Sound wave device and manufacturing process for it

Abstract

Sound wave device (1), comprising: a piezoelectric substrate (3) with an electrode formation surface (3a) and an IDT electrode (2) provided on the electrode formation surface (3a) of the piezoelectric substrate (3), wherein the IDT electrode (2) comprises a near contact layer (4) provided on the electrode formation surface (3a) of the piezoelectric substrate (3) and a main electrode layer (6) arranged on the near contact layer (4), wherein the near contact layer (4) comprises a first layer (4A) in close contact with the piezoelectric substrate (3) and a second layer (4B) in close contact with the main electrode layer (6), wherein the first layer (4A) has a first lateral surface (4Ac) and the second layer (4B) has a second lateral surface (4Bc), wherein at least parts of the first and second lateral surfaces (4Ac, 4Bc) are inclined relative to a normal direction (Z) of the electrode formation surface (3a) such that a region of a surface of the second layer (4B), wherein the surface is in close contact with the main electrode layer (6), is smaller than a region of a surface of the first layer (4A), wherein the surface is in close contact with the piezoelectric substrate (3), and assuming that the angles (θ1, θ2) formed by the parts inclined with respect to the normal direction (Z) of the electrode formation surface (3a) are defined as the inclination angles of the first and second lateral surfaces (4Ac, 4Bc), the inclination angle (θ2) of the second lateral surface (4Bc) is smaller than the inclination angle (θ1) of the first lateral surface (4Ac).

Description

TECHNICAL AREA

[0001] The present invention relates to a sound wave device and a manufacturing method for the sound wave device. STATE OF THE ART

[0002] Sound wave devices are still widely used today in mobile phones and other devices. For example, JP 2001-217672A discloses an example of a sound wave device that includes an IDT (interdigital transducer) electrode. The disclosed sound wave device includes a piezoelectric substrate, an intermediate layer arranged on the piezoelectric substrate, and an electrode film arranged on the intermediate layer.

[0003] US Patent 2009 / 0121584A1 discloses a surface acoustic wave (SAW) element comprising an inductively coupled membrane (ICD) electrode with electrode fingers on a piezoelectric substrate. These fingers are formed by laminating an interlayer and an electrode layer with a higher coefficient of thermal expansion than the interlayer. The electrode fingers have a trapezoidal cross-section that widens towards the piezoelectric substrate. Technical problem

[0004] When the sound wave device of the type disclosed in JP 2001-217 672 A is manufactured using a deposition process, a metal film for the interlayer and a metal film for the electrode film are deposited onto the piezoelectric substrate and a resist structure, respectively. A metal with a high melting point is used as the metal for the interlayer. Therefore, it sometimes occurs that during an interlayer formation step, the resist structure is severely deformed due to radiant heat from a deposition source and heat conduction from the deposited particles. In some cases, such deformation causes a side face of the interlayer to be significantly tilted. This can lead to an increase in electrode film distortion caused by the excitation of the IDT electrode and a deterioration of the intermodulation distortion (IMD) characteristics.

[0005] An object of the present invention is to provide a sound wave device in which distortion of an IDT electrode caused by the excitation of a sound wave can be reduced regardless of the melting point of the metal used for the above-mentioned intermediate layer, and in which the IMD properties can be improved, and to provide a manufacturing method for the sound wave device. Solution to the problem

[0006] According to a general embodiment of the present invention, a sound wave device is provided comprising a piezoelectric substrate with an electrode formation surface and an IDT electrode arranged on the electrode formation surface of the piezoelectric substrate, wherein the IDT electrode comprises a near-contact layer arranged on the electrode formation surface of the piezoelectric substrate and a main electrode layer arranged on the near-contact layer, wherein the near-contact layer comprises a first layer in direct contact with the piezoelectric substrate and a second layer in direct contact with the main electrode layer, wherein the first layer has a first side surface and the second layer has a second side surface, wherein at least parts of the first and second side surfaces are inclined relative to a normal direction of the electrode formation surface such thatthat a region of a surface of the second layer, where the surface is in direct contact with the main electrode layer, is smaller than a region of a surface of the first layer, where the surface is in direct contact with the piezoelectric substrate, and wherein, assuming that angles formed by the inclined parts of the first and second side surfaces with respect to the normal direction of the electrode formation surface are defined as the inclination angles of the first and second side surfaces respectively, the inclination angle of the second side surface is smaller than the inclination angle of the first side surface.

