RESEARCH OF CHALCOGENIDE MATERIALS FOR MEMORY DEVICES WITH RANDOM ACCESS BASED ON PHASE TRANSITIONS

Abstract.

Purpose. SbxSe(Te)100−x (x ≥ 50) thin films are suitable for creation of PRAM devices that works on the basis of reversible “amorphous↔crystalline” phase transformation. This paper presents the results of investigations of electrical resistence and optical transmission temperature dependences under termal cycling and heat conditions changes. Methods. Crystallization of SbxSe(Te)100−x (x ≥ 50) thin films was investigated by the method, which allows simultaneously measurements of electrical resistance and optical transmission on the one sample. Investigations of R(T) and Θ(T) dependences were carried out on planar structures “Cr layer-SbxSe(Te)100−x film” in the temperature range 293–493 K, both in continuous regime at heating rates (q) 3 and 6 K/min, in thehermal cycling regime and in heating regime with temperature scanning stops at selected stabilization temperatures (Tst) for a certain temperature stabilization time (tst). Results. Nonisothermal crystallization of SbxSe(Te)100−x (x ≥ 50) amorphous films is accompanied by a sharp decrease in resistance and transmission. The transition parameters (the starting temperature Tph from amorphous to crystalline state, temperature range of transition ∆Tph, resistance ∆R and transmission ∆Θ changes) depend on the chemical composition of films and heating rate. For the studied materials, the value of ∆T is 4-18 K and ∆R is 2-3 orders of magnitude. As the heating rate increases Tph and ∆Tph shift to higher temperatures. Investigations have shown that crystallization of SbxSe(Te)100−x amorphous films (partial or complete) under certain conditions can occur at temperatures below Tph. The fraction of crystallized volume of films, the values of R, Θ, ∆R and ∆Θ depend on the temperature and time parameters (for example, Tst, tst) of the heating process. Conclusions. It is established that SbxSe(Te)100−x (x ≥ 50) amorphous films crystallize under certain heat conditions. The phase transition from an amorphous state to a crystalline one is accompanied by a sharp decrease in electrical resistance and optical transmission. The crystallization processes and phase transition parameters depend on the chemical composition of films and the heating conditions. The results testify that SbxSe(Te)100−x films can be used as materials for temperature sensors and PRAM devices

Keywords: chalcogenide materials, amorphous films, phase transformations, crystallization, memory cells, temperature sensors

https://doi.org/10.24144/2415-8038.2020.47.7-20