JPH0478212A - Electrode structure for surface acoustic wave filter - Google Patents

Abstract

PURPOSE:To obtain excellent resonance phenomenon by forming separate regular electrodes so as to keep the state of a propagation path for a surface acoustic wave uniform against fluctuation. CONSTITUTION:Electrodes for a surface acoustic wave are formed on a piezoelectric flat plate 100 by a metallic film and two regular electrode digits 120, 121 arranged in parallel are connected electrically in series. Moreover, 1st and 2nd ground terminals 114, 118 are provided to integrate a bus-bar conductor for the connected electrode fingers as a common electrode and to connect it across a common electrode 122 so as to connect to a case leading to ground. Furthermore, an input terminal 110 and an output terminal 109 are formed, which are connected to electrically open electrodes of the two regular electrode digits 120, 121. Moreover, the bus-bar conductor of the input and output side regular electrode fingers 120, 121 is broken at two points respectively and the bus-bar conductors at both ends are respectively connected to the 1st and 2nd ground terminals 114, 118.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an electrode structure of a dual mode filter that utilizes one surface acoustic wave.

[Conventional technology]

Conventional electrode structures for surface acoustic wave filters include Japanese Patent Laid-Open No. 56-206816 and Japanese Patent Laid-Open No. 57-131855.

[Problems to be Solved by the Invention] However, in the above-mentioned conventional technology, the potential independent of the potential associated with the surface acoustic wave immediately below, which is applied by the connecting conductor running across the vibration region of the surface acoustic wave, does not cause normal resonance. In addition to interfering with the vibration displacement of the child, there are other problems such as mismatching of the acoustic impedance of the surface acoustic wave propagation path. or,
In the example of JP-A-57-131855, it is clear that if a part of the bus bar conductor of the electrode of an interdigital transducer is integrated with part or all of the reflector, the above-mentioned problems will naturally occur. be. The present invention is intended to solve these problems, and its purpose is to provide the market with a surface acoustic wave dual mode filter that is stable, has a high Q value, and has excellent filter characteristics.

[Means for Solving the Problems 1] The electrode structure of the surface acoustic wave filter of the present invention comprises two surface acoustic wave resonators adjacent to each other on a piezoelectric flat plate, and utilizes the elastic lateral coupling effect between the two surface acoustic wave resonators. In the surface acoustic wave filter which is a dual mode filter, the surface acoustic wave electrode is formed of gold 12EIIJj on a piezoelectric flat plate, and two regular electrode fingers arranged in parallel are electrically connected in series. In addition to the connection, the bus bar conductors of the connected electrode fingers are integrated to form a common electrode, and first and second ground terminal portions are provided for connecting to both ends of the common electrode and grounding the case. , are connected to the electrically open electrodes of the two regular type electrode fingers to form input and output terminal parts, respectively, and furthermore, the bus bar conductors of the regular type electrode fingers on the input and output sides are connected at two places each. After cutting, connect the bus bar conductors at both ends to the first
and a second ground terminal.

[For production]

According to the above configuration of the present invention, since the connecting conductor does not run across the vibration region of the surface acoustic wave resonator, good filter characteristics can be obtained without interfering with the vibration of the resonator.

[Embodiment] Fig. 1 is a plan view of a surface acoustic wave filter according to an embodiment of the present invention. To explain each part in Fig. 0, 100 is a piezoelectric flat plate, which includes crystal, LiTaO3, LiNbO
It is made of piezoelectric material of grade 5. 120 and 121 are regular type electrode fingers 101, 102, 103 are output side bus bar conductors, 10
4. 105 and 106 are the input side bus bar conductors, which are made by cutting the bus bar conductor of the regular electrode finger at four places. 0 Next, 107 and 108 are connected to the output side and input side bus bar conductors, respectively. An output terminal section (107) and an input terminal section (108) are connected to the output terminal 1 by means of wire bonding, cab bonding, etc.
09 and the zero-order 122 connected to the input terminal 110 are common electrodes, which are formed by integrating the bus bar conductors on the phase-connecting side of the two regular electrode fingers 120 and 121. 113 and 117 are the first ground terminal section and the second ground terminal section, respectively.
, and is connected to the 122 common electrodes. Furthermore, 114 and 118 are grounding portions on the side of a metal or ceramic case on which the chip of the surface acoustic wave filter of this embodiment is mounted, and are connected to the above-mentioned 117 and 113 by wire bonding, canning bonding, or the like. Next, the conductors 111.112.115 and 116 are conductors 101.104 and 103.106 (7), respectively, for connecting each bus bar conductor to the first ground terminal section and the second ground terminal section 6 The manufacturing method of each electrode and conductor described above is based on the piezoelectric flat plate 100 having a mirror surface.
．． A thin film of a metal such as L, Au, or Ag is formed by means such as vapor deposition or sputtering, and then a pattern is formed by processing such as photolithography. The regular type electrode fingers 120 and 121 in Section 8 do not necessarily have to have a constant pitch, but may have a variable pitch or a pitch that changes stepwise, and the regular type electrode fingers may have a film thickness of 120 or 121. It's not uniform (
However, it should be set properly.

