The role of sputter pressure in influencing electrical and optical properties of ITO on glass
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1256-N11-53
The role of sputter pressure in influencing electrical and optical properties of ITO on glass
S. Elhalawaty1, K. Sivaramakrishnan1, N. D. Theodore2 and T. L. Alford1,a) 1
School of Materials and Flexible Display Center at ASU, Arizona State University, Tempe,
Arizona 85287, U. S. A 2
CHD-Fab., Freescale Semiconductor Inc., 2100 East Elliot Rd., Tempe, Arizona 85284, U.S.A
ABSTRACT Thin layers of indium tin oxide (ITO) were deposited onto glass substrates by RF magnetron sputtering with the pressure varying from 6 mTorr to 15 mTorr. The films were annealed in a reducing atmosphere at 500 °C for 30 minutes. Sheet resistance was determined by four-pointprobe measurement. Resistivity, mobility, and carrier concentration were obtained by Hall effect measurements. Transmission of the films in the visible spectrum was determined by photospectrometry. The structure of the films was characterized by X-ray diffraction. X-ray photoelectron spectroscopy was used to determine the oxidation state of Sn, which was used to determine the fraction of active tin clusters. The effect of additional anneals was investigated. The results reveal that the lowest resistivity obtained was 1.69×10-4 Ω-cm at 9 mTorr and the highest transmittance of 90% was obtained after a second anneal. However, the second anneal decreased the mobility and conductivity for high sputter pressures.
INTRODUCTION Transparent conducting oxides (TCOs) have been widely used in the optoelectronics industry due to their high electrical conductivity combined with high transmission in the visible and near–IR regions of the electromagnetic spectrum. ITO is one of the most used transparent conducting oxides. It is a degenerate wide band-gap (3.5-4.3 eV) n-type semiconductor due to oxygen vacancies and substitutional tin dopants [1]. Sn4+ ions substitute for In3+ ions on cation sites and create donor levels in the energy band-gap. Oxygen vacancies act as doubly ionized donors and donate two electrons per oxygen vacancy to the electrical conduction band [2,3]. Given ITO films’ unique transparent and conducting properties, they have been utilized in many applications such as: solar cells, flat panel displays, surface heaters for automobile windows, transparent heat reflecting window material for buildings, lamps, and solar collectors [1,4]. ITO films can have different conductivity, transparency, and surface structures depending upon deposition method. There are many deposition techniques such as reactive DC or RF sputtering [5], reactive evaporation [6], sol-gel process [7], chemical vapor deposition [8], and recently pulsed laser deposition [9,10]. However, the most frequently used deposition technique is RF magnetron sputtering which provides high deposition rates, large deposition areas, and less damaged areas [11]. The properties of RF sputtered ITO films are sensitive to sputtering a)
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parameters: total sputtering pressure, oxygen content in the sputtering gas, target to substrate distance, substrate temperature, depositi
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