Sonic speaker device

Abstract

To provide a sound wave speaker device capable of emitting broadband sound waves while miniaturizing the body.SOLUTION: A sound wave speaker device 10 includes a sound wave speaker 11, and a voltage adjustment unit 12 that amplifies a signal Vpp input from a sound source 100 and applies the amplified signal to the sound wave speaker 11. The sound wave speaker 11 includes a plurality of elements 20 which are formed by using MEMS technology and have different resonance frequencies. The element 20 includes a piezoelectric vibrator 30 and a vibrating region 41. The voltage adjustment unit 12 can individually adjust the amplification factor of the signal Vpp to be applied to the element 20. The voltage adjustment unit 20 individually adjusts the value of the signal Vpp to be applied so that the variation in sound pressure at each resonance frequency is smaller in a frequency range than when a common signal Vpp is applied to all the elements 20.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The disclosure herein relates to an acoustic speaker device. [Background technology]

[0002] Patent Document 1 discloses an acoustic speaker device that radiates sound waves in a predetermined frequency range, i.e., a wide band. The contents of the prior art document are incorporated by reference as explanations of technical elements in this specification. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2003-223174 A Summary of the Invention [Problem to be solved by the invention]

[0004] The size of an acoustic speaker device that radiates a wide band of sound waves is generally large. In the above-mentioned respects and in other respects not mentioned, further improvements in the acoustic speaker device are required.

[0005] One disclosed object is to provide a sonic speaker device that can radiate sound waves over a wide band while being compact in size. [Means for solving the problem]

[0006] The sonic speaker device disclosed herein includes a sonic speaker (11) that radiates sound waves, and a voltage adjustment unit (12) that amplifies a signal Vpp input from a sound source (100) and applies the amplified signal to the sonic speaker.

[0007] The sonic speaker is A plurality of piezoelectric films (31); a vibration section (40) having a first surface (40a), a second surface (40b) opposite to the first surface, and a plurality of vibration regions (41) each having a piezoelectric film individually disposed on the first surface and vibrating in response to expansion and contraction of the piezoelectric film; a support (50) having a main surface (50a) and a plurality of cavities (51) that open onto the main surface and are adjacent to a second surface of the vibration region, the cavities (51) defining the vibration region such that the resonant frequencies are different from one another by having opening areas in the main surface different from one another, and supporting the vibration section on the main surface; Sound waves in a frequency range are radiated from the piezoelectric film side, with the lower limit being the resonant frequency of the maximum vibration region, which is the vibration region defined by the cavity with the largest opening area among the multiple cavities, and the upper limit being the resonant frequency of the minimum vibration region, which is the vibration region defined by the cavity with the smallest opening area.

[0008] The voltage regulator is The amplification factor of the signal Vpp applied to the piezoelectric film can be adjusted individually. The value of the applied signal Vpp is individually adjusted so that the variation in sound pressure at each resonance frequency in the frequency range is smaller than when a common signal Vpp is applied to all the piezoelectric films. do. The acoustic speaker has a dummy cavity (51d) that opens to a main surface of the support, a dummy vibration area (41d) that is defined by the dummy cavity in the vibration part, and a dummy piezoelectric film (31d) that is arranged on the dummy vibration area and to which a signal Vpp is not applied, The resonant frequency of the dummy vibration area is set to a frequency between two adjacent resonant frequencies in the frequency range, or a frequency outside the frequency range and near the upper or lower limit of the resonant frequency. do.

[0009] According to the disclosed sonic speaker device, the sonic speaker is formed by MEMS technology. Specifically, a plurality of cavities are provided in a support, and a vibrating portion is provided on a main surface of the support. In the vibrating portion, a vibration region that vibrates with expansion and contraction of the piezoelectric film is defined by adjacent cavities. The opening areas of the cavities are different from one another so that the resonant frequencies of the vibration regions are different from one another. In this way, a single (common) vibrating portion is provided with a plurality of vibration regions with different resonant frequencies. This makes it possible to reduce the size of the sonic speaker, and ultimately the sonic speaker device.

[0010] Furthermore, the voltage adjustment unit can individually adjust the value of the signal Vpp applied to the piezoelectric film arranged individually with respect to the vibration region. In other words, the sound pressure at each resonance frequency can be individually adjusted. By the voltage adjustment unit individually adjusting the value of the signal Vpp, the variation in sound pressure in the above-mentioned frequency range is reduced, and the sonic speaker functions as a speaker that can radiate a wideband sound wave. As a result, it is possible to provide a sonic speaker device that can radiate a wideband sound wave while being compact in size.

[0011] The various aspects disclosed in this specification adopt different technical means to achieve their respective objectives. The claims and the parenthetical symbols described in this section are merely illustrative of the corresponding relationship with the embodiments described below, and are not intended to limit the technical scope. The objectives, features, and effects disclosed in this specification will become clearer with reference to the following detailed description and the accompanying drawings. [Brief description of the drawings]

[0012] [Figure 1] 1 is a diagram showing a schematic configuration of an ultrasonic speaker device according to a first embodiment. [Diagram 2] FIG. 1 is a plan view showing an acoustic speaker. [Diagram 3] FIG. 3 is a cross-sectional view taken along line III-III in FIG. [Figure 4] FIG. 4 is a block diagram showing a voltage adjustment unit. [Diagram 5] FIG. 4 is a diagram showing an example of the value and phase of a signal Vpp applied to each element. [Figure 6] FIG. 13 is a diagram showing the variation in sound pressure in a predetermined frequency range after voltage adjustment. [Figure 7] FIG. 11 is a diagram for explaining a sound pressure adjustment method. [Figure 8] FIG. 11 is a diagram for explaining a sound pressure adjustment method. [Figure 9] FIG. 11 is a diagram for explaining a sound pressure adjustment method. [Figure 10]13 is a diagram showing another example of the value and phase of the signal Vpp applied to each element. FIG. [Figure 11] FIG. 13 is a diagram showing the variation in sound pressure in a predetermined frequency range after voltage adjustment. [Figure 12] FIG. 13 is a reference diagram showing the result of applying a common voltage as the signal Vpp. [Figure 13] FIG. 13 is a diagram showing the relationship between the voltage applied to one element and the sound pressure at the resonant frequency when all elements are driven. [Figure 14] FIG. 1 is a diagram showing frequency characteristics of one element. [Figure 15] FIG. 11 is a plan view showing an acoustic speaker in an acoustic speaker device according to a second embodiment. [Figure 16] FIG. 16 is a cross-sectional view taken along line XVI-XVI in FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, several embodiments will be described with reference to the drawings. In addition, by assigning the same reference numerals to corresponding components in each embodiment, duplicated explanations may be omitted. When only a part of the configuration is described in each embodiment, the configuration of the other embodiment described above can be applied to the other parts of the configuration. In addition to the combination of configurations explicitly stated in the description of each embodiment, configurations of several embodiments can be partially combined together even if not explicitly stated, as long as there is no particular problem with the combination.

[0014] (First embodiment) First, a schematic configuration of the acoustic speaker device will be described with reference to FIG.

[0015] <Sound wave speaker device> As shown in FIG. 1, the sonic speaker device 10 includes a sonic speaker 11 and a voltage adjustment unit 12.

[0016] As described below, the sonic speaker 11 includes a plurality of elements 20 that emit sound waves and are formed using MEMS technology. The elements 20 have different resonance frequencies. The sonic speaker 11 can emit sound waves in a specific frequency range, that is, sound waves in a wide band, by utilizing a plurality of resonance points. MEMS is an abbreviation for Micro Electro Mechanical Systems. The sonic speaker 11 is used, for example, in the atmosphere.

