Electrodes and their lead structures of an ultrathin piezoelectr

Details Electrodes and their lead structures of an ultrathin piezoelectr Electrodes and their lead structures of an ultrathin piezoelectr

1992-01-24

1993-08-10

Budd, Mark O.

Electrical generator or motor structure

Non-dynamoelectric

Piezoelectric elements and devices

310366, 310367, 310344, H01L 4108

Patent

active

052352404

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

The present invention relates to electrodes and their lead structure of an ultrathin piezoelectric resonator whose fundamental frequency is as high as tens to hundreds of megahertz.


PRIOR ART

In recent years there has been a strong and growing demand for high frequency operation and high frequency stability of various pieces of electronic and communication equipment. An ordinary AT cut quartz crystal resonator, which has heretofore been used widely as a piezoelectric device (such as a resonator or filter), has a very excellent temperature-frequency characteristic; however, since its resonance frequency is in inverse proportion to the thickness of AT cut quartz crystal plate, the fundamental frequency of this kind of resonator with a mechanical strength sufficient for practical use is around 40 MHz at the highest.
There has also been widely employed what is called overtone oscillation means which extracts a higher order harmonic mode vibration of an AT cut quartz crystal resonator to obtain a frequency which is an odd multiple of the fundamental resonance frequency, but its oscillation circuit calls for an LC tuning circuit including a coil, and hence is not suitable for fabrication as a semiconductor IC, besides the overtone oscillation circuit may sometimes be difficult to activate because such a resonator has a large capacitance ratio and consequently a high impedance level.
On the other hand, a surface acoustic wave resonator, whose oscillation frequency is determined by the pitch of electrode fingers of an interdigital transducer, has come to be able to output a maximum of 1 GHz or so due to the progress in photolithography, the resonator of this kind possesses a problem as a piezoelectric substrate usable therefor is remarkably inferior to the AT cut quartz crystal in terms of temperature-frequency characteristic.
To solve the above-mentioned problems, study has been given such a piezoelectric resonator as shown in FIGS. 16(a) and (b).
The piezoelectric resonator has a cavity 2 provided by machining or etching in one side of a block of AT cut quartz crystal 1 centrally thereof to form a vibratory portion 3, which has a thickness of about 17 .mu.m, if a fundamental resonance frequency of, say, 100 MHz is desired to obtain.
On the side of the block where the cavity 2 is provided, the ultrathin vibratory portion 3 is edged with and mechanically supported by a thick frame-like marginal portion (or rib) 4 formed integrally therewith.
By depositing a conductive film 5 all over the piezoelectric substrate on the side where the cavity 2 is provided and by depositing a partial electrode 6 and an electrode lead 7 extending therefrom, through use of, for example, vacuum evaporation on the flat surface of the vibratory portion 3 opposite from the cavity 2, it is possible to obtain a resonator of a very high resonance frequency substantially equal to the fundamental resonant frequency of the ultrathin vibratory portion 3 or a filter element of such a high center frequency.
As can be imagined from its structure, the above-said piezoelectric resonator is suitable for housing in such a flat package as depicted in FIG. 17.
It is customary and technically advantageous to house the piezoelectric resonator upside down--with the cavity 2 of the quartz crystal block 1 facing downward--in the bottom of ceramic or similar dish-like case 8 which is concave centrally thereof and to mechanically bond and electrically connect the overall electrode 5 and a conductive film 10 exposed on the bottom of the concavity of the case 8, by a conductive adhesive 9 laid down in line on the top of one side of the frame-like marginal portion 4.
Incidentally, the conductive film 10 on the bottom of the concavity of the case 8 is connected to a terminal 11 formed at one corner of the case 8 on the underside thereof via a connecting conductor hermetically passing through the case 8.
A pad 7a at one end of the electrode lead 7 extending from the partial electrode 6 of the resonator has a minimum area necessary for connection,

REFERENCES:
patent: 3694677 (1972-09-01), Guttwein et al.
patent: 3891872 (1975-06-01), Nagata et al.
patent: 4439706 (1984-03-01), Matsuoka et al.
patent: 4517485 (1985-05-01), Berte et al.
patent: 4720651 (1988-01-01), Nakazawa et al.

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