Can anyone tell me how to decide the area of the memristor cell. What considerations should I take while deciding on the area of memristor in sky130B. And how small could I go in terms of area ?

The minimum size is determined by the RERAM layer itself, which is 0.23um x 0.23um with a minimum spacing of 0.23. I don't know if it's physically possible to make an array at minimum width and space.

Usually memory cells are of unique size, because any geometrical differencies change the behavior of the cell and heavy characterization is needed. Moreover process is tuned to have a working cell. Making it bigger or smaller will very likely lead to a non functional cell. At least this is my past experience as a memory designer. Sky130 might have different approaches.

@Stefan Schippers: It may be due to the experimental nature of the ReRAM process, but SkyWater really does have a "minimum width" rule on the ReRAM layer, like an implant, and not an "exact width" rule like a via. Like you, I would expect the dimension to have a large impact on the model, but for what it's worth, that's the way the rule is written in the ReRAM DRC deck and in the documentation. I would guess that the model is based on a minimum sized device of 0.23um x 0.23um, but I'm not sure.