Applications of parylene films in the manufacture of organic field-effect transistors

• Parylene C is used as gate dielectric in various organic field-effect transistors.
• Unusual cleanness of the parylene process is due to a lack of external initiator.
• High quality semiconductor/dielectric contact results from the purity of parylene.
• Parylene covered with top silver gate provides a long term transistor protection.

Along with the technology of microscopic electromechanical systems and that of brain–machine interface, the area of organic electronics presents a major development direction of high-tech applications of parylene coatings. Within this area, a fabrication of organic field-effect transistors (OFETs), where parylene C is applied as a gate dielectric, makes the most common use of these materials. The main advantage of parylene coatings in the OFET technology is their very high purity. Depending on a transistor design, films of parylene C may play a role of the gate dielectric material, that of a protective insulator coating, and/or that of a device substrate. The work presents a number of applications of parylene C in different OFET devices, namely in organic thin film transistors (OTFTs) and organic single-crystal transistors developed by the authors. A combination of zone-cast films of active materials, both n-type and p-type, with parylene C gate dielectric makes a principal design of the OTFTs. In this group, the best performance parameters and namely μFE = 0.18 cm2/Vs, Ion/off = 104 and turn-on voltage < 5 V were obtained for the n-type OFET based on a naphthalene bisimide derivative. Another group of devices developed is comprised of transistors based on active material single crystals. In this case, dithiophene-tetrathiafulvalene (DT-TTF) was used as a semiconductor, with the effect of its crystalline form on the transistor performance being investigated. Of the two DT-TTF polymorphs, monoclinic α form and hexagonal β form, the OFETs based on the α form were characterized by field-effect charge carrier mobility nearly an order of magnitude higher. In general, the results presented in the paper show both a broad applicability of parylene films in the technology of organic field-effect transistors and a versatile role these films may play in that technology.

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