CN1016032B - Surface acoustic wave device - Google Patents

Abstract

The interdigital transducers 3, 4 and the reflectors 5, 6 are formed on the piezoelectric substrate 2 with an aluminum film. The aluminum film is oriented in a certain direction in terms of crystal orientation. And thus, the stress migration of the aluminum film can be suppressed.

Description

The present invention relates to a surface acoustic wave device, and more particularly to a surface acoustic wave device in which electrodes made of aluminum are formed on a piezoelectric substrate.

Surface acoustic wave devices widely used in recent years are surface acoustic wave devices such as filters and resonators using surface acoustic waves (hereinafter, may be abbreviated as SAW).

In these surface acoustic wave devices, interdigital electrodes and/or grating electrodes composed of a plurality of metal strips arranged in parallel are generally formed on the surface of a piezoelectric substrate.

The material used for the piezoelectric substrate can be crystal, single crystal such as lithium tantalate (LiTaO ₃ ), lithium niobate (LiNbO ₃ ), lithium tetraborate (Li ₂ B ₄ O ₇ ), or sapphire (Al ₂ O ₃ ) ZnO/Al ₂ O ₃ etc. on which zinc oxide (ZnO) is formed on the substrate.

Also, aluminum is generally used as a metal for forming the above-mentioned interdigital electrodes and grid electrodes. The reason why aluminum is used in this way is that it is easy to photolithography, its specific gravity is small so that the electrode loading mass effect is small, and its electrical conductivity is high.

However, it has been found that when a signal of a high voltage level is applied to a surface acoustic wave device such as a SAW filter or a SAW resonator, the aluminum electrode is subjected to strong stress due to the action of the surface acoustic wave device and migration occurs. Since this migration is caused by stress, it is called stress migration in order to distinguish it from electromigration. If this phenomenon occurs, it will cause an electrical short circuit, an increase in insertion loss, and a decrease in the Q value of the resonator. Furthermore, since stress migration occurs more easily at higher frequencies, it becomes a serious problem especially in surface acoustic wave devices used at high frequencies.

Especially for the harmonic oscillator, in order to use it to generate stable oscillation, it is necessary to increase the gain of the oscillation circuit to increase the voltage level Very high signal. In the resonator with reflectors arranged on both sides of the transducer, the surface wave is trapped between the reflectors, and standing waves are added to the transducer and reflector, so strong stress is applied to them. For this reason, in the case of a resonator, stress migration is particularly likely to occur. Therefore, in the existing SAW resonator, in order to suppress the phenomenon of stress migration as much as possible, it is necessary to make it work at a low voltage level, so that the C/N ratio (carrier-to-noise ratio) cannot be improved or the SSB phase noise can be suppressed. .

Also, for SAW filters, particularly in filters for transmission, since a signal of a high voltage level is applied, stress migration is likely to occur.

A countermeasure to prevent the above-mentioned stress migration is to add a small amount of Cu, Ti, Ni, Mg, Pd, etc. to the aluminum of the electrode material, but the effect is still not satisfactory.

Also, recently, an approximately 105° rotation Y-cut (LST cut) crystal substrate has attracted attention as a substrate of a surface acoustic wave device having good temperature characteristics. A surface acoustic wave device using such an LST-cut crystal substrate is a device in which a leaky surface acoustic wave (LSAW) propagates along the surface of its substrate, and is characterized by having better temperature characteristics than a surface acoustic wave device with an ST-cut crystal substrate.

However, when an ST-cut crystal substrate is used, no particular problem occurs even if the thickness of the aluminum electrode is set to about 2% of the wavelength of the surface acoustic wave. On the contrary, when an LST-cut crystal plate is used, it is known that Making the aluminum electrode thicker than 1% of the wavelength causes a drastic drop in the Q value and deteriorates the characteristics in, for example, a resonator. When reducing the thickness of the aluminum electrode on the LST cut crystal substrate in order to avoid such deterioration of characteristics, in the conventional polycrystalline aluminum, the apparent electrical resistivity becomes large due to the large volume of aluminum crystal grains forming the electrode. Large, thus causing an increase in insertion loss or a decrease in Q value. Such disadvantages are particularly noticeable in the high-frequency range where the wavelength becomes shorter.

