JP5156478B2 - Surface acoustic wave device - Google Patents

Description

  The present invention relates to a surface acoustic wave device, and more particularly to an acoustic wave device including an insulator at the tip of an electrode finger of a comb-shaped electrode.

  A surface acoustic wave device having an IDT (Interdigital Transducer) composed of a pair of comb-shaped electrodes on a surface of a piezoelectric substrate and a pair of reflectors sandwiching the IDT in the propagation direction of the surface acoustic wave as an acoustic wave device using an acoustic wave There is. Surface acoustic wave devices are used in mobile communication devices and the like. With the recent development of mobile communication devices, surface acoustic wave devices are required to have low loss in order to improve the reception sensitivity of mobile communication devices and reduce power consumption.

  In order to reduce the loss of a surface acoustic wave device, it is required to suppress leakage of the surface acoustic wave in a direction other than the propagation direction of the surface acoustic wave. That is, it is required to efficiently confine the energy of the surface acoustic wave in the IDT opening.

  Patent Document 1 discloses a technique for confining the energy of a surface acoustic wave in the vicinity of an opening of an IDT by defining the thickness of a bus bar of a comb electrode. In Patent Document 2, by providing a dummy electrode between the electrode finger of the comb-shaped electrode and the bus bar, radiation of the surface acoustic wave in an oblique direction is suppressed, and the energy of the surface acoustic wave is made near the opening of the IDT. A confinement technique is disclosed. Patent Document 3 discloses a technique for confining the energy of surface acoustic waves in the vicinity of the IDT opening by narrowing the gap from the tip of the electrode finger of the comb electrode to the bus bar or dummy electrode finger. .

Patent Document 4 discloses a technique for forming a comb-shaped electrode by anodizing a predetermined region of an aluminum thin film.
JP 2002-1000095 A2 JP 2006-080873 A JP 2004-328196 A JP 2002-084156 A

  However, according to the techniques of Patent Documents 1 and 2, the surface acoustic wave energy is concentrated in the gap region between the tip of the electrode finger of the comb electrode and the bus bar or the dummy electrode finger. This concentrated energy results in degradation of the filter insertion loss. According to the technique of Patent Document 3, energy concentration in the gap region can be suppressed, but if the gap region is narrowed, an ESD (Electrostatic Discharge) withstand voltage is lowered.

  The present invention has been made in view of the above problems, and suppresses the concentration of surface acoustic wave energy in the gap region between the tip of the electrode finger of the comb-shaped electrode and the bus bar or the dummy electrode finger, thereby achieving a low-loss elastic surface. An object is to provide a wave device.

  The present invention includes at least one set of comb-shaped electrodes formed on a piezoelectric substrate, each including a plurality of electrode fingers and a bus bar for commonly connecting the plurality of electrode fingers, wherein the plurality of electrode fingers are alternately arranged. And an insulator that is not embedded between the plurality of electrode fingers but is embedded between the tips of the plurality of electrode fingers and the bus bar. It is a device. According to the present invention, leakage of surface acoustic wave energy can be suppressed, and concentration of surface acoustic wave energy in the region between the tip of the electrode finger of the comb electrode and the bus bar can be suppressed.

  The said structure WHEREIN: The said insulator can be set as the structure continuously embedded and provided between the front-end | tip of these electrode fingers, and the said bus-bar. According to this configuration, leakage of surface acoustic wave energy can be suppressed.

  The said structure WHEREIN: It can be set as the structure by which the said insulator is provided so that it may have the space | gap part which is not embedded with the said insulator between the front-end | tip of these electrode fingers and the said bus bar.

  The said structure WHEREIN: The distance of the front-end | tip of these electrode fingers and the said bus-bar can be set as the structure longer than the distance between adjacent electrode fingers among these electrode fingers. According to this configuration, ESD breakdown between the electrode finger and the bus bar can be suppressed.

