JP4297137B2 - Surface acoustic wave device and manufacturing method thereof - Google Patents

Description

  The present invention relates to a surface acoustic wave device used for, for example, a resonator and a bandpass filter, and a method for manufacturing the same, and more specifically, an elastic surface having a structure in which an insulator layer is formed so as to cover an IDT electrode. The present invention relates to a wave device and a manufacturing method thereof.

A DPX or RF filter used in a mobile communication system is required to satisfy both a wide band and good temperature characteristics. Conventionally, in a surface acoustic wave device that has been used for DPX and RF filters, a piezoelectric substrate made of 36 ° -50 ° rotated Y-plate X-propagating LiTaO ₃ is used. This piezoelectric substrate had a frequency temperature coefficient of about −40 to −30 ppm / ° C. In order to improve temperature characteristics, a method of forming a SiO ₂ film having a positive frequency temperature coefficient so as to cover an IDT electrode on a piezoelectric substrate is known. FIG. 109 shows an example of a method for manufacturing this type of surface acoustic wave device.

As shown in FIG. 109A, a resist pattern 52 is formed on the piezoelectric substrate 51 except for the portion where the IDT electrode is formed. Next, as shown in FIG. 109B, an electrode film 53 for forming IDT electrodes is formed on the entire surface. Thereafter, the resist 52 and the metal film adhering to the resist 52 are removed using a resist stripping solution. In this way, the IDT electrode 53A is formed as shown in FIG. 109 (c). Next, as shown in FIG. 109 (d), the SiO ₂ film 54 is formed so as to cover the IDT electrode 53A.

On the other hand, a method for manufacturing a surface acoustic wave device in which an insulating or anticonductive protective film is formed so as to cover the IDT electrode of the surface acoustic wave device for the purpose different from the improvement of the frequency temperature characteristic is as follows. It is disclosed in Patent Document 1. FIG. 110 is a schematic cross-sectional view showing the surface acoustic wave device described in this prior art. In the surface acoustic wave device 61, an IDT electrode 63 made of Al or an alloy containing Al as a main component is formed on a piezoelectric substrate 62. An insulating or anticonductive interelectrode finger film 64 is formed in a region other than the region where the IDT electrode 63 is provided. Further, an insulating or anticonductive protective film 65 is formed so as to cover the IDT electrode 63 and the electrode finger film 64. In the surface acoustic wave device 61 described in this prior art, it is described that the electrode finger film 64 and the protective film 65 are made of an insulating material such as SiO ₂ or an anticonductive material such as silicone. Here, it is said that the formation of the electrode finger film 63 suppresses the deterioration of characteristics due to the discharge between the electrode fingers caused by the pyroelectric property of the piezoelectric substrate 61.

On the other hand, Patent Document 2 below, on a piezoelectric substrate composed of quartz or lithium niobate, and electrodes made of a metal such as aluminum or gold is formed, after further forming a SiO ₂ film, the SiO ₂ film A 1-port surface acoustic wave resonator formed by flattening is disclosed. Here, it is said that good resonance characteristics can be obtained by flattening.
Japanese Patent Laid-Open No. 11-186866 JP-A-6-258355

As shown in FIG. 109, in the conventional method for manufacturing a surface acoustic wave device in which a SiO ₂ film is formed in order to improve the frequency temperature characteristics, there are a portion where the IDT electrode 53A is present and a portion where the IDT electrode 53A is not present. Therefore, the height of the surface of the SiO ₂ film 54 is different. Therefore, there is a problem that the insertion loss is deteriorated due to the presence of irregularities on the surface of the SiO ₂ film 54. Moreover, this unevenness | corrugation becomes large as the film thickness of an IDT electrode becomes large. Therefore, the film thickness of the IDT electrode could not be increased.

  On the other hand, in the surface acoustic wave device described in Document 1, the protective film 65 is formed after the interelectrode finger film 64 is formed between the electrode fingers of the IDT electrode 63. Therefore, the surface of the protective film 65 can be planarized.

  However, in the configuration described in Document 1, the IDT electrode 63 is made of Al or an alloy containing Al as a main component. Although the electrode finger film 64 is formed so as to be in contact with the IDT electrode 63, a sufficient reflection coefficient cannot be obtained in the IDT electrode 63. For this reason, for example, there is a problem that ripples tend to occur in the resonance characteristics.

  Furthermore, in the manufacturing method described in Document 1, the resist formed on the inter-electrode finger film 64 must be removed using a resist stripping solution before the protective film 65 is formed. The electrode 63 may be corroded by the resist stripping solution. Therefore, a metal that easily corrodes cannot be used as the metal constituting the IDT electrode. That is, there are restrictions on the type of metal constituting the IDT electrode.

  On the other hand, the 1-port surface acoustic wave resonator described in Patent Document 2 described above uses quartz or lithium niobate as the piezoelectric substrate, and the electrode is made of aluminum or gold. In this embodiment, only an example in which an electrode made of Al is formed on a quartz substrate is shown. That is, there is no particular mention of surface acoustic wave devices using other substrate materials or other metal materials.

  An object of the present invention is to provide a surface acoustic wave device in which an insulating layer is formed between electrode fingers of an IDT electrode and on the IDT electrode, and a method for manufacturing the same, in view of the above-described state of the prior art, and the reflection of the IDT electrode Accordingly, it is an object of the present invention to provide a surface acoustic wave device having a sufficiently large coefficient and hardly causing deterioration of characteristics due to ripples appearing in resonance characteristics and the like, and a method for manufacturing the same.

  Another object of the present invention is that not only the reflection coefficient of the IDT electrode is sufficiently large and has good characteristics, but also there are few restrictions on the selection of the metal material constituting the IDT electrode, and the elasticity that does not easily cause adverse effects due to corrosion of the IDT electrode. The object is to provide a surface acoustic wave device and a method of manufacturing the same.

  Still another object of the present invention is that the IDT electrode has a sufficiently large reflection coefficient, good characteristics, and is not only susceptible to deterioration of characteristics due to corrosion of the IDT electrode, but also has excellent frequency temperature characteristics. The object is to provide a surface acoustic wave device and a method of manufacturing the same.

As described above, Patent Document 2 shows that good resonance characteristics can be obtained by flattening the SiO ₂ film. Therefore, the inventors of the present application use a LiTaO ₃ substrate having a large electromechanical coupling coefficient as a piezoelectric substrate in order to obtain a broadband filter, and otherwise perform the 1-port surface acoustic wave similarly to the structure described in Patent Document 2. A resonator was fabricated and the characteristics were investigated. That is, an electrode made of Al was formed on a LiTaO ₃ substrate, a SiO ₂ film was formed, and the surface of the SiO ₂ film was flattened. However, after forming the SiO ₂ film, the inventors have found that the characteristics are greatly deteriorated and are not practical.

When a LiTaO ₃ substrate or a LiNbO ₃ substrate having a larger electromechanical coupling coefficient than quartz is used, the specific bandwidth is remarkably increased. However, as a result of the present inventors have made a detailed study, as shown in FIGS. 2 and 3, to form an electrode made of Al in the LiTaO ₃ substrate, may further the formation of the SiO ₂ film, a SiO ₂ film It was found that the reflection coefficient drastically decreased to about 0.02 by flattening the surface of the film. 2 and 3, IDT electrodes made of aluminum, gold, or platinum are formed in various thicknesses on a LiTaO ₃ substrate with Euler angles (0 °, 126 °, 0 °), and an SiO ₂ film is further formed. It is a figure which shows the relationship between the electrode film thickness H / (lambda) of a surface acoustic wave apparatus formed, and a reflection coefficient. Note that the solid lines in FIGS. 2 and 3 shows the change in the reflection coefficient if not flattened as shown schematically the surface of the SiO ₂ film in FIGS. 2 and 3, a broken line indicates a surface of the SiO ₂ film The change in reflection coefficient when flattened is shown.

As is apparent from FIGS. 2 and 3, when a conventional electrode made of Al is used, the reflection coefficient is 0.02 regardless of the electrode film thickness by flattening the surface of the SiO ₂ film. It can be seen that it drastically decreases to the extent. For this reason, it is considered that a sufficient stop band cannot be obtained, and a sharp ripple is generated in the vicinity of the anti-resonance frequency.

Conventionally, it is known that the reflection coefficient increases as the electrode film thickness increases. However, as is apparent from FIGS. 2 and 3, when an electrode made of Al is used, even if the film thickness of the electrode is increased, the reflection coefficient is reduced when the surface of the SiO ₂ film is flattened. It can be seen that does not increase.

On the other hand, as is apparent from FIGS. 2 and 3, when an electrode made of Au or Pt is formed, the thickness of the electrode increases even when the surface acoustic wave of the SiO ₂ film is flattened. It can be seen that the reflection coefficient increases with time. As a result of various studies based on such knowledge, the inventors of the present application have made the present invention.

  According to the first invention of the present application, a piezoelectric substrate, and at least one IDT electrode formed on the piezoelectric substrate and made of a metal having a higher density than Al or an alloy containing the metal as a main component; In the remaining region excluding the region where the at least one IDT electrode is formed, a first insulator layer formed with a film thickness substantially equal to the IDT electrode, and the IDT electrode and the first insulator layer are provided. There is provided a surface acoustic wave device including a second insulator layer formed so as to cover the IDT electrode and having a density of 1.5 times or more that of the first insulator layer. In the first invention, ripples appearing in the resonance characteristics and filter characteristics are moved out of the band, and the ripples are suppressed. Therefore, good characteristics can be realized.

  According to a broad aspect of the second invention of the present application, a piezoelectric substrate, at least one IDT electrode formed on the piezoelectric substrate, and formed on the IDT electrode and constitutes an IDT electrode In the remaining region excluding the region where the at least one IDT electrode is formed, a protective metal film made of a metal or alloy having a higher corrosion resistance than the metal or alloy, and the IDT electrode and the protective metal film A first insulator layer formed to have a film thickness substantially equal to the total film thickness; and a second insulator layer formed to cover the protective metal film and the first insulator layer. A surface acoustic wave device is provided.

  In a specific aspect of the second invention, the average density of the laminated structure composed of the IDT electrode and the protective metal film is 1.5 times or more the density of the first insulator layer, whereby resonance characteristics and Unnecessary ripples appearing on the filter characteristics are shifted out of band and resonated.

In another specific aspect of the first and second inventions, the first and second insulator layers are formed of the same material. Also, preferably, the second insulator layer is formed by SiO _2.

  The surface acoustic wave device according to the first and second inventions is preferably a surface acoustic wave device using reflection of surface acoustic waves. The structure using the surface acoustic wave reflection is not particularly limited, and an end surface reflection type surface acoustic wave device using the reflection of the two opposing end surfaces of the piezoelectric substrate may be configured, or the surface acoustic wave propagation of the IDT. A surface acoustic wave device provided with a reflector on the outside in the direction may be used.

  The surface acoustic wave devices according to the first and second inventions can be used for various surface acoustic wave resonators and surface acoustic wave filters. Such a surface acoustic wave resonator may be a one-port resonator or a two-port resonator, and the surface acoustic wave filter may be a two-port resonator filter. A ladder type filter or a lattice type filter may be used.

  On the specific situation with the surface acoustic wave apparatus concerning the 1st, 2nd invention, the said electrode is an IDT electrode. The IDT electrode may be a unidirectional electrode, thereby reducing insertion loss.

  The electrode may be a reflector.

  On the specific situation with the surface acoustic wave apparatus concerning the 1st, 2nd invention, the said electrode is an IDT electrode and a reflector electrode.

  In the surface acoustic wave device according to the first aspect of the present invention, the first insulator layer formed to have a film thickness substantially equal to the IDT electrode is provided in the remaining region except the region where the IDT electrode is formed. In the configuration in which the second insulator layer is provided so as to cover the IDT electrode and the first insulator layer, the IDT electrode has a metal having a higher density than the density of the first insulator layer or the metal as a main component. Therefore, the reflection coefficient of the IDT electrode can be made sufficiently large. Therefore, it is possible to provide a surface acoustic wave device with good frequency temperature characteristics in which characteristics are not easily deteriorated due to undesired ripples.

  In addition, since the IDT electrode and the first insulator layer have substantially the same thickness, and the second insulator layer is laminated so as to cover the IDT electrode and the first insulator layer, the second insulator The outer surface of the layer can be flattened, whereby the deterioration of the characteristics due to the unevenness of the surface of the second insulator layer hardly occurs.

  In the surface acoustic wave device according to the second aspect of the invention, the first insulator layer having a film thickness substantially equal to the IDT electrode is provided in the remaining region except for the region where the IDT electrode is formed. And a protective metal film made of a metal or alloy having better corrosion resistance than the metal or alloy constituting the IDT electrode, and the second insulator so as to cover the protective metal film and the first insulator layer. A layer is formed. Therefore, since the IDT electrode is covered with the protective metal layer and the first insulator layer, the IDT electrode is hardly corroded by the resist stripping solution when the resist is stripped by the photolithography technique. Therefore, it is easily corroded by a resist stripping solution such as Cu, but an IDT electrode can be formed using a metal or alloy having a sufficiently large density compared to Al, effectively reducing the characteristics of the surface acoustic wave device. Can be suppressed.

  When the IDT electrode is made of Cu or an alloy containing Cu as a main component, the density is higher than that of Al, which has been widely used as an electrode material for a surface acoustic wave device, so the first and second inventions are followed. The surface acoustic wave device can be easily constructed, and an IDT electrode having a sufficient reflection coefficient can be easily formed.

  In the manufacturing method according to the third invention, after the first insulator layer is formed on the piezoelectric substrate 2, the portion of the insulator layer where the IDT electrode is formed is removed using the resist pattern, and the remaining region has the first insulator layer. Forming a metal having a higher density than Al or an electrode film containing the metal as a main component in a region where the laminated structure of the one insulator layer and the resist remains and then the first insulator layer is removed; Thus, the IDT electrode is formed, and then the resist remaining on the first insulating layer is removed. And since the 2nd insulator layer is formed so that the 1st insulator layer and IDT electrode may be covered, the unevenness of the 2nd insulator layer upper surface is hard to arise. Therefore, the deterioration of the characteristics due to the unevenness on the surface of the second insulating layer hardly occurs. In addition, since the IDT electrode is made of a metal having a higher density than Al or an alloy containing the metal as a main component, the reflection coefficient of the IDT electrode can be increased, and deterioration of characteristics due to undesired ripples can be suppressed.

  According to the fourth invention, after the IDT electrode is formed, a protective metal film made of a metal or alloy having higher corrosion resistance than the metal or alloy constituting the IDT electrode is formed. The resist on the insulating layer and the protective metal film laminated on the resist are removed. Therefore, when this removal step is performed with the resist stripping solution, the side surface of the IDT electrode is covered with the first insulator layer and the upper surface is covered with the protective metal layer, and therefore the IDT electrode is hardly corroded.

  Therefore, it is possible to provide the surface acoustic wave device according to the second invention without causing corrosion of the IDT electrode.

  According to the fifth invention, after forming the electrode on the piezoelectric substrate and forming the insulating layer so as to cover the electrode, the surface roughness of the insulating layer above the portion where the electrode is present and the portion where the electrode is not present Is flattened. Therefore, as in the first invention, the deterioration of the characteristics due to the unevenness on the surface of the insulating layer hardly occurs.

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

  A method for manufacturing a surface acoustic wave device according to a first embodiment of the present invention will be described with reference to FIGS.

As shown in FIG. 1A, first, a LiTaO ₃ substrate 1 is prepared as a piezoelectric substrate. In this embodiment, a LiTaO ₃ substrate of 36 ° Y-plate X propagation and Euler angles (0 °, 126 °, 0 °) is used. However, as the piezoelectric substrate, a LiTaO ₃ substrate having another crystal orientation may be used, or a substrate made of another piezoelectric single crystal may be used. Alternatively, a piezoelectric substrate formed by laminating a piezoelectric thin film on an insulating substrate may be used. Note that there is a relation of Euler angles (φ, θ, ψ) θ = cut angle + 90 °.

