JP7625942B2 - Sonic speaker device - Google Patents

Description

The disclosure in this specification relates to an acoustic speaker device.

Patent document 1 discloses an acoustic speaker device that emits 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 the technical elements in this specification.

JP 2003-223174 A

Sonic speaker devices that emit wideband sound waves are generally large in size. In the above respects, and in other respects not mentioned, further improvements in sonic speaker devices are required.

One disclosed objective is to provide a sonic speaker device that can emit sound waves over a wide frequency range while being compact in size.

The sonic speaker device disclosed herein comprises a sonic speaker (11) that emits sound waves, and a voltage adjustment unit (12) that amplifies a signal Vpp input from a sound source (100) and applies it to the sonic speaker.

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) in which piezoelectric films are individually arranged on the first surface and vibrate in accordance with expansion and contraction of the piezoelectric films;
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.

The voltage regulator is
The amplification factor of the signal Vpp applied to the piezoelectric film can be individually adjusted.
The value of the applied signal Vpp is adjusted individually 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.
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 vibrating region is set to a frequency between two adjacent resonant frequencies in the frequency range, or a frequency outside the frequency range and in the vicinity of the upper or lower limit resonant frequency .

According to the disclosed sonic speaker device, the sonic speaker is formed by MEMS technology. Specifically, a plurality of cavities are provided in the support, and a vibrating portion is provided on the main surface of the support. In the vibrating portion, a vibration region that vibrates in response to 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.

The voltage adjustment unit can also individually adjust the value of the signal Vpp applied to the piezoelectric films that are individually arranged relative to the vibration area. In other words, the sound pressure at each resonant 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 emit a wide band of sound waves. As a result, it is possible to provide a sonic speaker device that can emit a wide band of sound waves while being compact in size.

The various aspects disclosed in this specification employ different technical means to achieve their respective objectives. The claims and the reference characters in parentheses in this section are illustrative of the corresponding relationships with the embodiments described below, and are not intended to limit the technical scope. The objectives, features, and advantages disclosed in this specification will become clearer with reference to the detailed description that follows and the accompanying drawings.

1 is a diagram showing a schematic configuration of an ultrasonic speaker device according to a first embodiment; FIG. 1 is a plan view showing an acoustic speaker. FIG. 3 is a cross-sectional view taken along line III-III in FIG. 2 . FIG. 4 is a block diagram showing a voltage adjustment unit. FIG. 11 is a diagram showing an example of the value and phase of a signal Vpp applied to each element. FIG. 13 is a diagram showing the variation in sound pressure in a predetermined frequency range after voltage adjustment. FIG. 11 is a diagram for explaining a sound pressure adjustment method. FIG. 11 is a diagram for explaining a sound pressure adjustment method. FIG. 11 is a diagram for explaining a sound pressure adjustment method. 11A and 11B are diagrams illustrating another example of the value and phase of the signal Vpp applied to each element. FIG. 13 is a diagram showing the variation in sound pressure in a predetermined frequency range after voltage adjustment. FIG. 13 is a reference diagram showing the result of applying a common voltage as the signal Vpp. 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. FIG. 1 is a diagram showing frequency characteristics of one element. FIG. 11 is a plan view showing an acoustic speaker in an acoustic speaker device according to a second embodiment. FIG. 16 is a cross-sectional view taken along line XVI-XVI in FIG. 15 .

Below, several embodiments will be described with reference to the drawings. Note that in each embodiment, corresponding components are given the same reference numerals, and duplicated descriptions may be omitted. When only a portion of the configuration is described in each embodiment, the configuration of the other embodiment described above can be applied to the other portions of the configuration. In addition to the combinations 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.

First Embodiment
First, a schematic configuration of the acoustic speaker device will be described with reference to FIG.

<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 .

As described below, the sound speaker 11 has multiple elements 20 that emit sound waves and are formed using MEMS technology. The elements 20 have different resonant frequencies. By utilizing multiple resonant points, the sound speaker 11 is capable of emitting sound waves in a specific frequency range, i.e., sound waves over a wide band. MEMS is an abbreviation for Micro Electro Mechanical Systems. The sound speaker 11 is used, for example, in the atmosphere.

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. As described below, the voltage adjustment unit 12 can individually adjust the voltage applied to the piezoelectric film 31.

