Extremely low drift of resistance and threshold voltage in amorphous phase change nanowire devices

Time-dependent drift of resistance and threshold voltage in phase change memory (PCM) devices is of concern as it leads to data loss. Electrical drift in amorphous chalcogenides has been argued to be either due to electronic or stress relaxation mechanisms. Here we show that drift in amorphized Ge2Sb2Te5 nanowires with exposed surfaces is extremely low in comparison to thin-film devices. However, drift in stressed nanowires embedded under dielectric films is comparable to thin-films. Our results shows that drift in PCM is due to stress relaxation and will help in understanding and controlling drift in PCM devices. Disciplines Engineering | Materials Science and Engineering Comments Suggested Citation: Mitra, M., Y. Jung, D.S. Gianola, R. Agarwal. (2010). "Extremely low drift of resistance and threshold voltage in amorphous phase change nanowire devices." Applied Physics Letters. Vol. 96, 222111. © 2010 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in Applied Physics Letters and may be found at http://dx.doi.org/10.1063/ 1.3447941. This journal article is available at ScholarlyCommons: http://repository.upenn.edu/mse_papers/181 Extremely low drift of resistance and threshold voltage in amorphous phase change nanowire devices Mukut Mitra, Yeonwoong Jung, Daniel S. Gianola, and Ritesh Agarwal Department of Materials Science and Engineering, University of Pennsylvania, 3231 Walnut Street, Philadelphia, Pennsylvania 19104-6272, USA Received 15 April 2010; accepted 15 May 2010; published online 4 June 2010 Time-dependent drift of resistance and threshold voltage in phase change memory PCM devices is of concern as it leads to data loss. Electrical drift in amorphous chalcogenides has been argued to be either due to electronic or stress relaxation mechanisms. Here we show that drift in amorphized Ge2Sb2Te5 nanowires with exposed surfaces is extremely low in comparison to thin-film devices. However, drift in stressed nanowires embedded under dielectric films is comparable to thin-films. Our results shows that drift in PCM is due to stress relaxation and will help in understanding and controlling drift in PCM devices. © 2010 American Institute of Physics. doi:10.1063/1.3447941 Electric-field induced structural phase transformations in chalcogenides have attracted significant interest due to their potential use in nonvolatile phase change memory PCM devices. Chalcogenides e.g., Ge–Sb–Te alloys are particularly important for PCM owing to their fast and reversible crystalline to amorphous phase change properties via Joule heating to produce electrically distinct states. However, various challenges including understanding their structural, electronic, thermal, and mechanical properties especially in the amorphous state, the effect of field on electrical switching, and device scalability needs to be addressed before PCM can become a viable alternative to flash technology. Chalcogenide glasses are affected by relaxation processes that occur on a large distribution of timescales resulting in time-dependent electrical, optical, mechanical, and thermal behavior. For PCM device operation, the amorphous state resistance and the field strength at which it switches to a higher conducting state threshold voltage, Vth are fundamental parameters that determine device reliability. Any phenomenon that affects these critical parameters leading to temporal drift in PCM is an important issue that needs to be investigated as they lead to changes in the measurable device characteristics used for recording and reading the information. This issue becomes particularly important for multilevel memory devices, as drifts in resistance would lead to states being overwritten causing serious errors. Therefore, it becomes important to understand the physical origin of phenomena that cause drift in material properties to eventually minimize such effects. The drift of amorphous phase resistance in PCM has been described by a power law,