3874 IEEE TRANSACTIONS ON MAGNETICS, VOL. 42, NO. 12, DECEMBER 2006 Side-Track Erasure Processes in Perpendicular Recording Shaoping Li, H. Zhang, P. Lu, W. Zhu, H. Edelman, Chris Rea, Ned Tabat, S. Mao, D. Brown, M. Montemorra, and D. Palmer Seagate Technology, Inc., Bloomington, MN 55435 USA In perpendicular recording, substantial erasure of the stored data patterns can occur during the writing process. Among all those erasure processes, sidetrack erasure (STE) is one of the critical issues in drive head/media integration. Unlike the adjacent track erasure (ATE) process, the locations of the STE affected areas are often many tens of tracks away from the central writing track location. In this work, we report on an experimental investigation and quantification of the general attributes and the origins of the STE processes in various situations. Particularly, we thoroughly characterize some distinctive signatures and behaviors of STE processes by employing both the amplitude- and BER-based STE measurement methods in combination with a novel magnetic force microscope characterization technique. Index Terms—Magnetic force microscope, perpendicular recording, side track erasure, side writing. I. INTRODUCTION I N perpendicular recording, the side track erasure (STE) is one of major engineering concerns in drive integration [1]–[5]. The problem arises when the stray field from the sides of a recording head causes erasure on both the adjacent and other side-tracks. However, unlike adjacent track erasure (ATE) process, STE effect extends well beyond the closest neighbor tracks. Such a STE effect can cause significant amplitude drop of the previously written data and substantial increase of the noise, inevitably translating into a sizable bit error rate (BER) degradation and resulting in severe degradation of the electrical performance of disk drives. Fundamentally the STE effect in perpendicular recording is directly connected with the vertical writing scheme itself so that it is a unique problem for per- pendicular recording. Furthermore, in practice, due to design complexity of perpendicular heads and media, it is not easy to experimentally diagnose relevant STE root causes in different situations. The complex interactions between recording heads and the soft underlayer could make the matter even worse. To resolve the intrinsic characteristics of the STE process and deepen our understanding of the underlying physics in STE processes, in this work, we have experimentally investigated some inherent attributes of the STE process in various situations and quantified some of its distinctive signatures. II. EXPERIMENT All STE measurements are conducted on high precision spin- stand testers equipped with some servo capabilities. Their non- repeatable run-out is less than 2–8 nm. The STE measurements are evaluated on various disk loca- tions of inner diameter (ID), middle (MD), and outer diameter (OD), respectively. Thus, the spatial distributions of STE can be examined and obtained precisely on recording disk. The perpendicular recording media and heads are used for this study. The merged read/write heads consist of a tunneling Digital Object Identifier 10.1109/TMAG.2006.883836 magnetoresistive (TMR) reader and a multiturn single pole writer, with 2.0 to 2.4 T moments, as well as the return pole(s). The granular type recording media consist of a 200-nm-thick magnetically soft underlayer (SUL) and a 25-nm-thick CoCrPt recording layer spaced by a 10-nm-thick nonmagnetic in- terlayer. The recording layer has a saturation moment of 500 emu/cm , the coercive field H of 4000–7000 Oe and the nucleation field H of 1000 to 2200 Oe. The current employed in our STE measurements are ranging from 20 to 60 mA - . Various overshoot magnitude and overshot duration settings are also employed in our STE measurements in order to ex- plore the impact of variable operational stress. To ensure the maximum tracking capability and measurement precision, the servo patterns between each sector were established and its quality and bursts’ waveforms were fully optimized prior to our STE measurements. The STE measurement is performed in such sequence that a numbers of tracks are first written around the central track location and subsequently obtain the BER or narrow-band amplitude for each written track. Then the recording head is moved to the central location where it is cycled many times through the write process. Following that the STE induced BER or the amplitude reduction can be obtained after many continuous writes. In order to unambiguously identify the contributing factors to STE, we have conducted a coherent writing scheme combined with a magnetic force microscope (MFM) imaging process to capture the STE footprints of the head on the media. The experiment was prepared in such a way that a series of different bit length pulse sequences were coherently written multiple times on a dc erased background from 10 000 to 500 000 cycles in specific radius on recording media. Subsequently the induced STE signatures were then captured by MFM imaging process. Note that the media background is prepared by dc magnetizing in order to enhance the erasure effect and increase the resolution of the tool. For writing coherent data tracks precisely in hundreds of thousands of revolutions, the writing signal is synchronized by using an additional clock head. Its average jitter variation is less than 2 ns at our measurement conditions. 0018-9464/$20.00 © 2006 IEEE