Optical and Electrical Properties of Cr-SiO Thin Films for Flat Panel Displays
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Optical and Electrical Properties of Cr-SiO Thin Films for Flat Panel Displays Richard Wood, Peter Hofstra and David Johnson Luxell Technologies Inc. 5170A Timberlea Blvd. Mississauga, CANADA, L4W 2S5 ABSTRACT Low temperature fabrication of transparent conducting materials is a key issue in flat panel display production. Though Cr-SiO cermet thin films have predominantly been used as thin film resistors in a variety of microelectronics applications, it is shown in this paper that the material can successfully be used as a transparent to semi-transparent conductor in some applications if the value of the extinction coefficient, k, can be kept low (98% for thickness, optical properties and conductivity) these films were successfully grown over an area exceeding 1 m in diameter, allowing for full-scale production. Furthermore, deposition at room temperature produced stable films compatible with lift off processes employed in patterning the rear electrode of these displays. Black Layer™ has also been successfully integrated into organic light emitting diodes, with no change in the I-V characteristics. A low resistance transparent layer is crucial to these current driven devices. The required Black Layer™ materials have also been deposited without thermal damage to the underlying organic layers. CONCLUSIONS Lower resistance in films deposited at higher rates, from both source concentrations, can be attributed to the presence of more chromium, acting like metal bridges, and formation of more Cr3Si centres. Oxidation of metals, Si and Cr, likely produces a lower k in films deposited at low rates. Resistance decreases by an order of magnitude in films deposited at low rates when switching from the 60/40 to 70/30 mixtures suggesting that a lack of chromium, in 60/40, increases the concentration of silicon rich sites that don't contribute to conduction. In addition, in the chromium rich, 70/30, films, more chromium is present, likely being the cause of increased absorption. At high rates, both films have excess chromium that appears to remain elemental. Conduction reaches a peak with increasing deposition rate, suggesting that the dominant mechanism is the formation of CrxSiy complexes and not elemental chromium: the Cr3Si crystals likely reach a concentration and size maximum. A high atom arrival rate at the surface will limit crystal growth. It has been shown that electron beam evaporation conditions can be changed to alter the material concentrations and states in the films, unlike sputtering and flash evaporation. Results also indicate that deposition conditions could be further adjusted to reduce resistance while keeping the extinction coefficient low. Addition of oxygen during the deposition of 70/30 could reduce the free silicon and chromium content. REFERENCES 1. L. K. Thomas, W. Pekruhn, T. Chunhe and A. Schroder, Solar Energy Mater. 16(1-3) 133 (1987). 2. M.Milosavljevic, T. M. Nenadovic, N. Bibic and T. Dimitrijevic, Thin Solid Films 101(2) 167 (1983). 3. A. G. Taylor, R. E. Thurstans and D. P. Oxley, J. Phys. E: S
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