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RF superimposed DC sputtering of zinc tin oxide (ZTO) and indium zinc oxide (IZO)

: Heimke, B.; Kopte, T.; Hartung, U.; Nyderle, R.; Junghähnel, M.; Krause, U.; Braun, J.

Advanced Coatings for Large-Area or High-Volume Products. ICCG 2008, 7th International Conference on Coatings on Glass and Plastics. Proceedings : June 15-19, 2008, NH Conference Centre Koningshof, Eindhoven/Veldhoven, the Netherlands
Eindhoven, 2008
ISBN: 978-90-5986-281-4
International Conference on Coatings on Glass and Plastics (ICCG) <7, 2008, Eindhoven>
Conference Paper
Fraunhofer FEP ()
RF superimposed DC; transparent conducting oxide; IZO; TZO; sputtering

Transparent conductive oxide layers are widely used for transparent front contact layers in display technologies as well as in solar cell Systems and other applications. Beside the most commonly used material, tin doped indium oxide (ITO), other alternative materials such as zinc doped tin oxide (ZTO) and zinc doped indium oxide (IZO) came into consideration, due to the lower material costs or the good electrical and optical properties.
In a combined approach of a RF superimposed DC sputter process the benefits of better film growing properties in RF plasmas and the high deposition rate of DC processes were used to deposit thin IZO and ZTO films on glass Substrates.
To obtain more detailed Information about the deposited films, the UV-VIS and IR spectra have been analysed using an oscillator model and an extended Drude model. Together with four point probe and Hall measurements the free carrier concentration n, the carrier mobility u and the resistivity p of the deposited thin films could be determined. It was shown fhat DC sputtered IZO thin films present quite similar properties like ITO thin films with regards to the obtained resistivity and the transmittance in the visible spectral ränge. With a Superimposed RF ratio of 50% of the total input power, thin films with a resistivity of 3.5xlO~4 ficm and a transparency of 89% at 550 nm could be obtained, without additional heating of the glass Substrate. The carrier concentration reaches approximately 7xlO20 cm3 and the carrier mobility was about 25 cm2/Vs. The DC sputtered ZTO thin films show a relatively high resistivity of 9xlO"3 Ocm with limited free carrier concentration of 8xl019cm3 and carrier mobility of 8 cmWs. DC superimposed RF sputtered films with a RF ratio of 30% of the total input power show an increased carrier concentration as well as an increase in the carrier mobility. With vacuum annealing at 300°C the resistivity can be reduced to 3.5xlO"3 Qcm with a transparency of 85%.