Data Storage Systems Center

In hard disc drives (HDD), it is imperative to reduce total head media spacing (HMS) in order to achieve higher recording density. However, HMS of the current state of the art HDD, physical fly height (PFH) is almost the lowest limit due to the adoption of thermal fly height control, and therefore the major portion is occupied by carbon overcoat for physical/chemical surface protection and lubricant thcknesses, meaning that a very small room is left for further HMS reduction. A researcher in the DSSC proposed a new concept for realizing continuous contact head media interface (HMI) utilizing surface acoustic wave. This concept, name as surface acoustic wave – active bearing (SAW-AB) project, in principle requires no lubricant layer yet can achieve zero friction/wear while maintaining continuous mechanical contact. Some basic theoretical calculations suggest that the linear speed of a few tens of m/s may be achievable, which is comparable with the current HMI linear velocity, without requiring large power injection. In order to prove this concept, a feasibility study has already begun. One experiment showed that the attractive surface interaction due to Van der Waals force for insulators and metal-to-metal bonding for conductors can be diminished by SAW excitation. Another experiment showed that SAW excitation actually generates lateral traction force even when the SAW frequency is as high as about 300MHz. These promising results are presented in the poster in more details.

Electric charging can occur during the operation of magnetic recording heads due electron transfer from the head to the underlying disk surface. The work function (Φ) of the recording head material acts as a barrier to electron transfer, and thus directly impacts the extent of the charging.

As a means of modifying the work function, we subjected the carbon film-covered surface to fluorination with XeF2 under ultrahigh vacuum (UHV) conditions. Introduction of electronegative species such as fluorine is known to raise the work function by creating a negatively-charged surface layer. The changes in surface composition were monitored with X-ray photoemission spectroscopy (XPS), while the work function was measured with UV photoemission spectroscopy (UPS).

We find that fluorination with XeF2 increases the work function of the diamond-like carbon (DLC) layer by as much as 1.5 eV. In addition, most of the increase occurs at very low surface concentrations of fluorine, suggesting that a small number of highly reactive DLC sites have a controlling influence with respect to the surface work function.

The effect of fluorination can be reversed by annealing the sample at high temperatures, leading to the loss of surface fluorine.

Chemical mechanical polishing (CMP) is a manufacturing process that is commonly used to planarize integrated circuits and data storage devices during fabrication. The CMP process involves the wafer sample being mounted onto a rotating carrier and pressed against a rotating polyurethane pad that is flooded with slurry. The slurry itself is a chemically reactive fluid containing suspended abrasive particles. The relative motion between the wafer, pad, and particles causes surface wear in both surfaces. In order to develop a predictive capability for CMP, a number of models have been formulated which focus on certain aspects of the CMP process. However, there are very few models that integrate all of the important aspects of CMP into a single framework. Therefore, the focus of this study involves the development of a multi-physics modeling tool that models all of the important interactions in CMP—namely fluid mechanics, contact mechanics, and particle dynamics—and incorporates all of them into a single framework for predicting wear. Each of the constituent models was formulated separately and compared to experiment before being combined into the integrated framework. The resultant model, called the Particle-Augmented Mixed Lubrication (PAML) model, was used to predict wear in silico from a measured surface topography during CMP. The results from the PAML simulation were compared to experimental measurements.