JP2022091026A - Sound wave speaker - Google Patents

Abstract

To miniaturize a sound wave speaker discharging a sound wave in a wide band.SOLUTION: A sound wave speaker 10 comprises: a plurality of piezoelectric films 21; a vibration part 30; and a support body 40. The vibration part 30 includes a plurality of vibration regions 31 which vibrate in accordance with a telescopic motion of piezoelectric films 21. The support bodies 40 open to main surfaces 40a and are adjacent to the vibration regions 31, and includes a plurality of cavity parts 41 regulating the vibration regions 31 so that resonance frequencies become different from each other by making open areas in the main surfaces 40a difference from each other. Then, a sound wave in a frequency range having a resonance frequency in a first vibration region as the vibration region 31 of which the open area is regulated by the maximum cavity part 41 as a lower limit and a resonance frequency of a second vibration region of which the open area is the vibration region 31 regulated by the minimum cavity part 41 as an upper limit, is discharged from each piezoelectric film 21 side.SELECTED DRAWING: Figure 2

Description

The disclosure herein relates to a sonic speaker.

Patent Document 1 discloses a sound wave speaker that emits sound waves in a predetermined frequency range, that is, a wide band. The content of the prior art document is incorporated by reference as an explanation of the technical elements in this specification.

Japanese Patent Application Laid-Open No. 2003-223174

The physique of a sound wave speaker that emits sound waves in a wide band is generally large. Further improvements are required for sound wave speakers in the above-mentioned viewpoints or in other viewpoints not mentioned.

One object disclosed is to miniaturize a sound wave speaker that emits a wide band of sound waves.

The sound wave speaker disclosed here is
With a plurality of piezoelectric films (21),
A plurality of piezoelectric films are individually arranged on the first surface (30a), the second surface (30b) opposite to the first surface, and the first surface, and vibrate as the piezoelectric film expands and contracts. A vibrating portion (30) having a vibrating region (31),
A plurality of cavities that are open to the main surface (40a) and adjacent to the second surface of the vibration region and define the vibration region so that the resonance frequencies are different from each other because the opening areas on the main surface are different from each other. (41), and a support (40) that has and supports the vibrating portion on the main surface.
Equipped with
Of the plurality of cavities, the resonance frequency of the first vibration region, which is the vibration region defined by the cavity having the largest opening area, is set as the lower limit, and the second vibration region defined by the cavity having the smallest opening area. Sound waves in the frequency range with the resonance frequency in the vibration region as the upper limit are radiated from the piezoelectric film side.

According to the disclosed sound wave speaker, a plurality of cavities are provided in the support, and a vibrating portion is provided on the main surface of the support. Of the vibrating portions, the vibrating region that vibrates with the expansion and contraction of the piezoelectric film is defined by the adjacent cavity portion. The opening areas of the cavities that open on the main surface of the support are different from each other so that the resonance frequencies of the plurality of vibration regions are different from each other. This structure is formed by MEMS technology. Therefore, it is possible to miniaturize a sound wave speaker that emits sound waves in a predetermined frequency range, that is, sound waves in a wide band.

The disclosed embodiments herein employ different technical means to achieve their respective objectives. The claims and the reference numerals in parentheses described in this section exemplify the correspondence with the parts of the embodiments described later, and are not intended to limit the technical scope. The objectives, features, and effects disclosed herein will be further clarified by reference to the subsequent detailed description and accompanying drawings.

It is a top view which shows the sound wave speaker which concerns on 1st Embodiment. It is sectional drawing which follows the II-II line of FIG. It is a figure which shows the relationship between the radius of the vibration region and the resonance frequency for each element. It is a figure for demonstrating a standing wave. It is a figure which shows the standing wave by the reflection on the back surface of the vibration region. It is a figure which shows the measurement result of the reference example. It is a figure which shows the relationship between a frequency and a specific acoustic impedance. It is sectional drawing which shows the sound wave speaker which concerns on 2nd Embodiment. It is sectional drawing which shows the modification. It is sectional drawing which shows the modification. It is sectional drawing which shows the modification. It is sectional drawing which shows the sound wave speaker which concerns on 3rd Embodiment.

Hereinafter, a plurality of embodiments will be described with reference to the drawings. By assigning the same reference numerals to the corresponding components in each embodiment, duplicate description 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. Further, not only the combination of the configurations specified in the description of each embodiment but also the configurations of a plurality of embodiments can be partially combined even if the combination is not specified. ..

(First Embodiment)
First, the sound wave speaker will be described with reference to FIGS. 1 to 3. In the following, the stacking direction of the vibrating portion and the piezoelectric film (piezoelectric vibrator), that is, the thickness direction of the support (cavity portion) is referred to as the Z direction. It is orthogonal to the Z direction, and the arrangement direction of a plurality of vibration regions is indicated as the X direction. The direction orthogonal to both the Z direction and the X direction is referred to as the Y direction. Unless otherwise specified, a shape viewed from the Z direction in a plane, that is, a shape along the XY plane defined by the X and Y directions is simply referred to as a plane shape. Further, the plan view from the Z direction may be simply referred to as a plan view. FIG. 1 is a plan view of the sound wave speaker of the present embodiment as viewed from the piezoelectric vibrator side in the Z direction. FIG. 2 is a cross-sectional view taken along the line II-II of FIG. FIG. 3 is a diagram showing the relationship between the radius of the vibration region and the resonance frequency for 11 types of elements configured in the sound wave speaker.