  The present invention includes a plurality of electrode fingers, a plurality of dummy electrode fingers, and a bus bar in which the plurality of electrode fingers and the plurality of dummy electrode fingers are alternately connected in common. At least one pair of comb-shaped electrodes in which electrode fingers are alternately arranged; and tips of the plurality of dummy electrode fingers not embedded between the plurality of electrode fingers and corresponding to tips of the plurality of electrode fingers; And a surface acoustic wave device characterized by comprising an insulator embedded in between. According to the present invention, surface acoustic wave energy leakage can be suppressed, and concentration of surface acoustic wave energy in a region between the tip of the electrode finger of the comb-shaped electrode and the tip of the dummy electrode finger can be suppressed.

  The said structure WHEREIN: The said insulator can be set as the structure continuously embedded and provided between the front-end | tip of these electrode fingers, and these dummy electrode fingers. According to the above configuration, leakage of surface acoustic wave energy can be suppressed.

  The said structure WHEREIN: It can be set as the structure by which the said insulator is provided so that it may have the space | gap part which is not embedded with the said insulator between the front-end | tip of these electrode fingers and these dummy electrode fingers. .

  In the above configuration, the distance between the tips of the plurality of electrode fingers and the plurality of dummy electrodes may be longer than the distance between adjacent electrode fingers of the plurality of electrode fingers. According to this configuration, ESD breakdown between the electrode finger and the dummy electrode finger can be suppressed.

  The said structure WHEREIN: The said insulator can be set as the structure which consists of an oxide of the metal which comprises these electrode fingers. According to this configuration, the insulator can be easily formed.

  The said structure WHEREIN: The film thickness of the said insulator can be set as the structure more than the film thickness of these electrode fingers. According to this configuration, leakage of surface acoustic wave energy can be suppressed.

  According to the present invention, it is possible to suppress leakage of surface acoustic wave energy and to suppress concentration of surface acoustic wave energy in a region between the tip of the electrode finger of the comb electrode and the tip of the bus bar or dummy electrode finger. it can.

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

  FIG. 1A is a plan view of the surface acoustic wave device according to the first embodiment. FIG. 1B and FIG. 1C are an AA sectional view and a BB sectional view of FIG. 1A, respectively. Referring to FIG. 1A, on a piezoelectric substrate 10 such as lithium niobate or lithium tantalate, a reflector 22 made of a metal material mainly containing aluminum or the like and an IDT 21 sandwiched between the reflectors 22 are provided. Yes. The IDT 21 has a pair of comb electrodes 20. Each set of comb-shaped electrodes 20 includes a plurality of electrode fingers 12 and a bus bar 14 that commonly connects the plurality of electrode fingers 12. The plurality of electrode fingers 12 of each pair of comb-shaped electrodes 20 are alternately arranged. Here, the propagation direction of the surface acoustic wave is defined as the x direction, and the direction perpendicular to the propagation direction of the surface acoustic wave is defined as the y direction. The opening length in the y direction, which is the overlap of the electrode fingers 12 of a pair of comb-shaped electrodes 20, is WL, the width in the y direction of the bus bar 14 is WB, and the distance in the x direction between adjacent electrode fingers 12 is L 1. The distance in the y direction between the electrode finger 12 and the bus bar 14 is L2, and the wavelength of the surface acoustic wave is λ.

  Referring to FIG. 1B, an insulator 18 mainly containing, for example, aluminum oxide is embedded between the tips of the plurality of electrode fingers 12 and the bus bar 14. Here, the film thickness of the insulator 18 is T1, and the film thickness of the electrode finger 12 is T2. On the other hand, referring to FIG. 1C, the insulator 18 is not embedded between the plurality of electrode fingers 12. That is, the space 30 is between the plurality of electrode fingers 12.

  FIG. 2A and FIG. 2B are diagrams showing the results of simulating the deformation amount with respect to the coordinate y of Comparative Example 1 and Example 1, respectively. In Example 1, the wavelength λ is 2 μm, the electrode finger 12 and the bus bar 14 are made of aluminum and the film thickness T2 is 0.13 μm, the insulator 18 is made of aluminum oxide, the film thickness T1 is 0.13 μm, the opening length WL is 20λ, Bus bar width WB is 10λ, and distances L1 and L2 are λ / 4. A lithium tantalate substrate is used as the piezoelectric substrate 10. Comparative Example 1 has the same configuration as Example 1 except that insulator 18 is not provided.

