JPH03128519A - Saw resonator and saw filter - Google Patents

Abstract

PURPOSE:To improve characteristics such as sprious or Q value, etc., by providing a ceryain number, which is not fixed by a position in a breadthwise direction, of reflection structure bodies in a reflector to reflects surface acoustic waves and to generate a resonance phenomenon. CONSTITUTION:The reflection structure bodies of reflectors 103 and 104 are provided so that the lengths can be variously changed according to the position in an (x) axis direction. A number [n (y)] of the reflection structure bodies corresponding to a position (y) of a SAW resonator in the breadthwise direction is set like the example of 502. Thus, instead of conventional almost trapezoidal vibration displacement distribution 503, displacement distribution 504 close to a sine function sin can be realized by decreasing the number (n) in both ends in the breadthwise direction of the reflector. Namely, by weighting the number (n) of the reflection structure bodies in the reflector to the position of the SAW resonator in the breadthwise direction, the vibration displacement of a high-dimensional lateral mode can be suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to the structure of a SAW device that utilizes surface acoustic waves.

[Summary of the invention]

In a SAW resonator and a SAW filter, the present invention provides a reflector for reflecting surface acoustic waves to generate a resonance phenomenon, and by providing the number of reflecting structures that are not constant depending on the position in the width direction, spurious This is intended to improve characteristics such as Q value.

[Prior Art 1] An example of the configuration of a conventional SAW resonator and a conventional SAW filter is shown in FIG. 3 and FIG. 4, respectively. Furthermore, regarding the dual mode SAW filter, which is one of the SAW filters, i
There is a detailed report by Yamada, Shimizu, etc. in the Japan Society of Information and Communication Engineers US77-33. First, the configuration of a conventional SAW resonator will be explained with reference to Fig. 3. The names of the parts in Fig. 6 are as follows: 300 is a piezoelectric flat plate, 301 and 302 are positive and negative electrode fingers of IDT (interdigital electrode), 303 and 304. are reflectors, 305 and 3
06. 307, 308, etc. are reflective conductor strips that are reflective structures. Figure 4 shows the configuration of a dual mode filter using elastic coupling, which is one of the zero-order SAW filters. The names are: 400 is a piezoelectric flat plate, 401
is the input electrode of the IDT, 402 is the common electrode of the IDT,
403 is an output electrode of the IDT. Also, 404 and 4
05 shows a reflector of two cavity-type SAW resonators connected in phase.

[Problems to be Solved by the Invention] However, in the above-mentioned conventional technology, the displacement distribution in the width direction perpendicular to the traveling direction of the surface acoustic wave that is excited and propagated by the IDT is caused by high-order transverse modes that are high-order vibrations. Easy to occur, S
When an AW resonator and a SAW filter are configured, spurious light is generated and the characteristics are deteriorated. In addition, in the above-mentioned dual mode filter using elastic coupling, leakage of surface acoustic waves in the left and right longitudinal directions occurs at the central longitudinal connection between the two cavity-type SAW resonators, resulting in filter intrusion loss. The disadvantage was that it increased. Therefore, the present invention aims to solve these problems, and its purpose is to:
SAW with improved spurious and filter insertion loss characteristics
Our objective is to provide resonators and SAW filters to the market.

[Means to solve the problem]

The SAW resonator and SAW filter of the present invention are as follows.

1) In a cavity type SAW resonator having at least 61 IDTs and one pair of reflectors, the number of reflective structures of the reflector is not constant depending on the position in the width direction perpendicular to the propagation direction of the surface acoustic wave. 2) having a weighted reflector; 2) an SA having a plurality of IDTs and a reflector according to paragraph 1;
W filter, 3) In a SAW filter consisting of a dual mode filter in which two cavity-type SAW resonators are arranged in parallel and laterally, the reflection structures of adjacent reflectors of the two SAW resonators are connected and , having a reflector in which the number of the reflecting structures is weighted to be non-constant depending on the position in the width direction orthogonal to the propagation direction of the surface acoustic wave; 4) two cavity-type SAW resonators are arranged in parallel and laterally; In a SAW filter consisting of a dual mode filter, a bus conductor of a common electrode formed by connecting adjacent IDTs is connected to a part of a conductive strip which is a reflective structure of a reflector described in item 1. 5) A SAW filter comprising a reflector having a specific number of reflective structures at the location of the common pole bus conductor as described in paragraph 41.

