Bidirectional threshold switching in Pt/Ag:Ni(OH) ₂ /Pt structure

Abstract In this study, an Ag-doped Ni(OH) ₂ (Ag:Ni(OH) ₂ ) thin film is fabricated by solution process with Ag concentration of 2% at 200 °C and applied to threshold switching selector devices. X-ray photoelectron spectroscopy and high-resolution transmission electron microscopy analysis confirm that the matrix contains 72% Ni(OH) ₂ and 28% NiO, while the Ag is doped as ion state. As the processing temperature increases, the Ni(OH) ₂ matrix changes to NiO, and the doped Ag tends to metal state. Selector devices with Pt bottom and top electrodes were fabricated and measured. Compared with a Pt/Ag:NiO/Pt device, which shows non-volatile resistive switching characteristics, bi-directional threshold switching behavior is demonstrated in the Pt/Ag:Ni(OH) ₂ /Pt device. The selectivity is larger than 10 ⁴ . The high/low resistance state cycles have been measured by half-bias pulse stimulation without obvious deterioration. Since Ag ion in Ni(OH) ₂ matrix shows fast diffusion, a thin Ag filament could be formed at low voltage, which then disperses and fractures after the voltage is removed. It corresponds to the main mechanism of bi-directional threshold switching. For the Pt/Ag:NiO/Pt device, the formation of thicker Ag filaments at higher electric fields leads to non-volatile resistive switching.