As shown in FIGS. 1 and 2, the sound wave speaker 10 includes a plurality of piezoelectric vibrators 20, a vibrating portion 30, a support 40, and a base member 50. The sound wave speaker 10 is configured to be able to radiate a sound wave in a predetermined frequency range, that is, a sound wave in a wide band by forming a plurality of elements using the MEMS technique. MEMS is an abbreviation for Micro Electro Mechanical Systems. The sound wave speaker 10 is used in the atmosphere.

The plurality of piezoelectric vibrators 20 are individually provided with a vibrating region 31 included in the vibrating portion 30 so as to be vibrable. The piezoelectric vibrator 20 has a piezoelectric film 21, an upper electrode 22, and a lower electrode, respectively. The sound wave speaker 10 of the present embodiment includes 11 piezoelectric vibrators 20. The piezoelectric vibrator 20 individually has a piezoelectric film 21 and an upper electrode 22. That is, the sound wave speaker 10 has 11 piezoelectric films 21 and 11 upper electrodes 22.

The piezoelectric film 21 is a thin film formed by using, for example, an AlN-based material such as ScAlN, or a piezoelectric material such as lead titanium zirconate (PZT) or ZnO. The piezoelectric film 21 of the present embodiment is formed by a sputtering method using ScAlN as a material. The thickness of the piezoelectric film 21 is, for example, about 1 μm. The piezoelectric film 21 has a substantially perfect circular shape in a plane. In the 11 piezoelectric vibrators 20, the diameters, that is, the areas of the piezoelectric films 21 are different from each other. The piezoelectric film 21 has an area corresponding to the vibration region 31. The plurality of piezoelectric films 21 are arranged in three rows in the Y direction. In the middle row, three piezoelectric films 21 are arranged side by side in the X direction. In the rows at both ends in the Y direction, four piezoelectric films 21 are arranged side by side in the X direction. In each row, the piezoelectric films 21 are arranged in order of area.

The upper electrode 22 is arranged on one surface of the piezoelectric film 21 in the Z direction. The upper electrode 22 is formed by a sputtering method, a vapor deposition method, or the like using a well-known electrode material. The layer structure of the upper electrode 22 may be a single layer or a multi-layer structure. The upper electrode 22 of this embodiment is formed of a TiAl alloy as a material. The upper electrode 22 has a shape that substantially matches the piezoelectric film 21 in a plan view. The upper electrode 22 of the present embodiment has a substantially perfect circular shape in a plane. Each of the upper electrodes 22 also serves as an upper electrode pad when a driving voltage is applied.

The lower electrode is arranged in the Z direction on the other surface of the piezoelectric film 21, that is, on the back surface of the surface on which the upper electrode 22 is arranged. The lower electrode sandwiches the piezoelectric film 21 between the lower electrode and the upper electrode 22. The lower electrode of the present embodiment is a portion of the semiconductor film 300 imparted with conductivity that overlaps with the piezoelectric film 21 in a plan view, as will be described later. At least a portion of the other portion of the semiconductor film 300 functions, for example, as wiring. The lower electrode pad 23 is formed on the semiconductor film 300 at a position different from that of the piezoelectric film 21. The lower electrode pad 23 is formed at a position that does not overlap with the vibration region 31. The lower electrode pads 23 of the present embodiment are arranged side by side in the X direction together with the three piezoelectric films 21 forming the middle row. The lower electrode pad 23 is formed by using the same electrode material as the upper electrode 22. When a driving voltage is applied between the upper electrode 22 and the lower electrode pad 23, the piezoelectric film 21 to which the voltage is applied expands and contracts. The piezoelectric film 21 expands and contracts in the XY in-plane direction, for example.

Of course, the semiconductor film 300 may not be provided with conductivity, and a lower electrode may be provided separately from the semiconductor film 300. In this case, the lower electrode is formed by using the same electrode material as the upper electrode 22.

The vibrating portion 30 has a first surface 30a and a second surface 30b which is the back surface of the first surface 30a in the Z direction. The piezoelectric film 21 and the lower electrode pad 23 are arranged on the first surface 30a of the vibrating portion 30. The vibrating portion 30 is composed of, for example, a film formed on the support 40. The film constituting the vibrating portion 30 may be a single layer or a multilayer. Such a vibrating portion 30 may be referred to as a vibrating membrane or a movable membrane. The vibrating portion 30 of the present embodiment includes a semiconductor film 300 and an insulating film 301.

The semiconductor film 300 is a film formed by using a semiconductor material such as silicon (Si). The semiconductor film 300 of the present embodiment is doped with impurities to provide sufficient conductivity to function as a lower electrode and wiring. Specifically, conductivity is imparted by doping the silicon film with p-type impurities. The semiconductor film 300 has a thickness capable of vibrating in the Z direction. For example, it is about 20 to 25 μm.

The insulating film 301 is a film having electrical insulating properties such as an oxide film and a nitride film. The insulating film 301 electrically separates the semiconductor film 300 and the semiconductor substrate 400 constituting the support 40. The insulating film 301 of this embodiment is a silicon oxide film. The insulating film 301 has a thickness capable of vibrating in the Z direction in a laminated structure with the semiconductor film 300.

