Ultrasonic elements, information equipment, and highly directional speakers

Abstract

To provide an ultrasonic element capable of stably outputting ultrasonic waves with frequencies below 500 kHz. [Solution] The ultrasonic element comprises a substrate having a vibrating region and a non-vibrating region surrounding the vibrating region, a first electrode disposed inside the vibrating region, a piezoelectric body disposed on the substrate covering the first electrode, and a second electrode provided on the piezoelectric body, wherein the direction in which the substrate, the first electrode, the piezoelectric body, and the second electrode are stacked is defined as the stacking direction, and the thickness of the substrate along the stacking direction is 2.0 μm or more and 10.0 μm or less.

Description

Technical Field

[0001] The present invention relates to an ultrasonic element, an information device including the ultrasonic element, and a super-directional speaker including the ultrasonic element.

Background Art

[0002] Conventionally, an information device that limits the sound wave transmission position to a narrow range has been known (for example, Patent Document 1). Patent Document 1 relates to a small electronic device including a super-directional speaker, which modulates an audio signal and a high-frequency signal into an amplitude-modulated wave signal, amplifies the amplitude-modulated wave signal to obtain an amplified signal, and converts the amplified signal into acoustic vibrations for radiation. In the device of Patent Document 1, a super-directional beam-shaped sound field is formed by inputting it into an ultrasonic element composed of a small ceramic piezoelectric element. In the process of the amplitude-modulated sound wave propagating in the air, a non-linear interaction occurs to generate a distortion component, so that the low-frequency component therein becomes audible to the listener.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, it is difficult to stably drive ultrasonic waves with a frequency of 200 kHz or less by the ultrasonic element mounted on a conventional small electronic device. That is, conventionally, in order to stably output ultrasonic waves with a frequency of 40 kHz to 500 kHz with directivity, it is necessary to make the diameter of the speaker aperture 15 mm or more, which has been difficult to mount on a small device.

Means for Solving the Problems

[0005] An ultrasonic element according to one aspect of the present disclosure comprises a substrate having a vibrating region and a non-vibrating region surrounding the vibrating region, a first electrode disposed inside the vibrating region, a piezoelectric body disposed on the substrate covering the first electrode, and a second electrode provided on the piezoelectric body, wherein the direction in which the substrate, the first electrode, the piezoelectric body, and the second electrode are stacked is defined as the stacking direction, and the thickness of the substrate along the stacking direction is 2.0 μm or more and 10.0 μm or less. [Brief explanation of the drawing]

[0006] [Figure 1] A schematic diagram showing the general configuration of the super-directional speaker of the first embodiment. [Figure 2] A diagram showing an example of the ultrasonic output range of the super-directional speaker of the first embodiment. [Figure 3] A plan view showing the schematic configuration of the ultrasonic element of the first embodiment. [Figure 4] A diagram showing the relationship between the resonant frequency of the ultrasonic element and the thickness of the substrate in the first embodiment. [Figure 5] This figure shows an example of the relationship between the substrate thickness and the width of the vibration region when the resonant frequency H of the ultrasonic element is 40 kHz, according to the first embodiment. [Figure 6] This figure shows an example of the relationship between the substrate thickness and the width of the vibration region when the resonant frequency H of the ultrasonic element is set to 75 kHz in the first embodiment. [Figure 7] This figure shows an example of the relationship between the substrate thickness and the width of the vibration region when the resonant frequency H of the ultrasonic element is 100 kHz, according to the first embodiment. [Figure 8] This figure shows an example of the relationship between the substrate thickness and the width of the vibration region when the resonant frequency H of the ultrasonic element is 500 kHz, according to the first embodiment. [Figure 9] A diagram showing the displacement of the vibration region for outputting ultrasonic waves of a predetermined frequency in the ultrasonic element of the first embodiment and the ultrasonic element of the comparative example. [Figure 10] Figure 9 shows a schematic configuration of the ultrasonic element in the comparative example. [Figure 11]A schematic diagram showing the general configuration of the ultrasonic element of the second embodiment. [Figure 12] A schematic diagram showing the general configuration of the information equipment of the third embodiment. [Figure 13] A schematic diagram showing an example of a wireless speaker equipped with the super-directional speaker of this disclosure. [Figure 14] A schematic diagram showing an example of a car navigation system equipped with the super-directional speaker of this disclosure. [Figure 15] A schematic diagram showing an example of an indoor content output device equipped with the super-directional speaker of this disclosure. [Figure 16] A schematic diagram showing an example of an operation panel equipped with the information equipment disclosed herein. [Modes for carrying out the invention]

[0007] [First Embodiment] The first embodiment of this disclosure will be described below. Figure 1 is a schematic diagram showing the general configuration of the super-directional speaker 1 of this embodiment. As shown in Figure 1, the super-directional speaker 1 comprises an ultrasonic element 10 and a control device 20 that controls the ultrasonic element 10. The super-directional speaker 1 of this embodiment is a speaker that generates audible sound only in a predetermined audible field, and can be suitably incorporated into small devices and portable devices such as smartphones, tablet terminals, and notebook computers.

[0008] Figure 2 shows an example of the output range of the ultrasonic waves emitted from the super-directional speaker 1. In this embodiment, the super-directional speaker 1, in the control device 20, combines and modulates an audio signal in the audible frequency band based on audible sound and an ultrasonic signal in the ultrasonic frequency band to create a modulated signal. The amplified modulated signal is input to the ultrasonic element 10, thereby outputting ultrasound as acoustic vibrations from the ultrasonic element 10. Because ultrasound has high directivity, it exhibits higher directivity compared to low-frequency audible sounds. The directivity angle of the ultrasound output from the ultrasound element 10 depends on the frequency of the ultrasound. As the frequency of the ultrasound increases, the spread of the ultrasound beam narrows, and therefore the directivity angle also narrows. For this reason, it is preferable to set the ultrasound frequency band to be used appropriately according to the purpose of the super-directional speaker 1.

