Memristor

Program a resistance with a voltage pulse and read the stored value afterward at a lower voltage.

Circuit operation

V1 normally supplies a 0.5 V read level, below the 1 V programming threshold. A 3 V pulse programs MR1 through RS = 100 Ω. The initial resistance is 5 kΩ; positive voltage increases it.

Expected behavior

$$i(t)=\frac{v(t)}{R(t)}$$ $$\frac{dR}{dt}=0\quad\text{when }|v|<V_t$$

Read current is initially about 98 µA. After the programming pulse it is lower, because the resistance has increased. The lower read voltage reveals the stored state without changing it. Calculate MR1 resistance from its measured voltage and current during either read interval.

Reading the results

The first voltage probe is green; the second, when present, is red. The first current probe is blue. The schematic opens fitted to its extents. The saved transient spans 6 ms with a maximum step of 2 µs. The chart uses separate voltage and current lanes, and the table retains the same probe order.

Try a change

Set MR1 initial resistance to 2 kΩ. Compare the first read current and the resistance retained after the same write pulse. Restore the saved values after comparison.

Model limits

MR1 uses the ngspice voltage-threshold memristor model. Alpha is zero, so subthreshold reads preserve state. Rmin, Rmax, Rinit, Vt, and Beta are illustrative values. This is a memristive-system model, not a material-specific or thermal model.

Reference: ngspice memristor model and threshold-model paper.