JPH10145171A - Surface acoustic wave element and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the surface acoustic wave element that has an insulating film to prevent a short-circuit defect, due to metallic trash dropped from a cover after or at sealing of a package by solder and to provide its manufacture. SOLUTION: After a positive photosensing resin has been coated on a piezoelectric substrate 1 on which interdigital transducer electrodes 21 are formed, an insulating film 31 is formed only on the electrodes, by exposing and developing the substrate from its rear side. Alternatively, a negative photosensing resin is coated on the substrate 1 on which the interdigital transducer electrodes 21 are formed, the insulating film 31 is formed by the method, such as sputtering by exposing and developing the substrate from the rear side after exposing the electrode surface, and the photosensing resin is removed to form the insulating film 31 on the electrode faces. Furthermore, the element is adjusted to have a desired frequency by etching the insulating film 31.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a surface acoustic wave device (SAW device) and a method for manufacturing the same, and more particularly, to a protective film for an electrode and a method for manufacturing the same.

[0002]

2. Description of the Related Art In order to reduce the size of a SAW device, a surface mount type using a ceramic package has become mainstream. In such a package structure, the interdigital transducer electrode portion of the SAW device is short-circuited due to minute metal scraps due to plating of the lid portion and the splash of solder when the lid is soldered to the package.
It has become impossible to withstand use.

[0003] As a method for preventing such a defect due to metal scrap, a method described in Japanese Patent Application Laid-Open No. 6-132775 has been conventionally known. FIG. 9 shows a structure of a conventional system, wherein 1 is a first package, 2 is a second package, 3 is a pattern of a surface acoustic wave element, 4 is a conductive adhesive, 5 is a lead wire, and 6 is an elasticity. This is a small piece of the substrate on which the pattern of the surface acoustic wave element is formed.

In this conventional method, a first package 1 and a second package 2 are respectively formed, and a part or all of the pattern 3 of the surface acoustic wave element is joined to the first package 1 by anodic bonding. In addition, a second package 2 made of metal has a two-stage configuration in which the entire surface acoustic wave element is sealed.

[0005]

To prevent the occurrence of defects due to short-circuiting of metal scraps, it is required that the SAW characteristics be not affected as much as possible and that the device can be manufactured by a simple process at a low cost. SUMMARY OF THE INVENTION It is an object of the present invention to provide a SAW device for preventing short-circuiting in a simple process by forming an insulating film only on an electrode surface and without causing a large variation in characteristics, and a method for manufacturing the same. .

[0006]

In order to solve this problem, the present invention provides a method of applying a photosensitive resin after forming an electrode pattern of a comb-shaped interdigital transducer electrode.
By exposing only the photosensitive resin between the electrodes by exposing from the back surface of the piezoelectric substrate by a self-alignment method that masks the electrode pattern, it is possible to selectively form a film and form an insulating film only on the electrode surface It is what it was.

Accordingly, since the insulating film is not formed on the surface of the piezoelectric substrate, it is possible to prevent a short circuit without greatly changing the characteristics of the surface acoustic wave element, and to etch the frequency by etching the insulating film formed on the surface. Adjustment of characteristics is also possible.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention according to claim 1 of the present invention is directed to a piezoelectric substrate, a comb-shaped interdigital transducer electrode and an external connection electrode provided on the piezoelectric substrate, and at least the interdigital transducer. A surface acoustic wave device having a structure in which an insulating film is formed on an electrode film and no insulating film is formed on the piezoelectric substrate surface between the interdigital transducer electrodes. This has the effect of preventing defects due to short-circuits of the interdigital transducer electrodes due to metal chips without increasing the element characteristics, particularly insertion loss.

According to a second aspect of the present invention, there is provided a surface acoustic wave device according to the first aspect, wherein the insulating film is made of a positive photosensitive polyimide, an organic resin material, silicon oxide, silicon nitride oxide, or organosilicate. In addition, by using an insulating film having heat resistance and low density, it is possible to realize an element which does not greatly affect the surface acoustic wave element characteristics even when the film thickness varies.

