UV/Ozone Based Facile Surface Modulation Technique for Efficient Organic Thin Film Transistor

Abstract

The capacity to actualize a comprehensive range of electronic functions based on organic devices is important to the development of fully functional organic electronic circuits. Specifically low voltage, quick switching transistors, in particular, have previously been demonstrated but a critical function, i.e. dependable data storage, is currently lacking. Organic thin-film transistors (OTFTs) have received a lot of interest for possible use in memory, flexible electronics such as sensors, and light-emitting diodes because of their inexpensive production costs, lightweight, mechanical flexibility, and other advantages.The most often utilised active ingredient in organic TFTs is pentacene (C22H14). The electrical properties of organic TFTs based upon pentacene, such as field-effect mobility, are equivalent to those of amorphous silicon thin film transistors (a-Si TFTs), which are typically employed for the backplane of liquid crystal displays (LCDs), but far inferior to those of generic inorganic TFTs. As a result, electrical properties for high-performance flexible electronics must be improved. The interfacial properties of active layer and gate insulator layer plays a very crucial role in determining the electrical properties of organic TFTs. Therefore in this work we report an UV/ozone treatment on the surface of gate dielectric layer so as to improve the interfacial properties.At first the glass substrate was cleaned in an ultrasonic cleaner with acetone, ethanol, isopropyl alcohol and DI water. Then by using thermal evaporation technique a gate electrode with thickness of approximately 80 nm was deposited on the substrate. Later a solution of Poly 4-vinylphenol (PVP) was spin coated with a thickness of 140 nm, this organic layer was deposited as the bottom insulator layer. Now an ozone treatment (wavelength = 253nm) for 5,10 and 20 min was done over the PVP layer. Subsequently a layer of PMMA was coated over the UV treated layer. Finally with a coating of 70nm thick pentacene active layer 100 nm thick silver drain/source electrodes with channel length of 50µm were also deposited using thermal deposition.Further the morphology and topography was studied using AFM images and element analysis was done from XPS spectra. The device performance (output and transfer characteristics) was characterized using Kiethley 4200 SCS semiconductor parameter analyser. The changes in performance of transistor devices before and after UV/ozone treatment could be explained using XPS spectra, AFM images and water contact angle measurement. It is evident from the AFM images that the grain size of pentacene on UV/Ozone treated dielectric surface are larger than the untreated surface, thus reducing the boundary scattering and enhancing the field effect mobility. Thus surface treatment with UV/Ozone could acts as simple, low cost method to enhance the performance of a organic thin film transistors.