[0017] The voltage adjustment unit 12 applies a drive voltage to the sonic speaker 11 based on an input signal from a sound source, i.e., an electrical signal of sound. The sound is sound in the ultrasonic range and / or sound in the audible range. The voltage adjustment unit 12 can individually adjust the voltage applied to the piezoelectric film 31, as described later.

[0018] <Sound wave speaker> Next, the sound wave speaker 11 will be described with reference to Fig. 2 to Fig. 4. Fig. 2 is a plan view of the sound wave speaker 11 as viewed from the piezoelectric vibrator 30 side in the Z direction. Fig. 3 is a cross-sectional view taken along line III-III in Fig. 2.

[0019] As shown in Fig. 2 and Fig. 3, the acoustic speaker 11 includes a plurality of elements 20, a plurality of piezoelectric vibrators 30, a vibration section 40, a support 50, and a base member 60. In the following, the stacking direction of the vibration section 40 and the piezoelectric film 31 (piezoelectric vibrator 30), that is, the thickness direction of the support 50 (hollow section 51), is referred to as the Z direction. The direction perpendicular to the Z direction and in which the plurality of vibration regions are arranged is referred to as the X direction. The direction perpendicular to both the Z direction and the X direction is referred to as the Y direction. Unless otherwise specified, the shape viewed in plan from the Z direction, that is, the shape along the XY plane defined by the X direction and the Y direction, is simply referred to as the planar shape. The planar view from the Z direction may also be simply referred to as the planar view.

[0020] The multiple elements 20 have different resonant frequencies. The sonic speaker 11 of this embodiment includes eleven elements 20. Each of the elements 20 includes a piezoelectric vibrator 30 and a vibration region 41. Since the elements 20 radiate sound waves, they may be referred to as sonic elements or radiating elements. When radiating sound waves with frequencies above the audible range, the elements 20 may be referred to as ultrasonic elements. Since the elements 20 are formed using MEMS technology, they may be referred to as MEMS elements.

[0021] The plurality of piezoelectric vibrators 30 are provided so as to be capable of individually vibrating the vibration regions 41 of the vibration section 40. Each of the piezoelectric vibrators 30 has a piezoelectric film 31, an upper electrode 32, and a lower electrode. The acoustic speaker 11 of this embodiment includes eleven piezoelectric vibrators 30. Each of the piezoelectric vibrators 30 has a piezoelectric film 31 and an upper electrode 32. In other words, the acoustic speaker 11 has eleven piezoelectric films 31 and eleven upper electrodes 32.

[0022] The piezoelectric film 31 is a thin film formed using, for example, an AlN-based material such as ScAlN, lead zirconate titanate (PZT), ZnO, or other piezoelectric material. The piezoelectric film 31 of this embodiment is formed by a sputtering method using ScAlN as the material. The thickness of the piezoelectric film 31 is, for example, about 1 μm.

[0023] The piezoelectric film 31 has a substantially perfect circular shape in plan view. The diameters, i.e. areas, of the piezoelectric films 31 in the eleven piezoelectric vibrators 30 are different from one another. The piezoelectric films 31 have an area according to the vibration region 41. The multiple piezoelectric films 31 are arranged in three rows in the Y direction. In the middle row, three piezoelectric films 31 are arranged side by side in the X direction. In the rows at both ends in the Y direction, four piezoelectric films 31 are arranged side by side in the X direction. In each row, the piezoelectric films 31 are arranged in order of area.

[0024] The upper electrode 32 is disposed on one surface of the piezoelectric film 31 in the Z direction. The upper electrode 32 is formed by sputtering, deposition, or the like using a commonly known electrode material. The layer structure of the upper electrode 32 may be a single layer or a multilayer. The upper electrode 32 of this embodiment is formed from a TiAl alloy. The upper electrode 32 has a shape that is substantially the same as that of the piezoelectric film 31 in a plan view. The upper electrode 32 of this embodiment has a substantially perfect circular shape in plan view. The upper electrode 32 may also serve as an upper electrode pad when applying a drive voltage. An upper electrode pad may be provided separately from the upper electrode 32.

[0025] The lower electrode is disposed on the other surface of the piezoelectric film 31 in the Z direction, i.e., on the back surface of the surface on which the upper electrode 32 is disposed. The lower electrode sandwiches the piezoelectric film 31 between the upper electrode 32 and the lower electrode. The lower electrode in this embodiment is a portion of the semiconductor film 400 that has been given electrical conductivity as described below, which overlaps with the piezoelectric film 31 in a plan view. At least a part of the other portion of the semiconductor film 400 functions as, for example, wiring.

[0026] A lower electrode pad 33 is formed on the semiconductor film 400 at a position different from the piezoelectric film 31. The lower electrode pad 33 is formed at a position that does not overlap with the vibration region 41 in a plan view. The lower electrode pad 33 of this embodiment is arranged in the X direction together with the three piezoelectric films 31 forming the middle row. The lower electrode pad 33 is formed using the same electrode material as the upper electrode 32. When a drive voltage is applied between the upper electrode 32 and the lower electrode pad 33, the piezoelectric film 31 to which the voltage is applied expands and contracts. The piezoelectric film 31 expands and contracts, for example, in the XY in-plane direction.

[0027] Of course, the semiconductor film 400 may not be made conductive, and a lower electrode may be provided separately from the semiconductor film 400. In this case, the lower electrode is formed using the same electrode material as the upper electrode 32.

[0028] The vibration section 40 has a first surface 40a and a second surface 40b which is the back surface of the first surface 40a in the Z direction. A piezoelectric film 31 and a lower electrode pad 33 are arranged on the first surface 40a of the vibration section 40. The vibration section 40 is composed of, for example, a film formed on a support 50. The film constituting the vibration section 40 may be a single layer or a multilayer. Such a vibration section 40 may be called a vibration film or a movable film. The vibration section 40 of this embodiment is composed of a semiconductor film 400 and an insulating film 401.

[0029] The semiconductor film 400 is a film formed using a semiconductor material such as silicon (Si). The semiconductor film 400 of this embodiment is doped with impurities to provide sufficient conductivity to function as a lower electrode and wiring. Specifically, the silicon film is doped with p-type impurities to provide conductivity. The semiconductor film 400 has a thickness that allows it to vibrate in the Z direction. For example, the thickness is about 20 to 25 μm.

[0030] The insulating film 401 is an electrically insulating film such as an oxide film or a nitride film. The insulating film 401 electrically separates the semiconductor film 400 from the semiconductor substrate 500 constituting the support 50. The insulating film 401 in this embodiment is a silicon oxide film. The insulating film 401 has a thickness that allows vibration in the Z direction in a laminated structure with the semiconductor film 400.

[0031] The vibrating section 40 has a plurality of vibrating regions 41. The vibrating regions 41 are regions of the vibrating section 40 that vibrate in the Z direction in response to expansion and contraction of the piezoelectric film 31. The vibrating regions 41 are defined by a cavity 51 in the support 50. In the vibrating region 41, the cavity 51 is adjacent to the second surface 40b. In the portion other than the vibrating region 41, the semiconductor substrate 500 is adjacent to the second surface 40b. In this way, the cavity 51 exists directly below the vibrating region 41, and the vibrating region 41 can vibrate in the Z direction.

