Note: Descriptions are shown in the official language in which they were submitted.
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MAGNETIC DEVICE, AND PROCESS AND
APPARATUS FOR PRODUCING THE SAME
FIELD OF THE INVENTION
This invention relates to a magnetic device which
utilizes an abrupt change in magnetization that occurs in
response to a change in an externally applied magnetic field.
The invention also relates to a process and an apparatus for
producing the magnetic device.
BAC~GROUND OF THE INVENTION
The magnetization behavior of magnetic materials has
been extensively utilized in various devices. Magnetic
materials that are recently drawing the attention of
researchers include those which, when the strength of a
magnetic field exceeds a certain critical value, exhibit a
sudden magnetic flux reversal as a discontinuous response.
If a pickup coil is placed in the neighborhood of such a
magnetic material, a sharp voltage pulse is induced by the
discontinuous magnetic flux reversal in the magnetic
material. The resulting signal finds wide use in various
magnetic devices for measuring magnetic fields (e.g., the
earth's field), rotational speeds and flow rates.
Electronic article surveillance systems for
preventing the theft of merchandise and article
identification systems for enabling rapid delivery have
recently gained in popularity. In addition to oscillation
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circuits, LC resonant circuits, magnetostrictive resonance
materials and high permeability materials, magnetic materials
which exhibit the above-described discontinuous magnetic flux
reversal are used as identification markers. For example,
Examined Japanese Patent Publication No. Hei-3-27958
(corresponding to U.S. Patents 4,660,025, 4,686,516 and
4,797,658) teaches a marker in the form of a filament of an
Fe-based amorphous metal and a system using the marker.
The magnetization of the metal filament in a
longitudinal direction is sufficiently stable so as not to
readily undergo magnetic flux reversal, but the moment an
externally applied magnetic field reaches a certain
magnitude, a 180~ magnetic flux reversal occurs very
abruptly. This property, which is also called a "large
Barkhausen reversal", is utilized in the anti-theft systems
described above. If an alternating magnetic field
transmitted as an interrogating signal in the surveillance
zone reaches a critical value, the metal filament undergoes a
discontinuous magnetic flux reversal and an abrupt voltage
pulse is induced in the detection coil. The waveform of the
resulting pulse is subjected to frequency analysis and in
accordance with the intensity or proportion of higher-order
harmonic waves, the marker signal is used to determine
whether an alarm should be sounded. This system is
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advantageous in that the marker is inexpensive and provides a
highly discriminating performance.
In addition to the above-described amorphous metal
filament, many other magnetic materials have been found to
exhibit a discontinuous magnetization response. For example,
Unexamined Published Japanese Patent Application No. Hei-
1-150881 (corresponding to U.S. Patent 4,980,670) and No.
Hei-6-94841 (corresponding to U.S. Patent 5,313,192) teach
materials obtained by annealing elongated amorphous metal
ribbons in a magnetic field. According to Unexamined
Published Japanese Patent Application No. Hei-4-218905
(corresponding to U.S. Patent 5,181,020), a thin film having
a strong uniaxial magnetic anisotropy which is formed on a
flexible polymeric substrate such as a resin film exhibits a
discontinuous magnetic flux reversal and has good square
hysteresis loop characteristics similar to the metal
filament.
The thin film described in Unexamined Published
Japanese Patent Application No. Hei-4-218905 (corresponding
to U.S. Patent 5,181,020) produces an abrupt and
discontinuous magnetization response similar to the amorphous
metal filament if it is rendered in an elongated form
measuring, for example, 1 mm wide by 50 mm long by 0.5 ~m
thick along the axis that is easily magnetized (the magnetic
easy axis). However, the magnetic characteristics of the
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thin film are highly sensitive to a demagnetizing field and
have been found to deteriorate markedly when provided in a
shorter, wider and thicker form. Although there is a strong
need today for miniaturizing sensors and anti-theft markers,
S it cannot be met by the above noted magnetic materials
because they cannot provide an abrupt and discontinuous
magnetization response unless provided in an elongated form.
SUMMARY OF THE INVENTION
The present invention has been accomplished in view
of the above problems of the prior art.
It is therefore an object of the present invention to
provide a magnetic device which exhibits satisfactory
magnetic characteristics despite its compact size. Another
object of the invention is to provide a process for easily
producing the magnetic device. A further object of the
invention is to provide an apparatus for easily producing the
magnetic device.
The above objects have been achieved, in a first
embodiment of the present inventions, by providing a magnetic
device comprising a soft magnetic thin film formed on a
substrate, said soft magnetic thin film includes a central
area and a second area having a film thickness that is
smaller than that of the central area, and wherein said
magnetic device has a magnetic hysteresis loop which exhibits
a discontinuous magnetization reversal.
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In a second embodiment of the present invention, the
soft magnetic thin film of said second area has a film
thickness gradient.
In a third embodiment, the present invention provides
a process for producing the above-described magnetic device,
which comprises:
positioning a mask member having an opening over said
substrate with sufficient clearance so as not to contact the
substrate, and
depositing a magnetic thin film through the opening
of said mask member and onto said substrate.
In a fourth embodiment, the present invention
provides a process for producing the above-described magnetic
device, which comprises:
winding a substrate on a cylindrical can,
winding a mask member having an opening corresponding
to the shape of said thin film onto said substrate via a
spacer so as not to contact the substrate, and
depositing a soft magnetic thin film through the
opening of said mask member and onto said substrate.
In a fifth embodiment, the present invention provides
a process for producing the above-described magnetic device,
which comprises:
winding a substrate on a cylindrical can,
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positioning a mask member having an opening
corresponding to the shape of said thin film over said
substrate with sufficient clearance so as not to contact said
substrate, and
depositing a soft magnetic film through the opening
of said mask member and onto said wound substrate.
In a sixth embodiment, the present invention provides
an apparatus for producing the above-described magnetic
device, which comprises:
means for superposing, in the followiny order, (1) a
substrate, (2) a spacer and (3) a mask member having an
opening corresponding to the shape of said thin film around a
cylindrical can in such manner that the mask member does not
contact the substrate,,
means for depositing a soft magnetic thin film
through the opening of said mask member and onto said .
substrate, and
means for winding the superposed substrate, spacer
and mask member.
