Variable capacitor and associated fabrication method

• Main Authors: E.A. HILL, V.R. DHULER, A.B. COWEN
• Format: Patent
• Language: English
• Published: 02.04.2003
• Edition: 7
• Subjects: BASIC ELECTRIC ELEMENTS; BLASTING; CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES ORLIGHT-SENSITIVE DEVICES, OF THE ELECTROLYTIC TYPE; ELECTRIC SWITCHES; ELECTRICITY; EMERGENCY PROTECTIVE DEVICES; HEATING; LIGHTING; MACHINES OR ENGINES FOR LIQUIDS; MECHANICAL ENGINEERING; MECHANICAL-POWER PRODUCING DEVICES OR MECHANISMS, NOTOTHERWISE PROVIDED FOR OR USING ENERGY SOURCES NOT OTHERWISEPROVIDED FOR; MICROSTRUCTURAL DEVICES OR SYSTEMS, e.g. MICROMECHANICALDEVICES; MICROSTRUCTURAL TECHNOLOGY; OR A REACTIVE PROPULSIVE THRUST, NOT OTHERWISE PROVIDED FOR; PERFORMING OPERATIONS; PRODUCING MECHANICAL POWER; RELAYS; SELECTORS; SPRING, WEIGHT, INERTIA OR LIKE MOTORS; TRANSPORTING; WEAPONS; WIND, SPRING WEIGHT AND MISCELLANEOUS MOTORS

A variable capacitor having low loss and a correspondingly high Q is provided. In addition to a substrate, the variable capacitor includes at least one substrate electrode and a substrate capacitor plate that are disposed upon the substrate and formed of a low electrical resistance material, such as HTS material or a thick metal layer. The variable capacitor also includes a bimorph member extending outwardly from the substrate and over the at least one substrate electrode. The bimorph member includes first and second layers formed of materials having different coefficients of thermal expansion. The first and second layers of the bimorph member define at least one bimorph electrode and a bimorph capacitor plate such that the establishment of a voltage differential between the substrate electrode and the bimorph electrode moves the bimorph member relative to the substrate electrode, thereby altering the interelectrode spacing as well as the distance between the capacitor plates. As such, the capacitance of the variable capacitor can be controlled based upon the relative spacing between the bimorph member and the underlying substrate. A method is also provided for micromachining or otherwise fabricating a variable capacitor having an electrode and a capacitor plate formed of a low electrical resistance material such that the resulting variable capacitor has low loss and a correspondingly high Q. The variable capacitor can therefore be employed in high frequency applications, such as required by some tunable filters.