Biased rotatable combdrive actuator methods

#This invention relates generally to Micro-Electro-Mechanical-Systems (MEMS). More particularly, it is related to a novel class of vertical combdrive devices serving as rotating actuators and/or position sensors and methods for operating any combdrive.

#The advent of silicon fabrication technologies has made possible a line of integrated devices in which micro-actuators and micro-mechanical structures are fabricated using processing technology similar to that used in the integrated-circuit industry. These integrated actuators have been employed in a variety of applications, such as fiber-optic switching, optical tracking for applications such as free-space communications, inertial sensors, and magnetic disk drives. They offer small size, low cost, high reliability, and superior performance. Furthermore, micro-machined structures may be integrated with Integrated Circuits (ICs) fabricated on the same substrate.

#Various actuation methods can be employed in these integrated actuators, including electrostatic, electromagnetic, thermal, and thermo-pneumatic means. Electrostatic actuation becomes particularly attractive on a small size scale, since the electrostatic force increases as the gap between two charged elements decreases. Combdrive electrodes are widely used for generating electrostatic driving forces.

#FIGS. 1A-1B show a prior art rotating actuator employing a two-layer combdrive in nominal and rotating states respectively;

#FIG. 2 depicts an exemplary embodiment of a uni-axial rotating device employing a biased combdrive in a nominal state according to an embodiment of the present invention;

#FIG. 3 shows an exemplary embodiment of a uni-axial rotating actuator employing a biased combdrive in a rotating state according to an embodiment of the present invention;

#Although the following detailed description contains many specific details for the purposes of illustration, anyone of ordinary skill in the art will appreciate that many variations and alterations to the following details are within the scope of the invention. Accordingly, the exemplary embodiments of the invention described below are set forth without any loss of generality to, and without imposing limitations upon, the claimed invention.

#FIG. 2 shows an exemplary embodiment of a uni-axial biased rotating actuator 200 employing a biased combdrive in a nominal state according to the present invention. In biased combdrive rotating actuator 200, a plurality of first comb fingers 20, extending from a first micro-machined structure 21, are substantially co-planar with a plurality of second comb fingers 22 extending from a second micro-machined structure 23. According to one embodiment of the present invention, second comb fingers 22 and first comb fingers 20 may be fabricated from a single layer of a substrate 27, thereby substantially interdigitated and self-aligned according to a predetermined engagement. Although much of the following discussion relates to self-aligned electrostatic combdrives, the advantages of biased actuation may be applied to other types of cob drives that are not self-aligned.

#The substrate 27 may be, for example from a single-layer structure or multi-layer structure, such as a silicon-on-insulator (SOI) substrate having two conductive layers separated by an insulating layer. Both sets of comb fingers 20, 22 may be defined in the same step by etching a pattern in the substrate 27. The first and second comb fingers 20, 22 may be substantially co-planar. Alternatively, one of the sets of comb fingers may be selectively etched to remove portions of one of the structure so that the two sets of comb fingers are vertically offset with respect to each other, although they are still self-aligned.