Therefore, the inventors of the present invention refer again to the cause of the stress migration mentioned above. As a result, it was found that aluminum to be an electrode formed by electron beam evaporation, sputtering, etc. is not oriented in a fixed direction crystallographically, but is in an amorphous polycrystalline state. Therefore, it is considered that stress migration due to grain boundary diffusion easily occurs in such an aluminum electrode.

Therefore, an object of the present invention is to provide a surface acoustic wave device including an aluminum electrode that hardly causes stress migration.

The present invention is directed to a surface acoustic wave device including a piezoelectric substrate and electrodes formed on the piezoelectric substrate to constitute, for example, a transducer, wherein the electrodes include an aluminum film oriented in a certain direction in crystal orientation.

In this way, it is considered that an aluminum film whose crystal axes are oriented in a certain direction exhibits properties similar to those of a single crystal film. Therefore, such an aluminum film hardly causes stress migration. Therefore, according to this invention, an electrical short circuit and an increase in insertion loss due to stress migration can be prevented. Also, when the present invention is applied to a harmonic oscillator, it can prevent its Q value from decreasing due to stress migration. Therefore, the lifetime of the surface acoustic wave device can be extended by suppressing the occurrence of stress migration.

Also, in general, the higher the frequency of stress migration, the more prominent it is. However, according to the present invention, since the occurrence of such stress migration can be suppressed, the high-frequency characteristics of the surface acoustic wave device can be well maintained.

Also, according to the present invention, the occurrence of stress migration can be suppressed even when a signal of a high voltage level is applied. Therefore, the surface acoustic wave device according to the present invention can be practically used even in a circuit with a high signal level. Therefore, when the present invention is applied to a surface acoustic wave resonator, since a signal of a high voltage level can be applied without any problem, the C/N ratio can be increased and the SSB phase noise can be reduced. Furthermore, since the resonator can be used in a state where the gain is large and overexcited, the resonator can be stably oscillated. In addition, the present invention can be suitably applied to a filter for transmitting a high-voltage signal.

As piezoelectric substrates, single crystal substrates such as crystal substrates, lithium tantalate LiTaO ₃ substrates, lithium niobate LiNbO ₃ substrates, lithium tetraborate Li ₂ B ₄ O ₇ substrates, or sapphire (Al ₂ O ₃ ) substrates are used. A ZnO/Al ₂ O ₃ substrate with a ZnO thin film epitaxially grown on it is better.

When using a crystal substrate as the piezoelectric substrate, it is preferable to use a rotary Y-cut crystal substrate. When using a crystal substrate as the piezoelectric substrate in this way, the aluminum film may be a (311) oriented film.

In the case of cutting the crystal substrate with the rotation Y, a better embodiment is that the rotation angle of the rotation Y-cut crystal can be selected in the range of 25°-39°.

Another preferred embodiment is that the rotation angle of the rotated Y-cut crystal for the substrate can be selected in the range of 103°-107°. It is therefore possible to provide a surface acoustic wave device in which a leaky surface acoustic wave propagates on a substrate. At this time, the aluminum film whose crystal axis points to a certain direction exhibits properties close to that of a single crystal film, and since it is not a collection of crystal grains, it can maintain good electrical conduction even when its thickness is very thin. Therefore, it is possible for a surface acoustic wave device using an LST-cut crystal substrate to exhibit its inherently good temperature characteristics. In particular, it is significant in the high-frequency field, and a surface acoustic wave device using an LST-cut crystal substrate and used in the high-frequency field can be realized.

When using a Li ₂ B ₄ O ₇ substrate as a piezoelectric substrate, it is better to use a 45° rotation X to cut the substrate.

