PRODUCT CATALOG
Oct/2020
TMR Basic Principles
Tunnel Magneto-Resistance (TMR) sensors exploit the barrier layer, whereas the resistance depends on
a special form of the Magneto-Resistive (MR) effect the degree of magnetization of the free layer and its
based on quantum-mechanical processes. The MR orientation with respect to the pinned layer: When
effect appears when the change of a magnetic field both free and pinned layer magnetization orienta-
applied to a conductive material leads to a change in tions point in the same direction, the resistance is
its electrical resistance, thus transducing a magnetic minimal, while opposite magnetization directions
stimulation into an electrical response.
evoke maximum resistance. A TMR sensor is com-
posed of a number of individual TMR elements
forming the four branches of a Wheatstone bridge,
where the fixed layers of the elements within each
branch are identically aligned.
In a TMR element, a stack of magnetic material is sep-
arated by an electrical insulator – the so-called tunnel
barrier – into two overlapping layers (see Fig. 1–1).
One of these magnetic layers (the “pinned” layer) is
processed to show a well aligned in-plane magne- Applying a rotating magnetic field in the plane
tization that is invariant when exposed to external of the Wheatstone bridge allows to tap periodic
magnetic fields. In contrast, the magnetization of voltage signals from the two bridges that are phase-
the other magnetic layer (the “free” layer) is flexible shifted by 90° (see Fig. 1–2). These four signals
and can be modified by applying external magnetic finally allow to unambiguously extract the orienta-
fields. Applying a voltage between the two magnetic tion of the stimulating field, i.e., the angular position
layers causes a current flowing (tunneling) through of the rotating permanent magnet.
B
N
TMR element
α
S
VCC
VCC
Free Layer
Barrier Layer
Pinned Layer
Sin+
Sin- Cos+
Cos-
Current flow
direction
Fig. 1–1: TMR element
Fig. 1–2: Wheatstone bridge structure of TAS214x
GeneralTMR Features
◆ High output at 1.5 Vpp / 3.0 Vpp @ 5 V
◆ Low temperature drifts
(Analog output sensorTAS2141 /TAS2143)
◆ Low power consumption
◆ Good angular accuracy of 0.6 deg. (1.5 Vpp differential
output @ 5 V), 0.ꢀ deg. (3.0 Vpp differential output @ 5 V)
(Analog output sensorTAS2141 /TAS2143)
◆ Detections can be made from 0 to 360°
n=5pc
1.0
0.8
0.6
0.4
0.2
0.0
1.0
0.8
0.6
TMR
0.4
0.2
AMR
0.0
–0.2
–0.4
–0.6
–0.8
–1.0
GMR
150°C
-40°C
25°C
0
90
180
(
270
360
10
20
30
40
50
60
)
70
80
90
)
Angle deg
(
Magnetic Field mT
20 times the AMR element, 6 times the GMR element, 500 times the Hall element
Fig. 2–1: Output wave pattern comparison TAS2141-AAAB
(1.5 Vpp differential output)
Fig. 2–2: Angle error graph TAS2141-AAAB
(1.5 Vpp differential output)
2
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