[0009] Furthermore, when sound waves are output into the air, the compression and expansion of the air occur linearly. If the frequency of the audible sound is f1 and the frequency of the ultrasound is f2, and the amplitude is modulated, sideband components (f2±f1) are generated. However, if the sound wave is ultrasound and the ultrasound is output at a high sound pressure, the high frequency and large amplitude of the ultrasound cause the compression and expansion of the air to become nonlinear, and the waveform of the ultrasound during propagation is distorted (nonlinear effect). As in this embodiment, when an amplified signal obtained by amplitude modulating and amplifying the audio signal and the ultrasound signal is input to the ultrasound element 10, as shown in Figure 2, the ultrasound propagates linearly in the range up to a predetermined distance from the ultrasound element 10 (near field 91), and an audible field 92 is formed in front of the near field 91 (away from the ultrasound element 10). In the audible field 92, distortion of the ultrasound waveform occurs due to the nonlinear effect described above. As a result, an audible sound frequency f1 is generated, which is the difference between the ultrasound frequency f2 and the sideband components (f2±f1).

[0010] Incidentally, in the super-directional speaker 1 described above, it is necessary to form a beam width with an appropriate directivity range, and the higher the ultrasonic frequency, the stronger the directivity. Also, in order to form the target audible field 92 (to determine the distance of the near-field 91), the sound pressure of the speaker output needs to be appropriately increased. Furthermore, in order to reproduce audible sound in the audible field 92, the ultrasonic frequency f2 also needs to be appropriately selected, and conditions are required that allow for stable driving within a range of at least 40kHz to 500kHz. In this embodiment, an ultrasonic element 10 having a configuration that can be stably driven within a range of 40 kHz or more and 500 kHz or less is provided. Hereinafter, a specific configuration of such an ultrasonic element 10 will be described.

[0011] [Configuration of Ultrasonic Element 10] FIG. 3 is a plan view showing a schematic configuration of the ultrasonic element 10 of this embodiment. As shown in FIG. 1, the ultrasonic element 10 of this embodiment includes a substrate 11, a first electrode 121, a piezoelectric body 122, a second electrode 123, a vibration suppression portion 13, and a support substrate 14. Here, in this embodiment, the first electrode 121, the piezoelectric body 122, and the second electrode 123 are laminated on the substrate 11. The lamination direction of the substrate 11, the first electrode 121, the piezoelectric body 122, and the second electrode 123 is defined as the Z direction. Also, a plane intersecting (orthogonal in this embodiment) the Z direction is defined as the XY plane, and the two orthogonal axial directions included in the XY plane are defined as the X direction and the Y direction, respectively.

[0012] The substrate 11 includes a base portion 111 and a surface layer portion 112. The base portion 111 is a flat plate-like substrate made of a semiconductor substrate, and in this embodiment, it is made of Si as the semiconductor substrate. The surface layer portion 112 is a portion obtained by surface processing the surface of the base portion 111. For example, in this embodiment, one side of the base portion 111 made of Si is subjected to an oxidation treatment to form a SiO2 layer, and further, a ZrO2 layer is laminated by sputtering or the like. That is, in this embodiment, the surface layer portion 112 is composed of a SiO2 layer and a ZrO2 layer. In this embodiment, the dimension (thickness) of the substrate 11 along the Z direction is 2.00 μm or more and 10.00 μm or less, and more preferably 2.08 μm or more and 6.77 μm or less. Note that the surface layer portion 112 has a sufficiently small thickness dimension with respect to the base portion 111, and the thickness of the substrate 11 is dominated by the base portion 111.

[0013] 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.

[0014] As shown in Figures 1 and 3, the substrate 11 includes a vibrating region 11A and a non-vibrating region 11B surrounding the vibrating region 11A. The vibrating region 11A is a region that vibrates when a voltage is applied to the piezoelectric element 122 via the first electrode 121 and the second electrode 123, and ultrasonic waves are output from the ultrasonic element 10 due to the vibration of the vibrating region 11A. In Figure 3, the boundary between the vibrating region 11A and the non-vibrating region 11B is shown by the dashed line Q.

[0015] On the other hand, the non-vibration region 11B is a region where vibration is restricted. In this embodiment, vibration suppression portion 13 is provided on the first surface 113 of the non-vibration region 11B of the substrate 11, thereby suppressing vibration in the non-vibration region 11B. The vibration suppression section 13 uses a resin that has a vibration suppression effect. The resin used is not particularly limited, and for example, resist resins such as epoxy resins, acrylic resins, and novolac resins can be used. The vibration suppression section 13 is provided to cover the entire non-vibration region 11B, but not in the vibration region 11A. In this embodiment, an example is shown in which the vibration suppression portion 13 is provided on the first surface 113 of the substrate 11, but the support legs 141 that join the substrate 11 and the support substrate 14 may also function as the vibration suppression portion.

[0016] The first electrode 121 is located on the surface layer 112 of the substrate 11, within the vibration region 11A of the substrate 11, as viewed from the Z direction. In other words, the width W1 of the first electrode 121 is smaller than the width W0 of the vibration region 11A. In this embodiment, the vibration region 11A and the first electrode 121 are circular when viewed from the Z direction. In this case, the width W1 of the first electrode 121 represents the diameter of the first electrode 121, and the width W0 of the vibration region 11A represents the diameter of the vibration region 11A. The vibration region 11A is not limited to a circle, but may have other shapes, such as a rectangle. If the vibration region 11A has a shape with a short axis and a long axis, such as a rectangle or an ellipse, the first electrode 121 is also made to be similar in shape to the vibration region 11A, and the short axis and long axis of the first electrode 121 are made to coincide with the axis and long axis of the vibration region 11A. In this case, the first electrode 121 is positioned relative to the vibration region 11A such that (dimension of the short axis of the first electrode 121) < (dimension of the short axis of the vibration region 11A).