According to a third aspect of the present invention, a step of forming a comb-shaped interdigital transducer electrode and an external connection electrode on the surface of a piezoelectric substrate, and forming the interdigital transducer electrode and the external connection electrode Applying and drying a positive photosensitive resin on the surface of the piezoelectric substrate, and irradiating light from the surface of the piezoelectric substrate on which the electrodes are not formed to expose the photosensitive resin to the piezoelectric substrate. A method of manufacturing a surface acoustic wave device, comprising: exposing a photosensitive resin formed thereon, removing an exposed portion of the photosensitive resin by development, and heating and curing the photosensitive resin on the electrode. With the interdigital transducer electrode pattern as a mask, the desired insulation is achieved only by forming a pattern in a self-alignment system and curing by heating. Simple manufacturing method for obtaining an effect that is achieved.

According to a fourth aspect of the present invention, a step of forming a comb-shaped interdigital transducer electrode and an external connection electrode on the surface of a piezoelectric substrate, and forming the interdigital transducer electrode and the external connection electrode Apply a negative photosensitive resin on the surface of the piezoelectric substrate
Drying, and irradiating the photosensitive resin formed on the piezoelectric substrate by irradiating light for sensitizing the photosensitive resin from a surface of the piezoelectric substrate on which the electrodes are not formed; and Removing the negative photosensitive resin formed on the electrodes by development; forming an insulating film on the surface of the piezoelectric substrate on which the electrodes are formed by vacuum deposition or sputtering; A method of manufacturing a surface acoustic wave device having a step of dissolving and removing a conductive resin and simultaneously removing an insulating film formed on the photosensitive resin, and forming an inorganic insulating film having excellent heat resistance and stability. This has the effect of enabling the use of very demanding elements such as surface acoustic wave elements using a quartz substrate.

According to a fifth aspect of the present invention, there is provided a step of forming a comb-shaped interdigital transducer electrode and an external connection electrode on the surface of a piezoelectric substrate, and forming the interdigital transducer electrode and the external connection electrode. Applying and drying a negative photosensitive resin on the surface of the formed piezoelectric substrate, exposing the photosensitive resin from a surface of the piezoelectric substrate on which no electrode is formed, and forming the photosensitive resin on the electrode. Removing the negative photosensitive resin by development, applying and drying a liquid inorganic or organic material on the surface of the piezoelectric substrate on which the electrodes are formed, and forming an insulating film; This is a method for manufacturing a surface acoustic wave device having a process of dissolving and removing the resin and at the same time removing the insulating film formed on the photosensitive resin, using a non-photosensitive material as the insulating film. The choice of materials that can be used since that can spread, an effect that can be used optimal materials depending on the material of the piezoelectric substrate.

According to a sixth aspect of the present invention, the thickness of the dried negative photosensitive resin formed on the piezoelectric substrate on which the interdigital transducer electrode and the external connection electrode are formed is determined by changing the thickness of the interdigital transducer electrode. 6. The method of manufacturing a surface acoustic wave device according to claim 5, wherein the thickness of the electrode is smaller than the thickness of the electrode of the interdigital transducer electrode. This has the effect that the effect of preventing short-circuiting of the electrode due to metal scrap can be more reliably achieved.

According to a seventh aspect of the present invention, there is provided a method of manufacturing a surface acoustic wave device according to any one of the third to fifth aspects, wherein the thickness of the insulating film is set to 20 to 400 nm, more preferably 30 to 200 nm. This method is effective in preventing short-circuiting by setting the film thickness to 20 nm or more, and can be made up to 400 nm without greatly affecting the surface acoustic wave characteristics depending on the material of the piezoelectric substrate to be used. Has an action.

According to an eighth aspect of the present invention, the surface is adjusted to a desired frequency by shaving an insulating film formed on the interdigital transducer electrode by etching. This is a method of manufacturing an acoustic wave device. If the frequency characteristics obtained from the thickness of the interdigital transducer electrode and the thickness of the insulating film are not the desired values, etching only the insulating film increases the electrode resistance and withstands electric power. The frequency adjustment can be performed without affecting the characteristics and insertion loss. In this case, by selecting a material that selectively etches only the insulating film with respect to the electrode and the piezoelectric substrate, the insulating film can be etched without damaging the electrode and the piezoelectric substrate, and a large change in characteristics does not occur. Has the effect of adjusting the frequency.

