JP2005020547A - Surface acoustic wave device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface acoustic wave device which has high frequency precision as well as frequency stability, simple manufacturing process, and low manufacturing cost. <P>SOLUTION: A surface acoustic wave element in which an IDT (Interdigital Transducer) electrode formed on a main face of piezoelectric substrate of rectangular form is covered with a protecting film, is mounted on a substrate as it is held only at an end side or the center part. An arbitration film of identical composition to the protecting film is attached on the other main face of the piezoelectric substrate. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a surface acoustic wave device used for mobile communication devices such as mobile phones, network devices, in-vehicle devices, medical devices, and the like, and more specifically, used for an oscillation circuit or the like that requires high frequency accuracy. The present invention relates to a surface acoustic wave device.
[0002]
[Prior art]
Surface acoustic wave devices such as surface acoustic wave resonators and surface acoustic wave filters are widely used in various wireless communication devices, network devices, in-vehicle devices, medical devices, etc. that use the microwave band. Surface acoustic wave devices used for circuits and the like are required to have higher frequency accuracy and stability.
[0003]
In order to satisfy this requirement, surface acoustic wave devices having a structure in which only a part of a surface acoustic wave element is held on a substrate have been proposed (see, for example, Patent Document 1 and Patent Document 2). ).
[0004]
FIG. 5 is a cross-sectional view schematically showing a conventional surface acoustic wave device disclosed in Patent Document 1, which is mounted on the upper surface of a base so as to hold only a part of the surface acoustic wave element. FIG. 2 is a plan view schematically showing the structure of an electrode formed on the upper surface of a surface acoustic wave element.
[0005]
A surface acoustic wave device 100 shown in FIG. 5 has a structure in which one end of a surface acoustic wave element 110 is fixed to a case 130 with an adhesive 120 and hermetically sealed with a lid 140. Here, as shown in FIG. 6, the surface acoustic wave element 110 includes a pair of comb-like electrodes 112a and 112b each having a plurality of electrode fingers, and the other comb-like electrode between the electrode fingers of one comb-like electrode. The interdigital transducer (IDT) electrode 112, which is disposed so that the electrode fingers of the electrode are positioned, and the reflector electrode 113 formed at both ends so as to sandwich the IDT electrode 112, and the IDT electrode 112 are electrically connected. The pad electrode 114 thus formed is formed on the upper surface of the piezoelectric substrate 111. The surface acoustic wave element 110 and the case 130 are electrically connected by connecting the pad electrode 114 of the surface acoustic wave element 110 and the connection electrode 131 of the case 130 by the bonding wire 150.
[0006]
When the entire lower surface and both ends of the surface acoustic wave element 110 are fixed to the case 130, the adhesive 120 that fixes the surface acoustic wave element 110 contracts, the case 130 warps due to a difference in thermal expansion coefficient from the lid 140, and the like. The surface acoustic wave element 110 is stressed and the frequency characteristic of the surface acoustic wave device 100 changes. However, the above-described structure can suppress the frequency change of the surface acoustic wave device 100. A surface acoustic wave device having high frequency accuracy and frequency stability can be obtained.
[0007]
[Patent Document 1]
Japanese Patent Laid-Open No. 11-330882 (FIGS. 1 and 11)
[0008]
[Patent Document 2]
JP 2002-26656 A (FIG. 1)
[0009]
[Problems to be solved by the invention]
However, the conventional surface acoustic wave device described above has the following problems.
[0010]
In other words, since the surface acoustic wave device described in Patent Document 2 has no countermeasure against conductive foreign matter, the foreign matter having electrical conductivity is held at different potentials by adhering to the electrode fingers of the IDT electrode. There is a problem that the pair of comb-like electrodes to be short-circuited with each other and the characteristics are not obtained.
[0011]
In addition, as in the surface acoustic wave device described in Patent Document 1, when an oxide film is formed by anodization on the surface of the IDT electrode, there is no problem of short circuit due to conductive foreign matter. Liquid composition (mixed solution of phosphate aqueous solution, borate aqueous solution, etc.) and temperature control, manual attachment of voltage-applying electrode to each wafer, cleaning after anodic oxidation treatment Since work is required, the manufacturing process becomes complicated, man-hours increase, and manufacturing costs increase.
