JP2009194895A - Surface acoustic wave device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface acoustic wave device employing an LiNbO<SB>3</SB>substrate, in which not only the reflection coefficient but also the electromechanical coupling coefficient k<SP>2</SP>of an IDT are large, and the range of Euler angles of the LiNbO<SB>3</SB>substrate for realizing a large electromechanical coupling coefficient k<SP>2</SP>can be enlarged. <P>SOLUTION: The surface acoustic wave device 1 wherein a plurality of grooves 2b are formed on an upper surface 2a of an LiNbO<SB>3</SB>substrate 2, an IDT 3 having a plurality of electrode fingers composed of a metal material filling the plurality of grooves 2b is provided, wherein the metal material is composed of Ta, Mo or an alloy principally comprising at least one of these metals. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a surface acoustic wave device used as, for example, a resonator or a bandpass filter. More specifically, the surface acoustic wave device has a structure in which an IDT is formed using a metal filled in a groove on a piezoelectric substrate. About.

  Conventionally, surface acoustic wave devices have been widely used as resonators and bandpass filters. For example, Patent Document 1 below discloses a surface acoustic wave device 1001 that schematically shows a cross-sectional structure in FIG.

In the surface acoustic wave device 1001, a plurality of grooves 1002 b are formed on the upper surface 1002 a of the LiTaO ₃ substrate 1002. A plurality of grooves 1002b are filled with a metal, whereby an IDT 1003 having a plurality of electrode fingers made of the metal is formed. A SiO ₂ film 1004 is laminated so as to cover the upper surface 1002a of the LiTaO ₃ substrate 1002. Since the LiTaO ₃ substrate 1002 has a negative frequency temperature coefficient TCF, an SiO ₂ film 1004 having a positive frequency temperature coefficient TCF is laminated, and the absolute value of the frequency temperature coefficient TCF of the surface acoustic wave device 1001 is reduced. .

  Further, it is said that a large reflection coefficient can be obtained in the IDT by forming the IDT using the metal embedded in the plurality of grooves 1002b. Specifically, when the wavelength of the surface wave is λ and the thickness of Al filled in the groove 1002b, that is, the thickness of the IDT made of Al is 0.04λ, the reflection coefficient per electrode finger is It is shown that 0.05 is obtained, and a larger reflection coefficient is obtained as the electrode thickness is larger.

On the other hand, the following Patent Document 2 discloses a surface acoustic wave device shown in FIG. In the surface acoustic wave device 1101, an IDT 1103 is formed on a piezoelectric substrate 1102 made of LiTaO ₃ or LiNbO ₃ . A protective film 1104 is formed so as to cover the IDT 1103. On the other hand, a first insulating layer 1105 made of SiO ₂ having the same thickness as the laminated metal film formed by laminating the IDT 1103 and the protective film 1104 is formed in the remaining region excluding the portion where the IDT 1103 and the protective film 1104 are formed. Has been. A second insulator layer 1106 made of SiO ₂ is laminated so as to cover the first insulator layer 1105. Here, it is shown that by using a metal having a density higher than that of Al as IDT 1103, the absolute value of the reflection coefficient can be increased and unwanted ripples can be suppressed.
WO2006 / 011417A1 JP 2004-112748 A

  In the surface acoustic wave device 1001 described in Patent Document 1, it is shown that the absolute value of the reflection coefficient can be increased as the thickness of the IDT made of Al is increased. However, the inventor of the present application has found that good resonance characteristics cannot be obtained simply by increasing the absolute value of the reflection coefficient. That is, in the surface acoustic wave device described in Patent Document 1, the absolute value of the reflection coefficient can be increased by increasing the thickness of the electrode made of Al. However, since the sign of the reflection coefficient is negative, there are many in the passband. It has been found that ripples are generated and good resonance characteristics cannot be obtained.

In Patent Document 1, the relationship between the thickness of the IDT and the reflection coefficient is merely described for the case where an IDT made of Al is used on a LiTaO ₃ substrate. Note that paragraph 0129 of Patent Document 1 suggests that an IDT may be formed using another metal such as Au on a LiNbO ₃ substrate, but only an IDT made of Au is disclosed.

  On the other hand, in Patent Document 2, as described above, when an IDT made of a metal having a density higher than that of Al is used, it is shown that the absolute value of the reflection coefficient can be increased. No particular mention is made of increasing the electromechanical coupling coefficient.

In addition, in the structure in which the trench provided on the LiNbO ₃ substrate is filled with Au to form the IDT, the Euler angle range of the LiNbO ₃ substrate that can be used for obtaining a sufficiently large electromechanical coupling coefficient k ² is narrow. There was a problem.

