JP2008294538A - Elastic boundary wave device and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an elastic boundary wave device which has a suitably small reflection coefficient ¾κ<SB>12</SB>¾/k<SB>0</SB>, a large electromechanical coupling coefficient K<SP>2</SP>, and a desired bandwidth, and can suppress spuriousness on a pass-band low-range side and increase insertion loss. <P>SOLUTION: The elastic boundary wave device 1 has an IDT electrode 4 formed by forming a plurality of grooves 2b on the top surface 2a of a piezoelectric body and charging metal in the plurality of grooves 2b, has a dielectric 3 formed on the IDT electrode 3 and the top surface 2a of the piezoelectric body 2, and uses an SH type elastic boundary wave propagated on the interface between the dielectric 2 and piezoelectric body 3, wherein when the wavelength of the elastic boundary wave is denoted as λ, a thickness H of the IDT electrode 4 is >8261.744p<SP>-1.376</SP>, the density ρ is >3745 kg/m<SP>3</SP>, and a thickness H of the IDT electrode is different from the depth of the grooves 2b. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a boundary acoustic wave device used as, for example, a resonator or a bandpass filter and a manufacturing method thereof, and more particularly to a boundary acoustic wave device using an SH type boundary acoustic wave and a manufacturing method thereof.

  In recent years, boundary acoustic wave devices have attracted attention because they can be miniaturized instead of surface acoustic wave devices. In the boundary acoustic wave device, the IDT electrode is disposed between the first and second mediums made of solid, and the boundary acoustic wave propagating on the boundary between the first and second media is used.

For example, Patent Document 1 below discloses a boundary acoustic wave device 1001 shown in FIG. In the boundary acoustic wave device 1001, a piezoelectric body 1002 made of LiNbO ₃ and a dielectric body 1003 made of SiO ₂ are laminated. An IDT electrode 1004 and reflectors 1005 and 1006 made of a metal having a high density such as Au are formed at the interface between the piezoelectric body 1002 and the dielectric body 1003. By using a metal having a high density such as Au as the IDT electrode 1004, the boundary acoustic wave is excited by concentrating vibration energy on the portion where the IDT electrode 1004 is provided.

In the boundary acoustic wave device described in Patent Document 1, it is preferable that H> 826.744ρ- ^1.376 and ρ> 3745 kg / m ³ when the film thickness H and density ρ of the IDT electrode are set. By ^setting H> 826.744ρ- ^1.376 , it is possible to propagate the SH type boundary acoustic wave with a propagation loss of 0, and it is possible to reduce the propagation loss by setting the density ρ to the above specific value or more. It is shown.
WO2004 / 070946

As described in Patent Document 1, in the structure in which the IDT electrode 1004 made of Au is provided at the boundary between the piezoelectric body 1002 made of LiNbO ₃ and the dielectric body 1003 made of SiO ₂ , for example, the wavelength of the elastic boundary wave is λ. When the thickness of the IDT electrode 1004 is 0.06λ and the duty ratio is 0.6, the reflection coefficient | κ ₁₂ | / k ₀ that is an index of the reflection amount of the electrode finger of the IDT is as large as about 0.175. It was. Here, the reflection coefficient | κ ₁₂ | / k ₀ is an index of the reflection amount of the electrode finger, κ ₁₂ indicates an inter-mode coupling coefficient based on the mode coupling theory, and k ₀ is an elastic boundary that propagates through the IDT electrode. The wave number 2π / λ is shown.

Conventionally, in a surface acoustic wave filter device used in an RF stage of a mobile phone, a structure in which an IDT electrode made of Al is provided on a LiTaO ₃ substrate has been frequently used. In this structure, the absolute value of the reflection coefficient κ ₁₂ / k ₀ of the leaky surface acoustic wave was only about 0.03 to 0.04.