Adding a trace amount of additives such as Cu, Ti, Ni, Mg, and Pd to the aluminum film is effective for further suppressing migration. The amount of this additive can be selected within the range of 0.1% by weight to 10% by weight.

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

FIG. 2 shows the transmission characteristics of the 50Ω system of the surface acoustic wave device shown in FIG. 1 .

FIG. 3 is a circuit diagram of a device used to evaluate the electric resistance characteristic of a surface acoustic wave device.

FIG. 4 is a graph showing a graph used to determine the end of life due to stress migration.

FIG. 5A is a photo obtained by reflection high-enery electron diffraction of an aluminum film according to an embodiment of the present invention.

FIG. 5B is an explanatory view of FIG. 5A.

6A is a photograph obtained by reflection high-speed electron diffraction of an aluminum film according to a comparative example.

FIG. 6B is an explanatory view of FIG. 6A.

FIG. 7A is a photograph obtained by reflective high-speed electron diffraction of an aluminum film according to another embodiment of the present invention.

FIG. 7B is an explanatory view of FIG. 7A.

Fig. 8 is a graph showing the relationship between the film thickness of the aluminum electrode and its resistivity in the example shown in Fig. 7A.

Referring to FIG. 1 , a surface acoustic wave device 1 includes a piezoelectric substrate 2 . On the surface of the piezoelectric substrate 2, for example, two interdigital transducers 3 and 4 and two reflectors 5 and 6 positioned to sandwich these transducers 3 and 4 are formed. The IDT 3 is provided with a pair of interdigital electrodes 7 and 8 . The electrode fingers provided on the interdigital electrode 7 partially face the electrode fingers provided on the interdigital electrode 8 . On the other hand, the interdigital transducer 4 is provided with a pair of interdigital electrodes 9 and 10 . The electrode fingers provided on the interdigital electrode 9 are partially opposed to the electrode fingers provided on the interdigital electrode 10 . The interdigital electrodes 7, 8, 9 and 10 are connected to lead terminals 11, 12, 13 and 14, respectively.

The reflectors 5 and 6 are formed by grid electrodes provided with a plurality of parallel parallel metal strips 15 and 16, respectively.

Such a surface acoustic wave device 1 can be used not only as a 2-port SAW resonator, but also as a 2-port SAW filter. In the case of a SAW resonator, either one of the transducers 3 and 4 can be omitted to form a 1-port SAW resonator. Also the reflectors 5 and 6 may not be formed by metal strips but given by a plurality of grooves formed on the piezoelectric substrate. In the case of a SAW filter, either one of the transducers 3 and 4 may be used as an input transducer and the other as an output transducer. In the case of a filter, the reflectors 5 and 6 can also be omitted. And it can also be composed of more than three transducers.

Next, details of the surface acoustic wave device 1 shown in FIG. 1 will be described in the order of its manufacture.

A 33.5°-rotated Y-cut crystal substrate after mirror grinding was used as the piezoelectric substrate 2.

On the surface of the piezoelectric substrate 2, about 1000 The thickness of the aluminum film is formed.

/秒且基板2的温度设定为80℃时，得到了（311）取向的铝膜。When forming the above-mentioned aluminum film, the evaporation rate and the temperature of the substrate 2 were usually selected to be 10 /sec and +160°C, compared with such conditions, by making the vapor deposition rate higher and the temperature of the substrate 2 lower, it is possible to orient the aluminum film in a certain direction in terms of crystal orientation. According to the experiments carried out by the inventor, the evaporation speed was set to 40

/s and the temperature of the substrate 2 is set at 80°C, a (311)-oriented aluminum film is obtained.

The epitaxial growth of the (311) plane of the aluminum film has been confirmed by the reflection high-speed electron diffraction (RHEED) method. Fig. 5A is a photograph obtained by such a RHEED method. FIG. 5B is an explanatory view of FIG. 5A.

