JPH08162881A - Thin film surface acoustic wave element filter and its manufacture - Google Patents

Abstract

PURPOSE: To attain a low loss without deterioration the crystalline of a piezoelectric layer in the surface acoustic wave(SAW) filter of a structure where a piezoelectric layer grown epitaxially is formed on a substrate. CONSTITUTION: Electrodes 5W, 5E formed by doping impurity to a piezoelectric layer 20 are arranged to a boundary between a substrate 1 being a propagation layer of a surface acoustic wave and a piezoelectric layer 20 formed by expitaxial growing on the substrate 1. Thus, the stimulated surface acoustic wave is directly propagated onto the substrate and since no deterioration in the crystalline of the piezoelectric layer 20 is caused, the piezoelectric efficiency is improved and the SAW filter with a low loss is manufactured.

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 filter and a method for manufacturing the same, and more particularly to an electrode formed at the interface portion of the piezoelectric layer with the substrate so as not to affect the crystal structure of the piezoelectric layer. The present invention relates to a thin film surface acoustic wave filter having the above and a manufacturing method thereof.

[0002]

2. Description of the Related Art FIGS. 7 (a) and 7 (b) are sectional views showing a conventional surface acoustic wave filter (hereinafter referred to as SAW filter). 1 is a substance having a high propagation velocity of an oscillating wave, for example, α-Al
It is a substrate made of ₂ O ₃ and is generally called a sapphire substrate. Reference numeral 2 is a piezoelectric layer formed by epitaxial growth of ZnO, AlN, or the like formed on the substrate 1 by vapor deposition or sputtering, or having an orientation.
W and 3E are comb-shaped electrodes made of a conductive material such as Al and Au formed on the piezoelectric layer 2 or at the interface between the piezoelectric layer 2a and the substrate 1.

FIG. 7 (c) is a top view of FIG. 7 (a) seen from above. 3W and 3E are made of a conductive material, and form comb-shaped electrodes made of electrode portions 3w, 3w ', 3e, and 3e', respectively.

Here, the conventional thin film SA shown in FIG.
A method of manufacturing the W filter will be described. FIG. 8 shows the manufacturing steps for manufacturing the thin film SAW filter as shown in FIG. 7 (a) in order from FIG. 8 (a) to FIG. 8 (f). As shown in FIG. 8 (a), the piezoelectric layer 2 is formed on the substrate 1 by epitaxial growth, and then, as shown in FIG. 8 (b), the electrode metal 3 made of a conductive material such as Al or Au is deposited. And the like.

After the resist 4 is applied thereon as shown in FIG. 8 (c), the resist 4 is applied as shown in FIG. 8 (d).
By patterning, a resist mask 4a is formed. Next, as shown in FIG. 8E, the electrode metal 3 is etched using the patterned resist mask 4a as a mask. Then, the resist mask 4a is removed to form the electrodes 3W and 3E. Here, the etching of the electrode metal 3 shown in FIG. 8 (e) is performed by a method such as dry etching such as ion milling using Ar gas when the piezoelectric layer 2 is an amphoteric oxide.

Next, the operation of such a conventional thin film SAW filter will be described. Comb type electrode part 3w, 3w '
When a high frequency signal is applied between the electrodes, the electrode width (d1) of the comb-shaped electrode, the electrode spacing (d2) and the propagation velocity (Vp) of the vibration wave
) Etc., the vibration of the resonance frequency (f) determined by the following equation is obtained.

[0007]

[Equation 1]

Only the resonance frequency (f) surface acoustic wave determined by this is excited by the resonance action utilizing the piezoelectricity of the piezoelectric layer 2. This oscillating wave propagates through the substrate 1 having a high propagation speed, reaches the electrode 3E side, and is again extracted as an electric signal and excited by the comb-shaped electrode 3E composed of the electrode portions 3e and 3e '. Only electrical signals of frequency are output.

In order to increase the resonance frequency (f), it is necessary from the above equation that the propagation velocity (Vp) of the surface acoustic wave in the medium is high. Therefore, a substance having both high piezoelectricity necessary for converting an electric signal into a surface acoustic wave and a high propagation velocity of an oscillating wave should be used, but substances excellent in such respective characteristics are limited. Has been. Therefore, conventionally, as shown in FIG. 7A, ZnO, which has high piezoelectricity, is formed on the substrate 1 such as α-Al ₂ O _{3 which is} non-piezoelectric but has a high propagation velocity of vibration waves (large Vp). A structure in which a single crystal film of AlN or the like is grown and an electrode is formed thereon, or as shown in FIG. 7 (b), an electrode is formed on a substrate 1 of α-Al ₂ O ₃ or the like, A structure having a structure in which the electrode gap and the upper part thereof are filled with a piezoelectric layer 2a made of an alignment film is used.

