U.S. patent application number 14/097332 was filed with the patent office on 2017-02-09 for low-noise magnetic sensors.
The applicant listed for this patent is King Abdullah University of Science and Technology. Invention is credited to Jurgen Kosel, Jian Sun.
Application Number | 20170038439 14/097332 |
Document ID | / |
Family ID | 50338222 |
Filed Date | 2017-02-09 |
United States Patent
Application |
20170038439 |
Kind Code |
A9 |
Kosel; Jurgen ; et
al. |
February 9, 2017 |
LOW-NOISE MAGNETIC SENSORS
Abstract
Magnetic sensors are disclosed, as well as methods for
fabricating and using the same. In some embodiments, an EMR effect
sensor includes a semiconductor layer. In some embodiments, the EMR
effect sensor may include a conductive layer substantially coupled
to the semiconductor layer. In some embodiments, the EMR effect
sensor may include a voltage lead coupled to the conductive layer.
In some embodiments, the voltage lead may be configured to provide
a voltage for measurement by a voltage measurement circuit. In some
embodiments, the EMR effect sensor may include a second voltage
lead coupled to the semiconductor layer. In some embodiments, the
second voltage lead may be configured to provide a voltage for
measurement by a voltage measurement circuit. Embodiments of a Hall
effect sensor having the same or similar structure are also
disclosed.
Inventors: |
Kosel; Jurgen; (Thuwal,
SA) ; Sun; Jian; (Thuwal, SA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
King Abdullah University of Science and Technology |
Thuwal |
|
SA |
|
|
Prior
Publication: |
|
Document Identifier |
Publication Date |
|
US 20140084913 A1 |
March 27, 2014 |
|
|
Family ID: |
50338222 |
Appl. No.: |
14/097332 |
Filed: |
December 5, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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13187329 |
Jul 20, 2011 |
9164153 |
|
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14097332 |
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61365914 |
Jul 20, 2010 |
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61733973 |
Dec 6, 2012 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G01R 33/0052 20130101;
G01R 33/095 20130101; G01R 33/072 20130101; G01R 33/07 20130101;
H01L 43/02 20130101 |
International
Class: |
G01R 33/09 20060101
G01R033/09; H01L 43/02 20060101 H01L043/02; G01R 33/07 20060101
G01R033/07 |
Claims
1. A sensor, comprising: a semiconductor layer; a conductive layer
on a first side of the semiconductor layer, the conductive layer
coupled to the first side of the semiconductor layer; a voltage
lead coupled to the conductive layer opposite the semiconductor
layer, the voltage lead configured to provide a voltage for
measurement by a voltage measurement circuit; a first current lead
coupled to a second side of the semiconductor layer, the current
lead configured to provide a current for measurement by a current
measurement circuit; and a second current lead coupled to the
second side of the semiconductor layer.
2. The sensor of claim 1, wherein the second side of the
semiconductor layer is opposite the first side of the semiconductor
layer.
3. The sensor of claim 1, wherein the voltage measurement is
between the voltage lead and the second current lead.
4. The sensor of claim 2, wherein the voltage measurement is
between the voltage lead and the second current lead.
5. The sensor of claim 1, wherein the conductive layer comprises a
material selected from the group consisting of gold (Au), copper
(Cu), silver (Ag), and titanium (Ti).
6. The sensor of claim 1, wherein the semiconductor layer comprises
a material selected from the group consisting of silicon (Si),
indium antimonide (InSb), indium arsenide (InAs), gallium asrsenide
(GaAs), aluminum indium antimonide (AlInSb), and aluminum indium
antimonide (AlInSb).
7. The sensor of claim 1, where the semiconductor layer is
n-doped.
8. The sensor of claim 1, where the semiconductor layer comprises a
plurality of n-doped layers.
9. The sensor of claim 8, where the plurality of n-doped layers
comprises a first n-doped layer, a second n-doped layer formed upon
the first n-doped layer, and a third n-doped layer formed upon
second n-doped layer.
10. The sensor of claim 1, where the semiconductor layer comprises
a n-type high mobility two-dimensional electron gas (2DEG)
heterostructure.
11. The sensor of claim 1, wherein the first and second current
leads are coupled to the semiconductor layer at opposing edges of
the second side of the semiconductor layer.
12. The sensor of claim 1, wherein the first and second current
leads are asymmetrically located on the second side of the
semiconductor layer about a center of the sensor.
13. The sensor of claim 1, further comprising another voltage lead
coupled to the second side of the semiconductor layer between a
center of the sensor and the second current lead.
14. The sensor of claim 1, wherein the sensor is an extraordinary
magnetoresistance (EMR) sensor.
15. A method for detecting a magnetic field comprising: providing a
sensor of any of claims 1 through 13; measuring a voltage at the
voltage lead coupled to the conductive layer opposite the
semiconductor layer; measuring a current flowing through the first
and second current leads, where the current and voltage are
measured in different directions; and calculating a resistance
based upon the measured voltage and the measured current.
16. The method of claim 15, wherein the second current lead is
grounded.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation-in-part (CIP) to U.S.
patent application Ser. No. 13/187,329 filed on Jul. 20, 2011, and
claims priority to U.S. Provisional Application No. 61/733,973
filed Dec. 6, 2012, the entire contents of which are specifically
incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates generally to magnetic sensors,
more particularly, to extraordinary magnetoresistance (EMR) effect
and Hall effect sensors and methods for making and using the
same.
[0004] 2. Description of the Related Art
[0005] Generally, there are at least two types of magnetic sensors
that can be used to measure a magnetic field, including an EMR
sensor and a Hall sensor. An EMR sensor operates based on an EMR
effect. Broadly speaking, the EMR effect quantifies scattering of
electrons at a material interface when an electric current is
applied to the material. The scattering occurs due to an
interaction between the magnetic field and electrons in at least
one of the materials comprising the sensor. Generally, a the Hall
effect quantifies a shearing force caused by interaction between
the magnetic field and electrons in the current applied to the
material. Each of these effects are described in greater detail in
the sections below.
EMR Effect Sensors
[0006] EMR is a large magnetoresistance effect that may arise in a
nonmagnetic semiconductor metal hybrid structure. In an EMR effect
sensor, the Lorentz force induced by a magnetic field may cause a
redistribution of the electric current density between adjacent
semiconductor and metal layers resulting in resistance changes. The
EMR effect may be described by equation (1):
E M R ( H e ) = R ( H ) - R ( 0 ) R ( 0 ) ( 1 ) ##EQU00001##
where H.sub.e is the external magnetic field (e.g., external to the
sensor), R(H) is the measured resistance of the sensor in the
presence of a magnetic field H, and R(0) is the measured resistance
of the sensor at zero magnetic field.