In FIG. 5B, 17 is a direct spot of electron beams, and what is seen in the area 18 is a reflection pattern. As shown in FIGS. 5A and 5B in the reflection pattern, spots appear because of periodicity in the crystal structure. From this point, it can be confirmed that the obtained aluminum film is growing epitaxially.

On the other hand, it has been confirmed that at the above vapor deposition rate of 10 /s and the substrate temperature is +160°C, the aluminum film evaporated does not undergo epitaxial growth, but becomes random orientation (amorphous). The RHEED photo of this comparative example is Fig. 6A. FIG. 6B is an explanatory view of FIG. 6A.

In FIG. 6B, 19 is a direct spot of the electron beam, and what is seen in the region 20 is a reflection pattern. No spots of electron rays appear on this reflection pattern. The reflection patterns in the area 20 are in the shape of rings or halos. When a ring-shaped or halo-shaped reflection pattern is obtained in this way, it can be judged that the aluminum film is polycrystalline or amorphous.

Next, each of the Examples and Comparative Examples of the present invention was subjected to the following processing.

That is, by processing the aluminum film by photolithography, two interdigital transducers 3 and 4 and reflectors 5 and 6 composed of grid electrodes are formed on the surface of the piezoelectric substrate 2 as shown in FIG. 1 .

In the SAW device 1 thus obtained, the wavelength of the SAW is about 4.7 μm, the width of the electrode fingers is about 1.17 μm, and the length of the aperture is about 100 wavelengths. In Fig. 1, although the illustration is simplified, actually the interdigitated electrodes 7, 8, 9 and 10 included in the transducers 3 and 4 are provided with 50 electrode fingers respectively, and the reflectors 5 and 6 are respectively provided with 50 electrode fingers. 300 gold genus.

The 50Ω series transmission characteristics of the 2-port SAW resonator 1 of this embodiment thus obtained are shown in FIG. 2 . It can be seen from Figure 2 that the peak value of the attenuation appears at a frequency of about 674 MHz, and the insertion loss at this peak frequency is about 6 decibels dB. The vertical axis on the left in Fig. 2 represents the relative attenuation, and the insertion loss at the peak frequency is zero dB. The SAW resonator of the comparative example also showed substantially the same characteristics as those shown in FIG. 2 .

Next, using the apparatus shown in FIG. 3 , the withstand power characteristics, ie, the stress migration suppression characteristics in each of the Examples and Comparative Examples were evaluated. In the device shown in FIG. 3 , the output of the oscillator 21 is amplified by the power amplifier 22 , and the output of the power amplifier 22 is added to the SAW resonator 1 . The output P(t) of the SAW resonator 1 is input to the power meter 23, and its output level is measured there. The output of the power meter 23 is fed back to the oscillator 21 via the computer 24, and the frequency of the oscillator 21 is controlled accordingly, so that the frequency of the signal applied to SAW1 is always the peak frequency in the transmission characteristic. The SAW resonator 1 is placed in the constant temperature bath 25 so that the ambient temperature of the SAW resonator 1 is as high as 85°C. This is to give the SAW resonator 1 a condition for increasing the speed at which the SAW resonator 1 deteriorates.

In this way, the output of the power amplifier 22 is 1W (50Ω series), the initial output level Po is measured in advance, and the output P(t) after a certain time t is P(t)≤Po-1(dB) is the lifetime td of the SAW resonator 1 . This is because it is generally considered that the curve of P(t) will be as shown in FIG. 4 . Therefore, it is appropriate to estimate the time when the initial output Po decreases by 1 dB as the life td.

The evaluated samples A, B, and C are samples in which the interdigital transducers 3 and 4 and the reflectors 5 and 6 are composed of aluminum films as shown below, respectively.

A: Randomly oriented pure aluminum

B: Randomly oriented pure aluminum + 1Wt% copper

C: epitaxially grown pure aluminum

Samples A and B are samples corresponding to comparative examples of the present invention. Here, sample B is a sample to which copper having an effect of inhibiting migration was added. On the other hand, sample C is a sample corresponding to an example of the present invention.

