Resistive switching memory characteristics of Ge/GeO(x) nanowires and evidence of oxygen ion migration

The resistive switching memory of Ge nanowires (NWs) in an IrO(x)/Al(2)O(3)/Ge NWs/SiO(2)/p-Si structure is investigated. Ge NWs with an average diameter of approximately 100 nm are grown by the vapor–liquid-solid technique. The core-shell structure of the Ge/GeO(x) NWs is confirmed by both scanning electron microscopy and high-resolution transmission electron microscopy. Defects in the Ge/GeO(x) NWs are observed by X-ray photoelectron spectroscopy. Broad photoluminescence spectra from 10 to 300 K are observed because of defects in the Ge/GeO(x) NWs, which are also useful for nanoscale resistive switching memory. The resistive switching mechanism in an IrO(x)/GeO(x)/W structure involves migration of oxygen ions under external bias, which is also confirmed by real-time observation of the surface of the device. The porous IrO(x) top electrode readily allows the evolved O(2) gas to escape from the device. The annealed device has a low operating voltage (<4 V), low RESET current (approximately 22 μA), large resistance ratio (>10(3)), long pulse read endurance of >10(5) cycles, and good data retention of >10(4) s. Its performance is better than that of the as-deposited device because the GeO(x) film in the annealed device contains more oxygen vacancies. Under SET operation, Ge/GeO(x) nanofilaments (or NWs) form in the GeO(x) film. The diameter of the conducting nanofilament is approximately 40 nm, which is calculated using a new method.