[0012]
As a countermeasure against conductive foreign matter, there is also a simple method of depositing a protective film such as silicon or silicon oxide on the surface of the IDT electrode by sputtering or vapor deposition as used in a general surface acoustic wave device. However, this method has the following problems. That is, the piezoelectric substrate is deformed and the resonance frequency of the surface acoustic wave device is also shifted by the stress generated when the protective films having different thermal expansion coefficients are applied to the piezoelectric substrate at a high temperature and then returned to room temperature. Next, the stress is released little by little with the passage of time, so that the deformation of the piezoelectric substrate is also little by little. As a result, the resonance frequency of the surface acoustic wave device also changes little by little. Due to this phenomenon, there is a problem that the high frequency accuracy and frequency stability realized by holding only a part of the surface acoustic wave element are lost.
[0013]
The present invention has been devised in view of the above-mentioned problems, and an object thereof is to provide a surface acoustic wave device having high frequency accuracy and frequency stability, a simple manufacturing process, and low manufacturing cost. It is in.
[0014]
[Means for Solving the Problems]
In the surface acoustic wave device according to the present invention, an IDT electrode and a pad electrode are attached to and formed on one main surface of a rectangular piezoelectric substrate, and the IDT electrode is protected with a non-formation region on the pad electrode. A surface acoustic wave element covered with a film is held only on one end side or the central part thereof, and is mounted on a substrate having a connection electrode electrically connected to the pad electrode. In the surface wave device, an adjustment film having the same composition as that of the protective film is deposited on the other main surface of the piezoelectric substrate.
[0015]
The surface acoustic wave device according to the present invention is characterized in that the adjustment film has a non-formation region corresponding to the non-formation region of the protective film on a one-to-one basis.
[0016]
[Action]
According to the surface acoustic wave device of the present invention, the IDT electrode and the pad electrode are deposited and formed on one main surface of the rectangular piezoelectric substrate, and the IDT electrode is not formed on the pad electrode. The surface acoustic wave element covered with the protective film is held on only one end side or the central part thereof, and mounted on a substrate having a connection electrode electrically connected to the pad electrode, An adjustment film having the same composition as that of the protective film is deposited on the other main surface of the piezoelectric substrate. Therefore, the stress due to the protective film deposited on the one main surface of the piezoelectric substrate and the stress due to the adjustment film deposited on the other main surface of the piezoelectric substrate balance at the initial value and are released in the same way as time passes. Therefore, the deformation of the piezoelectric substrate is suppressed, and the change with time of the frequency characteristics of the surface acoustic wave element is also suppressed. Therefore, a surface acoustic wave device excellent in frequency accuracy and frequency stability can be obtained.
[0017]
According to the surface acoustic wave device of the present invention, since the adjustment film has a non-formation area corresponding to the non-formation area of the protective film, the stress exerted on the piezoelectric substrate by the adjustment film. Can be further made equal to the stress exerted on the piezoelectric substrate by the protective film, and the temporal change of the frequency characteristics of the surface acoustic wave device can be further suppressed. Therefore, it is possible to obtain a surface acoustic wave device with further excellent frequency accuracy and frequency stability.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail with reference to the drawings.
[0019]
(First embodiment)
FIG. 1 is a plan view schematically showing a surface acoustic wave device according to a first embodiment of the present invention, and FIG. 2 is a perspective view of a surface acoustic wave element used in the surface acoustic wave device of FIG.
[0020]
In FIG. 1, a surface acoustic wave device 1 has a structure in which a surface acoustic wave element 10 is mounted on a base body 40 by a spacer 20 and an adhesive 30 so as to be held only at one end, and is hermetically sealed by a lid 50. Has been.
[0021]
As shown in FIG. 2, the surface acoustic wave element 10 is formed with various electrodes 60 including an IDT electrode 61, a reflector 62, a pad electrode 63, and the like on the upper surface of the piezoelectric substrate 11, and the upper surface is further formed with a pad electrode. 63 is covered with a protective film 70 so as to be exposed, and an adjustment film 80 is attached to the lower surface of the piezoelectric substrate 11.
[0022]
The pad electrode 63 and the connection electrode 44 formed on the base body 40 are connected by a bonding wire 90, and the surface acoustic wave element 10 and the base body 40 are electrically connected.
[0023]
The piezoelectric substrate 11 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 or lead zirconate. In addition to functioning as a support base material that supports the various electrodes 60, the protective film 70, and the like on the upper surface, when electric power is applied to the piezoelectric substrate 11 through the various electrodes 60, a predetermined surface acoustic wave is generated on the upper surface. To act.
