Solution Processable High Dielectric Constant Nanocomposites Based on ZrO2 Nanoparticles for Flexible Organic Transistors

A solution-based strategy for fabrication of high dielectric constant (kappa) nanocomposites for flexible organic field effect transistors (OFETs) has been developed. The nanocomposite was composed of a high-kappa polymer, cyanoethyl pullulan (CYELP), and a high-kappa nanoparticle, zirconium dioxide (ZrO2). Organic field effect transistors (OFETs) based on neat CYELP exhibited anomalous behavior during device operation, such as large hysteresis and variable threshold voltages, which yielded inconsistent devices and poor electrical characteristics. To improve the stability of the OFET, we introduced ZrO2 nanoparticles that bind with residual functional groups on the high-kappa polymer, which reduces the number of charge trapping sites. The nanoparticles, which serve as physical cross-links, reduce the hysteresis without decreasing the dielectric constant. The dielectric constant of the nanocomposites was tuned over the range of 15.6-21 by varying the ratio of the two components in the composite dielectrics, resulting in a high areal capacitance between SI and 74 nF cm(-2) at 100 kHz and good insulating properties of a low leakage current of 1.8 X 10(-6) A cm(-2) at an applied voltage of -3.5 V (0.25 MV cm(-1)). Bottom-gate, top-contact (BGTC) low operating voltage p-channel OFETs using these solution processable high-kappa nanocomposites were fabricated by a contact film transfer (CET) technique with poly(3-heicylthiophene) (P3HT) as the charge transport layer. Field effect mobilities as high as 0.08 cm(2) V-1 s(-1) and on/off current ratio of 1.2 X 10(3) for P3HT were measured for devices using the high-kappa dielectric ZrO2 nanocomposite. These materials are promising for generating solution coatable dielectrics for low cost, large area, low operating voltage flexible transistors.