JPH1197973A - Surface wave device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a surface wave device having satisfactory characteristics using a leaking surface acoustic wave, by using a piezoelectric substrate constituted of dielectric thin films layered on a specific piezoelectric single crystal substrate. SOLUTION: An edge face reflection type surface wave resonator 1 is constituted by using a piezoelectric substrate 2 in which an electromechanical connection coefficient is large. In the piezoelectric substrate 2, a ZnO thin film 2b being a dielectric thin film constituted of materials whose surface wave propagating speed is slower than that of a substrate 2a is layered on a 41 deg.±3 rotation Y board Z propagation LiNbO3 substrate 2a. A pair of comb-shaped electrodes 3a and 3b are formed on the lower surface of the piezoelectric thin film 2b, that is, the upper surface of the substrate 2a. The comb-shaped electrodes 3a and 3b are not weighed, and formed so that a normal type interdigital transducer (IDT) can be constituted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface acoustic wave device using a leaky surface acoustic wave, and more particularly, to a surface acoustic wave device using a piezoelectric substrate obtained by laminating a dielectric thin film on a specific piezoelectric single crystal substrate. The present invention relates to a surface acoustic wave device capable of forming a piezoelectric resonance component having good characteristics using a leaky surface acoustic wave.

[0002]

2. Description of the Related Art As a surface acoustic wave device using a piezoelectric substrate, various devices such as a surface acoustic wave resonator, a surface acoustic wave filter, and an elastic convolver have been put to practical use. In order to obtain good characteristics in the surface acoustic wave device, it is required that the substrate used has a large electromechanical coupling coefficient Ks.

[0003] Japanese Patent Application Laid-Open No. 8-139565 discloses 41
° On the rotating Y plate X-propagating LiNbO ₃ substrate, the LiNbO ₃
There is disclosed a surface acoustic wave device using a piezoelectric substrate formed by forming a piezoelectric thin film made of a material having a lower surface wave propagation speed than _three substrates, and utilizing a Love wave. Here, by forming a piezoelectric thin film on the specific LiNbO ₃ substrate, the electromechanical coupling coefficient Ks in the case of utilizing Love waves
It is possible to increase.

However, the L of the 41 ° rotation Y plate X propagation
When a piezoelectric thin film such as a ZnO thin film is formed on an iNbO ₃ substrate, an epitaxial film cannot be formed, and when the thickness of the piezoelectric thin film is increased, there is a problem that attenuation accompanying surface wave propagation increases. In particular, when the thickness of the piezoelectric thin film is H and the wavelength of the Love wave is λ, H / λ = 0.045
In a preferred range of about 0.09, an interdigital transducer (hereinafter abbreviated as IDT) is used.
When the Love wave was excited using, the attenuation was large.

Further, since the thickness of the piezoelectric thin film is relatively large, the attenuation of the surface wave due to the formation of the piezoelectric thin film is also large. Conventionally, when a piezoelectric thin film of ZnO or the like is formed on a piezoelectric single crystal substrate and a leaky surface acoustic wave is excited, the attenuation is considered to be further increased.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a surface acoustic wave device using a leaky surface acoustic wave, which uses a piezoelectric substrate having a sufficient electromechanical coupling coefficient Ks to reduce the leaky surface acoustic wave. It is an object of the present invention to provide a surface acoustic wave device that is suppressed and can achieve good characteristics.

[0007]

The present invention SUMMARY OF] is the surface wave propagation velocity than the 41 ° ± 3 rotation Y plate X propagation LiNbO ₃ substrate, the LiNbO ₃ is formed on the substrate, and the LiNbO ₃ substrate A piezoelectric substrate having a dielectric thin film made of a slow material, and an IDT provided on the piezoelectric substrate, wherein the surface acoustic wave device is configured to use a leaky surface acoustic wave. is there.

That is, the present inventor studied a surface acoustic wave device that excites a leaky surface acoustic wave using various piezoelectric substrate materials in order to achieve the above-mentioned object.
The use of a piezoelectric substrate obtained by laminating a dielectric film on a 3 ° rotation Y-plate X-propagating LiNbO ₃ substrate makes it possible to suppress the attenuation accompanying the propagation of leaky surface acoustic waves and to provide a sufficient electromechanical coupling coefficient. It has been found that Ks can be obtained, and thus a surface acoustic wave device having good characteristics can be constructed, and based on the findings, the present invention has been accomplished.