The object of the present invention is to eliminate the drawbacks of the prior art, use a LiNbO ₃ substrate as a piezoelectric substrate, and not only have a sufficiently large reflection coefficient of IDT, but also a large electromechanical coupling coefficient k ^2. An object of the present invention is to provide a surface acoustic wave device in which the Euler angle range of a LiNbO ₃ substrate that can be used is relatively wide and the degree of freedom in design can be increased.

According to the present invention, a piezoelectric substrate made of a LiNbO ₃ substrate and having a plurality of grooves formed on the upper surface thereof, and a plurality of electrode fingers made of a metal material filled in the plurality of grooves on the upper surface of the piezoelectric substrate. A surface acoustic wave device is provided, wherein the metal material is made of Ta or Mo or an alloy mainly composed of at least one of these metals.

In the surface acoustic wave device according to the present invention, when the wavelength of the surface acoustic wave is λ, the normalized film thickness that is normalized by λ of the IDT and the Euler angle (0 ° ± 10 °, LiNbO ₃ substrate) θ, 0 ° ± 10 °) is one of the combinations shown in Table 1 below. In this case, the Euler angle range of the LiNbO ₃ substrate capable of obtaining a large electromechanical coupling coefficient k ² can be further expanded.

The surface acoustic wave device according to the present invention preferably further includes a dielectric film made of an inorganic material mainly composed of SiO ₂ or SiO ₂ that covers the IDT and the piezoelectric substrate. In this case, the frequency temperature coefficient of the dielectric film made of an inorganic material mainly composed of SiO ₂ or SiO ₂ is a positive value, and the frequency temperature coefficient TCF of LiNbO ₃ is a negative value. A surface acoustic wave device having a small absolute value of the frequency temperature coefficient TCF can be provided.

When the dielectric film, particularly, a dielectric film made of SiO ₂ is formed on a LiNbO ₃ substrate, the normalized film thickness obtained by normalizing with the IDT λ according to the type of the metal material constituting the IDT. The normalized film thickness of the dielectric film made of SiO ₂ and the Euler angles (0 ° ± 10 °, θ, 0 ° ± 10 °) of the LiNbO ₃ substrate are shown in Tables 2 to 7 below. One of the combinations shown.

More specifically, when the wavelength of the surface acoustic wave is λ, a standardized film thickness normalized by λ of the IDT and a standard normalized by λ of the SiO ₂ film as the dielectric film One of the combinations shown in Table 2 to Table 4 or Table 5 to Table 7 below is that the formed film thickness and the Euler angle (0 ° ± 10 °, θ, 0 ° ± 10 °) of the LiNbO ₃ substrate. It is a seed.

As described above, a LiNbO ₃ substrate capable of realizing a large electromechanical coupling coefficient k ² by using one of the combinations shown in Tables 2 to 7 according to the type of the metal material constituting the IDT. The Euler angle range can be further expanded.

According to the present invention, in an IDT having a plurality of electrode fingers made of a metal material filled in a groove on the upper surface of a LiNbO ₃ substrate, the metal material is Ta or Mo or an alloy mainly composed of at least one of these metals. Therefore, not only the reflection coefficient of IDT is large, but also a large electromechanical coupling coefficient k ² can be obtained. Moreover, the Euler angle of the LiNbO ₃ substrate can be selected from a wide range in order to realize a range where the electromechanical coupling coefficient k ² is large. Therefore, not only can the characteristics of the surface acoustic wave device be improved, but also the degree of freedom in designing the surface acoustic wave device can be increased.

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

  FIGS. 1A and 1B are schematic partial front sectional views of a portion where an IDT of a surface acoustic wave device according to a first embodiment of the present invention is formed, and FIG. It is a schematic plan view of a surface acoustic wave device.

As shown in FIG. 1A, the surface acoustic wave device 1 includes a LiNbO ₃ substrate 2. A plurality of grooves 2 b are formed on the upper surface 2 a of the LiNbO ₃ substrate 2. The IDT 3 having a plurality of electrode fingers is formed by filling the plurality of grooves 2b with metal. The upper surface of the IDT ₃ and the upper surface 2a of the LiNbO ₃ substrate 2 are flush with each other.

A SiO ₂ film 4 is formed so as to cover the upper surface 2a and the IDT 3. In the present invention, the SiO ₂ film 4 may not be formed.

  As shown in FIG. 1B, the surface acoustic wave device 1 includes the IDT 3 and first and second reflectors 5 and 6 disposed on both sides of the IDT 3 in the surface wave propagation direction. This is a surface acoustic wave resonator. Each of the reflectors 5 and 6 is a grating reflector formed by short-circuiting both ends of a plurality of electrode fingers.

