Thin film read/write head for minimizing erase fringing and method of making the same

The present invention pertains to a thin film magnetic recording head which minimizes erase fringing and the process for manufacturing the thin film magnetic recording head. The head is used to record and read information made up of alternating magnetization patterns on a magnetic recording medium. Known recording heads cause erase fringing of the magnetic medium during the write operations. The structure of the recording head of the present invention has the ABS portion of one of two magnetic poles beveled away from ABS at the gap to zero throat, reduces erase fringing of the magnetic recording medium and is easily manufactured. By reducing erase fringing, the present invention enables an increase in disk density of information without risking loss of data integrity.

FIELD OF THE INVENTION 
The present invention relates to the structure of and process for 
manufacturing a thin film read/write head, and more particularly to the 
structure of a thin film head which minimizes erase fringing of the 
magnetic recording medium and the process for easily and reliably 
manufacturing the head. 
BACKGROUND OF THE INVENTION 
Information is stored on a magnetic recording medium such as a disk as 
alternating magnetization patterns. As is well known, when a thin film 
head passes over the recording medium, the magnetization patterns on the 
medium are sensed to read the information stored on the medium. 
Alternatively, information is written onto the recording medium by passing 
a thin film head over the medium to store appropriate magnetization 
patterns. 
A typical disk drive system includes a plurality of magnetic disks and a 
head assembly. The typical head assembly used with a disk drive moves 
radially towards or away from the axis of rotation of the disks. At any 
given discrete distance away from the axis of rotation, the recording head 
is positioned to read or write data from or to a discrete area on one of 
the almost concentric tracks of the disk. 
To record information onto the magnetic medium, the recording head applies 
a magnetic field to the portion of the medium within the boundary of the 
desired track. Ideally, the width of the track should equal the width of 
the recording head so that the induced magnetic field of the head only 
alters magnetization patterns of the desired track. The trend in the data 
storage field is to increase the density of the information stored on a 
disk. One way to accomplish increased density is to increase the number of 
tracks on the disk. Accordingly, in a high density disk, the distance 
between adjacent tracks is smaller than in a low density disk. 
If the induced magnetic field of the thin film head extends beyond the 
width of the head and affects the magnetization position on an adjacent 
track, the information stored on the adjacent track may be corrupted or 
destroyed. This problem is referred to as erase fringing. The distance 
away from the sides of the recording head in the track width direction 
where the magnetic field erases data on the sides of the recording head is 
called the erase width of the recording head. The problem caused by erase 
fringing increases as the ratio of the track spacing to the optical width 
of the heads decreases in high density disks. Therefore, erase fringing 
limits the potential density of the magnetic medium or disk because 
sufficient space between the tracks must be maintained to avoid corrupting 
or erasing adjacent tracks. 
Conventional thin film heads contain two rectangular magnetic poles, P1 and 
P2, which are separated by a thin gap. Pole P1 is typically made a few 
microns wider than pole P2 in order to avoid magnetic contact between the 
two poles due to misalignment in the pole P2 process. The erase fringing 
that occurs when a magnetic field is applied between poles P1 and P2 
increases as the difference in the width of the two magnetic poles at the 
gap increases. This erase fringing occurs because the magnetic field 
extends beyond the width of the pole P2 at the gap. 
One known method to reduce the amount of erase fringing involves modifying 
the design of the read/write head. In one such modified design, the air 
bearing surface (ABS) geometry of pole P1 is modified. The ABS geometry 
denotes the geometry as seen by the magnetic recording medium looking 
toward the thin film recording head. The rectangular poles P1 and P2 are 
milled together so that the width of the resulting rectangular pole P1 is 
equal to the width of rectangular pole P2 at the ABS. The excess material 
of rectangular pole P1 and P2 that is milled away extends further away 
from the ABS past the zero throat point. In this known structure, the 
length from the ABS to where the milling ceases is approximately 4-6 
microns. Accordingly, a relatively large amount of material from pole P1 
and P2 must be milled away. 
In another modified design for a thin film recording head reducing erase 
fringing, the ABS geometry of pole P1 is milled to form a relatively 
rectangular portion adjacent the gap and a relatively trapezoidal portion 
with a larger cross-section area adjacent the rectangular portion. Again, 
in this design, the length from the ABS to where the milling ceases is 
approximately 4-6 microns. 
