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PCM progress report no. 6: Recent advances in phase change memory (Part 2)

Posted: 15 Mar 2012 ?? ?Print Version ?Bookmark and Share

Keywords:phase change memory? array? physical vapor deposition?

Hynix did provide the sensing voltage at the sense amplifier as a function of number of write/erase cycles at decade intervals up to 108 cycles. The problem is they started to report results in arbitrary units (AU), making independent assessment difficult and, without a product, requiring a blind acceptance of statements like, "We confirmed the set and reset sensing window compatible with product level specifications..." What is reported is a resistance window of two decades from the write/erase tests at 90o C is reduced to a difference of 1.4 AU at the sense amplifier.

True to their word, Hynix researchers produced a fabrication platform and used it to demonstrate the fabrication of a 1-Gb PCM array that raises an immediate question: Will it be the stage on which a commercial PCM array, scaled and competitive in price and performance, eventually appears. or will the 1 Gb be the fourth in the industry-wide list of 1-Gb PCM demonstration devices? At the time of writing the answer to that question is "not yet," and it must remain open.

PCM originally targeted a scaling advantage over flash as a raison d'etre; the ability of Flash memory to scale has left PCM trailing in its bit-capacity wake. Even if the warnings of the possibility of PCM problems with scaling, thermal cross talk, complexity, and element separation are ignored and it is possible to bring together the best of all the disparate pieces of work reported in a single fabrication plant, will there be a management team brave enough to commit to an 8-Gb-plus PCM array? Given fabrication and performance success, the result would be that they would only be able to bring to the market a memory device that would not be a significant improvement over products based on a different technology.

An additional problem for those contemplating entering the market is IBM has now added a caveat to its earlier very positive statements with respect to the future application of PCM in servers in 2016. The caveat runs as follows: "...the enterprise timeline hinges on mobile phone and memory manufacturers taking up MLC-PCM as a NOR flash replacement in the next couple of years." Perhaps after the International Solid-State Circuits Conference 2012 (ISSCC2012), one company might surprise us all, but I somehow doubt it. The 8-Gb paper from Samsung at ISSCC2012 and the commercial PCM product that it might spawn in the subsequent months, will certainly give all PCM watchers, as well as non-volatile memory competitors, something to look forward to.

1. S. H. Lee et al., "Highly Productive PCRAM Technology Platform and Full Chip Operation:based on 4F2 (84-nm pitch) cell scheme for 1Gb and Beyond," Proc IEDM, pp 47-50 (2011).
2. DerChang Kau et al., "A stackable cross point Phase Change Memory," Proc IEDM, pp 1-4 (2009).
3. K. Gopalakrishman et al., "Highly scalable Novel Access Device based on mixed ionic Electronic Conduction for High Density PCM Arrays," Proc VLSI, pp 205-206 (2010).
4. H. Y. Cheng et al., "A High Performance Phase Change memory with Fast switching Speed and High Temperature Retention by engineering the GexSbyTe Phase Change Material," Proc IEDM, pp51-54 (2011).
5. Stefan Lai, "Current status of the phase change memory and its future," Proc IEDM (2003).
6. J.Y.Wu et al., "A Low Power Phase Change memory Using Thermally Confined TaN/TiN Bottom Electrode," Proc IEDM, pp43-46 (2011).

About the author
Ron Neale is the former editor-in-chief of Electronic Engineering. Also, he is the co-author of "Nonvolatile and reprogrammable, the read-mostly memory is here", by R.G.Neale, D.L.Nelson and Gordon E. Moore, Electronics, pp56-60, Sept. 28, 1970.

To download the PDF version, click here.

Here are the other parts of this series:
PCM progress report no. 1: Temperatures rise and constituents on the move
PCM progress report no. 2: Review of PCM-related activities in early 2011
PCM progress report no. 3: New direction with polyamorphic states
PCM progress report no. 4: Simulating the brain
PCM progress report no. 5: Scaling issues
PCM progress report no. 6: Recent advances in phase change memory (Part 1)
PCM progress report no. 7: A look at Samsung's 8-Gb array

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