Pressure wave generating element

Abstract

This pressure wave generating element comprises a substrate, a heat insulating layer that is provided on the substrate, and a heat generating layer that is provided on the heat insulating layer such that the heat insulating layer is positioned between the heat generating layer and the substrate. Cr is dispersed in the heat generating layer.

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 heat generating layer provided on one surface side of the silicon substrate.

[0003] JP 2006-94399 A

[0004] The pressure wave generating element of Patent Document 1 does not take into consideration the suppression of changes in resistance value in a high temperature environment.

[0005] An object of the present disclosure is to provide a pressure wave generating element that can suppress changes in resistance value in a high-temperature environment.

[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 so that the insulating layer is positioned between the substrate and the insulating layer, with Cr diffused into the heat generating layer.

[0007] According to the present disclosure, it is possible to provide a pressure wave generating element that can suppress changes in resistance value in a high-temperature environment.

[0008] FIG. 1 is a plan view showing a pressure wave generating element according to one embodiment of the present disclosure. FIG. 2 is a cross-sectional view taken along line II-II in FIG. 1. FIG. 3 is a flowchart illustrating an example of a manufacturing method for the pressure wave generating element of FIG. 1. FIG. 1 is a first view showing a cross-sectional image and EDX mapping of a heat generating layer of an example embodiment. FIG. 2 is a second view showing a cross-sectional image and EDX mapping of a heat generating layer of an example embodiment. FIG. 3 is a third view showing a cross-sectional image and EDX mapping of a heat generating layer of an example embodiment. FIG. 1 is a first view showing a cross-sectional image and EDX mapping of a heat generating layer of a comparative example. FIG. 2 is a second view showing a cross-sectional image and EDX mapping of a heat generating layer of a comparative example. FIG. 3 is a third view showing a cross-sectional image and EDX mapping of a heat generating layer of a comparative example.

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

[0010] The pressure wave generating element of the first aspect comprises a substrate, an insulating layer provided on the substrate, and a heat generating layer provided on the insulating layer so that the insulating layer is positioned between the substrate and the insulating layer, and Cr is diffused into the heat generating layer.

[0011] The pressure wave generating element of the second aspect is the pressure wave generating element of the first aspect, wherein Cr is contained in a surface of the heat generating layer opposite to a surface facing the heat insulating layer.

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

[0013] A fourth aspect of the pressure wave generating element is the pressure wave generating element of the second or third aspect, wherein the heat generating layer contains Au, and the ratio of Cr to Au on the surface of the heat generating layer is 0.1 or more.

[0014] A fifth aspect of the manufacturing method is a method for manufacturing a pressure wave generating element comprising a substrate, an insulating layer provided on the substrate, and a heat generating layer provided on the insulating layer, the insulating layer being located between the substrate and the heat generating layer, the heat generating layer containing Au and Cr, wherein a laminated film is formed on the insulating layer in which Cr and Au are stacked in order from the substrate side, and the laminated film is heat treated to form the heat generating layer.

[0015] 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.

[0016] 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).

[0017] 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 (not shown) located between the heat insulating layer 20 and the heat generating layer 30. The adhesive layer contains, for example, NiCr, Cr, or Ti.

[0018] 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.

[0019] The heat insulating layer 20 includes, for example, an organic material. In this embodiment, the heat insulating layer 20 includes polyimide (for example, the heat insulating layer 20 is made of polyimide).

[0020] The heat generating layer 30 is formed of a conductive material and is configured to generate heat when an electric current flows through it when electrically driven, thereby radiating pressure waves caused by the periodic expansion and contraction of air. Cr is diffused into the heat generating layer 30. For example, the heat generating layer 30 has a stacked structure of Cr oxide / AuCr / Cr, Cr oxide / AuCr, or Cr oxide / Au / Cr. The heat generating layer 30 contains Cr (in this embodiment, Cr oxide) on a surface 31 located opposite the surface facing the thermal insulating layer 20 in the stacking direction Z. As an example, the heat generating layer 30 is configured so that the ratio of Cr to Au (Cr / Au ratio) on the surface 31 of the heat generating layer 30 is 0.1 or greater. Cr is more diffused in a heat generating layer 30 with a Cr / Au ratio of 0.1 or greater than in a heat generating layer 30 with a Cr / Au ratio of less than 0.1.

