Download or read book Application of Rarefied Gas Dynamics to the Head Disk Interface in Hard Disk Drives written by Nan Liu and published by . This book was released on 2010 with total page 206 pages. Available in PDF, EPUB and Kindle. Book excerpt: To compete with solid state drives (SSDs), hard disk drives (HDDs) must improve their performance in capacity, speed and reliability, which requires the spacing between the magnetic disk, used to store information, and the magnetic transducer, used to read information from and write information onto the disk, to decrease. This distance is now approaching 5nm, and, accordingly, the distance between a slider, embedding the transducer, and the disk ranges from several nanometers to several micrometers, which makes the gas flowing between the slider and the disk rarefied. This dissertation applies rarefied gas dynamics to investigate several issues related to HDDs' performance. Particle contamination on the slider may scratch the disk and induce loss of data. An improved model is proposed to numerically study particle contamination on a thermal flying-height control (TFC) slider, which adjusts the transducer-disk spacing by use of a small heater embedded in the slider near the transducer. It is found that the currently used model is sufficiently accurate despite its simple form. The temperature increase inside HDDs during operation may affect their reliability. This dissertation derives an analytical formula for the gas-flow induced shear force in the head-disk interface (HDI) and uses it to investigate how the raised temperature affects the slider's flying attitude and the shear forces on the slider and the disk. Numerical prediction of a TFC slider's flying performance lays the foundation for commercial designs of TFC sliders. An improved model is proposed to calculate the heat flux on the TFC slider and it is found that the currently used model is accurate enough for this purpose. Finally, a general approach is proposed to numerically investigate a TFC slider flying in gas mixtures.

Download or read book Study of Dynamics and Nanoscale Heat Transfer of Head Disk Interface in Hard Disk Drives written by Yuan Ma and published by . This book was released on 2018 with total page 104 pages. Available in PDF, EPUB and Kindle. Book excerpt: Since its introduction in 1956, hard disk drives have become one of the dominant products in the industry of data storage. The capacity of the hard disk drives must keep evolving to store the exploding data generated in the era of big data. This demand pushes the development of technologies including heat assisted magnetic recording (HAMR), microwave assisted magnetic recording (MAMR) and bit-patterned media (BPM) to increase the areal density beyond 1Tb/in2. In the development of these technologies, it is essential to have a clear understanding of the dynamics and nanoscale heat transfer behavior across the head-disk interface. In this dissertation, dynamics and nano-scale heat transfer in the head disk interface are discussed. Experimental study of nano-scale heat transfer is conducted with the specifically designed static touchdown experiment. Simulation strategy that incorporates the wave-based phonon conduction theory was also developed. In the flying condition, correlation between the temperature and head disk spacing was found at both passive flying stage and modulation stage. When the flying height increases due to either disk surface microwaviness or contact induced modulation, head temperature will increase, with a slight time delay, indicating the existence of a cooling effect as the head approaches the disk. The static touchdown experiment, which decouples the complicated air bearing from the nano-scale interface was further designed and performed. The heat transfer behavior across a closing nano-scale gap between head and disk was observed and measured. Experimental and simulation results showed general agreement with the theoretical predictions of the wave based theory for radiation and phonon conduction. The effect of different factors including humidity, air pressure, lubricant layer and disk substrate in the static touchdown experiment were also studied separately. Furthermore, the dynamics of HAMR condition was studied with waveguide heads. The laser induced protrusion was found to be around 1~2 nm in height. The findings of this dissertation could be applied to future HAMR head/media design, and the static touchdown experiment could be potentially improved to be a new approach to measure material conduction coefficient and emissivity with high special resolution.

