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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