On the other hand, in the boundary acoustic wave device 1001 described in Patent Document 1, the absolute value of the reflection coefficient κ ₁₂ / k ₀ can be increased by using the IDT electrode made of Au as described above. When the reflection coefficient increases, the blocking area in the reflectors 1005 and 1006 can be widened. Therefore, when a longitudinally coupled resonator type filter in which reflectors are arranged on both sides of the boundary acoustic wave propagation direction in the region where the IDT electrode 1004 is provided, a wide band can be easily achieved. In addition, the number of electrode fingers in the reflector can be reduced, and downsizing can be promoted.

  However, when a resonator type boundary acoustic wave filter device is configured, a passband is formed in the vicinity of the stopband of the IDT electrode 1004. Therefore, the wider the stopband, the greater the line width of the electrode finger and the film. There has been a problem that frequency variation becomes large due to variation in thickness.

Note that the stopband edge of the IDT electrode 1004, and shows the upper or lower end of the stop band when the grating reflectors are short-circuited and the positive terminal and the negative side of the IDT electrode terminal, kappa ₁₂ is Positive is the lower end, negative is the upper end.

When the longitudinally coupled resonator type boundary acoustic wave filter is configured, when κ ₁₂ is positive, the radiation conductance characteristic of the IDT electrode 1004 has a peak at a lower frequency side than the pass band of the filter. Accordingly, there is a problem that a large spurious is generated on the low band side of the pass band, and the attenuation in the stop band on the low band side is deteriorated.

In order to reduce the spurious due to the radiation conductance peak of the IDT electrode 1004, there are a method of reducing the reflection coefficient | κ ₁₂ | / k ₀ and a method of reducing the electromechanical coupling coefficient K ² . However, if the electromechanical coupling coefficient K ² is reduced, the insertion loss of the boundary acoustic wave device increases. Conversely, when the reflection coefficient | κ ₁₂ | / k ₀ is reduced, the boundary acoustic wave is increased in speed, the propagation loss is increased, and the insertion loss is also deteriorated.

The object of the present invention is to make the absolute value of the reflection coefficient κ ₁₂ / k ₀ moderately small and the electromechanical coupling coefficient K ² is relatively large in view of the current state of the above-described prior art, and therefore, is appropriate. It is an object of the present invention to provide a boundary acoustic wave device having a bandwidth and capable of reducing insertion loss and a method for manufacturing the same.

The boundary acoustic wave device according to the present invention includes a piezoelectric body as a main component, a plurality of grooves formed on an upper surface of the piezoelectric body, and an IDT electrode formed by filling the plurality of grooves with metal. The IDT electrode and a dielectric formed so as to cover the upper surface of the piezoelectric body, and utilizing an SH type boundary acoustic wave propagating through the boundary between the dielectric and the piezoelectric body, Assuming that the wavelength of the wave is λ, the thickness of the IDT electrode normalized by λ is H, and the density of the IDT electrode is ρ (kg / m ³ ), H> 826.744ρ- ^1.376 and ρ> 3745 kg / m is ^3, wherein the thickness H of the IDT electrode is different from the depth of the groove.

In the boundary acoustic wave device according to the present invention, the thickness H of the IDT electrode may be larger than the depth of the groove. In this case, adjustment can be made to reduce the amount of decrease in the reflection coefficient | κ ₁₂ | / k ₀ .

Conversely, in the present invention, the thickness H of the IDT electrode may be smaller than the depth of the groove. In this case, the reduction amount of the reflection coefficient | κ ₁₂ | / k ₀ can be increased.

  In the boundary acoustic wave device according to the present invention, preferably, the dielectric is a dielectric formed by a deposition method. Therefore, the upper surface of the IDT electrode and the upper surface of the piezoelectric body can be reliably covered with the dielectric regardless of the thickness of the IDT electrode with respect to the depth of the groove. Therefore, it is easy to change the thickness of the IDT electrode with respect to the groove depth.