[0017] Furthermore, a first lead electrode 121A is connected to the first electrode 121. The first lead electrode 121A extends from the vibration region 11A to the non-vibration region 11B on the surface layer 112 and is electrically connected to the control device 20 via a first terminal portion (not shown) provided at a predetermined position in the non-vibration region 11B of the substrate 11.

[0018] The piezoelectric element 122 is provided on the surface layer 112 of the substrate 11, extending from the vibrating region 11A to the non-vibrating region 11B. In other words, the piezoelectric element 122 covers the entire vibrating region 11A and the first electrode 121. The piezoelectric element 122 may be formed over the entire surface of the substrate 11. The piezoelectric element 122 is composed of a perovskite-type transition metal oxide containing Pb, for example, in this embodiment, it is PZT containing Pb, Zr, and Ti.

[0019] The second electrode 123 is provided on the piezoelectric body 122, extending from the vibrating region 11A to the non-vibrating region 11B. In other words, the width W2 of the second electrode 123 is greater than the width W1 of the first electrode 121 and the width W0 of the vibrating region 11A when viewed from the Z direction (W1 <W0<W2)。 Furthermore, the edge of the second electrode 123 is located on the piezoelectric element 122, and support legs 141, described later, are provided so as to cover the piezoelectric element 122 from the edge 123A of the second electrode 123. As a result, the edge 123A of the second electrode 123 is protected by the support legs 141, thereby suppressing burnout and cracking of the piezoelectric element 122 near the edge 123A of the second electrode 123.

[0020] Furthermore, a second lead electrode 123B is connected to the second electrode 123. This second lead electrode 123B extends from the piezoelectric element 122 to a second terminal portion (not shown) provided at a predetermined position in the non-vibration region 11B of the substrate 11, and is electrically connected to the control device 20 via the second terminal portion. When viewed from the Z direction, the portion in the vibration region 11A where the first electrode 121, piezoelectric element 122, and second electrode 123 overlap functions as a piezoelectric element 12. By applying a driving voltage between the first electrode 121 and the second electrode 123, the vibration region 11A flexes in the Z direction, and ultrasonic waves are output in the Z direction.

[0021] In this embodiment, as shown in Figure 3, the vibration region 11A and the first electrode 121 are circular, but the second electrode 123 does not have to be circular. That is, the shape of the second electrode 123 is not limited as long as it covers the vibration region 11A and the first electrode 121. Also, if the vibration region 11A and the first electrode 121 have a shape with a short axis direction and a long axis direction when viewed from the Z direction, the second electrode 123 should be installed relative to the vibration region 11A such that (dimension in the short axis direction of the first electrode 121) < (dimension in the short axis direction of the vibration region 11A) < (dimension in the short axis direction of the second electrode 123).

[0022] The support substrate 14 has a sufficiently larger thickness in the Z direction compared to the substrate 11, and is joined to the piezoelectric element 122 and the second electrode 123 via the support legs 141. In the example shown in Figure 1, the piezoelectric element 122 covers the entire substrate 11, but a part of the surface layer 112 of the substrate 11 may be exposed. In this case, the support legs 141 may also be joined to the surface layer 112. As described above, the support leg 141 covers the area from the edge 123A of the second electrode 123 to the piezoelectric element 122, so that the boundary between the edge 123A of the second electrode 123 and the piezoelectric element 122 is not exposed, thereby suppressing problems such as burnout and cracking.

[0023] Furthermore, as shown in Figure 1, the support substrate 14 may have a hole 142 that penetrates in the Z direction at a position opposite the vibration region 11A. In this case, the vibration of the vibration region 11A can output ultrasonic waves not only to the -Z side but also to the +Z side.

[0024] Incidentally, the resonant frequency H of the ultrasonic element 10 can be expressed as a function of the thickness d of the substrate 11 and the width W0 of the vibration region 11A (H=f(d,W0)). The width W0 of the vibration region 11A is the minimum width of the vibration region 11A, and in this embodiment, since the vibration region 11A is circular, it is the diameter. There are multiple combinations of the thickness d of the substrate 11 and the width W of the vibration region 11A to obtain a specific resonant frequency, but in this embodiment, a configuration is required to stably output ultrasonic waves with frequencies from 40kHz to 500kHz from the ultrasonic element 10.

[0025] Therefore, the inventors of this disclosure have newly discovered conditions for the thickness d of the substrate 11 in order to stably output ultrasonic waves with frequencies from 40 kHz to 500 kHz from the ultrasonic element 10. Figure 4 shows the relationship between the resonant frequency of the ultrasonic element 10 that satisfies the above conditions and the thickness d of the substrate 11 in this embodiment. In other words, in this embodiment, the relationship between the resonant frequency H of the ultrasonic element 10 and the thickness d of the substrate 11 is determined to satisfy the condition of equation (1) below.

[0026]

number

[0027] Furthermore, Figures 5 to 8 show the relationship between the thickness d of the substrate 11 in the ultrasonic element 10 and the width W0 of the vibration region 11A. Figure 5 shows the case when the resonant frequency H of the ultrasonic element 10 is 40 kHz, Figure 6 shows the case when the resonant frequency H of the ultrasonic element 10 is 75 kHz, Figure 7 shows the case when the resonant frequency H of the ultrasonic element 10 is 100 kHz, and Figure 8 shows the case when the resonant frequency H of the ultrasonic element 10 is 500 kHz. The relationship between the thickness d of the substrate 11 and the width W of the vibration region 11A, with respect to the resonant frequency of the ultrasonic element 10, can be determined in advance, as shown in Figures 5 to 8. Therefore, in this embodiment, the thickness d of the substrate 11 corresponding to the target resonance frequency (center frequency of the ultrasound output from the ultrasonic element 10) is determined based on equation (1) from the resonance frequency corresponding to the frequency band of the ultrasound output from the ultrasonic element 10. Then, the width W0 of the vibration region 11A is determined from the relationship between the thickness d of the substrate 11 corresponding to the target resonance frequency and the width W0 of the vibration region 11A. For example, if the ultrasonic resonance frequency is 75 kHz, the thickness d of the substrate 11 and the width W0 of the vibration region 11A satisfy the conditions of equation (2) below.

