Thermal degradation behavior of silicon dioxide-coated indium-tin-oxide thin films on glass in a storage status under highly accelerated life testing

Thermal degradation behavior in a storage status of silicon dioxide-coated indium-tin-oxide (ITO) thin films prepared by an electron-beam evaporation technique on K9 glass substrate has been investigated under highly accelerated life testing (HALT) in the temperature range of 40 ∼ 300 °C in air. Surface topographies, optical transmittances, and electrical resistances were measured by a metallographic microscope, a 3-D surface profiler, a spectrophotometer, and a digital voltmeter. Surface topography deterioration, transparency enhancement, and conductivity decrease were observed, and increasing temperature can accelerate the degradation. Moreover, the degradation rates of resistance relative variations have been studied as a function of temperature using Arrhenius relationship. The activation energies in different temperature ranges implied three main degradation mechanisms: (a) oxidation and structure relaxation below 180 °C; (b) oxidation and grain growth between 180 ∼ 270 °C; and (c) oxygen chemisorption and grain growth above 270 °C. Here, oxidation can lead to transparency enhancement in a NIR region and is dominant in resistance increase below 270 °C; oxygen chemisorption is the main factor of resistance increase above 250 °C; structure relaxation at low temperature and grain growth above 180 °C can enhance transparency in whole waveband, where grain growth has larger contribution and induces serious surface topography deterioration.