JP4581099B2 - Surface acoustic wave device - Google Patents

Description

  The present invention relates to a surface acoustic wave device.

  The current communication system is premised on the use of a highly selective filter in order to realize high-reliability and high-speed information transmission in a limited frequency resource. It is no exaggeration to say that it is used in large numbers and is now indispensable to dominate the performance of communication equipment.

  In general, a surface acoustic wave device has a pair of reflectors and an interdigital transducer disposed between the pair of reflectors formed on a piezoelectric substrate. A surface acoustic wave (hereinafter referred to as “SAW”) is excited, and the SAW is reflected between a pair of reflectors to generate a resonance wave having a desired frequency. This resonance wave is SAW generated in a direction parallel to the surface of the piezoelectric substrate (Shear Horizontal type SAW, hereinafter referred to as “SH type SAW”).

  However, such a surface acoustic wave device can generate a resonance wave having a desired frequency, but an unnecessary response may impede its characteristics. As this unnecessary response, there is a Rayleigh type SAW (hereinafter referred to as “Rayleigh type SAW”). A Rayleigh-type SAW is a SAW that is generated and vibrates in a direction perpendicular to the surface of the piezoelectric substrate.

  In the case of a Rayleigh-type SAW, unnecessary responses may be suppressed by appropriately selecting the orientation when cutting out the piezoelectric substrate, the thickness of the electrode formed on the piezoelectric substrate, and the like. However, when the surface acoustic resonators having various resonance frequencies are arranged for the filter characteristics, it is difficult to suppress the Rayleigh type SAW at the same time only with these. In addition, since the performance of the surface acoustic wave device is governed by the substrate to be used, if the direction of cutting out only for the purpose of suppressing the Rayleigh SAW is determined, the performance obtained for the SH SAW is reduced. May also cause problems.

  Therefore, an object of the present invention is to provide a surface acoustic wave device that solves the above problems and suppresses the influence on the SH type SAW while efficiently suppressing the Rayleigh type SAW.

  As a result of intensive studies on the above problems, the present inventors have conceived that Rayleigh-type SAW can be suppressed by disposing an organic layer on an elastic surface resonator, and the present invention has been completed. It was.

  That is, a surface acoustic wave device as one means for solving the problem is arranged between a pair of reflectors having a plurality of linear electrodes and a pair of reflectors, and the pair of common electrodes and the pair of common electrodes. An interdigital transducer having a plurality of crossing electrodes connected to each other and an organic layer disposed on at least one of a pair of reflectors and interdigital transducers are provided.

  In this means, the thickness of the organic layer is preferably less than half of the distance between the crossing electrodes of the interdigital transducer, and the viscosity of the organic layer is preferably in the range of more than 0 and not more than 40 cp.

  In addition, a surface acoustic wave device as another means for solving the above-described problem includes a pair of reflectors having a plurality of linear electrodes and a pair of common electrodes and the pair of common electrodes disposed between the pair of reflectors. An interdigital transducer having a plurality of crossing electrodes connected to each of the common electrodes, an inorganic layer formed between the plurality of linear electrodes in the reflector and between the multiple crossing electrodes in the interdigital transducer, and a pair of And an organic layer formed on the reflector, the interdigital transducer and the inorganic layer.

  In this means, the thickness of the organic layer is preferably less than half of the distance between the crossing electrodes of the interdigital transducer, and the viscosity of the organic layer is preferably in the range of more than 0 and not more than 40 cp.

  As described above, according to the present invention, it is possible to provide a surface acoustic wave device that suppresses the influence on the SH type SAW while efficiently suppressing the Rayleigh type SAW.

  Embodiments of the present invention will be described below with reference to the drawings. However, the present invention can be implemented in many different modes and is not limited to the embodiments shown below. Note that in this specification, portions having the same or similar functions are denoted by the same reference numerals, and repeated description thereof is omitted.

