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Phase change memory (PCM) is a high speed, high endurance, high density non-volatile memory technology that utilizes chalcogenide materials such as Ge 2 Sb 2 Te 5 (GST) that can be electrically cycled between highly resistive amorphous and low resistance crystalline phases. The resistance of the amorphous phase of PCM cells increase (drift) in time following a power law [1] , which increases the memory window in time but limits in the implementation of multi-bit-per-cell PCM. There has been a number of theories explaining the origin of drift [1] - [4] , mostly attributing it to structural relaxation, a thermally activated rearrangement of atoms in the amorphous structure [2] . Most of the studies on resistance drift are based on experiments at or above room temperature, where multiple processes may be occurring simultaneously. In this work, we melt-quenched amorphized GST line cells with widths ~120-140 nm, lengths ~390-500 nm, and thickness ~50nm ( Fig. 1 ) and monitored the current-voltage (I-V) characteristics using a parameter analyzer ( Fig. 2 ) in 85 K to 350 K range. We extracted the drift co-efficient from the slope of the resistance vs. time plots (using low-voltage measurements) and observed resistance drift in the 125 K -300 K temperature range ( Fig. 3 ). We found an approximately linear increase in drift coefficient as a function of temperature from ~ 0.07 at 125 K to ~ 0.11 at 200 K and approximately constant drift coefficients in the 200 K to 300 K range ( Fig. 3 inset). These results suggest that structural relaxations alone cannot account for resistance drift, additional mechanisms are contributing to this phenomenon [5] , [6] .
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Structural relaxation of amorphous phase change materials at room temperature
Owing to their ability for fast switching and the large property contrast between the crystalline and amorphous states that permits multi-level data storage, in-memory computing and neuromorphic computing, the investigation of phase change materials (PCMs) remains a highly active field of research. Yet, the continuous increase in electrical resistance (called drift) observed in the amorphous phase has so far hindered the commercial implementation of multi-level data storage. It was recently shown that the resistance drift is caused by aging-induced structural relaxation of the glassy phase, which is accompanied by a simultaneous decrease in enthalpy and fictive temperature. This implies that resistance is related to enthalpy relaxation. While the resistance is known to drift even at room temperature and below, evidence for enthalpy relaxation at room temperature in amorphous PCMs is still missing. Here, we monitor changes in enthalpy induced by long-term room-temperature aging in a series of PCMs. Our results demonstrate the simultaneity of resistance drift and enthalpy relaxation at room temperature, and thus provide further insights into the mechanism of resistance drift and its possible remediation.
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- Award ID(s):
- 1832817
- PAR ID:
- 10553367
- Publisher / Repository:
- AIP
- Date Published:
- Journal Name:
- Journal of Applied Physics
- Volume:
- 135
- Issue:
- 13
- ISSN:
- 0021-8979
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1063/5.0198312
