JP2000165195A - Surface acoustic wave device, surface acoustic wave filter, duplexer and communication equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide optimal TCF by providing a margin in manufacturing precision by forming an interdigital transducer on a piezoelectric substrate using a langasite single crystal and specifying the Euler angles of the langasite single crystal in this case. SOLUTION: A surface acoustic wave device 1 is constituted by forming one interdigital transducer IDT 3 on the piezoelectric substrate 2 made of La3 Ga5SiO14 single crystal and reflectors 4 on both sides of the IDT 3. The IDT 3 is formed by electrode materials like Al, Au, etc., and constituted by arranging one set of comb line electrodes 3a, 3b so that comb line parts of each electrode are arranged opposite to each other. A value of TCF becomes <=|3|ppm/ deg.C by defining values of the Euler angles (ϕ, θ, ψ) of the langasite La3Ga5SiO14 single crystal as a range of (28 deg.<=ϕ<=38 deg., θ=25 deg., 48 deg.<=ψ<=58.5) and the excellent TCF of the Euler angle is provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a surface acoustic wave device, and more particularly to a langasite single crystal (La) having good temperature characteristics.
_{The present invention} relates to a surface acoustic wave device, a surface acoustic wave filter, a duplexer, and a communication device using ₃ Ga ₅ SiO ₁₄ ).

[0002]

2. Description of the Related Art Conventionally, surface acoustic wave devices have been widely used for band-pass filters and the like of mobile communication equipment. As one of such surface acoustic wave devices, an interdigital transducer (ID) comprising a comb-shaped electrode on a piezoelectric substrate
A surface acoustic wave device and a surface acoustic wave filter having a structure formed with T) are well known.

As a piezoelectric substrate of such a surface acoustic wave device or a surface acoustic wave filter, lithium niobate (LiNb) is used.
A piezoelectric single crystal such as O ₃ ), lithium tantalate (LiTaO ₃ ), quartz, or lithium tetraborate (Li ₂ B ₄ O ₇ ) is used.

In the surface acoustic wave device and the surface acoustic wave filter, an electromechanical coupling coefficient (K) mainly representing conversion efficiency of electric energy and mechanical energy is as large as possible, and a group delay time temperature characteristic (TCF) indicating a rate of change of frequency with temperature. ) Is required to be small.

The surface acoustic wave filter using LiNbO ₃ or LiTaO ₃ has the advantage that the difference between the resonance frequency and the antiresonance frequency is large because K is large and the bandwidth is wide, but the TCF is large compared to quartz. There is a disadvantage that the frequency fluctuates greatly depending on the temperature.

[0006] The surface acoustic wave filter using the above quartz has the merit that the TCF is very small and the frequency hardly fluctuates depending on the temperature. There was a disadvantage that the width was narrow.

[0007] Therefore, smaller TCF than LiNbO ₃ or LiTaO _3, as the material K is greater than quartz, L
a ₃ Ga ₅ SiO ₁₄ has attracted attention. That is, La ₃
Ga ₅ SiO ₁₄ has a higher T than LiNbO ₃ or LiTaO _3.
It has the characteristics that CF is small and K is larger than quartz. There have been many reports of theoretical analysis and experimental results on the promising Euler angles and propagation directions of such a La ₃ Ga ₅ SiO ₁₄ single crystal substrate.

In these reports, La ₃ Ga ₅ Si
O ₁₄ in the single crystal (0 °, 140 °, 24 °) TCF = 2 Euler angles of a temperature range from -20 ° C. to 80 ° C..
At 8 ppm / ° C., K = 6.1% is regarded as the best Euler angle.

[0009]

However, in these reports, it is assumed that the Euler angles of (0 °, 140 °, 24 °) are the optimum values, and if the Euler angles deviate from these values, TC
It is said that F deteriorates rapidly. That is, according to these reports, a good TCF is obtained only at (0 °, 140 °, 24 °), but in order to obtain this effect, the Euler angle must be accurately set. There was a problem.

