U.S. patent application number 10/790040 was filed with the patent office on 2004-09-09 for magnetic sensor and method for fabricating the same.
This patent application is currently assigned to DENSO CORPORATION. Invention is credited to Ao, Kenichi.
Application Number | 20040174164 10/790040 |
Document ID | / |
Family ID | 32866662 |
Filed Date | 2004-09-09 |
United States Patent
Application |
20040174164 |
Kind Code |
A1 |
Ao, Kenichi |
September 9, 2004 |
Magnetic sensor and method for fabricating the same
Abstract
The magnetic sensor is fabricated such that a magnetic sensor
chip, having a one-chip structure in which MRE bridges and a
comparator are included, is mounted onto a lead frame using an
adhesive material, and then the magnetic sensor chip mounted on the
lead frame is encapsulated by molding in a molded material. The
magnetic sensor includes a magnetic-field generating portion formed
by magnetizing at least one of the chip mounting member, the
adhesive material, and the encapsulating material.
Inventors: |
Ao, Kenichi; (Tokai-city,
JP) |
Correspondence
Address: |
POSZ & BETHARDS, PLC
11250 ROGER BACON DRIVE
SUITE 10
RESTON
VA
20190
US
|
Assignee: |
DENSO CORPORATION
|
Family ID: |
32866662 |
Appl. No.: |
10/790040 |
Filed: |
March 2, 2004 |
Current U.S.
Class: |
324/252 ;
29/592.1; 324/262; 335/284 |
Current CPC
Class: |
H01L 2224/73265
20130101; H01L 2924/181 20130101; G01D 11/245 20130101; G01D 5/145
20130101; H01L 24/73 20130101; H01L 2924/1305 20130101; H01L
2924/13091 20130101; H01L 2224/48091 20130101; H01L 2224/48247
20130101; H01L 2224/32245 20130101; Y10T 29/49002 20150115; H01L
2224/48091 20130101; H01L 2924/00014 20130101; H01L 2924/13091
20130101; H01L 2924/00 20130101; H01L 2224/73265 20130101; H01L
2224/32245 20130101; H01L 2224/48247 20130101; H01L 2924/00012
20130101; H01L 2924/181 20130101; H01L 2924/00012 20130101; H01L
2924/1305 20130101; H01L 2924/00 20130101 |
Class at
Publication: |
324/252 ;
324/262; 029/592.1; 335/284 |
International
Class: |
G01R 033/09; G01R
033/06; G01B 007/30 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 3, 2003 |
JP |
2003-55823 |
Claims
What is claimed is:
1. A magnetic sensor comprising: a magnetic sensor chip; a chip
mounting member on which the magnetic sensor chip is mounted; an
adhesive material for bonding the magnetic sensor chip to the chip
mounting member; an encapsulating material for encapsulating the
magnetic sensor chip; and a magnetic-field generating portion
formed by magnetizing at least one of the chip mounting member, the
adhesive material, and the encapsulating material.
2. The magnetic sensor according to claim 1, wherein the
encapsulating material is magnetized at a portion opposite to the
position at which the magnetic sensor chip is mounted.
3. The magnetic sensor according to claim 1, wherein the
encapsulating material is magnetized at a portion that is located
on a side of the magnetic sensor chip.
4. The magnetic sensor according to claim 1, wherein the chip
mounting member is magnetized at a portion on which the magnetic
sensor chip is mounted.
5. The magnetic sensor according to claim 1, wherein the adhesive
material is formed on a surface on which the magnetic sensor chip
is mounted, and is entirely magnetized.
6. A magnetic sensor comprising: a magnetic sensor chip; a chip
mounting member, for mounting the magnetic sensor chip thereon,
with a magnetized portion on which the magnetic sensor chip is
mounted; a magnetized adhesive material for boding the magnetic
sensor chip to the chip mounting member; and an encapsulating
material for encapsulating the magnetic sensor chip therein, the
encapsulating material having a magnetized portion on a surface
opposite to the mounting surface of the magnetic sensor chip on the
chip mounting member, the magnetized portion of the encapsulating
material corresponding to the magnetized portion of the chip
mounting member.
7. A method for fabricating a magnetic sensor comprising: mounting
a magnetic sensor chip on a chip mounting member by using an
adhesive material for bonding; encapsulating the chip mounting
member and the magnetic sensor chip mounted thereon by using an
encapsulating material; and forming a magnetic-field generating
portion by magnetizing at least one of the chip mounting member,
the adhesive material, and the encapsulating material.
