Memristor

A memristor - the name is a portmanteau word from English- memory ( memory) and resistor ( electrical resistance) - is a passive electrical component whose electrical resistance is not constant, but depends on its past. The current resistance of this device is dependent on how many charges have flowed in the direction. So that the resistance value across the time course of the flowed current is adjustable. This resistance is retained even without power supply.

Memristors are sometimes described in addition to the resistance, capacitor and the coil, the fourth fundamental passive component.

History

Leon Chua of the University of California, Berkeley, already described in 1971, the not yet existing at the time as a passive component memristor and its properties. The first physical realization of a thin film composite with such properties was not informed until 2007. In April 2008, researchers from Hewlett -Packard have presented a relatively simple structure layer composite of titanium dioxide with platinum electrodes as a memristor. End of August 2010 was shown in work by Jun Yao of Rice University that also works as a simple silicon dioxide layer material. In July 2012, criticism was that the physical concept of so-called " memristive systems " contrary to the Landauer principle, a fundamental principle of information processing could stand. This criticism with regard to the fundamental problem of Memristorkonzepts was confirmed in 2013 by Di Ventra and Pershin.

Construction

In 2007, a static version of the memristor was produced by Stanley Williams for the first time. This memristor stores its state in a chemical form by incorporation of dopant atoms in a semiconductor.

The memristor, manufactured by Hewlett -Packard is composed of a few nanometers thick titanium dioxide layer between two platinum electrodes. The right image in the colored part of the titanium dioxide layer is doped with oxygen vacancies (p- doping) and has a high electrical conductivity. The left part of the titanium dioxide layer is an insulator. When an electric field is applied, the oxygen vacancies drift, which shifts the space charge zone. This reduces the thickness of the insulation layer. With decreasing thickness of the insulating layer increases the conductivity of the memristor, where the tunneling ( field emission ) plays an essential role.

Experimentally, such a memristor is characterized in an u / i - diagram by a hysteresis curve that passes through the coordinate origin ( pinched hysteresis loop), shown in the diagram. At the zero crossing of the u / i - curve one can see that it is a passive electrical component in the memristor. The state of the memristor is characterized by the location of the dividing line between the differently doped areas.

The memristor Rice University in 2010 is characterized by an even simpler structure. It consists of a 5 to 20 -nanometer-thick silicon dioxide layer between conductive doped silicon layers. A really active than originally envisaged, additional layer of graphene proved to be unnecessary. The device then only needs two connections like a resistor (as opposed to three in a flash memory cell) and can be implemented extremely inexpensive on an area of ​​about 10 nm edge length and because of the simple structure. The function of which is that (each about 5 nanometers in length without the oxygen, the crystals ) to arrange in the oxide layer upon application of the programming voltage paths of pure silicon nanocrystals to a conductive structure, which can be re- reproducible and repeated destroyed by a different voltage.

Functional equations

A memristor is defined as a device in which the flux and the electric charge q for a period independent in general non-linear function are coupled. Memristanz this function is defined by the rate of change of flow with the charge.

The size is called the ( incremental ) Memristanz or Memristivität and has in the SI system, the units of ohms ( Ω ). The magnetic flux is the time integral of the voltage applied to the terminal memristor defined (see voltage time area ) and has in the SI unit system, the Weber ( Wb). In fact arises at the memristor when an electrical voltage ideally but not considered a magnetic field. Because unlike the electric coil is also formed within the memristor, an electrical field that corresponds to the externally applied voltage. The current -voltage (induced voltage) in the circuit is therefore equal to zero, so that no induction occurs.

The behavior of the memristor thus complements the other three fundamental components

Here, the electric charge, the electric current, the electric voltage and the (magnetic) flux.

As shown, the correlations are

And

The voltage U at a memristor depends on the current I directly on the Memristanz:

For every moment a memristor behaves like a normal resistance, but (q ) be "resistance" M depends on the past of the stream from. A linear memristor ( constant- M) can not be distinguished by an electrical resistor with M = R.

For the current I and vice versa:

With

The variable W is referred to as an incremental conductance and has the Siemens unit (S).

The stored charge in the memristor is calculated as the integral of the electric current over time

Is given as the flow existing in memristor by the integral of the voltage across the time.

This integration is in the practical implementation due to the limited number of charge carriers neither unlimited nor linear, has very well but a monotonous course on.

The conversion in the memristor electrical power P is given by

Since it is a passive component in the memristor, applies also due.

Hypothetical application

The first prototypes and patterns of memristors were produced in 2007. As of the end of 2010, there are currently no practical applications. However, it is conceivable that memristors - in areas where no reinforcement is required - may replace transistors. However, the practical proof of this release in the form of available on the market memristors missing.

In May 2008, the scientists at Hewlett -Packard had advanced in the 15 - nanometer range; as the limit of conventional manufacturing processes are 16 nanometers ( see: photolithography ). A feature of memristors is not only to be able to store the binary values ​​0 and 1, but - in the form of analogue - any intermediate values ​​.

Patents memristors include applications in the field of programmable logic, the electronic signal processing, artificial neural networks and control systems.

Neuristoren

In the form of Neuristoren it should be possible memristors how biological synapses to function and predestine them allegedly for applications in the field of artificial intelligence.

However, it should be noted that this is the memristor is a simple device is capable of providing such functionality is not of itself, but only in the form of components in complex circuits. References such as on artificial intelligence may therefore be considered as tags, which serve to bring attention to the general public.

The application of memristors is rather considered in the field of artificial neural networks. This is about an application in the field of control engineering, the audio processing (eg noise reduction, speech recognition ), image processing (eg, object recognition ) or the Neuromorphings conceivable. This memristors replace transistors for simulation of synapses. Since such a simulation requires many transistors, the use of memristors can reduce the size of the circuit and thus the costs.

Memory

The power consumption in memories as a memory element memristors is far smaller than the current consumption of the conventional DRAM chips. However, the non-volatile memristor currently reach only about a tenth of the speed of the latter. A further advantage is the high packing density. The presented by HP " crossbar " memory has a packing density of 100 Gibit · cm -2, while the available memory in the same period have a density of 16 Gibit · cm -2. Memristors can be manufactured with the same processes as well as semiconductor structures and can be integrated into microelectronic circuits, therefore.

In addition to the much lower power consumption would computers that are equipped with memristors, including also offer the advantage after switching without booting to be immediately operational. A further advantage is that the memristor if it is read with the aid of alternating current, maintains its memory contents.