Head-tape Interface Research Articles

Tape-Head With Sub-Ambient Air Pressure Cavities

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.

Where Tape and Hard-Disk Technology Meet: The HDD Head–Tape Interface

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 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> BER for PRBS data on perpendicularly oriented particulate barium-ferrite tape.

Magnetic evaluation of advanced metal-evaporated tape in an advanced linear tape drive

Demand for increased data storage has resulted in the development of various types of magnetic tapes. To achieve higher recording density, tape manufacturers are developing thin-film tapes, such as advanced metal-evaporated (AME) tape, for use in linear tape drives. In recent studies, these new AME tapes have demonstrated sustainable mechanical durability at low tensions suitable for use in linear tape drives. An evaluation of the magnetic performance of these AME tapes including the impact of tape cupping and initial edge quality was the goal of this study. Head output, dropouts, head–tape interface friction, and lateral tape motion (LTM) were monitored throughout testing. As track widths continue to narrow, LTM has become one of the critical limitations of magnetic performance. To more accurately measure LTM during drive development, a new method involving the output voltage of a head-read element that has been adjusted to be halfway off the recorded track on tape was implemented (LTM M). It is shown that positively cupped AME tapes will result in similar head output and fewer dropouts than the current MP tapes. The negatively cupped AME sample produced the lowest head output data and the highest amount of dropouts of all the tapes evaluated in this investigation. All the tapes evaluated demonstrated similar values of LTM when monitored at the center of the tape. When LTM was monitored at the lower edge of the tape, the positively cupped AME tape with the worst relative edge contour length resulted in the highest LTM M. As found in previous studies, AME tapes produced slightly lower values of coefficient of friction than the MP tapes. From this investigation, positively cupped AME tapes with good initial relative edge contour length are recommended for use in linear tape drives, similar to those used in this study.

Comparative analysis and associated failure mechanisms of magnetic media in advanced linear tape drives

Flexible magnetic tape is widely used for data storage and archival, as future generation of tapes and drives will continue to increase overall storage capacities and data transfer rates. Tape portability, robust drive operation, longevity of magnetic media, and improved performance of head–tape interface under long-term use are required for magnetic tape to maintain a stronghold in the field of storage devices. Comparative studies were performed to investigate differences in performance of various cartridges in impact, tapes under long-term durability, and contamination of head–tape interface in advanced linear tape drives. A drop test was performed in which various cartridges were dropped from varying heights. Cartridge damage was recorded and indexed. Reinforced cartridge casing promotes good stability at low height impact, while casing significant plastic deformation in increased-height drops. Contamination and durability studies were performed in which debris generation, tape edge damage, tape cupping profiles, and error data was collected and analyzed for studies of head–tape interface. Most significant loose debris generation occurs as a result of wear at the tape edges, while adherent debris is related to tape binder system, and causes increases in drive error rate. Cleaning brushes have been incorporated into the design of drives to reduce the accumulation of all types of debris. A study was performed to determine the effectiveness of brushes on head surface cleaning. The use of brushes in drives was shown to be helpful in removal of both loose and adherent debris types. The effect of relative humidity at the interface was examined, and it was found that high relative humidity acts as a lubricant at the head–tape interface, helping to reduce tape wear. Low relative humidity can have differing effects on the interface performance, as it has shown to either increase or decrease debris accumulation, depending upon tape characteristics.

Durability studies of metal evaporated tapes in a linear tape drive: Role of head contour and tape tension

Magnetic performance of metal evaporated (ME) tape makes it a prominent storage media candidate for future data recording systems. However, the durability of ME tapes, limited by a number of tribological issues, is a major concern. A preliminary investigation on durability of ME tapes in a linear tape drive has been carried out. The effect of head contour and tape tension on the durability of the head-tape interface has been studied. An optical microscopy based technique has been used to measure the quality of factory-slit tape edges and after use in a liner tape drive. Debris distribution over the head surface at the end of the testing has been monitored. The ME tapes are found to be sensitive to both head contour and tape tension. Some desirable attributes of ME tapes required to improve durability are discussed.

