JP2003198323A - Surface acoustic wave device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface acoustic wave device using a leakage surface acoustic wave that the frequency temperature characteristic is satisfactory, the electromechanical coupling coefficient K<SP>2</SP>is large, and the damping constant αis small. <P>SOLUTION: In a surface acoustic wave device 11, at least one of the IDTs 13a, 13b composed of AI that a film thickness H/λ standardized by the wavelength of the surface wave is within the range from 0.04 to 0.12 is formed on an LiTaO<SB>3</SB>substrate 12 of 20° to 40° rotation Y board, i.e., Euler's angles (0°±3°, 110° to 132°, 0°±3°). SiO<SB>2</SB>film 15 is formed on the LiTaO<SB>3</SB>substrate so as to cover the IDTs 13a, 13b. The film thickness H/λ standardized by the wavelength of the surface wave of the SiO<SB>2</SB>film 15 is within the range from 0.15 to 0.40. <P>COPYRIGHT: (C)2003,JPO

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 used for a resonator, a bandpass filter and the like, and more specifically, a surface acoustic wave device using a rotating Y plate X propagating LiTaO ₃ substrate and a method for manufacturing the same. Regarding

[0002]

2. Description of the Related Art In mobile communication devices such as mobile phones,
Surface acoustic wave filters are used as bandpass filters and duplexers in the RF stage. As this kind of surface acoustic wave filter, LiTa of 30 ° to 50 ° rotating Y plate X propagation is used.
An IDT (interdigital transducer) made of Al is formed on an O ₃ substrate, and a surface acoustic wave filter utilizing leaky acoustic waves has been put into practical use.

However, in this surface acoustic wave filter, the frequency temperature characteristic is as bad as -30 to -40 ppm / ° C., and improvement thereof has been demanded. Therefore, in order to improve the frequency-temperature characteristic, a rotation of 30 ° to 50 ° Y plate X propagation L
A structure has been proposed in which an IDT made of Al is formed on an iTaO ₃ substrate and then a SiO ₂ film is further laminated. The frequency-temperature characteristic is improved by forming the SiO ₂ film.

The leaky surface acoustic wave has a higher sound velocity than the Rayleigh wave and has a large electromechanical coupling coefficient K ² . However, the leaky surface acoustic wave propagates while radiating energy inside the substrate, and thus has a damping constant that causes a propagation loss.

Therefore, it is required not only that the frequency-temperature characteristic is good, but that the electromechanical coupling coefficient K ² is large and the damping constant α is small. JP-A-9-167903
No. 6 publication discloses that LiTa having a cut angle of 39.5 ° to 46 °.
ID consisting of Al, Cu or Au on O ₃ substrate
It has been shown that when T is formed, the damping constant α can be suppressed.

[0006]

As described above, 30 °
˜50 ° rotation Y plate X propagation on LiTaO ₃ substrate, Al
It is said that the frequency temperature characteristic is improved when an IDT made of is formed and a SiO ₂ film is further laminated.

Therefore, even in the surface acoustic wave device disclosed in Japanese Unexamined Patent Publication No. 9-1679036, if the SiO ₂ film is laminated so as to cover the IDT, the frequency temperature characteristic can be improved and the damping constant α can be suppressed. Conceivable.

However, as described in JP-A-8-167936, 39.5 ° to 46 ° LiTaO ₃
When the IDT made of Al was formed on the substrate, the attenuation constant α was small, but when an SiO ₂ film was further stacked on the IDT, the attenuation constant α was not small but was large.

In view of the above situation, an object of the present invention is a surface acoustic wave device using a rotating Y-plate X-propagating LiTaO ₃ substrate, which can improve frequency-temperature characteristics by forming a SiO ₂ film. , The damping constant α is smaller, and ID
The electromechanical coupling coefficient at T is sufficiently large,
An object is to provide a surface acoustic wave device and a method for manufacturing the same.

[0010]

According to a broad aspect of the present invention, an Euler angle (0 ± 3 °, 110 ° to 132 °, 0 ±).
3 °) LiTaO ₃ substrate and at least one I formed of Al and formed on the LiTaO ₃ substrate.
DT and a SiO ₂ film formed on the LiTaO ₃ substrate so as to cover the IDT and having a film thickness H / λ normalized by the wavelength of the surface wave in the range of 0.15 to 040. A surface acoustic wave device is provided.

In the present invention, preferably the above Al
Film thickness H / standardized by the wavelength of surface wave of IDT
λ is in the range of 0.04 to 0.12, whereby the electromechanical coupling coefficient is effectively increased.

