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Memristor
1. MEMRISTOR
The fourth fundamental circuit element
Presented by,
Mahesh K C 1BM10EC058
Reviewers
Mrs. K. P. Lakshmi Mr. K N Madhusudhan
Associate professor Assistant professor
A seminar on
2. Contents
• Introduction
• A brief look at the basic elements
• The invention
• Features
• Physics of the Memristor
• An analogous system
• Comparison between Resistor and Memristor
• Applications
3. Introduction
• The MEMRISTOR stands for MEMory ResISTOR.
• It is the fourth passive fundamental circuit element.
• It is basically a semi-conductor whose resistance depends on the device history.
• The resistance is a function of its state variable.
• Circuit symbol
4. A brief look at the basic elements
• The three basic elements are RESISTOR, INDUCTOR and CAPACITOR
• Resistor was invented by Georg Ohm in 1827.
• Inductor was invented by Joseph Henry in 1831.
• Capacitor was invented by Ewald Georg von Kleist in 1745.
Resistor Inductor Capacitor
5. The invention
• The four fundamental variables of circuit theory are
Charge (Q) Voltage (V) Current (I) Flux (𝜑)
• The relation between the variables are defined as follows
𝒗 =
𝒅𝝋
𝒅𝒕
(1) 𝒊 =
𝒅𝒒
𝒅𝒕
….(2)
𝒅𝒗 = 𝑹𝒅𝒊….(3) 𝒅𝒒 = 𝑪𝒅𝒗…..(4) 𝒅𝝋 = 𝑳𝒅𝒊….(5)
• There was no relation to relate the flux with the charge.
6. • Leon Chua postulated the memristor on grounds of symmetry in 1971.
• The Memristor relates the flux with the charge.
• Thus it completed the interrelation between the pair of variables.
• R Stanley Williams devised the first ever memristor at the HP labs in 2008.
Tetrahedron of symmetry
8. Features of the Memristor
• It is a fundamental two terminal element.
• It retains its resistance level even after power had been shut down.
• But it does not store energy.
• It is characterized by a quantity called as Memristance.
𝑴 𝒒,𝝋 = 𝒅𝝋/𝒅𝒒
• The memory is characterized by one or more state variable.
9. Contd..
• Memristor is characterized by a constitutive relation ⱷ ⱷ, 𝑞 = 0
• The memristor is charge-controlled if this relation can be expressed as a single-valued
function ⱷ = ⱷ 𝑞
• The memristance of a charge controlled Memristor is given by 𝑴 𝒒 =
𝒅𝝋 𝒒
𝒅𝒒
• It is flux-controlled if this relation can be expressed as a single-valued function 𝑞 =
𝑞 ⱷ
• The memductance of a flux controlled Memristor is given by 𝑾 𝝋 = 𝒅𝒒(𝝋)/𝒅𝝋
10. Physics of the memristor
• R. Stanley Williams found an ideal memristor in titanium dioxide (TiO2) which is a wide band gap
semiconductor.
• Ti belongs to the group 4 elements. It is a transition metal with an atomic number of 22
• TiO2in its pure state is highly resistive but its conductivity can be increased by doping.
• In TiO2, the dopants do not stay stationary in a high electric field; they tend to drift in the direction
of the current.
TiO2
11. A B
Figure
𝑣 = 𝑅 𝑜𝑛
𝑤
𝐷
+ 𝑅 𝑜𝑓𝑓 1 −
𝑤
𝐷
𝑖Electronic current
𝑑𝑤 𝑡
𝑑𝑡
= 𝜇 𝑣
𝑅 𝑜𝑛
𝐷
𝑖(𝑡)Ionic drift
12. Working
• When an oxygen atom, which is negatively charged, is removed from its substantial site
in TiO2, a positively charged oxygen vacancy is created (V0
+) is created, which act as a
carrier.
• When a negative potential is applied to electrode, the positively charged oxygen
vacancies (V0
+) are attracted towards electrode A, the length of undoped region
increases thus resistance increases.
• When a positive potential is applied at electrode A the positively charged oxygen
vacancies are repelled and moved into the undoped TiO2. This ionic movement towards
electrode B reduces the length of undoped region decreasing the resistance.
15. • Water pressure is analogous to voltage and the water flowing is analogous to the charge.
• When water flows in forward direction, the diameter of the pipe increases thus decreasing
the resistance.
• When water flows in reverse direction, the diameter of the pipe decreases thus increasing
the resistance.
• When the water is shut off, the pipe retains its most recent diameter.
• It starts from the same diameter when the water flows through for the next time.
16. Comparison between Resistor and Memristor
• They are passive two terminal elements.
• The SI unit is ohms.
• The resistor has a fixed value of resistance, whereas the memristance depends on the device history.
• The I-V curve for a resistance is linear and it is non-linear for a memristor. (Also called the pinched
hysteresis loop)
17. Applications
• Nano scale nature
• Replacement for flash memory
• Replacement for DRAM
• Neural networks
18. References
[1] Chua, Leon O (September 1971), "Memristor-The Missing Circuit Element", IEEE Transactions on Circuit
Theory CT-18
(5): 507–519, doi:10.1109/TCT.1971.1083337
[2] An introduction to the memristor – a valuable circuit element in bioelectricity and bioimpedance Gorm K.
Johnsen 1,2
1. Institute of Energy Technology, 2007 Kjeller, Norway
2. Department of Physics, University of Oslo, 0316 Oslo, Norway
[3] Robust Hybrid Memristor-CMOS Memory: Modeling and Design Baker Mohammad, Member, IEEE, Dirar
Homouz,
and Hazem Elgabra
[4] Memristor-based IMPLY Logic Design Procedure, Shahar Kvatinsky, Avinoam Kolodny and Uri C. Weiser
Department of
Electrical Engineering Technion – Israel Institute of Technology Haifa 32000 ISRAEL