[0032] In FIG. 3, the region surrounded by the dashed line is the vibration region 41. The vibration region 41 of this embodiment has a two-layer structure of the semiconductor film 400 and the insulating film 401 described above. The vibration regions 41 are provided in the same number as the piezoelectric films 31. The vibration section 40 has eleven vibration regions 41 with different areas. The area is the area in a plan view. The piezoelectric films 31 are individually arranged on the first surface 40a of the vibration region 41. The vibration region 41 has a substantially perfect circular shape in a plan view. In a plan view, the center of the vibration region 41 and the center of the piezoelectric film 31 arranged on the vibration region 41 are substantially aligned. The multiple vibration regions 41 have different radii and diameters of the circles. Since the film configuration is the same, the thicknesses of the vibration regions 41 are substantially equal to each other.

[0033] The larger the radius of the vibration region 41 (the element 20), that is, the larger the area, the lower the resonance frequency of the vibration region 41. In this embodiment, the radii of the vibration region 41 are different from each other, so that the resonance frequencies of the elements 20 are set in the range of 40 kHz to 140 kHz at intervals of 10 kHz. Specifically, the resonance frequencies of the three elements 20 in the center row in the Y direction are set to 40 kHz, 50 kHz, and 60 kHz. The resonance frequencies of the four elements 20 arranged at one end in the Y direction are set to 140 kHz, 110 kHz, 100 kHz, and 70 kHz. The resonance frequencies of the four elements 20 arranged at the other end in the Y direction are set to 130 kHz, 120 kHz, 90 kHz, and 80 kHz. Note that each resonance frequency and the intervals between the resonance frequencies are not limited to a mode in which they completely match the above-mentioned numerical values, and an error of the order of manufacturing variation is acceptable.

[0034] As described above, the vibration region 41, together with the piezoelectric vibrators 30, constitutes the element 20 that radiates sound waves. Since the vibration regions 41 (elements 20) have different resonant frequencies, the sound wave speaker 11 can radiate sound waves in a predetermined frequency range by applying a drive voltage to the multiple piezoelectric vibrators 30. For example, by applying a drive voltage to all of the piezoelectric vibrators 30 of the eleven types of elements 20, sound waves having the above-mentioned frequency range of 40 to 140 kHz can be radiated. The sound wave speaker 11 radiates (emits) sound waves from the piezoelectric vibrators 30 side.

[0035] The support 50 supports the piezoelectric vibrator 30 and the vibration section 40. The support 50 has a main surface 50a and a back surface 50b that is the surface opposite to the main surface 50a in the Z direction. The vibration section 40 is disposed on the main surface 50a of the support 50. Specifically, an insulating film 401 is disposed on the main surface 50a of the support 50, and a semiconductor film 400 is laminated on the insulating film 401. The planar shape of the support 50 is not particularly limited. The support 50 is formed using a material that can be processed by MEMS technology, such as a semiconductor or glass.

[0036] The support 50 of this embodiment is configured to have a semiconductor substrate 500. One surface of the semiconductor substrate 500 forms a main surface 50a, and the opposite surface forms a back surface 50b. Such a support 50 may be called a support substrate. The thickness of the semiconductor substrate 500, that is, the support 50, is, for example, about 300 μm. The semiconductor substrate 500 of this embodiment is a silicon substrate. The semiconductor substrate 500 is provided as a so-called SOI substrate together with the semiconductor film 400 and the insulating film 401 described above. In other words, the acoustic speaker 11 is provided as one semiconductor chip. SOI is an abbreviation for Silicon on Insulator. The support 50 has a substantially rectangular shape in plan view.

[0037] The support 50 has a plurality of cavities 51. The support 50 has a configuration in which a plurality of cavities 51 are provided in a flat plate. Each of the plurality of cavities 51 has a predetermined thickness (depth) in the Z direction, and opens at least to the main surface 50a. The cavities 51 are formed in the support 50 by etching. The plurality of cavities 51 have different opening areas in the main surface 50a. The opening area in the main surface 50a may be simply referred to as the opening area hereinafter. The opening portion of the main surface 50a in the cavity 51 is blocked by the vibration part 40.

[0038] In the cavity 51, an opening portion in the main surface 50a defines the vibration region 41. The opening portion in the main surface 50a of the cavity 51 defines the overlapping portion (matching portion) of the vibration section 40 in a plan view as the vibration region 41. The same number of cavities 51 as the vibration regions 41 are provided. The vibration region 41 defined by the cavity 51 with the largest opening area corresponds to the maximum vibration region, and the resonant frequency of the element 20 including this vibration region 41 is 40 kHz, which is the lower limit of the frequency range. The vibration region 41 defined by the cavity 51 with the smallest opening area corresponds to the minimum vibration region, and the resonant frequency of the element 20 including this vibration region 41 is 140 kHz, which is the upper limit of the frequency range.

[0039] The support 50 (semiconductor substrate 500) of this embodiment has eleven cavities 51 with different opening areas. The vibration region 41 is adjacent to each of the cavities 51. In the cavities 51, the opening portion in the main surface 50a has a substantially perfect circular shape in plan view. Each of the cavities 51 extends in the Z direction and opens to the back surface 50b of the support 50. The cavities 51 have a substantially perfect circular columnar shape in plan view and have a predetermined thickness while maintaining a planar shape. The thicknesses of the multiple cavities 51 are substantially equal to each other. The cavities 51 are formed by dry etching such as reactive ion etching (RIE).

[0040] The cavity 51 has a thickness t1 as shown in FIG. 2. In this embodiment, the thickness t1 is equal to the thickness of the semiconductor substrate 500 forming the support 50. The thickness t1 is set to a predetermined value. The thickness t1 is set to be less than λ×1 / 4. The wavelength λ is a value obtained by dividing the sound speed c by the upper limit of the frequency range of the sound wave emitted by the sound wave speaker 11. The upper limit is the resonance frequency of the vibration region 41 defined by the cavity 51 with the smallest opening area. For example, when emitting sound waves in the frequency range of 40 to 140 kHz as described above, the value obtained by dividing the sound speed c by 140 kHz is the wavelength λ.

[0041] The base member 60 is a member to which a structure including the piezoelectric vibrator 30, the vibration portion 40, and the support 50 is fixed. The base member 60 is, for example, a package or case that protects the above structure. The base member 60 in this embodiment is a ceramic package. The support 50 (above structure) is fixed to one surface of the base member 60 via a fixing member 70. The fixing member 70 may be any member capable of fixing the support 50 to the base member 60. The fixing member 70 is provided so as to avoid the hollow portion 51.

[0042] The fixing member 70 in this embodiment is a bonding material. As shown in Fig. 2 and Fig. 3, the fixing member 70 is arranged, for example, at the four corners of the back surface 50b of the support body 50. In a fixed state, the back surface 50b of the support body 50 floats with respect to the base member 60. The support body 50 is fixed to the base member 60 so that gas can flow between the multiple cavities 51. The cavities 51 communicate with each other through the gap between the back surface 50b and the base member 60. By arranging the fixing member 70 at the four corners, the cavities 51 can also flow with the periphery of the support body 50 in a plan view.

[0043] The arrangement of the fixing members 70 is not limited to the four corners described above. Any arrangement that can stably fix the support 50 on the base member 60 may be used. For example, the fixing members 70 may be arranged along two opposing sides of the support 50 having a substantially planar shape.

[0044] <Voltage adjustment section> Next, the voltage adjustment unit 12 will be described with reference to Fig. 4. Fig. 4 is a block diagram showing the voltage adjustment unit 12. Fig. 4 also shows the sonic speaker 11 and the sound source 100.