The above-mentioned 41 ° ± 3 used in the present invention.
The rotating Y-plate X-propagating LiNbO ₃ substrate includes not only a 41 ° rotating Y-plate X-propagating LiNbO ₃ substrate but also a rotating Y-plate X-propagating LiNb having a rotation angle of 38 to 44 ° as described above.
A bO ₃ substrate can be used.

Further, the above-mentioned LiNbO_ThreeFormed on the substrate
For the dielectric film, LiNbO _ThreeSurface compared to substrate
The material is not particularly limited as long as the material has a low wave propagation speed.
It may be a dielectric thin film having electrical conductivity, or a piezoelectric thin film.
A dielectric thin film having no property may be used.

As a dielectric thin film having piezoelectricity, that is, a piezoelectric thin film, one made of ZnO, CdS or Ta ₂ O ₅ can be exemplified. Examples of the dielectric thin film having no piezoelectricity include SiO ₂ , PbS, and Nb ₂ O ₅ .

Preferably, when the piezoelectric thin film is a ZnO thin film, the thickness of the ZnO thin film is defined as H, and the wavelength of the leaky surface acoustic wave to be excited is λ. The film thickness, that is, H / λ is larger than 0,
It is set to be 0.045 or less.

When the piezoelectric thin film is a CdS thin film, when the thickness is H and the wavelength of the leaky surface acoustic wave to be excited is λ, H / λ is larger than 0 and 0.035 or less. It is said.

Further, when the piezoelectric thin film is a Ta ₂ O ₅ thin film, and its thickness is H and the wavelength of the leaky surface acoustic wave to be excited is λ, preferably, H / λ is larger than 0 and 0 0.035 or less.

The specific structure of the surface acoustic wave device according to the present invention is not particularly limited, and may be an end surface reflection type surface acoustic wave device utilizing reflection of two opposing end surfaces.
Alternatively, it may be a surface acoustic wave resonator or a surface acoustic wave filter provided with a reflector formed on both sides of the IDT in the direction of propagation of the surface acoustic wave.

The IDT provided on the piezoelectric substrate may be formed on the piezoelectric substrate,
It may be formed between the iNbO ₃ substrate and the dielectric thin film,
Further, the number and shape of the IDTs are not particularly limited.

The present invention can be generally applied to a surface acoustic wave device using a leaky surface acoustic wave, and can be applied to various surface acoustic wave devices such as a surface acoustic wave resonator, a surface acoustic wave filter, and an elastic convolver. it can.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be clarified below by giving non-limiting embodiments of the present invention with reference to the drawings.

A 41 ° rotated Y plate X-propagating LiNbO ₃ substrate (hereinafter simply referred to as a 41 ° YX LiNbO ₃ substrate)
Are known as surface acoustic wave substrates that generate leaky surface acoustic waves (leaky waves) with attenuation. However, conventionally, leaky surface acoustic waves have large attenuation due to propagation,
It was considered unusable.

When various dielectric thin films were formed on the above 41 ° YX LiNbO ₃ substrate, not only a leaky surface acoustic wave was excited but also a sufficient electromechanical coupling coefficient K
s was obtained.

Hereinafter, a case where a ZnO thin film is formed on the 41 ° YX LiNbO ₃ substrate will be described as an example.
For both the 41 ° YX LiNbO ₃ substrate and the ZnO thin film, the following piezoelectric basic equation, equation of motion and Maxw
The equation of ell holds.

[0022]

(Equation 1)

In order to excite a leaky surface acoustic wave, these equations are expressed as follows:
At the boundary with the LiNbO ₃ substrate, a sound velocity that satisfies each boundary condition may be obtained.

On the other hand, when an IDT is formed on a piezoelectric substrate, based on the following equation, the sound velocity V _f when electrically short-circuited at the boundary where the interdigital electrode exists,
The electromechanical coupling coefficient K is obtained from the sound speed _Vf when the motor is opened.

