NANOSCALE, SPATIALLY-CONTROLLED GA DOPING OF UNDOPED TRANSPARENT CONDUCTING OXIDE FILMS

Controlled Nanoscale Doping of Transparent Conducting Oxides NU 2008-091 Inventors Norma Cortes Mark Hersam* Tobin Marks* Abstract Transparent conducting oxides (TCOs) are employed as optically transparent electrodes in flat panel displays, OLEDs, photovoltaic cells, and electrochromic windows. TCOs possess a wide bandgap, and become electrically conducting when doped while retaining optical transparency >85% in the visible range. These properties are potentially well suited for functional invisible circuitry. However, TCO interconnects with suitable spatial and electrical properties that can be precisely positioned, have not been realized. Focused ion beam (FIB) is a widely used manufacturing technique for local ion implantation, etching, and metal deposition on conductive or semiconducting substrates on the nanometer scale. However, charging issues have plagued FIB doping of electrically insulating substrates, such as indium oxide films. Northwestern researchers have overcome this by introducing a thin Au anti-charging layer which enables nanoscale controlled doping of resistive indium oxide. This method writes precise 110-160 nm wide doped regions with implantation limited to a nominal depth of 7 nm below the oxide surface. Additionally, computer lithographic control of the ion beam affords diverse features of theoretically unlimited length, connectivity, and curvature. It has been shown that these Ga doped regions have enhanced electrical conductivity relative to the undoped background material. The spatial dimensions and electrical properties exhibited provide an ideal process for fabrication of transparent electrical interconnects and related devices. Applications o Transparent conducting oxide doping o Conducting oxide nanowire writing Advantages o Provides precise spatial control for writing embedded, optically transparent, and conducting oxide nanowires o Virtually unlimited ability to produce features of varying lengths, connectivity, and curvature Publications Cortes NES, Liu J, Chen C, Marks TJ, Hersam MC (2009) Nanoscale Writing of Transparent Conducting Oxides Features with a Focused Ion Beam. Advanced Materials. 21: 271-275. IP Status Patent applications have been filed.