Electrochromism of DC magnetron sputtered TiO2 thin films: Role of deposition parameters

•Sputter deposited titanium dioxide films have electrochromic properties.•High pressure in the sputter plasma and low substrate temperature are needed for good performance.•These parameters give amorphous films with an expected columnar structure.•The maximum coloration efficiency is ∼25 cm2/C.

We performed a comprehensive study on the electrochromism in TiO2 thin films made by reactive DC magnetron sputtering and elucidated the roles of sputter gas pressure p, O2/Ar gas ratio γ and substrate temperature τs. Good mid-luminous optical modulation—taken to be ∼50% in ∼200-nm-thick films—was obtained under charge exchange in a Li+ electrolyte for p>15 mTorr and τs<100 °C, whereas γ was less important. The deposition rate dropped for increasing p, and hence p≈15 mTorr was optimal. These films were X-ray amorphous and contained some water. The coloration efficiency η was ∼25 cm2/C, which exceeds data on η in most prior studies on sputter deposited TiO2 and verifies that such films can display the same values of η as those of TiO2 films made by several chemical techniques.

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