  The coordinate y indicates a direction perpendicular to the propagation direction of the surface acoustic wave, and the end of the bus bar 14 opposite to the electrode finger 12 is zero. The amount of deformation indicates the amount of deformation of the surface of the piezoelectric substrate 10 caused by the surface acoustic wave. Of the coordinates y, the range X indicates the range of the opening where the electrode fingers 12 of the IDT 21 overlap, and the range Y indicates the range of the bus bar 14. The range Z is a range assumed as a damper region in which surface acoustic waves are absorbed in the simulation. A large amount of deformation indicates that the energy of the surface acoustic wave at the corresponding coordinate y is large. The solid line fr is the resonance frequency (2000 MHz) of the surface acoustic wave resonator shown in FIG. 1, the dotted line fa is the anti-resonance frequency (2080 MHz), and the broken line f0 is the amount of deformation at the intermediate frequency (2040 MHz) between the resonance frequency and the anti-resonance frequency. Is shown.

  Referring to FIGS. 2A and 2B, the amount of change in f0 and fa is substantially the same in Comparative Example 1 and Example 1, and is not large. The surface acoustic wave energy mainly appears in the amount of deformation at fr. In Comparative Example 1 and Example 1, the amount of fr deformation in the range X of the opening (the amount of deformation in fr) is substantially equal. On the other hand, the amount of fr deformation in the range Y of the bus bar 14 is smaller in Example 1 than in Comparative Example 1. This indicates that the surface acoustic wave energy in Example 1 is smaller than that in Comparative Example 1 in the y direction outside the opening, and the energy is confined in the opening. Thereby, by making a filter using the resonator according to the first embodiment, insertion loss can be suppressed as compared with the first comparative example.

  FIG. 3A to FIG. 3C are diagrams illustrating manufacturing steps of the surface acoustic wave device according to the first embodiment. 3A is a plan view, and FIG. 3B and FIG. 3C are an AA sectional view and a BB sectional view of FIG. 3A, respectively. Referring to FIG. 3A, a metal film 32 mainly containing, for example, aluminum is formed on the piezoelectric substrate 10. The metal film 32 includes a reflector metal pattern 32a and a metal pattern 32b to be an IDT. Referring to FIG. 3B, a bus bar and an electrode finger are continuously formed as a metal film 32 in a region to be an electrode finger. With reference to FIG.3 (c), the space | gap part 30 is formed between the metal films 32 which should become a bus-bar in the area | region which should be between electrode fingers.

  Referring to FIGS. 3A and 3B, the region 34 to be between the tip of the electrode finger and the bus bar in the metal pattern 32b is selectively anodized. As a result, the aluminum in region 34 is oxidized to aluminum oxide. Thus, Example 1 shown in FIGS. 1A to 1C is completed. In FIG. 1C, the film thickness T1 of the insulator 18 and the film thickness T2 of the electrode finger 12 are illustrated in the same manner. However, when the insulator 18 is formed by anodizing the metal pattern 32b, insulation is performed. The film thickness T1 of the body 18 is larger than the film thickness T2 of the electrode finger 12.

  As described above, according to the first embodiment, the insulator 18 is embedded between the tips of the plurality of electrode fingers 12 and the bus bar 14. Thereby, the energy of the surface acoustic wave can be confined in the opening, and leakage of energy in the y direction (outside the opening) can be suppressed and loss can be suppressed. Further, as in Patent Documents 1 and 2, the surface acoustic wave energy is not concentrated in the gap region between the tip of the electrode finger of the comb electrode and the bus bar. Therefore, the insertion loss of the filter due to concentrated energy can be suppressed. Further, the surface acoustic wave energy can be confined in the opening without narrowing the gap region as in Patent Document 3. Therefore, insertion loss can be suppressed and ESD withstand voltage can be improved.