[0045] The sound source 100 shown in FIG. 4 outputs sound as an electrical signal. The sound source 100 outputs, for example, an audio signal and / or an acoustic signal. The sound source 100 provides, for example, music to the sonic speaker device 10. In this embodiment, the sound source 100 provides music including sounds in the ultrasonic range. The sound source 100 is built into, for example, a mobile terminal, a PC, a media player, etc. The sound of the music is input from the sound source 100 to the voltage adjustment unit 12 of the sonic speaker device 10 as an electrical signal Vpp.

[0046] The voltage adjustment unit 12 adjusts the signal Vpp input from the sound source 100 and applies it to the element 20 (piezoelectric vibrator 30) as a drive voltage. The voltage adjustment unit 12 includes a plurality of adjustment circuits 80. The adjustment circuits 80 are provided individually for the elements 20 of the sound speaker 11. That is, the voltage adjustment unit 12 includes eleven adjustment circuits 80 corresponding to the eleven elements 20. The same signal Vpp (common signal) is input to the plurality of adjustment circuits 80. Vpp is an abbreviation for Voltage peak to peak. The signal Vpp is an AC signal, and when it is input from the sound source 100, that is, before amplification, the peak-to-peak voltage is, for example, 0.5 V.

[0047] Each of the adjustment circuits 80 has an amplifier 81 and a phase shifter 82. The amplifier 81 amplifies and outputs the signal Vpp. The amplifier 81 is, for example, an operational amplifier. The voltage adjustment unit 12 can individually adjust the amplification factor of the amplifier 81. The voltage adjustment unit 12 adjusts the value of the signal Vpp applied to the element 20 individually by adjusting the amplification factor of the amplifier 81. The value of Vpp is a peak-to-peak voltage value. Adjusting the value of the signal Vpp is equivalent to adjusting the maximum voltage, which is the peak value on the positive phase side of the amplified signal Vpp. The voltage adjustment unit 12 individually adjusts the amplification factor of the signal Vpp applied to the element 20 so that the variation in sound pressure at each resonant frequency in the above-mentioned frequency range is reduced. The amplifier 81 adjusts the value of the signal Vpp in accordance with the characteristics of the corresponding element 20.

[0048] The phase shifter 82 adjusts the phase of the signal Vpp. The phase shifter 82 of this embodiment is provided between the amplifier 81 and the sound source 100. The phase shifter 82 is configured to be able to switch the phase shift angle for the signal Vpp between 0° and 180°. When the shift angle is 0°, the phase shifter 82 outputs the signal Vpp without shifting its phase. When the shift angle is 180°, the phase shifter 82 shifts the phase of the signal Vpp by 180° (π), that is, inverts the phase and outputs it. A signal with a shift angle of 180° has an opposite phase to a signal with a shift angle of 0°.

[0049] The voltage adjustment unit 12 can individually adjust the shift angle of the phase shifter 82. The voltage adjustment unit 12 individually adjusts the phase of the signal Vpp applied to the elements 20 so that the drop, so-called dip, between adjacent resonant frequencies in the above-mentioned frequency range is reduced. The voltage adjustment unit 12 adjusts the phase of the signal Vpp applied to some of the elements 20 so that it is opposite to the phase of the signal Vpp applied to the remaining elements 20.

[0050] A common signal Vpp is input to each element 20 of the sonic speaker 11 from the sound source 100 almost simultaneously via the voltage adjustment unit 12. The elements 20 function as bandpass filters that react only to a frequency band near the resonant frequency. Each element 20 does not radiate sound waves even if a frequency different from the resonant frequency of the element 20 is input, but radiates sound waves due to resonance when a frequency band near the resonant frequency is input.

[0051] 4, the phase shifter 82 is provided between the amplifier 81 and the sound source 100, but the present invention is not limited to this. The phase shifter 82 may be provided between the amplifier 81 and the element 20.

[0052] <How to adjust the sound pressure> To provide a sonic speaker device that emits sound waves over a wide frequency range, the variation in sound pressure must be small over a wide frequency range. In other words, the frequency characteristics of sound pressure must be approximately flat. However, in a configuration in which multiple elements with different resonant frequencies are fabricated on a single chip using MEMS technology, when a common voltage is applied to each element, the vibration mode and amplitude differ depending on the size of the element (such as the area of ​​the vibration region), resulting in variation in sound pressure at each resonant frequency. In addition, the sound pressure drops at frequencies between the resonant frequencies.

[0053] In contrast, in this embodiment, the voltage adjustment unit 12 adjusts the value and phase of the signal Vpp applied to each element 20 so that the variation in sound pressure is reduced in the above-mentioned frequency range. In other words, the voltage adjustment unit 12 executes a process of averaging the resonant frequency and the dip therebetween. FIG. 5 shows an example of the adjustment of the signal Vpp by the voltage adjustment unit 12. FIG. 6 shows the frequency characteristics when each element 20 is driven under the conditions of FIG. 5.

[0054] In-phase in Fig. 5 indicates that the shift angle of the phase shifter 82 is 0°, that is, the input signal from the sound source 100 is output without phase shift. Anti-phase indicates that the shift angle of the phase shifter 82 is 180°, that is, the phase of the input signal is inverted and output. Fig. 6 shows the measured value of the sound waves emitted from the sonic speaker 11 collected by a microphone. In this measurement, the distance between the sonic speaker 11 and the microphone was set to 50 cm. Also, the upper limit of the signal Vpp was set to 32 V, and the amplification factor of the signal Vpp (voltage) applied to each element 20 was adjusted.

[0055] As shown in FIG. 5, the signal Vpp value applied to the element 20 with a resonant frequency of 40 kHz was 32.0 V and the phase was in-phase. The signal Vpp value applied to the element 20 with a resonant frequency of 50 kHz was 24.0 V and the phase was in-phase. The signal Vpp value applied to the element 20 with a resonant frequency of 60 kHz was 22.9 V and the phase was in-phase. The signal Vpp value applied to the element 20 with a resonant frequency of 70 kHz was 14.7 V and the phase was reversed. The signal Vpp value applied to the element 20 with a resonant frequency of 80 kHz was 11.0 V and the phase was in-phase. The signal Vpp value applied to the element 20 with a resonant frequency of 90 kHz was 25.1 V and the phase was reversed. The signal Vpp value applied to the element 20 with a resonant frequency of 100 kHz was 14.5 V and the phase was in-phase. The signal Vpp value applied to the element 20 with a resonant frequency of 110 kHz was 21.6 V and the phase was reversed. The signal Vpp value applied to element 20 with a resonant frequency of 120 kHz was 32.0 V and the phase was in-phase. The signal Vpp value applied to element 20 with a resonant frequency of 130 kHz was 4.0 V and the phase was in-phase. The signal Vpp value applied to element 20 with a resonant frequency of 140 kHz was 6.2 V and the phase was out-of-phase.

[0056] As a result, as shown in Fig. 6, in the frequency range of 36 kHz to 133 kHz, the sound pressure was 76.2 ± 12.6 dB. In other words, the sound pressure variation was ± 12.6 dB. When a common voltage, for example, a common voltage of 32.0 V in phase was applied to all elements 20, the maximum sound pressure was the same as the result shown in Fig. 6 (not shown), but the variation was about ± 25 dB.

[0057] The higher the applied voltage (signal Vpp), the higher the sound pressure at the resonant frequency, and the lower the voltage, the lower the sound pressure. As shown in FIG. 5, by individually adjusting the value of the signal Vpp applied to the element 20, the variation in sound pressure at the resonant frequency can be suppressed. Also, by adjusting the phase, the dip can be reduced and the sound pressure at frequencies between the resonant frequencies can be kept within the above-mentioned variation range. A method for adjusting the phase will be described below.