In Samples A, B, and C, crystal substrates with the same cut angle were used as piezoelectric substrates, and the patterns of transducers and reflectors were also the same.

When the life td of each sample is evaluated with the device shown in Fig. 3, then:

A: Below 5 points

B: About 150 points

C: More than 900 points.

Here, if samples A and B are compared, the service life can be increased by more than 30 times by adding copper, and if samples B and C are compared, the service life can be further improved by making the aluminum film epitaxial growth More than 6 times. In other words, when samples A and C using pure aluminum are compared, it can be seen that sample C indeed achieves a lifetime exceeding 180 times that of sample A.

Next, the addition of copper is also applicable to sample C, because it has been confirmed by sample B that such addition of copper has the effect of inhibiting migration. That is, a sample identical to sample C was produced except that an aluminum epitaxial growth film added with 1 wt % of copper was formed. With regard to this sample, since it is known that the life is too long when the power of 1W is applied, it is not suitable for the experiment, so the power of 2.5W is applied. Based on this, it has been confirmed that the life span of 8000 points or more can be achieved. Generally, the acceleration coefficient due to power is said to be 3 to 4 powers, so the acceleration coefficient in the case of 2.5W is 2.5 ³ to 2.5 ⁴ times that of 1W, that is, about 15 to 39 times. Therefore, if the lifetime of 8,000 minutes or more is converted to 1W at 2.5W, the lifetime is equivalent to about 120,000 to 312,000 minutes or more.

In this way, when copper is added to the aluminum epitaxial growth film, it is possible to obtain a lifetime approximately 130 to 340 times that of the pure aluminum epitaxial growth film. It is known that adding additives such as titanium Ti, nickel Ni, magnesium Mg, and palladium Pd in addition to copper has the same effect of extending the life. If the addition amount of such an additive is too small, there will be no substantial effect. Therefore, it is usually necessary to add more than 0.1wt%, and if it is too much, the resistivity of the aluminum film will increase, so it is usually better to be below 10wt%.

It is also possible to form a very thin titanium Ti film or chromium Cr film on the piezoelectric substrate in advance as the substrate of the aluminum orientation film, which is so thin that it does not hinder its orientation.

The aluminum epitaxial growth film has a (311) orientation on a 25° to 39° rotated Y-cut crystal substrate, and can also be oriented on crystal substrates with other cut angles.

In general, for epitaxial growth of an aluminum film, the lattice between the substrate and the aluminum film must be matched to each other. Between the rotated Y-cut crystal substrate and the aluminum film, since the (311) plane of the about 30° rotated Y-cut crystal substrate and the aluminum epitaxial growth film matches on the lattice, the aluminum on the 25° to 35° rotated Y-cut crystal substrate The film is oriented on the (311) plane and grown epitaxially. However, the (311) plane of the aluminum epitaxial growth film is not necessarily parallel to the surface of the crystal substrate. When the cut plane of the crystal substrate deviates from the above angle, the orientation of the (311) plane of the aluminum epitaxial growth film is inclined with the cut plane of the crystal substrate. Therefore, in the case of other rotary cutting angles, the orientation of the corresponding aluminum film can also be determined. direction, and therefore the crystal substrate is not particularly limited to the rotational Y cut. For example, when the crystal is cut by two rotations, the (311) plane of the aluminum film can be epitaxially grown in a direction that basically satisfies the lattice matching condition.

In connection with this, a SAW device 1 as shown in FIG. 1 can be obtained by using a mirror-polished 105° rotation cut (LST cut) crystal substrate as a piezoelectric substrate and performing the same treatment as in the above-mentioned embodiment. On the contrary, the 105° rotary cut crystal substrate used here has the advantages of good temperature characteristics as mentioned above, but the Q value of the resonator may also decrease when the thickness of the aluminum electrode formed on it becomes 1% or more of the wavelength of the SAW. shortcoming.

