Transcript Integrated Magnetodiode Carrier

Magnetic Sensors
•
by Kuen-Hsien Wu
Galvano-magnetic effect:
1.
2.
3.
Lorentz deflection
– Lorentz force on charge carrier carrier deflection
Magneto-resistance
– Modulation of resistance by a magnetic field
Magneto-concentration
– Producing a gradient of carrier concentration perpendicular
to the magnetic inductor vector and original current direction
Magnetic Sensors and Effects
Main Magnetic Sensors
1.
2.
Hall Plates
Integrated Hall Sensors
1)
2)
3.
4.
5.
6.
Hall devices
MAGFET
Magneto-transistor
Magneto-diode
Carrier-domain Magnetometer
Super Magneto-resistor
Hall Plate
Geometric Effects
• VH = -GIBrn(qnt)-1
• rn: scattering factor
• Geometric correction factor G
– Describe the shapes effect
of the plate
• G depends on
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Plate length
Plate width
Contact size
Position of the sensor contact
Hall angle H
Biasing and Amplification Circuitry
• Hall-voltage operation is
preferred in mordern Hall
devices.
– Biased with a constant
current source.
• The left sensor contact is
virtually grounded by an
operational ampliier (OA)
– The full Hall voltage appears
at the right sensor contact.
– Without the OA, a large
common-mode voltage will
appear at the amplifier input.
Sensitivity
• Absolute sensitivity
– SA
• Supply-current related sensitivity
– SI
• Supply-voltage related sensitivity
– SV
Limiting Effects
• Noise
• Offset Voltage
• Temperature Coefficient
• Nonlinearity
Integrated Bulk Hall Sensor
Integrated Hall Switch
• A binary output
signal is produced.
Vertical Hall Device
Equipotential line
Differential Amplification Magnetic Sensor (DAMS)
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With a Magnetic induction, the
Hall voltage appears across the
base region.
If the two emitters are kept at the
same potential, the Hall voltage
acts as the differential emitterbase voltage of the transistor pair.
Under proper bias conditions, this
results in a corresponding
collector-current difference,
which can be converted into a
final voltage difference by load
resistors.
Base Region
Magnetic Field-Effect Transistor (MAGFET)
• The surface inversion layer or channel of a MOSFET can be used as
the active region of a Hall sensor.
• This device exploits the Hall effect and the Lorentz deflection of
carriers in the inversion layer.
• Such a device is compatible with MOS bias and signal-conditioning
circuitry.
• Disadvantages:
– High 1/f noise
– Low channel mobility  Magnetic Heterojunction Device (2DEG)
– Surface instability
Hall MAGFET
Dual-Drain MAGFET
• A magnetic induction
perpendicular to the inversion
layer produces a current
imbalance.
ID = ID1 – ID2
• ID=Gnch*(L/W)B ID
Split-Drain MOSFET
Magnetic Heterojunction Device
2DEG
Magnetotransistor (MT)
• Lorentz deflection
– Lorentz force deflects minority carriers toward one collector and
away from the other collector.
• Injection modulation
– The magnetic induction acting on the majority carriers moving in
the base region creates a Hall voltage, which modulates the
emitter-base voltage
– Creating an asymmetry in the minority-carrier injection.
• MT’s
– Vertical Magnetotransistor
– Lateral Magnetotransistor
– Suppressed-Sidewall-Injection MT (SSIMT)
Vertical Magnetotransistor
• The Lorentz deflects the
injected carriers in the base and
the subsequent epi-layer
causing a collector-current
imbalance
IC = IC1 – IC2
• IC=Gnch*(L/WE)B ICO
Lateral Magnetotransistor
(sensitive to perpendicular field)
• The two n+ base contacts are
used to create an accelerating
field across the large base
region. (different from the
vertical MT)
• Due to the accelerating voltage,
most minority carriers injected
from the emitter are directed
towards the two collectors and
only a small amount flows into
the substrate.
Large Base Region
Lateral Magnetotransistor
(sensitive to parallel field)
• The device has only one collector
and uses the substrate as a second
collector.
• The minority carriers flowing
laterally through the base region
are deflected either towards the
collector or the substrate.
• Thus, the ratio IC/IS is modulated
by the magnetic field.
Suppressed-Sidewall-Injection MT (SSIMT)
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IC = IC1 – IC2  B
The highly-doped n+ guard ring
surrounding the emitter prevents
the lateral injection of minority
carriers from the emitter into the
base.
– Improving the sensitivity
An accelerating field is formed
between the guard and the base
contacts to boost the magnetic
response.
The substrate current deflection
also cooperate the IC formation
B
Magnetodiode (MD)
Integrated Magnetodiode
Carrier-Domain Magnetometer (CDM)
• Carrier Domain
– A region of high, nonequilibrium carrier density.
• A CDM
– exploiting the action of Lorentz force on the charge carriers moving
in the domain.
– This force moves the entire carrier domain through the
semiconductor or modulates a domain migration caused by some
other effect.
– Detection the domain motion provides information on the magnetic
field.
Vertical Four-Layer CDM
• A perpendicular magnetic field
produces a displacement of the
domain, thus resulting in the
current imbalance in Ip1 andIp1
(or In1 andIn1).
• The current imbalance indicates
the domain displacement, and
hence the presence of the
magnetic field.
Carrier domain
Circular, Horizontal Four-Layer CDM
• Under the action of the
magnetic induction, the domain
travels around the
circumference of the structure.
• The frequency of this rotation is
proportional to the applied
magnetic induction.
• This generation of a frequency
output is a unique feature of thr
circular CDM.
• Disadvantage:
– High threshold field
– Large temperature coefficient
Circular, Horizontal Three-Layer CDM
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No threshold magnetic induction is
required.
Operated in the collector-emitter
breakdown regime with shortcircuited emitter and base contacts.
The angular frequency of the
carrier domain rotation is
modulated by the magnetic field.
Disadvantages:
– High current (need cooling)
– Breakdown voltage is not precise.
short-circuited emitter and base contacts
Supermagnetoresistor
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The sensor operates at the
temperature of 77K and responses
to very small fields (below 10 mT)
A week magnetic field will disturb
the superconductivity of a
superconductor material.
– This leads to an abrupt change in
the resistance of the sample with
magnetic field.