Micromachined variable capacitor

Details Micromachined variable capacitor Micromachined variable capacitor

1999-03-26

2001-04-03

Kincaid, Kristine (Department: 2831)

Electricity: electrical systems and devices

Electrostatic capacitors

Variable

C361S278000, C361S280000

Reexamination Certificate

active

06212056

ABSTRACT:

TECHNICAL FIELD
This invention relates to microminiature electronic components and, more particularly, to a micromachined variable capacitor.
BACKGROUND OF THE INVENTION
Microminiature capacitors whose capacitance values can be controllably varied are used in a variety of applications of practical importance. Thus, for example, voltage-controlled capacitors (varactors) are employed as tunable components in circuits such as voltage-controlled oscillators. They are also used as discrete tunable elements in filters and loaded-line phase shifters.
Micromachining techniques have been utilized to fabricate very small variable capacitors for high-frequency use. (See, for example, “A Micromachined Variable Capacitor For Monolithic Low-Noise VCOS” by Young and Boser, Solid-State Sensor and Actuator Workshop, Hilton Head, S.C., Jun. 2-6, 1996, pages 86-89.) But heretofore it has proven difficult, if not impossible, to micromachine a variable capacitor that exhibits a sufficiently high quality factor (Q) and a wide enough tuning range to satisfy the requirements of some important high-frequency applications. In some such applications, operation in the gigaHertz range with a monotonic capacitance-versus-voltage characteristic and a high Q (1000 or higher) may be specified. Furthermore, in some such cases, a wide tuning range (for example, 0.1-to-5 picoFarads) may be required.
Accordingly, continuing efforts have been directed by workers skilled in the art aimed at trying to provide an improved microminiature variable capacitor. In particular, these efforts have focussed on attempting to provide a reliable, low-cost micromachined variable capacitor exhibiting advantageous characteristics such as linearity, high Q and a wide tuning range. It was recognized that these efforts, if successful, could provide an improved variable capacitor for use in a variety of practical high-frequency applications.
SUMMARY OF THE INVENTION
In accordance with the principles of the present invention, a first wafer is processed by standard integrated-circuit fabrication techniques to form therein a flexible membrane that is integral with and mechanically supported by the wafer. A metal pattern, comprising a capacitor plate on the flexible membrane and an associated electrical connection thereto, is then defined on the wafer. A second wafer is processed by standard integrated-circuit fabrication techniques to form in the surface thereof a well with a flat bottom and sloped walls. A metal pattern, comprising a capacitor plate on the bottom of the well and an associated electrical connection thereto extending up one sloped wall of the well, is then defined on the second wafer. Subsequently, the two wafers are bonded together, with the respective capacitor plates thereon positioned in facing alignment with each other to form a parallel-plate capacitor with an air-gap between the plates. Applying a control signal to the electrical connections that respectively extend to the capacitor plates causes the plates to be electrostatically attracted to each other. The flexible membrane and the capacitor plate thereon are thereby moved toward the other plate, which controllably changes the air-gap between the plates and thus varies the capacitance of the element.
In another specific illustrative embodiment of the present invention, separate control and signal plates are fabricated on the aforementioned membrane on the first wafer. Corresponding control and signal plates are formed on the bottom of the well in the second wafer. The air-gap between the control plates may be chosen to be considerably greater (for example, three times greater) than that between the signal plates. In operation, the membrane is flexed and the control plate thereon is thereby moved over a limited and stable region of the air-gap distance between the control plates. At the same time, the signal plates are thereby able to be moved over substantially the entire extent of the distance therebetween without incurring any instability of operation.


REFERENCES:
patent: 4196632 (1980-04-01), Sikorra
patent: 4203128 (1980-05-01), Guckel et al.
patent: 4814845 (1989-03-01), Kutrtz
patent: 5277068 (1994-01-01), Fukiura et al.
patent: 5383364 (1995-01-01), Takahasi et al.
patent: 5594171 (1997-01-01), Ishida et al.
patent: 5636099 (1997-06-01), Sugawara et al.
patent: 5901031 (1999-05-01), Ishige et al.
“Tunable Capacitors with Programmable Capacitance-Voltage Characteristic” by E.S. Hung et al, Solid-State Sensor and Actuator Workship, Hilton Head Island, SC, Jun. 8-11, 1998, pp. 292-295.
“A Micromachined Variable capacitor for Monolithic Low-Noise VCOS” by D.J. Young et al, Solid-State Sensor & Actuator Workship, Hilton Head, SC, Jun. 2-6, 1996, pp. 86-89.

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