[0007] In a specific embodiment of the present invention, the main electrode layer of the sound wave device described above has a side surface, and assuming that an angle formed by the side surface of the main electrode layer with respect to the normal direction of the electrode formation surface of the piezoelectric substrate is defined as an inclination angle of the side surface of the main electrode layer, the inclination angle of the side surface of the main electrode layer is no greater than the inclination angle of the second side surface. In this case, distortion of the main electrode layer caused by the excitation of a sound wave can be further reduced.

[0008] In a further specific embodiment of the present invention, in the sound wave device described above, the elastic modulus of a metal forming the near-contact layer is greater than the elastic modulus of a metal forming the main electrode layer. In this case, the distortion of the main electrode layer caused by the excitation of the sound wave can be effectively reduced.

[0009] In a further specific embodiment of the present invention, in the sound wave device described above, the melting point of a metal forming the near-contact layer is at least as high as the melting point of a metal forming the main electrode layer. In this case, the distortion of the main electrode layer caused by the excitation of the sound wave can be reduced more reliably.

[0010] In a further specific embodiment of the present invention, the near-contact layer of the sound wave device described above consists of either NiCr or Ti, and the main electrode layer consists of Al. In this case, the distortion of the main electrode layer caused by the excitation of the sound wave can be further reduced.

[0011] The present invention further provides a manufacturing method for a sound wave device in which an IDT electrode, comprising a near-contact layer and a main electrode layer, is arranged on a piezoelectric substrate, wherein the manufacturing method comprises the steps of producing the piezoelectric substrate, which has an electrode formation surface, and forming the IDT electrode on the electrode formation surface of the piezoelectric substrate, wherein the step of forming the IDT electrode comprises these steps: laminating a resist layer on the electrode formation surface of the piezoelectric substrate, structuring the resist layer, and laminating a metal film for the near-contact layer on both the piezoelectric substrate and the resist layer by a vapor deposition process.Laminating a metal film for the main electrode layer onto the metal film for the near-contact layer by a vapor deposition process, and detaching the resist layer from the piezoelectric substrate, wherein the near-contact layer comprises a first layer in direct contact with the piezoelectric substrate and a second layer in direct contact with the main electrode layer, wherein the first layer has a first side surface, wherein the second layer has a second side surface, and wherein in the step of laminating the metal film for the near-contact layer, the metal film for the near-contact layer is laminated onto both the piezoelectric substrate and the resist layer, while conditions of the vapor deposition process are modified to form the first and second side surfaces in a state inclined relative to a normal direction of the electrode formation surface, and to form a region of a surface of the second layer.The area where the surface is in direct contact with the main electrode layer should be designed smaller than the area of ​​the first layer where the surface is in direct contact with the piezoelectric substrate. Assuming that the angles formed by the first and second side surfaces with respect to the normal direction of the electrode formation surface are defined as the inclination angles of the first and second side surfaces, respectively, the inclination angle of the second side surface should be smaller than the inclination angle of the first side surface. In this case, the distortion of the main electrode layer caused by the excitation of the sound wave can be further reduced.

[0012] In a further specific embodiment of the present invention, during the lamination step of the metal film for the near-contact layer, both on the piezoelectric substrate and on the resist layer in the manufacturing process for the sound wave device described above, the film formation rate in the deposition process is set to be slower when the second layer is formed than when the first layer is formed. In this case, the distortion of the main electrode layer caused by the excitation of the sound wave can be reduced more reliably. Advantageous effects of the invention

[0013] According to the present invention, a sound wave device can be obtained in which the distortion of the IDT electrode caused by the excitation of the sound wave can be reduced, and in which the IMD properties can be improved. A manufacturing method for the sound wave device can also be obtained. BRIEF DESCRIPTION OF THE DRAWING Fig. Figure 1 is a front sectional view of a sound wave device according to a first embodiment of the present invention. Fig. 2(a) is an enlarged front sectional view of an IDT electrode in the first embodiment of the present invention, and Fig. 2(b) is a partially opened, enlarged front sectional view of the IDT electrode in the first embodiment of the present invention. Fig. Figure 3 is an enlarged front sectional view of an IDT electrode in a comparative example. Fig. 4(a) and Fig. 4(b) are diagrams showing relations between a position of an electrode finger of the IDT electrode along a propagation direction of a sound wave and an S4 component of the distortion in an area of ​​a main electrode layer on the side closer to the piezoelectric substrate in the first embodiment of the present invention and the comparative example. Fig. Figure 5 is a curve diagram showing a relationship between the S4 component of the distortion and a level of a third harmonic. Fig. Figures 6(a) to 6(c) are partially opened, cutaway front views of the IDT electrode, which illustrate a manufacturing method for the sound wave device according to the first embodiment of the present invention. Fig. 7(a) and Fig. Figure 7(b) shows partially opened, cutaway front views of the IDT electrode, which illustrate the manufacturing process for the sound wave device according to the first embodiment of the present invention. Fig. Figure 8 is a front sectional view of an IDT electrode in a second embodiment of the present invention. DESCRIPTION OF EXECUTION FORMS

[0014] The present invention is illustrated by the following description of practical embodiments of the present invention with reference to the drawings.