Mechanical, hygroscopic, and thermal properties of metal particle and metal evaporated tapes and their individual layers

AbstractMechanical and thermal properties of magnetic tapes and their individual layers strongly affect the tribology of magnetic head–tape interface and reliability of tape drives. Dynamic mechanical analysis, longitudinal creep, lateral creep, Poisson's ratio, the coefficient of hygroscopic expansion (CHE), and the coefficient of thermal expansion (CTE) tests were performed on magnetic tapes, tapes with front coat or back coat removed, substrates (with front and back coats removed), and never‐coated virgin films of the substrates. Storage modulus and loss tangent values were obtained at a frequency range from 0.016 to 28 Hz, and at a temperature range from −50 to 150 or 210°C. Longitudinal creep tests were performed at 25°C/50% RH, 40°C/25% RH, and 55°C/10% RH for 50 h. The Poisson's ratio and lateral creep were measured at 25°C/50% RH. CHE was measured at 25°C/15–80% RH. CTE values of various samples were measured at a temperature range from 30 to 70°C. The tapes used in this research included two magnetic particle (MP) tapes and two metal evaporated (ME) tapes that were based on poly(ethylene terephthalate) and poly(ethylene naphthalate) substrates. The master curves of storage modulus and creep compliance for these samples were generated for a frequency range from 10−20 to 1015 Hz. The effect of tape manufacturing process on the various mechanical properties of substrates was analyzed by comparing the data for the substrates (with front and back coats removed) and the never‐coated virgin films. A model based on the rule of mixtures was developed to determine the storage modulus, complex modulus, creep compliance, and CTE for the front coat and back coat of MP and ME tapes. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1319–1345, 2004

Dynamic mechanical and thermal analyses of magnetic particle and metal evaporated tapes and their individual layers

AbstractThe mechanical and thermal properties of magnetic tapes and their individual layers strongly affect the tribology of the magnetic head–tape interface. Dynamic mechanical analysis and thermomechanical analysis tests were performed on magnetic tapes, tapes with front coat or back coat removed, substrates (with front and back coats removed), and never‐coated virgin films of the substrates. Storage modulus and loss tangent were obtained at a frequency range from 0.016 to 28 Hz, and at a temperature range from −50 to 150 or 210°C. Coefficients of thermal expansion (CTE) of various samples were measured at a temperature range from 30 to 70°C. The tapes used in this research include two magnetic particle (MP) tapes and two metal evaporated (ME) tapes based on poly(ethylene terephthalate) and poly(ethylene naphthalate) substrates. The master curves of storage modulus for these samples were generated for a frequency range from 10−20 to 1015 Hz. The effect of the tape manufacturing process on the dynamic mechanical properties of substrates was analyzed by comparing the data for the substrates (with front and back coats removed) and the never‐coated virgin films. A model based on the rule of mixtures was developed to determine the storage modulus, complex modulus, and CTE for the front coat and back coat of MP and ME tapes. To validate the procedure, data for these individual layers were then used to calculate the corresponding properties of the finished tape. The predicted results were compared with the experimental measurements. The data obtained in the study are also discussed in light of previously published lateral contraction, Poisson's ratio, CTE, and CHE (coefficient of hygroscopic expansion) data. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 548–567, 2003

Effect of magnetic tape thickness on friction and wear in a linear tape drive

The effect of magnetic tape thickness and tape substrate material on friction and wear is very important in functioning of future linear tape drives with ultra-thin tapes. This effect is studied using a magnetoresistive (MR) type head with metal particle (MP) tapes of two different substrate materials, and two different substrate thicknesses for each material. A new technique to measure friction directly from cantilever deflection is developed and employed successfully. Head-tape interface friction was monitored during short pass (10 m) shuttling tests for 50,000 passes. Surface analysis of worn head and tape surfaces was carried out using optical microscopy, atomic force microscopy and scanning electron microscopy to assess the damage and to determine the debris composition. A possible mechanism of crack formation at the tape edge, crack propagation and material removal is discussed.

