Surface Modification on Solution Processable ZrO2 High‑k Dielectrics for Low Voltage Operations of Organic Thin Film Transistors

High quality zirconium oxide (ZrO2) high-k dielectrics have been fabricated by chemical solution processes. The ZrO2 thin films annealed at various temperatures were studied from microstructure properties to electric properties in detail. The dielectric film annealed at 700 °C features a smooth surface, low leakage current density (1.89 × 10–6 A/cm2 @ −3 MV/cm) and high dielectric constant (20). Organic thin film transistors (OTFTs) based on ZrO2 with different surface modifications were characterized to investigate the interfacial effects between the high-k dielectric and organic semiconductors. The OTFTs with poly­(α-methylstyrene) (PαMS) coated ZrO2 show much higher carrier mobility and on/off ratio than those with bare-ZrO2 or with hexamethyldisilazane-treated ZrO2. The ZrO2/PαMS layers offer a low surface energy to grow large crystals and benefit the charge transport in organic semiconductors, whereas the dielectric surface roughness and dipole scattering are less important. The resulting OTFTs show high current on/off ratio (1.2 × 105), low threshold voltage (−0.38 V), and low SS (0.26 V/dec). Our work has deepened the understanding on the complex interfacial effects between high-k dielectric and organic semiconductor. Finally, we demonstrate low temperature fabrication of ZrO2 -OTFTs on a flexible substrate, demonstrating solution processable high-k ZrO2 dielectric films offer great potentials for low-cost organic electronic devices, especially for low voltage organic electronic devices.