  A method of manufacturing a boundary acoustic wave device according to the present invention includes a step of forming a resist film having a plurality of openings on an upper surface of a piezoelectric body, and etching the resist film as a mask to form the resist film on the upper surface of the piezoelectric body. A step of forming a plurality of grooves according to a plurality of openings, a step of forming a metal film having a thickness different from the depth of the grooves on the piezoelectric body and the resist film, and removing the resist film and resist film An unnecessary metal film is removed, an IDT electrode having a plurality of electrode fingers is formed by the metal film filled in the groove, and a dielectric is formed by a deposition method so as to cover the IDT electrode and the piezoelectric body And a step of forming a film.

In the boundary acoustic wave device according to the present invention, a plurality of grooves formed on the upper surface of the piezoelectric body are filled with metal to form an IDT electrode, and the thickness H and density ρ of the IDT electrode are such that H> 8261. 744ρ ^-1.376 and ρ> 3745 kg / m ³ , and the thickness H of the IDT electrode is different from the depth of the groove, so that the reflection coefficient | κ ₁₂ | / k ₀ can be appropriately reduced, and The electromechanical coupling coefficient K ² can be increased. Therefore, it is possible to reduce the spurious due to the radiation conductance peak of the IDT electrode, and it is possible to suppress the deterioration of the attenuation amount and the deterioration of the insertion loss on the low bandwidth side.

  Therefore, it is possible to provide a boundary acoustic wave device having an appropriate bandwidth according to various uses and a small insertion loss.

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

  1A and 1B are a schematic front sectional view showing a boundary acoustic wave device according to an embodiment of the present invention and a schematic plan view showing an electrode structure thereof.

The boundary acoustic wave device 1 includes a piezoelectric body 2 mainly composed of LiNbO ₃ and a dielectric body 3 composed of SiO ₂ . A plurality of grooves 2 b are formed on the upper surface 2 a of the piezoelectric body 2. The plurality of grooves 2b are filled with metal to form the IDT electrode 4 and the reflectors 5 and 6.

  As shown in FIG. 1B, the IDT electrode 4 has a plurality of electrode fingers that are interleaved with each other. The reflectors 5 and 6 have a structure in which both ends of a plurality of electrode fingers are short-circuited.

  In the present embodiment, the IDT electrode 4 and the reflectors 5 and 6 are made of Au.

The characteristics of the boundary acoustic wave device 1 are standardized by the fact that the IDT electrode 4 is formed by filling a groove 2b provided in the upper surface 2a of the piezoelectric body 2 with the metal, and the wavelength λ of the boundary acoustic wave. When the thickness of the IDT electrode 4 is H and the density ρ (kg / m ³ ), H> 826.744ρ- ^1.376 and ρ> 3745 kg / m ^3, and the thickness H of the IDT electrode 4 is the groove 2b. The depth is different. Thereby, the reflection coefficient | κ ₁₂ | / k ₀ is appropriately reduced, and the electromechanical coupling coefficient K ² (%) is sufficiently increased. For this reason, it is possible to suppress an undesired spurious on the low pass band side with an appropriate bandwidth and to increase the amount of attenuation, and to further suppress deterioration of insertion loss. This will be described more specifically.

In the boundary acoustic wave device 1, when the laminated structure is expressed as SiO ₂ / Au / LiNbO _{3 in} order from the top, the density of SiO ₂ is 2210 kg / m ³ , the density of Au is 19300 kg / m ³ , and LiNbO ₃ Since the density of this is 4700 kg / m ^3, it is a laminated structure of low density layer / high density layer / medium density layer. Since the IDT electrode 4 is formed by filling the groove 2b with a metal, high-density Au is embedded in the groove of LiNbO ₃ which is a medium density layer.

  Table 1 below shows the specifications of the boundary acoustic wave device of the present embodiment.

The acoustic velocity V _s1 , electromechanical coupling coefficient K ² and reflection coefficient | κ ₁₂ | / k ₀ from the lower end of the stop band of the boundary acoustic wave device 1 were determined as follows.

