Polymer dielectric materials for organic thin-film transistors: Interfacial control and development for printable electronics

Organic thin-film transistors (OTFTs) have been extensively studied for organic electronics. In these devices, organic semiconductor-dielectric interface characteristics play a critical role in influencing OTFT operation and performance. This study begins with exploring how the physicochemical characteristics of the polymer gate dielectric affects the thin-film growth mode, microstructure, and OTFT performance parameters of pentacene films deposited on bilayer polymer (top)-SiO2 (bottom) dielectrics. Pentacene growth mode varies considerably with dielectric substrate, and correlations are established between pentacene film deposition temperature, the thin-film to bulk microstructural phase transition, and OTFT device performance. Furthermore, the primary influence of the polymer dielectric layer glass transition temperature on pentacene film microstructure and OTFT response is shown for the first time.;Following the first study, the influence of the polymer gate dielectric viscoelastic properties on overlying organic semiconductor film growth, film microstructure, and TFT response are investigated in detail. From the knowledge that nanoscopically-confined thin polymer films exhibit glass transition temperatures that deviate substantially from those of the corresponding bulk materials, pentacene (p-channel) and cyanoperylene (n-channel) films grown on polymer gate dielectrics at temperatures well-below their bulk glass transition temperatures (Tg(b)) have been shown to exhibit morphological/microstructural transitions and dramatic OTFT performance discontinuities at well-defined temperatures (defined as the polymer "surface glass transition temperature," or Tg(s)). These transitions are characteristic of the particular polymer architecture and independent of film thickness or overall film cooperative chain dynamics. Furthermore, by analyzing the pentacene films grown on UV-curable polymer dielectrics with different curing times (hence, different degrees of crosslinking), clear correlations between pentacene film deposition temperature, degree of polymer dielectric film crosslinking, and the corresponding pentacene film growth mode, phase composition, and carrier mobilities are established. Based on the results, TFT measurements have been demonstrated to represent a new and sensitive methodology to probe polymer surface viscoelastic properties as well as the degree of polymer dielectric film crosslinking.;In the final study, the synthesis and dielectric properties of optimized crosslinked polymer blend (CPB) dielectrics for printable TFTs are reported. Novel silane crosslinking reagents with tuned reactivity enable the fabrication of CPB films having excellent quality and tunable thickness, fabricated both by spin-coating and gravure-printing. The CPB dielectric films fabricated by blending crosslinking reagent with poly(4-vinyl)phenol (PVP) require very low-curing temperatures (∼110°C), tenaciously adhere to a variety of TFT gate contact materials and exhibit excellent insulating properties with tunable capacitance values. The CPB film quality is correlated with the PVP-crosslinking reagent reactivity. Devices fabricated with both p- and n-channel organic semiconductors on the CPB dielectrics function at low operating voltages and the device performance is strongly correlated with the morphology and microstructure of the representative semiconductor films.