Magnetic headwith specified tapered pole tip width ratio

A magnetic head includes an elongate pole extending from an upper magnetic pole layer. The elongate pole has a tapered portion formed whose width is minimum width at the tip end of the pole. A ratio of the width of the narrowest section of the tapered portion to the width of the widest section (root) of the tapered portion is less than 1.0 but not less than 0.75.

FIELD OF THE INVENTION 
The invention relates to a magnetic recording system and a magnetic head 
for use in conjunction with the magnetic recording system. 
BACKGROUND OF THE INVENTION 
Magnetic recording media such as magnetic disks have been extensively used, 
and efforts have been made to increase bit density on such magnetic media. 
Today, the bit density on a magnetic disk, for example, often exceeds 1 G 
bits/in.sup.2. In order to further increase the bit density on a magnetic 
medium, it seems necessary to provide an improved magnetic write/read 
head. The most promising one is an induction type magnetic head. 
A typical induction type magnetic head utilizes a coil wound on a block of 
magnetic core. In order to minimize the dimensions of the head, however, 
many of recent induction type magnetic heads incorporate a thin film. 
As shown in FIG. 1, a magnetic head incorporating a thin film has a spiral 
induction coil 101, part of which is configured to pass through in between 
a lower core layer 102 and an upper core layer 103. Since the lower core 
layer 102 and the upper core layer 103 are made of conductive magnetic 
materials such as NiFe, the induction coil 101 is electrically insulated 
from the core layers 102 and 103 by an insulating layer 104. This type of 
induction type magnetic heads has a face that faces a magnetic disk such 
that the face has a write/read gap g between the lower core layer 102 and 
the upper core layer 103 for performing write and read operations, as 
shown in FIG. 1A. 
The upper core layer 103 has on the face thereof a section which has an 
elongate pole 103a, as shown in FIG. 1B. The elongate pole 103 is 
configured such that the magnetic flux density H through it becomes 
greatest at the tip thereof. 
A well known technique to form such elongate pole 103 is a 
photo-lithography in which the upper layer 103 is etched using a 
photo-resist mask. 
In order to increase bit density in magnetic recording, it is necessary to 
make the width W of the elongate pole 103a small, as shown in FIGS. 1C and 
1D, which may be attained by forming the tip of the elongate pole 103a in 
the form of thin rectangle having a narrow tip (called elongate pole-tip) 
103b, as described in IEEE TRANSACTIONS ON MAGNETICS, Vol. 26, No. 5, 
September 1990 by James L. Su et al. According to this article, the 
maximum ratio of the width W2 of the elongate pole-tip 103b to the width 
W1 of the elongate pole 103a, W2/W1, is found to be 0.46, with W1 being 26 
micrometers and W2 12 microns. 
If a further increase in bit density is intended, the width W2 of the 
elongate pole-tip 103b must be further narrowed. However, it is difficult 
to form a elongate pole-tip having a width less than 2.5 microns in the 
photo-lithographic method, since the thickness of the upper core layer 103 
is then of order of a few micron. 
Furthermore, if the rectangular elongate pole-tip 103b is made about 2.5 
micrometers wide, it is likely that the magnetic flux can saturate at the 
root section of the elongate pole 103b, and, should the magnetic flux 
saturate, change in magnetic field would not propagate beyond the 
saturated region, so that the tip of the elongate pole-tip 103b would 
become insensitive, thereby degrading over-write characteristic of the 
head. 
Another related technology for providing a elongate pole configuration is 
described in U.S. Pat. No. 5,600,519. This patent discloses a thin film 
magnetic head having three sections defined by a flare point and a zero 
throat height. The width of the intermediate section between the flare 
point and the zero throat height progressively increases toward the flare 
point, as shown in FIGS. 12 and 13 of the aforementioned patent. This 
increase in the elongate pole dimension is to equalize the flux density in 
the elongate pole. However, this patent does not teach any influence of 
the head configuration on the over-write characteristic. 
There is disclosed in Japanese Patent Publication Laid Open No. 2-105308 
another form of the pole tip in which the elongate pole changes its width 
towards the pole tip at a given angle. This prior art also fails to teach 
any influence of the angle of the elongate pole on the over-write 
characteristic. 
