A Forming-Free Bipolar Resistive Switching in HfO_x-Based Memory with a Thin Ti Cap

The electroforming process of Ti/HfO_x stacked RRAM devices is removed via the combination of low temperature atomic layer deposition and post metal annealing. The Pt/Ti/HfO_x/Pt RRAM devices show a forming-free bipolar resistive switching behavior. By x-ray photoelectron emission spectroscopy analysis, it is found that there are many oxygen vacancies and nonlattice oxygen pre-existing in the HfO_x layer that play a key role in removing the electroforming process. In addition, when the thickness ratio of the Ti and HfO_x layer is 1, the uniformity of the switching parameters of Pt/Ti/HfO_x/Pt devices is significantly improved. The OFF/ON window maintains about 100 at the read voltage of 0.1 V.