Download or read book Experimental Study of Head disk Interface Dynamics Under the Condition of Near contact Recording for Magnetic Hard Disk Drives written by Mark Joseph Donovan and published by . This book was released on 1995 with total page 300 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Dynamic Load Head disk Interactions and Interface Durability in Magnetic Disk Drives written by Ta-Chang Fu and published by . This book was released on 1995 with total page 128 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book A Study of the Head Disk Interface in Heat Assisted Magnetic Recording Energy and Mass Transfer in Nanoscale written by Haoyu Wu and published by . This book was released on 2018 with total page 114 pages. Available in PDF, EPUB and Kindle. Book excerpt: The hard disk drive (HDD) is still the dominant technology in digital data storage due to its cost efficiency and long term reliability compared with other forms of data storage devices. The HDDs are widely used in personal computing, gaming devices, cloud services, data centers, surveillance, etc. Because the superparamagnetic limit of perpendicular magnetic recording (PMR) has been reached at the data density of about 1 Tb/in^2 , heat assisted magnetic recording (HAMR) is being pursued and is expected to help increase the areal density to over 10 Tb/in^2 in HDDs in order to fulfill the future worldwide data storage demands. In HAMR, the magnetic media is heated locally (~50nm x 50nm) and momentarily (~10ns) to its Curie temperature (~750K) by a laser beam. The laser beam is generated by a laser diode (LD) and focused by a near field transducer (NFT). But the energy and mass transfer at high temperature from the laser heating can cause potential reliability issues. The design temperature of the NFT is much lower than the media’s Curie temperature. However, the distance between the NFT and the media is less than 10nm. As a result, the heat can flow back from the media to the NFT, which is called the back-heating effect. This can cause undesired additional temperature increase on the NFT, shortening its lifetime. Additionally, depletion, evaporation and degradation can happen on the lubricant and the carbon overcoat (COC) layer of the media. The material can transfer from the media to the head at high temperature and cause solid contamination on the head, adversely affecting its reliability. Since the laser heating in HAMR happens at nanoscale spatially and temporally, it is difficult to measure experimentally. In this dissertation, a comprehensive experimental stage, called the Computer Mechanics Laboratory (CML)-HAMR stage, was built to study different aspects of HAMR systems, including the heat and mass transfer in the head-disk interface during laser heating. The CML-HAMR stage includes an optical module, a spinstand module and a signal generation/acquisition module. And it can emulate the HAMR scenario. The head’s temperature was measured during the laser heating using the stage and heads with an embedded contact sensor (ECS). It was estimated, based on a linear extrapolation, that the ECS temperature rise is 139K, 132K, 127K and 122K when the disk is heated to the Curie temperature (~750K) and the head-disk clearance is 0nm, 1nm, 2nm and 3nm, respectively. The heating effect of the ECS was also studied and a related heat transfer experiment was performed. The normalized ECS self heating temperature rise, an indicator of the heat transfer in the head-disk interface (HDI), was measured. It was concluded that the heat transfer coefficient across the HDI strongly depends on the width of the gap size, especially when the gap size is smaller than 1nm. The head disk interaction during the laser heating was studied using a waveguide head, i.e., a HAMR head without the NFT. It showed that the laser heating can cause head surface protrusion. This lowers the fly-height (FH) and results in early touchdown (TD). It was shown that the ratio of touchdown power (TDP) change to the laser current is 0.3mW/mA. The dynamics of the head also changes during the laser heating. It was found that the magnitude of the 1st-pitch-mode vibration on the head increases over time both in short term and long term. The accumulation of material transferred to the head was also investigated. It was found that the solid contamination caused by the laser heating forms in the center of the waveguide. The round-shaped contamination formed on the head surface after laser heating. Finally the disk lubricant reflow after laser heating was studied. In the experiment, a beam of free space laser shines on the rotating disk at different laser powers, disk rotating speeds and repetitions. Then the disk was examined by an optical surface analyzer (OSA). It was found that 80% of the displaced lubricant recovers within 20 minutes. A simulation was also performed. The experiments and the simulation are in good agreement.

Download or read book Head disk Interface Dynamics of Ultra low Flying Air Bearing Sliders for Hard disk Drive Applications written by Brian Hayes Thornton and published by . This book was released on 2003 with total page 430 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Numerical Simulations of the Head disk Interface in Hard Disk Drives written by Puneet Bhargava and published by . This book was released on 2008 with total page 490 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Handbook of Lubrication and Tribology written by Robert W. Bruce and published by CRC Press. This book was released on 2012-07-06 with total page 1173 pages. Available in PDF, EPUB and Kindle. Book excerpt: Since the publication of the best-selling first edition, the growing price and environmental cost of energy have increased the significance of tribology. Handbook of Lubrication and Tribology, Volume II: Theory and Design, Second Edition demonstrates how the principles of tribology can address cost savings, energy conservation, and environmental protection. This second edition provides a thorough treatment of established knowledge and practices, along with detailed references for further study. Written by the foremost experts in the field, the book is divided into four sections. The first reviews the basic principles of tribology, wear mechanisms, and modes of lubrication. The second section covers the full range of lubricants/coolants, including mineral oil, synthetic fluids, and water-based fluids. In the third section, the contributors describe many wear- and friction-reducing materials and treatments, which are currently the fastest growing areas of tribology, with announcements of new coatings, better performance, and new vendors being made every month. The final section presents components, equipment, and designs commonly found in tribological systems. It also examines specific industrial areas and their processes. Sponsored by the Society of Tribologists and Lubrication Engineers, this handbook incorporates up-to-date, peer-reviewed information for tackling tribological problems and improving lubricants and tribological systems. The book shows how the proper use of generally accepted tribological practices can save money, conserve energy, and protect the environment.

