Understanding the crystallization behavior and structure of titanium addition in germanium antimony phase change thin films

The effects of a titanium dopant on the phase transition behavior and crystallization mechanism of Ge8Sb92 films were systematically investigated. The crystallization behavior induced by heat was studied by in situ resistance measurements. With the incorporation of titanium atoms, both the crystallization activation energy and electrical resistance increase, resulting in a higher amorphous thermal stability and a lower of the programming energy consumption. A broadening of the optical bandgap causes the enhancement in the amorphous resistance. X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy analysis reveal that a small amount of titanium addition can retard the grain growth and refine the crystal size, owing to the formation of amorphous Ge and Sb components. The shift in the Raman modes associated with Sb upon crystallization was observed. X-ray reflectivity and atomic force microscopy results illustrate that the volume fluctuation becomes smaller and the surface morphology becomes smoother after titanium doping. A reversible phase transition can be achieved by picosecond laser pulses. Phase change memory cells based on a titanium-doped Ge8Sb92 film were also fabricated to evaluate the electrical characteristics. The results indicate that the suitable incorporation of titanium in Ge8Sb92 thin films is an effective way to tune and optimize the crystallization performance for phase change memory applications.