JP5283972B2 - Surface acoustic wave device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface acoustic wave device having improved insertion loss by reducing the resistance of an IDT (Inter Digital Transducer). <P>SOLUTION: The surface acoustic wave device includes: a piezoelectric substrate 2; the IDT (interdigital transducer) 3 provided on the piezoelectric substrate 2; and a plurality of bridges 16 and 20 which are electrically connected to each of a plurality of interdigital electrodes 4 and 10 facing each other to form the IDT 3 and are provided on the IDT 3 so as to cover at least partially a plurality of electrode fingers 6 and 12 forming the plurality of interdigital electrodes 4 and 10. The surface acoustic wave device is provided which has improved insertion loss by reducing resistance of the IDT. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a surface acoustic wave device, and more particularly to a surface acoustic wave device having a structure in which a comb electrode is provided on a piezoelectric substrate.

  A surface acoustic wave device including an IDT (Inter Digital Transducer) composed of comb-shaped electrodes on a piezoelectric substrate is widely used as a duplexer, a bandpass filter, and the like in mobile communication devices typified by mobile phones. With the progress of information society in recent years, surface acoustic wave devices are required to reduce insertion loss and improve frequency characteristics.

Patent Document 1 discloses a technique for forming a wiring with low electrical resistance and high migration resistance by forming a wiring with oriented Al.
Japanese Patent No. 2937613

  Prior art will be described. FIG. 1A is a perspective view showing a surface acoustic wave device 100 according to a conventional example, and FIG. 1B is a front end portion of an electrode finger 6 (portion surrounded by a dotted line in FIG. 1A). It is an enlarged view.

As shown in FIG. 1A, an IDT _{3 made} of a metal such as Al is provided on a piezoelectric substrate 2 made of, for example, 42 ° rotated Y-cut LiTaO ₃ (42 ° Y-LiTaO ₃ ). The IDT 3 includes a comb electrode 4 and a comb electrode 10 that face each other. The comb-shaped electrode 4 is formed by a bus bar 8 and electrode fingers 6 extending from the bus bar 8. Similarly, the comb electrode 10 is formed by a bus bar 14 and electrode fingers 12. When an electric signal is input between the terminals of the comb electrodes 4 and 10, elastic waves are excited by the electrode fingers 6 and 12, and an electric signal having a passband frequency is output.

  However, in the surface acoustic wave device as described in the conventional example, the insertion loss of the pass band increases due to the electrical resistance of the IDT 3 itself. The resistance of IDT 3 is composed of the resistance r of the electrode fingers 6 and 12.

  As shown in FIG. 1B, when the film thickness of the electrode finger 6 is h, the width is d, and the intersection width between the electrode finger 6 and the electrode finger 12 is W as shown in FIG. The resistance r of 6 is expressed as r = ρ · W / (d · h). The same applies to the electrode fingers 12. That is, the resistance r is inversely proportional to the cross-sectional area d · h of the electrode finger. As described above, the conventional surface acoustic wave device has a problem that the insertion loss of the pass band increases due to the resistance of the IDT itself.

  In order to improve the insertion loss, it has been studied to use a metal having a low resistivity ρ such as Au, Ag, Cu or the like as a material for forming the IDT. However, the use of these metals has problems such as difficulty in processing and cost increase due to the expensiveness of these metals. Further, it has been studied to connect a plurality of IDTs in parallel, but there is a problem that it is not suitable for downsizing a surface acoustic wave device.

  In view of the above problems, an object of the present invention is to provide a surface acoustic wave device capable of reducing the resistance of an IDT and improving insertion loss.

The present invention is electrically connected to each of a piezoelectric substrate, an IDT provided on the piezoelectric substrate, and a plurality of comb electrodes facing each other forming the IDT, thereby forming the plurality of comb electrodes. A plurality of conductors provided on the IDT so as to cover at least a part of the plurality of electrode fingers, and each of the plurality of conductors is provided on each of the plurality of electrode fingers. The surface acoustic wave device is electrically connected to each of the plurality of comb-shaped electrodes via a connecting conductor . According to the present invention, it is possible to reduce the resistance of the IDT and improve the insertion loss of the surface acoustic wave device.

  In the above configuration, each of the plurality of conductors is electrically connected to each of the plurality of comb-shaped electrodes via a connection conductor provided on each of the plurality of electrode fingers. be able to. According to this configuration, since the cross-sectional area of the electrode finger can be increased, the resistance of the IDT can be reduced.

  The said structure WHEREIN: The said connection conductor can be set as the structure provided in at least one part of the area | region where the said conductor and the said electrode finger overlap.

  The said structure WHEREIN: Each of the said connection conductor provided on each of these electrode fingers can be made into a single conductor. According to this configuration, since the cross-sectional area of the electrode finger can be increased, the resistance of the IDT can be reduced.

