JPH0321112A - Manufacture of surface acoustic element - Google Patents

Abstract

PURPOSE:To simplify the formation of an air gap and to improve the production yield and yield rate by arranging space forming parts on plural prescribed positions between a non-piezo-electric substrate and a piezo-electric substrate and bonding both the substrates through the space forming parts to form the air gap. CONSTITUTION:In the manufacturing method of an surface acoustic wave element obtained by arranging the piezo-electric substrate 1 oppositely to a comb line electrode 3 formed on the non-piezo-electric substrate 4 through the air gap 2, an electrode 3 and a lead guiding part 30 are formed on the substrate 4, the space formation parts 5 having height necessary for forming height necessary for forming the air gap 2 are arranged on plural positions excluding the electrode 3 formed between both substrates 4, 1 and a surface wave propagation part and both the substrates 4, 1 are bonded and fixed through the space formation parts 5. Since the space formation parts 5 are formed on plural prescribed position and both the substrates are bonded and fixed through the space formation parts 5 in said constitution, the air gap can be extremely simply formed.

Description

[Detailed Description of the Invention] (Summary) Regarding a method for manufacturing a surface acoustic wave device, the objective is to eliminate the mass effect of the electrodes of the surface acoustic wave device, improve the internal characteristics and spurious characteristics, and In a method for manufacturing a surface acoustic wave device, in which a piezoelectric substrate and a comb-shaped electrode formed on a non-piezoelectric substrate are disposed facing each other with an air gap therebetween, the comb-shaped electrode and a lead lead-out portion are formed on the non-piezoelectric substrate. and space forming portions having a height necessary for forming the air gap are arranged at multiple locations between the non-piezoelectric substrate and the piezoelectric substrate, excluding the comb-shaped electrode and the surface wave propagation portion. The method for manufacturing a surface acoustic wave element is configured such that the j1 piezoelectric break plate and the piezoelectric substrate are bonded and fixed with the space forming portion in between.

[Industrial Field of Application] The present invention relates to a method for manufacturing a surface acoustic wave device, particularly an air gap electrode type surface acoustic wave device.

In recent years, with the increase in speed of information processing equipment and communication equipment,
Frequencies 411f of carrier waves and signal waves have been softened to high frequency ranges, and correspondingly, highly stable reference signals have been generated at high frequencies. Phase synchronization elements or filters are required, and recently surface acoustic wave elements such as surface acoustic wave filters and surface acoustic wave resonators have come to be used for these purposes.

In the future, by taking advantage of its small size and low cost, it is expected that it will be used in mobile radio applications such as car phones and mobile phones. development is required.

[Conventional technology]

A surface acoustic wave element, for example, a surface acoustic wave filter, uses a substrate having a large electrical-mechanical coupling coefficient and a relatively small temperature coefficient of frequency, for example, a 36° rotation Y cut-X
Propagation LiTa03 (36°Y X LiTaO:+
) It is a three-terminal or four-terminal device in which comb-shaped electrodes for excitation and reception are provided on a single crystal substrate.

The width (L) of the comb teeth of the comb-shaped electrode, the space between the comb teeth (S), and the pitch (P) of the comb teeth are usually expressed as follows, where λ is the wavelength of the surface wave.
There are many design values such as L=S-λ/4 and P-λ/2. For example, the center frequency 1 6 0 M I-1 z
In order to obtain the sound velocity of the X-propagating surface wave of the substrate 1,
λ-26 μm is calculated from 90 m/s, the electrode pitch is 13 μm, and the inside and electrode spacing is 6.5 μm.

FIG. 7 is a diagram showing two examples of the structure of a conventional surface acoustic wave element, in which figure (a) is a perspective view of the conventional example, figure (b) is an AA' cross-sectional view of the conventional example, FIG. 3(C) is a sectional view of another conventional example at 818'. In the figure, 100 (a piezoelectric substrate, for example, a 36°Y-X LiTaOa board. 110
1 is a comb-shaped electrode for excitation, 111 and 1124; 1 its lead lead-out portion; 120 is a comb-shaped electrode for reception; 121 and 12
2 is its lead lead-out portion.

