‘(N)ow all the EE textbooks need to be changed ‘
by Ducky Paredes
Professor Leon Chua is a graduate of MIT — Mapua Institute of Technology and, for his PhD, that other MIT in Massachusetts.
In 1972, as a University of Californina, Berkley professor, Dr. Chua wrote a paper in which he argued that in addition to the resistor, the capacitor and the inductor, there had to be a 4th element which would be a memory resistor or memristor.
An article in the IEEE Spectrum on “The Mysterious Memristor” by Sally Adee explains what this is all about:
“The memristor’s story starts nearly four decades ago with a flash of insight by IEEE Fellow and nonlinear-circuit-theory pioneer Leon Chua. Examining the relationships between charge and flux in resistors, capacitors, and inductors in a 1971 paper, Chua postulated the existence of a fourth element called the memory resistor. Such a device, he figured, would provide a similar relationship between magnetic flux and charge that a resistor gives between voltage and current. In practice, that would mean it acted like a resistor whose value could vary according to the current passing through it and which would remember that value even after the current disappeared.
“But the hypothetical device was mostly written off as a mathematical dalliance. Thirty years later, HP senior fellow Stanley Williams and his group were working on molecular electronics when they started to notice strange behavior in their devices. ‘They were doing really funky things, and we couldn’t figure out what [was going on],’ Williams says. Then his HP collaborator Greg Snider rediscovered Chua’s work from 1971. ‘He said, ‘Hey guys, I don’t know what we’ve got, but this is what we want,’ ‘ Williams remembers. Williams spent several years reading and rereading Chua’s papers. ‘It was several years of scratching my head and thinking about it.’ Then Williams realized their molecular devices were really memristors. ‘It just hit me between the eyes.’
“The reason that the memristor is radically different from the other fundamental circuit elements is that, unlike them, it carries a memory of its past. When you turn off the voltage to the circuit, the memristor still remembers how much was applied before and for how long. That’s an effect that can’t be duplicated by any circuit combination of resistors, capacitors, and inductors, which is why the memristor qualifies as a fundamental circuit element.
“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.’
“Chua deduced the existence of memristors from the mathematical relationships between the circuit elements. The four circuit quantities (charge, current, voltage, and magnetic flux) can be related to each other in six ways. Two quantities are covered by basic physical laws, and three are covered by known circuit elements (resistor, capacitor, and inductor), says Columbia University electrical engineering professor David Vallancourt. That leaves one possible relation unaccounted for. Based on this realization, Chua proposed the memristor purely for the mathematical aesthetics of it, as a class of circuit element based on a relationship between charge and flux.
“Chua calls the HP work a paradigm shift; he likens the addition of the memristor to the circuit design arsenal to adding a new element to the periodic table: for one thing, ‘now all the EE textbooks need to be changed,’ he says.
“So why hadn’t anyone seen memristance? Chua actually produced a memristor in the 1970s with an impractical combination of resistors, capacitors, inductors, and amplifiers as a proof of concept. But memristance as a property of a material was, until recently, too subtle to make use of. It is swamped by other effects, until you look at materials and devices that are mere nanometers in size.
“No one was looking particularly hard for memristance, either. In the absence of an application, there was no need. No engineers were saying, ‘If we only had a memristor, we could do X,’ says Vallancourt. In fact, Vallancourt, who has been teaching circuit design for years, had never heard of memristance before this week.
“But the smaller the scales of the devices scientists and engineers were working with got, the more the devices started behaving with the postulated ‘memristor’ effect, says Chua, who is now a senior professor at Berkeley.
There had been clues to the memristor’s existence all along. ‘People have been reporting funny current voltage characteristics in the literature for 50 years,’ Williams says. ‘I went to these old papers and looked at the figures and said, ‘Yup, they’ve got memristance, and they didn’t know how to interpret it.’
“’Without Chua’s circuit equations, you can’t make use of this device,”’ says Williams. ‘It’s such a funky thing. People were using all the wrong circuit equations. It’s like taking a washing machine motor and putting it into a gasoline-powered car and wondering why it won’t run.’
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Will someone please take note of this great achievement by a Filipino so that we will be known for greater achievements than beating people up in the ring or for singing and dancing.
It may be indicative of what is important to us that while we have a National Artist Award and have heaped all sorts of awards on a boxer, we do not have anything as significant for achievements in the sciences.
Says a science professor: “This is really a once in a lifetime accomplishment for anyone. Practically arguing by symmetry, he argued that this device ought to exist. It took HP Research labs to make it happen 37 years after his paper. Right now it is the hottest new technology development of 2008. We really ought to give him a major award for this work. To my knowledge this may be the most significant contribution made by a Filipino to science and engineering ever.”
Leon Chua is a great Filipino, someone that all Pinoys can be proud of. By recognizing his great achievement, we honor the country and ourselves.
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hvp 08.20.08)
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