Record Resistance Ratio and Bipolar/Unipolar Resistive Switching Characteristics of Memory Device Using Germanium Oxide Solid Electrolyte

The bipolar and unipolar resistive switching characteristics of a memory device using a Cu filament in a new Cu/GeO x /W structure under low-voltage operation (<1.5 V) have been investigated. The germanium oxide (GeO x ) solid electrolyte with a thickness of approximately 12 nm has been observed by both high-resolution transmission electron microscopy (HRTEM) and energy-dispersive X-ray spectroscopy analyses. A small device size of 150×150 nm 2 has been observed by HRTEM. The composition of Ge:O has been investigated by X-ray photoelectron spectroscopy analysis. The memory device shows bipolar switching under current compliances of 1 nA–50 µA with a large SET voltage of approximately 0.5 V and unipolar switching with a larger current compliance of >100 µA. This memory device has excellent uniformity in SET/RESET voltages, low resistance state/high resistance state (LRS/HRS), long read endurance of >1×10 5 cycles, and good data retention of >1×10 4 s with high resistance ratios of >10 5 in the bipolar mode and >10 9 in the unipolar mode.