Printable cross-linked polymer blend dielectrics. Design strategies, synthesis, microstructures, and electrical properties, with organic field-effect transistors as testbeds

We report here the synthesis and dielectric properties of optimized, cross-linked polymer blend (CPB) dielectrics for application in organic field-effect transistors (OFETs). Novel silane cross-linking reagents enable the synthesis of CPB films having excellent quality and tunable thickness (from 10 to ∼500 nm), fabricated both by spin-coating and gravure-printing. Silane reagents of the formula X₃Si-R-SiX₃ (R = -C ₆H₁₂- and X = Cl, OAc, NMe₂, OMe, or R = -C₂H₄-O-C₂H₄- and X = OAc) exhibit tunable reactivity with hydroxyl-containing substrates. Dielectric films fabricated by blending X₃Si-R-SiX₃ with poly(4-vinyl)phenol (PVP) require very low-curing temperatures (∼110°C) and adhere tenaciously to a variety of FET gate contact materials such as n ⁺-Si, ITO, and Al. The CPB dielectrics exhibit excellent insulating properties (leakage current densities of 10^-7 ∼ 10^-8 A cm^-2 at 2.0 MV/cm) and tunable capacitance values (from 5 to ∼350 nF cm^-2). CPB film quality is correlated with the PVP-cross-linking reagent reactivity. OFETs are fabricated with both p- and n-type organic semiconductors using the CPB dielectrics function at low operating voltages. The morphology and microstructure of representative semiconductor films grown on the CPB dielectrics is also investigated and is correlated with OFET device performance.