The material for these electrodes is preferably a metal with low electrical resistance such as Au, but metals with high density have a negative effect on in-band ripple characteristics and insertion loss characteristics due to the mass effect on surface wave vibration. For this reason, light Al or A42 alloy is usually used. Additionally, a thin film of 100 to 150 nm is deposited by vapor deposition or the like.

In the conventional example shown in the cross-sectional view of the figure (opening), a piezoelectric substrate 10
This is the most common electrode construction method for surface wave filters, in which comb-shaped electrodes 110 and 120 are directly and tightly formed on the surface of a surface wave filter.

On the other hand, in another conventional example shown in the cross-sectional view of FIG. It is organized. The most well-known example of such a structure is LiTaO3 with a piezoelectric base + ti 1o
When used as an insulating layer 101, the thickness is several μm.
This is an example in which a silicon dioxide (SiO■) film is interposed;
The temperature coefficient of the surface wave propagation velocity of the iO film has the opposite sign to that of LiTa03, and this is a device structure proposed to improve the frequency temperature characteristics (for example, IEEE +
1975 Ultrasonics Symposium
mProceedings, pp 503-507, S
ept. , 1975).

In all of the above conventional examples, the comb-shaped electrode is formed in close contact with the surface wave transmission substrate, so even though it is made of light Al, the weight of the comb-shaped electrode is directly or SiO. Since the piezoelectric material is flush with the surface of the piezoelectric material through the film, the influence of the mass effect occurs.

Therefore, surface acoustic wave elements having a structure in which an air gap is provided between a piezoelectric substrate and a comb-shaped electrode have recently been proposed.

FIG. 6 is a diagram illustrating a conventional manufacturing method of an air gap type surface acoustic wave element, which has already been proposed by the present inventors.

In the figure, 1 is a piezoelectric band substrate, for example, 36°Y-XL
It is an iTa03 board. 200 is air gap, 130a
, 130b are comb-shaped electrodes for excitation and reception, respectively;
Reference numerals 13L and 132 indicate respective lead lead-out portions, 140 and 150 openings in the piezoelectric bridge 140, respectively.

As can be seen from the figure, the lead lead-out parts 131 and 132 are directly fixed on the piezoelectric substrate 1, whereas the comb-shaped electrodes 130a and 130b are suspended on the back surface of the piezoelectric body 140. is fixed to the piezoelectric substrate 1 to form an air gap 200 between the piezoelectric substrate 1 and the piezoelectric substrate 1. There is.

In order to form the air gap 200 in this conventional example, first, a layer (not shown in the figure) that can be removed later by selective etching is applied on the piezoelectric substrate 1 to a thickness and range corresponding to the air gap 200. material, for example, polysilicon as a space material or carbon
A film is formed using a VD method or the like, and an electrode metal film, for example, Au having a thickness of 2 am, is deposited on the second layer using an electron beam evaporation method.

Next, the comb-shaped electrode 130a,
130b and the lead-out portion 13L 132 are patterned.

Next, the comb-shaped electrodes 130a, 130 of the processed substrate
b, and a part of the lead lead-out portions 13] and 132, an insulating film is formed, for example, a SiOz film having a thickness of about 5 μm and is resistant to the selected polysilicon film (not shown).
Deposit to a thickness of m.

Next, the comb-shaped electrodes 130a and 130b of the treated substrate are
For example, an opening 150 of an appropriate size that does not touch the electrode part is formed in the insulating film made of SiO2 in the middle of C.
It is formed by ion etching in F.