The actual measurement results and the like in these reports are L
The results obtained with only the a ₃ Ga ₅ SiO ₁₄ single crystal substrate are those in which the TCD is optimal when only the single crystal substrate is used, and those in which the TCD is optimal when other elements are added. There was another problem.

The present invention has been made in view of the above-described problems, and has an aspect of (0 °,
140 °, 24 °) and La ₃ Ga ₅ S
In a surface wave device or the like using an iO ₁₄ single crystal, it is an object to provide a margin in the manufacturing accuracy of the Euler angle and to obtain an optimum TCD.

[0012]

Therefore, the present invention according to claim 1 is a surface acoustic wave device having a piezoelectric substrate using a langasite single crystal, and an interdigital transducer formed on the piezoelectric substrate. , The Euler angles (φ, θ, ψ) of the langasite single crystal are 2
8 ° ≦ φ ≦ 38 °, θ = 25 °, 48 ° ≦ ψ ≦ 58.5
° range.

According to a second aspect of the present invention, there is provided a surface acoustic wave device having a piezoelectric substrate using a langasite single crystal and an interdigital transducer formed on the piezoelectric substrate, wherein the langasite single crystal Euler is used. Angles (φ, θ, ψ) are 33 ° ≦ φ ≦ 42 ° and θ, respectively.
= 26 °, 43.5 ° ≦ ψ ≦ 52.5 °.

According to a third aspect of the present invention, there is provided a surface acoustic wave device having a piezoelectric substrate using a langasite single crystal and an interdigital transducer formed on the piezoelectric substrate, wherein the langasite single crystal oiler is used. Angles (φ, θ, ψ) are 34 ° ≦ φ ≦ 45 ° and θ, respectively.
= 27 °, 40 ° ≦ ψ ≦ 51 °.

According to a fourth aspect of the present invention, there is provided a surface acoustic wave device including a piezoelectric substrate using a langasite single crystal, and an interdigital transducer formed on the piezoelectric substrate, wherein the langasite single crystal oiler is used. Angles (φ, θ, ψ) are 37 ° ≦ φ ≦ 45 ° and θ, respectively.
= 28 °, 39.5 ° ≦ ψ ≦ 47.5 °.

According to a fifth aspect of the present invention, there is provided a surface acoustic wave device having a piezoelectric substrate using a langasite single crystal and an interdigital transducer formed on the piezoelectric substrate, wherein the langasite single crystal Euler is used. Angles (φ, θ, ψ) are 27 ° ≦ φ ≦ 33 ° and θ, respectively.
= 22 ° to 24 °, and 54 ° ≦ ψ ≦ 60 °.

With the above configuration, the TCF is further improved as compared with a conventional langasite single crystal.

Further, in the invention according to claim 6, there is provided a surface acoustic wave device comprising a piezoelectric substrate made of a langasite single crystal and an interdigital transducer formed on the surface of the piezoelectric substrate, wherein the piezoelectric substrate has an oiler. When the angles (30 °, θ, 57 °) are plotted on the horizontal axis, and the ratio H / λ of the film thickness H of the interdigital transducer to the wavelength λ excited by the piezoelectric substrate is plotted on the vertical axis, A (Θ = 23.1 °, H / λ = 0.00
5), B (θ = 23.6 °, H / λ = 0.005), C
(Θ = 23.1 °, H / λ = 0.216), D (θ = 2
(2.6 °, H / λ = 0.216) within or on a region surrounded by a straight line connecting the points.

Thus, a surface acoustic wave device having a small frequency fluctuation can be obtained.

[0020]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a perspective view of a surface acoustic wave device according to a first embodiment of the present invention. As shown in FIG. 1, a surface acoustic wave device 1 has one IDT 3 on a piezoelectric substrate 2 made of La ₃ Ga ₅ SiO ₁₄ single crystal and reflectors 4, 4 on both sides thereof.
Is formed.