（波长的约0.7%）的铝膜。并可用RHEED法确认，此铝膜正在外延生长。图7A为所得到的铝膜的RHEED照片。图7B为图7A的说明图。Such a crystal substrate is used as the piezoelectric substrate 2 shown in FIG. 1, and a thickness of about 400 is formed on the piezoelectric substrate by the same electron beam evaporation conditions as in the above-mentioned embodiment.

(approximately 0.7% of the wavelength) of the aluminum film. It was confirmed by the RHEED method that the aluminum film was growing epitaxially. Fig. 7A is a RHEED photograph of the obtained aluminum film. FIG. 7B is an explanatory view of FIG. 7A.

In Fig. 7B, 26 denotes a direct irradiation spot of an electron beam. A reflective pattern appears on the area 27 . In this reflection pattern, spots indicating epitaxial growth of the aluminum film can be confirmed.

Next, the aluminum film obtained as described above was processed by photolithography to fabricate a 2-port SAW resonator 1 as shown in FIG. 1 . This resonator 1 is the same as the above embodiment except that the wavelength of the SAW is about 5.9 μm, the width of the electrode fingers is 1.47 μm, and the number of grid electrode metal strips constituting the reflectors 5 and 6 is 500.

The characteristics shown by this SAW resonator 1 are substantially the same as those shown in FIG. 2 .

Next, using the apparatus shown in FIG. 3, the lifetime was evaluated in the same manner as in the above-mentioned examples.

First, for a sample in which transducers 3 and 4 and reflectors 5 and 6 were formed by epitaxial growth of pure aluminum film, a lifetime of 800 minutes or more was obtained when a power of 1 W was applied. Also with respect to the sample that has formed transducer 3 and 4 and reflector 5 and 6 from the epitaxial growth aluminum film that adds 1Wt% copper, because life-span is too long when adding 1W power and is not suitable for carrying out experiment, so add up to 2.5W of power. Accordingly, the life of the sample reached 7000 minutes or more. When this life is converted to 1 W based on the above-mentioned acceleration coefficient, the life is equivalent to about 105,000 to 273,000 minutes or more.

Same as the above-mentioned embodiment, when adding copper to the aluminum epitaxial growth film, the amount of copper added is preferably between 0.1wt% and 10wt%. Furthermore, instead of adding copper, Ti, Ni, Mg, Pd, etc. may be added.

厚度形成随机取向的铝膜，得到了同样2端口SAW谐振子。但是此谐振子的插入损失大且完全没能显示2端口SAW谐振子本来所具有的特性。As a comparative example, cut the crystal substrate as a piezoelectric substrate with the same LST as that used in the above-mentioned embodiments, and use the same 400

The thickness of the randomly oriented aluminum film is obtained, and the same 2-port SAW resonator is obtained. However, the insertion loss of this resonator is large, and the characteristics originally possessed by the 2-port SAW resonator cannot be exhibited at all.

），在纵轴上表示电阻率（Ω·cm）。又实线为铝外延生长膜的场合，虚线为铝随机取向膜的场合。Therefore, the relationship between the thickness of each film and the resistivity was studied for the aluminum epitaxial growth film and the aluminum random orientation film. As a result, the results shown in FIG. 8 were obtained. In Figure 8, the film thickness is represented on the horizontal axis (

), and the resistivity (Ω cm) is represented on the vertical axis. Also, the solid line represents the case of an aluminum epitaxially grown film, and the dotted line represents the case of an aluminum randomly oriented film.

As shown in Figure 8, in the case of aluminum epitaxial growth film (solid line), even if the film thickness is 400 , can also maintain low resistivity. On the contrary, in the case of aluminum random orientation film (dotted line), at a film thickness of 400 , the resistivity shown is already very large. The reason for this is considered to be that since the aluminum random orientation film is composed of aggregates of crystal grains, when the film thickness is small, the film has an island-like structure and good electrical conductivity cannot be achieved.