  In the above configuration, each of the connection conductors provided on each of the plurality of electrode fingers may be a plurality of columnar conductors. According to this configuration, since the cross-sectional area of the electrode finger can be increased, the resistance of the IDT can be reduced.

  In the above configuration, the plurality of conductors can be configured not to be electrically connected to each other. According to this configuration, conduction between opposing comb electrodes can be prevented.

  ADVANTAGE OF THE INVENTION According to this invention, the surface acoustic wave device which can reduce resistance of IDT and can improve insertion loss can be provided.

  Embodiments of the present invention will be described with reference to the drawings.

  FIG. 2A is a perspective view showing the surface acoustic wave device 200 according to the first embodiment, and FIG. 2B is a side view seen from the direction of arrow A in FIG. The description of the same configuration as in FIG. In addition, the bridge 16 is shown through.

  As shown in FIGS. 2A and 2B, on the IDT 3, bridges 16 and 20 (conductors) made of metal such as Al are provided so as to cover a part of the electrode fingers 6 and 12. Is provided. The bridge 16 is electrically connected to the comb electrode 4 via a connection conductor 18 provided on each of the plurality of electrode fingers 6 forming the comb electrode 4. The connection conductor 18 is a plurality of columnar conductors made of a metal such as Al provided in a region where the bridge 16 and the electrode finger 6 overlap. Similarly, the bridge 20 is electrically connected to the comb electrode 10 via a plurality of columnar connection conductors 22 provided on each of the plurality of electrode fingers 12 forming the comb electrode 10. A portion where the connection conductor 18 between the electrode finger 6 and the bridge 16 is not provided, a portion where the connection conductor 22 between the electrode finger 12 and the bridge 20 is not provided, between the electrode finger 6 and the bridge 20, The gap between the electrode finger 12 and the bridge 16 is an air gap. The bridge 16 and the bridge 20 are spaced apart. That is, the bridge 16 and the bridge 20 are not electrically connected. Thereby, conduction between the comb electrode 4 and the comb electrode 10 can be prevented.

  According to the first embodiment, by connecting the connection conductors 18 and 22 and the bridges 16 and 20 to the electrode fingers 6 and 12, the cross-sectional area of the electrode fingers 6 and 12 can be increased. As described in the conventional example, the resistance r of the IDT 3 is inversely proportional to the cross-sectional area of the electrode finger. Therefore, by connecting the connection conductors 18 and 22 and the bridges 16 and 20 to the electrode fingers 6 and 12, the resistance r can be reduced, and the insertion loss of the surface acoustic wave device can be improved.

  Next, the calculation result of the resistance when Example 1 is used will be described. FIG. 3A is a top view showing a surface acoustic wave device used for calculation, and FIG. 3B is a schematic diagram showing an equivalent circuit. FIG. 4 is a diagram showing calculation results of resistance values. As a calculation method, a general-purpose three-dimensional electromagnetic field analysis tool was used. In FIG. 3A, the bridges 16 and 20 are shaded and seen through.

As shown in FIG. 3A, a terminal 24 is connected to the bus bar 8 of the comb electrode 4 and a terminal 26 is connected to the bus bar 14 of the comb electrode 10, and an electric signal is transmitted between the terminals 24 and 26. Apply. The piezoelectric substrate 2 is made of 42 ° Y-LiTaO _3, and the IDT ₃ , the connecting conductors 18 and 22, and the bridges 16 and 20 are all made of Al. The film thickness of Al, that is, the thickness of each of the electrode fingers 6 and 12, the connection conductors 18 and 22, and the bridges 16 and 20 is 0.18 μm. The width d of the electrode fingers 6 and 12 is 0.5 μm, the pitch p between the adjacent electrode fingers 6 and the electrode fingers 12 is 1 μm, and the intersection width W is 50 μm. The total number of electrode fingers 6 and 12 is 45. Further, the connection conductors 18 and 22 are columnar (cylindrical) shapes, and the diameter is 0.5 μm. The bridge 16 is provided so as to cover a region near the bus bar 8 of the electrode finger 6, and the bridge 20 is provided so as to cover a region near the bus bar 14 of the electrode finger 12. The distance between the bridge 16 and the bridge 20 is s.

  As shown in FIG. 3B, the surface acoustic wave filter of FIG. 3A can be expressed as an equivalent circuit having a capacitance component C and a resistance component R with respect to an electrical signal. The resistance component R when the frequency is changed.

