Investigation of Bit Patterned Media, Thermal Flying Height Control Sliders and Heat Assisted Magnetic Recording in Hard Disk Drives PDF Download
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Author: Hao Zheng
Publisher:
ISBN: 9781267070210
Category :
Languages : en
Pages : 230
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Book Description
Many advanced technologies in the field of magnetic disk recording are being studied in order to achieve areal densities in excess of 1.6 gigabits per square millimeter (1 terabits per square inch). Bit patterned media (BPM) is one of these promising technologies. By using disks with physically separated magnetic patterns instead of conventional continuous media, bit patterned media avoid magnetic interference between adjacent bits and improve the thermal stability of the media. Currently, thermal flying height control (TFC) sliders are commonly used to compensate thermal effects during reading and writing and to maintain a stable and ultra-low head/disk spacing during drive operation. Heat assisted magnetic recording (HAMR) has been introduced in order to address difficulties in writing of information on magnetic media with high coercivity. By using a laser beam to locally heat the media above its Curie temperature, the magnetic material momentarily reduces its coercivity and permits writing of information on the disk. However, the method raises concerns about the stability of the lubricants on the disk. In this dissertation, we focus on the investigation of the head/disk interface for bit patterned media, the design of thermal flying height control sliders, and the implementation of heat assisted magnetic recording. In particular, we use a finite-element-based air bearing simulator to study the steady-state flying characteristics of sliders flying over bit patterned media. This air bearing simulator is then combined with a thermo-mechanical model of a slider in order to analyze thermal flying height control sliders featuring dual heater/insulator elements. Next, a finite element model of a thermal flying height control slider with an integrated heat assisted magnetic recording optical system is developed to study the effect of heat dissipation along the laser delivery path on the performance of the HAMR-TFC slider. The design parameters of the dual thermal flying height control heaters are optimized in order to minimize the dependence of the head/disk spacing on laser induced thermal effects. Finally, experimental techniques are developed to investigate the photo-thermo stability and tribological properties of HAMR-type lubricants which are designed to be resistant to the high temperatures experienced under laser exposure.
Author: Hao Zheng
Publisher:
ISBN: 9781267070210
Category :
Languages : en
Pages : 230
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Book Description
Many advanced technologies in the field of magnetic disk recording are being studied in order to achieve areal densities in excess of 1.6 gigabits per square millimeter (1 terabits per square inch). Bit patterned media (BPM) is one of these promising technologies. By using disks with physically separated magnetic patterns instead of conventional continuous media, bit patterned media avoid magnetic interference between adjacent bits and improve the thermal stability of the media. Currently, thermal flying height control (TFC) sliders are commonly used to compensate thermal effects during reading and writing and to maintain a stable and ultra-low head/disk spacing during drive operation. Heat assisted magnetic recording (HAMR) has been introduced in order to address difficulties in writing of information on magnetic media with high coercivity. By using a laser beam to locally heat the media above its Curie temperature, the magnetic material momentarily reduces its coercivity and permits writing of information on the disk. However, the method raises concerns about the stability of the lubricants on the disk. In this dissertation, we focus on the investigation of the head/disk interface for bit patterned media, the design of thermal flying height control sliders, and the implementation of heat assisted magnetic recording. In particular, we use a finite-element-based air bearing simulator to study the steady-state flying characteristics of sliders flying over bit patterned media. This air bearing simulator is then combined with a thermo-mechanical model of a slider in order to analyze thermal flying height control sliders featuring dual heater/insulator elements. Next, a finite element model of a thermal flying height control slider with an integrated heat assisted magnetic recording optical system is developed to study the effect of heat dissipation along the laser delivery path on the performance of the HAMR-TFC slider. The design parameters of the dual thermal flying height control heaters are optimized in order to minimize the dependence of the head/disk spacing on laser induced thermal effects. Finally, experimental techniques are developed to investigate the photo-thermo stability and tribological properties of HAMR-type lubricants which are designed to be resistant to the high temperatures experienced under laser exposure.
