In
this study, we fabricate and characterize a Ti/TiO2/Si
device with different dopant concentrations on a silicon surface
for neuromorphic systems. We verify the device stack using transmission
electron microscopy (TEM). The Ti/TiO2/p++Si
device exhibits interface-type bipolar resistive switching with long-term
memory. The potentiation and depression by the pulses of various amplitudes
are demonstrated using gradual resistive switching. Moreover, pattern-recognition
accuracy (>85%) is obtained in the neuromorphic system simulation
when conductance is used as the weight in the network. Next, we investigate
the short-term memory characteristics of the Ti/TiO2/p+Si device. The dynamic range is well-controlled by the pulse
amplitude, and the conductance decay depends on the interval between
the pulses. Finally, we build a reservoir computing system using the
short-term effect of the Ti/TiO2/p+Si device,
in which 4 bits (16 states) are differentiated by various pulse streams
through the device that can be used for pattern recognition.
In this work, we emulate biological synaptic properties such as long-term plasticity (LTP) and short-term plasticity (STP) in an artificial synaptic device with a TiN/TiO2/WOx/Pt structure. The graded WOx layer with oxygen vacancies is confirmed via X-ray photoelectron spectroscopy (XPS) analysis. The control TiN/WOx/Pt device shows filamentary switching with abrupt set and gradual reset processes in DC sweep mode. The TiN/WOx/Pt device is vulnerable to set stuck because of negative set behavior, as verified by both DC sweep and pulse modes. The TiN/WOx/Pt device has good retention and can mimic long-term memory (LTM), including potentiation and depression, given repeated pulses. On the other hand, TiN/TiO2/WOx/Pt devices show non-filamentary type switching that is suitable for fine conductance modulation. Potentiation and depression are demonstrated in the TiN/TiO2 (2 nm)/WOx/Pt device with moderate conductance decay by application of identical repeated pulses. Short-term memory (STM) is demonstrated by varying the interval time of pulse inputs for the TiN/TiO2 (6 nm)/WOx/Pt device with a quick decay in conductance.
In this work, we propose a self-rectifying Ni/SiNx/HfO2/p++Si resistive memory device to alleviate the sneak-path current occurring in crossbar array. The bilayer (Ni/SiNx/HfO2/p++Si) device exhibits a much higher rectification ratio (>104) in the low-resistance state for DC sweep mode and pulse mode than single-layer devices (Ni/SiNx/p++Si and Ni/HfO2/p++Si). The suppressed current of the bilayer device can be explained by the high Schottky barrier of the HfO2 layer under a negative bias. The modified read bias scheme in the crossbar array structure ensures a large number of word line (∼3971 at a read margin of 10%) using the advantage of the high rectification of the bilayer device. The bilayer device with the proposed read bias scheme is promising for high-density memory applications.
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