Inxsey alloy thin films for phase change random access memory (pram) applications
Wekunda, B. Z. Buya
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Indium Selenide (InxSey) has shown great advantages over the conventionally used Ge2Sb2Te5 as a phase change memory material (PCM). It has been established that the electrical resistivity of Indium-Selenide based memory cell can be varied by a factor of 105 related with the degree of crystallization as compared with 103 for Ge2Sb2Te5. It is this wider change of electrical resistivity and higher electrical resistivity that has attracted great attention to Indium-Selenide based phase change material. However, little if any, has been reported about the concentration of indium and selenium in the film and its effect on the resistivity of the InxSey phase change alloy. In this study, the relationship between indium and selenium concentration, and electrical resistivity of thin films has been investigated. Also, the optical properties like the reflectance, transmittance, energy band gaps of the films have been studied. The films were fabricated by vacuum evaporation after synthesizing Indium and Selenium in various ratios by mass. Synthesis was done by melting them together in silica tube above 600 0C then left to cool before evaporating them on glass substrates in a high vacuum chamber maintained at ultra low pressure. The resistivity measurements were performed using the four point probe technique where the voltage and current were sourced from a sourcemeter interfaced to a labVIEW running computer. The film thickness measurements were carried out using Alpha IQ Surface Profiler and ranged from 80 nm to 120 nm. Films with a high concentration of indium were more reflective beyond the visible region while those with high concentration of selenium show more transmission beyond the visible region. The film with the highest concentration of selenium had a high energy band gap at 2.67 eV whereas that with the highest concentration of indium had the lowest band gap at 2.07 eV. The films with the highest concentration of indium exhibited greater resistance with sheet resistivity of about 109.6 Ωcm at room temperature and had the highest crystallization temperature of 203.3 0C. The fabricated PRAM device had static mode on voltage at 0.9 V and an off voltage of -0.4 V.