Recent growth in the cloud storage industry has created a massive demand for higher capacity hard disk drives (HDD). A sub-nanometer head media spacing (HMS) remains the most critical pre-requisite to achieve the areal density needed to deliver the next generation HDD products. Designing a robust head-disk interface (HDI) with small physical clearance requires a deeper understanding of slider dynamics, especially when the head flies in proximity to the disk surface. This paper describes a method using the magnetic read-back signal to characterize the head fly-height modulations as it undergoes a transition from a free-flying state to soft contact with the disk surface. A technique based on the magnetic fly-height sensitivity is introduced to identify the transition plane that corresponds to the onset of the touchdown process. Additionally, the proposed magnetic spacing based meteorology is used to study the effect of the air bearing stiffness and lubricant properties on the slider vibrations induced by intermittent head-disk interactions. The ability to accurately determine the transition plane corresponding to minimum stable flying conditions can help design a low clearance head-disk interface.

Growth in the demand for higher capacity hard disk drives has pushed the requirement for head-media spacing to sub-nanometer levels. The drop in operational clearance makes a head-disk interface more susceptible to potential head-wear and contamination related issues. Such degradation processes are often accompanied by a noticeable shift in the head-disk clearance. Hence monitoring an interface for a spacing change can be helpful in early detection of its imminent failure. In this paper, we present a method to detect the change in head-disk spacing using an embedded contact sensor (ECS). This technique involves the analysis of ECS dynamic response for an interface that is subjected to heater induced spacing modulations. As the head moves closer to the disk surface, the magnitude of the ECS frequency components can be used to determine the ‘characteristic spacing’ which can be used as a metric to detect any physical change for a given interface.

Recent growth in the cloud storage industry has created a massive demand for higher capacity hard disk drives (HDD). A sub-nanometer head media spacing (HMS) remains the most critical pre-requisite to achieve the areal density needed to deliver the next generation of HDD products. Designing a robust head-disk interface (HDI) with small physical clearance requires the understanding of slider dynamics, especially when the head flies in proximity to the disk surface. In this paper, we describe a method using the magnetic read-back signal to characterize the head fly-height modulations as it undergoes a transition from a free-flying state to soft contact with the disk surface. A technique based on the magnetic fly-height sensitivity is introduced for the identification of the transition plane that corresponds to the onset of the touchdown process. Additionally, the proposed magnetic spacing based meteorology is used to study the effect of the air bearing stiffness on the magnitude of the slider vibrations induced by intermittent head-disk interactions. The information about the minimum spacing while maintaining the stable flying conditions can help in reducing the head-disk interaction risk that can enable a low clearance interface.

We utilize thermal fly-height control (TFC) technology to perform in situ measurements of carbon overcoat wear at the angstrom level at the read–write area of magnetic recording heads. We also study the durability of the molecularly thin lubricated disk surface. Experimental findings reveal a linear relationship between the quantified carbon wear depth on the flying head versus the head–disk contact level produced by the TFC power. It is demonstrated that this method can serve as a measurement and probing technique of wear resistance for different types of lubricants. Lubricants possessing more polar hydroxyl end-groups and less mobility tend to show a superior surface stability under head–disk contacts, but raise concerns on head carbon overcoat wear.

Current hard disk drives use thermal fly-height control (TFC) during read/write operations. In this study, we use TFC technology during the disk glide process to determine sub-5 nm height defects. We also utilize TFC to measure the height of the defect during glide operation. Additionally, we magnetically mark the disk locations where defects are detected for further post-processing of the defects using optical surface analysis, atomic force microscopy (AFM), and scanning electron microscopy (SEM). The defect height estimation during the glide was confirmed to be accurate by AFM and SEM analysis. Finally, we will present the TFC glide sensitivity showing capability of detecting smaller defects than conventional non-TFC glide technologies.

