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 degrees 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/m(2) 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/cm(2) at -5 V, high gate capacitance of 106 nF/cm(2), 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 cm(2) V(-1)s(-1), very low threshold voltage of 0.5 V, high on/off current ratio of 10(6), 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.