(Embodiment 1)
FIG. 1 is a top view of a surface acoustic wave device (hereinafter referred to as “the present surface acoustic wave device”) 1 according to the present embodiment, and FIG. 2 is a cross-sectional view of the surface acoustic wave device taken along line AA in FIG.

  As shown in FIG. 1, the surface acoustic wave device 1 includes a pair of reflectors 3 on a piezoelectric substrate 2 and an interdigital transducer (hereinafter referred to as “IDT”) 4 disposed between the pair of reflectors 3. Furthermore, as shown in FIG. 2, an organic layer 5 is provided on the reflector 3 and the IDT 4. The surface acoustic wave device 1 generates a surface acoustic wave (hereinafter referred to as “SAW”) by applying a voltage to the IDT 4 and reflects the generated SAW with a pair of reflectors 3 to generate a wave having a specific frequency. Can be extracted as a resonance wave.

The piezoelectric substrate 2 in the surface acoustic wave device 1 is not particularly limited as long as the surface acoustic wave can be generated, but a material having high piezoelectricity and good temperature stability is preferable, for example, a LiNbO ₃ substrate. A LiTaO substrate or the like can be preferably used.

  The IDT 4 has a pair of common electrodes 42 each having a plurality of cross electrodes 41 connected in a comb-like shape. The pair of common electrodes 42 is connected to the other common electrode 42. Are arranged so as to mesh with each other. Note that the distance between adjacent crossing electrodes 41 (referred to as the distance between the center lines of the electrodes, hereinafter also referred to as “interelectrode distance”, see d in FIG. 1) is the resonance wave extracted from the surface acoustic wave resonator. This distance corresponds to a half wavelength, and this distance can be appropriately adjusted and is not limited, but it is preferably approximately 0.5 μm to 100 μm. Further, a dummy electrode 43 is formed on the common electrode of the IDT 4 so as to face the cross electrode 41 of the opposite common electrode.

  The pair of reflectors 3 are formed such that two reflectors 3 form a pair on a piezoelectric substrate, and the structure of each reflector 3 is as shown in FIG. The linear electrode 31 and the common electrode 32 that commonly connects the linear electrodes 31 are formed in a rectangular shape. The plurality of linear electrodes 31 are also arranged substantially parallel to the plurality of linear electrodes 31 in the other reflector 3.

  The pair of reflectors 3 and IDT 4 are formed on the piezoelectric substrate 2 as described above, and are formed of a conductive material. There are no particular limitations on the conductive material, and for example, a metal such as Al or Cu or an alloy thereof can be suitably used. The pair of reflectors 3 and IDT 4 can be formed using a known method such as photolithography or etching after a thin film made of a conductive material is formed on the piezoelectric substrate 2.

  In addition, as shown in FIG. 2, the surface acoustic wave device has an organic layer 5 containing an organic substance covering the reflector 3 and the IDT 4, thereby suppressing the influence on the SH type SAW. Rayleigh type SAW can be suppressed. More specifically, since the organic matter contained in the organic layer 5 generally has viscoelasticity, unnecessary SAW in a direction perpendicular to the surface of the piezoelectric substrate 2 can be attenuated by this viscoelasticity. On the other hand, SH-type SAWs are less susceptible to surface contamination than Rayleigh-type SAWs and are not greatly attenuated even if organic layer 5 is disposed.

  The organic layer 5 is not particularly limited as long as it needs to have viscoelasticity. For example, polyamide, parylene, resist material, or the like can be suitably used. A desirable range of the thickness of the organic layer 5 is not particularly limited as long as the Rayleigh-type SAW can be attenuated, but it is preferably greater than 0 and less than or equal to ½ of the distance between the electrodes, and more desirably from 0. It is largely 1/4 or less, more preferably 1/8 or less. If it is thicker than 1/2, not only the Rayleigh type SAW but also the SH type SAW may be attenuated.

  Moreover, although the desirable range of the viscosity of the organic layer 5 depends on the thickness of the organic layer 5, for example, it is desirably in the range of greater than 0 and not greater than 40 cP, and more desirably not greater than 20 cP. This is because when the viscosity is higher than 40 cP, the SH-type SAW may be attenuated more than necessary.

