JPH06283955A - Surface acoustic wave device - Google Patents

Abstract

PURPOSE:To provide a surface acoustic wave device capable of quickly and exactly performing the melting and peeling of resist film by minimizing the area of the resist film peeled by resist peeling solution. CONSTITUTION:The surface acoustic wave device is constituted in such a way that plural electrode finger groups 2-5 are fomed on a rectangular piezoelectric crystal substrate 1 by a lift-off method. and a dummy electrode 6 formed with the same material as that of the electrode finger groups 2-5 is arranged in the periphery of the electrode finger groups 2-5.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a SAW filter, SA
The present invention relates to a surface acoustic wave device such as a W resonant element and a SAW delay element, and particularly to a surface acoustic wave device (S
AW device).

[0002]

2. Description of the Related Art A SAW resonant element, which is an example of a surface acoustic wave device, has a piezoelectric crystal (Li ₂ B ₄ O) as shown in FIG.
₇ , LiTaO _3, etc.) A plurality of electrode finger groups were formed on the substrate 1. Examples of the electrode finger group include the input comb-teeth electrode 2, the output comb-teeth electrode 3 intersecting with the input comb-teeth electrode 2, the input / output comb-teeth electrodes 2 and 3, and the reflective electrodes 4 and 5 arranged so as to sandwich the comb-teeth electrodes 2 and 3. .

The width of one electrode finger of such an electrode finger group and the distance between the electrode fingers are determined (λ / integer) according to the wavelength λ of the surface acoustic wave. The characteristics of fluctuate greatly.

Conventionally, the lift-off method has been used as a method of forming the electrode finger group which requires such dimensional accuracy. In the lift-off method, a positive-type resist film is applied on the surface-polished piezoelectric crystal substrate 1, dried, and then developed in an overhang shape to expose the resist film in the exposed portion (electrode finger group portion). To remove.

In this way, the piezoelectric single crystal substrate 1 from which the resist film has been removed at the portion where the electrode finger group is to be formed is deposited on the entire surface with an aluminum film thickness of about 0.3 μm by a vapor deposition apparatus or the like. After that, the resist film is dissolved using a resist stripping solution to remove the aluminum film deposited on the resist film to form a plurality of electrode finger groups having a predetermined shape.

[0006]

From the perspective of the piezoelectric single crystal substrate as a whole, a plurality of electrode finger groups, that is, the area where aluminum should be adhered to the substrate, has a marginal portion, that is, the resist film is removed by the stripping solution. The area removed is extremely large.
Further, in the vicinity of the periphery of the piezoelectric single crystal substrate 1 or the like, an unnecessary resist film to be dissolved or peeled is continuously formed.

Therefore, in the conventional resist film dissolving / peeling process, the resist peeling liquid is heated or ultrasonic vibration is applied so as to prevent the resist from remaining, so that the progress speed of the peeling of the resist film is increased. The piezoelectric single crystal substrate has been soaked early or soaked in the resist stripping solution for a long time. Therefore, the resist film dissolving / peeling process has a great influence on the productivity.

Further, even if the device is inevitably increased in substrate area even if it is heated or subjected to ultrasonic vibration as described above, the resist film remains in the device,
It was reducing the yield.

The present invention has been devised in view of the above-mentioned problems, and an object thereof is to minimize the area of an unnecessary resist film which is stripped by a resist stripping solution and to quickly and surely form a resist film. An object of the present invention is to provide a surface acoustic wave device capable of melting and peeling.

[0010]

A surface acoustic wave device of the present invention is one in which a plurality of electrode finger groups are formed on a rectangular piezoelectric crystal substrate by a lift-off method, and the electrode finger groups are surrounded. , A dummy electrode made of the same material as the electrode finger group was arranged.

[0011]

As described above, by forming a dummy electrode made of the same material as the electrode finger group around the electrode finger group on the piezoelectric single crystal substrate, unnecessary resist to be dissolved or peeled off is formed. Since the area of the film is reduced, the resist film can be stripped in a short time.

[0012] Further, the resist and the electrode material other than the design do not remain on the piezoelectric single crystal substrate, and the decrease in the yield can be suppressed.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The surface acoustic wave device of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a plan view of a SAW resonant element which is an example of the surface acoustic wave device of the present invention. The same parts as those in FIG. 4 are described with the same reference numerals.