[0012] Preferably, the Euler angle of the LiTaO ₃ substrate and the normalized film thickness of the SiO ₂ film are any one of the combinations represented by (a) to (f) shown in Table 2 below.

[0013]

[Table 2]

In another specific aspect of the present invention, a leaky surface acoustic wave whose main component is SH wave is used as the surface acoustic wave.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be clarified by describing specific embodiments of the present invention with reference to the drawings.

FIG. 1 is a plan view for explaining a longitudinally coupled resonator filter as a surface acoustic wave device according to an embodiment of the present invention. In the surface acoustic wave device 11, LiTaO _{3 is used.}
On the upper surface of the substrate 12, the IDTs 13a and 13b and the reflector 1
4a and 14b are formed. IDT 13a, 13b
And the SiO ₂ film 1 so as to cover the reflectors 14a and 14b.
5 is formed.

As the LiTaO ₃ substrate 12, 2
0 ° to 42 ° rotated Y plate, that is, Euler angle is (0 °,
A 110 ° to 132 °, 0 °) LiTaO ₃ substrate is used. Rotating Y plate X propagation LiT with a cut angle outside this range
In the aO ₃ substrate, the damping constant α becomes large. Preferably, a 23 ° to 39 ° rotated Y plate, that is, a LiTaO ₃ substrate having an Euler angle of (0 °, 113 ° to 129 °, 0 °) is used.

The IDTs 13a and 13b and the reflector 14a,
14b is composed of Al. IDT 13a, 13
The film thickness H / λ normalized by the wavelength of the surface wave of b is 0.0
The range is from 4 to 0.12. As will be apparent from an experimental example described later, the electromechanical coupling coefficient K ² of the leaky surface acoustic wave is increased by setting the film thickness in this range.

Further, the SiO ₂ film 15 has a wavelength λ of the surface wave.
The film thickness normalized by is set in the range of 0.15 to 0.40. With such a film thickness range, the frequency-temperature characteristic is improved.

In the surface acoustic wave device of this embodiment, as described above, since the thickness of the SiO ₂ film is within the above specified range, the frequency temperature characteristic is improved and the I
Since the film thickness of DT is within the above specific range, the electromechanical coupling coefficient K ² is sufficiently large. Furthermore, Si
Even if the O ₂ film is laminated, since the LiTaO ₃ substrate having the above-mentioned specific cut angle is used, the attenuation constant α can be greatly reduced and the loss can be reduced. This will be described based on a concrete experimental example.

FIG. 2 shows the relationship between the Euler angles (0 °, θ, 0 °) θ in the rotating Y-plate X-propagating LiTaO ₃ substrate and the damping constant when the substrate surface is electrically short-circuited. In addition, between the cut angle and θ, the cut angle = θ−9
There is a relationship of 0 °.

As is apparent from FIG. 2, the angle θ is 124
It can be seen that the damping constant α decreases in the range of ° to 126 °, and that the damping constant α increases outside this range.

The thickness of the IDT made of Al is 10%.
It is known that the damping constant α decreases when θ = 129 ° to 136 ° when the thickness is made relatively thick. Therefore, conventionally, the IDT composed of Al, when using a LiTaO ₃ substrate, theta is LiTaO ₃ substrate of 129 ° ~136 ° has been used.

FIG. 3 is a diagram showing changes in the electromechanical coupling coefficient K ² when the angle θ is changed. θ is 100 ° ~
A large electromechanical coupling coefficient K ² is obtained in the range of 120 °. However, in the range of θ = 100 ° to 120 °, as is apparent from the result of FIG. 2, the damping constant α is large and it cannot be used.

FIG. 4 shows a 36 ° rotated Y plate X propagating LiTaO.
₃ substrates, namely Euler angles (0 °, 126 °, 0
°) LiTaO ₃ substrate on the IDT made of Al
FIG. 5 is a diagram showing the relationship between the normalized film thickness H / λ and the electromechanical coupling coefficient K ² . The wavelength λ of the surface acoustic wave means the wavelength at the center frequency of the surface acoustic wave filter.

As is apparent from FIG. 4, the thickness H of Al is H /
When λ is 0.04 or more, H / λ = 0, that is, the electromechanical coupling coefficient K ² is 1.3 as compared with the case where the Al film is not formed.
It is a value more than double. Further, the thickness H / λ of the Al film is 0.
If it exceeds 12, in reality, it becomes difficult to manufacture an IDT made of an Al film. Therefore, in order to obtain a large electromechanical coupling coefficient, the film thickness H / λ of the Al film is preferably set in the range of 0.04 to 0.12.

