Electrostatic slider fly height control

Details Electrostatic slider fly height control Electrostatic slider fly height control

2001-12-11

2004-08-10

Hudspeth, David (Department: 2651)

Dynamic magnetic information storage or retrieval

Automatic control of a recorder mechanism

Controlling the head

Reexamination Certificate

active

06775089

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a disc drive system. In particular, the present invention relates to an improved slider design that provides increased control of slider fly height in a disc drive system.
Disc drive systems are well known in the art and comprise several discs, each disc having concentric data tracks for storing data. The discs are mounted on a spindle motor, which causes the discs to spin. As the discs are spun, a slider is positioned above a data track on the disc by moving an actuator arm on which the slider is suspended. The actuator arm is moved using a large scale actuator motor, such as a voice coil motor. A transducing head carried by the slider is used to read from or write to a data track on the disc.
In a typical disc drive system, as the disc rotates, the disc drags air in a “wind” along the surface of the slider. Due to this windage, the slider lifts and “flies” a small distance above the disc surface. The distance between the slider and the rotating disc is termed the “fly height”.
The amount of data that can be stored on a disc is a measure of the areal recording density of the disc. In most applications, such as desk top or lap top computers, there is a continual desire to increase areal recording density on discs. Areal recording density is inversely proportional to the fly height of the transducing head. Therefore, there is a constant pressure to minimize and control fly height of the transducing head to afford higher areal recording density.
There have been many attempts to minimize and control fly height, to varying degrees of success. Often, attempts at minimizing fly height are very expensive to manufacture and do not address all of the variables that adversely affect fly height. These variables include atmospheric pressure, curvature or roughness of the disc surface, mechanical shock and vibration, and variation in the aerodynamics of the slider due to change in the orientation and position of the slider relative to the rotating disc. Fly height of the slider is also affected by thermal pole tip recession, which manifests itself in sliders constructed of commonly used materials such as silicon or an Al
2
O
3
/TiC composite as a protrusion of the pole tip at higher temperatures due to differential thermal expansion. The protrusion of the pole tip can reduce the fly height margin to below safe levels and possibly even cause catastrophic failure of the disc drive system.
Traditionally, several methods of fly height control have been employed. For example, a preload force is often applied to the slider to counteract the air bearing force. The magnitude of the preload force is designed to be in equilibrium against the air bearing force at a desired fly height, positioning the transducing head as close as reliably possible to the moving disc surface. Attempts have also been made to minimize and control fly height by adjusting the aerodynamic properties of the actuator arm and by adjusting the geometry of the slider assembly. Other attempts involve the use of micro-actuators to provide fine position control of the slider relative to the disc.
In the past, electrostatic fly height control has also been proposed. Applying a voltage to the slider creates an electrostatic potential in the slider which results in an attractive force between the slider and the disc. However, traditional methods of electrostatic fly height control have had only limited success. The slider becomes increasingly difficult to control as fly height is decreased because the electrostatic attractive force between the slider and the disc increases very rapidly as more voltage is applied. As a result, typical disc drive systems employing electrostatic control of fly height can only reduce fly height in a stable manner by about 30%. Applying more voltage to reduce fly height beyond that point risks a sudden and disastrous crash, with the slider suddenly being forced into full contact with the disc.
Thus, there is a need in the art to increase stability and control of the slider at low fly heights, thereby increasing areal recording density and increasing the performance of the disc drive system.
BRIEF SUMMARY OF THE INVENTION
The present invention is a design for a slider for use in a disc drive system and a method of electrostatically controlling the slider. The slider may be constructed of conductive or semi-conductive material. The slider contains a connection for applying a voltage and an actuation surface for providing electrostatic control. The slider also contains a transducing head, which may be located near the trailing edge of the slider and which may be encased in an insulating layer. The slider also contains a recessed area between the trailing edge and the actuation surface.
A voltage is applied to the slider that affects fly height of the slider by creating an electrostatic attraction force between the slider and the disc. By controlling voltage applied to the slider, it is possible to control the fly height as well, based on the electrostatic attraction between the slider and the disc. As voltage is increased, the electrostatic attraction between the slider and the disc increases, decreasing the fly height of the slider. The recessed area on the slider causes the majority of electrostatic attractive force between the slider and the disc to generate away from the trailing edge. As a result, the recessed area on the slider increases the stable range of electrostatic control, thereby providing increased control of the slider at lower fly heights.


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Lin, C. and Massaro, J., IBM Technical DIsclosure Bulletin, Electrostatically Loaded Slider Bearing, vol. 12, No. 7, Dec. 1969.

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