Investigation of Vertical Current Phenomena in the Insulator/Oxide Semiconductor Heterojunction Using XPS Analysis and an Atmospheric-Pressure Plasma Treatment System

Transferring charge carriers through an insulator film between two metal electrodes is a major issue in various electronic devices, including metal/insulator/metal (MIM) diodes and resistive switching memories. Recently, a concept has been proposed that can unidirectionally control the direction and magnitude of the vertical current in a metal/insulator/oxide semiconductor/metal (MIOSM) structure by utilizing a bulk-limited conduction mechanism, which depends on the trap and subgap states in the insulator. This shows the potential to expand the processing window of conventional electronic devices, which follow the electrode-limited conduction mechanism, but is still insufficient to provide direct evidence that the flow of the electrical current in the MIOSM structure is due to the bulk-limited conduction within the insulator. In this study, we fabricated P++ Si/AlOx/Al (MIM) and P++ Si/AlOx/a-IGZO/Al (MIOSM) thin film diodes using a solution-processed aluminum oxide as an insulator layer, which has relatively rich subgap states. After the AlOx thin film was fabricated, atmospheric-pressure plasma (APP) treatment was performed for different times on the AlOx thin film. Through XPS analysis of AlOx, we confirmed the correlation between the atmospheric plasma treatment time on the insulator, and the defect state was thereby controlled. Furthermore, we observed that this correlation directly affects the I–V curves of MIM and MIOSM diodes. These results provide a clue for employing an approach of the current flow through an insulating film to applications such as rectifiers, switching devices, amplifiers, and oxide thin film diodes.