Download or read book Partial contact Head Disk Interface for Ultrahigh Density Magnetic Recording written by Du Chen and published by . This book was released on 2008 with total page 342 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Numerical and Experimental Investigations of the Head disk Interface written by Maik Duwensee and published by . This book was released on 2007 with total page 230 pages. Available in PDF, EPUB and Kindle. Book excerpt: Experimental techniques were developed for the investigation of slider dynamics for ultra-low spacing head/disk interfaces. Voltage pulsing and mapping techniques were established for the investigation of clearance and flying height modulation as functions of head/disk interface parameters. Numerical methods were developed to analyze forces acting on sliders of discrete track recording head/disk interfaces. A finite-element-based air bearing simulator was used to predict the steady state flying characteristics of arbitrarily shaped slider contours flying over discrete track recording disks. The direct simulation Monte Carlo method was used to simulate the rarefied gas flow in nano-channels.

Download or read book Handbook of Lubrication and Tribology Volume II written by Robert W. Bruce and published by CRC Press. This book was released on 2012-07-06 with total page 1139 pages. Available in PDF, EPUB and Kindle. Book excerpt: Since the publication of the best-selling first edition, the growing price and environmental cost of energy have increased the significance of tribology. Handbook of Lubrication and Tribology, Volume II: Theory and Design, Second Edition demonstrates how the principles of tribology can address cost savings, energy conservation, and environmental pr

Download or read book Head disk Interface Studies in Magnetic Disk Drives written by Mike Suk and published by . This book was released on 1991 with total page 320 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Head disk suspension Dynamics written by Yong Hu and published by . This book was released on 1996 with total page 218 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Numerical Investigation of the Effects of Operational Shock and Disk Surface Pattern on the Dynamics of Head Disk Interface in Hard Disk Drives written by Liping Li and published by . This book was released on 2013 with total page 121 pages. Available in PDF, EPUB and Kindle. Book excerpt: This dissertation investigates the effects of shock and the disk surface pattern on the head disk interface (HDI) response in hard disk drives (HDDs). A new local adaptive mesh method is proposed at the end to improve the accuracy and efficiency of the algorithm to simulate the sliders' steady flying attitudes. Over the past decades, there has been an increase in the demand of HDDs used in portable devices. In such applications, the work performance of a HDD mainly depends on its ability to withstand external disturbances. Studies of the HDD's responses and failures during external shocks can be very beneficial for improving the HDD's design. A multi-body operational shock (op-shock) model is developed for this purpose in this thesis. The Guyan reduction method is used to model all the components considered in the op-shock model (a disk, a spindle motor, a base plate, a pivot and a head actuator assembly (HAA)). A fluid dynamic bearing (FDB), between the rotating and stationary units in the spindle motor, is simplified as a spring-dashpot system to save computation efforts. The same simplification is applied to a ball bearing (BB) system between the rotating and stationary units in the actuator pivot. Then the reduced models for all the components are assembled to obtain a complete multi-body op-shock model. Four models which include different components are introduced in this thesis to investigate various components' effects on the HDD's operating performance. The HDDs' failure mechanisms are also studied. It is found that different components influence the HDI responses in different ways. The ramp load/unload (LUL) technology has been proved to be a better alternative to the contact start-stop (CSS) approach due to the advantages of increasing areal density and greater durability. However, the application of the LUL ramps in the HDDs increases the possibility of collisions between the disk and the ramps since the ramps sit closely to the disk's outer radius. Therefore, it is important to study the ramp effects on the HDD's response during a shock. A reduced model of a deformable ramp is developed and implemented to the multi-body op-shock model. Numerical analyses using three ramp models (no-ramp model, rigid ramp model and deformable ramp model) are carried out to study the HDD's failure dependence on different ramp models. Bit patterned media (BPM) recording is one of the promising techniques for future disk drives in order to increase the areal density above 4 Tbit/in2. In patterned media, an individual recorded bit is stored in a distinct magnetic island. Thus, the BPM can change the topography of the disk surface and has an effect on the flying characteristics of the air bearing sliders. Proper designs of sliders and disks in the HDDs are required in order to achieve a stable work performance. So a simulator to model a slider's flying condition over a BPM disk is particularly important. Three methods (the averaging method, the Homogenization method and the Taylor expansion Homogenization methods) are implemented to simulate a slider's flying attitude, and finally an economical accurate method is chosen (the Taylor expansion Homogenization method) to investigate the slider's dynamics on partially planarized patterned media. In modern HDDs, the requirement of small and steady head disk spacing leads to more complicated air bearing surface designs. Thus it is challenging for an air bearing simulator to accurately capture the pressure under a slider's surface. A new local adaptive grid-generating algorithm is developed and is used to simulate the sliders' steady flying attitude. Local finer meshes (mesh's dimension decreases to half) are created on the nodes of the current grids, which have pressure gradients or geometry gradients larger than a pre-defined tolerance. Two sliders are used to demonstrate the applicability of this method. It is found that this new local adaptive grid-generating method improves the stability and efficiency of the simulation scheme.

