Robert G. Biskeborn

Scaling tape-recording areal densities to 100 Gb/in 2

We examine the issue of scaling magnetic tape-recording to higher areal densities, focusing on the challenges of achieving 100 Gb/in2 in the linear tape format. The current highest achieved areal density demonstrations of 6.7 Gb/in2 in the linear tape and 23.0 Gb/in2 in the helical scan format provide a reference for this assessment. We argue that controlling the head-tape interaction is key to achieving high linear density, whereas track-following and reel-to-reel servomechanisms as well as transverse dimensional stability are key for achieving high track density. We envision that advancements in media, data-detection techniques, reel-to-reel control, and lateral motion control will enable much higher areal densities. An achievable goal is a linear density of 800 Kb/in and a track pitch of 0.2 µm, resulting in an areal density of 100 Gb/in2.

Hard-disk-drive technology flat heads for linear tape recording

IBM thin-film tape heads have evolved from the ferrite-based heads first used in the IBM Model 3480 Tape Drive to the hard-disk-drive (HDD) technology flat-profile heads used in IBM Linear Tape-Open® (LTO®) products. This paper describes that transition and discusses the flat tape head manufacturing processes, drive implementation, performance, and outlook. Thin-film head technology for hard-disk drives was first used in tape heads in the early 1990s, when IBM built quarter-inch cartridge head images on HDD-type wafers. This was a springboard for the next step, flat-lapped tape heads, which use not only HDD wafers, but also HDD post-wafer machining technologies. With the emergence of LTO, flat heads entered mainstream tape head production in IBM. These have proven to have high performance and durability.

Flat profile tape recording head

In conventional recording, tape wraps a cylindrically contoured head. The authors describe an implementation in which tape contacts a flat-profile bidirectional recording head. Magnetic transducers are located away from the air-scraping edges in the region of uniform head-tape spacing. Optical measurements on glass heads confirm intimate contact between head and smooth media below approximately 3 m/s. Wallace spacing losses show an increase with tape speed, but contact is still evidenced by head wear at 6 m/s. Air leakage and tape mechanical effects lift the tape edges. The width of the lost-contact region is controlled by the design. Flat heads are fabricated using hard-disk-drive head materials, methods, and facilities, and are implemented in the IBM TotalStorage 3580 Linear Tape Open Ultrium drive.

Head and Interface for High Areal Density Tape Recording

A tape recording head in which reading and writing functions are provided by separate modules is presented. The read-only module may be fabricated with a thinner gap than conventional read-write modules. This was shown to provide >; 40% less gap recession in a controlled wear test. Writing modules are configured to contact tape in one tape motion direction only, thus reducing the wear duty cycle twofold. Modeling indicates that broadband signal-to-noise ratio decline due to wear can be up to several dB less for the separated reading-writing head, which therefore may enable advances in linear and thus areal density.

Planar Thin-Film Servo Write Head for Magnetic Tape Recording

We present a planar thin-film servo write head for writing timing-based servo patterns. The planar head operates at low current ( ~ 100 mA) with nanosecond switching times. The planar head can handle dc current, enabling trailing-edge writing. Magnetic force microscopy measurements of the transitions written by the planar head and a conventional commercial servo write head on longitudinal metal particle and nonoriented barium ferrite media were made to assess the quality of the written transitions. The transition response width PW50 is found to be independent of the tape velocity during write for the planar head. For the conventional head, PW50 is larger and increases with the tape write velocity. The reduced PW50 results in larger readback signal amplitude and hence an improved track-follow performance. The faster switching capability of the planar head enables formatting at higher tape velocity.

Crosstalk Between Write Transducers

Recording experiments on modern tape heads having closely spaced write transducers reveal the presence of writer-to-writer crosstalk. The data suggest that crosstalk arises from changes in write gap fields caused by the leakage of magneto-static flux between neighbors. Crosstalk recording simulations agree with the observed trends. Finite-element method (FEM) modeling of linear heads predicts smaller crosstalk than is experimentally observed, suggesting that nonlinear pole response is needed for explaining the phenomenon. Dependence of crosstalk on writer-to-writer spacing is computed and is consistent with the observations.

Tunnel Valve Sensors in Contact Recording

Results of experiments in which hard-disk drive (HDD) tunnel valve (TV) sensors were run in continuous contact with magnetic recording tape are presented. In one mode, suspended HDD sliders were run against tape backed by a supporting air film in a novel configuration. In another, tape was run in an air-skiving mode over HDD rowbars mounted on support beams, similar to the way tape wraps a conventional tape head. The data indicate that HDD TV sensors can successfully operate in continuous contact with running tape media. Measurements show that roughness of older generation metal particle tape limits the signal-to-noise ratio achievable using existing narrow HDD TV sensors. However, TV sensors optimized for running on smoother barium ferrite tape are now a viable candidate for future high areal density tape recording platforms.

TMR tape drive for a 15 TB cartridge

This paper highlights the development of tunnel magnetoresistive (TMR) sensors for magnetic tape recording applications. This has led to the introduction of a tape drives supporting a 15 TB native tape cartridge, currently the highest capacity available. Underscoring this development is the fact that the TMR sensors must run in continual contact with the tape media. This is contrasted with modern hard disk drive (hdd) sensors, which fly above the disk platters. Various challenges encountered in developing and deploying TMR are presented. In addition, advances to the write transducer are also discussed. Lastly, the authors show that future density scaling for tape recording, unlike that for hdd, is not facing limits imposed by photolithography or superparamagnetic physics, suggesting that cartridge capacity improvements of 4 to 6x will be achieved in the next 4 to 8 years.This paper highlights the development of tunnel magnetoresistive (TMR) sensors for magnetic tape recording applications. This has led to the introduction of a tape drives supporting a 15 TB native tape cartridge, currently the highest capacity available. Underscoring this development is the fact that the TMR sensors must run in continual contact with the tape media. This is contrasted with modern hard disk drive (hdd) sensors, which fly above the disk platters. Various challenges encountered in developing and deploying TMR are presented. In addition, advances to the write transducer are also discussed. Lastly, the authors show that future density scaling for tape recording, unlike that for hdd, is not facing limits imposed by photolithography or superparamagnetic physics, suggesting that cartridge capacity improvements of 4 to 6x will be achieved in the next 4 to 8 years.