In FIG. 1, 1 is a piezoelectric single crystal substrate, 2 to 5 are electrode finger groups, and in particular, 2 is an input comb-teeth electrode, 3 is an output comb-teeth electrode, and 4 and 5 reflections. It is an electrode.

The piezoelectric single crystal substrate 1 is made of Li ₂ B ₄ O ₇ ,
LiTaO ₃ , quartz, or the like, which is cut in a predetermined crystal orientation and has a polished rectangular surface.

Each of the electrode finger groups 2 to 5 is made of an electrode material such as aluminum. The input comb-teeth electrode 2 and the output comb-teeth electrode 3 are formed so as to intersect each other in the vicinity of the central portion of the substrate, and further, both ends of the intersected input comb-teeth electrode 2 and output comb-teeth electrode 3 are formed. Are formed with reflective electrodes 4 and 5. The width of each of the electrode fingers forming each of the electrode finger groups 2 to 5 and the distance between the electrode fingers are determined by the wavelength λ of the elastic wave propagating on the surface of the substrate, and the film thickness thereof is
It is set to an optimum value in order to suppress unnecessary elastic waves. As an example thereof, in a resonance element having a resonance frequency of 250 MHz, the width of the electrode fingers is set to 3.5 μm, the distance between the electrode fingers is set to 3.5 μm, and the film thickness is 0.3 μm.

With such a configuration, an externally applied signal is applied to the input comb-teeth electrode 2, and the substrate surface is provided between the input / output comb-teeth electrodes 2 and 3 and the reflective electrodes 4 and 5 which intersect each other. It propagates as a traveling wave and a reflected wave as elastic waves. That is, since the electrode fingers of the electrode finger groups 2 to 5 and the space between the electrode fingers are set according to the resonance wavelength λ, the signal corresponding to the resonance wave frequency is finally extracted from the output comb-teeth electrode 3. You can

A characteristic point of the present invention is the marginal portion of each of the electrode finger groups 2 to 5 formed on the piezoelectric single crystal substrate 1, which is a portion which does not affect the propagation of elastic waves, for example, That is, the dummy electrode 6 is formed around each of the electrode finger groups 2 to 5.

By forming this dummy electrode 6,
The area of the blank portion (the exposed area of the piezoelectric single crystal substrate 1) can be reduced without affecting the propagation of the elastic wave.

Here, the operation of the present invention will be described while explaining the method of manufacturing the above-described SAW resonant element with reference to FIGS. 2 (a) to 2 (f). 2A to 2F are partial cross-sectional views.

First, as shown in FIG. 2A, a piezoelectric single crystal substrate 11 having a size capable of extracting a plurality of elements is prepared. This substrate 11 is cut in a predetermined crystal orientation as described above and surface-polished.

Next, the electrode finger groups 2 to 5 are formed in the regions to be the respective elements.
And a step of forming the dummy electrode 6 is performed.

As shown in FIG. 2B, a positive resist film 12 'is printed on the entire surface of the substrate 11 to a thickness of about 1.0 .mu.m.
Dry and apply.

Next, exposure is performed as shown in FIG. The exposure is performed using a pattern mask (not shown) so that the portions where the electrode finger groups 2 to 5 and the dummy electrode 6 are formed are exposed. The exposed resist film is shown by 12.

Next, as shown in FIG. 2D, the resist film 12 exposed by the developing solution is removed. By this development, the unexposed portion of the resist film 12 'remains, and the substrate 11 in the portion where the electrode finger groups 2 to 5 and the dummy electrode 6 are formed is exposed.

Here, since the resist film 12 'remaining after the development is eroded by the developing solution from the end surface thereof, it has a trapezoidal shape (overhang shape) close to a substantially inverted triangular shape.

Next, after washing and drying, as shown in FIG. 2 (e), electrode materials 13 and 13 'such as aluminum are electrode-attached to a film thickness of 0.3 μm by a thin film technique such as vapor deposition and sputtering. . Electrode material 13, 1 such as aluminum
Since 3'is deposited on the entire surface of the substrate 11, it is also formed on the exposed portion of the substrate 11 by development and on the remaining resist film 12 '.

