Brian H. Thornton

Nonlinear aspects of air-bearing modeling and dynamic spacing modulation in sub-5-nm air bearings for hard disk drives

A new analytical model and method of analysis are proposed for understanding the dynamical behavior of ultralow flying height air-bearing sliders in proximity based on nonlinear dynamics. It is found that for sub-5-nm flying height air-bearing sliders, the nonlinear effects cannot be neglected. These nonlinear effects cause a sliders response to become highly nonstationary, making frequency domain analysis by fast Fourier transforms (FFTs) an insufficient means of analysis. Joint time-frequency analysis is applied for accurately analyzing the nonstationary slider responses and to verify the nonlinear nature of the air bearing for both experimental and simulation results. One degree-of-freedom (DOF) and 2-DOF nonlinear lumped parameter models are proposed showing the effect of nonlinearities on the FFT representations of air-bearing slider responses. The 2-DOF model is used to further investigate the nonlinear coupling effect, and it shows high correlation with experimental results from two different slider designs when in unsteady proximity. These findings suggest that the nonlinearities of the air-bearing slider must be considered when modeling slider-disk interface dynamics. Also, complex frequency domain representations of slider responses in proximity can be explained by the nonlinear nature of the air-bearing slider without contact between the slider and disk as previously proposed by other models.

Flyability and flying height modulation measurement of sliders with sub-10 nm flying heights

An experimental system is set up, and a procedure is proposed for measuring the flying height modulation (FHM) at the head-disk interface of a magnetic disk drive by using laser Doppler vibrometry (LDV). A precision trigger, a large number of averages, and a suitable filter are key to successfully measuring the FHM. Better results can be obtained from the velocity output of the LDV as opposed to the displacement output.

Some tribology and mechanics issues for 100-Gb/in/sup 2/ hard disk drive

The requirements of the mechanical head-disk interface design for a magnetic recording hard disk drive with a data density of 100 Gb/in/sup 2/. are presented. The research toward achieving this design in the Computer Mechanics Laboratory in collaboration with the National Storage Industry Consortium is summarized: 1) optimization of a 5-nm-flying-height ABS design; 2) experimental and numerical simulations of slider dynamics to reduce the flying height modulation; 3) tribological studies of sputtered, nitrogenated carbon (CN/sub x/) overcoats and their interaction with ZDOL lubricant; and 4) optimal strain sensor placement on an instrumented suspension for suppression of track misregistration.

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 (1.25×1 mm) has been successfully used for several generations of products and the question arises-should the formfactor 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 X0.66 mm) 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 wariness wavelengths (longer than the slider body length, L), the FHM is proportional to L β 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 pica 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.

Head-disk interface instability due to intermolecular forces

In this paper, we investigate the effects of intermolecular forces on the dynamic stability of the HDI.

Some tribology and mechanics issues for 100 Gbit/in/sup 2/ HDD

Summary form only given. The goal of 100 Gbit/in/sup 2/ storage density places severe requirements on the tribology and mechanics in hard disk drives. The physical air bearing spacing needed to achieve the required bit density along the track is about 5 nm, while the track density required is about 175 k tracks per inch. The head-disk interface assumes that the protective overcoat on the media is only 2 nm, with less on the slider to protect against catalytic degradation of the disk lubricant, which is itself assumed to be about 1 nm thick. This paper describes some of the developments needed to accomplish these goals.