Flexible high capacitance nanocomposite gate insulator for printed organic field-effect transistors

Ceramic-polymer nanocomposite dielectric consisting of an epoxy solution with propylene glycol methyl ether acetate as the solvent and barium titanate nanoparticles with capacitance in excess of 60 pF/mm² was developed and utilized as the gate insulator for organic field-effect transistors (OFETs). The high relative permittivity (κ = 35), bimodal nanocomposite utilized had two different filler particle sizes 200 nm and 1000 nm diameter particles. Bottom gate organic filed-effect transistors were demonstrated using a commercially available printing technology for material deposition. A metal coated plastic film was used as the flexible gate substrate. Solution processable, p-type arylamine-based amorphous organic semiconductor was utilized as the active layer. Fabricated OFETs with the solution processed nanocomposite dielectric had a high field-induced current and a low threshold voltage; these results suggest that the low operating voltage was due to the high capacitance gate insulator. In this paper, we review the characteristics of the nanocomposite dielectric material and discuss the processing and performance of the printed organic devices.     

Vacuum lamination approach to fabrication of high-performance single-crystal organic field-effect transistors

A novel vacuum lamination approach to fabrication of high-performance single-crystal organic field-effect transistors has been developed. The non-destructive nature of this method allows a direct comparison of field-effect mobilities achieved with various gate dielectrics using the same single-crystal sample. The method also allows gating delicate systems, such as n -type crystals and SAM-coated surfaces, without perturbation.     

Charge transport physics of conjugated polymer field-effect transistors

Field‐effect transistors based on conjugated polymers are being developed for large‐area electronic applications on flexible substrates, but they also provide a very useful tool to probe the charge transport physics of these complex materials. In this review we discuss recent progress in polymer semiconductor materials, which have brought the performance and mobility of polymer devices to levels comparable to that of small‐molecule organic semiconductors. These new materials have also enabled deeper insight into the charge transport physics of high‐mobility polymer semiconductors gained from experiments with high charge carrier concentration and better molecular‐scale understanding of the electronic structure at the semiconductor/dielectric interface.     

Ultra-thin films of polysilsesquioxanes possessing 3-methacryloxypropyl groups as gate insulator for organic field-effect transistors

Polysilsesquioxanes (PSQs) possessing 3-methacryloxypropyl groups as an organic moiety of the side chain were synthesized by sol-gel condensation copolymerization of the corresponding trialkoxysilanes. The ultra-thin PSQ film with a radical initiator and a cross-linking agent was prepared by a spin-coating method, and the film was cured integrally at low temperatures of less than 120 °C through two different kinds of polymeric reactions, which were radical polymerization of vinyl groups and sol-gel condensation polymerization of terminated silanol and alkoxy groups. The obtained PSQ film showed the almost perfect solubilization resistance to acetone, which is a good solvent of PSQ before polymerization. It became clear by atomic force microscopy observation that the surface of the PSQ film was very smooth at a nano-meter level. Furthermore, pentacene-based organic field-effect transistor (OFET) with the PSQ film as a gate insulator showed typical p-channel enhancement mode operation characteristics and therefore the ultra-thin PSQ film has the potential to be applicable for solution-processed OFET systems.