Both of the above modified geometries for a thin film recording head reduce 
the extent of the magnetic field outside the width at the gap and 
accordingly reduce erase fringing. However, both of the above head 
geometries require both poles P1 and P2 to have substantially parallel 
walls adjacent the gap and to be milled away from the ABS well beyond the 
zero throat point. Both of these head geometries are difficult and time 
consuming to manufacture and result in a relatively low yield of 
satisfactory products during high volume manufacturing. 
In one known process for making conventional thin film recording heads with 
plated poles, a base layer of insulating material such as Al.sub.2 O.sub.3 
is deposited on a substrate such as ALSIMAG. A seed layer of material such 
as NiFe is sputtered over the base layer. Photoresist is next coated over 
the NiFe seed layer. Next, through a photolithographic process, a window 
for a pole is formed in the photoresist. After the photoresist is 
developed, pole material is deposited in the window by electroplating. Now 
a thin gap layer of material such as Al.sub.2 O.sub.3 is deposited. Then, 
a coil structure surrounded by insulation is formed at the yoke region of 
the poles. Finally, the second pole is plated following the same procedure 
as described above. Normally, the width of the second pole at its tip is 
plated to be narrower than the width of the first pole at its tip in order 
to avoid magnetic contact between the poles at the gap. At this point, a 
conventional thin film head structure has been formed. 
If a more specific head geometry is desired, additional track trimming must 
be done. Using one known technique for trimming the head to the desired 
geometry, a thick photoresist mask is placed on the desired portion of the 
second pole and completely over the yoke. Ion milling is now used to 
remove excess magnetic material not covered by the photoresist along the 
width of the two pole portions. Therefore, the width of this photoresist 
pattern determines the final width of the poles at the gap. The ion 
milling proceeds along the entire excess depth of the first pole portion 
to achieve two rectangular pole portions of equal width. 
SUMMARY OF THE INVENTION 
The present invention is a read/write thin film head having a pole piece 
structure that reduces erase fringing during the write operation over 
conventional thin film heads. The thin film head of the present invention 
has two pole pieces P1 and P2 separated by a gap. Both pole pieces have 
equal widths at the gap. The sides of the bottom pole P1 are beveled 
outward away from the gap in the track width direction and the beveling 
continues away from the ABS to a point where pole P2 angles away from pole 
P1 and the gap, called the zero-throat point. The geometry or structure of 
the recording head of the present invention minimizes the magnetic field 
extending beyond the width of the head thereby minimizing erase fringing. 
The beveling of pole P1 extends over only a short portion of the length of 
the rectangular part of the pole and, accordingly, reduces manufacturing 
time and improves the accuracy of the fabrication process. 
The method of manufacturing the thin film head is similar to the 
conventional track trimming process except the second pole P2 is plated 
about a micron thicker than is required for adequate magnetic performance. 
Instead of using a photoresist, the plated pole P2 itself is then used as 
the mask for pole P1 during ion milling to achieve the above described 
geometry. Since the beveling extends only up to the zero throat point, a 
chemical, such as hydrofloric acid, is used to remove the gap material 
above pole P1 that is not covered by pole P2 up to the zero throat point 
before beginning the ion milling process. This reduces the manufacturing 
process time and improves the accuracy of the resulting thin film head 
geometrics. Since both poles P1 and P2 are made from the same material 
they etch at about the same rate and after a micron of ion milling, the 
desired thickness of pole P2 and beveling of pole P1 is achieved.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIG. 1 shows a perspective view along a line of symmetry of a conventional 
thin film recording head 10 having a first pole (P1) 12 and a second pole 
(P2) 14. The arrow A points in the direction of the view as seen by the 
magnetic recording medium, commonly called the Air Bearing Surface (ABS) 
view. The ABS view shows that poles 12 and 14 have substantially 
rectangular tip portions 16 and 18, respectively. A gap g separates poles 
12 and 14. The width of the front edge 20 of pole 12 is greater than the 
width of the front edge 22 of pole 14 at the gap g. 
FIG. 2 shows the side view of the same conventional thin film recording 
head 10 of FIG. 1. A point T is shown on the tip 18 of pole 14 and a point 
ZT is shown at a position where pole 14 angles away from the gap g and 
pole 12. The area between points T and ZT define the throat 24 of pole 14. 
Point ZT is commonly referred to as zero throat. The remaining standard 
portions or elements of the head 10 are not illustrated for the sake of 
simplicity and clarity in the drawings. As is well known in the field, 
this head design results in significant erase fringing due to the magnetic 
field between pole 12 and pole 14 extending beyond the width of the head 
10. 
