This paper presents a dual-stage approach to nanopositioning in which the tradeoff between the scanner speed and range is addressed by combining a slow, large-range scanner with a short-range scanner ...optimized for high-speed, high-resolution positioning. We present the design, finite-element simulations, and experimental characterization of a fast custom-built short-range scanner. The short-range scanner is based on electromagnetic actuation to provide high linearity, has a clean, high-bandwidth dynamical response and is equipped with a low-noise magnetoresistance-based sensor. By using advanced noise-resilient feedback controllers, the dual-stage system allows large-range positioning with subnanometer closed-loop resolution over a wide bandwidth. Experimental results are presented in which the dual-stage scanner system is used for imaging in a custom-built atomic force microscope.
The recording performance of a new prototype magnetic tape based on perpendicularly oriented strontium ferrite particles is investigated using a 29 nm wide tunneling magnetoresistive reader. At a ...linear density of 702 kbpi, a post-detection byte-error rate (BER) of 2.8e−2 is demonstrated based on measured recording data and a software read channel. The read channel uses a 64-state implementation of an extended version of a data-dependent noise-predictive maximum-likelihood detection scheme that tracks the first- and second-order statistics of the data-dependent noise. At the demonstrated post-detection BER, a post-error-correction-coding BER of less than 1e−20 can be achieved using an iterative decoding architecture. To facilitate aggressive track-density scaling, we made multiple advances in the area of track following. First, we developed a new timing-based servo pattern and implemented a novel quad channel averaging scheme. Second, we developed a new field programmable gate array prototyping platform to enable the implementation of quad channel averaging. Third, we enhanced our low disturbance tape transport with a pair of 20 mm diameter air bearing tape guides and a prototype track-following actuator. Fourth, we developed a novel low friction tape head and, finally, we designed a set of tape speed optimized track-following controllers using the model-based <inline-formula> <tex-math notation="LaTeX">H_{\infty } </tex-math></inline-formula> design framework. Combining these technologies, we achieved a position error signal (PES) characterized by a standard deviation ≤ 3.18 nm over a tape speed range of 1.2-4.1 m/s. This magnitude of PES in combination with a 29 nm wide reader enables reliable recording at a track width of 56.2 nm corresponding to a track density of 451.9 ktpi, for an equivalent areal density of 317.3 Gb/in 2 .
We describe a planar microelectromechanical systems (MEMS)-based x/y nanopositioner designed for parallel-probe storage applications. The nanopositioner is actuated electromagnetically and has x/y ...motion capabilities of plusmn60 mum. The mechanical components are fabricated from a single-crystal silicon wafer using a deep-trench-etching process. To render the system robust against vibration, we utilize a mass-balancing concept that makes the system stiff against linear shock, but still compliant for actuation, and therefore results in low power consumption. We present details of the finite-element model used to design the device as well as experimental results for the frequency response, actuation, and vibration-rejection properties of the nanopositioner
The recording performance of a new magnetic tape based on perpendicularly oriented barium ferrite particles was investigated using a 90-nm-wide giant-magnetoresistive reader and a prototype ...enhanced-field write head. A linear density of 600 kb/in with a postdetection byte-error rate <;3 × 10 -2 was demonstrated based on measured recording data and a software read channel that used a noise-predictive maximum likelihood detection scheme. Using a new iterative decoding architecture, a user bit-error rate of <;1 × 10 -20 can be achieved at this operating point. To facilitate aggressive scaling of the track density, we made several advances in the area of the track-following servo. First, we developed an experimental low-noise tape transport. Second, we implemented an optimized servo channel that together with an experimental timing-based servo pattern enables the generation of position estimates with nanoscale resolution at a high update rate. Third, we developed a field-programmable gate array-based prototyping platform in which we have implemented the servo channel and an H ∞ -based track-following controller, enabling real-time closed-loop track-following experiments. Combining these technologies, we achieved a position-error signal (PES) with a standard deviation of 10.3 nm. This magnitude of PES in combination with a 90-nm-wide reader allows the writing and reading of 177-nm-wide tracks at 600 kb/in, for an equivalent areal density of 85.9 Gb/in 2 . This paper clearly demonstrates the continued scaling potential of tape technologies based on low-cost particulate media.
In this paper, we study the mechanical interface between a hard-disk drive (HDD) head and magnetic recording tape to enable the use of HDD heads to investigate future tape operating points. Tape ...surface height measurements were obtained using an interferometer microscope for varying wrap angle configurations, tape velocities, and tape tensions. Simultaneously, the readback signal from the read element of the HDD head was captured to study the quality of the contact between the tape and the head. The signal-to-noise ratio (SNR) and bit-error rate (BER) performance of pseudorandom bit sequence (PRBS) data readback experiments are presented. An analytical model is described for estimating the magnetic spacing from the PRBS readback spectrum. In contrast to current commercial tape heads, the HDD head surface has a pronounced topography containing cavities. When tape passes in close proximity, subambient pressures are formed inside these cavities and the resulting pressure differences force the tape toward the head and deform the tape into remarkable shapes. For the topography of the HDD head used, the shape of tape is predominantly determined by the leading and trailing wrap angles. Readback was obtained only in the backward direction (i.e., opposite to the direction of operation in an HDD), with positive leading but negative trailing wrap angles. Better readback is obtained for shallow wrap angles, lower tape velocity, and higher tape tension. Good readback is obtained for leading and trailing wrap angles ~0.3° and -0.2°, respectively. Fits of the analytical model to the spectrum of the readback signal of PRBS data lead to a magnetic spacing estimate of ~30 nm. At 600 kb/in linear density, we measured 11 dB SNR and 7 × 10 -3 BER for PRBS data on perpendicularly oriented particulate barium-ferrite tape.
