Electrochromic properties of SnO2-incorporated Ni oxide films grown using a cosputtering system

SnO 2 -incorporated Ni oxide (NiO:SnO2) films were grown by means of a cosputtering system, consisting of two rf sputter guns, and their electrochromic properties were compared with those of a Ni oxide film. The Ni oxide films crystallized with an increased film thickness due to a plasma heating effect, leading to a decreased maximum bleached transmittance and coloration efficiency (CE). However, the NiO:SnO2 films grown by cosputtering showed acceptable maximum bleached transmittance and CE values, which were independent of film thickness. This indicates that SnO2 adatoms generated by the side sputter gun interfere with the movement of Ni oxide adatoms deposited by the main sputter gun, preventing the crystallization of the films. This was verified by x-ray diffraction and scanning electron microscopic data. We propose that the cosputtering technique described herein has the capability of providing good maximum bleached transmittance and CE properties in thick electrochromic films with no degradation due to the plasma heating effect.