JP5454413B2 - Piezoelectric and parametric array speakers - Google Patents

Description

  The present invention relates to a piezoelectric speaker and a parametric array speaker including a piezoelectric element.

  As a conventional piezoelectric speaker, a housing in which a housing capable of absorbing ultrasonic waves is provided on the back side of an ultrasonic transducer has been proposed (see Patent Document 1 and FIG. 12). Leakage sound waves to the back side of the ultrasonic transducer could be reduced by providing a housing capable of absorbing ultrasonic waves.

JP 2008-20429 A

However, there is a problem that part of the ultrasonic waves penetrates the housing, and the leakage of sound waves is insufficiently reduced.
The present invention was created to solve such problems, and an object of the present invention is to provide a piezoelectric speaker and a parametric array speaker that sufficiently reduce leaked sound waves.

  (1) A piezoelectric speaker for achieving the above object includes a reflection layer, an absorption layer that is laminated on the surface of the reflection layer, and has a higher density of voids included than the reflection layer, and on the surface of the absorption layer. A thick portion and a thin portion whose thickness in the interlayer direction is thinner than the thick portion is distributed in the in-plane direction, and forms a hollow space between the absorbing layer and the thin portion, and And a piezoelectric element that vibrates integrally with the thin portion.

  According to the present invention, the sound wave transmitted to the hollow space as the back cavity by the vibration of the thin portion is absorbed by the absorption layer that encloses the gap. The sound wave penetrating the absorption layer is reflected on the surface of the reflection layer having a void density lower than that of the absorption layer, and is absorbed again by the absorption layer. That is, leakage of the sound wave transmitted to the hollow space due to the vibration of the thin portion can be sufficiently reduced.

(2) In the piezoelectric speaker for achieving the above object, the reflection layer, the absorption layer, and the base are formed of zirconia.
With this configuration, the reflective layer, the absorption layer, and the base can be formed by a single firing. In addition, the thermal expansion coefficients of the reflective layer, absorption layer, and base are the same, and the thermal expansion coefficients of the reflective layer, absorption layer, and base are close to the thermal expansion coefficients of the piezoelectric materials that make up the piezoelectric element, thus preventing warpage it can. Furthermore, since zirconia has a large flexural modulus, the vibration frequency of the thin portion can be increased, and since the bending strength is also large, a large amplitude of the thin portion can be obtained. Since zirconia is a stable substance even at high temperatures, the piezoelectric element can be formed by printing / firing with a simple process without the reflective layer, the absorbing layer, and the base portion reacting with the material constituting the piezoelectric element.

  (3) Sound leakage of sound waves can be sufficiently reduced even in a parametric array speaker in which a plurality of the piezoelectric speakers are arranged.

(1A) is a structural schematic diagram of the piezoelectric speaker of the first embodiment, and (1B) is a sectional view of the piezoelectric speaker of the first embodiment. (2A) to (2D) are cross-sectional views of the piezoelectric speaker of the first embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In addition, the same code | symbol is attached | subjected to the corresponding component in each figure, and the overlapping description is abbreviate | omitted.

(1) Configuration of parametric array speaker:
1A and 1B are a structural schematic diagram and a cross-sectional view showing a configuration of the parametric array speaker 10. FIG. The parametric array speaker 10 is a MEMS (Micro Electro Mechanical Systems) manufactured by using a semiconductor manufacturing process or a printing process, and is housed in a case (not shown) and used as a super-directional speaker for a small electronic device or the like.
In addition, in this specification, when it sees from the base 13, the side by which the piezoelectric element 14 is laminated | stacked is described as an upper side, and the opposite side of an upper side is described as a lower side. Further, unless otherwise indicated, the expression “thickness” means the thickness in the interlayer direction.

The parametric array speaker 10 includes a reflection layer 11, an absorption layer 12, a base portion 13, and a piezoelectric element 14. The reflective layer 11 has a uniform thickness over the entire area in the in-plane direction, and constitutes the lowermost layer of the parametric array speaker 10. The reflective layer 11 is made of zirconia (ZrO ₂ ). For example, the thickness of the reflective layer 11 is 100 μm.

  The absorption layer 12 has a uniform thickness over the entire region in the in-plane direction, and is formed on the upper surface of the reflection layer 11. The absorption layer 12 is formed of zirconia and includes a large number of fine voids. The density of the voids included in the absorption layer 12 is higher than that of the reflective layer 11, and the volume ratio representing the density of the voids is 20 to 80%. For example, the thickness of the absorption layer 12 is 100 μm, and the average diameter of the voids included in the absorption layer 12 is 50 μm.