[0010]

In the thin film SAW filter having the structure shown in FIG. 7 (b), the electrodes 3W,
By forming 3E and 3E at the interface between the piezoelectric layer 2 and the substrate 1, the surface acoustic wave can be directly transmitted to the substrate 1 which is a propagation medium, and the surface acoustic wave can be directly converted from the substrate 1 into an electric signal. Therefore, the conversion efficiency from the electric signal to the surface acoustic wave or from the surface acoustic wave to the electric signal is good, which is very advantageous for reducing the pass loss of the filter.
There are restrictions on the material of the piezoelectric layer. That is, the higher the crystallinity of a piezoelectric material, the higher its piezoelectricity.
In the case of an AW filter, the piezoelectric layer 2 is preferably made of a single crystal film epitaxially grown on the substrate 1,
Due to the electrodes 3W and 3E formed on the substrate, the piezoelectric layer 2
7 (b) because the crystallinity of the piezoelectric layer 2 is significantly deteriorated and the piezoelectricity is lowered when the film is formed by epitaxial growth.
In the structure shown in (1), it is difficult to form a piezoelectric layer made of an epitaxially grown single crystal film, and there is a problem in that an alignment film having a piezoelectricity lower than that must be used.

Therefore, conventionally, electrodes 3W, 3 are formed on the piezoelectric layer 2 formed by epitaxial growth shown in FIG. 7 (a).
The structure forming E has been mainly used. However, in the case of FIG. 7A, although the main vibration direction of the excited surface acoustic wave is the horizontal direction in the figure, this main horizontal vibration is transmitted to the substrate 1 through the piezoelectric layer 2. At this time, since the vibration propagates in a direction deviated from the horizontal direction, the vibration is greatly attenuated, and there is a problem that the piezoelectric layer 2 reduces the propagation efficiency of the surface acoustic wave.

Further, a SAW having a structure as shown in FIG.
In the manufacturing process of the filter, since the etching rate of the piezoelectric layer 2 is higher than that of the electrode metal 3 in the electrode forming process, it is difficult to control during etching, and dry etching such as ion milling using Ar gas should be performed. There was a problem that it had to be.

The present invention has been made to solve the above problems, and an electrode is formed at the interface between the piezoelectric layer and the substrate so as not to deteriorate the crystallinity of the upper piezoelectric single crystal film. As a result, thin film SAW that is highly efficient and easy to manufacture
An object of the present invention is to provide a filter and a manufacturing method thereof.

[0014]

Means for Solving the Problems Thin film SA according to the present invention
The W filter is provided with a piezoelectric layer made of a semiconductor formed by epitaxial growth on a substrate, and an electrode portion formed by doping impurities in the interface portion of the piezoelectric layer with the substrate.

Further, the present invention further comprises a second electrode portion formed by doping impurities in the piezoelectric layer, which is separated from the electrode portion above the electrode portion, in the thin film SAW filter. It is a thing.

Further, according to the present invention, in the above thin film SAW filter, a surface electrode portion is further provided on the upper surface of the piezoelectric layer. In the thin film SAW filter according to the present invention, the material of the substrate is α-Al ₂ O ₃ and the material of the piezoelectric layer is ZnO.

In the method of manufacturing a thin film SAW filter according to the present invention, a step of forming a piezoelectric layer made of a semiconductor by epitaxial growth on a substrate, a step of forming a resist on the step, and patterning the resist to form a resist mask. And a step of implanting ions into the piezoelectric layer using the resist mask as a mask to form a low resistance electrode portion at the interface between the substrate and the piezoelectric layer.

A method of manufacturing a thin film SAW filter according to the present invention comprises a step of forming an electrode layer made of a semiconductor containing impurities and having a low resistance by epitaxial growth on a substrate, and forming a resist on the electrode layer. Patterning a resist mask to form a resist mask, etching the electrode layer using the resist mask as a mask to form a low resistance electrode on the substrate, and epitaxially growing to cover the low resistance electrode. And a step of forming a piezoelectric layer made of a semiconductor.

According to the present invention, in the method of manufacturing a thin film SAW filter, after the above steps, a step of forming a second electrode layer made of a semiconductor containing impurities and having a low resistance by epitaxial growth, and above the steps. A resist is formed on the substrate, and the resist is patterned to form a resist mask.
Etching the electrode layer to form a second electrode on the piezoelectric layer, and forming a piezoelectric layer made of a semiconductor by epitaxial growth so as to cover the second electrode.

Further, according to the present invention, in the method of manufacturing a thin film SAW filter described above, after the above steps, ion implantation is further performed using a resist mask, and a low layer is formed in the piezoelectric layer above the electrodes and apart from the electrodes. It includes the step of forming the second electrode of the resistor.