In a seventh embodiment, the present invention
provides an apparatus for producing the above-described
magnetic device,
means for winding a substrate or a cylindrical can,
means for positioning a mask member having an opening
corresponding to the shape of said thin film over said
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substrate with sufficient clearance so as not to contact said
substrate, and
means for depositing a soft magnetic film through the
opening of said mask member and onto said wound substrate
In an eighth embodiment, the present invention
provides a process for producing a magnetic device comprising
a thin film formed on a substrate, including a central area
and a second area having a film thickness that is smaller
than that of the central area, which comprises:
positioning a mask member between said substrate and
a thin film deposition source, to thereby selectively block
deposition from said deposition source, and
depositing a thin film onto said substrate while
moving said mask member and said substrate relative to each
other, to thereby vary the area blocked by said mask member
over time and form said second area having a reduced film
thickness.
The magnetic device of the present invention has a
discontinuous magnetization response characteristic which is
not overly sensitive to the shape of the magnetic device.
Hence, the magnetic device of the invention exhibits
satisfactory magnetic characteristics despite its compact
size.
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The process and apparatus of the present invention
enable easy production of a compact magnetic device having a
discontinuous magnetization response characteristic.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a simplified schematic diagram showing an
example of the magnetic device of the present invention.
Fig. 2 is a simplified schematic diagram showing
another example of the magnetic device of the present
lnventlon .
Fig. 3 is a simplified schematic diagram showing yet
another example of the magnetic device of the present
invention.
Fig. 4 is a simplified schematic diagram showing an
example of the apparatus for producing the magnetic device of
the present invention.
Fig. 5 shows a partially enlarged view of the film
forming zone of the apparatus of Fig. 4, and particularly the
relative positions of a substrate, mask member and spacer
provided therebetween.
Fig. 6 is a simplified schematic diagram illustrating
the operating principle of the second production process of
the present invention.
Fig. 7 is a simplified schematic diagram showing
another example of the apparatus for producing the magnetic
device of the present invention.
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Fig. 8 is a simplified schematic diagram showing two
different ways to cut out the magnetic device of the present
invention from a substrate with a thin film produced with the
apparatus of Fig. 7.
Fig. 9 is a simplified schematic diagram showing an
example of thin film deposition with a mask member fixed on a
substrate.
Fig. 10 is a simplified schematic diagram showing an
example of thin film deposition with a rod of a mask member
set on a substrate such that its longitudinal direction
coincides with the direction of movement of the substrate.
Fig. 11 is a simplified schematic diagram showing an
example of thin film deposition with a rod of a mask member
set obliquely on a substrate such that its longitudinal
direction forms a certain angle with the direction of
movement of the substrate.
Fig. 12 is a simplified schematic diagram showing an
example of thin film deposition with a sawtooth edged a mask
member set on a substrate.
Fig. 13 is a diagram showing the hysteresis loop of
the magnetic device manufactured in Example 1.
Fig. 14 is a diagram showing the hysteresis loop of
the magnetic device manufactured in Comparative Example 1.
Fig. 15 is a graph showing the thickness gradient of
the thin film formed in Example 2.
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Fig. 16 is a diagram showing the hysteresis loop of
the magnetic device manufactured in Example 2.
Fig. 17 is a diagram showing the hysteresis loop of
the magnetic device manufactured in Comparative Example 2.
Fig. 18 is a diagram showing the hysteresis loop of
the magnetic device manufactured in Example 3.
Fig. 19 is a diagram showing the hysteresis loop of
the magnetic device manufactured in Example 4.
Fig. 20 is a diagram showing the hysteresis loop of
the magnetic device manufactured in Comparative Example 3.
DETAILED DESCRIPTION OF THE INVENTION
The present invention will now be described in
further detail with reference to the accompanying drawings.
The magnetic devices according to the first and second
embodiments of the present invention are described first.
The magnetic device of the present invention
comprises a soft magnetic thin film formed on a substrate
comprising an area having a smaller film thickness than the
central area of the soft magnetic thin film. The soft
magnetic thin film formed in that area desirably has a film
thickness gradient.
Fig. 1 is a simplified schematic diagram showing an
example of the magnetic device of the present invention.
Fig. l(a) is a plan view of the magnetic device and Fig. l(b)
is a section A-A' of Fig. l(a). The magnetic device
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generally indicated by l in Fig. 1 is circular and an area 2
extending from position C to either end E has a smaller film
thickness than the central area 3, and the film thickness of
the area 2 progressively decreases toward either end.
Fig. 2 is a simplified schematic diagram showing
another example of the magnetic device of the present
invention. Similar to Fig. l, Fig. 2ta) is a plan view of
the magnetic device, and Fig. 2(b) is a section A-A' of Fig.
2(a). The magnetic device generally indicated by 1 in Fig. 2
is rectangular, and an area 2 extending from position C to
either end E has a smaller film thickness than the central
area 3. Furthermore, the film thickness of the area 2
decreases progressively toward either end of the longer side.
Fig. 3 is a simplified schematic diagram showing yet
another example of the magnetic device of the present
invention. Similar to Fig. 1, Fig. 3(a) is a plan view of
the magnetic device and Fig. 3(b) is a section A-A' of Fig.
3(a). The magnetic device generally indicated by 1 in Fig. 3
is rectangular and two areas 2 extending from position C to D
have a smaller film thickness than the central area 3.
Furthermore, the area between position D and either end E has
the same film thickness as the central area.
With an area or areas thus formed being a smaller
film thickness than the central area, the direction of
magnetization of the magnetic device is reversed momentarily
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in a critical magnetic field, whereupon an abrupt magnetic
pulse is radiated to the surroundings.
It should be noted that in the magnetic device of the
invention, the soft magnetic thin film is present even in the
area or areas which have a smaller film thickness than the
central area. The magnetic device shown in Fig. 3 has a film
thickness that is controlled to be smaller not at opposite
ends but in areas slightly offset toward the center. If the
film thickness of these areas is zero, the thin film is
interrupted in the middle, such that the first object of the
invention is not attained. On the other hand, the magnetic
devices shown in Figs. 1 and 2 have a film thickness that is
controlled to be smaller at opposite ends such that the film
thickness decreases progressively toward either end until it
becomes zero at the farthest end. These magnetic devices
produce sufficiently abrupt magnetic pulses to attain the
first object of the present invention.
