JPH10107582A - Surface acoustic wave device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture a surface acoustic wave(SAW) device at a low cost with a simple process in which a short-circuit between electrode fingers due to deposition of a conductive foreign material is suppressed. SOLUTION: A photosensing resist for lift-off is coated on a piezoelectric substrate 10 made of a 36 deg. Y-cut - X propagation LiTaO3 crystal, a negative pattern of an interdigital transducer(IDT) electrode is formed and the width of electrode fingers 1a, 1b is selected to 1.1μm, and the interval between the electrode fingers 1a, 1b is selected to 1.1μm. Then an aluminum film is formed on the surface of the piezoelectric substrate on which the negative pattern is in existence by the thickness of 460nm by the vacuum vapor-deposition method and a silicon film for a protection film 13 is formed 35nm thick without breaking the vacuum state. The photosensing resist, the conductor film and the protection film 13 equivalent to the negative pattern of the piezoelectric substrate 10 are lifted off to manufacture the SAW device. The film thickness of the IDT electrodes of the SAW device is selected to 460nm and a half of the interval between the electrode fingers 1a and 1b of the SAW device is selected to 550nm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface acoustic wave device for a resonator and a frequency band filter incorporated in a mobile radio device such as an automobile telephone and a portable telephone, and an electrode formed on a piezoelectric substrate. However, the present invention relates to a surface acoustic wave device configured to suppress a short circuit due to adhesion of a conductive foreign matter.

[0002]

2. Description of the Related Art Conventional surface acoustic waves (Surface Acoustic W)
ave (hereinafter abbreviated as SAW) is shown in FIG. 2 and its manufacturing process is shown in FIG. 2A is a partially enlarged sectional view of a SAW device, FIG. 2B is a partially enlarged sectional view of a device provided with a protective film,
(C) is a plan view of the basic configuration of the entire device.

In FIG. 1A, a plurality of parallel electrode fingers 11a and 11b are arranged on a piezoelectric substrate 10 such as a LiNbO ₃ crystal or a LiTaO ₃ crystal at a predetermined interval L so as to mesh with each other. ID of comb-shaped electrode
A T (Inter Digital Transducer) electrode 11 is provided. (B) shows the case where the IDT electrode 11 is provided in order to maintain the insulation between the electrode fingers 11a and 11b when the conductive fine particles 12 adhere to the electrode fingers 11a and 11b or between the electrode fingers 11a and 11b. In this configuration, an insulating or semiconductive protective film 13 is provided on the entire surface of the substrate.

In FIG. 1C, reference numeral 11a denotes, for example, an input-side electrode finger, and 11b denotes, for example, an output-side electrode finger.
The characteristics as a resonator or a frequency band filter (hereinafter referred to as a filter) have been deteriorated. In general, the number of IDT electrode pairs is several tens to several hundreds, but is schematically illustrated in (c).

[0005] Such a SAW device is manufactured by steps shown in FIG. In step (a), a photosensitive resist for lift-off is applied on the piezoelectric substrate 10, and in step (b), a negative pattern of the IDT electrode 11 is formed by photolithography. Thereafter, in step (c), a conductive film made of a metal or an alloy for the IDT electrode 11 is formed in a vacuum atmosphere by a thin film forming method such as an evaporation method or a sputtering method, and the piezoelectric substrate 10 is formed in step (d). The photosensitive resist and the conductive film in the negative pattern portion are removed by a lift-off method (or an etching method) from the vacuum atmosphere, and the IDT electrode 11 having a desired pattern is formed. Then, in step (e), the protective film 13 is formed on the IDT electrode 11 by a vapor deposition method, a sputtering method, or the like. At this time, the piezoelectric substrate 10 was put in a vacuum atmosphere in two steps (c) and (e).

[0006]

SUMMARY OF THE INVENTION However, the IDT
If the protective film 13 is not provided on the electrode 11 and the substantially spherical conductive fine particles 12 adhere, the radius R becomes R
When ≧ L / 2 (L is the distance between the electrode fingers 11a and 11b), there is a problem that the electrode fingers 11a and 11b are electrically connected and short-circuited. Further, a protective film 13 is provided on the entire surface of the substrate on which the IDT electrode 11 is provided, and the electrode fingers 11a, 11
Even if an attempt is made to maintain insulation between b, the effect of the protective film 13 on the resonator characteristics and filter characteristics cannot be ignored.
For example, the thickness of the protective film 13 has to be reduced, for example, the thickness of the protective film 13 is set to about 50 nm for the thickness of the IDT electrode 11 of about 500 nm. Therefore, the coverability of the protective film 13 is insufficient, and the protective film 13 is not sufficiently formed on the side surfaces of the electrode fingers 11a and 11b.
When they were fitted between the electrodes b, the short-circuit occurred through the side surfaces of the electrode fingers 11a and 11b.