The vibrating unit 30 has a plurality of vibrating regions 31. The vibration region 31 is a region of the vibrating portion 30 that vibrates in the Z direction as the piezoelectric film 21 expands and contracts. The vibration region 31 is defined by the cavity 41 of the support 40. In the vibration region 31, the cavity 41 is adjacent to the second surface 30b. A semiconductor substrate 400 is adjacent to the second surface 30b in a portion other than the vibration region 31. As described above, since the cavity 41 exists directly below the vibration region 31, the vibration region 31 can vibrate in the Z direction. In FIG. 2, the region surrounded by the alternate long and short dash line is the vibration region 31. The vibration region 31 of the present embodiment has a two-layer structure of the semiconductor film 300 and the insulating film 301 described above. The same number of vibration regions 31 are provided as the piezoelectric films 21.

The vibrating unit 30 has 11 vibrating regions 31 having different areas from each other. The area is an area in a plan view. Piezoelectric films 21 are individually arranged on the first surface 30a of the vibration region 31. The vibration region 31 has a substantially perfect circular shape in a plane. In a plan view, the center of the vibration region 31 and the center of the piezoelectric film 21 arranged on the vibration region 31 substantially coincide with each other. The plurality of vibration regions 31 have different circle radii and diameters. As shown in FIG. 3, the larger the radius of the vibration region 31, that is, the larger the area, the lower the resonance frequency. In the present embodiment, the resonance frequency is set in the range of 40 kHz to 130 kHz by setting the radius of the vibration region 31 to a value different from each other in the range of 800 μm to 1530 μm.

The vibration region 31 constitutes an element that radiates a sound wave together with the piezoelectric vibrator 20. Since the resonance frequency of each of the vibration regions 31 (elements) is different, the sound wave speaker 10 can radiate a sound wave in a predetermined frequency range by applying a driving voltage to the plurality of piezoelectric vibrators 20. For example, by applying a driving voltage to all the piezoelectric vibrators 20 of 11 types of elements, it is possible to radiate a sound wave having a frequency range (40 to 130 kHz) shown in FIG. The sound wave speaker 10 radiates (exits) sound waves from the piezoelectric vibrator 20 side.

The support 40 supports the piezoelectric vibrator 20 and the vibrating portion 30. The support 40 has a main surface 40a and a back surface 40b which is a surface opposite to the main surface 40a in the Z direction. The vibrating portion 30 is arranged on the main surface 40a of the support 40. Specifically, the insulating film 301 is arranged on the main surface 40a of the support 40, and the semiconductor film 300 is laminated on the insulating film 301. The planar shape of the support 40 is not particularly limited. The support 40 is formed by using a material that can be processed by the MEMS technique, such as a semiconductor or glass.

The support 40 of this embodiment is configured to have a semiconductor substrate 400. One side of the semiconductor substrate 400 forms the main surface 40a, and the opposite side to the one side forms the back surface 40b. Such a support 40 may be referred to as a support substrate. The thickness of the semiconductor substrate 400, that is, the support 40 is, for example, about 300 μm. The semiconductor substrate 400 of this embodiment is a silicon substrate. The semiconductor substrate 400 is provided as a so-called SOI substrate together with the semiconductor film 300 and the insulating film 301 described above. SOI is an abbreviation for Silicon on Insulator. The support 40 has a substantially rectangular shape in a plane.

The support 40 has a plurality of cavities 41. The support 40 has a structure in which a plurality of hollow portions 41 are provided on a flat plate. Each of the plurality of cavities 41 has a predetermined thickness (depth) in the Z direction, and is open to at least the main surface 40a. The cavity 41 is formed in the support 40 by etching. The plurality of cavities 41 have different opening areas on the main surface 40a. The opening area on the main surface 40a may be simply referred to as an opening area below. The opening portion of the main surface 40a in the cavity portion 41 is closed by the vibrating portion 30. In the cavity 41, the opening portion in the main surface 40a defines the vibration region 31. As for the opening portion in the main surface 40a of the cavity portion 41, the overlapping portion (matching portion) in the plan view of the vibrating portion 30 is defined as the vibration region 31. The same number of cavities 41 as the vibration regions 31 are provided.

The support 40 (semiconductor substrate 400) of the present embodiment has 11 hollow portions 41 having different opening areas. The vibration region 31 is adjacent to each of the cavity portions 41. In the cavity 41, the opening portion in the main surface 40a has a substantially perfect circular shape in a plane. Each of the cavities 41 extends in the Z direction and opens to the back surface 40b of the support 40. The cavity 41 has a first cavity region 41a having a predetermined thickness while maintaining a planar shape. The first cavity region 41a has a predetermined thickness (depth) in the Z direction from the main surface 40a, and the planar shape is a region having a constant thickness direction. Since the first cavity region 41a also includes the opening portion in the main surface 40a, the vibration region 31 is defined. The first cavity region 41a has a cylindrical shape having a substantially perfect circular plane. The first cavity region 41a of the present embodiment extends to the back surface 40b. That is, the first cavity region 41a corresponds to the cavity portion 41. In the plurality of cavity portions 41, the thicknesses of the first cavity regions 41a are substantially equal to each other. The cavity 41 is formed by dry etching such as reactive ion etching (RIE).

