Fig. 4
a A simplified diagram of a biological synapses based on Pt/a-HfSiOx/TaN memristor with two terminal structures. b I–V characteristics were replicated for 100 cycles before implement of biological synapses. c Gradual reset method using positive sweeping voltages that are increased (+ 1.0 V to + 1.7 V, step value = 0.01 V). d Variations in conductance levels during a string of successful sweeps. e Gradual set with CC increased (0.2 mA to 2 mA with a 0.01 mA increment) while the set operation is in progress. f Modifications to conductance levels by CC control during set-process. The 30 negative pulses followed by 30 positive pulses, each with variable g pulse width and h pulse amplitude features of potentiation and depression. i A Pt/a-HfSiOx/TaN memristor with a high pulse amplitude of − 1.1 V/100 µs for potentiation and + 1.2 V/200 µs for depression produced synaptic weight update nonlinearity