According to a ninth aspect of the present invention, there is provided the method for manufacturing a surface acoustic wave device according to the eighth aspect, wherein the etching is performed by dry etching. It has the effect of being accurate and improving the frequency adjustment system.

According to a tenth aspect of the present invention, a piezoelectric substrate on which an insulating film is formed is divided, and after bonding to a package and lead connection between an external connection portion and the package, electrical characteristics are measured. 10. The method for manufacturing a surface acoustic wave device according to claim 9, wherein the device is adjusted to a desired frequency by performing dry etching while performing the frequency adjustment while performing measurement. It has the effect of improving reliability and yield.

FIG. 1 shows an embodiment of the present invention.
This will be described with reference to FIG. (Embodiment 1) FIG. 1 shows a cross-sectional structure of an interdigital transducer electrode portion of a surface acoustic wave device according to Embodiment 1 of the present invention, 1 is a piezoelectric substrate, 21 is an interdigital transducer electrode, and 31 is the present invention. Is an insulating film.

In FIG. 1, an insulating film 31 functions to prevent metal chips (not shown) from dropping from the lid during or after soldering and short-circuiting on the interdigital transducer electrode 21. It is composed of a positive photosensitive polyimide film.

In the above description, the example in which the insulating film is made of a positive photosensitive polyimide has been described. However, the present invention can be similarly carried out by using other organic resins, silicon oxide, silicon nitride oxide, organosilicate, or the like. .

(Embodiment 2) FIG. 2 shows a cross-sectional structure of an interdigital transducer electrode portion of a surface acoustic wave device according to Embodiment 2 of the present invention, 1 is a piezoelectric substrate, 21 is an interdigital transducer electrode, and 31 is Is an insulating film according to the present invention.

In FIG. 2, an insulating film 31 functions to prevent metal chips (not shown) from dropping from a lid upon solder sealing or after sealing and short-circuiting on the interdigital transducer electrode 21. It is composed of a silicon oxide film.

In the present embodiment, the insulating film 31 is formed not only on the surface of the interdigital transducer electrode 21 but also on a part of both side surfaces, so that short-circuiting due to metal chips can be more reliably prevented. Have.

Although the above description has been made with reference to an example in which the insulating film is formed of a silicon oxide film, the present invention can be similarly implemented by using other organic resin, silicon nitride oxide, organosilicate, or the like.

[0025]

Next, specific examples of the present invention will be described.

(Embodiment 1) The first embodiment shown in FIG.
Was produced as follows. First,
A 872 MHz ladder type surface acoustic wave filter having an electrode pattern configuration (a) and an equivalent circuit configuration (b) as shown in FIG. 3 was used. Reference numeral 1 denotes a piezoelectric substrate, and in this embodiment, a 36 ° YX lithium tantalate crystal was used. 2 is an interdigital transducer electrode, 3 is a reflector electrode, and these are made of an aluminum film.

FIG. 4 shows a cross-sectional structure of an element for explaining a manufacturing process in which the filter element is formed using a substrate on which such a filter element is formed. FIG. 4A shows a cross section of an interdigital transducer electrode portion of the filter shown in FIG. Reference numeral 1 denotes a piezoelectric substrate, and reference numeral 21 denotes an interdigital transducer electrode. A positive photosensitive polyimide (manufactured by Nissan Chemical Industries, Ltd.) is spin-coated on the surface on which the electrodes are formed to form an interdigital transducer electrode 2.
1 was applied to the entire surface of the piezoelectric substrate, prebaked and dried. This film formation state is shown in FIG.

Next, as shown in FIG. 4 (c), the positive photosensitive resin between the electrodes was exposed by irradiating the back surface of the piezoelectric substrate 1 with ultraviolet light. Thereafter, the exposed portion was removed with a developing solution and cured by heating at about 300 ° C., thereby producing a surface acoustic wave device having the configuration shown in FIG. The insulating film 3 at this time
1, the thickness of the polyimide film was set to 70 nm, but the frequency change became smaller than the initial value by about 2.5 MHz, but the insertion loss increased only by less than 0.1 dB, and the surface acoustic wave characteristics were not practical. No problem was seen.