FIG. 3 shows a perspective view along a line of symmetry of a modified thin 
film recording head 30 having a first pole (P1) 32 and a second pole (P2) 
34. The arrow A points in the direction of the ABS view. The ABS view of 
FIG. 3 shows that poles 32 and 34 have substantially rectangular tips 36 
and 38 and front edges 40 and 42, respectively. A gap g separates poles 32 
and 34. The width of pole 32 and the width of pole 34 are equal at the tip 
and away from the tip well past zero throat. 
FIG. 4 shows the side view of the same modified thin film recording head 30 
of FIG. 3. A point T is shown on the tip portion 38 of pole 34 and a point 
ZT is shown at a position where pole 34 angles away from the gap g and 
pole 32. The throat of pole 34 lies between points T and ZT. The remaining 
standard portions or elements of the head 30 are not illustrated for the 
sake of simplicity and clarity in the drawings. The above modified 
geometry of the thin film head 30 reduces erase fringing over the 
conventional thin film head design shown in FIGS. 1 and 2. To achieve the 
width of rectangular pole (P1) 32 equal to the width of rectangular pole 
(P2) 34 a substantial amount of expensive and time-consuming milling and 
trimming of P1 and P2 is required. The trimming of pole P1 away from ABS 
must proceed well past zero throat about 4-6 microns. 
FIG. 5 shows a perspective view along a line of symmetry of a thin film 
recording head 50 of the present invention. The head 50 has a first pole 
(P1) 52 and a second pole (P2) 54. The poles 52 and 54 are separated by a 
gap g. The ABS view of FIG. 5 shows that the tip portion 56 pole (P1) 52 
is not rectangular and that the tip portion 58 of pole (P2) 54 is 
substantially rectangular. The width of front edge 60 of pole (P1) 52 and 
the width of front edge 62 of pole (P2) 54 at the gap g are substantially 
equal. However, the width of back edge 64 of pole (P1) 52 opposite the gap 
is greater than the width of front edge 60 of pole (P2) 54 at the gap. In 
the preferred embodiment, back edge 64 of pole (P1) 52 is about a micron 
wider than the width of front edge 60 of pole (P2) 54. A joinder portion 
66 of pole (P1) 52 angles away at approximately a 45 degree angle from 
front edge 62 of pole (P2) 54. FIG. 5 further shows a side wall portion 70 
of pole (P1) 52 lying in a plane. The top edge 72 of the wall 70 also is 
lying in the plane. The material removed from the corner of pole (P1) 52 
during manufacturing results in an edge 74 extending away from the surface 
56 to the zero throat point illustrated by line 76. The edge 74 is lying 
in a plane substantially parallel to and spaced from the plane containing 
edge 72. The joinder portion 66 connects the plane of edge 72 with the 
plane of edge 74. 
FIG. 6 shows the side view of the recording head FIG. 5. As shown in FIG. 
6, pole (P1) 52 is beveled to approximately the point ZT at zero throat, 
about a micron and a half away from ABS. Thus, with the present invention, 
only a small amount of ion milling is required compared to the extensive 
ion milling required for thin film recording heads of the design shown in 
FIG. 3. The erase fringing which occurs with the present invention is also 
dramatically decreased as compared with the erase fringing caused by the 
recording head shown in FIG. 1. 
FIG. 7 shows an ABS view of the thin film recording head of the present 
invention shown in FIG. 5. The ABS view shows the tip portions 56 and 58 
of pole portions 52 and 54, respectively. The front edges 60 and 62 of 
pole portions 52 and 54, respectively, are also shown and are of 
substantially equal width at the gap. The left and right side edges of 
pole 52 include the portions or legs 61 and 63 which are substantially 
normal to the back edge 64 and angled portions or legs 65 and 67. The legs 
65 and 67 are preferably at approximately a 45 degree angle. In the 
preferred embodiment, the back edge 64 is 2 microns wider than the front 
edge 62 of pole (P2) 58 and the distance d that each side edge is beveled 
equals one micron. 
Of course, the angle of the bevel can be any other degree without departing 
from the scope of the present invention. If the angle of the beveling is 
increased, additional material from pole (P1) 52 is removed. This results 
in a marginal reduction of erase fringing. If the angle of the beveling is 
decreased, less material from pole (P1) 52 would be removed. As the angle 
approaches zero, the geometry of the present invention approaches that of 
the conventional thin film recording head shown in FIG. 1 and the ability 
of the resulting recording head to reduce erase fringing is substantially 
decreased. 
