Electrical properties of piezoelectric aluminium nitride films deposited by reactive dc magnetron sputtering

Abstract

Piezoelectric AlN films crystallised in a hexagonal wurtzite structure with the c-axis oriented perpendicular to the surface were deposited on silicon substrates by dc reactive magnetron sputtering. The evolution of the crystallographic and electrical properties of these films with a nitrogen concentration between 10 and 100% in the Ar–N2 gas mixture was studied using X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDXS) and four-point probe methods. It was found that the electrical properties are correlated to the film structure and to the deposition parameters. The AlN films having a high electrical resistivity (>1014 Ω cm at room temperature) also exhibit a high crystallographic orientation, as determined from the XRD peak intensity. An optimum for the nitrogen concentration is identified in the range 60–80% of N2 in the gas mixture. The Arrhenius plots of electrical resistance give an activation energy of 2.2 eV between 200 °C and 450 °C. This energy is attributed to oxygen impurities. EDXS analysis reveals that oxygen is the only element present in the deposited films, along with Al and N.