Pu-Ling Lu

Commercial TMR heads for hard disk drives: characterization and extendibility at 300 gbit/in/sup 2/

Tunneling magnetoresistive (TMR) reading heads at an areal density of 80-100 Gbit/in/sup 2/ in a longitudinal magnetic recording mode have for the first time been commercialized for both laptop and desktop Seagate hard disk drive products. The first generation TMR products utilized a bottom TMR stack and an abutted hard bias design. These TMR heads have demonstrated three times the amplitude of comparable giant magnetoresistive (GMR) devices, resulting in a 0.6 decade bit error rate gain over GMR. This has enabled high component and drive yields. Due to the improved thermal dissipation of current-perpendicular-to-plane geometry, TMR runs cooler and has better lifetime performance, and has demonstrated the similar electrical static discharge robustness as GMR. TMR has demonstrated equivalent or better process and wafer yields compared to GMR. The TMR heads is proven to be a mature and capable reader technology. Using the same TMR head design in conjunction with perpendicular recording, 274 Gbit/in/sup 2/ has been demonstrated. Advanced design can reach 311 Gbit/in/sup 2/.

Perpendicular media: alloy versus multilayer

Properties and performance for alloy and multilayer perpendicular recording media designs utilizing a soft magnetic underlayer are compared. Among samples considered here, grain size and grain size dispersion are more highly refined for alloy media deposited at high substrate temperature, and are beginning to approach those now available in longitudinal recording. Multilayer media made at ambient temperature typically sacrifice film density and surface smoothness for interface quality. Although microstructural development and the manufacturing process for multilayer media are less mature versus alloy, multilayer media remain attractive due to their high anisotropy potential and the ease with which H/sub n/ and H/sub c/ can be controlled. For thermally stable alloy media made on a pilot production sputtering machine, a spin-stand areal density of 61 Gb/in/sup 2/ has been demonstrated at 350 Mb/s data rate with an on-track bit-error-rate reference level of 1e-6. Using the same media, a working perpendicular drive has been demonstrated at 32 Gb/in/sup 2/ and 500-800 Mb/s data rate.

Recording Performance of a Pulsed HAMR Architecture

In most heat-assisted magnetic recording (HAMR) systems, the laser is ON and kept constant during the entire sector. In this architecture, the transitions are defined whenever the magnetic writer changes polarity. In a pulsed HAMR system, the laser pulses once per bit. In this architecture, the transition is defined by the rising edge of the first laser pulse after a magnetic writer current transition. In this paper, we compare the bit error rate (BER) and areal density capability (ADC) of both continuous wave (CW) HAMR and pulsed HAMR. For our testing conditions, we find that there is no penalty for using a pulsed HAMR system over a CW HAMR system in terms of BER and ADC capability.

Areal-Density Limits for Heat-Assisted Magnetic Recording and Perpendicular Magnetic Recording

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.

Direct and reverse overwrite processes in perpendicular recording

Excellent overwrite (OVW) performance has to be guaranteed for two cases, namely, the case where a low frequency (LF) background data pattern is overwritten by a high frequency (HF) data pattern and the reverse case, e.g., the reverse overwrite (ROVW) situation where a high linear density background pattern is overwritten by a low linear density data pattern. In this work, the spectra of both OVW and ROVW processes have been investigated experimentally to identify the intrinsic characteristics of residual noise in the OVW and ROVW processes in perpendicular recording. Specifically the spectra of both OVW and ROVW processes have been quantitatively analyzed to quantify the characteristics of relevant amplitude modulation or amplitude cancellation process.

Using Ensemble Waveform Analysis to Compare Heat Assisted Magnetic Recording Characteristics of Modeled and Measured Signals

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.

Radius and Skew Effects in an HAMR Hard Disk Drive

Over the past year, heat-assisted magnetic recording (HAMR) has continued to make significant progress toward production and remains the most promising technology to enable areal density growth beyond 1 Tb/in2. In this paper, we present an experimental study on the effects of disk radius and head skew angle in a HAMR hard disk drive. We demonstrate the dependence of laser power on disk radius and the sensitivities to several additional factors that can potentially change that characteristic. We also contrast adjacent track interference and areal density capability performance in drive to conventional perpendicular recording and their respective sensitivities to radius and skew angle.