Ag/HfO₂-based conductive bridge memories elaborated by atomic layer deposition: impact of inert electrode and HfO₂ crystallinity on resistive switching mechanisms

Resistance switching is studied in conductive bridge memory structures made from atomic layer deposited HfO₂ and Ag active electrode. Inert electrode is varied by using different substrates (TiN, W, Pt). HfO₂ crystallinity is modified by varying the deposition temperature (300/350 °C) and the film thickness (10/20 nm). Current–voltage characteristics, as well as current–time characteristics (to access to the switching kinetics), are studied according to the inert electrode nature and HfO₂ structural properties. Results are discussed along resistance transition mechanisms which imply (i) the generation of oxygen vacancies by electronic injection at the inert electrode, (ii) Ag diffusion along oxygen vacancy paths, and (iii) the reduction of silver ions controlled by the inert electrode/HfO₂ interface. Best characteristics, in terms of stability, are observed with Pt inert electrode and 10 nm films. Crystalline and amorphous films (10 nm) provide similar characteristics. In 10 nm films, TiN and W inert electrodes lead to variability in electrical properties (parasitic sets during reset, switching time dispersion). Such a variability is related to high electronic injection at the TiN/HfO₂ and W/HfO₂ interfaces which creates a high density of oxygen vacancy paths (Ag diffusion paths). In thicker and well-crystallized films (20 nm), progressive set is observed. This is ascribed to conduction along oxygen vacancy paths, which dominates over conduction along Ag conductive bridges.