Similarly to the IDT ₃ , the reflectors 5 and 6 are also formed by filling a plurality of grooves provided on the upper surface 2 a of the LiNbO ₃ substrate 2 with the same metal. Therefore, also in the reflectors 5 and 6, the electrode surface and the upper surface 2a of the LiNbO ₃ substrate 2 are substantially flush with each other. Therefore, the upper surface of the SiO ₂ film 4 is substantially flattened over the entire surface acoustic wave device 1.

Although the frequency temperature coefficient TCF of the LiNbO ₃ substrate 2 is a negative value, the frequency temperature coefficient TCF of the SiO ₂ film 4 is a positive value, so that the absolute value of the frequency temperature coefficient TCF is reduced as a whole. Therefore, in the surface acoustic wave device 1, the change in the frequency characteristic due to the temperature change is small.

  The surface acoustic wave device 1 of this embodiment is a surface acoustic wave device using SH waves, and the feature thereof is that the metal material constituting the IDT 3 is Pt, W, Ta, Mo, Ag, Cu. Ni, Cr and Ti or an alloy mainly composed of at least one of these metals. The IDT 3 may be added with a metal layer made of another metal material such as an adhesion layer or a diffusion prevention layer, or the IDT 3 may have a laminated structure with another metal layer.

Thereby, in the surface acoustic wave device 1 of the present embodiment, not only the absolute value of the reflection coefficient of the IDT 3 is increased, but also a large electromechanical coupling coefficient k ² can be obtained. Also, the following concrete experimental examples of, as shown in, in obtaining an electromechanical coupling coefficient k ² is large SAW device 1, it is possible to widen the Euler angle range of the LiNbO ₃ substrate that may be utilized. Therefore, the degree of freedom in design can be increased. This will be described with reference to FIGS.

6 and 7 have the same structure as that of the surface acoustic wave device 1 of the above embodiment, except that an IDT electrode and a reflector are made of Al and LiNbO in a surface acoustic wave device using a leaky surface acoustic wave. ₃ Euler angles of the substrate (0 °, θ, 0 ° ) is a diagram showing respectively theta, reflection coefficient and the relationship between the electromechanical coefficient k ² of.

6 and 7 show results when the normalized film thickness standardized by the wavelength λ of the surface wave of the IDT 3 made of Al is 0.04λ or 0.08λ. In addition, the result of the structure in which the SiO ₂ film 4 having a normalized film thickness of 0.25λ is formed is indicated by a solid line, and the result of the structure in which the SiO ₂ film 4 is not formed is indicated by a broken line.

  As can be seen from FIG. 6, when Al is used as the electrode material, the reflection coefficient is not so high.

Further, as apparent from FIG. 7, by changing the θ of Euler angles, the electromechanical coupling coefficient k ² can be increased to 0.2 or more. However, as shown in FIG. 6, even when the SiO ₂ film 4 is not formed, the reflection coefficient is 0.1 or less regardless of the value of the Euler angle θ and the film thickness of the IDT made of Al. I understand that it is small.

On the other hand, FIG. 8 and FIG. 9 show the results when Au having a normalized film thickness of 0.04λ or 0.08λ standardized at the wavelength λ of the surface wave is used as the electrode material. That is, the result when the IDT electrode 3 and the reflectors 5 and 6 shown in FIG. 1 are made of Au is shown. Figure 8 shows the relationship between θ and the reflection coefficient of the Euler angles, Figure 9 shows the relationship between θ and the electromechanical coupling coefficient k ² of the Euler angles.

8 and 9, the result of the structure in which the SiO ₂ film 4 having the normalized film thickness 4 of 0.25λ is shown by a solid line, and the result of the structure not formed by a broken line.

  As can be seen from FIG. 8, when Au is used as the electrode material, the reflection coefficient can be increased regardless of the Euler angle θ as compared with the case where the electrode material Al shown in FIG. 6 is used. .

However, as shown in Figure 9, the electromechanical coupling coefficient k ² is large area, i.e. the area is larger than the electromechanical coupling coefficient k ² is 0.2, the normalized film thickness of electrodes made of Au 0 In the case of .04λ, the structure in which the SiO ₂ film 4 is not formed is in the range of 72 ° to 131 °, and in the case where the normalized film thickness of the electrode made of Au is 0.08λ, 85 ° to 119. It is in the range of °. Accordingly, when the normalized film thickness is changed in the range of 0.04λ to 0.08λ, the electromechanical coupling coefficient k ² is selected unless the Euler angle θ is selected in the range of 85 ° to 119 °. It can be seen that cannot be made 0.2 or more.