In the case of controlling the film thickness at
either end as shown in Figs. 1 and 2, the film thickness of
the magnetic device preferably decreases progressively over a
length of about 1 to 20 mm, more preferably 2 to 10 mm, and
it becomes almost zero at the farthest end of the device.
The gradient of such a decrease in film thickness is
desirably low.
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In the case of controlling areas slightly offset from
either end toward the center as shown in Fig. 3, the film
thickness of the magnetic device preferably changes over a
length of about 0.1 to 5 mm, more preferably 0.5 to 2 mm such
that the smallest thickness ranges preferably from about 10%
to about 80% of the thickness in the central area. This
range is more preferably from about 20% to about 70%, and
most preferably about 30~ to about 65%.
The composition of the magnetic device of the present
invention is selected in consideration of both the magnetic
characteristics of the thin film per se and the
characteristics required by the magnetic device. For
example, the soft magnetic thin film either has uniaxial
magnetic anisotropy or it may be isotropic. If the magnetic
device is to be manufactured using an isotropic thin film,
satisfactory device characteristics are easier to obtain with
the circular shape shown in Fig. 1 than with the rectangular
shapes shown in Figs. 2 and 3. On the other hand, if the
magnetic device is to be manufactured using a thin film
having uniaxial magnetic anisotropy, satisfactory device
characteristics can be easily obtained even if the thin film
is rectangular as shown in Figs. 2 and 3. In this case, the
magnetic easy axis of the rectangular thin film may be
aligned with the direction A-A' such that the areas with a
controlled thin film cross the magnetic easy axis to cover
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the entire width of the magnetic device. Preferably, the
magnetic easy axis forms an angle of no more than 20~, more
preferably no more than 10~, with the lengthwise direction of
the magnetic device. Most preferably, the two directions are
S parallel to one another.
The areas of the magnetic device where the film
thickness is controlled to be smaller than in the central
area may be at either end of the device as shown in
Fig. 2 or slightly offset therefrom toward the center as
shown in Fig. 3. In the case of Fig. 3, the device
characteristics thus obtained tend to be highly reproducible.
On the other hand, more abrupt magnetic pulses are sometimes
obtained in the case of Fig. 2. Therefore, the areas of the
magnetic device where the film thickness is controlled to be
smaller than in the central area may be determined as
appropriate depending on the intended application.
The general size of the magnetic device of the
present invention is as follows. In the case of the circular
ones, the diameter is generally within the range of from 8 mm
to 70 mm, preferably 20 mm to 40 mm. In the case of the
rectangular ones, the length of the shorter side is generally
within the range of from 0.5 mm to 40 mm, preferably from
1 mm to 20 mm, and the length of the longer side is generally
within the range of from 10 mm to 70 mm, preferably from
20 mm to 50 mm. Too short diameter of the circular magnetic
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device or too short length of the shorter side of the
rectangular magnetic device is not preferable since the
abrupt magnetization reversal would not be obtained or the
intensity of the signal radiated to the surroundings by the
magnetization reversal is not sufficient. On the other hand,
too long diameter of the circular magnetic device or too long
length of the shorter side of the rectangular magnetic device
is not preferable since the abrupt magnetization reversal
would not be obtained or the large device is not easy to
handle. In addition, too short length of the longer side of
the rectangular magnetic device is not preferable since the
abrupt magnetization reversal would not be obtained, and too
long length of the longer side of the rectangular magnetic
device is not preferable since the large device is not easy
to handle. In addition to the circular magnetic devices and
rectangular magnetic devices described above, magnetic
devices of other shapes have similar tendencies.
The operating mechanism of the magnetic device of the
present invention is discussed below as follows. With
respect to a magnetic material which experiences magnetic
flux reversal as a result of the motion of magnetic domain
walls, when the walls of reverse domains generated at either
end of a sample of the magnetic material jump by moving very
fast the moment the applied magnetic field reaches a critical
value, abrupt magnetic pulses are radiated to the
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surroundings. On the other hand, the shorter and wider the
shape of the sample, the greater the demagnetizing field that
works on the sample. This makes the sample less likely to be
magnetized but, at the same time, the discontinuous behavior
of reverse domains is suppressed. Because of this effect, it
has been extremely difficult to realize satisfactorily
compact magnetic devices as discussed above.
In order to avoid the influence of the demagnetizing
field, it would be effective to constrain the magnetic walls
of reverse domains by a certain kind of force, and to have
them jump by releasing the constraint the moment a magnetic
field having a particular strength is reached. This force
which constrains the magnetic walls is called a "pinning"
force, and in the present invention, the film thickness is
controlled in selected areas to thereby provide an effect
that is comparable to a pinning force. The coercivity of the
thin film largely depends on its thickness and increases with
an increasing film thickness. If the film thickness is
reduced at either end, the coercivity of that area becomes
greater than that of the other areas. As a result, the
movement of the magnetic walls of the reverse domains present
in that area is restricted such that they will move slowly as
the strength of the external magnetic field increases. with
the gradual increase in the external magnetic field, the tips
of the reverse domains move inwardly. The moment they reach
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the central area beyond the areas having a controlled film
thickness, the magnetic domain walls move fast enough to
complete a magnetic flux reversal. This is because the
central area has a smaller coercivity due to a sufficient
film thickness. As a result of this rapid movement of the
magnetic flux domains, abrupt magnetic pulses are radiated to
the surroundings.
The above-described mechanism is realized in any of
the magnetic devices shown in Figs. 1 to 3. It should also
be noted that in magnetic devices which have a controlled
film thickness at either end as in Figs. 1 and 2, an
additional mechanism may come into play depending on the
composition of the device to thereby generate magnetic
pulses. For example, in a magnetic device having a geometry
such that the film thickness decreases progressively toward
either end, the magnetic field leakage will act on both ends.
This produces a local distribution of the demagnetizing field
which is entirely different from what develops in a geometry
having no changes in film thickness. Because of these
effects, the domain structure at the farthest ends of the
magnetic device becomes very stable and will not easily
change. Ideally, such a magnetic device does not develop a
closure domain structure, but develop a single domain at the
farthest ends. Thus, upon the application of an external
magnetic field, new reverse domains will nucleate. If the
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nucleating magnetic field is greater than the coercivity of
the film, the magnetic domain walls will move very fast the
moment the reverse domains have nucleated and magnetic pulses
subsequently radiate.
