Use of Multilayer Oxide Films Prepared by RF-Magnetron Sputtering as Transparent IR-Reflector

Abstract

A transparent-conducting indium tin oxide (ITO)/Titanium di-oxide (TiO2) multilayer optical filter has been developed using conducting and transparent ITO and transparent insulating TiO2 films grown by RF-magnetron sputtering. The objective is to cut off the infrared portion of the solar spectrum to avoid the heating effect. The electrical resistivity of ITO film is 1.2×10-4 Ω·cm, the sheet resistance is below 8 Ω/□ and the visible optical transmission is above 85%. The refractive index of this film is 1.9. On the other hand, TiO2 is highly resistive (resistivity is of the order of 1010 Ω·cm), and has 85% visible optical transmission and very low absorption in the visible and infrared regions. The refractive index of TiO2 film is 2.6 at a substrate temperature 250°C and 2.9 at 450°C. At 450°C, the rutile titanium dioxide structure was formed which was confirmed on the basis of diffraction rings. In the multilayered ITO/TiO2 structure ITO and TiO2 layers were alternately deposited. Thicknesses of the ITO and TiO2 layers were optimized to achieve the best result. The multilayer has the same sheet resistance as that of ITO film and about 92% visible transmission with the plasma resonant frequency at 840 nm. The X-ray diffraction (XRD) pattern of the ITO/TiO2 multilayer indicates a the random orientation of crystal growth.