Modeling of virgin state and forming operation in embedded phase change memory (PCM)

Baldo, M.; Melnic, O.; Scuderi, M.; Nicotra, Giuseppe; Borghi, Massimo; Petroni, Elisa; Motta, A.; Zuliani, P.; Redaelli, A.; Ielmini, Daniele

doi:10.1109/iedm13553.2020.9372089

Cited by 13 publications

(7 citation statements)

References 4 publications

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“…The trend of extracted metrics is also compatible with observed Ge clustering, which is in turn a forming mechanism (Fig. 8), as extensively studied from Baldo et al [8]. Given a total amount of segregated germanium (as reported with blue and red pictures on the left), differences in the virgin and postforming median resistance are obtained (as reported on the right with same color code).…”

Section: Introductionsupporting

confidence: 84%

“…Also, the Arrhenius plots in Fig. 12 further supports a modification in the amorphous crystallization response, consistent with a change in the active material, induced by process segregation and forming [8]. Note that the activation energy of process B is similar to process A but the Arrhenius pre-factor is much improved (shift up in the Arrhenius plot of Fig.…”

Section: Electrical Characterizationsupporting

confidence: 60%

“…Given a total amount of segregated germanium (as reported with blue and red pictures on the left), differences in the virgin and postforming median resistance are obtained (as reported on the right with same color code). The post forming cell behavior is thus the result of the forming pulse and the obtained distribution of elements after process integration [8]. This effect must be thus carefully considered.…”

Section: Introductionmentioning

confidence: 99%

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BEOL Process Effects on ePCM Reliability

Redaelli

Gandolfo

Samanni

et al. 2022

IEEE J. Electron Devices Soc.

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The effect of back-end of line (BEOL) process on cell performance and reliability of Phase-Change Memory embedded in a 28nm FD-SOI platform (ePCM) is discussed. The microscopic evolution of the Ge-rich GST alloy during process is the focus of the first part of the paper. A new metric for quantification of active material modifications is introduced to better follow its evolution with process sequence. Ge clustering has been shown to occur during the fabrication, impacting the pristine resistance and the after forming cell performance. Two different BEOL processes are then benchmarked in terms of key performance. An optimized process is identified, and an extensive electrical characterization of array performance and reliability is done on the full 16MB chip. The optimized BEOL process results in a memory cell fully compatible with the requirements for demanding automotive applications.

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Section: Introductionsupporting

confidence: 84%

Section: Electrical Characterizationsupporting

confidence: 60%

Section: Introductionmentioning

confidence: 99%

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BEOL Process Effects on ePCM Reliability

Redaelli

Gandolfo

Samanni

et al. 2022

IEEE J. Electron Devices Soc.

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“…This issue poses a significant problem for programming operations in an active device. The local composition variation and phase separation into Ge-rich and Sb-rich regions compromise the device’s functionality [ 10 , 22 , 28 , 29 ]. Moreover, the excess Ge content in Ge-rich alloys increases oxidation susceptibility with lowered crystallization temperature and Te enrichment [ 9 , 30 ].…”

Section: Introductionmentioning

confidence: 99%

Phase Separation in Ge-Rich GeSbTe at Different Length Scales: Melt-Quenched Bulk versus Annealed Thin Films

et al. 2022

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Integration of the prototypical GeSbTe (GST) ternary alloys, especially on the GeTe-Sb2Te3 tie-line, into non-volatile memory and nanophotonic devices is a relatively mature field of study. Nevertheless, the search for the next best active material with outstanding properties is still ongoing. This search is relatively crucial for embedded memory applications where the crystallization temperature of the active material has to be higher to surpass the soldering threshold. Increasing the Ge content in the GST alloys seems promising due to the associated higher crystallization temperatures. However, homogeneous Ge-rich GST in the as-deposited condition is thermodynamically unstable, and phase separation upon annealing is unavoidable. This phase separation reduces endurance and is detrimental in fully integrating the alloys into active memory devices. This work investigated the phase separation of Ge-rich GST alloys, specifically Ge5Sb2Te3 or GST523, into multiple (meta)stable phases at different length scales in melt-quenched bulk and annealed thin film. Electron microscopy-based techniques were used in our work for chemical mapping and elemental composition analysis to show the formation of multiple phases. Our results show the formation of alloys such as GST213 and GST324 in all length scales. Furthermore, the alloy compositions and the observed phase separation pathways agree to a large extent with theoretical results from density functional theory calculations.

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“…This analysis has demonstrated the crucial role of microscopic investigation in the characterization of PCM materials, especially because the results can be directly related to programmed cells' physical properties. The microscopic study of non-programmed (or "bulk") material properties in integrated devices has gathered increasing interest both from structural and chemical points of view [13,14]. In particular, the latter represents a real challenge for out-of-stoichiometry alloys such as Ge-rich GST, which result at the end of the process in segregated materials characterized by significantly spread composition [9].…”

Section: Introductionmentioning

confidence: 99%

Metrics for Quantification of By-Process Segregation in Ge-Rich GST

et al. 2022

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Ge-rich GST alloys are the most promising materials for phase-change memory (PCM) to fulfill the soldering compliance and the tough data retention requirements of automotive applications. Significant efforts have been made to engineer those materials and optimize their integration inside the fabrication process of PCM. In this perspective, the physical characterization of the device and the material is instrumental in understanding the underlying physics, improving the process, and optimizing the interactions between the device, the process, and the material itself. Especially, microscopic investigations have gathered increasing interest, giving detailed descriptions of local material modulations that have a crucial role in cell programming and reliability performances. In this work, a deep analysis of Ge-rich GST microscopic alloy evolution during the integration process has been performed, exploiting analysis by EELS with TEM supported by a novel statistical data post-processing method. The new proposed statistical-based methodology also introduces new simple metrics for elemental compositional evaluations that have been exploited for process engineering.

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Modeling of virgin state and forming operation in embedded phase change memory (PCM)

Cited by 13 publications

References 4 publications

BEOL Process Effects on ePCM Reliability

BEOL Process Effects on ePCM Reliability

Phase Separation in Ge-Rich GeSbTe at Different Length Scales: Melt-Quenched Bulk versus Annealed Thin Films

Metrics for Quantification of By-Process Segregation in Ge-Rich GST

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