JP2000315934A - Surface acoustic wave device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a surface acoustic device wave with minimum loss, a wide band and excellent angle ratio by providing an electrode pattern with the thickness of a specified range of wavelength of excited LSAW and providing a piezoelectric substrate with the azimuth formed by rotating an LiTaO3 single crystal from a Y axis to a Z axis centering around an X axis with an angle within the specified range. SOLUTION: In the surface acoustic wave device consisting of the piezoelectric substrate and the electrode pattern mainly composed of Al formed on the surface of the piezoelectric substrate, a resonator to excite the LSAW is constituted on the surface of the piezoelectric substrate by the electrode pattern. The electrode pattern has the thickness within the rage of 0.03 to 0.15 of the wavelength of the excited LSAW and the piezoelectric substrate has the azimuth formed by rotating the LiTaO3 single crystal from the Y axis to the Z axis centering around the X axis with the angle within a range between 39 to 46 degrees. Thus, the surface acoustic wave device with small attenuation of surface acoustic waves and a higher Q factor even in a GHz band is formed by setting a rotation angle of the LiTaO3 single crystal large.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention generally relates to a surface acoustic wave device, and more particularly to a surface acoustic wave device having excellent pass band characteristics in a high frequency band including a GHz band.

[0002]

2. Description of the Related Art A surface acoustic wave device is a small-sized and
It is widely used as a filter or a resonator in a high-frequency circuit of a wireless communication device that is lightweight and operates in a very high frequency band. While such a surface acoustic wave device is generally formed on the piezoelectric single crystal or polycrystalline substrate, the electromechanical coupling coefficient k ² is large, therefore high excitation efficiency of the surface waves, also a small propagation loss of the surface wave in a high frequency band As a substrate material, in particular, in a 64 ° rotation Y-cut plate of LiNbO ₃ single crystal, the propagation direction of the surface wave was set to X direction.
4 ° YX LiNbO ₃ substrate (K. Yamanouti and K. Shi
bayama, J. Appl. Phys. vol.43, no.3, March 1972, p
p.856) Alternatively, in a 36 ° rotation Y-cut plate of LiTaO ₃ single crystal, the propagation direction of the surface wave is 36 ° in the X direction.
YX LiTaO ₃ substrates are widely used.

[0003]

However, these cut angles are optimal when the additional mass effect of the electrodes formed on the piezoelectric crystal substrate can be neglected, and are several hundred MHz.
In the low frequency band below z, the surface acoustic wave to be excited is effective because of its long wavelength. However, in the operation near the GHz band required by recent mobile phones and the like, the thickness of the electrode is increased. It cannot be neglected for the elastic wave wavelength to be used, and is not always optimal. In the operation in such a high frequency band, the effect of the additional mass of the electrode is remarkably exhibited.
In such a very short wavelength operation, the passband of a surface acoustic wave filter or the surface acoustic wave is increased by increasing the thickness of the electrode on the piezoelectric substrate and increasing the apparent electromechanical coupling coefficient. Although it is possible to reduce the capacitance ratio γ of the resonator, such a configuration causes a problem that the bulk wave radiated from the electrode toward the inside of the substrate increases and the propagation loss of the surface wave increases. . Such a bulk wave is called an SSBW (surface skimming bulk wave), and a surface wave accompanied by the SSBW is called an LSAW (Leak
y surface acoustic wave). Regarding the propagation loss of LSAW in a surface acoustic wave filter using a thick electrode film, 36 ° YX LiTaO ₃ and 64 ° YX L
About iNbO ₃ substrate, Plessky et al. or Edmons
on Analyzed by others (VS Plessky and
CS Hartmann, Proc. 1993 IEEE Ultrasonics Symp.,
pp.1239-1242; PJ Edmonson and CK Campbel
l, Proc. 1994 IEEE Ultrosonic Symp., pp75-79).

Incidentally, such a conventional 36 ° YXL
LS such as iTaO ₃ or 64 ° YX LiNbO ₃
In the conventional surface acoustic wave filter using AW, when the electrode film thickness is small, the sound velocity value of the surface wave and the sound velocity value of the bulk wave approach, and as a result, a spurious peak due to the bulk wave appears in the pass band of the filter. (M. Ueda et al., Pro
c. 1994 IEEE Ultrasonic Symp., pp. 143-146).

FIG. 20 shows spurious peaks A and B due to a bulk wave appearing near the filter pass band in the surface wave filter according to the above Ueda et al. The filter is formed on a 36 ° YX LiTaO ₃ substrate, and has a comb-shaped electrode made of an Al—Cu alloy having a thickness of 0.49 μm corresponding to 3% of the excitation wavelength.

Referring to FIG. 20, a spurious peak B
Is generated outside the pass band formed near 330 MHz, while the spurious peak A is generated within the pass band.
As a result, it can be seen that ripple occurs in the pass band characteristic.

In the surface acoustic wave filter, the sound velocity of the surface wave depends on the additional mass of the electrode, that is, the film thickness.
Since the sound speed of the SBW does not depend on the thickness of the electrode, in operation in a high frequency band such as the GHz band, the thickness of the electrode increases with respect to the excitation surface wave wavelength, and the sound speed of the surface wave with respect to the bulk wave. Decrease relatively. As a result, the pass band of the filter shifts with respect to the spurious peak, and the pass band characteristics are flattened. However, when the thickness of the electrode is increased with respect to the surface wave wavelength, the loss of the LSAW due to the bulk radiation increases as described above.

In particular, in a surface acoustic wave filter operating in a very high frequency band such as the GHz band, it is necessary to secure a certain thickness of the electrode in order to reduce the resistance of the comb-shaped electrode. The problems of increased loss and degraded squareness described above are unavoidable.

Accordingly, it is a general object of the present invention to provide a new and useful surface acoustic wave device which solves such a conventional problem.

A more specific object of the present invention is to provide a piezoelectric single crystal substrate cut at a cut angle optimized with respect to the film thickness of an electrode, and to prevent a pass band from being spurious due to a bulk wave. It is another object of the present invention to provide a surface acoustic wave device set as follows.