8. The method for fabricating a magnetic sensor according to claim
7, wherein the encapsulating material is magnetized at a portion
opposite to the position at which the magnetic sensor chip is
mounted.
9. The method for fabricating a magnetic sensor according to claim
7, wherein the encapsulating material is magnetized at a portion
that is located on a side of the magnetic sensor chip.
10. The method for fabricating a magnetic sensor according to claim
9, wherein the chip mounting member has a predetermined portion
reduced in shape relative to its peripheral portion to make the
predetermined portion highly resistive, the method further
comprising: allowing a large current to flow through the chip
mounting member while externally applying a magnetic field to the
encapsulated magnetic sensor chip, thereby generating heat at the
portion reduced in shape of the chip mounting member to magnetize
the vicinity of the portion reduced in shape.
11. The method for fabricating a magnetic sensor according to claim
7, wherein the chip mounting member is magnetized at a portion on
which the magnetic sensor chip is mounted.
12. The method for fabricating a magnetic sensor according to claim
7, wherein the adhesive material is formed on a surface on which
the magnetic sensor chip is mounted, and is entirely
magnetized.
13. A method for fabricating a magnetic sensor comprising:
magnetizing a portion of a chip mounting member on which a magnetic
sensor chip is mounted; magnetizing an adhesive material for
bonding the magnetic sensor chip to the chip mounting member;
mounting the magnetic sensor chip on the chip mounting member by
using the adhesive material; encapsulating the chip mounting member
and the magnetic sensor chip mounted thereon by using an
encapsulating material; and magnetizing a portion of the
encapsulating material on a surface opposite to the mounting
surface of the magnetic sensor chip on the chip mounting member,
the portion of the encapsulating material corresponding to the
magnetized portion of the chip mounting member.
14. The method for fabricating a magnetic sensor according to claim
13, wherein the magnetized portion is demagnetized once and
magnetized again.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is based upon, claims the benefit of
priority of, and incorporates by reference Japanese Patent
Application No. 2003-55823 filed Mar. 3, 2003.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a magnetic sensor, and more
particularly, to a magnetic sensor that is employed as a rotation
sensor for providing control to an automobile engine or ABS control
in an automobile brake system.
[0004] 2. Description of the Related Art
[0005] FIG. 1A is across-sectional view of the configuration of a
magnetic sensor disclosed in Japanese Patent Laid-Open Publication
No. Hei 9-79865 (1997), while FIG. 10B is a cross-sectional view of
a modified example of FIG. 10A. As shown in FIG. 10A, a magnetic
sensor 50 is fabricated in a manner such that a magnetic sensor
chip 51 having a magneto-resistance element (MRE) and mounted on a
lead frame 52 is packaged by molding in a molded material 53 of an
epoxy-based thermosetting resin. Additionally, using an adhesive
material 54, a bias magnet 55 is fixedly bonded into a recessed
portion on a surface of the molded package as opposed to the
magnetic sensor chip 51 mounted on the lead frame 52. A modified
example shown in FIG. 10B is adapted to include the bias magnet 55
fixed onto the lead frame 52 in the molded package.
[0006] However, the conventional technique shown in FIG. 10A
provides the bias magnet 55 outside the molded package, raising a
problem that the magnetic sensor 50 is increased in size by the
dimensions of the bias magnet 55. Furthermore, the detection
accuracy of the magnetic sensor 50 depends on the positional
relationship between the bias magnet 55 and the magnetic sensor
chip 51. In aligning and bonding the bias magnet 55 using the
adhesive material 54, the bias magnet 55 may be dislocated while
the adhesive material 54 is being hardened, thereby raising another
problem of providing reduced detection accuracy.
[0007] On the other hand, the bias magnet 55 may also be provided
in the molded package as shown in the modified example illustrated
in FIG. 10B. In this case, the magnetic sensor 50 can be reduced in
size; however, the bias magnet 55 needs to be aligned with and then
fixed to the lead frame 52. This raised still another problem of
complicating the fabrication process as well as increasing the
number of components required.
SUMMARY OF THE INVENTION
[0008] The present invention was developed in view of the
aforementioned problems. It is therefore an object of the present
invention to provide a magnetic sensor that is reduced in size as
well as in dislocation to thereby provide improved detection
accuracy, and that can be fabricated with less number of man-hours
and components.
