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New Memristor Makes Low-Cost, High-Density Memory
KentuckyFC writes "A group of electronics engineers have discovered that a thin layer of vanadium oxide acts as a memristor, the fourth basic component of circuits after resistors, capacitors, and inductors that was discovered last year. At a critical temperature, a current passing through the layer causes it to change from an insulating state to a metal-like state, thereby changing its resistance (abstract). The effect lasts many hours — which is what makes the layer a memristor (a resistor with memory). The team says this could be scaled up to make resistive random access memory, or RRAM, at very low cost, from little more than layers of vanadium oxide."
The article suggests use as resistive RAM rather than a solid state drive. As long as it doesn't need to be a permanent memory element it might be possible to refresh periodically on a schedule that's safely less than the lifetime of the state transition, i.e. boost the phenomenon every hour or two. Shouldn't cause much of a power hit.
I thought the more exciting announcement was that memristors could be tripled up to create transistors that were (despite being tripled up) still much smaller than a standard transistor.
Then, there were bits about them supporting more than just binary states, which would increase complexity and density yet again.
Denser memory may be the first pratical consumer product, but if the other possiblities work out, I'm pretty sure that memory will also be the least significant.
correction:
it's actually 0.6 mA, so that would be 0.24W/byte, and only during the (very short) write pulse. Still some work to do, but it could possibly end up more efficient than flash memory.
No more need to supercool RAM on seized computers in order to extract passwords - the RAM will just naturally hold state for hours.
If they're going to use this, (some) people are going to want to have more secure operating systems that don't leak security data all over the place.
http://en.wikipedia.org/wiki/Memristor#Potential_applications
[27] http://www.nytimes.com/2008/05/01/technology/01chip.html
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Not really; if you only have to refresh it once every four hours, you can do that for a LONG time on a battery. What I really see as the potentially big win is if they can get the speeds up to SRAM levels. Technically it would be a kind of DRAM, but if you only have to refresh it once every four hours, then just using a LRU scheme when allocating memory might mean that in practical usage you would never need a refresh anyway.
"You're right," Fisheye says. "I should have set it on 'whip' or 'chop.'"
Yes. Resistance is fusile.
Kevin Smith on Prince
Sorry to be so harsh, but the specific experiment reported here is of little to none value outside of science. Why?
Hysteretic resistive switching in metal oxide systems is a well known phenomenon (RRAM) and occurs in all transition metal oxides with noble eletrodes. This is what has been recristened as "Memrestor" by HP. It is widely agreed upon that this switching mechanism is due to a redox reaction where oxygen is added or removed from the insulator. The specifics (filament, interfacial barrier lowering etc.) are still subject of current research though.
The experiment in the paper takes a slightly different approach: vanadium oxide has a very interesting property where its resistance switches apruptly by orders of magnitude at a certain temperature due to a reorganisation of its electronic structure. This phenomenon is known as metal to insulator (MTI) transition and has been research for at least 50 years.
The MTI has a hysteretic behavior which means that it retains its state if you vary the temperature only a little above or below the critical MTI temperature Tc. The researchers have now shown that if you keep the temperature of the system close to Tc, you can use an additional electric current to switch the resistivity of the system. A possible explanation could be self heating.
Why is it useless for practical application?
1) The phenomenon instrinsically only works at a certain temperature. Deviations by fractions of degrees K will destroy all information.
2) As far as I can see they only demonstrated electrical switching into one direction. To erase the memory both would be required.
All in all a nice experiment, but again with typical university style hype, piggybacking on the Memristor craze.
I am also relatively certain that current driven MTI switching has been reported before. I am aware of a couple of experiments where a field switched MTI transition was proposed for transistors. Those devices should exhibit exactly the same hysteresis and "memory" properties.
i = current
q = charge
V = voltage
phi = magnetic flux
dq = i dt (current)
dphi = V dt (voltage)
dV = r di (resistance)
dq = C dv (capacitance)
dphi = L di (inductance)
(see http://www.spectrum.ieee.org/may08/6207)
It was hypothesized that some device should exist that connects charge and flux, and follows the relationship: dphi = M dq. This is "memristance." It was predicted in 1971 as the "fourth basic circuit element"; see: http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?arnumber=1083337
They were fundamentally theoretically new then. They just had not been physically realized and connected with that theory until recently.
Please don't dismiss them as "pure marketing hype" without some research.
There are four basic quantities that are of concern in an electrical circuit: charge(q), current(i), voltage(v), and magnetic flux(phi). Those four quantities can be matched into pairs 6 different ways. Two of those pairs are time constrained by basic physical law: dq = i dt and dphi = v dt. Three of the remaining are determined by the properties of resistance(R), capacitance(C), and inductance(I): dv = R di, dq = C dv, and dphi = L di. Resistors, capacitors, and inductors are ultimately just devices that have a lot of one of those three properites and nearly none of the others.
It was speculated in the early 70's that there must be a fourth property, called memristance(M), that describes the 'missing' relationship: dphi = M dq. The memristor, then, is the corresponding device that has a lot of memristance but none of the other three properties. While memristance has been previously measured in complex systems, no one figured out how to build an feasible isolated memristor until just recently.
The four are considered fundamental in that none of the four can be built from a combination of the other three (e.g. you can't make a resistor from some combination of capacitors, inductors, and memristors) but any device can be built from some combination of the four (e.g. you CAN make a diode from L's, C', R's, and M's).
The memristor is is just a way to model nonlinear circuit elements and is one of many components in a nonlinear expansion for circuit modeling. See this paper by Leon Chua, the memristor's inventor. Note that in this paper the fourth element of the four element torus is negative resistance and not the memristor. All of the publicity over the memristor has been (sucessfull) marketing by some researchers at HP. .
From the talk page for the memristor on wikipedia
"Resistance, Capacitance and Inductance are regarded as fundamental because to each there corresponds a different picture of what is going on with the energy. Resistance refers to the loss of energy to Joule heating. Capacitance refers to storage of energy in the electric field. Inductance refers to storage of energy in the magnetic field.
If memristance is the "fourth fundamental" circuit element then memristors must do something with the energy they are imparted other than turn it into heat, or store it in electric or magnetic fields. So what do memristor supporters have to say about this? nothing. This is not surprising, since the concept of memristance stems from a purely mathematical argument bent on taming the current/voltage relationships of nonlinear circuit elements. The concept of memristance was invented out of convenience to avoid dealing with frequency-dependent (time-dependent) resistance, inductance, and capacitance. Thus the memeristor is not "fundamental", unless in your book fundamental is synonymous with convenient."