Properties of atomic layer deposited Al<inf>2</inf>O<inf>3</inf>/ZnO dielectric films grown at low temperature for RF MEMS

Al2O3/ZnO alloy films were grown at 100°C using atomic layer deposition (ALD) techniques. It has been previously established that the resistivity of these films can be tuned over a wide range by varying the amount of Zn in the film. Al2O3/ZnO ALD alloy films can therefore be designed with a dielectric constant high enough to provide a large down-state capacitance and a resistivity low enough to promote the dissipation of trapped charges. The material and electrical properties of the Al2O3ZnO ALD films were investigated using Auger electron spectroscopy (AES), nanoindentation, and mercury probe measurements. Chemical analysis using AES confirmed the presence of both Al and Zn in the alloys. The nanoindentation measurements were used to calculate the Young's modulus and hardness of the films. Pure Al2O3 ALD was determined to have a modulus between 150 and 155 GPa and a hardness of ∼8 GPa, while the results for pure ZnO ALD indicated a modulus between 120 and 140 GPa and a hardness of ∼5 GPa. An Al2/ZnO ALD alloy displayed a modulus of 140-145 GPa, which falls between the two pure films, and a hardness of ∼8 GPa, which is similar to the pure Al2O3 film. The dielectric constants of the ALD films were calculated from the mercury probe measurements and were determined to be around 6.8. These properties indicate that the Al2O3/ZnO ALD films can be engineered as a property specific dielectric layer for RF MEMS devices.