JP2010081086A - Acoustic wave device and method for manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an acoustic wave device in which not only contact resistance in a contact part is reduced but also an electrode hardly corrodes with an etchant when being manufactured by a photolithography method for instance, and to provide a method for manufacturing the acoustic wave device. <P>SOLUTION: In the acoustic wave device 1, a first laminated metal film 11 is formed so as to include the electrode finger part of an IDT electrode 3 on a piezoelectric substrate 2, the contact part is formed at a part overlapped with the first laminated metal film 11, and a second laminated metal film is formed on the piezoelectric substrate 2. A metal film at the top part of the first laminated metal film is a Ti film, a metal film at the bottom layer of the second laminated metal film 12 is a Ti film, and the Ti films are brought into contact with each other at the contact part C. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an acoustic wave device used for a bandpass filter, a resonator, and the like, and more specifically, a first electrode made of a laminated metal film including an Al film, a laminated metal film, and the first electrode. The present invention relates to an acoustic wave device having a second electrode stacked on a first electrode so as to be electrically connected, and a method for manufacturing the same.

  In recent years, with the downsizing of mobile phones, there is a strong demand for downsizing of bandpass filters used in mobile phones. As this type of band-pass filter, surface acoustic wave devices using surface acoustic waves are widely used. In order to promote miniaturization, in a surface acoustic wave device, a surface acoustic wave filter chip in which a conductive film for forming an IDT or the like is formed on a piezoelectric substrate uses bumps instead of wire bonding for the package. They are connected by flip chip bonding.

  An example of this type of surface acoustic wave device is disclosed in Patent Document 1 below.

  FIG. 8 is a partially cutaway front sectional view for explaining the surface acoustic wave device disclosed in Patent Document 1. As shown in FIG. The surface acoustic wave device 1001 includes a piezoelectric substrate 1002. An IDT 1003 is formed on the piezoelectric substrate 1002 by a laminated conductive film. The IDT 1003 has a main electrode layer 1003a made of Cu. An adhesion layer 1003b made of Ti is stacked below the main electrode layer 1003a. By forming the adhesion layer 1003b made of Ti, the adhesion strength of the IDT 1003 to the piezoelectric substrate 1002 is increased.

  A protective layer 1003c made of Al is stacked on the upper side of the main electrode layer 1003a. Since Al is less oxidized than Cu, the main electrode layer 1003a can be protected by the protective layer 1003c. In the surface acoustic wave device 1001, the IDT 1003 is covered with a silicon oxide film 1004 in order to improve frequency temperature characteristics and to protect the surface temperature wave device 1001.

On the other hand, in Patent Document 2 described below, the IDT has a base layer made of Ti formed on a piezoelectric substrate and a main electrode layer made of Al formed on the base layer. That is, IDT having an Al / Ti laminated structure is shown in order from the top. In Patent Document 2, an electrode pad electrically connected to the IDT is laminated between a lower electrode made of Al, an upper electrode made of Al, and a lower electrode and an upper electrode, and made of Ti. And a barrier layer. That is, the electrode pad has an Al / Ti / Al laminated structure in order from the top. This is because the lower electrode made of relatively soft Al is formed on the piezoelectric substrate to prevent cracks in the piezoelectric substrate during bonding using bumps during flip chip bonding.
JP 2006-115548 A JP 2003-174056 A

  As described in Patent Document 2, in the electrode pad portion where bump bonding is performed, cracking of the piezoelectric substrate can be prevented by using Al as the lowermost electrode layer.

  Now, a wiring pattern connected to the IDT of the surface acoustic wave device is a first wiring pattern, and a wiring pattern connected to the electrode pad is a second wiring pattern.

  The first wiring pattern connected to the electrode pad is formed simultaneously with the electrode pad. Therefore, when the electrode pad portion is formed as described in Patent Document 2, the second wiring pattern connected to the electrode pad similarly has an Al / Ti / Al laminated structure. In a contact portion where such a second wiring pattern is overlapped with and electrically connected to the first wiring pattern connected to the IDT, an Al film which is a conductive film in the lowermost layer of the second wiring pattern is formed. Then, it is overlaid on the uppermost conductive film of the first wiring pattern.

  Therefore, as described in Patent Document 1, when the laminated conductive film constituting the IDT has an Al / Cu / Ti laminated structure, the first wiring pattern also has the same laminated structure. The Al film and the Al film are stacked. In such a structure, the contact resistance at the contact portion increases, and the insertion loss of the surface acoustic wave device tends to deteriorate.

