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.
Highlights
Circle-shaped dots that show a brighter contrast than the surrounding area are exhibited in the carbon-doped GeSbTe (CGST) film and are assumed to be voids because of the contrast is due to the low density of the dot area since this area projects the thickness of the transmission electron microscopy (TEM) sample
The coalescence of micro-voids and the formation of excess vacancies during the deposition process resulted in the formation of voids in CGST films when the annealing temperature is increased
It becomes clear that the conditions used for the deposition of CGST films is another key factor in the formation of voids in Phase Change Memory (PCM) devices
Summary
As memory cell density increases in mobile and system applications, phase change memory (PCM) has been focused on as an alternative for use in generation memories because the current types of commercialized memories, such as Dynamic Random Access Memory (DRAM), have limitations due to problems associated with integration complexity and poor scalability.[1,2,3,4,5,6,7,8,9] PCM has been shown to be structurally simpler and more amenable to size scaling compared to DRAM, which contributes to high density cells with a lower cost per bit.[10,11,12] Owing to enormous development efforts that have been made, PCMs are currently available for use in mobile applications on a 45 nm scale,[13,14,15] and full functionality has been extended to 20 nm cells.[16,17,18,19]To expand PCM applications further, the poor cyclic endurance of PCM needs to be improved. 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.
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