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# Memristor Memory Circuits

## Applications of Memristor Circuits In Computer Memory

Any electronics hobbyist or engineer used to be able to tell you that there were 3 fundamental components in all electronic devices upon which everything else is built upon: the resistor, the capacitor, and the inductor. Those with a little more in-depth electrical background may also know of Leon Chua who is a electrical engineering professor at the University of California Berkeley campus. He joined the electrical engineering and computer sciences department there in 1971 and that was the same year that he generalized the idea of the memristor as a fourth electrical component that would bring mathematical symmetry to the basic devices, and now 40 years later it looks like the memristor may be ready to go mainstream with Hewlett-Packard (HP) and memory chip partner Hynix putting the theory into production leaving designers wondering whether memristor memory will be the technology to replace nand flash memory as the non-volatile data storage solution of choice.

## Introduction To Memristor Theory

By way of a simple definition, a memristor can be classified as a resistor with memory. Depending on the direction of current flow through the memristor circuit component the electrical resistance (Ohms) will either increase or decrease. When the current source is removed then the memory aspect will take precedence and retain the level of resistance that was last produced. Mathematically this equates to a function which relates the charge and flux (time integral of current and time integral of voltage). The slope of said function is what is known as memristance.

So for many years after being imagined the memristor remained elusive because no engineer was able to find a physical compound that would produce the necessary effects as required by the theory. There had been memristives systems which showed such behavior but it was not until nanoscales were reached that the memristors were truly discovered. Above nanoscale the memristance is dominated by other electrical and field effect "anomalies." But, in 2012 HP Labs released information that they had indeed built working prototypes of memristors on a scale of 3nm by 3nm with 1ns switching time which sets the stage for the HP and Hynix partnership to rival the competition. Their implementation is a titanium dioxide memristor which utilizes the unique behavior of nanoscale thin films. It is a thin double layer of titanium dioxide film placed between electrodes. Due to the fast ion conduction at such a small scaled the HP memristor is a solid state device belonging to the nanoionic device category.

So from this new invention analysts can see that there are a variety of advantages that memristors bring to the market.

1) Can be you used as memristor memory data storage like SDRAM or nand flash and does not require constant power (non-volatile)

2) Can be scaled down to geometries much smaller than currently available allowing designers to overcome modern Moore's Law limits. For example, nand flash has a minimum limit due to memory cell disturbance and other degradation during read and write operations. The thin film technology of a memristor changes the game by orders of magnitude and actually improves in performance as it is scaled downwards.

3) 3d layering - The HP implementation can be stacked in vertical as well as horizontal layers allowing for chips and circuits to grow upwards on circuit boards and packages

4) Logic operations are possible as well as the memory usages. This will allow complex calculations and even allow the component to act as a processor. It seems to be a missing link in mapping brain activity and some even envision programming brains from the small pieces as a method of mapping a neural network.

## Fun Applications And Use Cases

The ideas of what memristors will be able to do in the near-future are big thinking at its finest. Within the past few months, researchers at the Korea Advanced Institute of Science and Technology (KAIST) in South Korea have made progress in designing new wearable electronics. The nanoscale of memristor memory allows it to be used in a bendable circuit similar to the emerging bendable LCD displays. The team designed a compact grid from amorphous titanium dioxide with aluminum electrodes. Such a cross-point configuration is being pursued by researchers but it needs to overcome a stumbling block problem with "sneak paths" before being fully ready for mainstream. Similarly, electronic paper is another area of advancement that could see memristors bringing things like the video commercial on the cereal box of Tom Cruise in Minority Report where nutrition information and interactive ads combine during breakfast. Despite obvious memristor paths of deliver like CPUs and computer RAM replacements, the devices could be used in fields like medicine where a flexible implant is needed to measure or manipulate biological functions or the neural network and synapses. The future looks ripe with possibility and it will be interesting to watch and see what role memristors will eventually hold.

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