Research at the Precision Engineering Center
In modern hard disk drives, higher speeds and tolerances are critical in meeting the increasing demands of consumers. A major influence on the data density and access time is the flying height of the read/write head. The read/write head is contained within a small ceramic slider that acts as an air bearing when the storage disk is rotated; therefore, the shape of the slider directly determines the flying height of the read/write head. Previously, sliders were polished to their final shapes, but to keep pace with the rapidly increasing data density required by users, both mechanical and laser scribing techniques have been employed to more accurately control the final curvature of the slider.
Mechanical scribing relies on a diamond indenter to create localized plastic deformation, which results in an overall curvature for the slider. Previous work at the PEC has developed a model for long mechanical scribes, but through the use of numerical techniques such as finite element analysis this model is being extended to more complicated scribing geometries (partial and asymmetrical scribes).
Laser scribing is a much newer technique that has been developed by IBM. A laser focused on the surface of the slider melts a small area of the ceramic, and the resolidification of this material results in residual stresses which produce a net curvature of the slider. Currently, this process is used in production, but more and more stringent demands require a better understanding of the process. Using finite element analysis, students and faculty at the PEC are developing a model which, when calibrated with experimental results, can predict the deflection generated by a laser scribe placed anywhere on the surface of the slider.
Past work has shown that the residual stresses induced by mechanical scribes can be modeled using an experimentally calibrated force system. Austin and Scattergood developed a 2D model for the deflections created by mechanically scribing of a slider. Extending the model to three dimensions involves the use of numerical methods; in this case, finite element analysis was used to model a similar force system. The use of FEA allows solution of scribing geometries impossible by closed form solution.
A similar method was used to model laser scribing–several force systems were devised that would produce curvatures similar to laser scribes. Due to the parameters seen in laser scribing, all theoretical calculations and models were conducted using finite element models. Experimental work in conjunction with IBM-San Jose allowed the verification and calibration of a force system. With a calibrated force system, any scribe length or placement can be modeled and the resulting curvature predicted.
Current results show that the laser scribing model can predict deflections within 10% of experimental values and the results can be improved significantly using different calibrations for different scribing directions (two calibrations yields approximately 5% error from experimentally measured sliders). It is important to note that the repeatibility of the current metrology employed in measurement of the scribed sliders is approximately 10%. Final results will be available by May 2001.
The following faculty, students, and PEC affiliates are involved in this project:
| Faculty | Students | Affiliates |
| Dr. Jeff W. Eischen | Bryan M. Love | IBM |