There is an inherent contact potential difference between the head and the disk surfaces in hard disk drives (HDD's). Current HDD's use thermal fly-height control (TFC) during read/write operations. In this study, we show a method to determine the contact potential for the head disk interface (HDI) using TFC technology. We utilize TFC to measure the flying height of the slider via touchdown power by applying a DC voltage bias to either the head or the disk or both. The DC voltage condition where the TFC clearance is maximized corresponds to the balancing of the HDI contact potential. In other words, the opposite polarity of that DC voltage bias condition is the HDI contact potential. Additionally, we show that the contact potential of HDI can be determined by either applying the DC voltage bias to the head or to the disk

Accurate touchdown power detection is a prerequisite for read-write head-to-disk spacing calibration and control in current hard disk drives, which use the thermal fly-height control slider technology. The slider air bearing surface and head gimbal assembly design have a significant influence on the touchdown behavior, and this paper reports experimental findings to help understand the touchdown process. The dominant modes/frequencies of excitation at touchdown can be significantly different leading to very different touchdown signatures. The pressure under the slider at touchdown and hence the thermal fly-height control efficiency as well as the propensity for lubricant pickup show correlation with touchdown behavior which may be used as metrics for designing sliders with good touchdown behavior. Experiments are devised to measure friction at the head-disk interface of a thermal fly-height control slider actuated into contact. Parametric investigations on the effect of disk roughness, disk lubricant parameters, and air bearing surface design on the friction at the head-disk interface and slider burnishing/wear are conducted and reported.

The use of patterned media is a new approach proposed to extend the recording densities of hard disk drives beyond 1 Tb/in.(2). Bit-patterned media (BPM) overcome the thermal stability problems of conventional media by using single-domain islands for each bit of recorded information, thereby eliminating the magnetic transition noise (Albrecht et al., Magnetic Recording on Patterned Media, 2003). Considering steady state conditions, we have transferred the pattern from the disk surface onto the slider surface and have investigated the pressure generation due to the bit pattern. To reduce the numerical complexity, we have generated the bit pattern only in the areas of the slider near the trailing edge, where the spacing is small. Cylindrical protrusions were modeled using very small mesh size on the order of nanometers to obtain the flying characteristics for the entire slider air bearing surface (ABS) using the "CMRR" finite element Reynolds equation simulator (Duwensee et al., Microsyst Technol, 2006; Wahl et al., STLE Tribol Trans, 39(1), 1996). The effect of pattern height, pattern diameter, slider skew angle, and slider pitch angle on flying height of a typical slider is investigated. Numerical results show that the flying height decreases for a patterned slider and the change in flying height is a function of the pattern height and ratio of the pattern diameter to the pattern pitch. In comparison to discrete track media, the flying height loss is larger for a patterned slider disk interface for the same recessed area of pattern.

In this article, we explore the physical mechanisms for lubricant migration on recording head slider surfaces and how this migration leads to increased slider–disk spacing during disk drive operations. This is done using both a new experimental methodology, called the “droplet stress test,” and through simulation. In our simulations, we compare the air shear-induced lubricant migration modeled either as viscous flow of a continuum liquid film with zero slip or as wind driven slippage of molecules across the surface. The experimental data are best fitted using the viscous flow model to determine an effective viscosity for the sub-nanometer thick lubricant films. This effective viscosity tends to be somewhat less than the lubricant bulk viscosity due to air shear promoting the slippage of lubricant molecules across the surface. Our experimental results also indicate that the potential spacing increase from the pickup of disk lubricant on the slider is limited by the mobile fraction of the dewetting thickness of the lubricant film on the slider.