A first insulator layer 2 is formed on the entire surface of the LiTaO ₃ substrate 1. In the present embodiment, the first insulator layer 2 is formed of a SiO ₂ film.

  The formation method of the 1st insulator layer 2 may be performed by appropriate methods, such as printing, vapor deposition, or sputtering. Moreover, the thickness of the 1st insulator layer 2 is made equal to the thickness of the IDT electrode formed later.

  Next, as shown in FIG. 1B, a resist pattern 3 is formed by using a photolithography technique. In the resist pattern 3, the resist pattern 3 is configured so that the resist is located except for the region where the IDT is formed.

  Next, as shown by an arrow in FIG. 1C, a portion of the first insulator layer 2 positioned below the resist 3 is formed by a reactive ion etching method (RIE) that irradiates an ion beam. Remove the remaining parts.

When SiO ₂ is etched by RIE using a fluorine-based gas, a residue may be generated due to a polymerization reaction. In this case, after performing RIE, it can respond by processing with BHF (buffered hydrofluoric acid) etc.

  Thereafter, a Cu film and a Ti film are formed to a thickness equal to that of the first insulator layer 2. As shown in FIG. 1D, the Cu film 4 is applied to the region where the first insulator layer 2 is removed, that is, the region where the IDT is formed, and at the same time, the Cu film 4 is also applied to the resist pattern 3. Is done. Next, a Ti film 5 is formed as an overall protective metal film. As shown in FIG. 1E, the Ti film 5 is applied on the upper surface of the IDT electrode 4 </ b> A and the Cu film 4 on the resist pattern 3. Therefore, the IDT electrode 4 </ b> A has a side surface covered with the first insulating layer 2 and an upper surface covered with the Ti film 5. Thus, the IDT electrode 4A and the protective metal film are formed, and the total thickness of the IDT electrode 4A and the Ti film 5 as the protective metal film is the same as the thickness of the first insulator layer 2. It is comprised so that it may have.

  Thereafter, the resist pattern 3 is removed using a resist stripping solution. In this way, as shown in FIG. 1F, the IDT electrode 4A is formed in the remaining region except the region where the first insulator layer 2 is provided, and the upper surface of the IDT electrode 4A is Ti. A structure covered by the membrane 5 is obtained.

Thereafter, as shown in FIG. 1G, a SiO ₂ film is formed as a second insulator layer 6 on the entire surface.

  Thus, the 1-port surface acoustic wave resonator 11 shown in FIG. 6 was obtained.

  In FIGS. 1A to 1G, only the portion where the IDT electrode 4A is formed is extracted and described. However, as shown in FIG. 6, the surface acoustic wave resonator 11 includes reflectors 12 and 13 on both sides of the IDT electrode 4 </ b> A in the surface acoustic wave propagation direction. The reflectors 12 and 13 are also formed by the same process as the IDT electrode 4A.

In the above embodiment, since the 1-port surface acoustic wave resonator 11 is configured, one IDT electrode 4A is formed on the LiTaO ₃ substrate 1, but depending on the use of the surface acoustic wave device. A plurality of IDT electrodes may be formed, and the reflector may be formed in the same process as the IDT as described above, or the reflector may not be provided.

For comparison, a 1-port surface acoustic wave resonator was manufactured in accordance with the conventional method for manufacturing a surface acoustic wave device having a SiO ₂ film shown in FIG. However, also in this comparative example, as a substrate material, a LiTaO ₃ substrate of 36 ° rotation Y-plate X propagation (Euler angles (0 °, 126 °, 0 °)) was used, and the IDT electrode was formed of Cu. As is apparent from the manufacturing method shown in FIG. 109, after the IDT electrode 53A is formed, since the SiO ₂ film 54 is formed, irregularities on the surface of the SiO ₂ film 54 was forced to occur. In the comparative example, the normalized film thickness h / λ of the IDT electrode made of Cu is 0.042, where h is the thickness of the IDT electrode and λ is the wavelength of the surface acoustic wave, and the normalized film thickness Hs / λ of the SiO ₂ film. FIG. 4 shows impedance characteristics and phase characteristics when (Hs is the thickness of the SiO ₂ film) is 0.11, 0.22, and 0.33. As is apparent from FIG. 4, as the normalized film thickness Hs / λ of the SiO ₂ film increases, the impedance ratio, which is the ratio between the impedance at the antiresonance point and the impedance at the resonance point, decreases.

FIG. 5 shows the relationship between the normalized film thickness Hs / λ of the SiO ₂ film of the surface acoustic wave resonator manufactured in the comparative example and the MF (Figure of Merit) of the resonator. As can be seen from FIG. 5, the MF decreases as the thickness of the SiO ₂ film increases.

That is, when the IDT electrode and the SiO ₂ film are formed according to the conventional method shown in FIG. 109, even if the IDT electrode is formed of Cu, the characteristics greatly deteriorate as the thickness of the SiO ₂ film increases. did. This is considered to be due to the fact that the above-mentioned unevenness must be generated on the surface of the SiO ₂ film.

On the other hand, according to the manufacturing method of the present embodiment, even when the thickness of the SiO ₂ film is increased, the characteristics are hardly deteriorated, as shown in FIGS.

FIG. 7 is a diagram showing changes in impedance characteristics and phase characteristics when the thickness of the SiO ₂ film when the surface acoustic wave resonator 11 is obtained according to the above-described embodiment, that is, the thickness of the second insulator layer 6 is changed. It is. The broken lines in FIGS. 8 and 9 are diagrams showing changes in γ and MF of the resonator when the film thickness Hs / λ of the SiO ₂ film is changed in the example.

  8 and 9, the result of the comparative example is shown by a solid line.

As is clear from comparison of FIG. 7 with FIG. 4, in the above-described embodiment, the impedance is lowered even when the normalized film thickness Hs / λ of the SiO ₂ film is increased, compared with the comparative example. I find it difficult.

Further, as is apparent from the results of FIGS. 8 and 9, compared with the comparative example, the manufacturing method of the example suppresses the deterioration of the characteristics due to the increase in the normalized film thickness Hs / λ of the SiO ₂ film. You can see that

That is, according to the manufacturing method of the present embodiment, even when the thickness of the SiO ₂ film is increased as described above, the impedance ratio is hardly lowered and the deterioration of the characteristics can be suppressed.

On the other hand, FIG. 10 is a diagram showing the relationship between the film thickness of the SiO ₂ film and the frequency temperature characteristics TCF of the surface acoustic wave resonators obtained by the manufacturing methods of the comparative example and the example.

  In FIG. 10, the solid line indicates the result of the comparative example, and the broken line indicates the result of the example.

As is apparent from FIG. 10, according to the manufacturing method of the example, when the film thickness of the SiO ₂ film is increased, the frequency temperature characteristic TCF can be ideally improved as the film thickness increases. .

  Therefore, it can be seen that by adopting the manufacturing method of the above embodiment, it is possible to provide a surface acoustic wave resonator capable of effectively improving the temperature characteristic without causing the characteristic deterioration.

  In addition, in the manufacturing method of the present embodiment, the IDT electrode is made of Cu having a higher density than Al. Therefore, the IDT electrode 4A has a sufficient reflection coefficient, and can suppress unwanted ripples appearing on the resonance characteristics. This will be described below.

A surface acoustic wave resonator of a second comparative example was fabricated in the same manner as in the above example except that an Al film was used instead of Cu. However, the normalized film thickness Hs / λ of the SiO ₂ film was 0.08. That is, the normalized film thickness of the first insulator layer was set to 0.08. The impedance and phase characteristics of the surface acoustic wave resonator thus obtained are shown by solid lines in FIG.

Further, the impedance and phase characteristics of the surface acoustic wave resonator configured in the same manner as in the second comparative example except that the SiO ₂ film is not formed are shown by broken lines in FIG.

As is clear from the solid line in FIG. 11, even if the manufacturing method of the above embodiment is followed, when the IDT electrode is formed of Al and the SiO ₂ film is formed, a large ripple indicated by an arrow A in FIG. Can be seen between the resonance point and the antiresonance point. Further, it can be seen that such ripple does not appear in the surface acoustic wave resonator having no SiO ₂ .

Therefore, it can be seen that even if the frequency temperature characteristic is improved by forming the SiO ₂ film, when the IDT electrode is formed of Al, the ripple A appears and the characteristic is deteriorated. As a result of further study on this point, the present inventor has found that if a metal having a higher density than Al is used as the IDT electrode, the reflection coefficient of the IDT electrode can be increased, thereby suppressing the ripple A. I found it.

That is, according to the same manufacturing method as in the above example, the surface acoustic wave resonator was manufactured in the same manner as in the above example by varying the density of the metal constituting the IDT electrode 4. The impedance characteristics of the surface acoustic wave resonator thus obtained are shown in FIGS. Figure 12 (a) ~ (e), respectively, the ratio [rho ₁ / [rho ₂ for the density [rho ₂ of the IDT electrode and the protective metal film first insulator layer having an average density [rho ₁ of the laminated structure of, 2.5, The results for 2.0, 1.5, 1.2 and 1.0 are shown.

  12A to 12E, the ripple A is shifted out of the band in FIGS. 12A to 12C, and the ripple A is remarkably suppressed in FIG. 12A. You can see that

  Therefore, from the result of FIG. 12, if the density ratio of the laminated structure of the IDT electrode and the protective metal film to the first insulator layer is 1.5 times or more, the ripple A is outside the resonance frequency-antiresonance frequency band. It can be seen that good characteristics can be obtained. More preferably, it can be seen that if the density ratio is 2.5 times or more, the ripple itself can be reduced.

  In FIGS. 12A to 12E, the Ti film was laminated on the IDT electrode 4A according to the above embodiment, so the average density was used. In the present invention, on the IDT electrode 4A, The protective metal film may not be provided. In that case, the thickness of the IDT electrode 4A is preferably the same as the thickness of the first insulator layer, and the ratio of the density of the IDT electrode to the density of the first insulator layer is preferably 1.5 times or more. More preferably, it should be 2.5 times or more, and it was confirmed that the same effect as described above was obtained.

Therefore, in the surface acoustic wave resonator in which the IDT electrode is covered with the SiO ₂ film, the density of the IDT electrode or the average density of the stacked body of the IDT electrode and the protective metal film is the first located on the side of the IDT electrode. It can be seen that if the density is higher than the density of the insulator layer, the reflection coefficient of the IDT electrode can be increased, thereby suppressing the deterioration of the characteristics appearing between the resonance point and the antiresonance point.

  Examples of metals or alloys having a higher density than Al include Cu, Ag, Au, and alloys mainly composed of these.

  Further, preferably, if the protective metal film is laminated on the IDT electrode as in the above embodiment, a resist pattern is obtained as apparent from the manufacturing method shown in FIGS. When peeling 3, the side surface of the IDT electrode 4 </ b> A is covered with the first insulator layer 2 and the upper surface is covered with the protective metal film 6, so that the corrosion of the IDT electrode 4 </ b> A can be prevented. . Therefore, it can be seen that a surface acoustic wave resonator having even better characteristics can be provided.

Further, the first and second insulator layers may be formed of other insulating materials having an effect of improving temperature characteristics such as SiO _x N _y other than SiO ₂ . The first and second insulator layers may be made of different insulating materials, or may be made of the same material as described above.

FIG. 13 shows the normalized thickness H / λ of IDT when IDT electrodes are formed using various metals with various thicknesses on a LiTaO ₃ substrate with Euler angles (0 °, 126 °, 0 °). It is a figure which shows the relationship of an electromechanical coupling coefficient.

When the normalized film thickness of the electrode obtained from FIG. 13 and having an electromechanical coupling coefficient larger than that of Al was examined for each metal, the result shown in FIG. 14 was obtained. That is, FIG. 14 shows that when an IDT electrode made of metal of various densities is formed on the LiTaO ₃ substrate, the electromechanical coupling coefficient is larger than that when an IDT electrode made of Al is formed as described above. It is a figure which shows the electrode film thickness range which becomes.

In FIG. 14, the upper limit of the film thickness range of the electrodes made of each metal is the limit value in the range where the electromechanical coupling coefficient is larger than that of Al, and the lower limit of the electrode film thickness range of each metal indicates the production limit. When the electrode film thickness range with a large electromechanical coupling coefficient is y, the density is x, and the upper limit is approximated by a quadratic equation, y = 0.00025x ² −0.01056x + 0.16473.

Therefore, as will be apparent from the description of specific examples of each electrode material described later, the 14 ° -50 ° rotated Y-plate X propagation (Euler angle (0 °, 104 ° -140 °, 0 °)) In the structure in which the electrode is formed on the piezoelectric substrate made of LiTaO ₃ and the SiO ₂ film is formed in the range of the normalized film thickness Hs / λ 0.03 to 0.45, the normalized film thickness of the electrode H / λ is
0.005 ≦ H / λ ≦ 0.00025 × ρ ² −0.01056 × ρ + 0.16473 Formula (1)
When satisfying, the electromechanical coupling coefficient can be increased as is apparent from the results of FIG. Note that ρ represents the average density of the electrodes.

  In the present invention, the electrode is formed using a metal having a higher density than the above-described aluminum. In this case, the electrode may be made of a metal having a higher density than aluminum, or may be made of an alloy mainly composed of aluminum. Moreover, you may be comprised by the laminated structure of the main metal film which consists of aluminum or the alloy which has aluminum as a main component, and the subordinate metal film which consists of a metal different from this metal film. When the electrode is composed of a laminated film, when the average density of the electrode is ρ and the density of the metal of the main electrode layer is ρ0, the average density satisfying ρ0 × 0.7 ≦ ρ ≦ ρ0 × 1.3 I just need it.

  In the present invention, the surface of the second insulator layer is flattened as described above, and this flattening may be any as long as it has irregularities of 30% or less of the film thickness of the electrode. If it exceeds 30%, the effect of planarization may not be sufficiently obtained.

  Furthermore, as described above, the planarization of the second insulator layer is performed by various methods. For example, a flattening method by etch back, a flattening method using an oblique incidence effect by a reverse sputtering effect, a method for polishing the surface of the insulating layer, a method for polishing an electrode, and the like can be given. Two or more of these methods may be used in combination. Details of these methods will be described with reference to FIGS.

102A to 102C show a method of planarizing the surface of the insulator layer by an etch back method. First, as shown in FIG. 102A, an electrode 42 is formed on a piezoelectric substrate 41, and then an insulating layer 43 is formed. As shown in FIG. 102B, a resist 44 is formed on the insulator layer 43 by spin coating or the like. The surface of the resist 44 is flat. Therefore, from this state, the surface of the insulator layer 43 made of SiO ₂ or the like can be planarized by etching by reactive ion etching, that is, by etch back (FIG. 102 (c)).

  103A to 103D are schematic cross-sectional views for explaining the reverse sputtering method. Here, the electrode 42 is formed on the piezoelectric substrate 41, and then the insulating layer 43 is formed. Then, the surface of the insulating layer 43 is irradiated with argon ions or the like by sputtering. These ions are used for sputtering the substrate 41. When ions collide with the substrate and perform sputtering, a larger sputtering effect can be obtained when incident on an oblique surface than on a flat surface. This is known as the oblique incidence effect. Due to this effect, the surface of the insulator layer 43 is planarized as the sputtering proceeds, as shown in FIGS.

  104 (a) and 104 (b) are schematic cross-sectional views for explaining a method for planarizing an insulating layer by polishing. As shown in FIG. 104A, after the electrode 42 and the insulator layer 43 are formed on the substrate 41, the surface of the insulator layer 43 can be planarized by mechanically or chemically polishing. it can.

  105 (a) to 105 (c) show a method of flattening by polishing the electrode. Here, as shown in FIG. 105A, after the first insulator layer 45 is formed on the substrate 41, a metal film 42A made of an electrode material is formed on the entire surface by vapor deposition or the like. Thereafter, as shown in FIG. 105 (b), the metal film 42A is mechanically or chemically polished to thereby form the electrode 42 and the first region formed around the region where the electrode 42 is provided. An insulating layer 45 is formed. In this way, the upper surfaces of the first insulator layer 45 and the electrode 42 are flush with each other and flattened. Thereafter, as shown in FIG. 105C, by forming the second insulator 46, an insulator layer having a flat surface can be formed.

