Advanced protective coatings for reflectivity enhancement by low temperature atomic layer deposition of HfO2 on Al surfaces for micromirror applications

We report on the implementation of thin atomic layer deposited coatings for environmental protection and reflectivity enhancement of Al-based micromirror devices. The reflectance characteristics of HfO2 and SiO2 thin layers on Al surfaces has been simulated by Rigorous Coupled-Wave Analysis (RCWA). Reflectance enhancement, especially in the 420-675 nm wavelength region, has been predicted by fine-tuning the layer thickness in HfO2/SiO2 dual layer stacks. This engineered solution has been developed and then implemented on real micro-electro-mechanical system (MEMS) devices demonstrating an enhancement of the reflectivity. Our approach suggests that atomic layer deposition is a valid method for both protecting and enhancing the performances of reflective surfaces of micro-opto-electro mechanical systems.