JP4557691B2 - Surface acoustic wave device - Google Patents

Description

  The present invention relates to a surface acoustic wave device used for mobile communication devices such as mobile phones, in-vehicle devices, medical devices, and the like.

There are various types of surface acoustic wave devices such as surface acoustic wave resonators and surface acoustic wave filters. A pair of reflectors are formed on a piezoelectric substrate along the propagation direction of the surface acoustic wave, and the reflectors A device in which an IDT (interdigital transducer) is formed between the two is often used. In this type of surface acoustic wave device, the surface acoustic wave excited by the IDT can be confined by multiple reflection between the reflectors disposed on both sides thereof. A low-loss surface acoustic wave filter can be constructed.
JP 2002-76818 A

  However, the conventional surface acoustic wave device described above has a problem that a part of the surface acoustic wave generated by the IDT changes its propagation direction due to diffraction and leaks out of the surface acoustic wave device. As a result, the surface acoustic wave energy is not completely confined by the surface acoustic wave device, and the Q of the surface acoustic wave resonator and the insertion loss of the surface acoustic wave filter are reduced due to this.

  The present invention has been devised in view of the above-described drawbacks, and it is an object of the present invention to provide a surface acoustic wave device in which leakage of surface acoustic waves is reduced.

One aspect of the surface acoustic wave device of the present invention is a pair of comb teeth formed by connecting one end of a plurality of electrode fingers arranged at equal intervals along a propagation direction of a surface acoustic wave on a piezoelectric substrate with bus bar electrodes. The electrode electrodes are formed so as to face each other so that the electrode fingers mesh with each other, and are arranged at equal intervals along the surface acoustic wave propagation direction on both sides of the surface acoustic wave propagation direction of the IDT. In the surface acoustic wave device in which a pair of reflectors are formed by connecting both ends of a plurality of reflective electrodes with a common electrode, at least one slit is provided in each of the pair of bus bar electrodes. And formed vertically.

In another aspect of the surface acoustic wave device of the present invention, a pair of electrode fingers connected at one end to a piezoelectric substrate at equal intervals along the propagation direction of the surface acoustic wave is connected by a bus bar electrode. Are formed so that the electrode fingers face each other so that the electrode fingers mesh with each other, and are formed at equal intervals along the surface acoustic wave propagation direction on both sides of the surface acoustic wave propagation direction of the IDT. in a pair of reflectors formed surface acoustic wave device comprising a formed by connecting a pair of common electrodes to both ends of the plurality of reflective electrodes disposed on each of the pair of common electrodes, at least one slit, It is formed perpendicular to the plurality of electrode fingers.

Furthermore, another aspect of the surface acoustic wave device of the present invention is formed by connecting one end of a plurality of electrode fingers arranged at equal intervals along the propagation direction of the surface acoustic wave on the piezoelectric substrate with a bus bar electrode. An IDT is formed by making a pair of comb-like electrodes face each other so that the electrode fingers mesh with each other, and equidistant along both sides of the surface acoustic wave propagation direction of the IDT along the surface acoustic wave propagation direction. In the surface acoustic wave device formed with a pair of reflectors formed by connecting both ends of the plurality of reflective electrodes with a pair of common electrodes, each of the pair of bus bar electrodes and the pair of common electrodes, At least one slit is formed perpendicular to the plurality of electrode fingers.

  Furthermore, the surface acoustic wave device of the present invention is characterized in that the width of the slit is smaller than ½ of the arrangement pitch of the electrode fingers.

  Furthermore, in the surface acoustic wave device of the present invention, a plurality of the slits are formed in each of the bus bar electrodes and / or the common electrode, and the arrangement pitch thereof is smaller than the arrangement pitch of the electrode fingers. It is characterized by.

According to one aspect of the surface acoustic wave device of the present invention, each of the pair of bus bar electrodes,
At least one slit is formed perpendicular to the plurality of electrode fingers. Therefore, it is possible to reflect the surface acoustic wave, which travels out of direction due to diffraction and leaks through the bus bar electrode, to be reflected by the slit and returned to the surface acoustic wave device. A surface acoustic wave device with high performance can be obtained.