  The present invention can be applied to various surface acoustic wave devices. Examples of such surface acoustic wave devices are shown in FIGS. 106 (a) and (b) to FIG. FIGS. 106A and 106B are schematic plan views showing the electrode structures of the 1-port surface acoustic wave resonator 47 and the 2-port surface acoustic wave resonator 48, respectively. A two-port surface acoustic wave resonator filter may be configured using the same electrode structure as that of the two-port surface acoustic wave resonator 48 shown in FIG.

  Further, FIGS. 107 and 108 are schematic plan views showing electrode structures of a ladder type filter and a lattice type filter, respectively. By forming an electrode structure such as the ladder filter 49a and the lattice filter 49b shown in FIGS. 107 and 108 on the piezoelectric substrate, the ladder filter and the lattice filter can be configured according to the present invention.

  However, the present invention is not limited to the surface acoustic wave device having the electrode structure shown in FIGS. 106 and 107 but can be applied to various surface acoustic wave devices.

  In the surface acoustic wave device according to the present invention, preferably, a surface acoustic wave device using a leaky acoustic wave is configured. Japanese Laid-Open Patent Publication No. 6-164306 discloses a surface acoustic wave device having a electrode made of a heavy metal such as Au and using a Love wave having no propagation attenuation. Here, by using heavy metal as an electrode, the sound velocity of the propagated surface acoustic wave is made slower than the slow transverse wave bulk wave of the substrate, thereby eliminating leakage components and using love waves as non-leakage surface acoustic waves. Has been.

  However, in the Love wave, the speed of sound is inevitably slow, and the IDT pitch must be reduced accordingly. Therefore, the difficulty of processing increases and the processing accuracy deteriorates. In addition, the line width of the IDT is reduced and the loss due to resistance is also increased. Therefore, the loss must be large.

  In contrast, in the present invention, unlike a surface acoustic wave device using a love wave as described above, a leaky surface acoustic wave having a high sound velocity is used despite the use of an electrode made of a metal heavier than Al. In this case, it is possible to reduce the propagation loss. Therefore, a low-loss surface acoustic wave device can be configured.

  Hereinafter, based on the above-described results, individual examples in the case where the electrode is made of a metal having a density higher than that of Al will be described for each metal material.

The metal having a density higher than that of Al used in the present invention is (1) a density of 15000 to 23000 kg / m ³ and a Young's modulus of 0.5 × 10 ^{11 to} 1.0 × 10 ¹¹ N / m ² or a shear wave velocity. Is a metal having 1000 to 2000 m / s, for example, Au, (2) density 5000 to 15000 kg / m ³ and Young's modulus 0.5 × 10 ^{11 to} 1.0 × 10 ¹¹ N / m ² or shear wave speed of 1000 to 2000 m / 3, for example, Ag, (3) density 5000-15000 kg / m ³ and Young's modulus 1.0 × 10 ¹¹ -2.05 × 10 ¹¹ N / m ² or shear wave velocity is 2000-2800 m / s Metal such as Cu, (4) Metal having a density of 15000 to 23000 kg / m ³ and Young's modulus of 2.0 × 10 ^{11 to} 4.5 × 10 ¹¹ N / m ² or a shear wave speed of 2800 to 3500 m / s For example, tungsten, (5) a metal having a density of 15000 to 23000 kg / m ³ and a Young's modulus of 1.0 × 10 ^{11 to} 2.0 × 10 ¹¹ N / m ² or a shear wave velocity of 2000 to 2800 m / s, such as tantalum, (6) A metal having a density of 15000 to 23000 kg / m ³ and a Young's modulus of 1.0 × 10 ^{11 to} 2.0 × 10 ¹¹ N / m ² or a shear wave velocity of 1000 to 2000 m / s, such as platinum, (7) density Examples thereof include metals having a Young's modulus of 5,000 to 15000 kg / m ³ and a Young's modulus of 2.0 × 10 ^{11 to} 4.5 × 10 ¹¹ N / m ² or a shear wave velocity of 2800 to 3500 m / s, such as Ni and Mo.

[Example where the electrode is mainly Au]
FIG. 15 is a plan view for explaining a longitudinally coupled resonator filter as a surface acoustic wave device according to another embodiment of the present invention.

The surface acoustic wave device 21 has a structure in which IDTs 23 a and 23 b and reflectors 24 a and 24 b are formed on the upper surface of a LiTaO ₃ substrate 22. An SiO ₂ film 15 is formed so as to cover the IDTs 23a and 23b and the reflectors 24a and 24b. As the LiTaO ₃ substrate 22, a 25 ° to 58 ° rotated Y-plate X propagation (Euler angles (0 °, 115 ° to 148 °, 0 °)) LiTaO ₃ substrate is used. In the rotating Y plate X propagation LiTaO ₃ substrate having a cut angle outside this range, the attenuation constant is large and the TCF is also deteriorated.

  The IDTs 23a and 23b and the reflectors 24a and 24b are made of a metal having a higher density than Al. Such a metal includes at least one metal selected from the group consisting of Au, Pt, W, Ta, Ag, Mo, Cu, Ni, Co, Cr, Fe, Mn, Zn, and Ti, or at least the metal An alloy having one type as a main component can be mentioned.

  As described above, since the IDTs 23a and 23b and the reflectors 24a and 24b are made of a metal having a higher density than that of Al, the film thicknesses of the IDTs 23a and 23b and the reflectors 24a and 24b are compared with those using Al. Even when the thickness is reduced, the electromechanical coupling coefficient and the reflection coefficient can be increased as shown in FIGS.

As described above, the electrode film thickness can be reduced. Regarding the thickness of the SiO ₂ film 25, it is preferable that the film thickness Hs / λ normalized by the wavelength of the surface acoustic wave is in the range of 0.03 to 0.45, as will be apparent from experimental examples described later. Hs represents the total thickness when the first and second insulating layers are made of SiO ₂ , and λ represents the surface acoustic wave wavelength. By setting it within this range, the attenuation constant can be made much smaller than when there is no SiO ₂ film, and the loss can be reduced.

  Although it differs depending on the material constituting the IDT, for example, when it is made of an Au film, the film thickness standardized with the surface acoustic wave wavelengths of the IDTs 23a and 23b is preferably 0.013 to 0.030. If the Au film is thin, the IDT has a drag resistance, so 0.021 to 0.03 is more preferable.

In the surface acoustic wave device according to the present invention, as described above, the IDTs 23a and 23b are made of a metal having a density higher than that of Al on the LiTaO ₃ substrate 22, and the electrode thicknesses of the IDTs 23a and 23b are reduced. Can do. Therefore, good frequency temperature characteristics are realized by forming the SiO ₂ film 25 with good characteristics. This will be described based on a specific example.

When an IDT made of Al is formed on a LiTaO ₃ substrate of 36 ° rotation Y plate X propagation, Euler angles (0 °, 126 °, 0 °), and Au, Ta, Ag, Cr, W, Cu, FIGS. 16, 18 and 17 show changes in the electromechanical coupling coefficient K _{saw, the} attenuation constant (α), and the reflection coefficient | ref | when the IDTs made of Zn, Mo, and Ni are formed in various film thicknesses. . The numerical calculation was performed according to the method of JJ Champbell and WR Jones: IEEE Trans. Sonic & Ultrason. SU-15.p209 (1968), assuming that the electrodes were uniform over the entire surface.

As is clear from FIG. 16, in the IDT made of Al, when the normalized film thickness H / λ is 0.10, the electromechanical coupling coefficient K _saw is about 0.27. H represents thickness, and λ represents the surface acoustic wave wavelength. On the other hand, in an IDT composed of Au, Ta, Ag, Cr, W, Cu, Zn, Mo, and Ni, when H / λ is in the range of 0.013 to 0.035, a larger electromechanical coupling coefficient K _Saw can be realized. However, as is apparent from FIG. 18, the attenuation constant α is almost 0 in the IDT made of Al regardless of the film thickness H / λ, whereas Au, Ta, Ag, Cr, W, Cu, In the IDT composed of Zn, Mo, and Ni, the attenuation constant becomes very large.

FIG. 25 is a diagram showing a relationship between θ and an electromechanical coupling coefficient in a structure in which an IDT and SiO ₂ film made of Au is formed on a LiTaO ₃ substrate with Euler angles (0 °, θ, 0 °). It is. Here, the normalized thickness of the IDT composed of Au, when the 0.022,0.025 and 0.030, and the normalized thickness Hs / lambda of the SiO ₂ film, 0.00 (SiO ₂ film ), 0.10, 0.20, 0.30, and 0.45.

As can be seen from FIG. 25, as the SiO ₂ film becomes thicker, the electromechanical coupling coefficient K _saw becomes smaller. As will be described later, let us consider a case where the film thickness of the IDT is reduced in order to suppress the deterioration of characteristics due to the SiO ₂ film. As is apparent from FIG. 16 described above, when the standardized film thickness is reduced to 0.04 in the conventional IDT made of Al, the electromechanical coupling coefficient K _saw is 0. Even when the SiO ₂ film is not formed. It becomes 245 and becomes small. Further, when the standardized film thickness of IDT made of Al is set to 0.04 and the SiO ₂ film is formed, the electromechanical coupling coefficient K _saw is further reduced, and it is difficult to increase the bandwidth practically.

On the other hand, as is apparent from FIG. 25, in the structure in which the IDT made of Au is formed and the SiO ₂ film is formed, the Euler angle θ is set to 128.5 ° or less, so that the specification of the SiO ₂ film can be obtained. It can be seen that even when the chemical thickness Hs / λ is about 0.45, the electromechanical coupling coefficient K _saw is 0.245 or more. Further, when an SiO ₂ film having a normalized film thickness of about 0.30 is formed, the electromechanical coupling coefficient K _saw can be set to 0.245 or more by setting the Euler angle θ to 132 ° or less. it can. As will be described later, when the Euler angle θ is smaller than 115 °, the damping constant increases, which is not practical. Accordingly, the Y plate X propagation at 25 ° to 42 ° rotation (Eulerian angle (0 ± 3 °, 115 ° to 132 °, 0 ± 3 °)), more preferably the 25 ° to 38.5 ° rotation Y plate X propagation. It can be seen that it is preferable to use a LiTaO ₃ substrate (Euler angle (0 ± 3 °, 115 ° -128.5 °, 0 ± 3 °)).

On the other hand, the frequency temperature characteristic (TCF) of the LiTaO ₃ substrate with a 36 ° rotation Y plate X propagation and Euler angles (0 °, 126 °, 0 °) is −30 to −40 ppm / ° C., which is not sufficient. In order to improve the frequency temperature characteristic TCF to be within a range of ± 20 ppm / ° C., on a LiTaO ₃ substrate of 36 ° rotation Y plate X propagation, Euler angles (0 °, 126 °, 0 °), FIG. 19 shows changes in frequency temperature characteristics when an IDT made of Au is formed and SiO ₂ films are formed in various thicknesses. In FIG. 19, ◯ represents a theoretical value, and x represents an experimental value. Here, the normalized film thickness of the IDT made of Au is H / λ = 0.020.

As is apparent from FIG. 19, it can be seen that the formation of the SiO ₂ film improves the frequency temperature characteristics. In particular, it can be seen that when the normalized film thickness Hs / λ of the SiO ₂ film is in the vicinity of 0.25, the TCF is 0.

Further, as the rotating Y plate X propagation LiTaO ₃ substrate, the cut angles are 36 ° (Euler angles (0 °, 126 °, 0 °)) and 38 ° (Euler angles (0 °, 128 °, 0 °)). Using the two types of Euler angle LiTaO ₃ substrates, numerically analyzed the change in the attenuation constant α when the thickness of the IDT made of Au and the thickness of the SiO ₂ film were variously changed. The results are shown in FIGS. Note that the film thickness value of Au in FIGS. 20 and 21 is H / λ. As is apparent from FIGS. 20 and 21, it can be seen that the attenuation constant α can be reduced by selecting the thickness of the SiO ₂ film regardless of the thickness of the IDT made of Au. That is, as apparent from FIG. 20 and FIG. 21, if the film thickness Hs / λ of the SiO ₂ film is 0.03 to 0.45, more preferably 0.10 to 0.35, It can be seen that the attenuation constant α can be made extremely small even when an IDT made of an Euler angle LiTaO ₃ substrate and any film thickness of Au is formed.

  Furthermore, it can be seen from FIG. 17 that when using IDT made of Au, a sufficiently large reflection coefficient is obtained even with a thin film thickness as compared with Al.

Accordingly, from the results shown in FIGS. 16 to 21, when an IDT made of Au having a film thickness H / λ of 0.013 to 0.030 is formed on the LiTaO ₃ substrate, the film thickness Hs / λ of the SiO ₂ film is If the range is 0.03 to 0.45, not only a large electromechanical coupling coefficient can be obtained, but also the attenuation constant α can be made very small and a sufficient reflection coefficient can be obtained.

In the embodiment described above, an IDT made of Au having a normalized film thickness of H / λ = 0.020 is formed on a LiTaO ₃ substrate having a cut angle of 36 ° (Euler angles (0 °, 126 °, 0 °)). The attenuation-frequency characteristics of the surface acoustic wave device 11 of the example formed by further forming the SiO ₂ film having the normalized film thickness Hs / λ = 0.1 are shown by broken lines in FIG. For comparison, in the surface acoustic wave filter, the attenuation frequency characteristic of the structure before forming the SiO ₂ film is shown by a solid line.

As is apparent from FIG. 22, the insertion loss is improved although the electromechanical coupling coefficient is slightly reduced from 0.30 to 0.28 by the formation of the SiO ₂ film. Therefore, as is clear from FIG. 22, it is confirmed that the attenuation constant α is reduced if the thickness of the SiO ₂ film is in the specific range.

The inventor of the present application forms IDT made of Au with a normalized film thickness of 0.02 on a rotating Y-plate X-propagating LiTaO ₃ substrate with various Euler angles based on the above-described knowledge, and further with various thicknesses. A one-port surface acoustic wave resonator was fabricated by forming a SiO ₂ film. In this case, the normalized film thickness of the SiO ₂ film was 0.10, 0.20, 0.30, and 0.45. The Q value of each 1-port surface acoustic wave resonator thus obtained was measured. The results are shown in FIG.

In general, the larger the Q value of the resonator, the higher the steepness of the filter characteristics from the pass band to the attenuation band when used as a filter. Therefore, when a steep filter is required, a larger Q value is desirable. As is clear from FIG. 26, the Q value is maximized in the vicinity of (0 °, 138 °, 0 °) when the cut angle is 48 ° rotated Y plate and Euler angles regardless of the thickness of the SiO ₂ film. It can be seen that the Q value is relatively large in the range of cut angles of 42 ° to 58 ° (Euler angles (0 °, 132 ° to 148 °, 0 °)).

Accordingly, as is clear from FIG. 26, a cut angle 42 ° to 58 ° rotation Y plate (Euler angles (0 °, 132 ° ~148 ° , 0 °)) LiTaO 3 substrate is used, the LiTaO ₃ substrate In addition, it is possible to obtain a large Q value by forming at least one IDT made of a metal having a higher density than Au and further forming a SiO ₂ film on the LiTaO ₃ substrate so as to cover the IDT. I understand. Preferably, as apparent from FIG. 26, the cut angle is a 46.5 ° to 53 ° rotated Y plate (Euler angles (0 °, 136.5 ° to 143 °, 0 °)).

In the present invention, an adhesion layer may be formed on the upper surface of the IDT. That is, as shown in FIG. 27A, the IDT 33 may be formed on the LiTaO ₃ substrate 32, and the adhesion layer 34 may be formed on the upper surface of the IDT 33. The adhesion layer 34 is disposed between the IDT 33 and the SiO ₂ film 35. The adhesion layer 34 is provided to increase the adhesion strength of the SiO ₂ film 35 to the IDT 33. As a material constituting such an adhesion layer 34, Pd, Al, or an alloy thereof is preferably used. Further, the adhesion layer 34 may be configured using not only a metal but also a piezoelectric material such as ZnO, or other ceramics such as Ta ₂ O ₃ or Al ₂ O ₃ . By forming the adhesion layer 34, the adhesion strength between the IDT 33 made of a metal having a higher density than Al and the SiO ₂ film 35 is increased, thereby suppressing the film peeling of the SiO ₂ film.

