Accurately detecting irregularities in the media - thermal asperities and delamination - and mapping them out from further usage is critical to prevent data loss and minimize head disk interaction (HDI). Defect growth is a common concern in hard disk drives (HDD) and the immediate vicinity of media defects are also mapped out to provide sufficient protection against defect growth. A class of media defects that prove more complex to protect against defect growth is scratches on the media. Margining a media scratch involves filling in the gaps between the components of a scratch and margining the vicinity of the scratch in the defect growth direction. While Hough transform based techniques and deeplearning models have been developed to identify media patterns, they cannot be implemented in the hard disk drive firmware due to memory and computational limitations. Here, we present a computationally simple and efficient alternative to identify scratches on the media by combining clustering and an iterative parameter estimation to fit a line to the scratch in noisy conditions. The result is a method that is capable of modeling linear, spiral and parabolic scratches on a media and fill gaps in the scratch and extend the margining at either end of the scratch.

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.

HDD heads have various interaction modes with thermal asperities (TAs), and protection mechanisms need to be put in place to ensure the head–disk interaction (HDI) resulting from them is eliminated or minimized to the highest extent possible. We propose a method to reduce such head–disk interaction (HDI) during TA detection and classification by flying higher at low thermal fly-height control (TFC) power, which minimizes the interaction of the TA with the head. The key idea is to scan the head at higher fly height, but with higher ECS bias voltage. By mapping out these TAs and ensuring the head does not fly over them again to prevent HDI, the fly height can then be lowered, and the rest of the TA cluster can be scanned. Following this method iteratively, the entire TA cluster can be mapped out with minimal interaction with the head. Although this method entails an increase in the test time to detect and map all TAs, compared to detecting them with TFC being on, this can help improve the reliability of the drive by protecting the sensitive read/write elements especially for energy assisted recording from HDI. Other than track follow, TA interactions also occur when the head seeks across the tracks. Typical seek avoidance attempts to eliminate TA interaction during seeking, however it is not straightforward to determine which of the seek mechanism: TFC on during short seeks, retract/arrival during long seeks, interaction with high TAs (HTAs), whose height is more than the fly height of the head during long seeks with TFC off, or idle TA interaction causes the greatest HDI. Through theoretical analysis and experimental corroboration, this paper intends to rank the various modes of TA interaction, so by developing features for eliminating or minimizing them in that order could help bring the maximum benefit for achieving minimum lifetime reduction of the head due to such interaction.

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.

HDD heads have various interaction mechanisms with thermal asperities (TAs), and protection mechanisms need to be put in place to ensure the head-disk interaction (HDI) resulting from them is eliminated or minimized to the highest extent possible. It is straightforward to not allow the head sit-on-track on cylinders that have such TAs on them, and the same principle can be extended to so-called high TAs (HTAs), whose height is more than the fly height of the head, so heads do not inadvertently interact with the TA even when motion is triggered on another head, since the entire head stack moves together. Similar TA interactions also occur when the head seeks across the tracks. Typical short seeks have thermal fly-height control (TFC) turned on while it is turned on during long seeks, which is greater than a few hundred tracks. Heads can also interact with TAs during retract and arrival of the head during such long seeks. Finally, background media scan (BGMS), which is an industry standard, when the drive enters an idle state. Interaction with HTAs can also occur when the drive enters such a state. Typical seek avoidance attempts to eliminate TA interaction during seeking, however it is not straightforward to determine which of the seek mechanism: TFC On during short seeks, retract/arrival during long seeks, HTA interaction during long seeks with TFC off, or idle TA interaction causes the greatest HDI. Through theoretical analysis and experimental corroboration, this paper intends to rank the various modes of TA interaction, so by developing features for eliminating or minimizing them in that order could help bring the maximum benefit for achieving minimum lifetime reduction of the head due to such interaction.

