Reducing sensor temperature in magnetoresistive recording heads

Details Reducing sensor temperature in magnetoresistive recording heads Reducing sensor temperature in magnetoresistive recording heads

2000-07-14

2002-05-28

Evans, Jefferson (Department: 2652)

Dynamic magnetic information storage or retrieval

Head

Magnetoresistive reproducing head

Reexamination Certificate

active

06396670

ABSTRACT:

BACKGROUND OF THE INVENTION
Magnetoresistive recording heads are well known to be useful in reading back data from a magnetic media mass storage devices such as disk drives or magnetic tape drives. Popular designs include a standard giant magnetoresistive (GMR), vertical giant magnetoresistive (VGMR), advanced magnetic (AMR), vertical advanced magnetic recording (VAMR), and spin valve type heads. Typically, a magnetic read back sensor is used to detect a direction and amount of magnetic flux as a magnetic media passes by in close proximity to the sensor. This sensor is biased by a current which changes in direction and magnitude in the presence of a magnetic flux. Changes in magnetic field signals are sensed by the bias current and are correlated to meaningful data by a data processing device with access to the magnetic media mass storage device.
A basic design of a standard AMR or spin valve head (
FIG. 1A
) includes a sensor element
4
adjacent to an air bearing surface (“ABS”)
8
with electrical contacts
22
touching the sides of the sensor
4
. The sensor
4
lies between upper and lower shields
2
,
6
.
In contrast, a basic design of a vertical GMR head (
FIG. 1B
) includes a sensor element
4
comprising a front contact
9
adjacent to an ABS
8
, an optional bias winding
3
and a rear contact
5
. The vertical GMR sensor element
4
runs away from the ABS
8
between the front and rear contacts
9
and
5
. An upper metal shield
2
and a lower metal shield
6
surround the sensor element
4
and bias winding
3
. The lower recessed region
21
is optional, but is known to improve the magnetic efficiency of the device. Another design generally referred to as flux guide heads (FIG.
2
), comprises two contacts
14
between a front flux guide
16
and a rear flux guide
15
. The flux guides
15
,
16
are bounded by an upper metal shield
2
and a lower metal shield
6
.
A problem that is encountered in all AMR and GMR heads, including vertical GMR and Flux Guide heads is the heating of the sensor element due to Joule heating from the bias current. Joule heating is the resultant heating on matter in which current flows from energy loss due to electron-ion collisions. The resultant power loss is:
P=I
b
2
R
se
,
where I
b
is the bias current through the sensor element and R
se
is the resistance of the sensor element. In the case of most standard AMR and GMR-spin valve type heads, much of the Joule heat is removed from the sensor via direct thermal conduction to metal shields through two half-gap insulators
19
,
21
,
23
. Half-gap insulator refers to the insulators between the MR/GMR element and the lower/upper shield respectively. The gap is the distance between the two shields. Normally, the insulator material is Al
2
O
3
, or any pin-hole free dielectric with an adequately high breakdown voltage, such as AlN, Si
3
N
4
, SiO
2
, or diamond-like carbon (DLC). These half gap insulators
19
,
21
,
23
can comprise a low thermal conductivity thermal path
7
(the width of the half-gap insulator regions
21
,
23
) of typically 100 Angstroms or more, that can significantly limit heat dissipation. Some cooling is realized by thermal radiation and convective cooling from the ABS
8
adjacent to the front sensor of the head to the recording medium as well as heat conduction out to the sides through the contacts
22
. However, performance and reliability of the head are limited by the temperature increase resulting from normal use of the sensor. In general, the head reliability decreases as it heats due to accelerated interdiffusion of GMR film layers. The result of overheating can have results ranging from signal loss to melting of the heads.
Vertical AMR and Vertical GMR read back heads experience even more severe Joule heating of the sensor. For optimum magnetic efficiency and high signal output, shield recesses
21
,
23
(
FIG. 1B
) are necessary. This design, however, increases the thermal paths
7
. As a result, the rate of heat extraction from the sensor
4
is reduced and the sensor
4
operates hotter than if there were no shield recesses. Because the sensor
4
is longer than a standard GMR sensor and has consequently higher resistance, the VGMR sensor with recessed shields will also operate hotter than a standard horizontal GMR sensor. In a typical vertical GMR design, a front contact
9
is sided by an upper metal shield
2
and lower metal shield
6
adjacent area comprising an ABS
8
. The part of the sensor
4
and front contact
9
that are adjacent to the ABS
8
are separated from the shields
2
,
6
by front half gaps
19
. A bias winding
3
, if present (it is optional), is set back from the front contact
9
and sided by the upper and lower metal shields
2
,
6
. A rear contact
5
may extend beyond the metal shields
2
,
6
and is connected to the front contact
9
via a vertical giant magnetoresistive sensor (“VGMR”)
4
that runs adjacent to the bias winding
3
and perpendicular to the ABS
8
. The recessed design causes the upper recessed metal shield
2
and lower recessed metal shield
6
to be spaced at a relatively large distance away from the sensor element
4
, separated by the recessed gap insulators
21
and
23
.
Whereas if the metal shields
2
,
6
were located in close proximity to the sensor, the shields could act as effective heat sinks, instead the shields are recessed, forming an increased area that is filled with a gap insulator
21
,
23
that inhibits heat dissipation. The vertical design also positions the heat-producing part of the element
4
including the bias winding
3
such that it is not exposed at the ABS
8
where it can radiate heat away.
VGMR heads are designed so that they have a much wider sensor-to-shield gap
7
in the region away from the ABS
8
in relation to the sensor-to-shield air gap
19
in close proximity to the ABS
8
. This wider gap
7
inhibits the inherent role of heat dissipater that the metal shields
2
,
6
would otherwise perform.
The wider gap from sensor to shield incorporated into the VGMR design is necessary to address considerations of magnetic flux propagation. In order to limit flux propagation, the VGMR type designs typically require that both the upper and lower metal shields be recessed to improve magnetic efficiency. The recess is required to ensure that magnetic flux from the media reaches the sensitive part of the VGMR sensor. The sensitive part, covered by the front contact
9
, generates no signal. Without recesses that start at the top of front contact
9
, all the flux leaks from the two shields
2
,
6
and lowers the signal output.
As a result, the buried portion of the sensor that lies within the wider gap
21
,
23
experiences more heat buildup than the sensor portion in the narrow gap
19
. The heat buildup is a direct result of the lessened thermal conductivity of the gap insulators
21
,
23
as compared to the metal shields
2
,
6
. The larger gap
21
,
23
between the sensor
4
and the heat sinking metal shields
2
,
6
results in a correspondingly longer thermal path
7
for removing a sensor's heat before the heat reaches the thermal sink of the shields
2
,
6
.
SUMMARY OF THE INVENTION
Accordingly this invention provides a method and apparatus for improved heat dissipation in a magnetoresistive recording head. Heat dissipation is improved by inclusion of a high thermal conductivity metal as a metal filler located between an upper and a lower metal shield and a sensor. A highly thermally conductive material might include an element metal such as aluminum or copper and should be specifically tailored to have a similar thermal expansion coefficient as the shield material. Moreover, the metal filler must be non-magnetic. In addition, to facilitate the magnetic efficiency of the head, recesses in the upper and lower shields are used.
One condition adding to the heating problem of the buried sensor is the long low thermal conductivity heat path between a sensor acting as a heat source and the upper and lower metal shields acting as a heat sink.

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