Crystallization Behavior and Physical Properties of Sb-Excess Ge[sub 2]Sb[sub 2+x]Te[sub 5] Thin Films for Phase Change Memory (PCM) Devices

Abstract

The crystallization behavior of antimony͑Sb͒-excess Ge 2 Sb 2+x Te 5 was examined. Sb-excess GST showed crystallization ͑T C ͒ and melting ͑T M ͒ temperatures of 205 and 550°C, respectively, slightly higher T C and lower T M values than stoichiometric Ge 2 Sb 2 Te 5 compounds. It also showed a substantially different crystallization behavior compared to the stoichiometric Ge 2 Sb 2 Te 5 composition. The resulting Sb-excess GeSbTe thin film showed a grain growth dominated crystallization behavior.

Characterization of Ge22Sb22Te56 and Sb-Excess Ge15Sb47Te38 Chalcogenide Thin Films for Phase-Change Memory Applications

“…The time required for programming was measured for reset (t reset ) and set (t set ) operations as a function of applied pulse width 56) has a slightly lower crystallization activation energy than GST(15/47/38), suggesting that crystallization of GST(22/22/56) occurs somewhat more readily than that of GST(15/47/38). 3 Consequently, the GST(22/22/56) device is expected to have faster setting performance. To resolve this discrepancy a more detailed microstructure analysis was performed.…”

“…The method of sample preparation has been previously described in detail. 3 The GST(22/22/56) and GST (15/47/38) films were freshly deposited by means of RF magnetron sputtering at room temperature. The prepared specimens were then moved into the TEM vacuum chamber.…”

“…2 However, as previously mentioned, nitrogen-doped GST(2/2/5) showed considerable compositional degradation during operation: the initial composition of GST(2/2/5) was completely altered to Ge 15 Sb 47 Te 38 (GST(15/47/38)). 3 The crystallization characteristics of the two materials with different compositions were analyzed using transmission electron microscopy (TEM) and calculation of nucleation activation energy. However, the relationship between the electrical properties and crystallization characteristics of this PCM device remains to be investigated.…”

Empirical investigation of SET seasoning effects in Phase Change Memory arrays

“…These effects give rise to the formation of a non-stoichiometric GST compound with different crystallization and melting temperature. An altered GST compound such as the Ge 15 Sb 47 Te 38 shown a lower crystallization temperature of about 70°C and a higher melting temperature of about 40°C, with respect to Ge 2 Sb 2 Te 5 [4,9]. Furthermore the sheet resistance in crystalline state is about 100 times lower than stoichiometric GST.…”

“…In deep, recent material studies [8] on cell structures very similar to that exploited in this work, shown that the proportion of Te (both in crystalline and amorphous phase) vary inversely with the temperature gradient during the cell programming, with consequent effects on the successive erase operations. Moreover, in [9] has been reported that the Te deficiency and the accompanying Sb enrichment are triggered by segregation reactions into Ti composing the heater element, arising the presence of intermetallic compounds. Measurements performed on single cell test structures proven that after multiple programming cycles, cross-sectional transmission electron microscopy and energy dispersive analysis show that electromigration as well as incongruent melting causes phase separation by mass movement by which the peak position of Sb and Ge lies shifted toward the cathode of the structure and that of Te toward the anode structure [10].…”