[0007] The dimensions of an EMR sensor, the thickness of its
layers, and the placement of the voltage and current leads may
significantly effect magnitude of the measured EMR. FIG. 1A and
FIG. 1B depict prior art EMR effect sensors 100A and 100B. As
depicted in both figures, EMR effect sensors 100A and 100B each
have a metal layer 102 and a semiconductor layer 104. In both
pictures, the voltage and current leads are arranged symmetrically
around center 110 of the EMR effect sensor.
[0008] Voltage leads 106 and current leads 108 are located on one
side of the device--coupled to semiconductor layer 104. FIG. 1A
depicts voltage leads 106 and current leads 108 in an V-I-I-V
formation, and FIG. 2A depicts the voltage and current in a I-V-V-I
formation. The voltage (V) between voltage leads 106 and the
current (I) through current leads 108 allow for the calculation of
the resistance R(H) in equation (1) by using equation (2):
R ( H ) = V ( H ) I ( H ) ( 2 ) ##EQU00002##
[0009] EMR effect sensors 100A and 100B can further be described by
width 112 of the metal layer 102, width 114 of the semiconductor
layer 104, and length 116 of the EMR effect sensor. FIG. 2
illustrates the simulated EMR effect for EMR effect sensor 100B
(e.g., having an I-V-V-I lead formation) for four different
magnetic fields as a function of the length (L) 116 of the EMR
sensor divided by the width (W.sub.s) 114 of the semiconductor
layer 104. In this example, metal layer 102 is gold, and
semiconductor layer 104 is indium antimonide. As shown, the EMR
effect is dependent on the dimensions of the sensor. In FIG. 2, the
EMR effect reaches a maximum of approximately 1.1.times.10.sup.5%
with a 1 T magnetic field and an L/W.sub.s ratio of 25.
[0010] FIG. 3A and FIG. 3B illustrate the change in current density
in semiconductor layer 104 of EMR effect sensor 100B. At a zero
magnetic field, the current density in semiconductor layer 104 is
low, as depicted by minimal current density flux lines in
semiconductor layer 104 in FIG. 3A. The presence of an external
magnetic field causes a redistribution of the current density due
to the Lorentz force yielding an increased current density in the
semiconductor, as depicted by more current density flux lines in
semiconductor layer 104 in FIG. 3B. In this example, a 0.3 T
external magnetic field creates an increased current density within
the semiconductor layer, and as a result, creates a higher
electrical resistivity.
Hall Effect Sensors
[0011] The Hall effect is the production of a voltage difference
(the Hall voltage) across an electrical conductor, transverse to an
electric current in the conductor and a magnetic field
perpendicular to the current. For an n-type semiconductor where
there is a dominate type of charge carrier-electron, the Hall
voltage V.sub.H is given by equation (3):
V H = - I B ned ( 3 ) ##EQU00003##
where I is the current input, B is the magnetic flux density, d is
the thickness of the plate, e is the electron charge, and n is the
carrier density of electrons.
[0012] The most frequently used Hall effect sensor consists of a
high mobility semiconductor conductive bar with four or six
contacts. Two of the contacts are current leads, which are used to
induce a current flow through the Hall bar, and the other contacts
are voltage probes which are used to measure the Hall voltage. FIG.
9 depicts the typical four contacts Hall effect sensor 900. As
depicted in the figure, Hall effect sensors 900 have a
semiconductor bar 901 and voltage probes 902 and current leads 903
are located on the edges of the semiconductor bar 901. The voltage
probes are arranged symmetrically along the centerline 904 of the
Hall sensor.
[0013] The Hall sensitivity S.sub.H is a very useful parameter for
judging the performance of the Hall sensor (equation (4)).
S H = .differential. V H .differential. B = - I ned ( 4 )
##EQU00004##
[0014] The Hall sensitivity is typically 1.about.5 mV/mT for a 1 mA
current with the commercial Hall sensors.
[0015] Another useful parameter is the thermal field noise (in T/
Hz, equation (5)):
S B = 4 K B TR S H ( 5 ) ##EQU00005##
where R is the resistance of the Hall sensor, T is the temperature
and K.sub.B is the Boltzmann constant. Two-dimensional quantum-well
multilayer heterostructures based on GaAs are promising for
low-noise Hall sensors with 100 nT/ Hz. In general, noise could be
significantly reduced with devices of lower resistance.
SUMMARY OF THE INVENTION
[0016] Embodiments of magnetic sensors are disclosed. In one
embodiment, the magnetic sensor includes a semiconductor layer. In
some embodiments, the sensor may include a conductive layer
substantially coupled to the semiconductor layer. In some
embodiments, the sensor may include a first voltage lead coupled to
the semiconductor layer. In some embodiments, the first voltage
lead may be configured to provide a voltage for measurement by a
voltage measurement circuit. In some embodiments, the sensor may
include a second voltage lead coupled to the conductive layer. In
some embodiments, the second voltage lead may be configured to
provide a voltage for measurement by a voltage measurement
circuit.
EMR Sensors
[0017] Extraordinary magnetoresistance (EMR) effect sensors are
disclosed. In some embodiments, the EMR effect sensor includes a
semiconductor layer. In some embodiments, the EMR effect sensor may
include a conductive layer substantially coupled to the
semiconductor layer. In some embodiments, the EMR effect sensor may
include a first voltage lead coupled to the semiconductor layer. In
some embodiments, the first voltage lead may be configured to
provide a voltage for measurement by a voltage measurement circuit.
In some embodiments, the EMR effect sensor may include a second
voltage lead coupled to the conductive layer. In some embodiments,
the second voltage lead may be configured to provide a voltage for
measurement by a voltage measurement circuit.
[0018] In some embodiments, the EMR effect sensor may include a
first current lead coupled to the semiconductor layer. In some
embodiments, the first current lead may be configured to provide a
current for measurement by a current measurement circuit. In some
embodiments, the EMR effect sensor may include a second current
lead. The second current lead may be coupled to the semiconductor
layer. In some embodiments, the second current lead may be
configured to provide a current for measurement by a current
measurement circuit.
[0019] In some embodiments, the conductive layer may include gold
(Au). In some embodiments, the conductive layer may include copper
(Cu). In some embodiments, the conductive layer may include silver
(Ag). In some embodiments, the conductive layer may include
Titanium (Ti).
[0020] In some embodiments, the semiconductor layer may include
indium antimonide (InSb). In some embodiments, the semiconductor
layer may include indium arsenide (InAs). In some embodiments, the
semiconductor layer may include gallium asrsenide (GaAs). In some
embodiments, the semiconductor layer may include aluminum indium
antimonide (AlInSb). In some embodiments, the semiconductor layer
may include aluminum indium arsenide (AlInAs). In some embodiments,
the semiconductor layer may include silicon (Si).
