Some more details from this group are at Adv. Mat. 23, 3847-3852 (2011). It largely reflects what has been reported here. However, capacitance measurements are missing which should be normally used to evaluate the charge trapping.
I see the distinction you are going after, a distributed vs. more focused filament path. But the way to show this is to compare R vs. size. If R is weakly dependent on size, as was shown in the thesis, it is more likely to be at least not so evenly distributed as would be imagined. I'll check this against the foils from the event, if they are available soon.
This paper and 11 other exciting talks are scheduled for the IEEE San Francisco Bay Area Nanotechnology Council's 8th Annual Full Day Symposium -"Emerging Non-volatile Memory Technology" on April 6th. Register at www.ieee.org/nano where you can find the abstracts for the other papers
Resistron-If you fabricate a device with a volume fraction of Pt in the range 30% close to the value of the percolation limit, (i.e 33%), where the probability of a continuous path becomes 1, then there will be in 3D many possible similar discontinuous shorter paths. I think it is wrong to describe this as a standard filamentary RRAM, whatever that is. Sure you could lump these under your definition of "predefined filaments". The results in work already published suggest a good correlation of resistance with area, suggesting the insulating state is NOT single filament like many of the reported RRAM and ReRAMs. I think you need to understand the role of the spreading resistance in the values reported by Prof Wei and colleagues for the conducting state, without that you might conclude the results for the conducting state are substantially independent of area and are therefore for a single conducting filament.
When operating near the 33% volume fraction limit there is also a probability of many paths where there are short continuous chains of Pt atoms that do not reach the distance between the electrodes, so they might be considered as nano metallic strands, there can still be traps between those chains that allow the device to work as reported, even if the strands become negatively charged the will offer some form of Coulombic repulsion.
I would suggest if you have the opportunity you follow Peter Clarke's advice here above and attend Prof Wei's presentation. Also read the report of the work from on Rice NV RAM, reported in EETimes today-that is clearly a single filament device. Your standard filamentary RRAM if you like.
I understand that there are characteristics of resistance switching behavior and V-I-R curves that can be used to distinguish between filamentary and non-filamentary behavior. These are things which I did not go into here.
I suggest that those who are interested in more detail get along to the TI Conference Center at
2900 Semiconductor Drive, Santa Clara, California on Friday, April 6. OR try and get hold of Professor Chen's slide set from the event, perhaps from the IEEE.
Having read his student's thesis, I think what they got is a standard filamentary RRAM, with pre-defined filaments, marked by Pt and pores characteristic of co-sputtered films. Filaments can consist of charge-trapping defects of course. But the defects they show are nm-scale rather than atomic.
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