With respect to this element, the effect of preventing short-circuit when metal scraps fell was examined. Evaluation method is about 20 μm
Was dropped on the interdigital transducer electrode, and a voltage at which insulation between the electrodes was destroyed was obtained by a CV charge method.

This result indicates that the insulation was broken at a voltage of 1 V or less when the polyimide film as the insulating film was not provided.
When formed to a thickness of 70 nm, no breakdown occurred even at a voltage of 100 V or more. In the present embodiment, the film thickness is set to 70 nm, but the film thickness for obtaining the short-circuit prevention effect may be 40 nm or more.
If the insertion loss is allowed to be less than 0.5dB, 150n
m or less is desirable. In the case where the coating was spin-coated under the same conditions and dried, and then heat-cured immediately to form an insulating film between the electrodes, the insertion loss was 0.5 dB.

Embodiment 2 Using a quartz substrate and a resonator having a center frequency of 224 MHz, a positive photosensitive polyimide is applied to the entire surface, dried, and then irradiated with ultraviolet light from the back surface of the substrate to form a gap between the electrodes. After exposing the resin to light, the resin was developed to remove the resin, and heat-cured at 300 ° C. to form an element having the structure described in Embodiment 1.

The polyimide film thus formed,
With respect to the device in which the entire surface was coated, dried and immediately heated and cured to leave an insulating film between the electrodes, the film thickness was changed to determine the relationship between the amount of frequency change and the insertion loss. The result is shown in FIG.

In the figure, (A) shows the characteristics of the device according to the present invention, and (B) shows the device characteristics when polyimide is left on the entire surface. Although the element (A) according to the present invention was produced under the same conditions, the result that the insertion loss did not change even when the frequency was changed was obtained, whereas the element (B) having the polyimide film formed on the entire surface was obtained. The insertion loss increased with the frequency change, and it was found that not forming a polyimide film between the electrodes had a great effect on reducing the influence on the device characteristics. The short-circuit prevention effect of this device was also evaluated.
nm.

(Embodiment 3) The first embodiment shown in FIG.
Was produced as follows. First,
An insulating film 31 was formed on a surface acoustic wave device having an electrode pattern configuration as shown in FIG. The piezoelectric substrate 1 is made of lithium niobate (LiNbO ₃ ) and has a center frequency of 902M.
At Hz, the electrode design is in longitudinal mode. Figure 7 shows the cross-sectional shape of the interdigital transducer electrode part of the device.
(A).

1 is a piezoelectric substrate, and 21 is an interdigital transducer electrode. The substrate was spin-coated using a negative photosensitive photoresist and dried. The cross-sectional shape at this time is shown in FIG. In the figure, reference numeral 41 denotes a negative resist.

Thereafter, as shown in FIG. 7C, ultraviolet light was irradiated from the back surface of the substrate to expose the resist formed between the electrodes. Thereafter, when development is performed, as shown in FIG. 7D, the resist on the electrode is removed and the surface of the electrode is exposed, and a silicon oxide film of about 40 nm is formed on this surface by sputtering (FIG. 7E )).

Finally, by removing the negative resist with acetone and simultaneously removing the silicon oxide film on the resist, the surface acoustic wave device of the second embodiment shown in FIG. 2 was produced. As for the characteristics of the device fabricated in this manner, the frequency change was 1.5 MHz and the insertion loss was only 0.02 dB or less. The short-circuit prevention effect was measured by the CV charge method, and the withstand voltage was 70 V or more.

In this embodiment, the silicon oxide film is formed by sputtering. However, the present invention is not limited to sputtering, but may be vacuum deposition or chemical vapor reaction (CVD). A method such as printing or dipping may be used, and the film forming method is not particularly limited. Further, the insulating film is not limited to silicon oxide, and is particularly limited as long as it is a material having heat resistance smaller than the density of the electrode film material and resistant to solder reflow, which is not attacked by the stripping and removing solution of the negative resist. Never.

