JPH0421366B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an electrode structure of a multimode filter that utilizes surface acoustic waves, such as SAW or shear waves (SSBW).

(Prior Art) Several types of structures have been proposed for surface acoustic wave multimode filters, but their basic form is as shown in FIG. By arranging devices 2 and 3 in parallel and close to each other along the propagation direction of the SAW that they excite, for example, the SAW was excited as shown in Figure b.
When acoustic coupling occurs between SAWs, the result is c.
As shown in symmetric mode (s-mode, resonant frequency
fs) and antisymmetric mode (a mode, resonant frequency
The purpose is to construct a passband filter by utilizing the well-known acoustic phenomenon in which two modes of vibration with different resonance frequencies, called fa, occur. In this case, it is known to obtain a filter in which fa>fs, fa is the center frequency, and fa−fs=Δf is approximately half of the passband.

However, according to the results of an experimental study conducted by the inventors of the present application regarding the conditions for generating acoustic coupling between the resonators 2 and 3 that are arranged close to each other, the conditions for generating acoustic coupling between the two electrodes 2 and 3 are as follows. It has been found that the g value depends on the intersecting finger width w and the width g between the electrode finger ends sandwiching the common bus bar 4 of both electrodes. (See Publication No. 2-16613).

Under such conditions, the width of the common bus bar 4 is such that the piezoelectric substrate 1 is a rotating Y-cut crystal.
If g is assumed to be one wavelength at a center frequency of 100MHz, it is necessary to set it to around 20μm.

This not only makes it impossible to bond the lead wire directly to the common bus bar 4, but also makes it impossible to bond the lead wire directly to the common bus bar 4.
If the number of electrode finger pairs is increased from 400 to 800 in order to make the ratio sufficiently high, this means that the inherent loss of the common bus bar 4 increases, resulting in an increase in the loss of the film itself.

(Object of the Invention) The present invention has been made in order to solve the above-mentioned problems, and in order to reduce the inherent loss caused by the extremely thin common bus bar, the electrodes of both the resonators are The number of finger pairs is kept as small as possible, and instead reflectors are provided at both ends of both electrodes to compensate for the drop in Q.The bus bar of both resonators, including the common bus bar, is used as part or all of the reflector. The purpose of the present invention is to provide an electrode structure for a multi-mode filter that utilizes SAW or SSBW, etc., integrated with.

(Examples) Hereinafter, the present invention will be explained in detail with reference to drawings showing examples.

FIG. 2 is a diagram showing an example of the electrode structure that is the basis of the SAW dual mode filter according to the present invention.

That is, the common bus bar 7 of a pair of interdigital transducer electrodes 5 and 6 formed on the piezoelectric substrate 1 and having a relatively small number of electrode fingers is provided at both ends of the electrodes 5 and 6. The bus bars 10 and 11 are configured to extend across the gratings and connect to them, and are grounded through one or both of bus bars 10 and 11 that connect them in parallel on both sides of the gratings. .

By doing so, a very small width portion of the common bus bar 7 is connected to the interdigital bus bar 7.
Only the width of the transducer electrodes 5 and 6 corresponds to the width of the transducer electrodes 5 and 6, and the rest is equivalent to an extremely large width, so the ohmic loss of the common bus bar 7, which is the grounding wire of this filter, can be kept to a minimum. , so that filter losses can also be minimized.

Furthermore, since the connecting portion of the electrode of the common bus bar 7 with the lead terminal can be directly wire bonded to the bus bar 10, 11 of the reflector 8 and/or 9, it is possible to make a special land for connection with the lead terminal. There is no need to provide one.

However, even if the electrode configuration as described above is used, the hot terminals A and B (input,
It goes without saying that the output terminals (of course, the input and output can be exchanged with each other) have to be arranged separately on the opposite edges of the piezoelectric substrate 1, which limits the freedom of arrangement of the lead terminals. This defect has become a problem that cannot be ignored as the demand for smaller filters and higher density mounting of electronic components on printed circuit boards increases.

In order to solve this problem, the filter according to the present invention has an electrode configuration as shown in FIG.

