Resistive random access memory (RRAM) has emerged as a promising candidate for next-generation nonvolatile memory (NVM) due to its low-voltage operation, fast switching speed and high-density integration . Two common resistive switching (RS) modes in RRAM are unipolar and bipolar modes . A unipolar RRAM in series with a rectifying diode, so-called one diode-one resistor (1D1R) cell, is particularly attractive for high-density applications because of the minimal 4F 2 cell size . However, high RESET current (I RESET) impedes the cell size scaling in 1D1R array. Recently, we have demonstrated a reliable Ni/HfO 2/Si unipolar RRAM, fully compatible with the Si technology [4, 5]. In this paper, we show that unipolar HfO 2 RRAM exhibits excellent NVM characteristics promising for low-I RESET, low-power operation in the future high-density 1D1R array. In addition, we show that the RS mode can be tailored by a bottom interfacial layer of Al 2O 3 between HfO 2 and Si. New evidence on the location of filament connections/ruptures and RS mechanism will be discussed in details.