The base 13 is formed on the upper surface of the absorption layer 12. The base 13 is made of zirconia. In a plan view (in-plane direction), the base portion 13 includes, for example, five circular thin portions 13a and a thick portion 13b that constitutes a region excluding the thin portions 13a. The thin part 13a is thinner than the thick part 13b. The thin portion 13a is formed by providing a cylindrical recess D that is recessed from the lower surface toward the upper side in the base portion 13. Since the thin part 13a is thinner than the thick part 13b, the thin part 13a is less rigid than the thick part 13b and is selectively vibrated. The zirconia constituting the thin portion 13a has a larger flexural modulus (210 GPa) than silicon (Si) and the like, and can vibrate the thin portion 13a at a high frequency. Can output. Moreover, since zirconia has a large bending strength (1120 MPa) among ceramics, a large amplitude of the thin portion 13a can be obtained, and the sound pressure can be increased.
The recess D corresponds to a hollow space formed between the thin portion 13a and the absorption layer 12. For example, the diameter of the thin portion 13a in plan view is 1000 μm, the thickness of the thin portion 13a is 15 μm, and the thickness of the thick portion 13b is 200 μm.

The piezoelectric element 14 includes a lower electrode 14a, a piezoelectric layer 14b, and an upper electrode 14c. The lower electrode 14 a is formed on the entire upper surface of the base portion 13. The lower electrode 14a is formed of gold (Au) or platinum (Pt). For example, the thickness of the lower electrode 14a is 1 μm.
The piezoelectric layer 14b is formed on the surface of the lower electrode 14a. The piezoelectric layer 14b has a uniform thickness, and five circular openings 14b1 and one square opening 14b2 are formed in the piezoelectric layer 14b in plan view. Each circular opening 14b1 is a concentric circle of each thin portion 13a of the base 13 in plan view, and has an opening diameter smaller than each thin portion 13a. That is, the thin portion 13a and the piezoelectric layer 14b overlap in the interlayer direction in an annular region having a predetermined width outside the circular opening 14b1 of the piezoelectric layer 14b in plan view.
The upper electrode 14c is formed on the surface of the piezoelectric layer 14b. The upper electrode 14c has the same pattern as the piezoelectric layer 14b in plan view, and the upper electrode 14c is also formed with five circular openings 14c1 and one square opening 14c2. When the square opening 14b2 of the piezoelectric layer 14b and the square opening 14c2 of the upper electrode 14c overlap in the interlayer direction, the lower electrode 14a is exposed to the upper side, and a conductor (not shown) can be connected to the lower electrode 14a.

  The parametric speaker 1 configured as described above operates as follows. When a drive voltage of a modulated wave obtained by amplitude-modulating an ultrasonic wave carrier wave with an audible sound wave is applied to the upper electrode 14c and the lower electrode 14a of the piezoelectric element 14 via a lead wire (not shown), the piezoelectric layer 14b of the piezoelectric element 14 is applied. As a result, in-plane expansion / contraction and expansion stress occurs. The expansion / contraction / expansion stress generated in the annular region having a predetermined width outside the circular opening 14b1 in the piezoelectric layer 14b is transmitted to each thin portion 13a overlapping the annular region in the interlayer direction, and vibrates each thin portion 13a. Since the lower electrode 14a and the upper electrode 14c of the piezoelectric element 14 are electrically integrated with each other, the thin portions 13a vibrate in the same phase. The ultrasonic wave of the modulated wave is transmitted upward from the vibrating thin part 13a, and an audible sound is generated by the parametric array effect in a narrow range near the upper perpendicular of the thin part 13a due to the strong directivity of the ultrasonic wave. The parametric array effect is due to non-linearity of sound waves, and an audible aerial sound source corresponding to the original sound wave is continuously generated in a linear region near the upper perpendicular of the thin portion 13a by self-demodulation. It is a phenomenon. By such a parametric array effect, the parametric speaker 1 with extremely strong directivity of the audible space of the output sound can be realized. Further, by forming the thin portion 13a with zirconia having a large bending strength, a practical sound pressure can be obtained even with the small parametric speaker 1.

  The ultrasonic waves are also transmitted to the lower side of the thin portion 13a by the vibration of the thin portion 13a. The ultrasonic wave transmitted to the lower side of the thin portion 13 a reaches the absorption layer 12 including a large number of voids and is absorbed by the absorption layer 12. A part of the ultrasonic waves penetrates the absorption layer 12, but is reflected upward at the bonding interface between the absorption layer 12 and the reflection layer 11. The ultrasonic waves reflected upward are again absorbed by the absorption layer 12, and leakage sound waves can be sufficiently reduced.