Further, when the protective film 13 is formed on the IDT electrode 11 by a thin film forming method using a vacuum apparatus such as a vapor deposition method or a sputtering method, the piezoelectric substrate 10 is again placed in a vacuum atmosphere. It was necessary to evacuate the vacuum device at least twice. Furthermore, foreign substances may adhere to the piezoelectric substrate 10 and the IDT electrodes 11 while the piezoelectric substrate 10 is being taken in and out of the vacuum atmosphere.

Accordingly, the present invention has been completed in view of the above circumstances, and an object of the present invention is to suppress a short circuit between electrode fingers due to the adhesion of a conductive foreign substance, and to provide a SAW having such a configuration.
An object of the present invention is to manufacture an apparatus at a low cost by a simple process.

[0009]

According to a first aspect of the present invention, there is provided a surface acoustic wave device, wherein a pair of comb-shaped electrodes having a plurality of parallel electrode fingers are arranged on a piezoelectric substrate so as to mesh with each other. A surface acoustic wave device comprising a protective film provided only on these comb-shaped electrodes, wherein the thickness of the comb-shaped electrodes is less than 1/2 of the distance between adjacent electrode fingers. Features.

In a surface acoustic wave device according to a second aspect of the present invention, a pair of comb-shaped electrodes having a plurality of parallel electrode fingers are arranged on a piezoelectric substrate so that both electrode fingers mesh with each other. A surface acoustic wave device comprising a protective film provided on the surface of a piezoelectric electrode and a piezoelectric substrate, wherein the difference between the thickness of the comb-like electrode and the film thickness of the protective film is set to の of the distance between adjacent electrode fingers. Less than.

[0011]

FIG. 1 shows a surface acoustic wave device according to the present invention.
Now, the manufacturing process will be described with reference to FIG. FIG. 1A is a partially enlarged sectional view of a SAW device, and FIG. 1B is a partially enlarged sectional view of a SAW device according to another embodiment. In FIGS. 1A and 1B, reference numerals 1a and 1b denote a plurality of parallel electrode fingers of an IDT electrode, which is a pair of comb-shaped electrodes arranged so as to be engaged with each other; Is the thickness of the IDT electrode, L is the distance between the electrode fingers 1a and 1b, P is the thickness of the protective film 13, and R is the radius of the conductive fine particles 12. FIGS. 3A to 3E briefly describe the contents of each step. In FIG. 1, the same members as those in FIG. 2 are denoted by the same reference numerals.

In FIG. 1A, when 2R <L, both electrode fingers 1a and 1b of the pair of comb-shaped electrodes do not short-circuit. When 2R> L, the fine particles 12 adhere over a plurality of electrode fingers, but on the IDT electrode (I
Since the protective film 13 is provided only on the DT electrode), no short circuit occurs. In 2R ≒ L, the fine particles 12 may contact the side surfaces of the electrode fingers 1a and 1b and short-circuit. However, in the present embodiment, H <L / 2, and the side surfaces of the electrode fingers 1a and 1b are It does not reach the maximum width of the fine particles 12. Therefore, the probability of short-circuiting through the side surfaces of the electrode fingers 1a and 1b is significantly reduced.

In FIG. 1B, 2R <L and 2R
In the case of> L, no short circuit occurs as in (a). The present embodiment is applied to the case where the thickness of the IDT electrode is relatively large such as H ≧ L / 2, and the height HP of the side surfaces of the electrode fingers 1a and 1b exposed to the outside is changed to HP. By setting L / 2, the side surfaces of the electrode fingers 1a and 1b
The maximum width of the part has not been reached. Therefore, the electrode fingers 1a,
The probability of short-circuiting through the side surface 1b is significantly reduced.

The protective film 13 is made of an electrically insulating or semiconductive (semiconductive) material, and has a resistivity ρ
(Ω · cm), it is preferable that ρ / P be 10 ⁹ (Ω) or more. The material is T
a, Mo and their oxides or nitrides, NiC
r, NiCr-Si, Cr-SiO, Cr-SiO ₂ ,
Si, SiO ₂ , SiN and the like.