[0011]

According to the present invention, the above object is achieved by a piezoelectric substrate and an electrode pattern mainly composed of Al formed on the surface of the piezoelectric substrate. In the surface acoustic wave device, the electrode pattern forms a resonator that excites an LSAW on the surface of the piezoelectric substrate, and the electrode pattern has a thickness in a range of 0.03 to 0.15 of a wavelength of the excited LSAW. The piezoelectric substrate has an orientation obtained by rotating the LiTaO ₃ single crystal at an angle in the range of 39 to 46 ° from the Y axis to the Z axis around the X axis. The surface acoustic wave device according to claim 1, wherein the electrode pattern forms a plurality of resonators on the surface of the piezoelectric substrate. Or claim 3 The said electrode pattern has a thickness of the wavelength of the surface acoustic wave excited on the said piezoelectric substrate in the range of 0.07-0.15 as described, The said electrode pattern of Claim 1 or 2 characterized by the above-mentioned. By a surface acoustic wave device or as described in claim 4, the electrode pattern is:
0.0 wavelength of the surface acoustic wave excited on the piezoelectric substrate
The piezoelectric substrate has a thickness in the range of 5 to 0.10.
The ITaO ₃ single crystal, about the X axis, one of three claims 1, wherein the one having an orientation rotated at an angle in the range of 40 to 44 ° to the Z axis direction from the Y-axis 6. The piezoelectric substrate according to claim 1, wherein the piezoelectric substrate comprises a LiTaO ₃ single crystal having an angle in the range of 42 ° from the Y axis to the Z axis around the X axis. The surface acoustic wave device according to claim 1, wherein the electrode pattern includes a multi-mode filter on the piezoelectric substrate. The electrode pattern is formed by the surface acoustic wave device according to claim 1 or as described in claim 7.
The surface acoustic wave device according to any one of claims 1 to 5, wherein the surface acoustic wave device is made of an alloy.
As described in the above, the resonator is connected in a ladder type, and the surface acoustic wave device according to any one of claims 1 to 7, or as described in the paragraph 9 above, , A piezoelectric substrate, and A formed on the surface of the piezoelectric substrate.
In a surface acoustic wave filter comprising an electrode pattern having l as a main component, the electrode pattern forms a resonator that excites an LSAW on the surface of the piezoelectric substrate, and the electrode pattern has a wavelength of 0.1 mm of the excited and excited LSAW. 03-0.1
Has a thickness of 5 range; said piezoelectric substrate, LiTaO ₃
The single crystal is placed in the direction of 39 to 4 from the Y axis to the Z axis around the X axis.
An electrode pattern rotated by an angle in the range of 6 °; said electrode pattern comprising a comb-shaped electrode, or by a surface acoustic wave filter, or as described in claim 10.
In a surface acoustic wave device comprising a piezoelectric substrate and an electrode pattern mainly composed of Al formed on the surface of the piezoelectric substrate, the electrode pattern excites an LSAW on the piezoelectric substrate, and a wavelength of the excited LSAW. 0.04-0.
The piezoelectric substrate has a thickness in the range of 12;
_{The three} single crystals are 66-
12. The piezoelectric substrate according to claim 11, wherein the piezoelectric substrate has an azimuth rotated at an angle in the range of 74 °.
_{The three} single crystals are arranged in a direction from the Y-axis to the Z-axis,
13. The surface acoustic wave device according to claim 10, wherein the electrode pattern has an azimuth rotated by an angle in a range of 72 [deg.]. The surface acoustic wave device according to claim 10 or 11, wherein the surface acoustic wave has a thickness in the range of 0.05 to 0.10 of the wavelength of the surface acoustic wave excited above, or as described in claim 13. The electrode pattern is made of Al.
The electrode pattern is made of an Al-Cu alloy, according to the surface acoustic wave device according to any one of claims 1 to 14, or as described in claim 14.
12, the electrode pattern forms a ladder-type filter using a plurality of resonators on the surface of the piezoelectric substrate by the surface acoustic wave device according to any one of claims 12 or 15. 2. The method according to claim 1, wherein
The surface acoustic wave device according to any one of 0 to 14, or as described in claim 16, wherein the electrode pattern forms a resonator on the surface of the piezoelectric substrate. A piezoelectric substrate formed by the surface acoustic wave device according to any one of claims 10 to 14 or as described in claim 17, and an electrode pattern mainly composed of Au formed on the surface of the piezoelectric substrate. Wherein the electrode pattern excites LSAW on the surface of the piezoelectric substrate, and the electrode pattern has a thickness in the range of 0.004 to 0.021 of a wavelength of the excited LSAW. The piezoelectric substrate is made of LiTaO ₃ single crystal;
A surface acoustic wave device characterized by having an azimuth rotated at an angle in the range of 39 to 46 ° from the Y axis to the Z axis around the axis, or as described in claim 18. In a surface acoustic wave device comprising a piezoelectric substrate and an electrode pattern mainly composed of Cu formed on the surface of the piezoelectric substrate, the electrode pattern excites LSAW on the surface of the piezoelectric substrate, and the electrode pattern is excited. The piezoelectric substrate has a thickness in the range of 0.009 to 0.045 of the wavelength of the LSAW; and the piezoelectric substrate is a LiTaO ₃ single crystal that is 39 to 46 ° from the Y axis to the Z axis around the X axis. 20. A piezoelectric substrate and a piezoelectric substrate formed on the surface of the piezoelectric substrate by a surface acoustic wave device having an azimuth rotated by an angle in the range of
In a surface acoustic wave device comprising an electrode pattern mainly composed of u, the electrode pattern
When the SAW is excited, the electrode pattern is
The piezoelectric substrate has a thickness in the range of 0.005 to 0.017 of the wavelength of the SAW; the piezoelectric substrate is formed by depositing LiNbO ₃ single crystal in the range of 66 to 74 ° from the Y axis to the Z axis around the X axis. 21. A piezoelectric substrate and a Cu substrate formed on the surface of the piezoelectric substrate by a surface acoustic wave device characterized by having an azimuth rotated at an angle of
A surface acoustic wave device comprising an electrode pattern mainly composed of:
AW is excited, and the electrode pattern is excited by the excited LS
The piezoelectric substrate has a thickness in the range of 0.012 to 0.036 of the wavelength of AW; the piezoelectric substrate is made of LiNbO ₃ single crystal in a range of 66 to 74 ° around the X axis from the Y axis to the Z axis along the X axis. The problem is solved by a surface acoustic wave device characterized by having an azimuth rotated at an angle of.

