Photocurable organic gate insulator for the fabrication of high-field effect mobility organic transistors by low temperature and solution processing

Demand for inexpensive electronic devices has driven interest in organic semiconductors that can be deposited by simple, low-cost, solution-based processes.([1-7]) Moreover, this allows the use of flexible substrates such as plastics, opening a route for the development of flexible, thin film electronic devices and information displays with the advantages of light weight, low cost, and low-temperature processing, which is a much sought-after goal. The potential applications of organic semiconductors have generated intense research interest in organic thin film transistors (OTFTs). To form a well-defined interface between the organic semiconductor and the gate insulator during solution processing, the gate insulator should not be soluble in the solvent used to dissolve the organic semiconductor. Although thermal curing can be used to prepare insoluble organic gate insulators, a high temperature process is still necessary to complete the chemical crosslinking, and this process distorts the plastic substrate.([8]) Here we introduce a photo-curable organic gate insulator for OTFTs that allows low-temperature and solution-based processing and provides high field-effect mobility in the devices. This photo-curable organic insulator can be patterned easily to make connections (i.e. vertical interconnectivity via holes) between the gate electrodes and the underlying bus lines in integrated circuits. Ibis patterning is achieved using a simple conventional photolithography process (i.e. photo-irradiation through a photomask and developing), and does not require the complicated lithography process typically used to pattern via holes during OTFT array fabrication (i.e. photolithography using a photo-resist, oxygen plasma etching, and lift-off method). Therefore, use of the insulator described here can simplify the fabrication of integrated circuit devices. When we used this organic insulator in pentacene TFTs, we observed a high field-effect mobility of 0.5 cm(2) V-1 s(-1) without hysteresis, and an on/off current ratio of 1.7 x 10(7), when we used a polycrystalline pentacene with a bottom-contact geometry as the semiconductor.