Failure mechanisms of the head-tape interface during head stepping in a linear tape drive

Improving the performance of computer tape drives is an ongoing process. The magnetic and tribological performance of metal particle (MP) tape during head stepping was evaluated in a commercial linear tape drive. Head output and head-tape interface friction were monitored during short-pass (10m) shuttling tests with stepping of the head. The test without stepping showed no signs of failure. To evaluate the effect of stepping on the head-tape interface, three different kinds of stepping test, namely normal stepping, reverse stepping and normal stepping with inverted drive, were performed. All these tests with head stepping failed far sooner than the test without stepping. Non-parallelism between the head and tape surfaces caused a reduction in hydrodynamic air bearing pressure. Less spacing between the lower tape edge and the head resulted in high wear of the lower edge of the tape and outer outrigger surfaces of the head. Additional sliding in a direction orthogonal to the tape motion from head stepping aggravated the friction and wear of the lower tape edge. The inability of the drive to overcome this high friction ultimately resulted in failure. On the head surface, different kinds of debris were found, and unsymmetrical debris distribution was observed. Some manufacturing improvements are presented to prolong drive durability.

Effect of operating environment on head–tape interface in a linear tape drive

Environment plays an important role in the functioning of tape drives and the exact reproduction of the stored data. The magnetic and tribological performance of metal particle tape at ambient and extreme temperature and humidity conditions was evaluated in a commercial tape drive. Head output and head–tape interface friction were monitored during short pass (10 m) shuttling tests. Optical microscopy, atomic force microscopy and scanning electron microscopy were used to evaluate the head and tape surfaces at the end of the tests. Magnetic and tribological performance of the head–tape interface is the best at low temperature and low relative humidity conditions. Increase in both temperature and humidity results in performance degradation. Low temperature and high relative humidity conditions generate more debris and cause more wear of the tape edges. High temperature and low relative humidity conditions show deposition of debris near the read head region and increase in head output. High temperature and high humidity conditions result in failure of the drive. Possible mechanisms responsible for the observed tribological behavior of the head–tape interface at various conditions are discussed.

Understanding the effect of the tape surface on the metal-particle tape medium noise

Spacing fluctuations resulting from the head–tape interface dominate the metal-particle tape medium noise. Utilizing narrow-gap record heads, the spatial correlation of the head-medium interface has been completely and accurately characterized using a magnetic recording measurement. The measurements show that the spacing fluctuations damp with shorter wavelength, or in other words, the tape head-medium noise possesses a long spatial correlation length. In addition, the results demonstrate that the roughness-induced spacing fluctuations originate from portions of the tape surface that contact the tape, i.e., the load-bearing surface. This understanding of the head-medium noise reveals that the majority of the tape medium noise occurs during the recording process, and not during signal playback. Spatial correlation measurements on low-density (5 kfci) recordings provide verification of these conclusions. The study offers a thorough understanding of the surface roughness role on producing the head-medium noise.

Effect of operating environment on failure mechanism of a head-tape interface in a linear tape drive with a belt-driven cartridge

The effect of the operating environment on the failure mechanism of a head-tape interface in a linear tape drive with a belt-driven cartridge was studied. A modified commercial drive with magnetoresistive head and metal particle tape were used. Durability tests for the full tape length were performed at ambient and extreme environmental conditions. Head output, coefficient of friction and number of dropouts per minute were measured during the test. Optical and atomic force microscopy and Auger electron spectroscopy were used to evaluate changes at the head-tape interface at the end of the tests. Magnetic and tribological performance of head-tape interface is the best at low temperatures and low relative humidities. Increases in both temperature and relative humidity result in performance degradation, with the worst performance at the highest temperature. At ambient conditions, sporadic variations in the coefficient of friction and the number of dropouts per minute are observed, associated with a cycle of stain formation and removal. Possible mechanisms responsible for the observed tribological behaviour of the interface at various environmental conditions are discussed.

Magnetic and tribological evaluation of metal particle and metal-evaporated tapes in a linear tape drive

Improving the performance of computer tape drives is an ongoing process that has recently involved the utilization of metal-evaporated (ME) tapes. The magnetic and tribological performance of the current metal particle (MP) tape and a new dual-magnetic-layer ME tape were evaluated in a Quantum DLT 4000 linear tape drive. Head output, drop-outs and head-tape interface friction were monitored during high-tension (1.7 N) high-speed (4 m/s) short-pass (10 m) shuttling tests without stepping the head. The severe MP test never showed signs of failure, but wear of the head's outriggers is believed to impact the stability of the head output signal. MP tape significantly outperformed ME tape; ME even performed poorly at nominal tension (0.8 N) and speed (2.5 m/s) conditions. ME tape lubricant was stripped away by corners on the DLT head, resulting in increased friction, wear and exposure of the relatively brittle diamond-like carbon layer. A high-tension high-speed MP test with head stepping was also performed to evaluate the effect of stepping; it failed far sooner than the non-step MP test. The nominal ME test and severe MP head step test are both believed to have failed because of the drive's inability to overcome high (wear-induced) static friction experienced during changes in tape direction. Modifications to the existing head or a new head design could improve the performance of ME tape in the DLT 4000 linear tape drive.

