Electrostatic Comb Drive Actuator Array with Integrated Cantilever for Scanning Probe Applications

Abstract

This paper illustrates an electrostatic comb-drive actuator array integrated with a scanning probe cantilever capable of $9.13\\mu \\mathrm{m}$ of unilateral displacement at as little as 55V. We have investigated and implemented several approaches to achieve this large displacement with the aim being to develop our own MEMS scanning probes with robust nanowires grown directly onto the cantilevers. By utilizing double folded flexures as our guiding mechanical parts, we reduced stiffness in the actuating direction. The fabrication of trapezoidal combs allows for longer combs with more actuating fingers to create a greater force without adding weight to the structures. The increased electrostatic force and thus displacement of the device is also due to a reduced finger gap size of $2\\mu \\mathrm{m}$ and development of a faster etch process to provide for smoother side walls and better structural stability of the numerous thin fingers. In addition, we shifted from the traditional approach of grounding the fixed combs to grounding the movable combs which is necessary to allow for integration of RF signals at a future date. Finally, by conducting such fabrication in-house we have demonstrated the ability to incorporate growth of a nanowire into this fabrication process.