[0025]

(Equation 2)

FIG. 1 shows the above-mentioned 41 ° YX LiNbO _3.
The measurement results of the sound velocities V _f and V _m of the surface wave when using a piezoelectric substrate having ZnO thin films of various thicknesses formed on the + surface of the substrate are shown. In FIG. 1, ○ and ● represent
The sound velocity of a surface wave (leakage surface acoustic wave or Love wave) when a ZnO thin film is formed on the + face of the LiNbO ₃ substrate is shown, ○ is the sound velocity V _f when the boundary is free, and ● is the metallized boundary. is the speed of sound V _m of the case was. Note that △
And ▲ show the sound speed of a Rayleigh wave when a ZnO thin film is formed on the + face of the LiNbO ₃ substrate, △ shows the sound speed V _f when the boundary is free, and ▲ shows the sound speed when the boundary is metallized. a V _m.

FIG. 3 is a diagram showing sound speeds of leaky surface acoustic waves, Love waves and Rayleigh waves when a ZnO thin film is formed on the negative surface of a LiNbO ₃ substrate. , Respectively, have the same meaning as in FIG.

As is apparent from FIGS. 1 and 3, the above L
LiNbO ₃ substrate of + side and - to any side of the plane even when forming a ZnO thin film, by the difference between V _f and V _m are present, it can be seen that the leaky surface wave or Love waves are excited .

As is clear from FIGS. 1 and 3,
For Rayleigh waves, the sound velocity V _f when the boundary is free
When almost no difference between the acoustic velocity V _m when being metallized, therefore, the Rayleigh wave is seen that almost not excited. Moreover, components of the Rayleigh wave has no existence between the acoustic velocity V _f and the sound velocity V _m of the leaky surface acoustic wave, in the structure to form a ZnO thin film on the 41 ° Y-X LiNbO ₃ substrate, the Rayleigh wave It is understood that it is hardly affected by the components of

FIG. 2 shows the above-mentioned 41 ° YX LiNbO _3.
FIG. 4 shows the electromechanical coupling coefficient K when the ZnO thin film is formed in various thicknesses on the + surface of the substrate, and FIG. 4 shows the electric power when the ZnO thin film is formed in various thicknesses on the negative surface of the same substrate. FIG. 4 is a diagram illustrating a mechanical coupling coefficient K.

As is apparent from a comparison of FIGS. 2 and 4, the electromechanical coupling coefficient K is almost the same regardless of whether the ZnO thin film is formed on the + face or the − face of the LiNbO ₃ substrate. , + Surface, the electromechanical coupling coefficient K is slightly increased.

As can be seen from FIG. 2, the maximum value of the electromechanical coupling coefficient K is about 0,0 at a film thickness H / λ = 0.045 normalized by the wavelength λ of the leaky surface acoustic wave of the ZnO piezoelectric thin film. 4
6, which is very large. In addition, when H / λ is 0.1.
At 045 or less, it can be seen that the leaky surface acoustic wave is favorably excited. In other words, it can be seen that even when the thickness of the ZnO thin film is extremely thin, the leaky surface acoustic wave can be effectively excited.

In addition, when H / λ is in the range of 0.45 or less, the electromechanical coupling coefficient K increases as the thickness of the ZnO thin film increases. Therefore, since the electromechanical coupling coefficient K is relatively large, the above 41 ° Y-XL is used.
It is understood that a surface wave device having a wide band can be provided by using the iNbO ₃ substrate.

Further, since the thickness of the ZnO thin film can be reduced, it is possible to suppress the attenuation of the leaky surface acoustic wave which is easily attenuated with the propagation, thereby providing a surface acoustic wave device having excellent characteristics. I understand.

It is widely known that the frequency temperature coefficient TCF of the 41 ° YX LiNbO ₃ substrate is positive, and that the ZnO thin film has a negative frequency temperature coefficient. Therefore, the above 41 ° YX LiNbO ₃ substrate and Z
It can also be seen that when combined with the nO thin film, frequency temperature characteristics can be improved.

Next, based on the above results, a 41 ° rotation Y
An experimental example in which an end face reflection type surface acoustic wave resonator is manufactured using a piezoelectric substrate having a ZnO thin film formed on a cut X-propagation LiNbO ₃ substrate will be described.

FIG. 5 is a schematic perspective view showing an end reflection type surface acoustic wave resonator. The end surface reflection type surface acoustic wave resonator 1 is configured using a piezoelectric substrate 2. The piezoelectric substrate 2 is 41 ° Y
-Has a structure in which a ZnO thin film 2b is laminated on an XLiNbO ₃ substrate 2a. The lower surface of the piezoelectric thin film 2b, that is, Li
As shown, a pair of comb electrodes 3a and 3b were formed on the upper surface of the NbO ₃ substrate 2a. Note that the plurality of electrode fingers of the comb electrode 3a and the plurality of electrode fingers of the comb electrode 3b are arranged so as to be inserted into each other. The outermost electrode finger of the comb electrodes 3a and 3b is LiNbO.
_{The three} substrates 2 are formed along the edge formed by the two opposing end surfaces 2c and 2d and the upper surface.

