JP2008125130A - Surface acoustic wave device and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface acoustic wave device having proper frequency temperature characteristics, a large electro-mechanical coupling coefficient, and small propagation loss. <P>SOLUTION: A surface acoustic wave device 1 comprises a piezoelectric substrate 2 made with 17°-58° rotated Y plate X propagation LiTaO<SB>3</SB>, an IDT 3 composed of tantalum, and a SiO<SB>2</SB>film formed on the piezoelectric substrate 2 to cover IDT 3. The standard film thickness H/λ of the IDT 3 is within the range of 0.004-0.055, and the standard film thickness Hs/λ of the SiO<SB>2</SB>film is within the range of 0.10-0.40, where H is the film thickness and λ is the wavelength of surface waves. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

The present invention relates to a surface acoustic wave device used for, for example, a surface acoustic wave filter, and more particularly to a surface acoustic wave device using a LiTaO ₃ substrate.

Conventionally, a surface wave device using a 40 ° to 42 ° rotated Y-plate X-propagating LiTaO ₃ substrate as a bandpass filter is known (for example, Non-Patent Document 1 below). In the RF bandpass filter, an Al film having a thickness H / λ normalized by the wavelength λ of 0.08 to 0.10 is formed on the 40 ° to 42 ° rotated Y-plate X-propagating LiTaO ₃ substrate. IDT was formed.

As described above, in the conventional surface wave device using the 40 ° -42 ° rotated Y-plate X-propagating LiTaO ₃ substrate, the frequency temperature characteristic TCF is relatively large as −33 ppm / ° C., so that the temperature characteristic is further improved. Some specifications could not be met sufficiently. Conventionally, as a method for improving the temperature characteristic TCF of a surface acoustic wave device, a method of forming an SiO ₂ layer after forming an IDT made of Al on a LiTaO ₃ substrate is known (Patent Document 1 below). .
1997 IEICE General Conference Proceedings: SA-10-6, p. 500-501 JP-A-2-295212

However, when forming a resonator or a filter using an IDT made of Al, in order to obtain a large electromechanical coupling coefficient K _saw or a reflection coefficient, as shown in FIGS. H / λ (H is the film thickness, and λ is the wavelength of the surface wave) must be considerably thick as 0.08 to 0.10. Since the IDT composed of Al is considerably thicker in the portion where the IDT which is shown in FIG. 13 (a) is formed, on the SiO ₂ film that in order to improve the frequency temperature characteristic Once formed, as shown in FIG. 13 (b), (c) , a large step in the SiO ₂ film occurs, there is a crack occurs in the SiO ₂ film. Therefore, the generation of cracks tends to deteriorate the filter characteristics of the surface acoustic wave filter.

In addition, since the electrode film thickness of the IDT made of Al is thick, the effect of covering the unevenness of the electrode surface of the IDT by the formation of the SiO ₂ film is not sufficient, and thereby the temperature characteristics may not be sufficiently improved. .

The object of the present invention is not only to improve the frequency-temperature characteristics by forming a SiO ₂ film in a surface acoustic wave device using a LiTaO ₃ substrate with a propagating rotating Y plate X in view of the current state of the prior art described above, By reducing the electrode film thickness of the IDT, cracks in the SiO ₂ film can be prevented and the attenuation constant can be greatly reduced, so that the desired electrical characteristics such as filter characteristics can be obtained, and To provide a surface acoustic wave device and a method for manufacturing the same, in which the electromechanical coupling coefficient and the reflection coefficient in the IDT are sufficiently large.

The surface wave device according to the present invention is formed on a piezoelectric substrate made of 17 ° -58 ° rotated Y-plate X-propagating LiTaO ₃ and the piezoelectric substrate, and the film thickness is H and the wavelength of the surface wave is λ. Sometimes, it is formed on the piezoelectric substrate so as to cover the IDT made of tantalum having a normalized film thickness H / λ of 0.004 to 0.055, and is normalized by the wavelength of the surface wave. And a SiO ₂ film having a thickness Hs / λ of 0.10 to 0.40.

  In a specific aspect of the surface acoustic wave device according to the present invention, the normalized film thickness H / λ of the IDT is in the range of 0.01 to 0.55, more preferably in the range of 0.016 to 0.045. The

In another specific aspect of the surface acoustic wave device according to the present invention, the piezoelectric substrate is composed of a 21 ° to 53 ° rotated Y-plate X propagation LiTaO ₃ substrate.