(Embodiment 4) The present embodiment 2 shown in FIG.
Was produced as follows. First,
An insulating film was formed on the surface acoustic wave device having the electrode pattern configuration as shown in FIG. The substrate is made of lithium niobate (LiN
bO ₃ ), the center frequency is 902 MHz, and the electrode design is a longitudinal mode method. FIG. 8A shows a cross-sectional shape of the interdigital transducer electrode portion of the element.

1 is a piezoelectric substrate, and 21 is an interdigital transducer electrode. The substrate was spin-coated using a negative photosensitive photoresist and dried. The resist film thickness at this time is formed to be slightly smaller than the electrode film thickness as shown in FIG. In the figure, reference numeral 41 denotes a negative resist.

Thereafter, ultraviolet light is irradiated from the back surface of the substrate to expose and develop the resist formed between the electrodes, and the resist on the electrodes is removed as shown in FIG. Was exposed, and a silicon oxide film of about 40 nm was formed on this surface by sputtering. At this time, silicon oxide is partially formed not only on the electrode surface but also on both side surfaces as shown in FIG. 8D.

Finally, by removing the negative resist with acetone and simultaneously removing the silicon oxide film on the resist, the surface acoustic wave device of the second embodiment shown in FIG. 2 was produced. The surface acoustic wave device thus formed does not have the insulating film 31 formed on the piezoelectric substrate, but is formed not only on the electrode surface but also on a part of both side surfaces. There was a greater effect, and a breakdown voltage of 100 V was obtained by the CV charge method even with a film thickness of 40 nm. The frequency change and the insertion loss were almost the same as those of the third embodiment.

Example 5 A positive photosensitive polyimide of about 150 nm was formed on an oscillator having a center frequency of 224 MHz using the quartz substrate shown in Example 2. The frequency at this time was 224.1 MHz, which was out of the standard. However, as a result of performing dry etching on the substrate in a mixed gas atmosphere of CF ₄ and O ₂ gas for 30 s, the frequency was brought to the standard value of 224.0 MHz. Was completed. About 50 nm of the polyimide film remained after etching, and the short-circuit preventing effect was sufficient.

In this embodiment, the etching is performed in the substrate state. However, each element is divided and die-bonded to the package.
After connecting the wires, measure the frequency in a vacuum while
By performing dry etching with ₄ and O ₂ gas and finishing the etching at a target frequency, more accurate frequency adjustment was possible.

In this embodiment, the polyimide film is dry-etched. However, the present invention is not limited to polyimide as long as it has etching selectivity with respect to the substrate and the electrode material. In addition, although quartz was used as the piezoelectric substrate, there is no particular problem to use a substrate such as lithium tantalate, lithium niobate, or lithium tetraborate used for the surface acoustic wave device.

[0046]

As described above, according to the present invention, an insulating film can be formed only on the electrode surface by the self-alignment exposure method, and the characteristics of the surface acoustic wave device can be increased without increasing the particularly important insertion loss. The advantageous effect that short-circuit can be prevented and the frequency can be adjusted to a desired value by etching the insulating film can greatly improve the yield.

[Brief description of the drawings]

FIG. 1 is a sectional structural view of an interdigital transducer part of a surface acoustic wave device according to a first embodiment of the present invention.

FIG. 2 is a sectional structural view of an interdigital transducer of a surface acoustic wave device according to a second embodiment of the present invention.

FIG. 3A is a diagram showing an electrode pattern configuration of the surface acoustic wave device used in the first embodiment of the present invention; FIG. 3B is a diagram showing an equivalent circuit configuration of the surface acoustic wave device;

FIG. 4 is a process chart for producing the surface acoustic wave device according to the first embodiment of the present invention;

FIG. 5 is a characteristic diagram comparing the relationship between the amount of frequency change and the insertion loss of the surface acoustic wave device according to the first embodiment of the present invention with the case where an insulating film is formed on the entire surface;

FIG. 6 is a configuration diagram of an electrode pattern used in the surface acoustic wave device according to the first embodiment of the present invention.

FIG. 7 is another process chart for producing the surface acoustic wave device according to the first embodiment of the present invention.

FIG. 8 is a process chart for producing the surface acoustic wave device according to the second embodiment of the present invention.