The first cavity region 41a has a thickness t1 as shown in FIG. In the present embodiment, the thickness t1 is equal to the thickness of the semiconductor substrate 400 forming the support 40. 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 velocity c by the upper limit of the frequency range of the sound wave emitted by the sound wave speaker 10. The upper limit is the resonance frequency of the vibration region 31 defined by the cavity 41 having the smallest opening area. For example, when radiating a sound wave in the frequency range of 40 to 130 kHz as described above, the wavelength λ is the value obtained by dividing the sound velocity c by 130 kHz.

The base member 50 is a member to which the structures of the piezoelectric vibrator 20, the vibrating portion 30, and the support 40 are fixed. The base member 50 is, for example, a package or case that protects the structure. The base member 50 of this embodiment is a ceramic package. The support 40 (the above structure) is fixed to one surface of the base member 50 via the fixing member 60. The fixing member 60 may be any as long as it can fix the support 40 to the base member 50. The fixing member 60 is provided so as to avoid the cavity 41.

The fixing member 60 of the present embodiment is a joining material. As shown in FIGS. 1 and 2, the fixing member 60 is arranged at the four corners of the back surface 40b of the support 40, for example. In the fixed state, the back surface 40b of the support 40 is floating with respect to the base member 50. The support 40 is fixed to the base member 50 so that gas can flow between the plurality of cavities 41. The cavities 41 communicate with each other through a gap between the back surface 40b and the base member 50. Since the fixing member 60 is arranged at the four corners, gas can flow around the support 40 in a plan view.

The arrangement of the fixing member 60 is not limited to the four corners described above. Any arrangement may be sufficient as long as the support 40 can be stably fixed on the base member 50. For example, the support 40 having a substantially planar shape may be arranged along two sides facing each other.

<Summary of the first embodiment>
According to the sound wave speaker 10 of the present embodiment, the piezoelectric film 21 is provided on the first surface 30a side of the vibration region 31, and the cavity 41 is provided on the second surface 30b side opposite to the first surface 30a. Therefore, the sound wave speaker 10 radiates sound waves from the piezoelectric film 21 side.

Further, a plurality of hollow portions 41 are provided in the support 40, and a vibration portion 30 is provided on the main surface 40a of the support 40. Of the vibrating portions 30, the vibrating region 31 that vibrates with the expansion and contraction of the piezoelectric film 21 is defined by the adjacent cavity portion 41. The plurality of cavities 41 have different opening areas of the main surface 40a. Therefore, it is possible to radiate a sound wave in a predetermined frequency range, that is, a sound wave in a wide band. The sound wave speaker 10 can, for example, radiate the above-mentioned sound wave having a frequency range of 40 kHz to 130 kHz from the piezoelectric film 21 side. In this case, the vibration region 31 having a radius of 1530 μm corresponds to the first vibration region, and the vibration region 31 having a radius of 800 μm corresponds to the second vibration region. The resonance frequency of 40 kHz in the vibration region 31 having a radius of 1530 μm corresponds to the lower limit of the frequency range. The resonance frequency of 130 kHz in the vibration region 31 having a radius of 800 μm corresponds to the upper limit of the frequency range.

Further, the sound wave speaker 10 is formed by using the MEMS technique. For example, a single support 40 (semiconductor substrate 400) is formed with a plurality of cavities 41 having different opening areas. From the above, the wide band sound wave speaker 10 can be miniaturized.

The number of vibration regions 31 and cavities 41 is not limited to the above example. The number of the vibration region 31 and the cavity 41 may be a plurality. For example, it may be configured to have two vibration regions 31 and two cavity portions 41. The two cavities 41 have different opening areas on the main surface 40a. As a result, the resonance frequencies of the two vibration regions 31 are different from each other. The vibration region 31 defined by the cavity 41 having a large opening area corresponds to the first vibration region, and the resonance frequency of this vibration region 31 is the lower limit of the frequency range. The vibration region 31 defined by the cavity 41 having a small opening area corresponds to the second vibration region, and the resonance frequency of this vibration region 31 is the upper limit of the frequency range. The same applies to the number of piezoelectric vibrators 20 including the piezoelectric film 21.

In this embodiment, an example in which a drive voltage is applied to all the piezoelectric vibrators 20 of the 11 elements configured in the sound wave speaker 10 at the same timing (energization period) to emit sound waves having a frequency range of 40 kHz to 130 kHz. Indicated. As described above, when the radiated sound wave exceeds the audible frequency and includes at least a frequency range up to 200 kHz, it can be applied as a sound wave speaker for obtaining a hypersonic effect. The upper limit of the audible frequency is generally 20 kHz.

The driving example of the element is not limited to the above-mentioned example. A drive voltage may be applied only to the piezoelectric vibrators 20 of a plurality of elements that are a part of the elements provided in the sound wave speaker 10 to radiate sound waves in a predetermined frequency range. The frequency range may be changed over time by switching the element to which the drive voltage is applied. The drive voltage may be temporarily applied to only one element.

