Atomic Layer Deposition of Nanocrystalline-As-Deposited (GeTe)_x(Sb₂Te₃)_1–x Films for Endurable Phase Change Memory

Abstract

This paper introduces a new atomic layer deposition process for highly conformal, nanocrystalline-as-deposited GeTe–Sb2Te3 pseudobinary film growth at a deposition temperature of 130 °C. The process utilizes Ge­(II)-amidoguanidinate (GeIIN­(CH3)2[(N i Pr)2CN­(CH3)2]), Te­(Si­(CH3)3)2, and Sb­(OC2H5)3 with an NH3 coreagent. The alternative GeTe and Sb2Te3 subcycles produced various film compositions, all consistent with the GeTe–Sb2Te3 tie lines, owing to the stoichiometric reactions between the precursors without involvement of undesirable side reactions. The density of the nanocrystalline Ge2Sb2Te5 (GST225) films was 6.2 g·cm–3, similar to the density of the bulk crystalline material. The crystallization behaviors indicated that the distribution of the constituent elements of the GST225 films was highly uniform at the atomic level, as opposed to the case of the low-temperature (100 °C)-deposited films. The cubic to hexagonal transition at 350 °C upon postannealing produced (0001) hexagonal planes highly aligned along the substrate. The demonstration of the phase change memory device achieved high cycling endurance (>107). Considering that further scaling and optimization of the cell design can improve the electrical performance, the nanocrystalline GST films introduced herein can provide potential utilities in the large-capacity three-dimensional vertical-type phase change memory.

Developing Precursor Chemistry for Atomic Layer Deposition of High-Density, Conformal GeTe Films for Phase-Change Memory

“…28 This broad scattering intensity could be ascribed to the short-range covalent networking structures (mostly from the nearest neighbor) in the amorphous GeTe film. 29,38 Overall, the typical crystallization temperature of these ALD films corresponds to the reported crystallization temperature of the sputtered GeTe film (180−190 °C). 30,31 The crystallization temperature is similar to that of the undoped GeTe despite the presence of the C and N impurities as observed in the AES.…”

“…While this is not a sufficiently high performance for the storage-class memory application where a switching cycle of >∼10 8 –10 10 is required, it is still promising for the mass-storage device, such as Intel’s recent Optane for solid-state drive application. More importantly, this work elucidated that fundamental chemical research for the new precursor synthesis and extensive engineering works for optimizing the ALD process can pave the way for implementing the ALD GeTe films for actual device application, which has not been the case in the previous works. ,,,,,− The GeTe ALD process described here has high potential utilities for building crystalline-as-deposited GST materials whose crystallization temperature is below 180 °C for further performance improvement as described in more detail in a separate paper …”

“…The estimated RESET current value was ∼45 μA, which is a quite promising value considering the relatively large diameter of the contact hole (130 nm) compared with that of the state-of-the-art device (<20 nm). A separate, sequential paper will describe the utility of the current GeTe process for the deposition of Ge 2 Sb 2 Te 5 , which hugely improves the cycling endurance of phase-change memory (>10 7 ) by forming low impurity, crystalline-as-deposited films …”

“…A separate, sequential paper will describe the utility of the current GeTe process for the deposition of Ge 2 Sb 2 Te 5 , which hugely improves the cycling endurance of phase-change memory (>10 7 ) by forming low impurity, crystalline-asdeposited films. 38…”

Bipolar Resistive Switching in the Ag/Sb2Te3/Pt Heterojunction

“…Generally, V-VI chalcogenide Sb 2 Te 3 is mostly used for a phase change memory (PCM) which shows unipolar switching − due to its rapid change in resistance caused by inherent phase transition between amorphous and crystalline states. PCM write speed varies from 100 ns up to 10 μs and its endurance is in the range of 10 6 to 10 9 cycles, while RRAM write speed varies from as short as 10 ns up to over 100 μs and endurance varies in the range of 10 5 to 10 9 cycles, which reflects its less-mature status and its larger variability .…”