JPS62130010A - Surface acoustic wave element and its manufacture - Google Patents

Abstract

PURPOSE:To improve the reflectance of a reflector and to miniaturize the titled element by selecting a line width ratio etaR of the reflector using metallic strip connected together to be a small value of 0.0<etaR<0.5. CONSTITUTION:A lithium tantalate of 36 deg. rotation Y axis cut applied with mirror polishment is used as a piezoelectric substrate 1 on which a shear horizontal surface acoustic wave propagates, and Al is sputtered and vapor-deposited with a film thickness of 2000Angstrom on the substrate 1. Then a photomask is used in response to the reflectors 3, 3' and a reed screen electrode, the pattern is transferred to a photoresist, and the reflectors 3, 3' and the red screen electrode 2 are formed as a pattern. In this case, the relation of the line width ratio etaR is expressed as 0.0<etaR<0.5, where LR is the metallic finger width, SR is the interval of the metallic fingers and R=LR/(LR+SR). The ratio etaR is preferably <=0.45 and also preferably >=0.1 to preclude the possibility of disconnection of a metallic strip constituting the reflector.

Description

Detailed Description of the Invention: ``Technicality+nJ The uninvented object is a resonator, a filter, and a reflector having a metal strip reflector, interdigital Ti, J4ihj, on a piezoelectric substrate in which a shear-horizontal type surface acoustic wave propagates. 〃
The present invention relates to surface acoustic wave elements such as wire extensions and methods of manufacturing the same.

"Prior art and its problems" Surface acoustic wave elements have traditionally been used for special purposes in military applications, but in recent years they have begun to be used in consumer equipment such as FM tuners and TVs, and have suddenly come into the spotlight. It has become. Specifically, the surface acoustic wave element includes an 8-element element, an oscillator,
It has been commercialized as a filter, etc. The characteristics of these various surface acoustic wave devices are that they are small, lightweight, and highly reliable, and that their manufacturing process is similar to that of integrated circuits, and that they have high I11 productivity. Nowadays, it has become the number one produced indispensable electronic component.

A surface wave propagating on the surface of a piezoelectric medium has a seed/, 1
However, the one commonly used is Rayleigh (Ra).
They are called waves. Incidentally, there are a coupling coefficient and a temperature coefficient as indicators for evaluating the performance of a piezoelectric substrate. The coupling coefficient is an index representing the efficiency with which air energy is converted into vibration energy, and the temperature coefficient is an index representing the temperature coefficient of the propagation delay time of a surface acoustic wave propagating in a piezoelectric medium. In addition, surface acoustic waves propagate in a shear-horizontal type of elasticity in which particles are displaced in a direction perpendicular to the direction in which surface acoustic waves propagate within the surface layer of the plate. It is beginning to attract attention because it has surface waves and has a large 1111 coupling coefficient.

? With the increasing frequency of mobile radio devices such as car phones, surface acoustic wave J (wavelength f-) is used in voltage-controlled oscillators, etc., to reduce size, weight, and cost. Although it is useful, there is a problem that the frequency variable width is narrow.

As an example of a surface acoustic wave device having a reflector using a metal strip in the prior art, surface acoustic wave resonance r.
An example of if < is shown in Figure 7, that is, this surface acoustic wave resonance r is the piezoelectricity in which the surface waves propagate (on the surface acoustic waves interdigital electrode 2;
It is constructed by forming a reflector 3.3' on the bullet, in which a large number of metal strips are periodically arranged at right angles to the propagation direction of one surface wave. When a voltage of a specific frequency is applied to the interdigital electrodes 2, an electric field is applied to the surface of the piezoelectric substrate 1 in the gap between the interdigital electrodes 2, and the piezoelectricity of the piezoelectric substrate 1 causes a strain proportional to the voltage. It propagates to both sides as a surface wave at a sound speed determined by the material of the substrate l. This surface wave is reflected by the grating reflectors 3, 3' on both sides, returns to the interdigital electrode 2 again, and resonates.