Further, the resonance frequency of all the elements is set to a frequency exceeding the audible frequency, but the frequency is not limited to this. The resonance frequency may be set as the audible frequency range for a part of the plurality of elements. For example, the opening area of the plurality of cavities 41 may be set so as to emit sound waves in a frequency range exceeding the audible frequency and having an upper limit of 200 kHz and sound waves in a frequency range within the audible frequency range. In this case, one sound wave speaker 10 can be expected to have a hypersonic effect. Further, the resonance frequencies of all the elements may be set within the range of the audible frequency. By configuring the plurality of cavities 41 in the common support 40, the physique of the sound wave speaker 10 can be miniaturized.

By increasing the applied drive voltage, the sound pressure can be increased. In the present embodiment, the plurality of cavities 41 are also open to the back surface 40b of the support 40. The support 40 is fixed to the base member 50 so that gas can flow between the plurality of cavities 41. By communicating the plurality of cavities 41 with each other, a large space is formed on the side opposite to the side from which the sound wave is emitted. Therefore, the resistance of the gas to vibration is smaller and the sound pressure can be increased as compared with the configuration in which the cavities 41 do not communicate with each other. In particular, in the present embodiment, since the cavity 41 communicates with the space around the support 40, it is easy to increase the sound pressure.

In the present embodiment, the cavity 41 has a first cavity region 41a. As described above, the first cavity region 41a has a predetermined thickness (depth) in the Z direction from the main surface 40a, and the planar shape is a region having a constant thickness direction. As described above, when a region having a predetermined thickness and opening to the main surface 40a is provided while maintaining the planar shape, it is easy to define the shape and the area of the vibration region 31 by etching. That is, it is easy to set a desired resonance frequency.

In the present embodiment, the first cavity region 41a has a cylindrical shape having a substantially perfect circular plane. As a result, the vibration region 31 also has a substantially perfect circular shape in a plane. Since it has a perfect circular shape, it is possible to suppress unnecessary vibration and frequency variation and increase the amplitude of a specific frequency. That is, the sound pressure can be increased.

FIG. 4 is a diagram for explaining a standing wave. The alternate long and short dash line shows the specific acoustic impedance due to backside reflection, and the solid line and broken line show the amplitude. The sound wave emitted from the second surface 30b of the vibration region 31 is reflected at the end portion (back surface 40b) of the first cavity region 41a and returns to the vibration region 31. When the distance from the second surface 30b of the vibration region 31 to the end of the first cavity region 41a becomes an odd multiple of λ / 4, the second surface 30b of the vibration region 31 has a phase shift of π between the time of emission and the reflection. Becomes a fixed end. Then, a standing wave is generated at the second surface 30b of the vibration region 31 and at the end of the first cavity region 41a, and the acoustic impedance becomes maximum. As a result, the amplitude of the vibration region 31 is suppressed, and the sound pressure at a specific frequency is lowered.

In the configuration in which a plurality of cavity portions 41 are spatially connected as in the present embodiment, the sound wave is transmitted to the vibration region 31 different from the vibration region 31 that vibrates. The second surface 30b of the vibration region 31 different from the vibration region 31 that radiates the sound wave becomes a reflection surface, and a standing wave may be generated. When the distance from the second surface 30b of the vibration region 31 reflecting the sound wave to the opening end of the first cavity region 41a of the cavity portion 41 defining the vibration region 31 becomes an odd multiple of λ / 4, a standing wave is generated. Occurs. As shown in FIG. 5, the reflected second surface 30b and the sound wave emitting second surface 30b are both nodes, and the end portion of the first cavity region 41a is the abdomen. If the space of the cavity 41 is small, the acoustic impedance becomes large and the influence of the standing wave becomes large. In particular, it is necessary to consider the reflection in the vibration region 31 defined by the cavity 41 having the smallest opening area. The alternate long and short dash line in FIG. 5 shows the emitted sound wave.

FIG. 6 is a diagram showing measurement results of frequency and amplitude for a reference example. In the reference example, the above-mentioned 11 types of elements are individually provided. That is, FIG. 6 shows the measurement result of the configuration in which the cavities corresponding to the respective elements do not communicate with each other. As shown in FIG. 6, 11 peaks were confirmed in the frequency range of 40 kHz to 130 kHz. In the configuration in which the plurality of cavities do not communicate with each other, the reflection at the end of the first cavity region 41a may be considered among the above reflections. By individually designing the distance from the second surface 30b of the vibration region 31 to the end of the first cavity region 41a so as not to be an odd multiple of λ / 4, it is possible to suppress a decrease in sound pressure due to a standing wave. Can be done.

FIG. 7 is a diagram showing an increase in acoustic impedance due to reflection. FIG. 7 is a simulation result. When a plurality of cavities were spatially connected without considering the thickness, an increase in acoustic impedance was confirmed at around 100 kHz, as shown in FIG. 7. This indicates that when a sound wave near 100 kHz is emitted, the condition of standing wave generation is satisfied in the cavity 41 having the smallest opening area. Although not shown for convenience, as in the present embodiment, when the frequency and the amplitude are measured for a configuration in which 11 types of elements are provided in a single sound wave speaker, the amplitude near 100 kHz shown in FIG. 6 decreases. It could be confirmed.

