Densely cross-linked polysiloxane dielectric for organic thin-film transistors with enhanced electrical stability
Journal
Journal of Materials Chemistry C
Date
2019.05.21
Abstract
A solution-processible organic？inorganic hybrid material consisting of polysiloxane urethane acrylate composite (PSUAC) with a dual cross-linking mechanism was developed, which satisfy all the requirements for use as a gate dielectric for flexible organic thin-film transistors (OTFTs). PSUACs incorporate urethane group for promoting adhesion to substrates and acrylate group for enhancing the degree of cross-linking via a photo-curing reaction. Aluminium acetoacetate is introduced as a thermal curing agent that reacts with the silanols at the end of the PSUA resin, thus realizing a reliable dielectric that is barely affected by the slow polarization induced by moisture absorption. Thin films of cross-linked PSUAC provided smooth surfaces with a root-mean-square roughness of < 0.3 nm and which exhibited high breakdown voltages of > 6.2 MV cm？1, while the capacitance was only slightly affected by the frequency. A self-assembled monolayer (SAM) of octadecytrichlorosilane (ODTS) was formed on the cross-linked PSUAC dielectric to provide a hydrophobic surface with a water-contact angle of 107°. OTFTs employing a small-molecule organic semiconductor of dibenzothiopheno[6,5-b:6′,5′-f]thieno[3,2-b]thiophene (DBTTT) were fabricated using the cross-linked PSUAC as a gate dielectric. These realized a high mobility of 3.3 cm2 V-1 s-1 and an on/off ratio of > 107 without any hysteresis in the transfer characteristics. The threshold voltage was shifted about 2 V in the bias stress measurement conducted for 10,000 sec on non-passivated devices exposed in air, verifying the stable characteristics of the gate dielectric layer even without passivation of the device. Flexible OTFTs on polyimide (PI) substrate were fabricated and identical electrical properties with a mobility of 3.3 cm2 V-1 s-1 were confirmed. PSUAC can be used as a reliable gate dielectric for high-performance OTFT devices including flexible applications.