In the structure in which the IDT 3 made of Au and the reflectors 5 and 6 are formed, and further the SiO ₂ film 4 is formed, the normalized film thickness of the Au film is 0 for the electromechanical coupling coefficient k ² to be 0.2 or more. In the case of .04λ, the Euler angle θ must be in the range of 77 ° to 117 °, and in the case where the normalized film thickness is 0.08λ, the Euler angle θ must be in the range of 90 ° to 114 °. Recognize. Therefore, it can be seen that when the normalized film thickness of the SiO ₂ film 4 is in the range of 0.04λ to 0.08λ, the Euler angle θ must be in the range of 90 ° to 114 °.

On the other hand, as described below, when a metal material constituting IDT 3 is Ta or Mo or an alloy mainly composed of at least one of these metals, the electromechanical coupling coefficient k ² is 0. The range of Euler angles that can be set to 2 or more can be widened. Accordingly, the degree of freedom in designing the surface acoustic wave device can be increased.

Note that when the electromechanical coupling coefficient k ² is 0.2 or more, to that to be good, in the surface acoustic wave device used as resonators and band filters, to obtain a bandwidth that is usually sought, electrical This is because the mechanical coupling coefficient k ² is preferably about 0.2 or more.

(When the metal material is Ta)
2 and 3 show the relationship between the Euler angle θ of the LiNbO ₃ substrate when Ta is used as the metal material constituting the IDT electrode 3 and the reflectors 5 and 6, the reflection coefficient, and the electromechanical coupling coefficient k ² . It is a figure which shows a relationship. 2 and 3, the standardized film thickness of Ta as the metal material constituting the IDT 3 and the reflectors 5 and 6 is set to 0.04λ or 0.08λ. Further, also in FIG. 2 and FIG. 3 shows the results when the SiO ₂ film 4 is formed by a solid line, the results when the SiO ₂ film 4 is not formed by a broken line. Also in FIGS. 2 and 3, the results of the comparative example in which the IDT ₃ made of Ta having a normalized film thickness of 0.08λ and the reflectors 5 and 6 are formed on the upper surface of the LiNbO ₃ substrate are indicated by a one-dot chain line. .

  As can be seen from FIG. 2, even when Ta is used as the metal material, a larger reflection coefficient can be obtained than when Al is used, regardless of the Euler angle θ range.

As apparent from FIG. 3, in the comparative example shown by a chain line, the range of the electromechanical coupling coefficient k ² can be as high as 0.2 or more, it can be very narrow and 80 ° to 101 ° in the Euler angle θ Recognize.

On the other hand, in the structure of the embodiment of the present invention in which the SiO ₂ film 4 is not formed, the Euler angle range in which the electromechanical coupling coefficient k ² can be 0.2 or more is a normalized film of the Ta film. It can be seen that when the thickness is 0.04λ, the range may be 70 ° to 140 °, and when the standardized film thickness is 0.08λ, the range may be 72 ° to 142 °. Therefore, when Ta is used as the metal material, when the normalized film thickness is in the range of 0.04λ to 0.08λ, the Euler angle θ may be in the range of 72 ° to 140 °. Recognize. Therefore, the range of Euler angle θ can be expanded compared to the range of 85 ° or more and 119 ° or less when Au is used.

Similarly, in the structure in which the SiO ₂ film 4 is laminated, the range of Euler angle θ that can expand the electromechanical coupling coefficient k ² to 0.2 or more is as follows when the normalized film thickness of Ta is 0.04λ. 78 ° to 122 ° and a normalized film thickness of 0.08λ, it can be seen that the angle may be set to 76 ° to 125 °. That is, when the normalized film thickness of Ta is in the range of 0.04λ to 0.08λ, it can be seen that the Euler angle θ should be 78 ° or more and 122 ° or less. Therefore, it can be seen that the Euler angle θ range can be expanded compared to the range of 90 ° or more and 114 ° or less when the Au film is used.

(When Mo is used as the metal material)
4 and 5 are diagrams showing the relationship between the Euler angle θ, the reflection coefficient, and the electromechanical coupling coefficient k ² , as in FIGS. 2 and 3. 4 and 5, the normalized film thickness of Mo as the metal material constituting the IDT 3 and the reflectors 5 and 6 is 0.02λ, 0.04λ, or 0.08λ. Further, also in FIG. 4 and FIG. 5 shows the results when the SiO ₂ film 4 is formed by a solid line in the solid line, the results when the SiO ₂ film 4 is not formed by a broken line.

