JPH036912A - Surface acoustic wave element - Google Patents

Abstract

PURPOSE:To improve the in-band ripple characteristic and the insertion loss characteristic or the like by inserting an air gap between a piezoelectric substrate and an interdigital electrode. CONSTITUTION:Leadout parts 31, 32 are fixed directly onto a piezoelectric substrate 1, while interdigital electrodes 3a, 3b are fixed onto a rear side of an insulator bridge 4 in a pending way to form an air gap 2 with the piezoelectric substrate 1. Then a surface acoustic wave on the piezoelectric substrate 1 is excited or received via the above-mentioned air gap.

Description

[Detailed Description of the Invention] [Summary] Regarding the structure of a surface acoustic wave device, the purpose is to eliminate the mass effect of the electrodes of the surface acoustic wave device and improve the in-band characteristics and spurious characteristics, and the present invention includes a piezoelectric substrate and the above-mentioned. A comb shape placed above the piezoelectric substrate through an air gap! and an insulator bridge made of a non-piezoelectric material that supports the comb-shaped electrode, the comb-shaped electrode is configured to excite or receive surface acoustic waves in the piezoelectric substrate via the air gap. Configure a surface wave element.

[Industrial application field]

The present invention relates to a surface acoustic wave device, and in particular to configurations of excitation and reception electrodes thereof.

In recent years, with the increase in speed of information processing equipment and communication equipment,
The frequency bands of carrier waves and signal waves are increasingly shifting to higher frequencies, and correspondingly, it is necessary to generate highly stable reference signals at high frequencies, elements for single-phase synchronization, filters, etc. Surface acoustic wave devices, such as surface acoustic wave filters and surface acoustic wave resonators, have come to be used for applications such as surface acoustic wave filters and surface acoustic wave resonators.

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 electro-mechanical coupling coefficient and a relatively small temperature coefficient of frequency, for example, a 36° rotation V cut-X.
It is a three-terminal or four-terminal device in which comb-shaped electrodes for excitation and reception are provided on a propagation LiTaO5 (36° Y −X LiTa0s) single crystal substrate.

The width of the comb teeth (L) of the comb-shaped electrode, and the space between the comb teeth (S).

When the wavelength of the surface wave of a comb-teeth (P) is λ, usually L = S - λ/4. There are many design values such as P=λ/2. For example, in order to obtain a center frequency of 835 MHz, the sound velocity of the X-propagating surface wave of the substrate 1 is 4090 m/s.
λ = 4.9 μm is calculated, and the electrode pitch is 2.45
μm, electrode width and electrode spacing are 1.23 μm.

FIG. 3 is a diagram showing two examples of the configuration of a conventional surface acoustic wave element, in which (a) is a perspective view of the conventional example, and (b) is a sectional view taken along line A-A' of the conventional example; Figure (c) is another conventional example ^-^
It is a sectional view. In the figure, 100" is a piezoelectric substrate, for example, a 36' Y-X LiTa0n plate. 11
0 is a comb-shaped electrode for excitation, 111 and 112 are lead-out portions thereof, 120 is a comb-shaped electrode for reception, 121 and 122
is its lead derivation part.

As the material for these electrodes, metals with low electrical resistance such as Au are preferable, but metals with high density have an adverse effect on the in-band ripple characteristics and insertion loss characteristics due to the mass effect on surface wave vibration. For this reason, a light film of Af (or Af gold alloy) is usually used, and 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 FIG.
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, another conventional example shown in the cross-sectional view of FIG. I'm taking it. The most well-known example of such a configuration is an example in which a silicon dioxide (Sing) film with a thickness of several μm is interposed as the insulating layer 101 when LiTa0= is used as the piezoelectric substrate 100. The temperature coefficient of the surface wave propagation velocity of the film is of the opposite sign to that of LiTa0z, and this is an element configuration proposed to improve the frequency-temperature characteristics (for example, IEELI975 U
ltrasonics SycsposiutsPro
ceedings, pp 503-5Q7.5ept,
, 1975).

[Problem to be solved by the invention]

However, in the conventional example described above, although the AII is light, the weight of the comb-shaped electrode is applied to the surface of the piezoelectric body either directly or through the 5i02 film, and the mass effect has an influence. especially,
In recent surface wave devices used in the vicinity of the GHz band, this influence has increasingly become a problem, and a solution to this problem was needed.

[Means to solve the problem]

The above problem is solved by a piezoelectric substrate 1 and a comb-shaped electrode 3 disposed above the piezoelectric substrate Fil with an air gap 2 in between.
and an insulator bridge 4 made of a non-piezoelectric material that supports the comb-shaped electrode 3, and the comb-shaped electrode 3 excites or receives surface acoustic waves in the piezoelectric substrate l via the air gap. This problem can be solved by a surface acoustic wave element characterized by the following.

[Effect]

The surface acoustic wave element of the present invention includes a piezoelectric substrate l and a comb-shaped electrode 3.
Since the air gap 2 is interposed between the piezoelectric substrate 1 and the piezoelectric substrate 1, the mass of the electrode is directly and indirectly
In addition, since the air gap 2 is provided, there are no restrictions on the electrode material or electrode thickness, and the polar resistance can be made sufficiently small. Ripple characteristics, insertion loss characteristics, etc. can be improved, and the power that can be input to the element can also be increased.