In the above description, a crystal substrate is used as the piezoelectric substrate. Moreover, LiTaO ₃ substrates, LiNbO ₃ substrates, LiB ₄ O ₇ substrates, ZnO/Al ₂ O ₃ substrates, etc. can also be used as piezoelectric substrates. Even on these latter piezoelectric substrates, an aluminum alignment film can be formed by appropriately selecting the film-forming conditions and/or film-forming methods (for example, methods such as ion beam sputtering and ion plating) of aluminum. In these cases, it may be an aluminum epitaxial growth film, and may not be limited to a (311) oriented film. In conclusion, the crystallographic orientation of the Al epitaxially grown film was determined to satisfy the conditions for each lattice match between the Al film and the substrate.

In particular, if a _LiT2O3 substrate _{, LiNb2O3} substrate or _{Li2B4O7 substrate} with a large electromechanical coupling coefficient is used, it is compared with _{the case} of using a crystal substrate. A SAW filter with wide passband and low loss and a harmonic oscillator with small capacity ratio can be realized. Especially if the Li ₂ B ₄ O ₇ substrate is cut with a 45° rotation, a SAW device with zero temperature coefficient can be realized.

Claims (15)

1. A surface acoustic wave device, comprising: Piezoelectric substrate; An electrode device formed on the above-mentioned piezoelectric substrate; It is characterized by: The above-mentioned electrode device includes an aluminum film oriented in a certain direction in a crystal orientation, and the above-mentioned aluminum film is a (311) oriented film. 2. A surface acoustic wave device, comprising: Piezoelectric substrate; Electrode device formed on the above piezoelectric substrate: It is characterized by: The above-mentioned electrode device includes an aluminum film oriented in a certain direction in a crystal orientation, and the above-mentioned aluminum film is a (311) oriented film and is epitaxially grown. 3. The surface acoustic wave device according to claim 1 or 2, wherein the piezoelectric substrate is a rotating Y-cut crystal substrate. 4. The surface acoustic wave device according to claim 3, wherein the rotation angle of said rotating Y-cut crystal is 25° to 39°. 5. The surface acoustic wave device according to claim 1 or 2, wherein the piezoelectric substrate is a LiTaO ₃ substrate. 6. The surface acoustic wave device according to claim 1 or 2, wherein the piezoelectric substrate is a LiNbO ₃ substrate. 7. The surface acoustic wave device according to claim 1 or 2, wherein the piezoelectric substrate is a Li ₂ B ₄ O ₇ substrate. 8. The surface acoustic wave device according to claim 7, wherein the Li ₂ B ₄ O ₃ substrate is a 45° spin cut substrate. 9. The surface acoustic wave device according to claim 1 or 2, wherein the piezoelectric substrate includes a sapphire substrate and a ZnO thin film epitaxially grown on the sapphire substrate. 10. The surface acoustic wave device according to claim 1 or 2, wherein the aluminum film contains an additive consisting of at least one selected from the group consisting of Cu, Ti, Ni, Mg and Pd. 11. The surface acoustic wave device according to claim 10, wherein said additive is contained in said aluminum film at 0.1% by weight to 10% by weight. 12. The surface acoustic wave device according to claim 3, characterized in that the rotation angle of the above-mentioned rotating Y-cut crystal is 103-107° 13. A surface acoustic wave harmonic oscillator, comprising: Piezoelectric substrate: and At least one transducer formed on the piezoelectric substrate and at least two reflectors positioned to sandwich the transducer. It is characterized by: The transducer includes an aluminum film oriented in a certain direction in terms of crystal orientation, and the aluminum film is a (311) oriented film. 14. The surface acoustic wave device according to claim 13, wherein said reflector includes an aluminum film oriented in a certain direction in terms of crystal orientation. 15. A surface acoustic wave filter, comprising Piezoelectric substrate: input and output transducers formed on the aforementioned piezoelectric substrate; It is characterized by: The above-mentioned input and output transducers contain an aluminum film oriented in a certain direction in terms of crystal orientation, and the above-mentioned aluminum film is a (311) oriented film.

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