Switching performance of bistable membranes activated with integrated piezoelectric thin film transducers

Abstract

In this paper we report on the fabrication of bistable micro electromechanical systems (MEMS) membranes, which have diameters in the range of 600–800 μm, a total thickness of 3.13 μm and feature integrated low power piezoelectric transducers based on aluminium nitride. To estimate the impact of the membrane asymmetry due to the integrated piezoelectric transducers, an asymmetric constant in the potential energy calculation of the bistable system is introduced, thus enabling a proper theoretical prediction of the membrane behaviour. To switch between the two bistable ground states, rectangular pulses with frequencies in the range of 50–100 kHz and a peak-to-peak voltage of 30 Vpp are applied. Two different actuation schemes were investigated, whereas one shows positive and the other negative pulse amplitudes. With a Laser-Doppler Vibrometer the velocity of the membranes during the bistable switching process is measured and integrated over time to calculate the membrane displacement in the centre. FFT (fast Fourier transform) spectra of an applied broadband white noise signal were determined in both ground states and showed a strongly decreased dominant resonance frequency in the lower ground state. The results also showed, that the asymmetry of the system causes different switching behaviours for each bistable ground state, whereas it requires less energy to switch from the lower to the upper ground state. Furthermore, it was demonstrated that a minimum of two pulses are needed for switching when using positive rectangular pulses of 30 Vpp in contrast to four when applying negative pulses. The pulse frequency causing switching was in the range of 60–110 kHz, strongly depending on the geometry and applied signal scheme. Additionally, a positive voltage offset applied to the pulse signal characteristics resulted in both a wider range of frequencies suitable for switching and in a decrease of the dominant resonance frequency, which is also beneficial for the switching process and indicates the potential for efficient switching of bistable MEMS membranes.