Where Tape and Hard-Disk Technology Meet: The HDD Head-Tape Interface

Abstract

In this paper, we study the mechanical interface between a hard-disk drive (HDD) head and magnetic recording tape to enable the use of HDD heads to investigate future tape operating points. Tape surface height measurements were obtained using an interferometer microscope for varying wrap angle configurations, tape velocities, and tape tensions. Simultaneously, the readback signal from the read element of the HDD head was captured to study the quality of the contact between the tape and the head. The signal-to-noise ratio (SNR) and bit-error rate (BER) performance of pseudorandom bit sequence (PRBS) data readback experiments are presented. An analytical model is described for estimating the magnetic spacing from the PRBS readback spectrum. In contrast to current commercial tape heads, the HDD head surface has a pronounced topography containing cavities. When tape passes in close proximity, subambient pressures are formed inside these cavities and the resulting pressure differences force the tape toward the head and deform the tape into remarkable shapes. For the topography of the HDD head used, the shape of tape is predominantly determined by the leading and trailing wrap angles. Readback was obtained only in the backward direction (i.e., opposite to the direction of operation in an HDD), with positive leading but negative trailing wrap angles. Better readback is obtained for shallow wrap angles, lower tape velocity, and higher tape tension. Good readback is obtained for leading and trailing wrap angles ∼ 0.3° and-0.2°, respectively. Fits of the analytical model to the spectrum of the readback signal of PRBS data lead to a magnetic spacing estimate of ∼ 30 nm. At 600 kb/in linear density, we measured 11 dB SNR and 7× 10^-3 BER for PRBS data on perpendicularly oriented particulate barium-ferrite tape.