Explosive Crystallization Characteristic of Ge–Cu–Te Thin Films for Phase-Change Memory

Abstract

Ge–Cu–Te thin films were investigated experimentally for their initial crystallization characteristics and their correlation with electrical behaviors as phase-change materials for application in phase-change random access memory (PCRAM). Explosive crystallization (EC) with random orientation was observed as an initiating effect on crystallization during the early stage of crystallization for Ge–Cu–Te thin films. Both the tetrahedral coordination environment and triangular Cu atoms clusters consisting of threefold rings for Ge–Cu–Te thin films contribute to the initiation of EC. Crystallization progresses from the surface toward the bulk of the thin films, resulting in grain growth through the thickness of the thin films. Thicker films can encourage EC by reducing heat loss and producing a thicker liquid layer as a result of more significant temperature gradients near the phase-change front. Moreover, providing additional external heat by extending the annealing time also pushes EC. Finally, electrical transport measurements using the Hall system demonstrated that conductivity is increased by a more continuous EC network that concentrates more carriers. The authors consider that the above results are beneficial for understanding the phase-change mechanism of Ge–Cu–Te phase-change materials.

Phase-Controlled Synthesis and Phase-Change Properties of Colloidal Cu–Ge–Te Nanoparticles

“…Figure D–F shows the representative X-ray diffractograms of amorphous, trigonal, and tetragonal Cu–Ge–Te nanoparticles. All three structures are highly relevant for PCM technology. − For example, the trigonal CGT material (α-GeTe phase) has improved data retention properties and smaller volumetric change upon phase transitions. , The amorphous CGT material is characteristic of an abundance of unusual threefold ring local coordination. , Finally, the Cu 2 GeTe 3 PCM material has a set of unconventional properties, such as negative reflectivity change upon crystallization and sp 3 -type bond hybridization. , Nevertheless, this tetrahedrally coordinated PCM material shows fast switching characteristics also in addition to the higher crystallization temperature with respect to octahedrally coordinated GST fragile glasses. Taken together, the unconventional switching mechanism in CGT materials points to the important role of Cu 3d orbitals, enabling p–d bond mixing and delocalization of d-electrons upon phase transitions. ,, In the next section, we discuss in detail how to achieve each of the three Cu–Ge–Te phases.…”

“…All three structures are highly relevant for PCM technology. 40 − 43 For example, the trigonal CGT material (α-GeTe phase) has improved data retention properties and smaller volumetric change upon phase transitions. 20 , 44 The amorphous CGT material is characteristic of an abundance of unusual threefold ring local coordination.…”

Low Energy Ion-Induced Crystallization of Ge in c-Al/a-Ge Bilayer Thin Films at Low Temperatures of ∼125 °C

“…Polycrystalline Ge ( poly -Ge) is an important material for its potential applications in low-cost semiconductor devices such as high density data storage devices, solar cells, flat panel displays, etc. − The performance of these devices can be significantly improved by reducing the fabrication temperature of poly -Ge near room temperature or at room temperature. The poly -Ge can be fabricated by different conventional process like solid phase crystallization (SPC), − laser crystallization, − and metal-induced crystallization (MIC). − Among these methods, the MIC process is an efficient, reliable, and well-known technique by which poly -Ge can be fabricated at relatively low temperatures (160–300 °C) from amorphous germanium ( a -Ge) film in the presence of certain transition metal (Al, Au, Cu, Ag, Ni, etc.)…”