Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
1999-06-11
2001-12-11
Ometz, David L. (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
Reexamination Certificate
active
06330137
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to magnetic data storage systems, more particularly to magnetoresistive read heads, and most particularly to structures incorporating an insulating barrier, as well as methods for making the same.
Magnetic disk drives are used to store and retrieve data for digital electronic apparatuses such as computers. In
FIGS. 1A and 1B
, a magnetic disk data storage system
10
of the prior art includes a sealed enclosure
12
, a disk drive motor
14
, and a magnetic disk, or media,
16
supported for rotation by a drive spindle S
1
of motor
14
. Also included are an actuator
18
and an arm
20
attached to an actuator spindle S
2
of actuator
18
. A suspension
22
is coupled at one end to the arm
20
, and at its other end to a read/write head or transducer
24
. The transducer
24
typically includes an inductive write element with a sensor read element (which will be described in greater detail with reference to FIG.
2
). As the motor
14
rotates the magnetic disk
16
, as indicated by the arrow R, an air bearing is formed under the transducer
24
causing it to lift slightly off of the surface of the magnetic disk
16
, or, as it is termed in the art, to “fly” above the magnetic disk
16
. Alternatively, some transducers, known as “contact heads,” ride on the disk surface. Data bits can be read along a magnetic “track” as the magnetic disk
16
rotates. Also, information from various tracks can be read from the magnetic disk
16
as the actuator
18
causes the transducer
24
to pivot in an arc as indicated by the arrows P. The design and manufacture of magnetic disk data storage systems is well known to those skilled in the art.
FIG. 2A
depicts a magnetic read/write head
24
including a write element
28
and a read element
26
. The edges of the write element
28
and read element
26
also define an air bearing surface ABS, in a plane
29
, which can face the surface of the magnetic disk
16
of
FIGS. 1A and 1B
.
The write element
28
is typically an inductive write element. A write gap
30
is formed between an intermediate layer
31
, which functions as a first pole, and a second pole
32
. Also included in write element
28
, is a conductive coil
33
that is positioned within a dielectric medium
34
. As is well known to those skilled in the art, these elements operate to magnetically write data on a magnetic medium such as a magnetic disk
16
.
The read element
26
includes a first shield
36
, the intermediate layer
31
, which functions as a second shield, and a read sensor
40
that is located between the first shield
36
and the second shield
31
. A common type of read sensor
40
used in the read/write head
24
is a magnetoresistive (MR) sensor. A MR sensor (e.g., AMR or GMR) is used to detect magnetic field signals by means of a changing resistance in the read sensor. When there is relative motion between the MR sensor and a magnetic medium (such as a disk surface), a magnetic field from the medium can cause a change in the direction of magnetization in the read sensor, thereby causing a corresponding change in resistance of the read element. The change in resistance can then be detected to recover the recorded data on the magnetic medium.
While some read sensors operate in current-in-plane (CIP) mode, others operate in current-perpendicular-to-plane (CPP) mode.
FIG. 2B
is a perspective view of a read sensor
40
that operates in CPP mode. A bottom lead
42
is in electrical contact with a bottom layer
44
of the read sensor
40
, while a top lead
48
is in electrical contact with a top layer
46
of the read sensor
40
. While the top and bottom leads
48
,
42
are shown electrically insulated from the second and first shields
31
,
36
, respectively, they can alternatively be coincident, with the shields operating as leads.
A sensing current I is passed between the top and bottom leads
48
,
42
, and therefore passes substantially perpendicular through the read sensor layers
50
, including the top and bottom layers
46
,
44
. As with other MR read sensors, this sensing current is used in conjunction with changing resistance of the read sensor to detect data from nearby magnetic media. Various read sensors can be used in the CPP mode, with various layers and their combinations. For example, a spin valve read sensor can be used, various configurations and formations of which are known to those skilled in the art.
Increasing read performance is a function of increase of the signal &Dgr;V that can be detected across the read sensor
40
. In turn, the signal &Dgr;V detected from operation of the read sensor is a function of the sensing current I that is passed through the read sensor, and the sensor resistance change &Dgr;Rs during operation. More particularly, as is well know in the art, the signal &Dgr;V is essentially equal to the product of the sensing current I and the sensor resistance change &Dgr;Rs.
Spin valve sensors rely on the magneto tunneling effect, which is believed to be a result of the asymmetry in the density of states of the majority and minority energy bands in a ferromagnetic material. Thus, the sensor resistance, which is inversely proportional to the spin-polarized tunneling probability, depends on the relative magnetization orientations of the two electrodes on either side of an insulating barrier layer. In the parallel orientation there is a maximum match between the number of occupied states in one electrode and available states in the other. In the antiparallel configuration the tunneling is between the majority states in one electrode and minority states in the other. W. J. Gallagher, S. S. Parkin et al., J Appl. Phys. 81 (8) April 1997, p.3741-6.
To maximize the effectiveness of such an insulating barrier layer it is desirable to minimize any defects that could create shorting through the layer, which would render it substantially ineffective. The thickness T of the insulating barrier, measured along the current path, is also desired to be minimized while maintaining a barrier. It is also desirable to maintain a band gap on the order of about 1 eV to about 10 eV, where the band gap is a measure of the separation between the energy of the lowest conduction band and the highest valence band. Further, it is desirable to maximize the smoothness of the surface of the insulating barrier on which a succeeding layer is to be formed.
In the past, read sensor designs have included insulating barriers formed of alumina. Alumina insulating barriers can be formed by known methods, including deposition of aluminum metal by physical vapor deposition, evaporation, or ion beam deposition, for example. After such deposition, the aluminum can then be oxidized in O
2
plasma. Such processes can result in an alumina layer having a thickness T in the range of about 10 Å to about 50 Å, and a band gap in the range of about 1 eV to about 5 eV. While such thicknesses and band gap values may be adequate, unfortunately these processes and materials result in significant defects, and therefore significant probability of shorting.
Alumina and other materials formed by reactive sputtering can alternatively be used to form an insulating barrier. For example, hafnium oxide (HfO
2
), zirconium oxide (ZrO
2
), or tantalum oxide (Ta
2
O
5
) can be formed by reactively sputtering from a metallic target using an RF or DC magnetron. However, while these oxides may be able to exhibit satisfactory band gap values and thicknesses, they still may be likely to include defects that may result in shorting. Further, each of these materials can be adversely affected by techniques that may be used in later processing operations of the read element, read/write head, or slider. For example, these materials may be soluble in one or more of the developers or strippers used in conjunction with photoresistive materials used during fabrication. Agents such as fluorine or chlorine would need to be used in the RIE processing, however these may cause undesirable corrosion of other device elements. Of cou
Knapp Kenneth E.
Rottmayer Robert E.
Ryan Francis
Carr & Ferrell LLP
Ferrell John S.
Hayden Robert D.
Ometz David L.
Read-Rite Corporation
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