Specific examples of the alloy composition of the
soft magnetic thin film of the magnetic device of the present
invention include crystalline materials such as NiFe, FeAlSi,
FeAl and FeSi, fine crystalline Fe or Co alloy materials
containing B, C, N, O, etc., and amorphous materials such as
CoFeSiB, CoZrNb and FeC.
To form thin films of these materials, evaporation,
plating and other commonly known techniques may be employed.
In the present invention, the use of a sputtering process is
particularly preferred.
Depending on its composition, the magnetic device of
the invention may desirably have uniaxial magnetic
anisotropy. This property can be imparted by various methods
such as the application of stress to the magnetic device,
annealing in a uniaxial magnetic field, and annealing under
an applied stress. An especially preferred sputtering method
is described in Unexamined Published Japanese Patent
Application No. Hei-4-218905 (corresponding to U.S. Patent
5,181,020), in which thin-film forming particles impinge on a
substrate at an angle. According to this method, strong
uniaxial magnetic anisotropy is readily induced in the
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sputtered film as such, to thereby produce a soft magnetic
thin film having satisfactory magnetic characteristics.
Unexamined Published Japanese Patent Application No.
Hei-7-220971 (corresponding to EP-A-737,949) teaches another
method of imparting uniaxial magnetic anisotropy. According
to this published patent application, a magnetostrictive thin
film is formed on a resin substrate having anisotropic
thermal shrinkage under appropriate conditions. As a result,
not only is uniaxial magnetic anisotropy induced in
compliance with the anisotropic thermal shrinkage of the
substrate, but a soft magnetic property is also ensured.
The magnetic device of the invention comprises a soft
magnetic thin film formed on a substrate. The substrate is
not limited to any particular type, and can be selected from
common types such as glass, metals and resins. The use of a
polyethylene terephthalate (PET) film is preferred since it
is flexible and suited to large-scale production.
The magnetic device of the present invention has
magnetic characteristics which exhibit an abrupt magnetic
flux reversal in magnetic hysteresis, and it is characterized
in that its discontinuous magnetization response
characteristics are not so sensitive to the device shape. As
already noted, conventional materials are highly affected by
a demagnetizing field, and their characteristics have been
found to abruptly deteriorate when fabricated in a wider and
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shorter form. However, the magnetic device of the present
invention is less affected by the shape factor, and will
effectively operate in sizes of one inch or less to produce a
discontinuous abrupt magnetic flux reversal even if it is of
a geometry having a high demagnetizing field coefficient.
Consequently, the present invention provides a very effective
solution for meeting the need for smaller sensors and markers
which is sure to become more pressing in the years to come.
Next, the process for producing the magnetic device
of the present invention is described below. The production
of the magnetic device of the present invention starts with
preparing a thin film having a thickness difference in
selected areas. This may be effectively accomplished by
plasma or acid etching of a thin film which is exposed in
only those areas where the film thickness needs to be
controlled, but which is covered in other areas. However, it
is more advantageous from the viewpoint of productivity and
the like to cover a selected area of the substrate with a
mask member during film formation so that the deposition of
particles in that area is restricted to reduce the thickness
of the film being formed in that area.
Thus, according to the first embodiment of the
process for producing the magnetic device of the present
invention, a mask member having a shape which restricts the
inflow of particles deposited on a substrate is set with a
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sufficient clearance to prevent contact with the substrate,
and wherein said clearance effectively controls the thickness
gradient of the film that is formed.
It is a commonly adopted practice to form a patterned
thin film on a substrate with a mask member placed in contact
with the substrate in order to restrict the inflow of
particles deposited on the substrate. However, according to
this method, there is no film deposition under the mask
member, whereas a film of the same thickness is deposited in
those areas corresponding to the mask openings. Hence,
cannot be used to produce a thin film for the magnetic device
of the present invention which has a thickness difference in
selected areas.
On the other hand, if a mask member having a desired
shape in accordance with the size and characteristics of the
magnetic device is set with a sufficient clearance to prevent
contact with the substrate as a thin film is formed thereon,
the vapourized film-forming particles will pass around behind
the shade of the mask member. This results in a deposit on
the corresponding areas of the substrate, to thereby form a
thin film having a thickness gradient which gradually
decreases in thickness. By cutting the substrate with the
thus obtained thin film to a device shape such that it has a
smaller film thickness in areas other than the central area,
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the magnetic device of the present invention can be produced
which exhibits a discontinuous abrupt magnetic flux reversal.
In the present invention, the gradient of film
thickness is chiefly controlled by the clearance (distance)
between the substrate and the mask member. On the other
hand, the amount of particles that pass around behind the
shade of the mask member to deposit on corresponding areas of
the substrate is largely influenced by the shape of the
apparatus employed and its characteristics such as the mean
free path and the plasma density which are determined by the
operating pressure. Therefore, the distance between the
substrate and the mask member cannot be specified by any
unique value, except that a distance of about 0.1 to 5 mm is
generally preferred.
If a thin film is formed with a flat substrate such
as a glass plate that is successively fed into the film
forming stage, a flat plate mask member can be superposed on
the substrate with a spacer typically interposed
therebetween to provide the necessary clearance from the
substrate. Hence, the production process of the present
invention is relatively easy to implement.
On the other hand, if a roll-to-roll apparatus is
employed such that a highly flexible resin film is fed into
the film forming stage as it is wound in a roll and a
deposited film is then taken up, the mask member is not easy
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to set since the film is formed on the substrate which is
wound around a cylindrical can. Therefore, the present
invention also provides a process and an apparatus for
efficiently producing the above-described magnetic device of
the present invention using a roll-to-roll apparatus. The
process and apparatus for attaining this aspect of the
invention are described in detail below.
According to the first embodiment of the process of
the present invention, a thin film is formed on a continuous
substrate which is wound onto a cylindrical can in the roll-
to-roll apparatus as follows. To produce the intended
magnetic device by this process, a mask member of a given
shape and having an opening of a given shape for restricting
the inflow of particles deposited on the substrate is wound
around the can superposed on the substrate with a spacer
provided therebetween to prevent contact with the substrate.
The thin film is formed on the substrate as the substrate,
the spacer and the mask member are taken up.
