Electricity: measuring and testing – Magnetic – Magnetometers
Reexamination Certificate
1998-11-19
2001-05-29
Oda, Christine (Department: 2862)
Electricity: measuring and testing
Magnetic
Magnetometers
C324S207210, C338S03200R
Reexamination Certificate
active
06239595
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a magnetic field sensing element for detecting a change in a magnetic field, and more particularly, to the element used in a device for detecting the rotation of a magnetic body.
2. Description of the Related Art
Generally, a magnetic resistance element (hereinafter referred to as an MR element) is an element whose resistance changes depending on an angle formed by the direction of magnetization of a ferromagnetic body (Ni-Fe or Ni-Co, for example) thin film and the direction of an electric current. The resistance of such an MR element is minimum when the direction of an electric current and the direction of magnetization cross at right angles to each other, and is maximum when the angle formed by the direction of an electric current and the direction of magnetization is 0°, that is, when the directions are the same or completely opposite. Such a change in resistance is referred to as an MR rate of change, and is typically 2-3% with respect to Ni-Fe and 5-6% with respect to Ni-Co.
FIGS. 34 and 35
are a side view and a perspective view, respectively, showing the structure of a conventional magnetic field sensing device.
As shown in
FIG. 34
, the conventional magnetic field sensing device comprises a rotation axis
41
, a magnetic rotating body
42
which has at least one concavity and convexity and which rotates synchronously with the rotation of the rotation axis
41
, an MR element
43
arranged with a predetermined gap between the magnetic rotating body
42
, a magnet
44
for applying a magnetic field to the MR element
43
, and an integrated circuit
45
for processing an output of the MR element
43
. The MR element
43
has a magnetic resistance pattern
46
and a thin film surface (magnetic-sensitive surface)
47
.
In such a magnetic field sensing device, rotation of the magnetic rotating body
42
causes a change in the magnetic field penetrating the thin film surface
47
which is the magnetic-sensitive surface of the MR element
43
, resulting in a change in the resistance of the magnetic resistance pattern
46
.
However, since the output level of the MR element as a magnetic field sensing element used in such a magnetic field sensing device is low, the detection can not be highly accurate. In order to solve this problem, a magnetic field sensing element using a giant magnetic resistance element (hereinafter referred to as a GMR element) having a high output level has been recently proposed.
FIG. 36
is a graph showing the characteristics of a conventional GMR element.
The GMR element showing the characteristics in
FIG. 36
is a laminated body (Fe/Cr, permalloy/Cu/Co/Cu, Co/Cu) as a so-called artificial lattice film where magnetic layers and non-magnetic layers with thicknesses of several angstroms to several dozen angstroms are alternately laminated. This is disclosed in an article entitled “Magnetic Resistance Effects of Artificial Lattices,” Japan Applied Magnetics Society Transactions, Vol. 15, No. 51991, pp. 813-821. The laminated body has a much larger MR effect (MR rate of change) than the above-mentioned MR element, and, at the same time, is an element which shows the same change in resistance irrespective of the angle formed by the direction of an external magnetic field and the direction of an electric current.
In order to detect a change in the magnetic field, the GMR element substantially forms a magnetic-sensitive surface. Electrodes are formed at the respective ends of the magnetic-sensitive surface to form a bridge circuit. A constant-voltage and constant-current power source is connected between the two facing electrodes of the bridge circuit. The change in the magnetic field acting on the GMR element is detected by converting a change in the resistance of the GMR element into a change in voltage.
FIGS. 37 and 38
are a side view and a perspective view, respectively, showing the structure of a magnetic field sensing device using a conventional GMR element.
In
FIGS. 37 and 38
, the magnetic field sensing device comprises a rotation axis
41
, a magnetic rotating body
42
as a means for imparting a change to a magnetic field, the body having at least one concavity and convexity and having rotatable synchronously with the rotation of the rotation axis
41
, a GMR element
48
arranged with a predetermined gap between the magnetic rotating body
42
, a magnet
44
as a magnetic field generating means for applying a magnetic field to the. GMR element
48
, and an integrated circuit
45
for processing an output of the GMR element
48
. The GMR element
48
has a magnetic resistance pattern
49
as a magnetic-sensitive pattern and a thin film surface
50
.
In such a magnetic field sensing device, rotation of the magnetic rotating body
42
causes a change in the magnetic field penetrating the thin film surface (magnetic-sensitive surface)
47
of the GMR element
48
, resulting in a change in the resistance of the magnetic resistance pattern
49
.
FIG. 39
is a block diagram showing the magnetic field sensing device using the conventional GMR element.
FIG. 40
is a block diagram showing the detail of the magnetic field sensing device using the conventional GMR element.
The magnetic field sensing device shown in
FIGS. 39 and 40
is arranged with a predetermined gap between the magnetic rotating body
42
and itself, and comprises a Wheatstone bridge circuit
51
using the GMR element
48
to which a magnetic field is applied by the magnet
44
, a differential amplification circuit
52
for amplifying the output of the Wheatstone bridge circuit
51
, a comparison circuit
53
for comparing the output of the differential amplification circuit
52
with a reference value to output a signal of either “0” or “1,” and an output circuit
54
that switches in response to the output of the comparison circuit
53
.
FIG. 41
shows an example of the structure of a circuit of the magnetic field sensing device using the conventional GMR element.
In
FIG. 41
, the Wheatstone bridge circuit
51
has on its respective sides GMR elements
48
a
,
48
b
,
48
c
, and
48
d
, for example, with the GMR elements
48
a
and
48
c
being connected with a power source terminal VCC, the GMR elements
48
and
48
d
being polished, the other ends of the GMR elements
48
a
and
48
b
being connected with a connection
55
, and the other ends of the GMR elements
48
c
and
48
d
being connected with a connection
56
.
The connection
55
of the Wheatstone bridge circuit
51
is connected with an inverting input terminal of an amplifier
59
of a differential amplification circuit
58
via a resistor
57
. The connection
56
is connected with a non-inverting input terminal of the amplifier
59
via a resistor
60
, and is further connected with a voltage dividing circuit
62
for forming a reference voltage based on the voltage supplied from the power source terminal VCC via a resistor
61
.
An output terminal of the amplifier
59
is connected with its own inverting input terminal via a resistor
63
, and is further connected with an inverting input terminal of a comparison circuit
64
. A non-inverting input terminal of the comparison circuit
64
is connected with a voltage dividing circuit
66
for forming a reference voltage based on the voltage supplied from the power source terminal VCC, and is further connected with an output terminal of the comparison circuit
64
via a resistor
67
.
An output end of the comparison circuit
64
is connected with a base of a transistor
69
of an output circuit
68
. The collector of the transistor
69
is connected with an output terminal of the output circuit
68
and is further connected with the power source terminal VCC via a resistor
71
. The emitter of the transistor
69
is polished.
FIG. 42
shows the structure of the conventional magnetic field sensing element.
FIG. 43
is a graph showing operating characteristics of the conventional magnetic field sensing element.
As shown in
FIG. 42
, the Wheatstone bridge comprises the GMR element
48
Fukami Tatsuya
Hatazawa Yasuyoshi
Hiraoka Naoki
Sakai Yuuichi
Shinjo Izuru
Jolly Anthony
Mitsubishi Denki & Kabushiki Kaisha
Oda Christine
Sughrue Mion Zinn Macpeak & Seas, PLLC
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