An Experimental and Simulation Study of Touchdown Dynamics
ABSTRACT Dynamic flying height technology has been widely employed for reducing the mechanical spacing between the magnetic heads and the disk. As the recording density of hard disk drives approach 1 Tbit/in2, the spacing is decreased to sub 1 nm. At such low spacing, the touchdown (TD) dynamics becomes extremely critical. First, it affects the accuracy of the spacing setting, or TD detection. Second, it affects the hard disk drive reliability, such as writing modulation, wear, instability, etc. It decides how low the slider can fly stably and reliably. In this paper, we tried to have a better understanding of the TD dynamics with several designs of experiments first. We found that there were two stages in the whole TD process. In the first TD stage, a low frequency (30-150 kHz) vibration appeared. It was a suspension mode that was excited by the lubricant on the disk. In the second stage, a high frequency vibration (200-400 kHz) appeared. It was the second pitch mode of the slider air bearing excited by the contact between the slider and the disk. Based on these experimental observations, we propose modeling and simulation procedures with a combination of a full suspension model and a simplified air bearing model. Simulation can predict these two TD frequencies very well. Therefore, it could be applied to design head/disk interface to help achieve preferred TD behaviors.
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- "During flying, slider may encounter the soft contact, or hard contact; the contact force may be in out-of-plane ( -direction) or in-plane (off-track and down-track) . In this paper, the out-of-plane force is denoted as , and the in-plane force is denoted as . "
ABSTRACT: To achieve the areal density of 1 TB/in<sup>2</sup> in hard disk drives (HDDs), the magnetic spacing between the slider and disk needs to reduce to 1 nm or smaller. At such small clearance, the contact between the slider and disk is inevitable. Slider-disk contact may induce a drastic slider response, which has a significant negative impact on the reading/writing performance. In this paper, the effect of a low-frequency vibration in the Z-direction (out-of-plane) brought by the tip of gimbal (TG) on slider dynamics is studied. The impacts of three different excitations on the TG resonance are explored. Under such excitations, the bending mode of TG can be easily excited, which consequently induces the vigorous slider vibration. The influences of the air-bearing stiffness on slider dynamics subject to TG mode are also studied. A slider designed with weaker air-bearing stiffness will suffer a stronger TG resonance than that of stiffer air bearing. These experimental and simulation results show that better TG design and more strict environmental or excitations control are required to achieve a robust head disk interface (HDI).IEEE Transactions on Magnetics 09/2013; 49(9-9):4977-4981. DOI:10.1109/tmag.2013.2252359 · 1.21 Impact Factor
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ABSTRACT: With the wide application of thermal flying-height control (TFC) technology in the hard disk drive industry, the head-disk clearance can be controlled to as low as ~1 nm. At this ultra-low clearance, the air bearing slider is subject to relatively large interfacial forces, and it experiences more complicated dynamics, compared with the flying case. In this study we conduct a numerical analysis to investigate the dynamics of TFC sliders during touchdown. The general trend of the slider’s motion predicted by the numerical simulation qualitatively agrees with experimental findings. The touchdown process begins with a slight intermittent contact between the slider’s trailing edge and the disk, followed by a partial slider-disk contact at the trailing edge accompanied by a large pitch motion at the 1st air bearing mode; this pitch motion gets suppressed and the slider comes into stable sliding on the disk as the protrusion is further increased.Microsystem Technologies 09/2012; 18(9-10). DOI:10.1007/s00542-012-1537-6 · 0.95 Impact Factor
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ABSTRACT: Future magnetic storage density targets (>4 Tb/in. 2) require subnanometer physical clearances that pose a tremendous challenge to the head disk interface (HDI) design. A detailed understanding of slider-lubricant interactions at small clearances and contact is important to not only address magnetic spacing calibration and long term HDI reliability but also to meet additional challenges imposed by future recording architectures such as heat assisted magnetic recording (HAMR). In this work, the behavior of the disk lubricant is investigated through controlled tests using TFC sliders which are actuated to proximity (i.e. backoff) and into contact (i.e. overpush) on one specific half of the disk per rotation by synchronization with the spindle index. Observations for lubricant distribution in contact tests (i.e. overpush) reveal an accumulation of lubricant on the disk near the onset of contact suggesting a migration of lubricant from the slider to the disk as the slider approaches the disk. Experiments also reveal that there is a similar deposition of lubricant even in the absence of contact for backoff tests. Furthermore, light contact tests result in significant lubricant rippling and depletion with associated slider dynamics. The lubricant rippling frequencies correlate well with the slider’s vibration frequencies. Interestingly, strong overpush may lead to stable slider dynamics (for certain air bearing designs) that is also associated with noticeably lower lubricant distribution (compared to the light contact case), and the greatest lubricant changes are observed only at the onset and the end of contact. This paper reveals the complex nature of slider-lubricant interactions under near-contact and contact conditions, and it highlights the need for further studies on the topic to help design a HDI for recording architectures of the future.Microsystem Technologies 09/2012; 18(9-10). DOI:10.1007/s00542-012-1582-1 · 0.95 Impact Factor