[0058] Figures 7 to 9 show the frequency characteristics of sound waves. Like Figure 6, Figures 7 to 9 show the measured values ​​of sound waves emitted from the sound wave speaker 11 collected by a microphone. In this measurement, the distance between the sound wave speaker 11 and the microphone was set to 10 cm. White noise was also input, generated with Vpp=1.1 V and a maximum frequency of 500 kHz.

[0059] FIG. 7 shows an example in which a signal Vpp is applied to an element 20 having a resonant frequency of 70 kHz and / or an element 20 having a resonant frequency of 80 kHz among a plurality of elements 20. The solid line shows the frequency characteristics when the phases of the signals Vpp applied to the two elements 20 are opposite to each other. The dashed line shows the frequency characteristics when the phases of the signals Vpp applied to the two elements 20 are the same. The dashed line shows the frequency characteristics when the signal Vpp is applied only to the 70 kHz element 20. Similarly, the dashed line shows the frequency characteristics when the signal Vpp is applied only to the 80 kHz element 20.

[0060] As shown by the dashed line in Figure 7, when the phases are in phase, the dip in the frequency between the resonant frequency of 70 kHz and the resonant frequency of 80 kHz is large. In contrast, as shown by the solid line, when the phases are out of phase (opposite to each other), the dip between the resonant frequencies becomes smaller. In this way, by adjusting the phase, it is possible to suppress the interference between two adjacent resonant frequencies and reduce the dip between the resonant frequencies.

[0061] FIG. 8 shows an example in which a signal Vpp is applied to an element 20 with a resonant frequency of 80 kHz and / or an element 20 with a resonant frequency of 90 kHz. As in FIG. 5, the solid line shows the frequency characteristics when the phases of the signals Vpp applied to the two elements 20 are opposite to each other. The dashed line shows the frequency characteristics when the phases of the signals Vpp applied to the two elements 20 are the same. The dashed line shows the frequency characteristics when the signal Vpp is applied only to the 80 kHz element 20. The dashed line shows the frequency characteristics when the signal Vpp is applied only to the 90 kHz element 20.

[0062] As shown by the dashed and solid lines in FIG. 8, the frequency dip between the resonant frequency of 80 kHz and the resonant frequency of 90 kHz hardly changes when the phase is in-phase and when the phase is out-of-phase. In this way, the dip may hardly change due to the adjustment of the phase. In at least one of the resonant frequencies adjacent to the dip, the larger the Q value of the element 20, the sharper the peak of the sound pressure at the resonant frequency becomes, and the larger the dip becomes. Therefore, it is advisable to adjust the configuration of the side opposite to the side emitting the sound wave so that the Q value of the element 20 becomes smaller. For example, the Q value can be reduced by adjusting the configuration and fixing method of the support 50 and the base member 60.

[0063] Furthermore, when the phase was reversed, a dip was observed near 72 kHz, as indicated by the solid arrow. This dip became more evident when the value of the signal Vpp applied to one of the two elements 20 was reduced to lower the sound pressure. Thus, adjusting the phase of two adjacent resonant frequencies may affect the dip between the adjacent resonant frequencies.

[0064] 9 shows an example in which a signal Vpp is applied to an element 20 with a resonant frequency of 70 kHz, an element 20 with a resonant frequency of 80 kHz, and an element 20 with a resonant frequency of 90 kHz. The solid line shows the frequency characteristics when the phase of the signal Vpp applied to the 90 kHz element 20 is opposite to the phase of the signal Vpp applied to the other two elements 20. The dashed line shows the frequency characteristics when the phases of the signal Vpp applied to the three elements 20 are the same.

[0065] 9, when the phase of the signal Vpp applied to the 90 kHz element 20 is reversed, the dip near 72 kHz can be made smaller as shown by the solid arrow, compared to when the phase of the signal Vpp applied to all elements 20 is the same. In this way, the dip can be made smaller by adjusting the phase of the signal Vpp applied to three consecutive elements 20. In other words, for a plurality of consecutive resonant frequencies that sandwich a dip, it is possible to make the dip smaller by adjusting the phase of the signal Vpp applied to the corresponding elements 20.

[0066] The adjustment of the dip is not limited to the frequencies shown in Figs. 7 to 9. The dips between other resonant frequencies can be adjusted in the same manner. The value and phase of the signal Vpp applied to each element 20 shown in Fig. 5 are the value and phase after the above-mentioned adjustment is performed. By such adjustment, the variation in sound pressure can be reduced to ±12.6 dB in the frequency range as shown in Fig. 6.

[0067] <Summary of the First Embodiment> In this embodiment, the sonic speaker 11 is formed by MEMS technology. Specifically, a plurality of cavities 51 are provided in a single support 50 (semiconductor substrate 500), and a vibrating section 40 is provided on a main surface 50a of the support 50. In the vibrating section 40, a vibration region 41 that vibrates with the expansion and contraction of the piezoelectric film 31 is defined by adjacent cavities 51. The opening areas of the cavities 51 are different from each other so that the resonant frequencies of the vibration regions 41 are different from each other. In this way, a plurality of vibration regions 41 with different resonant frequencies are provided in a single (common) vibrating section 40. Therefore, the size of the sonic speaker 11, and therefore the sonic speaker device 10, can be reduced.

[0068] Furthermore, the voltage adjustment unit 12 can individually adjust the value of the signal Vpp applied to the piezoelectric film 31 (piezoelectric vibrator 30) that is individually arranged with respect to the vibration region 41. In other words, the sound pressure at each resonance frequency can be individually adjusted. By the voltage adjustment unit 12 individually adjusting the value of the signal Vpp, the variation in sound pressure in the above-mentioned frequency range is reduced, and the sound wave speaker 11 functions as a speaker that can emit sound waves in a wide band. The sound wave speaker 11 can emit sound waves having a predetermined frequency range, for example, from the piezoelectric film 31 side. As described above, the sound wave speaker device 10 of this embodiment can emit sound waves in a wide band while being compact in size.

[0069] In this embodiment, the signal Vpp is applied to all the piezoelectric vibrators 30 of the eleven elements 20 at the same timing (energization period), and the sonic speaker 11 emits sound waves having a frequency range of 40 kHz to 140 kHz. In this way, if the emitted sound waves exceed the audible frequency and include at least a frequency range with an upper limit of 200 kHz, it can be used as a sonic speaker device for obtaining a hypersonic effect. The upper limit of the audible frequency is generally 20 kHz.

[0070] In this embodiment, the voltage adjustment unit 12 can adjust not only the value of the signal Vpp but also the phase individually. The voltage adjustment unit 12 adjusts the phase of the signal Vpp applied to some of the multiple elements 20 so that it is opposite to the phase of the signal Vpp applied to the remaining elements 20. In this way, the voltage adjustment unit 12 adjusts the phase of the signal Vpp individually, thereby reducing the dip between the resonance frequencies in a predetermined frequency range. Therefore, the variation in sound pressure in the frequency range can be further reduced.

[0071] 5, the voltage adjusting unit 12 adjusts the phase so that the phase of the signal Vpp applied to the element 20 (piezoelectric vibrator 30) having a resonant frequency of 70 kHz is opposite to the phase of the signal Vpp applied to the element 20 having a resonant frequency of 80 kHz. This makes it possible to reduce the dip (drop in sound pressure) at frequencies between 70 kHz and 80 kHz. In this example, the vibration region 41 in the element 20 having a resonant frequency of 70 kHz corresponds to the first vibration region, and the piezoelectric film 31 corresponds to the first piezoelectric film. The vibration region 41 in the element 20 having a resonant frequency of 80 kHz corresponds to the second vibration region, and the piezoelectric film 31 corresponds to the second piezoelectric film.

