Tuesday, February 21, 2017
In memoriam: Millie Dresselhaus
Millie Dresselhaus has passed away at 86. She was a true giant, despite her diminutive stature. I don't think anything I could write would be better than the MIT write-up linked in the first sentence. It was great to have had the opportunity to interact with her on multiple occasions and in multiple roles, and both nanoscience in particular and the scientific community in general will be poorer without her enthusiasm, insights, and mentoring. (One brief anecdote to indicate her work ethic: She told me once that she liked to review on average something like one paper every couple of days.)
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6 comments:
No joke - it's just that she must've reviewed 150 papers a year or something on that order, which is just phenomenal. She felt that refereeing was a form of mentoring, and like all such things she took it seriously and did a better job than just about anyone else.
Hi Doug,
We will all miss Millie Dresselhaus. I didn't know her personally, but she is my academic "grandmother", so I have always felt a connection with her.
On a somewhat related note (since Millie worked on carbon nanotubes), we have been hearing quite a bit lately about Nantero's new NRAM memory technology. This is potentially revolutionary for the electronics industry, since NRAM cells could potentially replace DRAM, with zero static power dissipation, but the mechanism behind switching in these cells seems mysterious to me. They work by "snapping" carbon nanotubes together when a certain voltage is applied, which is fairly intuitive, but the part that puzzles me is how they manage to reset the cell by reverting the current and voltage. They claim it has to do with some kind of thermal ("phonon") mechanism, but I think that is only part of the story.
Have you heard about this technology, and do you understand the mechanism behind the reset operation?
Looking forward to your post as always!
Anon, Nantero has been working on this for something like 15 years. As you say, the idea is that "set" comes about from electrostatic attraction between tubes that ends up with them sticking together, and "reset" happens at high bias, presumably when they heat the heck out of the tube network via current. If there is one junction, for example, that limits the current, the heating will happen most near there. I agree with your skepticism about the reset mechanism. Really where the electronic energy goes into phonons is not trivial and can be tens of nm away from a tube-tube junctions. There are many "resistive switching" structures that show qualitatively similar properties, with conducting filaments disrupted at high bias because of thermally driven processes.
I'd also wonder about the process tolerance of making these structures en masse. Seems like you'd need great control over the junction environment (to avoid adsorbates, etc. that might change the adhesion properties of the tubes, and to avoid doing oxidative chemistry). To be fair, though, environmental control and packaging are also critical to technologies like flash. Functionally, Intel's reported crosspoint memory structures sound operationally similar, even though they have nothing to do with nanotubes.
Yes, I realize that Nantero has been promoting their technology for many years now, but I hear that this time they are indeed much closer to large-scale implementation:
http://spectrum.ieee.org/nanoclast/semiconductors/materials/nrams-ship-may-have-finally-come-in
My understanding of these devices is that they function similarly to a ReRAM cell, which turn on by forming a filament of vacancies or metal atoms, but use the nanotubes as some sort of additional "stabilizer" in the cell. This is very speculative, but I am still suspecting some sort of electrochemical (or possibly PCM-like) process in the cell, since the SET/RESET mechanism requires asymmetry after all.
I did not work for her, but as a post doc I collaborated closely with her group for a couple of years. She was the real deal. Not only brilliant, but also kind and supportive, and somehow also demanding in a way that brought the best out in people. I knew she wasn't young, but I still find myself shocked and depressed over her passing.
Seems worth mentioning that a very nice ad starring her came out just a few days ago: http://www.popsugar.com/tech/GE-Millie-Dresselhaus-Scientist-Commercial-2017-43232611
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