9A is a plan view showing a planar shape of a conventional surface acoustic wave device. FIG. 9B is a cross-sectional view showing a sectional shape of a conventional surface acoustic wave device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Piezoelectric substrate 2 Interdigital transducer electrode 3 Reflector electrode 21 Interdigital transducer electrode 31 Insulating film 41 Negative photosensitive resin

Continued on the front page (72) Inventor Takashi Okada 1006 Kazuma Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd.

Claims (10)

[Claims] A piezoelectric substrate, a comb-shaped interdigital transducer electrode and an external connection electrode provided on the piezoelectric substrate, and an insulating film formed on at least the interdigital transducer electrode film;
A surface acoustic wave device having a structure in which an insulating film is not formed on a surface of a piezoelectric substrate between electrodes of an interdigital transducer electrode. 2. The surface acoustic wave device according to claim 1, wherein the insulating film is made of a positive photosensitive polyimide, an organic resin material, silicon oxide, silicon nitride oxide, or organosilicate. 3. A step of forming a comb-shaped interdigital transducer electrode and an external connection electrode on the surface of the piezoelectric substrate, and forming a positive photosensitive film on the surface of the piezoelectric substrate on which the interdigital transducer electrode and the external connection electrode are formed. Applying and drying a photosensitive resin, and irradiating the photosensitive resin formed on the piezoelectric substrate by irradiating light for sensitizing the photosensitive resin from a surface of the piezoelectric substrate where the electrodes are not formed. A method for manufacturing a surface acoustic wave device, comprising: a step of exposing; a step of removing an exposed portion of the photosensitive resin by development; and a step of heating and curing the photosensitive resin on the electrode. 4. A step of forming a comb-shaped interdigital transducer electrode and an external connection electrode on the surface of the piezoelectric substrate, and a step of forming a negative type on the surface of the piezoelectric substrate on which the interdigital transducer electrode and the external connection electrode are formed. A step of applying and drying a photosensitive resin, and a step of irradiating light for sensitizing the photosensitive resin from a surface of the piezoelectric substrate on which the electrodes are not formed, and forming the photosensitive resin on the piezoelectric substrate. Exposing, removing the negative photosensitive resin formed on the electrodes by development, and forming an insulating film by vacuum evaporation or sputtering on the surface of the piezoelectric substrate on which the electrodes are formed. And a step of dissolving and removing the photosensitive resin and simultaneously removing an insulating film formed on the photosensitive resin. 5. A step of forming a comb-shaped interdigital transducer electrode and an external connection electrode on the surface of a piezoelectric substrate, and forming a negative photosensitive film on the surface of the piezoelectric substrate on which the interdigital transducer electrode and the external connection electrode are formed. Applying and drying a conductive resin, exposing the photosensitive resin from the surface of the piezoelectric substrate on which the electrodes are not formed, and removing the negative photosensitive resin formed on the electrodes by development. Forming an insulating film by applying and drying a liquid inorganic or organic material on the surface of the piezoelectric substrate on which the electrodes are formed, and dissolving and removing the photosensitive resin and simultaneously forming the photosensitive resin. A method for manufacturing a surface acoustic wave device, comprising: a step of also removing an insulating film formed on a resin. 6. A dry thickness of a negative photosensitive resin formed on a piezoelectric substrate on which an interdigital transducer electrode and an external connection electrode are formed is smaller than an electrode film thickness of the interdigital transducer electrode portion. 6. The method for manufacturing a surface acoustic wave device according to claim 5. 7. The insulating film according to claim 3, wherein the thickness of the insulating film is 20 nm to 400 nm, more preferably 30 nm to 200 nm.
The method for manufacturing a surface acoustic wave device according to any one of the above. 8. The method for manufacturing a surface acoustic wave device according to claim 3, wherein a desired frequency is adjusted by shaving off an insulating film formed on the interdigital transducer electrode by etching. 9. The method according to claim 8, wherein the etching is performed by dry etching. 10. After dividing a thick electric substrate on which an insulating film is formed, bonding to a package, and connecting a lead to an external connection portion and a package, dry etching is performed while measuring electric characteristics to perform a desired frequency. The method for manufacturing a surface acoustic wave device according to claim 9, wherein the adjustment is performed to: