Piezoelectric ultra-sensitive aluminum nitride thin film on flexible aluminum substrate

Abstract

Development of ultra-sensitive mechanical pressure sensors is required for various technological fields such as medical diagnosis and gas leakage. Aluminum nitride (AlN) thin films deposited by rf reactive sputtering on flexible aluminum substrates show a piezoelectric response to an ultra-small mechanical pressure in the scale of few Pa. This result is achieved only in the case where the residual average stress in the AlN film is close to zero. The deposition temperature determines the crystallographic orientation of the grains relative to the AlN film plane and consequently the type and magnitude of the residual stress in the film. Various sources of mechanical pressures were applied on the AlN films including a stream of air from a narrow diameter nozzle, sound waves in air and a piezoelectric actuator. In addition, a thermally induced pressure was tested. The scale of the applied mechanical pressures was calibrated and found to be in the range of few Pascals. The piezoelectric response of the AlN film is correlated with the mismatch of atomic arrangement at the AlN film/Al substrate interface.