Quasi-Self-Aligned Organic Thin-Film Transistors in Coplanar Top-Gate Configuration

Besides charge carrier mobility and contact resistance, parasitic overlap capacitance is a key factor limiting the dynamic behavior of organic thin-film transistors. The most effective away to reduce parasitic overlap capacitances between source/drain and gate electrode is to employ self-aligned transistor architectures. However, so far, self-alignment in organic transistors has only been achieved using nonscalable or complex fabrication processes. Here we demonstrate quasi-self-aligned OTFTs in a coplanar top-gate architecture fabricated with reliable and scalable state-of-the-art fabrication techniques such as wet-chemical etching. Self-alignment is achieved by carrying out a wet-chemical etching process on top of the channel interface. We prove that for the proper choice of etchant, the charge carrier transport properties of the channel interface are not deteriorated. The benefit of the self-aligned design lies in the reduction of the specific overlap capacitances which are 2 orders of magnitude (0.13 nF cm–2) lower than for nonself-aligned devices (15 nF cm–2). Furthermore, we highlight the potential of this approach for high-frequency operation of organic transistors and quantify the gain in cutoff frequency compared to non-self-aligned devices.