Crystalline-as-deposited ALD phase change material confined PCM cell for high density storage class memory

Sky, M. Bright; Sosa, Norma; Masuda, Takeshi; Kim, W.; Kim, S.; Ray, A.; Bruce, Robert L.; Gonsalves, J.; Zhu, Yu; Suu, Koukou; Lam, C.

doi:10.1109/iedm.2015.7409621

Cited by 16 publications

(12 citation statements)

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“…As the physical integrity of the films can be deteriorated by crystallization during postannealing or repeated write operations, which involve the volumetric shrinkage of the film, the ALD process that can be performed at higher temperatures is critically important for depositing high-density films and fabricating the high-performance PcRAM. In this regard, the recent report by Sky et al is eye catching . They reported an ALD process for crystalline-as-deposited GST films that achieved >10 11 programming endurance after postannealing at above melting temperature .…”

Section: Introductionmentioning

confidence: 95%

“…In this regard, the recent report by Sky et al is eye catching. 17 They reported an ALD process for crystalline-as-deposited GST films that achieved >10 11 programming endurance after postannealing at above melting temperature. 8 Unfortunately, they did not disclose the process details, including the types of precursors and process conditions, perhaps due to the confidentiality issues.…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2019

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Atomic layer deposition (ALD) of phase-change materials has been suggested as the most feasible technique for the construction of high-aspect-ratio architectures required for ultrahigh-density phase-change random access memory (PcRAM). The recent advances in the ALD technique have established the foundations for the formation of conformal Ge–Te or Ge–Sb–Te films, but their electrical performance as a phase-change memory device has been rarely reported, especially with prolonged cycles. This study introduced Ge(II)–amido guanidinate (Ge(guan)NMe2 (guan = ( i PrN)2CNMe2, Me = CH3)) as a new ALD Ge precursor that was compatible with the high ALD temperature of up to 170 °C, which was necessary for achieving the high-density and stoichiometric as-deposited GeTe thin films. The films were deposited in an amorphous state. Coinjection of NH3 gas with the Te precursor (Te(SiMe3)2) was essential to initiate the feasible ALD reaction with the new Ge(II) precursor. Ab initio calculation proposed plausible exergonic chemical reaction pathways where NH3 actively participated in the dissociation of both −SiMe3 and guanidinate ligands from Te and Ge precursors, respectively. The ALD process showed self-limiting growth behavior and produced highly uniform and conformal morphologies. Low impurity levels (<5%) and a low crystallization temperature (180 °C) were observed for the samples deposited at 170 °C. The prototypical memory device showed a current–voltage curve with a voltage snapback region followed by switching to a low resistance state. Over 104 cycling endurance was achieved for the 170 °C grown GeTe film, whereas inferior endurance (<103) was observed for the low-temperature-grown GeTe.

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Section: Introductionmentioning

confidence: 95%

Section: Introductionmentioning

confidence: 99%

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

et al. 2019

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“…[11] The novel PCM device that we have recently developed has shown promising results by using a metallic surfactant layer, which confines the Ge-Sb-Te (GST) phase change material into a nanopillar, in contrast to the thin film of the mushroom device (Figure 1a). [12] The benefits of the metallic surfactant layer have been studied based on electrical testing, which include improved atomic layer deposition (ALD) yield of a dense GST inside a pore [13] , excellent reliability achieving more than 2x10 12 programming cycles as shown in Figure 1b [14] , demonstration of drift and noise mitigation for multi-level cell operation [15] , and no etching damage due to the improved ALD yield. [13] The new device structure and added materials complexity of the confined PCM device compared to the mushroom device requires a systematic investigation of the relationship between the microstructure of the GST nanopillar and corresponding electrical properties during phase change.…”

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confidence: 99%

Self‐Healing of a Confined Phase Change Memory Device with a Metallic Surfactant Layer

Xie

Kim²,

Kim

et al. 2018

Advanced Materials

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Understanding and possibly recovering from the failure mechanisms of phase change memories (PCMs) are critical to improving their cycle life. Extensive electrical testing and postfailure electron microscopy analysis have shown that stuck-set failure can be recovered. Here, self-healing of novel confined PCM devices is directly shown by controlling the electromigration of the phase change material at the nanoscale. In contrast to the current mushroom PCM, the confined PCM has a metallic surfactant layer, which enables effective Joule heating to control the phase change material even in the presence of a large void. In situ transmission electron microscope movies show that the voltage polarity controls the direction of electromigration of the phase change material, which can be used to fill nanoscale voids that form during programing. Surprisingly, a single voltage pulse can induce dramatic migration of antimony (Sb) due to high current density in the PCM device. Based on the finding, self-healing of a large void inside a confined PCM device with a metallic liner is demonstrated for the first time.

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“…An example of the impact of massively parallel fabrication of 3D memory architectures can be seen in vertical NAND Flash arrays, where the conformal deposition of electronic materials has transformed this technology increasing the number of layers into the hundreds . Unfortunately, while highly conformal high-performance films have been developed for PCM memories, − many attempts have failed in producing an actual OTS selector which shows stable, repeatable switching. , OTS selectors are two-terminal devices exhibiting high selectivity and a sharp on/off transition at a threshold voltage. The mechanism of conduction in the subthreshold region is fairly understood, being dominated by trap-assisted phenomena typical of amorphous solids; several models have instead been proposed for the switching mechanism such as field-assisted tunneling between trap states, , thermal induced threshold switching, the formation of a metastable filament, − or models bridging between the electronic and filamentary frameworks .…”

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confidence: 99%

ALD Heterojunction Ovonic Threshold Switches

Adinolfi

Laudato

Clarke

et al. 2020

ACS Appl. Electron. Mater.

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Conformal atomic layer deposition (ALD) of chalcogenide films would enable aggressive 3D integration of nonvolatile memories; unfortunately, the fabrication of high-performance ALD OTSs remains an unsolved problem. Here we present an ALD process to incorporate As in a quaternary GeAsSeTe (GAST) film showing excellent conformality, controllable thickness, and composition homogeneity. The films were used to produce a GeSe/GAST heterojunction-OTS selector. We demonstrate low leakage current (∼10–9 A over a 0.01 μm2 area measured at VTH/2), a VTH ∼ 3 V, a switching time of ∼2 nsand an outstanding endurance exceeding 109 cycleson par with the current OTS state-of-the-art.

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Crystalline-as-deposited ALD phase change material confined PCM cell for high density storage class memory

Cited by 16 publications

References 0 publications

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

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

Self‐Healing of a Confined Phase Change Memory Device with a Metallic Surfactant Layer

ALD Heterojunction Ovonic Threshold Switches

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