The calculation is an extension of the finite element method proposed in "Fine Element Analysis of Periodically Structured Piezoelectric Waveguides" (The IEICE Transactions Vol.J68-C No1,1985 / 1, pp.21-27). Then, as shown in FIG. 1, one strip was arranged in the half-wavelength section, and the sound velocities at the upper end and the lower end of the stop band of the electrically released strip and the shorted strip were obtained. Let V _{o1 be} the sound velocity at the lower end of the release strip, V _{o2 be} the sound velocity at the upper end, V _{s1 be} the sound velocity at the lower end of the stop band of the short-circuit strip, and V _s2 be the sound velocity at the upper end. Since most of the energy is concentrated in the vicinity of 1λ above and below the IDT in the vibration of the boundary wave, the boundary condition between the front and back surfaces is fixed elastically, with 8λ being sufficiently large in the vertical direction. Next, based on the method proposed in "Excitation characteristics evaluation of surface acoustic wave interdigital electrode by mode coupling theory" (Technical Report of IEICE, NW90-62, 1990, pp.69-74) | Κ ₁₂ | / k ₀ and the electromechanical coupling coefficient K ² representing the amount of reflection of the boundary wave at 1 were obtained. Note that κ ₁₂ represents an inter-mode coupling coefficient based on the mode coupling theory, and k ₀ represents the wave number 2π / λ of an elastic wave propagating through the IDT electrode. Note that the κ ₁₂ / k ₀ was determined in consideration of the influence of the frequency dispersion, since the frequency dispersion of the sound velocity is larger in the structure shown in Table 1 than the structure dealt with in the above document. The TCD was determined by the formula [1] from the phase velocities V _{15 ° C.} , V _{25 ° C.} and V _{35 ° C. at the} lower end of the short-circuit strip stop zone at ₁₅ , ₂₅ and _{35 ° C.}

Here, α _s is the linear expansion coefficient of the LiNbO ₃ substrate in the boundary wave propagation direction.

  The characteristics of the boundary acoustic wave of the boundary acoustic wave device 1 obtained by the above calculation are shown in Table 2 below.

As is apparent from Table 2, the reflection coefficient | κ ₁₂ | / k ₀ is 0.133, and the electromechanical coupling coefficient K ² is 18.6%.

  For comparison, the conventional boundary acoustic wave device shown in FIG. 9 is calculated in the same manner as in the above embodiment according to the calculation conditions shown in Table 3 below corresponding to the calculation conditions in the above embodiment, The propagation characteristics of boundary acoustic waves were obtained. The results are shown in Table 4 below.

As is clear from Table 4, in the boundary acoustic wave device 1001, the reflection coefficient | κ ₁₂ | / k ₀ was as large as 0.175, and the electromechanical coupling coefficient K ² (%) was 15.8%.

Therefore, as is clear from the comparison between the results in Table 2 and the results in Table 4, the boundary acoustic wave device 1 of the above embodiment has a reflection coefficient κ ₁₂ / k ₀ as compared with the conventional boundary acoustic wave device 1001. It can be seen that it is reduced from 0.175 to 0.133 and the electromechanical coupling coefficient K ² is increased from 15.8% to 18.6%. Therefore, it can be seen that the insertion loss can be reduced while securing an appropriate bandwidth.

Next, according to the boundary acoustic wave device 1 of the above-described embodiment, it will be described that the spurious on the low pass band side that has occurred in the conventional boundary acoustic wave device 1001 can be suppressed. This is because the reflection coefficient | κ ₁₂ | / k ₀ is appropriately reduced. This will be described with reference to FIGS.

FIG. 4 is a diagram showing attenuation-frequency characteristics of the conventional boundary acoustic wave device 1001 prepared as the comparative example. Here, a large spurious as indicated by an arrow A appears on the low pass band side. On the other hand, FIG. 5 is a diagram in which the attenuation frequency characteristics when the reflection coefficient | κ ₁₂ | / k ₀ is 0.10 or 0.15 in the boundary acoustic wave device 1 are obtained by calculation. As is apparent from FIG. 5, when the reflection coefficient | κ ₁₂ | / k ₀ is either 0.15 or 0.10, that is, 0.15 or less, it is indicated by an arrow A in FIG. It turns out that the spurious that existed does not exist. Therefore, also in the above embodiment, since the reflection coefficient | κ ₁₂ | / k ₀ is 0.133, the spurious A appears as in the case of 0.15 or 0.10 shown in FIG. Not expected.

