ee698a advanced electron devices magnetic sensors and logic gates ling zhou ee698a
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EE698A Advanced Electron Devices
Magnetic sensors and logic gates
Ling Zhou
EE698A
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EE698A Advanced Electron Devices
Outline
• Anisotropic magnetoresistive sensors
• Giant magnetoresistive sensors
• Colossal magnetoresistive sensors
• Using magnetoresistive elements to build up logic gates
• Hall sensors and devices
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EE698A Advanced Electron Devices
Conventional Vs. Magnetic sensing
The output of conventional sensors will directly report desired parameters
On the other hand, magnetic sensor only indirectly detect these parameters
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EE698A Advanced Electron Devices
Magnetic sensor technology field ranges
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EE698A Advanced Electron Devices
Anisotropic magnetoresistive (AMR) sensor
Current Iθ
Magnetization MR=R┴+ΔRAMRcos2 θ
Magnetoresistance variation with angle between M and I
The theory of the AMR sensor is based on the complex ferromagnetic process in a thin film
AMR ratio for typical ferromagnetic materials at room temperature is around 1-3%
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EE698A Advanced Electron Devices
AMR sensor circuit
Wheatstone bridge configuration is used to ensure high sensitivityand good repeatability
Disadvantage of AMR sensor: can only sense the magnitude, but not the direction; non-linear output.
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EE698A Advanced Electron Devices
AMR effect for small wire
“Effect of bar width on magnetoresistance of nanoscale nickel and cobalt bars” J. Appl. Phys. 81(8) 1997
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EE698A Advanced Electron Devices
Giant magnetoresistive (GMR) sensor
Two different ferromagnetic materials sandwiched by a thin conduction layer
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EE698A Advanced Electron Devices
GMR circuit technique
Due to their outstanding sensitivity, Wheatstone Bridge Circuits are very advantageous for the measurement of resistance, inductance, and capacitance.
GMR resistors can be configured as a Wheatstone bridge sensor. Two of which are active. Resistor is 2 µm wide, which makes the resistors sensitive only to the field along their long dimension.
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EE698A Advanced Electron Devices
Obtaining parallel, antiparallel magnetic alignment
• pinned sandwiches– Consist of two magnetic layers, soft layer and hard layer
• Antiferromagnetic multilayers– Consist of muliple repetitions of alternating magnetic and
nonmagnetic layers
– The polarized conduction electrons cause antiferromagnetic coupling between magnetic layers
• Spin valves– An additional layer of an antiferromagnetic material is
provided on the top or bottom
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EE698A Advanced Electron Devices
Antiferromagnetic multilayers
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EE698A Advanced Electron Devices
Use GMR in hard drive read head
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EE698A Advanced Electron Devices
Parameters for GMR sensor
• Magnetic layers: 4~6 nm
• Conductor layer 3~5 nm in sandwich structure– This thickness is critical in antiferromagnetic
multilayer GMR sensors, typically 1.5~2 nm
• Switching field 3~4 KA/m (35~50 Oe) for sandwich structure and 250 for multilayer structures
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EE698A Advanced Electron Devices
Magnetic tunnel junction (MTJ)
Insulation Layer
Soft Ferromagnetic LayerHard Ferromagnetic Layer
Sandwiches of two ferromagnetic layers separated by a very thininsulation layer as tunneling barrier
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EE698A Advanced Electron Devices
Use MR element as logic gates
Hc1<Hc2 , layer 1 is easier to be switched
Only IA and IB together can switch layer 1
For rotation of layer 2, an additional input line IC is required
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EE698A Advanced Electron Devices
AND gate
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EE698A Advanced Electron Devices
OR gate and NAND, NOR gates
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EE698A Advanced Electron Devices
Advantages of MR element
• A single MR element is sufficient to realize and store four basic logic functionalities. Integration density is increased.
• The output is non-volatile and repeatedly readable without refreshing, which reduces the heat evolution.
• Fast operation: the switching of frequency of magnetic films can be pushed to several GHZ.
• Low power consumption.
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EE698A Advanced Electron Devices
Colossal magnetoresistive (CMR) and extraordinary magnetoresistive
(EMR)
• Under certain conditions, mixed oxides undergo a semiconductor to matallic transition with the application of an external magnetic field.
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EE698A Advanced Electron Devices
Hall sensor
The Hall voltage is generated by the effect of an external magnetic field acting perpendicularly to the direction of the current.
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EE698A Advanced Electron Devices
Hybrid hall effect devices
Can be used as magnetic field sensor, storage cell and logic gates
An HHE device is a layered structure composed of an input wire, ferromagnetic element, insulation layers, and a conducting output channel.
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EE698A Advanced Electron Devices
Magnetic p-n junction