Low-Temperature Deposition of Inorganic–Organic HfO₂–PMMA Hybrid Gate Dielectric Layers for High-Mobility ZnO Thin-Film Transistors

Low-temperature solution-processed inorganic–organic hybrid gate dielectrics are considered as emerging candidates for future low-cost flexible electronic devices, which are alternatives to high-temperature inorganic-based gate dielectric materials. In the present work, we developed a novel inorganic–organic HfO2–PMMA hybrid dielectric material by an efficient eco-friendly sol–gel method, deposited by spin-coating technique and converted into dielectric thin films at a very low thermal annealing temperature of 185 °C. The HfO2–PMMA hybrid thin-film formation was systematically investigated by FTIR and XPS techniques. Subsequently, a very low surface roughness of 0.8 nm and high uniformity of hybrid thin films were observed by tapping-mode AFM. Also, the thin films showed a hydrophilic nature with a high surface energy of 59.9 mJ/m2 as observed by the contact angle technique. The insulating properties of this hybrid film, studied by C–V and I–V measurements, showed very low leakage current density under 1 nA/cm2 at −5 V, high gate capacitance of 106 nF/cm2, and high dielectric constant of 11.3 at 1 kHz. With such dielectric properties, the hybrid thin films were tried as dielectric gate layers in room-temperature-sputtered ZnO thin-film transistors (TFTs). As-fabricated devices achieved low operating voltage, less than 5 V, with high saturation field effect mobility of 15.5 cm2 V–1 s–1, very low threshold voltage of 0.5 V, high on/off current ratio of 106, and low subthreshold slope of 0.37 V/dec. These results reveal the promising application of the HfO2–PMMA hybrid material as the gate dielectric for the fabrication of ZnO-based TFTs at low temperature.