Memristor is an English word, made by merging two words or formed from the two words memory and resistor. It is similar to a resistor but with memory.
A memory resistor (Memristor) is a passive two-terminal solid-state nonlinear electrical component. Besides resistors, capacitors, and inductors, the memristor is considered a fourth fundamental element in electrical circuits.
The capacitor, resistor, and inductor are the three basic passive elements that every electrical engineer is familiar with. They are called fundamental elements because they cannot be built with a combination of any other. As these are independent and passive because they do not need an external power supply to function.
The memristor can “remember” the electronic state and represent it using analog signals. A circuit of this type makes it possible to produce computers with instantaneous ignition, without it being necessary to reload the operating system at each start. The circuit retains information even without an electric current when the computer is turned off.
The possibility of storing analog signals makes it possible to store and process a quantity of data much larger than that processed by digital circuits, capable of representing only two states (0 and 1). The memristor is a new generation of memory and computing power.
Symbol of Memristor
Principle of Memristor
The memristor regulates the value of the electrical flow corresponding to a datum according to the history of voltages applied to them. Data can be stored and processed simultaneously. It makes memristor much more efficient than legacy systems.
Dynamic electronic devices are typically passive electronic components that work exactly like a variable resistor to manage data storage.
Similar to a resistor, it executes and maintains a safe current flow through a device, also remembering the last charge it passed.
A memristor differs from an ordinary resistor. It can “remember” charges even when no current or voltage is present. Therefore, the information can still be stored even when the device is turned off.
Construction and Working of Memristor
The memristor is a two-terminal device. The resistance of this element depends on the polarity, duration of time and the magnitude of the voltage applied.
We take a resistive titanium dioxide as a memristor element. This material is placed between the two electrodes made of platinum. The internal section of the titanium dioxide is divided into two parts. One part of the element is doped with titanium dioxide and the second is left undoped. When we apply a voltage across the electrodes, the oxygen atom present in titanium dioxide starts diffusing. The direction of oxygen atom diffusion depends on the polarity of the applied voltage. The diffusion of the oxygen atom cause to change in the resistance of the doped portion of titanium oxide.
History of Memristor
Dr. Leon Chua professor at California University introduced the memory resistor theory foremost in 1971. He described it as an electrical passive element, which he named memristor.
Professor Chua noticed a missing relationship in circuit theory, which led to predict the existence of a fourth passive fundamental element.
Although memory resistors always follow the fundamental circuit, and variables of voltage, current, and their time integrals, they have a dynamic function with memory and can be described as a net load function. The same is not found in the three other fundamental circuit elements (resistor, inductor, and capacitor).
The memristor is also capable of logical functions. This can significantly change the current compartmentalized structure of computing, as this allows the creation of devices capable of both processing and storing data in the same space. Currently, there is no standard memory resistor, but each device implements a particular function. In such a case the voltage integral determines the current integral, and vice versa.
Characteristic Voltage and Current (V-i) of the memristor
An important demonstration of the memristor is its characteristic V-i hysteresis curve for a memristor excited by a periodic signal such as square, sinusoidal, etc.
For a Memristor turned on by a periodic signal (square or sinusoidal), it can be seen from the above figure that when the voltage is zero, the current is also zero, and vice versa. So the voltage and the (v, i) current comply with identical zero crossing.
Characteristics of Magnetic flux and charge (Φ-q) of Memristors
A Memristor is a two-terminal passive circuit element that has a non-linear relationship between electrical charge (q) and magnetic flux (Φ) connection. It can be seen from the above figure that the charge slowly becomes zero as the magnetic flux y-axis.
Types of Memristor
Memristors are classified into several types based on their design and an overview of these types is given below. We can classify the memristor into two categories. They are-
- Molecular and Ionic Thin-film Memristors
- Spin and Magnetic
Now, we will discuss the sub-categories of the memristor.
Molecular and Ionic Thin-film Memristors
Molecular and Ionic Thin-film Memristors depend on the different properties of the materials and the hysteresis initiation in the material after incorporating charge in it.
This type of memristor has titanium dioxide as the main element. The hysteresis in this memristor happens due to the transfer of oxygen between the layers after its charging.
The ions are of two types anions and cations. The ion, when in the solid state, has the capacity to move a charge and it can move the charge from one place to another in any direction. The hysteresis in the material can be developed by dynamic doping. It has a single passive layer in between the electrode and the polymer as an active material. The polymer forces the ions. and as a result, it moves from the electrode to the film. It functions on the principle of the ‘Electrolytic process”.
Manganite is similar in construction and functionality to titanium dioxide. In Manganite, in place of titanium oxide, a film of manganite oxide is used.
It utilizes the multiple-quantum-well diodes, and therefore it can utilize dynamic doping and generate hysteresis among the film layers.
Magnetic Effect and Spin Technology
The development of this type of memristor is based on the degree of freedom technology. The polarization of the spinning electrons can be controlled by the magnetic field created by the moving magnet, and thus hysteresis is generated.
The spintronic technology is similar to titanium dioxide memristors. In this, we can change the direction of the spinning electron by using a movable magnet. As a result, this hysteresis generates between the device.
Spin Torque Transfer
MRAM (magnetoresistive random access memory) is a memristive component by nature. The hysteresis is generated by the Spin Valve Technology of MRAM. The spin valve technology varies the resistance and as a result, the current is induced through the junction made up of magnets. The MRAM inherently has magnetic and ionic characteristics.
In 1960, Bernard widrow designed a memristor with three terminals using Electroplating technology. The ‘non-solid states generate the hysteresis. The time integration of the current controls the conduction of the system.
Advantages of Memristors devices
Memristors have many advantages. They are-
- The Memristor uses power when the device is active similar to ‘non-volatile memory. Therefore, Memristors require less energy to operate.
- Memristor produces less heat.
- They are faster than current technologies such as SSD memories. Memristors are less expensive.
- They can store twice as much data on the same surface.
- Memristors are insensitive to radiation like transistors.
- Because they provide nonvolatile memory, Memristors can prevent computers from needing to be rebooted. The user would find his files and his applications in the state where he had left them. This would allow us to reboot a PC as quickly as we turn on a light bulb.
Disadvantages with Memristors
- Since memristors are still in development, their future depends on determining the best hardware implementation.
- The speed and the performance of memristors are not at par with the speed of DRAM and transistors.
- The memristors are not commercially available.
Applications of Memristors
Potential areas of application of Memristors are
- It can be used as a switch and it is possible to connect the multiple inputs and the outputs in the matrix. It is also called a ‘Matrix Switch’.
- In the PLC device signal processing
- In the super-resolution imaging
- Physical neural networking
- In the Control systems
- In Digital Circuits
- Biological and neuromorphic systems.
- Computer and networking technology