Hard disk drives must be designed to be resistant to operational and non-operational shock (Jayson et al. in IEEE Trans Magn 38(5):2150–2152, 2002). Numerical and experimental results show that “lift-tab separation” and “dimple separation” are two possible failure modes of presently used head suspension assemblies (Murthy in Ph.D. thesis, Center for Magnetic Recording Research, University of California, San Diego, 2007). In addition, “dimple and tongue wear” at the interface of gimbal and dimple are areas of concern in the design and operation of high performance suspensions during shock. In this investigation, an improved numerical model for non-operational shock response of a load/unload hard disk drive is implemented by including design parameters of suspension such as dimple preload, suspension material, dimple height and the surface diameter of the dimple in the model. Results for dimple and lift-tab separation, as well as the maximum impact stress at the dimple region, as a function of preload and suspension design parameters, will be presented.

A numerical model is developed to study the effect of texture on air bearing sliders for large Knudsen numbers. The effect of texture location, texture size, and density on the pressure generation is studied. First, a textured plane slider parallel to the disk surface is investigated, and the texture parameters are determined that result in optimum pressure generation. Then, a plane inclined slider is studied using optimum texture parameters found in the parallel slider case. Thereafter, the effect of texture on the steady state flying characteristics of an actual magnetic recording slider is investigated. Finally, the flying height modulation, pitch, and roll motion of a textured slider (pico and femto form factors) are determined numerically by exciting the slider using a step on the disk. Comparison of the results for textured and untextured sliders is made. It is found that textured sliders show better dynamic performance compared to the untextured sliders in terms of stiffness and damping.

Commercially available microdrives were tested using linear and rotary shock and vibration testing equipment. Several microdrives designed with different slider and disk configurations were tested to track hard and soft errors as well as head/disk failures. The shock amplitude for operational and non-operational shock was gradually increased to determine the maximum shock that a microdrive could withstand before failure. After failure, the microdrive was examined to determine whether a mechanical failure occurred or whether the failure was due to a magnetic hard/soft error. During a shock event, the displacement and frequency of the vibrations of the microdrive were examined at various locations on the arm and suspension. A scanning laser Doppler vibrometer (LDV) was also used to determine the amplitude and frequency of the vibrations of the front cover and to investigate whether these vibrations contribute to failure of the head/disk interface. A finite element model of the disk drive was also developed to simulate the shock response. The maximum amplitude for failure to occur was determined numerically for operational and non-operational conditions using a pulse width of 2 ms. A comparison of experimental and numerical results is given.

The dynamic response of the head disk interface is investigated numerically for two different designs of 1-in. hard disk drive enclosures, the so-called "thin" enclosure and the "thick" enclosure. First, the in-plane and out-of-plane vibration response is determined. Then, the effects of linear shock and head slap are studied. Simulation results show that the thinner enclosure has better performance with respect to forced vibrations in terms of reduced amplitude of slider vibrations. In addition, the effect of operational shock on the dynamic characteristics of textured and untextured sliders is studied. A finite element formulation of the time-dependent Reynolds equation (with Boltzmann slip flow correction) was used to obtain the air bearing response. The results show that the dynamic flying characteristics of textured sliders are improved compared to that of untextured sliders.

The shock performance of the head/disk interface (HDI) of 3.5 and 2.5 in. hard disk drives (HDDs) is investigated. The displacement of the actuator arm, the suspension, and the disk due to linear shock loads is studied experimentally for both non-operating and operating states of the disk drive. A finite element model of the disk drive was developed to simulate the shock response. Numerical simulation results and experimental results are compared and presented.

Most hard disk drives manufactured in the last few years have Load/Unload (L/UL) technology. As opposed to the Contact Start/Stop (CSS) technology, L/UL technology has the advantage of improved areal density because of more disk space availability and better shock performance. The latter characteristic has significant benefits during the non-operational state of the hard disk drive since head/disk interactions are eliminated and the head is parked on a ramp adjacent to the disk. However, even if head/disk interactions are absent, other failure modes may occur such as lift-tab damage and dimple separation leading to flexure damage. A number of investigations have been made to study the response of the head disk interface with respect to shock when the head is parked on the disk ([1], [2]). In this paper, we address the effect of non-operational shock for L/UL disk drives.