The recent Flash Memory Summit in Santa Clara paid a lot of attention to the future of NAND and successor technologies (as indeed one would think it should). For those of us unable to be there the conference has posted almost all the presentations on-line at www.flashmemorysummit.com/English/Conference/Proceedings_Chrono.html although I suspect some have been edited from the actual presentations. In any case, it allowed me to catch up! I’ve discussed the SK Hynix keynote presentation in a previous Blog based on the informative set of slides posted. Here are a few comments on some of the other more interesting presentations.
It is of course difficult to fully capture the content of a presentation from just looking at the slides. A good example is the keynote from David Eggleston of Rambus (formerly Unity Semiconductor). The slides contain some great imagery (see above) and the basic message is that one needs to understand (control?) the way that a system interfaces with the information stored in the non-volatile memory cells to be successful. He points to ways that ReRAM can be configured differently from NAND to improve memory array efficiency and handling. Interestingly he appears to concede the middle ground between DRAM and NAND to PCRAM (phase change) based on a lower write speed (SK Hynix’s presentation contains a similar comment).
The last two slides are worth looking out for. The penultimate shows an ReRAM roadmap with niche applications starting in 2013 and moving to NAND replacement in 2017. Any presentation that ends with a couple of Bob Dylan quotes can’t be all bad but reading without the context of Dr. Eggleston’s actual remarks left me a bit bemused.
4DS is a subsidiary of an Australian company of virtually the same name. There presentation includes an impressive level of materials detail of their rather catchily titled ‘MOHJO’ approach to ReRAM. A lot of the results appear to be from a 2009 publication from the group of the present Chief Scientist, Dongmin Chen who is a Fellow at the Rowland Institute at Harvard. Their devices are based on PCMO (Pr – Ca – Mn Oxide) but I was perplexed by the slide towards the end which describes their proprietary PCMO process and ReRAM cell which only exhibits a ~12% resistance change.
A couple of University groups made detailed presentations on the resistive switching process in ReRAM. Professor Nishi’s group from Stanford described some ab-initio modeling with a nice introduction that reviews the different binary oxides in which resistive switching has been observed (there are quite a lot!). Professor Jha (University of Toledo) also has a mechanism focused presentation describing the conduction mechanisms of the various states of a ReRAM cell.
One of the presentations on line that I suspect is not exactly as presented is that from Amigo Tsutsui of Sony Corporation (it’s much shorter than the others!) Without going into any real detail, Dr Tsutsui describes CuTe based ReRAM where the mobility of Cu ions is responsible for resistive switching.
Last but by no means least is the presentation by Janice Nickel from HP. This is actually a rather useful update on recent work by HP on their ReRAM technology. Several slides provide a ‘one slide’ summary of recent publications. Highlights I picked up on are the move from TiOx and TaOx based cells to those containing a TaOx/TiOx bilayer which give a more non-linear I-V characteristic (and hence help reduce the impact of sneak paths in a cross bar array). Another couple of slides describe so ultra fast measurements on a specially configured ReRAM cell. While impressive, this does emphasise the fact that taking advantage of such high speed switching in a chip is going to be challenging! Also, Dr Nickel makes the point that the devices are really analogue devices where the resistance can be accurately controlled by the compliance current over several orders of magnitude. However, I did not follow the slides on switching energy but can well believe the statement that almost all the applied energy does not get consumed by the actual switching process.
So some interesting presentations and my appreciation goes out to the summit organizers for making them available but I am left with the feeling that there is no substitute for actually attending a conference!
Christie Marrian, www.ReRAM-Forum.com Moderator