In this embodiment, the thickness t1 is set to be less than λ × 1/4 based on the above findings. As described above, the wavelength λ is a value obtained by dividing the sound velocity c by the upper limit of the frequency range of the sound wave emitted by the sound wave speaker 10, that is, the resonance frequency of the vibration region 31 having the smallest opening area. In this embodiment, it is a value obtained by dividing the sound velocity c by 130 kHz. Since the speed of sound is 331 m / s, the wavelength λ (minimum wavelength) is 2.55 mm in dry air. λ × 1/4 is 638 μm. As described above, the thickness of the support 40 is 300 μm, and the thickness t1 is set to be less than λ × 1/4.

As described above, the wavelength λ is the smallest wavelength in a sound wave in a predetermined frequency range. Therefore, by satisfying t1 <λ × 1/4, it is possible to suppress the generation of a standing wave at any wavelength, that is, at any frequency.

The thickness t1 may be λ × 1/8 or less. According to this, the standing wave can be suppressed more effectively. When emitting a sound wave having a frequency range of 40 kHz to 130 kHz, λ × 1/8 is 319 μm. In the present embodiment, since the thickness of the support 40 (semiconductor substrate 400) is set to 300 μm, the thickness t1 is λ × 1/8 or less.

In the present embodiment, an example in which the vibrating portion 30 includes the insulating film 301 is shown, but the present invention is not limited thereto. The support may be configured to include an insulating film and a semiconductor substrate. In this case, the insulating film is also etched with the semiconductor film as the bottom, and a cavity is formed over the semiconductor substrate and the insulating film. The vibrating portion is composed of a semiconductor film, and a cavity portion is adjacent to the back surface of the semiconductor film.

(Second Embodiment)
This embodiment is a modification based on the preceding embodiment, and the description of the preceding embodiment can be incorporated. In the prior embodiment, the first cavity region 41a coincided with the cavity portion 41. Alternatively, the cavity 41 may have a second cavity region 41b that is continuous with the first cavity region 41a.

FIG. 8 is a cross-sectional view showing the sound wave speaker 10 of the present embodiment. The cavity 41 has a first cavity region 41a and a second cavity region 41b, respectively. The first cavity region 41a does not open to the back surface 40b. In the Z direction, the area from the main surface 40a to the middle of the cavity 41 is the first cavity region 41a. The second cavity region 41b is connected to the first cavity region 41a and is open to the back surface 40b. The second cavity region 41b includes the first cavity region 41a in a plan view.

In the present embodiment, the first cavity region 41a and the second cavity region 41b both form a cylindrical shape having a substantially perfect circular plane. The second cavity region 41b also extends in the Z direction while maintaining a planar shape. The opening area of the back surface 40b of the second cavity region 41b is larger than the opening area of the main surface 40a of the first cavity region 41a. The first cavity region 41a is a reduced diameter region, and the second cavity region 41b is a diameter-expanded region having a diameter longer than that of the first cavity region 41a. The cavity 41 has a stepped structure with a first cavity region 41a and a second cavity region 41b having different diameters.

Further, in the present embodiment, the vibrating portion 30 has the semiconductor film 300. One surface of the semiconductor film 300 forms the first surface 30a, and the surface opposite to the one surface forms the second surface 30b. The support 40 has a semiconductor substrate 400 and an insulating film 401. The insulating film 401 is also etched with the semiconductor film 300 as the bottom, and the hollow portion 41 is formed over the semiconductor substrate 400 and the insulating film 401. One surface of the insulating film 401 forms the main surface 40a. The portion of the semiconductor film 300 adjacent to the cavity 41 (first cavity region 41a) forms the vibration region 31. Other configurations are the same as the configurations described in the prior embodiments.

<Summary of the second embodiment>
In the present embodiment, the cavity portion 41 has the above-mentioned second cavity region 41b. Since the area of the second cavity region 41b is larger than that of the first cavity region 41a, the interface between the first cavity region 41a and the second cavity region 41b serves as a sound wave reflecting surface. This interface corresponds to the end portion of the first cavity region 41a on the back surface 40b side described in the prior embodiment. In FIG. 8, the interface is shown by a alternate long and short dash line. Therefore, by setting the thickness t1 of the first cavity region 41a to less than λ × 1/4 in all the cavity portions 41, a standing wave due to reflection at the end portion (interface) of the first cavity region 41a and a standing wave and It is possible to suppress the generation of standing waves due to reflection on the second surface 30b of the other vibration region 31.

Further, since the cavity portion 41 has the second cavity region 41b, the thickness of the support 40 can be made thicker as compared with the configuration having only the first cavity region 41a. This makes it easier to secure the rigidity of the support 40 even if the thickness t1 is reduced in order to suppress the standing wave. In particular, it becomes easy to set the thickness t1 to λ × 1/8 or less.

Further, by having the second cavity region 41b, the space of the cavity portion 41 is expanded, so that the sound pressure can be increased.

In the present embodiment, the support 40 has a stepped structure formed by the first cavity region 41a and the second cavity region 41b. The stepped structure can reduce the reflection intensity at a specific frequency. Therefore, it is possible to suppress a decrease in sound pressure due to reflection on the back surface side.

<Modification example>
An example is shown in which the support 40 includes the insulating film 401 and the cavity 41 is formed from the semiconductor substrate 400 to the insulating film 401, but the present invention is not limited thereto. Similar to the preceding embodiment (see FIG. 2), in a configuration in which the vibrating portion 30 has the semiconductor film 300 and the insulating film 301 and the support 40 has only the semiconductor substrate 400, even if the above-mentioned second cavity region 41b is applied. good.