The thickness of the adhesion layer 34 is desirably about 1% or less of the wavelength of the surface acoustic wave so as not to affect the entire surface acoustic wave. In FIG. 27A, the adhesion layer 34 is formed on the upper surface of the IDT 33. However, as shown in FIG. 27B, the adhesion layer 34A is also formed on the LiTaO ₃ substrate at the interface with the SiO ₂ film 35. May be formed. Further, as shown in FIG. 27C, the adhesion layer 34 may be formed so as to cover not only the upper surface of the IDT 33 but also the side surfaces thereof.

As another configuration for improving the adhesion strength of the SiO ₂ film, in a plurality of electrodes including a bus bar other than IDT and a pad for connection to the outside, each of the plurality of electrodes is a base metal made of the same material as IDT. A layer and an upper metal layer made of Al or an Al alloy may be used. That is, for example, as an electrode film constituting the reflectors 24a and 24b shown in FIG. 15, a base metal layer made of the same material as the IDTs 23a and 23b, and an Al film may be laminated on the base metal layer. Thus, by providing the upper metal layer made of Al or Al alloy, the adhesion strength with the SiO ₂ film can be increased. In addition, the electrode cost can be reduced, and the Al wedge bond property can be further improved.

  Examples of electrodes other than the IDT include not only reflectors, bus bars, and external electrode connection pads, but also lead electrodes formed as necessary. The Al alloy is not particularly limited, and examples thereof include an Al—Ti alloy and an Al—Ni—Cr alloy.

Even when an Euler angle rotating Y-plate X-propagating LiTaO ₃ substrate other than the experimental example described above is used, when an IDT made of Au is formed, the SiO ₂ film that minimizes the attenuation constant α is formed. The present inventors have confirmed that there is a thickness. That is, if the film thickness Hs / λ of the SiO ₂ film is in a specific range, the attenuation constant α can be reduced as in the case of the experimental example. On the other hand, FIGS. 28 to 36 show the relationship between Euler angles and α when the film thickness Hs / λ of the SiO ₂ film is 0.1 to 0.45. From these figures, it became clear that the Euler angle θ at which α is minimized decreases as the thickness of the SiO ₂ film increases. Therefore, even when a rotating Y-plate X-propagating LiTaO ₃ substrate having another Euler angle is used, the thickness of the SiO ₂ film is selected in the structure in which the IDT made of Au is formed and the SiO ₂ film is laminated. Thus, a surface acoustic wave device having a frequency temperature characteristic TCF as good as half or less, a large electromechanical coupling coefficient, and a large reflection coefficient can be formed as compared with the conventional surface acoustic wave device. Preferred combinations of the Euler angle of the LiTaO ₃ substrate capable of exhibiting such an effect, the electrode thickness of the IDT made of Au, and the thickness of the SiO ₂ film are as shown in Tables 16 and 17 below. It has been confirmed.

  The Euler angle θ may deviate from −2 ° to + 4 ° from a desired angle. This deviation is calculated from the result of calculation in the present specification based on the metal film formed on the entire surface of the substrate. Therefore, an error may occur in the above range in an actual surface acoustic wave device.

In manufacturing the surface acoustic wave device according to the present invention, after an IDT made of a metal mainly composed of Au is formed on a rotating Y-plate X-propagating LiTaO ₃ substrate, the frequency is adjusted in that state, and then the attenuation constant is set. It is desirable to form a SiO ₂ film having a thickness within a range where α can be reduced. This will be described with reference to FIGS. FIG. 23 shows a 36 ° rotated Y-plate X propagation (Euler angle (0 °, 126 °, 0 °)) LiTaO ₃ substrate, an IDT made of various thicknesses of Au, and various thicknesses of SiO ₂ films. The change of the sound velocity of the leaky surface acoustic wave when forming is shown. FIG. 24 shows a case where IDTs made of various thicknesses of Au are formed on a LiTaO ₃ substrate having the same Euler angle, and the normalized film thickness of the SiO ₂ film formed thereon is changed. Changes in the sound velocity of leaky surface acoustic waves are shown. As is clear from comparison between FIG. 23 and FIG. 24, the change in the sound velocity of the surface acoustic wave is much greater when the film thickness of Au is changed than when the film thickness of the SiO ₂ film is changed. large. Therefore, it is desirable to adjust the frequency prior to the formation of the SiO ₂ film. For example, it is desirable to adjust the frequency after forming an IDT made of Au by laser etching or ion etching. Particularly preferably, when the normalized film thickness of Au is in the range of 0.015 to 0.03, the change in the sound speed due to the SiO ₂ film is reduced, and the frequency fluctuation due to variations in the SiO ₂ film can be reduced. .

  The Euler angle θ may deviate from −2 ° to + 4 ° from a desired angle. This deviation is calculated from the result of calculation in the present specification based on the metal film formed on the entire surface of the substrate. Therefore, an error may occur in the above range in an actual surface acoustic wave device.

  In addition, during manufacture, Euler angles φ and ψ varied from 0 ° to ± 3 °, but almost the same characteristics as those of 0 ° were obtained.

[Example where the electrode material is Ag]
The surface acoustic wave device of this embodiment is the same as the surface acoustic wave device 21 shown in FIG. However, in this embodiment, the IDTs 23a and 23b are made of Ag.

  As will be described later, when the IDTs 23a and 23b are made of Ag, the film thickness H / λ normalized by the surface acoustic wave wavelengths of the IDTs 23a and 23b is preferably 0.01 to 0.08.

In the surface acoustic wave device according to the present invention, as described above, the IDTs 23a and 23b are made of Ag on the LiTaO ₃ substrate 22, and the electrode film thickness of the IDTs 23a and 23b can be reduced. Since an Euler angle LiTaO ₃ substrate is used, the attenuation constant can be significantly reduced, and a reduction in loss can be achieved. Further, the formation of the SiO ₂ film 25 realizes good frequency temperature characteristics. This will be described based on a specific experimental example.

The surface acoustic wave transmitted through the LiTaO ₃ substrate includes a leaky surface acoustic wave (LSAW) in addition to the Rayleigh wave. The leaky surface acoustic wave has a faster sound speed and a larger electromechanical coupling coefficient than the Rayleigh wave, but propagates while radiating energy into the substrate. Therefore, the leaky surface acoustic wave has an attenuation constant that causes a propagation loss.

FIG. 36 shows the normalized film thickness H / of the Ag film when an IDT made of Ag is formed on a 36 ° rotated Y-plate X-propagating LiTaO ₃ substrate (Euler angles (0 °, 126 °, 0 °)). The relationship between λ and the electromechanical coupling coefficient K _saw is shown. Note that λ represents the wavelength at the center frequency of the surface acoustic wave device.

As is apparent from FIG. 36, when the thickness H / λ of the Ag film is in the range of 0.01 to 0.08, the electromechanical coupling coefficient K _saw has no Ag film (H / λ = 0). It can be seen that it is 1.5 times or more. Further, when the thickness of the Ag film is in the range of H / λ = 0.02 to 0.06, the electromechanical coupling coefficient K _saw is 1.7 times or more compared to the case where the Ag film is not formed. It can be seen that when the film thickness H / λ of the Ag film is in the range of 0.03 to 0.05, the value is 1.8 times or more that when the Ag film is not formed.

  When the normalized film thickness H / λ of the Ag film exceeds 0.08, it is difficult to produce an IDT made of the Ag film. Therefore, since a large electromechanical coupling coefficient can be obtained and the IDT can be easily manufactured, the thickness of the IDT made of the Ag film is desirably in the range of 0.01 to 0.08, and more preferably The range is 0.02 to 0.06, more preferably 0.03 to 0.05.

Next, FIG. 37 shows changes in the frequency temperature coefficient TCF when an SiO ₂ film is formed on a LiTaO ₃ substrate. FIG. 37 shows SiO ₂ films on three types of LiTaO ₃ substrates with Euler angles (0 °, 113 °, 0 °), (0 °, 126 °, 0 °) and (0 °, 129 °, 0 °). The relationship between the normalized film thickness Hs / λ of the SiO ₂ film and TCF in the case where is formed is shown. Here, no electrode is formed.

As is apparent from FIG. 37, the TCF is within the range of the normalized film thickness Hs / λ of the SiO ₂ film of 0.15 to 0.45 regardless of whether θ is 113 °, 126 °, or 129 °. It can be seen that the range is from -20 to +20 ppm / ° C. However, since the formation of the SiO ₂ film takes time, the film thickness Hs / lambda of the SiO ₂ film 0.15 to 0.40 is desirable.

By depositing SiO ₂ film on the LiTaO ₃ substrate, but it has been known that TCF such Rayleigh waves is improved, the LiTaO ₃ substrate, and forming an electrode made of Ag, further SiO ₂ film In the structure in which the layers are laminated, there has been no report actually tested in consideration of the film thickness of the electrode made of Ag, the film thickness of SiO ₂ , the Euler angle, and the damping constant of the leaky elastic wave.

FIG. 38 shows an electrode made of Ag having a normalized film thickness H / λ of 0.10 or less on a LiTaO ₃ substrate with Euler angles (0 °, 120 °, 0 °), and a normalized film thickness Hs / λ of 0. The change of the attenuation constant α when an SiO ₂ film of ˜0.5 is formed is shown. As apparent from FIG. 38, when the film thickness Hs / λ of the SiO ₂ film is 0.2 to 0.40 and the film thickness H / λ of the Ag film is 0.01 to 0.10, the attenuation constant α is You can see that it is getting smaller.

On the other hand, FIG. 39 shows a case where an Ag film having a normalized film thickness H / λ of 0 to 0.10 is formed on a LiTaO ₃ substrate having an Euler angle of (0 °, 140 °, 0 °). A change in the attenuation constant α when a SiO ₂ film having a chemical thickness Hs / λ of 0 to 0.5 is formed is shown.

As is apparent from FIG. 39, when a LiTaO ₃ substrate with Euler angle θ = 140 ° is used, the thickness of the SiO ₂ film is changed as described above when the thickness of the Ag film is 0.06 or less. Even so, it can be seen that the attenuation constant α is large.

That is, in order to realize a good TCF, a large electromechanical coupling coefficient, and a small attenuation constant, the cut angle of the LiTaO ₃ substrate, that is, the Euler angle, the film thickness of the SiO ₂ film, and the film thickness of the electrode made of Ag, respectively. It can be seen that it is necessary to combine them optimally.

40 to 47, the normalized film thickness Hs / λ of the SiO ₂ film is 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4 or The relationship between θ and the attenuation constant α when an Ag film having a normalized film thickness H / λ of 0.1 or less on a LiTaO ₃ substrate is 0.45 is shown.

As apparent from FIGS. 40 to 47, when the thickness H / λ of the Ag film is 0.01 to 0.08, the thickness of the SiO ₂ film and the Euler angle θ are shown in Table 18 below. It can be seen that if any combination is selected, the frequency temperature characteristic TCF is good, the electromechanical coupling coefficient is large, and the attenuation constant α can be effectively suppressed. Desirably, even better characteristics can be obtained by selecting a more preferred Euler angle on the right side of Table 18 below.

More preferably, when the normalized film thickness of the Ag film is 0.02 to 0.06, the thickness of the SiO ₂ film and the Euler angle θ are any combination shown in Table 19 below. It is even more preferable that it is selected, and more desirably, by selecting a more preferable Euler angle on the right side of Table 19 below, even better characteristics can be obtained.

More preferably, when the normalized film thickness of the Ag film is 0.03 to 0.05, the thickness of the SiO ₂ film and the Euler angle θ are any combination shown in Table 20 below. If it is selected, better characteristics can be obtained. Even in this case, the characteristics can be further improved by selecting a more preferable Euler angle shown on the right side of Table 20 below.

  In the present invention, the IDT may be composed only of Ag, but may be composed of an Ag alloy or a laminate of Ag and another metal as long as Ag is mainly used. The IDT mainly composed of Ag may be 80% by weight or more of the entire IDT. Therefore, an Al thin film or a Ti thin film may be formed on the Ag base, and in this case as well, 80% by weight or more of the total of the base thin film and Ag may be composed of Ag.

In the above experiment, a LiTaO ₃ substrate having Euler angles (0 °, θ, 0 °) was used. However, in the Euler angles of the substrate material, variations of 0 ± 3 ° usually occur in φ and ψ. The effect of the present invention can be obtained even in a LiTaO ₃ substrate within such a variation range, that is, (0 ± 3 °, 113 ° to 142 °, 0 ± 3 °).

  The Euler angle θ may deviate from −2 ° to + 4 ° from a desired angle. This deviation is calculated from the result of calculation in the present specification based on the metal film formed on the entire surface of the substrate. Therefore, an error may occur in the above range in an actual surface acoustic wave device.

[Examples when Cu is used as an electrode material]
The surface acoustic wave device shown in FIG. 15 was configured in the same manner as in the case of using Au except that the electrode was formed of Cu. Since the electrode is made of Cu having a higher density than Al, the electromechanical coupling coefficient and the reflection coefficient can be increased.

FIG. 58 is a diagram showing the relationship between the electrode film thickness and the reflectance per one electrode film of the Cu electrode and the Al electrode when the normalized film thickness of the SiO ₂ film is 0.20.

  As shown in FIG. 58, when the electrode made of Cu is used as compared with the conventionally used electrode made of Al, the reflectance per electrode finger is increased, so the number of electrode fingers in the reflector is also increased. Can be reduced. Therefore, it is possible to reduce the size of the reflector, and hence the surface acoustic wave device.

  As will be described later, the film thickness H / λ normalized by the surface acoustic wave wavelengths of the IDTs 23a and 23b is preferably 0.01 to 0.08.

FIG. 48 shows an electrode made of Cu having a normalized film thickness H / λ of 0.10 or less on a LiTaO ₃ substrate with Euler angles (0 °, 120 °, 0 °), and a normalized film thickness Hs / λ of 0. The change of the attenuation constant α when an SiO ₂ film of ˜0.5 is formed is shown. As apparent from FIG. 48, when the film thickness Hs / λ of the SiO ₂ film is 0.2 to 0.40 and the film thickness H / λ of the Cu film is 0.01 to 0.10, the attenuation constant α is You can see that it is getting smaller.

On the other hand, FIG. 49 shows a case where a Cu film having a normalized film thickness H / λ of 0 to 0.10 is formed on a LiTaO ₃ substrate having an Euler angle of (0 °, 135 °, 0 °). A change in the attenuation constant α when a SiO ₂ film having a chemical thickness Hs / λ of 0 to 0.5 is formed is shown.

As is clear from FIG. 49, when the LiTaO ₃ substrate of θ = 135 ° is used, even if the film thickness of the Cu film and the film thickness of the SiO ₂ film are changed as described above, the attenuation constant α is You can see that it ’s big.

That is, in order to realize a good TCF, a large electromechanical coupling coefficient, and a small attenuation constant, the cut angle of the LiTaO ₃ substrate, that is, the Euler angle, the film thickness of the SiO ₂ film, and the film thickness of the electrode made of Cu, respectively. It can be seen that it is necessary to combine them optimally.

50 to 57, the normalized film thickness Hs / λ of the SiO ₂ film is 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4 or The relationship between θ and the attenuation constant α when a Cu film having a normalized film thickness H / λ of 0.08 or less is formed on a LiTaO ₃ substrate is 0.45.

As apparent from FIGS. 50 to 57, when the thickness H / λ of the Cu film is 0.01 to 0.08, the thickness of the SiO ₂ film and the Euler angle θ are shown in Table 21 below. If it is selected in this way, the frequency temperature characteristic TCF is good within the range of ± 20 ppm / ° C., the electromechanical coupling coefficient is large, and the attenuation constant α can be effectively suppressed. Desirably, even better characteristics can be obtained by selecting a more preferable Euler angle on the right side of Table 21 below.