Next, the temperature coefficient of frequency TC when a SiO ₂ film is laminated without forming an IDT on a LiTaO ₃ substrate
The change in F is shown in FIG. In FIG. 5, θ = 113 °, 126
9 shows changes in the frequency temperature coefficient TCF when a SiO ₂ film was formed with various thicknesses on each LiTaO ₃ substrate of 90 ° and 129 °.

As is apparent from FIG. 5, θ = 113 °,
In both cases of 126 ° and 129 °, Si
It is understood that the TCF falls within the range of −20 to +17 ppm / ° C. when the normalized film thickness H / λ of the O ₂ film is within the range of 0.15 to 0.45. However, more preferably, it takes time to deposit the SiO ₂ film, a SiO ₂ film thickness H / lambda
Is preferably in the range of 0.15 to 0.40.

It has been conventionally known that TCF is improved by forming a SiO ₂ film on a LiTaO ₃ substrate. However, in a structure in which an IDT made of Al is formed on a LiTaO ₃ substrate and a SiO ₂ film is further laminated, the Al film thickness H / λ, the SiO ₂ film thickness, the substrate cut angle, and the leakage surface acoustic wave No experiments have been reported considering the damping constant α.

6 and 7 show Euler angles (0 °, 12
2 °, 0 °) on a LiTaO ₃ substrate with Al
In a surface acoustic wave device in which DT is formed with various film thicknesses,
Is a graph showing changes in attenuation constant α in the case of further laminating a SiO ₂ film of various thickness. Note that FIG. 7 is an enlarged view of a main part of FIG.

As is apparent from FIGS. 6 and 7, θ = 1
When a 22 ° LiTaO ₃ substrate is used, the thickness H / λ of SiO ₂ is in the range of 0 to 0.3, and the thickness H / λ of the Al electrode is H / λ.
It can be seen that the damping constant α is small in the range of 0 to 0.10.

FIG. 8 shows Euler angles (0 °, 136 °, 0
°) LiTaO ₃ substrate, the normalized film thickness H / λ is 0
A change in the attenuation constant α when an IDT made of an Al film having a range of 0.12 is formed and further a SiO ₂ film having a normalized film thickness H / λ in the range of 0 to 0.12 is formed. Show.

As is apparent from FIG. 8, when the LiTaO ₃ substrate with θ = 136 ° is used, even if the thickness of the Al film and the thickness of the SiO ₂ film are changed within the above range, the damping constant It can be seen that α becomes large.

That is, the frequency temperature coefficient TCF is improved,
It can be seen that it is necessary to select the Euler angle of the LiTaO ₃ substrate in order to realize a sufficient magnitude of the electromechanical coupling coefficient K ² and a reduction of the damping constant α.

FIGS. 9 to 16 show (0 °,
theta, theta is the LiTaO ₃ substrate in the range of 110 ° to 140 ° in 0 °), the normalized thickness H / lambda is 0-0.
FIG. 9 is a diagram showing changes in the attenuation constant α when an IDT made of an Al film in the range of 12 is formed and SiO ₂ having various normalized film thicknesses are stacked.

As is apparent from FIGS. 9 16, the film thickness H / lambda of the Al film is 0.12 or less, and when the film thickness of the SiO ₂ film while varying the thickness of the SiO ₂ film It is understood that there is a range in which the damping constant α can be effectively lowered by selecting θ in a specific range according to the above. The results are shown in the table as shown in Table 3 below.

[0037]

[Table 3]

Therefore, using a LiTaO ₃ substrate having Euler angles (0 °, θ, 0 °) of θ in the range of 110 ° to 132 °, the SiO ₂ film thickness H / λ is 0.15 to 0.4.
It can be seen that when the value is 0, the damping constant α can be suppressed and the frequency temperature characteristic can be improved. Further, preferably, when the film thickness H / λ of the IDT made of Al is 0.12 or less, SiO is satisfied so as to satisfy the conditions (a) to (f) shown in Table 3 above.
By selecting the normalized film thickness H / λ of the _two films and the Euler angle θ of the LiTaO ₃ substrate, it can be seen that the electromechanical coupling coefficient can be improved, the frequency temperature coefficient TCF can be improved, and the damping constant α can be reduced. . It is more preferable that the ranges of Euler angles shown on the right side of Table 3 are more preferable in the SiO ₂ film thicknesses of (a) to (f) as is clear from Table 3.

In the above experimental example, the IDT made of Al was formed. However, when forming the IDT, a very thin Ti film or Cr film may be formed under the Al film in order to enhance the adhesion strength of the electrode. Good. That is, the IDT may be made of a material mainly composed of Al, and 80% by weight or more of the IDT is Al.
It may be composed of.