Download or read book Tribological Investigations of the Head disk Interface of Hard Disk Drives written by Qing Zhao and published by . This book was released on 1999 with total page 424 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Numerical and Experimental Investigations of a Hard Disk Drive Subject to Shock and Vibration written by Eric Michael Jayson and published by . This book was released on 2003 with total page 372 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Some Tribological Aspects of the Hard Disk Drive Head Disk Interface for Quasi Contact Conditions written by YUNG-KAN CHEN and published by . This book was released on 2015 with total page 125 pages. Available in PDF, EPUB and Kindle. Book excerpt: The magnetic recording hard disk drive has been one of the most important storage strategies since 1956. Among all storage solutions, hard disk drives possess the unrivaled advantageous combination of storage capacity, speed, reliability and cost over optical strategies and flash memory. Unlike other storage solutions, hard disk drives utilize a mechanical interface to perform the magnetic read/write process, and therefore its success relies heavily on the stability of the head-disk interface (HDI) which is composed of a magnetic transducer carried by an air bearing slider, an air gap of a few nanometers thick, and a disk surface coated with multiple layers of molecularly-thin films. This dissertation addresses the physics of the interface in terms of contact detection, lubricant modulation and wear. Contact detection serves as one of the core requirements in HDI reliability. The writing process demands a strict spacing control, and its accuracy is based on a proper choice of a contact reference from slider dynamics and therefore the heads’ signal. While functioning in a real drive the only feedback signal comes from sensors neighboring the read-write transducer, and a high speed head-disk contact is associated with complex structural responses inherent in an air-bearing/suspension/lubricant system that may not be well explained solely by magnetic signals. Other than studying the slider-disk interaction at a strong interplay stage, this dissertation tackles the contact detection by performing component-level experimental and simulation studies focusing on the dynamics of air-bearing sliders at disk proximity. The slider dynamics detected using laser Doppler vibrometry indicates that a typical head-disk contact can be defined early as in-plane motions of the slider, which is followed by vertical motions at a more engaged contact. This finding confirms and is in parallel with one of the detection schemes used in commercial drives by magnetic signals. Lubricated disk surfaces play an important role in contact characteristics. As the nature of contact involves two mating surfaces, the modulation of disk lubricant films should be investigated to further understand the head-disk contact in addition to the slider dynamics. In this dissertation, the lubricant modulation is studied under various contact conditions with reference to slider dynamics. It is found that lubricant modulation can be directly associated with the slider’s dynamics in a location specific way, and its evolution is likely to affect the slider’s stable back-off fly-height as the contact is retracted. In addition to modulations at contact proximities, the lubricant response to passive flying and continuous contacting conditions are also addressed for different lubricant types and thicknesses. By integrating the observations from slider dynamics and lubricant modulations, we can establish an insightful understanding towards the transition from flying to the onset of contact. Head wear is also a concern when an erroneous contact detection occurs or imperfections from disk surface exists. Typically a protective diamond-like carbon (DLC) layer of thickness 1-2 nm is coated over the area of the reader/writer shields, and this film loss poses a threat to long term reliability. In this dissertation, in-situ methods of monitoring head wear is proposed in two ways. One method is to evaluate the touchdown power variations as a measure of spacing increase by DLC wear, which was verified by using Auger Electron Spectroscopy, and the other method studies the temperature contact sensor response to gauge mechanical wear. The later possesses the advantage of detecting wear without going into actual contact, but it may be affected by the location difference between the touchdown sensor and wear area.