[0009] According to a first aspect of the present invention, a
magnetic sensor includes a magnetic sensor chip, a chip mounting
member on which the magnetic sensor chip is mounted, an adhesive
material for bonding the magnetic sensor chip to the chip mounting
member, an encapsulating material for encapsulating the magnetic
sensor chip, and a magnetic-field generating portion formed by
magnetizing at least one of the chip mounting member, the adhesive
material, and the encapsulating material.
[0010] This feature enables the magnetic-field generating portion,
which is otherwise provided outside the molded package, to be
formed inside the molded package, thereby reducing the sensor in
size by the dimensions of the magnetic-field generating portion.
Furthermore, although the conventional technique uses the adhesive
material to bond the magnetic-field generating portion to the
molded material, the invention forms the magnetic-field generating
portion by directly magnetizing at least one of the chip mounting
member, the adhesive material, and the encapsulating material. This
allows for eliminating dislocations while the adhesive material is
being hardened, thereby providing improved detection accuracy.
Furthermore, since any one of the chip mounting member, the
adhesive material, and the encapsulating material can constitute
the bias magnet, the number of components can be reduced when
compared with the case of employing a separately prepared bias
magnet.
[0011] A magnetic sensor according to a second aspect of the
present invention allows the encapsulating material to be
magnetized at a portion opposite to the position at which the
magnetic sensor chip is mounted. According to this feature, the
magnetic-field generating portion is formed near the magnetic
sensor chip, thereby allowing the magnetic force required of the
magnet to be reduced.
[0012] A magnetic sensor according to a third aspect of the present
invention allows the encapsulating material to be magnetized at a
portion that is located on the mounting side of the magnetic sensor
chip and on a side of the magnetic sensor chip. According to this
feature, the magnetic-field generating portion can be provided
closer to the magnetic sensor chip, thereby allowing the magnetic
force required of the magnet to be further reduced.
[0013] A magnetic sensor according to a fourth aspect of the
present invention allows the chip mounting member to be magnetized
at a portion on which the magnetic sensor chip is mounted.
According to this feature, since the chip mounting member is
employed as the magnetic-field generating portion, the
conventionally employed lead frame can also be used to form the
magnetic-field generating portion, thereby facilitating
fabrication.
[0014] A magnetic sensor according to a fifth aspect of the present
invention allows the adhesive material to be formed on a surface on
which the magnetic sensor chip is mounted as well as to be entirely
magnetized. According to this feature, the magnetic-field
generating portion can be provided closer to the magnetic sensor
chip, thereby allowing the magnetic force required of the magnet to
be reduced.
[0015] A magnetic sensor according to a sixth aspect of the present
invention includes a magnetic sensor chip; a chip mounting member,
for mounting the magnetic sensor chip thereon, with a magnetized
portion on which the magnetic sensor chip is mounted; a magnetized
adhesive material for boding the magnetic sensor chip to the chip
mounting member; and an encapsulating material for encapsulating
the magnetic sensor chip therein, the encapsulating material having
a magnetized portion on a surface opposite to the mounting surface
of the magnetic sensor chip on the chip mounting member, the
magnetized portion of the encapsulating material corresponding to
the magnetized portion of the chip mounting member. According to
this feature, since the member formed on the reverse side of the
magnetic sensor chip mounted portion serves as the magnetic-field
generating portion, the magnetic-field generating portion is
increased in volume, thereby allowing the bias magnet to create an
increased magnetic force.
[0016] A method for fabricating the magnetic sensor according to
any one of the first to sixth aspects corresponds to one of the
seventh to thirteenth aspects of the present invention except for
the tenth aspect below. The method can provide the same operation
and effects as those described above with reference to the first to
sixth aspects, which will not be explained again.
[0017] In a method for fabricating a magnetic sensor according to
the tenth aspect of the invention, the magnetic sensor is provided
with a chip mounting member having a predetermined portion reduced
in shape relative to its peripheral portion to make the
predetermined portion highly resistive. The method further entails
the step of allowing a large current to flow through the chip
mounting member while externally applying a magnetic field to the
encapsulated magnetic sensor chip, thereby generating heat at the
portion reduced in shape of the chip mounting member to magnetize
the vicinity of the portion reduced in shape. According to this
feature, a desired position inside the encapsulating material can
be magnetized.