  On the other hand, in order to improve the reliability and power durability, the inventor of the present application forms the first wiring pattern connected to the IDT and IDT in order from the top by a laminated conductive film of Al / Ti / Pt / NiCr. investigated. By using an Al film and a Pt film as the main electrode layer, it is possible to increase the reflection coefficient, particularly by using a Pt film having a high density of Al. However, even in this case, when the second wiring pattern connected to the electrode pad is Al / Ti / Al, the Al film is still overlaid on the Al film at the contact portion which is the connection portion between them. Thus, it was found that the contact resistance is increased and the insertion loss of the surface acoustic wave device is deteriorated.

  The first and second wiring patterns are usually formed by a photolithography method. That is, after forming the first wiring pattern, a photoresist layer is formed, and an opening is formed by etching or the like in a portion where the second wiring pattern is to be formed in the photoresist layer. Thereafter, a metal film constituting the second wiring pattern is formed in the entire region including the inside of the opening. Then, the photoresist layer and the unnecessary second wiring pattern forming metal film thereon are removed by a lift-off method.

  In such a manufacturing method, when the opening is formed by etching, the first wiring pattern is exposed in the opening, but when the Al film in the first wiring pattern is exposed, acid, alkali, or the like is exposed. There was also a problem that the Al film was corroded by the etching solution.

  An object of the present invention is to provide an acoustic wave device capable of reducing contact resistance at a contact portion where electrodes such as wiring patterns are electrically connected to each other, thereby reducing loss, and a method for manufacturing the same. Is to provide.

  Another object of the present invention is to provide an acoustic wave device and a method of manufacturing the same that can not only reduce the contact resistance at the contact portion but also hardly cause corrosion of the electrode due to an etching solution when manufactured by a photolithography method, for example. There is.

  According to the present invention, a piezoelectric substrate, a first laminated metal film formed on the piezoelectric substrate and formed by laminating a plurality of metal films, the first electrode including at least an IDT electrode, A second electrode made of a second laminated metal film formed by laminating a plurality of metal films, and the second electrode overlaps the first electrode. The contact portion for electrically connecting the first and second electrodes is formed by the portion, and the first laminated metal film has an Al film and a Ti film as the uppermost layer, An elastic wave device is provided in which the second laminated metal film has a Ti film as a lowermost layer.

  In a specific aspect of the acoustic wave device according to the present invention, the first laminated metal film has a noble metal film, and the noble metal is Pt or Au. In this case, the electrical resistance of the first electrode can be reduced and the loss can be reduced.

  In another specific aspect of the acoustic wave device according to the present invention, the outer edge of the second electrode is located inside the outer edge of the first electrode in the contact portion. In this case, when the first and second electrodes are formed by the photolithography method, when the opening is formed in the resist layer with the etching solution, the portion exposed to the opening is the Ti provided in the uppermost layer. Since it is a film, corrosion of the first electrode hardly occurs.

  In still another specific aspect of the acoustic wave device according to the present invention, when the thickness of the Ti film located in the uppermost layer of the first electrode is λ, the wavelength of the acoustic wave is The Ti film in the lowermost layer of the second electrode is in the range of 0.5 to 10% of the wavelength λ. Therefore, the electrical resistance can be lowered without impairing the reflection coefficient of the elastic wave.

  According to still another specific aspect of the acoustic wave device according to the present invention, an insulating film is further provided on the piezoelectric substrate so as to cover the first electrode. In this case, the first electrode can be protected by the insulating film.

  In still another specific aspect of the surface acoustic wave device according to the present invention, the surface acoustic wave is a surface acoustic wave, thereby providing a surface acoustic wave device that exhibits the effects of the present invention.

  In the method for manufacturing an acoustic wave device according to the present invention, the step of forming the first electrode made of the first laminated metal film on the piezoelectric substrate and the formation of a resist layer so as to cover the first electrode A step of forming an opening in a portion of the resist layer where the second laminated metal film is formed, and forming a second laminated metal film on the opening and the upper surface of the resist layer. And a step of removing the resist layer and the second laminated metal film on the resist layer by a lift-off method.