The mask member for use in the present invention may
be selected from among metal (e.g. stainless steel~ folls,
glass cloths, resin films, etc. The mask member is wrapped
around the cylindrical can with the interposed spacer to
provide sufficient clearance from the substrate and, hence,
may occasionally fail to be thoroughly cooled with the can.
If, on account of this insufficient cooling, the mask member
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is heated during deposition by sputtering, evaporation and
the like methods, the mask member is preferably made of a
heat-resistant material such as glass, metal or a polyimide.
An example of the spacer for use in the present
invention is a beam-like element consisting of a plurality of
metal wires running parallel to each other. Metal wires such
as copper wires are preferred as the spacer because the
distance from the substrate can be controlled by the wire
diameter and because the metal wires have a high heat
resistance. As discussed above, the preferred range of the
wire diameter is not uniquely determined since it depends on
the apparatus used to produce the magnetic device of the
invention. Generally speaking, the range of the wire
diameter is from about 0.5 to about 5 mm.
Fig. 4 is a simplified schematic diagram showing an
example of the roll-to-roll apparatus for producing the
magnetic device of the present invention. Fig. 5 shows a
partially enlarged film forming zone of the apparatus of Fig.
4, particularly the relative positions of the substrate 4,
mask member lO and spacer 9 provided therebetween.
As shown in Fig. 5, the mask member 10 has a circular
opening 13 because the magnetic device to be produced is of
the circular type shown in Fig. 1; however, the present
invention is not so limited, and an opening of a desired
shape may be provided in the mask member 10.
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Because vapourized film-forming particles will pass
around behind the mask member and deposit in corresponding
areas of the substrate, the area where the particles are
deposited to form a thin film accordingly becomes larger than
the opening in the mask member. Considering this fact, the
opening provided in the mask member may be rendered somewhat
smaller than the magnetic device that is to be finally
produced. As an example, a circular opening having a size of
about 15 to 22 mm will suffice if a magnetic device with a
diameter of 25 mm is required.
In Fig. 5, only one opening is provided in the mask
member but this is just for the sake of convenience in
explanation. In order to realize mass production of magnetic
devices, a plurality of openings are preferably arranged side
by side so that many magnetic devices can be simultaneously
manufactured in one step. In this case, utmost care must be
exercised in determining the distance between openings
provided in the mask member. As discussed above, due to the
clearance between the mask member and the substrate, a thin
film will be deposited considerably outward from the opening
in the mask member. If the distance between openings is
unduly small, the individual devices will overlap.
Therefore, the distance between openings formed in the mask
is preferably as large as possible, and are generally spaced
by at least 10 mm, possibly at least 15 mm. As an example,
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CA 02218302 1997-10-14
if magnetic devices having a diameter of 25 mm are to be
manufactured on a film substrate having a width of 1 m, about
20 to 30 openings can be provided per 1 m of the mask member
in both horizontal and vertical directions. Hence, about 400
to 900 magnetic devices can be manufactured simultaneously
per square meter of the mask member.
As shown in Figs. 4 and 5, metal wires as spacers 9
are placed on top of the substrate 4 and the mask member 10
having a circular opening 13 is placed on the spacers 9 such
that the substrate 4, the spacers 9 and the mask member 10
are wound around a can 11 in superposition on each other.
Thin-film forming particles 14 pass through the circular
opening 13 to deposit on the substrate 4. Because the
spacers 9 provide a certain clearance between the substrate 4
and the mask member 10, the particles 14 will pass around
behind the mask member in an area near the circular opening
13 to deposit in a corresponding area of the substrate 4. As
a result, a thin film is deposited on the substrate 4 to a
larger extent than the diameter of the circular opening 13,
and the area of the deposited thin film which is near the
circumference decreases in film thickness towards the
peripheral edge thereof.
The apparatus for producing magnetic devices by the
above method has both means for winding the substrate, the
spacer and the mask around the can in superposition, and
CA 02218302 1997-10-14
means for taking up the overlapping substrate, spacer and
mask member. In order to wind the respective materials for
the substrate, spacer and mask member around the can in
superposition and to take them up after a thin film has been
formed, a roll of the respective superposed materials may be
fed into the film coater unit. In the film coater unit, the
superposed materials are wound onto the can, and the
substrate is taken up together with the deposited film.
Alternatively, the respective materials may be separately fed
into the film coater unit such that they are superposed on
the can 11 and, after a thin film has been formed, the
respective materials are separately taken up (this is the
method illustrated in Fig. 4).
Referring to Fig. 4, the substrate 4, the spacer 9
and the mask member 10 are supplied by associated feed rolls
8 and guide rolls 7, and are superposed on each other on the
peripheral surface of the can 11. As the can 11 rotates in
the direction of the arrow shown in Fig. 4, the superposed
materials are fed onto a deposition source 12, where a thin
film is deposited on the substrate. Thereafter, the
substrate with the deposited film, the spacer and the mask
member pass on associated guide rolls 6 and are wound up by
associated take-up rolls S.
Thus, the mask member is supplied in a continuous
form such as a film or a foil and onto a deposition source
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CA 02218302 1997-10-14
simultaneously with the substrate on which a thin film is
being formed. This method provides great latitude in
selecting the shape of the magnetic device depending upon the
shape of the opening in the mask member and, hence, is
suitable for producing circular magnetic devices. In
addition, the clearance between the mask member and the
substrate can be held constant, and this is very effective
for controlling the film thickness.
If rectangular magnetic devices of the types shown in
Figs. 2 and 3 are to be produced by a roll-to-roll apparatus,
a more simplified process and apparatus can be employed. The
process and the apparatus of this second embodiment are
described below.
The simplified process for producing the magnetic
device of the invention with a roll-to-roll apparatus is
realized. A thin film is formed on a substrate as it is
wound onto a cylindrical can. A mask of a given shape for
restricting the inflow of particles deposited on the
substrate is set below the can with a sufficient clearance to
prevent contact with the substrate, and where the thin film
is formed as the substrate is taken up.
Fig. 6 is a simplified schematic diagram illustrating
the operating principle of this production process. A thin
film is deposited on the substrate 4 using deposition source
12 such as a sputtering cathode. As shown, a mask member 10
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CA 02218302 1997-10-14
is placed in a selected area below the can, preferably just
underneath it, with sufficient clearance to prevent contact
with the substrate 4. In those areas of the substrate 4
which are not covered with the mask member 10, vapourized
film-forming particles 14 travel directly to the substrate 4,
thereby forming a thin film (having a greater thickness as
indicted by 15), whereas in the area of the substrate which
is just above the mask member 10, the particles 14 are
blocked by the mask member 10 and fail to form a thin film.