Such a surface acoustic wave resonator can be expressed as shown in FIG. 9, similar to the case of a crystal resonator, when 1 is expressed as an air-bacteria equivalent circuit. In FIG. 8, G.

is the electrostatic capacitance r- of the interdigital electrode 2, the inductance is /C is called the volume li1 ratio, expressed as γ, volume jji
The ratio γ is an important parameter that determines the resonance J,', ] wave number characteristics of the resonator, etc. If γ is small, when used in a voltage controlled oscillator, the oscillation frequency will be 'if you can change it. Therefore, 11Lγ is y=(π'/8 to 2) eyelid r ・−(, D (r
≧1) T can be approximated, where k2 is the above-mentioned coupling coefficient, and r is a constant determined by the performance of the reflector.

r=1 represents the theoretical limit. ■As can be seen from the formula, the volume ratio γ is determined by the coupling coefficient of the piezoelectric board used and the performance of the reflector, but conventionally only the coupling coefficient of the piezoelectric substrate has been focused on, and the reflection due to the structure of the reflector etc. They are not paying attention to the second aspect of their performance.

The reflector becomes large, making it impossible to miniaturize the element, and the capacitance ratio is large, so when used in a voltage controlled oscillator, there are drawbacks such as the inability to obtain a large variable frequency.

A partially enlarged view of a conventional reflector is shown in FIG.
The width of the metal strips used in the reflector and the spacing between the metal strips are approximately equal, and the line width ratio of the reflector is ηR or ηR=0.5. This causes the performance of the reflector, specifically the reflectance, to deteriorate from its original characteristics.In order to increase the reflectance of the entire reflector, a large number of metal strips must be used, which increases the size of the element and increases the capacitance. The disadvantage was that the ratio γ was not reduced.

"Objective of the Invention" The object of the present invention is to solve the problems of the prior art described above, to improve the reflectance of a reflector using metal strips, to reduce the size of the element, and to reduce the capacitance ratio. To provide a surface acoustic wave element which, when used in a voltage controlled oscillator, has improved performance such as widening the frequency variable width, reducing the size of a filter having a surface acoustic wave reflector, and lowering insertion loss, and a method for manufacturing the same. It is in.

"Structure of the Invention" The surface acoustic wave element of the present invention has a piezoelectric substrate on which a shear-horizontal type surface acoustic wave propagates, and a large number of mutually connected substrates whose center spacing is approximately 1/2 of the propagation wavelength of the surface acoustic wave. A reflector consisting of connected metal strips is provided, the metal finger width of the reflector is LR1, the metal finger spacing is SR, and the line width ratio η
When R is expressed as ηR=LR/(LR+SR), 0
．． 0<ηR(0, 5).

The further improved surface acoustic wave element of the present invention has a piezoelectric substrate on which a shear-horizontal surface acoustic wave propagates, and a large number of interconnected elements whose center spacing is approximately 1/2 of the propagation wavelength of the surface acoustic wave. a reflector made of a metal strip, and at least one set of interdigital electrodes, where the metal finger width of the reflector is LR1, the metal finger spacing is SR, and the line width ratio η
If R is expressed as ηR=R/(LR+SR), then 0
．． 0<ηRcO, 5, and when the electrode finger width of the interdigital electrode is LT, the electrode finger width interval is ST, and the line width ratio η is expressed as ηT=LT/ (LT + ST). , ηT>ηR.

The method of manufacturing a surface acoustic wave device according to the present invention includes a piezoelectric plate (1) on which a shear-horizontal surface acoustic wave propagates, and a plurality of piezoelectric plates whose center spacing is approximately 1/2 of the propagation wavelength of the surface acoustic wave. A method of manufacturing a surface acoustic wave device having a reflector made of interconnected metal strips, wherein the reflector has a metal finger width of LR, a metal finger spacing of SR, and a line width ratio ηR of ηR= Manufactured by photolithography using a photomask created by setting the line width ratio of the reflector pattern so that when expressed as LR/(LR+SR), 0.0<ηR<0, 5 It is characterized by

