FILM COMPOSITION AND UNDERLAYER EFFECTS ON OFF-TRACK ERROR-RATE PERFORMANCE IN CoCrPtTa MEDIA ON GLASS-CERAMIC SUBSTRATES

摘要

In recent years, alternatives to NiP/Al substrates have been introduced and higher coercivity alloys have been employed to push recording density to higher levels [1,2]. The flatter alternative substrates, such as glass or glass-ceramic, allow the head to fly lower and Pt additions to CoCrTa alloys increase coercivity (Hc) to ensure a shorter recording transition length. To make full use of these advances, more information is needed on the quaternary alloy composition dependence of media noise behavior and off-track-error-rate performance, especially in the high recording density regime. Buffer/underlayer/CoCrPtTa/C film structures were DC magnetron sputter deposited onto 65 mm glass-ceramic substrates in a static sputtering system. The base pressure was typically 5×10~(-7) mTorr. The substrates were preheated to 200-300°C and the sputtering pressure was about 13 mTorr. Transmission electron microscope and atomic force microscope were used to examine the film grain microstructure and morphology. Magnetic properties were tested using a non-destructive rotating disc magnetometer. The recording characteristics and media noise were measured at a linear density of 125 kfci using a Guzik 1601 tester with a magnetoresistive (MR) head with a 0.35 μin gap length and flying at a nominal height of 2.1 μin. Off-track error-rate performance was obtained using a SAL-MR head flying also at nominal 2.1 μin with a speed of 13.9 m/sec utilizing a commercial PRML channel with 60.8 Mbps data rate [3,4]. The accompanying table summarizes magnetic properties, signal-to-media-noise ratio (SNR) and off-track capability (OTC) of the films prepared with different film compositions and choice of buffer and underlayers. Similar magnetic properties were obtained for all samples to minimize media noise and OTC variations directly due to different magnetic properties. Discs 1-6 are the films with Cr both as buffer and underlayer. A clear trend is observed in these samples; (1) higher Cr content leads to a significantly better SNR and OTC; (2) higher Ta content also leads to a better SNR and OTC but to a lesser extent; and (3) higher Pt content significantly degrades SNR and OTC. Discs 7 and 8, with CrV underlayer, are the two best noise performing films compared with the films with Cr underlayer, SNR was improved by 1.7 dB and OTC was improved by 12%. In disc 9, CrV was used for both the buffer layer and underlayer. An enhancement of 4.9 dB SNR and 23% OTC were the result. The figure plots OTC versus SNR for all alloys, indicating the strong correlation between OTC and the broad band noise. The choice of CrV as both buffer and underlayer for Co_(76)Cr_(15)Pt_(5)Ta_(4) film clearly exhibits the best performance.