Finally, from the opening 150 and the side surfaces on both sides of the processed substrate, from the exposed portion of the space material (not shown in the figure),
Selective engineering, e.g. rillW solution (ethylene cyan≧1-pitecarol + water) or KO at 80'C}
If only the polysilicon space material (not shown) is selectively dissolved and removed in one solution, the polysilicon space material (not shown) remains as an air gap 200 with a thickness of approximately 50 to 150 nm. Comb-shaped electrodes 130a, 13
0b is in a state of floating in the air, and an air-gap electrode type surface acoustic wave element is formed on the piezoelectric substrate 1 that has no mass effect at all.

[Problems to be solved by the invention] However, the conventional air-gap electrode type surface acoustic wave device described above has many manufacturing steps and is complicated, making it difficult to manufacture with a high yield and making the product expensive. There was a problem that needed to be solved.

[Means to solve the problem]

``2'' is a method for manufacturing a surface acoustic wave element in which a piezoelectric substrate 1 and a comb-shaped electrode 3 formed on a non-piezoelectric substrate 4 are disposed facing each other with an air gap 2 interposed therebetween.
A comb-shaped electrode 3 and a lead lead-out portion 30 are disposed on a non-piezoelectric substrate 4.
, and the non-piezoelectric substrate 4Fl. /I and piezoelectric substrate 1
Space forming portions 5 having a height necessary for forming the air gap 2 are provided at multiple locations between the comb-shaped electrode 3 and the surface wave propagation portion, and the non-piezoelectric substrate 4
This problem can be solved by a method of manufacturing a surface acoustic wave element, which is characterized in that the piezoelectric substrate 1 and the piezoelectric substrate 1 are adhesively fixed with the space forming portion 5 interposed therebetween.

[Effect]

According to the manufacturing method of the present invention, the piezoelectric substrate 1 and the comb-shaped electrode 3
The air gap 2 interposed between the non-piezoelectric substrate 4 and
Space forming portions 5 having a height necessary for forming the air gap 2 are arranged at predetermined plural locations between the non-piezoelectric substrate 4 and the piezoelectric substrate 1. Since it is only necessary to adhesively fix the space forming portion 5 between the two, it can be formed extremely easily.

[Embodiment] Figure (2) shows a first embodiment of the present invention, where (A) is an assembled perspective view, and (1) is a side view.

In the figure, ■ is a piezoelectric substrate, for example, 36°Y-X L
It is an iTa03 board. 2 is an air gap, 3a3b is a comb-shaped electrode for excitation and reception, 31 and 32 are respective lead lead-out portions, 4 is a non-piezoelectric substrate, 5 is a space forming portion, and 6 is a recessed portion.

As can be seen from the figure, the air gap 2 is a distance S obtained by subtracting the electrode thickness of the comb-shaped electrode 3 from the height of the space-shaped hollow portion 5 formed on the non-piezoelectric substrate 4.

Next, an example of the above manufacturing process will be described in order.

First, in the same figure (A), a non-piezoelectric substrate 4, for example,
A comb-shaped electrode 3a is placed on one surface of a glass substrate with a thickness of 0.45 mm.
A recess 6 for forming the comb-shaped electrode 3b and its lead lead-out portion 31, and the comb-shaped electrode 3b and its lead lead-out portion 32 are formed to have a smooth bottom surface.

For example, the recess 6 is formed by setting the surface wave propagation velocity of the 36° YX LiTaOs plate to 4090 m/sec, and the center frequency is 1.
In the case of a 60MHz surface wave filter, approximately 2.6μm
The depth shall be . That is, there are 2.6 μm-high grooves at six locations excluding the comb-shaped electrode 3a and its lead lead-out portion 31, the comb-shaped electrode 3b and its lead lead-out portion 32, and the surface wave propagation portion between the comb-shaped electrode 3a and the comb-shaped electrode 3b. Processing is performed so that a space forming portion 5 is formed. Processing may be carried out using chemical etching using hydrofluoric acid or ion etching using an appropriate etching gas after performing resist work.

