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Historical variations of HMS versus bit length from [6].

Historical variations of HMS versus bit length from [6].

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Article
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This paper reviews the state of the head-disk interface (HDI) technology, and more particularly the head-medium spacing (HMS), for today’s and future hard-disk drives. Current storage areal density on a disk surface is fast approaching the one terabit per square inch mark, although the compound annual growth rate has reduced considerably from ~100%...

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Heat assisted magnetic recording (HAMR) is expected to increase the storage areal density to more than 1 Tb/in2 in hard disk drives (HDDs). In this technology, a laser is used to heat the magnetic media to the Curie point (~400-600 °C) during the writing process. The lubricant on the top of a magnetic disk could evaporate and be depleted under the...
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Citations

... The demand for higher density hard disk drives (HDDs) pushes the requirements for the head-disk spacing. The greater the HDDs' density, the smaller the head-disk spacing required (see [1][2][3]). The head-disk spacing can be designed by setting the slider's flying height. ...
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This paper discusses a passive vibration control method to improve the shock tolerance of hard disk drives (HDDs) in operating condition (op-shock tolerance). Past works in improving the HDDs’ op-shock tolerance includes (i) parking the head when shock is detected, (ii) installing a lift-off limiter, (iii) structural modification of the suspension, and (iv) installing an external vibration isolation. Methods (i) and (iv) have practical issues, method (ii) works only on single shock direction, and method (iii) requires major engineering design/manufacturing work. Compared to these works, this paper proposes a method which has no practical issues and without requiring major engineering design/manufacturing work. The proposed method is to apply a polymer-based dampening layer on the backside of the baseplate with the purpose of increasing the damping ratio of the 1st bending mode of the baseplate. The location of the dampening layer on the baseplate is first determined by modal analysis and then fine-tuned by non-op-shock tests. The op-shock tolerance improvement is confirmed by op-shock tests where 2.5″ HDD with the dampening layer on the baseplate can withstand a 300G 0.5-ms shock without failure while unmodified HDD can only withstand 250G 0.5-ms shock without failure.
... Currently, to reach ∼1 Tb/in 2 areal density, ∼2.5 nm-thick PECVD-grown a-C:H coatings are used on commercial disks (massdensity of ∼2.1 g/cm 3 ; hydrogen content of ∼40 at.%) [94] while ∼2.7-nm thick FCVA-deposited ta-C films are used on the heads (mass-density of 3.0 g/cm 3 ) [95] . Based on industry roadmaps, the average carbon coating thickness should be reduced down to ∼1.6 nm to achieve an areal density of 4 Tb/in 2 [96] . However, the reduction of the thickness below 2 nm may introduce many challenges regarding the resulting tribology and corrosion resistance [97] . ...
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While graphene has held the center stage in nanocarbon material research since its isolation in 2004, less attention has been paid to nanometer-thick carbon films in which at least part of the carbon atoms are sp³-hybridized, whatever the crystallographic structure. However, because of their composition, structure, physical and chemical properties, those nanomaterials exhibit competitive features that should be considered for the development of future sustainable technologies based on 2D materials. The purpose of this review is to provide a snapshot of the main advances in the synthesis of sub-10 nm thick sp³-C-rich films, which include amorphous carbon hydrogenated or not, nanocrystalline diamond films, graphane, diamanes and diamanoids. Physical properties and applications (i.e. existing or potential) are also highlighted.
... costs. Affected by the superparamagnetic effect [20], the areal data density of CMR (see Fig. 1(a)) has reached the limitation [14,23]. To further expand disk storage capacity and reduce costs, academia and storage manufacturers are trying to explore new technologies and methodologies. ...
