ABSTRACT
Resistive random access memory (R-RAM) denotes all of the random access memories that rely on the resistance differences to store data. Usually, a R-RAM storage device has a sandwich metal–insulator– metal structure. Filament is a key word when describing the conduction of R-RAM. A filament is not a traditional conducting material such as a metal or a transportation carrier of a semiconductor. Unipolar operation executes programming/erasing by using short/long pulses or by using high/low voltage with the same voltage polarity. The threshold voltage is usually defined for R-RAM material that represents the state transition point. Once the supplying voltage surpasses the threshold voltage, the resistance could change abruptly. This is a continuous process, but the transition is usually completed in a short period of time; that is, less than a nanosecond. For the high density requirement, the crossbar array structure is dominant in R-RAM design, and 3D stacking can further improve the memory capacity within the given area constraint.
