Yawshing Tang

Overview of Fly Height Control Applications in Perpendicular Magnetic Recording

The ability to control head-to-media spacing through a heating element has many technical implications. Properly applying this capability can significantly improve bit error rate (BER) performance in perpendicular magnetic recording (PMR). It also calls for the development of techniques associated with clearance control. A good touchdown detection method and an accurate measurement of spacing change are essential for proper clearance control. This paper analyzes the potential performance improvement through the application of clearance reduction during writing and reading. Touchdown detection methods and spacing calculation accuracy will also be analyzed

Study of Lithographically Defined Data Track and Servo Patterns

We report on fabrication of discrete tracks on perpendicular magnetic recording (PMR) media with an e-beam lithographical process. We studied the recording performance of the e-beam media on a spinstand in parallel with conventional PMR media. Discrete track media show significant reduction in adjacent track erasure (ATE). We studied and quantitatively measured the source of the ATE improvement, and developed a triple track geometrical model to calculate achievable track density for both discrete track recording (DTR) and continuous media. From the model, we identify two factors of DTR that contribute to reaching a higher TPI. Using the same fabrication technique, we also studied servo burst design and its playback waveform quality. At 250 ktpi, we compare DTR servo bursts with servo bursts written with a conventional method. DTR servo bursts show better edge definition, which can translate to better position error signal sensitivity and support higher TPI in the future.Discrete tracks are fabricated on conventional PMR media with an e-beam litho graphical process. The recording performance is studied on a spinstand in parallel with conventional PMR media. Discrete track media shows significant reduction in adjacent track erasure (ATE). The source of the ATE improvement is studied and quantitatively measured. A triple track geometrical model is developed to calculate achievable track density for both DTR and continuous media. From the model, we identify two factors of DTR, which contribute to reaching a higher TPI. Using the same fabrication technique, we also study servo burst design and its playback waveform quality. At 250 ktpi, we compare DTR servo bursts and servo bursts written with a conventional method. DTR servo bursts show better edge definition, which can translate to better PES signal sensitivity and support higher TPI in the future.

Fabrication of Flyable Perpendicular Discrete Track Media

Discrete track media offers many potential recording advantages over conventional continuous media in hard disk drives. In this study, we present a novel fabrication process for discrete track perpendicular magnetic media via electron beam lithography, ion milling, and the use of a protective Al sacrificial layer. Physical characterization of the media confirms the process is able to produce patterned tracks with no damage to the media. Spin stand analysis verifies the disks are flyable and capable of recording sharp transitions without any degradation in the magnetic signal

Write Synchronization in Bit-Patterned Media

Writing bit-patterned media has been a challenging problem because it is necessary to synchronize write timing with physical bit-pattern locations on disk. This timing requirement must be addressed not only in disk drives but also in testing environments such as a spin stand. This paper first describes a technique for synchronizing write timing on a spin stand. Testing results show that, with data block length similar to a disk drive sector, the write timing jitter due to synchronization error is much smaller than the magnetic transition jitter. We then discuss the potential timing jitter sources in a disk drive, including disk speed variation, head vibration, and write clock stability. Experimental data show that the head vibration is potentially the most difficult jitter source for the write clock to handle. The possibility and difficulty in applying coding techniques to correct write timing error is also investigated. While it is possible to create codes for this purpose, practical considerations can limit its usefulness.

Perpendicular write-head remanence characterization using a contact scanning recording tester

In this study, an experimental method for characterizing perpendicular write-head pole-tip remanence using a contact scanning recording tester is presented. The head remanence is characterized by imaging the written patterns generated by perpendicular write heads on dc-saturated perpendicular media. Write-head footprints are recorded with pulsed unidirectional currents while the head is stationary, followed by scanning the head in various directions at current-off state. Sufficient head remanent field yields written traces during the current-off scan. Projection of traces in multiple scanning directions enables pinpointing of the pole-tip remanence locations. It is found that the traces written by the remanent field appear only when pulse current amplitudes exceed a certain threshold value. The strength of remanent field also shows a dependence on current pulse polarity. The “stiffness” of the remanence is characterized by the amplitude of the opposite write current needed to eliminate the remanent field.

Recording Performance Study of PMR Media With Patterned Tracks

Discrete track recording technology offers a potential advantage in reducing adjacent track erasure/interference. As nano-imprinting technology advances, fabrication of such media has been demonstrated. In recent years, discrete track recording has generally been viewed as one of the next promising technologies for areal density advancement. In this study, we evaluated the recording performance of PMR media with patterned tracks. To accurately assess the advantage of discrete track performance and compare with current continuous media, both recording performances were measured on one single track. The head flying height is monitored on the patterned and continuous media regions. At 100-nm data track width, patterned tracks show noticeably better signal-to-noise ratio and significantly lower adjacent track erasure compared with continuous media at the same track width. Such measured performance advantages are critical to increase track density beyond 300-400 ktpi

Lithographically patterned servo position error signal patterns in perpendicular disks

For discrete track media to become a viable alternative, it is essential to produce accurate servo patterns in a cost effective manner. This study presents a spin stand analysis and comparison of position error signals generated from various lithographically defined servo patterns and servo bursts written on continuous regions of the same perpendicular recording media. It is demonstrated that the edge variation on the patterned servo elements is much less than that found on conventional servo bursts. In addition, evidence shows that despite some amplitude loss resulting from the removal of magnetic material, patterned servo bursts produce good quality position error signals when compared to servo bursts written on continuous media.

Thermal stability enhancement of perpendicular media with high-order uniaxial anisotropy

The effect of second-order uniaxial anisotropy energy K/sub 2/ on thermal stability and writability of perpendicular media has been studied. Due to the high orientation of crystalline easy axes, both energy barrier and dynamic coercivity of perpendicular media increases with K/sub 2/. With relatively more increase in energy barrier, improvement of the tradeoff between thermal stability and writability can be achieved by increasing K/sub 2/. The field angle dependence with nonzero K/sub 2/ is also quantitatively investigated.

Characterization of Mechanically Induced Timing Jitter in Synchronous Writing of Bit Patterned Media

Potential sources of timing errors in writing bit-patterned media are experimentally characterized. This paper describes a time-domain analysis of jitter in a disk drive that is identified as the effect of spindle speed variation. The jitter during head-disk interaction is characterized by a frequency modulation analysis. The impact of head vibration on write timing is also demonstrated using images reconstructed from read signal.

Writability in Discrete Track Media

Discrete track recording has emerged as a promising candidate for high storage capacity since it reduces adjacent track erasing (ATE) and alleviates narrow head requirements. In this paper, the writability of discrete lines was studied in discrete track media (DTM) fabricated by e-beam lithography and ion-milling on perpendicular magnetic recording (PMR) media. The writability of discrete lines with finite length and three kinds of line width (50, 100, and 150 nm) is compared with continuous media on the same track. When writing current is small (less than 12 mA), the narrowest discrete lines (50 nm) are not easily magnetized, most likely due to deformed magnetic layer created by a shallow wall angle. Conversely, wider discrete lines ( ges 100 nm) are magnetized like continuous media. No difference in the level of magnetization was observed for the narrowest lines if writing current was large enough (more than 12 mA). This smooth magnetization of the narrowest line at sufficient writing current flow makes it certain that narrow discrete line can be used for high capacity storage.