Further, the present invention includes, in the method for manufacturing a thin film SAW filter, a step of further forming a surface electrode made of metal on the upper surface of the piezoelectric layer after the above steps.

In addition, in the method for manufacturing a thin film SAW filter according to the present invention, after the above steps, a step of forming a surface electrode layer made of a semiconductor containing impurities and having a low resistance is further performed by epitaxial growth; And forming a resist mask by patterning the resist, and using the resist mask as a mask to etch the surface electrode layer to form a surface electrode on the piezoelectric layer.

According to the present invention, in the method for manufacturing a thin-film SAW filter, after the steps described above, ion implantation is further performed using a resist mask, and a surface portion of the piezoelectric layer above the electrodes and apart from the electrodes. In addition, a step of forming a low-resistance surface electrode is included.

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiment 1. Configuration 1. Referring to FIG. 1, the thin film SAW filter according to the first embodiment of the present invention includes a piezoelectric layer (2) made of a semiconductor formed by epitaxial growth on a substrate (1).
0) and the piezoelectric layer (20) at the interface between the substrate (1) and the electrode portion (5W, 5W) formed by doping impurities.
E), it is possible to obtain a thin film SAW filter in which electrodes are formed at the interface between the piezoelectric layer and the substrate without disturbing the crystallographic direction of the piezoelectric layer by epitaxial growth.

Configuration 2. Thin film SA in the first embodiment
Referring to FIG. 2, the method of manufacturing the W filter is performed by forming a piezoelectric layer (20) made of a semiconductor on a substrate (1) by epitaxial growth, forming a resist (4) on the piezoelectric layer (20), and patterning the resist (4). Forming a resist mask (4a) with a resist mask (4a)
Using the as a mask, the piezoelectric layer (20) is ion-implanted,
A step of forming low-resistance electrode portions (5W, 5E) at the interface between the substrate (1) and the piezoelectric layer (20), whereby the piezoelectric layer can be formed without disturbing the crystallographic direction of the piezoelectric layer by epitaxial growth. Electrodes (5W, 5E) can be formed at the interface between (20) and the substrate (1).

Configuration 3. Further, referring to FIG. 3, the method of manufacturing the thin film SAW filter according to the first embodiment includes a step of forming on the substrate (1) an electrode layer (5) made of a semiconductor containing impurities and having a low resistance by epitaxial growth. And a step of forming a resist (4) thereon and patterning the resist (4) to form a resist mask (4b),
The electrode layer (5) is etched using the resist mask (4b) as a mask, and the low resistance electrode (5W, 5) is formed on the substrate (1).
E) and a step of forming a piezoelectric layer (20) made of a semiconductor by epitaxial growth so as to cover the low resistance electrodes (5W, 5E). An electrode can be formed in the interface portion of the piezoelectric layer with the substrate in a small number of steps without disturbing the crystal orientation.

Example 1. FIG. 1 is a cross-sectional view showing a thin film SAW filter according to a first example of the first embodiment, and in FIG. 1, reference numeral 1 denotes a surface acoustic wave having a high propagation velocity α.
A single crystal substrate made of -Al ₂ O ₃ , and 20 a piezoelectric material made of ZnO, for example, on the substrate 1, α-Al ₂ O ₃
The piezoelectric layers 5W and 5E, which are epitaxially grown on the (0001) plane or the (0/112) plane and are made of a semiconductor having a piezoelectric property, are doped with Al as an impurity in the piezoelectric layer 20 epitaxially grown on the substrate 1. It is a semiconductor electrode having a resistance value of about 10 ⁻³ Ω / cm.

The surface direction of the above-mentioned substrate is shown as (0 /
112) is

[0029]

[Equation 2]

In this specification, "/" in parentheses "()" indicates a bar.

Next, a method of manufacturing the SAW filter according to the first embodiment will be described with reference to FIG. 2, the same reference numerals as those in FIG. 1 denote the same or corresponding parts,
Reference numeral 4 is a resist, and 4a is a resist mask obtained by patterning the resist 4.

As shown in FIG. 2 (a), a piezoelectric layer 20 made of ZnO single crystal is formed on the (0001) plane or (0/112) plane of the substrate 1 made of α-Al ₂ O ₃ . Epitaxial growth is performed to a thickness of several μm. After that, as shown in FIG. 2B, a resist 4 is formed on the piezoelectric layer 20.
Apply. The resist 4 is exposed to light and patterned to form a resist mask 4a for electrode formation as shown in FIG. 2 (c).

