Thermally Assisted Magnetic Recording Research Articles

Flying stability of a slider with a damaged diamond like carbon layer induced by confined optical energy in a thermally assisted magnetic recording system

Thermally assisted magnetic recording (TAMR) is one possible solution for overcoming the limitation of higher storage density. However, in TAMR systems, several problems arise in association with the heat generated by the laser. This paper investigates the effect of damaged diamond like carbon (DLC) layer induced by confined optical energy in TAMR slider using derived equation of material loss in DLC layer. It is found that because of the confined optical energy in the near field transducer, DLC layer under the bottom of the slider can be damaged. The damaged DLC layer can lead the increment of flying height and decrement of pitch angle. These changes of slider attitude change the air bearing stiffness (ABS) between slider and disk. As the result, the changed ABS has a bad effect on the flying stability of the slider. And in higher energy, the effect is intensified.

Study of Flying Stability of a Thermally Assisted Magnetic Recording System with Laser Diode Mount Light Delivery

The laser diode (LD) is a key component in thermally assisted magnetic recording (TAMR) systems. However, heating from the LD can induce thermal deformation of the slider assembly, and change the gap separation between the slider and disk medium. In this paper, we analyzed the relationship between the slider–medium gap and the optical efficiency of the TAMR head, by considering the thermal effects of epoxy, the adhesive layer, and the near-field transducer (NFT) on the TAMR slider. The epoxy effect was modeled by using finite element (FE) analysis. Five different epoxy models were simulated, and the optimal epoxy model was selected, on the basis of its thermal performance. FE analysis was also carried out to simulate the TAMR slider assembly, which consisted of the LD, NFT, adhesive layer, epoxy, and TAMR head. On the basis of iterative analysis, an FE model was constructed with optimized representation of the epoxy, TAMR head component, and NFT. Thermal analysis of the simulation representation indicated that the epoxy, adhesive layer, and NFT played a significant role in the performance of the TAMR system.

8-${\rm Tb/in}^{2}$-Class Bit-Patterned Medium for Thermally Assisted Magnetic Recording

Three-dimensional optical/thermal spot profiles obtained by thermally assisted magnetic recording (TAMR) on bit-patterned media (BPM) with dot densities of 6 to 15 Tb/in <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> were numerically analyzed. Introduction of a spacing layer with higher thermal conductivity than that of the recording dots leads to narrow temperature distribution (i.e., steep temperature profile) in the dots. A temperature profile with FWHM of less than 5 nm was obtained on a patterned dot array under areal densities of 6 to 15 Tb/in <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . In addition, introduction of a thermal-control layer beneath the recording layer decreased vertical temperature difference within a recording bit while keeping a narrow temperature distribution. Feasibility of 8-Tb/in <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> -class TAMR on a BPM was verified by LLG simulation with a triangular antenna-type near-field optical element.

Head and Granular Media for Thermally Assisted Magnetic Recording for Recording Density of 6 Tb/in$^{2}$

Optimum structural dimensions and characteristics of a granular thermally-assisted-magnetic-recording (TAMR) medium for a recording density of more than 6 Tb/in <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> were investigated by using optical, thermal, and Landau-Lifshitz-Gilbert (LLG) simulators. A sharp thermal profile in the medium could be obtained by using a heat-sink layer with heat conductivity greater than 100 W/m K. The ratio of in-plane κ to out-of-plane κ(κ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">xy</sub> /κ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</sub> ) of the recording layer and thickness (Tm <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">MgO</sub> ) of the MgO layer should both be decreased. The targets for magnetic-write width (MWW) and signal-to-noise ratio (SNR) are 18 nm and 12 dB for a recording density greater than 6 Tb/in <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , respectively. In the case of Tm <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">MgO</sub> of 12 nm, the conditions for achieving these targets are ΔT of 450 K and H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">eff</sub> of 1.36 MA/m. In the case of Tm <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">MgO</sub> of 5 nm, the conditions are ΔT of 600 K and H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">eff</sub> of 1.4 MA/m (namely, MWW of 18 nm and recording density of 6.0 Tb/in <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ); ΔT of 550 K and H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">eff</sub> of 1.48 MA/m (namely, MWW of 16.5 nm and recording density of 6.5 Tb/in <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ); and ΔT of 500 K and H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">eff</sub> of 1.58 MA/m (namely, MWW of 15.0 nm and recording density of 7.2 Tb/in <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ). It is also clear that the thermal profile is a determinant factor in MWW.