  In a specific aspect of the method for manufacturing an acoustic wave device according to the present invention, in the contact portion, the opening is arranged so that an outer edge of the second electrode is located inside an outer edge of the first electrode. It is formed on the resist layer. Therefore, the etching solution used for forming the opening comes into contact with the Ti film of the first electrode exposed in the opening, but the Ti film is hardly corroded by acid, alkali, or the like. Therefore, it is possible to reliably obtain the acoustic wave device according to the present invention while preventing corrosion of the electrode.

  In the acoustic wave device according to the present invention, the first laminated metal film has the Ti film as the uppermost layer, and the second laminated metal film has the Ti film as the lowermost layer. Since contact is made, the contact resistance between the first and second electrodes can be lowered, thereby making it possible to reduce the insertion loss.

  According to the method for manufacturing an acoustic wave device according to the present invention, after forming the first laminated metal film, the second laminated metal film is formed by photolithography. Since they overlap, the acoustic wave device according to the present invention having a contact portion with low contact resistance can be easily provided according to the photolithography method.

  Hereinafter, the present invention will be clarified by describing specific embodiments of the present invention with reference to the drawings.

FIG. 1 is a schematic plan view showing a state where an insulating film, which will be described later, is removed in an elastic wave device according to an embodiment of the present invention. The acoustic wave device 1 has a piezoelectric substrate 2. The piezoelectric substrate 2 can be formed of an appropriate piezoelectric material. Examples of the piezoelectric material include piezoelectric single crystals such as LiTaO ₃ or LiNbO ₃ or piezoelectric ceramics such as PZT. In this embodiment, the piezoelectric substrate is 126. ° LiNbO ₃ substrate was used.

  An IDT electrode 3 is formed on the piezoelectric substrate 2. The IDT electrode 3 has a plurality of first electrode fingers 4 and a plurality of second electrode fingers 5 arranged so as to be interleaved with the plurality of first electrode fingers 4. In the present embodiment, the surface acoustic wave is excited by the IDT electrode 3, and thus a surface acoustic wave device is formed.

  In the IDT electrode 3, a first dummy electrode 6 is formed with a gap from the tip of the first electrode finger 4. Similarly, a second dummy electrode 7 is formed with a gap from the tip of the second electrode finger 5.

  On the other hand, the IDT electrode 3 is subjected to cross width weighting so that the electrode finger cross width gradually decreases from the center of the surface acoustic wave propagation direction toward the end of the IDT electrode 3. However, in the present invention, the IDT electrode 3 may be weighted in other forms, or may not be weighted.

  Since the weighting is performed as described above, the envelope A connecting the tips of the plurality of first electrode fingers 4 and the tips of the second electrode fingers 5 are shown in FIG. 2 is extended in an oblique direction, and the envelope A and the envelope B are getting closer to the end of the IDT electrode 3.

  On the other hand, reflectors 8 and 9 are formed on both sides of the IDT electrode 3 in the surface acoustic wave propagation direction. Therefore, a surface acoustic wave resonator having the IDT electrode 3 and the reflectors 8 and 9 is formed.

  In this embodiment, as described above, the wavelength λ of the IDT electrode finger is 3.958 μm, the maximum cross width of the electrode finger is 120 μm, the number of electrode finger pairs is 134, the resonance frequency is 900 MHz, A one-port surface acoustic wave resonator having an antiresonance frequency of 934 MHz is formed.

  Incidentally, the IDT electrode 3 includes a first laminated metal film 11 formed by laminating a plurality of metal films on the piezoelectric substrate 2 as shown in a schematic front sectional view of FIG. The electrode made of the first laminated metal film 11 is defined as the first electrode. The first electrode includes the IDT electrode 3. That is, as shown in FIG. 1, the first electrode is formed so as to reach not only the IDT electrode 3 but also the electrode finger portions of the reflectors 8 and 9.

  In the present embodiment, as shown in FIG. 3, the first laminated metal film 11 has a structure in which a Ti film 11a, an AlCu film 11b, a Ti film 11c, a Pt film 11d, and a NiCr film 11e are laminated in order from above. The thickness of each metal film was Ti / AlCu / Ti / Pt / NiCr = 10/102/10/78/10 nm. The unit of film thickness is a value in nm. The AlCu film 11b is an AlCu alloy film containing 1% by weight of Cu and the balance being Al. The NiCr film 11e is a NiCr alloy film containing 50% by weight of Ni and the balance being Cr.