Preprint
The emerging interlaced magnetic recording (IMR) technology achieves a higher areal density for hard disk drive (HDD) over the conventional magnetic recording (CMR) technology. IMR-based HDD interlaces top tracks and bottom tracks, where each bottom track is overlapped with two neighboring top tracks. Thus, top tracks can be updated without restraint, whereas bottom tracks can be updated by the time-consuming read-modify-write (RMW) or other novel update strategy. Therefore, the layout of the tracks between the IMR-based HDD and the CMR-based HDD is much different. Unfortunately, there has been no related disk simulator and product available to the public, which motivates us to develop an open-source IMR disk simulator to provide a platform for further research. We implement the first public IMR disk simulator, called IMRSim, as a block device driver in the Linux kernel, simulating the interlaced tracks and implementing many state-of-the-art data placement strategies. IMRSim is built on the actual CMR-based HDD to precisely simulate the I/O performance of IMR drives. While I/O operations in CMR-based HDD are easy to visualize, update strategy and multi-stage allocation strategy in IMR are inherently dynamic. Therefore, we further graphically demonstrate how IMRSim processes I/O requests in the visualization mode. We release IMRSim as an open-source IMR disk simulation tool and hope to attract more scholars into related research on IMR technology.
... Head-media spacing (HMS), another commonly used term in the industry, differs from the fly height. The HMS is the distance between the bottom of the reader in the head and the top of the magnetic layer in the disk [29], while the fly height refers to the physical distance between the two bodies in the HDI. Thus, the HMS is the sum of the head carbon overcoat thickness, the fly height, the lubricant thickness and the disk carbon overcoat thickness. ...
... Thus, the HMS is the sum of the head carbon overcoat thickness, the fly height, the lubricant thickness and the disk carbon overcoat thickness. It is noted that the reader performance can improve approximately by a factor of two when the HMS decreases by 0.3-0.5 nm [29]. Therefore, the HDD industry devotes much effort to the development of ultrathin protective films and further reduction of the fly height. ...
... Therefore, the HAMR head-disk interface is a system that combines nanoscale spacing (< 15 nm), high temperatures (head ∼ 150-250 • C, disk ∼ 400-500 • C), steep thermal gradient (∼ 10 K/nm), and a high-speed sliding condition (5-40 m/s) [4,14]. The HDI performance directly determines the lifetime of the HAMR product [14,29]. The introduction of the laser brings several reliability issues to the head-disk interface [14,29,35]. ...
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Thesis
As data generated worldwide are growing explosively, it is crucial to increase the areal density of traditional storage devices to satisfy the requirements. Conventional hard disk drive (HDD) technology, perpendicular magnetic recording (PMR), has reached the superparamagnetic limit of ~ 1 Tb/in2. To realize the areal density over 1 Tb/in2, the size of the media bits must be further decreased to tens of nanometers, which requires high coercivity magnetic media. The high coercivity can avoid superparamagnetism and thus store data safely at the small bit size under room temperature, but it makes data writing challenging. To assist the writing process, energy is input to the media to lower its coercivity temporarily. Current technologies such as heat-assisted magnetic recording (HAMR) and microwave-assisted magnetic recording (MAMR) utilize two different methods to lower the coercivity. HAMR integrates a laser to locally heat the media to its Curie temperature (400–500 °C), while MAMR uses a spin torque oscillator to induce ferromagnetic resonance in the media grains. In the HAMR head-disk interface (HDI), a recording head flies over a rotating disk with a relative velocity of 5–40 m/s and an initial spacing of 10–15 nm controlled by an air bearing. Then, the spacing is reduced by energizing a joule heater inside the head. The heater generates a protrusion on the head surface to lower the initial spacing to 1–2 nm so that data reading/writing can be performed using the read/write transducers in the head. The head is also integrated with a laser diode, a waveguide (WG) and a near-field transducer (NFT) for laser delivery. The laser beam is launched from the recording head and is focused on the recording disk to locally heat the disk (400–500 °C), which is even hotter than the head temperature (150–250 °C). Therefore, the head-disk interface of HAMR is a system that combines nanoscale spacing (< 15 nm), high temperatures (head ∼ 150–250 °C, disk ∼ 400–500 °C), steep thermal gradient (∼ 10 K/nm), and a high-speed sliding condition (5–40 m/s). Furthermore, the introduction of the laser affects thermal transport and thermal protrusion, and causes thermally-induced material transfer in the interface, which needs to be