It is an object of the invention to provide a magnetic head which has an 
enhanced magnetic flux density in the pole tip, even when the width of the 
pole tip is 2.5 microns or less. 
SUMMARY OF THE INVENTION 
The above object of the invention may be attained by providing a magnetic 
head, comprising: a lower magnetic pole layer; an insulation layer formed 
on the lower magnetic pole layer; a conductive coil embedded in the 
insulation layer; an upper magnetic pole layer formed on the insulation 
layer; a elongate pole extending from the upper magnetic pole layer, the 
elongate pole having a taper portion at the tip, and near the tip, of the 
elongate pole, the taper portion having the smallest width at the tip 
thereof; and a non-magnetic gap layer formed between the taper portion and 
the lower magnetic pole layer, as shown in FIGS. 2, and 3. 
The taper portion of the magnetic head may have two sides meeting with the 
tip end face at an angle between 45.degree. and 90.degree.. 
It is preferable that the ratio of the width Wb of the tip end of The taper 
portion of to the width Wa of the root section of the taper portion, 
Wb/Wa, is less than 1, but not less than 0.75. 
The width Wb of the taper portion is preferably not more than 2.5 microns. 
Each of the sides of the taper portion preferably has a linear or a curved 
configuration. 
It is preferable to have the taper portion formed on the underside of the 
elongate pole. 
The object of the invention may be fulfilled also by a magnetic head, 
comprising: a lower magnetic pole layer; an insulation layer formed on the 
lower magnetic pole layer; a conductive coil embedded in the insulation 
layer; an upper magnetic pole layer formed on the insulation layer; a 
elongate pole extending from the upper magnetic pole layer; and a 
non-magnetic gap layer formed between the taper portion and the lower 
magnetic pole layer, as shown in FIGS. 2, and 3. 
The object of the invention may be fulfilled also by a magnetic head, 
comprising: a lower magnetic pole layer; an insulation layer formed on the 
lower magnetic pole layer; a conductive coil embedded in the insulation 
layer; an upper magnetic pole layer formed on the insulation layer; a 
elongate pole extending from the upper magnetic pole layer; and a 
non-magnetic gap layer formed between the taper portion and the lower 
magnetic pole layer, wherein the lower magnetic pole layer is provided, on 
the side thereof facing the pole tip, with recesses, as shown in FIGS. 2, 
3, and 8. 
In this case, the tip of the elongate pole is smaller in width than the 
root section of the elongate pole. 
The object of the invention is fulfilled by steps of: forming a first 
insulation layer on a lower magnetic pole layer; forming a conductive coil 
on the first insulation layer; forming a second insulation layer for 
covering the conductive coil; forming a magnetic layer on the second 
insulation layer; patterning the upper magnetic pole layer into a 
predetermined pattern by photo-lithographically etching the magnetic 
layer; and forming a tapered section having a width equal to or less than 
2.5 microns by impinging an ion beam onto the tip of the elongate pole. 
In this method, the sides of the taper portion may be linear or curved. 
Also, the ion beam may be impinged onto the lower magnetic pole layer 
simultaneously so that a recess may be formed in the upper portion of the 
lower magnetic pole layer. 
Further, the ion beam may be impinged on to the lower portion of the tip of 
the elongate pole, as shown in FIG. 10. 
The magnetic head of the invention has several features. 
First, the tip portion of the upper magnetic pole layer of the magnetic 
head is tapered, instead of having a stepped configuration, so that the 
magnetic flux at the root section of the elongate pole is less likely to 
saturate. As a result, the magnetic flux at the tapered tip may vary 
easily and, in addition, the magnetic flux density is enhanced. 
It would be appreciated that with the tapered pole making an angle with the 
tip end face less than 90.degree. but not less than 45.degree., over-write 
characteristic of the head is not degraded, as verified by experimental 
results shown in FIG. 4. 
If the elongate pole is configured such that the ratio of the width at the 
tip to the width at the root section of the elongate pole is made less 
than 1 but not less than 0.75, the over-write characteristic is further 
enhanced, as verified by the experimental results shown in FIG. 5. 
In another aspect of the invention, it is not difficult to make the width 
of the tip of the taper portion not to exceed 2.5 microns due to the fact 
that the elongate pole is tapered by means of ion beam bombardment, 
thereby minimizing the width of the track recorded on a magnetic recording 
medium. 