It is characterized by

[Embodiment] Fig. 1 is a plan view showing an embodiment of the SAW resonator of the present invention.
01 and 102 are positive and negative EDT electrodes, 103 and 104, respectively.
is a reflector, and 105 and l○6 and 107 and 108 are anti-Q1 structures of the reflector. In the figure, the piezoelectric flat plate lOO is formed by mirror-polishing the surface of a flat plate obtained by cutting a piezoelectric material such as quartz, LiTa01, LiNb0-, etc. in a specific direction. 101
and 102 are Al1. A metal conductor film such as Ag or Au is formed by a method such as vapor deposition, and then a pattern is formed by etching. The reflectors 103 and 104 may be formed by the same forming means as the IDT, or may be formed by etching the surface of a piezoelectric flat plate as shown in FIG. 1. This method is generally called group processing. The reflective structure of the reflector thus consists of an array of strips or groups (parallelly arranged elongated grooves) or the like of metal conductors. In the present invention, the length of the reflective structures of reflectors 103 and 104 is
Figure 5 shows the vibration displacement distribution of the SAW resonators that occur in such a case, where the SAW resonators are arranged to vary depending on their axial position and are not arranged in a fixed length arrangement as in the conventional Figure 3. Ta. The horizontal axis AA' in FIG. 5 indicates the position coordinates of the center position of the IDT in FIG. 1 in the width direction. In a SAW resonator, a surface acoustic wave excited by an IDT, that is, a transducer consisting of interdigital electrodes, propagates in the X-axis direction and is reflected by the reflective structure of the reflector, causing a resonance phenomenon. In the invention, the number n(y) of reflective structures corresponding to the position y in the width direction of the SAW resonator is as shown in an example of FIG. 5 502. 501 is the conventional number distribution, which is a constant number. The number distribution function n (y) of the SAW resonator (A
-A') The state of the vibration displacement distribution at the position will be explained. A curve 503 in FIG. 5 is a vibration displacement distribution of a SAW resonator with a conventional distribution of a constant number of reflective structures.
04 is an example of vibration displacement of the present invention. The reason why the vibration displacement distribution u (y) of 504 occurs can be explained as follows.

Corresponding to the number n (y) of reflective structures at position y in the width direction, the reflection coefficient r (n) of the reflector is ``(n) = ta
nh (rn (3/)) (1) where y is the reflectance of one reflective structure.

The closer F(n) is to 1, the more surface acoustic waves excited by the IDT will be reflected at the center of the IDT without leaking out of the left or right ends of the reflector, so the displacement u (y) will be .

u (y) = KF (n) (2) However, K is a proportional constant, so n (y) corresponding to the target u (y) can be found using equations (1) and (2) above. Therefore, the vibration displacement distribution 5 is close to the conventional trapezoidal shape.
03, a displacement distribution 504 close to the sine function sin can be realized by reducing the number n at both ends of the reflector in the width direction.

Next, the SAW filter of the present invention will be explained using a dual mode SAW filter made of elastic coupling as an example. FIG. 2 is a plan view showing one embodiment of the dual mode SAW filter of the present invention. The names of the parts in FIG.
204 is a common electrode, 206 and 207 are reflectors, and 208 and 209 are reflective structures provided on extensions of the bus conductor of the common electrode. Also, the portions 201 and 211 are connecting portions of the bus conductor that serve to provide electrical connection to the reflective structure of the reflector. 201 and 202 surrounded by broken lines
each constitute a SAW resonator. The reflective structure may be a conductive strip made of metal such as Aε, Au, or Ag, or a group of grooves formed on the surface of a piezoelectric flat plate. The dual-mode SAW filter of the present invention has the SAW resonators shown in FIG. 1 of the present invention arranged in parallel in the lateral direction and is monolithically constructed on the same piezoelectric flat plate 200, but it has the following improvements. being done. First, a reflective structure of a reflector is formed at the position of the common electrode 205 in the X-axis direction to provide a surface acoustic wave reflecting function. Second
The number n (y) of the reflecting structures is set depending on the position y of the reflector in the y-axis direction so that symmetrical and antisymmetrical transverse modes are easily excited. This situation will be further explained with reference to FIG. Fig. 6 shows the standing wave amplitude of the surface acoustic wave at the BB' position in Fig. 2, that is, the amplitude value of the vibration displacement.
Distribution of the number n of reflector structures of the filter, and 603 and 6
04 shows the functional form of vln of the present invention.