In the above experiment, Euler angles (0 °, θ, 0
Although the LiTaO ₃ substrate of (°) was used, the Euler angle of the substrate material usually has a variation of 0 ± 3 °. Within the range of such variation, that is, (0 ± 3
The effect of the present invention can be obtained even with a LiTaO ₃ substrate having a temperature of 110 °, 110 ° to 132 °, 0 ± 3 °.

The present invention is not limited to the longitudinally coupled resonator type surface acoustic wave filter shown in FIG. 1, but may be a surface acoustic wave resonator, a laterally coupled surface acoustic wave filter, a ladder type filter, a lattice type filter or the like. It can be applied to various surface wave devices.

[0042]

According to the surface acoustic wave device of the present invention, at least one I made of Al is formed on a LiTaO ₃ substrate having Euler angles (0 ± 3 °, 110 ° to 132 °, 0 ± 3 °).
DT is formed and LiT covers the IDT
Film thickness H / λ standardized by wavelength of surface wave on aO ₃ substrate
There SiO ₂ film in the range of 0.15 to 0.40 is formed. Therefore, since the SiO ₂ film is in the above specific thickness range, the frequency-temperature characteristic is effectively improved,
And the damping constant α is reduced.

Further, in the present invention, since the film thickness standardized by the wavelength of the surface wave of the IDT is set in the range of 0.04 to 0.12, a large electromechanical coupling coefficient can be obtained. .

Further, preferably, the film thickness of the IDT is set to 0.
When the Euler angle and the film thickness of the SiO ₂ film are selected to be 12 or more and as shown in (a) to (f) above, the electromechanical coupling coefficient is large, the frequency temperature characteristic is excellent, and the attenuation constant α is An even smaller surface acoustic wave device can be obtained.

[Brief description of drawings]

FIG. 1 is a plan view showing a surface acoustic wave device according to an embodiment of the present invention.

FIG. 2: LiTaO _{3 with} Euler angles (0 °, θ, 0 °)
The figure which shows the relationship between (theta) in a board | substrate, and the damping constant (alpha).

FIG. 3: LiTaO _{3 with} Euler angles (0 °, θ, 0 °)
Diagram showing the relationship between θ and the electromechanical coupling coefficient K ² of the substrate.

Fig. 4 LiT with Euler angles (0 °, 126 °, 0 °)
The normalized film thickness H / λ is 0.0 to 0.12 on the aO ₃ substrate.
Electromechanical coupling coefficient K ² when an Al film in the range of
FIG.

FIG. 5 Euler angles (0 °, 113 °, 0 °), (0
°, 126 °, 0 °) and (0 °, 129 ° 0 °) 3
In the type of LiTaO ₃ substrate, shows the change in the frequency-temperature characteristic TCF in the case normalized thickness H / lambda of the SiO ₂ film is in the range of 0.0 to 0.5.

FIG. 6 LiT with Euler angles (0 °, 122 °, 0 °)
On the aO ₃ substrate, the IDT made of Al has a standardized film thickness of 0.
In the configuration that is formed in the range of 0 to 0.12, shows the change of the attenuation constant α in the case of further laminating a SiO ₂ film of the normalized thickness 0.0 to 0.5.

FIG. 7: LiT with Euler angles (0 °, 122 °, 0 °)
On the aO ₃ substrate, the IDT made of Al has a standardized film thickness of 0.
FIG. 7 is a diagram showing changes in the attenuation constant α when a SiO ₂ film having a normalized film thickness of 0.0 to 0.5 is further stacked in a structure formed in the range of 0 to 0.12. It is a figure which expands and shows the result shown.

FIG. 8: LiT with Euler angles (0 °, 136 °, 0 °)
On the aO ₃ substrate, the IDT made of Al has a standardized film thickness of 0.
In the configuration that is formed in the range of 0 to 0.12, shows the change of the attenuation constant α in the case of further laminating a SiO ₂ film of the normalized thickness 0.0 to 0.5.

FIG. 9: LiTaO _{3 with} Euler angles (0 °, θ, 0 °)
An IDT made of Al having a normalized film thickness H / λ in the range of 0.0 to 0.12.
FIG. 6 is a diagram showing the relationship between θ and the attenuation constant α in the case where the SiO ₂ film of 1 is laminated.

FIG. 10: LiTaO with Euler angles (0 °, θ, 0 °)
_{3 An} IDT made of Al having a normalized film thickness H / λ in the range of 0.0 to 0.12.
In the case of laminating the 15 SiO ₂ film, diagram showing the relationship between θ and the attenuation constant alpha.