investigated both for fundamental understanding and for practical applications such as HAMR and other microelectronics devices. To study the thermal transport across a closing gap between the head and the disk, we conducted static touchdown experiments using a custom-made setup where the disk is not rotating to exclude the air cooling effect. The head temperature rise was measured as a function of the heater power under various conditions such as different substrate materials, relative humidity and laser on/off. An enhanced thermal transport due to phonon heat conduction is observed for the gap < ∼ 2 nm. The thermal transport across the gap becomes stronger when a better thermal conductor is used as the substrate or when the humidity is higher than 75%. With the presence of the laser, the head undergoes a joule heat dissipation inside the head and a back-heating from the hot spot on the substrate. In the HAMR operations, the laser delivery involves energy loss, which leads to a localized angstrom-level laser-induced protrusion (LIP) and a fly height change (FHC). They need to be considered and compensated in the spacing control. Flying touchdown experiments were performed to evaluate their overall effect on the spacing change, then they were separated using their different time constants in microseconds and milliseconds. In addition, HAMR operations may utilize two heaters in the head. It is demonstrated that the head protrusion shape can be modulated by use of the dual heaters, and that the touchdown area can be controlled precisely. During the laser exposure under HAMR operations, material transfer also happens due to the high level of thermal transport. The temperature of the hot spot on the disk is much higher than the lubricant evaporation temperature, so the lubricant is evaporated from the disk and then condenses on the head surface. The material accumulation on the head surface, also known as smear, is a challenging reliability issue for HAMR. We experimentally investigate the smear formation mechanism and propose two smear mitigation strategies. The results show that the smear forms when the lubricant evaporation occurs for a certain time, and that the smear can be mitigated by a mechanical burnishing approach or a thermal approach. Next, we report a thermal mapping technique using a phase change material Ge2Sb2Te5. Ge2Sb2Te5 undergoes a crystalline transition at 149 °C with changes in its density and optical reflectivity. By use of these changes, we can map surface temperatures from nanoscale to microscale with minimal calibration, which is demonstrated using a recording head. Finally, we propose a near-field thermal transport based scheme for lubricant thickness measurement. The thermal effect of the lubricant is investigated when the head approaches the disk in the flying touchdown experiments, which is then used to determine the lubricant thickness. Most previous lubricant measurements require an ex-situ tool such as optical surface analyzer (OSA), but the proposed scheme is an in-situ method with a sub-angstrom resolution and a faster response time. Using the scheme, we performed in-situ measurements of the lubricant depletion and reflow dynamics under HAMR operations.
... In scaling magnetic handshake materials down to micron-scale panels, it is important to consider the maximum achievable density of non-crosstalking lock-key pairs (M c ) given state-of-the-art magnetic recording technology. The current areal bit density of perpendicular magnetic recording media, where one bit represents a magnetic moment oriented into or out of the plane of the disk, is on the order of 1Tb/in 2 [27]. At this density, one bit comprises an area of 645nm 2 , with typical recording layer thicknesses of 10-30nm [28]. ...
Preprint
The ability to rapidly manufacture building blocks with specific binding interactions is a key aspect of programmable assembly. Recent developments in DNA nanotechnology and colloidal particle synthesis have significantly advanced our ability to create particle sets with programmable interactions, based on DNA or shape complementarity. The increasing miniaturization underlying magnetic storage offers a new path for engineering programmable components for self assembly, by printing magnetic dipole patterns on substrates using nanotechnology. How to efficiently design dipole patterns for programmable assembly remains an open question as the design space is combinatorially large. Here, we present design rules for programming these magnetic interactions. By optimizing the structure of the dipole pattern, we demonstrate that the number of independent building blocks scales super linearly with the number of printed domains. We test these design rules using computational simulations of self assembled blocks, and experimental realizations of the blocks at the mm scale, demonstrating that the designed blocks give high yield assembly. In addition, our design rules indicate that with current printing technology, micron sized magnetic panels could easily achieve hundreds of different building blocks.