[0072] 5, the voltage adjusting unit 12 adjusts the phase so that, for example, the phase of the signal Vpp applied to some of the elements 20 of three consecutive elements 20 having resonant frequencies of 70 kHz, 80 kHz, and 90 kHz is opposite to the phase of the signal Vpp applied to the remaining elements 20. Specifically, the phase is adjusted so that the phase of the signal Vpp applied to each of the elements 20 having resonant frequencies of 70 kHz and 90 kHz is opposite to the phase of the signal Vpp applied to the element 20 having a resonant frequency of 80 kHz. This can further reduce the dip in the frequency between 70 kHz and 80 kHz.

[0073] In this embodiment, the plurality of cavities 51 are also open to the back surface 50b of the support 50. The support 50 is fixed to the base member 60 so that gas can flow between the plurality of cavities 51. The plurality of cavities 51 communicate with each other, forming a large space on the side opposite to the side from which the sound waves are emitted. Therefore, the gas resistance to vibration is smaller than in a configuration in which the cavities 51 do not communicate with each other, and the sound pressure can be increased. Particularly in this embodiment, the cavities 51 communicate with the space around the support 50, making it easier to increase the sound pressure.

[0074] In this embodiment, the cavity 51 has a predetermined thickness while maintaining its planar shape. Therefore, it is easy to define the shape and therefore the area of ​​the vibration region 41 by etching. In other words, it is easy to set a desired resonance frequency. Particularly in this embodiment, the cavity 51 has a cylindrical shape that is approximately a perfect circle in plan. As a result, the vibration region 41 also has an approximately perfect circle in plan. Because of the perfect circle shape, unnecessary vibrations and frequency variations can be suppressed, and the amplitude of a specific frequency can be increased. In other words, the sound pressure can be increased.

[0075] <Modification> The adjustment of the value and phase of the signal Vpp by the voltage adjustment unit 12 is not limited to the above example. FIG. 10 is a diagram showing another example of the value and phase of the signal Vpp applied to each element 20. FIG. 11 shows the frequency characteristics when each element 20 is driven under the conditions of FIG. 10. FIG. 12 is a diagram showing the frequency characteristics of a reference example. In the reference example, the conditions of the signal Vpp applied to each element 20, that is, the value and phase of the signal Vpp, are common to each other. FIG. 11 and FIG. 12 are measurements of sound waves emitted from the sonic speaker 11 collected by a microphone. In this measurement, the distance between the sonic speaker 11 and the microphone is 10 cm. In addition, the value of the signal Vpp before amplification is set to 0.5 V, and the upper limit of the signal Vpp after amplification is set to 5 V. In the reference example, the same configuration as FIG. 11 is used except that the conditions of the signal Vpp applied to each element 20 are different. In the reference example, the applied signal Vpp=5 V.

[0076] As shown in FIG. 10, the signal Vpp value applied to the element 20 with a resonant frequency of 40 kHz was 2.4 V and the phase was in-phase. The signal Vpp value applied to the element 20 with a resonant frequency of 50 kHz was 3.8 V and the phase was in-phase. The signal Vpp value applied to the element 20 with a resonant frequency of 60 kHz was 2.8 V and the phase was reversed. The signal Vpp value applied to the element 20 with a resonant frequency of 70 kHz was 2.1 V and the phase was in-phase. The signal Vpp value applied to the element 20 with a resonant frequency of 80 kHz was 1.4 V and the phase was reversed. The signal Vpp value applied to the element 20 with a resonant frequency of 90 kHz was 2.2 V and the phase was in-phase. The signal Vpp value applied to the element 20 with a resonant frequency of 100 kHz was 4.7 V and the phase was in-phase. The signal Vpp value applied to the element 20 with a resonant frequency of 110 kHz was 5.0 V and the phase was in-phase. The signal Vpp value applied to element 20 with a resonant frequency of 120 kHz was 1.9 V and the phase was reversed. The signal Vpp value applied to element 20 with a resonant frequency of 130 kHz was 2.0 V and the phase was in-phase. The signal Vpp value applied to element 20 with a resonant frequency of 140 kHz was 2.1 V and the phase was reversed.

[0077] As a result, as shown in Fig. 11, in the frequency range of 34 kHz to 146 kHz, the sound pressure was 75.0 ± 12.0 dB. In other words, the variation in sound pressure was ± 12.0 dB. On the other hand, as shown in Fig. 12, in the reference example in which the applied signal Vpp was common, in the frequency range of 32 kHz to 160 kHz, the sound pressure was 84.6 ± 18.6 dB. In other words, the variation in sound pressure was ± 18.6 dB.

[0078] 11 and 12, it is clear that individually adjusting the value of the signal Vpp applied to the element 20 can suppress the variation in sound pressure of the resonance frequency in the frequency range of 40 kHz to 140 kHz, compared to using a common value for the signal Vpp. It is also clear that individually adjusting the phase of the signal Vpp can reduce the dip in the frequency between the resonance frequencies, compared to using a common phase for the signal Vpp (all in phase).

[0079] In this embodiment, since the value of the signal Vpp applied to each element 20 is adjusted individually, the sound pressure is lower than that of a configuration in which the upper limit (5V) of the amplified signal Vpp is applied as a common signal. However, what is important in a sonic speaker device that radiates a wideband sound wave is that the sound pressure variation is small in a wide frequency range. Therefore, the sonic speaker device 10 of this embodiment is suitable as a speaker device that radiates a wideband sound wave. In addition, the sound pressure can be adjusted by the amplification factor of the applied signal Vpp. For example, if the value of the applied signal Vpp is doubled from the value in FIG. 10, the sound pressure can be increased by 6 dB while keeping the variation the same. In other words, by increasing or decreasing the voltage applied to each element 20 at an equal ratio, the sound pressure can be increased or decreased without changing the variation.

[0080] Although an example has been shown in which the voltage adjustment unit 12 individually adjusts both the value (amplification factor) and phase of the signal Vpp applied to each element 20, the present invention is not limited to this. The voltage adjustment unit 12 only needs to individually adjust at least the value (amplification factor) of the signal Vpp applied to each element 20. This reduces the variation in sound pressure at the resonant frequency within the frequency range, and the sound speaker 11 functions as a speaker capable of emitting sound waves in a wide band.

[0081] The number of the vibration regions 41 and the cavities 51 is not limited to the above example. The number of the vibration regions 41 and the cavities 51 may be more than one. For example, a configuration having two vibration regions 41 and two cavities 51 may be used. The two cavities 51 have different opening areas on the main surface 50a. This causes the resonance frequencies of the two vibration regions 41 to differ from each other. The vibration region 41 defined by the cavities 51 with a large opening area corresponds to the maximum vibration region, and the resonance frequency of this vibration region 41 is the lower limit of the frequency range. The vibration region 41 defined by the cavities 51 with a small opening area corresponds to the minimum vibration region, and the resonance frequency of this vibration region 41 is the upper limit of the frequency range. The same applies to the number of piezoelectric vibrators 30 including the piezoelectric film 31.

[0082] Examples of driving the elements 20 are not limited to the above examples. Each of the adjustment circuits 80 may be provided with a switch that turns on and off the application of the signal Vpp to the corresponding element 20 (piezoelectric vibrator 30). This makes it possible to apply the signal Vpp only to the piezoelectric vibrators 30 of the elements 20 that are part of the elements 20 provided in the sound speaker 11. In other words, the frequency range of the radiated sound waves can be changed. The frequency range may be changed over time by switching the element 20 to which the signal Vpp is applied. The signal Vpp may be applied temporarily to only one element 20.

