JPS6172408A - Surface acoustic wave element - Google Patents

Abstract

PURPOSE:To change easily the impedance characteristic without giving effect to the frequency characteristic by providing an auxiliary electrode connected to an input electrode or an output electrode at the outside of the range of an input counter electrode and an output counter electrode. CONSTITUTION:Auxiliary electrodes 17a, 17b are connected to one end of input comb line electrodes 12a, 12b and not covered by a piezoelectric thin film 14. That is, the auxiliary electrodes 17a, 17b are provided at a position at the outside of the input counter electrode 15. Since the auxiliary electrodes 17a, 17b not covered by the piezoelectric thin film 14 are provided while being connected electrically to the electrodes 12a, 12b in this way, only the static capacitance is adjusted without generating a surface acoustic wave from the electrodes 17a, 17b. Thus, the impedance characteristic is changed easily without giving any effect onto the frequency characteristic of the surface acoustic wave element.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a surface acoustic wave device (hereinafter simply referred to as a SAW device), and particularly relates to a surface acoustic wave device whose impedance characteristics can be changed without affecting frequency characteristics. It is related to the element.

[Prior art and its problems]

SAW elements can be applied to filters, resonators, delay lines, etc., and have many advantages in that they are small and do not require adjustment.

Such a SAW element applies a voltage to a piezoelectric material to generate a surface acoustic wave, and converts this surface acoustic wave back into an electric signal to obtain a desired frequency characteristic. LiTaOx, LiNbO3, single crystals such as quartz, PZT-based piezoelectric ceramics, ZnO, AiN
Piezoelectric thin films such as

A conventional SAW element using such a piezoelectric thin film, for example, a SAW filter, as shown in FIGS. An output comb-shaped electrode 3 that converts the surface acoustic wave into an electric signal again is provided, and both output comb-shaped electrodes 2
. An input counter electrode 5 and an output counter electrode 6 are provided to face each other.

By the way, the input/output comb-shaped electrodes 2 and 3 are formed of a vapor-deposited film of metal, such as Au, and a piezoelectric thin film 4 is formed by CVD (chemical vapor deposition) so as to cover the entirety of both output comb-shaped electrodes 2 and 3. P V' such as phase growth method), ion blating method, or sputtering method using DC, RF, magnetron, etc.
In addition to forming the electrode by the D method, a counter electrode 5 for both outputs is also formed.
, 6 are formed by depositing a metal film such as At or Au so as to cover the upper surfaces of the intersecting portions of the input/output comb-shaped electrodes 2 and 3.

The comb shape of the input/output comb-shaped electrodes 2.3 is constructed by Fourier transforming the required frequency characteristics of the filter and making the impulse response on the time axis correspond to the length of the comb-shaped electrodes. 5 and 6 are provided to increase the electromechanical coupling coefficient representing the efficiency of conversion between an electric signal and a surface acoustic wave.

By the way, the impedance of the conventional SAW filter mentioned above is affected by radiation resistance, capacitance, electrical resistance, acoustic susceptance, etc.
When a W filter is attached to a device and used, it is the capacitance that becomes a problem in terms of impedance characteristics. Therefore, it is possible to change the impedance characteristics by adjusting this capacitance, but the factors that determine capacitance, such as the capacitance per pair of electrodes, the number of effective pairs, and the crossover width, are simply It is not only a factor that determines capacitance, but also a factor that determines frequency characteristics, so changing these determining factors and changing capacitance to change impedance characteristics also changes frequency characteristics at the same time. Therefore, with conventional SAW filters, it is impossible to change only the impedance characteristics.

[Failure to solve the problem]

In a surface acoustic wave element comprising an input electrode, an output electrode, and an input counter electrode and an output counter electrode via a piezoelectric body, an auxiliary electrode connected to the input electrode or the output electrode outside the range of the input counter electrode and the output counter electrode. Provide electrodes.

[Example 1] FIGS. 1a and 1b are explanatory diagrams of a first example of a surface acoustic wave element according to the present invention.

In FIGS. 1a and 1b, 11 is a non-piezoelectric substrate that serves as the base of the SAW element, and on the surface of this non-piezoelectric substrate 11 are input comb-shaped electrodes 12a that convert electrical signals into surface acoustic waves.
12b and output comb-shaped electrodes 13a and t3b for converting the surface acoustic waves into electrical signals again.

14 has a film thickness of h/λ(0,1(λ: surface acoustic wave wavelength,
The piezoelectric thin film 14 is formed to entirely cover the input comb-shaped electrodes 12a, 12b and the output comb-shaped electrodes 13a, 13b.

Reference numeral 15 denotes an input counter electrode, and this input counter electrode 15 is formed to cover the intersection of the manual comb-shaped electrodes 12a and 12b.

16 is an output counter electrode, and this output counter electrode 16 is formed to cover the intersection of the output comb-shaped electrodes 13a and 13b.

Reference numerals 17a and 17b are auxiliary electrodes provided with one end (electrical connection) of the input comb-shaped electrodes 12a and 12b, and these auxiliary electrodes 17a and 17b are made of a non-piezoelectric substrate like the input comb-shaped electrodes 12a and 12b. 11, input comb-shaped electrodes 12a, 1
It is not covered with a piezoelectric thin film 14 like 2b. The claw 9 auxiliary electrodes 17a and 17b are the input counter electrodes 15
It is located outside of the

By the way, the input/output comb-shaped electrodes 12a, 12b,
The auxiliary electrodes 13a, 13b and the auxiliary electrodes 17a, 17b are formed by a metal vapor deposition film of, for example, At or Au. It is formed by a PVD method such as the method.

