Diamond ultra-small electrodes for integration with GaN electronics

Abstract

As a novel electrode material, diamond possesses unique properties, such as the widest potential window of water dissociation in all electrode materials, extreme chemical stability, low background current density and biocompatibility, being all in the wish-list of biologists, who want to perform biochemical sensing. And it would be significant to combine the diamond sensor technology with other mainstream technologies for biochemical sensing, e.g. parallel sensing with fluorescence microscopy, potentiometry sensing, on-wafer signal conditioning, even the realisation of LOC (Lab On Chip) concept etc. However, traditional diamond micro devices are deposited mostly on silicon substrate, which is not transparent to visible light and also show limited biocompatibility. Particularly, monolithic integration into Si-based CMOS circuits may not be possible since silicon-based electronics can hardly withstand the CVD conditions of diamond deposition. In this study, a new substrate for CVD diamond electrodes-single crystalline sapphire is adopted. Sapphire is a wide-bandgap semiconductor, besides being highly transparent and robust, it serves as a substrate material for a wide range of electronics. Among them, high-performance GaN electronics are especially interesting for this study, since they may withstand the harsh growth conditions of CVD diamond films, thus allowing the monolithic integration of GaN electronics into diamond sensors for signal conditioning and processing. As a precondition of the monolithic integration, electrode-grade diamond film needs to be deposited on the sapphire substrate. In this study, technologies are developed, leading to realization of large-area (up to 2 inch) DOS (diamond-on-sapphire) materials with well-preserved diamond material properties for electrode applications. Based on DOS (diamond on sapphire), several state-of-art diamond ultra-small electrode devices have been realized, targeting several novel applications.