The operation of the present invention will be described below with reference to FIGS.

FIG. 1 is a diagram for explaining a cut-out angle of a piezoelectric crystal substrate.

FIG. 1 shows a piezoelectric single crystal, such as LiTaO ₃ , having crystal axes X, Y, and Z cut out from the Y axis at an angle inclined from the Y axis by the rotation angle θ. It shows the state that it was turned on. Such a piezoelectric crystal substrate is rotated by θ rotation Y−
It is called an X substrate.

FIG. 2 shows the θ rotation YX of the LiTaO ₃ single crystal.
The insertion loss of the resonator formed on the substrate is shown for various cutting angles or rotation angles θ.

As described above, LiTa has been conventionally used.
When forming a surface acoustic wave device on an O ₃ substrate, 36 ° Y
If -X substrate, also to form a surface acoustic wave device in LiNbO ₃ substrate, 64 ° Y-X substrate but is generally used, which is the mass effect of electrodes formed on the substrate surface The propagation loss for a relatively long wavelength surface wave which can be ignored is minimized at these rotation angles. See, for example, Nakamura et al., IEICE Technical Report, US 77-42.

In FIG. 2, the curve shown by a black circle is LiTaO
₃ is a calculation result of the LSAW propagation loss when a virtual electrode having a zero film thickness is uniformly formed on the surface of the 36 ° YX substrate. When the rotation angle θ is 36 °, the propagation loss is minimized. It turns out that it becomes. However, in this calculation, the crystal constant reported by Kovacs et al. Was used (G. Kovacs, eta
l., Proc. 1990 IEEE Ultrasonic Symp.pp.435-43
8).

However, in a short wavelength region such as a GHz band, as described above, the thickness of the electrode cannot be ignored with respect to the wavelength of the excited surface wave, and the effect of the additional mass of the electrode is remarkable. Appears in According to the inventor of the present invention, due to the effect of the additional mass, the propagation loss characteristic in FIG. 2 changes in the direction of the arrow, and as shown by the white circle in FIG. I found that it shifted to the side. However, in FIG. 2, the curve shown by a white circle shows the case where an Al electrode is formed uniformly on the piezoelectric substrate and the thickness of the electrode is 10% of the wavelength of the excitation surface wave.

Further, FIG. 3 shows that A on a LiTaO ₃ substrate
6 shows the relationship between the propagation loss and the rotation angle θ when a grating electrode of 1 is formed. In FIG. 3, the broken line indicates the case where the electrode thickness is zero, and the solid line indicates the case where the electrode thickness is 10% of the excitation surface wave wavelength. Obviously, as a result of forming a grating having a finite thickness on the substrate with respect to the wavelength of the excitation surface wave, the rotation angle at which the propagation loss is minimized is shifted to a higher angle side.

That is, by setting the rotation angle θ of the LiTaO ₃ single crystal substrate to be higher than the conventional angle of 36 °, a surface acoustic wave device having less Q in the GHz band and a high Q is formed. Can be. Also, with the added mass effect of the electrode at such high frequencies,
Since the position of the pass band of the filter shown in FIG. 18 shifts to the lower frequency side with respect to the spurious peaks A and B, the spurious peak A is not increased in the surface acoustic wave device formed on the LiTaO ₃ substrate having such a large rotation angle. , B out of the pass band of the filter. As described above, the spurious peaks A and B are caused by bulk waves and are not affected by the additional mass of the electrode.

Further, in the present invention, the squareness ratio of the pass band characteristic also changes depending on the rotation angle θ, and particularly in the GHz band, Li cut out at an angle higher than the conventionally used rotation angle θ.
It has been found that a TaO ₃ substrate provides excellent pass bandwidth and squareness. 4 and 5 respectively show such LiT
5 shows the frequency temperature characteristics and the temperature characteristics of the minimum insertion loss of a surface acoustic wave filter formed on an aO ₃ substrate. However,
The surface acoustic wave filter has a configuration shown in FIG. 7 described later, and is formed on a LiTaO ₃ substrate having various rotation angles θ such that the electrode film thickness becomes 10% of the wavelength of the surface acoustic wave to be excited. Formed.

As can be seen from FIG. 4, the filter has a substrate rotation angle, that is, a cut angle θ of 36 ° Y, 40 ° Y,
In both cases of 42 ° Y and 44 ° Y, substantially the same temperature characteristics are exhibited. The various changes in the center frequency are considered to be due to the difference in the sound speed in the substrate and the variation in the sample preparation conditions.

As can be seen from FIG. 5, LiTaO
_When the rotation angle θ of the _three substrates is set in the range of 40 ° Y to 44 ° Y, at least the normal temperature range, that is, −35 °
In the range of C to 85 ° C., the loss is smaller than when the rotation angle θ is set to 36 ° Y in the related art. In particular, when the rotation angle θ is set in the range of 40 ° Y to 42 ° Y, it can be seen that the fluctuation width of the minimum insertion loss also decreases.

FIG. 6 shows the insertion loss of the resonator formed on the θ-rotated YX substrate of LiNbO ₃ single crystal for various cut-out angles or rotation angles θ.

In FIG. 6, the curve shown by the broken line is LiNbO
₃ is a calculation result of LSAW propagation loss when a virtual electrode having zero film thickness is uniformly formed on the surface of the 64 ° YX substrate, and the propagation loss is minimum when the rotation angle θ is 64 °. It turns out that it becomes. However, in this calculation, the crystal constant reported by Warner et al. Was used (J. Acoust. Soc.
Amer., 42, 1967, pp.1223-1231)).

However, in a short wavelength region such as the GHz band, as described above, the thickness of the electrode cannot be ignored with respect to the wavelength of the excited surface wave, and the effect of the additional mass of the electrode is remarkable. Appears in According to the inventor of the present invention, due to the effect of the additional mass, the propagation loss characteristic in FIG. 6 changes in the direction of the arrow, and as shown by the solid line in FIGS. We found that it shifted to the high angle side. However, the curve shown by the solid line in FIG. 2 shows the case where the thickness of the electrode is 3% of the wavelength of the excitation surface wave.