  As can be seen from FIG. 4, even when Mo is used as the metal material, a larger reflection coefficient can be obtained than when Al is used, regardless of the Euler angle θ range.

Further, as apparent from FIG. 5, in the structure in which the SiO ₂ film 4 is not formed, the Euler angle range in which the electromechanical coupling coefficient k ² can be 0.2 or more has a normalized film thickness of 0. In the case of 02λ, the range may be 70 ° to 144 °. In the case of 0.04λ, the range may be 70 ° to 160 °. When the normalized film thickness is 0.08λ, It can be seen that it may be in the range of 70 ° to 160 °. Therefore, when Mo is used as the metal material, when the normalized film thickness is in the range of 0.02λ to 0.04λ, the Euler angle θ should be in the range of 70 ° or more and 144 ° or less. In the case of more than 0.04λ and 0.08λ or less, it is understood that the angle may be set to 70 ° or more and 160 ° or less. Therefore, the range of Euler angle θ can be expanded compared to the range of 85 ° or more and 119 ° or less when Au is used.

Similarly, in the structure in which the SiO ₂ film 4 is laminated, the Euler angle range in which the electromechanical coupling coefficient k ² can be expanded to 0.2 or more is shown in FIG. 5 when the normalized film thickness of Mo is 0.02λ. In the case of 80 ° to 113 ° and 0.04λ, 78 ° to 125 °, and in the case where the normalized film thickness is 0.08λ, 77 ° to 125 ° may be set. That is, when the normalized film thickness of Mo is in the range of 0.02λ to 0.04λ, the Euler angle θ should be 80 ° or more and 113 ° or less, more than 0.04λ, and 0.08λ. In the following cases, it is understood that the angle may be 78 ° or more and 125 ° or less. Therefore, it can be seen that the Euler angle θ range can be expanded compared to the range of 90 ° or more and 114 ° or less when the Au film is used.

Summarizing the results described with reference to FIGS. 2 to 5, a metal material constituting an electrode having an electromechanical coupling coefficient k ² of 0.2 or more, a normalized film thickness of the electrode made of the metal material, The combination of Euler angles θ is one of the combinations shown in Table 8 below. Table 8 shows the result in the case of the structure in which the SiO ₂ film is not laminated.

  Table 8 also shows the case where Au is used as the metal material for comparison.

[Combination of electrode film thickness, normalized film thickness of SiO ₂ film, and Euler angle θ range when SiO ₂ film is formed]
In Table 8 above, when the SiO ₂ film is not formed, the electrode film thickness at which the electromechanical coupling coefficient k ² is 0.2 or more and the Euler angle θ range are shown for each electrode material.

The present inventors have further in the formed structure so as to cover the IDT electrode of the SiO ₂ film as the dielectric film, also considered an electrode material, in addition to the electrode film thickness, the normalized thickness of the SiO ₂ film Then, the range of each Euler angle θ in which the electromechanical coupling coefficient k ² is 0.2 or more was examined. A result is demonstrated for every metal material below.

(When SiO ₂ film is formed and the metal material is Ta)
10 (a), 10 (b) to 17 (a), 17 (b) show the Euler angles θ and Ta when the metal material is Ta and the SiO ₂ film is formed with various standardized film thicknesses. illustrates the reflection coefficient and the relationship between the electromechanical coupling coefficient k ^2, respectively.

Incidentally, FIG. 10 (a), (b) shows the results when the normalized thickness of the SiO ₂ film is 0, i.e. no SiO ₂ film is formed, 11 to 17, the SiO ₂ film The results are shown when the normalized film thicknesses are 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, and 0.35, respectively. Moreover, the standardized film thickness of Ta as a metal material which comprises IDT3 and the reflectors 5 and 6 was made into various thickness, as described in FIGS. As shown in FIG. 2 described above, when Ta is used as the metal material, a larger reflection coefficient can be obtained than when Al is used regardless of the range of the Euler angle θ. 10A to 17A, it can be seen that a large reflection coefficient is obtained even when the Ta film is variously changed regardless of the value of the Euler angle θ.

On the other hand, as is apparent from FIGS. 10B to 17B, when the normalized film thickness of Ta is in the range of 0.04 to 0.08, the normalized film thickness of the SiO ₂ film is , if one of the combinations showing the range of θ of Euler angles shown in Table 9 below, the electromechanical coefficient k ² it can be seen that a 0.2 or higher. In Table 9, the lower limit value and the upper limit value of the Euler angle θ range are shown. For example, when the thickness of the SiO ₂ film is 0.05 or less, the Euler angle θ should be in the range of 74 ° or more and 138 ° or less.