In the present invention, the IDT electrode is made of Al or an Al alloy (Al-Cu system, Al-Ti system, etc.), and Al is particularly preferable because of its high excitation efficiency and low material cost. The electrode shape is such that input / output comb-like electrodes (IDT electrodes) as shown in FIG. 1 are alternately engaged with each other. In the present invention, a plurality of electrode fingers are arranged in parallel. It can also be applied to a slit type device such as a vessel. Further, the cross-sectional shape of the electrode fingers 1a and 1b is preferably an inverse taper type tapering toward the surface of the piezoelectric substrate in order to suppress short-circuiting through the side surfaces of the electrode fingers 1a and 1b.

The logarithm of the IDT electrode is 50 to 200.
The width of the electrode fingers 1a and 1b is about 0.1 to 10.0 μm, and the interval between the electrode fingers 1a and 1b is 0.1 to 10.0 μm.
It is preferable that the width of the electrode fingers 1a and 1b be about 10 to 80 μm and the thickness of the IDT electrode be about 0.2 to 0.4 μm in order to obtain desired characteristics as a resonator or a filter. is there. In addition, reflectors for reflecting the SAW and efficiently resonating the SAW may be appropriately provided at both ends of the SAW propagation path of the IDT electrode.
If a piezoelectric material such as ZnO or AlO is formed between the layers b, SA
This is preferable because the resonance efficiency of W is improved.

The piezoelectric substrate 10 includes a 36 ° Y cut-X propagation LiTaO ₃ crystal, a 64 ° Y cut-X propagation LiNbO ₃ crystal, and a 45 ° X cut-Z propagation Li
B ₄ O ₇ crystal, quartz and the like are preferable. In particular, a 36 ° Y cut-X propagation LiTaO ₃ crystal has a wide pass band width, and a 45 ° X cut-Z propagation LiB ₄ O ₇ crystal is electromechanical coupling. This is preferable because the coefficient is large and the group delay time temperature coefficient is small. The thickness of the piezoelectric substrate 10 is 0.3 to 0.5 mm
If less than 0.3 mm, the piezoelectric substrate 10 becomes brittle,
If it exceeds 0.5 mm, the cost increases.

Thus, the present invention has the effect of significantly suppressing a short circuit between electrode fingers due to adhesion of a conductive foreign matter.

Further, the SAW device of the present invention is manufactured as follows. In the case of FIG. 1A, the process of FIG. 3 is followed.
First, in step (a), a photosensitive resist for lift-off is applied on the piezoelectric substrate 10, and in step (b), a negative pattern of the IDT electrode is formed by photolithography. Then, in a step (c), a vapor deposition method, a sputtering method, a CVD method,
A conductive film made of Al or the like for an IDT electrode is formed in a vacuum atmosphere by a thin film forming method such as a method. At this time, the thickness of the conductive film is set to be less than 1/2 of the interval between the electrode fingers 1a and 1b. Next, in step (d), without breaking the vacuum,
A protective film 13 is formed on the surface of the piezoelectric substrate on which the T electrode is formed by an evaporation method or the like. The film thickness is preferably from 10 to 100 nm, and if it is less than 10 nm, it will not be sufficient to function as the insulating protective film 13, and if it exceeds 100 nm, it greatly affects the resonator characteristics and filter characteristics. Then, in a step (e), a photosensitive resist corresponding to the negative pattern portion,
The conductive film and the protective film 13 are lifted off at the same time,
Obtain an AW device.

In the case of FIG. 1B, the following steps are performed.
First, a photosensitive resist for lift-off is applied on the piezoelectric substrate 10, and a negative pattern of the IDT electrode is formed by photolithography. Thereafter, a conductive film for an IDT electrode made of Al or the like is formed by a thin film forming method such as an evaporation method, a sputtering method, and a CVD method. The conductive film corresponding to the negative pattern is lifted off together with the photosensitive resist and removed to form an IDT electrode. The IDT electrode is formed by first forming a conductive film, applying a photosensitive resist, forming a positive pattern of the IDT electrode by a photolithography method, and then leaving a conductive film corresponding to the positive pattern by an etching method. It doesn't matter.

Next, vapor deposition, sputtering, CVD
The protective film is formed by a thin film forming method such as a method. The film thickness is preferably 10 to 100 nm as in the case of FIG. At this time, the difference between the thickness of the IDT electrode and the thickness of the protective film 13 is set to be less than の of the interval between the electrode fingers 1a and 1b, and the surface acoustic wave device of the present invention is obtained.

It should be noted that the present invention is not limited to the above embodiment, and various changes may be made without departing from the scope of the present invention.

[0023]

Embodiments of the present invention will be described below.