Thermal Deformation of Thermally Assisted Magnetic Recording Head in Binary Gas Mixture at Various Temperatures

Helium-filled drives and thermally assisted magnetic recording (TAMR) systems are the most promising next-generation magnetic recording technologies. Currently, a fused TAMR system under helium- or air-helium-filled conditions is expected. In the fused system, it is important to accurately predict thermal deformation for a full TAMR head model and change of flying height (FH) at near filed transducer (NFT). In this paper, we first constructed an iterative coupled-field analysis process and a more realistic TAMR head model, including the NFT and even the epoxy components. The heat transfer coefficient was calculated using derived gas mixture properties. And the thermal deformation and protrusion of TAMR head was investigated for various temperature and helium fraction ratios. From the simulation results, the maximum temperature at the laser diode (LD decreased up to 20% due to changes in the heat transfer coefficient and environmental temperature. The epoxy effect induced by the LD heating was around 40%, which is in no way negligible. A thermal protrusion of 1.0–1.5 nm occurred at the NFT at various conditions. After considering the thermal deformation of the epoxy and the protrusion at the NFT, we found that the total FH was reduced with increasing helium fraction ratio and temperature.

6PM2-C-3 熱アシスト磁気記録におけるレーザ照射による潤滑膜減耗特性(6PM2-C OS6 マイクロナノトライボロジー(3))

To achieve magnetic recording densities of more than 10 Tb/in^2, the head-disk interface (HDI) spacing should be less than 2-3 nm. Thus far, thermally assisted magnetic recording (TAMR) technology has been studied and developed to achieve such ultra-high magnetic recording densities. However, the use of ultra-thin liquid lubricant films as well as DLC thin films on the disk surface in TAMR leads to critical issues with regard to the HDI. In addition, HDD technology with head-disk assembly mechanism in which He gas is enclosed has been developed. In this study, the effect of lubricant bonding mechanisms on lubricant depletion has been studied. Furthermore, the mechanisms of lubricant depletion due to laser heating have bean investigated and discussed.

Fundamental Study of Vapor Lubrication by PFPE Lubricants in Hard Disk Drives

Thus far, it has been shown that lubricant depletion occurs at a relatively low temperature of approximately 200°C in thermally assisted magnetic recording (TAMR). Because the lubricant on the disk surface plays an important role in maintaining the reliability and durability of the head-disk interface (HDI), lubricant depletion is one of the critical issues in hard disk drives. Thus, there is a great need to develop technology that supplies lubricant to the HDI as the amount of lubricant decreases, so that the thickness of the lubricant film remains constant. In this study, we conducted a fundamental study of vapor lubrication using perfluoropolyether (PFPE) lubricants as the first step. In other words, we conducted an experimental study to elucidate the fundamental mechanism of vapor lubrication and to investigate the technological feasibility of applying vapor lubrication to hard disk drives. In addition, the possibility of using vapor lubrication in hard disk drives with contact sliders was also investigated. As a result, it was confirmed that vapor lubrication would be useful to overcome the lubricant depletion issue.

Ultra-high coercivity small-grain FePt media for thermally assisted recording (invited)

Thermally assisted magnetic recording (TAR), a promising approach to extend data storage densities beyond 1 terabit/in.2, requires high anisotropy granular magnetic media with small grains and a tight grain size distribution. We demonstrate sputtered chemically ordered granular L10 Fe45Pt45Ag10 media using carbon segregant on glass substrates. X-ray diffraction and transmission electron microscopy reveal high chemical ordering, an average grain size of 〈D〉 = 7.2 nm and a size distribution as low as σD/〈D〉=16%. Magnetic properties studied with a vibrating sample magnetometer show Hc = 4.8 T, Hk &amp;gt; 9 T, and Ku &amp;gt; 4.5 × 107 erg/cm3. Drag testing of this media shows recording areal densities of 620 Gb/in.2.

1204 熱アシスト磁気記録におけるHDIトライボロジーに関する研究 : 潤滑材付着特性の変化(GS-16 トライボロジー特性(1))

1204 熱アシスト磁気記録におけるHDIトライボロジーに関する研究 : 潤滑材付着特性の変化(GS-16 トライボロジー特性(1))

FePtAg-C Nanogranular Film as Thermally Assisted Magnetic Recording (TAR) Media

We studied highly L10 -ordered FePtAg-C nanogranular film as a potential high-density storage medium for thermally assisted magnetic recording (TAR). A 6.4-nm-thick FePtAg-C film was fabricated on an oxidized silicon substrate with a 10-nm MgO underlayer at 550°C, with the perpendicular coercivity of 35 kOe, and average grain size of 6.2 ± 1.4 nm. The time-dependence measurement of remnant coercivity results in the energy barrier Eb=5.1 eV ~ 200 kB T, meaning excellent thermal stability for long-term data storage. The static tester experiments by TAR head demonstrated an areal density of 550 Gb/in2.

