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

Abstract

Zinc oxide (ZnO) was incorporated into metal-insulator-semiconductor (MIS) structures featuring high dielectric constant (high-κ) barium tantalate (BaTa 2 O 6 )or alumina (Al 2 O 3 )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 BaTa 2 O 6 and Al 2 O 3 structures were on the order of 10 −7 A/cm 2 . The trap density and trapped charge concentration at the BaTa 2 O 6 /ZnO interface were determined to be 6.18 × 10 11 eV −1 cm −2 and 5.82 × 10 11 cm −2 from conductance–voltage and capacitance–voltage measurements. At the Al 2 O 3 /ZnO interface the trap density and trapped charge were more than an order of magnitude smaller at 1.09 × 10 10 eV −1 cm −2 and 1.04 × 10 10 cm −2 respectively. The BaTa 2 O 6 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 BaTa 2 O 6 MIS structure. Overall, the results indicate that Al 2 O 3 would be better suited for transparent thin film transistors deposited at low temperature or without substrate heating.