The interdigital transducer 3 is
It is formed of an electrode material such as Al or Au, and is configured by arranging a pair of comb-shaped electrodes 3a and 3b such that respective comb teeth portions face each other.

Next, a second embodiment of the present invention will be described. FIG. 2 is a perspective view of a longitudinally-coupled surface acoustic wave filter according to a second embodiment of the present invention. As shown in FIG. 2, a longitudinally-coupled surface acoustic wave filter 11 includes two IDTs 13 and 13 on a piezoelectric substrate 12 made of a La ₃ Ga ₅ SiO ₁₄ single crystal.
And reflectors 14 and 14 formed on both sides thereof.

The IDT 13 is made of an electrode material such as Al, Au or the like, and is configured by arranging a pair of comb-shaped electrodes 13a and 13b such that respective comb-tooth portions face each other. The IDTs 13 and 13 are arranged in parallel at regular intervals in the surface wave propagation direction.

Further, a third embodiment of the present invention will be described. FIG. 3 is a perspective view of a laterally coupled surface acoustic wave filter according to a third embodiment of the present invention. As shown in FIG.
The lateral coupling type surface acoustic wave filter 21 is formed by forming an IDT 23 on a piezoelectric substrate 22 made of a La ₃ Ga ₅ SiO ₁₄ single crystal.

The IDT 23 is formed of an electrode material such as Al or Au, and has comb electrodes 23a, 23c and 23c.
c and 23b are configured by disposing the respective comb teeth portions so as to face each other.

Next, fourth and fifth embodiments of the present invention will be described. FIG. 4 is a block diagram of a duplexer according to a fourth embodiment of the present invention and a communication device according to a fifth embodiment of the present invention.

As shown in FIG. 4, the communication device 31 includes a surface acoustic wave filter 32 for reception and a surface acoustic wave filter 3 for transmission.
3 is connected to the antenna 35, the output terminal is connected to the receiving circuit 36, and the input terminal is connected to the transmitting circuit 37. Such a receiving surface acoustic wave filter 3 of the duplexer 34
2 and the surface acoustic wave filter 33 for transmission use the surface acoustic wave filters 11 and 21 of the second and third embodiments.

Table 1 shows the characteristics according to the cut angle of the material used as the substrate of the surface acoustic wave device used in the above applications. Those marked with * before the sample number indicate those outside the scope of the present invention.

[0029]

[Table 1]

As can be seen from Table 1, the Euler angles (φ, θ, θ) of the langasite single crystal (La ₃ Ga ₅ SiO ₁₄ )
ψ) is (28 ° ≦ φ ≦ 38 °, θ = 25 °, 48 °
≦ ψ ≦ 58.5 °), that is, sample numbers 5 to 7
, The TCF value is | 3 | ppm / ° C. or less. Therefore, the conventional good Euler angle (0
°, 140 °, and 24 °).

Further, as can be seen from Table 1, the Euler angles (φ, φ) of the langasite single crystal (La ₃ Ga ₅ SiO ₁₄ )
θ, ψ) (33 ° ≦ φ ≦ 42 °, θ = 26 °, 4
3.5 ° ≦ ψ ≦ 52.5 °), that is, in the range of sample numbers 10 to 12, the value of TCF was | 3 | ppm / ° C.
It is as follows. Therefore, it can be seen that it has a TCF equivalent to the conventional good Euler angles (0 °, 140 °, 24 °).

Further, as can be seen from Table 1, the values of the Euler angles (φ, θ, ψ) of the langasite single crystal (La ₃ Ga ₅ SiO ₁₄ ) are (34 ° ≦ φ ≦ 45 °, θ = 27).
°, 40 ° ≤ ψ ≤ 51 °), that is, in the range of sample numbers 15 to 17, the TCF value is | 3 | ppm / ° C or less. Therefore, it can be seen that it has a TCF equivalent to the conventional good Euler angles (0 °, 140 °, 24 °).