That is, by setting the rotation angle θ of the LiNbO ₃ single crystal substrate to be higher than the conventional angle of 64 °, a surface acoustic wave device having a low Q in the GHz band and a high Q can be formed. Can be.

[0028]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to preferred embodiments.

FIG. 7A is a plan view showing a configuration of a ladder type surface acoustic wave filter according to a first embodiment of the present invention.
(B) is an equivalent circuit diagram thereof.

Referring to FIG. 7 (A), the surface acoustic wave filter is a rotation Y of LiTaO ₃ or LiNbO ₃ single crystal.
Is formed on the plate, the first comb-shaped electrodes R ₁ where the input-side electrode connected to the input terminal IN, the input-side electrode and the interdigital electrode R
_A second comb-shaped electrode R ₁ ′ connected to the output terminal of the _first comb-shaped electrode R ₁ , and an output-side electrode connected to the input-side electrode of the comb-shaped electrode R _1. third comb-shaped electrodes R ₂ of which is grounded, is connected to the input side electrode to the output electrode of the interdigital electrode R _1, fourth comb-shaped electrodes R _{2 'of} which it is grounded output-side electrode, an input-side electrode A fourth comb-shaped electrode R ₂ ″ connected to the output-side electrode of the comb-shaped electrode R ₁ ′ and having the output-side electrode grounded.

Each of the comb electrodes R ₁ , R ₁ ′, R ₂ ,
In R ₂ ′, R ₂ ″, the input electrode i is, as usual, a first group of electrode fingers extending in parallel in a first direction intersecting the path of the surface acoustic wave propagating in the X-axis direction. The output-side electrode o also includes, as usual, a second group of electrode fingers extending parallel to a second direction opposite to the first direction, and the first group of electrode fingers The two groups of electrode fingers are arranged alternately, and each of the comb electrodes R ₁ ,
In R ₁ ′, R ₂ , R ₂ ′, R ₂ ″, a reflector Re having a configuration in which a plurality of parallel electrode fingers are short-circuited at both ends in the X-axis direction is formed. In the example, the comb-shaped electrodes R ₁ , R ₁ ′, R ₂ , R ₂ ′, R ₂ ″ are Al-1% Cu
It is formed of an alloy and has a thickness of about 0.4 μm corresponding to 10% of the pass band wavelength of the filter.

FIG. 7B shows an equivalent circuit diagram of the filter shown in FIG.

Referring to FIG. 7B, the comb-shaped electrodes R ₁ and R ₁ ′ are connected in series, and furthermore, the comb-shaped electrodes R ₂ ,
R ₂ ′ and R ₂ ″ are connected in parallel.

FIG. 8 shows the minimum insertion loss experimentally obtained for the surface acoustic wave filters of FIGS. 7A and 7B by Li
Various cut angles θ of the TaO ₃ single crystal substrate 11 will be described. The minimum insertion loss includes the effects of both the propagation loss of the surface wave and the matching loss of the filter, but the cut angle θ of the substrate does not substantially contribute to the matching loss.

Referring to FIG. 8, it can be seen that the minimum insertion loss decreases as the cut angle of the substrate increases, and becomes minimum at a cut angle around 42 °. Cut angle is 42
Beyond °, the minimum insertion loss increases again. Therefore, from the viewpoint of filter insertion loss, the LiTaO ₃ substrate 11
Is set in the range of 38 ° to 46 °, the minimum insertion loss of the filter can be suppressed within 1.6 dB.

According to the present invention, it has been found that the cut angle of the LiTaO ₃ single crystal substrate also affects the squareness ratio of the surface acoustic wave filter.

FIG. 9A shows the definition of the squareness ratio.

Referring to FIG. 9A, the squareness ratios are as follows: a bandwidth BW ₂ that provides 1.5 dB of attenuation with respect to the minimum insertion loss of the pass band, and a bandwidth BW ₁ that provides 20 dB of attenuation.
And given by BW ₁ / BW ₂ . The larger the squareness ratio, the broader the filter, the lower the selectivity, and the narrower the passband at the same time. That is, it is desirable to design the surface acoustic wave filter so that the squareness ratio approaches 1 as much as possible.

FIG. 9B shows the squareness ratio experimentally obtained for the surface acoustic wave filters of FIGS. 7A and 7B as a function of the cut angle θ of the piezoelectric substrate 11.

As can be seen from FIG. 9B, the squareness ratio approaches 1 as the cut angle θ increases, and reaches a minimum value of 1.47 at a cut angle of θ = 42 °. On the other hand, when the cut angle increases beyond 42 °, the squareness ratio also increases, and the selectivity of the filter deteriorates. In the surface acoustic wave filter according to the present invention, the minimum insertion loss is 1.6 dB or less, and the squareness ratio is 1.0.
It is desirable that the cut angle θ of the LiTaO ₃ substrate is 39 to 4 from FIG.
It can be seen that a range of 6 °, particularly a range of 40 to 44 °, is preferable. In particular, by setting the cut angle θ to 42 °, the minimum insertion loss can be minimized, and the squareness ratio can also be minimized.

FIG. 10 shows experimentally obtained pass band characteristics of the surface acoustic wave filters shown in FIGS. 7A and 7B. In FIG. 10, the solid line indicates the case where a 42 ° YX substrate of LiTaO ₃ is used as the substrate 11, and the dashed line indicates the same L
The case where a 36 ° YX substrate of iTaO ₃ is used as the substrate 11 is shown.

Referring to FIG. 10, the pass band characteristic is 88.
It has a center frequency at 0 MHz and is characterized by a flat passband of about 40 MHz. Outside of the passband, the attenuation increases sharply, but the filter using the 42 ° YX substrate has steeper characteristics than the conventional one using the 36 ° YX substrate, and therefore has a better squareness ratio. It shows that it shows. In FIG. 10, spurious peaks A and B due to SSBW are observed outside the pass band of the filter.

