Crystallization kinetics of inxsey thin films for phase change memory (pram) applications
Muchira, Irene Wanjiku
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Chalcogenide phase change memory is a potential replacement to flash memory due to excellent properties such as high storage density, rapid phase transition and archival stability. Phase change non-volatile semiconductor memory technology is based on an electrically initiated, reversible rapid amorphous-to-crystalline phase change process in multicomponent chalcogenide alloy materials similar to those used in rewritable optical disks. For over a decade Ge2Sb2Te5 (GST) compound has been used in fabrication of phase change memory devices. However the material has drawbacks such as low crystallization temperature that reduces its ability to retain data at high temperatures and low crystalline resistance which increases the reset current of phase change memory devices. Therefore there is a quest for a new material which overcomes these drawbacks. In this work, a systematic investigation of crystallization kinetics of In40Se60, In60Se40 and, In80Se20, alloys has been made. These alloys have been prepared by thermal evaporation using Edward Auto 306 evaporation system. Temperature dependent electrical resistance measurements have been carried out based on the four point probe using Keithley 2400 source meter interfaced with computer using LabView software. A sudden drop in sheet resistance at critical transition temperature corresponding to the phase transformation at varied heating has been observed for all the alloys. The alloys have shown an electrical contrast of six orders of magnitude between the resistance of the as deposited and annealed phases. Such a high contrast is a requisite for the sufficient high signal to noise ratio during reading. From the heating rate dependence of crystallization temperature (Tc) the activation energy for crystallization was determined using the Kissinger analysis. The activation energies were determined to be 0.538±0.063eV for In40Se60 and 0.354±0.018eV for In60Se40. The In80Se20 alloy exhibited two transitions with activation energy of 0.523±0.103eV and 0.425±0.042eV for first and second transitions respectively. The In40Se60 alloy is the most suitable for PRAM applications since it has the highest activation energy which make memory cell from this material stable. We recommend fabrication and characterisation of In40Se60 memory cell as an alternative material for phase change memory applications.