Effects of different interlayers on indium-tin oxide thin films sputtered on flexible PET substrates

Abstract

Using radio-frequency magnetron sputtering, various interlayer materials (Cu, Al, Ag, and ZnO) were added to indium-tin oxide (ITO) films on a polyethylene terephthalate (PET) flexible substrate, and were compared to examples made without an interlayer. The effects of the interlayer on the ITO were investigated with X-ray diffractometry (XRD), visible wavelength photospectrometry, four-point probe electrical resistivity, and micro-scratch adhesion tests, which were all conducted at four temperatures (25°C, 35°C, 55°C, and 75°C). The ITO crystallographic texture was overwhelmingly found to be (2 2 2), for all combinations considered. The grain size was reduced in the ITO films having interlayers of Ag or Cu, and was enlarged by the ZnO. The visible light transmittance remained almost unchanged for the Al and ZnO buffers, but Ag and Cu failed to maintain the industry standard of 75–80% for a transparent film. Cu, ZnO, and especially Ag, effectively reduced, whereas, Al increased the sheet resistance of the ITO. Upon heating, the scratch resistance diminished in all cases, excluding Cu, while the sheet resistance grew with respect to temperature, for all films except those with Ag. The XRD intensity and the light transmittance were not significantly affected by temperature.