Further, as estimated from FIG. 25 for Au, it can be seen that when the Euler angle θ is 125 ° or less, the electromechanical coupling coefficient K _saw is remarkably increased. Therefore, more preferably, the combination of the normalized film thickness Hs / λ and the Euler angle of the SiO ₂ film shown in Table 22 below is desirable.

Further, from the results shown in FIGS. 48 to 56, the Euler angle at which the attenuation constant is 0 or the minimum, that is, θ _min is determined based on the normalized film thickness Hs / λ of the SiO ₂ film and the normalized film thickness H / of the Cu film. The results obtained for λ are shown in FIG.

By approximating the curves shown in FIG. 59 when the normalized film thickness H / λ of the Cu film is 0, 0.02, 0.04, 0.06, and 0.08 by a cubic equation, A to E are obtained.
(A) When 0 <H / λ ≦ 0.01 θ _min = −139.713 × Hs ³ + 43.07132 × Hs ²
-20.568011 × Hs + 125.8314 ... Formula A
(B) When 0.01 <H / λ ≦ 0.03 θ _min = −139.660 × Hs ³ + 46.002985 × Hs ²
-21.141500 × hs + 127.4181 ... Formula B
(C) When 0.03 <H / λ ≦ 0.05 θ _min = −139.607 × Hs ³ + 48.988838 × Hs ²
-21.714900 × Hs + 129.0048 ... Formula C
(D) When 0.05 <H / λ ≦ 0.07 θ _min = −112.068 × Hs ³ + 39.660355 × Hs ²
-21.186000 × Hs + 1299.9397 Formula D
(E) When 0.07 <H / λ ≦ 0.09 θ _min = −126.995 × Hs ³ + 67.4040488 × Hs ²
−29.432000 × Hs + 131.5686 Formula E
Therefore, it is preferable that the Euler angle (0 ± 3 °, θ, 0 ± 3 °) θ is set to θ _min represented by the above-described expressions A to E, but θ _min −2 ° < If θ ≦ θ _min + 2 °, the attenuation constant can be effectively reduced.

In the present invention, the IDT may be composed only of Cu, but may be composed of a Cu alloy or a laminate of Cu and another metal as long as it is mainly composed of Cu. The IDT mainly composed of Cu is defined as ρ (Cu) × 0.7 ≦ ρ (average) ≦ ρ (Cu) × 1.3 when the average density of the electrode is ρ (average).
That is,
6.25 g / cm ³ ≦ ρ (average) ≦ 11.6 g / cm ³
As long as the above is satisfied. In addition, an electrode made of a metal such as W, Ta, Au, Pt, Ag, or Cr having a density higher than that of Al is laminated so that ρ (average) of the entire electrode is in the above range on or below Cu. Also good. Even in this case, the same effect as in the case of the Cu electrode single layer can be obtained.

  The Euler angle θ may deviate from −2 ° to + 4 ° from a desired angle. This deviation is calculated from the result of calculation in the present specification based on the metal film formed on the entire surface of the substrate. Therefore, an error may occur in the above range in an actual surface acoustic wave device.

  In addition, during manufacture, Euler angles φ and ψ varied from 0 ° to ± 3 °, but almost the same characteristics as those of 0 ° were obtained.

[Examples using tungsten as an electrode material]
The surface acoustic wave device shown in FIG. 15 was configured in the same manner as in the previous embodiment. However, the IDT and the reflector were made of tungsten. The normalized film thickness H / λ of IDT was in the range of 0.0025 to 0.06.

As the LiTaO ₃ substrate, 22 ° to 48 ° rotation Y plate X propagation, at Euler angles (0 °, 112 ° ~138 ° , 0 °) was used LiTaO ₃ substrate.

In the present embodiment, as described above, the piezoelectric substrate 22 made of 22 ° -48 ° rotated Y-plate X-propagating LiTaO ₃ , the IDTs 3a, 3b made of tungsten with H / λ = 0.0025-0.06, and Hs Surface acoustic wave device having a small frequency temperature coefficient TCF, a large electromechanical coupling coefficient K _saw and a small propagation loss because of using the SiO ₂ film 4 in the range of /λ=0.10 to 0.40 Can be provided. This will be described based on the following specific experimental example.

FIG. 60 and FIG. 61 show that an IDT made of tungsten having various thicknesses on each LiTaO ₃ substrate with Euler angles (0 °, 120 °, 0 °) and (0 °, 140 °, 0 °), is a diagram illustrating the attenuation constant in the case of forming a SiO ₂ film of various thickness.

As is apparent from FIG. 60, when θ = 120 °, the SiO ₂ film thickness Hs / λ is 0.1 to 0.40 and the normalized film thickness H / λ of tungsten is 0.0 to 0.00. It can be seen that in the range of 10, the attenuation constant is small. On the other hand, as is apparent from FIG. 61, when θ = 140 °, the normalized film thickness H / λ of the tungsten electrode is in the range of 0.0 to 0.10 regardless of the film thickness of the SiO ₂ film. It can be seen that the damping constant is increased.

That is, in order to reduce the TCF as ± 20 ppm / ° C., obtain a large electromechanical coupling coefficient, and reduce the attenuation constant, the Euler angle of the LiTaO ₃ substrate, the thickness of the SiO ₂ film, and the thickness of the electrode made of tungsten It can be seen that three conditions must be considered.

62 to 65 show the relationship between θ (degrees) and the attenuation constant when the normalized film thickness Hs / λ of the SiO ₂ film and the normalized film thickness H / λ of the electrode film made of tungsten are changed. Show.

As apparent from FIGS. 62 to 65, when the normalized film thickness H / λ of the electrode made of tungsten is 0.012 to 0.053 and 0.015 to 0.042, the film thickness of the SiO ₂ film and the optimum The relationship with θ is as shown in Table 23 and Table 24 below. The optimum θ may vary by about −2 ° to + 4 ° due to variations in the electrode finger width of the tungsten electrode and variations in the single crystal substrate. In the figure, the film thickness not shown is based on proportional distribution.

That is, as is clear from Tables 23 and 24, when the film thickness H / λ of the electrode made of tungsten is 0.012 to 0.053, the frequency temperature characteristic TCF is in the range of ± 20 ppm / ° C. When the film thickness Hs / λ of the SiO ₂ film is in the range of 0.1 to 0.4, θ in the Euler angle of LiTaO ₃ is in the range of 112 ° to 138 °, that is, the rotation angle. It can be seen that the Euler angles shown in Table 23 may be selected in the range of 20 ° to 50 °.

Similarly, as apparent from Table 24, the normalized film thickness of the electrode made of tungsten film is 0.015 to 0.042, and the frequency temperature characteristic TCF is improved to be within a range of ± 20 ppm / ° C. Therefore, when the film thickness Hs / λ of the SiO ₂ film is in the range of 0.1 to 0.4, the Euler angle of the LiTaO ₃ substrate may be in the range of 112 ° to 138 °, and more preferably It can be seen that the Euler angles in Table 24 may be selected according to the thickness of the SiO ₂ film.

Here, the range of “LiTaO ₃ Euler angle” in Table 23 and Table 24 defines a range where the attenuation constant is 0.05 or less. Further, the “more preferable” range of the Euler angles of LiTaO ₃ in Table 23 and Table 24 is that in which the attenuation constant is specified to be 0.025 or less. Further, the relationship between the film thickness Hs / λ of the SiO ₂ film and the Euler angle when the normalized film thickness of the electrode film made of tungsten is 0.012, 0.015, 0.042, 0.053 is shown in FIG. 65 is obtained by conversion from the normalized film thickness of the electrode film made of tungsten shown in FIG. 65, and thereby the values of the film thickness and Euler angle of the SiO ₂ film in Tables 23 and 24 are obtained.

In manufacturing the surface acoustic wave device according to the present invention, after an IDT made of a metal containing tungsten as a main component is formed on a rotating Y-plate X-propagating LiTaO ₃ substrate, the frequency is adjusted in that state, and then the attenuation constant is set. It is desirable to form a SiO ₂ film having a thickness within a range where α can be reduced. This will be described with reference to FIGS. 66 and 67. FIG. FIG. 66 shows an IDT made of tungsten with various thicknesses H / λ and SiO _{2 with} various thicknesses Hs / λ on a rotating Y plate X-propagating LiTaO ₃ substrate with Euler angles (0 °, 126 °, 0 °). The change of the sound velocity of the leaky surface acoustic wave when a film is formed is shown. FIG. 67 shows the normalized film thickness Hs / λ of the SiO ₂ film formed on an IDT made of tungsten having various film thicknesses H / λ on a LiTaO ₃ substrate having the same Euler angle. The change of the sound velocity of the leaky surface acoustic wave when changing is shown. As is apparent from a comparison between FIGS. 66 and 67, the change in the sound velocity of the surface acoustic wave is much greater when the film thickness of tungsten is changed than when the film thickness of the SiO ₂ film is changed. large. Therefore, it is desirable to adjust the frequency prior to the formation of the SiO ₂ film. For example, it is desirable to adjust the frequency after forming an IDT made of tungsten (W) by laser etching or ion etching.

In addition, as described above, the present invention is a piezoelectric substrate made of LiTaO _{3 of} 22 ° to 48 ° rotated Y-plate X propagation, Euler angles (0 °, 112 ° to 138 °, 0 °), H / λ = It has an IDT made of tungsten with 0.0025 to 0.06 and an SiO ₂ film with Hs / λ = 0.10 to 0.40, and therefore the number and structure of IDTs Etc. are not particularly limited. That is, the present invention can be applied not only to the surface acoustic wave device shown in FIG. 15 but also to various surface acoustic wave resonators, surface acoustic wave filters, and the like as long as the above conditions are satisfied.

  The Euler angle θ may deviate from −2 ° to + 4 ° from a desired angle. This deviation is calculated from the result of calculation in the present specification based on the metal film formed on the entire surface of the substrate. Therefore, an error may occur in the above range in an actual surface acoustic wave device.

  In addition, during manufacture, Euler angles φ and ψ varied from 0 ° to ± 3 °, but almost the same characteristics as those of 0 ° were obtained.

[Example when Ta is used as an electrode material]
The surface acoustic wave device shown in FIG. 15 was constructed. However, a substrate made of LiTaO ₃ with 14 ° to 58 ° rotated Y-plate X propagation and Euler angles (0 °, 104 ° to 148 °, 0 °) is used as the piezoelectric substrate 22, and IDT is tantalum (Ta). The normalized film thickness H / λ is in the range of 0.004 to 0.055.

In the present embodiment, as described above, the piezoelectric substrate 2 made of LiTaO _{3 with} 14 ° to 58 ° rotated Y-plate X propagation, Euler angles (0 °, 104 ° to 148 °, 0 °), and H / λ = Since the IDTs 3a and 3b made of tantalum of 0.004 to 0.055 and the SiO ₂ film 4 in the range of Hs / λ = 0.10 to 0.40 are used, the frequency temperature coefficient TCF is small, A surface acoustic wave device having a large electromechanical coupling coefficient K _saw and a small propagation loss can be provided. This will be described based on the following specific experimental example.

68 and 69 show an Euler angle (0 °, 120 °, 0 °) and IDT made of tantalum having various thicknesses on each LiTaO ₃ substrate of (0 °, 140 °, 0 °), is a diagram illustrating the attenuation constant in the case of forming a SiO ₂ film of various thickness.

As is apparent from FIG. 68, when θ = 120 °, the SiO ₂ film thickness Hs / λ is 0.1 to 0.40, and the normalized film thickness H / λ of the tantalum electrode is 0.0 to 0.00. It can be seen that in the range of 10, the attenuation constant is small. On the other hand, as is apparent from FIG. 69, when θ = 140 °, the normalized film thickness H / λ of the electrode made of tantalum is in the range of 0.0 to 0.06 regardless of the film thickness of the SiO ₂ film. It can be seen that the damping constant is increased.

That is, in order to reduce the absolute value of TCF, obtain a large electromechanical coupling coefficient, and reduce the attenuation constant, the Euler angle of the LiTaO ₃ substrate, the thickness of the SiO ₂ film, and the film thickness of the electrode made of tantalum It can be seen that the conditions must be taken into account.

70 to 73 show the relationship between θ and the attenuation constant when the normalized film thickness Hs / λ of the SiO ₂ film and the normalized film thickness H / λ of the electrode film made of tantalum are changed.

As is apparent from FIGS. 70 to 73, when the normalized film thickness H / λ of the electrode made of tantalum is 0.01 to 0.055 and 0.016 to 0.045, the film thickness of the SiO ₂ film is optimal. The relationship with θ is as shown in Table 25 and Table 26 below. Note that this optimum θ may vary by about −2 ° to + 4 ° due to variations in the electrode finger width of the tantalum electrode and variations in the single crystal substrate.

That is, as apparent from Table 25 and Table 26, when the film thickness H / λ of the electrode made of tantalum is 0.01 to 0.055, the frequency temperature characteristic TCF is set within a range of ± 20 ppm / ° C. When the normalized film thickness of the SiO ₂ film is in the range of 0.1 to 0.4, θ at the Euler angle of LiTaO ₃ is in the range of 104 ° to 148 °, that is, the rotation angle. It can be seen that the Euler angles shown in Table 25 may be selected in the range of 14 ° to 58 °, more preferably, according to the SiO ₂ film thickness Hs / λ.

Similarly, as apparent from Table 26, the normalized film thickness of electrodes made of tantalum film is from 0.016 to 0.045, in order to improve the frequency temperature characteristic TCF, of the SiO ₂ film thickness Hs / When λ is in the range of 0.1 to 0.4, the Euler angle of the LiTaO ₃ substrate may be in the range of 107 ° to 144 °, and more preferably according to the film thickness Hs / λ of the SiO ₂ film. It can be seen that the Euler angles in Table 26 should be selected.

The range of Euler angles of LiTaO ₃ defines a range where the attenuation constant is 0.05 or less. Further, the more preferable range of the Euler angles of LiTaO ₃ in Table 25 and Table 26 is that in which the attenuation constant is specified to be 0.025 or less. The relationship between the film thickness Hs / λ of the SiO ₂ film and the Euler angle when the normalized film thickness of the electrode film made of tantalum is 0.012, 0.015, 0.042, 0.053 is shown in FIG. The values of the film thickness Hs / λ and Euler angles of the SiO ₂ films in Table 25 and Table 26 are obtained by conversion from the normalized film thickness of the electrode film made of tantalum shown in FIG.

In manufacturing the surface acoustic wave device according to the present invention, an IDT made of a metal containing tantalum as a main component is formed on a rotating Y-plate X-propagating LiTaO ₃ substrate, and then the frequency is adjusted in that state, and then the damping constant is set. It is desirable to form a SiO ₂ film having a thickness within a range where α can be reduced. This will be described with reference to FIGS. 74 and 75. FIG. FIG. 74 shows the normalized film thickness H / of tantalum when an IDT and SiO ₂ film made of tantalum is formed on a rotating Y plate X-propagating LiTaO ₃ substrate with Euler angles (0 °, 126 °, 0 °). The relationship between λ, the normalized film thickness Hs / λ of the SiO ₂ film, and the sound velocity of the leaky surface acoustic wave is shown. Further, FIG. 75 shows leakage when an IDT made of tantalum having various film thicknesses is formed on a LiTaO ₃ substrate having the same Euler angle and the normalized film thickness of the SiO ₂ film formed thereon is changed. Changes in the speed of sound of surface acoustic waves are shown. As is clear from a comparison of FIGS. 74 and 75, the change in the sound velocity of the surface acoustic wave is much greater when the tantalum film thickness is changed than when the SiO ₂ film thickness is changed. large. Therefore, it is desirable to adjust the frequency prior to the formation of the SiO ₂ film. For example, it is desirable to adjust the frequency after forming an IDT made of tantalum by laser etching or ion etching.

