A Numerical Study of Air-Bearing Slider Form-Factors

This paper presents a numerical study comparing the performance of air bearing slider form-factors. The air bearing slider and air bearing surface (ABS) design has gone through drastic changes in recent years in order to achieve the performance required by lower flying heights. In the past, improvements have been seen by scaling down the form-factors of air bearing sliders. The pico form-factor $1.25×1mm$ has been successfully used for several generations of products and the question arises—should the form-factor be scaled down further? The dynamic characteristics and flying-height modulation (FHM) performance of two different ABS designs in the pico and femto $0.82×0.66mm$ form-factors were numerically investigated. It was found that for the smaller form-factor designs, greater damping of the air bearing film and slider body system was achieved but with an undesirable decrease in modal frequencies. However, depending on the ABS design, beneficial dynamic properties can be achieved by scaling down the form-factor from pico to femto. Maximizing the total air bearing force (the sum of negative and positive) with a design featuring a large number of transverse pressure gradients can obtain high stiffness and damping. Geometric FHM was also investigated using both sinusoidal disk waviness and an actual measured disk topography. It was found that the FHM depends not only on the form-factor, but also on the ABS design. For long disk waviness wavelengths (longer than the slider body length, L), the FHM is proportional to $Lβ$ where β was found to be between 2.6 and 4; hence, FHM is dependent on form-factor. For short disk waviness wavelengths, the FHM is a function of the ABS design and flying attitude and not form-factor. A disk waviness wavelength of 3 mm demarks the transition above which the FHM is a function of form-factor and below which the FHM is a function of the ABS design and the superposition of these two effects compose the geometric FHM. Simulations with an actual measured disk topography showed that the femto form-factor exhibited 22–32 percent less FHM than the pico form-factor for a similar design. However, by changing the ABS design, 35–40 percent less FHM was achieved within the same form-factor. By scaling down a pico slider to a femto slider, we do not necessarily achieve enhanced overall performance. Significant performance improvements in the pico form-factor can be attained if the ABS is properly designed. However, in designing a dynamically stable and low FHM air bearing slider a femto slider ultimately yields better performance when care is taken in designing the ABS.