[0024]
The various electrodes 60 are made of, for example, a metal material such as aluminum or an alloy containing aluminum as a main component. The IDT electrodes 61 excite surface acoustic waves, and are formed on both sides of the IDT electrodes 61 along the propagation direction of the surface acoustic waves. The reflector 62, the pad electrode 63 for external connection electrically connected to the IDT electrode 61, etc. are comprised.
[0025]
The IDT electrode 61 includes a pair of comb-like electrodes 61a and 61b each formed of a strip-shaped common electrode and a plurality of electrode fingers extending in a direction orthogonal to the common electrode, and the common electrodes are parallel to each other. And the electrode fingers of the comb-like electrodes 61a and 61b are arranged to face each other so as to be alternately arranged in the propagation direction of the surface acoustic wave in the facing region of both the common electrodes.
[0026]
When a predetermined power is applied from the outside to the IDT electrode 61, a predetermined surface acoustic wave corresponding to the arrangement pitch of the electrode fingers on the upper surface of the piezoelectric substrate 11, specifically, the arrangement pitch of the electrode fingers is 1 / It acts to generate surface acoustic waves with two wavelengths.
[0027]
On the other hand, the reflector 62 is for confining the surface acoustic wave generated in the region where the IDT electrode 61 is formed between the pair of reflectors 62a and 62b to generate a standing wave satisfactorily. A plurality of strip-like reflective electrodes are arranged at substantially the same pitch as the electrode fingers of the IDT electrode 61, and are spaced outside the IDT electrode 61 by approximately the same interval as the arrangement pitch of the electrode fingers of the IDT electrode 61. Arranged.
[0028]
The pair of reflectors 62a and 62b and the IDT electrode 61 disposed therebetween constitute a one-terminal pair resonator.
[0029]
The pad electrode 63 is a portion to which bonding wires and bumps that are electrically connected to the outside are joined, and is electrically connected to the IDT electrode 61.
[0030]
For the various electrodes 60 as described above, a resist is spin-coated on an electrode film formed on the piezoelectric substrate 11 by well-known vapor deposition or sputtering, and after exposure and development using a stepper device or the like, an RIE device or the like is used. It can be formed by etching.
[0031]
The protective film 70 is made of an inorganic material such as an insulating material such as silicon oxide or silicon nitride, or a semiconductive material such as silicon, and is formed by conventionally known sputtering or vapor deposition. The protective film 70 is formed on the upper surface of the piezoelectric substrate 11 so as to expose the pad electrode 63, and even after the protective film 70 is formed, the bonding wire 90 and the bump are connected to the pad electrode 63 so as to be externally connected. It can be connected electrically.
[0032]
Note that the protective film 70 is for preventing a short circuit or damage of the IDT electrode 61 due to conductive foreign matter or the like. For this purpose, the thickness is preferably set to 200 mm or more.
[0033]
Similarly to the protective film 70, the adjustment film 80 is made of an inorganic material such as an insulating material such as silicon oxide or silicon nitride or a semiconductive material such as silicon, and is formed by sputtering or vapor deposition. Since the adjustment film 80 is for offsetting the influence of the stress of the protective film 70, the same composition as that of the protective film 70 is preferably used to make the stress of the adjustment film 80 coincide with the stress of the protective film 70. Is done. Furthermore, the stress canceling effect of the adjustment film 80 can be further enhanced by matching the film forming conditions and thickness of the adjustment film 80 with those of the protective film 70.
[0034]
The surface acoustic wave element 10 as described above is supported by the spacer 20 on the lower surface of a portion slightly inside from one end in the longitudinal direction, and the base 40 is formed on the lower surface and side surface near the one end by the adhesive 30. The other end is lifted from the base body 40 and mounted.
[0035]
The spacer 30 protrudes about 30 μm from the base body 40 and functions to support the surface acoustic wave element 10 like a fulcrum of a seesaw. Although materials such as metal, ceramic, and epoxy resin can be used, they can be easily formed by applying and baking or curing a metal paste in the same manner as the wiring electrode formed on the substrate 40.
[0036]
A silicon-based adhesive or the like is preferably used as the adhesive 30, and the surface acoustic wave element 10 is cured by being pulled in a state where one end of the surface acoustic wave element 10 is pulled toward the substrate 40 due to shrinkage during curing. The surface acoustic wave element 10 functions to be fixed to the base 40 in a state where the other end of the surface is lifted from the base 40.
