Enhancement of a cyclic endurance of phase change memory by application of a high-density C15(Ge21Sb36Te43) film

Abstract

The lower cyclic endurance of Phase Change Memory (PCM) devices limits the spread of its applications for reliable memory. The findings reported here show that micro-voids and excess vacancies that are produced during the deposition process and the subsequent growth in sputtered carbon-doped GeSbTe films is one of the major causes of device failure in PCM with cycling. We found that the size of voids in C15(Ge21Sb36Te43) films increased with increasing annealing temperature and the activation energy for the growth rate of voids was determined to be 2.22 eV. The film density, which is closely related to voids, varies with the deposition temperature and sputtering power used. The lower heat of vaporization of elemental Sb and Te compared to that for elemental Ge and C is a major cause of the low density of the film. It was possible to suppress void formation to a considerable extent by optimizing the deposition conditions, which leads to a dramatic enhancement in cyclic endurance by 2 orders of magnitude in PCM devices prepared at 300oC-300W compared to one prepared at 240oC-500W without change of compositions.

Carbon ion implantation as healing strategy for improved reliability in phase-change memory arrays

“…Based on same endurance tests, we report in Fig. 10a the cycles number obtained for each C implantation energy, confirming the benefits of C, compatible with previous results obtained on GeSbTe doped by sputtering [8] [12]. Such improvement at device level is mandatory for an implementation of PCM in large arrays to deploy reliable products [13].…”

“…sputtering of the phase change layer, prone to improve the thermal stability by increasing the crystallization temperature of the target alloy [6] [7]. However, the introduction and control of carbon (C) in the GST layer at really low concentrations becomes challenging with standard co-sputtering techniques, which moreover can give rise to residual micro-voids and excess vacancies in the film [8].…”

Review of memristor devices in neuromorphic computing: materials sciences and device challenges

“…These voids can lead to PCM cells getting stuck at the high resistance state. To solve this issue, carbon dopants were used inside the GST to limit the micro-void formation [36]. The ageing issue of multi-bit PCM is also severe when there is a resistance drift if the GST amorphous state is unstable at a given temperature.…”

Phase-Change Memory by GeSbTe Electrodeposition in Crossbar Arrays

“…Plasma sputtering has commonly been used for depositing PCMs demonstrating strong switching properties. − Atomic layer deposition (ALD) has shown good composition control over the PCM in high-aspect-ratio structures. − Other PCM deposition methods that have been explored include chemical vapor deposition. , However, there are several limitations associated with these methods. For example, sputtering deposit material at an angle making it unsuitable in filling high density or high-aspect-ratio structures.…”