Direct Patterning on Top-Gate Organic Thin-Film Transistors: Improvement of On/Off Ratio, Subthreshold Swing, and Uniformity

Indacenodithiophene-co-benzothiadiazole (IDT-BT), diketopyrrolopyrrole-thieno[3,2-b]thiophene (DPPT-TT), and poly{[N,N'-bis(2-octyldodecyl)-naphthalene-1,4, 5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5'-(2,2'-bithiophene)} (N2200) organic thin-film transistors (OTFTs) with a top-gate structure were patterned by simple oxygen plasma treatment instead of conventional processes such as photolithography and inkjet printing. The ungated layer, which is known to cause leakage current paths, was efficiently removed by oxygen plasma treatment. After patterning, the gate leakage current in OTFTs was suppressed below the order of 10(-9) A, the on/off current ratio of DPPT-TT OTFTs increased from 5 x 10(4) to 2 x 10(7), and the subthreshold swing extracted from N2200 OTFTs decreased from 1.6 to 0.3 V dec(-1). All the measured electrical parameters of the patterned OTFTs were distributed in narrower ranges than those of the corresponding non-patterned devices, indicating the high uniformity and reproducibility of the patterned OTFTs. Our low-cost and simple patterning method can be widely used to improve the electrical performance of OTFTs.