<Sound wave speaker>
Next, the acoustic speaker 11 will be described with reference to Fig. 2 to Fig. 4. Fig. 2 is a plan view of the acoustic 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.

2 and 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), i.e., 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, i.e., 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.

The multiple elements 20 have different resonant frequencies. The sonic speaker 11 of this embodiment includes eleven elements 20. Each element 20 is configured with 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.

The multiple piezoelectric vibrators 30 are arranged so that they can individually vibrate the vibration area 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 has eleven piezoelectric vibrators 30. Each piezoelectric vibrator 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.

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. In this embodiment, the piezoelectric film 31 is formed by sputtering using ScAlN as the material. The thickness of the piezoelectric film 31 is, for example, about 1 μm.

The piezoelectric film 31 has a substantially circular shape in plan view. The diameter, i.e., area, of the piezoelectric film 31 is different for each of the eleven piezoelectric vibrators 30. The piezoelectric film 31 has an area corresponding 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.

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, vapor 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 approximately the same as the piezoelectric film 31 in a plan view. The upper electrode 32 of this embodiment has a planar shape that is approximately a perfect circle. 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.

The lower electrode is disposed on the other surface of the piezoelectric film 31 in the Z direction, i.e., the surface opposite to 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. In this embodiment, the lower electrode is a portion of the semiconductor film 400 that has been made conductive as described below, and that overlaps with the piezoelectric film 31 in a planar view. At least a portion of the other portion of the semiconductor film 400 functions, for example, as wiring.

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. In this embodiment, the lower electrode pad 33 is arranged in the X direction together with the three piezoelectric films 31 that form 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.

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.

The vibration part 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 part 40. The vibration part 40 is composed of, for example, a film formed on a support 50. The film constituting the vibration part 40 may be a single layer or may be multi-layered. Such a vibration part 40 may be called a vibration film or a movable film. The vibration part 40 of this embodiment is composed of a semiconductor film 400 and an insulating film 401.

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

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 that constitutes the support 50. In this embodiment, the insulating film 401 is a silicon oxide film. The insulating film 401 has a thickness that allows vibration in the Z direction in a stacked structure with the semiconductor film 400.

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

3, the region surrounded by the dashed line is the vibration region 41. The vibration region 41 in this embodiment has a two-layer structure of the semiconductor film 400 and the insulating film 401 described above. The vibration region 41 is provided in the same number as the piezoelectric film 31. The vibration section 40 has eleven vibration regions 41 with different areas. The area is the area in a plan view. The piezoelectric film 31 is 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.

The larger the radius of the vibration region 41 (element 20), that is, the larger the area, the lower the resonant frequency of the vibration region 41. In this embodiment, the radii of the vibration region 41 are different from each other, so that the resonant frequencies of the elements 20 are set in the range of 40 kHz to 140 kHz at intervals of 10 kHz. Specifically, the resonant frequencies of the three elements 20 in the middle row in the Y direction are set to 40 kHz, 50 kHz, and 60 kHz. The resonant 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 resonant 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 the resonant frequencies and the intervals between the resonant frequencies are not limited to being exactly the same as the above values, and errors of the order of manufacturing variability are acceptable.

As described above, the vibration region 41, together with the piezoelectric vibrator 30, constitutes the element 20 that radiates sound waves. Since the vibration regions 41 (elements 20) each have a different resonant frequency, by applying a drive voltage to the multiple piezoelectric vibrators 30, the sound speaker 11 can radiate sound waves in a predetermined frequency range. 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 frequency range of 40 to 140 kHz described above can be radiated. The sound speaker 11 radiates (emits) sound waves from the piezoelectric vibrator 30 side.

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 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.

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 is sometimes 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 a single semiconductor chip. SOI is an abbreviation for Silicon on Insulator. The support 50 has a substantially rectangular planar shape.

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 below. The opening portion of the main surface 50a in the cavity 51 is blocked by the vibration section 40.

In the cavity 51, the openings in the main surface 50a define the vibration region 41. The openings in the main surface 50a of the cavity 51 define the overlapping (matching) portions of the vibration section 40 in a planar view as the vibration region 41. The same number of cavity sections 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.

The support 50 (semiconductor substrate 500) of this embodiment has eleven cavities 51 with different opening areas. Each of the cavities 51 is adjacent to a vibration region 41. In the cavities 51, the opening portion in the main surface 50a has a substantially perfect circular shape in plan. 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 cylindrical shape that is substantially perfect circular in plan and has 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).

