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Track width measurement in heat-assisted magnetic recording systems using the cross-track DC noise method
(2022-07-01)
Kampun, Prasit
;
Lekawat, Lertsak
;
Tongsomporn, Damrongsak
This paper uses a cross-track DC noise measurement technique to determine the written track width in heat-assisted magnetic recording (HAMR). The method is approached as a simple, no-extra-hardware-required technique on a spin-stand to determine the written track width as well as the DC noise amplitude at the center track in a HAMR system. The track width data show the expected trends with changing laser operating current (Iop) and write current (Iw), and they are strongly correlated with track density capabilities and physical near-field transducer (NFT) peg width. The written track width is essentially defined by the Iop, which increases as Iop increases. The method is useful for comparing the magnetic responses of different writer pole or NFT peg geometries, as well as media design comparison to provide insight into the head/component necessary to improve HAMR system performance, which is useful HAMR recording parameters for head/media designers and test engineers.
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Influence of Recorded Pattern on Background Interference impact in Magnetic Recording
(2021-11-05)
Chaiduangsri, Nuttapon
;
Kaitwanidvilai, Somyot
;
Tongsomporn, Damrongsak
This paper discusses the impact of background interference on a recorded pattern for heat-assisted magnetic recording technology (HAMR). Several patterns of the background track were examined, with the log bit error rate and signal to noise ratio measured via a spin-stand tester using HAMR head and media. It was found that the low frequency pattern gave the highest BER and SNR loss due to the strong magnetic field from the adjacent tracks. Similar to its practical use, the PRBS pattern also showed high interference. These observations may be used to support HDD areal density growth.
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Magnetic write field characterization in heat-Assisted magnetic recording systems
(2020-01-01)
Kampun, Prasit
;
Lekawat, Lertsak
;
Tongsomporn, Damrongsak
Magnetic write field is a critical factor in determining the quality of the magnetic write transitions, which determine the linear density (LD) limit in heat-Assisted magnetic recording (HAMR). We introduce a reversed DC band approach as a simple, no extra-hardware-Required technique in a spin-stand to assess the magnetic write field contributions, independently in an HAMR system. Heads with different distances between near-field transducer and writer pole, and media with and without soft magnetic under layer were characterized. The estimated result strongly correlates with LD and signal-To-noise ratio, which agrees with previous modeling studies. These results give insight into the head/component required to optimize the HAMR's system performance. The technique provides qualitative ranking of magnetic write fields and recording temperature, as well as laser operating current at Curie temperature for head/component designs.
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Experimental study of media heat sink thickness impact on signal-To-noise ratio in heat-Assisted magnetic recording
(2020-01-01)
Kaitwanidvilai, Somyot
;
Chaiduangsri, Nuttapon
;
Tongsomporn, Damrongsak
Recently, heat-Assisted magnetic recording (HAMR) has been demonstrated to extend the areal density growth over the superparamagnetic limited. One key component of this technology is a heat sink layer in HAMR media, which benefits the thermal gradient and transition noise. However, the disadvantage of the heat sink layer (HS) has not been fully explored. In this paper, we investigate the background interference (BGI) impact as a result of the heat sink layer via the spin-stand tester. HAMR heads included a light delivery system that have measured a signal-To-noise ratio and down-Track thermal gradient on a variety of HS thickness. Subsequently, we found that a thicker HS is a trade-off between the BGI and thermal gradient. Thus, it remains challenging to achieve an ultra-high areal density using the thermal media design.
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An effective track width with a 2d modulation code in Two-Dimensional Magnetic Recording (TDMR) systems
(2019-01-01)
Pituso, Kotchakorn
;
Warisarn, Chanon
;
Tongsomporn, Damrongsak
When the track density of two-dimensional magnetic recording (TDMR) systems is increased, intertrack interference (ITI) inevitably grows, resulting in the extreme degradation of an overall system performance. In this work, we present coding, writing, and reading techniques which allow TDMR systems with multi-readers to overcome severe ITI. A rate-5/6 two-dimensional (2D) modulation code is adopted to protect middle-track data from ITI based on cross-track data dependence. Since the rate-5/6 2D modulation code greatly improves the reliability of the middle-track, there is a bit-error rate gap between middle-track and sidetracks. Therefore, we propose the different track width writing technique to optimize the reliability of all three data tracks. In addition, we also evaluate the TDMR system performance using an user areal density capability (UADC) as a main key parameter. Here, an areal density capability (ADC) can be measured by finding the bit-error rate of the system with sweeping track and linear densities. The UADC is then obtained by removing redundancy from the ADC. Simulation results show that a system with our proposed techniques gains the UADC of about 4.66% over the conventional TDMR systems.
