The influence of substrate bias and sputtering pressure on the deposited aluminium nitride for magnetoelectric sensors

A residual stress of Aluminium nitride (AlN) thin films has been a problem in the magnetoelectric (ME) composites that are used in the AC magnetic field sensors. The present work aims to optimize the deposition process of AlN in order to fabricate a nearly-zero stress of AlN thin films as well as ME composites without losing the microstructural and piezoelectric properties. The influences of RF bias power and sputtering pressure on the residual stress, microstructure, and piezoelectric response have been investigated. Two different stacks are deposited on Si/SiO2 substrates: Ta/Pt/AlN and Ta/FeCoSiB/Ta/Pt/AlN. Pulsed DC reactive sputter depositions have been performed to deposit AlN films. With increasing the substrate bias, stress of the AlN films and the stacks with the magneto strictive layer are augmented. A variation of the sputtering pressure is a promising way to fabricate nearly zero stress of the AlN films and the stacks without the magneto strictive layer. A transition from tensile to compressive stress has been observed at the low sputtering pressure. Sputtering pressure also affects the stress of AlN films and the stacks with the magneto strictive layer. FWHM of AlN (0002) peaks are nearly constant within the ranges of the substrate bias. By reducing the sputtering pressure, FWHM is broadened due to lower ionization degree associated with AlN formation and greater number of micro-arcs. However, the magnitude of e_31,f is increased due to a lower residual stress at the low sputtering pressure.