However, in the neighborhood of either end of the mask member
10, the particles 14 pass around behind the mask and are
deposited in the corresponding areas of the substrate, to
form a thin film (having a smaller thickness as indicated by
2) which progressively decreases in thickness. This effect
is utilized by the subject production method of the
invention.
Fig. 7 is a simplified schematic diagram showing an
example of a (roll-to-roll) apparatus for producing the
magnetic device of the invention by the method described
above. In Fig. 7, the substrate 4 is wound onto can 11 after
passing on guide roll 7, and a thin film is deposited on the
substrate 4 by deposition source 12. In the apparatus shown
in Fig. 7, a plurality of linear mask members 10 (four mask
members are shown in Fig. 7) are set just beneath the can 11
such that they do not contact the substrate 4, and films
CA 02218302 1997-10-14
having a smaller thickness 2 similar to the one shown in Fig.
6 are formed in those areas of the substrate which correspond
to the shades of the mask members 10. The substrate having
the thin film formed thereon is sent to a take-up roll via
guide roll 6. The thin film on the substrate 4 wound up by
the take-up roll consists of alternating bands of the thicker
portion 15 and the thinner portion 2, and the magnetic device
of the invention is cut out from the substrate 4.
Fig. 8 is a simplified schematic diagram showing two
deferent ways to cut out the magnetic device of the present
invention from the substrate with the thin film that was
manufactured with the apparatus of Fig. 7. As described
above, the thin film formed on the substrate 4 consists of
alternating bands of the thicker portion 15 and the thinner
portion 2. If a magnetic device of the shape indicated by 16
is cut out from this substrate, the device 1 has a thin film
of the smaller thickness 2 at each of the farthest ends as
shown in Fig. 8(a) and this is the magnetic device shown in
Fig. 2. If, on the other hand, a magnetic device of the
shape indicated by 17 is cut out from the substrate, the
device 1 has a thin film having a smaller thickness in areas
slightly offset toward the center as shown in Fig. 8(b) and
this is the magnetic device shown in Fig. 3.
As seen from Fig. 8, the width of the mask member 10
determines the shape of the areas 2 of the thin film having a
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CA 02218302 1997-10-14
controlled thickness, and it ranges preferably from 0.1 to 30
mm, with the range of 0.5 to 10 mm being more preferred. If
the width of the mask member 10 is less than 0.1 mm, it is
too narrow to provide the intended film thickness gradient.
On the other hand, if the width of the mask member 10 exceeds
30 mm, the overall size of the magnetic device increases to
the extent that a compact magnetic device is not realized
which is a primary objective of the invention.
As described above, the distance between the mask
member 10 and the substrate 4 cannot be uniquely determined
because it varies with the characteristics of the specific
film coater unit that is employed. However, in most cases, a
range of from about 0.1 to about 5 mm is preferred.
The mask member 10 may be rectangular or in the form
of a round bar. Alternatively, it may assume any cross-
sectional shape such as a triangle or an ellipse. A suitable
shape may be selected as appropriate in consideration of the
gradient of the film thickness of the magnetic device or the
shape of the areas of the thin film which are to have a
controlled thickness. Fig. 7 shows the case of using linear
masks. Because the surface of the can is curved, the
clearance between the mask member and the can increases
progressively with increasing distance from the center line
of the can and this may occasionally deteriorate the film
thickness control. If this possibility exists, it is
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CA 02218302 1997-10-14
effective to install a protector to ensure that a thin film
is formed only in the neighborhood of the central position of
the can.
Forming a mask member having the same curvature as
the can is a very effective means because it permits the
clearance between the mask member and the substrate to be
-held constant.
In addition to the first process described above, the
magnetic device of the invention can also be produced by a
second process which is described below.
In this second process, the magnetic device
comprising a substrate and a thin film formed thereon
including a central area and an area having a film thickness
that is smaller than that of the central area is preferably
produced by either evaporation or sputtering. In order to
prepare this thin film on the substrate, a mask member for
selectively blocking the deposition of a thin film is used.
The second process for producing the magnetic device of the
invention is characterized in that the mask member for
selective blocking of the deposition of the thin film LS
provided between the substrate and an evaporation source or a
sputtering cathode. In this case, either the substrate or
the mask member is moved such that the region of the
substrate which is shaded by the mask member varies over
time.
CA 02218302 1997-10-14
Consider the case shown in Fig. 9, where masks 19 are
fixed on a stationary substrate 18 and particles are
deposited on the substrate to form a thin film. No film is
deposited at all in the areas of the substrate which are
beneath the mask members 19. However, in the open areas
which are not covered with the mask members 19, a film of
uniform thickness is deposited on the substrate 18. As a
result, the deposited thin film is interrupted at areas 20
where no film is formed, and the film has a discontinuous
thickness profile in which the thickness of the film changes
discontinuously from one region to another. Hence, this
method is not capable of producing a thin film having a
thickness gradient that is needed for the magnetic device of
the invention which should exhibit an abrupt magnetic flux
reversal when the strength of an external magnetic field
reaches a critical value.
If a thin film is formed by moving either of the
substrate or the mask member, the thickness of the thin film
thus formed is affected by the relative positions of the mask
member and the substrate. Consider the case shown in Fig.
10, where rods of mask member 19 are set such that their
lengthwise direction is aligned with the direction of
movement of the substrate 18. The substrate travels in the
direction shown by the arrow in Fig. 10. Even if the mask
member 19 or the substrate 18 move relative to each other, a
- 33 -
CA 02218302 1997-10-14
given point on the substrate 18 is at all times in a position
such that it is shaded or not shaded by the mask members 19.
In this case, the film formed on the substrate 19 is of the
same type as shown in Fig. 9 and no thin film will form that
has the desired thickness gradient.