Next, in the state shown in FIG. 2 (c), ion implantation is performed using the resist mask 4a as a mask, and as shown in FIG. 2 (d), the interface between the substrate 1 and the piezoelectric layer 20 is formed. Impurities are doped and electrodes 5W and 5
Form E. At this time, the thickness of the electrode is 0.1 to 1.0 μm.
m. After that, as shown in FIG. 2 (e), the resist mask 4a is removed and a heat treatment is applied to the electrode portion 5
The impurities of W and 5E are activated to reduce the resistance of the electrode portions 5W and 5E.

Here, the electrode portion has a crystal orientation similar to that of the semiconductor crystal of the piezoelectric layer 20 even when Al is used as an impurity to be doped by ion implantation.
1-doped ZnO (ZnO: Al) is, for example, ZnO.
By doping Al with 0.2 wt%, it is possible to reduce the resistance to about 1 × 10 ⁻³ Ω / cm.

Since the electrodes 5W and 5E are directly formed on the substrate in this way, when the surface acoustic wave is excited by the high frequency applied between the electrodes 5w and 5w 'due to the piezoelectricity of the piezoelectric layer 20, This vibration can be directly transmitted to the substrate. Moreover, the electrodes 5W and 5E are made of the same material as the piezoelectric layer 20 and are epitaxially grown on the substrate in the same crystal orientation as the piezoelectric layer 20.
There is almost no lattice mismatch between W and 5E, and the piezoelectric layer 20
Has a good crystallinity. Therefore, the deterioration of the crystallinity of the piezoelectric layer, which has been a problem in the conventional device as shown in FIG. 7B, can be eliminated.

In this first embodiment, impurities are ion-implanted into the piezoelectric layer 20 which is a semiconductor to reduce the resistance, so that the crystallinity of the piezoelectric layer 20 is not impaired and the substrate 1 of the piezoelectric layer 20 is not damaged. Since it is possible to manufacture a thin film SAW filter in which the electrodes 5W and 5E are directly formed on the interface portion of the substrate 1, when the high frequency applied between the electrodes 5w and 5w 'is converted into surface acoustic waves, the thin film SAW filter is directly connected to the substrate 1. Since the electrodes 5W and 5E are made of the same material as the piezoelectric layer 20 and are epitaxially grown on the substrate like the piezoelectric layer 20, the lattice mismatch between the piezoelectric layer 20 and the electrodes 5W and 5E can be achieved. The crystallinity of the piezoelectric layer 20 is extremely good, and the piezoelectricity does not deteriorate due to poor crystallinity of the piezoelectric layer 20. Therefore, there is an effect that a thin film SAW filter having good operating characteristics can be easily manufactured.

Example 2. FIG. 3 is a cross-sectional view showing a manufacturing process of the thin film SAW filter according to Example 2 of the first embodiment, and 5 in the drawing is a low resistance semiconductor electrode having a low resistance, for example, by doping Al as an impurity. It is a layer.

First, as shown in FIG. 3A, the semiconductor electrode layer 5 containing impurities is epitaxially grown on the substrate 1 and post-annealing activates the impurities to reduce the resistance.

Thereafter, as shown in FIG. 3 (b), a resist 4 is applied, and this is exposed and patterned to form a resist, as shown in FIG. 3 (c).
A resist mask 4b as shown in is formed. afterwards,
As shown in FIG. 3D, the semiconductor electrode layer 5 is patterned by wet or dry etching to form an electrode. Then, the resist 4b is removed and the electrode portion 5 is removed.
W and 5E.

Next, the piezoelectric layer 20 is formed on the substrate 1 and the electrodes 5.
Epitaxial growth is performed on W and 5E to obtain a thin film SAW filter having the structure shown in FIG.

Here again, as described in the first embodiment, the crystal directions of the electrode portions 5W and 5E and the piezoelectric layer 20 are the same, and even when the piezoelectric layer 20 is grown, the crystallinity is maintained by the electrode portions 5W and 5E. It does not deteriorate.

In the second embodiment as described above, the same material as that of the piezoelectric layer 20, which is a semiconductor, is doped with impurities to reduce resistance and is epitaxially grown on the substrate, and the electrodes 5W and 5E are formed by etching. Further, by epitaxially growing the piezoelectric layer 20 having the same crystal structure as that of the electrode material on the upper portion thereof, it is possible to manufacture a thin film SAW filter in which the electrodes 5W and 5E are formed directly on the substrate at the interface between the piezoelectric layer 20 and the substrate 1. Therefore, when the high frequency wave applied between the electrodes 5w and 5w ′ is converted into the surface acoustic wave, this can be directly transmitted to the substrate 1, and the electrode 5
Since W and 5E are made of the same material as the piezoelectric layer 20 and are epitaxially grown on the substrate similarly to the piezoelectric layer 20, the piezoelectric layer 20
Lattice mismatch between the electrodes and the electrodes 5W and 5E is small, the crystallinity of the piezoelectric layer 20 is extremely good, and the piezoelectricity does not deteriorate due to poor crystallinity of the piezoelectric layer 20. Therefore,
There is an effect that a thin film SAW filter having good operating characteristics can be easily manufactured.