Other embodiments of the present invention can be achieved by removing 
additional material from pole P1. For example, in another embodiment of 
the present invention, pole P1 is ion milled so that the width of pole P1 
equals the width of pole P2 at the gap. The ion milling of P1 achieves an 
almost 90 degree angle with respect to side 60 of pole P2 and also removes 
a few microns of material from pole P1. The resulting geometry of pole P1 
has a substantially rectangular portion at the gap and a substantially 
rectangular portion of greater width away from the gap. In the above 
described embodiments of the present invention, the ion milling proceeds 
away from the ABS to about zero throat. Further, the exact geometries of 
the above described embodiments of the present invention are aspirational. 
The actual milling and manufacturing of thin film recording heads is 
imprecise due to their deminimis size. In actual practice, exact 
geometries or precise angles are difficult to achieve. 
The magnetic field which causes erase fringing is made up of vertical, 
transverse and longitudinal components. The longitudinal component is 
directed along the recording medium direction of motion, the vertical 
component is directed normal to the plane of the medium, and the 
transverse component is directed along the track width direction. 
In FIG. 8, an ABS view along a line of symmetry of a recording head 50 of 
the present invention is shown. The head is comprised of two poles P1 and 
P2 and a gap g therebetween. During the recording process, the magnetic 
recording medium will pass by the pole P1 across the gap g and to pole P2 
in the direction indicated by the arrow DOR. The influence that pole P1 
has upon the medium during recording in the central region is overridden 
by the flux at the gap and at the adjacent region of pole P2. The track 
width of recorded data created in the medium caused by the action of 
recording head 50 is approximately the width Wg of the recording head at 
the gap plus the write fringing caused by magnetic fields outside the 
width of the gap. 
Longitudinal field contours in the midplane of the magnetic medium in 
relation to poles P1 and P2 and gap g are shown by dotted lines. 
Corresponding contours exist for transverse fields of magnetic recording 
head 50, but have been omitted for simplicity of description only. FIG. 8 
shows that a contour of +50 encompasses a portion of pole P1 and a portion 
of pole P2 substantially centered about gap g. Within this +50 contour, a 
+80 contour is defined. The two aforementioned contours are all 
substantially centered about gap g. Of course, gradients exists within and 
between the contours as shown. For example, the flux density in a thin 
region 55 located adjacent front edge 62 of pole piece P2 will be between 
+80 and +250 units. In FIG. 8, the contour +80 represent the extent of the 
erase/write width for the magnetic medium whose coercivity is equal to 
+80. 
Under similar operating conditions, the longitudinal magnetic field 
contours for a conventional thin film recording head extend further away 
from the sides of the recording head than the contours shown in FIG. 8 and 
contribute significantly to additional erase fringing. The longitudinal 
magnetic field contours for plus 80 of the present invention are 
comparable to the plus 80 contours for the head geometry shown in FIG. 3. 
Therefore, the present invention has a similar erase width as the head 
geometry shown in FIG. 3. 
Similarly, the design of the present invention reduces the extent of 
transverse magnetic fields outside the width of the recording head. The 
reduction of the transverse magnetic fields contributes to the reduction 
of erase fringing and also helps to minimize inter-symbol interference 
during the writing of closely spaced bits and reduce the width of the 
pulse during readback (PW50). Minimizing inter-symbol interference and 
reducing the width of (PW50) provides for increased linear density of the 
recording medium. 
By reducing the extension of longitudinal and transverse magnetic fields 
outside of the width of the head, the present invention substantially 
reduces erase width over conventional thin film heads and also has an 
erase width comparable to thin film recording heads shown in FIG. 3 which 
require an extensive and less reliable manufacturing process. 
Table 1 shows the erase widths of thin film recording heads shown in FIGS. 
1, 3 and 5 for various ratios of Hg/Hc. Hg/Hc represents the ratio of the 
strength of the magnetic field at the midplane of the medium to the 
coercivity of the recording medium. As is well known in the field, to 
achieve a successful overwrite on the recording medium Hg/Hc should be 
greater than or equal to 2.5. Of course, for higher ratios of Hg/Hc the 
magnetic medium coercivity is more easily overcome; however, the erase 
width is also increased. For Hg/Hc equal to 2.5, Table 1 shows that the 
erase width for conventional thin film recording heads equals 292 micro 
inches, the erase width for the present invention equals 265 micro inches, 
and the erase width for the thin film recording head of FIG. 3 equals 262 
micro inches. Thus, Table 1 shows that 90% (27/30) of the improvement 
achieved by extensive and substantial ion milling of the recording head in 
FIG. 3 can be obtained by the present invention which simply bevels pole 
P1 one micron at 45 degrees to zero throat. 