  As shown in FIG. 4, the horizontal axis represents frequency and the vertical axis represents resistance value. In the conventional example shown by the dotted line in the figure, the resistance component R is about 0.70Ω in the entire frequency band. On the other hand, when the distance between the bridges in Example 1 was s = 10 μm, the resistance component R was about 0.34Ω as shown by the broken line, and the resistance was about half that of the conventional example. Further, when s = 0.5 μm, as indicated by the solid line, the resistance component R was about 0.3Ω, and the resistance could be further reduced.

  As this result shows, according to the first embodiment, the resistance can be reduced to about half that of the conventional example, and the resistance can be further reduced by narrowing the distance between the bridge 16 and the bridge 20. It was. Further, since the connection conductors 18 and 22 and the bridges 16 and 20 can be formed of Al, processing is easy and inexpensive. Therefore, the cost increase of the surface acoustic wave device can be suppressed. Furthermore, since the resistance can be reduced with only one IDT without connecting a plurality of IDTs, the surface acoustic wave device can be downsized.

  In FIG. 2A to FIG. 3, the connection conductors 18 and 22 are cylinders, but the connection conductors 18 and 22 are not limited to columns as long as they are a plurality of columnar conductors.

  As a modification of the first embodiment, an example in which the shape of the connection conductor is changed will be described. FIG. 5 is an enlarged perspective view of the vicinity of the tip of the electrode finger 6 of the surface acoustic wave device according to the modification of the first embodiment.

  As shown in FIG. 5, the connection conductor 28 that connects the electrode finger 12 and the bridge 20 is a single conductor provided in a part of a region where the electrode finger 12 and the bridge 20 overlap. Although illustration is omitted, the connection conductor connecting the electrode finger 6 and the bridge 16 has the same configuration. In FIG. 5, the connection conductor 28 is provided in a part of the region where the electrode finger 12 and the bridge 20 overlap, but may be provided in the entire region.

  Thus, the connection conductor is not limited to a plurality of columnar conductors, and can be a single conductor provided in at least a part of the region where the electrode fingers and the bridge overlap.

  Example 2 uses a surface acoustic wave device according to Example 1 when a surface acoustic wave device according to a conventional example is used in a surface acoustic wave filter in which a plurality of surface acoustic wave devices are connected in parallel and cascade connected. This is an example in which the frequency characteristics are calculated and compared with those obtained. FIG. 6A is a top view illustrating the surface acoustic wave filter according to the second embodiment, and FIG. 6B is a schematic diagram illustrating the configuration of each surface acoustic wave device. In FIG. 6B and FIG. 7 described later, the bridge and the connection conductor are omitted.

As shown in FIG. 6A, an input terminal 30, an output terminal 32, a ground terminal 34, and surface acoustic wave devices 210, 220, 230, and 240 are provided on a piezoelectric substrate 2 made of 42 ° Y-LiTaO _3. It has been. Each surface acoustic wave device is a portion indicated by shading in the figure. As shown in FIG. 6B, each surface acoustic wave device includes a double mode filter including an IDT 37 located at the center, IDTs 36 disposed on both sides thereof, and reflectors 35 disposed on both sides of the three IDTs. In this example, a 1.9 GHz band filter was used. A connection conductor and a bridge are provided on the electrode fingers of the comb-shaped electrode. The IDT, each surface acoustic wave device and the wiring 31 for connecting the terminals (the hatched portion in the figure), the input terminal 30, the output terminal 32, the ground terminal 34, the bridge and the connection conductor are all formed of Al. .

  FIG. 7 shows an enlarged view of a portion related to the surface acoustic wave device 210 of FIG. 6A (a portion surrounded by a dotted line in FIG. 6A). As shown in FIG. 7, one of the comb electrodes forming each IDT and the reflector 35 are connected to the ground terminal 34 by a wiring 31. Further, the input terminal 30 is connected to an IDT 37 located at the center by a wiring 31. A surface acoustic wave is excited by an electrical signal input from the input terminal 30 to the IDT 37 and is output from the IDT 36 to the surface acoustic wave devices 230 and 240. Each surface acoustic wave device has the same configuration.

  As shown in FIG. 6A, the surface acoustic wave devices 210 and 220 excite acoustic waves by the electrical signal input from the input terminal 30. The excited elastic wave is converted into an electric signal and input to the IDTs 36 located on both sides of the surface acoustic wave devices 230 and 240, where the elastic wave is excited again. Finally, an electrical signal having a frequency in the pass band is output from the IDT 37 located at the center of the surface acoustic wave devices 230 and 240 to the output terminal 32. That is, the surface acoustic wave filter 400 is a surface acoustic wave filter having an unbalanced input terminal and an unbalanced output terminal in which two double mode filters are connected in parallel and two double mode filters are connected in cascade at the same time. is there.

