Recording Head Operations

Bloomington, MN, United States

Recording Head Operations

Bloomington, MN, United States
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Rea C.,Recording Head Operations | Subedi P.,Recording Head Operations | Zhou H.,Recording Head Operations | Saunders D.,Recording Head Operations | And 13 more authors.
IEEE Transactions on Magnetics | Year: 2017

Differences in the areal density capability limits for heat-assisted magnetic recording (HAMR) and conventional perpendicular magnetic recording (PMR) are explored using spinstand measurements and micromagnetic modeling. The written track curvature and the transition width are measured with a special technique that mitigates cross-track averaging effects due to finite read sensor width. Tracks written with HAMR heads are shown to have more curvature compared with those written with modern PMR writers. Both broadening and transition curvatures are present cross track, that can be described reasonably well using Landau-Lifshitz-Gilbert modeling and indicates the effective gradient profile dominates. However, as we get to the track edge, we see disagreement between the model and the experiment, which is not currently reconciled. The curvature and broadening effects appear to challenge not only the downtrack bit resolution during readback, but also the cross-track written width with increased linear density. We discuss different near field transducer (NFT) designs, and comparing narrow versus wide thermal profile NFT designs, we can see that track pitch appears to weakly optimize to a maximal cross-track gradient point. Experimental measurements of constant bit error rate for different linear and track densities indicate a significant opportunity for high track density recording using HAMR. The difference appears to be related to the ability for HAMR to address high track pitches with a minimal increase in risk of adjacent track interference compared with PMR. We revise NFT head-to-media spacing requirements when we attempt to account for interference effects. © 1965-2012 IEEE.


Hernandez S.,Research Storage Group | Lu P.-L.,Research Storage Group | Granz S.,Research Storage Group | Krivosik P.,Recording Head Operations | And 4 more authors.
IEEE Transactions on Magnetics | Year: 2017

Ensemble waveform analysis is used to calculate signal to noise ratio (SNR) and other recording characteristics from micromagnetically modeled heat assisted magnetic recording waveforms and waveforms measured at both drive and spin-stand level. Using windowing functions provides the breakdown between transition and remanence SNRs. In addition, channel bit density (CBD) can be extracted from the ensemble waveforms using the di-bit extraction method. Trends in both transition SNR, remanence SNR, and CBD as a function of ambient temperature at constant track width showed good agreement between model and measurement. Both model and drive-level measurement show degradation in SNR at higher ambient temperatures, which may be due to changes in the down-track profile at the track edges compared with track center. CBD as a function of cross-track position is also calculated for both modeling and spin-stand measurements. The CBD widening at high cross-track offset, which is observed at both measurement and model, was directly related to the radius of curvature of the written transitions observed in the model and the thermal profiles used. © 1965-2012 IEEE.


Rea C.,Recording Head Operations | Holfeld J.,Recording Head Operations | Kalarickal S.,Twin Cities Operations | Benakli M.,Recording Head Operations | And 13 more authors.
IEEE Transactions on Magnetics | Year: 2014

Heat-assisted magnetic recording (HAMR) is a fast evolving technology, and has been established as the next enabler of higher areal density in magnetic recording. After achieving high areal density capability, HAMR drive integration was recently demonstrated. In this paper, we discuss some of the recent learning from component performance and drive integration. We identify a key challenge in HAMR integration: erasure due to thermal background heating. The background heating was introduced to improve near-field transducer reliability and reduce laser power requirement. We present experimental and modeling data on the impact of thermal background, both in the cross-track (adjacent-track erasure) and down-track (self-erasure) dimensions. © 2014 IEEE.


Kiely J.D.,Recording Head Operations | Jones P.M.,Recording Media Operations | Wang H.,Recording Media Operations | Yang R.,Recording Head Operations | And 4 more authors.
IEEE Transactions on Magnetics | Year: 2014

Heat-assisted magnetic recording involves the transfer of energy to the recording medium via optical means. To enable high areal density, the recorded track must be smaller than the diffraction limit of focused light, which is accomplished by using a near-field transducer (NFT) with a corner or peg with small dimension. Energy transfer using such a transducer is a near-field effect, and therefore is highly sensitive to the spacing between the NFT and the medium. Since the recording medium has some surface roughness, there will be a variation in the NFT-to-medium spacing and this will impact the amount of energy transferred from the NFT. We model the effect of Gaussian surface roughness on NFT energy transfer and predict surface temperature variations for a rough surface. In addition, we illustrate how changing the head-medium spacing changes the impact that roughness has on surface temperature variation. We combine these modeled predictions with spinstand measurements of recorded data and conclude that the effect of media roughness results in only limited temperature excursions above the nominal recording medium temperature. © 2014 IEEE.


