JPH0421367B2 - - Google Patents

Description

[Detailed description of the invention] (Industrial application field) The present invention is a surface acoustic wave, that is, a Rayleigh wave.
SAW or slip wave (SSBW), love wave, etc., SH
(Shear Horizontal) Multiple modes using waves
This invention relates to the electrode structure of a filter.

(Prior Art) As shown in FIG. The resonators in which the resonators 4, 5 and 6, 7 are arranged are arranged close to each other at right angles to the propagation direction of the surface acoustic wave, for example, "SAW" excited by these resonators, and parallel to each other, and a common bus bar for both of these resonators is used. By making the width of 8 sufficiently small, the SAWs excited by these two resonators are acoustically coupled to each other (see b in the same figure), and as a result, the symmetrical mode (S-mode, resonant frequency fs) that appears is opposite to We are continuing our research on constructing a bandpass filter by utilizing two modes of vibration with different resonance frequencies, called the symmetrical mode (a mode, resonance frequency fa) (see c in the same figure). (Please refer to Publication No. 131213/1983).

It is already widely known that in this type of filter, fa>fs, fa is the center frequency, and fa−fs=Δf is approximately half of the passband. Further, the Δf increases or decreases depending on the magnitude of the acoustic coupling between the two resonators, but in order to obtain the widest possible passband, the width of the common bus bar 8 must be made as small as the IDT electrode finger. As a result, there was a drawback that the inherent loss increased and the insertion loss of the filter increased.

In order to alleviate this defect to some extent, a common bus bar 8 is connected to the gratings of the reflectors 4 to 7 as shown in FIG. Although efforts have been made to do so, the effects have not yet been sufficient.

(Object of the Invention) As mentioned above, the present invention has been made to eliminate the defects of surface acoustic wave multimode filters that have been developed by the inventors of the present invention. busbar length
Limited to the IDT electrode part, a relatively wide pattern is formed between the both ends of the IDT electrode and the lead terminal near the periphery of the piezoelectric substrate between the IDT electrode and the reflector.
It is an object of the present invention to provide a surface acoustic wave multimode filter having an electrode structure in which the common bus bar is shortened to the maximum by connecting through the common bus bar, thereby reducing the electrical loss in this part.

(Embodiments of the Invention) The present invention will be described in detail below with reference to embodiments shown in the drawings.

FIG. 2 is an electrode configuration diagram showing one embodiment of the SAW multimode filter according to the present invention, in which two IDT electrodes 2 and 3 are arranged in parallel on the surface of a single piezoelectric substrate 1 via a fine common bus bar 11. Reflectors 12 and 13 are placed close to each other, and reflectors 12 and 13 are placed on both sides of these IDT electrodes 2 and 3. At this time, the supply bus bar 11
Both ends of the IDT electrodes 2, 3 are cut off near both ends of the IDT electrodes 2, 3, and between both ends of this common bus bar and bonding pads 14, 15 provided near one edge of the piezoelectric substrate 1, the IDT electrodes 2, 3 and the reflector 12, Between 13 and 16 and 1, respectively, a relatively wide pattern
7.

By doing this, the common bus bar 11, which has a small width, has the minimum necessary length, and the patterns 16 and 17 that connect both ends of the bus bar with the bonding pads 14 and 15 have a large width, so that The inherent loss can be suppressed to a sufficiently small value compared to the electrode configuration method as shown in FIG. 1a described above.

In addition, for this type of filter, the input
Since the output hot terminals 18 and 19 are essential, the common bus bar 11 has to be grounded, and the input and
It will be obvious that the output terminals 18 and 19 can exchange input and output with each other.