Studies on Degradation Mechanisms of Tape Lubricants in a High Vacuum Environment

Degradation and tribological performance of several tape lubricants were studied during sliding in a high vacuum environment. Gaseous products generated from the head–tape interface and friction force were detected and monitored as function of sliding distance by using a quadrupole mass spectrometer and strain gauges. Chemical analyses of the commercial tape lubricants were done to better understand the degradation processes and degradation products in the sliding tests. Experimental results showed that the commercial metal evaporated (ME) tape lubricants include fatty acid and perfluoropolyether (PFPE) compounds. The degradation products from the commercial tape include small fluorine containing fragments from the PFPE lubricant and small hydrocarbon fragment from fatty acid. In addition, three other species, H2, C2H5 and CO2 were detected in the case of ME tapes and they were generated from the degradation of the diamond-like carbon (DLC) coating on the tape surface. The commercial metal-particle (MP) tape used fatty acid and fatty acid ester lubricants. Only hydrocarbon fragments were detected in the MP tapes' sliding tests, no H2, C2H5 and CO2 were found. The coefficient of friction of these two tapes increased with sliding and depletion of lubricant on the tape surface. The trend of the coefficient of friction was different for ME and MP tapes because of the differences in the lubricant and lubricant distribution on these two tape surfaces. Z-Dol and stearic acid were used to lubricate ME tapes, their test results were analyzed and compared with the commercial tapes' test results.

Effect of Magnetic-Head Slot Orientation on Pole Tip Recession and Debris Generation in Linear Tape Drives

Pole tip recession (PTR) and debris generation lead to signal loss at the head-tape interface. Accelerated tape drive experiments and measurements of head-tape spacing were conducted using heads with different slot orientations. PTR was higher for blind-slotted (slots in the direction of tape travel) heads than for transverse-slotted (slots in the direction transverse to tape travel) heads. More tape debris was found on the surface of transverse-slotted heads, but most of this debris resided in the slots rather than on the bearing surface. The slots in the transverse-slotted heads act as tape cleaners, which accounts for the large debris buildup in the slots. This leaves fewer loose debris particles at the interface for the transverse-slotted heads. Little difference was found in the head-tape spacing for the two types at the conditions used in the drive experiments. It is proposed that the greater amount of loose debris available at the interface for use in three-body abrasive wear, which is believed to cause PTR, results in higher PTR in blind-slotted heads. Presented as a Society of Tribologists and Lubrication Engineers Paper at the ASME/STLE Tribology Conference in Seattle, Washington, October 1–4, 2000

Analysis of stain formation and wear mechanisms in a linear tape drive

Magnetic reliability of a linear tape drive is intimately related to the tribology at the head-tape interface because an increase in the spacing between the read element of the head and the magnetic particles in the tape reduces the strength of the magnetic signal read from the tape. In this study, Co-γ-Fe2O3 tape was worn against magnetoresistive (MR) heads in a modified commercial tape drive. Friction, the head output and the number of drop-outs were used to determine the wear mechanisms at the head-tape interface. Additionally, atomic force microscope (AFM) measurements, Auger material composition analysis and stain thickness measurement using a nanoindentation scratch test were used to support the friction and magnetic data. Using these methods, it was found that three different wear mechanisms occur at the head-tape interface, which first involves adhesion building a stain on the head surface, followed by the cyclic wearing and accumulation of the stain. Finally, the tape binder is sufficiently worn away, causing the stain to be permanently removed by abrasion of the hard magnetic particles. The life of the head-tape interface can be improved by cleaning the stain from the head with an abrasive tape before the stain becomes too thick. Therefore, if only one tape was used in the lifetime of the head, the head would need to be cleaned only once because the tape has a finite amount of stain-producing material available. However, if the stain thickness is reduced too much, the head-tape interface will not function without an increase in stain material because the presence of the stain provides lubrication without which the friction at the head-tape interface exceeds the motor force, causing the drive to stop.