[0018] In a method for fabricating a magnetic sensor according to a
fourteenth aspect of the invention, the magnetized portion is
demagnetized once and magnetized again. According to this feature,
even when a dislocation is found after the desired portion is
aligned and magnetized, the demagnetization allows
re-alignment.
[0019] Further areas of applicability of the present invention will
become apparent from the detailed description provided hereinafter.
It should be understood that the detailed description and specific
examples, while indicating the preferred embodiment of the
invention, are intended for purposes of illustration only and are
not intended to limit the scope of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] The present invention will become more fully understood from
the detailed description and the accompanying drawings,
wherein:
[0021] FIG. 1 is a cross-sectional view of the arrangement of a
magnetic sensor and a magnetic rotor according to a first
embodiment of the present invention;
[0022] FIG. 2A is a plan view of a magnetic sensor chip according
to an embodiment of the present invention;
[0023] FIG. 2B is a circuit diagram of the arrangement of MRE
bridges according to the first embodiment of the present
invention;
[0024] FIG. 3A is a characteristic diagram of the characteristics
of the MRE bridges placed in proper alignment with a bias magnet
according to an embodiment of the present invention;
[0025] FIG. 3B is a characteristic diagram of the characteristics
of the MRE bridges placed in improper alignment with the bias
magnet;
[0026] FIG. 4A is a cross-sectional view of a one-chip structure of
an MRE formation region and a processing-circuit formation region
made up of a MOSFET or the like, in the magnetic sensor chip
according to an embodiment of the present invention;
[0027] FIG. 4B is a cross-sectional view of a one-chip structure of
the MRE formation region and a processing-circuit formation region
made up of a bipolar transistor or the like, in the magnetic sensor
chip;
[0028] FIG. 5 is a diagram of the characteristics of the relation
between the magnetic force and the variation in resistance of an
MRE bias magnet;
[0029] FIG. 6 is a cross-sectional view of the structure of a
magnetic sensor according to a second embodiment of the present
invention;
[0030] FIG. 7 is a cross-sectional view of the structure of a
magnetic sensor according to a third embodiment of the present
invention;
[0031] FIG. 8 is a cross-sectional view of the structure of a
magnetic sensor according to a fourth embodiment of the present
invention;
[0032] FIG. 9 is a cross-sectional view of the structure of a
magnetic sensor according to a fifth embodiment of the present
invention;
[0033] FIG. 10A is a cross-sectional view of the structure of a
magnetic sensor according to the prior art; and
[0034] FIG. 10B is a cross-sectional view of a modified example of
FIG. 10A of the prior art.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0035] The following description of the preferred embodiments is
merely exemplary in nature and is in no way intended to limit the
invention, its application, or uses.
First Embodiment
[0036] Now, the present invention will be described with reference
to the accompanying drawings in accordance with a magnetic sensor
according to a first embodiment. FIG. 1 is a cross-sectional view
of a magnetic sensor and a magnetic rotor (an object to be
detected) according to the first embodiment of the present
invention. FIG. 2A is a plan view of the magnetic sensor chip
according to the first embodiment of the present invention, while
FIG. 2B is a circuit diagram of the circuit configuration of a
magnetoresistive pattern according to the first embodiment of the
present invention.
[0037] This embodiment provides a magnetic sensor 1 which can be
employed as a rotation detector, for detecting the rotation of a
rotating object (including gears) to be sensed, such as an engine
rotation sensor, a cam angle sensor, a crank angle sensor, an
automobile speed sensor, an AT sensor, and a wheel speed sensor.
Referring to FIG. 1, on the right hand side of a gear-shaped (its
teeth not shown) magnetic rotor (an object to be detected) 8, the
magnetic sensor 1 is disposed opposite to the magnetic rotor 8 at a
certain distance therefrom. The magnetic rotor 8 is coupled to a
spinning body (not shown) via a rotary shaft 7. The magnetic sensor
1 includes a magnetic sensor chip 2, a lead frame 3, and a molded
material 5. A portion of the molded material 5 is magnetized to
serve as a bias magnet 6 for producing a bias magnetic field.
