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PCM Progress Report No. 6: Afterthoughts

2/13/2012 08:20 PM EST
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R G.Neale
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re: PCM Progress Report No. 6: Afterthoughts
R G.Neale   2/17/2012 9:24:07 AM
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eista-The reason why refractory metals or metal silicides and nitrides are used as phase change memory (PCM) electrodes is because during reset they need to interface with molten chalcogenide without reaction. I think the materials you suggest(SiGe,BiTe)would react and result in an unstable device. I think the IBM innovation of mixing two refractories in a composite structure is as close as it is possible to get to your suggestion at the moment.

rbtbob
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re: PCM Progress Report No. 6: Afterthoughts
rbtbob   2/16/2012 4:59:57 PM
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Maybe IBM/Macronix should add a thin layer of permanently crystallized chalcogenide like what HP says develops in their memristor: "...in one-to-two nanometers thick region, the film cools in an annealing-like like process which leaves the film in a fixed crystalline state that should remain that way indefinitely...." It would even out both the heat and current transfer. AND they should dope their Golden Composition with Terbium in a way that gets it uniformly distributed. Someday I will again find the materials paper that found it to cause a wildly anomalous but beneficial behavior. Lastly, has HP said anything more about the "newly developed structural phase" that forms around the memristor's conductive piller? It seems like that mass could have a major effect on the electric field. http://www.eetimes.com/electronics-news/4216057/HP-discovers-memristor-mechanism

resistion
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re: PCM Progress Report No. 6: Afterthoughts
resistion   2/16/2012 4:52:18 PM
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Normally, electrical and thermal conductivity go together, supported by the electrons.

resistion
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re: PCM Progress Report No. 6: Afterthoughts
resistion   2/16/2012 4:46:31 PM
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Despite the bucket arrangement, they still have the issues, the voltage and power consumption is higher from the added resistance, which is not completely bypassed.

eista
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re: PCM Progress Report No. 6: Afterthoughts
eista   2/16/2012 4:06:49 PM
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Nice analysis, Dr. Neale Following the thought, is the thermal-electric material good for bottom electrode (good electrical conductivity and poor thermal conductivity), such as SiGe, BiTe?

R G.Neale
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re: PCM Progress Report No. 6: Afterthoughts
R G.Neale   2/16/2012 2:45:28 PM
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Kinnar-IBM did report a comparison test that involved baking cells from a 128M-bit PCM array with their new Golden Composition for 6 hrs at 190 degrees C and similar cells using GST225 that demonstrated its superiority give or take a few tail-bits. The GST225 based devices failing the test at 160 C test. The IBM team was very conservative in their conclusion suggesting that their work should generate further interest in material engineering as a way forward for PCM. IBM did not state the number of write/erase cycles that the devices they tested had accrued. I was more concerned about the vulnerability of the Golden Composition to element separation, especially with scaling, and the possibility, using my fig 3, that element separation might push the GC into the valley in the crystallization temperature surface where lies GST225 and compromise the performance. The answer to your question regarding the ability to withstand a practical industrial environment will only be found when the Golden Composition is used to fabricate a useful size array or the IBM 128M-bit PCM arrays are subjected to that environment.

Kinnar
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re: PCM Progress Report No. 6: Afterthoughts
Kinnar   2/16/2012 11:24:11 AM
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Is this Golden Composition is realizable in a practical industrial environment?

R G.Neale
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re: PCM Progress Report No. 6: Afterthoughts
R G.Neale   2/16/2012 10:32:03 AM
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resistion-If you mean the poor conductor both electrical and thermal (TaN) in the IBM/Macronix PCM electrode design then they mitigate the downside by having it spread as a thin large diameter layer at the contact point “the base of the bucket” then the (TiN) is used as the low resistance electrical conductor. I think the problem with scaling this structure is the thermally insulating sidewall layer of TaN with a thickness of 7 to 8nm will have to be reduced just as the area/volume heat loss problem worsens. If not the minimum diameter device will be 16nm plus the diameter of any TiN that is carrying the reset current. What will be very interesting next week at ISSCC2012 is to see if Samsung stay with the concave dash structure for the 8G-bit or have moved to the bucket structure.

resistion
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re: PCM Progress Report No. 6: Afterthoughts
resistion   2/16/2012 4:07:24 AM
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It is questionable to use the poor conductor, as that will up your voltage budget. You also can't RESET as fast.

Volatile Memory
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re: PCM Progress Report No. 6: Afterthoughts
Volatile Memory   2/15/2012 10:18:58 PM
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Mr. Neale: Ok, then I am declaring it. Nobody believes that PCM's "problems" can be solved. All efforts to commercialize PCM in volume have repeatedly failed since 1970. Anybody who pretends that PCM has even a slight chance to succeed is either totally uninformed or intentionally disingenuous. In other words, PCM is a techno-Ponzi.

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