Magnetic Sensor (3B) Magnetism Hall Effect AMR Effect GMR Effect
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Magnetism Ferro-magnetic material Permanent magnet Ferri-magnetic material Below Curie Temp: like ferromagnets Above Curie Temp: like paramagnets Para-magnetic material DC Josephson: I > I c then in the resistiv Optical Sensor 3
Hall Effect (1) Transient State I x v x F m Lorentz Force to charges E x Applied external magnetic field charges deflect charges are accumulated F ' m Lorentz Force to charges I x As E H increases, new (+) and ( ) charges are repelled by those previously accumulated charges. (balancing effect) electrical potential (E H ) are created Optical Sensor 4
Hall Effect (2) The force Fe counteracts Fm. Steady State F e : due to E H I x F m : due to external magnetic field Again charges travels straight, but with the Hall angle θ. E x E t E H E H v x F m Lorentz Force to charges F e F m : Lorentz Force Optical Sensor 5
Hall Effect (3) Transient State Steady State I x v x F m Lorentz Force to charges I x E x E t E x E H E H I x F ' m Lorentz Force to charges F e F m : Lorentz Force Optical Sensor 6
Hall Effect Geometric Factor (1) f H = function l w, l 1 w 1 l 2 w 2 l 3 w E H1 E H2 E H3 l 1 l 2 l 3 w 1 w 2 w 3 Optical Sensor 7
Hall Effect Geometric Factor (2) F e F m : Lorentz Force w l The force Fe counteracts Fm. F e : due to E H F m : due to external magnetic field More charges are accumulated at the both ends until they repel other new charges. w Optical Sensor 8
Physical Magneto-resistance Effect Ideal Case Real Case Semiconductor Different Lorentz Force to each charge Different charges travel different paths The total length of paths is increased The resistance increases slightly Optical Sensor 9
Geometrical Magneto-resistance Effect (1) Ideal Case Real Cases Metal Electrode Contact Optical Sensor 10
Geometrical Magneto-resistance Effect (2) Min R 1 : Max R 1 ratio R R o = max R 1 min R 1 Min R 2 : Max R 2 ratio R R o = max R 2 min R 2 Optical Sensor 11
Magnetic Anisotropy (1) Magneto-crystalline Anisotropy An intrinsic property of a ferri-magnet Magnetization curve along different crystal directions Easy direction Hard direction Intermediate direction Optical Sensor 12
Magnetic Anisotropy (2) Easy direction Magnetization Permalloy Resistor : NiFe (ferri-magnet) Optical Sensor 13
Permalloy Resistor (1) R max : small current Easy direction : parallel current direction R min : large current : perpendicular current direction Optical Sensor 14
Permalloy Resistor (2) Easy direction Fix the direction of current External Magnetic Field changes the magnetization direction of permalloy the resistance the current 45 θ H applied Optical Sensor 15
AMR Sensor (1) The current direction is fixed R max : small current : parallel current direction R min : large current : perpendicular current direction = 0 = 90 = 90 Optical Sensor 16
AMR Sensor (2) How the current direction is fixed? Shortening Bars Barber Pole Biasing : the shortest path Optical Sensor 17
Giant Magneto-resistance Effect Anti-parallel Magnetic Layers Parallel Magnetic Layers Current Magnetic Layer Non-magnetic Conductor Magnetic Layer Current High Interface Scattering : R max Low Interface Scattering : R min Optical Sensor 18
GMR Sensor Anti-parallel Magnetic Layers Parallel Magnetic Layers Current External Magnetic Field Change Current High Interface Scattering : R max Low Interface Scattering : R min Optical Sensor 19
References [1] http://en.wikipedia.org/ [2] Nam Ki Min, Sensor Electronics, Dong-il Press [3] http://www.sensorsmag.com/ articles