[0038] As shown in FIG. 2A, the magnetic sensor chip 2 has a
one-chip structure that includes a substrate 9 on which MRE bridges
10, 11 and a processing circuit 17 are formed. The MRE bridges 10,
11 include MREs 12-15, while the processing circuit 17 includes a
differential amplifier 18, a comparator 19 and the like, which are
known in the art. The centerline 2a of the magnetic sensor chip 2
lies on the magnetic center 2b of a magnetic field produced by the
bias magnet 6. The MRE bridges 10, 11 are disposed symmetrically
about the chip centerline 2a. Furthermore, each of the MRE bridges
10, 11 has a comb-shaped structure that is formed by sequentially
folding back a conductor trace to alternately define a plurality of
longer and shorter sides for connection.
[0039] The MREs 12 to 15 are constructed such that the MREs 12, 13
are connected in series, the MREs 14, 15 being also connected in
series, and the MREs 12, 14 on the power supply side and the MREs
13, 15 on the ground side are disposed symmetrically about the
centerline 2a of the magnetic sensor chip 2. The MREs 12, 13 and
MREs 14, 15, each having a serial connection, are arranged such
that their detection axes form an angle of 45 and -45 degrees to
the magnetic center 2b of the magnetic field produced by the bias
magnet 6, respectively, i.e., the detection axes form an angle of
90 degrees to each other as in the shape of a Japanese character
"HA()". This allows a vectorial variation in bias magnetic field to
result in increased variations in potential at the two middle
points between the serially connected MREs 12 and 13 and between
the serially connected MREs 14 and 15.
[0040] As shown in FIG. 2B, the first and second MRE bridges 10, 11
form a bridge circuit 16 in which the first MRE bridge 10 allows
current to flow from the MRE 12 toward the MRE 13, while the second
MRE bridge 11 allows current to flow from the MRE 14 toward the MRE
15. The bridge circuit 16 employs a midpoint potential Va between
the MREs 12 and 13 as the output from the MRE bridge 10, while
employing a midpoint potential Vb between the MREs 14 and 15 as the
output from the MRE bridge 11.
[0041] The magnetic sensor 1 constructed as described above
operates as follows. First, the magnetic rotor 8 rotating in a
given direction causes its peripheral crests (protruded portions)
and valleys (recessed portions) to alternately approach the bias
magnet 6. This causes a bias magnetic field produced by the bias
magnet 6 to be attracted by the protruded portion and thereby
varied. At this time, the magnetic vector passing through the MREs
12 to 15 is deflected in the direction of rotation of the magnetic
rotor 8, thereby causing variations in resistance of the MREs 12 to
15 due to the change in the direction of the magnetic vector. This
leads to variations in outputs Va, Vb from the two pairs of the MRE
bridges 10 and 11.
[0042] These outputs Va, Vb are supplied to the differential
amplifier 18 incorporated into the processing circuit 17. The
differential amplifier 18 differentially amplifies the midpoint
potentials Va, Vb from the two MRE bridges 10, 11 for output. A
signal amplified by the differential amplifier 18 and then supplied
to the comparator 19 is binary coded through a magnitude comparison
with a predetermined threshold voltage. This makes it possible to
employ the output from the processing circuit 17 as the output from
the magnetic sensor 1, thereby detecting the rotational state of
the magnetic rotor 8.
[0043] The binary coding of sensor outputs carried out in the
differential amplifier 18 or the like to provide binary output
raises a problem of the amount of shift in the rising and falling
edges of the binary output, the amount of shift in the edges having
an effect on the detection accuracy of sensors. One of the factors
having an effect on the shift in the edges is the positional
relation between the MRE bridges 10, 11 and the bias magnet 6. FIG.
3A is a characteristic diagram of the MRE bridges 10, 11 placed in
proper alignment with the bias magnet 6. FIG. 3B is a
characteristic diagram of the MRE bridges 10, 11 placed in improper
alignment with the bias magnet 6.
[0044] As shown in FIGS. 3A and 3B, the sensor output varies due to
a dislocation of the bias magnet 6 relative to the MRE bridges 10,
11 when a sinusoidal sensor output signal (amplified signal) is
translated into a binary coded signal using the predetermined
threshold value. This variation in the sensor output may cause an
actual threshold value to deviate from the true threshold value,
e.g., by a predetermined potential difference .DELTA.V (mV) (an
erroneous threshold value). This deviation in the threshold value
causes a shift in the position of the rising and falling edges when
compared with the case of binary coding using the true threshold
value.
