Evaluation of vibrational properties and local structure change during phase transition in Ge₂Sb₂Te₅ and In₃SbTe₂ phase change materials

Abstract

Temperature-dependent local structural details of In3SbTe2 (IST) and Ge2Sb2Te5 (GST) phase change materials are explored with the aid of Raman scattering and X-ray Photoelectron Spectroscopy (XPS) techniques. Significant temperature-induced changes occur in the local structure of the phase change material, facilitating the amorphous to crystalline phase transformation. These two phases exhibit a large resistivity contrast, which is utilized to store data in the Phase Change Memory (PCM) application. The Raman spectra recorded for IST material suggest that the as-deposited sample (amorphous phase) first crystallized around 300 ℃ annealing temperature with two binary phases InTe and InSb formations. InTe and InSb phases were obtained at ~85.5 cm-1 and ~180 cm-1 Raman shift, respectively, having vibration modes associated with B1g symmetry and TO phonons with Г15 symmetry. Further annealing at a higher temperature of 400℃, a ternary IST phase is obtained at ~163 cm-1 Raman shift indicating the transformation to a fully crystalline state. On the other hand, the amorphous GST material forms a metastable face-centered cubic (FCC) phase and stable hexagonal (HEX) phase upon crystallization. The Raman findings demonstrate the changes in vibration modes of Ge-Te and Sb-Te bonds during phase switching without any phase separation. Crystalline GST (HEX phase) comprises rising peaks of GeTe4 and GeTe4-nGen (n=1, 2) corner-sharing tetrahedra with A1 mode at ~104.5 cm-1 and ~137 cm-1 Raman shift, respectively, and a declining Sb2Te3 peak at ~175 cm-1, having A1g (2) vibration mode. Furthermore, the XPS analysis displays the changes in the bonding mechanism of the elements present in the phase change material during the amorphous to crystalline phase transition, firmly supporting the Raman observations.

Low‐Power Crystallization Process in In3SbTe2 Phase Change Memory Devices with Thin Oxide Layer

“…These two phases merge into the single IST phase at higher temperature. [9,[13][14][15] In-3d, Sb-3d, and Te-3d core-level spectra in amorphous IST layer are analyzed for devices with/without the oxide (HfO 2 ) layer. In-3d, illustrated in Figure 3a, consists of InSb and In 2 Te 3 bonds, [14,15] which are shifted by 0.33 and 0.11 eV, respectively, in the device with the oxide layer.…”

“…[9,[13][14][15] In-3d, Sb-3d, and Te-3d core-level spectra in amorphous IST layer are analyzed for devices with/without the oxide (HfO 2 ) layer. In-3d, illustrated in Figure 3a, consists of InSb and In 2 Te 3 bonds, [14,15] which are shifted by 0.33 and 0.11 eV, respectively, in the device with the oxide layer. Sb-3d spectrum displays InSb bond, [14,15] and Te-3d spectrum shows InTe and In 2 Te 3 bonds [14,15] with small binding energy displacements in the device with the oxide layer, portrayed in Figure 3b,c respectively.…”

“…In-3d, illustrated in Figure 3a, consists of InSb and In 2 Te 3 bonds, [14,15] which are shifted by 0.33 and 0.11 eV, respectively, in the device with the oxide layer. Sb-3d spectrum displays InSb bond, [14,15] and Te-3d spectrum shows InTe and In 2 Te 3 bonds [14,15] with small binding energy displacements in the device with the oxide layer, portrayed in Figure 3b,c respectively. Shifts in peak positions occur due to the atom's chemical nature, but compounds remain unchanged in IST spectra, with no Hf-or O-related bonds confirming that no atoms diffused from the oxide layer into the active layer in PCM device with oxide layer.…”

“…[4][5][6][7] Novel phase change materials like In 3 SbTe 2 (IST) are explored to solve these issues. [9][10][11][12][13][14][15] With a higher T c of 290 °C and significant resistance contrast between the phases, IST offers improved thermal stability and multiple data storage, making it suitable for high-density PCM device applications. [9][10][11][12][13][14][15] Although this technology has demonstrated a lot of potential, issues like reducing power usage are currently being addressed.…”

“…[9][10][11][12][13][14][15] With a higher T c of 290 °C and significant resistance contrast between the phases, IST offers improved thermal stability and multiple data storage, making it suitable for high-density PCM device applications. [9][10][11][12][13][14][15] Although this technology has demonstrated a lot of potential, issues like reducing power usage are currently being addressed. Researchers have focused on minimizing the power consumption in the PCM device by restructuring device geometry, [7,16,17] modifying material composition [18,19] and mitigating heat loss by incorporating an interfacial layer like TiO 2 , [20,21] HfO 2 , [22][23][24] Ta 2 O 5 , [25] Bi 2 Te 3 , [26] MoS 2 , [27] and graphene [28] below the phase change layer in the PCM device.…”