... Further advances in the hard disk industry require lower Head-Media Spacing (HMS) to obtain higher areal density. Based on the industry's roadmap, the current technology has achieved an areal density of more than 1Tb/in 2 which demands a HMS of less than 10 nm and a clearance of near 1 nm [1]. Clearance is defined as the effective spacing between the head and media surfaces, accounting for roughness, lubricant and protective coating thicknesses. ...
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Perfluoropolyether (PFPE) polymer lubricant performs an important role in protecting both the writing/reading elements in the recording head and the disk of magnetic storage devices from mechanical wear or damage, induced by direct contact. Under high-speed sliding, the nanometer thick lubricant shows complex behavior, such as shear thinning, slippage and bonding ratio, making it difficult to directly test or simulate its performance. Based on a numerical model, the present study obtains the mechanical response of the lubricant under normal and sliding contacts. The mechanical response is then entered into a finite element model (FEM) through definition of material behavior of the lubricant using a hyper-elastic constitutive model. By comparing the sliding contact simulations with lubricant and without lubricant, it is found that the presence of lubricant helps to reduce the contact stresses, mainly because the contact area is increased.
... For example: an FePt based granular thin film has a Curie temperature near 450 °C. However, the reliability of the tribological head disk interface (HDI), becomes a significant challenge to the success of HAMR technology [2,3]. Smear formation and material transfer between the head and media is one major concern of the HAMR HDI. ...
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Heat-assisted magnetic recording (HAMR) is on the magnetic recording industry’s roadmap of next generation recording technology. The high temperature writing condition creates several reliability challenges for the head disk interface (HDI). Material buildup, or so-called smear, that accumulates between the head and the media is one key challenge. Our previous studies found that the material transfer is mainly driven by the high temperature and mechanical interaction between the head and media. In this paper, we systematically studied the role of the media in the smear formation and transfer process. We identified at least two different types of smear and the critical temperatures for their formation and transfer. Furthermore, we found that optimizing the media process, particularly the magnetic layer and lubricant, could help to reduce smear. This study helps in understanding the smear formation mechanism and explores methods to mitigate smear for HAMR drives.
... Better thermal stability was reported in filtered cathodic vacuum arc (FCVA)-based COCs under laser irradiation in HAMR-like conditions 29 and thermal annealing up to~940 K 32 , consistent with the good thermal stability, i.e., no change in sp 3 content up to 1100°C, found in tetrahedral a-C (ta-C) films 33 . However, FCVA-based COCs are not yet used as HDM overcoats due to the presence of macro-particles 6,34 . ...
... The slider containing the read/write head and the head overcoat are shown as well. For 1 Tb/in 2 , the head-media spacing is~8.9-6.5 nm 6 , based on the sum of overcoat thickness (2.5-2 nm) 6 , lubricant thickness (1.2-1 nm) 6 , touch down height (2-1 nm) 6 , fly clearance (1.2-1 nm) 6 and head overcoat thickness (2-1.5 nm) 6 . b Full stack of bare CoCrPt:Oxide-based hard disk media comprising a glass substrate, seed bottom underlayer, and antiferromagnetic layer (A-FM) between two soft-magnetic under layers (SUL), followed by two intermediate layers and a co-based magnetic recording layer. ...
... The slider containing the read/write head and the head overcoat are shown as well. For 1 Tb/in 2 , the head-media spacing is~8.9-6.5 nm 6 , based on the sum of overcoat thickness (2.5-2 nm) 6 , lubricant thickness (1.2-1 nm) 6 , touch down height (2-1 nm) 6 , fly clearance (1.2-1 nm) 6 and head overcoat thickness (2-1.5 nm) 6 . b Full stack of bare CoCrPt:Oxide-based hard disk media comprising a glass substrate, seed bottom underlayer, and antiferromagnetic layer (A-FM) between two soft-magnetic under layers (SUL), followed by two intermediate layers and a co-based magnetic recording layer. ...
