The resistive switching behavior of cesium bromide and cesium iodide RRAM devices effectively suppresses current in the off state due to their inherent insulating properties. The addition of a thin layer of molybdenum trioxide improves the stability and electrical properties of the devices. The switching mechanism in these devices is dominated by silver conducting filaments, with a very low switching voltage (<0.18 V), extremely long retention time (>106 s), excellent endurance cycling (>105 cycles), and fast switching speed (<200 ns). The team also tested the multi-level storage capability of these devices using different compliance currents and applied them to MNIST handwritten recognition network testing, achieving a recognition rate of over 90%.
In contrast, the resistive switching mechanism in yttrium trifluoride RRAM devices is dominated by fluoride ion vacancies due to its amorphous structure, which prevents silver ions from effectively passing through. This device has two operating modes and can serve as both analog and digital memory. It also has a long retention time (>105 s) and stable endurance cycling. Notably, the retention time performance of the yttrium trifluoride RRAM devices is even better (>106 s) when used for multi-level storage, achieving a high on/off ratio of 7.2 and a very high recognition rate of 97% in MNIST handwritten recognition network testing.
Lead-free metal halide RRAM devices may have different operating mechanisms due to their crystal phase, but they all exhibit excellent performance, indicating their potential value in memory applications and the possibility of breaking through the von-Neumann bottleneck.