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 that constitutes 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 the value obtained by dividing the sound speed c by the upper limit of the frequency range of the sound waves radiated by the sound speaker 11. The upper limit is the resonant frequency of the vibration region 41 defined by the cavity 51 with the smallest opening area. For example, when radiating sound waves in the frequency range of 40 to 140 kHz as described above, the wavelength λ is the value obtained by dividing the sound speed c by 140 kHz.

The base member 60 is a member to which the structure including the piezoelectric vibrator 30, the vibration part 40, and the support 50 is fixed. The base member 60 is, for example, a package or case that protects the above structure. In this embodiment, the base member 60 is a ceramic package. The support 50 (the 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 to avoid the hollow portion 51.

The fixing member 70 in this embodiment is a bonding material. As shown in Figs. 2 and 3, the fixing member 70 is arranged, for example, at the four corners of the back surface 50b of the support body 50. In the 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 are in communication 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 surroundings of the support body 50 in a plan view.

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 is acceptable. For example, the fixing members 70 may be arranged along two opposing sides of the support 50 having a roughly planar shape.

<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 acoustic speaker 11 and the sound source 100.

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, music including sounds in the ultrasonic range is provided. 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.

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 sonic speaker 11. In other words, 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.

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 the peak-to-peak voltage value. Adjusting the value of the signal Vpp is equivalent to adjusting the maximum voltage, which is the peak value of 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 small. The amplifier 81 adjusts the value of the signal Vpp according to the characteristics of the corresponding element 20.

The phase shifter 82 adjusts the phase of the signal Vpp. In this embodiment, the phase shifter 82 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°.

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, or so-called dip, between adjacent resonant frequencies in the above-mentioned frequency range is small. 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.

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

In the example shown in FIG. 4, the phase shifter 82 is provided between the amplifier 81 and the sound source 100, but this is not limiting. The phase shifter 82 may also be provided between the amplifier 81 and the element 20.

<How to adjust sound pressure>
In order 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 one 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.

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 performs a process to average out the resonant frequency and the dip between them. Figure 5 shows an example of the adjustment of the signal Vpp by the voltage adjustment unit 12. Figure 6 shows the frequency characteristics when each element 20 is driven under the conditions of Figure 5.

In-phase in FIG. 5 indicates that the shift angle of the phase shifter 82 is 0°, i.e., 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°, i.e., 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 50 cm. 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.

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 the 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 the 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 the element 20 with a resonant frequency of 140 kHz was 6.2 V and the phase was reversed.

As a result, as shown in Figure 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 Figure 6 (not shown), but the variation was about ± 25 dB.

The higher the applied voltage (signal Vpp), the higher the sound pressure at the resonant frequency; 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. In addition, by adjusting the phase, the dip can be reduced and the sound pressure at frequencies between the resonant frequencies can be kept within the range of the variation described above. The method of adjusting the phase is described below.

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

Figure 7 shows an example in which a signal Vpp is applied to an element 20 with a resonant frequency of 70 kHz and/or an element 20 with a resonant frequency of 80 kHz among a plurality of elements 20. The solid line shows the frequency characteristics when the phases of the signal Vpp applied to the two elements 20 are opposite to each other. The dashed line shows the frequency characteristics when the phases of the signal 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 double-dashed line shows the frequency characteristics when the signal Vpp is applied only to the 80 kHz element 20.

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 interference between two adjacent resonant frequencies and reduce the dip between the resonant frequencies.

Figure 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 Figure 5, the solid line shows the frequency characteristics when the phases of the signal Vpp applied to the two elements 20 are opposite to each other. The dashed line shows the frequency characteristics when the phases of the signal 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.

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 or out-of-phase. In this way, the dip may hardly change due to phase adjustment. 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 and the larger the dip. Therefore, it is advisable to adjust the configuration of the side opposite the side emitting the sound waves so that the Q value of the element 20 is smaller. For example, it is possible to reduce the Q value by adjusting the configuration and fixing method of the support 50 and the base member 60.

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. In this way, adjusting the phase of two adjacent resonant frequencies can affect the dip between the adjacent resonant frequencies.

Figure 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.

As shown in Figure 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 indicated by the solid arrow, than 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 multiple 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.

