Electrical and optical characterisation of aluminium nitride piezoelectric films on silicon nitride membranes

摘要

Aluminium nitride (AlN) is a thin film piezoelectric material having excellent potential for integration with microelectronic systems. We have investigated flexural modes of Si_3N_4 membrane structures with and without an AlN active layer. AlN films typically 3 μm thick were deposited by RF sputtering. Mechanical excitation was provided acoustically by sweeping the excitation frequency of a 1 MHz air-coupled ultrasonic transducer. Mode shapes were verified by scanning laser vibrometry up to the [3,3] mode, in the frequency range 100 kHz to 1 MHz. Resonant frequencies were identified at the predicted values provided the tension in the layers could be estimated. For a membrane structure incorporating an AlN layer, acoustic and electrical excitation of flexural modes was confirmed by displacement measurements using laser vibrometry and resonant frequencies were compared with analytical calculations.