Next, an electrode metal film is applied to the four parts 6, for example, with a thickness of 2 μm.
of Au is deposited by electron beam weeding method.

Next, the electrode metal film is etched using a known etching method.
Alternatively, etching by ion etching method,
The comb-shaped electrodes 3a, 3h and the lead-out portion 3132 are patterned.

On the other hand, as the piezoelectric substrate 1, a 36° Y-X LiTa03 plate, which is slightly smaller in size than the non-piezoelectric substrate 4 and has a thickness of 0.35 mm and whose surface has been polished smooth, is separately prepared.

Next, the processed non-piezoelectric substrate 4 and the piezoelectric substrate 1 are arranged so that the comb-shaped electrodes 3a and 3b and the smooth surface of the piezoelectric substrate I face each other, and an adhesive is applied to the surface of the space forming portion 5. , For example, it is fixed with an epoxy resin adhesive.

Thus, the interval S of the air gap 2 of the air gap type surface acoustic wave element formed according to this embodiment is 2.6.
-2 = 0.6 μm, and if the wavelength of the surface wave is λ, then the S spacing is λ/40.

That is, the comb-shaped electrodes 3a, 3b are in a state of floating in the air, and do not exert any mass effect on the piezoelectric substrate 1.

Finally, the leads are pulled out from the lead lead-out portion 3L32, and if necessary, they are covered and inspected to complete the test.

It should be noted that if the air gap 2 in the present invention is about λ/40 from the calculation of the electric field distribution using the conformal mapping method, the excitation power of the surface acoustic wave can be sufficiently generated manually, and the electric signal from the receiving electrode can also be It is possible to convert to

FIG. 2 shows a second embodiment of the present invention, in which (a) is an assembled perspective view and (b) is a side view.

In this example, the non-piezoelectric substrate 4 has a flat surface, and the comb-shaped electrodes 3a, 3b and the lead lead-out portion 3L 32 are patterned on the flat surface in the same manner as in the first embodiment.

On the other hand, the piezoelectric substrate 1 is machined so that the recess 6 has a depth of approximately 2.6 μm. That is, the comb-shaped electrode 3a and its lead-out portion 3LIi! Processed so that space forming portions 5 with a height of 2.6 μm are formed at six locations excluding the il-shaped electrode 3b and its lead lead-out portion 32, and the surface wave propagation portion between the comb-shaped electrode 3a and the comb-shaped electrode 3b. do.

If both of the above are made to face each other and bonded using an epoxy resin adhesive, an air gap type surface acoustic wave element can be manufactured in the same manner as in the first embodiment.

FIG. 3 is a diagram showing a third embodiment of the present invention, where (A) is an assembled perspective view and the same figure (opening) is a side view.

This embodiment is characterized in that both the piezoelectric substrate 1 and the non-piezoelectric substrate 4 can have smooth surfaces.

That is, the non-piezoelectric substrate 4 has a flat surface, and the comb-shaped electrodes 3a, 3b, lead lead-out portions 31. 32 is the first
A pattern is formed in the same manner as in the example.

The height is 2 at six locations excluding the comb-shaped electrode 3a and its lead lead-out portion 3L, the comb-shaped electrode 3b and its lead lead-out portion 32, and the surface wave propagation portion between the comb-shaped electrode 3a and the comb-shaped electrode 3b.
．． A space forming portion 5 made of, for example, a SiO film having a thickness of 6 μm is formed by electron beam evaporation.

On the other hand, if a smooth plate is prepared separately as the piezoelectric substrate 1, and the above two are bonded together with an epoxy resin adhesive, an air gap type surface acoustic wave element can be manufactured in the same manner as in the first embodiment. can do.

FIG. 4 is a diagram showing a fourth embodiment of the present invention, and FIG.