[0028]

number

[0029] Therefore, if the ultrasonic resonance frequency is 75 kHz, then from equation (1), d = 5.05 μm can be calculated, and from equation (2), W0 = 948.69 μm can be calculated. Similarly, the thickness d of the substrate 11 and the width W0 of the vibration region 11A can be calculated for other resonant frequencies as well. Furthermore, the thickness d of the substrate 11 corresponding to the resonant frequency of 40 kHz is d = 6.77 μm, and the width W0 of the corresponding vibration region 11A, as shown in Figure 5, is W0 = 1670.84 μm. The thickness d of the substrate 11 corresponding to the resonant frequency of 500 kHz is d = 2.08 μm, and the width W0 of the corresponding vibration region 11A, as shown in Figure 8, is W0 = 240.05 μm. Based on the above, for the ultrasonic element 10 of this embodiment, which can output ultrasonic waves from 40 kHz to 500 kHz, the thickness d of the substrate 11 is preferably 2.08 μm ≤ d ≤ 6.77 μm, and the width W0 of the corresponding vibration region 11A is 1670.84 μm ≥ W0 ≥ 240.05 μm. The resonant frequency of the ultrasonic element 10 is the frequency at which the ultrasonic element 10 can output ultrasonic waves with maximum sound pressure. The ultrasonic waves actually output from the ultrasonic element 10 can be output within a predetermined bandwidth range centered on the resonant frequency. Therefore, as described above, even if the thickness of the substrate 11 is 2.0 μm or more and 10.0 μm or less, it is possible to output ultrasonic waves between 40 kHz and 500 kHz.

[0030] [Frequency determination of ultrasonic element 10] Next, the frequency characteristics of the ultrasonic element 10 in this embodiment will be described. Figure 9 shows the displacement of the vibration region required to output ultrasonic waves of a predetermined frequency in the ultrasonic element 10 of this embodiment and the ultrasonic element of the comparative example. In Figure 9, line L1 shows the characteristics of the ultrasonic element 10 of this embodiment, and line L2 shows the characteristics of the ultrasonic element 80 of the comparative example. Figure 10 shows the schematic configuration of the ultrasonic element 80 of the comparative example.

[0031] As shown in Figure 10, the comparative example ultrasonic element 80 comprises a substrate 81, a diaphragm 82, and a piezoelectric element 83 laminated on the diaphragm 82. Here, the substrate 81 is made of Si, as in this embodiment, and has an opening 811 that penetrates the substrate 81. The diaphragm 82 is made by laminating an SiO2 layer and a ZrO2 layer, and is provided on the substrate 11 so as to close the opening 811. Of the diaphragm 82, the portion that closes the opening 811 (the portion that overlaps with the opening 811 when viewed from the Z direction) becomes the vibration region 82A of the comparative example ultrasonic element 80. Furthermore, the piezoelectric element 83 is constructed by sequentially stacking a first electrode 831, a piezoelectric body 832, and a second electrode 833. The first electrode 831, the piezoelectric body 832, and the second electrode 833 are each stacked within the vibration region 82A to form the piezoelectric element 83. Although not shown in the figures, similar to this embodiment, a first connecting electrode connected to the first electrode 831 and a second connecting electrode connected to the second electrode 833 extend from the vibration region 82A to the non-vibration region 82B on the diaphragm 82 and are connected to corresponding terminals. By applying a driving voltage between the first electrode 831 and the second electrode 833, the vibration region 82A is vibrated and ultrasonic waves are output. The ultrasonic element 80 of the comparative example described above is formed as follows. Specifically, an SiO2 layer is formed by thermal oxidation of one side of a Si substrate 81, and a ZrO2 layer is laminated on the SiO2 layer to form a diaphragm 82. After this, an electrode material is deposited on the diaphragm 82 and patterned by etching or the like to form a first electrode 831. Furthermore, a piezoelectric body 832 is formed by repeatedly coating and firing the piezoelectric material and then patterning it by etching. In addition, a second electrode 833 is formed by depositing an electrode material and patterning it by etching or the like. After the above, the substrate 81 is etched from the side opposite to the diaphragm 82, with the SiO2 layer acting as an etching stopper, to form an opening 811.

[0032] In the comparative example ultrasonic element 80 described above, the thickness of the substrate 81 is controlled by etching, which increases the surface roughness of the surface of the diaphragm 82 on the substrate 81 side, making it difficult to achieve an arithmetic surface roughness of 0.4 ± 0.5 μm as in this embodiment. Therefore, the comparative ultrasonic element 80 has difficulty producing a stable ultrasonic output, especially in the low-frequency range. For example, as shown in Figure 9, the comparative ultrasonic element 80 does not operate normally below approximately 200 kHz. In other words, the comparative ultrasonic element 80 cannot stably output ultrasonic waves with frequencies between 40 kHz and 200 kHz. In contrast, the ultrasonic element 10 of this embodiment can stably output ultrasound even in a wide frequency band from 40 kHz to 500 kHz, as shown by line L1.

[0033] [Configuration of the control device 20] Next, the control device 20 of the super-directional speaker 1 will be described. The control device 20 includes a drive circuit unit 21 for driving the ultrasonic element 10, a memory 22 for recording various information, and a processor 23 for outputting control signals to the drive circuit unit 21 for controlling the driving of the ultrasonic element 10. As described above, the super-directional speaker 1 of this embodiment is incorporated into a small device such as a smartphone. The memory 22 and processor 23 may be incorporated for the control of the small device, or they may be incorporated independently for the control of the super-directional speaker 1.

