplitude in the vibration region 11A, allowing the ink to be properly ejected from the nozzle.

[0039] [Differentiation] It should be noted that the present invention is not limited to the embodiments described above, and any configurations obtained by modifying, improving, or appropriately combining the embodiments to the extent that the objectives of the present invention can be achieved are included in the present invention.

[0040] [Example 1] For example, in the second embodiment, a support substrate 17 and support legs 171 are provided, but similarly in the first embodiment, the support substrate 17 and support legs 171 may be provided on the +Z side of the substrate 11. In this case, in the non-vibration region 11B, the vibration suppression portion 16 and the support leg portion 171 are provided on the ±Z side of the substrate 11.

[0041] Furthermore, although the second embodiment illustrates a configuration in which a support substrate 17 is provided, a configuration in which only the support legs 171 are provided, without a support substrate 17, is also possible.

[0042] [Differentiation 2] In the first embodiment described above, an example was shown in which the vibration region 11A is circular, but the vibration region 11A may be formed in other shapes having a short axis direction and a long axis direction. Figure 9 is a plan view of the piezoelectric device 10C when the vibration region 11A is rectangular. In Figure 9, the piezoelectric element 14 and the third electrode 15 are not shown.

[0043] For example, in the piezoelectric device 10C shown in Figure 9, the vibration region 11A is configured in a rectangular shape with the X direction as the short axis and the Y direction as the long axis. In this case, the first electrode 12 is provided along a side parallel to the long axis, that is, a pair of long sides, spanning from the vibrating region 11A to the non-vibrating region 11B. The second electrode 13 is provided in the vibration region 11A, as in the embodiment described above. Since the first electrodes 12 are provided along a pair of long sides of the vibration region 11A, the second electrode 13 is provided in a rectangular shape with its length in the direction of the long axis, sandwiched between these first electrodes 12. The piezoelectric element 14 and the third electrode 15 are the same as in the above embodiment, and are arranged to cover the first electrode 12 and the second electrode 13 from the vibration region 11A to the non-vibration region 11B. Also, as in the first embodiment, a vibration suppression part 16 is placed in the non-vibration region 11B of the first surface 113 of the substrate 11. Alternatively, as in the second embodiment, a support substrate 17 facing the third electrode 15 may be placed, and support legs 171 may be joined to the portion corresponding to the non-vibration region 11B. As a result, the cross-section of the piezoelectric device 10C when viewed in the XZ plane is the same as that of the first embodiment shown in Figure 1 or the second embodiment shown in Figure 7.

[0044] In this case, let W1 be the sum of the widths W11 and W12 along the short axis direction of the portion of the first electrode 12 within the vibration region 11A, and let W2 be the width along the short axis direction of the second electrode 13. W1 <W2 0.25 ≤ W1 / W2 ≤ 1 0.5 < (W1 + W2) / Wc < 1 The vibration region 11A, the first electrode 12, and the second electrode 13 are configured to satisfy the following conditions. This allows the vibration amplitude in the vibration region 11A to be increased, similar to the embodiment described above, thereby improving driving efficiency.

[0045] In the example shown in Figure 9, a pair of first electrodes 12 are provided along the long side of the vibration region 11A. However, similar to the above embodiment, the first electrodes 12 may be arranged to surround the outer periphery of the vibration region 11A.

[0046] [Difference 3] The above embodiment and the modified example 2 shown in Figure 9 show an example in which the first electrode 12 is arranged on either side of the second electrode 13, but the embodiment is not limited thereto. For example, in the above embodiment, the first electrode 12 may be provided only on the +X side (or only on the -X side) of the second electrode 13. If the vibration region 11A is rectangular as shown in Figure 9, the first electrode 12 may be provided only along one of the long sides of the vibration region 11A. In this case, the width of the first electrode 12 in the vibration region 11A is W1. W1 <W2 0.25 ≤ W1 / W2 ≤ 1 0.5 < (W1 + W2) / Wc < 1 The vibration region 11A, the first electrode 12, and the second electrode 13 are configured to satisfy the following conditions.

[0047] [Summary of this disclosure] A piezoelectric device according to a first aspect of the present disclosure comprises: a substrate having a vibrating region and a non-vibrating region surrounding the vibrating region; a first electrode provided spanning the vibrating region and the non-vibrating region; a second electrode disposed inside the vibrating region and spaced apart from the first electrode; a piezoelectric body provided spanning the substrate, the first electrode, and the second electrode; and a third electrode on the piezoelectric body that, when viewed from the thickness direction of the substrate, overlaps with at least the first electrode and the second electrode within the vibrating region.

[0048] In such piezoelectric devices, by shifting the phase between the drive voltage applied between the first and third electrodes and the drive voltage applied to the second and third electrodes, it is possible to alternately generate stress that causes the vibration region to bend towards the piezoelectric body and stress that causes it to bend away from the piezoelectric body, thereby increasing the amount of deformation (vibration amplitude) in the vibration region.

[0049] In the piezoelectric device of this embodiment, when viewed from the thickness direction, the width of the portion of the first electrode that is positioned in the vibration region is less than or equal to the width of the second electrode, and it is preferable that the sum of the width of the first electrode positioned in the vibration region and the width of the second electrode is less than the width of the vibration region. This allows for a greater deformation of the piezoelectric device compared to the case where the width of the portion of the first electrode located in the vibration region is larger than the width of the second electrode.

[0050] In the piezoelectric device of this embodiment, it is preferable that the first electrode is provided sandwiching the second electrode. This results in a symmetrical stress balance in the vibration region, allowing for a larger displacement during vibration.

