Atomic layer deposition of Al2O3/ZnO nano-scale films for gold RF MEMS

Atomic layer deposition (ALD) was used to create an Al₂O₃/ZnO thin film for gold capacitive RF MEMS switches. These films exhibited a widely tunable range of physical properties, allowing the creation of a material capable of dissipating trapped charges and maximizing the on-capacitance of the switch. Predicted pull-down voltages of the ALD-coated switches underestimated the experimental findings due to residual stresses in the ALD film and annealing of the gold during the ALD deposition. Switch cycles to failure were measured using a 10 dBm, 10 GHz, CW signal with a bipolar actuation voltage of 25-55 V. Preliminary testing showed lifetimes of 400 million cycles using 50/50 ALD Al₂O₃/ZnO films, with ultimate failure due to moisture-induced stiction and particulate contamination, not dielectric charging. The insertion loss and isolation for the switches was typically <0.35 dB and > 25 dBm, respectively, over a 10-25 GHz frequency range.