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Monday, October 11, 2010

MEMRISTOR: The fourth component of the electrical circuit...

Researchers at Hewlett-Packard have developed a working unit of a memory circuit that has existed in theory for 37 years, which could ultimately replace RAM and make computers more intelligent by tracking data it has retained.
The technology, called memristor, could allow computers to make decisions by understanding past patterns of data it has collected, similar to human brains collecting and understanding a series of events.
For example, a memristor circuit could be capable of telling a microwave the heating time for different food types based on the information it has collected over time, said Stanley Williams, senior fellow at HP.
A memristor circuit requires lower voltage and less time to turn on than competitive memory like DRAM and flash, Williams said. "Because it [uses] less voltage and less time, of course, it uses much less power," Williams said. Denser cells also allow memristor circuits to store more data than flash memory.
Through prototypes, HP is trying to show circuit designers what memristor is capable of doing. "What we have done is confirmed a concept for a new electronic device that was originally proposed nearly 40 years ago," Williams said.
Memristor is the fourth fundamental circuit element, joining the other three -- resistor, capacitor and inductor -- that had been known for 150 years, Williams said. The element has properties that cannot be duplicated by any combination of the other three elements, Williams said.
"It is as fundamental to electronic engineering as a chemical element is to chemistry or an electron is to physics," Williams said.
In a 1971 academic paper, Leon Chua, a mathematician and professor at the University of California at Berkeley, wrote that memristor would have properties similar to a synapse in a brain. The synapse makes connections between two neurons, and the more often a signal is sent to a synapse, the stronger the synapse gets.
"That is a very different type of behavior than anything that had been observed before in circuit elements," Williams said.
HP is not going to reproduce all the functions of a brain in memristor, but the company is trying to build a relatively simple computing machine that operates on a different principle from today's computers, Williams said.
The scientists created the memory by applying a charge on a circuit with blocks of titanium dioxide. The actual resistance of the memristor changes depending on the amount of current flowing through the circuit, Williams said. When the current is turned off, the memory retains the information it has acquired.
Although the concept of memristor has existed for a while, the memory prototype is an academic device that will first work its way to academia. It could hit the commercial semiconductor market in five years, Williams said.

what is memristor...?
A memristor is a passive two-terminal circuit element in which the resistance is a function of the time history of the current and voltage through the device. Memristor theory was formulated and named by Leon chu in a 1971 paper.On April 30, 2008 a team at HP Labs announced the development of a switching memristor. Based on a thin film of titanium dioxide, it has a regime of operation with an approximately linear charge-resistance relationship.These devices are being developed for application in nanoelectric memories, computer logic, and nueromorphic computer architecture.

Background


Memristor symbol.
A memristor is a passive two-terminal electronic component for which the resistance (dV/dI) is proportional to the amount of charge that has flowed through the circuit. When current flows in one direction through the device, the resistance increases; and when current flows in the opposite direction, the resistance decreases. When the current is stopped, the component retains the last resistance that 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.
More generally, a memristor is a two-terminal component in which the resistance depends on the integral of the input applied to the terminals, rather than on the instantaneous value of the input at the terminals. Since the element "remembers" the amount of current that has passed through it in the past, it was tagged by Chua with the name "memristor." A general memristor is any of various kinds of passive two-terminal circuit elements that maintain a functional relationship between the time integrals of current and voltage. This function, called memristance, is similar to variable resistance. Specifically engineered memristors provide controllable resistance, but such devices are not commercially available. Other devices such as batteries and varistors have memristance, but it does not normally dominate their behavior. The definition of the memristor is based solely on fundamental circuit variables, similar to the resistor, capacitor, and inductor. Unlike those three elements, which are allowed in linear time-invariant or LTI system theory, memristors are nonlinear and may be described by any of a variety of time-varying functions of net charge. There is no such thing as a generic memristor. Instead, each device implements a particular function, wherein either the integral of voltage determines the integral of current, or vice versa. A linear time-invariant memristor is simply a conventional resistor.
In his 1971 paper, memristor theory was formulated and named by Leon Chua,extrapolating the conceptual symmetry between the resistor, inductor, and capacitor, and inferring that the memristor is a similarly fundamental device. Other scientists had already proposed fixed nonlinear flux-charge relationships, but Chua's theory introduced generality.
Like other two-terminal components (e.g., resistor, capacitor, inductor), real-world devices are never purely memristors ("ideal memristor"), but will also exhibit some amount of capacitance, resistance, and inductance.

Potential applications

Williams' solid-state memristors
They can also be fashioned into non-volatile solid-state memory, which would allow greater data density than hard drives with access times potentially similar to DRAM, replacing both components.HP prototyped a crossbar latch memory using the devices that can fit 100 gigabits in a square centimeter, and has designed a highly scalable 3D design (consisting of up to 1000 layers or 1 petabit per cm3).HP has reported that its version of the memristor is currently about one-tenth the speed of DRAM.The devices' resistance would be read with aternating current so that the stored value would not be affected.
Some patents related to memristors appear to include applications in programmable logic,signal processing,neural networks,and control systems.
Recently, a simple electronic circuit consisting of an LC network and a memristor was used to model experiments on adaptive behavior of unicellular organisms.It was shown that the electronic circuit subjected to a train of periodic pulses learns and anticipates the next pulse to come, similarly to the behavior of slime molds Physarum polycephalum subjected to periodic changes of environment.Such a learning circuit may find applications, e.g., in pattern recognition.

This technology can change the way we see the future and make our life easy by making fast and intelligent computers which will help to solve major research problems and help to generate newer technologies......

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