Simulation and measurement of a head-disk collision in magnetic data storage - General Developments - Brief Article

Journal of Research of the National Institute of Standards and Technology, Jan-Feb, 2003

Magnetic data storage technology has been following Moore's law, with data storage density doubling every 18 months. In the face of this, the National Storage Industry Consortium, now the Information Storage Industry Consortium, has set the ambitious goal of reaching 155 gigabit per square centimeter data storage in the next five years. For 155 Gb/[cm.sup.2] areal density technology, the head-disk interface becomes an important scientific and technological issue. The spacing between the head and the disk is shrinking to 3.5 nm with the disk spinning at speeds approaching 40 m/s. Occasional contacts will test the strength and robustness of the protective coating of carbon and lubricant on the disk, which are each only about a nanometer thick. Because of the reduced flight height, waviness of the disk, and rotational wobble, occasional contacts between the head and disk will occur, and sometimes catastrophically. Since this kind of random contact is difficult to measure and monitor, measurement tools are needed to simulate such events.

NIST has successfully developed an experimental technique and a numerical model to study the dynamic behavior of a head colliding with a disk. In the theoretical part of the study, a three-dimensional finite-element model was constructed to represent the overcoat, media and substrate, as well as a two-mass system, to represent the air-bearing slider. After solving the initial value problem, the model is capable of predicting the contact duration/frequency, contact forces, maximum penetration, energy dissipation and partition and underlying stress and deformation field for a given layered structure of the hard disk, asperity size and disk rotational speed.

In the experimental part of the study, a one-pass, high-speed impact test instrument and test method to evaluate materials responses on a hard disk surface have been developed. The basic concept is to artificially create a ridge (500 am to 2000 nm height and 0.002[degrees] to 0.010 angle of incline) on the disk surface by controlled scratching on the substrate side of the disk to create a ridge on the top surface with its multilayer intact. A 3 mm-diameter ruby ball collides with the ridge at 7200 rpm rotational speed. The impact force is measured with an acoustic emission sensor and the deformation volume is obtained with an AFM.

The bench test and the simulation model lead toward the goal of providing the necessary tools to optimize materials, lubricants, and mechanical design for future high-density storage technology.

CONTACT: Tze-jer Chuang, (301) 975-5773; chuang@nist.gov or Stephen Hsu, (301) 975-6125; hsu@nist.gov.