In fabricating the edge reflection type surface acoustic wave resonator 1, a LiNbO ₃ substrate 2a is 2.18 × 2.8.
× The thickness is 0.5 mm, and the comb electrodes 3a and 3b are formed using aluminum so that the surface wave propagates in the X direction. The comb electrodes 3a and 3b were formed without weighting so as to form a regular IDT. The thickness of aluminum is 6000 °, and λ is 85.
5 μm, the metallization ratio in the IDT was 0.5, the electrode finger cross width was 25λ, and the number of electrode fingers was 25.

The thickness H of the ZnO piezoelectric thin film 2b is H
/Λ=0.027. FIG. 6 shows the impedance-frequency characteristics of the end surface reflection type surface acoustic wave resonator 1 manufactured as described above.

For comparison, the edge reflection type surface acoustic wave resonance of the above embodiment was performed except that the ZnO piezoelectric thin film was not formed and that a plurality of grooves were formed by dicing on the back surface of the LiNbO ₃ substrate. Comparative Example 1
Was manufactured. FIG. 7 shows the impedance-frequency of the end surface reflection type surface acoustic wave resonator of Comparative Example 1.

When the resonance frequency is fr and the antiresonance frequency is fa, the (fa-fr) / fr is 8.1% in the resonance characteristic of the end face reflection type surface acoustic wave resonator of Comparative Example 1 shown in FIG. On the other hand, in the end face reflection type surface acoustic wave resonator of the embodiment shown in FIG. 6, (fa−fr) / fr is increased to 9.6%. That is, it can be seen that the band is widened.

6 and 7, a slight deterioration of Q at the resonance point and the anti-resonance point is observed in the end face reflection type surface acoustic wave resonator of the embodiment, but this is not a problem in practical use. It is about.

Accordingly, from a comparison of FIGS. 6 and 7, according to the present invention, the ZnO piezoelectric thin film was formed by the above-mentioned 41 ° YX LiN
It can be seen that the lamination on the bO ₃ substrate can provide a wider band surface acoustic wave device.

An edge reflection type surface acoustic wave resonator constructed in the same manner as in the example except that the back surface of the LiNbO ₃ substrate was not diced and the ZnO piezoelectric thin film was not laminated was compared. The surface acoustic wave resonator of Example 2 was manufactured, and its resonance characteristics were measured. FIG. 8 shows the results.

The solid line A in FIG. 8 indicates the resonance characteristic of the end-face reflection type surface acoustic wave resonator of Comparative Example 2, and the broken line indicates the resonance characteristic of the end-face reflection type surface acoustic wave resonator of Comparative Example 1 described above. As is clear from FIG. 8, when the ZnO piezoelectric thin film was not laminated, the dicing process was not performed on the back surface of the LiNbO ₃ substrate. As can be seen from FIG. This is the bulk wave LiNbO ₃
This is considered to be spurious due to reflection at the bottom surface of the substrate.

The bulk wave is different from the leaky surface acoustic wave,
Since the light propagates over almost the entire thickness of the LiNbO ₃ substrate and the reflection at the bottom surface of the bulk wave cannot be ignored, it is considered that the above-mentioned spurious appears. Therefore, when the ZnO thin film was not laminated, the spurious due to the reflection of the bulk wave could not be suppressed unless the bottom surface of the LiNbO ₃ substrate was roughened as described above.

On the other hand, as is apparent from FIG.
In the edge reflection type surface acoustic wave resonator of this embodiment, LiNbO ₃
It can be seen that the spurious due to the reflection of the bulk wave is suppressed by laminating the above-mentioned ZnO piezoelectric thin film without processing the bottom surface of the substrate into a rough surface. That is, Li
By forming a ZnO thin film on an NbO ₃ substrate, spurious due to reflection of bulk waves can be suppressed, and good resonance characteristics can be obtained. This is considered for the following reason.