[0015] It should be noted that the embodiments disclosed in this description are merely illustrative and that it is optional to partially replace or combine individual components between the different embodiments.

[0016] Fig. Figure 1 is a front sectional view of a sound wave device according to a first embodiment of the present invention.

[0017] The sound wave device 1 contains a piezoelectric substrate 3. The piezoelectric substrate 3 consists of LiTaO3. It should be noted that the materials of the piezoelectric substrate are not limited to specific types and that the piezoelectric substrate can consist of a suitable combination of piezoelectric single crystals or piezoelectric ceramics. More specifically, the piezoelectric substrate can consist of, for example, LiNbO3, KNbO3, quartz, langasite, ZnO, PZT (piezoelectric zirconium tanate), or lithium tetraborate.

[0018] The piezoelectric substrate 3 has an electrode formation area 3a. An IDT electrode 2 is formed on the electrode formation area 3a. A sound wave is excited when an alternating voltage is applied to the IDT electrode 2. In this embodiment, reflectors 8 are arranged on both sides of the IDT electrode 2 in one direction of sound wave propagation. With such an arrangement, a single-port sound wave resonator is formed. The reflectors do not always need to be present. Fig. 2(a) is an enlarged front sectional view of an IDT electrode in the first embodiment. Fig. 2(b) is a partially opened, enlarged front sectional view of the IDT electrode in the first embodiment. More precisely, each of the Fig. 2(a) and Fig. 2(b), on an enlarged scale, one of several electrode fingers of the IDT electrode. This applies in a similar way to Fig. 3, Fig. 6(a) to 6(c), Fig. 7(a) and Fig. 7(b) and Fig. 8, which will be described later.

[0019] As in Fig. As illustrated in Figure 2(a), the IDT electrode 2 comprises a near-contact layer 4 arranged on the electrode formation surface 3a of the piezoelectric substrate 3. A main electrode layer 6 is arranged on the near-contact layer 4. The near-contact layer 4 has a higher adhesion to the piezoelectric substrate 3 than the main electrode layer 6 has to the piezoelectric substrate 3. The near-contact layer 4 contains a first layer 4A in direct contact with the piezoelectric substrate 3. The near-contact layer 4 further contains a second layer 4B in direct contact with the main electrode layer 6. The first layer 4A and the second layer 4B are formed continuously in a normal direction Z to the electrode formation surface 3a.

[0020] In this embodiment, the near-contact layer 4 consists of Ti. Although the materials of the near-contact layer are not limited to specific ones, the near-contact layer preferably consists of a suitable metal with high adhesion to the piezoelectric substrate. More precisely, the near-contact layer advantageously consists, for example, of Ti, Cr, NiCr, Zr, Ta, W, or Mo.

[0021] In this description, the main electrode layer 6 serves as a dominant electrode layer during sound wave excitation. In this embodiment, the main electrode layer 6 consists of Al. The main electrode layer preferably consists of a suitable metal with low resistance. More precisely, the main electrode layer advantageously consists of, for example, Al, Cu, Au, or Ag. The resistance to stress migration can be improved by adding another element to the metal forming the main electrode layer. For example, an alloy containing Al as a major component and to which Cu is added is preferably used as the material for the main electrode layer.

[0022] In this embodiment, the near-contact layer 4 has a thickness of 30 nm, and the main electrode layer 6 has a thickness of 430 nm. A wavelength, specified by a distance between the electrode fingers of the IDT electrode 2, is 4.6 µm. The IDT electrode 2 has a metallization ratio of 0.5. The thicknesses of the individual layers of the IDT electrode, as well as the wavelength and metallization ratio of the IDT electrode, are not limited to specific values.

