Pressure-wave-generating element

Abstract

This pressure-wave-generating element includes a substrate, a heat insulating layer provided on the substrate, and a heat generating layer provided in the heat insulating layer. The heat insulating layer is positioned between the substrate and the heat generating layer, the substrate includes Si, the heat insulating layer includes an organic material, and the thickness of the heat insulating layer is 1 μm or more.

Description

Pressure wave generating element

[0001] The present disclosure relates to a pressure wave generating element.

[0002] Patent Document 1 describes a pressure wave generating element in which a heat insulating layer made of a porous silicon layer is provided between a silicon substrate and a heating element layer provided on one surface of the silicon substrate. In the pressure wave generating element of Patent Document 1, a metal material with a Young's modulus of not less than 170 GPa is used as the heating element layer. This enables a higher sound pressure output compared to when gold is used as the heating element layer material.

[0003] JP 2006-94399 A

[0004] The pressure wave generating element of Patent Document 1 has room for improvement in terms of increasing sound pressure.

[0005] An object of the present disclosure is to provide a pressure wave generating element that can improve sound pressure.

[0006] A pressure wave generating element according to one aspect of the present disclosure comprises a substrate, an insulating layer provided on the substrate, and a heat generating layer provided on the insulating layer, wherein the insulating layer is located between the substrate and the heat generating layer, the substrate contains Si, the insulating layer contains an organic material, and the thickness of the insulating layer is 1 μm or more.

[0007] According to the present disclosure, a pressure wave generating element capable of improving sound pressure can be provided.

[0008] 1 is a plan view showing a pressure wave generating element 1 according to an embodiment of the present disclosure.

[0009] Various aspects of the present disclosure will now be described.

[0010] A first aspect of the pressure wave generating element comprises a substrate, an insulating layer provided on the substrate, and a heat generating layer provided on the insulating layer, wherein the insulating layer is located between the substrate and the heat generating layer, the substrate contains Si, the insulating layer contains an organic material, and the thickness of the insulating layer is 1 μm or more.

[0011] A pressure wave generating element of a second aspect is the pressure wave generating element of the first aspect, wherein the thickness of the heat insulating layer is less than 50 μm.

[0012] A pressure wave generating element of a third aspect is the pressure wave generating element of the first or second aspect, wherein the heat insulating layer contains polyimide.

[0013] A fourth aspect of the pressure wave generating element is the pressure wave generating element of the third aspect, wherein the ratio of the peak intensity of the imide ring to the peak intensity of the aromatic ring in the heat insulating layer is 0.15 or more.

[0014] The pressure wave generating element of the fifth aspect is the pressure wave generating element of any one of the first to fourth aspects, further comprising an adhesive layer located between the heat insulating layer and the heat generating layer, the adhesive layer containing NiCr, Cr or Ti.

[0015] A sixth aspect of the pressure wave generating element is the pressure wave generating element of the fifth aspect, wherein the arithmetic mean roughness of the heat insulating layer is less than the thickness of the adhesive layer.

[0016] A seventh aspect of the pressure wave generating element is the pressure wave generating element of any one of the first to sixth aspects, wherein the ratio of the thermal conductivity of the substrate to the thermal conductivity of the heat insulating layer is 150 or more.

[0017] An example of the present disclosure will be described below with reference to the accompanying drawings. The following description is merely exemplary in nature and does not limit the present disclosure, its applications, and uses. The accompanying drawings are schematic drawings, and the illustrated configuration and actual products may differ in dimensional ratios, etc.

[0018] 1 and 2 , a pressure wave generating element 1 according to one embodiment of the present disclosure includes a substrate 10, a heat insulating layer 20, and a heat generating layer 30. The heat insulating layer 20 is provided on the substrate 10, and the heat generating layer 30 is provided on the heat insulating layer 20. The heat insulating layer 20 is located between the substrate 10 and the heat generating layer 30. As an example, the substrate 10, the heat insulating layer 20, and the heat generating layer 30 are stacked along a stacking direction (e.g., the Z direction).