605 and 606 are the amplitudes of conventional vibration displacement, respectively;
05 is the symmetric mode US, and 606 is the antisymmetric mode Ua, both of which exhibit a resonance phenomenon due to the elastic coupling of the dual mode SAW filter and perform a bandpass function for the input signal.
As shown in the figure, us and ua of 605 and 606 have a flat distribution at the center. On the other hand, the curves 607 and 608 are the vibration displacement of the transverse mode according to the embodiment of the present invention in FIG.
7 is the symmetric mode US, and 608 is the antisymmetric mode ua. Add that 607 and 608 are transverse mode fundamental waves. Furthermore, the above 603 and 604 are uS+u as an example.
It is given in al. Figure 7 shows the displacement distribution of higher-order transverse modes. In the figure, 801 is a fundamental wave, 802 is a second-order higher-order mode, and 803 is a third-order higher-order mode, and of course there is also a higher-order m-order mode, although not shown.

The conventional displacements 605 and 606 can be considered to be a combination of these transverse mode groups. Therefore, as a matter of course, unnecessary spurious resonance due to transverse higher-order modes occurs. FIG. 8 shows the transmission characteristics of the conventional dual mode SAW filter and the present invention.
902 is an example in which a conventional spurious is present, and 902 is an example in which spurious due to the higher-order transverse mode is removed by the present invention.

However, the horizontal axis shows the frequency f, and the vertical axis shows the insertion loss in dB.6 The method of weighting the number of reflector reflection structures of the present invention may be applied to a 2-port SAW filter having multiple rDTs. I would like to add that 6 things are of course true.

[Effects of the Invention] As described above, according to the present invention, the vibration displacement of higher-order transverse modes is suppressed by weighting the number n of reflection structures of the reflector with respect to the position in the width direction of the SAW resonator. be able to. Further, by using the weighted reflector used in the SAW resonator of the present invention in a two-boat SAW filter and a dual mode SAW filter having a plurality of IDTs, a SAW filter with suppressed spurious can be realized. Furthermore, in the dual mode filter, by forming a reflective structure of the reflector at the width position where the bus conductor of the common electrode is located, surface acoustic waves propagating along the bus conductor are reflected and a good effect is achieved. Since the resonance phenomenon can be realized, the insertion loss of the dual mode filter can be reduced. Especially the two S's
Narrowband filter with separated AW resonators improves characteristics'jh
The fruits are noticeable. In addition, in the dual mode SAW filter of the present invention, by connecting the bus conductor of the common electrode to a part of the reflective structure made of a metal conductor of the reflector, the GND connection of the reflector and the drawing effect of the common electrode can be achieved. This has been achieved and we can expect great profits in the future.

[Brief explanation of the drawing]

FIG. 1 is a plan view showing an embodiment of a SAW resonator of the present invention, FIG. 2 is a plan view showing an embodiment of a SAW filter of the present invention, and FIG. 3 is a plan view showing an embodiment of a conventional SAW resonator. FIG. 4 is a plan view showing an example of a conventional SAW filter, and FIG. 5 is a plan view showing a reflection structure of a reflector.
i n width direction distribution diagram and vibration displacement diagram, Figure 6 is a diagram similar to Figure 6 of the SAW filter, Figure 7 is the transverse mode vibration displacement diagram of the conventional SAW resonator, Figure 8 is the SAW filter. FIG. Figure 1 Figure 2 Poem 3 Figure 4 Figure 5ti0 Figure 6 (dB) Wj8F! J

Claims (1)

[Claims] 1) In a cavity type SAW resonator having at least one IDT and a pair of reflectors, the reflection structure of the reflector is determined by the position in the width direction orthogonal to the propagation direction of the surface acoustic wave. A SAW resonator characterized in that it has a weighted reflector whose number of bodies is not constant. 2) A SAW filter comprising a plurality of IDTs and the reflector according to claim 1. 3) In a SAW filter consisting of a dual mode filter in which two cavity-type SAW resonators are arranged in parallel and laterally, the reflective structures of adjacent reflectors of the two SAW resonators are connected, and the elastic surface A SAW filter comprising a reflector in which the number of reflecting structures is weighted to vary depending on the position in the width direction perpendicular to the wave propagation direction. 4) In a SAW filter consisting of a dual mode filter in which two cavity-type SAW resonators are arranged in parallel and laterally, the common electrode bus conductor formed by connecting adjacent IDTs is the reflector according to claim 1. A SAW filter, characterized in that the SAW filter is connected to a part of a conductive strip that is a reflective structure. 5) S characterized by having a reflector having a specific number of reflective structures also at the position of the common electrode bus conductor according to claim 4.
AW filter.