A variable capacitor device using MEMS or micromachining techniques wherein thin-films
of materials are deposited, patterned and etched to form movable micromechanical
elements on the surface of a substrate composed of either semiconductor, glass,
metal, or ceramic material. In one embodiment of the present invention to achieve
higher frequency performance as well as other benefits, the substrate is comprised
of Low-Temperature Co-Fired Ceramics (LTCC). The variable capacitor is an electrostatically
actuated micromechanical device and if fabricated on a LTCC multi-layered substrate
material has continuous electrical connections through the layers. The same LTCC
substrate material can also be used to enclose the device by selectively removing
a portion of the upper substrate so as to form a cavity. The two substrates are
then bonded together to enclose and protect the variable capacitor. An integrated
circuit can be incorporation onto the multi-level substrate structure to enable
a electronic closed-loop controlled variable capacitor module. The integrated circuit
is flip-chip bonded at the bottom of the substrate structure with appropriate electrical
connections between the integrated circuit and the MEMS variable capacitor device.
A variation of the present invention utilizes a zipper actuation method wherein
the tuning ratio of the variable capacitor is increased to very high levels. Yet
another variation of the present invention utilizes a differential gap between
the top and bottom electrodes such that the actuation electrodes do not physically
contact one another. Yet another implementation of the present invention uses an
extra set of electrodes or mechanical mechanism so as to lock the value of the
capacitor indefinitely. Yet another implementation uses shaped actuation electrodes
so as to linearize the relationship between the applied actuation voltage and the
resultant capacitance of the device.