[0019] In this embodiment, the pressure wave generating element 1 includes a pair of pads 40 provided on the heat insulating layer 20, and an adhesive layer 50 (see FIG. 2) located between the heat insulating layer 20 and the heat generating layer 30. The adhesive layer 50 contains, for example, NiCr, Cr, or Ti.

[0020] The substrate 10 is made of, for example, a semiconductor or an electrical insulator. Examples of semiconductors include Si. Examples of electrical insulators include glass, ceramics, and polymers.

[0021] The heat insulating layer 20 includes an organic material. In this embodiment, the heat insulating layer 20 has a thickness of 1 μm or more and less than 50 μm, and includes polyimide (for example, the heat insulating layer 20 is made of polyimide). Polyimide is a material whose product of thermal conductivity and heat capacity per volume is smaller than that of porous silicon, for example. Polyimide has a thermal conductivity of 0.3 W / m / K and a heat capacity per volume of 1600 kJ / K / m. ３ Porous silicon has a thermal conductivity of 1 W / m / K and a heat capacity per volume of 700 kJ / K / m ３ The thickness of the heat insulating layer 20 is the dimension of the heat insulating layer 20 in the stacking direction Z.

[0022] The thermal insulating layer 20 may be configured to satisfy one or more of the following conditions (1) to (3), or all of them: (1) The ratio of the peak intensity of the imide ring to the peak intensity of the aromatic ring in the thermal insulating layer 20 is 0.15 or more (peak intensity of imide ring / peak intensity of aromatic ring ≧ 0.15). (2) The arithmetic mean roughness Ra of the thermal insulating layer 20 (for example, the arithmetic mean roughness Ra of the portion of the thermal insulating layer 20 facing the adhesive layer 50) is equal to or less than the thickness of the adhesive layer 50. The thickness of the adhesive layer 50 is the dimension of the adhesive layer 50 in the stacking direction Z. (3) The ratio of the thermal conductivity of the substrate 10 to the thermal conductivity of the thermal insulating layer 20 is 150 or more (thermal conductivity of substrate 10 / thermal conductivity of the thermal insulating layer 20 ≧ 150).

[0023] The heat generating layer 30 is made of a conductive material and is configured to generate heat when an electric current flows through it and radiate pressure waves caused by the periodic expansion and contraction of air. Pads 40 are connected to both sides of the heat generating layer 30 in a direction (e.g., the X direction) intersecting the stacking direction Z. Each pad 40 is made of a conductive material and has a single-layer or multi-layer structure. An electric current is supplied to the heat generating layer 30 via a pair of pads 40.

[0024] The pressure wave generating element 1 can be manufactured, for example, by the following method.

[0025] A polyimide (PI) film (for example, 7 μm thick) is formed on a Si wafer by spin coating using PI varnish. The Si wafer constitutes the substrate 10, and the PI film constitutes the heat insulating layer 20. After the PI film is formed, an inert gas oven is used to heat the Si wafer at 150°C to 350°C for 1 hour, using N ２ The cure is carried out under "ambient" conditions.

[0026] After curing, a laminated film is formed on the PI film by sputtering. When forming the laminated film, a metal mask is used to form the heat generating layer 30. The laminated film is, for example, a laminated film (Au: 20 nm / Cr: 2 nm / PI: 7 μm / Si) in which Cr and Au are stacked in this order from the Si wafer side, with Au constituting the heat generating layer 30 and Cr constituting the adhesion layer 50. The heat generating layer 30 has, for example, a rectangular shape of 3.5 mm × 3.5 mm when viewed in plan along the stacking direction Z. Each side of the heat generating layer 30 extends along the X direction and the Y direction. The Y direction is a direction intersecting the stacking direction Z and the X direction.

[0027] A pair of pads 40 is formed on both sides of the heat generating layer 30. Each pad 40 has, for example, a rectangular shape measuring 4 mm x 1.4 mm in plan view along the stacking direction Z. The long sides of each pad 40 extend along the Y direction, and the short sides of each pad 40 extend along the X direction. The distance between the pair of pads 40 (in other words, the linear distance between the opposing long sides of the pair of pads 40) is, for example, 3.2 mm. Each pad 40 has, for example, a layered structure in which NiCr: 100 nm, NiCu: 200 nm, and Au: 100 nm are layered in this order from the Si wafer side (i.e., an Au / NiCu / NiCr layered structure).