According to another aspect of the surface acoustic wave device of the invention, at least one slit is formed in each of the pair of common electrodes perpendicular to the plurality of electrode fingers. Therefore, it becomes possible to reflect the surface acoustic wave that is traveling in the direction shifted by diffraction and leaks through the common electrode, and reflects it back to the surface acoustic wave device by the slit, which is excellent in confining the surface acoustic wave energy. A surface acoustic wave device with high performance can be obtained.

Furthermore, according to still another aspect of the surface acoustic wave device of the present invention, at least one slit is formed perpendicularly to the plurality of electrode fingers in each of the pair of bus bar electrodes and the pair of common electrodes. ing. Therefore, both the surface acoustic wave leaking through the bus bar electrode due to the deviation of the traveling direction due to diffraction and the surface acoustic wave leaking through the common electrode are reflected by the slit and returned to the surface acoustic wave device. Therefore, it is possible to provide a surface acoustic wave device with higher performance that is more excellent in confining surface acoustic wave energy.

Furthermore, according to the surface acoustic wave device of the present invention, when the width of the slit is smaller than half the arrangement pitch of the electrode fingers, the surface acoustic going leaks deviated traveling direction by the diffraction In some of the waves, the waves reflected on both sides of the slit are in phase, and the surface acoustic waves can be reflected more efficiently by the slits. A surface acoustic wave device can be obtained.

Furthermore, according to the surface acoustic wave device of the present invention, a plurality of the slits are formed in each of the bus bar electrodes and / or the common electrode, and the arrangement pitch is made smaller than the arrangement pitch of the electrode fingers. In this case, a part of the surface acoustic wave that leaks due to the deviation of the traveling direction due to diffraction can be Bragg reflected by a plurality of slits, and the surface acoustic wave can be reflected more efficiently by the slit. Therefore, it is possible to provide a high-performance surface acoustic wave device further excellent in confining surface acoustic wave energy.

  Hereinafter, the surface acoustic wave device of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is an external perspective view schematically showing a surface acoustic wave device according to an embodiment of the present invention. The surface acoustic wave device shown in FIG. 1 is connected to the pair of reflectors 20 arranged along the propagation direction of the surface acoustic wave on the upper surface of the piezoelectric substrate 10, the IDT 30 arranged therebetween, and further connected to the IDT 30. Are formed with various electrodes including a pad electrode 40 and the like for electrical connection.

  The piezoelectric substrate 10 is made of, for example, piezoelectric single crystal such as crystal, lithium tantalate single crystal, lithium niobate single crystal, lithium tetraborate single crystal, or piezoelectric ceramics such as lead titanate and lead zirconate, In addition to functioning as a support base material that supports the various electrodes on its upper surface, when an electric signal is applied to the piezoelectric substrate 10 via the IDT 30, it acts to generate a predetermined surface acoustic wave on its principal surface.

  The IDT 30 includes a pair of comb-like electrodes formed by connecting one ends of a plurality of electrode fingers 31 arranged at equal intervals along the propagation direction of the surface acoustic wave with a strip-shaped bus bar electrode 32. They are arranged so as to face each other in an interlocked state so as to be alternately arranged in the propagation direction of the surface acoustic wave. When a predetermined electrical signal is applied from the outside, a predetermined surface acoustic wave corresponding to the arrangement pitch of the electrode fingers 31 is generated on the upper surface of the piezoelectric substrate 10.

  On the other hand, the reflector 20 is configured by connecting both ends of a plurality of reflective electrodes 21 arranged at equal intervals at substantially the same pitch as the electrode fingers 31 of the IDT 30 along the propagation direction of the surface acoustic wave by the common electrode 22. ing. The surface acoustic wave generated in the IDT 30 formation region is reflected and confined between the pair of reflectors 20.

  The pad electrode 40 is a portion to which fine metal wires and bumps that are electrically connected to the outside are joined, and is electrically connected to the IDT 30.

  The various electrodes are made of, for example, a metal material such as aluminum or an alloy containing aluminum as a main component. A resist is spin-coated on an electrode film formed on the piezoelectric substrate 10 by vapor deposition or sputtering, and a stepper device or the like is provided. It is formed by etching using a RIE (Reactive Ion Etching) apparatus or the like after exposure and development. The pad electrode 40 may be covered with Ni, Cr, Au or the like on the upper surface in order to improve the bondability with a fine metal wire or bump, and the thickness is preferably thicker than other electrodes.

  Thus, a surface acoustic wave resonator is constituted by the pair of reflectors 20 and the IDT 30 disposed therebetween.

