Photo-crosslinkable polymer gate dielectrics for hysteresis-free organic field-effect transistors with high solvent resistance
Poly(N-(4-hydroxyphenyl)maleimide-co-4-vinylphenol) (PHPMIVP) and its derivatives were developed for polymer gate dielectrics exhibiting high chemical resistance to various organic solvents and hysteresis-free operations in FET. PHPMIVP were modified with photo-reactive side-groups including cinnamoyl (PHPMIVP-C), methacroyl (PHPMIVP-M) or 4-(6-(7-coumarinyloxyl)hexyloxy)benzoyl (PHPMIVP-CHB). Especially, PHPMIVP-CHB exhibited high thermal stability and very strong chemical resistance to various organic solvents including acetone, THF, tetraline, chloroform and chlorobenzene, which allow forming dielectric layers and semiconducting layers by sequential spin-casting processes without deterioration of device performance. Neither breakdown-voltage shift nor change in the leakage current density curve was observed after treating PHPMIVP-CHB film with various organic solvents, photoresist stripper (PRS2000) or Au etchant (KI solution). The field-effect transistors fabricated by sequential spin-casting of PHPMIVP-CHB insulating layers and PQTBTz-C12 semiconducting layers showed charge mobility with μFET = 0.029 cm2 V−1 s−1 and on/off ratio = 106 which are almost 10 times better than those of PQTBTz-C12 FETs fabricated on other polymers such as PHPMIVP, PHPMIVP-C and PHPMIVP-M.