However, if, as in the present invention, the
substrate or the mask member is moved such that the region of
the substrate which is shaded by the mask member varies with
time, a film is obtained which has an area of continuously
ranging thickness. Even if the mask member 19 consists of
rods as shown in Fig. 10, they may be set obliquely as shown
in Fig. 11 such that their lengthwise axes form an angle with
the direction of movement of the substrate 18. The substrate
travels in the direction shown by the arrow in Fig. 11. If
this requirement is met, the region of the substrate which is
shaded by the mask member 19 varies with time and the
thickness of the film thus formed can be adjusted by the
length of time over which the substrate 18 is covered by the
mask member 19. As a result, the thin film is provided with
areas 2 having the desired thickness gradient. The extent of
the areas 2 is determined by the angle that the lengthwise
axis of the mask member 19 forms with the direction of
movement of either the substrate 18 or the mask member 19.
The film thickness gradient can be adjusted more
precisely by using a nonlinear mask member, for example, one
- 34 -
CA 02218302 1997-10-14
having a sawtooth edge as indicated by 19 in Fig. 12. The
substrate travels in the direction shown by the arrow in Fig.
12. If the substrate 18 or the mask member 19 having such a
nonlinear shape is moved, the length of time over which the
substrate is covered by the shade of the sawtooth edge 21
varies continuously, to thereby form areas 2 having a film
thickness gradient. In this case, the lengthwise axis of the
mask member l9 may be in complete alignment with the
direction of movement of the substrate 18 or the mask member
19.
The foregoing description has been directed to a
method of forming a thin film on a substrate that is held in
a flat state. Flexible substrates such as resin films or
metal foils can be processed by the roll-to-roll method in
which a roll of the substrate is unwound and passed around a
cylindrical can so that a thin film is continuously formed on
the substrate as it is wound by a take-up roll, and the
invention is also effective for this method. In this case,
the mask member is set below the can around which the
substrate has been wound. In order to achieve more precise
adjustment of the film thickness, it is more effective to
bend the mask member in conformance with the curvature of the
can so that the mask member maintains a constant clearance
from the substrate.
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CA 02218302 1997-10-14
The following Examples and comparative Examples are
provided for the purpose of further illustrating the present
invention. However, the present invention should not be
construed as being limited thereto.
Example 1
A fluororesin impregnated glass cloth 75 ~m thick
(product of Yodogawa Kasei Co., Ltd.) was punched to form
circular holes (15 mm~) at intervals of 30 mm, and the thus
prepared sheet was used as a mask member. A roll-to-roll
apparatus was used in the coating process. A PET
(polyethylene terephthalate) film 100 ~m thick was wrapped as
a substrate onto a water-cooled can, and copper wires 0.9 mm
in diameter were placed as spacers on top of the substrate.
The separately prepared mask member was superposed on the
copper wires. Thus, the mask member was set on the substrate
with a clearance of about 0.9 mm provided therebetween.
Using a DC magnetron sputtering apparatus of the type
described in Unexamined Published Japanese Patent Application
No. Hei-4-218905 (corresponding to U.S. Patent 5,181,020), in
which magnets are positioned below a target and the magnetic
flux from the magnets is guided by yokes to generate a high-
density plasma on the target surface, an amorphous thin film
having the composition Co5lFe26SilOBl3 (the subscripts represent
atomic %) was formed in a thickness of 0.5 ~m on the
substrate, which was taken up continuously together with the
CA 02218302 1997-10-14
spacers and the mask member. The substrate with the thin
film formed thereon was cut out in a specified geometry to
manufacture magnetic device samples of the invention. Each
sample was circular with a diameter of about 25 mm, and in
the area extending over the range of 7.5 to 12.5 mm from the
center of the circle, the film thickness decreased
continuously to provide a thickness gradient.
The magnetic characteristics of each sample were
measured with an ac B-H tracer (AC, BH-lOOK of Riken Denshi
Co., Ltd.) at 60 Hz. Since each sample exhibited uniaxial
magnetic anisotropy, the measurement was conducted with a
pickup coil set in the center of the sample in the direction
of the magnetic easy axis. The result is shown in Fig. 13.
As seen in Fig. 13, in each sample of the invention, the
magnetic device had a satisfactory square hysteresis loop and
the magnetization changed abruptly at -1 Oe and +0.6 Oe to
provide discontinuous jumps in magnetization.
Comparative Example 1
An amorphous thin film having the composition
Co5lFe26SilOB13 (the subscripts represent atomic %) was formed
on a PET (polyethylene terephthalate) film using the same
apparatus and under the same conditions as in Example 1,
except that no spacer copper wires were not interposed
between the substrate and the mask member (i.e., the
substrate was in contact with the mask member). Circular
CA 02218302 1997-10-14
thin films were formed each having a diameter of 15 mm equal
to the diameter of the openings in the mask member. These
thin films had a substantially uniform thickness. Magnetic
device samples were cut out from the circular thin films and
their magnetic characteristics were measured using the same
method as in Example l. The result is shown in Fig. 14. As
seen from Fig. 14, the magnetic device samples made of the
thin films having a uniform thickness did not produce the
desired square hysteresis loop under the influence of a
strong demagnetizing field. In addition, the change in
magnetization was continuous, and no discontinuous jumps in
magnetization were observed.
Example 2
A 100-~m thick PET (polyethylene terephthalate) film
was set as a substrate on a roll-to-roll apparatus of the
same type as used in Example 1. Two stainless steel bars
each having a diameter of 4 mm were spaced apart by 20 mm and
set as masks just beneath the can, with the smallest
clearance from the substrate adjusted to 0.1 mm.
Then, by continuously taking up the substrate, an
amorphous thin film having the composition Co5lFe26SilOBl3 (the
subscripts represent atomic %) was formed in a thickness of
0.5 ~m on the substrate using a DC magnetron sputtering
apparatus of the same type as used in Example l. Two bands
of a film having a smaller thickness were observed on the
CA 02218302 1997-10-14
substrate at a spacing of about 20 mm in the direction of
travel of the substrate, and the change in the film thickness
was continuous.
The thickness profile of the thin film was evaluated
by the following procedure. A water-soluble ink was
preliminarily printed in a pattern of 1 mm x 50 mm on the
substrate PET film. The length of the ink pattern and that
of the mask were oriented in a vertical direction. After
film formation, the water-soluble ink and the overlying thin
film were washed away with water. Thus, a level difference
was established between the area retaining the thin film and
the area from which it was removed, and the difference was
measured with a surface profile measuring system Dektak 300
of Dektak Co., Ltd. As a result, the film thickness was
found to be 0.6 ~m in the central area between the traces of
the two masks (which corresponded to the central area of the
magnetic device). The thickness profile in the neighborhood
of each mask was measured by scanning at 0.5-mm intervals.
