Atomic layer deposited protective coatings for micro-electromechanical systems

This paper describes the novel fabrication approach of coating released micro-electromechanical systems (MEMS) devices with nanometer-thin films using atomic layer deposition (ALD). The ALD process is capable of depositing a variety of thin-film materials to protect MEMS devices from electrical breakdown, mechanical wear and stiction failure. ALD ensures conformal film coverage on all sides of a released MEMS device and can be performed at relatively low temperature of 177 C. The ALD film thickness can be precisely controlled at the atomic level as each reaction cycle deposits approximately one atomic monolayer. To demonstrate the concept of conformal layer deposition, ALD alumina (Al 2 O 3 ) films were deposited onto released MEMS cantilever beams and the coated devices were subsequently analyzed using cross-sectional scanning electron microscopy. Electrostatic testing of the coated MEMS cantilever beams revealed that the ALD Al 2 O 3 films prevented electrical shorting and failure when the devices were activated beyond the pull-in voltage. The curvature and increase in beam stiffness of MEMS devices resulting from the ALD Al 2 O 3 coating were also investigated.