  Moreover, since the reflection layer 11, the absorption layer 12, and the base 13 are formed of the same material (zirconia), the thermal expansion coefficients of the reflection layer 11, the absorption layer 12, and the base 13 coincide with each other. Further, since the thermal expansion coefficients of the reflective layer 11, the absorption layer 12, and the base portion 13 formed of zirconia approximate the thermal expansion coefficient of the piezoelectric layer 14b formed of zirconate-lead titanate, the parametric array speaker 10 Warpage can be prevented. Therefore, the parametric array speaker 10 can output sound with stable directivity and less energy loss.

(2) Parametric array speaker manufacturing method:
2A to 2E are cross-sectional views showing the manufacturing procedure of the parametric array speaker 10. FIG.
First, as shown in FIG. 2A, green sheets G11 to G13 corresponding to the reflective layer 11, the absorbing layer 12, and the base 13 are prepared. The green sheets G11 to G13 are formed by kneading zirconia, a sintering aid powder, an organic binder, and a solvent into a sheet shape. Here, the green sheet G12 corresponding to the absorbing layer 12 has a higher kneading ratio of the organic binder than the green sheets G12 and G13 corresponding to the reflective layer 11 and the base portion 13. The organic binder is thermally decomposed when the green sheets G11 to G13 are fired, and the space occupied by the organic binder becomes a void. Therefore, the density of the voids included in the absorption layer 12 formed by firing the green sheet G12 is higher than the density of the voids included in the reflective layer 11 and the base 13 formed by firing the green sheets G11 and G13. Can be high.

The green sheet G13 corresponding to the base 13 is constituted by three green sheets G13a to G13c. The uppermost green sheet G13a has a thickness corresponding to the thin portion 13a. That is, since the thickness of the thin part 13a can be managed by the thickness of the green sheet G13a, the thickness accuracy of the thin part 13a can be increased. Accordingly, the vibration characteristics of the thin portions 13a can be matched, and the parametric array effect of the ultrasonic waves emitted from the thin portions 13a can be obtained uniformly.
Of the two lower green sheets G13b and G13c, a region corresponding to the thin portion 13a in plan view is drilled by mechanical drilling such as punching or laser drilling. When each of the green sheets G11 to G13 is prepared, as shown in FIG. 2B, the green sheets G11 to G13 are stacked and fired at 1000 to 1300 ° C., for example, while pressing at 150 MPa in the interlayer direction. Thereby, the reflective layer 11, the absorption layer 12, and the base part 13 can be formed by one baking.

Next, as shown in FIG. 2C, the lower electrode 14a is formed by printing and baking a paste containing an electrode metal powder of gold or platinum over the entire area of the upper surface of the base 13 with a uniform thickness. The firing temperature of the lower electrode 14a is, for example, 900 to 1300 ° C.
Next, as shown in FIG. 2D, a paste containing zirconate-lead titanate powder is printed on the surface of the lower electrode 14a with a uniform thickness and fired to form the piezoelectric layer 14b. The firing temperature of the piezoelectric layer 14b is, for example, 900 to 1300 ° C.
Finally, as shown in FIG. 1B, the upper electrode 14c is formed by printing and baking a paste containing gold or platinum electrode metal powder on the surface of the piezoelectric layer 14b with a uniform thickness. The firing temperature of the upper electrode 14c is, for example, 900-1300 ° C. In addition, the paste corresponding to each layer 14a-14c is printed by performing screen printing using the printing mask which has the opening corresponding to each pattern of the in-plane direction of the lower electrode 14a, the piezoelectric layer 14b, and the upper electrode 14c. Can do.

  As described above, by forming the reflection layer 11, the absorption layer 12, and the base portion 13 with zirconia, the piezoelectric element 14 can be formed by printing and baking. That is, if the reflective layer 11, the absorption layer 12, and the base portion 13 are formed of zirconia, they will not react with lead vaporized during the firing of the piezoelectric layer 14b. If the piezoelectric element 14 is formed by printing and baking, it is not necessary to perform complicated photolithography. Furthermore, by forming the reflective layer 11, the absorption layer 12, and the base portion 13 with the same material zirconia, the thermal expansion coefficients of the respective layers 11 to 13 coincide with each other, and warpage during firing of the piezoelectric element 14 can be prevented. Therefore, the residual stress of the piezoelectric element 14 after firing can be relaxed. Furthermore, since zirconia has a thermal expansion coefficient close to that of zirconate-lead titanate constituting the piezoelectric layer 14b, warpage in the heat treatment step after the formation of the piezoelectric layer 14b can be prevented.

