Analysis of thermo-mechanical behavior of ITO layer on PET substrate

Mobile device's research should become advanced necessity for touch screen. Transparent conductive film is needed a touch screen panel that PET-ITO film is required transmittance (more than 85%) and sheet resistance (less than 400). The thermal stability of PET-ITO substrate has been issued on the industry of flexible electronics such as conducting films, display panels, interconnections, terminals, etc., which has more interested in the field engineer with increasing the needs of roll-to-roll manufacturing process. And also, the flexible products using PET-ITO substrate have been big matter to form fine pattern, pattern alignment and mass-productivity, which is strongly dependent on the thermal stability of the PET-ITO substrate such as thermal shrinkage and expansion. The previous works of PET-ITO substrate have been focused on the subjects such as ITO deposition process or ITO crack propagation rather than the thermo-physical behavior of PET-ITO substrate. Therefore, in this study, we used bare PET substrates and PET-ITO substrates for analyzing thermal strain quantitatively with the applied temperatures by thermo-mechanical analyzer (TMA). It was observed that the thermal strain of PET-ITO substrate was dependent on that of PET, even though the ITO layer on PET-ITO substrate has higher elastic modulus and lower coefficient of thermal expansion (CTE). And also, the thermal strain was observed to be unstable with increasing temperature after the glass temperature of PET. It was expected from these results that the improvement of the process, likely as the substitutive PET materials with high glass temperature or the change of an input temperature under the glass temperature of PET, should be needed when the PET-ITO substrate was applied into the mass production with fine pattern using roll-to-roll process.