Author: Sripathi Vangipuram Canchi
Publisher:
ISBN:
Category :
Languages : en
Pages : 304
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Book Description
The storage industry's density target of 10 Tb/sq.in. in hard disk drives within the next decade requires a significant change in head-disk interface (HDI) architecture, and it likely involves a combination of new technologies such as Heat Assisted Magnetic Recording and Bit Patterned Media Recording to mention a few. Independent of the actual recording technology, it is necessary to reduce the magnetic spacing to within 2nm, which implies a physical spacing as little as 0.25nm at the read-write transducer location. At such a small spacing intermittent contact between the slider and the lubricant layer or hard overcoat surface on the disk becomes inevitable. A continuous lubricant-contact HDI may in fact be necessary to meet future magnetic spacing needs. While the new recording technologies impose a significantly tighter budget on the slider dynamics in all three directions (vertical, down-track and off-track), the contacting HDI must be reliable, ensuring no degradation of lubricant or disk overcoats even after prolonged operation. The current slider technology uses Thermal Fly-height Control (TFC) to bring the read-write portion of the slider closer to the disk by resistive heating induced thermal deformation/protrusion. While subnanometer level clearance can be achieved using the TFC, slider stability and HDI reliability at very small spacing remains to be understood. In order to further reduce the magnetic spacing using the TFC architecture, a recording strategy with a small portion of the thermal protrusion in intermittent or continuous contact with the lubricant layer of the disk has been proposed, but there is limited theoretical and experimental work to verify the feasibility of this technique. The focus of this work is to advance the understanding of TFC slider dynamics and slider-lubricant interactions at a HDI with contact through experiments and modeling. Slider-lubricant contact is experimentally established by carefully controlling the TFC heater power, and the three dimensional slider dynamics under lubricant-contact is investigated. The degree of slider-lubricant contact is shown to influence the slider's vibration modes. A simple two degree of freedom model that accounts for nonlinearities at the HDI through quadratic and cubic approximations is used to analytically investigate the interesting features of this problem. It is shown that the thermal protrusion induced by the heater power can cause the system modes to couple unfavorably for certain heater power ranges, and this condition can manifest itself as large amplitude slider vibrations. Experiments are conducted to understand the interplay between slider dynamics and disk lubricant evolution under the thermal protrusion for contact and near contact conditions. Slider dynamics and lubricant rippling are shown to be well correlated and a mechanism of lubricant transfer from the slider to the disk at the onset of contact is demonstrated. Parametric investigations are conducted to understand the effect of lubricant type and thickness on lubricant distribution, lubricant depletion and subsequent lubricant recovery behavior at a contacting HDI.
Author: Reuben Jueyuan Yeo
Publisher: Springer
ISBN: 9811048827
Category : Technology & Engineering
Languages : en
Pages : 184
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Book Description
This book presents the latest research in ultrathin carbon-based protective overcoats for high areal density magnetic data storage systems, with a particular focus on hard disk drives (HDDs) and tape drives. These findings shed new light on how the microstructure and interfacial chemistry of these sub-20 nm overcoats can be engineered at the nanoscale regime to obtain enhanced properties for wear, thermal and corrosion protection – which are critical for such applications. Readers will also be provided with fresh experimental insights into the suitability of graphene as an atomically-thin overcoat for HDD media. The easy readability of this book will appeal to a wide audience, ranging from non-specialists with a general interest in the field to scientists and industry professionals directly involved in thin film and coatings research.