In general, a bulk wave is generated by being directly electrically excited in an IDT, or a mode conversion from a surface wave to a bulk wave upon reflection of the surface wave when the surface wave reaches a grating reflector. Is caused by the occurrence of Since the IDT is structurally regarded as being similar to the grating reflector, it is considered that the mode conversion of the surface wave into the bulk wave also occurs in the IDT. In this case, the acoustic impedance of the electrode finger portion of the IDT and
The greater the difference between the acoustic impedance in the gap between the electrode fingers (electric field short-circuit effect and mass load effect), the higher the conversion efficiency to bulk waves.

However, in this embodiment, the ZnO thin film is L
Since it is laminated on the iNbO ₃ substrate, the acoustic impedance difference between the electrode finger portion and the gap between the electrode fingers is reduced, the conversion efficiency of the surface wave into the bulk wave is reduced, and unnecessary spurious due to the bulk wave is reduced. Is considered to be suppressed.

In addition, the ZnO thin film also functions as a passivation film for the IDT,
Corrosion of the electrode fingers and short-circuiting due to metal powder hardly occur. A ladder-type filter was manufactured using seven end-face reflection type surface acoustic wave resonators 1 manufactured as the above examples. FIG. 9 shows the filter characteristics of the ladder-type filter thus obtained.

As is clear from FIG. 9, the ladder-type filter has an insertion loss of 1.9 dB, an out-of-band attenuation of about 30 dB, and a 3 dB pass band of 45.2 to 50.0 MH.
It can be seen that there is no practical problem with z. In other words, it can be seen that a ladder-type filter that can be put to practical use can be configured by using the above-mentioned end-face reflection type surface acoustic wave resonator using a leaky surface acoustic wave.

It should be noted that the present invention relates to the above-mentioned 41 ° YX Li
It is characterized by using a piezoelectric substrate formed on a NbO ₃ substrate and forming a dielectric thin film having a lower sound velocity of leaky surface acoustic wave than the LiNbO ₃ substrate. In addition to the ZnO piezoelectric thin film shown in the embodiment, another piezoelectric thin film such as a CdS thin film or a Ta ₂ O ₅ thin film may be used, or SiO ₂ , PbS, Nb ₂ O ₅
For example, a dielectric thin film having no piezoelectricity may be used.

FIG. 10 shows the relationship between the normalized film thickness H / λ and the sound velocity when the CdS piezoelectric thin film was formed on the positive surface of the LiNbO ₃ substrate, and FIG.
FIG. 11 shows the relationship with s. Similarly, when a Ta ₂ O ₅ thin film is formed on a 41 ° YX LiNbO ₃ substrate,
The relationship between the normalized film thickness H / λ of the Ta ₂ O ₅ thin film and the sound velocity, and the relationship between the normalized film thickness H / λ and the electromechanical coupling coefficient Ks are shown in FIGS. 12 and 13, respectively.

As is apparent from FIGS. 10 to 13, Cd
When the S thin film and the Ta ₂ O ₅ thin film are used, H / λ is set to 0.1.
It can be seen that if the ratio is 035 or less, the leaky surface acoustic wave can be efficiently excited, and a large electromechanical coupling coefficient can be obtained. Therefore, it can be seen that a surface acoustic wave device having a wide band and excellent resonance characteristics can be provided as in the above-described embodiment in which the ZnO thin film is formed.

The PbS or Nb ₂ O ₅ piezoelectric thin film is
Normalized film thickness H when formed on + surface of iNbO ₃ substrate
FIG. 14 shows the relationship between / λ and the speed of sound, and FIG. 15 shows the relationship between the normalized film thickness H / λ and the electromechanical coupling coefficient Ks.

As is clear from FIGS. 14 and 15, PbS
Also, it can be seen that even when an Nb ₂ O ₅ thin film is used, a leaky surface acoustic wave can be efficiently excited and a large electromechanical coupling coefficient can be obtained. Therefore, it can be seen that a surface acoustic wave device having a wide band and excellent resonance characteristics can be provided as in the above-described embodiment in which the ZnO thin film is formed.

The present invention relates to a surface acoustic wave device using the above-described piezoelectric substrate and utilizing a leaky surface acoustic wave.
The number and shape of the DT are not particularly limited, and a conventionally known structure can be appropriately adopted.

That is, the grating reflectors 1 are provided on both sides of the IDT 12 like the surface wave resonator 11 shown in FIG.
It may be a surface acoustic wave resonator with a reflector in which 3, 14 are arranged. In FIG. 16, reference numeral 16 denotes a piezoelectric substrate;
6a indicates a 41 ° YX LiNbO ₃ substrate, and 15b indicates a dielectric thin film.

