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Relation between bandgap and resistance drift in amorphous phase change materials.

Rütten M, Kaes M, Albert A, Wuttig M, Salinga M - Sci Rep (2015)

Bottom Line: A widening of the bandgap upon annealing accompanied by a decrease of the optical dielectric constant ε∞ is observed for all three materials.Quantitative comparison with experimental data for the apparent activation energy of conduction reveals that the temporal evolution of bandgap and activation energy can be decoupled.The case of Ag4In3Sb67Te26, where the increase of activation energy is significantly smaller than the bandgap widening, demonstrates the possibility to identify new phase change materials with reduced resistance drift.

View Article: PubMed Central - PubMed

Affiliation: Institute of Physics 1A, RWTH Aachen University, Sommerfeldstrasse 14, 52074 Aachen, Germany.

ABSTRACT
Memory based on phase change materials is currently the most promising candidate for bridging the gap in access time between memory and storage in traditional memory hierarchy. However, multilevel storage is still hindered by the so-called resistance drift commonly related to structural relaxation of the amorphous phase. Here, we present the temporal evolution of infrared spectra measured on amorphous thin films of the three phase change materials Ag4In3Sb67Te26, GeTe and the most popular Ge2Sb2Te5. A widening of the bandgap upon annealing accompanied by a decrease of the optical dielectric constant ε∞ is observed for all three materials. Quantitative comparison with experimental data for the apparent activation energy of conduction reveals that the temporal evolution of bandgap and activation energy can be decoupled. The case of Ag4In3Sb67Te26, where the increase of activation energy is significantly smaller than the bandgap widening, demonstrates the possibility to identify new phase change materials with reduced resistance drift.

No MeSH data available.


Related in: MedlinePlus

Temperature dependence of the optical bandgap of Ag4In3Sb67Te26, Ge2Sb2Te5 and GeTe before (squares) and after (dots) annealing at 353 K for 27 hours.Fits according to equation (1) by Varshni (see figure legend) show a transition from quadratic behaviour at low temperatures to linear behaviour at high temperatures. The resulting parameters for all fits are listed in Table 1.
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f4: Temperature dependence of the optical bandgap of Ag4In3Sb67Te26, Ge2Sb2Te5 and GeTe before (squares) and after (dots) annealing at 353 K for 27 hours.Fits according to equation (1) by Varshni (see figure legend) show a transition from quadratic behaviour at low temperatures to linear behaviour at high temperatures. The resulting parameters for all fits are listed in Table 1.

Mentions: We start by looking at the temperature dependent results for the optical bandgap of all three materials in Fig. 4. The bandgap widens consistently upon cooling with an increase of 26.7% for AIST, 20.8% for GST and 17.4% for GeTe, which is only slightly affected by annealing. Apart from that, we clearly observe a vertical shift between the pre and post annealing curves. A question we would like to answer quantitatively with these results is how the temperature dependence of the bandgap is influenced by relaxation. For that reason we fit the well-known Varshni model to the values of the bandgap 39 determined before and after the annealing.


Relation between bandgap and resistance drift in amorphous phase change materials.

Rütten M, Kaes M, Albert A, Wuttig M, Salinga M - Sci Rep (2015)

Temperature dependence of the optical bandgap of Ag4In3Sb67Te26, Ge2Sb2Te5 and GeTe before (squares) and after (dots) annealing at 353 K for 27 hours.Fits according to equation (1) by Varshni (see figure legend) show a transition from quadratic behaviour at low temperatures to linear behaviour at high temperatures. The resulting parameters for all fits are listed in Table 1.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4664898&req=5

f4: Temperature dependence of the optical bandgap of Ag4In3Sb67Te26, Ge2Sb2Te5 and GeTe before (squares) and after (dots) annealing at 353 K for 27 hours.Fits according to equation (1) by Varshni (see figure legend) show a transition from quadratic behaviour at low temperatures to linear behaviour at high temperatures. The resulting parameters for all fits are listed in Table 1.
Mentions: We start by looking at the temperature dependent results for the optical bandgap of all three materials in Fig. 4. The bandgap widens consistently upon cooling with an increase of 26.7% for AIST, 20.8% for GST and 17.4% for GeTe, which is only slightly affected by annealing. Apart from that, we clearly observe a vertical shift between the pre and post annealing curves. A question we would like to answer quantitatively with these results is how the temperature dependence of the bandgap is influenced by relaxation. For that reason we fit the well-known Varshni model to the values of the bandgap 39 determined before and after the annealing.

Bottom Line: A widening of the bandgap upon annealing accompanied by a decrease of the optical dielectric constant ε∞ is observed for all three materials.Quantitative comparison with experimental data for the apparent activation energy of conduction reveals that the temporal evolution of bandgap and activation energy can be decoupled.The case of Ag4In3Sb67Te26, where the increase of activation energy is significantly smaller than the bandgap widening, demonstrates the possibility to identify new phase change materials with reduced resistance drift.

View Article: PubMed Central - PubMed

Affiliation: Institute of Physics 1A, RWTH Aachen University, Sommerfeldstrasse 14, 52074 Aachen, Germany.

ABSTRACT
Memory based on phase change materials is currently the most promising candidate for bridging the gap in access time between memory and storage in traditional memory hierarchy. However, multilevel storage is still hindered by the so-called resistance drift commonly related to structural relaxation of the amorphous phase. Here, we present the temporal evolution of infrared spectra measured on amorphous thin films of the three phase change materials Ag4In3Sb67Te26, GeTe and the most popular Ge2Sb2Te5. A widening of the bandgap upon annealing accompanied by a decrease of the optical dielectric constant ε∞ is observed for all three materials. Quantitative comparison with experimental data for the apparent activation energy of conduction reveals that the temporal evolution of bandgap and activation energy can be decoupled. The case of Ag4In3Sb67Te26, where the increase of activation energy is significantly smaller than the bandgap widening, demonstrates the possibility to identify new phase change materials with reduced resistance drift.

No MeSH data available.


Related in: MedlinePlus