Functional Oxide Depositions on Dielectric Substrates for Optical Applications

Abstract

Complex oxides of the transition metals are essential materials in the fabrication of photonic devices due to their high transparency in the infrared and the exotic properties they exhibit. Unfortunately, integrating them onto semiconductor platforms has proven to be a challenge due to significant differences in lattice constant (12-15Å compared to 5Å) and thermal expansion coefficient (~10-5 compared to 10-6) leading to cracking in films during thermal processing. This work focuses on methods to integrate two complex oxides onto semiconductor platforms while minimizing crack formation and maximizing the optical properties used for photonic devices. The two oxides to be discussed are yttrium iron garnet (YIG), an oxide that exhibits the magneto-optical effect, and barium strontium titanate (BSTO), which exhibits the electro-optical effect. The discussion will begin with the fabrication procedures to make each oxide, focusing on the novel reactive sputter and rapid thermal anneal method used to achieve film crystallization. Film properties will then be discussed, including transparency, dielectric constant, and crystallization. Each of the two complex oxides exhibited extremely high photonic effects, magneto-optical for YIG and electro-optical for BSTO, respectively. From the work optimizing oxide thin films, methods to fabricate complex oxide waveguides were developed that resulted in high transparency and transmission of a guided mode. These materials are highly effective for use in semiconductor integrated photonics.