All-Inorganic Bismuth Halide Perovskite-Like Materials ABiI and ABiNaI (A = Rb and Cs) for Low-Voltage Switching Resistive Memory.

As silicon-based metal oxide semiconductor field effect transistors get closer to their scaling limit, the importance of resistive random-access memory devices increases due to their low power consumption, high endurance and retention performance, scalability, and fast switching speed. In the last couple of years, organic-inorganic lead halide perovskites have been used for resistive switching applications, where they outperformed conventional metal oxides in terms of large on/off ratio and low power consumption. However, there were scarce reports on lead-free perovskites for such applications. In this report, we prepared lead-free Au/ABiI/Pt/Ti/SiO/Si (A is either Cs or Rb) devices and tested their resistive switching characteristics. They showed a forming step prior to repeating switching, low operating voltage (0.09 V for RbBiI and 0.1 V for CsBiI), large on/off ratio (>10), relatively high endurance (200 cycles for RbBiI and 400 cycles for CsBiI cycles), and high retention (1000 s). Such low voltage could be explained by grain boundary-modulated ion drift. Difference in endurance was speculated to be due to the difference in the surface roughness of films because CsBiI films are smoother. To get rid of the forming step, 10% of the Bi cations were substituted with Na cations. However, this method only worked on Rb-based structures. This phenomenon was explained by the defect formation energy, which can only be negative in a corner-sharing RbBiI structure compared to a face-sharing octahedral CsBiI structure. As a result, the forming step was removed, and 100 cycles endurance and 1000 s retention performance were obtained. Similarly, the lower endurance is suspected to be due to the poor surface quality of the film.