It should be appreciated that a recess may be formed in the face of the 
lower magnetic pole layer facing the elongate pole, so that the magnetic 
flux coming out of the elongate pole of the upper magnetic elongate pole 
layer is less likely to diverge, that is, the write magnetic field between 
the elongate pole and the lower magnetic pole layer is better converged in 
the gap. As a result, leak of the flux from the gap is minimized and hence 
the induction magnetic head has a narrow write field.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
We will now describe first a composite magnetic head which includes an 
induced type magnetic head on top of a magnetoresistance effect type 
magnetic head, and then discuss optimization of the upper magnetic pole 
layer of the induction type magnetic head. 
FIG. 2 shows in perspective view a portion of a composite magnetic head 
incorporating an induction type magnetic head of the invention. FIG. 3 is 
a plan view of a main portion the induction type magnetic head. Formed on 
a head substrate 1 are magnetoresistance (MR) effect type magnetic head 10 
for replaying (or reading) data along with an induction type head 20 which 
is capable of recording (or writing) as well as reading data. 
The MR type magnetic head 10 consists of a first magnetic shield layer 11, 
a first non-magnetic insulation layer 12, a magnetoresistance effect 
element 13, and a second non-magnetic insulation layer 14. Connected on 
the opposite sides of the magnetoresistance effect element 13 are a pair 
of lead wires 13a. The magnetoresistance effect element 13 and the paired 
lead wires 13a are sandwiched between the first non-magnetic insulation 
layer 12 and the second non-magnetic insulation layer 14. 
On the other hand, the induction type magnetic head 20 includes a lower 
magnetic pole layer (lower core) 21 made of NiFe, a spiral coil 22 for 
electromagnetic conversion of electric energy into magnetic flux, an upper 
magnetic pole layer (upper core) 24, formed on the MR type magnetic head 
10 in the order mentioned. 
The lower magnetic pole layer 21 is formed on the second non-magnetic 
insulation layer 14 of the MR type magnetic head 10 and in a region which 
extends from the tip of the magnetoresistance effect element 13 to the 
center of the spiral coil 22, and may serve as a second magnetic shield 
layer of the MR type magnetic head 10. It should be understood, however, 
that the lower magnetic pole layer 21 may be formed independently of the 
second magnetic shield layer of the MR type magnetic head 10. 
Formed on the lower magnetic pole layer 21 is a gap layer 25 made of 
Al.sub.2 O.sub.3 and having a thickness of about 0.2 microns. 
Between the lower magnetic pole layer 21 and the upper magnetic pole layer 
24 is an insulation layer 23, which includes therein a portion of the 
spiral coil 22 that extends out of the upper magnetic pole layer 24, 
thereby insulating the spiral coil 22 from the insulation layer 23 and the 
upper magnetic pole layer 24. The upper magnetic pole layer 24 has a 
recess in the region thereof above the center of the spiral coil 22. The 
recessed portion of the layer 24 penetrates the insulation layer 23 and 
touches the central portion of the lower magnetic pole layer 21. Thus, the 
layer 24 and the 23 are connected there, and no gap layer 25 exists in 
this region. In this region, the spiral coil 22 is spaced apart from the 
upper magnetic pole layer 24 and lower magnetic pole layer 21. As a 
result, the lower magnetic pole layer 21 and the insulation layer 23, when 
coupled together, form a C-shaped cross section. 
It would be noted that the insulation layer 23 has a generally planar 
pentagonal shape as shown in FIG. 3(a), with an elongate pole 24a 
extending from one of the corner of the pentagon. The elongate pole 24a, 
having a length L of 5 microns and a width Wa of about 2.5 microns, is 
separated from the lower magnetic pole layer 21 by a gap layer 25. The 
space between the lower magnetic pole layer 21 and the elongate pole 24a 
serves as a read/write gap G, so that the dimension of the gap G equals 
the thickness of the gap layer 25. 
When disposed inside the magnetic recording system, the tip of the elongate 
pole 24a and one end of the lower magnetic pole layer 21 are placed to 
face the disk surface of the magnetic recording medium (which is a 
magnetic disk in the example shown herein.). 