  Returning to FIG. 1, the second electrode made of the second laminated metal film 12 is formed so as to partially overlap the first electrode made of the first laminated metal film 11. The second electrode 12 includes electrode pads 13 to 15 shown in FIG. 1, wiring patterns 16 to 18 that electrically connect the electrode pads 13 to 15 to the surface acoustic wave resonator, and a part of the IDT electrode 3, that is, It is formed in part of the bus bar.

  A portion where the second electrode is superimposed on the first electrode and the two are electrically connected is referred to as a contact portion C.

  In the present embodiment, the second stacked metal film 12 has a structure in which a plurality of these metal films are stacked in a thickness of Al / Ti / Al / Ti = 1140/200/500/100 nm in order from the top. As shown in FIG. 5 to be described later, in the second laminated metal film, reference numerals are assigned in order of the Al film 12a, the Ti film 12b, the Al film 12c, and the Ti film 12d from the top.

Further, as schematically shown in FIGS. 3 and 5, an insulating film 19 is formed so as to cover the IDT electrode 3 and the reflectors 8 and 9. In the present embodiment, the insulating film 19 has a structure in which a first insulating film 19a and a second insulating film 19b are stacked in order from the top. The first insulating film 19a is a SiN film, and the second insulating film 19b is a SiO ₂ film. The film thickness of both is SiN / SiO ₂ = 40/980 nm. However, the insulating film 19 may be formed of a single insulating material layer, and the thicknesses of the SiN film and the SiO ₂ film are not limited to the above.

  In the present embodiment, the IDT electrode 3 and the reflectors 8 and 9 are protected by the insulating film 19. Although not shown, the insulating film 19 is formed except for the portion where the electrode pads 13 to 15 are provided. That is, the electrode pads 13 to 15 are exposed upward.

  In the present embodiment, the electrode finger portion of the IDT electrode 3 is composed only of the first laminated metal film 11, and the wiring patterns 16 to 18 and the electrode pads 13 to 15 are the first and second laminated metal films 11. , 12 are laminated. The contact portion C described above is formed in the bus bar of the IDT electrode 3. In the contact portion C, the outer edge 12 A of the second multilayer metal film 12 is located on the first multilayer metal film 11. That is, the outer edge 12A of the second laminated metal film 12 is located on the inner side than the outer edge 11A of the first laminated metal film 11.

  In the present embodiment, in the contact portion, the uppermost layer of the first laminated metal film 11 is made of the Ti film 11a, and the lowermost layer of the second laminated metal film 12 is made of the Ti film 12d. Low enough. Therefore, insertion loss can be reduced.

  That is, in the elastic wave device described in Patent Document 1 or Patent Document 2, the contact resistance between the electrodes in the contact portion is high, and thus there is a problem that the insertion loss increases. The insertion loss can be reduced by reducing the contact resistance.

  In addition, according to the present embodiment, corrosion of the second electrode is unlikely to occur in the contact portion C to which the first and second electrodes are electrically connected. This will be clarified by explaining the manufacturing method.

  In manufacturing the acoustic wave device 1, first, a first laminated metal film is formed on the piezoelectric substrate 2 by vapor deposition, plating, sputtering, or the like. Thereafter, according to a known photolithography method, the first laminated metal film is patterned to form a first electrode including the IDT electrode 3.

  Thereafter, as shown in FIG. 4A, a photoresist layer 21 is formed on the entire upper surface of the piezoelectric substrate 2. Except for the portion where the second laminated metal film is scheduled to be formed above the photoresist layer 21, a mask which is an opening is placed and irradiated with light. Thereby, an uncured portion 21a and a cured portion 21b shown in FIG. 4A are formed. The uncured portion 21a is a portion shielded from light by the mask, and the cured portion 21b is a portion formed by curing the material constituting the photoresist layer 21 by light irradiation.

  Next, as shown in FIG. 4B, the uncured portion 21a of the photoresist layer 21 is etched with an etchant 22 such as acid or alkali. Thereby, the opening 21c is formed. The opening 21c corresponds to a region where the formation of the second laminated metal film 12 is planned. In this case, the upper surface of the first multilayer metal film 11 is exposed to the etching solution 22, but the uppermost layer of the first multilayer metal film 11 is the Ti film 11a. Since the Ti film 11a is hardly corroded by acid or alkali, the first laminated metal film 11 is hardly corroded.