[Embodiment] FIG. 1 is a diagram showing the configuration of an embodiment of the present invention, and FIG.
1 is a perspective view, (b) is a sectional view taken along line A-A, and (c) is a view taken along line xx'.

In the figure, 1 is a piezoelectric band substrate, for example, 36°Y −X
It is a LiTaO3 plate. 2 is air gap, 3a, 3b
are comb-shaped electrodes for excitation and reception, respectively, 3L32 is a lead lead-out portion, 4 is an insulator bridge, and 5 is an opening made in the insulator bridge 4.

As can be seen from the figure, the lead lead-out portions 31 and 32 are directly fixed on the piezoelectric base Fi1, whereas the comb-shaped electrodes i3a and 3b are suspended on the back surface of the insulator bridge 4. The air gap 2 is formed between the piezoelectric substrate Fi1 and the piezoelectric substrate Fi1.

Next, a specific example of the manufacturing process for constructing the above embodiment device will be explained step by step.

FIG. 2 is a diagram showing an embodiment of the manufacturing process of the surface acoustic wave device of the present invention.

Process (1): 36°'l-XL with a thickness of 0.35mm
iTa0. Polish the surface of the board smooth.

Step (2): Spread a spacer material 6 on the surface of the treated substrate to a thickness of S/10. That is, it is deposited around λ/40, for example, in the case of a surface acoustic wave filter with a center frequency of 835 MHz, about 50 to 150 nm to cover the propagation region of surface acoustic waves. For example, a film of polysilicon is formed by sputtering or CVD, and a region is formed by photoetching so that the material can be removed later by selective etching.

Step (3): An electrode metal film 30°, for example, 2 μm thick, is deposited on the treated substrate by electron beam evaporation.

Step (4): Patterning of the comb-shaped electrodes 3a, 3b, lead lead-out portions 31, 32, etc. is performed on the electrode metal film 30 of the treated substrate by a known photoetching method or ion etching method.

Step (5): Cover all of the comb-shaped electrodes 3a, 3b of the processed substrate and part of the lead lead-out portions 31, 32 with an insulating film 40 of, for example, a 530 g film that is resistant to the selective etching solution for the polysilicon film. The film is deposited to a thickness of approximately 5 μm.

Step (6): An opening 5 of an appropriate size that does not cover the electrode part is formed in the insulating film 40 made of Stag between the comb-shaped electrodes 3a and 3b of the processed substrate, for example, with CF4.
It is formed by ion etching in a chamber.

Process (selective etching from the exposed parts of the opening 5 and the spacer 6 on both sides of the treated substrate, for example, in an EPW solution (ethylenediamine + pitecarol water) or a KOH solution at 80'C, Only the polysilicon space material 6 is selectively dissolved and removed.

In this way, the polysilicon space material 6 remains as an air gap 2 with a thickness of about 50 to 150 nm, the comb-shaped electrodes 3a and 3b are suspended in the air, and the piezoelectric substrate 1 has a total (mass effect). A surface acoustic wave element of the present invention is formed which has no effect on the surface acoustic wave.

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 inputted sufficiently, and the electric signal from the receiving electrode can also be inputted into the air gap 2. It is possible to convert to

The above manufacturing process shows one example, and other materials,
It goes without saying that the surface acoustic wave device of the present invention may be similarly constructed by using a combination thereof or using other film forming techniques as appropriate.

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

〔Effect of the invention〕

As described above, in the surface acoustic wave element according to the present invention, since the air gap 2 is interposed between the piezoelectric substrate 1 and the comb-shaped electrode 3, the air gap 2 is interposed between the piezoelectric substrate 1 and the comb-shaped electrode 3. The mass does not have any influence on the surface acoustic waves propagating to the surface of the piezoelectric substrate 10, and the air gap 2
This eliminates restrictions on electrode materials and electrode thickness, making it possible to sufficiently reduce electrode resistance and contributing to improvements in the performance and quality of surface acoustic wave devices, such as in-band ripple characteristics, insertion loss characteristics, and power durability. There is a huge amount to do.

31.32 is the REET derivation part.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of an embodiment of the present invention, FIG. 2 is a diagram showing an embodiment of the manufacturing process of the surface acoustic wave device of the present invention, and FIG. 3 is a diagram showing the configuration of a conventional surface acoustic wave device. FIG. 2 is a diagram showing two examples. In the figure, 1 is a piezoelectric substrate, 2 is an air gap %, 3 (3a, 3b) is a comb-shaped electrode, 4 is an insulator bridge, 5 is an opening, 6 is a polysilicon film, c) A-A ~ location Motion 0 Country lsu ×- Figure 11 Old

Claims (1)

[Claims] A piezoelectric substrate (1), a comb-shaped electrode (3) disposed above the piezoelectric substrate (1) with an air gap (2) in between, and the comb-shaped electrode (3). and an insulator bridge (4) made of a non-piezoelectric material supporting the comb-shaped electrode (3).
), a surface acoustic wave element is characterized in that surface acoustic waves are excited or received in the piezoelectric substrate (1) via the air gap (2).