[0028] After the pair of pads 40 are formed, the pressure wave generating element 1 is manufactured by dicing into individual pieces. The pressure wave generating element 1 has, for example, a square shape of 6 mm x 7 mm in plan view along the stacking direction Z. The pressure wave generating element 1 is mounted on a mounting substrate after applying a conductive paste to each pad 40. After mounting on the mounting substrate, the conductive paste is dried at room temperature for 24 hours.

[0029] The ratio of the peak intensity of the imide ring to the peak intensity of the aromatic ring and the average failure power (n=5) were calculated for a plurality of pressure wave generating elements 1 produced by changing the temperature of the inert gas oven after forming the heat insulating layer 20 in the above-mentioned manufacturing method. The ratio of the peak intensity of the imide ring to the peak intensity of the aromatic ring was calculated from the FT-IR spectrum obtained by the ATR method (attenuated total reflection measurement method) using a Spotlight 150 manufactured by PerkinElmer. The absorption peak wave number of the imide ring was 1782 cm －１ The absorption peak wave number of the aromatic ring is 1500 cm －１ The average failure power was calculated from the voltage and resistance of each pressure wave generating element 1 when a voltage was applied to each of the fabricated pressure wave generating elements 1 and the elements were opened.

[0030] As shown in Table 1, it was found that the higher the temperature of the inert gas oven (shown as "heat treatment temperature" in Table 1), the greater the ratio of the peak intensity of the imide ring to the peak intensity of the aromatic ring (shown as "peak intensity ratio" in Table 1). For example, it was found that open circuit failures at low power (for example, around 20 W) can be suppressed by providing the pressure wave generating element 1 with a heat insulating layer 20 in which the ratio of the peak intensity of the imide ring to the peak intensity of the aromatic ring is 0.15 or more.

[0031] The pressure wave generating element 1 can exert the following effects.

[0032] The pressure wave generating element 1 includes a substrate 10, a heat insulating layer 20 provided on the substrate 10, and a heat generating layer 30 provided on the heat insulating layer 20. The heat insulating layer 20 is located between the substrate 10 and the heat generating layer 30. The substrate 10 contains Si, and the heat insulating layer 20 contains an organic material, with a thickness of 1 μm or more. In the pressure wave generating element 1, the heat insulating layer 20 contains an organic material (e.g., an organic material having a smaller product of thermal conductivity and heat capacity per volume than ceramics (e.g., porous silicon)), and the heat insulating layer 20 has a thickness of 1 μm or more, so that the transfer of heat generated in the heat generating layer 30 to areas other than the surrounding air can be suppressed. The pressure wave generating element 1 generates sound by instantaneously expanding and contracting the surrounding air using the heat generated in the heat generating layer 30. Therefore, by preventing the heat generated in the heat generating layer 30 from being transferred to areas other than the surrounding air, sound can be generated efficiently and sound pressure can be improved. Since the substrate 10 contains Si, which has high thermal conductivity, the steady-state temperature of the heat insulating layer 20 can be lowered, and a decrease in sound pressure can be suppressed. In other words, the above configuration makes it possible to realize a pressure wave generating element 1 that can improve sound pressure.

[0033] The thickness of the heat insulating layer 20 is less than 50 μm. If the heat insulating layer 20 is fabricated to have a thickness of 50 μm or more, stress may cause the substrate 10 and the heat insulating layer 20 to peel off during processing (e.g., during singulation). In other words, by making the thickness of the heat insulating layer 20 less than 50 μm, it is possible to more reliably realize a pressure wave generating element 1 that can improve sound pressure.

[0034] The heat insulating layer 20 contains polyimide. Polyimide has a high Tg (glass transition temperature) and decomposition temperature, so that the heat insulating layer 20 containing polyimide can be endowed with heat resistance against instantaneous heating.

