Photocatalytic device for disk drive contamination reduction

Details Photocatalytic device for disk drive contamination reduction Photocatalytic device for disk drive contamination reduction

2000-10-12

2002-08-13

Tupper, Robert S. (Department: 2652)

Dynamic magnetic information storage or retrieval

Record transport with head stationary during transducing

Disk record

Reexamination Certificate

active

06433957

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates generally to hard disk drives, and more particularly, to the reduction of contamination in hard disk drives.
BACKGROUND OF THE INVENTION
The internal environment of a modern computer hard disk drive (HDD) is critical to its function. The so-called head-disk interface (HDI) or area between the “head” which holds the reading and writing elements and the disk surface is very susceptible to contamination because the gap (height at which the head flies above the disk) is so small. The amount of data that can be stored on a disk is proportional to this gap. In present designs the gap is less than 30 nanometers (30×10
−9
meters). To allow this, the disks also must be very smooth. Most present designs require the head to land on the disk when the disk drive is shut off. Upon start up, it must easily lift off the disk and leave no residue or damage behind.
Liquid or gaseous contamination can cause failure by several modes:
The sticking of the head to the disk, usually due to vapor from liquids or low melting solids, is especially intractable in the disk drive industry.
Corrosion of the disks can roughen the surface; corrosion of the heads can affect electrical performance.
The fly height can be impacted by build-up of liquid or solid residue on the head, making data reading and writing unreliable.
Vapor concentrations as low as parts per billion of some common chemicals can cause catastrophic failure by one of these means. Changes in HDD technology such as lower flying heights, smoother disk surfaces, and lower power consumption by the spindle motor have all contributed to the greater sensitivity of new designs to these problems. Numerous schemes to minimize the hazard have been executed, and all have shortcomings as evidenced by the fact the HDI failures are a major limit to disk drive reliability.
One scheme common to almost all disk drives is to limit the use of materials inside the HDD known to “outgas” or generate vapors under operating conditions. This has been partly successful but notable problems are:
No other industry and hence no piece part vendor has knowledge of the sensitivity of this issue in the HDD, so subcomponent manufacturers cannot always provide adequate materials.
Testing methods are usually not as sensitive to contamination as is the HDI and small percentage failures can be very costly in terms of lost business.
Increasing sensitivity of advanced designs has meant that previously acceptable materials can result in failure when used for new designs.
Cost of well-controlled materials is much higher than less controlled materials. Market forces to reduce cost encourage the use of marginally acceptable materials (adhesives, plastics, and contaminated parts).
Common “dirt” such as hydrocarbon oils and silicones must be removed by careful and expensive cleaning processes.
Some necessary components are intrinsically vapor generating (e.g., bearing grease).
Another commonly used scheme has been to design the drive to leak with respect to the outside environment, ensuring that vapors from internal components are continuously diluted with fresh air. Obviously this scheme will fail if the outside environment, which is beyond the control of the HDD manufacturer, contains a harmful vapor or a material which in excess causes reliability problems (humidity is the best example).
A third commonly used scheme is to include a sorbent or adsorbent material, e.g., activated charcoal, inside the HDD. This is highly beneficial but demonstrably limited in its success. The sorbent is necessarily limited in its capacity for contaminants; it will eventually become saturated if continuously exposed. Also, the principal of sorption, whether physical or chemical, is reversible to varying degrees. Contaminants adsorbed at one temperature will be desorbed as the temperature rises. The present invention provides a solution to this and other problems as it comprises a device for purifying the internal atmosphere of an HDD.
SUMMARY OF THE INVENTION
The present invention comprises an assembly that includes a photocatalytic material and a device for activating photocatalytic material.
In accordance with one embodiment of the invention, an assembly of appropriate size and shape for mounting within a sealed or semi-sealed hard disk drive (HDD) is provided. More specifically, a photocatalytic surface is provided in close proximity or in contact with a light source which may be utilized as a means for activation.
The photocatalytic surface is preferably titanium dioxide (TiO
2
); it may be other metal oxide catalysts that can be photochemically activated such as zinc oxide (ZnO).
The invention comprises an assembly that contains a photocatalytic material and a means for activating thereof. The assembly is of appropriate size and shape for mounting within a sealed or semisealed HDD. The catalytic activity of the photocatalytic material is engineered to cause chemical reactions of the vapor contaminants within the disk drive enclosure, which impinge on it, converting them to harmless gaseous species. The most important photocatalytic process for this purpose is photocatalytic oxidation.
This approach has many inherent advantages over the current state of the art. The catalytic surface would never be exhausted, as would an absorbent. Elevated temperature would not cause re-release of contaminants because they would be destroyed. The HDD could be almost or entirely hermetically sealed against humidity and other environmental contaminants without concern that the HDD component outgassing would poison the drive. This could allow an inert atmosphere (e.g., helium) to be maintained in the drive to lower power consumption, reduce disk vibration and flutter, or reduce chemical reactions on the disk. The use of the catalyst could also permit the use of “dirtier” components, reducing manufacturing costs. Alternately, lifetime of a drive could be increased with the same quality and cleanliness of components presently used. The capacity of the catalyst would only be limited by the surface area, which could comprise a great portion of the interior illuminated surface, and the illumination power available. The location of the catalyst is chosen to allow maximum exposure to the atmosphere in the drive; preferably it is located in the flow paths to the drive consisting of a photocatalytic surface in close proximity or contact with a light source as a means for activation.
In one preferred embodiment, a non-friable, high surface area TiO
2
(titanium dioxide) coating is applied to a fluorescent lamp with substantial light output in the UV spectrum (below 400 nm wavelength, and most preferably below 300 nm wavelength) and of a size to fit within a disk drive. Such a coating can be applied by e.g., dipping the lamp in a sol-gel dispersion of TiO
2
and curing at elevated temperature.
Another preferred embodiment is substantially the same as above except the catalytic surface consists of a sheath of porous TiO
2
-containing ceramic that fits over the lamp.
In another embodiment, the catalytic surface consists of particulate TiO
2
enclosed in a mesh or porous material that wraps or slips around the lamp, preventing the particulate catalyst from escaping but allowing free exchange of gases.
In another embodiment similar to that above, the catalytic surface consists of a mesh (glass or fabric) impregnated with TiO
2
-catalyst.
In other embodiments otherwise similar to all of the above, the fluorescent lamp with substantial output below 300 nm could be replaced by one with substantial output below 400 nm but not 300 nm.
Alternatively, the fluorescent lamp could be replaced by an incandescent lamp with substantial output below 400 nm.
The lamp could also be replaced, in whole or in part, by a transparent window in the drive to allow ambient light or light from an external source to illuminate the catalytic surface(s) as described above. Banks of disk drives could be kept catalytically clean by this means.
In another embodiment of the invention, the method of ill

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