An example is shown in which the second cavity region 41b extends in the Z direction while maintaining a planar shape, but the present invention is not limited to this. As shown in FIG. 9, the second cavity region 41b may be configured in multiple stages. In FIG. 9, there are two stages as an example. Of the second cavity region 41b, the first stage opens in the back surface 40b and extends in the Z direction while maintaining a planar shape. The second stage extends in the Z direction while maintaining the planar shape. The second stage is connected to the first stage and the first cavity region 41a. The first stage contains the second stage in a plan view, and the second stage contains the first cavity region 41a in a plan view. According to this, since the number of stages is increased, the reflection intensity of a specific frequency can be further reduced. The number of stages in the second cavity region 41b is not limited to two. It may be 3 or more steps.

The structure for suppressing the decrease in sound pressure is not limited to the above-mentioned step structure. At least a part of the second cavity region 41b may have a tapered structure in which the area is continuously reduced from the back surface 40b toward the main surface 40a. The same effect as the step structure can be expected.

For example, in the example shown in FIG. 10, in the hollow portion 41, the portion inside the insulating film 401 forms the first hollow region 41a, and the portion of the semiconductor substrate 400 forms the second hollow region 41b. The second cavity region 41b has a tapered structure in the total length in the thickness direction thereof. In the example shown in FIG. 11, the second cavity region 41b is provided from the back surface 40b to the middle of the semiconductor substrate 400. The second cavity region 41b has a tapered structure in the total length in the thickness direction thereof. Further, a tapered structure may be formed up to the middle of the second cavity region 41b. The cavity 41 having the above structure can be formed, for example, by a combination of dry etching and anisotropic etching. A tapered structure may be formed up to the middle of the second cavity region 41b.

(Third Embodiment)
This embodiment is a modification based on the preceding embodiment, and the description of the preceding embodiment can be incorporated. In the prior embodiment, the second cavity regions 41b are provided independently of each other in the plurality of cavity portions 41. Alternatively, at least one of the second cavity regions 41b may be a common region connected to the plurality of first cavity regions 41a.

FIG. 12 is a cross-sectional view showing the sound wave speaker 10 of the present embodiment. The cavity 41 has a first cavity region 41a and a second cavity region 41b as in the second embodiment. In the example shown in FIG. 12, the second cavity region 41b is continuous with all the first cavity regions 41a. That is, the second cavity region 41b is a common region in all the cavity portions 41. The support 40 has a plurality of first cavity regions 41a defining a plurality of vibration regions 31 and one second cavity region 41b. The second cavity region 41b is provided so as to include all the first cavity regions 41a in a plan view. The configurations other than the above are the same as the configurations described in the prior embodiments.

<Summary of the third embodiment>
As described above, if at least one of the second cavity regions 41b is a common region connected to the plurality of first cavity regions 41a, the space of the cavity portion 41 can be further expanded. This makes it possible to increase the sound pressure.

In FIG. 12, the second cavity region 41b has a cylindrical shape having a substantially perfect circular plane. As a result, a stepped structure is formed by the first cavity region 41a and the second cavity region 41b. Therefore, the effect described in the preceding embodiment can be obtained. The second cavity region 41b forming the common region may be the tapered structure described in the prior embodiment.

In the present embodiment, an example in which the second cavity region 41b is common to all the cavity portions 41 is shown, but the present invention is not limited to this. The second cavity region 41b may be common to a plurality of cavity portions 41. For example, the second cavity region 41b may be shared with respect to the cavity portions 41 arranged in the X direction. According to this, the second cavity region 41b is shared in each row, and the support 40 has three second cavity regions 41b.

(Other embodiments)
The disclosure in this specification, drawings and the like is not limited to the exemplified embodiments. Disclosures include exemplary embodiments and modifications by those skilled in the art based on them. For example, the disclosure is not limited to the parts and / or combinations of elements shown in the embodiments. Disclosure can be carried out in various combinations. The disclosure can have additional parts that can be added to the embodiment. Disclosures include those in which the parts and / or elements of the embodiment are omitted. Disclosures include the replacement or combination of parts and / or elements between one embodiment and another. The technical scope disclosed is not limited to the description of the embodiments. Some technical scopes disclosed are indicated by the claims description and should be understood to include all modifications within the meaning and scope equivalent to the claims description.

Disclosure in the description, drawings, etc. is not limited by the description of the scope of claims. The disclosure in the description, drawings, etc. includes the technical ideas described in the claims, and further covers a wider variety of technical ideas than the technical ideas described in the claims. Therefore, various technical ideas can be extracted from the disclosure of the description, drawings, etc. without being bound by the description of the scope of claims.

An example is shown in which the cavity 41 has a first cavity region 41a, but the present invention is not limited thereto. The cavity 41 may have a tapered structure over the entire length in the thickness direction thereof. For example, by performing anisotropic etching on the semiconductor substrate 400 with the insulating film 301 as the bottom surface, it is possible to form the hollow portion 41 having a tapered structure in the entire length. In this case, the shape that opens to the main surface 40a of the cavity 41 and the planar shape of the vibration region 31 are substantially rectangular (rectangular). By making the opening areas different from each other, the wideband sound wave speaker 10 can be miniaturized.