[0021] In some embodiments, the semiconductor layer is n-doped. In
some embodiments, the semiconductor layer may include a first
n-doped layer, a second n-doped layer, and a third n-doped layer.
In some embodiments, the first n-doped layer, the second n-dope
layer, and the third n-doped layer may be doped with tellurium. In
some embodiments, the third n-doped layer is above the second
n-doped layer and the second n-doped layer is above the first
n-doped layer.
[0022] Methods for fabricating an EMR effect sensor are disclosed.
In some embodiments, the method may include forming an insulation
layer on a substrate. In some embodiments, the method may include
forming a semiconductor layer above the insulation layer. In some
embodiments, the method may include forming capping layer on the
semiconductor layer. In some embodiments, the method may include
forming a conductive layer coupled to the semiconductor layer. In
some embodiments, the method may include forming a first voltage
lead coupled to the semiconductor layer, the first voltage lead
configured to provide voltage for measurement by a voltage
measuring circuit. In some embodiments, the method may include
forming a second voltage lead coupled to the conductive layer. In
some embodiments, the second voltage lead may be configured to
provide voltage for measurement by a voltage measuring circuit.
[0023] In some embodiments of the method, the method may include
forming a first current lead coupled to the semiconductor layer. In
some embodiments, the first current lead may be configured to
provide current for measurement by a current measuring circuit. In
some embodiments, the method may include forming a second current
lead coupled to the semiconductor layer. In some embodiments, the
second current lead may be configured to provide current for
measurement by a current measuring circuit.
[0024] In some embodiments of the method, the conductive layer may
include Au. In some embodiments of the method, the conductive layer
may include Cu. In some embodiments of the method, the conductive
layer may include Ag.
[0025] In some embodiments of the method, the semiconductor layer
may include InSb. In some embodiments of the method, the
semiconductor layer may include InAs. In some embodiments of the
method, the semiconductor layer may include GaAs. In some
embodiments of the method, the semiconductor layer may include
AlInSb. In some embodiments of the method, the semiconductor layer
may include AlInAs. In some embodiments of the method, the
semiconductor layer may include Si.
[0026] In some embodiments of the method, the semiconductor layer
is n-doped. In some embodiments of the method forming the
semiconductor layer further may include forming a first n-doped
layer; forming a second n-doped layer; and forming a third n-doped
layer. In some embodiments of the method, forming the first n-doped
layer, the second n-dope layer, and the third n-doped layer may
include doping with tellurium. In some embodiments of the method,
the third n-doped layer is formed above the second n-doped layer
and the second n-doped layer is formed above the first n-doped
layer.
[0027] Some embodiments of the method may include forming a buffer
layer on top of the insulation layer and before forming the
semiconductor.
[0028] In some embodiments of the method, the insulator layer may
include aluminum oxide (Al.sub.2O.sub.3). In some embodiments of
the method, the substrate may include GaAs.
[0029] In some embodiments of the method, the capping layer may
include silicon nitride (Si.sub.3N.sub.4) and Al.sub.2O.sub.3.
[0030] Methods for detecting magnetic field are disclosed. In some
embodiments, the method includes providing a EMR effect sensor. The
EMR effect sensor, in some embodiments, may include a semiconductor
layer, a conductive layer substantially coupled to the
semiconductor layer, a first voltage lead coupled to the
semiconductor layer, a second voltage lead coupled to the
conductive layer, a first current lead coupled to the semiconductor
layer, and a second current lead coupled to the semiconductor
layer, the second current lead configured to provide current for
measurement by a current measurement circuit. In some embodiments,
the method may also include measuring the voltage across the first
voltage lead and the second voltage lead. In some embodiments, the
method may include measuring the current through the first current
lead and the second current lead. In some embodiments, the method
may include calculating resistance in response to the measured
voltage and the measured current.
Hall Effect Sensor
[0031] A low-noise Hall sensor is disclosed. It comprises a
conductive high mobility semiconductor layer with two current leads
contacted to the two ends of one side along the semiconductor
layer. The first voltage probe is placed on the center of one edge
of the bar; the second voltage probe is a shunt-like electrode,
which is coupled to the bar.
[0032] The output resistance of the low-noise Hall sensor is
reduced significantly compared to the conventional Hall sensor. Due
to the high conductivity of the metal, the current induced will
flow into the shunt-like electrode at zero field, which acts like a
short circuit in parallel to the semiconductor layer. This lowers
the resistance of the device and causes a decrease of the noise
level. When an external field is applied, the current flow will be
deflected by the Lorentz force, which will cause the voltage
difference at two voltage probes.
[0033] N-type III-V semiconductors are typically used as the
conductive bar in Hall sensor because of their high electron
mobility. In some embodiments, the semiconductor layer may include
n-type indium antimonide (InSb). In some embodiments, the
semiconductor layer may include n-type indium arsenide (InAs). In
some embodiments, the semiconductor layer may include an n-type
two-dimensional electron gas (2DEG) heterostructure, which is a
high-mobility quantum well. A typical 2DEG is formed of a InAs/AlSb
sandwich structure. Those materials are typically grown with
molecular beam epitaxy (MBE).
[0034] The metallic contacts need to be ohmic. For n-type InAs and
InSb, the metallic ohmic contact is typically formed with titanium
(Ti)/platinum (Pt)/gold (Au) by e-beam evaporation or sputtering.
For an InAs/AlSb 2DEG heterostructure, the metallic contact is
typically formed with palladium (Pd)/platinum (Pt)/gold (Au) by
e-beam evaporation or sputtering. Both of these two metallic
structures need a post-annealing process to form the ohmic
contact.
[0035] Methods for fabricating a Hall sensor are disclosed. Grow
the semiconductor layer with MBE on a semi-insulating substrate,
which could be gallium arsenide (GaAs). Pattern the conductive bar
with conventional photo-lithography for micro-scale device and
E-beam lithography for nano-scale device; the bar could be defined
with wet etching method in hydrogen fluoride solution or with dry
etching method using reactive ion etcher with a BCl.sub.3/Cl.sub.2
etchant gas. The metallic layer is deposited with e-beam
evaporation or sputtering. The patterns of the contact could be
defined with lift-off or etching process. A capping layer of
silicon nitride (SiN.sub.x) is deposit with plasma-enhanced
chemical vapor deposition (PECVD) to protect the device from
corrosion. Finally, the contact windows are opened for wire
bonding.
