Active solid-state devices (e.g. – transistors – solid-state diode – Responsive to non-electrical signal – Magnetic field
Reexamination Certificate
2002-11-04
2004-10-05
LeDynh, Bot (Department: 2862)
Active solid-state devices (e.g., transistors, solid-state diode
Responsive to non-electrical signal
Magnetic field
C324S244000, C324S251000
Reexamination Certificate
active
06800913
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to a Hall Effect device, and, in particular, to a modified Hall effect device which is a hybrid combination of a first conventional Hall plate and a second conventional Hall plate coupled to a ferromagnetic layer.
BACKGROUND OF THE INVENTION
Several different types of devices are available for the measurement of magnetic fields. Examples that operate at room temperature include flux gate magnetometers and magnetoresistors. A third family of devices is one of the oldest commercial field sensors, the Hall plate. All of these devices share a common trait; they measure a scalar value of magnetic field that represents a single component of the vector field to be measured. The family of Hall devices includes dozens, if not hundreds, of variations, for example, R. S. Popovic, “Hall-effect Devices,” Sens. Actuators 17, 39 (1989); and R. S. Popovic, “Hall Effect Devices”, (Adam Hilger, Bristol, 1991), both herein incorporated by reference. One limitation of all of these Hall devices is that these devices only can measure a scalar field value proportional to the component of vector field that is perpendicular to the plane of the Hall plate.
In the art, one-dimensional arrays of Hall devices have been used to achieve a moderate magnetic field spatial resolution. A one-dimensional array of Hall crosses has been described by E. Zeldov et al., “Thermodynamic observation of first-order vortex-lattice melting transition in BiSrCaCuO,” Nature 375, 373 (1995), herein incorporated by reference. In this study, an array of ten Hall crosses, with dimensions of 3 &mgr;m by 3 &mgr;m for each sensor, was used to detect the motion of fluxons in a small sample of single crystal superconducting BiSrCaCuO. The sensors were fabricated on a GaAs/AlGaAs chip and a macroscopic (0.7 mm by 0.3 mm by 0.1 mm) sample was placed on top. Each Hall sensor had a DC sensitivity of order 0.1 Oe and each was able to sense the presence of a single fluxon when in proximity to the sensor. The spatial resolution of the measurement was therefore of the order of magnitude of the Hall sensor dimensions, a few microns.
One recent advancement in the art of measuring magnetic fields is provided by a hybrid Hall effect device. A hybrid Hall device is a simple bilayer magnetoelectronic device. The physical principles of operation are described in the publication “Hybrid Hall Effect Device,” by Mark Johnson, B. Bennett, M. J. Yang, M. M. Miller and B. V. Shanabrook, Appl. Phys. Lett. 71, (1997) and in U.S. Pat. No. 5,652,445 entitled “Hybrid Hall Effect Device and Method of Operating,” both herein incorporated by reference, and are briefly described below with reference to FIGS.
1
(
a
) and (
b
).
An example of one prior art hybrid Hall effect device is generally denoted
10
in FIGS.
1
(
a
) and
1
(
b
). A thin, microstructured ferromagnetic film F, denoted
11
, is fabricated over a standard Hall cross
12
formed from a Hall plate
14
, and positioned such that edge
13
of film
11
is disposed over the central region of the Hall cross
12
. The film
11
is electrically isolated from the Hall cross
12
, typically by a thin insulating layer
15
.
The film
11
has a magnetization anisotropy in the film plane and acts as a local source of magnetic field. When an external magnetic field H
x
{circumflex over (x)} causes the magnetization M of F to be along −{circumflex over (x)}, there is a positive magnetic pole density on the edge over the Hall cross
12
, and a local negative field −|B
z
| is generated in the vicinity of the carriers in the Hall plate
14
which comprises an InAs layer
16
, a second insulating layer
17
and a substrate
18
(see FIG.
1
(
b
)). The result is a positive sense voltage V
s
=V
+
−V
−
. If the magnetization orientation is reversed, the sign of the pole density, the local field |B
z
|, and the sense voltage V; is reversed. Thus, device
10
translates a horizontal magnetic field into a vertical magnetic field, thereby providing for the detection and measurement of the convolution of the {circumflex over (x)} and {circumflex over (z)} field components comprising the magnetic field.
When fabricated with appropriate magnetic properties, the film
11
has bistable magnetization and the resulting hybrid Hall effect device
10
has digital applications, such as nonvolatile storage. When fabricated with other magnetic properties, the magnetization of film
11
responds linearly with an external field. A hybrid Hall effect device engineered in this way can act as a sensor of in-plane magnetic fields.
One limitation with prior art hybrid Hall effect devices, such as device
10
, is that these prior art devices cannot be used to determine the independent magnetic field vector components comprising a vector magnetic field, such as for determining the {circumflex over (x)} and the {circumflex over (z)} components of a magnetic field; device
10
merely measures the convolution of the {circumflex over (x)} and {circumflex over (z)} field components.
BRIEF SUMMARY OF THE INVENTION
The present invention concerns a modified hybrid Hall effect device, which is a hybrid combination of a first conventional Hall plate and a second conventional Hall plate coupled to a ferromagnetic layer, corresponding to film F. The modified Hall Effect device can be adapted for use as a magnetic field sensor capable of measuring the individual components of a vector magnetic field. Equivalently, the device is capable of measuring the magnitude of a vector magnetic field of any orientation.
In the present modified hybrid Hall effect device, the ferromagnetic film acts as a field transducer that translates a horizontal field into a vertical field. This is a function that can be combined with the sensitivity of Hall devices for use in applications where perpendicular and horizontal magnetic field components are present, to make a magnetometer that is sensitive to more than a single component of the field.
An object of the present invention is to provide an inexpensive, integrated combination of a Hall device that is adaptable for measuring two or three components of a vector magnetic field, {overscore (B)}. A magnetometor, incorporating the present invention, which is capable of measuring two or more vector components of a magnetic field, has several advantages over magnetometers which are capable only of scalar measurements. The single component to which a scalar magnetometer is sensitive may be the smallest component of the vector field to be measured. Therefore, measuring all three vector components, the vector magnetometer always measures the total field magnitude, and is therefore intrinsically more sensitive in any application.
An additional object of the present invention is to provide a microfabricated magnetometer cell with two or three components for measuring a vector field with high spatial resolution. A specific application is the calibration and characterization of magnetic force microscope (MFM) tips. A cell that measures a single component of field can also be used for this application, with diminished field sensitivity by comparison with the two or three component cells.
A further object of the present invention is to provide a device, which is adaptable to use any source of magnetic field and which generates a three-dimensional magnetic field that is dipolar but has properties unique to that source. The source may be either a macroscopic source, such as a vehicle, or a microscopic source such as a magnetic particle used to tag a molecule or bundle of molecules. While measuring a scalar field might permit the detection of a source of the field, measuring a vector field permits the detection of a source and, with a suitable model, also permits the identification of the object that is the source. Following this functionality, measurement of a vector field as a function of time and/or position permits an analysis of position and motion of the object, which is the field source.
An additional obje
Bennett Brian
Johnson Mark B.
Miller Michael
Karasek John J.
LeDynh Bot
Mills III John Gladstone
The United States of America as represented by the Secretary of
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