[0045] As shown in FIG. 3A, with the MRE bridges 10, 11 kept in
proper alignment with the bias magnet 6, the sensor output has a
large magnitude for the deflection of the magnetic vector with the
output signal having a steep gradient. Accordingly, a binary coded
signal (pulsed signal) is reduced in the amount of shift at its
edge position, thereby providing a desired level of detection
sensitivity. However, as shown in FIG. 3B, with the MRE bridges 10,
11 placed in improper alignment with the bias magnet 6, the sensor
output has a small magnitude for the deflection of the magnetic
vector with the output signal having a slanted gradient. This
causes an increase in the amount of edge shift and a drop in the
level of detection sensitivity, even when the amount of threshold
shift .DELTA.V is the same as that of the case of FIG. 3A.
[0046] Now, a method for fabricating the magnetic sensor 1 will be
explained below. FIGS. 4A and 4B are cross-sectional views of the
magnetic sensor chip 2 having a one-chip structure. First, as shown
in FIG. 4A, such a case is described in which an MRE formation
region 20 and a processing-circuit formation region 21 including a
MOSFET and the like are formed in a one-chip structure. In the
magnetic sensor chip 2, the substrate 9 is made of silicon. The MRE
formation region 20 in the magnetic sensor chip 2 has a LOCOS oxide
film 22 deposited on the N-type silicon substrate 9, with a
ferromagnetic thin film 23, formed such as of a Ni-Co alloy or
Ni-Fe alloy, deposited as an MRE on the LOCOS oxide film 22 by the
known vacuum deposition. On the ferromagnetic thin film 23, there
is formed a silicon oxide film 24. The ferromagnetic thin film 23
is connected to aluminum conductor trace materials 26a, 26b through
contact holes 25a, 25b.
[0047] The processing-circuit formation region 21 has a P-well
region 27 formed at a surface layer portion of the N-type silicon
substrate 9. On top of the P-well region 27, not the LOCOS oxide
film 22 but a thin gate silicon oxide film 29 is formed. On the
gate silicon oxide film 29, there is formed a polysilicon gate
electrode 32. On a surface layer portion of the P-well region 27 at
both the sides of the polysilicon gate electrode 32, there are
formed an N-type source region 30 and an N-type drain region 31,
which are connected to aluminum conductor trace materials 34, 35
through contact holes 33a, 33b. In this manner, an N-channel MOS
transistor Tr is formed, which in conjunction with a resistor (not
shown) or the like, forms an operational amplifier (the amplifier
18). It is also possible to form a gain-determining feedback
resistor, a gain-determining input resistor or the like in the MOS
process.
[0048] Now, as shown in FIG. 4B, such a case is described in which
the MRE formation region 20 and the processing-circuit formation
region 21 including a bipolar transistor or the like is formed in a
one-chip structure. For the processing-circuit formation region 21,
there are formed an N+ embedded layer 40 and an N- epitaxial layer
41 on the principal surface of the silicon substrate 9. On the
principal surface of the N- epitaxial layer 41, a silicon oxide
film 42 is deposited using CVD equipment. Then, the silicon oxide
film 42 is photo-etched using a desired circuit pattern and then
doped to form a P+ device isolation region 43, a P+ diffusion
region 44, and N+ diffusion regions 45, 46. In this manner, an NPN
bipolar transistor is made up of the N+ embedded layer 40, the N-
epitaxial layer 41, the P+ diffusion region 44, and the N+
diffusion regions 45, 46.
[0049] Then, in the MRE formation region 20, a contact portion is
formed on the silicon oxide film 42. A thin-film aluminum conductor
trace material 47 is evaporated onto the principal surface of the
P-type semiconductor substrate 9 and then photo-etched for
patterning. Additionally, on the silicon oxide film 42 including
the aluminum conductor trace material 47, a ferromagnetic thin film
48, formed such as of a Ni-Co alloy or Ni-Fe alloy, is deposited as
an MRE by the known vacuum deposition. The NPN transistor formed on
the principal surface of the P-type semiconductor substrate 9 and
circuit components (not shown) such as a PNP transistor, a
diffusion resistor, and a capacitor are electrically connected
using the aluminum conductor trace material 47 to serve as an
electric circuit.
[0050] The magnetic sensor chip 2 formed in this manner is placed
at a desired position on the lead frame 3 to be mounted thereon
with an adhesive material 4, and then electrically connected to the
lead frame 3 with a lead wire L. The lead frame 3 having the
magnetic sensor chip 2 mounted thereon is then put in place within
a mold having a predetermined shape to be encapsulated by molding
in the molded material 5. Thereafter, a predetermined portion of
the molded material 5 is magnetized to thereby form the bias magnet
6. At this time, a heat-resistant resin such as PPS (polyphenylene
sulfide) mixed with magnetic powder such as ferrite is employed as
the molded material 5.