[0034] Memory 22 stores various programs and data for controlling the super-directional speaker 1. The processor 23 controls the super-directional speaker 1 by reading and executing a program stored in the memory 22. Specifically, the processor 23 generates an audio signal based on, for example, user input instructions and outputs it to the drive circuit unit 21. The processor 23 also generates an ultrasonic signal corresponding to the audio signal and outputs it to the drive circuit unit 21. In other words, the processor 23 generates the ultrasonic frequency in synchronization with the generation of the audio signal so that the sideband components (f2±f1) generated by nonlinear effects in the audible field 92 become the frequency f1 of the audio signal. That is, the processor 23 in this embodiment functions as an audio generation unit and a high-frequency generation unit.

[0035] The drive circuit section 21 includes a signal modulation circuit 211 as a signal modulation section and an amplification circuit 212 as an amplification section. The audio signal and ultrasonic signal output from the processor 23 are input to the signal modulation circuit 211 of the drive circuit unit 21, which generates a modulated signal by combining and modulating the audio signal corresponding to the audible sound and the ultrasonic signal corresponding to the ultrasound. The amplification circuit 212 generates an amplified signal by amplifying the modulated signal and inputs it to the ultrasonic element 10. As described above, the ultrasonic waves output from the ultrasonic element 10 are transmitted at a predetermined directional angle due to the straight-line propagation of ultrasonic waves, and no ultrasonic waves are transmitted to areas outside of the directional angle. In addition, ultrasonic waves with frequencies that cannot be perceived by human hearing propagate in the near-field 91, and in the audible field 92 beyond the near-field 91, an audible sound corresponding to the speech signal is formed due to the nonlinear effect of the ultrasonic waves.

[0036] [Effects of this embodiment] In this embodiment, the ultrasonic element 10 comprises a substrate 11 having a vibrating region 11A and a non-vibrating region 11B surrounding the vibrating region 11A, a first electrode 121 disposed inside the vibrating region 11A, a piezoelectric body 122 disposed on the substrate 11 covering the first electrode 121, and a second electrode 123 provided on the piezoelectric body 122. In this embodiment, the thickness of the substrate 11 along the Z direction is configured to be 2.0 μm or more and 10.0 μm or less, more preferably 2.08 μm or more and 6.77 μm or less. In this embodiment of the ultrasonic element 10, the resonant frequency is in the range of 40 kHz to 500 kHz, and the ultrasonic element 10 can stably output ultrasound in the frequency band of 40 kHz to 500 kHz.

[0037] In this embodiment, the second electrode 123 is positioned across the vibration region 11A and the non-vibration region 11B. Furthermore, the width W2 of the second electrode 123 is greater than the width W1 of the first electrode 121, and the width W0 of the vibration region 11A is greater than the width W1 of the first electrode 121 and smaller than the width W2 of the second electrode 123. As a result, as described above, the ultrasonic element 10 can stably output ultrasound in the frequency band of 40kHz to 500kHz.

[0038] In this embodiment, the vibration suppression section 13 is provided on the first surface 113 of the substrate 11 opposite to the piezoelectric element 122, in a region that overlaps with the non-vibration region 11B when viewed from the Z direction. This allows the vibration region 11A to be defined by the vibration suppression unit 13 with a simple configuration. Furthermore, in this configuration, the substrate 11 is polished to a thickness of 2.0 μm to 10.0 μm, which allows for more precise control of the substrate thickness to the desired thickness compared to a configuration in which the substrate 11 is etched.

[0039] In this embodiment, the arithmetic surface roughness of the first surface 113 of the substrate 11 is within the range of 0.4 ± 0.5 μm. In such a substrate 11, as described above, the thickness of the substrate 11 can be precisely controlled to the desired thickness. Furthermore, such a first surface 113 is difficult to form by etching, and is formed by polishing.

[0040] In this embodiment, the material of the substrate 11 is Si. The substrate 11, made of Si, has high processing accuracy, is easy to form to the desired thickness as described above, and can stably output ultrasonic waves from 40kHz to 500kHz.

[0041] The super-directional speaker 1 of this embodiment comprises an ultrasonic element 10, a processor 23, a signal modulation circuit 211, and an amplification circuit 212. The processor 23 generates an audio signal in the audible range and an ultrasonic signal in the ultrasonic band, and inputs them to the signal modulation circuit 211. The signal modulation circuit 211 combines the audio signal and the ultrasonic signal to convert them into a modulated signal, and the amplification circuit 212 outputs the amplified acoustic signal to the ultrasonic element 10. The ultrasonic element 10 then radiates the input acoustic signal as acoustic vibrations. In such a highly directional speaker 1, the directivity of ultrasound causes acoustic vibrations (ultrasound) to be radiated within a predetermined directional angle. The radiated acoustic vibrations generate audible sound in the audible field 92 due to the nonlinear effects of ultrasound, becoming an audible sound that can be perceived by human hearing. This makes it possible to output sound that is audible only in a specific audible field 92. Furthermore, with low-frequency ultrasound such as 40kHz, it is usually difficult to achieve a directivity angle of 20 degrees or less. Therefore, conventionally, highly directional speakers utilizing the nonlinear effects of ultrasound could only be installed in vast spaces such as museums. In contrast, in this embodiment, it is possible to output ultrasound with frequencies from 40kHz to 500kHz from a small ultrasonic element 10 with a vibration region 11A width W0 of 2000μm or less, providing a highly directional speaker 1 that can be mounted in a small device.

