METHOD AND APPARATUS DETECTING BASE LINE POPPING NOISE IN A...

Details METHOD AND APPARATUS DETECTING BASE LINE POPPING NOISE IN A... METHOD AND APPARATUS DETECTING BASE LINE POPPING NOISE IN A...

2002-08-22

2004-12-07

Le, N. (Department: 2862)

Electricity: measuring and testing

Magnetic

Magnetic information storage element testing

C324S212000, C360S025000, C360S031000

Reexamination Certificate

active

06828784

ABSTRACT:

TECHNICAL FIELD
This invention relates to detection of base line popping noise by a read head and the stabilization of the magnetic domain of that read head for a merged type magneto-resistive head used in an assembled disk drive, including GMR (Giant Magneto-Resistive) read-write heads.
BACKGROUND ART
Disk drives are an important data storage technology. Read-write heads are one of the crucial components of a disk drive, directly communicating with a disk surface containing the data storage medium. This invention detects base line popping and corrects this and other Electro-Static Discharge (ESD) damage to the pinned layer of the read head in an assembled disk drive. Detection reconfigures and uses thermal asperity detection circuitry included in the channel interface. Correction uses a write current applied to the write inductive coil and a read current bias applied to the read head.
FIG. 1A
illustrates a typical prior art high capacity disk drive
10
including actuator arm
30
with voice coil
32
, actuator axis
40
, suspension or head arm
50
with slider/head unit
60
placed among the disks.
FIG. 1B
illustrates a typical prior art high capacity disk drive
10
with actuator
20
including actuator arm
30
with voice coil
32
, actuator axis
40
, head arms
50
-
56
and slider/head units
60
-
66
with the disks removed.
Since the 1980's, high capacity disk drives
10
have used voice coil actuators containing
20
,
30
,
32
,
40
,
50
,
52
,
54
,
56
,
60
,
62
,
64
, and
66
to position their read-write heads over specific tracks. The heads are mounted on head sliders
60
-
66
, which float a small distance off the disk drive surface when in operation. Often there is one head per head slider for a given disk drive surface. There are usually multiple heads in a single disk drive, but for economic reasons, usually only one voice coil actuator.
Voice coil actuators are further composed of a fixed magnet actuator
20
interacting with a time varying electromagnetic field induced by voice coil
32
to provide a lever action via actuator axis
40
. The lever action acts to move head arms
50
-
56
positioning head slider units
60
-
66
over specific tracks with speed and accuracy. Actuator arms
30
are often considered to include voice coil
32
, actuator axis
40
, head arms
50
-
56
and head sliders
60
-
66
. Note that actuator arms
30
may have as few as a single head arm
50
. Note also that a single head arm
52
may connect with two head sliders
62
and
64
.
Merged type heads possess different components for reading and writing, because the magneto-resistive effect only occurs during reading. A merged type head typically includes a thin film head and a spin valve sensor. The primary use of the thin film head is in the write process. The spin valve sensor is used for reading.
Merged Magneto-Resistive (MR) heads have several advantages over earlier approaches, using a single component, for both read and write. Earlier read-write heads were a study in tradeoffs. The single component, often a ferrite core, can increase read sensitivity with additional windings around the core. However, these added windings make the ferrite core write less efficiently.
Introduced in the 1990's, merged heads brought significant increases in areal density. A merged type head reads the disk surface using a spin valve, containing a conductive thin film, whose resistance changes in the presence of a magnetic field. By separating the functions of writing and reading, each function can be optimized further than would be possible for the older read-write heads. For all the improvement that merged heads bring, there remain problems. However, before discussing these problems, consider first how and what controls these devices in contemporary disk drives.
FIG. 2A
illustrates a simplified schematic of a disk drive controller
1000
controlling an analog read-write interface
220
, write differential signal pair (w+and w−), and the read differential signal pair (r+and r−) communicating resistivity found in the spin valve within MR read-write head
200
of the prior art.
Analog read-write interface
220
frequently includes a channel interface
222
communicating with pre-amplifier
224
. Channel interface
222
receives commands setting at least the read_bias, write_bias, and thermal asperity detection threshold(s), denoted as TA_threshold in FIG.
2
A.
Various disk drive analog read-write interfaces
220
may employ either a read current bias or a read voltage bias. By way of example, the resistance of the read head is determined by measuring the voltage drop (V_rd) across the read differential signal pair (r+and r−) based upon the read bias current setting read_bias, using Ohm's Law.
Most disk drives found in the prior art contain a Thermal Asperity Detection (TAD) signal as shown in FIG.
2
A. The Analog read/write interface
220
generates TAD, which is sent to the embedded disk controller
1000
. The embedded disk controller
1000
of the prior art contains a computer
1100
interacting
1122
with a memory
1120
. The memory
1120
contains the prior art program system
1200
.
FIG. 2B
illustrates a suspended head slider
60
containing the MR read-write head
200
of the prior art.
FIG. 2C
illustrates a perspective view of merged read-write head
200
from
FIG. 2B
including write inductive head
202
and magnetoresistive read head (or spin valve)
204
of the prior art.
FIG. 2D
illustrates a simplified cross section view of spin valve
204
with a region
206
composed of multiple layers forming the active region of spin valve
204
of
FIG. 2C
of the prior art.
FIG. 2E
illustrates a more detailed cross section view of region
206
of
FIG. 2D
, a typical GMR spin valve of the prior art.
Region
206
contains Anti-FerroMagnetic (AFM) exchange film
208
deposited on pinned Ferro-Magnetic (FM) layer
210
, over a copper (Cu) spacer layer
212
in turn deposited over free layer
214
on top of under layer
216
as typically found in a GMR spin valve of the prior art.
A GMR sensor is usually fabricated as follows: AFM layer
208
primarily composed of PtMn (Platinum Manganese). Pinned FM layer
210
is primarily composed of Co (Cobalt) NiFe (permalloy). The free layer
214
is primarily composed of NiFe permalloy. Under layer
216
is often composed primarily of Tantalum (Ta).
There is a distribution blocking temperature between layers
208
and
210
. When the temperature of spin valve
204
exceeds the distribution blocking temperature, the exchange coupling between AFM layer
208
and FM pinned layer
210
vanishes.
During the manufacture and handling of spin valve
204
, the magnetization of pinned layer (FM layer
210
) may be reversed or rotated by 180 degrees due to an ESD event. The magnetization of the free layer may also be altered by an ESD event.
Note that the entire spin valve
204
is vertically located between shields S
1
and S
2
of
FIG. 2C
as will be illustrated in
FIGS. 3A and 3B
.
FIG. 2F
illustrates normal magnetization of a spin valve read head as well as magnetization damage from ESD events as known in the prior art.
The AFM layer
208
will typically have a magnetization direction
300
. Pinned layer
210
will normally have magnetization direction
310
, but after one or more ESD events, may have a magnetization direction such as indicated by
312
or
314
. The Cu spacer layer
212
is not specifically relevant in this discussion and is not illustrated here. Free layer
214
normally has a magnetization direction
320
and after damage from one or more ESD events, may have an altered magnetization direction as indicated by
322
.
Normally, AFM layer
208
and pinned layer
210
have essentially parallel magnetization directions and free layer
214
is magnetized essentially perpendicular to layers
208
and
210
. Operation of the spin valve read head
204
depends upon these directional relationships.
FIG. 2G
illustrates an even more detailed cross section view of region
206
of
FIGS. 2D and

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