Synchronized Opto-Electro-Mechanical Measurements for Estimation of Energy Dissipation in Thin-Film-Piezoelectricon-Substrate MEMS/NEMS Devices

Piezoelectric microelectromechanical 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 dissipation in such devices and accurately determine them based on experimental data. Currently used methods to quantify energy dissipation from different sources and the properties of materials based on experimental data are set-up for piezoelectric devices, in which energy storage and dissipation 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 high motional impedance, or iii) a larger feedthrough capacitance, arising primarily from collocated electrodes, 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 and a Piezoelectric Micromachined Ultrasonic Transducers (PMUT).[2024-0063]

I. Introduction

Piezoelectric materials such as quartz, lead zirconate titanate (PZT), lead magnesium niobate-lead titanate (PMN-PT), and aluminum nitride have a wide range of applications, including for RF timing reference, sensors based on surface acoustic waves, bulk acoustic waves, and energy harvesting [1], [2], [3], [4], [5], [6]. Quality factor, a measure of energy loss in a resonator, is an important quantity that determines performance of MEMS/NEMS devices [7]. Thus, to design and engineer the Quality Factor (Q), it is important to study the energy loss mechanisms prevalent in the materials constituting the MEMS/NEMS device. Energy loss mechanisms in piezoelectric materials have been extensively studied since the 1950s [8], [9], [10], [11], [12].