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Flyer123
If the figures of merit are speed, size, energy and so on, calling something ...
Blaise
The "memristor" represents a mathematical model formulated by Leon Chua in the ...
UK researchers follow silicon-oxide ReRAM route
Peter Clarke
5/22/2012 5:58 AM EDT
LONDON – Researchers from University College London (UCL) have developed a silicon oxide based non-volatile resistive memory structure by following a promising line of research similar to that pursued by teams at Rice University and the University of Pennsylvania.
Resisitive RAM (ReRAM), sometimes called a memristor, is now being researched extensively as a potential replacement for flash memory which is not expected not to scale in plan much below 20-nm minimum dimensions. Some further memory capacity scaling may be achieved by stacking flash memory cells vertically but it is thought that resistive memory could displace flash memory if it can offer planar as well as z-directions scaling. Silicon oxide is now being researched as a potential alternative to metal-oxide types of ReRAM.
The UCL team has developed a silicon oxide memory, described in a recent paper in the Journal of Applied Physics, which they claim performs the switch in resistance much more efficiently than has been previously achieved.
The paper, entitled Resistive switching in silicon suboxide films, reports that the UCL team have worked with silcon-rich silicon dioxide. This differs from the work of Professor I-Wei Chen at the University of Pennsylvania who has reported the use of inclusions of atomically dispersed platinum in silicon oxide material. The UCL work appears to be closer to that of a team under James Tour at Rice University (see Making memory out of silicon oxide).
"The resistive switching phenomenon is an intrinsic property of the silicon-rich oxide layer and does not depend on the diffusion of metallic ions to form conductive paths. In contrast to other work in the literature, switching occurs in ambient conditions, and is not limited to the surface of the active material," the researchers state in the abstract to their paper.
They go on to propose a switch that is operated by field-driven formation and current-driven destruction of filamentary conductive pathways and report on/off resistence ratios of 10^4:1 and higher. The conductive pathways are 10-nanometers in diameter or smaller and programming currents can be as low as 2-microamps, with transition times on the order of nanoseconds.
"Our ReRAM memory chips need just a thousandth of the energy and are around a hundred times faster than standard flash memory chips," said Tony Kenyon, one of the researchers at UCL's department of electronic and electrical engineering, in statement. The UCL devices also display a continuously variable resistance that depends on the last voltage that was applied. This is an important property that allows the device to mimic how neurons in the brain function.
UCL ReRAM test circuits on broken wafer. Source: UCL/Adnan Mehonic
The behavior was discovered by accident as researchers at UCL were working on silicon-based light emitting diodes but noticed that devices appeared to be unstable. UCL PhD student, Adnan Mehonic, was asked to look specifically at the material's electrical properties and he discovered that the material was flipping between conducting and non-conducting states.
The technology has potential application beyond memory storage. The team is also exploring the use of silcon-rich silica as a logic switch for use in processors.
UCL team has been backed by UCLB, the technology transfer company of UCL, and has recently filed a patent. UCL said UCLB is in discussions with a number of semiconductor companies.
Related links and articles:
Abstract to UCL's Journal of Applied Physics paper
News articles:
Silicon dioxide 'nanometal' offers alternative ReRAM
Making memory out of silicon oxide
Elpida announces ReRAM chip, aims to enter market 2013
HP, Hynix plan to launch memristor memory in 2013
Job ad discloses SanDisk resistive RAM program
RRAM set to follow 3-D flash, says IMEC
Memristor 'brouhaha' bubbles under
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resistion
5/22/2012 7:15 AM EDT
A programming current of few uA means only nanoamps for reading, is that enough?
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peter.clarke
5/22/2012 8:37 AM EDT
Well the researchers have techniques for detecting the different states so there must be a way to create read circuitry. It might be challengingly different to conventional methods.
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resistion
5/22/2012 10:53 AM EDT
My understanding is high performance flash already requires tens of uAs for reading.
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jg_
5/22/2012 7:00 PM EDT
Here is an important detail, many seem to have overlooked :
["The UCL devices also display a continuously variable resistance that depends on the last voltage that was applied."]
Current Flash already allows Multi-Bit cells, so any alternative is going to have to have the same ability, in order to be far enough ahead of flash, to be worth the bother.
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resistion
5/22/2012 8:24 PM EDT
My lasting impression of MLC is someone showing a distribution with tail bits and saying "this shows MLC capability"..ok.
If the resistance depends on the last voltage applied, that may not be so useful for memory, but maybe for a memristor.