[0051] Now, the bias magnet 6 will be explained in more detail. The
molded material 5 is magnetized using a large current with the
magnetic sensor 1 placed in a predetermined gap of a magnetized
yoke formed in the shape of a toroidal core in order to
instantaneously establish a magnetic field greater than or equal to
1.times.106 (A/m) in the gap. On the other hand, as described
above, the positional relation between the bias magnet 6 and the
MRE bridges 10, 11 is one of the factors having an effect on the
detection accuracy of the sensor. Accordingly, it is necessary to
magnetize the bias magnet 6 in optimal alignment with the MRE
bridges 10, 11.
[0052] The optimal alignment can be achieved as follows. The
magnetic characteristics of the MREs 12 to 15 constituting the MRE
bridges 10, 11 exhibit the maximum resistance when a magnetic field
is applied in the direction of the longer sides of the comb-shaped
MRE pattern, and the minimum resistance when a magnetic field is
applied in the direction of the shorter sides. This means that with
the magnetic field being rotated, a large change in MRE resistance
is obtained most efficiency at an angle of 45 degrees between the
direction of the bias magnetic field and the MRE pattern.
Therefore, the bias magnet 6 is positioned so that the bias
magnetic field is inclined for biasing at an angle of 45 degrees to
the MREs 12 to 15. Incidentally, the detection device is not
limited to the MRE, but a barber pole may also be employed.
[0053] Furthermore, concerning the magnetic field strength of the
bias magnet 6, FIG. 5 shows a characteristic diagram of the
relation between the magnetic field strength and the variation in
resistance of the MRE bias magnet. As shown in FIG. 5, the MRE has
an output resistance exhibiting a hysteresis property. Accordingly,
to use it as the magnetic sensor, a magnetic field strength in the
region in which the output resistance is saturated (about 100 Gauss
or more) in consideration of reproducibility. On the other hand,
the magnetic field strength is greater with longer distances
between the S and N poles, and with greater permeance of the
magnet.
[0054] As described above, this embodiment allows the
magnetic-field generating portion, which is conventionally provided
outside the mold package, to be formed within the mold package,
thereby reducing the size of the sensor by the dimensions of the
magnetic-field generating portion. Furthermore, although the
magnetic-field generating portion is bonded to the molded material
with an adhesive material in the prior art, this embodiment allows
the magnetic-field generating portion to be formed by directly
magnetizing at least one of the chip mounting member, the adhesive
material, and encapsulating material. This eliminates dislocations
that would otherwise occur when the adhesive material is hardened,
thereby making it possible to provide improved detection accuracy.
Furthermore, since the bias magnet is made up of any one of the
chip mounting member, the adhesive material, and the encapsulating
material, it is possible to reduce the number of components when
compared with the case of employing a separately prepared bias
magnet.
Second Embodiment
[0055] Now, the present invention will be explained with reference
to FIG. 6 in accordance with a second embodiment. The portions of
the second embodiment common to those of the first embodiment are
not to be explained in detail. This embodiment is different from
the first embodiment in that the bias magnet 6 is formed at a
portion on a side of the magnetic sensor chip 2.
[0056] A method according to this embodiment makes use of the
property that a magnetic material is less magnetized when its Curie
temperature is reached, thereby being readily affected externally.
To reach the Curie temperature, the lead frame 3 is provided with a
heat-generating portion, which is part of the lead frame 3 reduced
in shape to have an increased resistance and generates heat by a
large current flowing therethrough. This heat-generating portion is
formed, within the lead frame 3, near the optimal position at which
the aforementioned bias magnet 6 is desirably formed.
[0057] First, as in the first embodiment, the magnetic sensor chip
2 is placed at a desired position on the lead frame 3 to be mounted
thereon with the adhesive material 4, and then electrically
connected to the lead frame 3 with the lead wire L. The magnetic
sensor chip 2 mounted on the lead frame 3 is then encapsulated by
molding in the molded material 5 of a heat-resistant resin such as
PPS (polyphenylene sulfide) mixed with magnetic powder such as
ferrite. Thereafter, a large current is allowed to instantaneously
flow through the lead frame 3 while a magnetic field is being
applied to the magnetic sensor 1 that has been encapsulated by
molding. This causes the heat-generating portion of the lead frame
3 to generate heat and the temperature of the molded material 5
present near the heat-generating portion to increase. This further
causes the molded material 5 present near the heat-generating
portion to be magnetized, thereby forming the bias magnet 6.