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Hard disk drives (HDDs) are used as secondary storage in digital electronic devices owing to low cost and large data storage capacity. Due to the exponentially increasing amount of data, there is a need to increase areal storage densities beyond ~1 Tb/in ² . This requires the thickness of carbon overcoats (COCs) to be <2 nm. However, friction, wear, corrosion, and thermal stability are critical concerns below 2 nm, limiting current technology, and restricting COC integration with heat assisted magnetic recording technology (HAMR). Here we show that graphene-based overcoats can overcome all these limitations, and achieve two-fold reduction in friction and provide better corrosion and wear resistance than state-of-the-art COCs, while withstanding HAMR conditions. Thus, we expect that graphene overcoats may enable the development of 4–10 Tb/in ² areal density HDDs when employing suitable recording technologies, such as HAMR and HAMR+bit patterned media
... Thus, improving the nanotribology of these protective films is crucial for realizing higher reliability in magnetic storage devices [4][5][6][7][8][9][10][11]. To reduce magnetic loss and increase the memory density, it is necessary to reduce the magnetic space at the magnetic head-disk interface, which requires a reduction in the film thickness to the nanometer scale [12][13][14]. However, it is difficult to maintain tribological durability with such thin films [11,13]. ...
... To reduce magnetic loss and increase the memory density, it is necessary to reduce the magnetic space at the magnetic head-disk interface, which requires a reduction in the film thickness to the nanometer scale [12][13][14]. However, it is difficult to maintain tribological durability with such thin films [11,13]. Therefore, it is necessary to gain a better understanding of the durability of extremely thin films under friction and wear. ...
Article
We studied the tribological properties of extremely thin DLC films at high temperature. The films were deposited on nickel phosphorus (NiP) or Si substrates using filtered cathodic vacuum arc (FCVA) or plasma chemical vapor deposition (P-CVD). The nanoindentation hardness values and elastic moduli of the films were lower on NiP than on Si. The nanofriction force of the FCVA-DLC film on NiP was low at room temperature, but very high at high temperature. In this hard film, the lubricous adsorbate was removed by sliding at high temperature, making it easily damaged through the large deformation of NiP. In contrast, the friction force of the P-CVD-DLC films on both substrates was low at high temperatures. In this case, the lubricous tribochemical products from the P-CVD-DLC film reduced friction and wear. The friction map dependences on load and number of reciprocating cycles were evaluated using a friction test and statistical cluster analysis. The friction durability of both films depended more strongly on load on NiP than on Si, with the friction coefficients on Si being almost independent of load. At high temperatures and load, the durability of the FCVA-DLC film on NiP decreased and this film was easily damaged.
... Further, the areal density associated with data storage has also been improved due to the miniaturization of mobile communication tools [1]. Therefore, there is a need to develop a highly sensitive device that can detect a small magnetic field within a nano-size range. ...
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Effect of the diameter on the CPP-GMR performance of electrodeposited Co/Cu multilayered nanowires was systematically investigated using our home-made anodized aluminum oxide (AAO) templates with the nanochannel diameter ranging from 35 to 130 nm. The nanochannel diameter was precisely controlled by tuning the anodization voltage ranging from 20 to 110 V. The Co/Cu multilayered nanowires with the aspect ratio of ∼1,000 were synthesized in the AAO nanochannels by applying a rectangular pulsed potential electrodeposition technique using an acidic aqueous solution containing Co²⁺ and Cu²⁺ ions. An ideal alternating Co/Cu multilayered structure with each layer thickness of several nanometers was clearly observed in the nanowires with the diameter ranging from 35 to 95 nm. The multilayered nanowires with the diameter ranging from 35 to 70 nm were spontaneously magnetized in the axial direction due to the preferential crystal orientation of hcp-Co (002) which was induced by the magnetic shape anisotropy. With decreasing the diameter down to 35 nm, the coercivity increased up to 1.37 kOe while the squareness reached 0.73 at the diameter of 50 nm. The CPP-GMR value reached 23.4% at room temperature in the Co/Cu multilayered nanowires with the diameter of 70 nm.