  The organic layer 5 can be formed by various known methods as long as it can be uniformly formed on the reflector 3 and the IDT 4, and examples thereof include spin coating.

  As described above, according to the surface acoustic wave device, the organic layer 5 having viscoelasticity can be disposed on the reflector 3 and the IDT 4 to suppress the influence on the SH type SAW traveling in the horizontal direction of the substrate. The Rayleigh type SAW generated in the direction perpendicular to the substrate can be efficiently suppressed.

(Example)
Here, the surface acoustic wave device according to Embodiment 1 was actually created and the effect was confirmed. It is shown below.

In the surface acoustic wave device according to this example, LiNbO ₃ was used as the piezoelectric substrate, and copper was used for the reflector 3 and the IDT 4. In this example, the distance between the electrodes was 2 μm. Further, 0.2 μm of an organic layer 5 made of a resist material (ZEP520, manufactured by Nippon Zeon Co., Ltd.) was formed using spin coating.

  After creating this surface acoustic wave device, an AC voltage of 5 dBm and 0.5 GHz to 1.5 GHz was applied between a pair of crossing electrodes of IDT 4 to evaluate the characteristics of the resonant wave. The result is shown in FIG. FIG. 4 shows the results of characteristic evaluation performed on a surface acoustic wave device (comparative example) having substantially the same configuration as the surface acoustic wave device of the present example except that the organic layer 5 is not formed.

  As shown in FIG. 3, it was confirmed that the surface acoustic wave device was able to suppress very sharp dip due to Rayleigh-type SAW observed in the vicinity of 920 MHz and 1120 MHz in FIG. In the surface acoustic wave device, the entire frequency characteristic is shifted by about 25 MHz due to the influence of the organic layer 5, but there is almost no change in the frequency bandwidth and loss. This frequency reduction can be corrected by adjusting the electrode period and the membrane pressure.

(Embodiment 2)
This embodiment is substantially the same as Embodiment 1, but the configuration of the organic layer 5 is different. Specifically, the difference is that the inorganic layer 6 made of an inorganic material is disposed between the linear electrodes of the reflector 3 and between the crossing electrodes 41 of the IDT 4 and the organic layer 5 is disposed thereon. FIG. 5 shows a cross-sectional view of a surface acoustic wave device according to the present embodiment (hereinafter referred to as “the present surface acoustic wave device”) (the top view of the surface acoustic wave device is substantially the same as FIG. 1 and is omitted). ).

  In the surface acoustic wave device, the Rayleigh type SAW generated in the direction perpendicular to the piezoelectric substrate can be suppressed by arranging the organic layer 5 on the reflector 3 and the IDT 4, while the linear electrode of the reflector 3. In the meantime, the inorganic layer 6 can be disposed between the crossed electrodes in the IDT 4 to suppress the attenuation of the SH type SAW, and the effect can be further enhanced as compared with the first embodiment. In the surface acoustic wave device, since the inorganic layer 6 is provided between the linear electrodes, the step between the linear electrodes and the piezoelectric substrate is eliminated, and the thickness control accuracy of the organic layer 5 is improved. There is also an advantage of being able to.

As the inorganic layer 6 used in the present embodiment, to suppress the contamination of organic substances, but are not limited to particular as long as it is possible to suppress the attenuation of the SH type SAW, for example SiN, inorganic insulating such as SiO ₂ A film or the like can be preferably used, and these inorganic layers can be formed by various methods such as sputtering and CVD.

(Embodiment 3)
This embodiment is substantially the same as Embodiment 1, but the configuration of the organic layer 5 is different. Specifically, the organic layer 5 is arranged only on the reflector 3 and the IDT 4. FIG. 6 shows a cross-sectional view of a surface acoustic wave device according to the present embodiment (hereinafter referred to as “the present surface acoustic wave device”) (the top view of the surface acoustic wave device is substantially the same as FIG. 1 and is omitted). ).