As can be seen from Table 1, the values of the Euler angles (φ, θ, ψ) of the langasite single crystal (La ₃ Ga ₅ SiO ₁₄ ) are (37 ° ≦ φ ≦ 45 °, θ = 28).
°, 39.5 ° ≦ ψ ≦ 47.5 °), that is,
In the range of sample numbers 20 to 22, the TCF value was | 3 | pp
m / ° C. or less. Therefore, T equal to the conventional good Euler angles (0 °, 140 °, 24 °)
It turns out that it has CF.

Accordingly, these langasite single crystals (La ₃ Ga ₅ SiO ₁₄ ) having the Euler angles can be used as the piezoelectric substrates 2, 12 and 12 of the surface acoustic wave device shown in FIG. 1 and the surface acoustic wave filters shown in FIGS. 22, the TCF is | 3 | p
pm / ° C. or less, for example, in a surface acoustic wave device with a center frequency of 100 MHz, for example, a temperature change of 50 ° C. requires only a change in frequency characteristics of about 15 KHz.
It is possible to sufficiently cope with use in an environment where temperature changes are large.

Next, another embodiment of the present invention will be described with reference to FIGS.
This will be described with reference to FIG. FIG. 5 shows how the curve of the frequency variation Δf / Δf with respect to the temperature changes according to the Euler angles in Table 1.

In FIG. 5, Euler angles (30 °, 23 °, 5
7 °) is represented by a black square, and the Euler angle (30 °,
24 °, 57 °) are represented by black circles, the actual values of Euler angles (30 °, 25 °, 57 °) are represented by black triangles,
The measured values of the Euler angles (30 °, 26 °, 57 °) are represented by black inverted triangles, and their approximate values are represented by lines.

As shown in FIG. 5, La ₃ G in the range of Table 1 is used.
In the a ₅ SiO ₁₄ single crystal, the black square (30
(°, 23 °, 57 °) the frequency variation is the least. In addition, black circles (30 °, 24 °,
57 [deg.]), Which is at a feasible level. In the case of (30 [deg.], 25 [deg.], 57 [deg.]) Indicated by a black triangle and the inverted triangle (30 [deg.], 26 [deg.], 57 [deg.]), The frequency is varied. Variations are too large to be feasible for implementation. Note that (30
°, 22 °, 57 °) (30 °, 24 °, 57 °)
And the frequency fluctuation is about the same as (30 °, 24 °, 57 °). Since the influence of φ on the Euler angles (φ, θ, 周波 数) on the frequency fluctuation is slightly smaller than that of θ, the effective range is about ± 3 ° with respect to θ = 23 ° ± 1 °. In addition, the propagation direction ψ
Similarly, since the influence on the frequency fluctuation is slightly smaller than that of θ, the effective range is about ± 3 ° with respect to θ = 23 ° ± 1 °.

FIG. 5 shows that La ₃ Ga _{5 in} the range of Table 1 is used.
In the SiO ₁₄ single crystal, it can be seen that as the Euler angle (φ, θ, ψ) of the La ₃ Ga ₅ SiO ₁₄ single crystal increases, the peak of this curve moves to the lower temperature side.

FIG. 6 shows how the curve of frequency variation with temperature changes depending on the film thickness H of the Al electrode formed on the La ₃ Ga ₅ SiO ₁₄ single crystal piezoelectric substrate.

In FIG. 6, the black squares are Euler angles (φ, θ,
ψ) is La ₃ Ga ₅ SiO with (30 °, 23 °, 57 °)
The measured values when a 150-nm Al electrode is formed on a _14- single-crystal piezoelectric substrate are shown. Solid circles indicate Euler angles (φ, θ, ψ).
Indicates the actual measurement values when a 450 nm Al electrode is formed on a (30 °, 23 °, 57 °) La ₃ Ga ₅ SiO ₁₄ single crystal piezoelectric substrate, and the black triangle indicates the Euler angles (φ, θ, ψ). Shows actual measured values when an Al electrode of 750 nm is formed on a piezoelectric substrate of (30 °, 23 °, 57 °) La ₃ Ga ₅ SiO ₁₄ single crystal. Δf / f indicates the rate of frequency fluctuation at 20 ° C. From FIG. 7, it can be seen that the curve shifts to the higher temperature side as the film thickness H of the Al electrode becomes thinner.