Next, the characteristics of the dual mode filter obtained by this embodiment will be explained using FIGS. 2 and 3. Figure 2 shows
A song Al201 showing the change in the amplitude of the polarization distribution P shown by one of the surface acoustic wave resonators when the horizontal direction of the embodiment in FIG. It is a curve 202 showing the voltage distribution v6 generated on the electrode 122. First, the polarization distribution P of the curve 201 is the polarization distribution P of the input terminal 110 and the ground terminal portions 114 and 118 under the normal type electrode finger mentioned above.
This is caused by displacement in a resonant state created by surface acoustic waves excited by an alternating voltage applied between them. In addition, when sufficient vibrational energy is trapped,
The displacement at the first and second ground terminal portions is extremely small and does not affect the characteristics.

For further improvement, the ground terminal portions 113 and 117 may be provided apart from the propagation path of the surface acoustic wave.Firstly, the above V6 will be explained as follows.

The width of the common electrode 122 in the embodiment of FIG. 1 is lO~50t.
It is a potential given by the product of im, the distributed resistance r of the common electrode that occurs because it is several times narrower than the bus bar conductor, and the resonant current i flowing through the common electrode. 1i4fly is a zero-order proportional to the curve obtained by integrating P from A to 0 or from B to 0. The function of the potential V0 will be explained using FIG. FIG. 3 is a cross-sectional view in the horizontal direction at the center of the regular type electrode finger on the input side in the embodiment shown in FIG. , 30
2 is an AC power supply, 303 is an input terminal, 304 is a ground terminal,
305, 306, 307, etc. are regular electrode fingers, 308 is the waveform of the polarization wave P of the surface acoustic wave that uses the resonance phenomenon, 309
．． 310, etc. are the distributed resistance r of the common electrode, and 320, 321, etc. are the direction and magnitude of the electric field intensity E generated directly under the regular electrode fingers. In particular, 330, 331, etc. are electric fields shown by regions where the bus bar conductors on the input and output sides are grounded.

Since the width of the busbar conductor is sufficiently wide, the distributed resistance can be considered to be almost zero, so it is omitted. First, the electric field E of 320 and 321 etc. is given by E, = (V-VO,)/2 press V/2,
t rattL6. Also, E,=V,,/'2F is given.

It should be noted that the direction of E2 is opposite to E. E2 is the phase of the displacement u of the surface acoustic wave of 308 and 18
An elastic surface displacement u2 having a 0° opposite phase is newly excited. Therefore, the sum of u and 10u becomes smaller than U, and a more rapid amplitude attenuation of the surface acoustic wave than before is obtained, increasing the energy confinement effect.

[Effects of the Invention] As described above, according to the present invention, by configuring the regular electrode by dividing it, the state of the propagation path of the surface acoustic wave is kept uniform and does not fluctuate, so that a good resonance phenomenon can be achieved. In addition, since the voltage generated at the common electrode is used to increase the energy confinement effect, a filter with a high Q value can be realized. Furthermore, since the voltage generated at the common electrode increases in accordance with the current flowing into the filter, it is possible to provide on the market a surface acoustic wave filter that is resistant to destruction even under excessive excitation voltage. Furthermore,
Since the electrode pattern basically has a square i-pole structure during manufacturing, the electrode can be processed uniformly by photoetching, and surface acoustic wave filters with less variation can be provided on the market.

[Brief explanation of the drawing]

FIG. 1 is a plan view showing an embodiment of the electrode structure of the surface acoustic wave filter of the present invention, FIG. 2 is a characteristic diagram of the embodiment of FIG. 1, and FIG. 3 is a diagram showing the operation of the embodiment of FIG. 1. It is an explanatory diagram. 100...Piezoelectric flat plate 120.121...Regular electrode finger 122...Common electrode or above Applicant: Seiko Epson Corporation

Claims (1)

[Claims] In a surface acoustic wave filter in which two surface acoustic wave resonators are constructed adjacent to each other on a piezoelectric flat plate and a double mode filter is created by utilizing the elastic lateral coupling effect between the two, the surface acoustic wave The electrode is formed of a metal film on a piezoelectric flat plate, and two regular electrode fingers arranged in parallel are electrically connected in series, and the bus bar conductors of the connected electrode fingers are further integrated to form a common electrode. In addition to providing first and second grounding terminals for connecting to both ends of the common electrode and grounding to the case, the terminals are connected to the electrically open electrodes of the two regular electrode fingers, respectively. After forming the input and output terminal portions, and cutting the busbar conductors of the regular type electrode fingers on the input and output sides at two places each, the busbar conductors at both ends are connected to the first
and a second ground terminal portion.