[0021] 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 formed of a conductive material and has a single-layer structure or a multi-layer structure. In this embodiment, each pad 40 has a stacked structure of Au / NiCu / NiCr. Current is supplied to the heat generating layer 30 via a pair of pads 40.

[0022] An example of a method for manufacturing the pressure wave generating element 1 will be described with reference to Fig. 3. In this manufacturing method, all steps may be performed automatically by controlling the manufacturing device using a program or the like, or some or all of the steps may be performed manually.

[0023] As shown in Fig. 3, a polyimide (PI) film (for example, 7 µm thick) is formed on a Si wafer by spin coating using PI varnish (step S1). The Si wafer constitutes the substrate 10, and the PI film constitutes the heat insulating layer 20. After the PI film is formed, the wafer is heated in an inert gas oven at 150°C to 350°C for 1 hour under N ２ The cure is carried out under "ambient" conditions.

[0024] After the PI film is formed, the heat generating layer 30 is formed on the PI film (step S2). The heat generating layer 30 is formed by using a metal mask when forming a laminated film on the PI film by sputtering. 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 laminated in this order from the Si wafer side, with Au constituting the heat generating layer 30 and Cr constituting the adhesion layer. The heat generating layer 30 has, for example, a rectangular shape measuring 3.5 mm x 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.

[0025] A pair of pads 40 are formed on the heat generating layer 30 (step S3). Each pad 40 has, for example, a rectangular shape measuring 4 mm x 1.4 mm in plan view along the stacking direction Z, and is formed on both sides of the heat generating layer 30. 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).

[0026] After the pair of pads 40 is formed, the device is diced into individual pieces (step S4). The individual pieces have, for example, a square shape of 6 mm x 7 mm in plan view along the stacking direction Z. The individual pieces are heated in an inert gas oven at 200°C for 24 hours with N ２The pressure wave generating element 1 is manufactured by performing an aging treatment under the condition of "heat-sensitive atmosphere" and heating the heat generating layer 30 (step S5). In the Au / Cr layer of the laminated film, Cr diffuses due to heat, and an AuCr alloy is formed. Heating the Au / Cr layer through the aging treatment promotes the alloying of AuCr.

[0027] The resistance change rate of a pressure wave generating element 1 (hereinafter referred to as an example) manufactured using the above-described manufacturing method was calculated and compared with the resistance change rate of a pressure wave generating element (hereinafter referred to as a comparative example) manufactured using the above-described manufacturing method without aging treatment, as shown below. The example and comparative example have the same configuration except for whether or not aging treatment was performed. - High-temperature tests were conducted to measure the resistance values ​​of the example and comparative example. Specifically, the example and comparative example were placed in a temperature bath set at 85°C, and 114 hours and 316 hours after placement, the example and comparative example were removed from the temperature bath and their resistance values ​​were measured. - The resistance values ​​of the example and comparative example were measured using a four-terminal method using a digital multimeter (Agilent 34410A). The resistance change rate ΔR=(R316h−R114h) / R114h×100 was calculated from the resistance value R114h 114 hours after input and the resistance value R316h 316 hours after input.

[0028] As shown in Table 1 below, the resistance change rate decreased in the comparative example, but did not decrease in the example.

[0029] The Au(111) peak positions were confirmed in the heat generating layers of the Examples and Comparative Examples. The Au(111) peak positions were confirmed by X-ray diffraction using a SmartLab Small Region XRD. As shown in Table 1 below, it was found that the Au(111) peak position in the heat generating layer of the Examples was shifted to a higher angle side than the Au(111) peak position in the heat generating layer of the Comparative Examples. In other words, it was found that the AuCr alloying was more advanced in the heat generating layer of the Examples than in the heat generating layer of the Comparative Examples, and that Cr had diffused into the heat generating layer.