  As shown in FIGS. 1A and 1B, the insulator 18 is preferably provided so as to be continuously embedded between the tips of the plurality of electrode fingers 12 and the bus bar 14. Thereby, the leakage of the energy of the surface acoustic wave in the y direction can be further suppressed.

  1A, the distance L2 between the tip of the electrode finger 12 and the bus bar 14 is preferably longer than the distance L1 between the adjacent electrode fingers 12 among the plurality of electrode fingers 12. Thereby, ESD destruction between the electrode finger 12 and the bus bar 14 can be suppressed.

  Furthermore, the film thickness T1 of the insulator 18 is preferably equal to or greater than the film thickness T2 of the plurality of electrode fingers 12. Thereby, the leakage of the energy of the surface acoustic wave in the y direction can be further suppressed.

  Furthermore, as described with reference to FIGS. 3A to 3C, the insulator 18 is preferably made of a metal oxide constituting the plurality of electrode fingers 12. Thereby, the insulator 18 can be easily formed by oxidizing the metal pattern 32b made of the same metal material as the electrode finger 12.

  Example 2 is an example in which the comb electrode has dummy electrode fingers. 4A to 4C, each set of comb-shaped electrodes 20a includes a plurality of dummy electrode fingers 16 in addition to a plurality of electrode fingers 12. The plurality of electrode fingers 12 and the plurality of dummy electrode fingers 16 are alternately connected to the bus bar 14 in common. The insulator 18 is embedded and provided between the tips of the plurality of electrode fingers 12 and the tips of the corresponding dummy electrode fingers 16. Other configurations are the same as those of the first embodiment shown in FIGS. 1A to 1C, and a description thereof will be omitted.

  FIG. 5A and FIG. 5B are diagrams showing the results of simulating the deformation amount with respect to the coordinate y in Comparative Example 2 and Example 2, respectively. In Example 2, the length of the dummy electrode finger 16 is 1λ. Other dimensions are the same as those in the first embodiment. A range W in FIGS. 5A and 5B shows a region between the electrode finger 12 and the bus bar 14. Comparative Example 2 has the same configuration as that of Example 2 except that the insulator 18 is not provided.

  With reference to FIG. 5A, in Comparative Example 2, the amount of fr deformation in the range Y corresponding to the bus bar 14 is smaller than in Comparative Example 1. However, in the range W, the fr deformation amount is large. Therefore, the loss caused by the leakage of the surface acoustic wave in the y direction cannot be suppressed only by providing the dummy electrode fingers 16 as in Comparative Example 2.

  Referring to FIG. 5B, according to the second embodiment, the fr deformation amount in the range W is smaller than that in the second comparative example. Furthermore, the fr deformation amount in the range Y is smaller than that in the first embodiment shown in FIG. Thereby, the loss resulting from the leakage of the surface acoustic wave energy in the y direction can be suppressed.

  FIG. 6A and FIG. 6B are diagrams showing the results of simulating the deformation amount with respect to the coordinate y in Modification Example 1 of Comparative Example 2 and Example 2, respectively. In the first modification of the second embodiment, the distance L2 between the tip of the electrode finger 12 and the tip of the dummy electrode finger 16 is λ / 8. Other dimensions are the same as in the second embodiment. Modification 1 of Comparative Example 2 has the same configuration as that of Modification 1 of Example 2 except that the insulator 18 is not provided.

  With reference to FIG. 6A, in the first modification of the comparative example 2, the fr deformation amount in the range W is smaller than that in FIG. 5A of the second comparative example. With reference to FIG. 6B, according to the first modification of the second embodiment, the fr deformation amount in the range W is further smaller than that of the first modification of the comparative example 2.

  FIG. 7A and FIG. 7B are diagrams showing the results of simulating the amount of deformation with respect to the coordinate y in Modification 2 of Comparative Example 2 and Example 2, respectively. In the second modification of the second embodiment, the distance L2 between the tip of the electrode finger 12 and the tip of the dummy electrode finger 16 is λ / 2. Other dimensions are the same as in the second embodiment. Modification 2 of Comparative Example 2 has the same configuration as that of Modification 2 of Example 2 except that the insulator 18 is not provided.