[0059]

According to the surface acoustic wave device of the present invention, 41 ° ±
On a 3 ° rotation Y plate X-propagating LiNbO ₃ substrate, the LiNb
Since a piezoelectric substrate on which a dielectric thin film made of a material whose surface wave has a lower sound velocity than that of the O ₃ substrate is used, a leaky surface acoustic wave can be efficiently excited and the electromechanical coupling coefficient is sufficient. Size. Therefore, it is possible to provide a wide-band surface acoustic wave device using a leaky surface acoustic wave.

Further, a 41 ° rotation Y-plate X-propagation LiNbO ₃
Since the substrate is known to have a small temperature coefficient Tc of 60 to 65 ppm, the frequency-temperature characteristics of the surface acoustic wave device are also good.

In particular, as described in claim 3, a piezoelectric thin film
As ZnO, CdS or Ta _TwoO_FivePiezo like
When a thin film is used, the frequency temperature characteristics of the piezoelectric thin film
The coefficient TCF is negative, and the above-mentioned YX LiNbO_ThreeBase
Since the coefficient TCF of the frequency temperature characteristic of the plate is positive,
A surface wave device having better temperature characteristics can be provided.
You.

When a ZnO thin film is used,
By setting the normalized film thickness H / λ to 0.045 or less.
Not only can stably excite the leaky surface acoustic wave, but also
Since the thickness of the nO thin film may be small, the propagation of leaky surface acoustic waves is
Attenuation due to transport can be suppressed, resulting in better resonance characteristics.
Sex can be obtained. Similarly, a CdS thin film or Ta_TwoO
_FiveWhen a thin film is used, the normalized film thickness H / λ is set to 0.1.
035 or less to improve the leakage surface acoustic wave
Can excite and suppress attenuation accompanying propagation
Therefore, it is possible to provide a surface acoustic wave device having good resonance characteristics.
You.

Further, when the surface acoustic wave device according to the present invention is an edge-reflection type surface acoustic wave device, it has no reflector, and is therefore small in size and leaky. Since the surface acoustic wave does not propagate outside the IDT, it is possible to provide a surface acoustic wave device having better resonance characteristics using the leaky surface acoustic wave.

[Brief description of the drawings]

FIG. 1 shows ZnO on a piezoelectric substrate having a ZnO thin film formed on a + surface of a 41 ° rotation Y-plate X-propagation LiNbO ₃ substrate.
The figure which shows the relationship between the relative film thickness H / (lambda) of a thin film, and the sound speed of various surface waves excited.

FIG. 2 shows a relationship between a relative thickness H / λ of a ZnO thin film of a piezoelectric substrate formed by forming a ZnO thin film on a + surface of a 41 ° rotation Y-plate X-propagation LiNbO ₃ substrate and an electromechanical coupling coefficient. FIG.

FIG. 3 shows a relative thickness H / λ of a ZnO thin film and a sound velocity of a surface wave when a piezoelectric substrate having a ZnO thin film formed on a negative surface of a 41 ° rotation Y plate X-propagation LiNbO ₃ substrate is used. FIG.

FIG. 4 is a view showing a relationship between a relative thickness H / λ of a ZnO thin film and an electromechanical coupling coefficient when a ZnO thin film is formed on a − surface of a 41 ° rotation Y-plate X-propagation LiNbO ₃ substrate.

FIG. 5 is a perspective view showing an edge reflection type surface acoustic wave resonator according to one embodiment of the present invention.

FIG. 6 is a diagram showing resonance characteristics of the end-face reflection type surface acoustic wave resonator shown in FIG. 5;

FIG. 7 is a diagram illustrating a resonance characteristic of an edge-reflection surface acoustic wave resonator in which a ZnO thin film is not stacked, prepared for comparison.

FIG. 8 is a diagram showing resonance characteristics of an edge-reflection type surface acoustic wave resonator in which a ZnO thin film is not formed and in which a bottom surface is grooved and where a groove is not formed, prepared for comparison.

