The effect of reactive ion etching parameters on the electrical properties and the removal of residual organics in spin-
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The effect of reactive ion etching parameters on the electrical properties and the removal of residual organics in spin-coated colloidal ITO films Salil M. Joshi and Rosario A. Gerhardt School of Materials Science and Engineering, Georgia Institute of Technology, 771 Ferst Drive NW, Atlanta GA 30332. USA. ABSTRACT Spheroidal colloidal indium tin oxide (ITO) nanoparticles, about 6 nm in diameter, were synthesized in-house and films were fabricated from them on glass substrates by spin coating. These films had high electrical resistivity due to the presence of organic capping ligands around each nanoparticle. Although high temperature annealing has been shown to reduce film resistivity by over eight orders of magnitude, lower temperature processing is desirable for applications like flexible electronics. Colloidal ITO films were subjected to a series of alternating RIE treatments in oxygen (5 minutes duration per cycle) and in argon (1 minute duration per cycle); and parameters such as gas pressure, RIE power and number of cycles were varied. These RIE treatments were found to reduce the film resistivity significantly. Among the parameters studied, gas pressure during RIE was found to be the most important parameter that determined the effectiveness of the treatment. Residual carbon content variation characterization done by XPS depth profiles also indicated similar trends. INTRODUCTION Indium tin oxide (ITO) is widely used as the material of choice for applications that need optical transparency combined with high electronic conductivity, such as displays, photovoltaic cells, and others1. Commercial deposition of ITO is typically carried out on glass substrates for applications such as flat panel displays or thin film solar cells, by pulsed laser, dc magnetron sputter systems, or by electron beam evaporation1, 2. These techniques need the substrates to be heated to a high temperature during deposition, as well as undergo a high temperature post annealing to achieve crystallization and conductivity enhancement in the ITO films3, 4, as low substrate temperatures can result in the deposition of amorphous ITO with inferior electro-optical properties5. These techniques are hence not suited for the fabrication of transparent conducting films and patterns on non-heat resistant substrates like polymers which may be used in applications like low-cost and flexible optoelectronic devices. In addition, techniques like sputtering are also wasteful6, 7 in terms of expensive ITO as a result of wasteful deposition on the chamber walls, as well as inefficient use of sputter targets due to non-uniform erosion1. It is proposed that transparent conducting circuits and films may be able to be fabricated through direct-write methods, starting from a pre-synthesized “ink” made from colloidal ITO nanoparticles. Colloidal ITO solutions used for this contain crystalline ITO nanoparticles, which are sterically stabilized in solution by passivating ligands on the surface of the nanoparticles. As described in previous publications8, 9, the as-co
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