Solution-processed lanthanum-doped Al2O3 gate dielectrics for high-mobility metal-oxide thin-film transistors

Solution-processed oxide gate dielectrics play an important in thin-film transistors (TFTs), determining their operation voltage, device performance and power consumption. Up to now, various solution-processed oxide gate dielectrics such as aluminum oxide (Al2O3) have been surveyed, however, they generally exhibit relatively high leakage current, low dielectric constant, and hysteresis which are unfavorable for stable device operation. Here, we demonstrate solution-processed lanthanum (La)-doped Al2O3 (LAO) gate dielectrics which exhibit low leakage current density, high dielectric constant, and relatively small frequency-dependent capacitance variation. In order to find the optimal doping concentration of lanthanum in Al2O3 film, various electrical, morphological, and spectroscopic analyses were carried out. We found that the addition of lanthanum in Al2O3 film effectively reduced the defective metal hydroxide bonding states within the film and significantly enhanced its dielectric characteristics. At an optimal doping concentration of lanthanum (20 at.%), gate dielectrics showing leakage current density, dielectric constant, and breakdown field of ~10−8 A/cm2 (at 2 MV/cm), 10.5, and >5 MV/cm were obtained. Using the LAO film as a gate dielectric, solution-processed indium-zinc-oxide TFTs having a field-effect mobility of 11.9 cm2/V-s, subthreshold slope of 0.38 V/dec, and on/off ratio of 104-105 were demonstrated.