Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Patent
1991-10-09
1993-02-09
Voeltz, Emanuel T.
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
310346, 310348, 310355, 310361, H01L 4104, H01L 4108
Patent
active
051855500
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a structure by which a resonator using an ultrathin piezoelectric plate capable of providing resonance frequencies as high as tens to hundreds of megahertz can be supported in a package.
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 inversely proportional to its thickness, 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 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 (SAW) resonator, whose oscillation frequency is determined by the pitch of electrodes of an interdigital transducer, has come to be able to output a maximum of 1 GHz or so due to the progress in photolithography, but a piezoelectric substrate usable for the SAW resonator is remarkably inferior to the AT cut quartz crystal in terms of temperature-frequency characteristic.
To solve the above-mentioned problems, there has been proposed such a piezoelectric resonator as shown in FIGS. 10(a) and (b).
That is, a cavity or recess 5 is formed, by machining or etching, in one side of a block 1 of AT cut quartz crystal substantially centrally thereof as depicted in FIGS. 10(a) and (b) and the thickness of a vibratory portion 2 forming the bottom of the cavity 5 is selected about 16 .mu.m, for example, if a fundamental resonance frequency of 100 MHz is desired.
On the side of the block where the cavity 5 is formed, the ultrathin vibratory portion 2 is edged with a thick frame-like marginal portion (or) rib 3 formed integrally therewith. The ultrathin vibratory portion 2 can be retained in its required shape by the frame-like rib 3. In this instance, it is preferable that excitation electrodes for the piezoelectric block be composed of an overall electrode 12 formed on the side of the block where the cavity 5 is provided and a partial electrode 14 and an electrode lead pattern 14a on the opposite side of the cavity 5, the electrode lead member 14a extending from the partial electrode 14 to one end face of the block.
It is customary and technically advantageous to house such a resonator of the above construction upside down--with the cavity 5 facing downward--in a ceramic or similar package 11 which has a concave housing space 10 centrally thereof and to mechanically bond and electrically connect the top 3a of one side of the frame-like marginal portion 3, by a conductive adhesive coated in line thereon, to a conductive film 16 which is exposed on the bottom of the housing space 10, hermetically passes through the package and is connected to an external lead member 17 projecting out of or exposed on the outside of the package, as shown in FIG. 11(a).
The piezoelectric device of such a construction has turned out to be defective in that since the resonator is very small, it is hard to control the amount of conductive adhesive used for bonding the top 3a of one side of the frame-shaped rib 3 to the bottom of the package 11, and consequently, the excess adhesive may sometimes flow into the cavity 5 and hence increases the thickness of the vibratory portion 2, causing a variation in the
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Ishii Osamu
Kurosaki Takebumi
Morita Takao
LaBalle C.
Toyo Communication Equipment Co., Ltd.
Voeltz Emanuel T.
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