Next, as shown in FIG. 2 (f), the substrate 11 is immersed in a resist stripping solution to dissolve and strip the resist film 12 '. Since the thickness of the resist film 12 ′ is, for example, 1.0 μm and the thickness of the electrode materials 13 and 13 ′ is, for example, 0.3 μm, the resist film 12 ′ dissolved from the electrode material 13 is projected. Further, due to the overhang shape of the resist film 12 ', a slight gap is formed between the resist film 12' and the electrode material 13, so that the stripping solution sufficiently penetrates and the resist film 1 does not interfere.
2'can be dissolved. Due to the dissolution and peeling of the resist film 12 ', the electrode material 13' deposited on the resist film 12 is also peeled at the same time, and in the end, the electrode fingers 2 to 5 and the electrode to be the dummy electrode 6 are formed. Material 13
Only that will be deposited on the substrate 11.

Finally, the substrate 11 is cut into a single element by cutting each element region with a diamond saw or the like.

Here, by forming the dummy electrode 6, the electrode material 13 finally deposited on the substrate 11 is formed.
Area increases. In other words, it remains after the development process,
And the resist film 1 to be dissolved in the dissolution / peeling process
The 2'area will be reduced.

Therefore, in the step of dissolving / peeling the resist film 12 ', it is possible to dissolve and peel in a short time without actively using a heating means and an ultrasonic wave applying means for increasing the rate of progress of dissolution as in the conventional case. Can be achieved. Of course, although the material can be dissolved and peeled in a short time, a heating means and an ultrasonic wave applying means may be used to further shorten the time.

Further, as a result, the resist film 12 ', the electrode material 13', etc., which are not designed, do not remain on the piezoelectric single crystal substrate 11, and the decrease in yield can be suppressed.

(Other Embodiments) (1) In the above-mentioned embodiment, the dummy electrode 6 is formed around the piezoelectric single crystal substrate 1, but the comb electrode 2 for input,
The input comb-teeth electrode 2, the output comb-teeth electrode 3 and the reflection electrodes 4, 5 are surrounded so as not to interfere with the propagation of the elastic wave between the output comb-teeth electrode 3 and the reflection electrodes 4, 5. Further, the formation position of the dummy electrode 6 can be variously changed such as by making them close to each other.

(2) In the above-mentioned embodiment, the dummy electrode 6 is formed as a continuous series of electrodes, but it may be formed intermittently.
As shown in (a) and (b), it may be an aggregate of stripes 61 or an aggregate of dots 62.

(3) In the above-mentioned embodiment, the dummy electrode 6 is in an electrically floating state, but it is unnecessary if it is not related to the propagating wave for deriving the resonance characteristic by being grounded to the ground potential. You may make it absorb an elastic wave.

(4) In the above embodiments, the SAW resonance element is explained, but it can be applied to a filter, a delay element, etc. In this case, the elastic wave required for the operation is disturbed. It is preferable to form a dummy electrode in a large area in a non-existing portion.

[0037]

As described above, in the present invention, since the dummy electrodes formed of the same material and in the same process as the electrode finger group are arranged around the electrode finger group, the resist film is dissolved / peeled during the lift-off process. The resist film to be dissolved / peeled in the process can be reduced, the dissolution / peeling can be reliably performed in a short time, and the manufacturing yield is improved.

[Brief description of drawings]

FIG. 1 is a plan view of a resonance element which is an example of a surface acoustic wave device of the present invention.

FIG. 2A to FIG. 2F are schematic views for explaining a process of forming an electrode finger group and a dummy electrode.

FIGS. 3A and 3B are partial plan views showing the configurations of other dummy electrodes, respectively.

FIG. 4 is a plan view of a resonance element that is an example of a conventional surface acoustic wave device.

[Explanation of symbols]

 1 ...- Piezoelectric single crystal substrate 2 ... Input comb-tooth electrode 3 ...- Output comb-tooth electrode 4, 5 ... Reflective electrode 6 ... Dummy electrode 11 ... Substrate

Claims (1)

[Claims] 1. A surface acoustic wave device in which a plurality of electrode finger groups are formed by a lift-off method on a rectangular piezoelectric crystal substrate, wherein the electrode finger group is surrounded by the same material as the electrode finger group. A surface acoustic wave device having a dummy electrode formed therein.