FIG. 9 is a diagram illustrating filter characteristics of a ladder-type filter configured by using a plurality of end-face reflection type surface acoustic wave resonators illustrated in FIG. 5;

FIG. 10: + of a 41 ° rotation Y-plate X-propagation LiNbO ₃ substrate
Cd on a piezoelectric substrate having a CdS thin film formed on its surface
The figure which shows the relationship between the relative film thickness H / (lambda) of S thin film, and the sound speed of various surface waves excited.

FIG. 11 shows a graph of + of a 41 ° rotation Y plate X propagation LiNbO ₃ substrate.
The figure which shows the relationship between the relative film thickness H / (lambda) of the CdS thin film of the piezoelectric substrate which forms a CdS thin film on a surface, and an electromechanical coupling coefficient.

FIG. 12 shows a diagram of + of a 41 ° rotation Y-plate X-propagation LiNbO ₃ substrate.
Shows the relative thickness H / lambda of the Ta ₂ O ₅ thin film of the piezoelectric substrate obtained by forming a Ta ₂ O ₅ thin film on the surface, the relationship between the acoustic velocity of Excited various surface waves.

FIG. 13: + of a 41 ° rotation Y-plate X-propagation LiNbO ₃ substrate
Of the piezoelectric substrate obtained by forming a Ta ₂ O ₅ thin film on a surface Ta ₂
O ₅ relative thickness H / lambda of the thin film, shows a relationship between the electromechanical coupling coefficient.

FIG. 14: + of a 41 ° rotation Y-plate X-propagation LiNbO ₃ substrate
Shows the relative thickness H / lambda of PbS or Nb ₂ O ₅ thin film of the piezoelectric substrate obtained by forming a PbS or Nb ₂ O ₅ thin film on the surface, the relationship between the acoustic velocity of Excited various surface waves.

FIG. 15 shows a graph of + of a 41 ° rotation Y plate X propagation LiNbO ₃ substrate.
Surface on the PbS or Nb ₂ O ₅ of the piezoelectric substrate on which a thin film is formed comprising PbS or Nb ₂ O ₅ thin film relative thickness H / lambda
FIG. 4 is a diagram showing a relationship between the coefficient and an electromechanical coupling coefficient.

FIG. 16 is a perspective view showing a surface acoustic wave resonator with a reflector as an example of a surface acoustic wave device to which the present invention is applied.

[Explanation of symbols]

1 ... edge reflection type surface acoustic wave resonator 2 ... piezoelectric substrate 2a ... 41 ° Y cut X propagation LiNbO ₃ substrate 2b ... ZnO thin films 3a as a surface acoustic wave device, 3b ... comb electrodes 11 ... surface wave resonator 12 ... IDT 13 , 14 ... reflectors 15 ... piezoelectric substrate 15a ... 41 ° rotation Y plate X propagation LiNbO ₃ substrate 15b ... dielectric thin film

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Mamoru Ikeura 2-26-10 Tenjin, Nagaokakyo-shi, Kyoto Inside Murata Manufacturing Co., Ltd.

Claims (7)

[Claims] 1. A 41 ° ± 3 rotation Y-plate X-propagation LiNbO ₃
Substrate and the LiNbO ₃ is formed on the substrate, and a piezoelectric substrate having a dielectric thin film surface-wave propagation velocity than that of the LiNbO ₃ substrate is slower material, interdigital provided on the piezoelectric substrate A surface acoustic wave device comprising: a transducer; and configured to use a leaky surface acoustic wave. 2. The surface acoustic wave device according to claim 1, wherein said dielectric thin film is a piezoelectric thin film. 3. The surface acoustic wave device according to claim 1, wherein the piezoelectric thin film is made of ZnO, CdS, or Ta ₂ O ₅ . 4. The piezoelectric thin film is a ZnO thin film, wherein H / λ is 0.045 or less, where H is the thickness, and λ is the wavelength of the leaky surface acoustic wave to be excited. 4. The surface acoustic wave device according to 3. 5. The piezoelectric thin film is a CdS thin film, wherein H / λ is 0.035 or less, where H is the thickness, and λ is the wavelength of the leaky surface acoustic wave to be excited. 4. The surface acoustic wave device according to 3. 6. The piezoelectric thin film is a Ta ₂ O ₅ thin film,
4. The surface acoustic wave device according to claim 3, wherein H / λ is 0.035 or less, where H is the film thickness, and λ is the wavelength of the leaky surface acoustic wave to be excited. 7. The surface acoustic wave device according to claim 1, wherein the surface acoustic wave device is an edge reflection type surface acoustic wave device.