When the thickness of the Ta film is greater than 0.08 and less than or equal to 0.12, the range of the SiO ₂ film thickness and Euler angle θ is one of the combinations shown in Table 10 below. When the standardized film thickness of the Ta film is larger than 0.12 and 0.16 or less, the standardized film thickness of the SiO ₂ film and the range of Euler angle θ are shown in Table 11 below. if one of combinations shown, likewise the electromechanical coefficient k ² may be 0.2 or more. Tables 9 to 11 are based on the results of FIGS. 10 to 17 described above.

(When SiO ₂ film is formed and the metal material is Mo)
18 (a), 18 (b) to 25 (a), 25 (b) show the Euler angles θ when Mo is used as the metal material and the SiO ₂ film is formed with various normalized film thicknesses. illustrates the reflection coefficient and the relationship between the electromechanical coupling coefficient k ^2, respectively.

Incidentally, FIG. 18 (a), (b) shows the results when the normalized thickness of the SiO ₂ film is 0, i.e. no SiO ₂ film is formed, 19 to 25, the SiO ₂ film The results are shown when the normalized film thicknesses are 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, and 0.35, respectively. Further, the standardized film thickness of Mo as a metal material constituting the IDT 3 and the reflectors 5 and 6 was set to various thicknesses as described in FIGS. As shown in FIG. 4 described above, when Mo is used as the metal material, a larger reflection coefficient can be obtained than when Al is used regardless of the range of the Euler angle θ. In FIGS. 18A to 25A, it can be seen that a large reflection coefficient is obtained even when the Mo film is variously changed regardless of the value of the Euler angle θ.

On the other hand, as is clear from FIGS. 18B to 25B, when the normalized film thickness of Mo is in the range of 0.04 to 0.08, the normalized film thickness of the SiO ₂ film is , if one of the combinations showing the range of θ of Euler angles shown in Table 12 below, the electromechanical coefficient k ² it can be seen that a 0.2 or higher. Table 12 below shows the lower limit value and the upper limit value of the Euler angle θ range. For example, when the film thickness of the SiO ₂ film is 0.05 or less, the Euler angle θ should be in the range of 70 ° or more and 153 ° or less.

When the film thickness of the Mo film is larger than 0.08 and 0.12 or less, the film thickness of the SiO ₂ film and the range of Euler angle θ are one of the combinations shown in Table 13 below. If the normalized film thickness of the Mo film is greater than 0.12 and less than or equal to 0.16, the normalized film thickness of the SiO ₂ film and the range of the Euler angle θ are shown in Table 14 below. if one of combinations shown, likewise the electromechanical coefficient k ² may be 0.2 or more. Tables 12 to 14 are based on the results of FIGS. 18 to 25 described above.

(About alloys)
As described above, in forming the IDT electrode, the groove provided on the upper surface of the LiNbO ₃ substrate was filled with the metal material. In this case, the metal material is not limited to the metal described above, but may be an alloy mainly composed of at least one of these metals.

Further, in the above experimental example, as a dielectric film, although SiO ₂ film is formed is not limited to the SiO ₂ film may be a dielectric film made of an inorganic material mainly containing SiO ₂ film. In any case, since these dielectric films have a positive frequency temperature coefficient, the absolute value of the frequency temperature coefficient of the surface acoustic wave device can be obtained by combining with a LiNbO ₃ substrate having a negative frequency temperature coefficient. The value can be reduced. That is, a surface acoustic wave device having excellent temperature characteristics can be provided.

  The electrode structure of the surface acoustic wave device formed according to the present invention is not limited to that shown in FIG. 1, and the present invention is applied to surface acoustic wave resonators and surface acoustic wave filters having various electrode structures. be able to.

As described above, in the present invention, it has been shown that the Euler angles (φ, θ, ψ) of LiTaO ₃ are not particularly limited, but in order to use Rayleigh waves and SH waves as surface waves, Euler angles are used. Is preferably in the range of 0 ° ± 10 °, θ in the range of 70 ° to 180 °, and ψ in the range of 0 ° ± 10 °. That is, the Rayleigh wave and the SH wave can be suitably used by setting the Euler angle to a range of (0 ° ± 10 °, 70 ° to 180 °, 0 ° ± 10 °). More specifically, the SH wave can be more suitably used at (0 ° ± 10 °, 90 ° to 180 °, 0 ° ± 10 °).

  Further, an LSAW wave may be used, and in that case, the Euler angle may be in the range of (0 ° ± 10 °, 110 ° to 160 °, 0 ° ± 10 °). In the above embodiment, the electrode structure of the 1-port SAW resonator is shown. However, the surface acoustic wave device of the present invention can be widely applied to other resonator structures or other resonator surface acoustic wave filters. Can do.