[0036] The term "coupled" is defined as connected, although not
necessarily directly, and not necessarily mechanically.
[0037] The terms "a" and "an" are defined as one or more unless
this disclosure explicitly requires otherwise.
[0038] The term "substantially" and its variations are defined as
being largely but not necessarily wholly what is specified as
understood by one of ordinary skill in the art, and in one
non-limiting embodiment "substantially" refers to ranges within
10%, preferably within 5%, more preferably within 1%, and most
preferably within 0.5% of what is specified.
[0039] The terms "comprise" (and any form of comprise, such as
"comprises" and "comprising"), "have" (and any form of have, such
as "has" and "having"), "include" (and any form of include, such as
"includes" and "including") and "contain" (and any form of contain,
such as "contains" and "containing") are open-ended linking verbs.
As a result, a device or method that "comprises," "has," "includes"
or "contains" one or more elements or steps possesses those one or
more steps or elements, but is not limited to possessing only those
one or more elements. Likewise, a step of a method or an element of
a device that "comprises," "has," "includes" or "contains" one or
more features possesses those one or more features, but is not
limited to possessing only those one or more features. Furthermore,
a device or structure that is configured in a certain way is
configured in at least that way, but may also be configured in ways
that are not listed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0040] The following drawings illustrate by way of example and not
limitation. For the sake of brevity and clarity, every feature of a
given structure is not always labeled in every figure in which that
structure appears. Identical reference numbers do not necessarily
indicate an identical structure. Rather, the same reference number
may be used to indicate a similar feature or a feature with similar
functionality, as may non-identical reference numbers.
[0041] FIG. 1A illustrates a prior art EMR effect sensor with
voltage and current leads in a V-I-I-V formation along one side of
the sensor.
[0042] FIG. 1B illustrates a prior art EMR effect sensor with
voltage and current leads in an I-V-V-I formation along one side of
the sensor.
[0043] FIG. 2 plots the simulated EMR effect of a prior art EMR
effect sensor as a function of the width of the sensor divided by
the length of the semiconductor layer for four external magnetic
fields.
[0044] FIG. 3A illustrates the current density flux lines through
an EMR effect sensor in the presence of zero external magnetic
field.
[0045] FIG. 3B illustrates the current density flux lines through
an EMR effect sensor in the presence of a magnetic field.
[0046] FIG. 4A illustrates an embodiment of the present EMR effect
sensor.
[0047] FIG. 4B illustrates another embodiment of the present EMR
effect sensor.
[0048] FIG. 5 is a flowchart illustrating an embodiment of a method
for fabricating an EMR effect sensor.
[0049] FIG. 6 illustrates another embodiment of the present EMR
effect sensor.
[0050] FIG. 7 is a flowchart illustrating an embodiment of a method
for measuring the EMR effect using an embodiment of the present EMR
effect sensor.
[0051] FIG. 8 compares the simulated EMR effect of an embodiment of
the present EMR effect sensor and a prior art EMR sensor as a
function of the external magnetic field.
[0052] FIG. 9 illustrates a conventional four contacts Hall sensor
with current leads and two voltage probes placed along the central
line.
[0053] FIG. 10 illustrates a low-noise Hall sensor.
[0054] FIG. 11A illustrates the current path lines and electric
field direction arrows in a low-noise Hall sensor in the presence
of zero magnetic field.
[0055] FIG. 11B illustrates the current path lines and electric
field direction arrows in a low-noise Hall sensor in the presence
of an external magnetic field.
[0056] FIG. 12 is a flowchart illustrating an embodiment of a
method for fabricating a low-noise Hall sensor.
[0057] FIGS. 13A and 13B illustrate examples of EMR effect sensors
with voltage and current leads in symmetrical and asymmetrical
configurations, respectively, along one side of the sensor.
[0058] FIG. 14A illustrates an example of an enhanced EMR effect
sensor.
[0059] FIG. 14B is an optical microscope image of a fabricated
example of an EMR sensor.
[0060] FIGS. 15(a), 15(b), and 15(c) are plots of voltages between
different electrodes of the EMR sensor of FIG. 14B as a function of
the homogenous magnetic field applied to the EMR sensor.
[0061] FIGS. 16(a) and 16(b) are plots of sensitivity of the EMR
sensor of FIG. 14B as a function of magnetic field in (a) a
low-field region and (b) a high-field region of the EMR sensor.
DETAILED DESCRIPTION
[0062] The present embodiments describe an advantageous structure
that may be useful for sensing magnetic fields. Advantageously, the
same or similar structure may be used for both an EMR sensor and a
Hall Effect sensor. For example, embodiments of a
semiconductor/metal hybrid structure, which comprises a conductive
semiconductor layer and a metallic shunt are described. Another
advantage of this structure may be the low-noise performance
characteristics achieved through use of the hybrid metallic shunt
structure, which may reduce the output resistance of the
sensor.
[0063] In one embodiment, the magnetic sensor includes a
semiconductor layer. In some embodiments, the sensor may include a
conductive layer substantially coupled to the semiconductor layer.
In some embodiments, the sensor may include a first voltage lead
coupled to the semiconductor layer. In some embodiments, the first
voltage lead may be configured to provide a voltage for measurement
by a voltage measurement circuit. In some embodiments, the sensor
may include a second voltage lead coupled to the conductive layer.
In some embodiments, the second voltage lead may be configured to
provide a voltage for measurement by a voltage measurement circuit.
As will become clear in the description below, such a structure may
be used as either an EMR sensor, a Hall effect sensor, or both.
EMR Effect Sensors
[0064] Extraordinary magnetoresistance (EMR) effect sensors are
disclosed. An embodiment of an EMR effect sensor 400A is depicted
in top view in FIG. 4A. The EMR effect sensor may also be referred
to as a Hall-bar type sensor. In some embodiments, EMR effect
sensor 400A may include semiconductor layer 404. Semiconductor
layer 404 may include indium antimonide (InSb), indium arsenide
(InAs), gallium arsenide (GaAs), aluminum indium antimonide
(AlInSb), aluminum indium arsenide (AlInAs), silicon (Si). The
length 416 of semiconductor layer 104 may be approximately 50 .mu.m
(e.g., between 30-70, between 40-60, and/or 45-55 .mu.m). The width
414 of semiconductor layer 404 may be 5 .mu.m (e.g., between 3-7,
between 4-6, and/or 4.5-5.5 .mu.m). As discussed with respect to
FIG. 2, the width 414 of semiconductor layer 404 may be selected
for optimum sensitivity as a function of the ratio between the
length 416 of the width 414 of the semiconductor layer
[0065] In some embodiments, conductive layer 402 may be
substantially coupled to the semiconductor layer 404. Conductive
layer 402 may be a metal layer with a width 412. Moreover,
conductive layer 404 may include gold (Au), copper (Cu), silver
(Ag), and/or other like conductive materials. Conductive layer 402
may also have a length 416 of approximately 50 .mu.m (e.g., between
30-70, between 40-60, and/or 45-55 .mu.m). As shown in the depicted
embodiment, the conductive layer may be substantially coupled to
the semiconductor layers. Both layers may be in substantial
contact.
