Hard Disk Drives - Magnetic Recording

Lubricant accumulation on the slider's surface of a hard disk drive (HDD) has a detrimental effect on its read/write performance. Air flow through the slider-disk clearance moves some of the lubricant from the air-bearing surface (ABS) toward the slider's lateral walls where it accumulates. In this article, we show by numerical simulations that the lubricant accumulation characteristics are strongly dependent on the slider's flying height, skew angle and ABS design. The lubricant flow on the slider's surface is quantified numerically. Air shear stress, air pressure and disjoining pressure are used as driving forces in the simulations. The lubricant thickness profile and volume evolution are calculated for two states of the HDD: operating and at rest. In the first state, lubricant is driven by air shear stress toward the trailing edge of the slider where it accumulates on the deposit end. In the second state, lubricant from the deposit end flows back into the ABS driven by the action of disjoining pressure. Lubricant accumulation on the four lateral walls of the slider is taken into account. The lateral walls are unfolded to study the flow using a two-dimensional lubrication model. The effects of flying height, skew angle and slider design on the accumulation removal of lubricant from the ABS are determined for the two states of the drive. Keywords Air bearings Á Lubricant transfer Á Head–disk interface Á Hard disk drive

A hard disk drive (HDD), hard disk, hard drive or fixed disk is a data storage device used for storing and retrieving digital information using one or more rigid ("hard") rapidly rotating disks (platters) coated with magnetic material. The platters are paired with magnetic heads arranged on a moving actuator arm, which read and write data to the platter surfaces. [2] Data is accessed in a random-access manner, meaning that individual blocks of data can be stored or retrieved in any order and not only sequentially. HDDs are a type of non-volatile memory, retaining stored data even when powered off. Introduced by IBM in 1956, [3] HDDs became the dominant secondary storage device for general-purpose computers by the early 1960s. Continuously improved, HDDs have maintained this position into the modern era of servers and personal computers. More than 200 companies have produced HDD units, though most current units are manufactured by Seagate, Toshiba and Western Digital. As of 2015, HDD production (exabytes per year) and areal density are growing, although unit shipments are declining. The primary characteristics of an HDD are its capacity and performance. Capacity is specified in unit prefixes corresponding to powers of 1000: a 1-terabyte (TB) drive has a capacity of 1,000 gigabytes (GB; where 1 gigabyte = 1 billion bytes). Typically, some of an HDD's capacity is unavailable to the user because it is used by the file system and the computer operating system, and possibly inbuilt redundancy for error correction and recovery. Performance is specified by the time required to move the heads to a track or cylinder (average access time) plus the time it takes for the desired sector to move under the head (average latency, which is a function of the physical rotational speed in revolutions per minute), and finally the speed at which the data is transmitted (data rate). The two most common form factors for modern HDDs are 3.5-inch, for desktop computers, and 2.5-inch, primarily for laptops. HDDs are connected to systems by standard interface cables such as PATA (Parallel ATA), SATA (Serial ATA), USB or SAS (Serial attached SCSI) cables. As of 2016, the primary competing technology for secondary storage is flash memory in the form of solid-state drives (SSDs), which have higher data transfer rates, better reliability, [4] and significantly lower latency and access times, but HDDs remain the dominant medium for secondary storage due to advantages in price per bit. [5][6] However, SSDs are replacing HDDs where speed, power consumption and durability are more important considerations. [7][8] Hybrid drive products have been available since 2007. [9] These are a combination of HDD and SSD technology in a single device, also known by the initialism SSHD.

A reliability model for the hard disk drive (HDD) is developed, focusing on head-disk separation as the primary independent variable. Among the many factors contributing to reliability, the role of water vapor is described for the first time. An experimental method based on magnetic spacing loss theory is used to characterize the head-media separation as a function of temperature, altitude, humidity, and HDD operating mode. A statistical model based on these empirical data is developed to predict HDD reliability for various operating conditions. The predictive capability of the model is verified experimentally through application to HDD product reliability test data.