As shown in FIGS. 3B or 3C, the tip of the elongate pole 24a has a taper 
portion 24b which progressively decreases in width towards the tip of the 
pole 24a. The sides of the taper portion 24b may be linear as shown in 
FIG. 3B or curved as shown in FIG. 3C. The width Wa of the elongate pole 
24a has a constant width of about 2.5 microns, except for the taper 
portion 24b. The width Wb of the tip end of the taper portion ranges 
between 1.87-2.5 microns, inclusive. 
The elongate pole 24a is provided with the above mentioned taper portion 
24b for the following reasons. 
The magnetic field Hw generated by an electric current through the coil 22 
passes through the lower magnetic pole layer 21 and the upper magnetic 
pole layer 24 to form a loop of magnetic field through the gap G, which is 
applied to a recording medium 2 (for example, magnetic disk) to store 
magnetically data carried by the electric current, as shown in FIG. 2. It 
should be noted that the magnetic flux density Hw through the lower 
magnetic pole layer 21 and the upper magnetic pole layer 24 is preferably 
maximum at the very tip of the elongate pole 24a. 
If, however, a sharp pole tip 103b is formed at or the end of the elongate 
rectangular pole 103a as in prior art head shown in FIG. 1C, the magnetic 
flux can easily saturate at the root of the elongate pole 103a. This is 
due to the fact that the width of the pole tip quickly decreases in 
stepped condition. Consequently, rise in magnetic flux density is 
suppressed at the tip 103b, thereby making it difficult to yield an 
intense magnetic write field from the gap G. 
In contrast, the upper magnetic pole layer 24 of the invention has a taper 
portion which gradually changes the width of the elongate pole. That is, 
the elongate pole 24a of the head is gradually tapered towards the tip of 
the upper magnetic pole layer 24 so that the magnetic flux does not 
saturate at the root (widest section) of the taper portion 24a, but 
instead the flux is allowed to converge towards the tip (narrowest 
section) of the elongate pole, thereby advantageously creating a 
high-density flux in the gap G for a write field. 
Referring to FIG. 4, we now discuss how the taper portion 24b at and near 
the tip of the elongate pole 24a affects the over-write characteristic of 
the head. 
Let the angle (hereinafter referred to as taper angle) that the line X 
connecting the initial and the final point of the tapered side 24b makes 
with the line Y passing through the tip end face be .theta.. Measurements 
done on the over-write characteristic for various taper angles reveal an 
apparent relationship between them, as shown in FIG. 4. 
It is seen in this figure that the over-write characteristic gradually 
decreases in a region where taper angle is greater than 90.degree.. On the 
other hand, the over-write characteristic undesirably drops far below 30 
dB in the region of taper angle less than 30.degree.. However, with the 
taper angle of 45.degree., the over-write characteristic drops below that 
of 90.degree. by a small amount of about 1.5 dB. 
Thus, it is advantageous to choose the taper angle greater than 45.degree.. 
The taper angle of 90.degree. must be excluded, since at that angle no 
taper portion 24b can exist on the elongate pole 24a. Accordingly, the 
taper angle .theta. must be chosen in the range given by the following 
inequality. 
EQU 45.degree..ltoreq..theta.&lt;90.degree. (1) 
In order to maintain over-write magnetic flux equal to or greater than 30 
dB, it is preferable to choose .theta. equal to or greater than 
60.degree.. 
FIG. 5 is a graphical representation of the experimental results showing 
how the ratio .alpha. (=Wb/Wa) affects the over-write characteristic, 
where Wa is the width of the elongate pole 24a and Wb is the tip width of 
the taper portion shown in FIGS. 2B and 2C. 
