Among the many possible phase‐change materials that can be used in digital memories, Ge‐rich GeSbTe (GGST) alloys are of special interest due to their much higher thermal stability, i.e., the higher crystallization temperature, they offer. However, in contrast to congruent materials which may transit from the amorphous to the crystalline state while keeping the same homogeneous chemical composition, GGST crystallization is obtained through the successive formation of the Ge and GST‐225 phases. For this reason, they show distinct properties and characteristics from those found in the canonical GST‐225 and GeTe alloys. Herein, some of these characteristics, their crystallization kinetics, the effect of N doping and oxidation, and their electrical properties are reviewed and highlighted.
The down scaling of complementary metal oxide semiconductor transistors requires materials such as porous low-k dielectrics for advanced interconnects to reduce resistance-capacitance delay. After the deposition of the matrix and a sacrificial organic phase (porogen), postcuring treatments may be used to create porosity by evaporation of the porogen. In this paper, Auger electron spectroscopy is performed to simultaneously modify the material (e-beam cure) and measure the corresponding changes in structure and chemical composition. X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy measurements in attenuated total reflection mode confirm the Auger results. The porogen removal and matrix cross-linking result in the formation of a Si–O–Si network under e-beam or ultra violet cure. The possible degradation of these materials, even after cure, is mainly due the presence of Si–C bonds.
Among the phase-change materials, Ge-rich GeSbTe (GST) alloys are of considerable interest as they offer a much higher thermal stability than their congruent contenders, a desirable characteristic for embedded digital memories and neuromorphic devices. Up to now, the mechanisms by which such alloys crystallize and progressively switch from one resistivity state to the other remain unclear and very controversial. Using in situ synchrotron X-ray diffraction during isothermal annealing and advanced transmission electron microscopy techniques, we solve this riddle and unveil the mechanisms leading to the overall crystallization of such alloys. During annealing at 310 °C, the initially homogeneous and amorphous material undergoes a progressive phase separation, leading to the formation of Ge-rich regions of different compositions. During this decomposition, the first formed GeTe embryos crystallize and trigger the heterogeneous crystallization of the Ge cubic phase. As the phase separation proceeds, these embryos dissolve and the Ge phase gradually builds up through the nucleation of small grains. Only when this Ge cubic phase is largely formed, the remaining amorphous matrix may locally reach the Ge 2 Sb 2 Te 5 composition at which it can crystallize as large grains. Our density functional theory calculations confirm that the quite exotic Pnma GeTe structure we have experimentally identified is more stable than the regular R3m structure at nanometric sizes.
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