[0042] [Second Embodiment] Next, a second embodiment will be described. In the first embodiment, an example was shown in which the shape of the vibration region 11A is defined by joining the vibration suppression part 13 to the non-vibration region 11B. Alternatively, the support legs 141 that join the support substrate 14 and the substrate 11 may be joined to the non-vibration region 11B to function as a vibration suppression unit. In the following explanations, items that have already been explained will be denoted by the same symbols, and their explanations will be omitted or simplified.

[0043] Figure 11 is a cross-sectional view showing the configuration of the ultrasonic element 10A of the second embodiment. In this embodiment, as shown in Figure 11, the vibration suppression portion 13 is not provided in the non-vibration region 11B of the first surface 113 of the substrate 11. Instead, in this embodiment, the support legs 141 connecting the support substrate 14 and the substrate 11 are joined to the portion of the substrate 11 corresponding to the non-vibration region 11B. As a result, the support legs 141 function as vibration suppressors, suppressing vibrations in the non-vibration region 11B and defining the shape of the vibration region 11A.

[0044] Furthermore, the support leg portion 141 of this embodiment is joined to the piezoelectric element 122 from the edge 123A of the second electrode 123, similar to the first embodiment. This suppresses burnout and cracking of the piezoelectric element 122 near the edge 123A of the second electrode 123.

[0045] In the second embodiment, the same effects and advantages as in the first embodiment can be achieved, and ultrasonic waves in the frequency band of 40kHz to 500kHz can be stably output from the ultrasonic element 10.

[0046] [Third Embodiment] In the first embodiment described above, a highly directional speaker 1 equipped with an ultrasonic element 10 was exemplified, but the invention is not limited thereto. In the third embodiment, an information device that transmits signals by ultrasound will be described as a small device equipped with an ultrasonic element 10.

[0047] Figure 12 shows a schematic configuration of the information device 1A of the third embodiment. As shown in Figure 12, the information device 1A of this embodiment comprises an ultrasonic element 10 and a control device 20A. The configuration of the ultrasonic element 10 is the same as in the first embodiment described above, and therefore will not be explained here. Alternatively, as in the second embodiment, the ultrasonic element 10 may be configured such that the vibration region 11A is defined by the support legs 141 instead of the vibration suppression part 13.

[0048] The control device 20A of the information device 1A in this embodiment includes, similar to the first embodiment, a drive circuit unit 21 for driving the ultrasonic element 10, a memory 22 for recording various information, and a processor 23A that outputs a control signal to the drive circuit unit 21 for controlling the driving of the ultrasonic element 10. In this embodiment, the processor 23A functions as the baseband signal generation unit and carrier signal generation unit of this disclosure by reading and executing the program recorded in the memory 22. In other words, the processor 23A generates a baseband signal based on, for example, user input instructions. The baseband signal is a signal containing various content data, and the content data can include various types of data such as text data, audio data, and image data. The processor 23A encrypts the content data into audio data using algorithms such as AES (Advanced Encryption Standard) or RSA (Rivest-Shamir-Adleman). Furthermore, the processor 23A generates a carrier signal corresponding to the generated baseband signal. The carrier signal is an ultrasonic signal, and the ultrasonic frequency is generated based on the frequency of the baseband signal, which is the audio data. This ultrasonic frequency can be set to a frequency band of 40kHz to 500kHz, as in the first embodiment described above.

[0049] The processor 23A then outputs these baseband signals and carrier signals to the signal modulation circuit 211 of the drive circuit unit 21. As a result, similar to the first embodiment, the signal modulation circuit 211 generates a modulated signal by combining the baseband signal and the carrier signal, and outputs the generated modulated signal to the amplification circuit 212. The amplification circuit 212 amplifies the modulated signal to obtain an acoustic signal, which is then output to the ultrasonic element 10. As a result, the ultrasonic element 10 vibrates in the vibration region 11A in response to the input acoustic signal, and outputs acoustic vibrations.

[0050] When using such information device 1A, as in the first embodiment described above, highly directional information communication becomes possible, allowing ultrasonic information to propagate within a predetermined directional angle range, and information is not received in the near field 91, while information is received in the audible field 92. In other words, due to the nonlinear effect of ultrasound, a baseband signal appears in the audible field 92, and by holding a receiver (not shown) over the audible field 92, the baseband signal output from the information device 1A can be received.

[0051] Such an information device 1A can receive information only in the direction of the ultrasonic output from the ultrasonic element 10 and within a predetermined audible field 92 at a set distance from the ultrasonic element 10, thus enabling the transmission and reception of highly confidential information.

[0052] [Differentiation] It should be noted that the present invention is not limited to the embodiments and modifications described above, and any configurations obtained by modifications, improvements, and appropriate combinations of the embodiments, to the extent that the objectives of the present invention can be achieved, are included in the present invention.

[0053] In the above embodiment, a highly directional speaker 1 and information device 1A equipped with an ultrasonic element 10 (or ultrasonic element 10A of the second embodiment) were exemplified, but the ultrasonic element 10 (or ultrasonic element 10A of the second embodiment) of this disclosure can be applied to any other device. Figures 13 to 15 show other application examples of the ultrasonic element 10. For example, the highly directional speaker 1 can be applied to small devices such as smartphones, tablet terminals, and notebook computers as described in the first embodiment, as well as wireless speakers as shown in Figure 11, car navigation systems as shown in Figure 12, and indoor content output devices as shown in Figure 13. Furthermore, the information device 1A can be applied to control panels as shown in Figure 14.

[0054] The wireless speaker 1B shown in Figure 13 is a neckband speaker, with the speaker unit 41 provided on a neckband 40 that is worn around the neck. The speaker unit 41 is provided with the ultrasonic element 10 used in the first embodiment or the ultrasonic element 10A of the second embodiment, and a drive circuit unit 21. The drive circuit unit 21 is capable of communicating with a mobile terminal device such as a smartphone, receives an audio signal and an ultrasonic signal from the mobile terminal device, generates a modulated signal by combining these, amplifies the modulated signal to generate an acoustic signal, and outputs it to the ultrasonic element 10. As a result, similar to the super-directional speaker 1 of the first embodiment, sound can be heard only in a predetermined audible field 92 (in this example, near the ears on the head).

