Fabrication of the flexible pentacene thin-film transistors on 304 and 430 stainless steel (SS) substrate

Flexible organic thin-film transistors (OTFT) were fabricated on 304 and 430 stainless steel (SS) substrate with aluminum oxide as a gate insulator and pentacene as an organic semiconductor. Chemical mechanical polishing (CMP) process was used to study the effect of the SS roughens on the dielectric properties of the gate insulator and OTFT characteristics. The surface roughness was decreased from 33.8 nm for 304 SS and 19.5 nm for 430 SS down to ∼2.5 nm. The leakage current of the metal–insulator–metal (MIM) structure (Au/Al2O3/SS) was reduced with polishing. Mobility and on/off ratio of pentacene TFT with bare SS showed a wide range of values between 0.005 and 0.36 cm2/Vs and between 103 and 105 depending on the location in the substrate. Pentacene TFTs on polished SS showed an improved performance with a mobility of 0.24–0.42 cm2/Vs regardless of the location in the substrate and on/off ratio of ∼105. With self assembled monolayer formation of octadecyltrichlorosilane (OTS) on insulator surface, mobility and on/off ratio of pentacene TFT on polished SS was improved up to 0.85cm2/Vs and ∼106. I–V characteristics of pentacene TFT with OTS treated Al2O3/304 SS was also obtained in the bent state with a bending diameter (D) of 24, 45 or 70 mm and it was confirmed that the device performed well both in the linear regime and the saturation regime.