  In particular, in the present embodiment, as shown in FIG. 1, the outer edge 12 </ b> A of the second laminated metal film 12 is positioned inside the outer edge 11 </ b> A of the first laminated metal film 11 in the contact portion C. Therefore, the AlCu film 11b and the like of the first laminated metal film 11 are not exposed to the etching solution. Thereby, corrosion of the first laminated metal film 11 can be reliably prevented.

  Next, as shown in FIG. 4C, a second laminated metal film 12 is formed on the entire surface. The second laminated metal film 12 is formed by sequentially forming the aforementioned metal films by a thin film forming method such as vapor deposition, plating, or sputtering.

Thereafter, the second laminated metal film portion located above the photoresist layer 21 is removed together with the photoresist layer 21 by a lift-off method. Next, annealing is performed by maintaining the temperature at 230 ° C. for 2 hours. In this way, as shown in FIG. 5, a structure in which the second laminated metal film 12 is laminated on the first laminated metal film 11 can be obtained. Thereafter, the insulating film 19 can be formed by sequentially forming the SiO ₂ film and the SiN film by an appropriate method such as sputtering. As described above, the elastic wave device 1 of the present embodiment can be obtained.

  According to the elastic wave device and the manufacturing method thereof of the present embodiment, as described above, the uppermost Ti film 11a of the first laminated metal film 11 and the lowermost Ti film 12d of the second laminated metal film 12 are used. Is in contact with each other, the contact resistance between the two is small, thereby reducing the insertion loss. This will be described based on a specific experimental example. In order to contrast with the above-described embodiment, as a first comparative example, the second laminated metal film is Al / Ti / Al = 1140/200/500 nm in order from above, except that An elastic wave device formed in the same manner as in the embodiment was prepared.

  As a second comparative example, the first laminated metal film is the same as the above embodiment except that the first laminated metal film is AlCu / Ti / Pt / NiCr = 102/110/78/10 nm in order from the top. The elastic wave device formed was prepared.

  The electrical characteristics of the elastic wave devices of the above embodiment and the first and second comparative examples were measured, and in particular, the return loss was evaluated. The results are shown in FIG. In FIG. 6, the solid line indicates the result of the above embodiment, the broken line indicates the result of the first comparative example, and the alternate long and short dash line indicates the result of the second comparative example. As can be seen from FIG. 6, according to the above embodiment, the return loss is small over almost the entire frequency region as compared with the first and second comparative examples. The reason is considered as follows.

  As described in Patent Document 2, when the Al films are in contact with each other in the contact portion, a thin Al oxide film is formed at the interface between them. For this reason, there is a problem that the contact resistance is increased and the insertion loss is deteriorated. This is because, after the first laminated metal film is formed, the uppermost Al film is exposed to the atmosphere, and an Al oxide film is formed on the surface of the Al film.

  In the first comparative example, the uppermost layer of the first laminated metal film is made of a Ti film, thereby suppressing oxidation of the surface of the AlCu film. However, the uppermost Ti film is oxidized, and the lowermost Al of the second laminated metal film in contact with the Ti oxide is affected by the Ti oxide, and an Al oxide is formed at the interface between the two. . Therefore, also in the first comparative example, it is considered that the Al oxide film is formed at the interface and the contact resistance is high.

  On the other hand, in the second comparative example, the uppermost layer of the first laminated metal film is made of an AlCu film and is subjected to a reducing action by the lowermost Ti film of the second laminated metal film. The film consisting of will be reduced. However, when the reduction action by Ti is not sufficient, the Al oxide film remains at the interface, and the contact resistance increases.

  As described above, in the portion where the first laminated metal film and the second laminated metal film are laminated, when an Al oxide film is formed at the interface between them, the contact resistance is increased.

  On the other hand, in the above embodiment, since the Ti films are in contact with each other, an Al oxide film is essentially not formed at the interface between the first and second laminated metal films. Therefore, the contact resistance can be sufficiently reduced, and the insertion loss can be reduced.

  In the present embodiment, Ti oxide is generated at the interface. However, the Ti oxide concentrated on the interface is spread and dispersed in the Ti film by the above-described annealing treatment. For this reason, it is considered that the contact resistance between the Ti films of the first and second laminated metal films is not so high.

  As described above, since the lowermost layer of the second laminated metal film is Ti, even when an Al film having a low resistivity is used in the second laminated metal film, the lowermost layer is used. The Ti film acts as a barrier layer and does not reach the Al film. Therefore, an increase in electrical loss can be prevented without increasing the wiring resistance of the second laminated metal film.

