Memory Devices with HfO2 Charge-Trapping and TiO2 Channel Layers: Fabrication via Remote and Direct Plasma Atomic Layer Deposition and Comparative Performance Evaluation

With the improvement of integration levels to several nanometers or less, semiconductor leakage current has become an important issue, and oxide-based semiconductors, which have replaced Si-based channel layer semiconductors, have attracted attention. Herein, we fabricated capacitors with a metal–insulator–semiconductor–metal structure using HfO2 thin films deposited at 240 °C and TiO2 thin films deposited at 300 °C via remote plasma (RP) and direct plasma (DP) atomic layer deposition and analyzed the effects of the charge-trapping and semiconducting properties of these films. Charge-trapping memory (CTM) devices with HfO2 (charge-trapping layer) and TiO2 (semiconductor) films were fabricated and characterized in terms of their memory properties. Al2O3 thin films were used as blocking and tunneling layers to prevent the leakage of charges stored in the charge-trapping layer. For the TiO2 layer, the heat-treatment temperature was optimized to obtain an anatase phase with optimal semiconductor properties. The memory characteristics of the RP HfO2–TiO2 CTM devices were superior to those of the DP HfO2–TiO2 CTM devices. This result was ascribed to the decrease in the extent of damage and contamination observed when the plasma was spaced apart from the deposited HfO2 and TiO2 layers (i.e., in the case of RP deposition) and the reduction in the concentration of oxygen vacancies at the interface and in the films.