[0066] In some embodiments, first voltage lead 408 may be coupled
to semiconductor layer 404. As shown in the depicted embodiment,
first voltage lead 408 may be arranged substantially along center
410 of EMR effect sensor 400A. First voltage lead 408 may be
substantially coupled to semiconductor layer 404. In some
embodiments, a second voltage lead 409 may be coupled to conductive
layer 402. As shown in the depicted embodiment, second voltage lead
409 may also be arranged substantially along center 410 of EMR
effect sensor 400A. Moreover, as shown in the depicted embodiment,
the first and second voltage leads are located on opposite sides of
EMR effect sensor 400A rather than being located on the same side
of the sensor.
[0067] First voltage lead 408 and second voltage lead 409 may be
configured to provide a voltage for measurement to a voltage
measurement circuit (not shown). Moreover, voltage may be measured
across the EMR sensor using first voltage lead 408 and second
voltage 409. A voltage measurement circuit may include a voltmeter,
a digital multimeter (DMM), or other analog or digital circuit
configured to measure voltage across two leads. In some
embodiments, first voltage lead 408 and second voltage lead 409 may
include Au, Cu, Ag, and/or other electrically conductive material.
First voltage lead 408 and second voltage lead 409 may include the
same material and/or materials as conductive layer 402, but the
leads may also include different materials. In some embodiments,
second voltage lead 409 may be substantially fused to conductive
layer 402. Moreover, second voltage lead 409 may be an extension of
conductive layer 402.
[0068] In some embodiments, EMR effect sensor 400A may further
include first current lead 406 and second current lead 407. First
current lead 406 and second current lead 407 may be similarly
configured to provide a current for measurement by a current
measurement circuit. As shown in the depicted embodiment, first
current lead 406 and second current lead 407 may be arranged
substantially symmetrically around center 410. FIG. 4A and FIG. 4B
illustrate two embodiments of arrangements of first current lead
406 and second current lead 407. As shown in FIG. 4B, first current
lead 406 and second current lead 407 are arranged more closely to
center 410 than in FIG. 4A. As shown in the depicted embodiment,
first current lead 406 and second current lead 407 are both coupled
to semiconductor layer 404.
[0069] In some embodiments, semiconductor layer 404 is n-doped. The
doping of the semiconductor layer may involve adding a dopant to
increase the charge carriers (e.g., electrons) within semiconductor
layer 404. Doping the semiconductor layer may increase the mobility
of the charger carriers within the semiconductor layer. For
example, tellurium (Te) or phosphorous (Ph) may be used as dopants.
In some embodiments, the semiconductor layer 404 includes multiple
n-doped layers: a first n-doped layer, a second n-doped layer, and
a third n-doped layer. For example, the first n-doped layer may
include Te-doped n-type InSb (Al0.09In0.91Sb) with a thickness of
approximately 2 .mu.m (e.g., 1-3 or 2.5-3.5 .mu.m). The second
n-doped layer may include Te-doped n-type InSb with a thickness of
approximately 1.5 .mu.m (e.g., 1-2 or 1.25-1.75 .mu.m). The third
n-doped layer may include InSb (Al0.09In0.91Sb) with a thickness of
approximately 50 nm (e.g., between 30-70, between 40-60, and/or
45-55 .mu.m). Moreover, in some embodiments, the third n-doped
layer may be above the second n-doped layer, and the second n-doped
layer may be above the third n-doped layer.
[0070] FIG. 5 illustrates one embodiment of a method 500 for
fabricating an embodiment of EMR effect sensor--such as for example
the embodiment illustrated in cross-section in FIG. 6. In some
embodiments, the method 500 may include forming 502 an insulation
layer 604 on a substrate. For example, insulation layer 604 may
include depositing a thin film Al.sub.2O.sub.3 or other insulating
materials known in the art. Forming 502 the insulation layer 604
may include a chemical vapor deposition process (CVD), a physical
vapor deposition process (PVD), atomic layer deposition process
(ALD), or other like process known in the art. Substrate 602 may
include GaAs or other semiconductors/insulators known in the art.
In some embodiments a buffer layer (not shown) may be grown on top
of the insulation layer. For example, the buffer layer (not shown)
may include a thin film of un-doped semiconductor (e.g., 200 nm of
In Sb). In some embodiments, the buffer layer may be grown with a
vapor-phase epitaxy process. The insulator layer may act to stop
the current flow into substrate. The buffer layer may be used to
accommodate the different lattice constants of the substrate and
the semiconductor layer, and thus, may be used as a strain relief
layer between the substrate layer and the semiconductor layer.
[0071] In some embodiments, the method 500 may also include forming
504 a semiconductor layer 606. Forming 504 the semiconductor layer
606 may include forming a variety of materials such as for example,
InSb, InAs, GaAs, AlInSb, AlInAs, and Si. In some embodiments,
forming 504 the semiconductor layer 606 may include forming a
n-doped semiconductor layer, and in some embodiments, forming 504
the semiconductor layer 606 may include forming a first n-doped
layer, forming a second n-doped layer, and forming a third n-doped
layer. For example, forming the first n-doped layer may include
growing a 2 .mu.m film of Te-doped n-type InSb (Al0.09In0.91Sb).
Forming the second n-doped layer may include growing a 1.5 .mu.m
film of Te-doped n-type InSb. Forming the third n-doped layer may
include forming a heavily doped n-type InSb (Al0.09In0.91Sb) film.
Each of the n-doped layers may be formed using a metalorganic vapor
phase epitaxy process.
[0072] In some embodiments, method 500 may also include forming 506
a conductive layer 608 on top of the semiconductor layer. For
example, forming 506 the conductive layer 608 may include forming a
metal layer such as Au, Cu, Ag, and/or other like conductive
material. The conductive layer may be formed using a PVD, CVD, ALD,
or like process known in the art. For example, a sputtering process
may be used and may help provide electrical contact between the
conductive layer and the semiconductor layer.
[0073] In some embodiments, method 500 may also include forming 508
a capping layer 610 on top of the semiconductor layer. The capping
layer 610 may form a passivating layer on top of conducting layer
608. In some embodiments, forming 508 the capping layer may include
depositing approximately 200 nm of Si.sub.3N.sub.4 and/or
Al.sub.2O.sub.3.