[0023] The first layer 4A of the near-contact layer 4 has a first side surface 4Ac. The second layer 4B has a second side surface 4Bc. The first and second side surfaces 4Ac and 4Bc are each inclined relative to the normal direction Z of the electrode formation surface 3a. More precisely, the first and second side surfaces 4Ac and 4Bc are inclined such that a region of a surface of the second layer 4B, where the surface is in direct contact with the main electrode layer 6, is smaller than a region of a surface of the first layer 4A, where the surface is in direct contact with the piezoelectric substrate 3. It is only required that at least portions of the first and second side surfaces are inclined relative to the normal direction Z of the electrode formation surface 3a. Furthermore, the main electrode layer 6 has a side surface 6c.

[0024] The angles formed by the first and second side surfaces 4Ac and 4Bc with respect to the normal direction Z of the electrode formation surface 3a are defined here as the inclination angles of the first and second side surfaces 4Ac and 4Bc, respectively. More precisely, as in Fig. Figure 2(b) illustrates that an angle formed between a dash-dot-dash line A extending in the normal direction Z of the electrode formation surface and the first side surface 4Ac is an angle of inclination θ1 of the first side surface 4Ac. Likewise, an angle formed between a dash-dot-dash line B and the second side surface 4Bc is an angle of inclination θ2 of the second side surface 4Bc. In the case where parts of the first and second side surfaces are inclined relative to the normal direction of the electrode formation surface, the angles formed by the inclined parts of the first and second side surfaces with respect to the normal direction of the electrode formation surface are the angles of inclination of the first and second side surfaces, respectively.

[0025] This embodiment is characterized in that the inclination angle θ2 of the second side surface 4Bc is smaller than the inclination angle θ1 of the first side surface 4Ac. In other words: Metals are laminated such that a width of the electrode finger in a direction extending from the electrode formation surface 3a is Fig. Figure 2(a) illustrates that the IDT electrode 2 gradually narrows along a lamination direction. This feature reduces distortion of the main electrode layer 6 in the IDT electrode 2 caused by sound wave excitation and improves IMD properties. This point is described below in comparison to a comparative example.

[0026] Fig. Figure 3 is an enlarged front sectional view of an IDT electrode in the comparison example.

[0027] A near-contact layer 104 of an IDT electrode 102 in a sound wave device of the comparative example comprises first and second layers 104A and 104B. The first and second layers 104A and 104B have first and second side surfaces 104Ac and 104Bc, respectively. In the sound wave device of the comparative example, there is no difference between the inclination angle of the first side surface 104Ac and the inclination angle of the second side surface 104Bc. Except for the point mentioned above, the sound wave device of the comparative example has a similar structure to the sound wave device 1 of the first embodiment.

[0028] Fig. 4(a) and Fig. Figure 4(b) shows diagrams that each depict the relationship between a position of the electrode finger of the IDT electrode along the propagation direction of the sound wave and an S4 component of the distortion in a surface of the main electrode layer on the side closer to the piezoelectric substrate in the first embodiment and the comparative example. A solid line represents the result obtained with the first embodiment, and a dashed line represents the result obtained with the comparative example. Assuming that a direction perpendicular to an extension direction of the electrode finger is a width direction of the electrode finger, a position where a value of a horizontal axis in each of the Fig. 4(a) and Fig. 4(b) zero (0) is, a mean position of the electrode finger in its width direction. Fig. Figure 4(a) shows the magnitude of the distortion in a region from the center of the electrode finger in the width direction to its end face. Fig. 4(b) shows the magnitude of the distortion in a region from the center of the electrode finger in the width direction to its end face on the side that is in Fig. 4(a) is opposite the illustrated end surface.

[0029] As described above, a sound wave is excited when a voltage is applied to the IDT electrode. At this moment, mechanical stresses act on the surface of the IDT electrode on the side closer to the piezoelectric substrate. This causes distortion in the main electrode layer. In this embodiment and the comparative example, the magnitude of the distortion increases as the aforementioned position moves from the center of the electrode finger towards the end face. Furthermore, as can be seen from the Fig. 4(a) and Fig. 4(b) to recognize that the distortion in this embodiment is reduced compared to the comparative example.

[0030] More precisely, as in Fig. 4(a) shows the distortion at one end face of the electrode finger 4.26 × 10 -3 in the comparison example and 3.99 × 10 -3 In this embodiment, the S4 component of the warping can thus be reduced by 0.27 × 10 according to this embodiment. -3 compared to the comparison example, the distortion can be reduced. Furthermore, it can be seen that in this embodiment, compared to the comparison example, the distortion can be effectively reduced in a region extending over approximately 10% of the total length of the electrode finger in the lateral direction from the end face of the electrode finger.

