Wednesday, 21 November 2012

Memristor, a brief description

A team from UCL experimented with silicon oxide to make LEDs, and accidentally caused the arrangement of the silicon atoms to change and form less resistive filaments within the solid silicon oxide. The switch in resistance is made much more efficiently than before, and the process has been described in a Journal of Applied Physics paper. The team were trying to make LEDs, but found that their devices appeared to be unstable.
A UCL PhD student in the department, Adnan Mehonic, was asked to look into this and found that the silicon oxide wasn’t unstable at all, and in fact was flipping predictably between various conducting and non-conducting states.
The work revealed that a material we had been looking at for some time could in fact be made into a memristor. The potential for this material is huge. During proof-of-concept development the team have shown they can program the chips using the cycle between two or more states of conductivity.
The memoristor was originally envisioned in 1971 by circuit theorist Leon Chua as a missing non-linear passive two-terminal electrical component relating electric charge and magnetic flux linkage. More recently the memristor definition was generalized by Leon Chua to cover all forms of 2-terminal non-volatile memory devices based on resistance switching effects and Chua has claimed that the memristor is the oldest known circuit element with its effects predating the resistor, capacitor and inductor. The memristor is currently under development by various teams including Hewlett-Packard, SK Hynix, and HRL Laboratories.
When current flows in one direction through a memristor, the electrical resistance increases; and when current flows in the opposite direction, the resistance decreases. When the current is stopped, the memristor 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. It has a regime of operation with an approximately linear charge-resistance relationship as long as the time-integral of the current stays within certain bounds. Effectively the memristor is a voltage dependent resistor or switch, whose characteristics
is similar to a diode but can be utilized in logic circuits for long term memory states. In 2008, a team at HP Labs announced the development of a switching memristor based on a thin film of titanium dioxide. These devices are being developed for application in nanoelectronic memories, computer logic, and neuromorphic computer architectures.
In October 2011, the same team announced the commercial availability of memristor technology within 18 months, as a replacement for Flash, SSD, DRAM and SRAM. In March 2012, a team of researchers from HRL Laboratories and the University of Michigan announced the first functioning memristor array built on a CMOS chip for applications in neuromorphic computer architectures. The CMOS chip which is a common form of integrated circuit can be easily refitted for memristor technology, and serve in current logic circuits (with a little adjustments for latency and memory density trade offs).
The definition of the memristor is based solely on the fundamental circuit variables of current and voltage and their time-integrals, just like the resistor, capacitor, and inductor.
The resistance of a memristor depends on the integral of the input applied to the terminals (rather than on the instantaneous value of the input as in a varistor). 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". Another way of describing a memristor is that it is any passive two-terminal circuit element that maintains a functional relationship between the time integral of current (called charge) and the time integral of voltage (often called flux, as it is related to magnetic flux). The slope of this function is called the memristance M and is similar to variable resistance. Batteries can be considered to have memristance, but they are not passive devices.

Some researchers have argued that biological structures such as blood and skin should also be considered to be memristors. Others have argued that the memory device under development by HP Labs and other forms of RRAM are not actually memristors or memristive systems but part of a broader class of variable resistance systems and that a broader definition of memristor is a scientifically unjustifiable land grab to favor the memristor patents of Hewlett-Packard.
The potential of arranging memristers in a lattice could replace a whole days worth of video roughly 100 Gigabyte of data in a space no bigger then a SD card. As one memristor can replace ten transistors, as a flop flop memory configuration. The potential space is already saved and power too.
The projected date for sale of this new memory will be in 2014, although the product maybe ready in summer 2013. Its expected that memristers will appear in small drives like flash drives or DRAM. Hopefully replacing spinning hard drives with its solid state memristor drives in a space of 5 years, which will make dvd and blue-ray discs obsolete.
The closest description in nature of what a memistor is a synapse, which when arranged in a computer can quicken boot up speeds in a traditional computer. Although its compatibility to work with existing hardware. The potential is to possibility integrate this technology in the artificial neurosynaptic computing chips, as a improved form of hardware for synthetic intelligence thus reducing power. The future of computing is to reduce size proving Moore's law is correct, but as this law will become to difficult this next decade. The use of memristors will still allow a continuation of Moore's law, at least for memory containment...

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