Simulation and modelling of pn junction actuators

The pn junction actuators are a new family of transducers with great potential for integration of micro- and nano-mechanical devices with electronics. In this paper, the finite element multiphysics simulation of our earlier work that employs a pn junction in order to bring a micro-cantilever under resonance is presented. The advantages and disadvantages of using this method over other possible actuation techniques are discussed. A theoretical model has been developed in order to describe the behaviour of a device comprised of a Schottky diode mounted on a cantilever. It was shown that the theoretical modelling is compatible with the experimental results. However, the theoretical modelling becomes exceedingly difficult or even impossible as more complicated configurations of junctions need to be studied. Consequently developing a reliable simulation method that can be applied to such cases is essential to fully harness the potential designs and applications of depletion region actuators. In this paper, a method to model the space charge regions of pn junction actuators is described and a method to couple the electrostatic and mechanical domains is described. An effective meshing method is presented which yields convergent results for narrow junction widths. The simulation data is shown to be congruent with experimental and theoretical results.