By ADITYA NAGARAJ MASKERI 1DS07EE006 A SEMINAR ON MEMRISTOR By ADITYA NAGARAJ MASKERI 1DS07EE006

Objectives Introduction and History of Memristor. Fundamental Circuit Elements The 4th New Fundamental Element Delay in Discovery Properties and Working Analogous System Potential Applications Conclusion

Introduction and History Currently known fundamental passive elements – Resistors, Capacitors & Inductors. Does a 4th passive element exist..? Leon O. Chua formulated Memristor theory in his paper “Memristor-The Missing Circuit Element” in 1971. Team of scientists headed by R. Stanley Williams of Hewlett Packard, realized Memristor made of Titanium Dioxide in 2008. Memristors are passive two terminal circuit elements. Behaves like a nonlinear resistor with memory.

Fundamental Circuit Elements

Resistor Resistor is a 2 terminal electronic component that produces a voltage across its terminals that is proportional to electric current through it in accordance with ohm’s law. Ohm’s Law: “ Voltage (V) across a resistor is proportional to the current (I) through it where constant of proportionality is the resistance (R)”. V=IR SI unit is ohm (Ω). Symbol

Capacitor Symbol Capacitor is a passive electronic component consisting of a pair of conductors separated by a dielectric. When a voltage potential difference exists between the conductors, and electric field is present in the dielectric. This electric field produced stores energy. Current- voltage relation: Where, C = Capacitance i(t) = Current v(t) = Voltage q(t) = Charge = C*v(t) SI unit of Capacitance is farad (F).

Inductor Symbol Inductor is a passive circuit element that can store energy in a magnetic field created by the current passing through it. Inductor is a conducting wire shaped as a coil. When current flows through a coil, it sets up a magnetic field inside the coil. Current-Voltage relation: Where, L = Inductance. SI unit of Inductance is henry (H).

The Missing Element Resistor – Voltage and Current Relation with the fundamental elements: Resistor – Voltage and Current Inductor – Current and Flux Capacitor – Voltage and Charge No relation between Flux and Charge.

The 4th New Fundamental Element: Memristor Leon Chua first theorized the existence of Memristors. In 2008, R. Stanley Williams & team at HP Labs developed a TiO2 Memristor. The memristance relates the Flux and the Charge. No combination of existing fundamental circuit elements can emulate the effect of Memristor.

Memristor An atomic force microscope image of a simple circuit with 17 memristors lined up in a row.  Each memristor has a bottom wire that contacts one side of the device and a top wire that contacts the opposite side.  The devices act as 'memory resistors', with the resistance of each device depending on the amount of charge that has moved through each one. The wires in this image are 50 nm wide, or about 150 atoms in total width.

Memristor Definition: “The Memristor is formally defined as a two-terminal element in which the magnetic flux Φm between the terminals is a function of the amount of electric charge q that has passed through the device.” Symbol: Equation: Memristance is a property of an electronic component to retain its resistance level even after power had been shut down or lets it remember (or recall) the last resistance it had before being shut off. Unit of measurement is ohm (Ω). Information can be written into the material as the resistance state in a few nanoseconds using few pico-joules of energy.

Properties Current v/s Voltage Characteristics Hysteresis model of Resistance v/s Voltage

Delay in Discovery The effect depends on atomic scale movements. Detectable only under nano-scale. M is 1 million times larger are nano-scale than at micrometer scale due to factor 1/D2. Where, D = Thickness of semiconductor film sandwiched between two metal contacts Memristance as a function of charge:

Working Semiconductor used is TiO2 . Two layers, one pure and another doped. Voltage applied with negative potential to doped region yields high resistance. Voltage applied with positive potential to doped region yields low resistance. Device remembers its previous state even after power is switched off.

Programmability of Memristor: Black Circles – Memristor VA – VD - Inputs V1, V2 – Transistor Power Supply Voltages

Analogous System Memristor behaves like a pipe whose diameter varies according to the amount and direction of current passing through it. The diameter of pipe remains same when the current is switched off, until it is switched on again. The pipe, when the current is switched on again, remembers what current has flowed through it.

Potential Applications Nano-Scale devices. Replacement of Flash Memory. Replacement for D-RAM. Brain-like Systems. Self-Learning Systems.

Conclusion “ Memristors are so significant that it would be mandatory to re-write the existing Electronics Engineering textbooks”. - Leon Chua & R. Stanley Williams

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