Impact of electrically formed interfacial layer and improved memory characteristics of IrO(x)/high-κ(x)/W structures containing AlO(x), GdO(x), HfO(x), and TaO(x) switching materials

Improved switching characteristics were obtained from high-κ oxides AlO(x), GdO(x), HfO(x), and TaO(x) in IrO(x)/high-κ(x)/W structures because of a layer that formed at the IrO(x)/high-κ(x) interface under external positive bias. The surface roughness and morphology of the bottom electrode in these devices were observed by atomic force microscopy. Device size was investigated using high-resolution transmission electron microscopy. More than 100 repeatable consecutive switching cycles were observed for positive-formatted memory devices compared with that of the negative-formatted devices (only five unstable cycles) because it contained an electrically formed interfacial layer that controlled ‘SET/RESET’ current overshoot. This phenomenon was independent of the switching material in the device. The electrically formed oxygen-rich interfacial layer at the IrO(x)/high-κ(x) interface improved switching in both via-hole and cross-point structures. The switching mechanism was attributed to filamentary conduction and oxygen ion migration. Using the positive-formatted design approach, cross-point memory in an IrO(x)/AlO(x)/W structure was fabricated. This cross-point memory exhibited forming-free, uniform switching for >1,000 consecutive dc cycles with a small voltage/current operation of ±2 V/200 μA and high yield of >95% switchable with a large resistance ratio of >100. These properties make this cross-point memory particularly promising for high-density applications. Furthermore, this memory device also showed multilevel capability with a switching current as low as 10 μA and a RESET current of 137 μA, good pulse read endurance of each level (>10(5) cycles), and data retention of >10(4) s at a low current compliance of 50 μA at 85°C. Our improvement of the switching characteristics of this resistive memory device will aid in the design of memory stacks for practical applications.