One of the issues in thermal asperity (TA) detection using an embedded contact sensor (ECS) is the degradation caused to the read/write elements of the head while interacting with the TA. We propose a method to reduce such head-disk interaction (HDI) during TA detection and classification by flying higher at low thermal fly-height control (TFC) power, which minimizes the interaction of the TA with the head. The key idea is to scan the head at higher fly height, but with higher ECS bias voltage. Initial experiments have shown that the TA count follows a negative cubic relationship with the backoff at various bias levels, and that it follows a square relationship with bias at various backoff levels. Using a sample set, the calibration curves i.e. the golden relationship between these parameters can be established. Using these, one can start the TA detection at the highest backoff and high ECS bias, and start to estimate the nominal TA count. By mapping out these TAs and ensuring the head does not fly over them again to prevent HDI, the fly height can then be lowered, and the rest of the TA cluster can be scanned. Following this method iteratively, the entire TA cluster can be mapped out with minimal interaction with the head. Although this method entails an increase in the test time to detect and map all TAs, compared to detecting them with TFC being on, this can help improve the reliability of the drive by protecting the sensitive read/write elements especially for energy assisted recording from HDI.

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.

In this investigation, we examine wear of thermal flying height control sliders as a function of DC bias voltage across the head–disk interface, relative humidity, and lubricant type. Wear tests were conducted using two different experimental setups, a load/unload tester, and a spin-stand tester with relative humidity control. Head wear was determined by measuring the change in the heater touch-down power (ΔTDP) before and after wear testing. After wear testing, selected recording heads were examined using atomic force microscopy and time of flight secondary ion mass spectrometry to investigate wear and deposit formation in the read/write region. Our results show that the polarity of the head–disk interface bias voltage and the relative humidity influence deposit formation and wear in the read/write region of recording heads.

A modeling and optimization approach is proposed and implemented for minimizing variations in flying height of thermal flying height control (TFC) sliders. The method utilizes the resistive heater element of TFC sliders for adjustment of spacing and the embedded thermal contact sensor (TCS) as a relative measurement for changes in flying height. In the modeling approach, the static and dynamic behavior of the TCS as a function of heater power is characterized. A model of the system is identified from experimental step excitation data using a realization algorithm. In the optimization approach, the optimal feedforward heater input profile is calculated via convex optimization techniques based on the static and dynamic behavior of the system. The modeling and optimization approach was verified experimentally, showing that the proposed approach reduces the difference between the maximum and the minimum value of the TCS measurements by a factor of two, indication a twofold reduction of flying height variations.

The effect of slider bias voltage and humidity on wear at the head/disk interface is investigated. Wear of thermal flying height control sliders is studied as a function of head/disk bias voltage, relative humidity, and heater power. The electrostatic force and the contact potential at the head/disk interface is monitored before and after head wear using the non-contact Kelvin probe method.

Head wear of thermal flying height control sliders is studied experimentally by (a) comparing the touch-down power before and after a wear test consisting of 300 consecutive touch-down cycles, (b) examining scanning electron microscopy (SEM) images, and (c) investigating atomic force microscopy (AFM) measurements of unworn and worn heads. The effect of bonded lubricant ratio, relative humidity, temperature, and heater power on head wear is investigated. The experiments were carried out on a commercial load/unload tester inside an environmental test chamber. We conclude that (a) head wear increases with increasing bonded lubricant ratio, (b) temperature has a minor effect on head wear for the temperature range of 30–50 °C, (c) head wear increases with decreasing relative humidity, and (d) head wear increases with increasing heater power during the wear test. SEM images show wear of the write shield for changes in touch-down power typically larger than 6 mW. AFM measurements show changes in surface roughness of heads with changes in touch-down power as small as 1.3 mW compared to new, unused head. A wear coefficient on the order of 10−11 to 10−13 was estimated.

