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 lowvoltage operation (<1:5 V) have been investigated. The germanium oxide (GeO _x) solid electrolyte with a thickness of approximately 12nm has been observed by both high-resolution transmission electron microscopy (HRTEM) and energy-dispersive X-ray spectroscopy analyses. A small device size of 150 × 150nm2 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 0.5V 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.