A theoretical and experimental study of piezoelectric microdiaphragm platforms for physical and biological sensing

Abstract

In recent years, development of new types of sensors based on microelectromechanical systems (MEMS) technology has found great popularity among researchers. These sensors have found extensive functionality in broad aspects of sensing; including thermal, tactile, chemical, and biological. Microcantilevers as the icon of MEMS sensors with advantages such as high sensitivity, label-free detection, robust structure and high reproducibility have benefited diverse fields of research since their inception. Recently, piezoelectric based microdiaphragms have been proposed with high sensitivity, low power consumption, and compact size in response of some drawbacks of microcantilevers, including their fragile structure, and their low quality factor in liquid. This thesis reports theoretical and experimental study of piezoelectric microdiaphragm platform for physical and biological sensing. The microdiaphragms were first designed and then fabricated by MEMS fabrication processes. Their different characteristics such as frequency behavior, mode shapes, coupling factor, quality factor (Q-factor), nonlinear vibrations, mass sensitivity, and pressure sensitivity were studied theoretically and experimentally. Finally, they have been applied for two different schemes of sensing; mass sensing and pressure sensing. These experimental results demonstrate promising perspective of piezoelectric microdiaphragms as physical and chemical sensors. Significant amount of residual stresses, which were generated in the microdiaphragm during the fabrication process, were characterized first. It was concluded that both flexural rigidity and tension contribute to the resonant frequency of the microdiaphragm. When the tension parameter k is less than 2, the resonant frequency almost remain constant with respect to k. However, when