[0043] Figure 11 is a Y rotation X board substrate surface of LiTaO _3, the electromechanical coupling coefficient k ² in the case where the thickness to the wavelength of the surface acoustic waves to form a 7% of the electrode, for θ varying cut angle The calculated results are shown. The calculations used the crystal constants reported by Kovacs et al. (Supra).

Referring to FIG. 11, the electromechanical coupling coefficient k
² shows a tendency to decrease as the cut angle increases. As the electromechanical coupling coefficient k ² is known, is a quantity indicating a ratio of the stored energy by the piezoelectric effect in the piezoelectric crystal, or pass bandwidth decreases as the value is small, the ripples in the passband Problems that arise. FIG.
It is understood from FIG. 1 that the cut angle θ is preferably set to 46 ° or less.

FIG. 12 shows the filter of FIGS. 7A and 7B in which the thickness of the comb-shaped electrode formed on the Y rotation-X propagation substrate 11 of LiTaO ₃ formed at various cut angles is changed. The result of calculation of the propagation loss in the case where it is performed is shown. In the calculation of FIG. 12, the crystal constants of Kovacs et al. Were used as in the previous calculation.

As can be seen from FIG. 12, the cut angle is 38
If the cut angle exceeds 40 °, the loss begins to decrease with the electrode thickness, and a minimum point appears on the characteristic curve. Understand. After the minimum, the losses begin to increase again. In particular, when the cut angle of the substrate 11 is set in the range of 40 ° to 46 °, which is the preferable angle described above, such a minimum point indicates that the thickness of the electrode with respect to the wavelength is 3 °.
Appears at% or more. In other words, in the filter of this embodiment, the thickness of the electrode normalized by the wavelength is 3%.
It is preferable to form so as to be as described above. On the other hand, if the thickness of the electrode is too large, it becomes difficult to pattern the electrode by etching, and the speed of sound in the substrate changes more sensitively to the film thickness of the electrode. It is preferable that the thickness be within 15%. FIG. 12 shows that in the case of an electrode using Al or an Al-1% Cu alloy, when the thickness of the electrode exceeds 15% of the wavelength, the propagation loss sharply increases at any cut angle. This shows that the emission of bulk waves from the electrodes becomes dominant. Especially the cut angle is 39-46 °
In the range, the electrode thickness is in the range of 0.07 to 0.15, and when the cut angle is in the range of 40 to 44 °, the electrode thickness is in the range of 0.05 to 0.10. preferable.

FIG. 13 shows a comb-shaped filter formed on the substrate 11 in the filters of FIGS. 7A and 7B, using a Y rotation-X plate of LiNbO ₃ formed at various cut angles as the substrate 11. The calculation result of the propagation loss when the thickness of the electrode is changed with respect to the wavelength of the excitation surface acoustic wave is shown. However, in the calculation of FIG. 13, the crystal constant of Warner et al. Is used.

As can be seen from FIG. 13, the propagation loss takes a minimum value once with an increase in the electrode film thickness, and then increases exponentially. It can be seen that the propagation loss is minimized when the electrode film thickness is 3.5% or less. However, in this case, if the electrode film thickness further increases and exceeds 4% of the wavelength of the pumped surface acoustic wave, the propagation loss sharply increases.
On the other hand, when the cut angle of the substrate is set to 66 ° or more, the propagation loss is minimized when the thickness of the electrode is 4% or more of the excited surface acoustic wave, that is, under the condition that the additional mass effect of the electrode becomes remarkable. In other words, under conditions where the electrode thickness is not negligible with respect to the wavelength of the excitation surface acoustic wave such that the electrode thickness normalized by wavelength is 4% or more, the cut angle of the LiNbO ₃ substrate is set to 66 ° or more. It is desirable to set. On the other hand, if the thickness of the electrode is too large, it becomes difficult to pattern the electrode by etching, and the speed of sound in the substrate changes more sensitively to the film thickness of the electrode. It is preferable that the thickness be within 12%. Accordingly, the cut angle of the LiNbO ₃ substrate is 66 °.
It is preferable to set the angle within a range of from 74 ° to 74 °.

In each of the above embodiments, the electrode composition was Al
Although −1% Cu was used, a similar relationship is established with pure Al. When the electrode is formed on the LiTaO ₃ substrate with another electrode material, for example, Au, the thickness of the electrode is in the range of 0.4 to 2.1% of the wavelength, and the thickness of the electrode is Au on the LiNbO ₃ substrate. When an electrode is formed, the thickness of the electrode is preferably set in the range of 0.5 to 1.7% of the wavelength. When an electrode is formed of Cu on a LiTaO ₃ substrate, the wavelength is set in the range of 0.9 to 4.5%. When an electrode is formed of Cu on a LiNbO ₃ substrate, the electrode is formed. Is preferably set in the range of 1.2 to 3.6% of the wavelength.

FIG. 14A shows a modification of the surface acoustic wave filter shown in FIG. 7A, and FIG. 14B shows an equivalent circuit diagram thereof. However, in FIGS. 14A and 14B, the same reference numerals are given to the parts described above, and the description will be omitted.

Referring to FIG. 14A, the surface acoustic wave filter is a LiTaO filter, similarly to the embodiment of FIG.
₃ or LiNbO ₃ single crystal formed on a rotating Y plate,
First comb-shaped electrodes R ₁ where the input-side electrode connected to the input terminal IN, the input-side electrode connected to said output side electrode of the interdigital electrode R _1, which is further connected the output-side electrode to the output terminal OUT 2 comb-shaped electrode R ₁ ′ and the input-side electrode
Is connected to the _first output-side electrode, the 3 _', an input-side electrode interdigital electrode R _1' interdigital electrode R ₂ in which a grounded output-side electrode is connected to the output electrode of which is grounded output-side electrode and a comb-shaped electrodes _{R 2} of the fourth.

Referring to FIG. 14B, the comb-shaped electrode R₁
And R₁′ Are connected in series and the comb-shaped electrode R₂And
And R₂’Are connected in parallel. However, comb-shaped electrode
R₁, R ₁’, R₂, R₂’Each form a transducer
And a comb-shaped electrode R₁’Is R₁About 1/2 of the capacity.
On the other hand, the comb-shaped electrode R₂’Is a comb-shaped electrode R₂About twice the capacity of
Have.