6 and 7 are diagrams showing the conductance characteristics of the IDT alone in the boundary acoustic wave device. In FIG. 6, the solid line shows the results when κ ₁₂ is 0.15, 0.10, or 0.05. For comparison, a LiTaO ₃ substrate is used, and leakage with IDT κ ₁₂ of 0.03 is shown. The conductance characteristics of the IDT alone in the surface wave device using the surface acoustic wave are also shown. Further, FIG. 7, the electromechanical coupling factor K ² is 13%, shows the IDT single conductance characteristic when 9% and 4%, for comparison, the electromechanical coupling factor K ² is 9.3% The conductance characteristics of a single IDT in a surface acoustic wave device using a LiTaO ₃ substrate are also shown.

As is apparent from FIG. 6, when κ ₁₂ is reduced, the conductance value of the IDT in the vicinity of the spurious response on the low passband side is reduced, and spurious can be suppressed. On the other hand, since the conductance value of the IDT in the pass band is increased, the electroacoustic conversion performance of the IDT in the pass band is improved and the loss can be reduced.

However, as is apparent from FIG. 7, even if the electromechanical coupling coefficient K ² is simply reduced, the conductance value only decreases as a whole, and the shape of the conductance characteristic itself does not change. Therefore, it can be seen that even if the electromechanical coupling coefficient K ² is reduced in order to suppress the spurious on the low side of the pass band, the electroacoustic conversion performance of the IDT in the pass band also deteriorates and the loss increases.

Therefore, it can be seen that | κ ₁₂ | / k ₀ needs to be an appropriate value for the required size and frequency characteristics of the boundary acoustic wave device.

In other words, by setting the reflection coefficient | κ ₁₂ | / k ₀ to a reasonably small value for the required size and frequency characteristics of the boundary acoustic wave device, spurious at the low pass band side is suppressed, and insertion loss is reduced. It can be seen that this can also be reduced.

  Next, an example of a method for manufacturing the boundary acoustic wave device 1 according to the above embodiment will be described with reference to FIGS.

As shown in FIG. 2A, a piezoelectric body 2 made of LiNbO ₃ is prepared. Next, a photoresist is applied on the upper surface of the piezoelectric body 2 and patterned by a photolithography method. In this way, a resist pattern 7 is formed as shown in FIG. The resist pattern 7 has a plurality of openings 7a. The plurality of openings 7a have a planar shape corresponding to the plurality of electrode fingers of the IDT electrode 4 and the reflectors 5 and 6 and electrode portions outside the electrode fingers.

  Next, an ion beam is irradiated using the photoresist pattern 7 as a mask to form a plurality of grooves 2b on the upper surface 2a of the piezoelectric body 2 as shown in FIG. By irradiation with this ion beam, the upper surface 2a of the piezoelectric body 2 is dug to form a plurality of grooves 2b, and the thickness of the resist pattern 7 is reduced.

  When the ion beam is irradiated, the resist pattern 7 may not be thin as long as the groove 2b is formed.

  Next, Au is vapor-deposited by an electron beam vapor deposition method to form an Au film 8 as a metal film. The IDT electrode 4 and the reflectors 5 and 6 are formed of Au filled in the groove 2b in the metal film 8 (see FIG. 2D).

Thereafter, the resist pattern 7 and the unnecessary metal film 8 on the resist pattern 7 are removed by a lift-off method. In this way, as shown in FIG. 3A, the IDT electrode 4 and the reflectors 5 and 6 are formed by filling the plurality of grooves provided on the upper surface 2a of the piezoelectric body 2 with Au as a metal. Is done. Thereafter, SiO ₂ as a dielectric is formed by a deposition method such as sputtering to form the dielectric 3 shown in FIG. In this way, the boundary acoustic wave device 1 of the above embodiment can be obtained.