A prototype perpendicularly oriented sputtered tape sample was investigated using a prototype high-moment tape write head and a 48 nm-wide tunneling magnetoresistive hard disk drive read head. A ...linear density of 818 kbpi with a post-detection byte-error rate <;0.023 was demonstrated based on measured recording data and a software read channel that used an extended version of the noise-predictive maximum-likelihood detection scheme that tracks the mean of the data-dependent noise. Using a previously reported iterative decoding architecture, a user bit-error rate of <;1e-20 can be achieved at this operating point. Track-following servo performance characterized by the standard deviation of the position error signal (σ-PES) ≤ 6.5 nm was also demonstrated over a tape speed range of 1.2-4.1 m/s. This magnitude of PES in combination with a 48 nm-wide reader enables reliable recording at a track width of 103 nm corresponding to a track density of 246.2 ktpi, for an equivalent areal density of 201.4 Gb/in 2 .
Tape-Head With Sub-Ambient Air Pressure Cavities Engelen, Johan B. C.; Jonnalagadda, V. Prasad; Furrer, Simeon ...
IEEE transactions on magnetics,
2016-Nov., 2016-11-00, 20161101, Letnik:
52, Številka:
11
Journal Article
A new tape-head design with surface cavities is presented as an alternative to the conventional skiving-edge flat-profile head design. The new head design is referred to as the vacuum head, inspired ...by the sub-ambient air pressure that develops in the surface cavities during operation. Two prototype head modules, a writer and a reader, were fabricated by modifying commercial tape-head modules and are compared with unmodified reference modules. A finite-element model is presented to simulate the head-tape interface and aid in the surface topography design of the vacuum head prototypes. The modeling results correspond qualitatively with experimental data from interferometer measurements of the shape of tape as it passes over the vacuum heads. The vacuum heads are operated successfully in data read/write experiments, with a slightly reduced signal-to-noise ratio performance compared with the reference heads. An indirect measure of head friction is obtained from tape velocity spectra that show a much reduced friction-induced compressional wave tape resonance for the vacuum modules compared with that for the reference modules. The results presented in this paper show that the new vacuum head design is a promising candidate for future heads with low friction, enabling the use of very smooth media for reduced magnetic spacing and increased areal densities.
The recording performance of a prototype magnetic tape based on perpendicularly oriented barium ferrite particles is investigated using an enhanced field tape write head and a 90 nm wide ...giant-magnetoresistive reader. A linear density of 680 kbits/in with a postdetection byte-error rate (BER) <;3.2e-2 is demonstrated based on recorded data processed by a software read channel with noise-predictive maximum likelihood detection. With this detector error rate, a user BER of <;1e-20 can be achieved by means of product error correction coding and iterative decoding. Several advances in the area of track-following servo control are also presented. Specifically, we describe a new timing-based servo pattern, which in combination with an optimized servo channel enables the generation of position estimates with nanoscale resolution and a high update rate. Track-following experiments are performed using an experimental low-noise tape transport, a prototype high-bandwidth actuator, and a set of speed-optimized H-infinity-based track-following controllers. Combining these technologies, we demonstrate a position-error signal (PES) with a standard deviation of 5.9 nm or less over a tape speed range of 1.23-4.08 m/s. This magnitude of PES in combination with a 90 nm wide reader allows operation with 140 nm wide tracks. Combined with a linear density of 680 kbits/in, this leads to an equivalent areal density of 123 Gbits/in 2 .
The friction and magnetic spacing between magnetic tape and a recording head are measured as a function of the wrap angle at several tape speeds and tape tensions for two tape samples with different ...roughnesses. An increase in friction and a decrease in magnetic spacing are measured for: 1) increasing wrap angle; 2) decreasing tape speed; and 3) increasing tape tension. The relation between the magnetic spacing and friction is fixed when varying the tape tension or wrap angle. For the rougher tape sample, reducing the tape speed (and adjusting the tape tension and wrap angle accordingly) reduces the magnetic spacing without increasing the friction. Although the smoother tape experiences more friction for a fixed wrap angle and tape tension, a smaller magnetic spacing at a specified friction is measured for it than for the rougher tape.
Aggressive track-density scaling in linear magnetic tape recording has been identified as a key means of sustaining capacity scaling. As the reader width decreases, the relative signal contribution ...of the written track region outside the lateral extent of the reader increases. We model, analyze and quantify side-reading effects of shielded magneto-resistive read heads reading narrow tracks on perpendicular-oriented tape media. We compare results from extended analytical models with experimental data. An understanding of these effects will be important in designing track misregistration budgets and SNR margins for future operating points of parallel-channel tape recording systems.
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