Evaluation of electromechanical transduction efficiency of p–n diode actuators with a silicon tuning fork resonator

Abstract

In this paper, we describe the electromechanical transduction efficiency of p–n diode actuators that are laterally driven by a force induced in a depletion layer. In order to experimentally evaluate the electromechanical transduction efficiency, we fabricated a U-shaped tuning fork resonator, which integrated the p–n diode and electrostatic actuators on a chip. The vibration amplitude was evaluated by measuring the output current passing through an electrostatic sensor. From an analytical model, the displacement generated by p–n diode actuators was shown to be independent of the DC bias voltage, and a constant output current passes even at a DC voltage of 0 V. Good agreement of the experimental results and the theory was confirmed. By comparing the measured values of the output current for p–n diode actuators with those for electrostatic actuators, it was found that p–n diode actuators with high impurity concentration have high electromechanical transduction efficiency. The resonant frequency for p–n diode actuators was also independent of the DC bias. Since these DC dependences are very different from those of widely used electrostatic actuators, p–n diode actuators are expected to be widely used, especially for applications requiring a low driving voltage including mobile applications.