In the present invention, as described above, the piezoelectric substrate made of LiTaO _{3 with} 14 ° to 58 ° rotated Y-plate X propagation and Euler angles (0 °, 104 ° to 148 °, 0 °), H / λ = It has an IDT made of tantalum of 0.004 to 0.055 and a SiO ₂ film of Hs / λ = 0.10 to 0.40. Therefore, the number and structure of IDTs Etc. are not particularly limited. That is, the present invention can be applied not only to the surface acoustic wave device shown in FIG. 15 but also to various surface acoustic wave resonators, surface acoustic wave filters, and the like as long as the above conditions are satisfied.

  The Euler angle θ may deviate from −2 ° to + 4 ° from a desired angle. This deviation is calculated from the result of calculation in the present specification based on the metal film formed on the entire surface of the substrate. Therefore, an error may occur in the above range in an actual surface acoustic wave device.

  In addition, during manufacture, Euler angles φ and ψ varied from 0 ° to ± 3 °, but almost the same characteristics as those of 0 ° were obtained.

[Examples using platinum as an electrode material]
The surface acoustic wave device shown in FIG. 15 has a piezoelectric substrate composed of a LiTaO ₃ substrate with 0 ° to 79 ° rotated Y-plate X propagation and Euler angles (0 °, 90 ° to 169 °, 0 °), and H / An IDT made of platinum with λ = 0.005 to 0.054 was used. The other points are the same as in the above-described embodiment.

Also in this embodiment, since the above configuration is provided, it is possible to provide a surface acoustic wave device having a small frequency temperature coefficient TCF, a large electromechanical coupling coefficient K _saw and a small propagation loss. This will be described based on the following specific experimental example.

76 and 77, an IDT made of platinum with various thicknesses on each LiTaO ₃ substrate of Euler angles (0 °, 125 °, 0 °) and (0 °, 140 °, 0 °), is a diagram illustrating the attenuation constant in the case of forming a SiO ₂ film of various thickness.

As is clear from FIG. 76, when θ = 125 °, the SiO ₂ film thickness Hs / λ is 0.1 to 0.40, and the normalized film thickness H / λ of the platinum electrode is 0.005 to 0.00. It can be seen that the attenuation constant is small in the range of 06. On the other hand, as is apparent from FIG. 77, at θ = 140 °, when the normalized film thickness H / λ of the electrode made of platinum is in the range of 0.005 to 0.06, the film thickness Hs / λ of the SiO ₂ film is In any case, it can be seen that the attenuation constant increases.

That is, in order to reduce the absolute value of TCF, obtain a large electromechanical coupling coefficient, and reduce the attenuation constant, the Euler angle of the LiTaO ₃ substrate, the thickness of the SiO ₂ film, and the film thickness of the electrode made of platinum It can be seen that the conditions must be taken into account.

78 to 83 show the Euler angle θ (degree) and the attenuation constant when the normalized film thickness Hs / λ of the SiO ₂ film and the normalized film thickness H / λ of the electrode film made of platinum are changed. The relationship is shown.

As is apparent from FIGS. 78 to 83, when the normalized film thickness H / λ of the electrode made of platinum is 0.005 to 0.054, θ is preferably in the range of 90 ° to 169 °. . Further, when the normalized film thickness H / λ of the electrode made of platinum is 0.01 to 0.04 and 0.013 to 0.033, the relationship between the film thickness Hs / λ of the SiO ₂ film and the optimum θ. Considering the reduction of the attenuation constant α, the results are as shown in Table 27 and Table 28 below. Here, the range of “LiTaO ₃ Euler angle” in Table 27 and Table 28 defines a range where the attenuation constant is 0.05 dB / λ or less. Further, the “more preferable” range of the Euler angles of LiTaO ₃ in Tables 27 and 28 defines a range in which the attenuation constant is 0.025 dB / λ or less. Note that the optimum θ may vary by about −2 ° to + 4 ° due to variations in the electrode finger width of the platinum electrode and variations in the single crystal substrate.

  In addition, during manufacture, Euler angles φ and ψ varied from 0 ° to ± 3 °, but almost the same characteristics as those of 0 ° were obtained.

That is, as is clear from Tables 27 and 28, when the film thickness H / λ of the electrode made of platinum is 0.01 to 0.04, the frequency temperature characteristic TCF is in the range of ± 20 ppm / ° C. When the film thickness Hs / λ of the SiO ₂ film is in the range of 0.1 to 0.4, θ in the Euler angle of LiTaO ₃ is in the range of 90 ° to 169 °, that is, the rotation angle. It can be seen that a range of 0 ° to 79 ° may be selected.

Similarly, as apparent from Table 27, the normalized film thickness of the electrode made of platinum is 0.01 to 0.04, and the frequency temperature characteristic TCF is improved to be within a range of ± 20 ppm / ° C. Therefore, when the film thickness Hs / λ of the SiO ₂ film is in the range of 0.1 to 0.4, the Euler angle θ of the LiTaO ₃ substrate may be in the range of 90 ° to 169 °. It can be seen that the Euler angles shown in Table 27 may be selected according to the thickness of the SiO ₂ film.

Similarly, the normalized film thickness of an electrode made of a platinum film is 0.013 to 0.033, and in order to improve the frequency temperature characteristic TCF to be in the range of ± 20 ppm / ° C., the film thickness of the SiO ₂ film When Hs / λ is in the range of 0.1 to 0.4, the Euler angle θ of the LiTaO ₃ substrate may be in the range of 102 ° to 150 °, and more preferably a film of SiO ₂ film. It can be seen that the Euler angles in Table 28 may be selected according to the thickness Hs / λ.

In addition, when the normalized film thickness of the electrode film made of platinum is 0.013 to 0.033, the relationship between the film thickness of the SiO ₂ film and the Euler angle is the same as that of the electrode film made of platinum shown in FIGS. It is calculated from the normalized film thickness, and the values of the film thickness Hs / λ and the Euler angle of the SiO ₂ film in Tables 27 and 28 are obtained.

In the production of the surface acoustic wave device according to the present invention, after an IDT made of a metal whose main component is platinum is formed on a rotating Y-plate X-propagating LiTaO ₃ substrate, the frequency is adjusted in that state, and then the damping constant is obtained. It is desirable to form a SiO ₂ film having a thickness Hs / λ within a range where α can be reduced. This will be described with reference to FIGS. 84 and 85. FIG. FIG. 84 shows an IDT made of platinum with various thicknesses H / λ and SiO _{2 with} various thicknesses Hs / λ on a rotating Y-plate X-propagating LiTaO ₃ substrate with Euler angles (0 °, 126 °, 0 °). The change of the sound velocity of the leaky surface acoustic wave when a film is formed is shown. FIG. 85 shows the normalized film thickness Hs / λ of the SiO ₂ film formed on an IDT made of platinum having various film thicknesses H / λ on a LiTaO ₃ substrate having the same Euler angle. The change of the sound velocity of the leaky surface acoustic wave when changing is shown. As is clear from comparison between FIG. 84 and FIG. 85, the change in the sound velocity of the surface acoustic wave is much greater when the thickness of the platinum film is changed than when the thickness of the SiO ₂ film is changed. large. Therefore, it is desirable to adjust the frequency prior to the formation of the SiO ₂ film. For example, it is desirable to adjust the frequency after forming an IDT made of platinum by laser etching or ion etching.

In the present invention, as described above, the piezoelectric substrate made of LiTaO _{3 with} 0 ° to 79 ° rotated Y-plate X propagation and Euler angles (0 °, 90 ° to 169 °, 0 °), H / λ = It has an IDT made of platinum of 0.005 to 0.054 and an SiO ₂ film of Hs / λ = 0.10 to 0.40. Therefore, the number and structure of IDTs Etc. are not particularly limited. That is, the present invention can be applied not only to the surface acoustic wave device shown in FIG. 1 but also to various surface acoustic wave resonators, surface acoustic wave filters, and the like as long as the above conditions are satisfied.

[Examples using nickel and molybdenum as electrode materials]
The surface acoustic wave device shown in FIG. 15 was constructed. Nickel or molybdenum was used as the electrode material. Further, as the piezoelectric substrate, a LiTaO ₃ substrate having a 14 ° -50 ° rotated Y-plate X propagation and Euler angles (0 °, 104 ° -140 °, 0 °) was used. The other points are the same.

The IDTs 23a and 23b and the reflectors 25a and 25b have a density of 8700 to 10300 kg to m ³ , a Young's modulus of 1.8 × 10 ¹¹ to 4 × 10 ¹¹ N / m ^2, and a shear wave velocity of 3170 to 3290 m / sec. It is comprised by. Examples of such a metal include nickel, molybdenum, and alloys mainly composed of these.

  The normalized film thickness H / λ (H is the IDT thickness, and λ is the wavelength at the center frequency) of the IDTs 23a and 23b is in the range of 0.008 to 0.06.

In the present embodiment, as described above, the piezoelectric substrate 22 made of LiTaO _{3 with} 14 ° -50 ° rotated Y-plate X propagation, Euler angles (0 °, 104 ° -140 °, 0 °), and H / λ = Since the IDTs 23a and 23b made of the specific metal and the SiO ₂ film 24 in the range of Hs / λ = 0.10 to 0.40 are used, the frequency temperature coefficient is 0.008 to 0.06. It is possible to provide a surface acoustic wave device in which the TCF is reduced to be within a range of ± 20 ppm / ° C., the electromechanical coupling coefficient K _saw is large, and the propagation loss is small. This will be described based on the following specific experimental example.

86 and 87, an IDT made of Ni of various thicknesses on each LiTaO ₃ substrate of Euler angles (0 °, 120 °, 0 °) and (0 °, 140 °, 0 °), is a diagram illustrating the attenuation constant in the case of forming a SiO ₂ film of various thickness Hs / lambda.

As is apparent from FIG. 86, when θ = 120 °, the SiO ₂ film thickness Hs / λ is 0.1 to 0.40, and the normalized film thickness H / λ of Ni is 0.008 to 0.00. It can be seen that the attenuation constant is small in the range of 08. On the other hand, as is apparent from FIG. 87, when θ = 140 °, the normalized film thickness H / λ of the electrode made of Ni is in the range of 0.008 to 0.08 regardless of the film thickness of the SiO ₂ film. It can be seen that the damping constant is increased.

88 and 89 show various examples of IDTs composed of Mo having various thicknesses on LiTaO ₃ substrates having Euler angles (0 °, 120 °, 0 °) and (0 °, 140 °, 0 °). is a graph showing changes in attenuation constant when the forming a SiO ₂ film with a thickness Hs / lambda.

As is apparent from FIG. 88, when θ = 120 °, the SiO ₂ film thickness Hs / λ is 0.1 to 0.40, and the normalized film thickness H / λ of Mo is 0.008 to 0.00. It can be seen that the attenuation constant is small in the range of 08. On the other hand, as is apparent from FIG. 89, when θ = 140 °, the normalized film thickness H / λ of the electrode made of Mo is within the range of 0.008 to 0.08, and the film thickness Hs / λ of the SiO ₂ film is In any case, it can be seen that the attenuation constant increases.

That is, in order to reduce the absolute value of TCF, obtain a large electromechanical coupling coefficient, and reduce the damping constant, the Euler angle of the LiTaO ₃ substrate, the thickness Hs / λ of the SiO ₂ film, the specific density, and the Young's modulus. It can also be seen that three conditions must be taken into consideration: the film thickness of the electrode made of metal in the shear wave velocity range.

90 to 93 show the relationship between θ (degrees) and the attenuation constant when the normalized film thickness Hs / λ of the SiO ₂ film and the normalized film thickness H / λ of the electrode film made of Ni are changed. Show.

94 to 97 show the relationship between θ (degrees) and the attenuation constant when the normalized film thickness Hs / λ of the SiO ₂ film and the normalized film thickness H / λ of the electrode film made of Mo are changed. Show.

As is apparent from FIGS. 90 to 97, when the normalized film thickness H / λ of the electrode made of Ni or Mo is 0.008 to 0.06, 0.017 to 0.06, and 0.023 to 0.06. The relationship between the thickness of the SiO ₂ film and the optimum θ is as shown in Table 29 below. Note that this optimum θ may vary by about −2 ° to + 4 ° due to variations in the electrode finger width of the electrodes and variations in the single crystal substrate.

  In addition, during manufacture, Euler angles φ and ψ varied from 0 ° to ± 3 °, but almost the same characteristics as those of 0 ° were obtained.

Further, the SiO ₂ film at the optimum film thickness H / λ = 0.008~0.06,0.02~0.06 and 0.027 to 0.06 of an electrode made of Ni shown in FIG. 90 view 93 The relationship between the film thickness and the optimum θ is as shown in Table 30 below.

Further, the SiO ₂ film at the optimum film thickness H / λ = 0.008~0.06,0.017~0.06 and 0.023 to 0.06 of an electrode made of Mo as shown in FIGS. 94-97 The relationship between the film thickness and the optimum θ is as shown in Table 31 below.

That is, as is clear from Table 29, the film thickness H / λ of the electrode made of a metal having the specific density, Young's modulus, and transverse wave speed is 0.008 to 0.06, 0.017 to 0.06, and In order to improve the frequency temperature characteristic TCF to be within the range of ± 20 ppm / ° C. at 0.023 to 0.06, when the film thickness of the SiO ₂ film is in the range of 0.1 to 0.4, It can be seen that θ in the Euler angle of LiTaO ₃ is in the range of 104 ° to 140 °, that is, the rotation angle is in the range of 14 ° to 50 °, and more preferably, the Euler angle shown in Table 29 is selected.

Similarly, when the normalized film thickness H / λ of the electrode made of Ni is 0.008 to 0.06, 0.02 to 0.06, and 0.027 to 0.06, the frequency temperature characteristic TCF is ± In order to improve it to be within the range of 20 ppm / ° C., θ at the Euler angle of the LiTaO ₃ substrate is 104 according to the film thickness Hs / λ of the SiO ₂ film with Hs / λ of 0.1 to 0.4. It can be determined that the angle is in the range of ° to 140 °, and more preferably, the Euler angles shown in Table 30 may be selected according to the film thickness Hs / λ of the SiO ₂ film.

Similarly, when the normalized film thickness H / λ of the electrode made of Mo is 0.008 to 0.06, 0.02 to 0.06, and 0.027 to 0.06, the frequency temperature characteristic TCF is ± In order to improve it to be within the range of 20 ppm / ° C., θ at the Euler angle of the LiTaO ₃ substrate is 104 according to the film thickness Hs / λ of the SiO ₂ film with Hs / λ of 0.1 to 0.4. It can be determined that the angle is in the range of ° to 141 °, and more preferably, the Euler angles shown in Table 31 may be selected according to the film thickness Hs / λ of the SiO ₂ film.

Here, the range of “LiTaO ₃ Euler angle” in Table 29 to Table 31 defines the range where the attenuation constant α is 0.1 dB / λ or less. Moreover, the “more preferable” range of the Euler angles of LiTaO ₃ in Tables 29 to 31 defines a range in which the attenuation constant is 0.05 dB / λ or less. The relationship between the film thickness Hs / λ of the SiO ₂ film and the Euler angles when the normalized film thicknesses of the electrode films are 0.095, 0.017, and 0.023 are shown in FIGS. 90 to 97. or are those obtained by converting the normalized thickness of the electrode film made of Mo, thereby seeking the value of the SiO ₂ film thickness of the film and the Euler angles of the table 29 to table 31.

In manufacturing the surface acoustic wave device according to the present invention, after the IDT made of the specific metal such as Ni or Mo is formed on the rotating Y-plate X-propagating LiTaO ₃ substrate, the frequency is adjusted in that state, and then It is desirable to form a SiO ₂ film having a film thickness that can reduce the attenuation constant α. This will be described with reference to FIGS. FIGS. 98 and 100 show an IDT made of Ni or Mo having various thicknesses H / λ and various film thicknesses Hs on a rotating Y plate X-propagating LiTaO ₃ substrate having Euler angles (0 °, 126 °, 0 °). 6 shows a change in sound velocity of a leaky surface acoustic wave when a / λ SiO ₂ film is formed. 99 and 101 show the standardization of the SiO ₂ film formed on an IDT made of Ni or Mo having various thicknesses H / λ on a LiTaO ₃ substrate having the same Euler angle. The change in the sound velocity of the leaky surface acoustic wave when the film thickness Hs / λ is changed is shown. As is apparent from a comparison between FIGS. 98 and 99, and FIGS. 100 and 101, the elastic surface is greater when the thickness of the electrode is changed than when the thickness of the SiO ₂ film is changed. The change in sound speed of the waves is much greater. Therefore, it is desirable to adjust the frequency prior to the formation of the SiO ₂ film. For example, it is desirable to adjust the frequency after forming an IDT made of Ni or Mo by laser etching or ion etching.

