Fig. 2

Neuron functions, “all-or-none”, “integrate”, and “integrate and fire”, implemented with a series resistance and a memristor. (a) “All-or-none” describes the “full response” of a neuron when the input signal is above a threshold. (b) Setup and input pulse shape for the “all-or-none” experimental measurement. (c) The input voltage consists of 10 pulses with increasing amplitude (black). The memristor turns on at a threshold of 1.2 V which can be seen by the sudden increase in current (blue) at the 6th pulse. The zoom-in shows the conductance of the device for each of the pulses above the threshold. One can see a “full response” in the conductance for all pulses. (d) The “integrate” function (blue) of a neuron is visualized for different timed input pulses. (e) Setup to measure the integration capabilities of the memristors with shown pulse signals. The pulse duration was reduced to 5 ms compared to the “all-or-none” measurement. (f) A voltage input pulse train consisting of 9 pulses is shown in black. As can be seen by the increasing current through the device (blue) the memristor is able to integrate. This can also be observed in the zoom-in where the conductance of the device increases with increasing pulses. (g) ”Integrate and Fire” (IF) operation for a neuron visualized. After an integration section (dark blue shade), the neuron reaches a firing threshold resulting in a spike (blue shade). This spike is followed by a refractory period (light blue shade) where the neuron recovers. After the recovery, the neuron is ready to “integrate and fire” again. (h) Setup and input pulse shape for IF measurements of the alloyed memristor. (i) Pulse packages with intervals of 100 µs and an increasing number of pulses are sent from the source e.g. one pulse in the first pulse package, two in the second, etc. The current through the device spikes at the 8th/9th pulse of a package and again at the 14th pulse. The zoom-in shows the conductance of the memristor for the last three packages. The integration can be observed by the conductance increasing at the beginning of the package (dark blue shade). After integration and upon reaching a threshold (dashed line), the spiking event (blue shade) takes place. The device then recovers in the refractory period (light blue shade).