Still, the input counter electrode 15 and the output counter electrode 16 are the input and output comb-shaped electrodes 12a, 12b, 13a,
For example, At, AU on the upper surface of the intersection in 13b
It is formed from a metal vapor deposited film such as.

Further, the input/output comb-shaped electrodes 12a, 12b,
The comb shapes in 13a and 13b are constructed by Fourier transforming the required frequency characteristics of the filter and making the impulse response on the time axis correspond to the length of the comb-shaped electrodes. This is provided to increase the electromechanical coupling coefficient, which represents the efficiency of conversion with surface waves.

The SAW filter configured as shown in the first embodiment has an auxiliary electrode 17a that is not covered with the piezoelectric thin film 14.

Since the auxiliary electrodes 17b are electrically connected to the input comb-shaped electrodes 12a and 12b, only the capacitance can be adjusted without generating surface acoustic waves from the auxiliary electrodes 17a and 17b. It becomes possible to easily change impedance characteristics without affecting frequency characteristics.

[Example 2] Figures 2a and 2b are explanatory diagrams of a second example of the surface acoustic wave element according to the present invention.

The SAW filter shown in this second embodiment has input comb-shaped electrodes 22a formed on a non-piezoelectric substrate 21.

Auxiliary electrodes 27a, 27b are electrically connected to 22b.
−, 1, and these auxiliary electrodes 27a and 27b are also covered with a piezoelectric thin film 24 having a film thickness of h/λ (0, 1 (λ: surface acoustic wave wavelength, repeating wavelength of the comb-shaped electrode)). It is composed of

In FIGS. 2a and 2b, 23a and 23b are output comb-shaped electrodes, 25 is an input counter electrode, and 26 is an output counter electrode, and these structures are the same as those of the first embodiment.

By the way, the input/output comb-shaped electrodes 22a, 22b,
23a.

23b and the auxiliary electrodes 27a, 27b are, for example, At,
The piezoelectric thin film 24 is formed of a metal vapor deposited film of Au, and is formed by a PVD method such as a CVD method (chemical vapor deposition method), an ion blasting method, or a DC, RF, or magnetron sputtering method. Further, the input counter electrode 25 and the output counter electrode 26 are formed on the upper surfaces of the intersection portions of the input/output comb-shaped electrodes 22a, 22b, 23a, and 23b, covered with a metal vapor deposition film such as A4Au.

Further, the input/output comb-shaped electrodes 22a, 22b, 23a,
The comb shape in 23b is constructed by Fourier transforming the required frequency characteristics of the filter and making the impulse response on the time axis correspond to the length of the comb-shaped electrode.
5.26 is provided to increase the electromechanical coupling coefficient representing the efficiency of conversion between an electric signal and a surface acoustic wave.

In the second embodiment, the auxiliary electrodes 27a and 27b are covered with the piezoelectric thin film 24, so that the auxiliary electrode 27a is different from the auxiliary electrodes 17a and 17b in the first embodiment.

It is thought that surface acoustic waves are generated from the auxiliary electrode 27b as well, but in the second embodiment, the auxiliary electrode 27a
, 27b, the film thickness of the piezoelectric thin film 24 is h/λ<0.1.
and the auxiliary electrode 27a.

Since the electrode 27b is arranged outside the input counter electrode 25 so that the electromechanical coupling coefficient is approximately zero, no surface acoustic waves are generated from the auxiliary electrodes 27a and 27b.

Therefore, like the auxiliary electrodes 17a and 17b of the first embodiment, the auxiliary electrodes 27a and 27b only contribute to adjusting the capacitance of the input comb-shaped electrodes 22a and 22b.
It becomes possible to easily change the impedance characteristics without affecting the frequency characteristics of the SAW filter.

In addition, in the first and second embodiments, the auxiliary electrodes 17a, 1
Input 7b, 27a, 27b comb-shaped electrodes 12a, 1
2b, 22a.

In the above description, the auxiliary electrodes are provided on the output comb electrodes 13a, 13b, 23a, 23b to change the impedance characteristics on the output side. The present invention is not limited to the first and second embodiments.

Further, in the above embodiment, a piezoelectric thin film was used as the piezoelectric material, but an auxiliary electrode similar to that in the above embodiment may be attached to a SAW filter using a single crystal material as the piezoelectric material. It is sufficient to provide a material or groove to prevent surface acoustic waves from propagating.

〔effect〕

Impedance characteristics can be changed extremely easily without affecting frequency characteristics.

[Brief explanation of the drawing]

1A and 1B are explanatory diagrams of a first embodiment of the surface acoustic wave device according to the present invention, FIGS. 2A and 2B are explanatory diagrams of a second embodiment of the surface acoustic wave device according to the present invention, FIGS. 3a and 3b are explanatory diagrams of a conventional surface acoustic wave element.・11.21-...Non-piezoelectric substrate, 12a, 12b, 22a, 2
2b - Input comb electrode, 13a, 13b, 23a,
23b - Output comb-shaped electrode, 14.24... Piezoelectric thin film, 15.25... Input counter electrode, 16.26...
・Output counter electrode, 17a, 17b, 27a, 27b...
・Auxiliary electrode.

Claims (1)

[Claims] In a surface acoustic wave element comprising an input electrode, an output electrode, and an input counter electrode and an output counter electrode via a piezoelectric body, an auxiliary electrode connected to the input electrode or the output electrode outside the range of the input counter electrode and the output counter electrode. A surface acoustic wave device characterized by being provided with electrodes.