Atomic layer deposition of thin films: from functional devices to protective coatings

Atomic layer deposition (ALD) is a self-limiting subset of chemical vapor deposition that has become widely popular in materials science applications such as device packaging, semiconductor passivation, transistor gate dielectrics, optical coatings, and protective barriers. ALD is capable of uniformly coating high-aspect ratio features, such as 1-dimensional nanostructures or pinhole-sized vias, across a macroscopic distance which is expected to only be limited by the size of the deposition chamber. This work reviews several applications of ALD used to deposit thin conformal layers of dielectric material which specifically capitalize on the precise, conformal nature of the deposition process. Semiconductor nanowire networks coated with aluminum oxide (AlOx) by plasma enhanced ALD (PEALD) show blue-shifted photoluminescence with increasing AlOx thickness. Novel memristor “edge” devices fabricated with an active switching layer of titanium dioxide deposited by PEALD yield an active device cross-section two orders of magnitude smaller than what is possible with conventional 2-dimensional thin film devices fabricated by similar photolithography methods. Protected silver mirrors coated with AlOx deposited by PEALD have superior durability when compared to mirrors coated with an identical layer of AlOx deposited by conventional physical vapor deposition. All of these applications benefit from the robust uniform coating properties of the ALD growth mechanism. Additional studies of dielectric barrier overlayers deposited by ALD on silver mirrors are discussed, and a figure of merit is proposed for judging overall mirror performance