(Embodiment 1) SA corresponding to FIG.
A W device was manufactured as follows. 36 ° Y-cut
On a piezoelectric substrate 10 made of an X-propagating LiTaO ₃ crystal,
A photosensitive resist for lift-off was applied, and a negative pattern of the IDT electrode was formed by photolithography. At this time, adjust the conditions such as the baking temperature of the photosensitive resist, the baking time, the ultraviolet intensity at the time of exposure, the exposure time, the developing solution, and the developing time, and make the cross-sectional shape of the photosensitive resist reversely tapered so that it is easy to lift off. Shaped. SA
Since W propagates in the X-axis direction of the LiTaO ₃ crystal, the longitudinal directions of the electrode fingers 1a and 1b are set to be perpendicular to the X-axis direction. Further, since a signal of about 900 MHz is passed, the electrode fingers 1a and 1a are required to obtain desired characteristics.
b is 1.1 μm, and the interval between the electrode fingers 1a and 1b is 1.
The thickness was set to 1 μm.

Next, the piezoelectric substrate 10 was set in a vacuum vapor deposition machine, and 460 nm of Al was formed on the surface of the piezoelectric substrate on which the negative pattern was formed. At this time, the degree of vacuum in the chamber of the vacuum evaporation machine was set to 10 ^-7 Torr. afterwards,
25 nm of Si for the protective film 13 was formed without breaking the vacuum. At this time, due to the pyroelectric effect of the piezoelectric substrate 10, the electrode finger 1
Heating of the piezoelectric substrate 10 was not performed in order to avoid the occurrence of discharge between the electrodes a and 1b and damage to the electrode fingers 1a and 1b. Then, the photosensitive resist, the conductive film, and the protective film 13 corresponding to the negative pattern of the piezoelectric substrate 10 are lifted off, and
The DT electrode and the protective film 13 were formed, and a SAW device was manufactured.

The above-mentioned SAW device has a (film thickness of IDT electrode)
= 460 nm, while (1/2 of the interval between the electrode fingers 1a and 1b) = 1.1 (μm) / 2 = 550 (nm). By adopting the above configuration, the defect rate in the related art was several percent, but was reduced to about 0.1%. In addition, since only one evacuation is required as compared with the related art, the SAW device can be manufactured at a lower cost.

(Embodiment 2) SA corresponding to FIG.
A W device was manufactured as follows. 36 ° Y-cut
On a piezoelectric substrate 10 made of an X-propagating LiTaO ₃ crystal,
A photosensitive resist for lift-off was applied, and a negative pattern of the IDT electrode was formed by photolithography. At this time, conditions such as a baking temperature, a baking time, an ultraviolet intensity at the time of exposure, an exposure time, a developing solution, and a developing time of the photosensitive resist were adjusted, and the cross-sectional shape thereof was formed into an inverse tapered shape so as to facilitate lift-off. SAW to LiTaO ₃
Since the light propagates in the X-axis direction of the crystal, the longitudinal directions of the electrode fingers 1a and 1b are perpendicular to the X-axis direction. Also, since a signal of about 900 MHz is passed, the width of the electrode fingers 1a and 1b should be 1.1 μm to obtain desired characteristics.
m, and the interval between the electrode fingers 1a and 1b was set to 1.1 μm.

Next, the piezoelectric substrate 10 was set in a vacuum evaporation machine, and 460 nm of Al was formed on the surface of the piezoelectric substrate on the side where the negative pattern was formed. At this time, the degree of vacuum in the chamber of the vacuum evaporation machine was set to 10 ^-7 Torr. The photosensitive resist corresponding to the negative pattern of the piezoelectric substrate 10 after the deposition was lifted off to form an IDT electrode. Thereafter, the piezoelectric substrate 10 was set in a vacuum evaporation machine, and the vacuum was evacuated to the order of 10 ⁻⁷ Torr, and a 25-nm thick Si film for the protective film 13 was formed to produce a SAW device. At this time, the piezoelectric substrate 10 was not heated in order to avoid the occurrence of discharge between the electrode fingers due to the pyroelectric effect of the piezoelectric substrate 10 and damage to the electrode fingers.

The above-mentioned SAW device has a (film thickness of IDT electrode)
− (Film thickness of protective film 13) = 460−25 = 435 (n
m), on the other hand, (１ ／ of the distance between the electrode fingers 1a and 1b)
= 1.1 (μm) / 2 = 550 (nm).
The difference of 435 nm between the thickness of the DT electrode and the thickness of the protective film 13 is
The value is smaller than 550 nm which is １ ／ of the interval between the electrode fingers 1a and 1b. With the above configuration, the same effect as in the first embodiment was obtained.