  In the present invention, by using a tantalum electrode, a larger electromechanical coupling coefficient and reflection coefficient can be obtained with a thinner electrode film thickness as shown in FIGS.

In still another specific aspect of the surface acoustic wave device according to the present invention, an adhesion layer is formed between the upper surface of the IDT and the SiO ₂ film, whereby the peeling of the SiO ₂ film can be controlled. In this case, the adhesion layer may be formed not only on the upper surface of the IDT but also on the interface between the LiTaO ₃ substrate and the SiO ₂ film. Further, the adhesion layer may be formed not only on the upper surface of the IDT but also in almost the entire region of the interface between the IDT and the SiO ₂ film. That is, an adhesion layer may be formed also on the side surface of the IDT.

In still another specific aspect of the surface acoustic wave device according to the present invention, a plurality of electrodes including at least a bus bar and an electrode pad for connection to the outside other than the IDT are further formed on the LiTaO ₃ substrate, A plurality of electrodes are formed on a base electrode layer made of tantalum and a base electrode layer, and a base metal layer having an upper metal layer made of Al or an Al alloy is formed in the same process as IDT. In addition, since the upper metal layer is made of Al or an Al alloy, the adhesion strength of the SiO ₂ film can be increased and the cost of the electrode can be reduced. Furthermore, the wedge bond property by Al is also improved.

  In the surface acoustic wave device according to the present invention, preferably, a leaky surface acoustic wave is used as the surface wave, and according to the present invention, the frequency constant is excellent, the IDT has a large electromechanical coupling coefficient and a large reflection coefficient. A surface acoustic wave device using a small leaky surface acoustic wave can be provided.

The method for manufacturing a surface acoustic wave device of the present invention includes a step of preparing a LiTaO ₃ substrate with 17 ° -58 ° rotated Y-plate X propagation, and at least one IDT on the LiTaO ₃ substrate, the main component of which is tantalum. A step of forming using a metal, a step of adjusting the frequency after forming the IDT, and a step of forming a SiO ₂ film on the LiTaO ₃ substrate so as to cover the IDT after the frequency adjustment. It is characterized by providing. The metal containing tantalum as a main component includes not only tantalum or an alloy containing tantalum as a main component, but also a layered structure of a tantalum layer and another metal, where the tantalum layer is the main layer.

In a specific aspect of the manufacturing method of the present invention, the IDT has a structure in which an electrode made of a metal having a density of 7100 kg / m ³ or more and a tantalum electrode are laminated.

Tantalum has a higher density than Al, and can easily form an IDT having a thin electrode film thickness, a large electromechanical coupling coefficient, and a large reflection coefficient, so that cracks in the SiO ₂ film can be prevented. Furthermore, the attenuation constant can be reduced by the SiO ₂ film.

In the surface wave device according to the present invention, the normalized film thickness H / λ is 0.004 to 0.055 on the piezoelectric substrate made of 17 ° to 58 ° rotated Y-plate X-propagating LiTaO ₃ and made of tantalum. An IDT is formed, and an SiO ₂ film of Hs / λ = 0.10 to 0.40 is formed so as to cover the IDT. The SiO ₂ film improves the frequency temperature coefficient TCF, and is made of a tantalum film. Since the film thickness H / λ of the IDT is in the specific range, the electromechanical coupling coefficient and the reflection coefficient are large, and the rotation angle of the LiTaO ₃ substrate is in the specific range, so the attenuation constant is small. Is done. Therefore, it is possible to provide a surface acoustic wave device that is excellent in frequency temperature characteristics, has a large electromechanical coupling coefficient, and has low propagation loss.

  In particular, when the film thickness H / λ of the IDT is in the range of 0.10 to 0.55, more preferably in the range of 0.016 to 0.045, the electromechanical coupling coefficient can be effectively increased. .

Further, when the rotation angle of the piezoelectric substrate made of LiTaO ₃ is in the range of 21 ° to 53 °, the attenuation constant can be further reduced.

Further, since the thin tantalum electrodes, deterioration of the characteristics of this for SiO ₂ can not be a large step or cracks SiO ₂ be deposited tantalum electrodes IDT on, insertion loss or the like due to their occurring when the Al electrode Nor.