Embodiment 2. Configuration 1. Referring to FIGS. 4 and 5, the thin film SAW filter according to the second embodiment of the present invention includes a piezoelectric layer (20) made of a semiconductor formed by epitaxial growth on a substrate (1), and a piezoelectric layer (20). An electrode portion (5) formed by doping impurities at the interface with the substrate (1)
W, 5E) and further the electrode part (5W, 5E) above the electrode part (5W, 5E), in a piezoelectric layer (20) separated from
Second electrode portion (5W-2, 5) formed by doping impurities
E-2) is provided so that the crystal orientation of the piezoelectric layer (20) by epitaxial growth is not disturbed,
The electrode (5) is provided in the piezoelectric layer (20) apart from the interface portion of the piezoelectric layer (20) with the substrate (1) and the electrodes (5W, 5E).
W-2, 5E-2) can be formed.

Configuration 2. Thin film SA in the second embodiment
Referring to FIG. 4, the method of manufacturing the W filter is the same as that of the first embodiment, except that the interface portion of the piezoelectric layer (20) with the substrate (1) is doped with impurities and then the electrode portion (5W, 5E) is formed. Further, ion implantation is further performed using the resist mask (4a), and the electrodes (5W, 5E) are formed on the electrodes (5W, 5E).
E) includes a step of forming a second electrode (5W-2, 5E-2) having a low resistance in a piezoelectric layer (20) separated from the piezoelectric layer (20), whereby a crystal of the piezoelectric layer (20) by epitaxial growth is formed. The piezoelectric layer at the interface between the substrate (1) and the piezoelectric layer (20) and the electrodes (5W, 5E) in a few steps without disturbing the direction.
Electrodes (5W-2, 5E-2) in the piezoelectric layer (20) apart from
Can be formed.

Configuration 3. In addition, referring to FIG. 5, the method of manufacturing the thin film SAW filter according to the second embodiment is different from that of the first embodiment in that the interface between the piezoelectric layer (20) and the substrate (1) is doped with impurities to form an electrode. Department (5W, 5E)
And then forming a second electrode layer (5-2) made of a semiconductor containing impurities and having a low resistance on the surface of the piezoelectric layer (20) by epitaxial growth, and a resist thereon. Is formed and a resist mask (4c) is formed by patterning this, and the second electrode layer (5-2) is etched using the resist mask (4c) as a mask to form a second layer on the piezoelectric layer (20). Electrodes (5W-2, 5
E-2) and the second electrode (5W-2, 5E)
-2), a step of forming a piezoelectric layer (20) made of a semiconductor by epitaxial growth so as to cover the
As a result, the piezoelectric layer (20) separated from the interface portion of the piezoelectric layer (20) with the substrate (1) and the electrodes (5E, 5W) without disturbing the crystal orientation of the piezoelectric layer (20) by epitaxial growth. ) Inside the second electrode (5W-2, 5E
-2) can be formed.

Example 1. FIG. 4 is a cross-sectional view showing the manufacturing process of the thin film SAW filter according to the first example of the second embodiment. In the figure, the same reference numerals as those in FIG. 2 indicate the same or corresponding portions.

First, in the same manner as that described in Example 1 in the first embodiment, a resist is applied on the piezoelectric layer 20 epitaxially grown on the substrate 1, and the resist is patterned to form the structure shown in FIG. Resist mask 4a
To form. Using this resist mask 4a as a mask,
The piezoelectric layer at the interface between the substrate 1 and the piezoelectric layer 20 is doped with impurities such as Al by ion implantation to form electrodes 5W and 5E as shown in FIG. 4 (b).

In Example 1 of the present Second Embodiment, subsequently, with a different implantation energy from the above-mentioned ion implantation, impurities such as Al are deposited at a position apart from the electrodes 5W and 5E above the electrodes 5W and 5E. After the second electrodes 5W-2 and 5E-2 are formed by doping, the resist mask 4a is removed, and heat treatment is performed to activate the impurities in the electrode portion, and as shown in FIG. Each electrode part (5W, 5E,
Lower resistance of 5W-2, 5E-2).

In Example 1 of the second embodiment, a plurality of electrode layers can be formed by changing the implantation energy at the time of ion implantation.

