Micro-electro-mechanical systems (MEMS), Piezoelectric, Vector sensor, Hydrophone
Micro-electro-mechanical-systems (MEMS) underwater vector sensors are capable of detecting the distance and the direction of sound signals generated by an underwater target. In this research, a piezoelectric MEMS vector sensor, which has four-clamped beams with a mushroom-shaped proof mass to improve receiving voltage sensitivity (RVS), was designed, fabricated and tested. In the design stage, two different designs were proposed and simulations were carried out using COMSOL Multiphysics® software to optimize the design parameters such as the beam length and the weight of the proof mass, which affect the resonance frequency. Based on the simulation results, the piezoelectric Pb(Zr¬0.52Ti0.48)O3 thin film was deposited by radio frequency (RF) magnetron sputtering and placed between two bottom and top platinum electrodes. The optimized fabrication process involved multiple etching steps and assembly process with mass structure. To investigate its performance as a MEMS vector sensor, its electrical and mechanical properties were characterized and the device showed promising results in resonance frequency and displacement when measured in air, although additional underwater experiments need to be conducted using theoretical algorithms to figure out the directivity in order to evaluate its capability as a hydrophone.
Table Of Contents
List of Contents Abstract List of Contents List of Figures List of Tables 1. Introduction 1 1.1 Hydrophone 1 1.2 Piezoelectric microelectromechanical system 2 1.2.1 Piezoelectric effect 2 1.2.2 Piezoelectric MEMS 6 1.3 Literature reviews 7 1.3.1 Piezoresistive MEMS hydrophone 7 1.3.2 Piezoelectric MEMS hydrophone 9 1.3.3 Piezoelectric device operating space 10 1.3.4 Stress distribution of clamped beam microstructure 11 1.4 Aim and objectives 14 2. Design and fabrication 15 2.1 Device concept and design 15 2.2 Simulation for optimization of design parameters 17 2.3 Fabrication process 10 2.3.1 Assembly with mass components 22 2.4 Packaging 23 3. Experimental methods 24 3.1 Experiment setup for measuring electrical properties 25 3.2 Experiment setup for measuring mechanical properties 25 4. Results and discussion 27 4.1 Fabrication results and discussion 27 4.2 Experimental results 42 4.2.1 Characteristics of microstructure 42 4.2.2 Electrical properties 43 4.2.3 Mechanical properties 47 4.2.4 Characteristics of PMVH devices with mushroom-shaped proof mass 52 5. Conclusions and future work 60 References 61 Appendices 67 요약문 70