Note that the thickness of the metal film 8 is made thinner than the depth of the groove 2b. Therefore, in this embodiment, the thickness H of the IDT electrode 4 is made smaller than the depth of the groove 2b. Thus, the depth of the groove 2b and the thickness H of the IDT electrode 4 are not equal and are different. Therefore, the reflection coefficient | κ ₁₂ | / k ₀ can be easily adjusted by the thickness H of the IDT electrode 4.

In addition, in this embodiment, since the thickness H of the IDT electrode 4 is smaller than the thickness of the groove 2b, the reduction amount of the reflection coefficient | κ ₁₂ | / k ₀ can be increased. In this case, when the depth of the groove 2b is made larger than the thickness of the IDT electrode 4, an increase in the reflection coefficient | κ ₁₂ | / k ₀ can be suppressed even when the thickness H of the IDT electrode is increased. . Therefore, it is desirable that both the reduction of the electric resistance due to the resistance of the electrode finger and the reduction of the reflection coefficient | κ ₁₂ | / k ₀ can be achieved.

For example, in the present invention, unlike the above embodiment, the thickness H of the IDT electrode 4 may be larger than the depth of the groove, as in the modification shown in FIG. Even in this case, the reflection coefficient | κ ₁₂ | / k ₀ can be adjusted.

As shown in FIG. 8, when the thickness H of the IDT electrode 4 is larger than the depth of the groove 2b, the amount of decrease in the reflection coefficient | κ ₁₂ | / k ₀ can be reduced. Therefore, according to the required bandwidth and size, the thickness H of the IDT electrode 4 may be increased or decreased with respect to the depth of the groove 2b. In any case, when the dielectric 3 is formed by the deposition method as in the above manufacturing method, the dielectric 3 is reliably deposited by the deposition method even if the thickness of the IDT electrode 4 is larger or smaller than the depth of the groove 2b. By forming, the upper surfaces of the IDT electrode 4 and the piezoelectric body 2 can be reliably covered.

In this embodiment, since the IDT electrode thickness H normalized by the wavelength λ of the boundary acoustic wave is H> 826.744ρ- ^1.376 , it is possible to effectively suppress the spurious due to the Stoneley wave while reducing the SH type. A boundary acoustic wave can be propagated. Further, since the density ρ is ρ> 3745 kg / m ³ , the film thickness of the electrode where the propagation loss is 0 can be reduced, and the electrode can be easily formed. Such an effect by H> 826.744ρ- ^{1.376 and} an effect by having ρ> 3745 kg / m ³ are as described in Patent Document 1 described above.

  In the above-described embodiment and modification, the boundary acoustic wave device as a longitudinally coupled resonator type filter has been described. However, the present invention provides a transformer using a longitudinally coupled filter, a laterally coupled resonator type filter, and a reflective SPUDT. The present invention can be widely applied to various devices using a boundary acoustic wave, such as a versatile boundary acoustic wave filter, a boundary acoustic wave resonator, a boundary acoustic wave optical switch, and a boundary acoustic wave optical filter.

In the above embodiment, the dielectric, which had been formed by SiO _2, may use other dielectric materials. That is, various dielectric materials such as SiO ₂ , Si, glass, SiC, ZnO, Ta ₂ O ₅ , AlN, and Al ₂ O ₃ can be used as the dielectric.

The piezoelectric body is not limited to LiNbO ₃ , and various piezoelectric bodies such as LiTaO ₃ , ZnO, Ta ₂ O ₅ , AlN, Kn, or piezoelectric ceramics such as PZT can be used.

  However, the piezoelectric body and the dielectric body need to be formed of different materials.

  The IDT electrode 4 may also be formed using a material other than Au. That is, the IDT electrode can be formed from various metals such as Pt, Ag, Cu, Ni, Ti, Fe, W, and Ta. Furthermore, the IDT electrode 4 may be formed of a laminated metal film formed by laminating a plurality of metal films. Further, in order to improve adhesion and power durability, a metal layer forming the IDT electrode 4 and the dielectric layer, a layer between the metal layer and the piezoelectric body, or a laminated metal film is formed. An adhesion layer made of a thin film such as NiCr, Ni, Ti, Cr, Pt, or Pd or a power durability improvement layer may be disposed between the metal films.

