We demonstrated analog memory, synaptic plasticity, and a spike-timing-dependent plasticity (STDP) function with a nanoscale titanium oxide bilayer resistive switching device with a simple fabrication process and good yield uniformity. We confirmed the multilevel conductance and analog memory characteristics as well as the uniformity and separated states for the accuracy of conductance change. Finally, STDP and a biological triple model were analyzed to demonstrate the potential of titanium oxide bilayer resistive switching device as synapses in neuromorphic devices. By developing a simple resistive switching device that can emulate a synaptic function, the unique characteristics of synapses in the brain, e.g. combined memory and computing in one synapse and adaptation to the outside environment, were successfully demonstrated in a solid state device.

We report, for the first time, the novel concept of ultrathin (~10nm) W/NbO x /Pt device with both threshold switching (TS) and memory switching (MS) characteristics. Excellent TS characteristics of NbO 2, such as high temperature stability (~160 o C), fast switching speed (~22ns), good switching uniformity, and extreme scalability of device area (φ~10nm)/thickness (~10nm) were obtained. By oxidizing NbO 2 , we can form ultrathin Nb 2 O 5 /NbO 2 stack layer for hybrid memory devices with both TS and MS. Without additional selector device, 1Kb cross-point hybrid memory device without SET/RESET disturbance up to 10 6 cycles was demonstrated.

HfO2 is the one of the potential high-k dielectrics for replacing SiO2 as a gate dielectric. HfO2 is thermodynamically stable when in direct contact with Si and has a reasonable band gap (∼5.65eV). In this study, MOS capacitors (Pt/HfO2/Si) were fabricated by depositing HfO2 using reactive DC magnetron sputtering in the range of 33∼135Å followed by Pt deposition. During the HfO2 deposition, O2 flow was modulated to control interface quality and to suppress interfacial layer growing. By optimizing the HfO2 deposition process, equivalent oxide thickness (EOT) can be reduced down to ∼11.2 Å with the leakage current as low as 1X10−2 A/cm2 at +1.0V and negligible frequency dispersion. HfO2 films also show excellent breakdown characteristics and negligible hysteresis after high temperature annealing. From the high resolution TEM, there is a thin interfacial layer after annealing, suggesting a composite of Si-Hf-O with a dielectric constant of ≈ 2 X K SiO2.

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