Study of SnxSey thin films for phase change memory (PCM) applications

Abstract

Phase Change Random Access Memory (PCM) is one of the most optimized candidates for the next generation non-volatile memory due to its fast operation speed, high scalability, low power operation and fabrication costs. The transition from the amorphous to the crystalline phase is induced by heating the material above its crystallization temperature for a long enough time, and the switching back to the amorphous phase is realized by melting and quenching the material fast enough that it solidifies in the amorphous state. In this study the electrical and optical properties of various SnXSey alloys at room temperature and during annealing from 25-250 °C was investigated and subsequent electrical characterization of fabricated SnSe4 PCM. An Edward Auto 306 RF/DC Magnetron evaporation chamber was used for thin film deposition. Transmission data in the range from 450 nm- 2500 nm was obtained using Shimadzu UV-VIS-NIR 3700/3700 DUV spectrophotometer. Optical bandgaps have been found to vary from 1.27-1.94 eV with decrease in tin concentration. IN characteristics measurements were performed on the films using Keithley 2400 source meter interfaced with four point probe using computer to determine sheet resistivity. Sheet resistivity varied from 1150-1600W cm. All the alloys have shown high sheet resistance at room temperature and low sheet resistance during annealing. This interprets that the samples were amorphous during deposition and changed to crystalline during annealing. The SnXSey alloys have different crystallization temperatures varying from 174-224 °C. Increase in tin concentration reduced the crystallization temperature. The PCM was fabricated based on SnSe4 alloy since it had high crystalline temperature, low crystallization temperature and a wide band gap hence a better choice than other alloys of SnXSey. The PCM was found to have a threshold voltage of 3.71 V and its voltage and pulse width of amorphization and crystallization processes were 3.71 V, 90 ns and 1.3 V, 26 p s, respectively