The adjustment of the dips is not limited to the frequencies shown in Figures 7 to 9. Dips between other resonant frequencies can be adjusted in the same way. The value and phase of the signal Vpp applied to each element 20 shown in Figure 5 are the value and phase after the above-mentioned adjustments are performed. By making such adjustments, it is possible to reduce the sound pressure variation to ±12.6 dB in the frequency range as shown in Figure 6.

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 vibration section 40 is provided on a main surface 50a of the support 50. In the vibration 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 resonance frequencies of the vibration regions 41 are different from each other. In this way, a single (common) vibration section 40 is provided with a plurality of vibration regions 41 with different resonance frequencies. Therefore, the size of the sonic speaker 11, and therefore the sonic speaker device 10, can be reduced.

The voltage adjustment unit 12 can also individually adjust the value of the signal Vpp applied to the piezoelectric film 31 (piezoelectric vibrator 30) that is individually arranged relative to the vibration region 41. In other words, the sound pressure at each resonant 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 speaker 11 functions as a speaker that can emit a wideband sound wave. The sound speaker 11 can, for example, emit sound waves having a predetermined frequency range from the piezoelectric film 31 side. As described above, the sound speaker device 10 of this embodiment can emit a wideband sound wave while being compact in size.

In this embodiment, the signal Vpp is applied to all 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, when 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.

In this embodiment, the voltage adjustment unit 12 can individually adjust not only the value of the signal Vpp but also the phase. 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 individually adjusts the phase of the signal Vpp, thereby reducing the dip between the resonant frequencies in a specified frequency range. Therefore, the variation in sound pressure in the frequency range can be further reduced.

As shown in FIG. 5, the voltage adjustment unit 12 adjusts the phase so that the phase of the signal Vpp applied to the element 20 (piezoelectric vibrator 30) with a resonant frequency of 70 kHz is opposite to the phase of the signal Vpp applied to the element 20 with a resonant frequency of 80 kHz. This reduces 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 with 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 with a resonant frequency of 80 kHz corresponds to the second vibration region, and the piezoelectric film 31 corresponds to the second piezoelectric film.

As shown in FIG. 5, the voltage adjustment 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 with 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 with resonant frequencies of 70 kHz and 90 kHz is opposite to the phase of the signal Vpp applied to the element 20 with a resonant frequency of 80 kHz. This can further reduce the dip in the frequency between 70 kHz and 80 kHz.

In this embodiment, the multiple 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 multiple cavities 51. The multiple cavities 51 communicate with each other, forming a large space on the side opposite to the side from which sound waves are emitted. Therefore, compared to a configuration in which the cavities 51 do not communicate with each other, the gas resistance to vibration is smaller, and the sound pressure can be increased. In particular, in this embodiment, the cavities 51 are also connected to the space around the support 50, making it easier to increase the sound pressure.

In this embodiment, the cavity 51 has a predetermined thickness while maintaining its planar shape. This makes it easy to define the shape and therefore the area of the vibration region 41 by etching. In other words, it is easy to set the desired resonance frequency. In particular, 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 circular shape in plan. Because of the perfect circular 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.

<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 measured values obtained by collecting sound waves emitted from the sonic speaker 11 with 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 0.5 V, and the upper limit of the signal Vpp after amplification is 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.

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 the element 20 with a resonant frequency of 120 kHz was 1.9 V and the phase was out-of-phase. The signal Vpp value applied to the 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 the element 20 with a resonant frequency of 140 kHz was 2.1 V and the phase was out-of-phase.

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 sound pressure variation 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 sound pressure variation was ±18.6 dB.

Comparing Figures 11 and 12, it is clear that individually adjusting the value of the signal Vpp applied to element 20 can suppress the variation in sound pressure at the resonant frequencies in the frequency range of 40 kHz to 140 kHz more effectively than if the signal Vpp value were common. It is also clear that individually adjusting the phase of the signal Vpp can reduce the dip in the frequency between the resonant frequencies more effectively than if the phase of the signal Vpp is common (all in phase).

In this embodiment, since the value of the signal Vpp applied to each element 20 is adjusted individually, the sound pressure is lower than, for example, 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 wideband sound waves is that the sound pressure variation is small over a wide frequency range. Therefore, the sonic speaker device 10 of this embodiment is suitable as a speaker device that radiates wideband sound waves. 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 the variation remains 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.