FIG. 4 shows a relationship between the ratio a and the over-write 
characteristic. With the ratio in the range from 0.75 to 1.0, the 
over-write characteristic changes little, whereas the characteristic 
greatly drops for the .alpha. smaller than 0.75. Thus, it is preferable to 
choose the ratio of the widths to be greater than 0.75. The value 
.alpha.=1 corresponds to no taper portion 24b on the elongate pole 24a, so 
that preferable range of .alpha. is 
EQU 2&gt;Wb/Wa.gtoreq.0.75 (2) 
FIG. 6 illustrates a magnetic field microscope (MFM) image of a reversed 
magnetization pattern caused by a write field applied to the magnetic disk 
2 for a magnetic head 20 of FIG. 2 for which an optical core width of the 
tip of the taper portion 24b of the upper magnetic pole layer was 2.0 
microns. The effective core width was found to be 2.0 microns and write 
spread was zero, where the "effective core width" is defined as the width 
of a bit recorded on a magnetic recording medium (disk), and the "optical 
core width" as the width of the tip of the elongate pole having a write 
magnetic elongate pole as measured on the optical photography, and the 
"write spread width" as the width of the effective core width less the 
optical core width. It is noted that a layer 16 made of a material such as 
Al.sub.2 O.sub.3 is formed between the substrate 1 and the magnetic shield 
layer 11, for protection of the substrate. 
Referring to FIGS. 7A-7C, FIGS. 8A-8C, and FIGS. 9A and 9B, a process of 
forming the taper portion will be now described. FIGS. 7A-7C are partial 
cross sections of the materials at various stages of the head fabrication 
process. FIGS. 7A-7C shows a section from which an upper magnetic pole 
layer is fabricated. FIGS. 8A-8C shows the end face of the magnetic head 
facing a magnetic disk. FIG. 9 is a perspective view of a major portion of 
the induction type magnetic head. 
A base protection layer 16, a first magnetic shield 11, a first 
non-magnetic insulation layer 12, a magnetoresistance effect element 13, a 
second non-magnetic insulation layer 14, and a lower magnetic pole layer 
21 are formed on the head base 1, as shown in cross section in FIG. 7A. 
Then, a gap layer 25 is formed by depositing Al.sub.2 O.sub.3 to a 
thickness of 0.5 microns, which is followed by formation of a first 
insulation layer 23a in a region where a spiral coil 22 will be formed. 
A spiral coil 22 of copper is then formed on the first insulation layer 
23a. A second insulation layer 23b is formed on top of the first 
insulation layer 23a, covering the spiral coil 22. The first and the 
second insulation layers 23a and 23b, respectively, constitute an 
insulation layer 23 shown in FIG. 2. 
The spiral coil 22 is lithographically formed by patterning a copper layer. 
The first and the second insulation layers 23a and 23b, respectively, are 
formed from photo-sensitive organic layers such as photoresist made of 
polyimide resin or novolac family resin. The layers are patterned by first 
depositing the materials to a thickness of about 2 microns, which are then 
exposed to light and developed. The first and the second insulation layers 
23a and 23b respectively, have openings 23c at the center of the spiral 
coil 22. The layers are partially removed above the magnetoresistance 
element 13. These layers are hardened by heat. 
Next, as shown in FIG. 7B, the top of the resultant piece is covered with 
an NiFe layer having a thickness of 3.5 microns. This layer extends over 
the central openings 23c located essentially at the center of the spiral 
coil 22, and connects to the second magnetic shield layer (lower magnetic 
pole layer) 21 and covers the gap layer 24 above the magnetoresistance 
effect element 13. 
The NiFe layer 30 may be patterned, using a photoresist mask and ion 
milling technique, into a generally pentagonal shape of an upper magnetic 
pole layer 24 as shown in FIG. 3A, with an elongate pole 24a extending 
from one of the five corners. The width of the elongate pole 24a, made by 
such lithographic patterning as described above, is at most 2.5 microns. 
At this stage, there is no taper portion 24b formed in the tip section of 
the elongate pole 24a or near the tip thereof. The taper portion 24b is 
formed as follows. 
A layer of Al.sub.2 O.sub.3 is deposited on the induction type magnetic 
head 20, forming a protective layer 31, as shown in FIG. 7C and FIG. 8A. 
The base 1 is fabricated in a configuration suitable for a head slider 32, 
as shown in FIG. 9A. The head slider 32 is then provided, on the surface 
that will face the disk 2, with a protruding rail face (or air bearing 
face) 33. The slider 32 is further provided at the rear end thereof with 
the induction type magnetic head 20 and the MR type magnetic head 10, and 
at the ends thereof, with pads 41-44 to which both ends of the spiral coil 
22 and a pair of terminals 13a of the MR element are connected. 