[0031] At the end surface of the electrode finger, as described by Fig. As shown in 4(b), the distortion is 4.26 × 10 -3in the comparison example and 3.99 × 10 -3 in this embodiment. Thus, according to this embodiment, the S4 component of the warping can also be reduced by 0.27 × 10 -3 compared to the comparison example at the Fig. 4(b) shown at the end surface. Furthermore, it can be seen that in this embodiment, the distortion in the lateral direction is also reduced compared to the comparison example in the region extending over approximately 10% of the total length of the electrode finger in the lateral direction of the end surface of the electrode finger, as shown by Fig. 4(b) shown, extends, and can be effectively reduced. The reason why distortion can be reduced according to this embodiment is suggested in the following theory.

[0032] In this embodiment, as in Fig. As illustrated in Figure 2(a), the inclination angle of the second side surface 4Bc of the near-contact layer 4 is smaller than that of its first side surface 4Ac. Accordingly, the mechanical stresses acting on and around the side surface of the electrode finger of the IDT electrode 2 upon excitation of the sound wave are distributed to a greater extent towards the piezoelectric substrate 3 than towards the main electrode layer 6. Therefore, because the concentration of mechanical stresses on the surface of the main electrode layer 6 is reduced on the side closer to the piezoelectric substrate 3 upon excitation of the sound wave, the distortion of the main electrode layer 6 is reduced.

[0033] As in Fig. As illustrated in Figure 2(b), an angle formed between the side surface 6c of the main electrode layer 6 and a dash-dot-dash line C extending in the normal direction Z of the electrode formation surface of the piezoelectric substrate 3 is an inclination angle θ3 of the side surface 6c of the main electrode layer 6. Under this assumption, as in this embodiment, the inclination angle θ3 of the side surface 6c of the main electrode layer 6 is preferably at most as large as the inclination angle θ2 of the second side surface 4Bc. With such a feature, the distortion of the main electrode layer 6 can be further reduced. The side surface of the main electrode layer can be inclined relative to the normal direction of the electrode formation surface such that only a portion of the side surface is inclined, or that the entire side surface is inclined.Alternatively, the side surface of the main electrode layer need not have a region that is inclined relative to the normal direction of the electrode formation surface. If the side surface of the main electrode layer is not inclined relative to the normal direction of the electrode formation surface, its angle of inclination is 0°.

[0034] The following describes a relationship between warping and IMD properties. Specifically, it illustrates the relationship between the S4 component of warping and the level of a third harmonic when using a horizontal shear (SH) wave. In the example described below, the third harmonic is an undesirable wave, and the IMD properties are improved as the third harmonic level decreases.

[0035] Fig. Figure 5 is a curve diagram showing the relationship between the S4 component of the distortion and the level of the third harmonic.

[0036] As from Fig. As can be seen in step 5, the level of the third harmonic decreases to the extent that the S4 component of the warping is reduced. Consequently, it follows that the IMD characteristics can be improved by reducing the warping of the IDT electrode.

[0037] As in Fig. As illustrated in Figure 2(a), the near-contact layer 4 is positioned closer to the piezoelectric substrate 3 than the main electrode layer 6. Furthermore, as described above, the mechanical stresses acting on and around the side surface of the electrode finger of the IDT electrode 2 are distributed to a greater extent towards the piezoelectric substrate 3 than towards the main electrode layer 6. In this embodiment, the near-contact layer 4 of the IDT electrode 2 is made of Ti, and its main electrode layer 6 is made of Al. Thus, the elastic modulus of the metal forming the near-contact layer 4 is preferably greater than that of the metal forming the main electrode layer 6. This makes it possible to reduce the mechanical stresses acting on the main electrode layer 6 from the side containing the piezoelectric substrate 3 upon excitation of the sound wave.As a result, distortion of the main electrode layer 6 can be effectively suppressed.

[0038] The following describes a manufacturing process for the sound wave device 1.

[0039] Fig. Figures 6(a) to 6(c) are partially opened, cutaway front views of the IDT electrode, which are used to explain the manufacturing process for the sound wave device according to the first embodiment. Fig. 7(a) and Fig. Figure 7(b) shows partially opened, sectioned front views of the IDT electrode, which illustrate the manufacturing process for the sound wave device according to the first embodiment. It should be noted that the Fig. 7(a) and Fig. 7(b) Describe the steps that follow the steps described in the Fig. The steps illustrated in 6(a) to 6(c) are carried out.