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, but this is not limiting. 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 that can emit sound waves over a wide band.

The number of vibration regions 41 and cavities 51 is not limited to the above example. The number of vibration regions 41 and 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 cavity 51 with the larger 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 cavity 51 with the smaller 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.

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 multiple 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 to only one element 20 temporarily.

The resonant frequencies of all the elements 20 are set to frequencies above the audible frequency, but are not limited to this. The resonant frequencies of some of the elements 20 may be in the audible frequency range. For example, the opening areas of the multiple cavities 51 may be set so as to emit sound waves in a frequency range above 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 also be set within the audible frequency range. By configuring the multiple 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.

In this embodiment, an example has been shown in which the vibration section 40 includes an insulating film 401, but this is not limiting. The support 50 may also 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.

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

Figure 13 shows the relationship between the voltage applied to element 20 at one resonant frequency and the sound pressure at the resonant frequency when all elements 20 are driven by applying a signal Vpp to them, as in the previous embodiment. Figure 13 shows the measured value 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 was 10 cm. Figure 13 shows an example of a resonant frequency of 90 kHz.

Normally, the sound pressure decreases as the applied voltage is lowered. However, as shown in Figure 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 even without applying the signal Vpp 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.

Figure 14 shows the frequency characteristics of sound waves emitted by one element 20. In Figure 14, an element 20 with a resonant frequency of 80 kHz is shown as an example. As shown in Figure 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) can be set within the range of sound pressure above the reference line. The range between the dashed lines in Figure 14, that is, the range indicated by the arrows, is the range of sound pressure above the reference line. This allows other elements having resonant frequencies within the frequency range above 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.

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

As shown in Figures 15 and 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 the word "dummy" is added to the name of each element to distinguish them. The dummy element 20d includes a dummy piezoelectric vibrator 30d and a dummy vibration area 41d.

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 above 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 dummy elements 20d has a resonant frequency of 85 kHz, and the other has a resonant frequency of 145 kHz.

<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. Therefore, the variation in sound pressure can be reduced. 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 reduces the dip.

Similarly, when the dummy element 20d with a resonant frequency of 145 kHz resonates, the sound pressure at frequencies near 140 kHz increases. 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.

In this embodiment, an example is shown in which the acoustic speaker 11 includes two dummy elements 20d, but the number of dummy elements 20d is not limited to the above example. It may be configured to include only one dummy element 20d, or it may be configured to include three or more dummy elements 20d.

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 specified frequency range. It may also be a frequency outside the frequency range, 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.

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.

The disclosure in the specification and drawings, etc. is not limited by the claims. The disclosure in the specification and drawings, etc. encompasses the technical ideas described in the claims, and extends to more diverse and extensive 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, etc., without being bound by the claims.

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, no intervening elements or layers are present. 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.

Spatially relative terms such as "inside," "outside," "back," "bottom," "low," "top," "top," and the like are utilized herein for ease of description to describe the relationship of one element or feature to other elements or features 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.

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 shape may be one in which the opening area changes in the thickness direction, for example, a shape in which the opening area changes in multiple steps.

Although an example in which the cavity 51 opens on the back surface 50b of the support 50 has been shown, this is not limiting. 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 part 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 and 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.

An example has been given 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, but this is not limiting. For example, the semiconductor substrate may be etched to form a diaphragm (thin part), and the part including the diaphragm may be a part of a predetermined thickness used as the vibration part, with the thick part connected to the vibration part used as the support. The cavity formed in the semiconductor substrate opens into the main surface of the support and defines the diaphragm, which is the vibration region.

An example has been shown in which the multiple cavities 51 communicate with the surroundings of the support 50, i.e., the external atmosphere, but this is not limiting. For example, a fixing member 70 (bonding material) may be placed around the entire edge of the back surface 50b of the support 50 to isolate the cavities 51 from the external atmosphere. Even in a state of isolation, the wider the space including the cavities 51, the higher the sound pressure can be.

An example in which air is placed inside the cavity 51 has been shown, but this is not limiting. A gas with a higher density than air may be placed inside the cavity 51. In this case, the resonant frequency shifts to the lower frequency side. A gas with a lower density than air may be placed 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).

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 (5)

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 into 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 . 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. 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. The acoustic speaker device according to 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. 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.

Images