In the present invention, as described above, the piezoelectric substrate made of LiTaO _{3 with} 14 ° -50 ° rotated Y-plate X propagation and Euler angles (0 °, 104 ° -140 °, 0 °), H / λ = An IDT made of a metal having a specific density, Young's modulus, and shear wave speed range of 0.008 to 0.06 such as Ni and Mo, and an SiO ₂ film having Hs / λ = 0.10 to 0.40. Therefore, the number and structure of the IDT are not particularly limited. That is, the present invention can be applied not only to the surface acoustic wave device shown in FIG. 15 but also to various surface acoustic wave resonators, surface acoustic wave filters, and the like as long as the above conditions are satisfied.

(A)-(g) is each typical partial notch sectional drawing for demonstrating the manufacturing method of the surface acoustic wave apparatus in one Example of this invention. IDT electrodes made of Al, Au or Pt with various film thicknesses are formed on a LiTaO ₃ substrate with Euler angles (0 °, 126 °, 0 °), and the normalized film thickness Hs / λ is 0.2. in one-port surface acoustic wave resonator obtained by forming a SiO ₂ film, diagram showing the relationship between the electrode thickness and the reflection coefficient when not the case with flattened planarizing the surface of the SiO ₂ film. IDT electrodes made of Al, Cu, or Ag with various film thicknesses are formed on a LiTaO ₃ substrate with Euler angles (0 °, 126 °, 0 °), and the normalized film thickness Hs / λ is 0.2. in one-port surface acoustic wave resonator obtained by forming a SiO ₂ film, diagram showing the relationship between the electrode thickness and the reflection coefficient when not the case with flattened planarizing the surface of the SiO ₂ film. Shows the normalized thickness of the SiO ₂ film of the surface acoustic wave resonator obtained by the manufacturing method of the comparative example, the relationship between the phase characteristic and the impedance characteristic. Shows the film thickness of the SiO ₂ film in the surface acoustic wave resonator prepared for comparison, the relationship between the MF resonator. 1 is a schematic plan view of a 1-port surface acoustic wave resonator obtained in an embodiment of the present invention. In the production process of Example, it shows the change in the impedance characteristic and the phase characteristic when changing the normalized thickness of the SiO ₂ film. It shows the relationship between the film thickness of the SiO ₂ film and γ resonators in the surface acoustic wave resonator obtained by the production method of the Examples and Comparative Examples. It shows the relationship between the film thickness of the SiO ₂ film and MF resonators in the surface acoustic wave resonator obtained by the production method of the Examples and Comparative Examples. Shows the thickness of the SiO ₂ film in the elastic surface wave resonator prepared in Examples and Comparative Examples, the relationship between the change in the frequency-temperature characteristic TCF. Diagram showing the frequency characteristics - and the surface acoustic wave resonator where the SiO ₂ film is formed, which is prepared in the second comparative example, no impedance SiO ₂ film. (A)-(e) is a figure which shows the change of an impedance characteristic at the time of changing the ratio with respect to the density of the 1st insulator layer of the average density of an IDT electrode and a protective metal film. Euler angles (0 °, 126 °, 0 °) LiTaO 3 shows the change in electromechanical coupling coefficient in the case of forming the IDT electrode composed of various metals on the substrate in different thickness. When an IDT electrode is formed of various metals on a LiTaO ₃ substrate, the relationship between the electrode film thickness range in which the electromechanical coupling coefficient is larger than the case where an electrode made of Al is used and the density of the electrode material is shown. Figure. The perspective view which shows the surface acoustic wave apparatus which concerns on the other Example of this invention. An IDT composed of Au, Ta, Ag, Cr, W, Cu, Zn, Mo, Ni on a LiTaO ₃ substrate of 36 ° rotation Y plate X propagation (Euler angles (0 °, 126 °, 0 °)) The figure which shows the relationship between the electrode film thickness of the standardized IDT at the time of forming IDT which consists of Al, and an electromechanical coupling coefficient. 36 ° rotation Y plate X propagation (Euler angles (0 °, 126 °, 0 LiTaO 3 shows the relationship between the reflection coefficient and the film thickness of the IDT electrode fingers one made of various electrode materials on a substrate °). An IDT composed of Au, Ta, Ag, Cr, W, Cu, Zn, Mo, Ni on a LiTaO ₃ substrate of 36 ° rotation Y plate X propagation (Euler angles (0 °, 126 °, 0 °)) The figure which shows the relationship between the electrode normalized film thickness of IDT, and an attenuation constant at the time of forming IDT which consists of Al. An IDT made of Au with a normalized film thickness of 0.02 is formed on a LiTaO ₃ substrate with a 36 ° rotation Y-plate X propagation (Euler angles (0 °, 126 °, 0 °)), and various films It shows the change in frequency temperature characteristics in the case of forming a SiO ₂ film having a thickness (TCF). On the LiTaO ₃ substrate of 36 ° rotation Y-plate X propagation (Euler angles (0 °, 126 °, 0 °)), an IDT made of Au of various thicknesses is formed, and an SiO ₂ film laminated thereon The figure which shows the change of the attenuation constant (alpha) when changing a normalized film thickness. An IDT made of Au of various thicknesses is formed on a LiTaO ₃ substrate of 38 ° rotation Y-plate X propagation (Euler angles (0 °, 128 °, 0 °)), and an SiO ₂ film laminated thereon The figure which shows the change of the attenuation constant (alpha) when changing a normalized film thickness. It shows the attenuation-frequency characteristic of the surface acoustic wave device for attenuation-frequency characteristics and the SiO ₂ film formation before the comparison of the surface acoustic wave device of Example. In a structure in which an IDT made of Au is formed on a LiTaO ₃ substrate of 36 ° rotation Y-plate X propagation (Euler angles (0 °, 126 °, 0 °)), and SiO ₂ films of various thicknesses are formed. The figure which shows the change of the sound velocity of the leaky surface acoustic wave at the time of changing the normalization film thickness of IDT which consists of Au. An IDT made of Au with various standardized film thicknesses is formed on a LiTaO ₃ substrate of 36 ° rotation Y-plate X propagation (Euler angles (0 °, 126 °, 0 °)), and a SiO ₂ film laminated in the structure, it shows a change in the sound velocity of the leaky surface acoustic wave in the case of changing the normalized thickness of the SiO ₂ film. Euler angles (0 °, θ, 0 ° ) view theta, indicating the change in electromechanical coupling coefficient in the case of changing the normalized thickness of the IDT normalized film thickness and SiO ₂ film made of Au. It shows the change in Q value of the resonator when changing the normalized thickness of θ and the SiO ₂ film of the Euler angles of the LiTaO ₃ substrate. (A)-(c) is each typical sectional drawing for demonstrating the surface acoustic wave apparatus which concerns on the modification of this invention provided with the contact | adherence layer. View showing the relationship between the attenuation constant alpha theta in various Au electrode film thickness in the film thickness H / lambda = 0.1 in the SiO ₂ film. View showing the relationship between the attenuation constant alpha theta in various Au electrode film thickness in the film thickness H / lambda = 0.15 for the SiO ₂ film. View showing the relationship between the attenuation constant alpha theta in various Au electrode film thickness in the film thickness H / lambda = 0.2 in the SiO ₂ film. View showing the relationship between the attenuation constant alpha theta in various Au electrode film thickness in the film thickness H / lambda = 0.25 for the SiO ₂ film. View showing the relationship between the attenuation constant alpha theta in various Au electrode film thickness in the film thickness H / lambda = 0.3 in the SiO ₂ film. View showing the relationship between the attenuation constant alpha theta in various Au electrode film thickness in the film thickness H / lambda = 0.35 for the SiO ₂ film. View showing the relationship between the attenuation constant alpha theta in various Au electrode film thickness in the film thickness H / lambda = 0.4 in the SiO ₂ film. View showing the relationship between the attenuation constant alpha theta in various Au electrode film thickness in the film thickness H / lambda = 0.45 for the SiO ₂ film. Normalized film thickness H / λ of an Ag film and electromechanical coupling coefficient when electrodes made of Ag films of various film thicknesses are formed on a LiTaO ₃ substrate with Euler angles (0 °, 126 °, 0 °) The figure which shows the relationship with K _saw . In three types of LiTaO ₃ substrates of Euler angles (0 °, 113 °, 0 °), (0 °, 126 °, 0 °) and (0 °, 129 °, 0 °), the electrode film thickness is 0, The figure which shows the relationship between the normalized film thickness Hs / λ of the SiO ₂ film and the frequency temperature coefficient TCF when the SiO ₂ film having various thicknesses is formed. On a LiTaO ₃ substrate with Euler angles (0 °, 120 °, 0 °), an Ag film having a normalized film thickness of 0.1 or less is formed, and an SiO ₂ film having a normalized film thickness of 0 to 0.5 is formed. The figure which shows the change of the attenuation constant (alpha) at the time of forming into a film. On a LiTaO ₃ substrate with Euler angles (0 °, 140 °, 0 °), an Ag film having a normalized film thickness of 0.1 or less is formed, and an SiO ₂ film having a normalized film thickness of 0 to 0.5 is formed. The figure which shows the change of the attenuation constant (alpha) at the time of forming into a film. Various Ag films having a normalized film thickness H / λ of 0.1 or less are formed on a LiTaO ₃ substrate having an Euler angle (0 °, θ, 0 °), and the normalized film thickness Hs / λ is 0.1. It shows the case of stacking an SiO ₂ film, the variation of the attenuation constant alpha. Various Ag films having a normalized film thickness H / λ of 0.1 or less are formed on a LiTaO ₃ substrate having an Euler angle (0 °, θ, 0 °), and the normalized film thickness Hs / λ is 0.15. It shows the case of stacking an SiO ₂ film, the variation of the attenuation constant alpha. Various Ag films having a normalized film thickness H / λ of 0.1 or less are formed on a LiTaO ₃ substrate having an Euler angle (0 °, θ, 0 °), and the normalized film thickness Hs / λ is 0.2. It shows the case of stacking an SiO ₂ film, the variation of the attenuation constant alpha. Various Ag films having a normalized film thickness H / λ of 0.1 or less are formed on a LiTaO ₃ substrate having an Euler angle (0 °, θ, 0 °), and the normalized film thickness Hs / λ is 0.25. It shows the case of stacking an SiO ₂ film, the variation of the attenuation constant alpha. Various Ag films having a normalized film thickness H / λ of 0.1 or less are formed on a LiTaO ₃ substrate having Euler angles (0 °, θ, 0 °), and the normalized film thickness Hs / λ is 0.3. It shows the case of stacking an SiO ₂ film, the variation of the attenuation constant alpha. Various Ag films having a normalized film thickness H / λ of 0.1 or less are formed on a LiTaO ₃ substrate with Euler angles (0 °, θ, 0 °), and the normalized film thickness Hs / λ is 0.35. It shows the case of stacking an SiO ₂ film, the variation of the attenuation constant alpha. Various Ag films having a normalized film thickness H / λ of 0.1 or less are formed on a LiTaO ₃ substrate having an Euler angle (0 °, θ, 0 °), and the normalized film thickness Hs / λ is 0.4. It shows the case of stacking an SiO ₂ film, the variation of the attenuation constant alpha. Various Ag films having a normalized film thickness H / λ of 0.1 or less are formed on a LiTaO ₃ substrate with Euler angles (0 °, θ, 0 °), and the normalized film thickness Hs / λ is 0.45. It shows the case of stacking an SiO ₂ film, the variation of the attenuation constant alpha. A Cu film having a normalized film thickness of 0.1 or less is formed on a LiTaO ₃ substrate having Euler angles (0 °, 120 °, 0 °), and a SiO ₂ film having a normalized film thickness of 0 to 0.5 is formed. The figure which shows the change of the attenuation constant (alpha) at the time of forming into a film. A Cu film having a normalized film thickness of 0.1 or less is formed on a LiTaO ₃ substrate having Euler angles (0 °, 135 °, 0 °), and a SiO ₂ film having a normalized film thickness of 0 to 0.5 is formed. The figure which shows the change of the attenuation constant (alpha) at the time of forming into a film. Various Cu films having a normalized film thickness H / λ of 0.1 or less are formed on a LiTaO ₃ substrate having an Euler angle (0 °, θ, 0 °), and the normalized film thickness Hs / λ is 0.1. It shows the case of stacking an SiO ₂ film, the variation of the attenuation constant alpha. Various Cu films having a normalized film thickness H / λ of 0.1 or less are formed on a LiTaO ₃ substrate having an Euler angle (0 °, θ, 0 °), and the normalized film thickness Hs / λ is 0.15. It shows the case of stacking an SiO ₂ film, the variation of the attenuation constant alpha. Various Cu films with a normalized film thickness H / λ of 0.1 or less are formed on a LiTaO ₃ substrate with Euler angles (0 °, θ, 0 °), and the normalized film thickness Hs / λ is 0.2. It shows the case of stacking an SiO ₂ film, the variation of the attenuation constant alpha. Various Cu films having a normalized film thickness H / λ of 0.1 or less are formed on a LiTaO ₃ substrate having an Euler angle (0 °, θ, 0 °), and the normalized film thickness Hs / λ is 0.25. It shows the case of stacking an SiO ₂ film, the variation of the attenuation constant alpha. Various Cu films having a normalized film thickness H / λ of 0.1 or less are formed on a LiTaO ₃ substrate having an Euler angle (0 °, θ, 0 °), and the normalized film thickness Hs / λ is 0.3. It shows the case of stacking an SiO ₂ film, the variation of the attenuation constant alpha. Various Cu films having a normalized film thickness H / λ of 0.1 or less are formed on a LiTaO ₃ substrate having an Euler angle (0 °, θ, 0 °), and the normalized film thickness Hs / λ is 0.35. It shows the case of stacking an SiO ₂ film, the variation of the attenuation constant alpha. Various Cu films having a normalized film thickness H / λ of 0.1 or less are formed on a LiTaO ₃ substrate having an Euler angle (0 °, θ, 0 °), and the normalized film thickness Hs / λ is 0.4. It shows the case of stacking an SiO ₂ film, the variation of the attenuation constant alpha. Various Cu films having a normalized film thickness H / λ of 0.1 or less are formed on a LiTaO ₃ substrate having an Euler angle (0 °, θ, 0 °), and the normalized film thickness Hs / λ is 0.45. It shows the case of stacking an SiO ₂ film, the variation of the attenuation constant alpha. Shows the relationship between the reflectance and the electrode film thickness per one electrode finger in the made of the electrode and the Cu electrode made of Al when the normalized thickness of the SiO ₂ film is 0.02. The figure which shows the relationship between the normalized film thickness Hs / λ of the SiO ₂ film and the normalized film thickness H / λ of the Cu film for realizing θ _min where the attenuation constant is 0 or the minimum. Euler angles (0 °, 120 °, 0 °) LiTaO on ₃ substrate, it shows the change of the attenuation constant α in the formation of the IDT composed of tungsten SiO ₂ film and various thicknesses of various thickness structure. Euler angles (0 °, 140 °, 0 °) LiTaO 3 substrate in the, shows the change of the attenuation constant α in the formation of the IDT composed of tungsten various SiO ₂ film and various thicknesses of structures. An electrode film made of tungsten having various thicknesses was formed on a LiTaO ₃ substrate having Euler angles (0 °, θ, 0 °), and a SiO ₂ film having a normalized thickness Hs / λ = 0.1 was formed. The figure which shows the relationship between (theta) in the surface acoustic wave apparatus, normalized thickness H / (lambda) of the electrode film which consists of tungsten, and attenuation constant (alpha). An electrode film made of tungsten having various thicknesses was formed on a LiTaO ₃ substrate having Euler angles (0 °, θ, 0 °), and a SiO ₂ film having a normalized thickness Hs / λ = 0.2 was formed. The figure which shows the relationship between (theta) in the surface acoustic wave apparatus, normalized thickness H / (lambda) of the electrode film which consists of tungsten, and attenuation constant (alpha). An electrode film made of tungsten having various thicknesses was formed on a LiTaO ₃ substrate having Euler angles (0 °, θ, 0 °), and a SiO ₂ film having a normalized thickness Hs / λ = 0.3 was formed. The figure which shows the relationship between (theta) in the surface acoustic wave apparatus, normalized thickness H / (lambda) of the electrode film which consists of tungsten, and attenuation constant (alpha). An electrode film made of tungsten having various thicknesses was formed on a LiTaO ₃ substrate having Euler angles (0 °, θ, 0 °), and a SiO ₂ film having a normalized thickness Hs / λ = 0.4 was formed. The figure which shows the relationship between (theta) in the surface acoustic wave apparatus, normalized thickness H / (lambda) of the electrode film which consists of tungsten, and attenuation constant (alpha). The film thickness of the tungsten film when the IDT made of tungsten is formed on the LiTaO ₃ substrate of Euler angles (0 °, 126 °, 0 °) and the SiO ₂ film is formed, the film thickness of the SiO ₂ film, The figure which shows the relationship with a sound speed. The film thickness of the tungsten film when the IDT made of tungsten is formed on the LiTaO ₃ substrate of Euler angles (0 °, 126 °, 0 °) and the SiO ₂ film is formed, the film thickness of the SiO ₂ film, The figure which shows the relationship with a sound speed. Euler angles (0 °, 120 °, 0 °) LiTaO on ₃ substrate, it shows the change of the attenuation constant α in the formation of the IDT composed of tantalum SiO ₂ film and various thicknesses of various thickness structure. Euler angles (0 °, 140 °, 0 °) LiTaO 3 substrate in the, shows the change of the attenuation constant α in the formation of the IDT composed of tantalum various SiO ₂ film and various thicknesses of structures. An electrode film made of tantalum having various thicknesses was formed on a LiTaO ₃ substrate having Euler angles (0 °, θ, 0 °), and a SiO ₂ film having a normalized thickness Hs / λ = 0.1 was formed. The figure which shows the relationship between (theta) in the surface acoustic wave apparatus, normalized thickness H / (lambda) of the electrode film which consists of tantalum, and attenuation constant (alpha). An electrode film made of tantalum with various thicknesses was formed on a LiTaO ₃ substrate with Euler angles (0 °, θ, 0 °), and a SiO ₂ film with a normalized thickness Hs / λ = 0.2 was formed. The figure which shows the relationship between (theta) in the surface acoustic wave apparatus, normalized thickness H / (lambda) of the electrode film which consists of tantalum, and attenuation constant (alpha). An electrode film made of tantalum having various thicknesses was formed on a LiTaO ₃ substrate having Euler angles (0 °, θ, 0 °), and a SiO ₂ film having a normalized thickness Hs / λ = 0.3 was formed. The figure which shows the relationship between (theta) in the surface acoustic wave apparatus, normalized thickness H / (lambda) of the electrode film which consists of tantalum, and attenuation constant (alpha). An electrode film made of tantalum having various thicknesses was formed on a LiTaO ₃ substrate having Euler angles (0 °, θ, 0 °), and a SiO ₂ film having a normalized thickness Hs / λ = 0.4 was formed. The figure which shows the relationship between (theta) in the surface acoustic wave apparatus, normalized thickness H / (lambda) of the electrode film which consists of tantalum, and attenuation constant (alpha). The tantalum normalized film thickness and the SiO ₂ standard in a structure in which an IDT made of tantalum is formed on an Euler angle (0 °, 126 °, 0 °) LiTaO ₃ substrate and an SiO ₂ film is formed thereon. The figure which shows the relationship between chemical conversion film thickness and sound speed. In a structure in which an IDT made of tantalum is formed on a LiTaO ₃ substrate with Euler angles (0 °, 126 °, 0 °) and an SiO ₂ film is formed thereon, _The figure which shows the relationship between the normalized film thickness of ₂ and a sound speed. Euler angles (0 °, 125 °, 0 °) LiTaO 3 substrate in the, shows the change of the attenuation constant α in the formation of the IDT composed of platinum SiO ₂ film and various thicknesses of various thicknesses structure. Euler angles (0 °, 140 °, 0 °) LiTaO 3 substrate in the, shows the change of the attenuation constant α in the formation of the IDT composed of platinum SiO ₂ film and various thicknesses of various thicknesses structure. An electrode film made of platinum with various thicknesses was formed on a LiTaO ₃ substrate with Euler angles (0 °, θ, 0 °), and a SiO ₂ film with a normalized thickness Hs / λ = 0.1 was formed. The figure which shows the relationship between (theta) in the surface acoustic wave apparatus, normalized thickness H / (lambda) of the electrode film which consists of platinum, and attenuation constant (alpha). An electrode film made of platinum having various thicknesses was formed on a LiTaO ₃ substrate having Euler angles (0 °, θ, 0 °), and an SiO ₂ film having a normalized thickness Hs / λ = 0.15 was formed. The figure which shows the relationship between (theta) in the surface acoustic wave apparatus, normalized thickness H / (lambda) of the electrode film which consists of platinum, and attenuation constant (alpha). An electrode film made of platinum with various thicknesses was formed on a LiTaO ₃ substrate with Euler angles (0 °, θ, 0 °), and a SiO ₂ film with a normalized thickness Hs / λ = 0.2 was formed. The figure which shows the relationship between (theta) in the surface acoustic wave apparatus, normalized thickness H / (lambda) of the electrode film which consists of platinum, and attenuation constant (alpha). An electrode film made of platinum having various thicknesses was formed on a LiTaO ₃ substrate having Euler angles (0 °, θ, 0 °), and an SiO ₂ film having a normalized thickness Hs / λ = 0.25 was formed. The figure which shows the relationship between (theta) in the surface acoustic wave apparatus, normalized thickness H / (lambda) of the electrode film which consists of platinum, and attenuation constant (alpha). An electrode film made of platinum having various thicknesses was formed on a LiTaO ₃ substrate having Euler angles (0 °, θ, 0 °), and a SiO ₂ film having a normalized thickness Hs / λ = 0.3 was formed. The figure which shows the relationship between (theta) in the surface acoustic wave apparatus, normalized thickness H / (lambda) of the electrode film which consists of platinum, and attenuation constant (alpha). An electrode film made of platinum having various thicknesses was formed on a LiTaO ₃ substrate having Euler angles (0 °, θ, 0 °), and a SiO ₂ film having a normalized thickness Hs / λ = 0.4 was formed. The figure which shows the relationship between (theta) in the surface acoustic wave apparatus, normalized thickness H / (lambda) of the electrode film which consists of platinum, and attenuation constant (alpha). When an IDT made of platinum is formed on a LiTaO ₃ substrate with Euler angles (0 °, 126 °, 0 °) and a SiO ₂ film is further formed, the thickness of the platinum film, the thickness of the SiO ₂ film, The figure which shows the relationship with a sound speed. When an IDT made of platinum is formed on a LiTaO ₃ substrate with Euler angles (0 °, 126 °, 0 °) and a SiO ₂ film is further formed, the thickness of the platinum film, the thickness of the SiO ₂ film, The figure which shows the relationship with a sound speed. Euler angles (0 °, 120 °, 0 °) LiTaO on ₃ substrate, shows the change of the attenuation constant α in the formation of the IDT composed of the SiO ₂ film and various thicknesses of various thicknesses nickel structure. Euler angles (0 °, 140 °, 0 °) LiTaO 3 substrate in the, shows the change of the attenuation constant α in the formation of the IDT composed of various of the SiO ₂ film and various thicknesses of nickel structure. Euler angles (0 °, 120 °, 0 °) LiTaO on ₃ substrate, it shows the change of the attenuation constant α in the formation of the IDT composed of molybdenum SiO ₂ film and various thicknesses of various thickness structure. Euler angles (0 °, 140 °, 0 °) LiTaO 3 substrate in the, shows the change of the attenuation constant α in the formation of the IDT composed of molybdenum SiO ₂ film and various thicknesses of various thicknesses structure. An electrode film made of nickel of various thicknesses was formed on a LiTaO ₃ substrate with Euler angles (0 °, θ, 0 °), and a SiO ₂ film with a normalized film thickness Hs / λ = 0.1 was formed. The figure which shows the relationship between (theta) in the surface acoustic wave apparatus, normalized thickness H / (lambda) of the electrode film which consists of nickel, and attenuation constant (alpha). An electrode film made of nickel having various thicknesses was formed on a LiTaO ₃ substrate having Euler angles (0 °, θ, 0 °), and a SiO ₂ film having a normalized thickness Hs / λ = 0.2 was formed. The figure which shows the relationship between (theta) in the surface acoustic wave apparatus, normalized thickness H / (lambda) of the electrode film which consists of nickel, and attenuation constant (alpha). An electrode film made of nickel with various thicknesses was formed on a LiTaO ₃ substrate with Euler angles (0 °, θ, 0 °), and a SiO ₂ film with a normalized thickness Hs / λ = 0.3 was formed. The figure which shows the relationship between (theta) in the surface acoustic wave apparatus, normalized thickness H / (lambda) of the electrode film which consists of nickel, and attenuation constant (alpha). An electrode film made of nickel with various thicknesses was formed on a LiTaO ₃ substrate with Euler angles (0 °, θ, 0 °), and a SiO ₂ film with a normalized thickness Hs / λ = 0.4 was formed. The figure which shows the relationship between (theta) in the surface acoustic wave apparatus, normalized thickness H / (lambda) of the electrode film which consists of nickel, and attenuation constant (alpha). An electrode film made of molybdenum with various thicknesses was formed on a LiTaO ₃ substrate with Euler angles (0 °, θ, 0 °), and a SiO ₂ film with a normalized thickness Hs / λ = 0.1 was formed. The figure which shows the relationship between (theta) in the surface acoustic wave apparatus, normalized thickness H / (lambda) of the electrode film which consists of molybdenum, and attenuation constant (alpha). An electrode film made of molybdenum having various thicknesses was formed on a LiTaO ₃ substrate having Euler angles (0 °, θ, 0 °), and a SiO ₂ film having a normalized thickness Hs / λ = 0.2 was formed. The figure which shows the relationship between (theta) in the surface acoustic wave apparatus, normalized thickness H / (lambda) of the electrode film which consists of molybdenum, and attenuation constant (alpha). An electrode film made of molybdenum having various thicknesses was formed on a LiTaO ₃ substrate having Euler angles (0 °, θ, 0 °), and a SiO ₂ film having a normalized thickness Hs / λ = 0.3 was formed. The figure which shows the relationship between (theta) in the surface acoustic wave apparatus, normalized thickness H / (lambda) of the electrode film which consists of molybdenum, and attenuation constant (alpha). An electrode film made of molybdenum with various thicknesses was formed on a LiTaO ₃ substrate with Euler angles (0 °, θ, 0 °), and a SiO ₂ film with a normalized thickness Hs / λ = 0.4 was formed. The figure which shows the relationship between (theta) in the surface acoustic wave apparatus, normalized thickness H / (lambda) of the electrode film which consists of molybdenum, and attenuation constant (alpha). When an IDT made of nickel is formed on a LiTaO ₃ substrate with Euler angles (0 °, 126 °, 0 °), and when SiO ₂ films having various thicknesses are formed, the thickness of the nickel film and the nickel The figure which shows the relationship between the film thickness of a film | membrane, and a sound speed. Euler angles (0 °, 126 °, 0 °) LiTaO 3 substrate to a is formed with IDT composed of different thickness of the nickel, in the structure it has a SiO ₂ film is formed thereon, the SiO ₂ film The figure which shows the relationship between the film thickness of and the sound speed. In the case where an IDT made of molybdenum is formed on a LiTaO ₃ substrate having Euler angles (0 °, 126 °, 0 °), and SiO ₂ films having various thicknesses are formed thereon, the molybdenum in the structure The figure which shows the relationship between a normalized film thickness and a sound speed. The normalized film thickness of the SiO ₂ film in a structure in which an IDT made of molybdenum of various film thicknesses is formed on a LiTaO ₃ substrate with Euler angles (0 °, 126 °, 0 °) and an SiO ₂ film is further formed. The figure which shows the relationship with sound speed. (A)-(c) is each typical sectional drawing for demonstrating the etch-back method as an example of the method which aims at the planarization of the surface of an insulator layer. (A)-(d) is each typical sectional drawing for demonstrating the reverse sputtering method as another example of the method of planarizing the surface of an insulator layer. (A) And (b) is typical sectional drawing which shows the further another example of the method of planarizing the surface of an insulator layer. (A)-(c) is each typical sectional drawing for demonstrating another method of planarizing the surface of an insulator layer. (A) And (b) is each typical top view for demonstrating the 1 port type resonator and 2 port type resonator as an example of the surface acoustic wave apparatus with which this invention is applied. The typical top view for explaining the ladder type filter as a surface acoustic wave device to which the present invention is applied. The typical top view for explaining the lattice type filter as a surface acoustic wave device to which the present invention is applied. (A)-(d) is typical sectional drawing for showing an example of the manufacturing method of the conventional surface acoustic wave apparatus. The typical front sectional view for explaining an example of the conventional surface acoustic wave device. .