[0035] If a polyimide having a ratio of the peak intensity of the imide ring to the peak intensity of the aromatic ring of less than 0.15 is used for the insulating layer 20, the imidization of the insulating layer 20 will be insufficient, and at the temperature at which the pressure wave generating element 1 is used (assumed to be below 100°C), the imidization of the insulating layer 20 may progress due to heat generated when the pressure wave generating element 1 is driven. As the imidization progresses, water is produced as a by-product, and the evaporation of the water may cause the insulating layer 20 to expand, potentially resulting in an open circuit failure. In the pressure wave generating element 1, the ratio of the peak intensity of the imide ring to the peak intensity of the aromatic ring in the insulating layer 20 is 0.15 or greater, so the insulating layer 20 is sufficiently imidized, and the imidization of the insulating layer 20 is suppressed at the temperature at which the pressure wave generating element 1 is used. As a result, sufficient power can be applied to the pressure wave generating element, thereby suppressing failures caused by low applied power.

[0036] The pressure wave generating element 1 includes an adhesive layer 50 located between the heat insulating layer 20 and the heat generating layer 30, and the adhesive layer 50 contains NiCr, Cr, or Ti. With this configuration, peeling of the heat generating layer 30 can be suppressed.

[0037] The arithmetic mean roughness of the heat insulating layer 20 is less than the thickness of the adhesive layer 50. With this configuration, peeling of the heat generating layer 30 can be more reliably suppressed.

[0038] If the ratio of the thermal conductivity of the substrate 10 to that of the insulating layer 20 is less than 150, the heat generated in the heat-generating layer 30 may escape to the substrate 10 side, or the steady-state temperature of the heat-generating layer 20 may increase, preventing the heat-generating layer 30 from cooling quickly, resulting in a decrease in sound pressure. In the pressure wave generating element 1, the ratio of the thermal conductivity of the substrate 10 to that of the insulating layer 20 is 150 or more, which prevents the heat generated in the heat-generating layer 30 from moving outside the surrounding air, thereby more reliably preventing a decrease in sound pressure.

[0039] The pressure wave generating element 1 can be configured as follows.

[0040] The thickness of the heat insulating layer 20 may be 1 μm or more, and is not limited to being less than 50 μm.

[0041] The thermal insulating layer 20 does not have to include polyimide.

[0042] The arithmetic mean roughness of the heat insulating layer 20 does not have to be less than the thickness of the adhesive layer 50 .

[0043] The adhesion layer 50 does not need to contain NiCr, Cr, or Ti.

[0044] Any of the various embodiments or modifications described above can be combined appropriately to achieve the effects of each. In addition, combinations of embodiments, combinations of examples, or combinations of embodiments and examples are possible, and combinations of features of different embodiments or examples are also possible.

[0045] Although the present disclosure has been described in each embodiment with a certain degree of detail, the disclosed contents of these embodiments may vary in structural details, and changes in the combination and order of elements in each embodiment may be made without departing from the scope and spirit of the claimed disclosure.

[0046] REFERENCE SIGNS LIST 1 pressure wave generating element 10 substrate 20 heat insulating layer 30 heat generating layer 40 pad 50 adhesive layer

Claims

1. A pressure wave generating element comprising: a substrate; a heat insulating layer provided on the substrate; and a heat generating layer provided on the heat insulating layer, wherein the heat insulating layer is located between the substrate and the heat generating layer, the substrate contains Si, the heat insulating layer contains an organic material, and the heat insulating layer has a thickness of 1 μm or more.

2. The pressure wave generating element according to claim 1, wherein the thickness of the heat insulating layer is less than 50 μm.

3. The pressure wave generating element according to claim 1 or 2, wherein the heat insulating layer comprises polyimide.

4. A pressure wave generating element according to claim 3, wherein the ratio of the peak intensity of the imide ring to the peak intensity of the aromatic ring in said heat insulating layer is 0.15 or more.

5. A pressure wave generating element according to any one of claims 1 to 4, comprising an adhesive layer located between the heat insulating layer and the heat generating layer, the adhesive layer containing NiCr, Cr or Ti.

6. The pressure wave generating element according to claim 5, wherein the arithmetic mean roughness of the heat insulating layer is less than the thickness of the adhesive layer.

7. A pressure wave generating element according to any one of claims 1 to 6, wherein the ratio of the thermal conductivity of the substrate to the thermal conductivity of the heat insulating layer is 150 or more.

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