An example is shown in which the cavity 41 opens in the back surface 40b of the support 40, but the present invention is not limited to this. For example, by forming an etching hole in the semiconductor film 300 of the vibrating portion 30 and etching the insulating film 401 from the first surface 30a side (so-called sacrificial layer etching), a part of the insulating film 401 is removed and the hollow portion 41 is formed. May be formed. By making the opening areas of the cavities 41 that open in the main surface 40a different from each other, the wideband sound wave speaker 10 can be miniaturized.

An example is shown in which the film on the support 40, specifically, the semiconductor film 300 and the insulating film 301 are used as the vibrating portion 30, but the present invention is not limited to this. For example, a semiconductor substrate may be etched to form a diaphragm (thin wall portion), a portion including the diaphragm may be used as a vibrating portion, and a thick portion connected to the vibrating portion may be used as a support. The cavity formed in the semiconductor substrate opens to the main surface of the support and defines a diaphragm which is a vibration region.

An example is shown in which the plurality of cavities 41 communicate with the surroundings of the support 40, that is, the external atmosphere, but the present invention is not limited thereto. For example, a fixing member 60 (joining material) may be arranged around the entire edge of the back surface 40b of the support 40 to block the external atmosphere from the cavity 41. Even in the blocked state, the wider the space including the cavity 41, the higher the sound pressure can be.

Although an example in which air is arranged in the cavity 41 is shown, the present invention is not limited to this. A gas having a higher density than air may be arranged inside the cavity 41. In this case, the resonance frequency shifts to the low frequency side. Further, a gas having a density lower than that of air may be arranged inside the cavity 41. In this case, the resonance frequency shifts to the high frequency side. By arranging a gas different from air, the frequency may be shifted so that a standing wave does not occur. These gases may be sealed in the cavity 41. The inside of the cavity 41 may be depressurized (vacuum).

10 ... sonic speaker, 20 ... piezoelectric vibrator, 21 ... piezoelectric film, 22 ... upper electrode, 23 ... lower electrode pad, 30 ... vibrating part, 300 ... semiconductor film, 301 ... insulating film, 30a ... first surface, 30b ... Second surface, 31 ... Vibration region, 40 ... Support, 400 ... Support substrate, 401 ... Insulating film, 40a ... Main surface, 40b ... Back surface, 41 ... Cavity, 41a ... First cavity region, 41b ... Second cavity Area, 50 ... base member, 60 ... fixing member

Claims (11)

With a plurality of piezoelectric films (21),
The piezoelectric film is individually arranged on the first surface (30a), the second surface (30b) which is a surface opposite to the first surface, and the first surface, and the piezoelectric film expands and contracts as the piezoelectric film expands and contracts. A vibrating portion (30) having a plurality of vibrating regions (31), and a vibrating portion (30).
The vibration region is defined so that the resonance frequency is different from each other by opening the main surface (40a) and the main surface adjacent to the second surface of the vibration region and having different opening areas in the main surface. A support (40) having a plurality of cavities (41) and supporting the vibrating portion on the main surface.
Equipped with
Of the plurality of cavities, the resonance frequency of the first vibration region, which is the vibration region defined by the cavity having the largest opening area, is set as the lower limit, and is defined by the cavity having the smallest opening area. A sound wave speaker that emits sound waves in the frequency range from the piezoelectric film side, with the resonance frequency of the second vibration region, which is the vibration region, as the upper limit. Further equipped with a base member (50)
The support has a back surface (40b) that is the opposite surface to the main surface.
The plurality of cavities are opened on the back surface thereof, respectively.
The sound wave speaker according to claim 1, wherein the support is fixed to the base member so that gas can flow between the plurality of cavities. The sound wave speaker according to claim 2, wherein the plurality of cavities have a predetermined thickness while maintaining a planar shape, and each has a first cavity region (41a) that defines the vibration region. The first cavity region has a cylindrical shape whose planar shape is a perfect circle.
The sound wave speaker according to claim 3, wherein the plurality of vibration regions have different diameters from each other. Let the wavelength λ be the value obtained by dividing the speed of sound by the resonance frequency of the second vibration region that defines the upper limit.
The sound wave speaker according to claim 3 or 4, wherein the thickness of the first cavity region is less than λ × 1/4. The sound wave speaker according to claim 5, wherein the thickness of the first cavity region is λ × 1/8 or less. Claimed that the plurality of cavities are connected to the first cavity region and open to the back surface thereof, and each has a second cavity region (41b) including the first cavity region in a plan view from the direction of the thickness. Item 6. The sound wave speaker according to any one of Items 3 to 6. The sound wave speaker according to claim 7, wherein each of the plurality of cavities has a stepped structure composed of the first cavity region and the second cavity region. The sound wave speaker according to claim 7, wherein the plurality of cavity portions are provided in the second cavity region and each have a tapered structure in which the area is continuously reduced from the back surface side toward the main surface side. The sound wave speaker according to claim 7, wherein at least one of the second cavity regions is a common region connected to the plurality of first cavity regions. The sound wave speaker according to any one of claims 1 to 10, wherein the opening area of the plurality of cavities is set so that the sound wave exceeds an audible frequency and includes at least a frequency range up to 200 kHz. ..

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