Electricity: measuring and testing – Magnetic – Magnetometers
Patent
1995-12-01
1997-07-08
O'Shea, Sandra L.
Electricity: measuring and testing
Magnetic
Magnetometers
338 32H, 327511, G01K 3307, H01L 4302, H03K 338
Patent
active
056465270
DESCRIPTION:
BRIEF SUMMARY
This is a National Application of PCT/EP94/00701.
FIELD OF THE INVENTION
The present invention relates to Hall-effect devices having a Hall plate or Hall element which is contacted by current connections and Hall voltage connections. Hall-effect devices of this kind of interest are also termed Hall generators or Hall probes.
DESCRIPTION OF THE RELATED ART
When a strip like electrical conductor through which a current I flows in its longitudinal direction and which is thin as compared to its width ("Hall element") is brought into a magnetic field having a component perpendicular to the plane of the conductor exhibiting the magnetic field strength B*, then due to the so-called Hall-effect between the side edges of the strip-like conductor a voltage, the so-called Hall voltage varied of purposes, e.g. for rugged magnetometers, magnetic-field actuated switches, position sensors and, more recently, also for highly precise resistance standards in which the quantum Hall-effect is made use of, see e.g. the publications of Kordic in "Sensors and Actuators", 10 (1986) pages 347-378 and of Popovic in "Sensors and Actuators" 17, (1989) pages 39-53.
In it simplest form a Hall-effect device (Hall generator) comprises where possible a thin, rectangular or strip-like electrical conductor ("Hall plate" or "Hall element") provided with four electrical connections and is usually fabricated of a semiconductor material such as e.g. Si, Ge, GaAs, Bi etc.
From the equation (1) one could assume that the sensitivity of a Hall device, i.e. the ratio of Hall voltage to magnetic field strength is able to be boosted to any extent by increasing the current I. In actual practice, however, it is evident that due to disturbing effects, particularly deficient alignment of the connections (positioning errors) and lack of homegenity of the conductor material a limit is very quickly reached, since these imperfections cause a resistance-induced voltage drop and thus a misalignment voltage (offset voltage) at the Hall voltage connections even in the absence of a magnetic field. When the Hall voltage attains the order of these misalignment voltages in the presence of a weak magnetic field, proper measurement is apparently no longer assured.
Various means of eliminating or compensating these misalignment voltages are already known. The simplest method involves measuring the signal at the Hall voltage connections for two opposing directions of the magnetic field, the misalignment voltage then being able to be eliminated by subtraction of the signals obtained. In actual practice, however, reversing the direction of the magnetic field is usually very difficult to carry out. Another, somewhat more complicated procedure works by swapping the current connections and the Hall voltage connections without a field reversal. For this purpose relatively complicated changeover switches are required, in addition to forming the signal difference. In conclusion it is known to compensate the misalignment voltages by employing paired Hall-effect devices connected to counteract each other. However, due to the inhomogenities in the material which are practically unavoidable it is hardly possible to fabricate Hall elements which are precisely identical, even when they are formed on the same substrate. Apart from this, such arrangements require twice the surface area and power.
For some applications such as e.g. measuring locally variable magnetic fields such as gradient fields better, especially simpler, more accurate and better-functioning Hall-effect devices are needed.
On the basis of this prior art the present invention is mainly based on the object of formulating Hall-effect devices of novel configurations with which the above-mentioned resistance-induced misalignment voltages are avoided by simple means and other measurement tasks are permitted.
SUMMARY OF THE INVENTION
A further object of the present invention is to formulate novel Hall-effect devices exhibiting new features or permitting new applications or better achieving known objects than hithert
REFERENCES:
patent: 4125821 (1978-11-01), Masuda
patent: 4599564 (1986-07-01), Kelleher et al.
patent: 4668914 (1987-05-01), Kersten et al.
Mani Ramesh G.
von Klitzing Klaus
Mani R. G.
O'Shea Sandra L.
Phillips Roger C.
von Klitzing K.
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