Author: Jinglin Zheng
Publisher:
ISBN:
Category :
Languages : en
Pages : 224
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Book Description
As a recent development to further reduce the flying height of a magnetic head in hard disk drives (HDDs) to nanometers, thermal flying-height (TFC) control technology is now widely applied in the HDD industry because it enables consistent read/write spacing, increased storage density and improved HDD reliability. The fast development of TFC technology presents new challenges to head designers because of the complicated structure of a TFC head, the thermo-mechanical-coupling effects and tribology issues arising at nanometer read/write spacing. A steady-state TFC solver dedicated to obtaining the steady-state flying attitude of a TFC slider is developed in this thesis. This solver uses a finite volume based solver (CML static solver) to solve the generalized Reynolds equation and obtain the pressure and spacing fields in the air bearing and a commercial coupled-field solver (ANSYS) to obtain the stress and strain fields due to internal heating. An iterative procedure is adopted to consider the cooling effect of the air bearing on the heater-induced protrusion. Accuracy of the solver is verified by drive-level magnetic tests on several combinations of air bearing and heater designs. TFC sliders' performances under different ambient conditions are investigated based on the TFC solver. It is found that the thermal actuation efficiency of a TFC slider increases with altitude because of the weakened cooling and reduced air bearing stiffness at the transducer area at a higher altitude. In addition, a TFC slider maintains a more consistent read/write spacing at different humidity levels, compared with a non-TFC slider, because the thermal actuation is able to compensate part of the pressure loss caused by water condensation. A TFC slider's flying height in air-helium mixtures is shown to be a highly nonlinear function of the fraction of helium in the gas mixture due to the combined effects of the gas mean free path, viscosity and heat conductivity. These results provide general guidelines for heater and ABS designers to reduce a TFC slider's sensitivity to ambient conditions and improve HDD reliability. A touchdown numerical model for predicting TFC sliders' dynamics at touchdown and over-pushed conditions is developed and implemented based on the CML dynamic simulator. It extends the solution of the time-varying generalized Reynolds equation to near-contact and contact conditions using a statistical multi-asperity approach. Various interfacial forces are considered by use and further development of a sub-boundary lubrication model to capture important tribological effects occurring at touchdown. This model is able to predict a TFC slider's unstable dynamics at the beginning of touchdown, which has been discovered in many related experimental studies. The effects of different head-disk interface factors are investigated using this numerical model. It is found that the suspension is actively involved in the TFC slider's bouncing vibrations and has a significant influence on the excited second air bearing pitch mode. It is also shown that adhesion force serves as an essential factor in exciting the second air bearing mode whereas other interfacial forces only affect details of the slider's bouncing behaviors. By changing the interfacial properties, namely, the interface roughness and lubricant thickness, the variation of interfacial forces with spacing reduction differs, which leads to very different touchdown patterns. With a rougher interface profile the slider smoothly transfers from a flying stage to a sliding stage. With a smoother interface profile the slider experiences a flying-bouncing-sliding transition. With the smoothest interface the slider goes through a flying-bouncing-surfing-sliding transition. The touchdown behaviors predicted by the numerical simulator are correlated with experiments conducted on industry-provided head parts with the same ABS and suspension design. Similar touchdown stages and excited modes are also discovered in the experiments. Though experiments showed a slider spectrum with richer frequency components, the modes missed from the numerical simulations are recovered by conducting a harmonic analysis on a full HGA model with air bearing included. The different touchdown dynamic patterns predicted here result in significant differences in the successful touchdown detection, which is very important for realizing reliable read/write operations, and therefore this work provides guidelines for head disk interface (HDI) optimization. The general approach proposed here is also applicable to studies on the effects of other important HDI factors, such as air bearing geometric features, heater-induced protrusion profiles, and suspension design parameters, and on the slider's touchdown dynamics behaviors, which will assist in obtaining solutions to performance and reliability issues in current hard disk drives.
Author: Haoyu Wu
Publisher:
ISBN:
Category :
Languages : en
Pages : 114
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Book Description
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.
