The present invention relates to disc storage systems for storing information. More particularly, the present invention relates to an improved disc drive slider design that includes pads having a contact surface that reduces stiction and dynamic friction between the slider and a surface of a disc.
Disc drives of the xe2x80x9cWinchesterxe2x80x9d and optical types are well known in the industry. Such drives use rigid discs, which are coated with a magnetizable medium for storage of digital information in a plurality of circular, concentric data tracks. The discs are mounted on a spindle motor, which causes the discs to spin and the surfaces of the discs to pass under respective hydrodynamic (e.g. air) bearing disc head sliders. The sliders carry transducers, which write information to and read information from the disc surfaces.
An actuator mechanism moves the sliders from track-to-track across the disc surfaces of the discs under control of electronic circuitry. The actuator mechanism includes an actuator arm and a suspension assembly. The slider is coupled to the suspension assembly through a gimbaled attachment. The suspension provides a load force to the slider which forces the slider toward the disc surface.
The slider includes a bearing surface, which faces the disc surface. As the disc rotates, the disc drags air under the slider and along the bearing surface in a direction approximately parallel to the tangential velocity of the disc. As the air passes beneath the bearing surface of the slider, air compression along the airflow path causes the air pressure between the disc and the bearing surface of the slider to increase, which creates a hydrodynamic lifting force that counteracts the load force and causes the slider to lift and xe2x80x9cflyxe2x80x9d in close proximity to the disc surface and enable the transducing head carried by the slider to perform read and write operations. The gimbaled attachment to the suspension assembly allows the slider to pitch and roll while following the topography of the disc.
Demands for increased disc storage capacity have led to lower slider fly heights and smoother disc surfaces. Unfortunately, the development of ultra-low flying sliders is impaired by a phenomenon called stiction. Stiction is caused by static friction and viscous sheer forces which cause the slider to stick to the disc surface after periods of non-use. Stiction can be overcome by the spindle motor provided that sufficient torque can be produced. However, the slider and/or the disc can be damaged when the slider is freed from the disc surface. In addition, dynamic friction between the disc surface and the slider can also cause problems in the form of reduced modulation on the read and write signals produced by the transducers.
Contact start/stop (CSS) disc drives operate with the slider in contact with the disc surface during start and stop operations when there is insufficient disc rotational speed to maintain the bearing that allows the slider to fly. To alleviate stiction problems, some CSS disc drives provide a dedicated landing zone near the inner diameter of the disc by generating, in a controlled fashion, asperities or texture, on the disc surface. The texture acts to reduce the area of contact at the slider-disc interface. Although this solution reduces the likelihood of disc drive failure due to stiction, there is also a reduction in the area of the disc surface that can be used for data storage. Furthermore, the presence of the asperities on the media surface can enhance the chance of slider-media contact during operation and thereby sets the limit to the true attainment of ultra-low flying sliders.
Another method of alleviating problems with stiction and dynamic friction is to include pads on the bearing surfaces of the slider. The pads act to reduce the area of contact with the disc surface and thereby reduce the stiction and dynamic friction that is encountered. Such pads are typically formed of diamond-like carbon (DLC). Unfortunately, DLC pads alone have been shown to lead to stiction and dynamic friction levels above reliability limits in systems using ultra high areal density interfaces which require the use of extremely smooth disc surfaces (e.g. Ra less than 3A).
Another method of alleviating stiction problems associated with CSS disc drives is disclosed in U.S. Pat. No. 5,991,118, which issued to Kasamatsu et al. The Kasamatsu Patent modifies the pads of a slider by etching the contact surface of the pads to thereby further reduce the contact area between the slider and the disc surface. The etched pattern on the pad has a depth that is less than the thickness of the pad. As the etched portion of the pad wears, the texture formed on the contact surface by the etched pattern deteriorates until it is completely worn away. Once the etched surface is eliminated, the slider acts in the same manner as the padded slider described above. As a result, this method will ultimately lead to stiction and dynamic friction levels that are above reliability limits in systems using ultra high aerial density interfaces.
Yet, another method for reducing problems caused by stiction is to use a ramp load or ramp load/unload disc drive. Ramp load disc drives eliminate the need of having to xe2x80x9cparkxe2x80x9d the slider on the disc surface by using a ramp, from which the slider is loaded above the disc surface and unloaded from the disc surface. The ramp is generally adapted to hold the slider by the suspension and is typically located adjacent the outer diameter of the disc. Prior to shutting the drive down, the actuator mechanism unloads the flying slider from the disc surface by rotating the suspension onto the ramp. Once the slider is unloaded, the disc is allowed to slow its rotational velocity from the full operating speed and the drive can be shut down. At start up, the actuator mechanism delays loading the slider onto the disc surface until the rotational velocity of the disc reaches the full operating speed. Although ramp load disc drives appear to be a solution to many of the problems associated with CSS drives, such as the need for a dedicated landing zone, ramp load disc drives have their drawbacks.
One problem that is encountered in ramp load disc drives is that the slider can contact the disc surface during ramp load operations when the required air bearing beneath the slider is not sufficiently formed. This contact is undesirable due to the possibility of damaging the disc surface and/or the slider, which could result in data loss and disc drive failure. One partial solution to this is to provide a dedicated loading zone at the outer diameter of the disc surface where no data is written. Unfortunately this solution decreases in the effective data storage area of the drive and does not solve the problem of potential damage to the slider. Ramp load disc drives can also encounter problems with stiction. This can occur, for example, when power to the disc drive is interrupted while the slider is flying over the disc surface or when the suspension is knocked off the ramp.
There exists a need for an improved disc drive slider design that reduces stiction and dynamic friction between the slider and the disc surface to provide reliable operation with ultra-smooth disc surfaces while further reducing the likelihood of damage caused by contact between the slider and a disc surface.
The present invention is directed to a disc drive slider that solves the problems discussed above. The slider includes a slider body and a rail formed on the slider body. The rail has a bearing surface that faces a surface of a disc. A textured portion is formed on the bearing surface of the rail. A pad is deposited on the textured portion and operates to reduce stiction, dynamic friction, and the likelihood of damage to the slider or the disc surface due to contact therebetween.