Experimental Investigation of Local Temperature Increase in Disk Surfaces of Hard Disk Drives Due to Laser Heating During Thermally Assisted Magnetic Recording

In this study, a novel method was developed to evaluate the local temperature increase under steady-state conditions on disk surfaces of hard disk drives due to laser heating during thermally assisted magnetic recording (TAMR). In particular, we evaluated changes in the refractive index and the extinction coefficient of disk substrates due to laser heating by varying the laser power, and determined the relationship between the laser power and the changes in these optical constants. Simultaneously, test disks were heated using a conventional heater, under heating conditions equivalent to those associated with laser heating, by varying the temperature. We evaluated the changes in the optical characteristics of the disk substrates due to heating, and formulated a relationship between the temperature and the changes in the optical characteristics. Then, the local temperature increase due to laser heating under steady-state conditions was evaluated by calibrating both sets of experimental results. In addition, the temperature increase was compared with the numerical simulation results, and good agreement was observed between the experimental and the simulation results. Thus, it was confirmed that, this method is useful and effective for estimating the temperature increase under steady-state conditions in disk surfaces of hard disk drives due to laser heating during TAMR. This method is also a first step toward understanding the occurrence of temperature phenomena in TAMR systems.

Operating Shock Analysis of a Thermally Assisted Magnetic Recording Head Gimbal Assembly Considering the Thermal Effects During Writing to Record the Data

In this paper, a thermally assisted magnetic recording (TAMR) head gimbal assembly (HGA) with an optical fiber and prism is proposed. The stiffness of a TAMR HGA is increased by an optical fiber and prism. Therefore, in this paper, operating shock analysis of a TAMR HGA considering the thermal effects during writing to record the data is numerically performed. Flying height (FH) analysis considering the thermal deformation by laser source also is investigated. As a result, judging from shock point of view, the shock characteristic of a TAMR HGA is better than that of conventional HGA. However, when considering the thermal effects during writing to record the data, the risk of contact for a TAMR HGA between media and slider is larger than that of conventional HGA. Hence, to solve these problems of a TAMR HGA, we should consider selection for material of media and TAMR slider, and design for head parts of TAMR slider.

L1-ordered FePtAg–C granular thin film for thermally assisted magnetic recording media (invited)

We studied highly L10-ordered FePtAg–C nanogranular film as a potential high-density storage medium in thermally assisted magnetic recording (TAR). A 6.4-nm-thick FePtAg–C film with a perpendicular coercivity of 37 kOe and an average grain size of 6.1±1.8 nm was fabricated on oxidized silicon substrate with a 10 nm MgO interlayer at 450 °C. The time-dependence measurement of remnant coercivity showed the energy barrier of Eb = 7.6 eV ∼300 kBT at room temperature, meaning the excellent thermal stability for long-term data storage. Static tester experiments on this film using a TAR head demonstrate the feasibility of recording at an areal density of ∼450 Gbits/in.2.

Tolerance Analysis of the Pitch Static Attitude of a Thermally Assisted Magnetic Recording System With an Optical Fiber and Prism

In this paper, we propose a thermally assisted magnetic recording (TAMR) system with an optical fiber and specially designed prism attachment. The TAMR system utilizes an optical fiber and prism to facilitate the delivery of light to the slider and media. However, problems such as increasing suspension stiffness were encountered. Using an optical fiber increases the TAMR suspension stiffness and affects the pitch torque of the system. The pitch torque affects the flying height (FH), which can lead to slider-disk contact. Therefore, we investigated the stiffness of the TAMR suspension and the relationship between FH and the pitch static attitude (PSA). The various factors affecting the FH loss and the environmental conditions were also investigated. Finally, to compensate the large pitch stiffness and prevent slider-disk contact, the air bearing surface (ABS) of the TAMR system was optimized for robust slider performance, and the tolerance of the TAMR system was analyzed for the PSA considering various parameters such as temperature, relative humidity, operating conditions and manufacturing errors. The final PSA tolerances of the conventional and TAMR suspension were calculated. These values were 1.58° and 0.37°, respectively. The sensitivity of the optimal PSA design was decreased by about 21.5%. The PSA tolerance using the optimal design was 0.47°. This indicates that the tolerance of the optimal model is larger than that of original model, which was about 21.3%.

