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On the path to creating more stable, compact HDDs

Posted: 01 Aug 2013 ?? ?Print Version ?Bookmark and Share

Keywords:lubricant transfer? hard disc drive? spectroscopic ellipsometry?

Researchers at the A*STAR Data Storage Institute have developed a technique to assess the impact of making hard disc drives (HDDs) more compact by measuring lubricant transfers in disc drives. The reason behind this is the need for the rapidly growing consumer demand for data storage. The findings will aim to guide the future design of stable disc drives, indicated the scientists.

The primary components of a HDD are a rotating disc coated with a thin film of magnetic material and a magnetic head on a moving arm, also called a slider. The slider includes magnetic write/read elements that can encode a single bit of binary information by altering the properties of the thin film at a small spot on the surface. A smaller spot enables a higher density of data storage.

Current technology is rapidly approaching one trillion bits per square inch, but this requires the separation between the head and disc to be less than 2nm. This narrow requirement, however, creates its own problems. Lubricant used on the surface of the disc to protect it from corrosion can attach to the slider, which adversely affects the reliability of the HDD. "We have carried out a systematic and quantitative study on how the variation of slider optical properties affects the accuracy of the measured lubricant thickness on the slider surface," noted Zhang.

Zhao, Zhang and their co-workers analysed a lubricant-coated slider using a technique known as spectroscopic ellipsometry. Measuring the intensity of light reflected from a sample slider provided a highly accurate estimate of the thickness of the lubricant film. Ellipsometry is a fast and non-destructive technique that, unlike some of the alternative approaches, does not require ultra-high vacuum conditions. This technique, however, does require accurate knowledge of the optical properties of the slider. A typical slider is made of aluminium oxide and grains of titanium carbide of many different shapes and sizes; thus, its optical properties vary from position to position.

Zhao and the team's study demonstrated that the uncertainty in lubricant thickness is nearly proportional to the uncertainty in the slider's optical constants, and it becomes particularly pronounced for thicknesses below 2nm.

"This lubricant transfer will be more serious in future heat-assisted magnetic recording," added Zhang. "The next step in this research will focus on how to reduce the lubricant transfer, especially in this type of device."

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