Light-activated self-rectifying resistive switching in HfxTayOz

Light-activated non-volatile bipolar self-rectifying resistive switching was demonstrated in Ag/HfxTayOz/Si metal/oxide/semiconductor (MOS) devices with HfxTayOz deposited via atomic layer deposition. Illumination with visible light enabled the Ag/HfxTayOz/Si device to be set to the low resistance state (LRS) at a low positive field. The set operation did not occur without illumination. The light-activated set field for HfxTayOz devices was much lower than that observed for devices with HfO2 as the oxide, while in devices with Ta2O5, the light-activated switching occurred at low field but suffered from nearly coincident set and threshold fields. The requirement of exceeding a threshold field to reveal the LRS has been referred to as threshold switching to distinguish from standard metal oxide resistive random-access memory devices in which the LRS shows an immediate rise in current. A separation of ∼0.23 MV/cm between the set and threshold fields in the HfxTayOz devices allowed operation as a light-activated non-volatile memory with an LRS/high resistance state ratio of 600:1. No photo-response was seen for metal/insulator/metal devices with a TiN bottom gate, and no light-activated switching was observed in MOS devices with Al top gates, pointing to Ag ion filament formation and dissolution as the primary mechanism for resistive switching.