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Impact of Background Interference on Signal-To-Noise Ratio in Heat-Assisted Magnetic Recording
(2018-01-01)
Kaitwanidvilai, Somyot
;
Chaiduangsri, Nuttapon
;
Tongsomporn, Damrongsak
We discuss background interference (BGI) arising from the read-back of preexisting data and adjacent tracks on a recording medium. A signal-To-noise ratio analysis is used to measure the impact of BGI in heat-Assisted magnetic recording in a spin-stand tester. The signal-To-noise ratio for a data track with an alternating field background was compared to a data track written over a pair of background tracks. We considered the effect of background track offsets: The distance between the background and data tracks. BGI, which depends on the background track offset, can degrade read-back performance. The dibit extraction technique is able to separate the linear dibit response and the BGI in the read-back waveform.
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A Soft-5/6 Modulation Code with Iterative ITI Subtraction Scheme in Multireader TDMR Systems
(2017-11-01)
Pituso, Kotchakorn
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Warisarn, Chanon
;
Tongsomporn, Damrongsak
The huge growth of the consumer electronic industry is driving the need for achieving ultrahigh areal storage densities. 2-D magnetic recording is a promising high-density storage technology where the shingled writing technique is employed for increasing the track per inch (TPI) and achieving higher areal densities. Nevertheless, high TPI causes a reader to cover higher number of tracks, which leads to the intertrack interference (ITI); hence the system performance is severely deteriorated. Therefore, we first propose the soft-5/6 modulation code together with iterative ITI subtraction scheme. Here, the soft information encoding and decoding schemes operate based on Boolean logic circuit for using in the iterative system. Furthermore, we also propose to move the upper and lower readers closer to the center reader to avoid the ITI effect from their outer tracks, which will then be performed together with ITI subtraction scheme. Moreover, this proposed reading technique is also applied together with the soft-4/5 modulation code. The simulation results show that the proposed systems are superior to the conventional system, especially at high user density.
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Simulation of magnetic footprints for heat assisted magnetic recording
(2017-05-01)
Pituso, Kotchakorn
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Khunkitti, Pirat
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Kruesubthaworn, Anan
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Chooruang, Komkrit
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Tongsomporn, Damrongsak
The heat assisted magnetic recording (HAMR) technology has been the promising candidate to overcome the thermal stability limitation at higher capacities of the hard disk drive. In this work, the characteristics of magnetic footprint of the medium written by HAMR were investigated through the micromagnetic simulations. The Voronoi granular media was firstly modeled, then the magnetic footprint technique was performed to observe the media behaviors at various linear densities. The results indicated that the pattern of magnetic footprint can be perverted at higher densities, which essentially causes a reduction of readback signal power. Also, the dependence of media grain size on the signal power shows that the larger grain size media can provide higher signal power at low linear density, while the smaller grain size media gives higher signal at high density. Thus, the magnetic footprint regarding the HAMR technology needs to be optimized to achieve the efficient recording system.
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An Intertrack Interference Subtraction Scheme for a Rate-4/5 Modulation Code for Two-Dimensional Magnetic Recording
(2016-01-01)
Pituso, Kotchakorn
;
Warisarn, Chanon
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Tongsomporn, Damrongsak
;
Kovintavewat, Piya
The performance of a rate-4/5 modulation code is evaluated in two-dimensional magnetic recording (TDMR) channels, where a magnetic medium is described by a discrete Voronoi model, and the two-dimensional sensitivity function of the reader is adopted to generate the TDMR readback signal. Since the read-head sensitivity function covers many tracks, it causes intertrack interference (ITI) that can deteriorate the system performance. Therefore, this letter proposes an ITI subtraction scheme in conjunction with the rate-4/5 modulation code in a coded TDMR channel to mitigate the ITI effect embedded in the readback signals before performing an iterative decoding process. We also investigate the data-dependent readback amplitude distributions and evaluate the TDMR system performance via computer simulation. Results show that the proposed scheme helps improve the TDMR system performance, especially when the areal density is high.
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An Experiment Study of Head-to-Media Spacing Sensitivity in Ultra-high Density Magnetic Recording Systems
(2016-01-01)
Nhunork, Pichet
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Warisarn, Chanon
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Tongsomporn, Damrongsak
The decrease in flying height due to the higher recording areal density of hard disk drives (HDDs) has had a huge impact on data storage technology. The head protrusion that induced by ambient temperature can further reduce flying clearance by a few nanometers. However, the head-disk interface reliability should be also emphasized; since when the head flies too close to the media, the recording head may be burnished. To investigate the head-to-media spacing sensitivity, we use the spin stand tester and analyze the sensitivity through the measurement of overwrite (OVW), micro-track profile (MTP), and signal-to-noise ratio (SNR). The experiment results imply the significant relationship between the OVW and the heater-induced writer protrusion (H-IWP). Furthermore, we verify that the properly reduction of head-to-media spacing can also enhance the both of writability and readability.

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