ee698a advanced electron devices magnetic sensors and logic gates ling zhou ee698a

EE698A Advanced Electron Devices

Magnetic sensors and logic gates

Ling Zhou

EE698A


Outline

• Anisotropic magnetoresistive sensors

• Giant magnetoresistive sensors

• Colossal magnetoresistive sensors

• Using magnetoresistive elements to build up logic gates

• Hall sensors and 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


Magnetic sensor technology field ranges


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%


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.


AMR effect for small wire

“Effect of bar width on magnetoresistance of nanoscale nickel and cobalt bars” J. Appl. Phys. 81(8) 1997


Giant magnetoresistive (GMR) sensor

Two different ferromagnetic materials sandwiched by a thin conduction layer


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.


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


Antiferromagnetic multilayers


Use GMR in hard drive read head


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


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


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


AND gate


OR gate and NAND, NOR gates


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.


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.


Hall sensor

The Hall voltage is generated by the effect of an external magnetic field acting perpendicularly to the direction of the current.


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.


Magnetic p-n junction

ee698a advanced electron devices magnetic sensors and logic gates ling zhou ee698a

Documents

conduction layer slide

head slide

barrier slide

gmr sensor magnetic

soft layer

magnetic sensing

ferromagnetic layers

magnetic layers spin