The Sputtering and Characterization of C-Axis Oriented Aluminium Nitride Thin Films On Top Of Cubic Silicon Carbide-On-Silicon Substrates for Piezoelectric Applications

Abstract

The growth of micro-scale wireless electronics is increasing significantly because of their miniaturisation and low power consumption. These devices currently draw power from batteries or chemical fuel cells. Their limited life-spans prompt active research to find an alternative solution by harvesting ambient energy from the environment. Numerous sources are available such as solar, thermoelectric, acoustic, and mechanical vibrations. Among them, mechanical vibration is perhaps the most practical to power these wireless electronic devices via piezoelectric transduction. Three most common piezoelectric materials are Lead zirconate titanate (PZT), zinc oxide (ZnO) and aluminum nitride (AlN). AlN is preferred over ZnO and PZT for several reasons. Chiefly among them is because it has the highest electromechanical coupling along the c-axis of wurzite AlN for longitudinal deformation. This thesis investigates the sputtering of c-axis oriented AlN on top of cubic-silicon carbide-on-silicon (3C-SiC-on-Si) substrates for piezoelectric applications. The 3C-SiC buffer layer was used to reduce the lattice mismatch and thermal expansion coefficient between AlN and Si. In the first part of the research, RF sputtering was utilised for depositing AlN. The low growth rate of RF sputtering prompted the switch to DC sputtering. The DC sputtering suffered from electrical arching problems, which were addressed by gradually decreasing the sputtering pressure. However, the system had the limitation of 1200 W of maximum power.