This embodiment is also characterized in that both the piezoelectric substrate 1 and the non-piezoelectric substrate 4 can be made smooth, and the non-piezoelectric substrate 4 has the same thickness as the electrode film, for example. , 2.
An Au film with a thickness of 0.071 m is formed simultaneously with the electrode film to form one space forming part 5a, and on the other hand, on the piezoelectric substrate 1 side, a SiO film with a thickness of d corresponding to the air gap 2, for example, 0.6 μm is formed. By forming the other space forming part 5b consisting of the above, and combining both, the required height of the space forming part 5 is 2.6 μm.

In this embodiment, the thickness of the SiO film can be reduced to 0.6 μm, so productivity is improved compared to the third embodiment.

FIG. 5 is a diagram showing a fifth embodiment of the wooden invention, where (A) is an assembled perspective view and the same figure (opening) is a side view.

This embodiment is also characterized in that both the piezoelectric substrate 1 and the non-piezoelectric substrate 4 can have smooth surfaces. Since it can be continuously formed on the soil of the body 2S plate 4, it is possible to further improve the domestic productivity.

The surface acoustic wave device manufacturing method of the present invention can be constructed by appropriately using +A materials or combinations thereof other than those shown in Examples 2 and 2, and other film forming techniques. Of course, you can do it.

Further, the size of the space forming portion 5, the thickness of the P'1 and the electrode are not limited to the above two embodiments, and may be set as appropriate according to the desired device performance. Just use the value.

It should be noted that although the above-mentioned embodiments show the case of a surface acoustic wave filter, it goes without saying that the manufacturing method of the present invention can be similarly applied to other surface acoustic wave resonators, delay elements, and the like.

(Effect of the invention) As described in detail below, according to the manufacturing method of the present invention,
The air gap 7 interposed between the piezoelectric substrate 1 and the comb-shaped electrode 3 is configured to provide the air gap 2 at a plurality of predetermined locations between the non-piezoelectric substrate 4 and the piezoelectric substrate 1. Since the space forming section 5 having the height necessary for forming the space forming section 5 is disposed and the non-piezoelectric substrate 4 and the piezoelectric substrate 1 are adhesively fixed to each other by sandwiching the space forming section 5, the air gap 2 can be formed extremely easily. Therefore, it greatly contributes to improving the quality stability, productivity, and yield of air-gap type surface acoustic wave elements, as well as reducing prices.

It is a figure which shows an example.

In the figure, 1 is a piezoelectric substrate; 2 is air gap, 3 (3a.3b) is a comb-shaped electrode, 4 is a non-piezoelectric substrate; 5 (5a, 5b) is the space forming part, 6 is the fourth part, 3L 32 is a lead lead-out section.

[Brief explanation of drawings]

Fig. 1 shows the first embodiment of the invention, Fig. 2 shows the second embodiment of the invention, Fig. 3 shows the third embodiment of the invention, and Fig. 4 shows the invention. A diagram showing a fourth embodiment of the invention, FIG. 5 a diagram showing a fifth embodiment of the invention, FIG. 6 a diagram explaining a conventional manufacturing method of an air gap type surface acoustic wave device, and FIG. 7 a diagram showing a conventional manufacturing method. Two Mi-1 configurations of surface acoustic wave elements:

Claims (1)

[Claims] In a method of manufacturing a surface acoustic wave element, a piezoelectric substrate (1) and a comb-shaped electrode (3) formed on a non-piezoelectric substrate (4) are arranged facing each other with an air gap (2) interposed therebetween,
A comb-shaped electrode (3) and a lead lead-out portion (30) are formed on a non-piezoelectric substrate (4), and the comb-shaped electrode (3) is located between the non-piezoelectric substrate (4) and the piezoelectric substrate (1). Space forming portions (5) having a height necessary to form the air gap (2) are provided at multiple locations excluding the surface wave propagation portion, and the non-piezoelectric substrate (4) and the piezoelectric Body board (1)
A method for manufacturing a surface acoustic wave device, comprising: adhesively fixing the space-forming portion (5) between the two.