Controlled Nanoscale Doping of Transparent Conducting Oxides by Focused Ion Beam Implantation (28091)
An effective method for the spatially-controlled writing of embedded, optically transparent, electrically conducting oxide nanowires and other patterns via focused ion beam implantation into highly resistive transparent metal oxide thin films.
ADVANTAGES: Nanoscale, spatially-controlled doping of highly resistive indium oxide films enables the fabrication of embedded, optically transparent, electrically conducting wires. The dimensions achieved combined with the electrical properties of the Ga-doped In2O3 system, potential length, connectivity, and shapes of lines make them ideal for transparent electrical interconnects and other applications.
SUMMARY: Transparent conducting oxides (TCOs) are employed on a vast scale as optically transparent electrodes in flat panel displays, OLEDs, photovoltaic cells, and electrochromic windows. TCOs possess a wide bandgap, 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, the requisite TCO interconnects of suitable spatial and electrical properties, that can be precisely positioned, have not been realized. Attempts to pattern blanket films of Sn-doped indium oxide (“ITO”) via wet and dry etch methods exhibit limited reliability and control compromising pattern fidelity and scale.
Focused ion beam (FIB) is a widely used manufacturing technique for local ion implantation, etching, and metal deposition on conductive or semiconducting substrates with nanometer scale spatial resolution. However, charging issues have confounded spatially-resolved FIB doping of electrically insulating substrates such as indium oxide films. The present invention overcomes this limitation by introduction of a thin Au anti-charging layer to enable nanoscale, controlled doping of resistive indium oxide with a Ga FIB (Figure 1). This method writes precise 110-160 nm wide doped regions with implantation limited to a nominal depth of 7 nm below the oxide surface. In addition, computer lithographic control of the ion beam affords diverse features of theoretically unlimited length, connectivity, and curvature (Figure 2). Conductive atomic force microscopy (AFM) imaging reveals the Ga doped regions have enhanced electrical conductivity relative to the undoped background material. Literature reported optimized GaxIn1-xO3 film conductivities (~103 S cm-1), carrier concentrations (~1019cm-3), and mobilities (65 cm2 V-1 s-1) demonstrate Ga doping imbues In2O3 with electrical properties suitable for device applications. This method, with proper dosing and beam energy, also generates transparent conductive nanowires that are embedded, essentially flush with the substrate and with minimal topographic damage. The spatial dimensions and electrical properties exhibited provide an ideal process for fabrication of transparent electrical interconnects and related devices.
Mark Hersam, Tobin Marks, Norma Cortes
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