[0074] In some embodiments, the method 500 may also include forming
510 a first voltage lead 612 and forming 512 a second voltage lead
614. The configuration of first voltage lead 612 and 614 are
described in more detail with respect to FIG. 4. Forming 510 first
voltage lead 612 and forming 512 second voltage lead 614 may
include using reactive ion etching (RIE) to smooth each side of the
structure 600, and diffuse conductive material (e.g., Au, Ag,
and/or Cu) and make electrical contact with the conductive layer
608.
[0075] In some embodiments, the method 500 may further comprise
forming a first current lead a second current lead (not shown). As
discussed in more detail with regards to FIG. 4, the first current
lead and second current both may be coupled to the semiconductor
layer. First current lead and second current lead may be formed
using the same processes used to form 510 first voltage lead
612.
[0076] FIG. 7 illustrates a method 700 for detecting a magnetic
field. In some embodiments, the method 700 includes providing 702
an EMR effect sensor. For example, an EMR effect sensor may include
sensors 400A, 400B, and 600. Moreover the EMR effect sensor may
include a semiconductor layer, a conductive layer, a first voltage
lead, a second voltage lead, a first current lead, and a second
current lead as discussed with regards to FIGS. 4A, 4B, and 6. In
some embodiments, the method 700 may include measuring 704 the
voltage across the first voltage lead and the second voltage lead.
In some embodiments, the method 700 may include measuring 706 the
current through the first current lead and the second current lead.
Next, in some embodiments, the method 700 may include calculating
resistance in response to the measured voltage and the measured
current. For example, the resistance of the EMR effect sensor may
be calculated using equation (2). Moreover, the EMR effect may be
measured by calculating the change in resistance in the presence of
a magnetic field using equation (1). Changes of the calculated
resistance may indicate a change in the magnetic field.
[0077] FIG. 8 illustrates the EMR effect of a claimed embodiment of
an EMR effect sensor compared to a prior art. As shown, when
compared to the claimed embodiment, the measured EMR effect of a
prior art EMR effect sensor appears to be a straight line as a
function of the magnetic field. As shown, the calculated EMR effect
of the prior art sensor in the presence of a -1 T external magnetic
field is 1.160.times.10.sup.5%. The claimed EMR effect sensor had a
calculated EMR effect of 728.times.10.sup.5% for the same external
magnetic field of -1 T. As shown, the claimed EMR effect sensors
may have a several hundred times improvement in detecting the
presence of a magnetic field when compared to the prior art.
Hall Effect Sensors
[0078] One of ordinary skill in the art will recognize that the
same or similar structure as found in FIG. 4 may be used for a Hall
sensor. One of ordinary skill in the art will also recognize
various minor configuration changes, such as changes in material or
orientation of the sensor with respect to the polarity of the
magnetic field, that may enhance either the Hall effect or the EMR
effect within the sensor. Thus, with only minor changes the sensor
may be optimized for sensing EMR effect or Hall effect. For
example, the Hall effect will typically be most pronounced when the
magnetic field is applied perpendicular to the direction of current
flow within the sensor. This is because the Hall effect typically
involves the cross-product of the magnetic field and the current.
On the other hand, one of ordinary skill in the art will recognize
that the EMR effect can be enhanced by selection of materials. For
example, a ferromagnetic metal materials, such as cobalt, nickel,
and iron will produce a very large EMR effect relative to the Hall
effect in the presence of an applied magnetic field. Paramagnetic
materials, such as gold, copper, or aluminum may be used for
sensing the Hall effect. One of ordinary skill in the art will
recognize a variety of material combinations and magnetic field
orientations that may be useful for optimizing sensing of either
the Hall effect or the EMR effect.
[0079] A low-noise Hall sensor is also disclosed. An embodiment of
the Hall sensor 1000 is depicted in the top view in FIG. 10. One of
ordinary skill in the art will appreciate the similarities between
the Hall sensor of FIG. 10 and the EMR sensor of FIG. 4. The
semiconductor layer 1001 is coupled with a metal shunt which acts
as a voltage probe 1002. The second voltage probe 1003 is placed at
the opposite side of the bar 1001 and along the central line 1005.
Current leads 1004 are placed at the two ends of the semiconductor
layer 1001 at the same side.
[0080] The semiconductor layer 1001 may be high mobility n-type
III-V semiconductors. In some embodiments, the semiconductor layer
may include n-type indium antimonide (InSb). In some embodiments,
the semiconductor layer may include n-type indium arsenide (InAs).
In some embodiments, the semiconductor layer may include n-type
two-dimensional electron gas (2DEG) heterostructure, which is a
high-mobility quantum well. The main type of 2DEG is formed of
InAs/AlSb sandwich structure.
[0081] The shunt-like voltage probe 1002, the second voltage probe
1003, and two current leads are all metallic ohmic contacts. For
n-type InAs and InSb, the metallic ohmic contact is formed with
titanium (Ti)/platinum (Pt)/gold (Au) by e-beam evaporation or
sputtering. For InAs/AlSb 2DEG heterostructure, the metallic
contact is formed with palladium (Pd)/platinum (Pt)/gold (Au) by
e-beam evaporation or sputtering. Both of these two metallic
structures may undergo a post-annealing process to form the ohmic
contact.
[0082] FIG. 11 illustrates the current path and electric field in
the Hall effect sensor when no external magnetic field is applied.
The vector diagram illustrating current flow is shown within the
structure of the device to illustrate current flow with respect to
the various features of the sensor, including the
semiconductor/metal interface.
[0083] FIG. 12 illustrates one embodiment of a method for forming a
Hall effect sensor 1000. In one embodiment, the method 1200 starts
by growing 1201 a semiconductor layer. For example the
semiconductor layer may be silicon. Next, the method 1200 includes
defining 1202 a patter on the semiconductor layer. The pattern may
be used for forming the contact leads. In a particular embodiment,
the pattern may be formed in photoresist. Next, the method 1200
includes depositing 1203 a metallic contact layer. The metallic
contact layer may comprise the metallic leads. The patterns of the
contacts may then be defined 1204, for example using a wet etch,
dry etch or lift-off process. Next, a capping layer may be
deposited 1205 over or around the sensor. Finally, contact windows
may be opened 1206 in the capping layer allowing access to the
metallic leads. One of ordinary skill in the art will recognize
alternative methods for forming the sensor, including those
described in FIG. 5.
