Thermal stability of amorphous metal chalcogenide thin films

Abstract Amorphous metal chalcogenides have good switching properties for resistive memories, but have low thermal stability. In this work, the response to rapid thermal stress, as high as 550 °C, of amorphous Cu-GeSe, Ag-GeSe, Cu-GeTe, Ag-GeTe thin films, is investigated. Metal-GeTe films, which are amorphous up to 280 °C, are the most stable. Metal-GeSe films start to crystallize at 190 °C and a Cu1.59Se phase, with 20.5% Cu vacancies and a structure similar to the c-Cu2-xSe superionic conductor, is formed. This might boost the performance of memory devices. Silver atoms migration is facilitated in Ag-GeSe by poor crystallization (below 5%, at all temperatures). Difussion of Ag is enhanced in Ag-GeTe, due to the crystallization of the cubic (Ag2Te)4-GeTe2 (Ag8GeTe6) phase, which has Ag+ vacancies. In Cu-GeTe, the formation of stoichiometric polycrystalline Cu0.67Ge0.33Te might hinder diffusion. An unusual anisotropic behaviour (increase in thickness, simultaneously with contraction of surface) is observed at 100 °C in Cu-GeSe and Cu-GeTe thin films, which suggests the orientation of the amorphous clusters package along a preferential direction.