[0040] As in Fig. As illustrated in Figure 6(a), the piezoelectric substrate 3 is fabricated. A resist layer 7 is then laminated onto the piezoelectric substrate 3. The resist layer 7 is then subjected to structuring. This structuring creates openings in subregions of the resist layer 7, exposing the piezoelectric substrate 3 in these open regions. For example, photolithography, which uses a negative photoresist, can be employed in the step of forming the structured resist layer 7 onto the piezoelectric substrate 3.

[0041] Then, as in the Fig. 6(b) and Fig. Figure 6(c) illustrates how metal films for the near-contact layer 4 are laminated onto both the piezoelectric substrate 3 and the resist layer 7 by a vapor deposition process. While the metal films are laminated onto the piezoelectric substrate 3, the near-contact layer 4 is formed in each of the open regions of the resist layer 7.

[0042] On this occasion, when a metal film with a high melting point is laminated onto the resist layer 7 by the vapor deposition process, the resist layer 7 is deformed due to radiant heat from the metal film. Here, a direction extending across the open region of the resist layer 7 is assumed to be a width direction W. With the deformation of the resist layer 7 described above, a minimum width W1 of the open region of the resist layer 7 is reduced. As the width W1 is reduced, the width of the open region where the piezoelectric substrate 3 is exposed, when viewed from the normal direction Z of the electrode formation surface 3a of the piezoelectric substrate 3, is also reduced.Therefore, because the deformation of the resist layer 7 described above progresses during the step of forming the near contact layer 4, the first and second side surfaces 4Ac and 4Bc of the near contact layer 4 are each inclined.

[0043] In the manufacture of the sound wave device 1 according to this embodiment, a film formation rate is achieved in the step of forming the first layer 4A, as in Fig. Figure 6(b) illustrates, adjusted so that it is larger than the one in the step of forming the second layer 4B, as in Fig. Figure 6(c) illustrates this. More precisely, for example, the film formation rate in the first layer 4A formation step is set to 5 As, and the film formation rate in the second layer 4B formation step is set to 0.5 As. The slower the film formation rate, the lower the heat conduction from the metal film deposited onto the resist layer 7 and the radiant heat from a deposition source. Therefore, a temperature rise of the resist layer 7 is also suppressed. The resist layer 7 deforms at a higher rate at a higher temperature. Thus, in this embodiment, the deformation rate of the resist layer 7 in the second layer 4B formation step can be designed to be slower than that of the resist layer 7 in the first layer 4A formation step.As a result, the inclination angle of the second side surface 4Bc of the second layer 4B can be reduced to a smaller value than that of the first side surface 4Ac of the first layer 4A.

[0044] Alternatively, the distance over which metal particles move after coming into contact with the piezoelectric substrate can be controlled by adjusting the conditions of the deposition process in the first layer formation step differently than those in the second layer formation step. With such control, the inclination angle of the second side face of the second layer can be reduced compared to that of the first side face of the first layer.

[0045] Referring again to the description of the manufacturing process for the sound wave device 1 according to this embodiment, it is then, as in Fig. Figure 7(a) illustrates a metal for the main electrode layer 6 being laminated onto the near-contact layer 4 by a vapor deposition process. In this embodiment, the near-contact layer 4 consists of Ti, and the main electrode layer 6 consists of Al. Thus, the melting point of the metal forming the main electrode layer 6 is preferably not higher than that of the metal forming the near-contact layer 4. With such a feature, the temperature to which the resist layer 7 is heated in the step of forming the main electrode layer 6 can be brought to a value that is not higher than the temperature to which the resist layer 7 is heated in the step of forming the near-contact layer 4. Accordingly, the inclination angle of the side surface 6c of the main electrode layer 6 can be more reliably brought to a maximum value equal to that of the second side surface 4Bc of the near-contact layer 4.Consequently, the distortion of the main electrode layer 6, which is caused by the excitation of the sound wave, can be suppressed more reliably.

[0046] Then, as in Fig. 7(b) illustrates the Fig. 7(a) illustrated resist layer 7 detached from the piezoelectric substrate 3.

[0047] Fig. Figure 8 is a partially opened, front sectional view of an IDT electrode in a second embodiment of the present invention.

[0048] According to a sound wave device of the second embodiment, an IDT electrode 12 includes an intermediate layer 15 arranged between a near-contact layer 14 and the main electrode layer 6. Furthermore, the near-contact layer 14 has a structure that differs from that of the near-contact layer 4 in the first embodiment. Except for the points mentioned above, the sound wave device according to the second embodiment has a structure similar to that of the sound wave device 1 according to the first embodiment.