FIG. 11: LiTaO with Euler angles (0 °, θ, 0 °)
_{3 An} IDT made of Al having a normalized film thickness H / λ in the range of 0.0 to 0.12.
The figure which shows the relationship between (theta) and damping constant (alpha) at the time of laminating | stacking the SiO2 film of No. ₂ .

FIG. 12: LiTaO with Euler angles (0 °, θ, 0 °)
_{3 An} IDT made of Al having a normalized film thickness H / λ in the range of 0.0 to 0.12.
In the case of stacking a SiO ₂ film 25, shows the relationship between θ and the attenuation constant alpha.

FIG. 13: LiTaO with Euler angles (0 °, θ, 0 °)
_{3 An} IDT made of Al having a normalized film thickness H / λ in the range of 0.0 to 0.12.
In the case of stacking three of the SiO ₂ film, diagram showing the relationship between θ and the attenuation constant alpha.

FIG. 14: LiTaO with Euler angles (0 °, θ, 0 °)
_{3 An} IDT made of Al having a normalized film thickness H / λ in the range of 0.0 to 0.12.
In the case of laminating the 35 SiO ₂ film, diagram showing the relationship between θ and the attenuation constant alpha.

FIG. 15: LiTaO with Euler angles (0 °, θ, 0 °)
_{3 An} IDT made of Al having a normalized film thickness H / λ in the range of 0.0 to 0.12.
4 is a diagram showing the relationship between θ and the attenuation constant α when the SiO ₂ films of No. 4 are laminated.

FIG. 16: LiTaO with Euler angles (0 °, θ, 0 °)
_{3 An} IDT made of Al having a normalized film thickness H / λ in the range of 0.0 to 0.12.
In the case of stacking a SiO ₂ film 45, shows the relationship between θ and the attenuation constant alpha.

[Explanation of symbols]

11 ... Surface acoustic wave device 12 ... LiTaO ₃ substrates 13a, 13b ... IDT 15 ... SiO ₂ film

[Procedure amendment]

[Submission date] January 28, 2002 (2002.1.2
8)

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] Claim 3

[Correction method] Change

[Correction content]

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0012

[Correction method] Change

[Correction content]

[0012] Preferably, the normalized thickness of the Euler angles and the SiO ₂ film of the LiTaO ₃ substrate is a either the combination being <br/> I Table in Table 2 below.

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0038

[Correction method] Change

[Correction content]

Therefore, using a LiTaO ₃ substrate having Euler angles (0 °, θ, 0 °) of θ in the range of 110 ° to 132 °, the SiO ₂ film thickness H / λ is 0.15 to 0.4.
It can be seen that when the value is 0, the damping constant α can be suppressed and the frequency temperature characteristic can be improved. Also preferably, if the IDT film thickness H / lambda of Al is 0.12 or less, so as to satisfy the conditions shown in Table 3, and the normalized thickness H / lambda of the SiO ₂ film, LiTaO ₃ If the Euler angle θ of the substrate is selected, the electromechanical coupling coefficient can be improved and the frequency temperature coefficient TC can be improved.
It can be seen that F can be improved and the damping constant α can be reduced. In addition, more preferably, as is clear from Table 3 , S
For the iO ₂ film thickness, the Euler angle range shown on the right side of Table 3 is desirable.

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0044

[Correction method] Change

[Correction content]

Further, preferably, the film thickness of the IDT is set to 0.
And 12 or more, as shown above SL, Euler angles and Si
By selecting the film thickness of the O ₂ film, it is possible to obtain a surface acoustic wave device having a large electromechanical coupling coefficient, excellent frequency-temperature characteristics, and a smaller attenuation constant α.

Claims (4)

[Claims] 1. Euler angles (0 ± 3 °, 110 ° -13
2 °, 0 ± 3 and LiTaO ₃ substrate °), the LiTaO ₃ is formed on the substrate, and at least one IDT made of a material whose main component is Al, said LiTaO ₃ so as to cover the IDT The film thickness H / λ formed on the substrate and normalized by the wavelength λ of the surface wave
Is a range of 0.15 to 040 and a SiO ₂ film. 2. The surface acoustic wave device according to claim 1, wherein the film thickness normalized by the wavelength of the surface wave of the IDT is 0.04 to 0.12. 3. The elasticity according to claim 1, wherein the Euler angle of the LiTaO ₃ substrate and the normalized film thickness of the SiO ₂ film are any of the combinations represented by the following (a) to (f). Surface wave device. [Table 1] 4. A leaky surface acoustic wave whose main component is SH wave is used as the surface acoustic wave.
The surface acoustic wave device according to any one of 1 to 3.