[0055] Furthermore, the navigation device 1C shown in Figure 14 is fixed to the vehicle's center panel 42 and is a device that guides the vehicle's driver along the vehicle's route. This navigation device 1C incorporates the ultrasonic element 10 used in the first embodiment (or the ultrasonic element 10A of the second embodiment), and the direction of ultrasonic wave transmission from the ultrasonic element 10 is directed toward the driver's seat 43 of the vehicle. The audible field 92 of the ultrasonic element 10 in this navigation device 1C is formed near the head of the driver seated in the driver's seat 43. In this configuration, only the driver inside the vehicle can receive voice guidance on the driving route from the navigation system 1C. Passengers seated in the front or rear seats will not hear the voice guidance on the driving route. Furthermore, passengers seated in the front or rear seats can only hear audio content such as music output from the car's speakers, and since the voice guidance on the driving route is not mixed in with this content, they can comfortably enjoy the content.

[0056] The indoor content output devices 1D shown in Figure 15 are provided in multiple locations within a single room 44. Examples of such rooms include the interior of an automobile. Each room 44 is equipped with a seat 45 corresponding to each indoor content output device 1D. Each indoor content output device 1D also incorporates an ultrasonic element 10 (or the ultrasonic element 10A of the second embodiment) used in the first embodiment, and the direction of ultrasonic wave transmission from the ultrasonic element 10 is directed toward the seat 45 corresponding to the indoor content output device 1D. As a result, users can only hear the audio output from the in-room content output device 1D corresponding to the seat 45 in which they are seated, and cannot hear the audio output from the in-room content output devices 1D corresponding to other seats. Therefore, when multiple users are seated in a closed space such as a car, each user can individually select the content they wish to view.

[0057] The control panel 1E shown in Figure 16 can be applied to, for example, a copier 46 installed in a store such as a convenience store. Users may print image data stored on mobile devices such as smartphones using a copier 46 installed in the store. In such cases, it is necessary to identify the copier 46 that will perform the printing. In the copier 46 shown in Figure 16, an information device 1A, as shown in the third embodiment, is built into the operation panel 1E, and information can be received by a receiver (for example, a mobile terminal device 47 such as a smartphone owned by the user) placed in a predetermined audible field 92. For example, information identifying the copier 46 is included in the baseband signal, and a modulated signal, which is a combination of the baseband signal and the carrier signal, is output from the ultrasonic element 10. As a result, the baseband signal can only be received in the audible field 92 formed at a predetermined distance E from the operation panel 1E, and by holding the mobile terminal device 47 over the audible field 92, the copier 46 can be identified by the mobile terminal device 47.

[0058] [Summary of this disclosure] An ultrasonic element 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 disposed inside the vibrating region, a piezoelectric body disposed on the substrate covering the first electrode, and a second electrode provided on the piezoelectric body, wherein the direction in which the substrate, the first electrode, the piezoelectric body, and the second electrode are stacked is defined as the stacking direction, and the thickness of the substrate along the stacking direction is 2.0 μm or more and 10.0 μm or less.

[0059] This makes it possible to realize an ultrasonic element with a resonant frequency of 40kHz to 500kHz, and to stably output ultrasound in the frequency band of 40kHz to 500kHz from the ultrasonic element.

[0060] In the ultrasonic element of this embodiment, the second electrode is arranged to span the vibration region and the non-vibration region. This allows for a reduction in the resonance frequency of the ultrasonic element compared to the case where the second electrode is provided only within the vibration region, and enables stable output of ultrasound in the frequency band of 40kHz to 500kHz from the ultrasonic element.

[0061] In the ultrasonic element of this embodiment, when viewed from the stacking direction, the width of the second electrode is greater than the width of the first electrode, and the width of the vibration region is greater than the width of the first electrode and less than the width of the second electrode. As a result, the width of the vibration region is greater than the width of the second electrode, and compared to the case where the first and second electrodes are contained within the vibration region, the resonance frequency of the ultrasonic element can be reduced, and ultrasonic waves in the frequency band of 40kHz to 500kHz can be stably output from the ultrasonic element.

[0062] In the ultrasonic element of this embodiment, a vibration suppression portion is provided on the surface of the substrate opposite to the piezoelectric element, in a region that overlaps with the non-vibration region when viewed from the stacking direction. This makes it possible to suppress vibrations in the non-vibration region outside the vibration region.

[0063] In the ultrasonic element of this embodiment, a support substrate may be disposed opposite to the surface of the piezoelectric body opposite to the substrate and the surface of the second electrode opposite to the substrate, and a vibration suppression portion may be disposed between the piezoelectric body, the second electrode and the support substrate in a region that overlaps with the non-vibration region when viewed from the stacking direction. Even with this configuration, it is possible to suppress vibrations in the non-vibration region outside the vibration region.

[0064] When using the vibration suppression portion that joins the substrate and the support substrate as described above, it is preferable that the vibration suppression portion is provided so as to cover the piezoelectric body from the edge of the second electrode. This makes it possible to suppress the problems of cracks and burnout occurring between the edge of the second electrode and the piezoelectric material.

[0065] In the ultrasonic element of this embodiment, the arithmetic surface roughness of the surface of the substrate opposite to the piezoelectric element is within the range of 0.4 ± 0.5 μm. This results in a uniform substrate thickness, enabling stable output of ultrasonic waves from 40kHz to 500kHz.

[0066] In the ultrasonic element of this embodiment, the material of the substrate is Si. By using a substrate made of Si, the processing accuracy of the substrate can be improved. Therefore, a substrate with an arithmetic surface roughness of 0.4 ± 0.5 μm and a thickness of 2.0 μm to 10.0 μm can be obtained.