The result is shown in Fig. 15. As seen from Fig. 15, the
thickness of the thin film deposited on the substrate varied
continuously on account of the masks, and the thickness was
smallest at an area corresponding to the center of either
mask (about 63% of the thickness at the areas not covered by
the mask). Thus, by providing the above masking structure,
areas having a smaller thickness than at the center of the
- 39 -
CA 02218302 1997-10-14
magnetic device were formed, and the film thickness
continuously varied to provide a gradient.
For the measurement of magnetic characteristics, a
PET film not having a printed pattern of a water-soluble ink
S was used as a substrate, and a thin film was formed thereon
under the same conditions described above. From the
substrate having the thin film formed thereon, rectangular
samples measuring about 28 mm long by 10 mm wide were cut out
such that the area having the smaller thickness would occur
at either, to thereby obtain magnetic device samples of the
invention.
The magnetic characteristics of these samples were
measured by the same method as employed in Example 1. Since
each magnetic device sample exhibited uniaxial magnetic
anisotropy in the longitudinal direction, the measurements
were conducted along the magnetic easy axis. The result is
shown in Fig. 16. As seen from Fig. 16, the magnetic device
samples of the invention each had a satisfactory square
hysteresis loop, and the magnetization changed abruptly at
-1 Oe and +1.1 Oe to provide discontinuous jumps in
magnetization.
Comparative Example 2
An amorphous thin film having the composition
Co5~Fe26Sil0B13 (the subscripts represent atomic %) was formed
on a PET film using the same apparatus and under the same
- 40 -
CA 02218302 1997-10-14
conditions as in Example 2, except that a mask member was not
set below the can. As a result, a thin film was uniformly
deposited on the substrate with no thickness gradient. From
this substrate, rectangular samples measuring 28 mm long by
10 mm wide as in Example 2 were cut out such that the length
of each sample was oriented parallel to the width of the
substrate. The magnetic characteristics of the cut out
samples were measured by the same method as used in Example
2. The result is shown in Fig. 17. As seen from Fig. 17,
the magnetic device samples made of thin films having a
uniform thickness did not produce the desired square
hysteresis loop, but rather produced a largely skewed loop
under the influence of a strong demagnetizing field. In
addition, the change in magnetization was continuous, and
discontinuous jumps in magnetization were not obtained.
Example 3
From the substrate prepared in Example 2, rectangular
magnetic device samples measuring about 38 mm long by 10 mm
wide were cut out such that areas having a smaller thickness
were located 5 mm from either end. The magnetic
characteristics of these samples were measured by the same
method as used in Example 1. Since each magnetic device
sample exhibited uniaxial magnetic anisotropy in the
longitudinal direction, the measurements were conducted along
the magnetic easy axis. The result is shown in Fig. 18. As
- 41 -
CA 02218302 1997-10-14
seen from Fig. 18, the magnetic device samples of the
invention each had a satisfactory square hysteresis loop, and
the magnetization changed abruptly at +0.4 Oe to provide
discontinuous jumps in magnetization.
Example 4
A 100-~m thick polyethylene terephthalate (PET) film
was set as a substrate on a roll-to-roll apparatus, and
stainless steel sheets measuring 10 mm wide by 30 cm long
which were bent to the curvature of the can were set as mask
members just beneath the can. The two stainless steel sheets
as mask members were spaced apart by 20 mm. The lengthwise
direction of each mask member formed an angle of 5~ with the
direction of travel of the substrate.
By continuously taking up the substrate on the setup
described above, an amorphous thin metallic film having the
composition Co5lFe26Sil0Bl3 (the subscripts represent atomic %)
was formed in a thickness of 0.5 ~m on the substrate using a
DC magnetron sputtering apparatus. Two bands of a film
having a smaller thickness were observed on the substrate at
a spacing of about 17 mm in the direction of travel of the
substrate, and the change in film thickness was continuous.
From the thus prepared substrate, rectangular samples
measuring 25 mm long on the longer side (across the width of
the substrate) by 10 mm wide were cut out such that the area
having the smaller thickness was located at either end. The
- 42 -
CA 02218302 1997-10-14
cut-out samples were magnetic devices. The magnetic
characteristics of these devices were measured with an ac B-H
tracer (AC, BH-100 K of Riken Denshi Co., Ltd.) at 60 Hz.
The result is shown in Fig. 19.
As seen from Fig. 19, the magnetic device samples
manufactured by the process of the invention had a
satisfactory square hysteresis loop, and the magnetization
changed abruptly at -0.7 Oe and +0.9 Oe to provide
discontinuous jumps in magnetization.
Comparative Example 3
An amorphous metallic thin film having the
composition Co5lFez6Sil0Bl3 (the subscripts represent atomic %)
was formed on a polyethylene terephthalate (PET) film using
the same apparatus and under the same conditions as in
Example 4, except that the length of the mask members was
adjusted parallel to the direction of travel of the substrate
(i.e., the angle between the lengthwise direction of the mask
members and the direction of travel of the substrate was zero
degrees). Because of this parallel alignment, the region of
the substrate which was shaded by the mask members did not
vary with time. The substrate having a thin film thus formed
thereon was characterized as having two bands of film-free
areas that were spaced apart by about 20 mm in the direction
of travel of the substrate, and the change in film thickness
at the boundary was clearly visible.
- 43 -
CA 02218302 1997-10-14
From the thus prepared substrate, rectangular samples
measuring 25 mm long on the longer side (across the width of
the substrate) by 10 mm wide were cut out such that a film-
free area was located at either end. The cut-out samples
were magnetic devices. The magnetic characteristics of these
devices were measured as in Example 1, and the result is
shown in Fig. 20.
As seen from Fig. 20, the magnetic device samples
manufactured without varying over time the region of the
substrate shaded by the mask members had hysteresis
characteristics exhibiting a lower degree of squareness as
compared to the samples of Fig. 19.
While the invention has been described in detail and
with reference to specific embodiments thereof, it will be
apparent to one skilled in the art that various changes and
modifications can be made therein without departing from the
spirit and scope thereof.
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