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The Memristor - they've found it! Answered

This came out quite a few days ago, but I haven't seen it until today.

HP's Henry Williams and his group have accidentally stumbled upon the fourth fundamental element in electronics - the memory resistor, or memristor. Basically, it's a resistor that changes its resistance with elapsed current flow, or total amount of charge that has passed through it, and retains its resistance even after current ceases to flow through it.

From the article:
"The classic analogy for a resistor is a pipe through which water (electricity) runs. The width of the pipe is analogous to the resistance of the flow of current—the narrower the pipe, the greater the resistance. Normal resistors have an unchanging pipe size. A memristor, on the other hand, changes with the amount of water that gets pushed through. If you push water through the pipe in one direction, the pipe gets larger (less resistive). If you push the water in the other direction, the pipe gets smaller (more resistive). And the memristor remembers. When the water flow is turned off, the pipe size does not change.

Such a mechanism could technically be replicated using transistors and capacitors, but, Williams says, “it takes a lot of transistors and capacitors to do the job of a single memristor.”

The memristor's memory has consequences: the reason computers have to be rebooted every time they are turned on is that their logic circuits are incapable of holding their bits after the power is shut off. But because a memristor can remember voltages, a memristor-driven computer would arguably never need a reboot. “You could leave all your Word files and spreadsheets open, turn off your computer, and go get a cup of coffee or go on vacation for two weeks,” says Williams. “When you come back, you turn on your computer and everything is instantly on the screen exactly the way you left it. "

Apparently, evidence of memristors has been around for quite a while, but it was only until now, during the age of nano-technological exploration, that we finally have labeled the "strange voltages" we've found in experimental circuits as a result of memristor behavior. The discovery was made while doping Titanium dioxide with some dopant that the article fails to cover. Anyhow, the resistance of TiO2 changes with the amount of dopant covering it. Since the dopant does not adhere perfectly to the TiO2 substrate, the flow of charges (electrons) can move the dopant, and cause it to cover more or less of the substrate, thus changing its resistance.

"Williams found an ideal memristor in titanium dioxide—the stuff of white paint and sunscreen. Like silicon, titanium dioxide (TiO2) is a semiconductor, and in its pure state it is highly resistive. However, it can be doped with other elements to make it very conductive. In TiO2, the dopants don't stay stationary in a high electric field; they tend to drift in the direction of the current. Such mobility is poison to a transistor, but it turns out that's exactly what makes a memristor work. Putting a bias voltage across a thin film of TiO2 semiconductor that has dopants only on one side causes them to move into the pure TiO2 on the other side and thus lowers the resistance. Running current in the other direction will then push the dopants back into place, increasing the TiO2's resistance.

HP Labs is now working out how to manufacture memristors from TiO2 and other materials and figuring out the physics behind them. They also have a circuit group working out how to integrate memristors and silicon circuits on the same chip. The HP group has a hybrid silicon CMOS memristor chip “sitting on a chip tester in our lab right now,” says Williams."

I think this is pretty awesome, considering the current breakthroughs in nanotechnology and downsizing of transistors, memristors would enable a whole new field to be born, and circuit theory may have to be re-designed.

Like Leon Chua said, the man who first came up with the idea of a memristor, "now all the EE textbooks need to be changed."

These next few years in the field of EE should be very interesting =)

Image from Spectrum Online


Cool, new compoenent, now I want to make a new type of component! so, it's not really used as a resistor, just as a value. Like high resistance is 0 and low resistance is 1? I still don't understand the whole point, for you still need transistors to operate it (or a relay).

It's not just 0 and 1, it's all positive real numbers. raw components aren't digital (1 or 0), they're analog. You can read the resistance of the memristor into a digital component via an a/d converter, which means a lot more data could possibly be stored, but it's all based on how long the current is flowing through the memristor.


10 years ago

I don't quite get it. First of all, I'm not seeing the desireable intuitive physical explanation for the memristor (similar to "electrons collect on the plate of the capacitors", although that's something of an over-simplification.) Second of all, it seems to me that any number of electrochemical things would behave similarly to the device they produced, including most rechargible batteries.

There's a good article in EE Times...

I would imagine there is an electrolytic or similar process going on, so current flowing causes movement of molecules across a barrier or dissimilar material boundary such that the barrier's resistance increases or decreases depending on the direction of current. Plenty of stuff in electronics doesn't have an explanation as easily accessible as that of the capacitor, just look at semiconductors. EDIT: OK I wrote that before reading the last paragraph of the quote above... seems my guess was right :)

Although it can be reproduced electromechanically, having a single component makes it "chipable" - I don't pretend to understand it properly, but a chip full of these could store a lot of data. I wonder if it could rival flash memory?

I saw this a couple of days ago, it's sweet because i'm heading off into Uni in 2 years to do EE, so it'll be cool using a new(ish) technology.

The Memistor - they've found it!

Had it been lost ???

Not so much lost as non-existent? They predicted its existence but never actually saw one until now.

That was just my variation of the old joke sign:

We Lost our Lease
( it was in the drawer just the other day )

I'd say "found" is an appropriate word - They predicted the existence of the device, and so no one ever "found" one. Now they have. ...or do my english skills fail to provide me with adequate words?

I bet it was in the last place they looked. BTW Titanium dioxide, is there anything it can't do? paint, sunscreen, eat smog, etc...

Ummm, april fools? (dude, its may)


I was talking electronics with a friend less than an hour ago, and I could not remember what it was called. The "memosistor" I came up with was close, though. It would help if I had actually pronounced the word at some point. I just did, so I'm good now.

haha - I got it wrong too! It's actually the memristor - I'm fixing all of that now.....

It looks like a pretzel stick with some kind of crackers on top of it....

kind of reminded me of thin strips of cheeze-whiz over a thin pretzel stick.