Author: Tan Duy Trinh
Publisher:
ISBN:
Category :
Languages : en
Pages : 185
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Book Description
International Data Corporation (IDC) estimates that hard disk drives will still be the main storage device for storing digital data in the next 10 years, holding approximately 80% of the data inside data centers. To increase the areal density of hard disk drives, the mechanical spacing between the head and disk surface has decreased to approximately 1nm. At such a small spacing, tribology of the head-disk interface, including head-disk contacts, wear, material buildup, and lubricant transfer, become increasingly more important for the reliability of hard disk drives. In addition to small spacing, heat-assisted magnetic recording (HAMR) technology aims to deliver higher areal density recording by heating up the media surface to a few hundred Celsius degrees, facilitating the writing process. High temperature at the head and disk surfaces cause serious reliability issues for the head-disk interface (HDI). Therefore, understanding of the main factors that affect the reliability of the head-disk interface is an essential task. In this dissertation, the effect of bias voltage and helium environment on the tribological performance of the head-disk interface is investigated. To do this, we first simulated the flying characteristics of the slider as a function of bias voltage in air and helium environment. Thereafter, an experimental study was performed using custom built tester located inside a sealed environmental chamber to study the effect of air and helium on wear and lubricant redistribution at the head-disk interface during load-unload. We investigated the effect of bias voltage and relative humidity on wear, material buildup, and nano-corrosion on the slider surface. Finally, we have studied laser current and laser optical power in heat-assisted magnetic recording as a function of operating radius, head-disk clearance, media design, and their effects on the life-time of the head-disk interface. The results of this dissertation provide guidance for the effect of bias voltage, relative humidity, and helium environment on wear, material buildup, corrosion, and lubricant transfer at the head-disk interface. More importantly, our experimental study in heat-assisted magnetic recording leads to a better understanding of the main factors that cause failure of the HAMR head-disk interface. Our results are important for the improvement of the tribological performance and reliability of perpendicular magnetic recording (PMR) and heat-assisted magnetic recording (HAMR) head-disk interface.
Author: Yuan Ma
Publisher:
ISBN:
Category :
Languages : en
Pages : 104
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Book Description
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.
Author: Uwe Boettcher
Publisher:
ISBN: 9781124584416
Category :
Languages : en
Pages : 221
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Book Description
In this dissertation, we focus on optimization of cross-track and vertical positioning of the read/write element over the data track. First, a data-based approach is presented for modeling and controller design of a dual-stage servo actuator in a hard disk drive. Based on discrete-time models, different dual-stage track-following controllers were designed using classic and H-infinity loop shaping techniques. The controllers were implemented in real-time. Next, an input shaping algorithm based on convex optimization techniques is presented for closed-loop discrete-time linear time-invariant (LTI) system. The proposed algorithm allows closed-loop signals to be subjected to linear constraints on amplitude and rate of change. As an illustrative example the seeking process in a hard disk drive is investigated and experimentally verified. To study the dependence of the read signal on cross-track and vertical motion, a straightforward analytical model for the read back signal is derived for perpendicular and longitudinal magnetic recording. The model captures the contribution of a single bit rather than the contribution of a bit transition which makes it applicable to patterned media as well as continuous media. In addition, a novel method of measuring the relative head-medium spacing based on the measurement of the read back signal from servo sectors is developed. The spacing measurement is tested experimentally on a spin stand where the flying height is varied using the resistance heater element in a thermal flying height control slider. In addition, voltage step response measurements were obtained for data based modeling. Finally, a dynamic model of the resistance heater in a thermal flying height control (TFC) slider is identified based on experimentally obtained step-input data. A generalized realization algorithm is used for identification of a discrete-time dynamic model of the resistance heater. Based on the identified model and convex optimization techniques, a computational scheme is proposed to obtain optimized feed forward input profiles to the heater element that minimize repeatable flying height variations. The optimized input signals were applied to the heater and greatly reduced flying height variations were observed in spinstand experiments.
Author: Jia-Yang Juang
Publisher:
ISBN: 9780542825187
Category :
Languages : en
Pages : 434
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Book Description
The key contributions of this dissertation are the identification of some of the mechanical challenges inherent in ultrahigh density magnetic recording required for the next generation of hard disk drives as well as some solutions to address these challenges.
Author: Nan Liu
Publisher:
ISBN:
Category :
Languages : en
Pages : 206
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Book Description
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.
