Jung Won Seo

Transparent resistive random access memory and its characteristics for nonvolatile resistive switching

This report covers the fabrication of a fully transparent resistive random access memory (TRRAM) device based on an ITO (indium tin oxide)/ZnO/ITO capacitor structure and its resistive switching characteristics. The fabricated TRRAM has a transmittance of 81% (including the substrate) in the visible region and an excellent switching behavior under 3V. The retention measurement suggests that the memory property of the TRRAM device could be maintained for more than 10years. We believe that the TRRAM device presented in this work could be a milestone of future see-through electronic devices.

Transparent flexible resistive random access memory fabricated at room temperature

We report the room temperature fabrication of highly transparent and flexible resistive random access memory devices based on an ITO (indium tin oxide)/ZnO (zinc oxide)/ITO/Ag/ITO capacitor structure on a polyethersulfone flexible substrate. The ITO/Ag/ITO multilayered bottom electrode provides superior flexibility as well as high transparency compared to devices with ITO single bottom electrode during repetitive bending tests. The devices exhibit a high transmittance and the excellent reliability of data retention. Moreover, they show consistent memory performance, even under thermal stress. The results of this study provide a breakthrough solution for the era of transparent and flexible electronic systems in the near future.

A ZnO cross-bar array resistive random access memory stacked with heterostructure diodes for eliminating the sneak current effect

We report cross-bar array resistive random access memory (RRAM) devices based on a ZnO thin film fabricated at room temperature. To prevent the sneak current path in a conventional cross-bar array device, two types of heterostructure diodes, a NiO/ZnO p-n junction and a WO3/ZnO tunnel barrier both stacked on cross-bar array RRAM were employed. With rectifying characteristics and high forward current density, the sneak current path was effectively eliminated. We believe that the proposed structures are promising for cross-bar type RRAM applications.

Tungsten oxide as a buffer layer inserted at the SnO2/p-a-SiC interface of pin-type amorphous silicon based solar cells

A thermally evaporated p-type amorphous tungsten oxide (p-a-WO3) film was introduced as a buffer layer between SnO2 and p-type amorphous silicon carbide (p-a-SiC) of pin-type amorphous silicon based solar cells. Using the Schottky barrier model, it is shown that the p-a-WO3 layer lowered the Schottky barrier height, which enhanced the open circuit voltage and the blue response compared to a bufferless cell. By inserting a 2-nm-thick p-a-WO3 layer between SnO2 and an 8-nm-thick p-a-SiC layer, the conversion efficiency was increased by 7.3% compared to the optimized bufferless cell only with a 10-nm-thick p-a-SiC window layer.

Evidence of Al induced conducting filament formation in Al/amorphous silicon/Al resistive switching memory device

We demonstrated that an Al/p-type amorphous silicon (p-a-Si)/Al switching device exhibits stable, nonvolatile resistive switching characteristics as well as reliable data retention at 85 °C. It is directly observed that the conducting filament is created after electroforming and incorporates the top metal migrated or diffused into a-Si layer. In addition, by analyzing the constitution of the conducting filament, we investigated the microscopic nature of the conducting filament. These results suggest that the Al/p-a-Si/Al device has potential for future nonvolatile memory applications.

Tunable work function of a WOx buffer layer for enhanced photocarrier collection of pin-type amorphous silicon solar cells

An in situ postdeposition ultraviolet treatment was proposed to improve the electrical properties of a tungsten oxide (WOx) buffer layer of pin-type amorphous silicon-based solar cell. Based on the x-ray and ultraviolet photoelectron spectroscopy and the activation energy measurements, it was found that the work function of WOx is tunable by ultraviolet light treatment, and the collection performance of solar cells incorporating WOx with the lower work function is further improved. Moreover, the optimal band alignment scheme for a window layer is discussed in terms of obtaining enhanced carrier collection without open circuit voltage degradation.