Electroforming of Memristors Based on Open TiN–SiO2–Mo Sandwich Structures in a Moderate Regime

Memristors based on open TiN–SiO2–Mo sandwich structures manufactured using thin-film technology were studied. The main feature of such structures was the high initial conductance (by several orders of magnitude higher than for similar TiN–SiO2–W structures). It is connected with the presence of Mo atoms, embedded into the open end surface of the SiO2 layer during the wet etching of SiO2. High initial currents are due to hopping conductance through Mo atoms. A moderate regime of electroforming was proposed, which takes place at relatively low voltages and currents using a subforming process. The subforming consisted in the electroforming process with the amplitude of 10 V and a small value current limitation of 10 nA. Measurements of the current for the TiN–SiO2–Mo structures at constant voltages for a time close to the subforming cycle time allowed to experimentally determine the threshold voltage for the formation of conductive phase particles, which turned out to be (about 1 V) significantly lower than in the TiN–SiO2–W structures (about 3 V). The mechanism of the threshold voltage decrease consists in that the height of the energy barrier between molybdenum atoms, embedded into the SiO2 surface, is significantly lower than on the boundary of an anode (Mo or W) with SiO2. Subsequently, the low threshold voltage value facilitates the conductive phase particles formation from organic molecules and makes a low-voltage subforming process sufficient for the electroforming of the open TiN‑SiO2‑Mo sandwich structures.