Direct evidence for abrupt postcrystallization germanium precipitation in thin phase-change films of Sb–15 at. % Ge

Cabral, C.; Krusin-Elbaum, L.; Bruley, J.; Raoux, S.; Deline, V.; Madan, A.; Pinto, T.
August 2008
Applied Physics Letters;8/18/2008, Vol. 93 Issue 7, p071906
Academic Journal
We present evidence for the instability in the crystalline (metallic) state of binary Te-free phase-change Ge–Sb thin films considered for integration into nonvolatile nanosized memory cells. We find that while the amorphous (semiconducting) phase of eutectic Sb–15 at. % Ge is very robust until Sb crystallization at 240 °C, at about 350 °C, germanium rapidly precipitates out. Ge precipitation, visualized directly with transmission electron microscopy, is exothermic and is found to affect the films’ reflectivity, resistance, and stress. It converts melting into a two-step process, which may seriously impact the switching reliability of a device.


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