By the way, if the electrode structure as described above is adopted, it is possible to reduce the ohmic loss of the common bus bar and reduce the insertion loss of the filter, but one of the hot terminals 18 is connected to the other hot terminal 19 and the ground terminal 14, 15 is present on the opposite edge of the substrate. This means that when this filter element is housed in a package and the bonding pads 15 to 18 of the filter element are connected to the bonding pads of the lead terminals exposed inside the package using bonding wires,・This means that the flow line of the head becomes complicated and the wire crosses the surface of the filter element, and in view of the recent situation where there is a strong demand for cost reduction by miniaturizing the package and improving productivity. I don't feel very well.

To solve this problem, the non-common bus bar 20 of one IDT electrode 2 is extended and connected to a part of the grating of the reflector 13, as shown in FIG. terminal 18
the other IDT electrode 3's hot terminal 19, ground terminal 1
All you have to do is concentrate on the same edges as 4 and 15.

By doing this, it becomes possible to align the lead terminals (pads) in the desired positions, thereby minimizing the flow line of the bonder head, increasing productivity, making the filter smaller, and improving reliability. can be achieved.

Although the present invention has been described above using a SAW multimode filter as an example, the present invention is not limited to this, and can be excited by an IDT electrode and basically exhibits the same behavior as SAW. It has been known. It is similarly applicable to filters using shear waves (SSBW), Love waves, and Bluestein-Gourier-Shimizu waves.

Incidentally, SSBW is excited by attaching an Al electrode to the -50 degree or +40 degree Y-cut crystal surface, and propagates inside the crystal substrate surface.
Love waves are excited by attaching electrodes made of a material such as Au to the surface of the Y-cut LiNbO ₃ substrate, and propagate directly below the surface of the LN substrate.
It has long been known that Brewstein-Gourier-Shimizu waves are excited by attaching an Al electrode to the surface of a 36-degree Y-cut LiTaO ₃ substrate and propagate directly beneath the LT substrate. When using these piezoelectric crystals, the degree of vibrational energy confinement in the IDT electrode is slightly different due to the difference in the electromechanical coupling coefficient of these piezoelectric crystals, so the logarithm of the IDT, the number of reflectors, the width of the common bus bar, etc. It is sufficient to find the optimum value by changing it somewhat.

(Effects of the Invention) Since the present invention is configured as described above, the length of the common bus bar of the filter is minimized to the necessary minimum value by using ordinary electrode pattern forming technology, thereby reducing the inherent loss. At the same time, it becomes possible to align the lead terminals for connecting the electrodes at desired positions, which has a remarkable effect on improving the filter characteristics, simplifying the manufacturing process, reducing the size, and improving the reliability.

[Brief explanation of drawings]

Figure 1a is an electrode configuration diagram of a conventional SAW multi-mode filter, Figures b and c are diagrams each explaining the operating principle of the SAW multi-mode filter, and Figure 2 is an electrode configuration diagram showing an embodiment of the present invention. , FIG. 3 is an electrode configuration diagram showing another embodiment of the present invention. 1... Piezoelectric substrate, 2, 3... IDT electrode, 8, 11...
Common busbars, 4 to 7 and 12, 13... reflectors, 16, 17... lead patterns.

Claims (1)

[Claims] 1. A plurality of resonators each having an interdigital transducer (hereinafter referred to as IDT) electrode and a reflector that reflects surface acoustic waves excited by the electrode on a single piezoelectric substrate. The resonators are arranged adjacently and at right angles to the propagation direction of the surface acoustic waves, and the width of the common bus bar of the adjacent resonators is set such that the required acoustic coupling occurs between the excited surface acoustic waves of the respective resonators. In the surface acoustic wave multi-mode filter, which is made small enough to accommodate the above-mentioned characteristics, a common busper of the adjacent resonators is formed so as to pass between the IDT electrode and the reflector and extend near the periphery of the piezoelectric substrate. An electrode structure of a surface acoustic wave multimode filter characterized by being connected to a lead pattern. 2 The surface acoustic wave excited by the IDT electrode is
The electrode structure of a surface acoustic wave multimode filter according to claim 1, characterized in that the electrode structure is a SAW, SSBW, Love wave, and Bluestein-Gourier-Shimizu wave.