Hall Effect Enhanced EMR Sensors
[0084] A strong magnetoresistance effect, the so-called
extraordinary magnetoresistance (EMR), can be demonstrated to exist
at room temperature in a certain kind of semiconductor/metal hybrid
structure. The orbital motion of carriers in a perpendicularly
applied external field causes a current deflection resulting in a
redistribution of the current from the metal shunt 102 (FIGS. 3A
and 3B) into the semiconductor layer 104 (FIGS. 3A and 3B), which
is the main reason for the resistance increase. The principle of
EMR sensing is based upon the change of the current path in the
hybrid structure upon application of a magnetic field rather than
the change of magnetoconductivity .sigma. of either the
semiconductor or the metal. This effect can be utilized to
implement sensors for the measurement of magnetic fields
perpendicular to the device.
[0085] The EMR effect was examined in a macroscopic composite Van
der Pauw disk made of a semiconductor disk with a concentric
metallic circular inhomogeneity embedded, and four electrodes were
used to apply current and measure voltage. Although this structure
provided good results, its realization in mesoscopic and
microscopic length scales was very difficult. Using bilinear
transformation, a bar-type geometry as illustrated in FIGS. 4 and
11, which includes a semiconductor bar shunted by a metal stack on
one side, can be derived, that shows a similar EMR effect while
being simpler in terms of fabrication. The EMR effect strongly
depends on the geometry of the device and the placement of the
electrical contacts. With respect to the placement of the
electrodes, two major kinds of configurations can be distinguished:
a symmetric configuration 1300A as shown in FIG. 13A, where the
placement of electrodes 106 and 108 are symmetric to the central
axis 110 of the bar-type device or an asymmetric configuration
1300B where the electrodes 106 and 108 are not symmetrically
located about the central axis 110 as illustrated in the example of
FIG. 13B.
[0086] At high fields of about 0.1 T, an outstanding sensitivity
can be achieved with symmetric EMR sensors 1300A made of group
III-V materials. For example, a two-contact EMR sensor may exhibit
a strong sensitivity of 85 .OMEGA./T at 0.1 T, which is comparable
to that of GMR sensors used in recording applications. Since the
symmetric EMR sensor 1300A has a parabolic magnetoresistance curve,
it suffers from a weak low-field sensitivity that may limit the
applicability of the EMR sensor 1300A and hinder commercialization.
aenhanced low-field sensitivity can be obtained with an asymmetric
electrode arrangement. Referring to FIG. 14A, shown is a graphical
representation of an example of an enhanced EMR sensor 1400A with a
three-contact configuration, which combines the EMR effect and the
Hall effect. The Hall effect has a linear response to a magnetic
field change producing considerable sensitivity in the low-field
region. Due to this, the three-contact sensor 1400A exhibits
significantly enhanced low-field sensitivity.
[0087] In the example of FIG. 14A, a voltage lead 409 is coupled to
the conductive layer 402 opposite the semiconductor layer 404, a
first current lead 406 is coupled to a second side of the
semiconductor layer, and a second current lead 407 is coupled to
the second side of the semiconductor layer. Current flowing between
the first and second current leads 406 and 407 may be measured at
the first current lead 406 and/or the second current lead 407.
Voltage may be measured between voltage lead 409 and the first
current lead 406 or between voltage lead 409 and the second current
lead 407. The current lead used for voltage measurement may be
referred to as a common lead. In some implementations, another
voltage lead coupled to the second side of the semiconductor layer
between the center 410 of the sensor 1400 and the second current
lead 407. Voltage may be measured between voltage lead 409 and the
other voltage lead. The other voltage lead may be located for the
desired sensing taking into account the EMR effect and Hall
effect.
[0088] Referring next to FIG. 14B, shown is an optical microscope
image of a fabricated sensor 1400B. A semiconductor sample was
deposited by solid-source molecular beam epitaxy on a
semi-insulating GaAs substrate with the following structure:
Substrate/In.sub.xGa.sub.1-xAs metamorphic buffer (1 .mu.m)/InAs
stabilizing buffer (0.2 .mu.m)/Si-doped InAs active layer (1.5
.mu.m, n=10.sup.16 cm.sup.-3). The metamorphic buffer was inserted
between GaAs and InAs to accommodate the large lattice mismatch
between them. A moderate mobility .mu. of 0.816 m.sup.2/Vs and
carrier density n.sub.s of 5.6.times.10.sup.16 cm.sup.-3 at 300K
has been observed in an unpatterned sample with the standard van
der Pauw technique.
[0089] After growth, the semiconductor 404 was patterned into a
rectangular mesa by photolithography followed by wet etching in
citric acid solution exploiting the semi-insulating GaAs as an etch
stop. The metal shunt 402 and electrodes 406, 407, and 409 were
metallized with a Ti (10 nm)/Au (150 nm) stack by magnetron
sputtering. A low contact resistivity of about 10.sup.-7
.OMEGA.cm.sup.2 was realized after a rapid thermal annealing
process at 250.degree. C.
[0090] In the embodiment of FIG. 14B, the current electrodes (or
leads) 406 and 407 were symmetrically placed at the two ends of the
semiconductor bar (or layer) 404 with a separation of 50 .mu.m from
the central line. At the central line, the voltage electrode 409
was connected to the metal shunt (or conductive layer) 402 while
electrode 408 was connected to the semiconductor bar 404. The
output voltage signal was measured between electrodes (or leads)
409 and 407. Electrode 407 may also be referred to as a common lead
for both current and voltage measurement. In the example of FIG.
14B, electrode 407 was grounded. Electrode 408 was added to the
sensor only to measure a reference signal for the sake of
comparison. The distances between each electrode 406, 407, and 408
on the semiconductor bar and the edge of the metal shunt were 10
.mu.m.
[0091] The sensor 1400B was wire bonded to a printed circuit board
and measurements and characterizations were carried out using a
physical property measurement system. A homogenous external field B
ranging from -1 T to 1 T was applied in a perpendicular direction
to the sensor 1400B in steps of 0.01 T. The external magnetic field
was applied perpendicularly to the illustration plane of FIG. 14B.
A constant current of 100 .mu.A was applied to the device via
electrodes 406 and 407 throughout the measurements. Arrow 1403
illustrates the direction of current flow. The current transport in
the hybrid structure is governed by Ohm's Law j=.sigma.E, where E
is the electric field and .sigma. is the conductivity matrix, which
is expressed as
.sigma. = .sigma. 0 1 + .beta. 2 [ 1 - .beta. .beta. 1 ] , ( 6 )
##EQU00006##
where .beta.=.mu.H and .sigma..sub.0=.mu.ne is the Drude
conductivity without magnetic field, .mu. is the mobility of the
carriers, n is the carrier density, and e is the electric charge.