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

FIG. 1 is a schematic cross-sectional view of a surface acoustic wave device according to an embodiment of the present invention. The surface acoustic wave device 1 is a longitudinally coupled resonator type surface acoustic wave filter, and includes a piezoelectric substrate 2 made of a 17 ° -58 ° rotated Y plate LiTaO ₃ . On the piezoelectric substrate 2, IDTs 3a and 3b and reflectors 5a and 5b made of a tantalum film (Ta film) are formed. The normalized film thickness H / λ (H is the IDT thickness and λ is the wavelength at the center frequency) of the IDTs 3a and 3b is in the range of 0.004 to 0.055. An SiO ₂ film 4 is formed on the piezoelectric substrate 2 so as to cover the IDTs 3a and 3b. The normalized film thickness Hs / λ (Hs is the thickness of the SiO ₂ film and λ is the wavelength of the surface wave at the center frequency) of the SiO ₂ film 4 is in the range of 0.10 to 0.40.

In the present embodiment, as described above, the piezoelectric substrate 2 made of 17 ° -58 ° rotated Y-plate X-propagating LiTaO ₃ , IDTs 3a, 3b made of tantalum with H / λ = 0.004-0.055, and Hs Since the SiO ₂ film 4 in the range of /λ=0.10 to 0.40 is used, a surface wave device having a small frequency temperature coefficient TCF, a large electromechanical coupling coefficient K ² , and a small propagation loss. Can be provided. This will be described based on the following specific experimental example.

As surface waves propagating through the LiTaO ₃ substrate, leaky surface acoustic waves exist in addition to Rayleigh waves. The leaky surface acoustic wave has a higher sound speed and a larger electromechanical coupling coefficient than the Rayleigh wave. However, a leaky surface acoustic wave is a wave that propagates while radiating energy into the substrate. Therefore, the leaky surface acoustic wave has an attenuation constant that causes propagation loss.

FIG. 2 shows the relationship between the Euler angle (0, θ, 0) θ in the rotating Y plate X propagation LiTaO ₃ and the attenuation constant (propagation loss) α when the substrate surface is electrically short-circuited. It should be noted that the rotation angle = θ−90 degrees.

  As is apparent from FIG. 2, the damping constant is small when the Euler angle θ is in the range of 124 ° to 126 °. Outside this range, the damping constant increases.

In addition, it is known that when an IDT made of Al having a relatively large thickness is formed, the attenuation constant becomes small at θ = 130 ° to 132 ° (for example, Non-Patent Document 1). Therefore, conventionally, in a configuration in which an IDT made of Al and a LiTaO ₃ substrate are combined, a rotating Y plate X propagation LiTaO ₃ substrate of θ = 130 ° to 132 ° has been used.

FIG. 3 shows the relationship between the Euler angle (0, θ, 0) θ and the electromechanical coupling coefficient K ² in the rotating Y-plate X-propagating LiTaO ₃ substrate. It can be seen that a large electromechanical coupling coefficient K ² is obtained when the Euler angle θ is in the range of 100 ° to 120 °. However, in the range of θ = 100 ° to 120 °, the damping constant is large as is apparent from FIG. Therefore, it can be seen that such an Euler angle LiTaO ₃ substrate cannot be used.

FIG. 4 shows a normalized film thickness H / λ of a tantalum film when a tantalum film is formed on a LiTaO ₃ substrate of 36 ° rotation Y-plate X propagation [Euler angles (0 °, 126 °, 0 °)]. (H represents the film thickness, and λ represents the wavelength at the center frequency of the surface acoustic wave device) and the electromechanical coupling coefficient K ² . In the range of the normalized film thickness H / λ = 0.004 to 0.08, the electromechanical coupling coefficient K ² is 1 of the electromechanical coupling coefficient when H / λ = 0 (when no film is formed). It becomes 3 times or more, and when H / λ = 0.01 to 0.055, it becomes 1.5 times or more, and when H / λ = 0.016 to 0.045, it becomes 1.75 times or more.

Therefore, it is understood that the electromechanical coupling coefficient K ² can be increased by setting H / λ = 0.004 to 0.08.

  Note that when the normalized film thickness of the tantalum film exceeds 0.055, it may be difficult to manufacture an IDT obtained from tantalum. Therefore, the normalized film thickness H / λ of the tantalum film is preferably 0.004 to 0.055, more preferably 0.012 to 0.055, and still more preferably 0.016 to 0.045. Recognize.

