Fig. 4
a Transition from STM to LTM of Au/Ti/HfAlOx/TiN-NP/HfAlOx/ITO RRAM device with the change of EPSC varying the spike number from 1 to 10 at the pulse voltage amplitude of ‒0.4 V/100 µs, along with the schematic of memory enhancement by repeated pulses. b EPSC gain (An/A1) plotted w.r.t. the pulse number at different pulse voltage from ‒0.3 V/100 µs to ‒0.7/100 µs V. c Synaptic plasticity EPSC measured with frequency from 2 to 100 Hz and d the EPSC gain (A10/A1) at pulse amplitude of ‒0.5 V/20 µs.