  A characteristic feature of this embodiment is that a plurality of slits 33 perpendicular to the electrode fingers 31 are formed in the bus bar electrode 32 of the IDT 30 at equal intervals, and a plurality of slits 23 perpendicular to the electrode fingers 31 are provided as reflectors. That is, the 20 common electrodes 22 are formed at equal intervals.

  In the surface acoustic wave device as described above, most of the surface acoustic waves generated by the IDT 30 propagate in the direction perpendicular to the electrode fingers 31 (the direction in which the electrode fingers 31 are arranged) and are multiplexed between the pair of reflectors 20. Reflected and trapped. However, the propagation direction of some surface acoustic waves changes due to diffraction, passes through the bus bar electrode 32 of the IDT 30 and the common electrode 22 of the reflector 20, and leaks to the outside of the surface acoustic wave device. The electrical characteristics of the wave device were deteriorated.

  In the surface acoustic wave device of this embodiment, the slit 33 is formed in the bus bar electrode 32 and the slit 23 is formed in the common electrode 22, so that the surface acoustic wave to be leaked to the outside is reflected by the slits 23 and 33. Thus, it can be confined in the surface acoustic wave device.

  The reflection of the surface acoustic waves at the slits 23 and 33 is generated on both side surfaces of the slits 23 and 33 by the same mechanism as the reflection at the reflective electrode 21. Therefore, a large number of slits 23 and 33 may be formed in order to improve the reflection amount, and in order to increase the reflection amount per slit, the thickness of the bus bar electrode 32 and the common electrode 22 is increased. Is desirable.

The arrangement pitch of the slits 23 and 33 may be approximately the same as the arrangement pitch of the electrode fingers 31, and the width of the slits 23 and 33 may be approximately the same as ½ of the arrangement pitch of the electrode fingers 31. More preferably, however, the arrangement pitch of the slits 23 and 33 is made smaller than the arrangement pitch of the electrode fingers 31, and the width of the slits 23 and 33 is approximately ½ of the arrangement pitch of the slits 23 and 33. (The width of the slits 23 and 33 is set to be smaller than ½ of the arrangement pitch of the electrode fingers 31.)
This is to efficiently reflect the surface acoustic wave incident obliquely on the slits 23 and 33. For example, in order to Bragg-reflect surface acoustic waves incident at an angle A with respect to a direction perpendicular to the slits 23 and 33, the arrangement pitch of the slits 23 and 33 is 1 / cosA of the arrangement pitch of the electrode fingers 31, and the slit 23 , 33 may be 1 / (2 cos A) of the arrangement pitch of the electrode fingers 31. Since the surface acoustic waves are incident on the slits 23 and 33 at various angles, it is impossible to Bragg-reflect all the surface acoustic waves. By making it smaller than the arrangement pitch, the surface acoustic wave incident at a specific angle can be Bragg reflected, and the surface acoustic wave can be efficiently reflected.

  The distribution of the angle of incidence of the surface acoustic wave on the slits 23 and 33 is such that the material of the piezoelectric substrate 10, the logarithm of the electrode fingers 31 of the IDT 30, the crossing width, the array pitch, the opening length, etc. Since it varies depending on various design matters such as the number, opening length, and arrangement pitch, the arrangement pitch and width of the slits 23 and 33 are set to appropriate values accordingly.

  Further, since the distribution of the surface acoustic wave incident angle with respect to the slit 33 in the IDT 30 and the surface acoustic wave incident angle distribution with respect to the slit 23 in the reflector 20 are different, the arrangement pitch and width of the slit 33 and the arrangement pitch of the slit 23 And by making the widths different, it becomes possible to reflect the surface acoustic wave more efficiently. In general, the incident angle of the surface acoustic wave to the slit 23 of the reflector 20 tends to be deeper than the incident angle of the surface acoustic wave to the slit 33 of the IDT 30. Therefore, by making the arrangement pitch and width of the slits 23 of the reflector 20 smaller than the arrangement pitch and width of the slits 33 of the IDT 30, surface acoustic waves can be reflected more efficiently.

  The slits 23 and 33 can be formed at the same time as forming the various electrodes by coating a resist on the electrode film formed on the piezoelectric substrate 10 by vapor deposition or sputtering and exposing, developing and etching. Well, this does not increase manufacturing equipment or manufacturing processes.

