Investigation of X-Ray Total Ionizing Dose Effects in Multistate 1T1R RRAM Arrays
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The emerging resistive random-access memory (RRAM) technology is a potential candidate for space applications due to its ion-based switching operation, non-volatility, and multi-bit capability. RRAM-based memory cells are usually a combination of a standard nMOS transistor and one RRAM device (1T1R). However, since the standard transistor is crucial to select the cell and control current compliance, especially for multistate applications, it represents the primary vulnerability to total ionizing dose (TID) effects due to radiation-induced charge trapping in the oxide. Therefore, the standard transistor can be replaced with a radiation-hardened-by-design (RHBD) device, the enclosed layout transistor (ELT), known for its effectiveness in mitigating TID effects. This work investigates the reliability of the radiation-hardened 9-by-4 1T1R array under X-ray radiation. The devices under study were fabricated using IHP’s 130 nm BiCMOS technology node, presenting a back-end-of-line (BEOL) integrated metal-insulator-metal (MIM) stack composed of TiN/Al:HfO2/Ti/TiN. The RRAM array was evaluated through periodic read operations under X-ray radiation up to an accumulated dose of 1000 krad(Si), which has been programmed into four resistance states. Experimental results validate the proposed non-volatile memory, as no significant increase in off-state leakage current or threshold voltage shifts were observed in the transistor. Furthermore, the array exhibited high stability across the resistance states, maintaining clear state separation without resistance drift throughout the irradiation process. In addition, post-irradiation transfer characteristics remained consistent with pre-irradiation data, confirming that switching mechanisms and reprogramming capabilities were preserved. Although these results are preliminary with respect to ongoing γ-ray test, they demonstrate favorable outcomes and progress toward robust RHBD memory for space applications. Future work will also focus on the set and reset operations under X-ray. This work was financially supported by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Project 551916740.