Memristor

Memristor is a combined word of Memory and Resistor. It is given name memristor because of its remembering property. Memristor can remember the amount of current passed through it!

Memristor is a two terminal passive circuit element which has non linear properties. When current through the device is in one direction, the resistance increases and when current through the device is in opposite direction, the resistance decreases.

But the main property which makes this component very special is when current passing through it stops, it retains the last resistance that it had, and when the flow of current starts again, the resistance of the circuit will be what it was when it was last active. That means it can remember the amount of current flowed through it. This property gives this component ability to work as memory device or data storage device.

Memristor was first theoretically invented in 1971 by Leon Ong Chua. He is a professor at university of California, Berkeley. Leon Ong Chua is widely known as father of nonlinear circuit theory and cellular neural networks. Leon Chua theoretically proved the existence of Memristor in a paper published by him in 1971. But unfortunately he could not find physical model of it.

But 37 years later, a team of researchers at Hewlett Packard (HP Labs) led by R Stanley Williams was able to make physical model of memristor in 2008. This model of memristor was developed by using a thin film of titanium dioxide and they are planning to launch it commercially as a memory device in the time frame of 2013 – 2014. The researchers also announced that memristor can be the replacement of flash memory, SSD, DRAM and SRAM.

Memristor is considered as fourth basic element of electronics. Resistor, Capacitor and Inductor are first three basic elements of electronic circuits.

This image is of a circuit with 17 memristors which is captured by an atomic force microscope.

RAM is a volatile memory that means the data stored in it disappears when the power is turned off. While memristor is a non-volatile memory, which means the data stored in it remains in it when power is turned off. It has a very fast read and write time so it can be used as a non-volatile RAM. Advantage of using memristor as RAM is computers don’t need to reboot every time when it is turned on.

”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.”

Memristor has ability to remember wide range of electrical states unlike only “on” and “off” in digital components. Memristor can remember values in analog way. This ability makes memristors able to perform more complex tasks than todays computers.

Memristors will be cheaper and far faster than flash memory, and allow far greater memory densities. Read time of memristor is less than 10 nanoseconds and wrier/erase time is about 0.1 nanoseconds which is faster than flash memory.

Conventional memory storage device use flip-flops which can store only one bit but memristor is able to store four bits which can increase storage capacity. Memristors are energy efficient than RAM because memristor doesn’t require any energy to maintain the data srorage.

Memristor chips can be made using three – dimensional layered structure which can process and store data. Making process of memristor is easy and completely compatible with today’s CMOS chip making process. It can be scaled to very small geometries without losing its properties.

Memristors can also be used as a microprocessor.

Researchers believe that the computers made using memristor can process and associate information in a manner similar to that of the human brain. Lots of researchers are trying to write a computer code which can simulate brain function on standard computer. These researchers have to use big machines which use enormous power to operate. But Williams suggests using hardware instead of computer code to simulate human brain. This hardware is made of memristor which can reduce the complexity of human brain simulator.