Thursday, March 18, 2010

DEMYSTIFYING THE MEMRISTOR

In the past, electronic circuit theory has revolved around three fundamental components: the resistor, the capacitor, and the inductor. Now a fourth has been added to that list, the memristor. First postulated in 1971 by Leon Chua at the University of California at Berkeley, a working example was recently created by Dmitri Strukov and colleagues at HP Labs.


A memristor is basically a two terminal device whose resistance depends on the magnitude and polarity of the voltage applied to it and the duration of the voltage applied to it. If the memristor is turn of, it remembers is most recent resistance until the next time you turn it on, whether that happens a day later or a year later .This fascinating feature which makes memristors a future promise for technology. As mentioned above it is regarded as the fourth circuit element.

Theoretically Memristors, a concatenation of " memory
resistors", are a type of passive circuit element that maintains a relationship between the time integrals of voltage and current across a two terminal element. This function called memristance is similar to resistance. Thus, a memristor's resistance varies according to devices memristance function. Memristance is a property of an electronic component. If the charge flows in one direction through a circuit, the résistance that component of the circuit will increase and if the charge flows in opposite direction in the circuit, the resistances will decrease. If the flow of the charge is stopped by turning off the applied voltage, the component will 'remember' the last resistance it had, and when the flow of charge starts again the resistance of the circuit will be what it was when it was last active.


Memristance of a material become more and more strong as its size reduces. At some points we scale into the realm of nanoelectronics, it will be necessary to take account of memristance in our circuit models in order to simulate and design electronic circuits properly. The definition of memristor is solely based on fundamental circuit elements like resistance, capacitance and inductance. Unlike those three elements, which are allowed in linear time invariant (LTI) system theory, memristor’s are nonlinear and may be defined by any variety of time varying functions of net charge. A linear time-invariant memristor is simply a resistor.


A common analogy for a resistor is pipe carrying water. The water it self is analogous to electric charge, pressure at the input of the pipe is similar to the applied voltage, and rate of flow of water through pipe is the electrical current. Just as with an electrical resistor, flow of water through a pipe is faster if the pipe is shorter and /or it has a larger diameter. An analogy for a memristor is an interesting kind of pipe that expands or shrinks when water flows through it. It the water flows in one direction, the diameter of the pipe increases, thus enabling the water to flow faster.If the water flows in opposite direction, the diameter of the pipe decreases, thus slowing down the flow of water. If the water pressure is turned off, the pipe will retain its most recent diameter until the water turned back on. Thus, the pipe does not store the water like a bucket (for a capacitor) -it remembers how much water flowed through it.


History of memristor’s goes back to 1971 when Leon Chua at the University of California at Berkeley, reasoned from the symmetry arguments that there should be fourth fundamental element, which he called a memristor. There are four fundamental circuit variables: electric current, voltage, charge, and magnetic flux. For these variables, we have resistors to relate current to voltage, capacitors to relate voltage to charge, and inductors to relate current to magnetic flux, but we were missing one to relate charge to magnetic flux. That is where the memristor comes in.


There had been clues for existence of memristor all along. People had been reporting funny current voltage characteristics in the literature for about 50 years. But it was only two years back, that the researchers at Hewlet Packard Labs surprised the electronics community with a fascinating candidate for such a device: the memristor. It had been theorized nearly 40 years ago, but because no one had managed to build one, it had long since become an esoteric curiosity. That all changed on 1 May 2008, when a group published the details of memristor.The group
succeeded in creating a nanoscale memristor switch in HP Labs. Titanium dioxide was used for this. On controlling the switch: HP scientists were able to determine both when the current flowed through the switch and how much current flowed through it, operating the switch more like a dial. They could set the switch 'ON' or 'OF' -' 12 or 02'- and they could dial up or down to any thing in between. "A conventional device has just 0 and 1 -two states -this can be 0.2 or 0.5 or 0.9", says Yang. This quality is what gives the memristor its potential for brain like information processing.


The greatest application of the memristor is in the field of non volatile high speed memory technology. A memristor’s memory is non volatile .We can think that non volatile ram made with types of memristor materials that are currently being studied by many groups around the world could be a strong competitor to the flash memory market in about five years. Materials used for fabricating memristors are compatible with present IC manufacturing facilities. In the future NVRAM's made using memristors would result in computers which could turn on and off like electric bulbs. Currently the good folk at HP Labs have exploited memristor concept to create simple data storage devices. Using memristors, they have been able to store 100 gigabits on a single die in one square centimeter. That is substantially more than the 16 gigabits for a single flash chip, and a comparable storage density to modern hard drives. In the future, HP thinks they can get that up to a terabit or more per centimeter... with the access speed of DRAM. Clearly, this will vie with other technologies such as IBM's racetrack memory. Of course, storage is only one possible role for memristors.


A final beauty of memristors comes from their response to decreasing size. The smaller the device, the more important memristance becomes. Conventional electronic circuits have ever increasing problems with heat and leakage at smaller sizes, but memristance is proportional to the inverse of the square of the film thickness, so smaller films mean a stronger memristance effect. By developing transistors based on memristors, we may be able to continue scaling down microprocessors for a (relatively) long time to come.


A memristor is still far beyond this. It could work well both in digital and as well as in analog mode .This analog support could be used in developing analog computer which will work more or less the way information processing occur in our brains. Memistor makes it possible to create systems with some pattern matching abilities of the human brain. This can lead to better facial recognizing technology. These capabilities can also help it to learn from experience and lead to computers that learn. The impact of memristor is so great which promises it to be a future hero of technology.



8 comments:

Digital Dan said...

2020 by then we will have devices that can truly rival human thinking. For about the price of a car you could purchase something smarter then yourself.

Anonymous said...

Maxwell's Demon says:

"A common analogy for a resistor is pipe carrying water. The water it self is analogous to electric charge, pressure at the input of the pipe is similar to the applied voltage, and rate of flow of water through pipe is the electrical current. Just as with an electrical resistor, flow of water through a pipe is faster if the pipe is shorter and /or it has a larger diameter. An analogy for a memristor is an interesting kind of pipe that expands or shrinks when water flows through it. It the water flows in one direction, the diameter of the pipe increases, thus enabling the water to flow faster.If the water flows in opposite direction, the diameter of the pipe decreases, thus slowing down the flow of water. If the water pressure is turned off, the pipe will retain its most recent diameter until the water turned back on. Thus, the pipe does not store the water like a bucket (for a capacitor) -it remembers how much water flowed through it."

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