Optical disk (OD) and drive (ODD) are important interfaces used for recording digital streams of bits that represent multimedia with analog nature or discrete data. Enhancing the ODDs in terms of reading/writing (operation) speed is vital as multi-layer (ML) ODs with high capacities are available in the market. This paper presents a simple strategy to enhance operation speed in ODDs by multi optical pickup unit (MOPU) 1 that leads to surprisingly higher transfer rates. The main considerations with different working modes plus theoretical and physical upper bounds are studied. To keep compatibility, the MOPU method is independent of the OD types or optical lens (OL) designs and based on the ODD hardware placement, so all ODs will be also readable at higher rates. Paper also discusses improvements achieved in experimental results based on prototypes.

The intermediaries are important organisations in mitigating systemic failures. Few of such failures
are those of university–industry linkages (UILs). Although there are several previous studies, they did
not pay adequate attention on how these intermediaries accumulate their capabilities that are necessary
to perform their roles over time. This study will try to partially fill in such gap by investigating
capabilities-building processes of intermediaries. The intermediaries in Hard Disk Drive (HDD)
industry in Thailand was selected as a case study. Qualitative data was collected from 20 semi-structured
and in-depth interviews of intermediaries’ management, university researchers and industrial companies
in the intermediaries’ networks. The findings show that the intermediaries play consulting, brokering,
mediating and resources providing roles. They assist to increase levels of interactions between university
and industry, transform informal to formal relationships and nurture potential human resources
for the industry. However, performing such activities depends on the intermediaries’ capabilities.
Four key capabilities encompass network capabilities, coordination capabilities, knowledge-building
capabilities and management capabilities. Underneath them, strategic capabilities, depending on
leadership, engender the intermediaries’ visions and strategies. Human resources development is
stimulated through individual and collective learning. These four capabilities are embedded into the
existing organisational systems by using mentoring and on-the-job training for newcomers, building
up the database system and arranging meetings for knowledge sharing on a regular basis. However,
discontinuity of government supports leads to a decrease in network members, transformation of
formal relationships back to informal ones and the close down of intermediary.

This paper presents a comprehensive non-exhaustive comparative study of hard disk drive read-channel equalization techniques used in the readback process of magnetically stored information. The main read channel architectures: partial-response maximum likelihood (PRML) and decision feedback equalization (DFE) based systems, are compared in power consumption, layout area, data signalling rate and data density. This work focuses on the key component of the read channel, presenting a continuous-time analog solution for the pulse-slimming equalizer capable of reducing power consumption and die area by a factor of ten, whilst showing equivalent response to a FIR filter implementation

We have investigated the effect of film thickness of a perfluoropolyether lubricant, Zdol 4000, on slider-disk spacing, or clearance.
The major conclusion of this work is that the Zdol lubricant impacts the slider-disk spacing. Adec rease in the film thickness of Zdol
4000 by
10A ˚ results in an increase in the effective slider-disk spacing by
1 nm. The effect of end groups on slider-disk spacing is
also investigated using the Zdol-TX and Z-Tetraol perfluoropolyether lubricants. At similar molecular weights and film thicknesses,
the end groups do not affect the slider-disk spacing by causing any additional interference. The slider-disk interference is therefore
attributed to the attractive van der Waals interaction between the slider and the disk surface that causes the Zdol main chain to
interact with the slider surface, giving rise to a friction force.

To achieve a feasible heat-assisted magnetic recording (HAMR) system, a near-field transducer (NFT) is necessary to strongly focus the optical field to a lateral region measuring tens of nanometres in size. An NFT must deliver sufficient power to the recording medium as well as maintain its structural integrity. The self-heating problem in the NFT causes materials failure that leads to the degradation of the hard disk drive performance. The literature reports NFT structures with physical sizes well below 1 micron which were found to be thermo-mechanically unstable at an elevated temperature. In this paper, we demonstrate an adiabatic NFT to address the central challenge of thermal engineering for a HAMR system. The NFT is formed by an isosceles triangular gold taper plasmonic waveguide with a length of 6 µm and a height of 50 nm. Our study shows that in the full optically and thermally optimized system, the NFT efficiently extracts the incident light from the waveguide core and can improve the shape of the heating source profile for data recording. The most important insight of the thermal performance is that the recording medium can be heated up to 866 K with an input power of 8.5 mW which is above the Curie temperature of the FePt film while maintaining the temperature in the NFT at 390 K without a heat spreader. A very good thermal efficiency of 5.91 is achieved also. The proposed structure is easily fabricated and can potentially reduce the NFT deformation at a high recording temperature making it suitable for practical HAMR application.

