To combat the large variability problem in RRAM,current compliance elements are commonly used to limit the inrush current during the forming operation. Regardless of the compliance implementation (1R-1R or 1T-1R), some degree of current overshoot is unavoidable. It is commonly believed that the peak value of the overshoot current is the most important factor affecting filament characteristics. This peak is linked to the parasitic capacitance of the test structure - larger parasitics lead to larger peak amplitudes. The widely reported detrimental effects of higher parasitic capacitance on the filament seems to support this concept. However, this understanding is inconsistent with the recent successes of compliance- free ultra-short pulse forming where a maximum peak current is guaranteed. In this work, using detailed circuit analysis and experimental measurements of 1R-1R and 1T-1R structures, we show that the overshoot amplitude is not dependent on the parasitic capacitance. Instead, it is the overshoot duration that depends most strongly on the parasitic capacitance. Thus, the impact of higher parasitic capacitance on the filament is due to overshoot duration rather than overshoot amplitude. In ultra-short pulse forming, the overshoot duration is always less than the applied pulse duration. Armed with the new insight on the importance of overshoot duration, the demonstrated success of ultra-short pulse forming becomes easier to understand.
Citation: IEEE Transactions on Electron Devices
Pub Type: Journals
Current overshoot, forming, Resistive random access memory (RRAM), short pulse switching, switching variability.