Electrical and chemical analysis of zinc oxide interfaces with high dielectric constant barium tantalate and aluminum oxide in metal-insulator-semiconductor structures fabricated at Low temperatures

Zinc oxide (ZnO) was incorporated into metal-insulator-semiconductor (MIS) structures featuring high dielectric constant (high-κ) barium tantalate (BaTa2O6)or alumina (Al2O3)as the insulator, and the structures were electrically evaluated for potential applications in transparent thin film transistors. The ZnO films were deposited by radio-frequency magnetron sputtering at 100 °C whereas the dielectric films were deposited by the same method at room temperature. The leakage currents of both the BaTa2O6 and Al2O3 structures were on the order of 10−7A/cm2. The trap density and trapped charge concentration at the BaTa2O6/ZnO interface were determined to be 6.18 × 1011 eV−1 cm−2and 5.82 × 1011 cm−2 from conductance–voltage and capacitance–voltage measurements. At the Al2O3/ZnO interface the trap density and trapped charge were more than an order of magnitude smaller at 1.09 × 1010 eV−1 cm−2and 1.04 × 1010 cm−2 respectively. The BaTa2O6 structures had significantly larger frequency dispersions due to the larger number of interface traps. Chemical analysis using X-ray photoelectron spectroscopy with depth profiling indicates that acceptor type defects associated with a deficiency of oxygen are related to the observed electron trapping in the BaTa2O6MIS structure. Overall, the results indicate that Al2O3 would be better suited for transparent thin film transistors deposited at low temperature or without substrate heating.