(3) Other embodiments:
The technical scope of the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the present invention. For example, the materials, dimensions, shapes, film forming methods, and pattern transfer methods shown in the above embodiments are merely examples, and it is obvious to those skilled in the art about the possibility of adding or deleting processes or changing the order of processes. Explanation is omitted.

  As another example of a parametric array speaker, two ultrasonic waves having a frequency difference corresponding to an audio wave in the audible range are transmitted from the thin portion 13a, and an audio wave in the audible range is generated by a beat phenomenon generated between the two ultrasonic waves. The configuration of the present invention may be applied to a parametric array speaker that demodulates the signal. In this case, it is necessary to vibrate two or more thin portions 13a at different frequencies by the two piezoelectric elements 14 to which drive voltages can be input independently. The configuration of the present invention can also be applied to piezoelectric speakers other than parametric array speakers. That is, by applying the configuration of the present invention to a piezoelectric speaker provided with one or more thin portions 13a that can vibrate, a piezoelectric speaker with sufficiently reduced leakage sound waves can be provided. That is, the sound wave that can reduce the leakage between the reflection layer 11 and the absorption layer 12 is not limited to the ultrasonic wave, and the effect of the present invention can be obtained in a piezoelectric speaker that directly transmits an audible sound.

Moreover, you may form any one or all of the reflective layer 11, the absorption layer 12, and the base 13 with ceramics other than a zirconia. For example, any or all of the reflective layer 11, the absorption layer 12, and the base 13 are made of alumina (Al ₂ O ₃ ), mullite (3Al ₂ O ₃ .2SiO ₂ ), aluminum nitride (AlN), silicon nitride (Si ₃ N ₄ ) It may be formed of zirconia toughened alumina (Al ₂ O ₃ .ZrO ₂ ), glass ceramic or the like. For example, a piezoelectric speaker can be manufactured by a process similar to that of the above embodiment using a green sheet formed by kneading these ceramic powders. Furthermore, any material can be used as long as the density of voids existing in the absorption layer 12 can be made higher than that of the reflection layer 11. Alternatively, it may be formed of a metal material or a semiconductor material.

  The piezoelectric element 14 may be formed by a method other than printing / firing, such as photolithography. Further, the upper electrode 14c, the piezoelectric layer 14b, and the lower electrode 14a may be fired at once, and further, the upper electrode 14c, the piezoelectric layer 14b, and the lower electrode 14a are fired on the reflective layer 11, the absorbing layer 12, and the base 13. You may carry out simultaneously with baking. Moreover, in the said embodiment, although the piezoelectric element 14 and the thin part 13a overlapped in the interlayer direction in the vicinity of the outer periphery of the thin part 13a, for example, the piezoelectric element 14 and the thin part 13a in the center part of the thin part 13a. Even if they overlap in the interlayer direction, the thin portion 13a can be vibrated. The shape of the thin portion 13a is not limited to a circle but may be a rectangle or the like. Further, the thin portion 13a only needs to be thinner than the thick portion 13b, the base portion 13 may have two or more thicknesses, or the base portion 13 has a continuous thickness change. Also good. The reflective layer 11 is not limited to the one that forms an independent hollow space for each thin portion 13a, but a common hollow space is formed in the plurality of thin portions 13a, and the sound waves transmitted to the common hollow space leak. And the absorption layer 12 may prevent this.

DESCRIPTION OF SYMBOLS 10 ... Parametric array speaker, 11 ... Reflection layer, 12 ... Absorption layer, 13 ... Base part, 13a ... Thin part, 13b ... Thick part, 14 ... Piezoelectric element, 14a ... Lower electrode, 14b ... Piezoelectric layer, 14b1 ... Circular opening , 14b2 ... square opening, 14c ... upper electrode, 14c1 ... circular opening, 14c2 ... square opening, G11-G13 ... green sheet.

Claims (3)

A reflective layer;
An absorption layer laminated on the surface of the reflective layer and having a higher density of voids included than the reflective layer;
Laminated on the surface of the absorbent layer, a thick portion and a thin portion whose thickness in the interlayer direction is thinner than the thick portion is distributed in an in-plane direction, and a hollow space is formed between the absorbent layer and the thin portion. A base forming
A piezoelectric element that vibrates integrally with the thin portion;
Comprising
Piezoelectric speaker. The reflective layer, the absorbing layer, and the base are formed of zirconia.
The piezoelectric speaker according to claim 1. The piezoelectric speakers according to claim 1 or 2 are arranged in a plurality of in-plane directions.
Parametric array speaker.

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