As described above, in the first embodiment, by changing the implantation energy in each of the ion implantation steps, in addition to the interface portion of the piezoelectric layer 20 with the substrate 1, the piezoelectric layer 20 is separated from the electrode above the electrode. Electrodes can be further formed at different positions, and a thin-film SAW filter having a plurality of electrode layers in the piezoelectric layer 20 can be manufactured by an easier process without impairing the crystallinity of the piezoelectric layer 20. Further, since this thin film SAW filter has a plurality of electrodes in the piezoelectric layer 20, in addition to the effects of the first embodiment,
The piezoelectric action can be simultaneously generated without being limited to the interface between the substrate 1 and the piezoelectric layer 20, so that the piezoelectric efficiency can be greatly improved.

Example 2. FIG. 5 is a cross-sectional view showing the manufacturing process of the thin film SAW filter according to the second example of the second embodiment. In the figure, the same reference numerals as those in FIG. 2 indicate the same or corresponding portions. First, as described in Example 1 in the first embodiment, the surfaces of the piezoelectric layer 20 in which electrodes 5W and 5E are formed in the interface portion between the piezoelectric layer 20 and the substrate 1 and the resist mask 4a is removed are prepared. Alternatively, as described in Example 2 in the first embodiment, the piezoelectric layer 20 covers the electrodes 5W and 5E formed on the substrate 1.
5 is formed on the surface of the piezoelectric layer 20 after the epitaxial growth of
As shown in (a), a low resistance semiconductor electrode layer containing impurities is further epitaxially grown on the piezoelectric layer 20 and the impurities are activated by post annealing to reduce the resistance.

After that, a resist is applied, and this is patterned to provide a resist mask 4c as shown in FIG. 5B, and the semiconductor electrode layer 5-2 is patterned by wet or dry etching to form an electrode 5W. -2,5E-2 is formed. Thereafter, the resist mask 4c is removed, and the piezoelectric layer 20 is further epitaxially grown on the electrodes 5W-2 and 5E-2 to obtain a thin film SAW filter having a structure as shown in FIG. 5 (c).

In the second embodiment, a plurality of electrodes are formed in the piezoelectric layer 20 by further performing the process shown in the second embodiment on the piezoelectric layer 20 in which the electrodes 5W and 5E are already formed. A thin film SAW filter having an electrode layer can be formed.

As described above, in the second embodiment, the piezoelectric layer 20 in which the electrodes 5W and 5E are already formed is formed.
A semiconductor electrode layer containing impurities is further epitaxially grown thereon, and the resistance of the semiconductor electrode layer is lowered, followed by etching using a resist mask to form electrodes 5W-2 and 5E-2, and the piezoelectric layer 20 is formed so as to cover the electrodes. By epitaxially growing the thin film S in which a plurality of electrode layers are formed in the piezoelectric layer 20 without impairing the crystallinity of the piezoelectric layer 20.
The AW filter can be manufactured by an easy process.

Further, since this thin film SAW filter has a plurality of electrodes in the piezoelectric layer 20, the piezoelectric action is not limited to the interface between the substrate 1 and the piezoelectric layer 20 as in the first embodiment. A plurality of them can be generated at the same time, and the piezoelectric efficiency can be greatly improved.

Embodiment 3. Configuration 1. Referring to FIG. 6, the thin-film SAW filter according to the third embodiment of the present invention is the thin-film SAW filter according to each of the above-described embodiments, and further has electrodes (5E-3, 5W-) on the surface of the piezoelectric layer (20). 3), which allows electrodes (5W, 5E) formed at the interface of the piezoelectric layer (20) with the substrate (1) without disturbing the crystallographic direction of the piezoelectric layer (20) by epitaxial growth. In addition, electrodes (5W-3, 5E-3) can be further formed on the surface of the piezoelectric layer (20).

Configuration 2. Thin film SA in the third embodiment
As for the method of manufacturing the W filter, referring to FIG. 6, after the process in each of the above-described embodiments, the surface electrode layer made of a semiconductor containing impurities and having a low resistance is further formed on the upper surface of the piezoelectric layer (20) by epitaxial growth. (5-3) is formed, a resist is formed thereon, and this is patterned to form a resist mask (4d). Using the resist mask (4d) as a mask, the surface electrode layer (5-3) is formed. ) Is etched, and the surface electrodes (5E-3, 5W- are formed on the piezoelectric layer (20).
3) is formed, whereby an electrode (5W, formed on the interface portion of the piezoelectric layer (20) with the substrate (1) without disturbing the crystallographic direction of the piezoelectric layer (20) by epitaxial growth. 5E) as well as the electrode (5E)
W, 5E) on the upper surface of the piezoelectric layer (20) apart from the electrode (5E)
-3,5W-3) can be formed.