[0049] The near-contact layer 14 exhibits higher adhesion to the piezoelectric substrate 3 than the intermediate layer 15 does to the piezoelectric substrate 3. The near-contact layer 14 has a side surface 14c. In contrast to the first embodiment, the angle of inclination of the side surface 14c of the near-contact layer 14 is constant. In the second embodiment, the near-contact layer 14 consists of a NiCr and Ti alloy. Although the metal forming the near-contact layer is not limited to a specific one, the near-contact layer preferably consists of a suitable metal that exhibits good adhesion to the piezoelectric substrate, as in the first embodiment.

[0050] In this embodiment, the intermediate layer 15 consists of Ti. The metal used to form the intermediate layer is not limited to a specific one. The near-contact layer and the intermediate layer can consist of the same metal.

[0051] The intermediate layer 15 has a side surface 15c. An angle formed between the side surface 15c and the normal direction Z of the electrode formation surface 3a of the piezoelectric substrate 3 is defined as the inclination angle of the side surface 15c. Under this assumption, the inclination angle of the side surface 15c of the intermediate layer 15 is smaller than that of the side surface 14c of the near-contact layer 14. As in the first embodiment, the distortion of the main electrode layer 6 caused by the excitation of the sound wave can therefore be reduced. Consequently, the IMD properties can be improved.

[0052] It is only required that at least a portion of the side surface of the near-contact layer is inclined relative to the normal direction of the electrode formation surface. With respect to the intermediate layer, it is likewise only required that at least a portion of the side surface of the intermediate layer is inclined relative to the normal direction of the electrode formation surface. If a portion of the side surface of the near-contact layer is inclined relative to the normal direction of the electrode formation surface, then the angle formed between the inclined portion of the side surface of the near-contact layer and the aforementioned normal direction is the angle of inclination of the side surface of the near-contact layer.If a part of the side surface of the interlayer is inclined relative to the normal direction of the electrode formation surface, then an angle formed between the inclined part of the side surface of the interlayer and the above-mentioned normal line is the inclination angle of the side surface of the interlayer.

[0053] Furthermore, the inclination angle of the side surface 6c of the main electrode layer 6 is no greater than that of the side surface 15c of the intermediate layer 15. As a result, the distortion of the main electrode layer 6 caused by the excitation of the sound wave can be effectively suppressed.

[0054] The melting point of the metal forming the near-contact layer 14 is at least as high as that of the metal forming the intermediate layer 15. Accordingly, the angle of inclination of the side surface 15c of the intermediate layer 15 can be easily made smaller than that of the side surface 14c of the near-contact layer 14 by using a method similar to the manufacturing process described above. The melting point of the metal forming the intermediate layer 15 is as high as that of the metal forming the main electrode layer 6. Accordingly, the angle of inclination of the side surface 6c of the main electrode layer 6 can be reliably adjusted to a value that is at most as large as that of the side surface 15c of the intermediate layer 15.

[0055] The elastic modulus of the metal forming the near-contact layer 14 is greater than that of the metal forming the intermediate layer 15. The elastic modulus of the metal forming the intermediate layer 15 is greater than that of the metal forming the main electrode layer 6. Accordingly, the distortion of the main electrode layer 6 caused by the excitation of the sound wave can be further reduced, as in the first embodiment. REFERENCE MARK LIST 1 sound wave device 2 IDT electrode 3 piezoelectric substrate 3a Electrode training area 4. Near contact layer 4A, 4B first and second layers 4Ac, 4Bc first and second face surfaces 6 Main electrode layer 6c side surface 7 Resist layer 8 Reflector 12 IDT electrode 14 Near contact layer 14c side surface 15 Intermediate shift 15c side surface 102 IDT electrode 104 Near contact layer 104A, 104B first and second layers 104Ac, 104Bc first and second face surfaces