  With reference to FIG. 7A, in the first modification of the comparative example 2, the fr deformation amount in the range W is substantially the same as that in the second modification shown in FIG. With reference to FIG. 7B, according to the second modification of the second embodiment, the fr deformation amount in the range W is larger than that of the second modification of the comparative example 2.

  FIG. 8 is a diagram showing a result of simulating a loss due to energy leakage in the y direction with respect to the distance L2 between the tip of the electrode finger 12 and the tip of the dummy electrode finger 16 in Comparative Example 2 and Example 2 and the modification thereof. is there. The loss due to energy leakage in the y direction was calculated based on the area of the fr deformation amount and the y coordinate in FIGS. 5 (a) to 7 (b).

  Referring to FIG. 8, in Comparative Example 2, the loss increases as the distance L2 increases. That is, in order to reduce the loss, it is required to reduce the distance L2. However, when the distance L <b> 2 is reduced, ESD damage tends to occur at the tip of the electrode finger 12 and the tip of the dummy electrode finger 16. On the other hand, in Example 2, the loss decreases as the distance L2 increases until the distance L2 reaches 0.25λ. That is, in Example 2, the distance L2 can be increased while suppressing loss. Therefore, in Example 2, it is possible to suppress a decrease in ESD withstand voltage and to reduce loss.

  Example 3 is an example in which an insulator and a gap are provided between the tip of the electrode finger and the bus bar. FIG. 9A is a plan view of the surface acoustic wave device according to the third embodiment, and FIG. 9B is a cross-sectional view taken along line AA of FIG. 9A. With reference to FIG. 9A and FIG. 9B, in Example 3, an insulator 18a and a gap portion 24 are provided between the tip of the electrode finger 12 and the bus bar. Other configurations are the same as those of the first embodiment, and the description thereof is omitted. As in the third embodiment, the insulator 18a may be provided so as to have a gap 24 that is not embedded with the insulator 18a. In order to suppress leakage of the energy of the surface acoustic wave in the y direction, the insulator 18a is preferably provided so as to be in contact with the electrode finger 12, and the gap portion 24 is preferably provided so as to be in contact with the bus bar 14.

  Example 4 is an example in which an insulator and a gap are provided between the tip of the electrode finger and the tip of the dummy electrode finger. FIG. 10A is a plan view of the surface acoustic wave device according to the fourth embodiment, and FIG. 10B is a cross-sectional view taken along line AA of FIG. Referring to FIGS. 10A and 10B, in Example 4, an insulator 18 a and a gap 24 are provided between the tip of the electrode finger 12 and the tip of the dummy electrode finger 16. Other configurations are the same as those of the second embodiment, and the description thereof is omitted. As in the fourth embodiment, the insulator 18a may be provided so as to have a gap 24 that is not embedded with the insulator 18a. In order to suppress leakage of the energy of the surface acoustic wave in the y direction, the insulator 18a is preferably provided so as to be in contact with the electrode finger 12, and the gap portion 24 is preferably provided so as to be in contact with the dummy electrode finger 16.

  In Examples 1 to 4, a resonator in which a pair of comb-shaped electrodes are sandwiched between reflectors is described as an example of a surface acoustic wave device. However, if a surface acoustic wave device has at least one pair of comb-shaped electrodes, Good. As the surface acoustic wave device, for example, a ladder filter having a plurality of the above-described resonators or a multimode filter in which a plurality of IDTs are provided between reflectors may be used.

  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.

