Characterization of switching parameters and multilevel capability in HfOx/AlOx bi-layer RRAM devices

HfO_x/AlO_x bi-layer RRAM devices were fabricated with the atomic layer deposition (ALD) method. Compared with the single-layer HfO_x devices, the bi-layer devices showed less variation of the switching voltages and resistances. Inspired by the fact that varying reset stop voltage in a DC sweep can achieve multilevel high resistance state, two equivalent pulse programming schemes were proposed: one linearly increases the reset pulse amplitudes; the other exponentially increases the reset pulse width. The transient current response waveform measurement suggests the former scheme is a more energy efficient programming method.