Homeothermic synaptic behaviors with a wide range of temperature were demonstrated in CMOS-compatible HfO _x /AlO _y memristors.

Atomic layer deposited (ALD) HfO₂/Al₂O₃/HfO₂ tri-layer resistive random access memory (RRAM) structure has been studied with a transparent indium tin oxide (ITO) transparent electrode. Highly stable and reliable multilevel conductance can be controlled by the set current compliance and reset stop voltage in bipolar resistive switching. Improved gradual resistive switching was achieved because of the interdiffusion in the HfO₂/Al₂O₃ interface where tri-valent Al incorporates with HfO₂ and produces HfAlO. The uniformity in bipolar resistive switching with I_on/I_off ratio (>10) and excellent endurance up to >10³ cycles was achieved. Multilevel conductance levels in potentiation/depression were realized with constant amplitude pulse train and increasing pulse amplitude. Thus, tri-layer structure-based RRAM can be a potential candidate for the synaptic device in neuromorphic computing.

In this letter, a bipolar resistive-switching random-access memory (RRAM) in Ni/Si₃N₄/SiO₂/p⁺-Si structure and its fabrication process are demonstrated. The proposed device with double-layer dielectrics consisting of Si₃N₄ layer (5 nm) as a resistive switching and SiO₂ (2.5 nm) layer for the tunnel barrier is investigated in comparison with that having a single layer of Si₃N₄. Double-layer cell shows ultra-low power operation under a compliance current (I_COMP) of 500 nA, which ensures the reset current (I_RESET) of sub-1 μA much lower than that of the single-layer cell. Also, large on/off ratio (∼10⁵) has been obtained since the SiO₂ layer efficiently suppresses the current in the high-resistance state. Moreover, maximum selectivity in double-layer cell is 122 when 1/2 read bias scheme is applied to the crossbar array. Highly nonlinear I-V characteristics of the double-layer Si₃N₄-based RRAM cell warrant the realization of selector-free RRAM cell in the crossbar array pursuing higher integration density.