A further improved method of manufacturing a monomorphic surface wave element of the present invention is to apply a shear-horizontal glue on a piezoelectric substrate on which a monomorphic surface wave propagates, the center spacing being approximately 1/2 of the propagation wavelength of the surface acoustic wave. In a method for manufacturing a surface acoustic wave device comprising a reflector made of a large number of mutually connected metal strips and at least one set of interdigital electrodes, the metal finger width of the reflector is defined as LR1 metal finger spacing. Let SR be the line width ratio η
When R is expressed as ηR=LR/(LR+SR),
0.0〈ηR (0.5, and ``1. The electrode finger width of the interdigital electrode is LT, the electrode finger width interval is ST,
When the line width ratio ηT is expressed as ηT; LT/(LT + ST), a photomask was created by setting the line width ratio of the reflector and interdigital electrode patterns so that 9 > ηR. It is characterized by being manufactured using photolithography technology.

By setting the pattern of the I/l'l surface wave large surface wave element radiator of the present invention as described above, the reflectance of the reflector can be improved. Furthermore, by setting the patterns of the reflector and interdigital electrodes as described in section 1 above, resonance resistance and attenuation outside the pass band can be stabilized, and a compact device with a small capacitance X11 ratio can be obtained. Furthermore, with the uninvented method for manufacturing a surface acoustic wave device, a surface acoustic wave device having the above-mentioned pattern can be easily manufactured with high viscosity.

Furthermore, by providing a photomask with an inspection pattern that effectively imitates the shape of the reflector or interdigital electrode described in 2.1, it is possible to easily and accurately conduct lines using electrical, mechanical, or optical methods. The width ratio can be increased to 414゛ite,
The quality of the element f- can be checked immediately after enching.

In the uninvention, it is preferable to form the reflective X) and interdigital electrodes made of metal strips with the same metal, or A1 or A1 as the metal from the viewpoint of reflector characteristics, ease of process, cost, etc. A1 alloy?i! frightfully,
Alternatively, it is preferable to have a multilayer structure of A1 or an A1 alloy and a high melting point metal.

"Embodiments of the Invention" Example 1 Figures 1, 2, and 3 show an example in which the present invention is applied to surface acoustic wave resonance. FIG. 2 is a sectional view, and FIG. 3 is a partially enlarged sectional view of the reflector portion.

Mirror-polished lithium tantalate with a 36-degree rotating Y cant is used as the piezoelectric substrate l on which shear-horizontal surface acoustic waves propagate, and A1 is coated with a film thickness of 2000 on the
It was sputter deposited to look like a person. Next, reflector 3.
Using a photomask made in advance with a line width ratio ηR of 3" and a line width ratio η of the interdigital electrode 2 changed in advance, the pattern is transferred to the photoresist, and a reflector 3.3' is formed by a normal wet etching method. A pattern of the interdigital electrode 2 and the interdigital electrode 2 was formed.At this time, an inspection pattern imitating the reflector 3.3' and the interdigital electrode 2 was also formed.This inspection pattern was formed using an optical method. 'A11 Table 1 shows the characteristics of the surface acoustic wave resonator with a fixed linewidth ratio.The propagation direction was approximately the X-axis direction.This surface acoustic wave resonator had one reflector 3.3 The number of metal strips connected to the W in ° is 200, and the number of pairs of interdigital electrodes 2 is 10.
The pitch of the reflector 3.3° and the interdigital electrode 2 was approximately 4 μm, and the resonant frequency was approximately 510 MHz.

Table 1 According to Table 1, it can be seen that the container 2 ratio decreases as the line width ratio ηR of the reflector 3.3° decreases. In other words, this indicates that the reflectance of the reflector is increasing.

In addition, as another example, the structure was similar to that of the previous example, but the number of metal strips constituting the 3.3° reflector was reduced to 150. When the line width ratio of the interdigital + lj pole 2 is set to 1); 0.5 as in Example i,
When the line width ratio ηR of the reflector 3゜3゛ is 0.5, the ratio is 15.
%, and there was almost no change when ηR was 0.3 or less.

From this, it can be seen that the reflectance of the reflector 3.3° according to the present invention is much higher than that of the conventional example, and it can be said that it is extremely effective for lowering the volume/cost ratio and downsizing. In this case, η
The size of R is within the scope of the present invention, 0, 0<ηR(0,
If it is 5, it is clear that the characteristics are better than the conventional example, but if it is 1
In order to fully obtain the effects of the present invention, ηR is preferably 0.45 or less; on the other hand, if ηR is too small, metal strips constituting the reflector may be disconnected (ri), which increases performance and reduces yield. Therefore, ηR is preferably 0.1 or more.