Even in the surface acoustic wave filter having such a configuration, when LiTaO ₃ is used for the substrate, the rotation angle θ is set to 38.
By more than 40 ° and less than 46 °, most preferably about 42 °, and when LiNbO ₃ is used for the substrate, the rotation angle θ is 66 °.
By setting the angle to 74 ° or less, more preferably about 68 °, it is possible to minimize the propagation loss even when used in a frequency band in which the additional mass effect of the electrode on the substrate becomes significant. .

The present embodiment is not limited to the ladder type surface acoustic wave filter described above, but can be applied to other types of surface acoustic wave filters, resonators or propagation delay lines. For example, the lattice filters shown in FIGS. 15A and 15B can be formed by modifying the filters of FIGS. 14A and 14B.

FIG. 16 shows a configuration of a surface acoustic wave filter 30 according to a second embodiment of the present invention. Referring to FIG. 16, the surface acoustic wave filter 30 Y rotation XLiTaO ₃ plates cut angle described above is 38 to 46 ° or over a substrate cut angle is made of Y rotation XLiNbO ₃ plates of 66 to 74 °, When a LiTaO ₃ substrate is used, a comb-shaped electrode having a thickness in the range of ₃ to 15% of the wavelength is formed. When a LiNbO ₃ substrate is used, the thickness of the comb-shaped electrode is in the range of 4 to 12% of the wavelength. Also in this embodiment, LSAW is excited as a surface wave, and the excited surface wave propagates in the X-axis direction.

The surface acoustic wave filter 30 has a configuration in which a pair of comb-shaped electrodes Rin and Rout are disposed adjacent to each other, and a pair of reflectors Re is disposed outside the pair. Also in this configuration, by optimizing the cut angle of the substrate and the film thickness of the electrodes as in the apparatus of FIGS. 7A and 7B, the loss is minimized and the wide passband characteristic with improved squareness is achieved. Is obtained.

FIG. 17 shows a configuration of a surface acoustic wave resonator 40 according to a third embodiment of the present invention.

Referring to FIG. 17, surface acoustic wave resonator 4
0 is the Y rotation X with the previously described cut angle of 38 to 46 °.
LiTaO ₃ plate or Y with a cut angle of 66 to 74 °
Formed on a substrate 11 made of a rotating XLiNbO ₃ plate,
When using a LiTaO ₃ substrate, ₃ to 15% of the wavelength
Is formed. On the other hand, when the LiNbO ₃ substrate is used, the wavelength of 4 to 1 is used.
Comb electrodes having a thickness in the range of 2% are formed. Also in this embodiment, LSAW is excited as a surface wave, and the excited surface wave propagates in the X-axis direction.

The surface acoustic wave filter 40 has a comb-shaped electrode Ro
ut, and a comb-shaped electrode Rin disposed on both sides thereof, and a pair of reflectors Re is disposed outside thereof. At that time, the comb-shaped electrode Rin is connected to the input terminal 41, while the comb-shaped electrode Rout is connected to the output terminal 42.

By optimizing the cut angle of the substrate and the film thickness of the electrode in the same manner as in the apparatus shown in FIGS. 7A and 7B, a resonator having a minimum loss and a high Q factor can be obtained. can get.

FIG. 18 shows a configuration of a one-port surface acoustic wave resonator 50 according to a fourth embodiment of the present invention.

Referring to FIG. 18, surface acoustic wave resonator 5
0 is the Y rotation XL having the cut angle of 38 to 46 degrees described above.
It is formed on a substrate 11 composed of an iTaO ₃ plate or a Y-rotated XLiNbO ₃ plate having a cut angle of 66 to 74 °, and L
When iTaO ₃ is used for the substrate, a comb-shaped electrode having a thickness in the range of ₃ to 15% of the wavelength is formed on the substrate 11. On the other hand, when a LiNbO ₃ substrate is used,
On the substrate 11, a comb electrode having a thickness in the range of 4 to 12% of the wavelength is formed. Also in this embodiment, LSAW is excited as a surface wave, and the excited surface wave propagates in the X-axis direction.

The surface acoustic wave resonator 50 is composed of a single comb-shaped electrode R formed on the substrate and a pair of reflectors Re provided on both sides of the single comb-shaped electrode R. The electrode on one side is connected to the first terminal 51, and the electrode on the other side is connected to the second terminal 52.

By optimizing the cut angle of the substrate and the film thickness of the electrode in the same manner as in the apparatus shown in FIGS. 7A and 7B, a resonator having a minimum loss and a high Q factor can be obtained. can get.

FIG. 19 shows a configuration of a two-port surface acoustic wave resonator 60 according to a fifth embodiment of the present invention.

Referring to FIG. 19, surface acoustic wave resonator 6
0 is the Y rotation XL having the cut angle of 38 to 46 degrees described above.
It is formed on a substrate 11 composed of an iTaO ₃ plate or a Y-rotated XLiNbO ₃ plate having a cut angle of 66 to 74 °, and L
When iTaO ₃ is used for the substrate, a comb-shaped electrode having a thickness in the range of ₃ to 15% of the wavelength is formed on the substrate 11. On the other hand, when a LiNbO ₃ substrate is used,
On the substrate 11, a comb electrode having a thickness in the range of 4 to 12% of the wavelength is formed. Also in this embodiment, LSAW is excited as a surface wave, and the excited surface wave propagates in the X-axis direction. The surface acoustic wave resonator 60 has a pair of comb-shaped electrodes R ₁ and R ₂ connected to an input terminal 61 and an output terminal 62, respectively.
e is provided. The resonator 60 is provided with a _first electrode of the comb-shaped electrode R1.
The first terminal 61 connected to the electrode finger group of FIG.
It is driven by applying a voltage between the second terminal 62 connected to the first electrode finger groups _2. Note that the second of the second electrode fingers group the electrode finger and the comb-shaped electrodes R ₂ comb-shaped electrodes R ₁ is grounded.

By optimizing the cut angle of the substrate and the film thickness of the electrode in the same manner as in the apparatus shown in FIGS. 7A and 7B, a resonator having a minimum loss and a high Q factor can be obtained. can get.