From the above, the Euler angles (φ, θ,
ψ) = (30 °, 24 °, 57 °) in the vicinity of La ₃ Ga ₅
As θ of the Euler angles (φ, θ, ψ) of the SiO ₁₄ single crystal increases, the peak temperature at which the frequency fluctuation becomes almost zero moves to the lower temperature side, and as the film thickness H of the Al electrode decreases, the peak temperature increases. It could be confirmed that it was moving to the high temperature side.

Therefore, the thickness H of the Al electrode is determined in accordance with the shift of the apex temperature to the higher temperature side depending on the magnitude of Euler angles (φ, θ, ψ) of the La ₃ Ga ₅ SiO ₁₄ single crystal. Thus, the peak temperature can be set to a desired value.

Therefore, the Euler angles (φ, θ, ψ) at which the characteristics of the La ₃ Ga ₅ SiO ₁₄ single crystal are good are (30 °, 24 °,
57 °), the peak temperature becomes an appropriate value.
The value of the film thickness H of the 1 electrode was calculated by an experiment.

As a result, the Euler angle (30 °, 22.6)
°, 24 °) and the peak temperature is 40 ° C. with H / λ = 0.216
It turned out to be. In addition, Euler angles (30 °, 2
(3.1 °, 24 °), the peak temperature was found to be 10 ° C. at H / λ = 0.216.

Further, the Euler angle (30 °, 23.1)
°, 24 °) and the peak temperature is 40 ° C. with H / λ = 0.005
It was found that the peak temperature was 10 ° C. at H / λ = 0.005 at Euler angles (30 °, 23.6 °, 24 °).

FIG. 7 shows the Euler angles and H / λ ranges in which the peak temperature is set in the range of 10 ° C. to 40 ° C. That is, A (Euler angle 3
0 °, 23.1 °, 24 °, H / λ = 0.005), B
(Eulerian angles 30 °, 23.6 °, 24 °, H / λ =
0.005), C (Eulerian angles 30 °, 23.1 °,
24 °, H / λ = 0.216), D (Eulerian angle 30
°, 22.6 °, 24 °, H / λ = 0.216) are located inside or on the line surrounded by a straight line connecting the points, the peak temperature is in the range of 10 ° C to 40 ° C. If this Euler angle and the film thickness of the electrode are adopted, the frequency fluctuation can be reduced.

In the first to third embodiments of the present invention, a surface acoustic wave device, a longitudinally coupled surface acoustic wave filter, and a laterally coupled surface acoustic wave filter have been described as examples, but the present invention is not limited thereto. For example, a transversal type surface acoustic wave filter having a plurality of sets of interdigital transducers or a surface acoustic wave device used for a ladder type filter in which surface acoustic wave devices are arranged in a ladder shape may be used. Has the same effect.

[0048]

As described above, according to the present invention, TCF is better than lithium niobate or lithium tantalate, and K can be larger than quartz. Since K can be increased as compared with quartz, when a surface acoustic wave device is formed, Q increases, and as a result,
The insertion loss of the surface acoustic wave device can be improved. It is also possible to obtain a temperature characteristic of TCF = | 3 | ppm or less, which is comparable to that of a conventional La ₃ Ga ₅ SiO ₁₄ single crystal having an Euler angle of (0 °, 140 °, 24 °). it can.

According to the invention of claim 6, La ₃ G
when forming an electrode on the piezoelectric substrate made of a ₅ SiO ₁₄ single crystal, it is possible to obtain a small surface wave device frequency variations.

[Brief description of the drawings]

FIG. 1 is a perspective view of a surface acoustic wave device for describing a first embodiment.

