Design and fabrication of GaN crystal ultra-small lateral comb-drive actuators

Ultra-small electromechanical comb-drive actuators made of GaN crystal were studied in order to apply them to optical micro-electromechanical systems. Using GaN crystals grown on Si substrates by metal-organic chemical vapor deposition, two kinds of electrostatic comb-drive actuators were designed and fabricated. In the fabrication, due to a residual stress of the grown crystal, the movable part of the actuator suffered considerable deformation depending on the growth conditions. The strain-stress issue of the grown crystal layer is discussed on the basis of lattice misfit and thermal expansion. To compensate for a convex deformation, crystallization tension of a thin HfO₂ film deposited on a GaN layer was investigated. The displacement of the actuator having dimensions of 52.2 m in width and 105.4 m in length was 1.3 m at 70 V. Several variable systems will be feasible by combining the actuators monolithically with GaN opt-electronic devices. Future applications are also briefly discussed.