1A is a plan view of the surface acoustic wave device according to the first embodiment, FIG. 1B is a cross-sectional view taken along the line AA in FIG. 1A, and FIG. It is -B sectional drawing. FIG. 2A is a diagram illustrating the deformation amount with respect to the coordinate y of the first comparative example, and FIG. 2A is a diagram illustrating the deformation amount with respect to the coordinate y of the first embodiment. 3A is a plan view of the surface acoustic wave device manufacturing process according to the first embodiment, FIG. 3B is a cross-sectional view taken along the line AA in FIG. 3A, and FIG. 3C is FIG. It is BB sectional drawing of). 4A is a plan view of the surface acoustic wave device according to the second embodiment, FIG. 4B is a cross-sectional view taken along line AA of FIG. 4A, and FIG. 4C is B of FIG. It is -B sectional drawing. FIG. 5A is a diagram illustrating the deformation amount with respect to the coordinate y in the comparative example 2, and FIG. 5B is a diagram illustrating the deformation amount with respect to the coordinate y in the second embodiment. 6A is a diagram illustrating the deformation amount with respect to the coordinate y of the first modification of the comparative example 2, and FIG. 6B is a diagram illustrating the deformation amount with respect to the coordinate y of the first modification of the second embodiment. FIG. 7A is a diagram illustrating a deformation amount with respect to the coordinate y of the second modification of the comparative example 2, and FIG. 7B is a diagram illustrating a deformation amount with respect to the coordinate y of the second modification of the second embodiment. FIG. 8 is a diagram showing a loss with respect to the distance L2 in Comparative Example 2 and Example 2. FIG. FIG. 9A is a plan view of the surface acoustic wave device according to the third embodiment, and FIG. 9B is a cross-sectional view taken along line AA of FIG. 9A. FIG. 10A is a plan view of the surface acoustic wave device according to the fourth embodiment, and FIG. 10B is a cross-sectional view taken along line AA of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Piezoelectric substrate 12 Electrode finger 14 Bus bar 16 Dummy electrode finger 18 Insulator 20 Comb electrode 21 IDT
22 Reflector 24 Cavity 30 Cavity 32 Metal Film 32a, 32b Metal Pattern 34 Region

Claims (10)

At least one pair of comb-shaped electrodes formed on the piezoelectric substrate, each including a plurality of electrode fingers and a bus bar for commonly connecting the plurality of electrode fingers, wherein the plurality of electrode fingers are alternately arranged;
An insulator that is not embedded between the plurality of electrode fingers, and is embedded between the tips of the plurality of electrode fingers and the bus bar;
A surface acoustic wave device comprising:   The surface acoustic wave device according to claim 1, wherein the insulator is continuously embedded between the tips of the plurality of electrode fingers and the bus bar.   2. The surface acoustic wave device according to claim 1, wherein the insulator is provided so as to have a gap portion that is not embedded with the insulator between the tips of the plurality of electrode fingers and the bus bar. .   The elastic surface according to any one of claims 1 to 3, wherein a distance between the tips of the plurality of electrode fingers and the bus bar is longer than a distance between adjacent electrode fingers of the plurality of electrode fingers. Wave device. A plurality of electrode fingers, a plurality of dummy electrode fingers, and a bus bar in which the plurality of electrode fingers and the plurality of dummy electrode fingers are alternately connected to each other are formed on the piezoelectric substrate, and the plurality of electrode fingers are staggered. At least one pair of comb electrodes arranged in
An insulator that is not embedded between the plurality of electrode fingers and is embedded between the tips of the plurality of electrode fingers and the tips of the plurality of dummy electrode fingers;
A surface acoustic wave device comprising:   6. The surface acoustic wave device according to claim 5, wherein the insulator is continuously embedded between the tips of the plurality of electrode fingers and the plurality of dummy electrode fingers.   The said insulator is provided so that it may have the space | gap part which is not embedded with the said insulator between the front-end | tip of these electrode fingers and these dummy electrode fingers. Surface acoustic wave device.   8. The distance between the tips of the plurality of electrode fingers and the plurality of dummy electrodes is longer than a distance between adjacent electrode fingers of the plurality of electrode fingers. Surface acoustic wave device.   The surface acoustic wave device according to any one of claims 1 to 8, wherein the insulator is made of an oxide of a metal constituting the plurality of electrode fingers.   10. The surface acoustic wave device according to claim 1, wherein a film thickness of the insulator is equal to or greater than a film thickness of the plurality of electrode fingers.

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