  Further, a protective layer may be formed outside the dielectric / IDT electrode / piezoelectric laminated structure in order to improve the strength of the boundary acoustic wave device and prevent the invasion of corrosive gas. In some cases, the laminated structure may be enclosed in a package. The protective layer can be formed of an organic material such as polyimide resin or epoxy resin, an inorganic insulating material such as titanium oxide, aluminum nitride, or aluminum oxide, or a metal film such as Au, Al, or W.

(A), (b) is a typical front sectional view of the boundary acoustic wave device concerning one embodiment of the present invention, and a typical top view showing electrode structure. (A)-(d) is each typical front sectional drawing for demonstrating the manufacturing method of the elastic boundary wave apparatus of embodiment shown in FIG. (A), (b) is each typical front sectional drawing for demonstrating each process for manufacturing the boundary acoustic wave apparatus of embodiment shown in FIG. The figure which shows the attenuation frequency characteristic of the conventional boundary acoustic wave apparatus prepared for the comparison. Shows the attenuation-frequency characteristic when │κ ₁₂ │ / k ₀ = 0.10 or 0.15 in the boundary acoustic wave device of the embodiment. The IDT in the surface acoustic wave device using the leaky surface acoustic wave as a reference example when | κ ₁₂ | / k ₀ of the IDT electrode in the boundary acoustic wave device is changed to 0.05, 0.10, or 0.15 Figure │κ ₁₂ │ / k ₀ of the electrode exhibits a conductance characteristic of the IDT electrode in the case of 0.03. In the boundary acoustic wave device, the electromechanical coupling coefficient K ² is 4%, 9%, 13%, and in the surface acoustic wave device using the leaky surface acoustic wave as a reference example, the electromechanical coupling coefficient is 9.3. The figure which shows the conductance characteristic of the IDT electrode in the case of%. The typical front sectional view for explaining the modification of the boundary acoustic wave device of the present invention. The typical front sectional view showing an example of the conventional boundary acoustic wave device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Elastic boundary wave apparatus 2 ... Piezoelectric body 2a ... Upper surface 2b ... Groove 3 ... Dielectric material 4 ... IDT electrode 5, 6 ... Reflector 7 ... Resist pattern

Claims (5)

A piezoelectric body;
A plurality of grooves formed on the upper surface of the piezoelectric body;
An IDT electrode formed by filling the plurality of grooves with metal;
A dielectric formed to cover the IDT electrode and the upper surface of the piezoelectric body;
Using SH type boundary acoustic waves propagating along the boundary between the dielectric and the piezoelectric body;
Assuming that the wavelength of the boundary acoustic wave is λ and the thickness of the IDT electrode normalized by λ is H, and the density of the IDT electrode is ρ (kg / m ³ ), H> 826.744ρ− ^1.376 and ρ> The boundary acoustic wave device according to claim ³ , wherein the thickness is 3745 kg / m ³ and the thickness H of the IDT electrode is different from the depth of the groove.   The boundary acoustic wave device according to claim 1, wherein a thickness H of the IDT electrode is larger than a depth of the groove.   The boundary acoustic wave device according to claim 1, wherein a thickness H of the IDT electrode is smaller than a depth of the groove.   The boundary acoustic wave device according to claim 1, wherein the dielectric is formed by a deposition method. Forming a resist film having a plurality of openings on the upper surface of the piezoelectric body;
Forming a plurality of grooves according to the plurality of openings on the upper surface of the piezoelectric body by etching using the resist film as a mask;
Forming a metal film having a thickness different from the depth of the groove on the piezoelectric body and the resist film;
Removing an unnecessary metal film on the resist film while removing the resist film, and forming an IDT electrode having a plurality of electrode fingers from the metal film filled in the groove;
And a step of forming a dielectric film by a deposition method so as to cover the IDT electrode and the piezoelectric body.

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