[0037]
The base body 40 is made of ceramic or the like, and is configured by laminating frames 42 and 43 on a flat plate 41 having a mounting portion for the surface acoustic wave element 10, and has a box shape with an open top surface. Of the base body 40, only the frame 43 has a structure in which gold or the like is plated on the surface of an alloy such as Kovar (iron / nickel / cobalt alloy). The lid 50 is plated with nickel or the like and joined by seam welding. Further, a connection electrode 44 to which a bonding wire 90 is connected is formed on the upper surface of the flat plate 41, and an external formed on the lower surface of the base body 40 via the wiring electrode 45 formed inside or on the surface of the base body 40. The terminal electrode 46 is electrically connected.
[0038]
With the above configuration, the surface acoustic wave device 1 having excellent frequency accuracy and frequency stability can be obtained by offsetting the influence of the stress of the protective film 70 by the stress of the adjustment film 80.
[0039]
(Second Embodiment)
Next, a surface acoustic wave element used in a surface acoustic wave device according to a second embodiment of the present invention will be described with reference to FIG. In the present embodiment, only the points different from the first embodiment described above will be described, and the same reference numerals will be used for the same components, and overlapping description will be omitted.
[0040]
A characteristic feature of the surface acoustic wave element 10 used in the surface acoustic wave device of the second embodiment shown in FIG. 3 is that the adjustment film 80 deposited on the lower surface of the surface acoustic wave element 10 is similar to the protective film 70. The non-formation region is provided. As a result, the protective film and the adjustment film are formed on the upper and lower surfaces of the piezoelectric substrate 11 in the same area, and the stress applied to the piezoelectric substrate 11 by each film can be further equalized. Is possible. Therefore, by mounting the surface acoustic wave element 10 on the substrate so as to be held only at one end as shown in FIG. 1, the surface acoustic wave device 1 having further excellent frequency accuracy and frequency stability is obtained. be able to.
[0041]
(Third embodiment)
Next, a surface acoustic wave device according to a third embodiment of the present invention will be described with reference to FIG. FIG. 4 is a sectional view schematically showing a surface acoustic wave oscillator to which the present invention is applied. Also in the present embodiment, only characteristic points different from the above-described embodiment will be described, and the same reference numerals will be used for the same components, and overlapping description will be omitted.
[0042]
In the surface acoustic wave oscillator 2 shown in FIG. 4, the surface shape of the surface acoustic wave element 10 having a surface acoustic wave resonator is formed on the upper side. On the lower side, an integrated circuit 3 incorporating an oscillation circuit is mounted. The integrated circuit 3 is electrically connected to a connection electrode 44 formed on the base body 40 via bonding wires 90, and further, via a wiring electrode (not shown) formed on the surface and inside of the base body 40. The surface acoustic wave element 10 and the external terminal electrode 46 are electrically connected to form a surface acoustic wave oscillator as a whole.
[0043]
Even in such a surface acoustic wave oscillator 2, a surface acoustic wave resonator having excellent frequency accuracy and frequency stability can be obtained by applying the present invention. Since it depends on the accuracy and stability of the resonance frequency of the resonator, a surface acoustic wave oscillator excellent in the accuracy and stability of the oscillation frequency can be obtained.
[0044]
(Experimental example)
Next, the results of experiments conducted to verify the operational effects of the present invention will be described. First, a surface acoustic wave device of a comparative example in which the product of the present invention as shown in FIG. 3 and the adjustment film 80 are not formed is prepared, and only one end thereof is held as shown in FIG. 40 and hermetically sealed. An ST-cut quartz substrate was used as the piezoelectric substrate, and aluminum was used as the material for the IDT electrode 61, the reflector electrode 62, and the pad electrode 63. Further, as the protective film 70 and the adjustment film 80, a silicon film having a thickness of 500 mm was formed by sputtering. The film forming conditions and thickness of the adjustment film 80 were the same as those of the protective film 70.
[0045]
Regarding the sample prepared as described above, the change in the resonance frequency from the sample creation time to 500 hours later was measured. In contrast, the comparative example without the adjustment film showed a change of 60 ppm with respect to the initial frequency. In the product of the present invention, the amount of change was about 20 ppm. This confirmed the remarkable effectiveness of the present invention.
