Study on optimizing c-axis oriented AlN thin film for piezoelectric sensing applications controlling the sputtering process parameters

The crystal orientation of aluminium nitride (AlN) thin film poses a challenge in piezoelectric applications, where the orientation of (002) is desired for obtaining a high piezoelectric coefficient of the order of 10(-12) V/m. Many processes to develop c-axis oriented AlN films with optimized parameters are reported specifically for piezoelectric applications. Of these, the sputtering has been a promising process with control over the target to substrate alignment angle and distance, sputtering parameters, the choice of bottom electrode, etc. The present study uses RF magnetron sputtering to investigate the impact of magnetron source orientation and the influence of working pressure on c-axis oriented AlN crystal growth. AlN thin films were deposited on Al and Mo bottom layers using magnetron sputtering under different source arrangements, namely parallel and confocal. Further, AlN was deposited under different working pressures with all other parameters being fixed. The structural and morphological properties of the prepared samples were studied. The analysis showed a parallel deposition set up with a smooth bottom layer and optimized working pressure promotes AlN to grow in (002) orientation suitable for piezoelectric applications.