Crystallization Kenetics and Structural Properties of SnxSey Thin Films for Phase Change Memory (pcm) Applications
Kundu, Masinde Joshua
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As the future size of phase change random access memory is scaled down, its reliability in data retention, archival life and power consumption is often disturbed by problems such as elemental segregation and compositional variation caused by repetitive phase transformation. These phenomena are closely related to the crystallization kinetics under various environments. The crystallization kinetics at low temperature and slow transition rates of Sn.Se, thin films have been investigated using sheet resistance measurements based on the van Pauw technique. The thin films were deposited on glass substrates at room temperature using thermal evaporation technique using Edwards auto 306 magnetron sputtering system. Results show that the crystallization temperature, specific sheet resistivity and the activation energy for Sn-Se alloys can be varied over a wide range by adjusting the composition of the binary alloy. The crystallization temperatures for Sn30Se70, Si14oSe6o and SnsoSeso were found to be: 195A±OAoC, 156.6±0.3°C and 129.8±0.5°C respectively. The electrical contrast obtained from the sheet resistance vs. temperature measurements between the amorphous phase and the crystalline phase was at least 105 for Sn30Se7o, and Sn40Se60 and less than 102 for the stoichiometric SnsoSeso. The value of activation energy obtained from Kissinger analysis was lowest for SnsoSeso at 0.43±0.05 eV and highest for Sn30Se70 at 0.63±0.06 eV. The activation energy for the films of the stoichiometric alloy Sn4oSe6o was 0.62±0.07 eV. From the alloys studied, the most promising stoichiometric alloys of Sn.Se, seems to be Sn30Se70 and Sn40Se60 because of their high electrical contrast of five orders of magnitude, high crystallization temperature better than the reported values of GST, and high activation energy that will increase the stability of the amorphousmark. The data stability at high temperatures is dependent on the crystallization temperature of the cell. The high values obtained for crystallization temperature will therefore ensure data stability and retention at elevated temperatures.