  In the above embodiment, the first multilayer metal film 11 includes a Pt film and an AlCu film. Thus, it is preferable to use Al or an Al alloy together with a noble metal such as Pt. Since noble metals such as Pt have a high density, the reflection coefficient of elastic waves can be increased, and they are excellent in power resistance, oxidation resistance, and corrosion resistance in humidity as compared with Cu. Therefore, the electrical characteristics and reliability of the acoustic wave device can be improved. On the other hand, since Al and AlCu alloys have low resistance, electrical loss can be reduced. In the present embodiment, the Ti film is provided between the Pt film and the AlCu film in order to prevent mutual diffusion of Pt and the AlCu alloy. That is, the intermediate Ti film functions as a barrier layer that prevents the diffusion.

  The noble metal combined with the Al or Al alloy is not limited to Pt but may be other noble metals such as Au. It is desirable to combine the above-mentioned noble metal with Al or AlCu alloy. However, since these two types of materials have a large difference in ionization tendency, there is a possibility that the Al or AlCu film is corroded by the battery effect at the time of development by photolithography. . However, as described above, in the acoustic wave device and the manufacturing method thereof according to the present embodiment, the inner metal such as the Al or AlCu film in the first laminated metal film is formed by the etching solution used when forming the second laminated metal film. Film corrosion is unlikely to occur. That is, since the uppermost part of the first laminated metal film is covered with the Ti film, corrosion of the Al film and the AlCu film in the first laminated metal film is difficult to occur. Therefore, the contact resistance between the first and second laminated metal films can be lowered, and further, corrosion in the first laminated metal film can be surely prevented, so that the reliability of the acoustic wave device is further improved. Can be enhanced.

  Preferably, the thickness of the uppermost Ti film 11a of the first multilayer metal film is in the range of 0.1% to 1% of λ when the wavelength λ of the elastic wave is used. The thickness of the lowermost Ti film 12d of the laminated metal film 2 is desirably 0.5% or more of λ. This is because the effect of preventing oxidation of Al or Al alloy located below the higher the Ti film thickness of the uppermost layer of the first laminated metal film becomes higher, but the reflection coefficient of the elastic wave For example, there is a possibility that the bandwidth when an elastic wave filter is formed becomes narrow. Therefore, in order to balance Al oxidation prevention and the elastic wave reflection coefficient, the normalized film thickness (%) of the uppermost Ti film 11a of the first laminated metal film is 0.1 (%) to 1%. It is desirable to be in the range of (%).

  On the other hand, even if the thickness of the lowermost Ti film 12d of the second laminated metal film 12 is increased, it does not contribute to the excitation of the surface wave, so that no major problem occurs. However, if the thickness is too thin, the second laminated metal film is likely to be oxidized in the metal film in the second layer from the lowest layer. Accordingly, it is desirable that the Ti film 12d has a certain thickness or more. FIG. 7 shows that, in the above embodiment, the thickness of the lowermost Ti film 12d of the second laminated metal film is 10 nm (0.25%), 20 nm (0.5%), or 100 nm (2.5%). It is a figure which shows the change of a return loss at the time. Figures in parentheses are wavelength λ ratios. It can be seen that almost the same characteristics are obtained when the thickness of the Ti film is 20 nm and 100 nm, whereas the return loss characteristics are deteriorated at 10 nm.

  Therefore, it is preferable that the thickness of the lowermost Ti film 12d of the second laminated metal film is 20 nm or more and the normalized film thickness is 0.5% or more of λ. It should be noted that even if the thickness of the lowermost Ti film 12d of the second laminated metal film 12 is large, the problem does not occur so much, but if it is too thick, the effect of suppressing electrical resistance by the Al film or the like may be impaired, so the normalized film The thickness is preferably about 10% or less.

In this embodiment, the IDT electrode is protected by the insulating film 19. That is, protection by the insulating film 19 is intended to prevent a short circuit due to the adhesion of metal powder and to improve moisture resistance. In this case, when the SiO ₂ film and the Al film are in contact with each other, there is a possibility that oxidation of Al is likely to occur. Therefore, in this embodiment, since the Ti film is provided on the top of the first laminated metal film forming the IDT, the oxidation of the Al film in the first laminated metal film is caused by the reduction action of Ti. Is effectively prevented.

