Ultra-high transparent sandwich structure with a silicon dioxide passivation layer prepared on a colorless polyimide substrate for a flexible capacitive touch screen panel

Abstract

Indium tin oxide (ITO)-based multilayer structures with ultrathin silver (Ag) deposition on colorless polyimide (CPI) were investigated as touch sensor electrode materials in this study. The electrical, optical, structural, and morphological properties of the ITO-based multilayer structures were compared. The figure of merit of the ITO/Ag/ITO(160)/CPI multilayer structure (bottom ITO film deposited at 160 °C), in which the bottom ITO layer was deposited at 160 °C, was calculated using Haacke's formula, and the value was found to be 63.6 × 10−3 Ω−1. Moreover, the sheet resistance and optical transmittance at 550 nm were 6.4 Ω/□ and 91.4%, respectively. Transmission electron microscopy measurements demonstrated that the continuous Ag layer had a uniform film of 10.9 nm. When an ITO/Ag/ITO(160) multilayer structure was used as a substitute for an X–Y ITO layer electrode for fabricating a flexible capacitive-type touch screen panel (FCTSP) and a low-refractive-index silicon dioxide (SiO2) layer was used as the passivation layer, the ultra-high optical transmittance of the SiO2/ITO/Ag/ITO(160) multilayer structure was measured to be 94.6% (at 550 nm), and the average optical transmittance over the visual region (400–700 nm) was measured to be 92.2%. An FCTSP with multiple touch points was successfully fabricated using an X–Y ITO/Ag/ITO(160) multilayer electrode and SiO2 passivation layer. Finally, we also derive the related theoretical formulas to fix our experimental data. Moreover, based on the theory, we can predict the optimized thickness to support the desirable ultra-high transparency of multilayer structures. This auxiliary simulation also paves an alternative route to explore the possibilities of optimized multilayer flexible devices.