[0083] Although the resonant frequencies of all the elements 20 are set to frequencies exceeding the audible frequency, this is not limiting. The resonant frequencies of some of the elements 20 may be in the audible frequency range. For example, the opening areas of the cavities 51 may be set so as to emit sound waves in a frequency range exceeding the audible frequency and with an upper limit of 200 kHz, and sound waves in a frequency range within the audible frequency range. In this case, a hypersonic effect can be expected from one sonic speaker device 10. The resonant frequencies of all the elements 20 may be set within the audible frequency range. By forming the cavities 51 into a common support 50, the size of the sonic speaker 11, and therefore the size of the sonic speaker device 10, can be reduced.

[0084] In this embodiment, an example in which the vibration section 40 includes the insulating film 401 has been shown, but the present invention is not limited to this. The support 50 may include an insulating film and a semiconductor substrate 500. In this case, the insulating film is also etched with the semiconductor film as the bottom, and a cavity is formed across the semiconductor substrate and the insulating film. The vibration section is made of a semiconductor film, and the cavity is adjacent to the back surface of the semiconductor film.

[0085] Second embodiment This embodiment is a modification based on the previous embodiment, and the description of the previous embodiment can be used. In the previous embodiment, the signal Vpp can be applied individually from the voltage adjustment unit 12 to all the elements 20. Instead of this, a dummy element to which the signal Vpp is not applied may be further provided.

[0086] Fig. 13 shows the relationship between the voltage applied to the element 20 at one resonance frequency and the sound pressure at the resonance frequency when all the elements 20 are driven by applying a signal Vpp to them as in the previous embodiment. Fig. 13 shows the measured value of the sound wave emitted from the sonic speaker 11 collected by a microphone. In this measurement, the distance between the sonic speaker 11 and the microphone was 10 cm. Fig. 13 shows an example of a resonance frequency of 90 kHz.

[0087] Normally, the sound pressure decreases as the applied voltage is lowered. However, as shown in Fig. 13, it has become clear that the sound pressure is lowest when the applied voltage is around 1 V, and the sound pressure rises when the applied voltage is 0 V. This is thought to be because resonance occurs due to the vibration of an element 20 with a close resonant frequency, for example, the vibration of an element 20 with a resonant frequency of 80 kHz or 100 kHz, even if the signal Vpp is not applied.

[0088] FIG. 14 shows the frequency characteristics of sound waves emitted by one element 20. FIG. 14 shows an element 20 with a resonant frequency of 80 kHz as an example. As shown in FIG. 14, the sound pressure is maximum at the resonant frequency, and the sound pressure decreases as it moves away from the resonant frequency. For example, a sound pressure 30 dB lower than the sound pressure of the resonant frequency is set as a reference line (a dashed line in the figure), and other resonant frequencies (resonant points) may be set within a range of sound pressures equal to or higher than the reference line. The range between the dashed lines in FIG. 14, that is, the range indicated by the arrows, is the range of sound pressures equal to or higher than the reference line. This allows other elements having resonant frequencies within a frequency range equal to or higher than the reference line to be driven by driving the element 20 without applying a voltage. In addition, the dip in the frequency between the resonant frequencies can be reduced.

[0089] Fig. 15 is a plan view showing the sonic speaker 11 of the sonic speaker device 10 according to this embodiment. Fig. 15 corresponds to Fig. 2. Fig. 16 is a cross-sectional view taken along line XVI-XVI shown in Fig. 15. Fig. 16 also shows a simplified view of the voltage adjustment unit 12 so that the input of the signal Vpp can be seen.

[0090] As shown in Fig. 15 and Fig. 16, the sonic speaker 11 of this embodiment further includes a dummy element 20d. As an example, the sonic speaker 11 includes eleven elements 20 and two dummy elements 20d. The dummy elements 20d have a similar configuration to the elements 20, and for distinction, "dummy" is added to the name of each element. The dummy element 20d includes a dummy piezoelectric vibrator 30d and a dummy vibration area 41d.

[0091] The support 50 has a dummy cavity 51d formed at a position different from the cavity 51 and opening to the main surface 50a. The dummy vibration region 41d is a portion of the vibration section 40 located on the dummy cavity 51d. The dummy vibration region 41d is defined by the adjacent dummy cavity 51d. A dummy piezoelectric film 31d and a dummy upper electrode 32d are arranged on the dummy vibration region 41d. The dummy piezoelectric vibrator 30d is composed of the dummy piezoelectric film 31d, the dummy upper electrode 32d, and a portion of the semiconductor film 400 forming the lower electrode. The dummy piezoelectric vibrator 30d is not electrically connected to the voltage adjustment section 12. The voltage adjustment section 12 does not have an adjustment circuit 80 corresponding to the dummy element 20d. As an example, in this embodiment, one of the resonant frequencies of the dummy elements 20d is set to 85 kHz, and the other resonant frequency is set to 145 kHz.

[0092] <Summary of the second embodiment> According to this embodiment, the vibration (drive) of the element 20 resonates the dummy element 20d to which the signal Vpp is not input from the voltage adjustment unit 12. The resonance of the dummy element 20d increases the sound pressure at the resonance frequency of the dummy element 20d. This makes it possible to reduce the variation in sound pressure. For example, the resonance of the dummy element 20d with a resonance frequency of 85 kHz increases the sound pressure at frequencies between the resonance frequencies of 80 kHz and 90 kHz of the two elements 20. When the dummy element 20d is provided, the Q value of the adjacent resonance frequency appears to be smaller. This makes it possible to reduce the dip.

[0093] Similarly, the dummy element 20d with a resonant frequency of 145 kHz resonates, increasing the sound pressure at frequencies near 140 kHz. The Q value of the adjacent resonant frequency of 140 kHz appears to be smaller. This makes it possible to reduce the drop at the boundaries (upper and lower limits) of the frequency range.

[0094] In the present embodiment, an example in which the acoustic speaker 11 includes two dummy elements 20d has been described, but the number of the dummy elements 20d is not limited to the above example. A configuration including only one dummy element 20d or a configuration including three or more dummy elements 20d may also be used.

[0095] The resonant frequency of the dummy element 20d is not limited to the above example. The resonant frequency of the dummy element 20d (dummy vibration region 41d) may be a frequency between two adjacent resonant frequencies in a predetermined frequency range. It may also be a frequency outside the frequency range and close to the upper or lower limit of the resonant frequency. For example, a dummy element 20d with a resonant frequency of 35 kHz may be provided. This can reduce the drop at the boundary on the lower limit side of the frequency range.

[0096] (Other embodiments) The disclosure in this specification and drawings, etc. is not limited to the exemplified embodiments. The disclosure includes the exemplified embodiments and modifications by those skilled in the art based thereon. For example, the disclosure is not limited to the combination of parts and / or elements shown in the embodiments. The disclosure can be implemented by various combinations. The disclosure can have additional parts that can be added to the embodiments. The disclosure includes the omission of parts and / or elements of the embodiments. The disclosure includes the substitution or combination of parts and / or elements between one embodiment and another embodiment. The disclosed technical scope is not limited to the description of the embodiments. Some disclosed technical scopes are indicated by the description of the claims, and should be interpreted as including all modifications within the meaning and scope equivalent to the description of the claims.

