Narrow track width magnetoresistive sensor and method of making

Details Narrow track width magnetoresistive sensor and method of making Narrow track width magnetoresistive sensor and method of making

2000-06-02

2004-03-02

Ometz, David L. (Department: 2653)

Dynamic magnetic information storage or retrieval

Head

Magnetoresistive reproducing head

Reexamination Certificate

active

06700759

ABSTRACT:

BACKGROUND
A key measure of the performance of an electromagnetic information storage system is the areal density. The areal density is the number of data bits that can be stored and retrieved in a given area. Areal density can be computed as the product of linear density (the number of magnetic flux reversals or bits per unit distance along a data track) multiplied by the track density (the number of data tracks per unit distance). As with many other measures of electronic performance, areal densities of various information storage systems have increased greatly in recent years. For example, commercially available hard disk drive systems have enjoyed a roughly tenfold increase in areal density over the last few years, from about 500 Mbit/in
2
to about 5 Gbit/in
2
.
Various means for increasing areal density are known. For instance, with magnetic information storage systems it is known that storage density and signal resolution can be increased by reducing the separation between a transducer and associated media. For many years, devices incorporating flexible media, such as floppy disk or tape drives, have employed a head in contact with the flexible media during operation in order to reduce the head-media spacing. Recently, hard disk drives have been designed which can operate with high-speed contact between the hard disk surface and the head.
Another means for increasing signal resolution is the use of magnetoresistive (MR) or other sensors for a head. MR elements may be used along with inductive writing elements, or may be independently employed as sensors. MR sensors may offer greater sensitivity than inductive transducers but may be more prone to damage from high-speed contact with a hard disk surface, and may also suffer from corrosion, so that conventional MR sensors are protected by a hard overcoat.
Recent development of information storage systems having heads disposed within a microinch (&mgr;in) of a rapidly spinning rigid disk while employing advanced MR sensors such as spin-valve sensors have provided much of the improvement in areal density mentioned above. Further increases in linear density and track density have been limited by constraints in reducing the size of transducer features that interact with the media in recording and reading magnetic patterns. For example, inductive pole-tips and MR sensors are conventionally defined by photolithography, which limits a minimum track width for which magnetic patterns on the media can be written or read.
FIG. 1
(Prior Art) depicts a design for a thin film head
50
as would be seen from a media from which the head is to read magnetic signals. The head contains a spin-dependent tunneling magnetoresistive sensor
52
formed in a series of layers between first and second magnetically permeable shields
55
and
58
which also serve as leads for the sensor, as described in U.S. Pat. No. 5,898,548, incorporated herein by reference. The sensor and adjacent layers include a template layer
64
that helps with formation of a subsequently deposited antiferromagnetic layer
66
. The antiferromagnetic layer
66
stabilizes the magnetic moment of a pinned ferromagnetic layer
68
. An alumina (Al
2
O
3
) tunneling layer
70
separates the pinned ferromagnetic layer
68
from a free ferromagnetic layer
72
that has a magnetic moment that can rotate in the presence of a magnetic field from the media. A cap layer
75
of tantalum (Ta) is formed to protect the sensor from damage, and electrically conductive spacer layers
60
and
62
separate the sensor from the shields.
Formation of the above-mentioned elements begins by depositing the first shield
55
, spacer layers
60
and
62
, sensor layers
64
,
66
,
68
,
70
and
72
, and cap layer
75
. After depositing the spacer, sensor and cap layers on the first shield
55
, a photoresist
77
is lithographically patterned and the sensor is defined by ion milling material not protected by the resist. A width W
0
of the sensor essentially corresponds to the width of the resist, although both may be thinned during the ion milling process. Alumina
88
is deposited to fill in around the sensor and a pair of hard bias layers
78
and
80
are formed to bias free layer
72
, leaving a thick deposit of material atop the resist
77
and pointed projections
82
and
84
along the sides of the resist. The resist is chemically removed, which frees the material atop the resist
77
, and the projections are broken off during chemically/mechanical polishing (CMP), after which the spacer
62
and second shield layer
58
are formed. An effective length L
0
of the sensor for linear resolution is the spacing between the first shield
55
and second shield
58
, which may be less than 0.1 micron.
Control of the ion milling for thinning the sensor
52
becomes difficult for widths W
0
that are less than 0.5 micron, and errors in mask definition increase with mask thickness, but thicker masks are useful to over-etch the sensor to attempt to create spacer
60
out of shield
55
. Therefore it has been difficult for such a prior art sensor to have a length-to-width ratio greater than ⅕. Moreover, forming spacer
62
from shield
58
requires the thin cap
75
to protect the sensor from damage during CMP, such as puncturing the cap with the broken off projections
82
and
84
. Contamination such as wash chemicals or alumina from the CMP may also degrade the performance of the conductive spacer
62
. While lithographic definition can be improved somewhat by using electron beam, X-ray or deep ultra violet lithography, such techniques are extremely capital intensive and require long lead times for equipment, development and facilities construction. Moreover, techniques such as X-ray and electron beam lithography are used to form individual sensors as opposed to more efficient simultaneous definition of all sensors on a wafer surface.
SUMMARY
In accordance with the present invention, a magnetoresistive (MR) sensor is defined by an electrically conductive sidewall layer that is oriented substantially perpendicular to most if not all other layers of the sensor, allowing the sensor to be made much thinner than conventional sensors. Such a thinner sensor can read narrower media tracks without interference from neighboring tracks, affording higher track density. The novel sidewall layer may be magnetically permeable and serve as an extension of a shield for the sensor, improving linear resolution and density. For this embodiment, an exact shield-to-shield spacing can be created based upon the sensor length, which is simply the sum of the accurately deposited sensor layers. Similarly, errors in sensor thickness can be much less than standard error tolerances for conventional sensors. The connection of the shields and the sensor can be tailored to create a device having a shape that is preferred for durability and yield as well as for electrical and magnetic considerations. Another advantage is that the sensor can be formed to a narrow width by mass production along with perhaps thousands of other sensors on a wafer, by employment of relatively inexpensive tools and processes. For conciseness this summary merely points out a few salient features in accordance with the invention, and does not provide any limits to the invention, which is defined below in the claims.


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Karpov et al., “Patterning of Vertical Thin Film Emitters in Fi

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