Fig. 2
From: Multi-level resistive switching in hafnium-oxide-based devices for neuromorphic computing
Illustration of spike-timing-dependent plasticity (STDP) and pulse timing. a STDP voltage profiles applied to a device. Δt is shifted consecutively for each data point in b. In the case of a two-terminal device, one of the profiles can be inverted, added to the other, and applied on only one of the electrodes instead of the two separate electrodes. In some demonstrations, the voltage profile was applied continuously, in others as a series of pulses, in yet others only as two rectangular pulses (one positive, one negative). b Schematic relative change of the device conductance G as a function of the time shift Δt in a. Often, ΔG is modelled according to the equations in the inset of b. c Timing illustration of filamentary switching as measured in [51]. After an initial delay Δtdelay after voltage application, the current increases rapidly during Δttrans until it reaches the compliance value. To achieve controlled filamentary multi-level RS, the timing and amplitude of the applied voltage pulse has to be such that it stops during the rapid current transition