(A) And (b) is a typical fragmentary front sectional view which shows the principal part of the surface acoustic wave apparatus concerning one Embodiment of this invention, (b) is a typical top view of this surface acoustic wave apparatus. is there. In one embodiment of the present invention, the relationship between the Euler angle θ and the reflection coefficient when Ta is used as the metal material constituting the IDT, and the solid line is the result in the case where the SiO ₂ film is laminated. a diagram showing the results when the dashed line is a structure that SiO ₂ film is not laminated. In one embodiment of the present invention, the relationship between the Euler angle θ and the electromechanical coupling coefficient k ² when Ta is used as the metal material constituting the IDT, and the solid line is a structure in which SiO ₂ films are laminated. It shows the results of the case of the result of the case, the dashed line is not stacked SiO ₂ film structure. In one embodiment of the present invention, the relationship between the Euler angle θ and the reflection coefficient when Mo is used as the metal material constituting the IDT, and the solid line is the result in the case where the SiO ₂ film is laminated. a diagram showing the results when the dashed line is a structure that SiO ₂ film is not laminated. In one embodiment of the present invention, the relationship between the Euler angle θ and the electromechanical coupling coefficient k ² when Mo is used as the metal material constituting the IDT, and the solid line is a structure in which the SiO ₂ film is laminated. It shows the results of the case of the result of the case, the dashed line is not stacked SiO ₂ film structure. In the conventional example, the relationship between the Euler angle θ and the reflection coefficient when Al is used as the metal material constituting the IDT is shown, and the solid line indicates the result in the case of the structure in which the SiO ₂ film is laminated. shows the results of the case of the structure SiO ₂ film is not laminated. In the conventional example, the relationship between the Euler angle θ and the electromechanical coupling coefficient k ² when Al is used as the metal material constituting the IDT, and the solid line is the result in the case where the SiO ₂ film is laminated. a diagram showing the results when the dashed line is a structure that SiO ₂ film is not laminated. In the conventional example, the relationship between the Euler angle θ and the reflection coefficient when Au is used as the metal material constituting the IDT is shown, and the solid line indicates the result in the case where the SiO ₂ film is laminated. shows the results of the case of the structure SiO ₂ film is not laminated. In the conventional example, the relationship between the Euler angle θ and the electromechanical coupling coefficient k ² when Au is used as the metal material constituting the IDT, and the solid line is the result in the case of the structure in which the SiO ₂ film is laminated. a diagram showing the results when the dashed line is a structure that SiO ₂ film is not laminated. In (a) and (b), in one embodiment of the present invention, Ta is used as the metal material constituting the IDT, and the normalized film thickness of the Ta film when the SiO ₂ film is not formed, and the Euler angle and theta, is a diagram showing respective relationships between the reflection coefficient and the electromechanical coupling coefficient k ^2. (A) and (b) are standardized Ta films when Ta is used as the metal material constituting the IDT and the standardized film thickness of the SiO ₂ film is 0.05 in one embodiment of the present invention. the film thickness, and θ of the Euler angles are diagrams respectively showing relationships between the reflection coefficient and the electromechanical coupling coefficient k ^2. (A) and (b) are standardized Ta films when Ta is used as the metal material constituting the IDT and the standardized film thickness of the SiO ₂ film is 0.1 in one embodiment of the present invention. the film thickness, and θ of the Euler angles are diagrams respectively showing relationships between the reflection coefficient and the electromechanical coupling coefficient k ^2. (A) and (b) show the standardization of the Ta film when Ta is used as the metal material constituting the IDT and the standardized film thickness of the SiO ₂ film is 0.15 in one embodiment of the present invention. the film thickness, and θ of the Euler angles are diagrams respectively showing relationships between the reflection coefficient and the electromechanical coupling coefficient k ^2. (A) and (b), in one embodiment of the present invention, Ta is used as the metal material constituting the IDT, and the normalized film thickness of the SiO ₂ film is 0.2. the film thickness, and θ of the Euler angles are diagrams respectively showing relationships between the reflection coefficient and the electromechanical coupling coefficient k ^2. (A) and (b), in one embodiment of the present invention, Ta is used as the metal material constituting the IDT, and the normalized film thickness of the SiO ₂ film is 0.25. the film thickness, and θ of the Euler angles are diagrams respectively showing relationships between the reflection coefficient and the electromechanical coupling coefficient k ^2. (A) and (b) show the standardization of the Ta film when Ta is used as the metal material constituting the IDT and the standardized film thickness of the SiO ₂ film is 0.3 in one embodiment of the present invention. the film thickness, and θ of the Euler angles are diagrams respectively showing relationships between the reflection coefficient and the electromechanical coupling coefficient k ^2. (A) and (b) are standardized Ta films when Ta is used as the metal material constituting the IDT and the standardized film thickness of the SiO ₂ film is 0.35 in one embodiment of the present invention. the film thickness, and θ of the Euler angles are diagrams respectively showing relationships between the reflection coefficient and the electromechanical coupling coefficient k ^2. (A) and (b) use Mo as a metal material constituting the IDT in one embodiment of the present invention, and the normalized film thickness of the Mo film when the SiO ₂ film is not formed, and the Euler angle. and theta, is a diagram showing respective relationships between the reflection coefficient and the electromechanical coupling coefficient k ^2. (A) and (b), in one embodiment of the present invention, Mo is used as the metal material constituting the IDT, and the normalized film thickness of the SiO ₂ film is 0.05. the film thickness, and θ of the Euler angles are diagrams respectively showing relationships between the reflection coefficient and the electromechanical coupling coefficient k ^2. (A) and (b) are standardization of the Mo film when Mo is used as the metal material constituting the IDT and the standardized film thickness of the SiO ₂ film is 0.1 in one embodiment of the present invention. the film thickness, and θ of the Euler angles are diagrams respectively showing relationships between the reflection coefficient and the electromechanical coupling coefficient k ^2. (A) and (b), in one embodiment of the present invention, using a Mo as the metal material constituting the IDT, when the normalized thickness of the SiO ₂ film is 0.15, standardization of Mo film the film thickness, and θ of the Euler angles are diagrams respectively showing relationships between the reflection coefficient and the electromechanical coupling coefficient k ^2. (A) and (b), in one embodiment of the present invention, Mo is used as the metal material constituting the IDT, and the normalized film thickness of the SiO ₂ film is 0.2. the film thickness, and θ of the Euler angles are diagrams respectively showing relationships between the reflection coefficient and the electromechanical coupling coefficient k ^2. (A) and (b), in one embodiment of the present invention, Mo is used as the metal material constituting the IDT, and the normalized film thickness of the SiO ₂ film is 0.25. the film thickness, and θ of the Euler angles are diagrams respectively showing relationships between the reflection coefficient and the electromechanical coupling coefficient k ^2. (A) and (b), in one embodiment of the present invention, Mo is used as the metal material constituting the IDT, and the normalized film thickness of the SiO ₂ film is 0.3. the film thickness, and θ of the Euler angles are diagrams respectively showing relationships between the reflection coefficient and the electromechanical coupling coefficient k ^2. (A) and (b), in one embodiment of the present invention, Mo is used as the metal material constituting the IDT, and the normalized film thickness of the SiO ₂ film is 0.35. the film thickness, and θ of the Euler angles are diagrams respectively showing relationships between the reflection coefficient and the electromechanical coupling coefficient k ^2. The typical front sectional view for explaining an example of the conventional surface acoustic wave device. The partial notch front sectional drawing which shows the other example of the conventional surface acoustic wave apparatus.

