Polymer Gate Dielectrics for High Performance Organic Field-Effect Transistors
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Polymer Gate Dielectrics for High Performance Organic Field-Effect Transistors Faruk Altan Yildirim1, Ronald Meixner2, Robert Roman Schliewe1, Wolfgang Bauhofer1, Holger Goebel2, and Wolfgang Krautschneider3 1 Institute of Optical and Electronic Materials, Hamburg University of Technology, Eissendorfer Str. 38, Hamburg, 21073, Germany 2 Department of Electronics, Helmut Schmidt University, University of the Federal Armed Forces Hamburg, Holstenhofweg 85, Hamburg, 22043, Germany 3 Institute of Nanoelectronics, Hamburg University of Technology, Eissendorfer Str. 38, Hamburg, 21073, Germany
ABSTRACT Solution-processed bottom-gate organic field-effect transistors (OFETs) with different polymeric dielectric materials were produced and characterized. As the active semiconductor layer, regioregular poly(3-hexylthiophene) (rr-P3HT) was used. Dielectric materials of high chemical stability with simple processing conditions were used as gate-insulation in OFETs. Also, the dielectric properties of the polymeric layers were investigated in metal-insulator-metal capacitor structures, where the thicknesses of the films were exactly the same as they were in the OFETs. The specific volume resistivity and dielectric constant values determined were then used to explain the electrical behavior of OFETs. The devices having BCB, SU-8 and NOA74 as dielectric layers exhibited the desired transistor characteristics, whereas the transistors with Avatrel dielectric did not, due to higher gate-leakages. As a result, SU-8 and NOA74 resins were proven to be good candidates for gate-dielectric usage in solution-processed all-polymer OFETs. INTRODUCTION The materials research for the solution-based processing of organic field-effect transistors (OFETs) has been of great interest in the last two decades [1-4]. In addition to the efforts for the synthesis of stable, high-mobility semiconductors, lately, the research on materials for the gate dielectric has increased explicitly, due to the better understanding of the influence of gate dielectric on the operation of OFETs. The challenge here has several dimensions: decreasing the operating voltages, forming a desired interface with the semiconductor and increasing the longterm stability and robustness of the transistor. Various organic polymers which had been used previously as dielectric materials include cross-linked poly(vinylphenol), benzocyclobutene, poly(methyl methacrylate), polyimides, low-κ dielectrics, silsesquioxane resins, photoresists, poly(vinylalcohol) and polypropylene [5, 6, 7]. In this work, the organic insulators studied were selected from “thermosetting resins”, which not only exhibit the desired insulating properties but also the chemical stability for keeping the stack integrity. Chemical stability of the dielectric layer is extremely important for the transistor since the solvents used for the deposition of the forthcoming layers may dissolve or swell the dielectric, which may lead to leakage currents or an undesired semiconductor/insulator interface. The dielectr
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