Interactions at the head–tape interface of a linear tape system

In this study, tape cycling experiments were performed using two different experimental metal particle media in combination with a Travan™ linear tape system. The aim was to investigate the effect of head/tape contact on the tribological properties and signal performance of the system. A combination of cycling at extreme environmental conditions, use of experimental media, and cycling beyond the normal limit of operation ensured a worst-case scenario for the head–tape interactions. Auger electron spectroscopy (AES) and atomic force microscopy (AFM) were used to characterize the chemical and physical surface changes that occurred on and in the head surfaces. X-ray photoelectron spectroscopy (XPS) was used to identify the chemical changes that occurred at the media surface and these changes were correlated to variation in signal dropout rate. Measurements were made as functions of number of cycles. The cycling experiments for the two different tapes were performed at conditions of 32°C, 80% RH and 5°C, 10% RH and transfer of material from the media to the head was observed at each condition for both tape types. The degree of material transfer was influenced by the environmental operating conditions, but was governed by localized heating effects, such as those originating from active magnetoresistive (MR) elements and frictional interactions between the head and media. XPS analyses of the surface of the media revealed a reduction of nitrogen with increasing number of cycles indicating binder depletion. Significant differences in elemental concentrations were also detected between areas corresponding to regions directly under the cartridge belt compared to those off belt.

Generation of magnetic tape debris and head stain in a linear tape drive

The presence of tape debris at the head-tape interface can cause an increase in spacing and consequently an increase in signal loss. In this study, the generation of tape debris in linear tape drives is analysed. Functional drive tests are conducted using thin-film AlO3-TiC and Ni-Zn ferrite heads run against commercial metal particle (MP) tape. Three types of tape debris are found: magnetic particle rich, polymer rich and adherent (stain). Each type is found at a distinct location on the head surface. Optical microscopy and computerized image analysis are used both to quantify the tape debris and to find its distribution on the head. Atomic force microscopy is used to measure the thickness of adherent debris. The Al2O3-TiC sample generates more of all three types than does the Ni-Zn ferrite sample. This is probably a result of the higher hardness of Al2O3-TiC. The differential wear of Al2O3 and TiC probably accounts for the presence of adherent debris on the Al2O3-TiC head. No adherent debris can be found on the Ni-Zn ferrite head. Since the adherent debris collects near the pole tip and is difficult to remove, it potentially poses the greatest head-tape spacing problem, even though its thickness is only of the order of a few nanometres. A relationship is found between the generation of loose debris and the tape speed, tape tension and head wrap. Loose debris generation increases as the tape speed decreases and as the tape tension and head wrap increase. Its generation is found to be approximately proportional to the frictional force. Loose debris, especially the magnetic-particle-rich type, continues to be generated in abundant amounts beyond the burnishing phase for MP tape. The use of an abrasive tape leader is found to reduce the amount of debris at the interface.

Finite element based head-tape interface simulation including head-tape surface asperity contacts

The finite-element method with a non-uniform mesh is used to analyze the two-dimensional (2D) linear head-tape interface including head-tape contacts. Numerical results for the head-tape spacing, the air-bearing pressure and the contact pressure for a 2D cylindrical head-tape interface are obtained and compared to the 1D calculation results. The effect of the tape edge on the head-tape spacing and pressure is investigated.

Tribology of the helical scan head tape interface

The performance of video helical scanner heads is strongly dependent on head wear and staining. In this study, the tribology of the helical scan head tape interface is investigated and the effect of environmental conditions on wear and transfer film formation is studied. Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM) are used to evaluate the morphology of deposits formed in the glass and ferrite regions of helical scan heads, and Energy Dispersive X-ray analysis (EDX) and Auger electron spectroscopy (AES) are applied for chemical characterization of the head and deposits, respectively. The tendency towards wear and deposit formation is investigated as a function of relative humidity (RH). Finally, lateral force microscopy is used to evaluate differences in friction between contaminated and clean regions of the head using a silicon nitride probe.