The pressure distribution in a squeeze film air bearing depends on the water vapor pressure and the saturation vapor pressure of water
at ambient temperature. When the water vapor pressure is compressed beyond the saturation vapor pressure, a portion of the water
vapor condenses, thus reducing the total gas pressure in the air bearing. This condensation mechanism thus reduces the flying height of
the slider. Using a magnetic recording system for experiments, we quantified the effect of condensation on flying height by measuring the
dependence of magnetic spacing on relative humidity.We developed a numerical model based on the proposed mechanism that matches
the experimental data and provides a detailed view of the air-bearing response to humidity.

Shingled magnetic recording is a promising option to sustain the historical areal density growth of hard disk drives while retaining conventional heads and media. Nevertheless, highly scaled shingled magnetic recording is subject to severe intertrack interference (ITI), fewer grains per channel bit and therefore lower signal-to-noise ratio (SNR). This naturally demands twodimensional (2D) read channel signal processing, which has an inherently large spectrum of detection performance vs. computational complexity trade-off. By concurrently detecting multi-track readback signals from a read head array, joint 2D signal detection can fully utilize the 2D interference to maximize the detection performance at the penalty of the highest computational complexity. Due to the justifiable concern on its practical feasibility, multi-track joint 2D detection has not been thoroughly studied from either the detection performance or silicon implementation perspective. To fill this missing link, this paper presents a comprehensive study of multi-track joint 2D signal detection performance and silicon implementation cost. We further present an interleaved pipelining strategy to reduce joint 2D signal detector silicon consumption. By carrying out comprehensive simulations and ASIC (applicationspecific integrated circuit) design, this study shows that multi-track joint 2D signal detection is a practically attractive option with superior detection performance and affordable silicon cost, especially when taking account of projected CMOS technology scaling towards 16nm and below.

We have investigated the tribological properties of a novel perfluoropolyether (PFPE) lubricant truncated on one end by a hydroxyl group and on the other end by a cyclotriphosphazene derivative. A measurement of the friction force as a function of molecular weight indicates that the dynamic clearance between the slider and the disk can be reduced by ∼1.5 nm by decreasing the molecular weight from 5300 to 2400 g/mol. However, the thermodynamic film stability of the novel PFPE lubricants, as determined by surface energy measurements and ellipsometric imaging of lubricant dewetting, becomes increasingly unstable at lower film thicknesses with decreasing molecular weight. Measurements conducted on lubricant mobility indicate that the novel PFPE lubricants are relatively immobile compared to the Zdol perfluoropolyether lubricants and hence resist film thinning to a greater degree. These data provide the direction for the optimization of the molecular weight of these novel PFPE lubricants.

This paper reviews the effect of the design evolution of modern magnetic hard disk drives on tribological challenges, such as wearless high-speed contact, ultra-thin lubrication, corrosion protection, and requirements of thinner carbon overcoat. We will present some data on slider wear measurements on the order of nanometers, lubricant migration and depletion as linked to tribological reliability, lubricant bonding kinetics on different carbon overcoats, corrosion protection using lubricant and thin carbon coatings, and lubricant de-wetting.

This paper presents a continuous time servo demodulator for magnetic disk drives implemented as a programmable current mode operated Gm C filter. This first order filter consists of pseudo differential balanced transconductors and of a MOSFET bank array to implement a variable integrating capacitor. Simulation results are presented.

