Mechanism of Nano-Structuring Manipulation of the Crystallization Temperature of Superlattice-like [Ge8Sb92/Ge]3 Phase-Change Films

Abstract

Superlattice-like (SLL) phase-change film is considered to be a promising phase-change material because it provides more controllabilities for the optimization of multiple performances of phase-change films. However, the mechanism by which SLL structure affects the properties of phase-change films is not well-understood. Here, four SLL phase-change films [Ge8Sb92(15 nm)/Ge (x nm)]3 with different x are fabricated. Their behaviors of crystallization are investigated by measuring sheet resistance and coherent phonon spectroscopy, which show that the crystallization temperature (TC) of these films increases anomalously with x, rather than decreases as the interfacial effects model predicted. A new stress effect is proposed to explain the anomalous increase in TC with x. Raman spectroscopy reveals that Raman shifts of all phonon modes in SLL films deviate from their respective standard Raman shifts in stress-free crystalline films, confirming the presence of stress in SLL films. It is also shown that tensile and compressive stresses exist in Ge and Ge8Sb92 layers, respectively, which agrees with the lattice mismatch between the Ge and Ge8Sb92 constituent layers. It is also found that the stress reduces with increasing x. Such a thickness dependence of stress can be used to explain the increase in crystallization temperature of four SLL films with x according to stress-enhanced crystallization. Our results reveal a new mechanism to affect the crystallization behaviors of SLL phase-change films besides interfacial effect. Stress and interfacial effects actually coexist and compete in SLL films, which can be used to explain the reported anomalous change in crystallization temperature with the film thickness and cycle number of periods in SLL phase-change films.

Improvement of Multilevel Memory Performance of MnTe Thin Films by Ta Doping

“…In fact, an increase in the surface/volume ratio of the film inhibits crystallization, while the substrate/film interface has a facilitating effect on crystallization. 37 As the film thickness decreases, both the surface−volume ratio and the substrate−interface ratio increase accordingly. It is clear that the latter is the main factor affecting crystallization in Ta 2.8% -MnTe films, thus exhibiting a decrease in crystallization temperature with decreasing thickness.…”

“…Typically, the crystallization temperature of films increases with decreasing thickness based on interfacial effects. , However, the Ta 2.8% -MnTe film in Figure showed the opposite. In fact, an increase in the surface/volume ratio of the film inhibits crystallization, while the substrate/film interface has a facilitating effect on crystallization . As the film thickness decreases, both the surface–volume ratio and the substrate–interface ratio increase accordingly.…”

Universal memory based on phase-change materials: From phase-change random access memory to optoelectronic hybrid storage*

“…[310] GeTe/ST superlattices have been investagated intensively till now. [317][318][319][320][321][322][323][324] Other SLL structure phase-change materials, such as Bi 2 Te 3 /ST, [325] Ge/ST, [326] GeTe/Sb 7 Te 3 , [327] Si/Sb 80 Te 20 , [328] GeTe/GST, [329] GST/SiO 2 , [330] Ga 30 Sb 70 /Sb 80 Te 20 , [331] GeTe/InTe, [332] Sn x Te 100−x /ST, [333] Si/Sb, [334] Ge 40 Te 60 /Cr, [335] and Ge 8 Sb 92 /Ge [336] were also reported having much better switching speed and thermal stability in comparison with GST. Cr-doped ST film may be one of the best phase-change materials candidates for optoelectronic hybrid storage due to its high crystallization temperature (235 • C), good data retention (120.8 • C, ten-years), and lower power consumption.…”