Being a diode structure with the rectifying contact at the bottom (a), it is vital that the set occurs in the (negative) forward polarity in order to operate in the area-scaling mode. Only in this mode, the self-rectification can be maintained during switching (Milestone 3).

With 8 layers (b) set occurred under positive bias and reset on negative voltage, which is characteristic for a filamentary switching mode. The device with 12 layers has the set operation on the negative voltage and it resets on the positive polarity. This preferential set in the negative polarity happened despite attempts to induce the set in the positive polarity. This preferential set in negative polarity for thicker devices is in accordance with the ZTO memristors fabricated with vacuum techniques [1] and represent to first realization of the area-scaling switching mechanism in ZTO processed by solution deposition. This important results shows that with the proper fine-tuning the ZTO conditions and thickness for area-scaling switching have been achieved.