[0046]
The present invention is not limited to the above-described embodiment, and various changes and improvements can be made without departing from the gist of the present invention.
[0047]
For example, in the above-described embodiment, the surface acoustic wave element 10 is mounted on the base 40 so as to be held only at one end portion thereof, but the surface acoustic wave element 10 is held only at the central portion thereof. 40 may be mounted.
[0048]
In the above-described embodiment, the surface acoustic wave element 10 and the base 40 are electrically connected using the bonding wire 90. However, the surface acoustic wave element 10 is flip-chip mounted on the base 40, and conductive bumps are used. Electrical connection and mechanical connection may be performed simultaneously. In this case, it is desirable to connect to the base body 40 at the center of the surface acoustic wave element 10.
[0049]
Further, in the above-described embodiment, the surface acoustic wave element 10 is mounted on the box-shaped base 40. However, the surface acoustic wave element 10 may be mounted on a flat base or mounted in a cavity formed on a module substrate or the like. It doesn't matter.
[0050]
Furthermore, in the above-described embodiment, the various electrodes 60 are formed of a metal such as aluminum or an aluminum alloy. However, the various electrodes 60 may be formed using other conductive materials.
[0051]
Furthermore, in the above-described embodiment, an example in which the present invention is applied to a one-terminal-pair resonator and an oscillator has been described, but other than that, for example, a surface acoustic wave filter such as a ladder filter or a multimode filter, Needless to say, the present invention can also be applied to a surface acoustic wave device such as a duplexer.
[0052]
Furthermore, in the above-described embodiment, if the adjustment film is provided with a non-formation area corresponding to the non-formation area of the protective film, an elastic surface with further excellent frequency accuracy and frequency stability. There is an advantage that a wave device can be obtained. Therefore, it is preferable that the adjustment film is provided with a non-formation region corresponding to the non-formation region of the protective film on a one-to-one basis.
[0053]
【The invention's effect】
According to the surface acoustic wave device of the present invention, the IDT electrode and the pad electrode are deposited and formed on one main surface of the rectangular piezoelectric substrate, and the IDT electrode is not formed on the pad electrode. The surface acoustic wave element covered with the protective film is held on only one end side or the central part thereof, and mounted on a substrate having a connection electrode electrically connected to the pad electrode, Since the adjustment film having the same composition as that of the protective film is deposited on the other main surface of the piezoelectric substrate, a surface acoustic wave device having excellent frequency accuracy and frequency stability can be obtained.
[0054]
Further, according to the surface acoustic wave device of the present invention, the adjustment film has a non-formation area corresponding to the non-formation area of the protective film on a one-to-one basis, so that frequency accuracy and frequency stability are further improved. An excellent surface acoustic wave device can be obtained.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view schematically showing a surface acoustic wave device according to a first embodiment of the present invention.
2 is a perspective view schematically showing a surface acoustic wave element used in the surface acoustic wave device of FIG. 1. FIG.
FIG. 3 is a perspective view schematically showing a surface acoustic wave element used in a surface acoustic wave device according to a second embodiment of the invention.
FIG. 4 is a cross-sectional view schematically showing a surface acoustic wave device according to a third embodiment of the present invention.
FIG. 5 is a cross-sectional view schematically showing a conventional surface acoustic wave device.
FIG. 6 is a plan view schematically showing a surface acoustic wave element used in a conventional surface acoustic wave device.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Surface acoustic wave apparatus 10 ... Surface acoustic wave element 20 ... Spacer 30 ... Adhesive 40 ... Base | substrate 50 ... Lid 60 ... Various electrodes 70 ... Protective film 80 ... Adjustment film 90 ... Bonding wire

Claims (2)

An elastic surface in which an IDT electrode and a pad electrode are deposited and formed on one main surface of a rectangular piezoelectric substrate, and the IDT electrode is covered with a protective film having a non-formation region on the pad electrode A surface acoustic wave device that is mounted on a substrate having a connection electrode that is electrically connected to the pad electrode so as to hold the wave element only at one end side or the center thereof,
2. A surface acoustic wave device according to claim 1, wherein an adjustment film having the same composition as that of the protective film is deposited on the other main surface of the piezoelectric substrate. 2. The surface acoustic wave device according to claim 1, wherein the adjustment film has a non-forming region corresponding to the non-forming region of the protective film on a one-to-one basis.

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