Synchronized Opto-Electro-Mechanical Measurements for Energy Loss Estimation in Thin-Film-Piezoelectric-on-Substrate MEMS/NEMS Devices

Abstract

Piezoelectric micro-electro-mechanical systems have significant market potential owing to their superior capabilities of transduction to those of standard capacitive and piezoresistive devices. However, piezoelectric films are often lossy, which reduces the quality factor of devices and affects their performance. It is thus important to examine all sources of energy losses in such devices and accurately determine them based on experimental data. Currently used methods to quantify energy loss from different sources and the properties of materials based on experimental data are set-up for piezoelectric devices, in which energy storage and loss primarily occur in the same piezoelectric material. Moreover, such methods rely on resonance-antiresonance measurements, and thus are unsuitable for thin-film-piezoelectric-on substrate (TPoS) micro/nano devices that have i) a significant portion of energy stored in the substrate/device layer, ii) a low signal-to-noise ratio owing to either lossy piezoelectric films or low motional impedance, or iii) a larger feedthrough capacitance in addition to the internal capacitance of the piezoelectric film. In this paper, we propose a method that overcomes these challenges based on synchronized optical and electrical measurements. We develop a comprehensive physics-based model to extract all the relevant parameters for the device, including the coefficient of piezoelectric coupling, internal and feedthrough capacitance, loss tangents (dielectric, piezoelectric, and mechanical), and the contributions of different sources to the quality factor of the device. We showcase the proposed method by using a PZT-based TPoS MEMS cantilever. It can be universally applied to all piezoelectric materials and arbitrary stacks of the device layer.