Compromise of electrical leakage and capacitance density effects: a facile route for high mobility and sharp subthreshold slope in low-voltage operable organic field-effect transistors

The effects of electrical leakage and capacitance density were investigated in the low-voltage operated organic field-effect transistors (OFETs) by using a gate dielectric with a bi-layer structure of atomic layer deposited alumina (ALD-Al2O3) and high-k polymeric cyanoethylated pullulan (CEP) layer. A significant improvement in the device performance was achieved by compromising the two effects, suppressing the leakage current with ALD-Al2O3 dielectric and maintaining the high capacitance with high-k polymeric layer. With the optimized thickness of similar to 5 nm alumina (C-i,C-CEP/Al2O3 similar to 85 nF cm(-2)), a high mobility of similar to 5 cm(2) V-1 s(-1) and sharp subthreshold slope (SS) of 0.066 V dec(-1) were obtained. The smoother surface of the polymeric dielectric surface enhanced the 2-dimensional vertical molecular layer growth and contributed to the better device performance.