[0030] The surface compositions of the heat generating layers in the examples and comparative examples were analyzed. The surface composition analysis of the heat generating layers was performed by qualitative analysis (wide scan spectrum measurement) and quantitative analysis (narrow scan spectrum measurement) using XPS (X-ray photoelectron spectroscopy) using a Quantes (measurement area: 100 μmφ, analysis depth: several nm) manufactured by ULVAC-PHI, Inc. As shown in Table 2 below, it was found that the surface of the heat generating layer in the examples contained more Cr than the surface of the heat generating layer in the comparative examples.

[0031] The cross sections of the heating layers of the example and comparative example were observed. The cross section observation of the heating layer was performed by FIB microsampling using an FE-TEM / EDX (JEOL JEM-F200 / Noran system 7). The sampled target area was used as the TEM observation material. Figures 4 to 6 show cross section images (STEM bright field images) and EDX mapping of the heating layer of the example, and Figures 7 to 9 show cross section images (STEM bright field images) and EDX mapping of the heating layer of the comparative example. As shown in Figures 4 to 9, Cr was confirmed to have diffused into the surface of the Au layer and heating layer in the heating layer of the example, but no Cr diffusion was confirmed in the heating layer of the comparative example.

[0032] The pressure wave generating element 1 can exert the following effects.

[0033] The pressure wave generating element 1 comprises 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 so that the heat insulating layer 20 is positioned between the substrate 10. Cr is diffused into the heat generating layer 30. With this configuration, it is possible to realize a pressure wave generating element 1 that can suppress changes in resistance value in a high-temperature environment.

[0034] Cr is contained in the surface 31 of the heat generating layer 30. With this configuration, it is possible to more reliably realize a pressure wave generating element 1 that can suppress changes in resistance value in a high-temperature environment.

[0035] Cr oxide is contained in the surface 31 of the heating layer 30. By forming Cr oxide (passive film) on the surface 31 of the heating layer 30, the progress of Cr oxide formation in the heating layer 30 can be suppressed, and changes in the resistance value can be suppressed. In addition, the Cr oxide (passive film) can suppress galvanic corrosion.

[0036] The heat generating layer 30 contains Au, and the ratio of Cr to Au on the surface 31 of the heat generating layer 30 is 0.1 or more. With this configuration, it is possible to more reliably realize a pressure wave generating element 1 that can suppress changes in resistance value in high-temperature environments.

[0037] The manufacturing method of the pressure wave generating element 1 can achieve the following effects.

[0038] The manufacturing method of the pressure wave generating element 1 includes the steps of forming a laminated film in which Cr and Au are laminated in this order from the substrate 10 side on the heat insulating layer 20, and then heat-treating the laminated film to form the heat generating layer 30. With this configuration, it is possible to manufacture a pressure wave generating element 1 that can suppress changes in resistance value in a high-temperature environment.

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

[0040] It is sufficient that Cr is diffused in the heat generating layer 30. For example, the surface 31 of the heat generating layer 30 may not contain Cr or may not contain Au, or the ratio of Cr to Au in the surface 31 of the heat generating layer 30 may be less than 0.1.

[0041] 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.

[0042] 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.

[0043] REFERENCE SIGNS LIST 1 pressure wave generating element 10 substrate 20 heat insulating layer 30 heat generating layer 31 surface 40 pad

Claims

1. A pressure wave generating element comprising: a substrate; an insulating layer provided on the substrate; and a heat generating layer provided on the insulating layer so that the insulating layer is positioned between the substrate and the insulating layer, wherein Cr is diffused into the heat generating layer.

2. A pressure wave generating element according to claim 1, wherein Cr is contained in the surface of the heat generating layer opposite to the surface facing the heat insulating layer.

3. A pressure wave generating element according to claim 1 or 2, wherein the surface of the heat generating layer contains chromium oxide.

4. A pressure wave generating element according to claim 2 or 3, wherein the heat generating layer contains Au, and the ratio of Cr to Au on the surface of the heat generating layer is 0.1 or more.

5. A method for manufacturing a pressure wave generating element comprising: 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, and the heat generating layer contains Au and Cr, comprising forming a laminated film on the insulating layer in which Cr and Au are stacked in order from the substrate side, and heat treating the laminated film to form the heat generating layer.

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