We investigate a tapered, hybrid plasmonic waveguide which has previously been proposed as an optically efficient near-field transducer (NFT), or component thereof, in several devices which aim to exploit nanofocused light. We numerically analyze how light is transported through the waveguide and ultimately focused via effective-mode coupling and taper optimization. Crucial dimensional parameters in this optimization process are identified that are not only necessary to achieve maximum optical throughput, but also optimum thermal performance with specific application towards heat-assisted magnetic recording (HAMR). It is shown that existing devices constructed on similar waveguides may benefit from a heat spreader to avoid deformation of the plasmonic element which we achieve with no cost to the optical efficiency. For HAMR, our design is able to surpass many industry requirements in regard to both optical and thermal efficiency using pertinent figure of merits like 8.5% optical efficiency.

We investigate the energy conversion process and subsequent thermal and bit-writing performance of a plasmonic near-field transducer (NFT) under steady-state operation within heat-assisted magnetic recording (HAMR) devices. The NFT is composed of metal-insulator-metal (MIM) layers that are designed to localize heating and produce optimal thermal gradients in order to relieve parasitic heating effects in the NFT. The thin-film MIM structure confines the electromagnetic energy in the down-track direction while cross-track confinement is achieved by tapering the insulator feature of the MIM. A comparative analysis using Gold and a number of novel Au alloys is undertaken. Modeled performance shows excellent thermal spot confinement (50 × 50 nm2) of temperatures above 650 K at an input laser power of 830 nm of less than 5 milliwatts. In addition, micromagnetic simulations using a stochastic Landau-Lifshitz-Bloch equation yield excellent signal to noise ratio with minimum jitter of under 2 nm when recording.

We have investigated the effect of the molecular weight (MW) and film thickness of a perfluoropolyether lubricant, Zdol, on the slider–disk spacing loss, or clearance. The major conclusion of this work is that Zdol films as thin as 10 Å can reduce the slider–disk clearance by 2 nm or more in the molecular weight range of 1000–5000 amu. This is attributed to the attractive van der Waals interaction between the slider and the disk surface that causes the Zdol main chain to interact with the slider surface, giving rise to a friction force. When the film thickness of the lubricant exceeds the monolayer thickness, dewetting can take place. The droplets that form occupy the space between the slider and disk surface reducing the slider–disk clearance by as much as ∼4 nm. There is a step increase in the acoustic emission signal at the dewetting thickness transition, indicative of a slider–disk interference.

A thin layer of lubricant is a critical element of the head/disk interface needed to improve its tribological durability and to prevent media corrosion. Local thinning of lubricant with its subsequent breakdown often leads to the immediate failure of the interface. This paper is devoted to the in situ quantitative analysis of nano-scale lubricant migration on the surface of a

A 3-V continuous-time Gm-C filter based on a seventh-order 0.05 equiripple response is presented for read channels. The design features a low-voltage, wide-dynamic-range transconductor, a stable biasing scheme, and a power-efficient filter architecture. The filter is tunable for cutoff frequencies from 10 to 100 MHz and provides up to 13 dB of magnitude boost and up to 6 6 630% of group delay adjustment for use in high-data-rate, extended partial-response maximum-likelihood channels. The filter is implemented in 0.29-m BiCMOS technology, occupies 0.5 mm 2 , and dissipates 120 mW.

This paper presents a comprehensive non-exhaustive comparative study of hard disk drive read-channel equalization techniques used in the readback process of magnetically stored information. The main read channel architectures: partial-response maximum likelihood (PRML) and decision feedback equalization (DFE) based systems, are compared in power consumption, layout area, data signalling rate and data density. This work focuses on the key component of the read channel, presenting a continuous-time analog solution for the pulse-slimming equalizer capable of reducing power consumption and die area by a factor of ten, whilst showing equivalent response to a FIR filter implementation.

This paper presents a comprehensive non-exhaustive comparative study of hard disk drive read-channel equalization techniques used in the readback process of magnetically stored information. The main read channel architectures: partial-response maximum likelihood (PRML) and decision feedback equalization (DFE) based systems, are compared in power consumption, layout area, data signalling rate and data density. This work focuses on the key component of the read channel, presenting a continuous-time analog solution for the pulse-slimming equalizer capable of reducing power consumption and die area by a factor of ten, whilst showing equivalent response to a FIR filter implementation.