[0051] In the piezoelectric device of this aspect, when the sum of the widths of the portions of the first electrode disposed in the vibration region is W1, the width of the second electrode is W2, and the width of the vibration region is Wc, it is preferable to satisfy 0.25 < W1 / W2 ≤ 1 and 0.5 < (W1 + W2) / Wc < 1. Thereby, when 0.25 > W1 / W2, the deformation amount of the piezoelectric device can be made larger than when 0.5 > (W1 + W2) / Wc.

[0052] The piezoelectric device of this aspect includes a voltage application unit that applies a voltage between the first electrode and the third electrode and between the second electrode and the third electrode, and it is preferable that the voltage application unit makes the phase of the voltage applied between the first electrode and the third electrode different from the phase of the voltage applied between the second electrode and the third electrode. In the piezoelectric device of this aspect, by applying a voltage between the second electrode, the piezoelectric body, and the third electrode, stress acts so that the vibration region is displaced to the side opposite to the piezoelectric body, and by applying a voltage between the first electrode, the piezoelectric body, and the third electrode, stress acts so that the vibration region is displaced to the piezoelectric body side. Therefore, by making the phase of the voltage applied between the first electrode and the third electrode different from the phase of the voltage applied between the second electrode and the third electrode, stress can be applied to the displacement direction of the vibration region respectively, and the displacement amount of the vibration region can be increased.

[0053] At this time, when the phase difference between the phase of the voltage applied between the first electrode and the third electrode and the phase of the voltage applied between the second electrode and the third electrode is Δφ, it is preferable to satisfy 150° ≤ Δφ ≤ 210°. Thereby, by applying a voltage between the second electrode, the piezoelectric body, and the third electrode, the vibration region is displaced to the side opposite to the piezoelectric body, and when the vibration region returns to the piezoelectric body side due to the spring force of the substrate, by applying a voltage between the first electrode, the piezoelectric body, and the third electrode, stress that causes the vibration region to be displaced to the piezoelectric body side due to the deformation of the piezoelectric body can be applied. Therefore, the deformation amount of the vibration region can be made larger by the combined force of the spring force of the substrate and the stress due to the deformation of the piezoelectric body.

[0054] In the piezoelectric device of this embodiment, the device may be configured to include a support substrate positioned opposite to the third electrode on the side opposite to the substrate, and support legs that join at least one of the substrate, the piezoelectric body, and the third electrode to the support substrate in the non-vibration region. In this configuration, the substrate can be reinforced by the support substrate, thereby suppressing damage to the substrate. Furthermore, by joining the support legs to a non-vibration region, they can function as vibration suppression members that suppress vibrations in the non-vibration region.

[0055] In this case, the support substrate may be configured to have through holes in the portion that overlaps with the vibration region when viewed from the thickness direction. This makes it possible to output ultrasonic waves generated by vibrations in the vibration region to both the piezoelectric side of the substrate and the side opposite the piezoelectric element.

[0056] An ultrasonic device according to a second aspect of the present disclosure comprises a piezoelectric device as described above, and transmits ultrasonic waves by driving the piezoelectric device. This allows for the output of high-pressure ultrasonic waves. [Explanation of symbols]

[0057] 10, 10A... Ultrasonic device, 10B, 10C... Piezoelectric device, 11... Substrate, 11A... Vibration region, 11B... Non-vibration region, 12... First electrode, 13... Second electrode, 14... Piezoelectric body, 15... Third electrode, 16... Vibration suppression section, 17... Support substrate, 20... Voltage control section, 21... First power supply, 22... Second power supply, 23... Common potential section, 171... Support leg section, 172... Through hole.

Claims

1. A substrate having a vibrating region and a non-vibrating region surrounding the vibrating region, A first electrode provided spanning the vibration region and the non-vibration region, A second electrode is positioned within the vibration region and spaced apart from the first electrode, A piezoelectric body provided spanning the substrate, the first electrode, and the second electrode, On the piezoelectric element, a third electrode is provided that, when viewed from the thickness direction of the substrate, overlaps with at least the first electrode and the second electrode within the vibration region, A piezoelectric device equipped with the following features.

2. Viewed from the thickness direction, the width of the portion of the first electrode that is positioned in the vibration region is less than or equal to the width of the second electrode, and the sum of the width of the first electrode positioned in the vibration region and the width of the second electrode is less than the width of the vibration region. The piezoelectric device according to claim 1.

3. The first electrode is provided sandwiching the second electrode, The piezoelectric device according to claim 2.

4. When W1 is the sum of the widths of the portion of the first electrode that is positioned in the vibration region, W2 is the width of the second electrode, and Wc is the width of the vibration region, 0.25<W1 / W2≦1, 0.5<(W1+W2) / Wc<1 A piezoelectric device according to claim 3, satisfying the requirements.

5. The device includes a voltage application section that applies a voltage between the first electrode and the third electrode, and between the second electrode and the third electrode, The voltage application unit makes the phase of the voltage applied between the first electrode and the third electrode different from the phase of the voltage applied between the second electrode and the third electrode. The piezoelectric device according to claim 1.

6. When the phase difference between the phase of the voltage applied between the first electrode and the third electrode and the phase of the voltage applied between the second electrode and the third electrode is Δφ, 150° ≤ Δφ ≤ 210° A piezoelectric device according to claim 5, satisfying the requirements.

7. A support substrate is positioned opposite to the third electrode on the side opposite to the substrate, In the non-vibration region, the support leg portion is provided for joining at least one of the substrate, the piezoelectric element, and the third electrode to the support substrate. The piezoelectric device according to claim 1.

8. The support substrate has through holes in the portion that overlaps with the vibration region when viewed from the thickness direction. The piezoelectric device according to claim 7.

9. A piezoelectric device according to any one of claims 1 to 8, An ultrasonic device that drives the piezoelectric device to transmit ultrasonic waves.

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