-[- The properties listed below are Al-3i (Si 1-3%),
Al[:u(CuO, 5~4$), AI-Ti(
(Ti0.5-2%) (7) Form an electrode material made of AI alloy type IA or a high-melting point metal such as Or, Mo, W, Ti, etc. to a thickness of 20-400 mm, and then apply A1 or Multi-layered electrode material made of bipedal A1 alloy, and more! - 50% high melting point metal such as Cr, No, W, Ti
A similar tendency was observed when electrode material 1 having a multilayer structure formed to a thickness of ~500 mm was used. Therefore, it can be seen that the effects obtained by the present invention do not depend on the jli electrode material.

Example 2 A surface acoustic wave element manufactured in such a manner that the piezoelectric substrate 1 in which shear-horizontal type surface acoustic waves propagates in Example 1 is replaced with 41-degree rotated Y-axis cut lithium niobate so that the waves propagate approximately in the X-axis direction. As a result of measuring the characteristics in the same manner as for the two feet, the characteristics showed the same tendency as in Example 1.

Example 3 A surface acoustic wave element manufactured in such a manner that the piezoelectric substrate l in which the shear-horizontal type surface acoustic waves of Example 1 propagates is replaced with 64-degree rotated Y-axis cut lithium niobate so that the waves propagate approximately in the X-axis direction. As a result of measuring the characteristics in the same manner as above, the characteristics showed the same tendency as in Example 1.

As described above, in the present invention, as the piezoelectric substrate 1 through which shear-horizontal surface acoustic waves propagate, the cut angle,
Various types with different propagation directions can be adopted.

Embodiment 4 FIG. 4 shows still another embodiment in which the present invention is applied to a resonant filter. This resonant filter is
It has two pairs of interdigital electrodes with an angle of 2.2°, and a reflector 3.3' is formed on the outside thereof.

In this resonant filter, the interdigital electrode 2.2°
Table 2 shows the results of measuring the characteristics by changing the line width ratio ηR of the reflector 3.3' with the line width ratio 1 set constant at 0.5.

Table 2 As is clear from Table 2, as the line width ratio ηR of one reflection Z+3.3' is decreased, the reflectance of the reflector 3.3' increases and the insertion loss of the filter decreases. I understand.

The piezoelectric substrate 1 of this embodiment is made of lithium tantalate with a Y cut of 36 degrees, and the propagation direction of surface acoustic waves is approximately in the X-axis direction. However, similar trends were obtained when other piezoelectric substrates were used.

Incidentally, the line width ratio of the interdigital electrodes is desirably set to the following limitations.

FIG. 5 shows the relationship between the line width ratio of the interdigital electrode and the electrode capacitance. According to this, when the line width ratio of the interdigital electrodes is increased, the electrode capacitance increases, and as a result, the capacitance ratio increases.

In addition, the amount of out-of-band attenuation also deteriorates.

FIG. 6 shows the relationship between the line width ratio ηT of the interdigital electrode and the radiation conductance. Here, the radiation conductance is, for example, inversely proportional to the resonance resistance of a surface acoustic wave resonator.The resonance resistance of a surface acoustic wave resonator is generally better to be small, but for that reason, the radiation conductance of the interdigital electrode is Bigger is better.

From the following I-, the m-width ratio ηT of the interdigital electrode is 0.
It can be said that the range of 3≦ηT≦0.7 is preferable from the viewpoint of capacitance ratio and resonance resistance.

"Effects of the Invention" As explained above, according to the present invention, the reflectance of one reflector can be increased by reducing the line width ratio of the reflectors using mutually connected metal strips. . Therefore, when applied to surface acoustic wave resonators, the capacitance ratio and resonant resistance are reduced, making it possible to downsize the leakage element, and when applied to voltage-controlled oscillators, the frequency variable width is much greater than conventional examples. It becomes wider. Furthermore, if applied to a resonant filter, an element that is smaller and has lower loss than the conventional one can be obtained.

