Development of PZT Based PiezoMEMS for Fluid Property Sensing
The research on Microelectromechanical Systems (MEMS) has resulted in several practical applications which have revolutionised the fi eld of sensors and actuators. Piezoresistive pressure sensors, capacitive micro-mirror devices, and accelerometers are a few of the earliest successful examples of practical MEMS devices. PiezoMEMS are a class of devices wherein thin piezoelectric films are used as active elements for transduction. These devices offer several advantages over capacitive MEMS such as low voltage operation, higher in-air Q-factor and relatively large actuation force. Lead Zirconate Titanate (PZT) is the most widely used bulk piezoelectric material owing to its high piezoelectric coupling coeffcients. The materials research community has been able to develop good quality thin fi lms of PZT for MEMS applications. How- ever, the introduction of PZT in MEMS devices has been mired with several challenges. These challenges were captured well by a Yole report from 2013 that stated, \The main difficulty for thin lm PZT technology is the integration of this exotic material into a ro- bust and reproducible process flow. There are major technological challenges associated with thin- lm PZT integration into a product: deposition, etching, process monitoring, test, reliability." The main goal of this thesis is to present engineering solutions to the challenges associated with the development of PZT based MEMS devices. Once a robust process for fabrication of different devices was achieved, we could scale up the process to fabricate several different devices on a single wafer, proving the viability of the process as a multiuser MEMS process. The results from several actuator/sensors realised using the process are presented in the thesis. One of our target applications was to develop a platform of self-actuating and self-sensing devices. Results from several such devices are presented, and challenges associated with such development are discussed. In the end, the design of a unique tip-coupled two-cantilever (TCTC) system working as a viscometer is presented. This viscometer design offers several advantages over the reported resonant MEMS sensors such as quick and direct measurement and the possibility to measure shear rate dependant viscosity. The thesis concludes with a roadmap for rapid development of PiezoMEMS devices on the technology platform created by this study.