Air Stable Cross-Linked Cytop Ultrathin Gate Dielectric for High Yield Low-Voltage Top-Gate Organic Field-Effect Transistors

Abstract

Wedemonstrate the use of a cross-linking chemistry for an amorphous fluoropolymer gate dielectric, poly(perfluorobutenylvinylether) commercially known as Cytop. Spin-coated films of Cytop exhibit good gate insulating properties as well as provide excellentOFET operational stability.However, these devices operate at large voltages because the dielectric layer thickness is typically ∼450-600 nm.When the thickness of a Cytop dielectric layer is decreased below 200 nm, the device yields are dramatically reduced due to pinhole formation. Our new cross-linked Cytop (C-Cytop) formulation deposited by spin-coating enables uniform thin films on top of various organic semiconductors that exhibits lowgate leakage current densities (<10 nA mm-2) and high dielectric breakdown strengths (>2 MV cm-1). Our approach results in C-Cytop dielectric films as thin as 50 nm, thus allowing the fabrication of reliable p- and n-channel top-gateOFETs operating at very low-voltages (<5 V).Themost remarkable properties of this new C-Cytop gate dielectric are the excellent device yields (∼100%) for thicknesses <100 nm and the dramatically reduced sensitivity to the underlying semiconductor film morphology. This new approach represents a significant advance compared to cross-linked PMMA films (C-PMMA) and other nonfluorinated polymer dielectrics on identical test structures. Furthermore, C-Cytop-based OFETs exhibit reduced bias stress and better air stability with respect to C-PMMA because of the inert perfluorinated chemical structure of this polymer. Finally, direct spectroscopic evidence of the cross-linking processwas obtained by Fourier transform infrared (FTIR) spectroscopy, demonstrating complete reaction in air and at room temperature.