Amorphous carbon is used as coating material for computer hard-disks magnetic media and recording heads. There has been significant improvement in understanding amorphous carbon's properties based on experimental observations. High data storage density requirement in the coming years necessitates the use of an ultrathin carbon overcoat while maintaining or enhancing its tribological, thermal, optical, and corrosion properties for better recording performance and reliability. Along with experimental techniques, atomistic simulations can be a useful tool to provide fundamental understanding, especially in the cases where experiments are not adequate. This review gives an overview of how atomistic modeling can provide insights into amorphous carbon properties and discuss challenges for such modeling.

In this investigation, we study head wear as a function of a dc bias voltage applied across the head-disk interface (HDI). Head-wear is determined by measuring the change in the heater touch-down power before and after 10 minute wear tests. It is found that applying a positive bias to the disk with respect to the slider results in reduced head wear.

In HDDs, during write operation, the transducer head flies over the media with no continuous monitoring on the adequacy of its flying height against sudden incidents. If the head hits an asperity or a lubricant spill drops from the head, the head momentarily oscillates around its intended fly height. This can compromise the data being written. Only by issuing a read command can the drive evaluate the quality of the data just written. This verification after write is not normally performed because it impacts drive performance. Heat-Assisted Magnetic Recording (HAMR) holds promises for higher data densities in magnetic media into the future and an “always-on” fly height monitoring system is desired. In HAMR, maintaining adequate fly height during write operation is a requirement from both the magnetic writing and the near-field heating antenna operation. The Radio-Frequency (RF) based system described in this work for fly height monitoring is non-magnetic in nature and, since the gap between head and media is smaller than the mean distance between air molecules, this system is also immune to temperature changes in the head or in the ambient. As shown in figure 1, the air gap between the flying head and the media is represented in electrical domain by capacitors (C1 and C2 in fig. 1). An RF signal of frequency significantly above the frequencies taken by the data signal's spectrum (cf. fig. 1) is injected onto the write lines. This RF signal capacitively couples onto all the elements on the head and the head-media interface (cf. fig. 1). When the head changes its fly height, the corresponding capacitance for the air gap changes its value. This varying capacitance behaves as a charge pump, which amplitude modulates (AM) the RF signal and injects this AM-modulated RF signal back into the head wiring. This signal travels back through the suspension and is detected at the pre-amplifier end. The amplitude of the sidebands carry information on fly height changes. The closer the head flies to the media, the stronger the AM sideband tones for the same disturbance in fly height.

Heat-assisted magnetic recording (HAMR) is a promising approach for enabling large increases in the storage density. In HAMR systems, the high temperature working condition brings challenges for head-media interface, where lubricant depletion and carbon graphitization may occur and cause failure. To explore the effect of laser heating on the change of lubricant and carbon overcoat layers, HAMR FID heads were used to heat the media with both CVD and sputtered carbon overcoat (COC) using different laser power. It is found that 90% of the optimized laser current is not enough to fully switch the magnetic medium or cause any visible thickness reduction in both media types. OSA Q-phase images and thickness profiles show increasing laser power induces greater thickness reduction, due to lubricant depletion or carbon wear. Compared with sputtered COC, CVD carbon is considered to be more stable, as lower conductivity was observed in PF TUNA AFM analysis.

Heat-assisted magnetic recording (HAMR) is a promising approach for enabling large increases in the magnetic data storage density. Amorphous carbon is the principal overcoat material of thin-film disks and magnetic heads in the HAMR systems. In this paper, we investigated the recording performance of media with a chemical vapor deposition (CVD) carbon overcoat (COC) and a sputtered COC. We observed that the carbon type has a significant impact on the HAMR recording performance and the heat absorption. Tunneling current atomic force microscopy analysis results show higher surface roughness and peak current in the disk with the sputtered carbon. Track profile and magnetic signal measurement results indicate 90% of the optimized laser current is not enough to fully write the disk with the CVD carbon, while the tracks on the sputtered carbon disk can be written using the same laser current. The difference in the two types of COC can be attributed to the difference in the carbon bonding structure, the optical and electrical properties, the roughness, and the heat absorption behavior.