Top-contact organic transistors and complementary circuits fabricated using high-resolution silicon stencil masks

The maximum operating frequency of a field-effect transistor is inversely proportional to its lateral dimensions. Organic thin-film transistors (TFTs) with dimensions of ∼1 µm or less have been fabricated by photolithography [1], electron-beam lithography (EBL) [2], nano-imprint lithography (NIL) [3], sub-femtoliter inkjet printing (SIJ) [4] and self-aligned inkjet printing (SAP) [5]. Some of these methods (EBL, SIJ, SAP) have small throughput, others (EBL, NIL, photolithography) involve solvents or high process temperatures. Since high-mobility small-molecule organic semiconductors often undergo phase transitions when exposed to solvents or heat [6,7], these methods are in general not suitable to pattern source and drain contacts on top of such semiconductors. As an alternative, high-resolution stencil masks offer the possibility to pattern top contacts with high throughput and without the need for solvents or elevated temperatures. For example, Jin et al. reported top-contact pentacene TFTs with a channel length of 1.8 µm fabricated by using a global silicon back gate and a high-resolution silicon nitride stencil mask [8]. For devices with short channel lengths, top-contact organic TFTs usually provide better performance than bottom-contact TFTs [9].