Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
2002-12-31
2004-11-30
Rickman, Holly (Department: 1773)
Stock material or miscellaneous articles
Composite
Of inorganic material
C428S690000, C428S690000, C428S690000, C428S336000, C428S900000, C428S611000, C428S667000, C427S129000, C427S131000
Reexamination Certificate
active
06824896
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to the field of disc drive storage, and more particularly to magnetic recording media on directly textured glass substrates.
2. Description of the Related Art
Conventional disc drives are used to magnetically record, store and retrieve digital data. Data is recorded to and retrieved from one or more discs that are rotated at more than one thousand revolutions per minute (rpm) by a motor. The data is recorded and retrieved from the discs by an array of vertically aligned read/write head assemblies, which are controllably moved from data track to data track by an actuator assembly.
The three major components making up a conventional hard disc drive are magnetic media, read/write head assemblies and motors. Magnetic media, which is used as a medium to magnetically store digital data, typically includes a layered structure, of which at least one of the layers is made of a magnetic material, such as CoCrPtB, having high coercivity and high remnant moment. The read/write head assemblies typically include a read sensor and a writing coil carried on an air bearing slider attached to an actuator. This slider acts in a cooperative hydrodynamic relationship with a thin layer of air dragged along by the spinning discs to fly the head assembly in a closely spaced relationship to the disc surface. The actuator is used to move the heads from track to track and is of the type usually referred to as a rotary voice coil actuator. A typical rotary voice coil actuator consists of a pivot shaft fixedly attached to the disc drive housing closely adjacent to the outer diameter of the discs. Motors, which are used to spin the magnetic media at rates of higher than 10,000 revolutions per minute (rpm), typically include brushless direct current (DC) motors. The structure of disc drives is well known.
Magnetic media can be locally magnetized by a read/write head, which creates a highly concentrated magnetic field that alternates direction based upon bits of the information being stored. The highly concentrated localized magnetic field produced by the read/write head magnetizes the grains of the magnetic media at that location, provided the magnetic field is greater than the coercivity of the magnetic media. The grains retain a remnant magnetization after the magnetic field is removed, which points in the same direction of the magnetic field. A read/write head that produces an electrical response to a magnetic signal can then read the magnetization of the magnetic media
Magnetic media structures are typically made to include a series of thin films deposited on top of aluminum substrates, ceramic substrates or glass substrates.
FIG. 1A
illustrates a conventional magnetic media structure built on top of a glass substrate including a glass substrate
110
, a nickel-phosphorous (NiP) layer
115
, a seed layer
120
, a magnetic layer
125
and a protective layer
130
. The glass substrate
110
is typically a high quality glass having few defects such as those produced by OHARA Disk (M) SDN. BHD of Melaka, Malaysia The nickel-phosphorous (NiP) layer
115
is an amorphous layer that is usually electrolessly plated or sputtered onto the glass substrate
110
. The NiP layer is used to enhance both the mechanical performance and magnetic properties of the disk. The NiP layer enhances the mechanical properties of the disk by providing a hard surface on which to texture. The magnetic properties are enhanced by providing a textured surface which improves the magnetic properties including the orientation ratio (OR) as is further discussed below. However, the disadvantage of applying the NiP layer
115
is that it adds another step in the process of making magnetic media, which adds to the cost of the magnetic media.
Seed layer
120
is typically a thin film made of chromium that is deposited onto the NiP layer
115
and forms the foundation for structures that are deposited on top of it. Magnetic layer
125
, which is deposited on top of seed layer
120
, typically include a stack of several magnetic and non-magnetic layers. The magnetic layers are typically made out of magnetic alloys containing cobalt (Co), platinum (Pt) and chromium (Cr), whereas the non-magnetic layers are typically made out of metallic non-magnetic materials. Finally, protective overcoat
130
is a thin film typically made of carbon and hydrogen, which is deposited on top of the magnetic layers
125
using conventional thin film deposition techniques.
FIG. 1B
is a flow chart illustrating the prior art conventional method of making the conventional magnetic media structure discussed with reference to
FIG. 1A
above. First in step
140
a substrate
110
is prepared for deposition prior to cleaning. Next in step
145
the substrate is cleaned using conventional cleaning procedures that clean the substrate and prepares it for thin film deposition. In step
150
, the NiP layer
115
is deposited onto the substrate. Typically, the NiP layer
115
is plated onto the substrate, if the substrate is aluminum and sputtered on if the substrate is glass or ceramic. Next in step
155
the NiP layer
115
is mechanically textured. Next in step
160
the seed layer
120
is deposited using conventional thin film deposition techniques. In step
165
the magnetic layer or layers
125
are deposited using similar techniques as used in step
160
to deposit seed layer
120
. In step
170
, the protective overcoat layer
130
is deposited over the magnetic layers
125
. Typically, this protective overcoat layer
130
consists of carbon with hydrogen and is deposited directly after of the previous layer while the substrate remains under vacuum. The protective overcoat layer
130
is typically deposited by transferring the substrate with thin films, while being kept under vacuum, to an adjacent chamber that is isolated from the chambers previously used to deposit films. Protective overcoat layer
130
is typically deposited in an isolated chamber because reactive gasses containing hydrogen or nitrogen can be used in the deposition process. Finally in step
175
the vacuum deposition process ends by moving the conventional media structure into a load lock and unloading the media structure from the vacuum chamber.
Generally, macroscopic in-plane magnetic anisotropy is induced when magnetic recording media are sputtered on mechanically textured NiP coated disk substrates. In such case, the remnant moment (M
rt
) is higher in the circumferential direction than in the radial direction. The orientation ratio OR
MRT
is defined as the ratio of the measured M
rt
in the circumferential direction to the measured M
rt
in the radial direction. Media with OR
MRT
>1 is called oriented media and media with OR
MRT
=1 is called isotropic media. One way of achieving orientated media on glass substrates
110
, is to mechanically texture the NiP layer
115
before films are sputtered onto them as was discussed with reference to
FIG. 1B
above However, this procedure of depositing a NiP layer
115
onto the glass substrate
110
and mechanically texturing the NiP layer
115
significantly increases the cost of making magnetic media. Magnetic recording media sputtered directly on glass substrates are usually isotropic (OR
MRT
=1).
The advantages of oriented media is that they have higher thermal stability and better recording performance such as narrow pulse width and low media noise compared to isotropic media. However, the disadvantages of making oriented media on glass substrates are the additional cost and processing which is associated with depositing the NiP layer
115
and consequently texturing the NiP layer.
There exists a particular need for a magnetic recording media comprising an alternate substrate, such as glass or ceramic, which exhibits OR
MRT
>1 and is suitable for high aerial density recording application. Therefore what is needed is a system and method that produces oriented media (OR
MRT
>1) having high coercivity and high SMNR on glass substrate
Freeman Eric Steck
Harkness Samuel Dacke
Hua Kien Vinh
Lee Li-Lien
Castillo Jesus Del
Minisandram Raghunath S.
Rickman Holly
Seagate Technology LLC
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