TABLE 1 
______________________________________ 
ERASE WIDTH 
(Hg/Hc) 
Head Type 2 2.5 3.0 4.0 
______________________________________ 
FIG. 1 270 .mu." 
292 .mu." 313 .mu." 
340 .mu." 
(Conventional 
thin film head 
6.0/8.0) 
FIG. 3 252 .mu." 
262 .mu." 274 .mu." 
292 .mu." 
(Rectangular 
thin film head 
6.0/6.0) 
FIG. 5 254 .mu." 
265 .mu." 280 .mu." 
317 .mu." 
(Present 
invention 
6/8 beveled) 
______________________________________ 
Moreover, the simplicity in the design of the present invention allows for 
ease in manufacturing. The main steps in one method of making the thin 
film recording head of the present invention shown in FIG. 5 is to deposit 
a base layer of insulating material such as Al.sub.2 O.sub.3 on a 
substrate such as ALSIMAG, sputter a seed layer of material such NiFe over 
the base layer, and coat the NiFe seed layer with a photoresist. Then, 
form a window in the photoresist for a pole P1 using a photolithographic 
process, and when developed, deposit the pole material in the window by 
electroplating. Next, add a thin gap layer of material such as Al.sub.2 
O.sub.3 and then add a coil structure surrounded by insulation at the yoke 
region of the poles. Then, plate the second pole P2 in a similar fashion. 
In the preferred method of making the thin film recording head of the 
present invention shown in FIG. 5, pole P2 should be plated about one 
micron thicker than the final desired thickness of pole P2 and also about 
2 microns narrower than the width of pole P1. 
To trim the head, use a chemical, such as Hydrofluoric Acid to remove much 
of the gap material above pole P1 not covered by pole P2 up to zero 
throat. Then, ion mill about one micron of the excess material from pole 
P2 to achieve the desired thickness of pole P2. Alternatively, pole P2 
could be plated slightly thicker and the gap material could be removed by 
ion milling. As the ion milling progresses, the portion of pole P1 
underneath P2 that is not protected from the ion beam will be beveled at 
approximately 45 degrees due to the angle of the ion milling reaching that 
portion of pole P1. The width of poles P1 and P2 at the gap will also be 
equal. The result is a design for a recording head which reduces erase 
fringing while minimizing the amount of complex ion milling required. Due 
to the simplicity of the manufacturing process, a higher quality product 
is produced with less defective recording heads. In the preferred 
embodiment shown in FIG. 5, the ion milling time is reduced to about 
one-sixth of the time required for ion milling the geometry shown in FIG. 
3. 
An alternate method of making the thin film recording head of the present 
invention is to repeat the method described above except increase the 
thickness of pole P2 before ion milling. By increasing the thickness of 
pole P2, a longer duration of ion milling will be required. As pole P2 is 
being ion milled, the material of pole P1 that is not protected by pole P2 
will be ion milled further away from the gap. Thus, various designs of 
pole P1 are achieved by varying the thickness of pole P2 and the duration 
of the ion milling. 
Another alternate method of making the thin film recording head of the 
present invention is to repeat the method described above and add an 
additional step of removing the photoresist material on top of pole P1. 
Before the gap material is removed by the Hydrofluoric Acid, a Plasma-Ash 
process is used to remove the photoresist material above pole P1 not 
covered by pole P2 and past zero throat. Then, the ion milling process 
shapes pole P1 at the ABS and also removes some of the material from pole 
P1 beyond zero throat. As previously explained, the geometry of the head 
shown in FIG. 5 is the preferred embodiment. Such a configuration and the 
realization that such a configuration substantially reduces or eliminates 
erase fringing is one of the fundamental improvements of the present 
invention. In addition, removing additional material from pole P1 beyond 
zero throat while requiring additional ion milling time does result in a 
marginal increase in recording head performance over the configuration 
shown in FIG. 5 while still providing a significant improvement over the 
prior art. 
The preferred embodiment of the present invention describes a thin film 
recording head geometry which substantially reduces erase fringing and is 
easily manufactured. The scope of the present invention is intended to 
cover all variations and substitutions which are and become apparent from 
the above illustrative embodiment of the present invention.