Lubricant Depletion Characteristics Induced by Rapid Laser Heating in Thermally Assisted Magnetic Recording

In this study, fundamental research was conducted on lubricant depletion due to rapid laser heating in thermally assisted magnetic recording (TAMR) systems. The effects of lubricant film thickness on lubricant depletion were investigated using a conventional lubricant, Zdol2000. The lubricant depletion characteristics resulting from laser heating were found to largely depend on the lubricant film thickness. Lubricant depletion mechanisms were also studied. In this study, it was found that lubricant depletion is predominantly due to lubricant evaporation for cases in which the lubricant film thickness is greater than one monolayer. In addition, the effect of laser irradiation duration on lubricant depletion was investigated using both continuous and 300-kHz pulsed laser irradiations, since actual TAMR systems require pulsed laser irradiation lasting a few nanoseconds. The differences between the fundamental lubricant depletion characteristics of continuous and pulsed laser irradiations were elucidated on the basis of the experimental results obtained in this study. Furthermore, it has been suggested that diamond-like-carbon (DLC) thin films on the disk surfaces are also affected by rapid laser heating, because the temperature of the films increases to more than 500 K upon laser heating. Therefore, we also studied the damage to DLC thin films due to rapid laser heating and found that the reflectivity of the DLC thin films changed; this change was presumably due to the decrease in the DLC density as well as the asperity in the laser-irradiated region.

B-2-4 熱アシスト磁気記録におけるヘッドディスクインターフェイスに関する研究 : DLC保護膜の構造におよぼす加熱の影響(B-2 ヘッド・ディスク・インタフェースに作用する相互作用他,口頭発表:ヘッド・ディスク・インターフェイス)

To further increase recording density of disk storage drives, thermally-assisted magnetic recording can solve the fundamental issues of thermal fluctuation and is regarded as the key technology for achieving recording density of more than 1 Tb/in^2. In this technology, it is suggested that there is critical issues for the ultra-thin liquid lubricant films and diamond-like carbon (DLC) films on the disk surfaces, because they are heated to high temperature with laser beams. In this study, we focused on the thermal stability of the three types of DLC films deposited by chemical vapor deposition (CVD), ion beam deposition (IBD) and filtered cathodic vacuum arc (FCVA) deposition. We also compared the optical properties of heated three DLC films characterized by ellipsometry, electron spectroscopy for chemical analysis and raman spectroscopy. As a result, the effects of heating temperature on the structure of DLC films were clarified.

Thermally assisted magnetic recording with bit-patterned media to achieve areal recording density beyond 5 Tb/in 2

Thermally assisted magnetic recording (TAR) with bit-patterned media was investigated by micromagnetic simulation. The media were assumed to be FePt layers. The effective head-field margin as well as the increase in temperature margin and down-track shift margin was investigated. Conditions of the head and medium that lead to a recording density beyond 5 Tb/in 2 were proposed.

열 보조 자기기록용 서스펜션의 PSA에 대한 분석

This paper presents the analysis of pitch static attitude(PSA) in thermally assisted magnetic recording(TAMR) suspension. The TAMR suspension using an optical fiber has high stiffness such as vertical, pitch and roll. Therefore, P-torque is greatly increased by the optical fiber. Also, flying height(FH) of the slider with TAMR suspension can be largely changed by PSA. In this paper, we focus on the FH by PSA of TAMR suspension. The FH is investigated using various PSA and proper PSA is proposed.

S1603-1-3 磁気ディスク装置用ヘッドサスペンションの機械特性に関する考察(情報機器コンピュータメカニクス,社会変革を技術で廻す機械工学)

S1603-1-3 磁気ディスク装置用ヘッドサスペンションの機械特性に関する考察(情報機器コンピュータメカニクス,社会変革を技術で廻す機械工学)

Automatic Design Optimization of Plasmon Antenna for Thermally Assisted Magnetic Recording

We developed auxiliary differential equation finite-difference time-domain (ADE-FDTD) method for dispersive Drude medium, and simulated the optical part of the plasmon antenna (PA) and waveguide (WG) system for thermally assisted magnetic recording (TAMR) heads. To achieve higher efficiency without sacrificing the small spot size, our newly developed automatic computational shape optimization program was carried out for the PA designs with a variety of configurations: no recording media, with-media, with magnetic write pole, and only-PA models. The optimized designs for these cases show an enhancement of the electrical field at the PA tip compared to the initial configuration. In addition, both the PA body as well as the tip affects the performance of the guiding and focusing of the plasmon. However, the optimized detail shape and the sensitivity of the dimension are dependent upon the configuration.