Further, the surface acoustic wave device of the present invention is not limited to the surface acoustic wave filter and the surface acoustic wave resonator described above, but may be applied to a surface acoustic wave delay line or a waveguide having a similar configuration. Useful.

[0069]

According to the first to fifth aspects of the present invention, the loss is minimized by optimizing the cut angle of the LiTaO ₃ substrate with respect to the additional mass of the electrode formed on the substrate surface. Thus, a surface acoustic wave device having a wide bandwidth and an excellent squareness ratio can be obtained.

According to the sixth and seventh aspects of the present invention, the electrodes formed on the surface of the LiTaO ₃ substrate are formed of an Al-based material, so that the electrodes can be easily patterned using an inexpensive material. Becomes possible.

According to the eighth and ninth aspects of the present invention, the loss angle is minimized by optimizing the cut angle of the LiTaO ₃ substrate with respect to the additional mass of the electrode formed on the substrate surface. A surface acoustic wave filter or a resonator having a wide bandwidth and an excellent squareness ratio and having various configurations can be formed.

According to the features of the present invention, by optimizing the cut angle of the LiNbO ₃ substrate with respect to the additional mass of the electrode formed on the substrate surface,
A surface acoustic wave device having a minimum loss, a wide bandwidth, and an excellent squareness ratio can be obtained.

According to the thirteenth and fourteenth features of the present invention, the electrodes formed on the surface of the LiNbO ₃ substrate are formed of an Al-based material, so that the electrodes can be easily patterned using an inexpensive material. Becomes possible.

According to the features of the present invention, the cut angle of the LiNbO ₃ substrate is optimized with respect to the additional mass of the electrode formed on the substrate surface.
Various surface acoustic wave devices having a small loss, a wide bandwidth, and an excellent squareness ratio can be configured.

According to the features of the present invention, the cut angle of the LiNbO ₃ substrate or the LiNbO ₃ substrate is changed to a higher angle side than the conventional one, and furthermore, the LSAW of which the electrode thickness is excited is increased. By optimizing for the wavelength, even when Au or Cu is used as the electrode material, it is possible to minimize the loss of the surface acoustic wave device, improve the bandwidth, and further improve the squareness ratio. Become.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining a cutting angle of a piezoelectric single crystal substrate.

FIG. 2 is a diagram illustrating the principle of the present invention.

FIG. 3 is another diagram illustrating the principle of the present invention.

FIG. 4 shows LiTaO ₃ substrates having various cut angles.
FIG. 4 is a diagram illustrating the temperature dependence of a formed surface acoustic wave filter, particularly the temperature dependence of a center frequency.

FIG. 5 shows LiTaO ₃ substrates having various cut angles.
FIG. 4 is a diagram showing the temperature dependency of a formed surface acoustic wave filter, particularly the temperature dependency of a minimum insertion loss.

FIG. 6 is a diagram showing the propagation loss of a surface acoustic wave filter formed on a LiNbO ₃ substrate as a function of the cut angle of the substrate.

FIGS. 7A and 7B are a diagram illustrating a configuration of a surface acoustic wave filter according to a first embodiment of the present invention and an equivalent circuit diagram thereof, respectively.

8 is a diagram illustrating a relationship between a minimum insertion loss of the surface acoustic wave filter of FIG. 7 and a cut angle of a piezoelectric substrate forming the filter.

9A is a diagram illustrating the definition of the squareness ratio in the filter passband characteristic, and FIG. 9B is a diagram illustrating the relationship between the squareness ratio and the substrate cut angle.

FIG. 10 is a diagram illustrating pass band characteristics of the filters shown in FIGS. 7 (A) and 7 (B).

FIG. 11 is a diagram illustrating a relationship between a substrate cut angle and an electromechanical coupling coefficient when a LiTaO ₃ substrate is used in the filters illustrated in FIGS. 7A and 7B.

FIG. 12 is a diagram showing the effect of electrode film thickness on propagation loss when using a LiTaO ₃ substrate in the filters shown in FIGS. 7A and 7B for various substrate cut angles.

FIG. 13 is a diagram showing the effect of electrode thickness on propagation loss when using a LiNbO ₃ substrate in the filters shown in FIGS. 7A and 7B for various substrate cut angles.

FIGS. 14A and 14B are a diagram illustrating a configuration of a surface acoustic wave filter according to a modification of the first embodiment of the present invention, and an equivalent circuit diagram thereof, respectively.

FIG. 15 is an equivalent circuit diagram of a surface acoustic wave filter according to a modification of FIG.

FIG. 16 is a diagram showing a configuration of a surface acoustic wave filter according to a second embodiment of the present invention.

FIG. 17 is a diagram showing a configuration of a surface acoustic wave resonator according to a third embodiment of the present invention.

FIG. 18 is a diagram showing a configuration of a one-port surface acoustic wave resonator according to a fourth embodiment of the present invention.

FIG. 19 is a diagram showing a configuration of a two-port surface acoustic wave resonator according to a fifth embodiment of the present invention.

FIG. 20 is a diagram illustrating an example of pass band characteristics of a conventional surface acoustic wave device.

[Explanation of symbols]

10,30,40,50,60 surface acoustic wave element 11 piezoelectric substrate 31, 41, 51, 61 input terminals 32, 42, 52, 62, the output terminal _{R 1, R 1 ', R} 2, R 2' comb electrodes Re Reflector

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Tsuyoshi Endo 4-1-1, Uedanaka, Nakahara-ku, Kawasaki-shi, Kanagawa Prefecture Inside Fujitsu Limited (72) Inventor Osamu Igata 4-chome, Kamiodanaka, Nakahara-ku, Kawasaki-shi, Kanagawa Prefecture No. 1 Fujitsu Limited (72) Inventor Kenya Hashimoto 4-31-1, Futawanishi, Funabashi City, Chiba Prefecture (72) Inventor Masanori Yamaguchi 3-10-4, Miyanodai, Sakura City, Chiba Prefecture

Claims (20)