Claims

[1] Sound wave device (1) comprising: a piezoelectric substrate (3) having an electrode formation surface (3a) and an IDT electrode (2) provided on the electrode formation surface (3a) of the piezoelectric substrate (3), wherein the IDT electrode (2) comprises a near contact layer (4) provided on the electrode formation surface (3a) of the piezoelectric substrate (3) and a main electrode layer (6) arranged on the near contact layer (4), wherein the close contact layer (4) comprises a first layer (4A) in close contact with the piezoelectric substrate (3) and a second layer (4B) in close contact with the main electrode layer (6), wherein the first layer (4A) has a first lateral surface (4Ac) and the second layer (4B) has a second lateral surface (4Bc), wherein at least parts of the first and second lateral surfaces (4Ac, 4Bc) are inclined relative to a normal direction (Z) of the electrode formation surface (3a) such that an area of ​​a surface of the second layer (4B), the surface being in close contact with the main electrode layer (6), is smaller than an area of ​​a surface of the first layer (4A), the surface being in close contact with the piezoelectric substrate (3), and wherein, assuming that angles (θ1, θ2) formed by the parts inclined with respect to the normal direction (Z) of the electrode formation surface (3a) are respectively defined as inclination angles of the first and second lateral surfaces (4Ac, 4Bc), the inclination angle (θ2) of the second lateral surface (4Bc) is smaller than the inclination angle (θ1) of the first lateral surface (4Ac). [2] The acoustic wave device (1) according to claim 1, wherein the main electrode layer (6) has a lateral surface (6c), and assuming that an angle (θ3) formed by the lateral surface (6c) of the main electrode layer (6) with respect to the normal direction (Z) of the electrode formation surface (3a) of the piezoelectric substrate (3) is defined as an inclination angle of the lateral surface (6c) of the main electrode layer (6), the inclination angle (θ3) of the lateral surface (6c) of the main electrode layer (6) is equal to or smaller than the inclination angle (θ2) of the second lateral surface (4Bc). [3] The acoustic wave device (1) according to claim 1 or 2, wherein a modulus of elasticity of a metal constituting the near contact layer (4) is larger than a modulus of elasticity of a metal constituting the main electrode layer (6). [4] The acoustic wave device (1) according to any one of claims 1 to 3, wherein a melting point of a metal constituting the near contact layer (4) is equal to or higher than a melting point of a metal constituting the main electrode layer (6). [5] The acoustic wave device (1) according to any one of claims 1 to 4, wherein the near contact layer (4) is made of one of NiCr and Ti, and wherein the main electrode layer (6) is made of Al. [6] A manufacturing method for an acoustic wave device (1) in which an IDT electrode (2) including a near contact layer (4) and a main electrode layer (6) is arranged on a piezoelectric substrate (3), the manufacturing method comprising the steps of: Producing the piezoelectric substrate (3) having an electrode formation surface (3a), and Forming the IDT electrode (2) on the electrode formation surface (3a) of the piezoelectric substrate (3), wherein the step of forming the IDT electrode (2) comprises the steps of: laminating a resist layer (7) on the electrode formation surface (3a) of the piezoelectric substrate (3), patterning the resist layer (7), laminating a metal film for the near contact layer (4) on both the piezoelectric substrate (3) and the resist layer (7) by a vapor deposition process, laminating a metal film for the main electrode layer (6) on the metal film for the near contact layer (4) by a vapor deposition process, and peeling the resist layer (7) from the piezoelectric substrate (3), wherein the near contact layer (4) comprises a first layer (4A) in direct contact with the piezoelectric substrate (3) and a second layer (4B) in direct contact with the main electrode layer (6), wherein the first layer (4A) has a first side surface (4Ac), and wherein the second layer (4B) has a second side surface (4Bc), and in the step of laminating the metal film for the near contact layer (4) on both the piezoelectric substrate (3) and the resist layer (7), the metal film for the near contact layer (4) is laminated while changing conditions of the vapor deposition process to form the first and second side surfaces (4Ac, 4Bc) in a state inclined relative to a normal direction (Z) of the electrode formation surface (3a), and to make an area of ​​a surface of the second layer (4B) where the surface is in direct contact with the main electrode layer (6) smaller than an area of ​​a surface of the first layer (4A) where the surface is in direct contact with the piezoelectric substrate (3), so that assuming that angles (θ1, θ2) formed by the first and second side surfaces (4Ac, 4Bc) with respect to the normal direction (Z) of the electrode formation surface (3a) are taken as inclination angles of the first and second side surfaces, respectively.second side surfaces (4Ac, 4Bc), the inclination angle (θ2) of the second side surface (4Bc) is smaller than the inclination angle (θ1) of the first side surface (4Ac). [7] The manufacturing method for the acoustic wave device (1) according to claim 6, wherein in the step of laminating the metal film for the near contact layer (4) on both the piezoelectric substrate (3) and the resist layer (7), a film forming speed in the evaporation process when the second layer (4B) is formed is set to be slower than a film forming speed in the evaporation process when the first layer (4A) is formed.

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