Rea C.,Recording Head Operations | Benakli M.,Recording Head Operations | Subedi P.,Recording Head Operations | Mendonsa R.,Recording Head Operations | And 13 more authors.
IEEE Transactions on Magnetics | Year: 2016

We collate multiple experimental measurements of heat-assisted magnetic recording (HAMR) near-field transducer (NFT) and reader sensitivity measurements on spinstand to compare and contrast with the conventional perpendicular magnetic recording (PMR). The readback process shares many similarities, but differences appear due to the increased measured curvature of the prewritten track, which increases the observed pulsewidth (Pw50), lower readback amplitude due to reduced flux from the media transition (MrT), and increased coating thicknesses. We find that the reader head-to-media spacing (HMS) sensitivities and requirements converge toward the conventional scaling requirements. The HAMR write process is more complex due to the uncertainties associated with the optical properties and protrusion position of the NFT. However, accumulating multiple studies varying write HMS with coatings, NFT changes, and media changes, we consistently observe lower sensitivities compared with the conventional writer HMS, in line with modeled comparisons, leading to more relaxed requirements on the NFT clearance than the PMR write HMS. A 1.5 Tbpsi basic technology demonstration demo is shared using the HMS numbers in the bounds of the claims. © 1965-2012 IEEE.


Hernandez S.,Research Storage Group | Lu P.-L.,Research Storage Group | Granz S.,Research Storage Group | Krivosik P.,Recording Head Operations | And 4 more authors.
IEEE Transactions on Magnetics | Year: 2016

Ensemble waveform analysis is used to calculate signal to noise (SNR) and other recording characteristics from micromagnetically modeled HAMR waveforms and waveforms measured at both drive and spin-stand level. Using windowing functions provides the breakdown between transition and remanence SNR. Also, channel bit density (CBD) can be extracted from the ensemble waveforms using the di-bit extraction method. Trends in both transition SNR, remanence SNR and CBD as a function of ambient temperature at constant track width showed good agreement between model and measurement. Both model and drive-level measurement show degradation in SNR at higher ambient temperatures, which may be due to changes in the down-track profile at the track edges compared to track center. CBD as a function of cross-track position is also calculated for both modeling and spin-stand measurements. The CBD widening at high cross-track offset, which is observed at both measurement and model, was directly related to the radius of curvature of the written transitions observed in the model and the thermal profiles used. © 2015 IEEE.


Rea C.,Recording Head Operations | Subedi P.,Recording Head Operations | Gao K.,Storage Research Group | Zhou H.,Recording Head Operations | And 12 more authors.
IEEE Transactions on Magnetics | Year: 2016

Differences in the areal-density capability limits for heat-assisted magnetic recording (HAMR) and conventional perpendicular magnetic recording (PMR) are explored using spinstand measurements, drive footprinting, and micromagnetic modeling. The written track curvature is measured with a special technique that mitigates the cross-track averaging effects due to a finite read sensor width. Tracks written with HAMR heads are shown to have more curvatures compared with those written with modern PMR writers. Mitigation of written track curvature is demonstrated with two different HAMR writer designs. The curvature effect appears to challenge not only the downtrack bit resolution during readback, but also the cross-track written width with increased linear density (LD). Experimental measurements of a constant bit error rate for different LDs and track densities (TDs) indicate a significant opportunity for high TD recording using HAMR. The difference appears to be related to the ability for HAMR to address high track pitches with a minimal increase in risk of adjacent track interference compared with PMR. © 2016 IEEE.


Hernandez S.,Storage Research Group | Krivosik P.,Recording Head Operations | Huang P.-W.,Recording Media Operations | Eppler W.R.,Recording Head Operations | And 2 more authors.
IEEE Transactions on Magnetics | Year: 2016

The auto-correlation signal-to-noise (ACSN) method is employed on micromagnetically modeled heat-assisted magnetic recording (HAMR) readback waveforms and compared with experimental ACSN data. The breakdown between transition signal-to-noise ratio (SNR) and remanence SNR is provided for both modeled and measured data. Good agreement is observed between both simulated and experimental SNRs as a function of laser power and as a function of linear density. An efficiency factor that relates maximum temperature observed in the media to the applied laser current is obtained by combining the modeled and experimental data. Usage of this methodology provides SNR metrics that allow a reliable comparison of micromagnetic modeling of HAMR recording systems to experimental measurements. © 2016 IEEE.


Rea C.,Recording Head Operations | Scholz W.,Recording Head Operations | Cao L.,Recording Head Operations | Peng C.,Recording Head Operations | And 14 more authors.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2014

Recent recording areal density and integrated drive performance demonstrations using Heat Assisted Magnetic Recording (HAMR) suggest that it is a viable technology to succeed conventional magnetic recording. However challenges still remain for the near field transducer, in particular reliability and sufficient thermal confinement. We explore a new NFT design, Near field Transducer Gap (NTG), which offers the potential to mitigate some of the issues in track confinement and thermal profile compared to earlier published studies [4]. The design offers efficiency improvements, and the potential to reduce unwanted background light and heating that can lead to erasure in the writing track, and neighbors. © 2014 SPIE.

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