Configuration 3. Thin film SA in the third embodiment
The method for manufacturing the W filter includes a step of further forming a surface electrode made of metal on the upper surface of the piezoelectric layer (20) after the steps of the above-described respective embodiments, whereby the piezoelectric layer (20) formed by epitaxial growth. In addition to the electrodes (5W, 5E) formed at the interface of the piezoelectric layer (20) with the substrate (1) without disturbing the crystal direction of the electrode (5W,
Electrodes may be formed on the upper surface of the piezoelectric layer (20) apart from 5E).

Structure 4. Thin film SA in the third embodiment
In the method for manufacturing the W filter, after the step in each of the above-described embodiments, ion implantation is further performed on the upper portion of the piezoelectric layer (20) by using a resist mask, and the piezoelectric element separated from the electrode on the upper portion of the electrode is separated. The method includes a step of forming a low-resistance surface electrode on the upper part of the layer, which allows the piezoelectric layer (2) to be formed without disturbing the crystallographic direction of the piezoelectric layer (20) by epitaxial growth.
Electrode (5) formed at the interface between the substrate (1) and the substrate (1)
In addition to W, 5E), an electrode can be further formed on the piezoelectric layer (20) apart from the electrode (5W, 5E).

Example 1. FIG. 6 is a cross-sectional view showing a process of manufacturing the thin film SAW filter according to Example 1 of the third embodiment. First, as shown in FIG. 6 (a), a semiconductor electrode layer containing impurities is further epitaxially grown on the upper surface of the piezoelectric layer 20 of the thin film SAW filter formed by each of the examples in the above-described second embodiment, and post-annealing is performed. The impurities are activated to form the electrode layer 5-3 having a low resistance. Next, a resist is applied on the formed electrode layer 5-3, and the resist is patterned to form a resist mask 4d as shown in FIG. 6 (b). The electrodes 5W-3 and 5E-3 shown in (c) are formed. Although the material of the electrode formed here is the one obtained by epitaxially growing the low-resistance semiconductor in the first embodiment, it may be formed of the metal material used in the conventional SAW filter.

When the electrodes are made of metal, the piezoelectric layer 20
Prepared by forming a metal layer for electrodes on the upper surface of FIG.
By providing the resist mask 4d as shown in (b) and etching the electrode metal layer by dry etching using Ar gas, the electrode 5W-3, shown in FIG. 6 (c),
A surface electrode is formed at the same position as 5E-3.

As described above, according to the first embodiment, in each of the above-described embodiments, the interface portion of the piezoelectric layer 20 with the substrate 1 and the piezoelectric layer 20.
Since the low resistance semiconductor electrode is formed therein, and the electrode is further formed on the piezoelectric layer 20, the thin film SAW filter having the electrode also on the surface of the piezoelectric layer 20 can be obtained. In addition, the piezoelectric effect can be generated simultaneously without being limited to the interface between the substrate 1 and the piezoelectric layer 20, so that the piezoelectric efficiency can be greatly improved.

Example 2. In Example 2 of the present third embodiment, the surface electrode is formed by ion implantation, and as described in Example 1 of the second embodiment, the resist mask 4a is provided on the piezoelectric layer 20 (see FIG. Four
(b)), using this as a mask, electrodes 5W, 5E, and electrodes 5W
After -2 and 5E-2 are formed, the implantation energy is further changed to form an electrode layer (not shown) formed by ion-implanting impurities such as Al near the surface of the piezoelectric layer 20.

As described above, in the second embodiment, as described in each of the above embodiments, the interface portion between the piezoelectric layer 20 and the substrate 1,
And an electrode layer formed by forming a low-resistance semiconductor electrode in the piezoelectric layer 20 and then ion-implanting impurities such as Al into the surface portion of the piezoelectric layer 20 using the resist mask formed on the piezoelectric layer 20 as a mask. Since it is formed, a thin film SAW filter having the same effect as that of the first embodiment can be manufactured by an easier process.

In the third embodiment, the substrate 1 of the piezoelectric layer 20 is used.
An example is shown in which the surface electrodes 5W-3 and 5E-3 are further formed on the surface of the piezoelectric layer 20 based on the one having the two-layer electrode in the interface portion with and in the piezoelectric layer 20. The underlying thin film SAW filter may have more electrodes in the piezoelectric layer, or may have electrodes formed only at the interface of the piezoelectric layer 20 with the substrate 1.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing the structure of a thin film SAW filter according to a first example of the first embodiment of the present invention.

2A to 2E are views for explaining the processing in each step in the method of manufacturing a thin film SAW filter according to Example 1 of the first embodiment of the present invention.

FIG. 3 is a diagram (a) to (f) illustrating processing in each step in the method of manufacturing the thin film SAW filter according to the example 2 of the first embodiment of the present invention.

