High‐Resolution Lithography for High‐Frequency Organic Thin‐Film Transistors

Abstract Organic thin‐film transistors are field‐effect transistors comprising a semiconductor in the form of a thin, typically polycrystalline layer of conjugated organic molecules. Since organic transistors can often be fabricated at temperatures no higher than about 100 °C, they are potentially useful for flexible, large‐area electronics applications. An important performance parameter of organic transistors is the transit frequency, which is the highest frequency at which the transistors can be operated. The transit frequency of organic transistors is determined in large part by the channel length and the parasitic gate‐to‐source and gate‐to‐drain overlap lengths. How small these dimensions can be made depends (at least in the case of transistors fabricated in the lateral device architecture) greatly on the resolution of the lithography method that is utilized for the patterning of the gate electrodes and the source and drain contacts. Patterning methods that have yielded organic transistors with lateral dimensions sufficiently small to provide transit frequencies above 10 MHz include photolithography, laser lithography, stencil lithography, and electron‐beam lithography. In this review, these four lithography methods and their roles in the fabrication of high‐frequency organic transistors, as well as their prospects for future improvements in the dynamic performance of organic transistors, will be illuminated.