  In the surface acoustic wave device, since the organic layer 5 is provided only on the linear electrode of the reflector 3 and the cross electrode of the IDT 4, the Rayleigh type SAW can be attenuated efficiently and the SH type SAW can be attenuated. Therefore, it is possible to provide a more efficient surface acoustic wave device.

(Embodiment 4)
The present embodiment is almost the same as the first embodiment, but the configuration of the IDT 4 is different. FIG. 7 shows a top view of the surface acoustic wave device according to this embodiment (the sectional view is the same as FIG. 2). More specifically, the IDT 4 in the surface acoustic wave device has a pair of common electrodes 42 to which a plurality of cross electrodes 41 are connected in a comb shape, and the pair of common electrodes 42 are connected. The plurality of cross electrodes 41 are arranged so as to mesh with the cross electrodes of the other common electrode 42. In addition, a dummy electrode 43 is formed on the common electrode of the IDT 4 so as to face the cross electrode 41 of the opposite common electrode. Furthermore, the length of the dummy electrode 43 of the IDT 4 is different from the length of the dummy electrode arranged next to it.

  In this embodiment, by making the lengths of the dummy electrodes 43 different in this way, it becomes possible to suppress unnecessary responses due to so-called transverse mode resonance (for example, unnecessary responses appearing in the range of 890 Hz to 1120 Hz in FIG. 4). Can be suppressed.) In particular, since the organic layer 5 according to this embodiment can independently suppress unnecessary responses in the vertical direction of the substrate and unnecessary responses in the horizontal direction, various unnecessary response means can be used simultaneously. It becomes. Therefore, a surface acoustic wave device that can suppress unnecessary responses can be obtained.

  FIG. 8 shows the result when the surface acoustic wave device according to this embodiment is formed by the same method as in Example 1 and the same measurement is performed. According to FIG. 8, it was confirmed that unnecessary responses in the vicinity of 920 MHz and 1120 MHz (dotted line) can be suppressed and unnecessary responses in the lateral mode can be suppressed as in the case of the first embodiment.

  As described above, it was confirmed that the surface acoustic wave device efficiently suppresses the Rayleigh-type SAW while suppressing the influence on the SH-type SAW.

1 is a top view of a surface acoustic wave device according to Embodiment 1. FIG. AA sectional view of the surface acoustic wave device according to the first embodiment. The figure which shows the insertion loss with respect to the frequency of the surface acoustic wave apparatus which concerns on Example 1. FIG. The figure which shows the insertion loss with respect to the frequency of the surface acoustic wave apparatus concerning a comparative example Sectional drawing of the surface acoustic wave apparatus which concerns on Embodiment 2. FIG. Sectional drawing of the surface acoustic wave apparatus which concerns on Embodiment 3. FIG. Top view of a surface acoustic wave device according to Embodiment 4 The figure which shows the insertion loss with respect to the frequency of the elastic surface apparatus which concerns on an example of Embodiment 4.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Surface acoustic wave apparatus, 2 ... Piezoelectric substrate, 3 ... Reflector, 4 ... Interdigital transducer, 5 ... Organic layer, 6 ... Inorganic layer, 31 ... Linear electrode, 41 ... Cross electrode, 42 ... Common electrode, 43 ... Dummy electrode

Claims (1)

A pair of reflectors having a plurality of linear electrodes;
An interdigital transducer having a plurality of crossing electrodes disposed between the pair of reflectors and connected to each of the pair of common electrodes and the pair of common electrodes;
An inorganic layer formed between the plurality of linear electrodes in the reflector and between the plurality of crossing electrodes in the interdigital transducer;
An organic layer that is disposed on the pair of reflectors, the interdigital transducer and the inorganic layer, and is at least one of polyamide, parylene, and a resist material , and
A surface acoustic wave device in which the thickness of the organic layer is not more than half of the distance between crossing electrodes of the interdigital transducer.

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