Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
1997-12-10
2001-02-13
Evans, Jefferson (Department: 2754)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
Reexamination Certificate
active
06188549
ABSTRACT:
TECHNICAL FIELD
The present invention relates to electromagnetic transducers or heads, and particularly to such transducers which employ a magnetoresistive effect for sensing signals.
BACKGROUND
The employment of magnetoresistive (MR) elements as sensors for electromagnetic transducers has led to improved performance of heads for disk and tape drives. As is well known, the resistance of an M element varies according to the magnetic field impinging upon the element, so that flowing an electric current through the element can be used to determine that magnetic field by measuring the change in resistance.
While bulk materials may exhibit some MR effect, such effects generally become more pronounced as an element becomes smaller relative to the applied electrical and magnetic flux. Thus it is known that films formed of materials such as Permalloy, which is an alloy of nickel and iron having a high permeability and low coercive force, are useful as sensors for heads when the film thickness is less than about 500 Å. Even thinner films exhibit quantum mechanical effects which can be utilized in devices such as spin valves for MR sensing. Higher storage density associated with smaller bit size also requires smaller MR elements.
Generally speaking, the thinner the film used for MR sensing, the more important that the film have a uniform thickness and structure. As such, the material surface or template upon which the film is formed is important. Heads for hard disk drives commonly include an MR sensor in a gap region located between or adjacent to a pair of magnetically permeable layers that are used for writing signals onto a disk. The conventional material forming the gap is alumina (Al
2
O
3
), which is known to be easy to form and work with, and which provides suitable template for forming thin MR films. Alumina, however, has a strong affinity for moisture and tends to form a columnar molecular structure, which is porous, both of which can undermine the quality and integrity of an adjoining MR sensor.
MR elements are also sensitive to a change in temperature, as such a change typically leads to a change in resistance, which can be misinterpreted as a change in magnetic flux or false signal. Thermal asperities caused by ephemeral contact between a head and disk, for example, can cause such signal errors, and for this reason it can be advantageous to thermally isolate an MR sensor. Higher magnetoresistance also generally implies increased heat generation by an MR film, however, and thus greater temperature increases during operation of the sensor. This higher operating temperature can also be deleterious to reading of signals.
SUMMARY OF THE INVENTION
The present invention employs an unconventional amagnetic material layer adjoining an MR sensor, the amagnetic layer designed to be thermally-conductive as well as electrically-insulative. Importantly, the amagnetic layer also provides a favorable surface upon which to form the delicate MR sensor. The amagnetic material is preferably an amorphous, solid oxide or nitride, such as AlN, SiC, SiO
2
, Si
3
N
4
, BeO or Ta
2
O
5
. These compounds can be formed by semiconductor processing techniques and are less prone than alumina to damage during the processing of other layers. Formation of these compounds into amorphous layers provides an advantageous template for creation of MR films having a thickness as little as a few atomic layers. These layers are also dense and impervious to water or oxygen, common contaminants to MR elements.
The amagnetic nature of these materials is in sharp contrast to the adjoining MR element, allowing the materials to be employed as gap layers. The materials also have similar coefficients of thermal expansion to that of the delicate MR sensor, so that changes in temperature during formation or operation do not lead to excessive stress or rupture of the sensor. These materials also may have a higher breakdown voltage than alumina and are less porous, reducing the possibility of shorting the sensor or damage from electrostatic discharge (ESD). The imperviousness of these materials to electrical shorting affords the formation of very thin gap layers, which can improve the resolution of the MR sensor, and also typically affords greater heat conduction to nearby heat-sink layers. Due to this symbiotic combination of attributes, these materials are used as high-performance gap layers.
The use of high-performance gap layers can be in a simple MR sensor employing permanent magnet or antiferromagnetic pinning, canted current bias or soft adjacent underlayer for orienting the magnetization of the sensor to provide a useful signal. The high-performance gap layers can instead be used with an MR sensor employing multiple, thinner films, such as a giant-magnetoresistive (GMR) sensor, which has greater need for draining heat from the sensor. Even more advantageous is the use of the high-performance gap layers with a spin-valve (SP) sensor, which can require extremely thin films that generate a high signal and thus a high proportion of heat. The quantum mechanical operation of SP sensors may be deleteriously affected by excess heat, and thus can benefit from the thermal conductivity of the high-performance gap layers. Depending upon thickness and other criteria, the formation of the high-performance gap layers may be accomplished via ion beam deposition or magnetron sputtering for at least the most critical layers.
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Evans Jefferson
Lauer Mark
Read-Rite Corporation
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