[Claims] 1. A surface acoustic wave device comprising a piezoelectric substrate and an electrode pattern mainly composed of Al formed on the surface of the piezoelectric substrate, wherein the electrode pattern includes a resonator for exciting an LSAW on the surface of the piezoelectric substrate. The electrode pattern has a wavelength of 0.03-0.
The piezoelectric substrate has a thickness in the range of 15;
_{The three} single crystals are arranged in a direction from the Y axis to the Z axis around the X axis.
A surface acoustic wave device having an azimuth rotated at an angle in a range of 46 °. 2. The surface acoustic wave device according to claim 1, wherein the electrode pattern forms a plurality of resonators on the surface of the piezoelectric substrate. 3. The electrode pattern according to claim 1, wherein the electrode pattern has a thickness in the range of 0.07 to 0.15 of the wavelength of the surface acoustic wave excited on the piezoelectric substrate. Surface acoustic wave device. 4. The electrode pattern has a thickness in a range of 0.05 to 0.10 of a wavelength of a surface acoustic wave excited on the piezoelectric substrate, and the piezoelectric substrate is made of LiTaO ₃ single crystal. 4. The elasticity according to claim 1, wherein the elastic member has an azimuth rotated about 40 degrees to 44 degrees from the Y axis to the Z axis around the X axis. Surface wave device. 5. The piezoelectric substrate according to claim 1, wherein the LiTaO ₃ single crystal has an orientation obtained by rotating the LiTaO ₃ single crystal at an angle in a range of 42 ° from the Y axis to the Z axis around the X axis. The surface acoustic wave device according to claim 1. 6. The surface acoustic wave device according to claim 1, wherein the electrode pattern forms a multi-mode filter on the piezoelectric substrate. 7. The surface acoustic wave device according to claim 1, wherein the electrode pattern is made of an Al—Cu alloy. 8. The surface acoustic wave device according to claim 1, wherein the resonator is connected in a ladder type. 9. A surface acoustic wave filter comprising a piezoelectric substrate and an electrode pattern mainly composed of Al formed on the surface of the piezoelectric substrate, wherein the electrode pattern includes a resonator for exciting an LSAW on the surface of the piezoelectric substrate. Wherein the electrode pattern has a wavelength of 0.03 to
Said piezoelectric substrate has a thickness in the range of 0.15;
The TaO ₃ single crystal has an orientation rotated about the X axis from the Y axis in the Z axis direction at an angle in the range of 39 to 46 °; the electrode pattern includes a comb-shaped electrode. Surface acoustic wave filter. 10. A surface acoustic wave device comprising a piezoelectric substrate and an electrode pattern mainly composed of Al formed on the surface of the piezoelectric substrate, wherein the electrode pattern excites LSAW on the surface of the piezoelectric substrate, The piezoelectric substrate has a thickness in the range of 0.04 to 0.12 of the wavelength of the LSAW obtained; the piezoelectric substrate is formed by depositing a LiNbO ₃ single crystal at 66 to 74 ° from the Y axis to the Z axis around the X axis. A surface acoustic wave device having an azimuth rotated by an angle in the range of. 11. The piezoelectric substrate according to claim 1, wherein the piezoelectric substrate has an orientation obtained by rotating the LiNbO ₃ single crystal at an angle in the range of 68 to 72 ° from the Y axis to the Z axis around the X axis. The surface acoustic wave device according to claim 10, wherein 12. The electrode pattern according to claim 10, wherein the electrode pattern has a thickness in the range of 0.05 to 0.10 of the wavelength of the surface acoustic wave excited on the piezoelectric substrate.
2. The surface acoustic wave device according to claim 1. 13. The surface acoustic wave device according to claim 10, wherein the electrode pattern is made of Al. 14. The surface acoustic wave device according to claim 10, wherein the electrode pattern is made of an Al—Cu alloy. 15. The elasticity according to claim 1, wherein the electrode pattern forms a ladder-type filter using a plurality of resonators on the surface of the piezoelectric substrate. Surface wave device. 16. The resonator according to claim 10, wherein the electrode pattern forms a resonator on the surface of the piezoelectric substrate.
15. The surface acoustic wave device according to claim 14. 17. A surface acoustic wave device comprising a piezoelectric substrate and an electrode pattern mainly composed of Au formed on the surface of the piezoelectric substrate, wherein the electrode pattern excites LSAW on the surface of the piezoelectric substrate, The pattern has a thickness in the range of 0.004 to 0.021 of the wavelength of the excited LSAW; the piezoelectric substrate comprises a LiTaO ₃ single crystal in a direction from the Y axis to the Z axis around the X axis. A surface acoustic wave device having an azimuth rotated at an angle in the range of 39 to 46 °. 18. A surface acoustic wave device comprising a piezoelectric substrate and an electrode pattern mainly composed of Cu formed on the surface of the piezoelectric substrate, wherein the electrode pattern excites an LSAW on the surface of the piezoelectric substrate, The pattern has a thickness in the range of 0.009-0.045 of the wavelength of the excited LSAW; the piezoelectric substrate comprises a LiTaO ₃ single crystal in which the X-axis is centered and the Y-axis is in the Y-axis direction. A surface acoustic wave device having an azimuth rotated at an angle in the range of 39 to 46 °. 19. A surface acoustic wave device comprising a piezoelectric substrate and an electrode pattern mainly composed of Au formed on the surface of the piezoelectric substrate, wherein the electrode pattern excites an LSAW on the surface of the piezoelectric substrate, The pattern has a thickness in the range of 0.005 to 0.017 of the wavelength of the excited LSAW; the piezoelectric substrate comprises a single crystal of LiNbO _{3 in} a direction from the Y axis to the Z axis around the X axis. A surface acoustic wave device having an azimuth rotated at an angle in the range of 66 to 74 °. 20. A surface acoustic wave device comprising a piezoelectric substrate and an electrode pattern mainly composed of Cu formed on the surface of the piezoelectric substrate, wherein the electrode pattern excites an LSAW on the surface of the piezoelectric substrate, The pattern has a thickness in the range of 0.012 to 0.036 of the wavelength of the excited LSAW; the piezoelectric substrate comprises a single crystal of LiNbO _{3 in} a direction from the Y axis to the Z axis around the X axis. A surface acoustic wave device having an azimuth rotated at an angle in the range of 66 to 74 °.