FIG. 4A to FIG. 4C are views for explaining the processing in each step in the method of manufacturing a thin film SAW filter according to Example 1 of the second embodiment of the present invention.

5 (a) to 5 (c) are diagrams for explaining the processing in each step in the method of manufacturing a thin film SAW filter according to Example 2 of Embodiment 2 of the present invention.

FIGS. 6A to 6C are diagrams for explaining the processing in each step in the method of manufacturing a thin film SAW filter according to Example 1 of the third embodiment of the invention. FIGS.

7A and 7B are diagrams showing a structure of a conventional thin film SAW filter, in which FIGS. 7A and 7B are sectional views and FIG. 7C is a view seen from above.

FIG. 8 is a diagram (a) to (f) for explaining the processing in each step in the conventional method of manufacturing a thin film SAW filter.

[Explanation of symbols]

1 substrate, 2 piezoelectric layer, 20 piezoelectric layer, 3 electrode metal, 3W input side electrode, 3E output side electrode, 4 resist, 4a to 4d resist mask, 5 low resistance semiconductor electrode layer, 5W input side low resistance semiconductor electrode, 5E Output side low resistance semiconductor electrode.

Claims (11)

[Claims] 1. A piezoelectric layer made of a semiconductor formed by epitaxial growth on a substrate, and an electrode portion formed by doping impurities into an interface portion of the piezoelectric layer with the substrate. Thin film surface acoustic wave filter. 2. The thin film surface acoustic wave filter according to claim 1, further comprising a second electrode portion formed above the electrode portion and separated from the electrode portion, the second electrode portion being formed by doping impurities into the piezoelectric layer. And a thin film surface acoustic wave filter further comprising: 3. The thin film surface acoustic wave filter according to claim 1, further comprising a surface electrode portion on an upper surface of the piezoelectric layer. 4. The thin film surface acoustic wave filter according to claim 1, wherein the substrate material is α-Al ₂ O ₃ and the piezoelectric layer material is ZnO. Thin film surface acoustic wave filter. 5. A step of forming a piezoelectric layer made of a semiconductor by epitaxial growth on a substrate, a step of forming a resist on the piezoelectric layer and patterning the resist to form a resist mask, and using the resist mask as a mask. And a step of implanting ions into the piezoelectric layer to form an electrode portion having a low resistance at the interface between the substrate and the piezoelectric layer. 6. A step of forming an electrode layer made of a semiconductor having a low resistance containing impurities by epitaxial growth on a substrate, and a step of forming a resist on the electrode layer and patterning the resist to form a resist mask. And a step of etching the electrode layer using the resist mask as a mask to form a low resistance electrode on the substrate, and a step of forming a piezoelectric layer made of a semiconductor by epitaxial growth so as to cover the low resistance electrode. A method of manufacturing a thin-film surface acoustic wave filter, comprising: 7. The method of manufacturing a thin film surface acoustic wave filter according to claim 5, wherein after the step, a second electrode layer made of a semiconductor containing impurities and having a low resistance is further formed by epitaxial growth. A step of forming a resist on the second electrode layer, patterning the resist to form a resist mask, and etching the second electrode layer using the resist mask as a mask to form a layer on the piezoelectric layer. A method of manufacturing a thin-film surface acoustic wave filter, comprising: a step of forming a second electrode; and a step of forming a piezoelectric layer made of a semiconductor by epitaxial growth so as to cover the second electrode. 8. The method for manufacturing a thin film surface acoustic wave filter according to claim 5, wherein after the step, ion implantation is further performed using a resist mask, and the ion is separated from the electrode above the electrode. A method of manufacturing a thin-film surface acoustic wave filter, comprising the step of forming a low-resistance second electrode in a piezoelectric layer. 9. The method of manufacturing a thin film surface acoustic wave filter according to claim 5, further comprising a step of forming a surface electrode made of metal on the upper surface of the piezoelectric layer after the step. A method for manufacturing a thin film surface acoustic wave filter, comprising: 10. The method for manufacturing a thin-film surface acoustic wave filter according to claim 5, further comprising a surface electrode layer made of a semiconductor containing impurities and having a low resistance by epitaxial growth after the step. Forming step, forming a resist on the surface electrode layer, patterning this to form a resist mask, and etching the surface electrode layer using the resist mask as a mask to form a surface electrode on the piezoelectric layer. And a step of forming the thin film surface acoustic wave filter. 11. The method for manufacturing a thin film surface acoustic wave filter according to claim 5, wherein after the step, ion implantation is further performed using a resist mask to form the electrodes above the electrodes. A method of manufacturing a thin film surface acoustic wave filter, comprising the step of forming a low-resistance surface electrode on the surface portion of the piezoelectric layer separated from each other.