The use of high K dielectric thin film prepared by RF sputtering as insulating layers for organic TFT devices

The performance of polymer thin-film transistors (TFTs) prepared on the high dielectric constant (high K) materials, such as tantalum oxide, tantalum oxide/silicon dioxide, and niobium oxide prepared by conventional magnetron RF sputtering taking into account the oxygen/argon ratio, substrate temperature during sputtering, gas pressure has been investigated in this study. The dielectric dispersion and the leakage current in the oxide layers were also measured to evaluate the sputtering condition feasible for TFTs. The leakage current of single layered Ta₂O₅ (200 nm) sandwiched between two Al electrodes becomes minimum at O₂/Ar = 30% and the T_s = 100°C. We successfully obtained the good quality of tantalum oxide films, having a relative dielectric constant of 20 and a leakage current of less than 50 nA/cm² at 1 MV/cm. Finally, we discuss the electrical properties of organic TFTs using poly(3 alkyl thiopene) (P3AT) and tantalum oxide as the gate. A field effect mobility of 7.5 × 10^-4 cm²/Vs and a threshold voltage of V_T = 7 V was obtained from saturation region. The FET properties were then discussed in terms of the surface roughness and the surface treatment of Ta₂O₅ layers.