  Next, a surface acoustic wave device according to another embodiment of the present invention will be described with reference to FIG. In the present embodiment, only differences from the above-described embodiment will be described, and the same components will be denoted by the same reference numerals, and redundant description will be omitted.

  FIG. 2 is an external perspective view schematically showing the surface acoustic wave device of the present embodiment. The surface acoustic wave device of this embodiment is different from the surface acoustic wave device of the above-described embodiment in that each slit 33 formed in the IDT 30 has a plurality of slit pieces 33a perpendicular to the electrode fingers 31. That is, they are arranged in a line in the side direction. With such a structure, the electrical path connecting each electrode finger 31 and the pad electrode 40 increases, and loss due to electrical resistance can be reduced.

  In addition, this invention is not limited to the above-mentioned embodiment, A various change and improvement are possible in the range which does not deviate from the summary of this invention.

  For example, in the surface acoustic wave device described above, an example in which a coating layer is not formed on the piezoelectric substrate 10 and the various electrodes has been shown, but a coating layer made of an insulating material or a semiconductive material may be formed. I do not care.

  In the above-described embodiment, an example in which a surface acoustic wave resonator is configured has been described. Needless to say, the present invention can also be applied to other surface acoustic wave devices such as a surface acoustic wave filter and a duplexer using the surface acoustic wave filter. Yes.

1 is an external perspective view schematically showing a surface acoustic wave device according to an embodiment of the present invention. It is an external appearance perspective view which shows typically the surface acoustic wave apparatus which concerns on another embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Piezoelectric substrate 20 ... Reflector 21 ... Reflective electrode 22 ... Common electrode 30 ... IDT
31 ... Electrode finger 32 ... Bus bar electrode 23, 33 ... Slit 33a ... Slit piece 40 ... Pad electrode

Claims (5)

A pair of comb-like electrodes formed by connecting one end of a plurality of electrode fingers arranged at equal intervals along the propagation direction of the surface acoustic wave on the piezoelectric substrate with bus bar electrodes so that the electrode fingers mesh with each other. In addition to forming IDTs facing each other, both ends of a plurality of reflective electrodes arranged at equal intervals along the surface acoustic wave propagation direction are connected to both sides of the IDT surface acoustic wave propagation direction by a common electrode. In the surface acoustic wave device formed by forming a pair of reflectors,
2. A surface acoustic wave device according to claim 1, wherein at least one slit is formed in each of the pair of bus bar electrodes perpendicular to the plurality of electrode fingers. A pair of comb-like electrodes formed by connecting one end of a plurality of electrode fingers arranged at equal intervals along the propagation direction of the surface acoustic wave on the piezoelectric substrate with bus bar electrodes so that the electrode fingers mesh with each other. The IDT is formed so as to face each other, and both ends of a plurality of reflective electrodes arranged at equal intervals along the propagation direction of the surface acoustic wave on both sides of the surface acoustic wave propagation direction of the IDT are a pair of common electrodes. In the surface acoustic wave device formed by forming a pair of reflectors connected,
A surface acoustic wave device, wherein at least one slit is formed in each of the pair of common electrodes perpendicularly to the plurality of electrode fingers. A pair of comb-like electrodes formed by connecting one end of a plurality of electrode fingers arranged at equal intervals along the propagation direction of the surface acoustic wave on the piezoelectric substrate with bus bar electrodes so that the electrode fingers mesh with each other. The IDT is formed so as to face each other, and both ends of a plurality of reflective electrodes arranged at equal intervals along the propagation direction of the surface acoustic wave on both sides of the surface acoustic wave propagation direction of the IDT are a pair of common electrodes. In the surface acoustic wave device formed by forming a pair of reflectors connected,
2. A surface acoustic wave device according to claim 1, wherein at least one slit is formed in each of the pair of bus bar electrodes and the pair of common electrodes perpendicular to the plurality of electrode fingers.   4. The surface acoustic wave device according to claim 1, wherein a width of the slit is smaller than ½ of an arrangement pitch of the electrode fingers.   The said slit is formed in each said bus-bar electrode and / or the said common electrode, and the arrangement pitch is made smaller than the arrangement pitch of the said electrode finger, The Claim 1 thru | or 4 characterized by the above-mentioned. Surface acoustic wave device.

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