A portion of the lower magnetic pole layer 21 of the induction type 
magnetic head 20 and the tip of the elongate pole 24a of the upper 
magnetic pole layer 24 are exposed at the end of the rail face 33. 
The opposite sides of the tip of the elongate pole 24a is then trimmed by 
bombarding a focused ion beam (FIB) while monitoring the tip using SEM, as 
shown in FIG. 8B and FIG. 9B, until the tip of the elongate pole 24a is 
trimmed to a thickness less than 2.5 microns. The trimmed tip has a shape 
as shown in detail in FIG. 2B and 2C. 
The tapered portion 24b may be formed along the entire length of the 
opposite sides of the elongate pole 24a, as shown in FIG. 8C, or may be 
formed only on the underside of the elongate pole 24a by trimming the tip 
as shown in FIGS. 10A and 10B. In either case, two sections of the lower 
magnetic pole layer 21 that face the taper portion 24b are trimmed to form 
the recesses 21a. 
After finishing the trimming, a diamond like carbon layer (not shown) is 
sputtered on the head. 
Experimental results on the write spread and over-write characteristic of a 
head thus formed are shown in FIG. 11. In this figure, a plot marked by 
diamonds represents the write spread for an untrimmed elongate pole; plots 
marked by squares and triangles represent write spreads for trimmed 
elongate poles, with square plots corresponding to elongate poles trimmed 
deeply compared with triangle plots. The width of the elongate pole 24a 
becomes smaller with trimming. 
As seen in FIG. 11, the amount of the write spread cause by a trimmed pole 
24a, or taper portion 24b, is smaller than that caused by an elongate pole 
which is not trimmed. In view of the fact that a magnetic field for use in 
over-write is less than 30 dB, tapered elongate pole 24a is better suited 
for high density recording on a magnetic recording medium than an elongate 
pole which is not trimmed, since a trimmed elongate pole exhibits less 
write spread than the latter by more than 30%. It should be appreciated 
that such a trimmed elongate pole 24a, with its tip trimmed by FIB to or 
less than 2.5 microns, not only has a small effective write core width but 
also has much less write spread. This may be understood from the following 
features of the invention. 
When the elongate pole of the upper magnetic pole layer is trimmed by FIB 
to form the taper portion 24b, the upper portion of the lower magnetic 
pole layer 21 is also trimmed, forming the recesses 21a, as described 
previously and shown in FIG. 8C and FIG. 10B. As a result, the magnetic 
field H1 extending out of the lower end of the taper portion 24b tends to 
converge towards the lower magnetic pole layer 21 between the recesses 
21a, instead of spreading around the tip. Accordingly, the write spread on 
the magnetic disk 2 is suppressed. 
The slider 32 equipped with the induction type magnetic head 20 and the MR 
head 21 is mounted on the tip of an arm 35 of a disk recording system as 
shown in FIG. 11. The arm 35 is mounted on an actuator 34 which actuate 
the arm 35 to move the slider 32 over the disk 2. 
Ones skilled in the art will appreciate that the induction type magnetic 
head 20 is not limited for use with magnetic disk systems, but it may 
equally be used for write and read on a magnetic tape system. 
The magnetic head described above has the following advantages. First, 
since the elongate pole for the upper magnetic layer of the head is 
tapered at its tip, it is less likely that the magnetic field will 
saturate at the root section of the elongate pole, thereby permitting the 
magnetic flux density to change easily at the tapered tip while preventing 
the magnetic flux density from decreasing at the tip. 
The tapered head having a taper angle with respect to the end face of the 
tip less than 90.degree. but not less than 45.degree., may avoid loss of 
over-write characteristic. The loss of over-write characteristic may be 
also prevented by setting the ratio of the width of the taper portion to 
the width of the root section of the taper portion less than 1.0 but not 
less than 0.75. 
In another aspect of the invention, the width of the tapered elongate pole 
may be made equal to or less than 2.5 microns by the use of ion beam 
trimming, thereby minimizing the width of tracks on a recording medium. 
In a still another aspect of the invention, the lower magnetic pole layer 
is provided, on the side thereof facing the pole tip, with recesses, such 
that the divergence of the write field that would otherwise escape from 
the gap between the elongate pole and the lower magnetic pole layer, is 
prevented, so that the write spread is suppressed for the head.