Next, the improvement effect of the frequency temperature coefficient TCF when the SiO ₂ film is formed on the LiTaO ₃ substrate will be described. FIG. 5 is a diagram showing changes in the frequency temperature coefficient TCF when a SiO ₂ film is formed on each (0, θ, 0) LiTaO ₃ substrate of θ = 113 °, 126 °, and 129 °.

As apparent from FIG. 5, theta is 113 °, in either case of 126 ° and 129 °, the film thickness of the SiO ₂ normalized thickness Hs / λ (Hs is SiO ₂ film, lambda surface waves It can be seen that the TCF is in the range of -24 to +17 ppm / ° C in the range of 0.10 to 0.45 (which indicates the wavelength at the center frequency of the device). However, since the formation of the SiO ₂ film it takes time, it is desirable that the thickness Hs / lambda of the SiO ₂ film is 0.40 or less. Therefore, preferably, the film thickness Hs / λ of the SiO ₂ film is in the range of 0.10 to 0.40, whereby the film can be formed in a short time and the TCF is in the range of −20 to +17 ppm / ° C. can do.

Conventionally, there are some reports that TCF such as Rayleigh waves can be improved by further forming a SiO ₂ film in a structure in which an IDT made of Al is formed on a LiTaO ₃ substrate (for example, the above-mentioned patent document). 1). However, in the laminated structure of LiTaO ₃ substrate-electrode made of tantalum-SiO ₂ film, there has been no report on an experiment taking into consideration the film thickness of the electrode and the attenuation constant of the leaky surface acoustic wave.

FIG. 6 and FIG. 7 show an IDT made of tantalum having various film 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.

As is apparent from FIG. 6, 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 electrode made of tantalum 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. 7, 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 cut 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.

8 to 11 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 apparent from FIGS. 8 to 11, 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 1 and Table 2 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 Tables 1 and 2, when the film thickness H / λ of the electrode made of tantalum is 0.01 to 0.055, the normalized film of the SiO ₂ film is used to improve the temperature characteristics. When the thickness is in the range of 0.1 to 0.4, the θ at the Euler angle of LiTaO ₃ is in the range of 107 ° to 148 °, that is, the rotation angle is in the range of 17 ° to 58 °, more preferably SiO. _It can be seen that the Euler angles shown in Table 1 may be selected according to the film thickness of ₂ .

Similarly, as is apparent from Table 2, the normalized film thickness of the electrode made of the tantalum film is 0.016 to 0.045, and the SiO ₂ film thickness is set to 0.000 in order to improve the frequency temperature characteristics. When it is in the range of 1 to 0.4, the Euler angle of the LiTaO ₃ substrate may be in the range of 109 ° to 144 °, and more preferably, the Euler angle in Table 2 is set according to the film thickness of the SiO ₂ film. It turns out that it only has to be selected.

The range of Euler angles of LiTaO ₃ defines a range where the attenuation constant is 0.05 or less. Moreover, the more preferable range of the Euler angles of LiTaO ₃ in Tables 1 and 2 is that in which the attenuation constant is specified to be 0.025 or less. The relationship between the film thickness 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 FIGS. The thickness of the SiO ₂ film and the Euler angle values in Tables 1 and 2 are obtained by conversion from the normalized film thickness of the electrode film made of tantalum shown in FIG.

FIGS. 14A, 14B, and 14C are scanning electron micrographs of the surface of the surface acoustic wave filter of the above example. Here, the results are shown before and after the SiO ₂ film having the normalized film thickness Hs / λ = 0.3 is formed on the IDT made of tantalum having the standardized film thickness of H / λ = 0.025. Has been. As is apparent from the post-deposition photograph in FIG. 14B, it can be seen that no cracks are observed on the surface of the SiO ₂ film, and therefore it is difficult for the characteristics to be deteriorated by the cracks. Compared with the Al electrode, the tantalum electrode has a thin film thickness and a large electromechanical coupling coefficient and reflection coefficient. Therefore, even if SiO ₂ is formed on a thin tantalum electrode, there is an advantage that a large step or crack does not occur in SiO ₂ as shown in FIGS. 14 (b) and 14 (c).

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. 15 and 16. FIG. 15 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. 16 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 apparent from a comparison between FIG. 15 and FIG. 16, the change in the sound velocity of the surface wave is much greater when the tantalum film thickness is changed than when the SiO ₂ film thickness is changed. . 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.