[0067] An information device in a second aspect of the present disclosure comprises the ultrasonic element of the first aspect described above, a baseband signal generation unit that generates a baseband signal, a carrier signal generation unit that generates a carrier signal in the ultrasonic band, a signal modulation unit that combines the baseband signal and the carrier signal and converts them into a modulated signal, and an amplification unit that amplifies the modulated signal and outputs an acoustic signal, wherein the ultrasonic element radiates the input acoustic signal as acoustic vibrations. In the ultrasonic element described above, when an acoustic signal is input, it emits acoustic vibrations. These acoustic vibrations propagate to the near field and to the audible field, which is further away from the ultrasonic element than the near field. In the near field, since the ultrasound propagates linearly, the baseband signal does not appear. On the other hand, in the audible field, the nonlinear effect of the ultrasound separates the carrier signal from the baseband signal, allowing the information contained in the baseband signal to be received by other devices such as receivers.

[0068] In the information device of this embodiment, the frequency of the carrier signal is 40 kHz or more and 500 kHz or less. By using such a carrier signal, the linearity of acoustic vibrations is increased, allowing them to propagate only within a predetermined directional angle.

[0069] A superdirectional speaker according to a third aspect of the present disclosure comprises the ultrasonic element of the first aspect described above, a sound generation unit that generates an audio signal in the audible range, a high-frequency generation unit that generates an ultrasonic signal in the ultrasonic band, a signal modulation unit that combines the audio signal and the ultrasonic signal and converts them into a modulated signal, and an amplification unit that amplifies the modulated signal and outputs an acoustic signal, wherein the ultrasonic element radiates the input acoustic signal as acoustic vibrations. Similar to the second embodiment described above, when an acoustic signal is input to the ultrasonic element, it emits acoustic vibrations that propagate to both the near field and the audible field. This makes it possible to output audible sound that is only audible in the audible field.

[0070] In the superdirectional speaker of this embodiment, the frequency of the ultrasonic signal is 40 kHz or more and 500 kHz or less. By using such ultrasound, the linearity of acoustic vibrations is increased, allowing them to propagate only within a predetermined directional angle. [Explanation of Symbols]

[0071] 1...Superdirectional speaker, 1A...Information equipment, 10,10A...Ultrasonic element, 11...Substrate, 11A...Vibration region, 11B...Non-vibration region, 12...Piezoelectric element, 13...Vibration suppression unit, 14...Support substrate, 20,20A...Control device, 21...Drive circuit unit, 23,23A...Processor (Baseband signal generation unit, Carrier signal generation unit, Voice generation unit, High frequency generation unit), 91...Near field, 92...Audible field, 111...Base, 112...Surface layer, 113...First surface, 121...First electrode, 122...Piezoelectric body, 123...Second electrode, 123A...Edge of the second electrode, 1141...Support leg, 211...Signal modulation circuit, 212...Amplification circuit.

Claims

1. A substrate having a vibration region and a non-vibration region surrounding the vibration region, A first electrode is disposed inside the vibration region, A piezoelectric body is placed on the substrate, covering the first electrode, The piezoelectric element comprises a second electrode provided on the piezoelectric element, An ultrasonic element in which the substrate, the first electrode, the piezoelectric material, and the second electrode are stacked in a direction defined as the stacking direction, and the thickness of the substrate along the stacking direction is 2.0 μm or more and 10.0 μm or less.

2. The second electrode is arranged to span the vibration region and the non-vibration region. The ultrasonic element according to claim 1.

3. When viewed from the stacking direction, the width of the second electrode is greater than the width of the first electrode, and the width of the vibration region is greater than the width of the first electrode and less than the width of the second electrode. The ultrasonic element according to claim 2.

4. The substrate is provided with a vibration suppression portion located on the side opposite to the piezoelectric element, in a region that overlaps with the non-vibration region when viewed from the stacking direction, The ultrasonic element according to claim 1.

5. A support substrate is disposed opposite to the side of the piezoelectric body opposite to the substrate, and opposite to the side of the second electrode opposite to the substrate. The system comprises a vibration suppression portion positioned between the piezoelectric element and the second electrode and the support substrate in a region that overlaps with the non-vibration region when viewed from the stacking direction, The ultrasonic element according to claim 1.

6. The vibration suppression portion is provided covering the piezoelectric body from the edge of the second electrode, The ultrasonic element according to claim 5.

7. The arithmetic surface roughness of the surface of the substrate opposite to the piezoelectric element is within the range of 0.4 ± 0.5 μm. The ultrasonic element according to claim 1.

8. The material of the substrate is Si. The ultrasonic element according to claim 1.

9. The ultrasonic element according to claim 1, A baseband signal generation unit that generates a baseband signal, A carrier signal generation unit that generates a carrier signal in the ultrasonic band, A signal modulation unit that combines the baseband signal and the carrier signal to convert them into a modulated signal, The system includes an amplification unit that amplifies the modulated signal and outputs an acoustic signal, The ultrasonic element is an information device that emits the input acoustic signal as acoustic vibrations.

10. The frequency of the carrier signal is between 40 kHz and 500 kHz. The information device according to claim 9.

11. The ultrasonic element according to claim 1, A sound generation unit that generates audio signals in the audible range, A high-frequency generation unit that generates ultrasonic signals in the ultrasonic band, A signal modulation unit that combines the aforementioned audio signal and the aforementioned ultrasonic signal and converts them into a modulated signal, The system includes an amplification unit that amplifies the modulated signal and outputs an acoustic signal, The ultrasonic element is a highly directional speaker that radiates the input acoustic signal as acoustic vibrations.

12. The frequency of the ultrasonic signal is between 40 kHz and 500 kHz. The super-directional speaker according to claim 11.

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