FIG. 2 is a perspective view of a longitudinally-coupled surface acoustic wave filter for explaining a second embodiment.

FIG. 3 is a perspective view of a laterally coupled surface acoustic wave filter for explaining a third embodiment.

FIG. 4 is a block diagram illustrating a duplexer according to a fourth embodiment and a communication device according to a fifth embodiment;

FIG. 5 shows a frequency variation Δf with respect to temperature due to Euler angles.
FIG. 6 is a characteristic diagram showing a change in a curve of / Δf.

FIG. 6 is a characteristic diagram showing a change in a curve of frequency fluctuation Δf / Δf with respect to temperature depending on a film thickness H of an Al electrode.

FIG. 7 is a characteristic diagram showing a relationship between an electrode film thickness and an Euler angle for explaining the present invention.

[Explanation of symbols]

 Reference Signs List 1 surface acoustic wave device 2 piezoelectric substrate 3 interdigital transducer 3a, 3b comb electrode

Claims (9)

[Claims] 1. A surface acoustic wave device having a piezoelectric substrate using a langasite single crystal and an interdigital transducer formed on the piezoelectric substrate, wherein the Euler angles (φ, θ, ψ)
Are in the ranges of 28 ° ≦ φ ≦ 38 °, θ = 25 °, and 48 ° ≦ ψ ≦ 58.5 °, respectively. 2. A surface acoustic wave device having a piezoelectric substrate using a langasite single crystal and an interdigital transducer formed on the piezoelectric substrate, wherein the Euler angles (φ, θ, ψ)
Are in the ranges of 33 ° ≦ φ ≦ 42 °, θ = 26 °, and 43.5 ° ≦ 表面 ≦ 52.5 °, respectively. 3. A surface acoustic wave device having a piezoelectric substrate using a langasite single crystal and an interdigital transducer formed on the piezoelectric substrate, wherein the Euler angles (φ, θ, ψ)
Are in the ranges of 34 ° ≦ φ ≦ 45 °, θ = 27 °, and 40 ° ≦ ψ ≦ 51 °, respectively. 4. A surface acoustic wave device having a piezoelectric substrate using a langasite single crystal and an interdigital transducer formed on the piezoelectric substrate, wherein the Euler angles (φ, θ, ψ)
Are in the range of 37 ° ≦ φ ≦ 45 °, θ = 28 °, and 39.5 ° ≦ ψ ≦ 47.5 °, respectively. 5. A surface acoustic wave device having a piezoelectric substrate using a langasite single crystal and an interdigital transducer formed on the piezoelectric substrate, wherein the Euler angles (φ, θ, ψ)
Are in the ranges of 27 ° ≦ φ ≦ 33 °, θ = 22 ° to 24 °, and 54 ° ≦ ψ ≦ 60 °, respectively. 6. A surface acoustic wave device comprising a piezoelectric substrate made of a Langasite single crystal and an interdigital transducer formed on the surface of the piezoelectric substrate, wherein the piezoelectric substrate has an Euler angle (30 °, θ, 57). °) on the horizontal axis, and the ratio H of the thickness H of the interdigital transducer to the wavelength λ excited by the piezoelectric substrate.
When / λ is represented on the vertical axis, A (θ = 23.1 °, H / λ = 0.005) B (θ = 23.6 °, H / λ = 0.005) C (θ = 23.1 °, H / λ = 0.216) D (θ = 22.6 °, H / λ = 0.216) Inside or on a line surrounded by a straight line connecting points A surface acoustic wave device. 7. A surface acoustic wave filter using at least one of the surface acoustic wave devices according to claim 1. Description: 8. A duplexer using the surface acoustic wave device according to claim 1 or the surface acoustic wave filter according to claim 7. 9. A surface acoustic wave device according to claim 1, a surface acoustic wave filter according to claim 7, or a surface acoustic wave filter according to claim 7.
A communication device using the shared device according to any one of the preceding claims.