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kinnar
5/23/2012 8:02 AM EDT
ReRAM is the most awaited replacement of Flash RAM if it get successful implementation as compared to FlashRAM. It really need Chemical Engineers and Nano Technology experts working behind the early invention of the possibilities associated with ReRAM.
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C VanDorne
5/23/2012 12:03 PM EDT
I think the key to a successful product introduction is the controller in front of the bucket-o-bits. As long as the controller interface is such that the CPU is indifferent to what's behind it then they can quickly get competitive products out into the market in standard storage formats. That'll free them up to sell the advantages of this technology over NAND - faster, lower-power, lower costs etc.
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xprmntl
5/23/2012 5:34 PM EDT
Interesting claims they have on being first. Others besides James Tour have published recently on SiOx RRAM--Jack Lee of UT-Austin, and Hyunsang Hwang of Gwangju University, Korea with Luigi Pantisano of IMEC. There are also a few published reports from the '70's, one by MJ Howes and another by RM Anderson.
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xprmntl
5/23/2012 6:37 PM EDT
Two more examples, which were previously cited by Blaise Mouttet, infamous Memristor denier:
D. R. Lamb and P. C. Rundle, "A non-filamentary switching action in thermally grown silicon dioxide films", Br. J. Appl. Phys. 18, 29-32 (1967)
Dow Corning also did work on SiO2 ReRAM in the early 1990's (US Patent 5283545).
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Blaise
5/28/2012 9:25 PM EDT
I prefer memristor realist rather than "memristor denier." I initially supported HP's work on memristors until I figured out that it was mostly propaganda to support their business agenda rather than legitimate science.
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Flyer123
5/29/2012 9:15 AM EDT
But why is it important how they call their device...
Isn't only important thing what device can do?
If HP produce device to match flash or to do something useful - call it memristor, or ReRAM or whatever it is irrelevant.
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Blaise
6/15/2012 8:10 PM EDT
The "memristor" represents a mathematical model formulated by Leon Chua in the 1970's. If the memristor model is a wrong mathematical model for ReRAM then its acceptance will probably hinder scientific development.
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Flyer123
6/25/2012 6:49 PM EDT
If the figures of merit are speed, size, energy and so on, calling something memristor or not wouldn't affect it.
Nobody really ended up with any real disadvantage for calling ReRAM 'a memristor' as nobody is using Chua's model to improve any important parameters anyway..
People are using name memristor (instead ReRAM) as it is more catchy but nobody really backs up anything on Chua's model.
I simply can't see any real problem with that.
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Flyer123
5/23/2012 6:51 PM EDT
If I got it right this is the bulk effect and Rice's study is more related to SiO2 substrates where the formation is on the surface - one of the reasons it doesn't work in the air.
NDR effect is known for many years but the operational device with properties to match flash and be cheap is different thing...
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Flyer123
5/23/2012 7:11 PM EDT
Moreover it seems they don't need current compliance as in case of Hwang's work.
It would be interesting to see if silicon has future as ReRam. That would reduce the cost significantly.
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resistion
5/29/2012 9:02 PM EDT
It got some compliance from the top contact.
Due to the high voltages involved, the silicon oxide type ReRAM will be harder to integrate into systems using typically lower voltages.
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Flyer123
5/30/2012 6:19 AM EDT
They got down to 3V, so it's pretty close to other metallic oxides.
3V is certainly ok for the flash...
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xprmntl
5/24/2012 10:11 AM EDT
In the overall cost of a RRAM chip, deposition of a few hundred angstroms of most metal oxides (eg. TiO2, Al2O3, HfO2, NiO, etc) is not significantly more expensive than deposition of silicon oxide, so it's not likely a cost driver.
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Flyer123
5/24/2012 11:28 AM EDT
In mass production it might be.
And there is no factory in the world which wouldn't rather deal with silicon than any other material.
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resistion
5/29/2012 9:04 PM EDT
It's an attractive proposal but if the ReRAM looks too much like the standard isolation, how can it be integrated.
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resistion
5/29/2012 10:28 AM EDT
What needs to be checked is resistance vs. Temperature, and how many times it can cycle.
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Flyer123
5/30/2012 6:12 AM EDT
On their website they stated 3k, Tour's group
10k, and Hwang's group 100k.
So silicon dioxide is more or less similar to other metallic oxides in these terms.
HP will come there first anyway - but it is interesting to see if silicon can fight back once again.
Very nice article in IEEE Spectrum about SiOx RRAM.
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Flyer123
5/30/2012 6:17 AM EDT
“The materials are as simple as can be: just silicon and silicon oxide. I hope that an entire community forms around this methodology, propelling it into commercial applications.” - J.Tour
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