3578 IEEE TRANSACTIONS ON MAGNETICS, VOL. 47, NO. 10, OCTOBER 2011 Dynamic Studies on Lube-Surfing Recording Wei Hua, Bo Liu, Shengkai Yu, Weidong Zhou, and Kyaw Sett Myo Data Storage Institute, (A*STAR) Agency for Science, Technology and Research, Singapore, 117608 This paper studies the full processes of touchdown, lube-surfing, and takeoff of thermal flying-height control sliders by simulation. It is observed that for a conventional slider, the lube-surfing process is not stable, and the slider may transfer to the full flying state or be in the solid contact with the disk. While for the spherical pad design, a stable lube-surfing state is achieved. It is taken into account that the spherical pad can further reduce the short-range forces, which play crucial roles in lube-surfing recording. The requirement and budget for the lube-surfing recording are discussed. Index Terms—Air bearing slider, head/disk interface, lube-surfing recording, spherical pad. I. INTRODUCTION I N a hard disk drive, a slider housing the read/write heads flies over a fast rotating disk surface due to a very thin layer of squeezed air bearing film between them. The head media spacing (HMS), a very important parameter related to the recording density, should be as small as possible. One of the main components of HMS is the flying height (FH). As a result, reducing the FH is an important work in the head/disk interface (HDI) and tribology research [1]–[3]. Naturally, contact recording [4] is considered to be an ideal scheme for reducing the FH. However, contact recording may not be able to reduce the FH without concerning with topo- graphic parameters of the interface. A typical case is the well- known tripad slider, which was widely used in the middle of 1990s. The tripad slider has a contact force of approximately 2.5 mN in its working state, but the FH could be as high as 25 nm [4], [5]. The reason is that the surface roughness also contributes to the FH, which normally refers to the clearance between the slider and disk roughness mean planes. On the other hand, if the surface roughness is significantly decreased, the FH will also be reduced correspondently. How- ever, lots of tribology issues will appear due to the smoothing surfaces. Typical challenges include the bouncing and wear of the slider, which attracts intensive studies in the 1990s [6]–[8]. Unfortunately, contact recording has not been employed in hard disk industry by the efforts of researchers for two decades. Another compromised method is to let the heads contact with lubricant only, as illustrated in Fig. 1. This state is called as lube-surfing recording [2], [3], [9], [10]. Even though the HMS will be a little larger than that of contact recording, the contact force and the wear can be significantly reduced. In the viewpoint of tribology, lube-surfing recording is much more promising. This paper studies the lube-surfing of two thermal flying- height control (TFC) sliders. One is the conventional design and the other is the spherical pad design [11], [12]. Simulation results show that for the conventional design, the lube-surfing Manuscript received February 10, 2011; revised April 20, 2011; accepted May 22, 2011. Date of current version September 23, 2011. Corresponding au- thor: W. Hua (e-mail: hua_wei@dsi.a-star.edu.sg). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TMAG.2011.2158069 Fig. 1. Schematic diagram showing a slider in contact with the disk lubricant. This is the ideal state for lube-surfing recording as the FH is minimized with acceptable contact force. process is not stable, while for the spherical pad design, the lube-surfing process is stable. The budget and demand for lube- surfing recording are given out. II. SIMULATION MODEL AND SIMULATION TOOL When a slider is flying over a fast rotating disk, the air bearing pressure is governed by the following normalized linearized Boltzmann equation [13] (1) where and are normalized air bearing pressure and FH functions, respectively. By solving the aforementioned non- linear partial differential equation, the air bearing pressure profile on the slider can be obtained. The solution of (1) is conducted on a self-developed air bearing simulation software ABSolution. The software is based on the finite-element method and the structured rectangular mesh. The Probability Model [14] is applied to deal with the air bearing force and the contact force, with both the air bearing surface (ABS) roughness and the disk surface roughness con- sidered. The intermolecular force and the electrostatic force are also considered in the code based on the Probability Model [15]. The slider-lubricant contact and the diamond-like carbon elastic/plastic deformations are taken into account [16]. In ad- dition, an implicit algorithm with second-order time accuracy is employed in the dynamic simulation to improve convergence, accuracy, and speed of the simulation [17]. Finally, a powerful user-friendly interface is developed for providing great conve- niences and flexibilities to a user. The software is verified to be well correlated to the experimental testing results [14], [18]. 0018-9464/$26.00 © 2011 IEEE