Offset-reduced hall element

Details Offset-reduced hall element Offset-reduced hall element

2002-04-30

2004-04-27

Pham, Long (Department: 2814)

Active solid-state devices (e.g., transistors, solid-state diode

Responsive to non-electrical signal

Magnetic field

C257S426000

Reexamination Certificate

active

06727563

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to Hall elements, and in particular to Hall elements with offset compensation.
BACKGROUND OF THE INVENTION AND PRIOR ART
Hall elements make use of the Hall effect, for example, for measuring a magnetic field. The Hall effect is understood to be the occurrence of an electric field perpendicular to the current density vector j as a result of the effect of a magnetic field. The perpendicular electric field E is calculated by the following equation:
E=−R
(
j×B
).
In this equation, R is the Hall constant. For impurity semiconductors, the Hall constant is proportional to the difference between the mobility of the holes in the semiconductor and the mobility of the electrons in the semiconductor.
Materials having Hall constants that are sufficiently high to be used as substrate or sensor region or simply as a region for a Hall element, are for example intrinsic-conduction InSb, In(AsP), InAs or lightly p- or n-doped regions on silicon. Two contacts are used to conduct an operating current through the region.
In contrast thereto, the two other contacts are used for tapping the Hall voltage formed due to the Lorentz force which leads to deflection of the moving charge carriers due to a magnetic field acting on the Hall element. After a short period of time, there is created an electric field in the Hall element that is directed perpendicularly to the operating current and has such an intensity that the Lorentz force acting on the charge carriers of the operating current is compensated.
The Hall effect or a Hall element, in addition to measuring a magnetic field in accordance with magnitude and sign thereof, may also be utilized for multiplication of two electric quantities, i.e. the magnetic field and the control current, or for contactless signal generators. An additional possibility consists in arranging a Hall element in the vicinity of a conductor track and to measure, in non-contacting manner, the current in this conductor track by detection of the magnetic field generated by the current through said conductor track.
FIG. 5
illustrates a planar Hall element
100
, comprising a region
100
formed of a material having a sufficiently high Hall constant. It is to be pointed out that, in the sense of the present description, the region of the Hall element having a non-zero Hall constant may either be a Hall substrate itself, which could be applicable for larger Hall elements, while however the region may also be a portion or region of an integrated circuit which in known manner is embedded in the IC substrate, e.g. in a well, or which has been modified by specific technological steps in order to have a corresponding Hall constant.
The region illustrated in
FIG. 5
is of cruciform shape, which affords the advantage that the Hall element shown in
FIG. 5
is also suited for so-called spinning current operation, i.e. that the operating current I can be passed through region
100
via contacts K
1
and K
3
, while however in a different mode of operation, the operating current I may also be passed through the region via contacts K
2
and K
4
, with the Hall voltage, of course, being present then at contacts K
1
and K
3
such that the same can be tapped at terminals A
1
and A
3
. For the following considerations, however, and without restriction to the general nature, it will be assumed for reasons of convenience that the operating current I is applied via terminals A
1
and A
3
, i.e. is fed to and removed from the region via the contacts K
1
and K
3
, while the Hall voltage is given by a potential difference between the contacts K
2
and K
4
, i.e. can be tapped at the terminals A
2
and A
4
.
In addition to a region
100
with a non-zero Hall constant and the contacts K
1
, K
2
, K
3
and K
4
for contacting the region
100
, a Hall element of course needs also leads
110
,
120
,
130
and
140
for electrically connecting the corresponding contacts K
1
to K
4
to the corresponding terminals A
1
to A
4
. In case of the known Hall element shown in
FIG. 5
, the leads
110
to
140
are designed in accordance with the practical circumstances. Practical circumstances consist in particular in that there is, for example, the requirement that all terminals A
1
to A
4
should be arranged closely together in order to be passed, for example, to a central switching unit for spinning current operation. In that case, it is necessary, as shown in
FIG. 5
, to pass at least one lead, namely lead
130
, around the Hall region
100
. In other words, lead
130
comprises a first section
130
a
corresponding to the direction of the current I, a second section
130
b
perpendicular thereto, as well as a section
130
c
directed parallel to current I, but having the current flowing therethrough in the direction opposite to the operating current I.
As has already been pointed out, Hall elements serve for measuring an external magnetic field acting on the Hall region. For carrying out such a magnetic field measurement, however, an operating current must be sent through the region so that a Lorentz force can act at all on moving charge carriers. Of course, this operating current I, like any current, also has a magnetic field which also leads to local Hall voltages in the region. However, as the effects of this local intrinsic field are symmetric with respect to the central axis of the current in the element proper, there is no Hall voltage created on the outside of the element, i.e. at the contacts K
2
and K
4
, that could be tapped via the terminals A
2
and A
4
. This local intrinsic field of the operating current I in the Hall region, however, acts in its full magnitude on neighboring Hall elements if arrays of Hall elements are used, as is the case in spinning current operation with mechanical pre-compensation. The intrinsic magnetic field of a Hall element in an array of Hall elements, due to its magnetic field generated and penetrating the neighboring element, leads to a measurement signal there that makes itself felt as an offset. The magnetic field generated by the operating current thus is superimposed on the external magnetic field to be measured in the first place. Thus, there is always an offset problem caused by the magnetic intrinsic field of the active sensor region when there are several sensors provided in the immediate vicinity, since the intrinsic fields of the sensors have the effect of an external magnetic field on the respective other sensors.
An additional problem in the known arrangement shown in
FIG. 5
arises due to the terminal leads
110
to
140
which any Hall element needs to have. For connecting the terminals A
1
to A
4
of the Hall element to a driving control, it is as a rule necessary, as already pointed out hereinbefore, to pass at least one of the current-carrying leads, in the example of
FIG. 5
lead
130
, around the region
100
. In the typical example of the prior art, as shown in
FIG. 5
, the unfavorable lead from terminal A
3
to contact K
3
consists of the differently aligned partial lengths
130
a
to
130
c.
Leads
130
a
to
130
c
deliver the following magnetic fields. The magnetic field generated by the operating current flowing through element
130
a
still is symmetric with the current flow in the active part of the Hall region and therefore generates in region
100
no Hall voltage that is externally measurable. However, this does no longer apply to the two partial lengths
130
b
and
130
c
. The magnetic field generated in these conductors acts on the region in its full magnitude and is measured by said region as well, i.e. itself produces a Hall voltage between the terminals A
2
and A
4
. Due to the fact that this additional field is always present when the element is in operation, it appears to the outside like a fixed offset which the element has. Only by changing the operating current is it possible to distinguish this share from a real offset, in that a normal offset changes linearly with the operating current, whereas the offset caused by the operating current d

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