As described above, the present invention provides a piezoelectric substrate made of 17 ° -58 ° rotated Y-plate X-propagating LiTaO ₃ , an IDT made of tantalum with H / λ = 0.004-0.055, and Hs / λ. = which is characterized by having a SiO ₂ film is 0.10 to 0.40, thus, there is no particular limitation on such IDT of number and structure. 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.

The meaning of tantalum as a main component means that when tantalum is laminated with another electrode, it does not mean the ratio of thickness, but means that the weight ratio multiplied by density and thickness is half or more. Note that the same layer as the tantalum electrode single layer is formed on the tantalum or below the tantalum even if it is laminated at the same rate as an electrode made of a metal such as W, Au, Pt, Cu, Ag, Cr having a density of 7100 kg / m ³ or more. Needless to say, it has an effect.

1 is a schematic plan view showing a surface acoustic wave device according to an embodiment of the present invention. Euler angles (0, θ, 0) shows a theta of LiTaO ₃ substrate, the relationship between the attenuation constant α of. Euler angles (0, θ, 0) shows the relationship between the LiTaO ₃ and the theta in the substrate electromechanical coefficient K ² of. The relationship between the normalized film thickness H / λ of the electrode film and the electromechanical coupling coefficient K ² in the structure in which the electrode film made of tantalum is formed on the LiTaO ₃ substrate with Euler angles (0 °, 126 °, 0 °). FIG. When a SiO ₂ film is formed on each LiTaO ₃ substrate of Euler angles (0 °, 113 °, 0 °), (0 °, 126 °, 0 °) and (0 °, 129 ° 0, 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. 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 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 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 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 wave apparatus, normalized thickness H / (lambda) of the electrode film which consists of tantalum, and attenuation constant (alpha). Euler angles (0 °, 126 °, 0 °) shows in LiTaO ₃ substrate, the relationship between the film thickness and the reflection coefficient of electrode fingers of the case of forming the electrodes made of tantalum or aluminum of various thicknesses electrodes . (A) shows the surface on which an IDT made of an aluminum electrode with a film thickness H / λ = 0.08 is formed on a LiTaO ₃ substrate with Euler angles (0 °, 126 °, 0 °), and (b) FIG. 4C is a view showing each scanning electron micrograph showing a cross section of the surface on which a SiO ₂ film having a thickness of Hs / λ = 0.3 is formed. (A) shows a surface on which an IDT made of tantalum having a thickness of H / λ = 0.025 is formed on a LiTaO ₃ substrate having Euler angles (0 °, 126 °, 0 °), and (b) FIG. 4C is a view showing each scanning electron micrograph showing a cross section of the surface on which SiO ₂ having a thickness of Hs / λ = 0.3 is formed. 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.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Surface wave apparatus 2 ... Piezoelectric substrate 3a, 3b ... IDT
4 ... SiO ₂ film 5a, 5b ... Reflector

Claims (6)

A piezoelectric substrate made of 17 ° -58 ° rotated Y-plate X-propagating LiTaO ₃ ;
IDT made of tantalum having a normalized film thickness H / λ of 0.004 to 0.055 when the film thickness is H and the wavelength of the surface wave is λ.
A surface acoustic wave device comprising: a SiO ₂ film formed on the piezoelectric substrate so as to cover the IDT and having a film thickness Hs / λ normalized by the wavelength of the surface acoustic wave of 0.10 to 0.40. .   2. The surface acoustic wave device according to claim 1, wherein the normalized thickness H / λ of the IDT is in a range of 0.01 to 0.055.   The surface acoustic wave device according to claim 2, wherein the normalized film thickness H / λ of the IDT is in a range of 0.016 to 0.045. The surface acoustic wave device according to claim 1, wherein the piezoelectric substrate is a 21 ° to 53 ° rotated Y-plate X-propagating LiTaO ₃ substrate. A step of preparing a LiTaO ₃ substrate for 17 ° -58 ° rotation Y-plate X propagation, a step of forming at least one IDT on the LiTaO ₃ substrate using a metal containing tantalum as a main component, and the IDT 5. The method according to claim 1, further comprising: adjusting the frequency after forming; and forming an SiO ₂ film on the LiTaO ₃ substrate so as to cover the IDT after the frequency adjustment. A method for manufacturing the surface acoustic wave device according to any one of the above. The method of manufacturing a surface acoustic wave device according to claim 5, wherein the IDT has a structure in which an electrode made of a metal having a density of 7100 kg / m ³ or more and a tantalum electrode are laminated.