Significant improvement of solution-processed organic thin-film transistors (OTFTs), exceeding the performance of a-Si:H thin-film transistors in the last few decades has attracted much attention to seek for inexpensive alternative. Owning to low-temperature processing of organic semiconductor and insulator and the compatibility with conformable/flexible substrates like plastics and paper, OTFTs have exhibited immense potential in applications such as backplane circuit for active-matrix displays, amplifiers for sensor arrays, image sensors, radio-frequency identification (RFID) tags etc. While there has been a sizable amount of work focusing on either individual device component or arrays of OTFTs with common gate structure, comparatively much less effort has been devoted to the development of array of identical OFETs consisting of isolated gate with patterned source/drain contact, which is essential from circuit application standpoint. The most favourable and scalable solution to adhere to such milestone is the integration of microelectronic technology with the existing organic semiconductor and insulator processing technology.

In this context, the advantage of down-scaling the channel length of OTFTs using the preferred bottom-gate bottom-contact (BGBC) architecture toward circuit application can be achieved using photolithography process. Among the handful of the solution-processed polymer dielectrics used for OTFT fabrication, poly-(methyl methacrylate) (PMMA) is the most widely studied polymer dielectric due to its excellent electrical and physio-chemical properties. However, incompatibility of pristine PMMA to the photoresists and the relevant solvents associated with photo-lithography process, limits its application as a gate dielectric layer in BGBC configuration for practical purposes. In this work, a novel approach to perform conventional photolithography process directly over the pristine PMMA gate dielectric layer is introduced without using any high-temperature/cross-linking method, capping layer, or chemical modification of pristine PMMA. Metal-insulator-metal (MIM) devices based on pristine PMMA is fabricated and characterized to ensure no degradation to the dielectric during the photolithography process steps. Finally the array of sub-10 µm channel length BGBC-OTFTs with isolated gate using pristine PMMA as a gate dielectric and poly-(3-hexylthiophene) (P3HT) as a solution-processed organic semiconductor is developed. The electrical characterization and stability behaviour of the devices will be discussed in this presentation. Photo-response of the OTFT in terms of responsivity and sensitivity will also be discussed at the end to realize its potential towards efficient photo-detection.