Explanation of symbols

1 ... LiTaO ₃ substrate 2 ... first insulating layer 3 ... resist pattern 4 ... metal film 4A ... Ti film 6 ... second insulator layer 11 ... surface acoustic wave resonators 12 and 13 as the IDT electrode 5 ... protective metal film Reflector 21 Surface acoustic wave device 22 LiTaO ₃ substrate 23a, 23b IDT
25 ... SiO ₂ film

Claims (9)

A piezoelectric substrate made of LiTaO ₃ or LiNbO ₃ having an electromechanical coupling coefficient of 15% or more;
A metal having a density higher than Al or an alloy containing the metal as a main component, or a metal having a density higher than Al or an alloy containing the metal as a main component and another metal formed on the piezoelectric substrate. At least one electrode comprising a laminated film comprising:
A first insulator layer formed in a film thickness substantially equal to the electrode in the remaining region excluding the region where the at least one electrode is formed;
A second insulator layer formed to cover the electrode and the first insulator layer;
A surface acoustic wave device in which a density of the electrode is 1.5 times or more that of the first insulator layer. A piezoelectric substrate;
At least one electrode formed on the piezoelectric substrate;
A protective metal film made of a metal or alloy that is formed on the electrode and has better corrosion resistance than the metal or alloy constituting the electrode;
A first insulator layer formed so as to have a film thickness substantially equal to the total film thickness of the electrode and the protective metal film in the remaining region excluding the region where the at least one electrode is formed;
A surface acoustic wave device comprising: the protective metal film and a second insulator layer formed so as to cover the first insulator layer.   3. The surface acoustic wave device according to claim 2, wherein an average density of the entire laminated structure of the electrode and the protective metal film is 1.5 times or more of a density of the first insulator layer.   The surface acoustic wave device according to any one of claims 1 to 3, which is a surface acoustic wave device using reflection of surface acoustic waves.   The electrode is composed of a laminated film of a main electrode layer made of a metal or alloy having a density higher than that of Al and at least one electrode layer made of another metal, and an average density ρ of the electrode and a density higher than that of the Al. 5. The surface acoustic wave device according to claim 1, wherein ρ0 × 0.7 ≦ ρ ≦ ρ0 × 1.3, where ρ0 is a density of a large metal.   The surface acoustic wave device according to any one of claims 1 to 5, wherein the unevenness of the surface of the second insulator layer is 30% or less of the film thickness of the electrode.   The surface acoustic wave device according to claim 1, wherein a leakage type surface acoustic wave is used as the surface acoustic wave.   The surface acoustic wave device according to claim 1, wherein the first insulator layer and the second insulator layer are made of the same material. The surface acoustic wave device according to claim 1, wherein the second insulator layer is made of SiO ₂ .

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