EP07.03.01 : Nitrogen-Doped Cr-Ge-Te Films for Phase Change Random Access Memory

5:00 PM–7:00 PM Apr 3, 2018 (America - Denver)

PCC North, 300 Level, Exhibit Hall C-E

Yi Shuang1 Shogo Hatayama1 Satoshi Shindo1 Daisuke Ando1 Yuji Sutou1 Junichi Koike1

1, Tohoku University, Sendai, , Japan

Dopants such as nitrogen, oxygen, transition metal and oxide have been demonstrated to effectively enhance the phase change properties of phase change material such as thermal stability, endurance and power consumption. [1] Usually, with dopant incorporation in phase change materials, the dynamic resistance in both phases can be raised several orders because of the grain refinement and formation of nitride in grain boundary. The reset current will be reduced as a result. The thermal retention also be greatly improved since some dopants have the ability to modify the crystallization kinetics, giving rise to a sizable increase in crystallization temperature. For example, N doped GeTe was confirmed to exhibit lower power consumption and better data retention property. The crystallization temperature of GeTe film increases markedly from 187 to 372 °C by moderate N doping and its high data retention is around 240 °C for 10 years, which is suitable for high temperature products and systems. [2] In this work, N dopant has been firstly used in the anomalous phase change material Cr-Ge-Te ternary compound which shows an inverse phase transition behavior, i.e., higher resistance crystalline phase and lower resistance amorphous phase. [3] The Cr-Ge-Te ternary compound has the advantages of high crystallization temperature and larger crystalline resistance in comparison with conventional phase change material Ge2Sb2Te5. So, we expected that N would enhance the performance of the Cr-Ge-Te compound.
Cr-Ge-Te ternary compound was deposited on a SiO2 (100 nm)/Si substrate by RF magnetron co-sputtering using Cr, Ge and Te target. Nitrogen flow rate was controlled by changing N2 gas flow rate from 0 to 0.9 SCCM. Resistance of the films as a function of temperature (R-T) was in-situ measured in a two-point probe method. The nitrogen content was determined by XPS. The crystallization temperature was measured from DSC. Simple memory cell was fabricated using a traditional lithograph technique based on N doped Cr-Ge-Te film (NCrGT).
By N doping, we found that phase change behavior of Cr-Ge-Te can be tuned by N content. When N content was in a relatively higher region, the resistance in the amorphous phase becomes higher than that in the crystalline. The crystallization temperature and thermal stability was also enhanced by N doping. The NCrGT based phase change memory cell was also demonstrated to show a typical switching behavior.
[1] Lee T H, Loke D, Elliott S R. Microscopic Mechanism of Doping-Induced Kinetically Constrained Crystallization in Phase-Change Materials[J]. Advanced Materials, 2015, 27(37): 5477-5483.
[2] Peng C, Wu L, Rao F, et al. Nitrogen incorporated GeTe phase change thin film for high-temperature data retention and low-power application[J]. Scripta Materialia, 2011, 65(4): 327-330.
[3] Hatayama S. et al. Phase change behaviors of Cr-Ge-Te compound thin film. Proceeding of the 28th Symposium on Phase Change Oriented Science (PCOS2016). 71 (2016).