That is, the reflector 9 is divided at appropriate locations, and the bus bar of one of the reflectors 9 is connected to the extension of the bus bar 12 of the interdigital transducer electrode 5. Further, the common bus bar 7 is configured to be connected only to the other grating 15 of the divided reflector 9.

By doing so, the input and output lead terminals A and B, respectively, to be attached to the non-common bus bar of each electrode 5 and 6 are ground terminals to be connected to the common bus bar 7.
C ₁ , C ₂ (Since it is a filter, it requires input/output terminals A and B, so when adopting an electrode configuration such as the dual mode SAW filter according to the present invention, the common bus bar 7
(grounding the non-common bus bar and using the non-common bus bar as an input/output hot terminal), as well as making it possible to concentrate all of the terminals on one edge of the board 1. Since the connection becomes easier and there is no need to connect the jumper wire over the electrode etc., it is possible to improve the reliability and yield of the filter without fear of short circuits.

Furthermore, between the electrode finger of the interdigital transducer electrode and the grating of the reflector,
Or between the gratings of divided reflectors
Needless to say, the intervals should be, for example, an integral multiple of 1/4 of the surface wave length so as not to disturb the uniformity of the propagation and reflection of the excited surface waves.

I have only explained the SAW filter above, but
The present invention need not be limited to this, but can also be applied to other waves that can be excited by interdigital transducer electrodes, such as by attaching aluminum electrodes to the -50 degree or +40 degree Y-cut crystal surface. SSBW that propagates inside near the substrate surface, Love waves that propagate just below the substrate surface by attaching electrodes made of material with high specific gravity such as gold to Y-cut LN (LiNbO ₃ ), and 36-degree Y-cut LT ( It is obvious that by attaching an aluminum electrode to LiTaO ₃ ), the present invention can also be applied to a filter that utilizes Blustein-Gourier-Shimizu waves propagating just below the surface of the substrate.

(Effects of the Invention) Since the present invention is constructed as described above, the connecting part with the lead terminal of the electrode of a multi-mode filter using SAW or SSBW equipped with a reflector requires special space and processing. Since the filter can be easily obtained without any problems, it has a significant effect on improving the reliability and yield, and the filter has a very small cross-sectional area. This is particularly effective in minimizing losses.

[Brief explanation of drawings]

Figures 1a to 1c are diagrams explaining the basic configuration and operating principle of a conventional SAW dual-mode filter, and Figure 2 is a dual-mode SAW filter electrode configuration that has been researched in the past and is the basis of the present invention. FIG. 3 is a diagram showing an embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Piezoelectric substrate, 2, 3, 5, and 6... Interdigital transducer electrode, 8, 9... Reflector, 7... Common bus bar, 12 and 13... Bus bar of electrode, 10 and 11... Bus bar of reflector.

Claims (1)

[Scope of Claims] 1. A plurality of interdigital transducer electrodes are disposed close to each other in parallel with each other and perpendicular to the propagation direction of the surface acoustic waves excited by the interdigital transducer electrodes on a piezoelectric substrate, and the interdigital transducer electrodes Reflectors for the surface acoustic waves excited by these transducer electrodes are arranged at both ends of the transducer electrodes, and the width of the common bus bar of the plurality of interdigital transducer electrodes is adjusted to reflect the surface acoustic waves excited by the transducer electrodes. In a surface acoustic wave multi-mode filter whose surface acoustic waves are small enough to produce the required acoustic coupling with each other, a portion of the non-common bus bar of each electrode is integrated with a portion of the reflector. Characteristic electrode structure of surface acoustic wave multimode filter. 2. Claims characterized in that a common bus bar of the adjacent interdigital transducer electrodes is integrated with the grating of the reflector and is grounded via a bus bar that connects the grating of the reflector. 1. Electrode structure of the surface acoustic wave multimode filter according to 1. 3 The surface acoustic waves excited by the interdigital transducer electrodes are SAW,
The electrode structure of a surface acoustic wave multimode filter according to claim 1 or 2, characterized in that the electrode structure is SSBW, Love wave, and Bloustein-Gourier Shimizu wave.