Explanation of symbols

1 ... the surface acoustic wave device 2 ... LiNbO ₃ substrate 2a ... top 2b ... groove 3 ... IDT
4 ... SiO ₂ film 5,6 ... Reflector

Claims (4)

A piezoelectric substrate made of a LiNbO ₃ substrate and having a plurality of grooves formed on the upper surface;
An IDT having a plurality of electrode fingers made of a metal material filled in a plurality of grooves on the upper surface of the piezoelectric substrate;
The surface acoustic wave device according to claim 1, wherein the metal material is made of Ta or Mo or an alloy mainly composed of at least one of these metals. When the wavelength of the surface acoustic wave is λ, the normalized film thickness normalized by λ of the IDT and the Euler angle (0 ° ± 10 °, θ, 0 ° ± 10 °) of the LiNbO ₃ substrate The surface acoustic wave device according to claim 1, which is one of combinations shown in Table 1 below.

The surface acoustic wave device according to claim 1, further comprising a dielectric film made of an inorganic material mainly composed of SiO ₂ or SiO ₂ that covers the IDT and the piezoelectric substrate. When the wavelength of the surface acoustic wave is λ, the normalized film thickness normalized by λ of the IDT, the normalized film thickness normalized by λ of the SiO ₂ film as the dielectric film, 4. The Euler angle (0 ° ± 10 °, θ, 0 ° ± 10 °) θ of the LiNbO ₃ substrate is one of the combinations shown in the following Table 2 to Table 4 or Table 5 to Table 7. A surface acoustic wave device according to claim 1.

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