[Brief explanation of drawings]

Fig. 1 is a plan view showing an embodiment in which the present invention is applied to a surface acoustic wave resonator, Fig. 2 is a cross-sectional view of a circular surface acoustic wave resonator, and Fig. 3 is a cross-sectional view of the same surface acoustic wave resonator. 4 is a partially enlarged sectional view, FIG. 4 is an f-plane view showing another embodiment in which the present invention is applied to a resonant filter, and FIG. 5 is a change in the spacing between the electrodes when the line width ratio of the interdigital electrodes is changed. Fig. 6 is a characteristic chart showing the change in radiation conductance when the line width ratio of the interdigital electrode is changed, Fig. 7 is a characteristic chart showing the conventional surface acoustic wave resonator. The figure is a partial enlarged sectional view of a pendulum, and figure fjS9 is an electrical equivalent circuit diagram of a surface acoustic wave element. The interdigital electrode, 3.3゛, is a reflector. Patent Applicant Alps Electric Co., Ltd. Agent: Kunio Sanyu Patent Attorney: Shigeru Matsui Figure 1 Figure 2 Ward 3 Figure 4 (1T) Figure 5 1 Line Width ('7T) ) Figure 6

Claims (6)

[Claims] (1) A reflector consisting of a large number of interconnected metal strips whose center spacing is approximately 1/2 of the propagation wavelength of the surface acoustic wave is placed on a piezoelectric substrate on which shear-horizontal surface acoustic waves propagate. In the surface acoustic wave element equipped with the above, when the metal finger width of the reflector is LR, the metal finger interval is SR, and the line width ratio ηR is expressed as ηR:LR/(LR+SR),
A surface acoustic wave element characterized in that 0.0<ηR<0.5. (2) In claim 1, 0.1≦ηR≦
A surface acoustic wave element that is said to be 0.45. (3) A reflector consisting of a large number of interconnected metal strips with a center-to-center spacing approximately 1/2 of the propagation wavelength of the surface acoustic wave, on a piezoelectric substrate on which shear-horizontal surface acoustic waves propagate. , and at least one set of interdigital electrodes, the metal finger width of the reflector is LR, the metal finger spacing is SR, and the line width ratio ηR is ηR:L.
When expressed as R/(LR+SR), 0.5<ηR<1
．． 0, and the electrode finger width of the interdigital electrode is LT, the electrode finger width interval is ST, and the line width ratio ηT is ηT=
A surface acoustic wave element characterized in that ηT>ηR when expressed as LT/(LT+ST). (4) In claim 3, 0.1≦ηR≦
0.45, and 0.3≦ηT≦0.7. (5) A reflector consisting of a large number of interconnected metal strips whose center spacing is approximately 1/2 of the propagation wavelength of the surface acoustic wave is placed on the piezoelectric substrate on which shear-horizontal surface acoustic waves propagate. In the method for manufacturing a surface acoustic wave device, the width of the metal fingers of the reflector is LR, and the distance between the metal fingers is SR.
If the line width ratio ηR is expressed as ηR=LR/(LR+SR), then the photomask is created by setting the line width ratio of the reflector pattern so that 0.0<ηR<0.5. 1. A method for manufacturing a surface acoustic wave device, characterized in that the surface acoustic wave device is manufactured using a photolithography technique. (6) A reflector consisting of a large number of interconnected metal strips with a center spacing of approximately 1/2 of the propagation wavelength of the surface acoustic wave, on a piezoelectric substrate on which shear-horizontal surface acoustic waves propagate. , at least one set of interdigital electrodes, wherein the metal finger width of the reflector is LR, the metal finger spacing is SR, and the line width ratio ηR
When expressed as ηR=LR/(LR+SR), 0.0
<ηR(0,5, and the electrode finger width of the interdigital electrode is LT, the electrode finger width interval is ST, and the line width ratio η
When T is expressed as ηT=LT/(LT+ST), ηT
A method for manufacturing a surface acoustic wave device, characterized in that the device is manufactured by photolithography using a photomask created by setting the line width ratio of the reflector and interdigital electrode patterns so that >ηR.