Herstellung und Charakterisierung von ScxAl1-xN basierten piezoelektrischen MEMS Energy Harvestern

Abstract

Micro electromechanical systems (MEMS) for sensor and actuator applications increasingly utilise piezoelectric thin-films. Main advantage of this approach is the possibility to sense and actuate with this functional material with a single structure. This work focuses on the manufacturing and characterisation of cantilevers with piezoelectric Aliminium Nitride (AlN) thin films. Furthermore, ScxAl1-xN (x = 27%) is employed to increase the piezoelectric constants of AlN which results in a further increase of the actuation potential. Initially, the fabrication of AlN and ScxAl1-xN cantilever series, employing varying process sequences is presented. Subsequently, the cantilevers are characterised by optical measurements of the deflection using a laser Doppler vibrometer (LDV) as well as electrically by impedance analyses. In both approaches, the cantilever are excited electrically. An analytical model for the deflection and conductance peak height of the cantilever close to a transverse eigenfrequency is introduced and used for a further evaluation of the measured data. Thereby, the piezoelectric coefficient d31 is determined for a representative fraction of the fabricated AlN and ScxAl1-xN cantilevers of each series. In addition, external actuation of the cantilever by a piezoelectric shaker and measurement of the ouput voltage to estimate the potential for vibrational energy harvesting is presented. In order to determine the output power at variable load resistors a new measurement setup is developed and employed to all cantilever series. An analytical model of the load resistance dependence of the output power is introduced and utilised for determination of model parameters. The superior properties of ScxAl1-xN thin-films for energy harvesting applications are validated. Finally, a tip mass is employed to further increase the power output at an optimized load resistance.