Measurement of intrinsic signal to noise ratios for high performance rigid recording media (abstract)

Abstract

Measurement of the noise spectrum of high performance oxide, thin-film longitudinal and perpendicular rigid recording media have been made in order to establish the frequency dependence of the noise, the intrinsic media signal-to-noise ratio, and the practical recording density limit set by error rate considerations. For the oxide media tested, the noise spectrum was flat with frequency at 0.7 μV rms/100 μV rms signal indicating it was close to the particle size determined noise limit. For plated Co-P and sputtered Co-Re thin-film longitudinal media the noise spectrum increases with frequency. At D70 (18 KFCI) the noise was 1.25 and 1 μV per 100 μV rms signal, respectively. For the vertical media the noise contribution came from shouldering around the fundamental frequency and was 2.5 μV/10 μV rms signal at D70 (22 KFCI) and increased with frequency. The measurements were made with both inductive and magnetoresistive heads (improved sensitivity) at 900 TPI and over a 20-MHz bandwidth. D70 for the oxide media was 13 KFCI. The flying height was maintained at 9μ in. Measurements were made at narrower trackwidths to confirm the square root dependence of S/N on trackwidth. Comparisons of both dc erase and high-frequency noise spectrums are presented and contrasted for oxide and metallic media. Evidence supporting proposed theories for the source of the media noise is discussed and the implications with respect to maximum achievable areal densities (without error correction) are presented.