  In the above embodiment, a 1-port surface acoustic wave resonator having an IDT electrode 3 and a reflector has been described. However, in the present invention, the first laminated metal film and the second laminated metal film are electrically connected at the contact portion. And can be widely applied to various acoustic wave devices in which the electrode fingers of the IDT electrode are formed by the first laminated metal film. That is, the present invention can be applied to a longitudinally coupled resonator type or ladder type surface acoustic wave filter or a transversal type surface acoustic wave filter. The present invention can also be applied to a boundary acoustic wave device using boundary acoustic waves instead of surface acoustic waves.

It is a top view for demonstrating the state which removed the insulating film in the elastic wave apparatus which concerns on one Embodiment of this invention. It is a partial notch top view which shows the principal part of the electrode structure of the elastic wave apparatus of embodiment shown in FIG. FIG. 2 is a partially cutaway cross-sectional view schematically showing an electrode finger forming portion of an IDT electrode in the embodiment shown in FIG. 1. (A)-(c) is each partial notch front sectional drawing for demonstrating the process of forming a 2nd laminated metal film on a 1st laminated metal film. In the manufacturing method of the elastic wave filter device of one embodiment of the present invention, it is a partial notch front sectional view showing the state where the 2nd laminated metal film was laminated on the 1st laminated metal film. It is a figure which shows the return loss characteristic in the elastic wave filter apparatus of embodiment of this invention and a 1st, 2nd comparative example. In the elastic wave filter apparatus of one Embodiment of this invention, it is a figure which shows the change of a return loss characteristic when changing the thickness of Ti film of the lowest layer of a 2nd laminated metal film. It is typical front sectional drawing for demonstrating the conventional surface acoustic wave filter apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Elastic wave apparatus 2 ... Piezoelectric substrate 3 ... IDT electrode 4 ... 1st electrode finger 5 ... 2nd electrode finger 6 ... 1st dummy electrode 7 ... 2nd dummy electrode 8, 9 ... Reflector 11 ... 1st 1 laminated metal film (first electrode)
11A ... Outer edge 11a ... Ti film 11b ... AlCu film 11c ... Ti film 11d ... Pt film 11e ... NiCr film 12 ... Second laminated metal film (second electrode)
12A ... Outer edge 12a ... Al film 12b ... Ti film 12c ... Al film 12d ... Ti film 13-15 ... Electrode pad 16-18 ... Wiring pattern 19 ... Insulating film 19a ... First insulating film 19b ... Second insulating film 21 ... Photoresist layer 21a ... Uncured part 21b ... Hardened part 21c ... Opening part 22 ... Etching solution

Claims (7)

A piezoelectric substrate;
A first electrode formed on the piezoelectric substrate, the first electrode including a plurality of metal films and including at least an IDT electrode;
A second electrode comprising a second laminated metal film formed by laminating a plurality of metal films, wherein the second electrode overlaps the first electrode. The contact portion that electrically connects the first and second electrodes is formed by the portion that is present,
The elastic wave device, wherein the first laminated metal film has an Al film and a Ti film as an uppermost layer, and the second laminated metal film has a Ti film as a lowermost layer.   The elastic wave device according to claim 1, wherein the first laminated metal film includes a noble metal, and the noble metal is Pt or Au.   3. The acoustic wave device according to claim 1, wherein an outer edge of the second electrode is positioned inside an outer edge of the first electrode in the contact portion.   The film thickness of the Ti film located in the uppermost layer in the first electrode is in the range of 0.1 to 1% of the wavelength λ when the wavelength of the elastic wave is λ, and the second electrode The acoustic wave device according to any one of claims 1 to 3, wherein the lowermost Ti film is in a range of 0.5 to 10% of the wavelength λ.   The acoustic wave device according to claim 1, further comprising an insulating film provided on the piezoelectric substrate so as to cover the first electrode. It is a manufacturing method of the elastic wave device according to claim 1,
Forming the first electrode made of the first laminated metal film on the piezoelectric substrate;
Forming a resist layer over the entire surface so as to cover the first electrode;
Forming an opening in a portion of the resist layer where the second laminated metal film is formed;
Forming a second laminated metal film on the opening and the upper surface of the resist layer;
And a step of removing the resist layer and the second laminated metal film on the resist layer by a lift-off method. 7. The acoustic wave device according to claim 6, wherein the opening is formed in the resist layer so that an outer edge of the second electrode is positioned inside an outer edge of the first electrode in the contact portion. Method.

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