  The parameters used for the calculation will be described. Each film thickness h of Al is 0.18 μm. The pitch p between the electrode fingers of the IDT is 1.02 μm, the width d of the electrode fingers is 0.51 μm, the crossing width W is 50 μm, and each surface acoustic wave device has 45 pairs of electrode fingers. The distance s between the bridges is 0.5 μm (see FIG. 3).

  FIG. 8A is a diagram showing the calculation results, and FIG. 8B is an enlarged view of the passband. The horizontal axis represents frequency and the vertical axis represents attenuation. As shown in FIGS. 8A and 8B, in the conventional example indicated by the dotted line, the attenuation amount is −1.537 dB at 1960 MHz and −2.165 dB at 1944 MHz. On the other hand, in Example 2 shown with the continuous line, it was -1.475 dB in 1960 MHz and -2.027 dB in 1944 MHz. As described above, the surface acoustic wave filter using the present invention was able to improve the insertion loss by about 0.1 dB as compared with the prior art.

  In the second embodiment, the surface acoustic wave device is a double mode filter, but a surface acoustic wave filter other than the double mode filter may be used.

  The third embodiment is an example in which the position of the bridge is changed. FIG. 9 is a perspective view illustrating the surface acoustic wave filter according to the third embodiment. The bridge 16 is shown through.

  As shown in FIG. 9, the bridge 16 is provided near the tip of the electrode finger 6, and the bridge 20 is provided near the tip of the electrode finger 12. Also with this configuration, since the cross-sectional areas of the electrode fingers 6 and 12 can be increased as in the first embodiment, the resistance of the IDTs 4 and 10 can be reduced.

  According to Example 3, as a result of calculating the resistance component R under the same parameters as those used in the calculation of FIG. 4 and the distance between the bridges s = 0.5 μm, R = 0.6Ω at 2 GHz. The resistance could be reduced by about 14% from the conventional example of R = 0.7Ω.

  When the bridge is provided near the bus bar of the electrode finger as in the first and second embodiments, and when provided near the tip of the electrode finger as in the third embodiment, the resistance can be reduced in either case. It was.

  Although the embodiments of the present invention have been described in detail above, the present invention is not limited to such specific embodiments, and various modifications and changes can be made within the scope of the gist of the present invention described in the claims. It can be changed.

FIG. 1A is a perspective view showing a surface acoustic wave device 100 according to a conventional example, and FIG. 1B is an enlarged view of a tip portion of an electrode finger. FIG. 2A is a perspective view showing the surface acoustic wave device 200 according to the first embodiment, and FIG. 2B is a side view. FIG. 3 is a plan view illustrating the surface acoustic wave device 200 according to the first embodiment. FIG. 4 is a diagram showing the result of calculating the resistance value of IDT. FIG. 5 is an enlarged perspective view of the tip portion of the electrode finger 12 of the surface acoustic wave device according to the modification of the first embodiment. FIG. 6A is a top view illustrating the surface acoustic wave filter 250 according to the second embodiment, and FIG. 6B is a schematic diagram illustrating the configuration of each surface acoustic wave device. FIG. 7 is an enlarged view of a portion related to the surface acoustic wave device 210 in FIG. FIG. 8A is a diagram illustrating a calculation result of the frequency characteristics of the surface acoustic wave filter 250 according to the second embodiment, and FIG. 8B is an enlarged view of the passband. FIG. 9 is a perspective view illustrating the surface acoustic wave device 300 according to the third embodiment.

Explanation of symbols

Piezoelectric substrate 2
IDT 3
Comb electrodes 4, 10
Electrode fingers 6, 12
Busbar 8, 14
Bridge 16, 20
Connecting conductor 18, 22, 28
Surface acoustic wave devices 100, 200, 210, 220, 230, 240, 300
Surface acoustic wave filter 250

Claims (5)

A piezoelectric substrate;
IDT provided on the piezoelectric substrate;
Provided on the IDT so as to cover at least a part of the plurality of electrode fingers forming the plurality of comb-shaped electrodes that are electrically connected to each of the plurality of mutually facing comb-shaped electrodes forming the IDT. comprising a plurality of conductors that are, a,
Each of the plurality of conductors is electrically connected to each of the plurality of comb-shaped electrodes via a connection conductor provided on each of the plurality of electrode fingers. Wave device. The surface acoustic wave device according to claim 1, wherein the connection conductor is provided in at least a part of a region where the conductor and the electrode finger overlap . The surface acoustic wave device according to claim 1, wherein each of the connection conductors provided on each of the plurality of electrode fingers is a single conductor . 3. The surface acoustic wave device according to claim 1, wherein each of the connection conductors provided on each of the plurality of electrode fingers is a plurality of columnar conductors . The surface acoustic wave device according to claim 1, wherein the plurality of conductors are not electrically connected to each other .

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