[0030]

According to the first aspect of the present invention, the protective film is provided only on the comb-shaped electrode, and the thickness of the comb-shaped electrode is set to be less than 1/2 of the distance between the electrode fingers. This has the effect that the occurrence of a short circuit between electrode fingers due to the adhesion of conductive foreign matter during assembly processing such as packaging can be remarkably suppressed. In addition, the comb-shaped electrode and the protective film can be formed continuously without breaking the vacuum, and the photolithography process can be performed only once, so that the process is simplified. Furthermore, when releasing the vacuum, contamination such as foreign matter entering the atmosphere from the outside and attaching to the atmosphere is reduced. Since the protective film is formed before the formation of the comb-shaped electrodes, there is no discharge between the electrode fingers due to the pyroelectric effect at the time of forming the protective film, and the electrode fingers are not damaged.

According to a second aspect of the present invention, a protective film is provided on the surfaces of the comb-like electrodes and the piezoelectric substrate, and the difference between the thickness of the comb-like electrodes and the thickness of the protective film is set to one of the distances between the electrode fingers. By setting the ratio to less than / 2, occurrence of a short circuit between the electrode fingers can be remarkably suppressed in the same manner as described above. In this case, it is not necessary to cover the side surface of the electrode finger with the protective film, or when the side surface of the electrode finger is not covered with the protective film for some reason, the film thickness of the comb-shaped electrode is adjusted as in the present invention. By doing so, short circuits can be suppressed. Therefore, since a film can be formed even by a film forming apparatus or a film forming method having poor coverage, the film can be manufactured at low cost without being restricted by the film forming equipment. Since it is not necessary to cover the side surfaces of the electrode fingers on which film formation is difficult, the thickness of the protective film can be reduced, and the tact time of film formation is shortened, resulting in good productivity. Further, by reducing the thickness of the protective film, the influence on the resonator characteristics and the SAW filter characteristics can be reduced, so that the degree of freedom in design is improved.

Further, according to the present invention, since the probability of short-circuiting even if conductive foreign matter adheres to a certain extent is considerably small, it is not necessary to wash the package which is a main source of the conductive foreign matter, and as a result, In addition, the manufacturing process can be simplified.

[Brief description of the drawings]

1A and 1B show a SAW device of the present invention, wherein FIG. 1A is a partially enlarged cross-sectional view of a SAW device having a protective film only on an IDT electrode, and FIG.
FIG. 3 is a partially enlarged cross-sectional view of a protective film on the entire surface.

2A and 2B show a conventional SAW device, in which FIG. 2A is a partially enlarged sectional view without a protective film, and FIG. 2B is a partially enlarged sectional view with a protective film over the entire surface.

FIG. 3 is a flowchart of a manufacturing process of the SAW device of the present invention;
(A) to (e) show the contents of each step.

FIG. 4 is a flowchart of a manufacturing process of a conventional SAW device;
(A) to (e) show the contents of each step.

[Explanation of symbols]

 1a: electrode finger 1b: electrode finger 10: piezoelectric substrate 12: conductive fine particles 13: protective film

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[Procedure amendment]

[Submission date] December 10, 1996

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Figure 2

[Correction method] Change

[Correction contents]

2A and 2B show a conventional SAW device, wherein FIG. 2A is a partially enlarged sectional view without a protective film, FIG. 2B is a partially enlarged sectional view with a protective film over the entire surface, and FIG. It is a top view of a structure.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Emi Kakai 3--5 Kodai, Seika-cho, Soraku-gun, Kyoto Prefecture Inside the Central Research Laboratories of Kyocera Corporation (72) Inventor Atsushi Hatate 3, Kodai-dai, Seika-cho, Soraku-gun, Kyoto 5-chome Kyocera Corporation Central Research Laboratory

Claims (2)

[Claims] A pair of comb-shaped electrodes having a plurality of parallel electrode fingers are arranged on a piezoelectric substrate so as to mesh with each other, and a protective film is provided only on these comb-shaped electrodes. A surface acoustic wave device comprising: a comb-shaped electrode having a thickness less than 1/2 of a distance between adjacent electrode fingers. 2. A pair of comb-shaped electrodes having a plurality of parallel electrode fingers arranged on a piezoelectric substrate so that both electrode fingers mesh with each other, and a protective film is formed on the surfaces of the comb-shaped electrodes and the piezoelectric substrate. Wherein the difference between the thickness of the comb-shaped electrode and the thickness of the protective film is less than の of the distance between adjacent electrode fingers. Surface wave device.