With a high mobility semiconductor sample, a strong EMR effect can
be expected. In steady state, the electrostatic potential
.phi.(x,y) is described by
.gradient.[.sigma..gradient..phi.(x,y)]=0. The output sensitivity
.delta. is defined as the rate of change of the output voltage
V=.phi.(i)-.phi.(j), where .phi.(i) and .phi.(j) are the potentials
at electrode i and j, respectively, (where i and j are 1, 2, 3 or 4
as indicated in FIG. 14B) with respect to the magnetic field. The
output voltage between electrodes 409 and 407 of the sensor 1400B
can be expressed as V.sub.3-2=V.sub.3-4+V.sub.4-2, where V.sub.3-4
is the Hall voltage of the hybrid structure and V.sub.4-2 is the
voltage arising from the asymmetric magnetoresistance R.sub.4-2.
The sensitivity of the sensor 1400B is calculated as
.delta..sub.3-2=.differential.V.sub.3-2/.differential.B=.delta..sub.3-4+.-
delta..sub.4-2. Thus, in addition to a component .delta..sub.4-2
resulting from the asymmetric EMR effect of common sensors, the
output sensitivity of this device is enhanced by a component
.delta..sub.3-4, which is caused by the Hall effect.
[0092] Referring now to FIG. 15, shown are the voltages V.sub.i-j
measured between different electrodes as a function of the magnetic
field B. The symmetric EMR voltage V.sub.1-2 of R.sub.1-2 was also
measured for comparison. In the magnetic field range of .+-.0.25 T,
the output of the symmetric EMR V.sub.1-2 is approximately
parabolic while the Hall voltage V.sub.3-4 has a linear behavior as
shown in FIG. 15(c). Asymmetric V vs. B curves were observed for
both asymmetric EMR voltages V.sub.4-2 and V.sub.3-2 as shown in
FIG. 15(a), which represents the output of the three-contact
geometry. The difference between them, V.sub.3-2-V.sub.4-2, is
equivalent to the Hall voltage V.sub.3-4 as shown in FIG. 15(b),
which was expected.
[0093] Moving to FIG. 16, shown are the sensitivities as a function
of the magnetic field. FIG. 16(a) illustrates sensitivity versus
magnetic field in a low-field region and FIG. 16(b) illustrates
sensitivity versus magnetic field in a high-field region with
different electrode configurations. Curve 1603 corresponds to
.delta..sub.3-4, curve 1606 corresponds to .delta..sub.4-2, curve
1609 corresponds to .delta..sub.3-2, and curve 1612 corresponds to
.delta..sub.2-1. The linear Hall response has a constant
sensitivity .delta..sub.3-4 of about 0.16 mV/T, while the outputs
of the EMR effect become more sensitive as the field gets stronger.
The asymmetric EMR sensitivity .delta..sub.1-2 is slightly
increased compared to the symmetric one .delta..sub.1-2 in the
range of 0 T-0.015 T. The highest sensitivity at zero field is
obtained between electrodes 409 and 407 with .delta..sub.3-2=0.19
mV/T, which is equivalent to the one of the symmetric EMR
.delta..sub.1-2 with a bias of 0.037 T and to the one of the
asymmetric EMR .delta..sub.4-2 at 0.061 T. At B=0.01 T, which is a
typical working range for low field applications like magnetic
beads detection, .delta..sub.3-2 is as high as 0.2 mV/T compared to
.delta..sub.1-2=0.067 mV/T and .delta..sub.1-2=0.048 mV/T. At the
very high field regime, the sensor is still extremely sensitive
though its performance is not quite as good as the one of a
symmetric EMR device.
[0094] Thus, enhanced EMR sensor 1400 with a three-contact
geometry, which combines the Hall effect and EMR effect, was
fabricated and characterized. The enhanced EMR sensor 1400 shows a
significant enhancement of the low-field output sensitivity. A
value of 0.2 mV/T at 0.01 T has been measured, which is 5 times
larger than that in a conventional symmetric EMR sensor 100. In
order to achieve a similar sensitivity, the conventional EMR sensor
100 needs an external bias field of at least 0.03 T. An even higher
sensitivity value can be expected in an enhanced EMR sensor 1400
made of a semiconductor epilayer with higher mobility and with an
optimized geometry that takes into account the EMR and Hall effect.
These results extend the applicability of the EMR sensor 1400 into
the low field region while maintaining an exceptional performance
in the high field region.
[0095] A magnetic field may be detected with an enhanced EMR sensor
1400 using, e.g., the method of FIG. 7. In some embodiments, an
enhanced EMR sensor 1400 is provided in 702. The voltage between
the voltage lead 409 and one of the leads 406, 407, or 408
connected to the semiconductor layer 404 may be measured in 704.
The current flowing between leads 406 and 407 may be measured in
706. A resistance may then be calculated in 708 based upon the
measured voltage and the measured current. For example, the
resistance of the EMR effect sensor may be calculated using
equation (2). Moreover, the EMR effect may be measured by
calculating the change in resistance in the presence of a magnetic
field using equation (1). Changes of the calculated resistance may
indicate a change in the magnetic field.
[0096] In some implementations, the enhanced EMR sensor 1400 can be
extended into the nano-scale regime to obtain a high spatial
resolution, which is of interest for applications like reading
heads. It should be noted that, as the device size is reduced to a
value smaller than the mean free path, ballistic transport
phenomena may become more relevant having an impact on the device
performance. The EMR effect still persists in such a case. However,
the EMR ratio is expected to be smaller than in case of the
diffusive transport regime.
[0097] Various features and advantageous details are explained more
fully with reference to the nonlimiting embodiments that are
illustrated in the accompanying drawings and detailed in the
following description. Descriptions of well known starting
materials, processing techniques, components, and equipment are
omitted so as not to unnecessarily obscure the invention in detail.
It should be understood, however, that the detailed description and
the specific examples, while indicating embodiments of the
invention, are given by way of illustration only, and not by way of
limitation. Various substitutions, modifications, additions, and/or
rearrangements within the spirit and/or scope of the underlying
inventive concept will become apparent to those skilled in the art
from this disclosure.
[0098] The apparatus disclosed and claimed herein can be made and
executed without undue experimentation in light of the present
disclosure. While the apparatus of this invention have been
described in terms of preferred embodiments, it will be apparent to
those of skill in the art that variations may be applied to the
methods and in the steps or in the sequence of steps of the method
described herein without departing from the concept, spirit and
scope of the invention. In addition, modifications may be made to
the disclosed apparatus and components may be eliminated or
substituted for the components described herein where the same or
similar results would be achieved. All such similar substitutes and
modifications apparent to those skilled in the art are deemed to be
within the spirit, scope, and concept of the invention as defined
by the appended claims.
* * * * *