[0097] The disclosure in the specification and drawings is not limited by the claims. The disclosure in the specification and drawings includes the technical ideas described in the claims, and extends to more diverse and broader technical ideas than the technical ideas described in the claims. Therefore, various technical ideas can be extracted from the disclosure in the specification and drawings without being bound by the claims.

[0098] When an element or layer is referred to as being "on," "coupled," "connected," or "bonded," it may be directly coupled, connected, or bonded to another element or layer, and intervening elements or layers may be present. In contrast, when an element is referred to as being "directly on," "directly coupled," "directly connected," or "directly bonded" to another element or layer, there are no intervening elements or layers. Other words used to describe relationships between elements should be construed in a similar manner (e.g., "between" vs. "directly between," "adjacent" vs. "directly adjacent," etc.). As used in this specification, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0099] Spatially relative terms such as "inside," "outside," "back," "bottom," "low," "top," "top," and the like are utilized herein to facilitate the description of the relationship of one element or feature to another element or feature as depicted in the figures. Spatially relative terms may be intended to encompass different orientations of the device during use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as "below" or "directly below" other elements or features would be oriented "above" the other elements or features. Thus, the term "bottom" can encompass both an orientation of top and bottom. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used in this specification would be interpreted accordingly.

[0100] The shape of the cavity 51 is not limited to the above example. For example, the planar shape of the cavity 51 is not limited to a substantially perfect circle. In addition, the cavity 51 may have a shape in which the opening area changes in the thickness direction, for example, a shape in which the opening area changes in multiple steps.

[0101] Although an example in which the cavity 51 opens on the back surface 50b of the support 50 has been shown, the present invention is not limited thereto. For example, in a configuration in which the support 50 has an insulating film on the semiconductor substrate 500 on the main surface 50a side, an etching hole may be formed in the semiconductor film 400 of the vibration section 40, and the insulating film of the support 50 may be etched from the first surface 40a side (so-called sacrificial layer etching) to remove a part of the insulating film to form the cavity 51. By making the opening areas of the cavities 51 opening on the main surface 50a different from each other, the wideband acoustic speaker 11 can be made smaller.

[0102] Although an example has been shown in which the film on the support 50, specifically the semiconductor film 400 and the insulating film 401, are used as the vibration part 40, this is not limiting. For example, a semiconductor substrate may be etched to form a diaphragm (thin part), a part of a predetermined thickness including the diaphragm may be used as the vibration part, and a thick part connected to the vibration part may be used as the support. A cavity formed in the semiconductor substrate opens to the main surface of the support and defines the diaphragm, which is the vibration region.

[0103] Although an example has been shown in which the multiple cavities 51 communicate with the periphery of the support 50, i.e., the external atmosphere, the present invention is not limited to this. For example, a fixing member 70 (bonding material) may be disposed around the entire edge of the rear surface 50b of the support 50 to isolate the cavities 51 from the external atmosphere. Even in the isolated state, the wider the space including the cavities 51, the higher the sound pressure can be.

[0104] Although an example in which air is disposed inside the cavity 51 has been shown, the present invention is not limited to this. A gas having a higher density than air may be disposed inside the cavity 51. In this case, the resonant frequency shifts to the lower frequency side. Also, a gas having a lower density than air may be disposed inside the cavity 51. In this case, the resonant frequency shifts to the higher frequency side. These gases may be enclosed (sealed) inside the cavity 51. The inside of the cavity 51 may be reduced in pressure (a vacuum). [Explanation of symbols]

[0105] 10...sound wave speaker device, 11...sound wave speaker, 12...voltage adjustment section, 20...element, 20d...dummy element, 30...piezoelectric vibrator, 30d...dummy piezoelectric vibrator, 31...piezoelectric film, 31d...dummy piezoelectric film, 32...upper electrode, 32d...dummy upper electrode, 33...lower electrode pad, 40...vibration section, 400...semiconductor film, 401...insulating film, 40a...first surface, 40b...second surface, 41...vibration region, 41d...dummy vibration region, 50...support, 500...semiconductor substrate, 50a...main surface, 50b...rear surface, 51...cavity, 51d...dummy cavity, 60...base member, 70...fixing member, 80...adjustment circuit, 81...amplifier, 82...phase shifter, 100...sound source,

Claims

1. The device comprises an ultrasonic speaker (11) that emits ultrasonic waves, and a voltage adjustment unit (12) that amplifies a signal Vpp input from a sound source (100) and applies the amplified signal to the ultrasonic speaker, The sonic speaker comprises: A plurality of piezoelectric films (31); a vibration section (40) having a first surface (40a), a second surface (40b) opposite to the first surface, and a plurality of vibration regions (41) in which the piezoelectric film is individually disposed on the first surface and vibrates in accordance with the expansion and contraction of the piezoelectric film; a support (50) having a main surface (50a) and a plurality of cavities (51) that open onto the main surface and are adjacent to the second surface of the vibration region, the cavities (51) defining the vibration region such that the resonant frequencies are different from one another by having opening areas in the main surface different from one another, and supporting the vibration section on the main surface; The sound waves are radiated from the piezoelectric film side within a frequency range in which a resonance frequency of a maximum vibration region, which is the vibration region defined by the cavity having the largest opening area among the plurality of cavities, is set as a lower limit, and a resonance frequency of a minimum vibration region, which is the vibration region defined by the cavity having the smallest opening area, is set as an upper limit, The voltage adjustment unit is The amplification factor of the signal Vpp applied to the piezoelectric film is individually adjustable; adjusting the value of the signal Vpp to be applied individually so that the variation in sound pressure at each resonance frequency in the frequency range is smaller than that in the case where the signal Vpp common to all of the piezoelectric films is applied; The acoustic speaker includes a dummy cavity (51d) that opens to the main surface of the support, a dummy vibration area (41d) that is defined by the dummy cavity in the vibration part, and a dummy piezoelectric film (31d) that is disposed on the dummy vibration area and to which the signal Vpp is not applied, An acoustic speaker device, wherein the resonant frequency of the dummy vibration region is a frequency between two adjacent resonant frequencies in the frequency range, or a frequency outside the frequency range and close to the upper or lower limit resonant frequency.

2. The voltage adjustment unit is The phase of the signal Vpp applied to the piezoelectric film is individually adjustable; 2. The acoustic speaker device of claim 1, wherein the phase of the signal Vpp applied to some of the piezoelectric films among the plurality of piezoelectric films is adjusted to be opposite to the phase of the signal Vpp applied to the remaining piezoelectric films so that the drop between adjacent resonant frequencies in the frequency range is reduced.

3. The plurality of piezoelectric films include a first piezoelectric film disposed in a first vibration region, which is the vibration region, and a second piezoelectric film disposed in a second vibration region, which is the vibration region adjacent to the first vibration region, and the resonance frequency of the second piezoelectric film is 3. The acoustic speaker device according to claim 2, wherein the voltage adjusting section adjusts the signal Vpp to be applied so that the phase of the signal Vpp is opposite to that of the first piezoelectric film and the second piezoelectric film.

4. 3. The acoustic speaker device of claim 2, wherein the voltage adjustment unit adjusts the phase of the signal Vpp applied to some of the piezoelectric films arranged in three or more vibration regions having continuous resonant frequencies so that the phase of the signal Vpp applied to the remaining piezoelectric films is opposite to the phase of the signal Vpp applied to the remaining piezoelectric films.

5. 5. The sonic speaker device according to claim 1, wherein the opening areas of the plurality of cavities are set so as to include at least a frequency range in which the sound waves exceed an audible frequency and have an upper limit of 200 kHz.

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