[0058] As described above, this embodiment allows the bias magnet 6
to be formed near the magnetic sensor chip 2, thereby allowing the
magnetic force required of the magnet to be reduced. Furthermore,
the lead frame 3 having the heat-generating portion according to
this embodiment allows for forming the bias magnet 6 at a desired
position inside the molded material.
Third Embodiment
[0059] Now, the present invention is explained with reference to
FIG. 7 in accordance with a third embodiment. The portions of the
third embodiment common to those of the aforementioned embodiments
will not be explained in detail. This embodiment is different from
the aforementioned embodiments in that the bias magnet 6 is formed
in the lead frame 3.
[0060] A method according to this embodiment includes the step of
using a magnetized yoke to magnetize the optimal position desired
to form the aforementioned bias magnet 6 in the lead frame 3 made
of known copper or 42 Ni-Fe or the like, thereby forming the bias
magnet 6. In this manner, the lead frame 3 is employed as the bias
magnet 6. Thus, a conventionally available lead frame 3 can be used
to form the bias magnet 6 without mixing magnetic powder into the
molded material 5, thereby facilitating manufacture.
Fourth Embodiment
[0061] Now, the present invention will be explained with reference
to FIG. 8 in accordance with a fourth embodiment. The portions of
the fourth embodiment common to those of the aforementioned
embodiments will not be explained in detail. This embodiment is
different from the aforementioned embodiments in that the bias
magnet 6 is formed in the adhesive material 4. A method according
to this embodiment includes the steps of mixing magnetic powder
such as ferrite into a known epoxy-based, silicone-based, or
polyimide-based adhesive material, and using a magnetized yoke to
magnetize the optimal position desired to form the aforementioned
bias magnet 6 in the adhesive material 4, thereby forming the bias
magnet 6. In this manner, the adhesive material 4 is employed as
the bias magnet 6. This allows for forming the bias magnet 6 close
to the magnetic sensor chip 2, thereby making it possible to reduce
the magnetic force required of the magnet.
Fifth Embodiment
[0062] Now, the present invention is explained with reference to
FIG. 9 in accordance with a fifth embodiment. The portions of the
fifth embodiment common to those of the aforementioned embodiments
are not to be explained in detail. This embodiment is different
from the aforementioned embodiments in that the bias magnet 6 is
formed in all of the adhesive material 4, the lead frame 3, and the
molded material 5.
[0063] A method according to this embodiment is implemented as
follows. First, the adhesive material 4 prepared as described in
the fourth embodiment is applied onto the lead frame 3 that is
formed as described in the third embodiment, and then the magnetic
sensor chip 2 is mounted thereon using the adhesive material 4.
Then, the magnetic sensor chip 2 mounted on the lead frame 3 is
encapsulated by molding in the molded material 5 as described in
the first embodiment. Additionally, as described in the first
embodiment, the magnetized yoke is used to magnetize the desired
portion, thereby forming the bias magnet.
[0064] In this manner, the predetermined portion in the adhesive
material 4, the lead frame 3, and the molded material 5, which are
present on the reverse side of the magnetic sensor chip 2, serves
as the bias magnet 6. This makes it possible to increase the volume
of the bias magnet 6, thereby allowing the bias magnet 6 to provide
an increased magnetic field.
[0065] The present invention is not limited to magnetizing all of
the lead frame 3, the adhesive material 4, and the molded material
5, as described above. Some of these components can also be
combined to be magnetized, e.g., such that the lead frame 3 and the
adhesive material 4, or the adhesive material 4 and the molded
material 5 are magnetized. As a modified example, the bias magnet 6
that has been once magnetized as described above can be
demagnetized. This demagnetization allows the bias magnet 6 to be
re-positioned even when dislocated after having been aligned for
the magnetization.
[0066] The description of the invention is merely exemplary in
nature and, thus, variations that do not depart from the gist of
the invention are intended to be within the scope of the invention.
Such variations are not to be regarded as a departure from the
spirit and scope of the invention.
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