Film Heads Research Articles

Integrating an MR head into a peak detection channel

Integrating an MR head into a peak detection channel requires the engineer to deal with basic differences between MR and thin film heads. These differences result from nonlinear sensor response, separate write and read elements, and having an active element at the ABS. A simple model for flux superposition can adequately address nonlinear effects and be used for equalization design. Timing budgets can be developed which demonstrate the dominance of media noise for present day systems. Single threshold qualification can handle most current system requirements, Separate read/write elements mean that more attention needs to be paid to offtrack equalization design and head dimensional tolerancing. An active element at the ABS requires better control of the head-disc potential and leakage currents. >

The effects of pole geometry on recording performance of narrow track thin film heads

The effects of pole trimming on the recording performance of thin film heads is investigated through experiment and modeling. Three dimensional head fields are computed numerically for various pole geometries, and are used by a simple two dimensional recording simulation to determine written width, erase width, read width and isolated pulse response. These parameters are then compared to experimental values measured on trimmed and untrimmed heads. Both modeled and experimental parameters are then used as input to a system error rate simulation to determine the effects of pole trimming on system error rate as a function of track density. Good agreement is found between model and experimental parameters. The error rate results suggest that in a system with a reasonable track misregistration (TMR), a track density increase of 7 to 9% can be obtained by trimming the inductive head poles.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Modeling study of isolated read-back pulses from keepered longitudinal thin film media using the boundary element method

The magnetic effects of a saturable magnetic keeper layer on the peak amplitude and shape of isolated read-back pulses from longitudinal thin film media were modeled as 2-dimensional magnetostatic field interactions using the boundary element method. The model assumes a standard thin film head and fly height of a 50% slider, a saturable NiFe keeper, and a perfectly sharp recorded transition in high-capacity longitudinal thin film media. Isolated pulses calculated from the model show that the keeper increases the peak amplitude (55%), decreases the half-height pulse width (46%), introduces pulse shape asymmetry, and eliminates undershoots from pole edges. The pulse shape is found to be very sensitive to changes in both the head-bias current and the head-disk spacing. >

Longitudinal recording performance of sputtered barium ferrite media on a carbon rigid disk substrate

We report the first measurement of the longitudinal magnetic recording properties of as-deposited crystalline thin film barium ferrite media. Using facing target sputtering, randomly oriented crystalline barium ferrite (BaFe/sub 12/O/sub 19/, BaM) has been deposited onto an Ultra Densified Amorphous Carbon substrate, producing high quality films in-situ at a substrate temperature of 660/spl deg/C without any post-deposition annealing. In order to prevent diffusion of carbon into the BaM film, an underlayer of silicon nitride was first reactively sputtered. The BaM sputtering was carried out using targets made from substituted BaM powder which had a powder H/sub c/=1860 Oe (from Toda Kogyo) in a 10% O/sub 2//Ar gas mixture at 3 mTorr. The sputtered films had an in-plane H/sub c/=2100 Oe. The performance of the disk was compared to a commercial disk with cobalt alloy media with H/sub c/=1760 Oe. At a flying height of 75 nm the isolated pulse width, PW/sub 50/, was 0.67 /spl mu/m vs. 0.88 /spl mu/m for the commercial media using a ReadRite M84 thin film head with a gap of 0.3 /spl mu/m. Near its measured D/sub 50/ of 66 kfci the BaM media had a broad band signal/noise ratio (SNR) of 20 dB vs. 13 dB for the commercial media. >

Electrochemical corrosion study of high moment thin film head materials

An electrochemical corrosion study of high moment, magnetically soft FeXN (X=metal) thin film head materials is presented. Potentiodynamic anodic polarization in aqueous 0.5M NaCl and 0.25M Na/sub 2/SO/sub 4/ solutions is studied for qualitative and quantitative measures of corrosion characteristics. The effect of annealing, composition, and a comparison with Permalloy and Fe thin films are also presented. A drastic improvement in corrosion characteristics result in the samples made with N/sub 2/ flow rate >10 sccm. >

Correlation between noise-after-write and magnetic domain structure conversions in thin-film heads by electron microscopy

Noise-after-write in thin film heads has been reported, but the sources have not yet been identified. Using an electron microscope, we observed the magnetic domain structure conversions after writing to find these noise sources. Magnetic domain observation consisted of an image lock-in technique for backscattered electron contrast (Type II) using a 200 kV scanning electron microscope. There was a strong correlation between noise-after-write and domain structure conversions, and noise-after-write is generated mainly near the backgap closure. >

A thin film head for HD-VCRs

A new design of the thin film magnetic head, embedded thin film head, having similar rubbing surface to the TSS (Tilted-Sputtered-Sendust) head is proposed. This head has high efficiency and low impedance by minimizing the size of the magnetic core and using a thin film coil. Both the normalized output voltage per root unit of inductance and the SNR showed +3.6 dB higher at 20 MHz than those of the TSS head for Hi-8 VCRs. This head, coupled with the other advantages, is one of the best candidates for the forthcoming digital HD-VCRs. >

Overwrite Modulation in Co-Based Thin Film Longitudinal Recording Media

Two mechanisms of overwrite, incomplete erasure and modulation, have been studied quantitatively for Co-based thin film longitudinal recording media with a variety of media parameters using thin film head. For all the media studied, the modulation component is larger than the incomplete erasure component under sufficient write current condition. As MrT or the head-medium spacing increases, the incomplete erasure component does not change, instead, overwrite degrades because of the increase in the modulation component. The increase in Hc affects overwrite performance through the increase in both incomplete erasure and modulation component. The relationship between overwrite and media noise performance is also discussed from the view point of media microstructure.

A model for threshold and timing error rate versus off-track position

A model to predict threshold and timing error rate versus position off-track is described. Missing bit and extra bit error rates are calculated separately, then combined to get the total threshold error rate. Timing error rate is calculated independent of threshold errors. The model illustrates the trade-offs in optimizing the threshold on-track versus off-track. The effect of erase width on off-track read performance is shown. The effect of thin film head undershoots on error rate is also shown. Results of the model compared favorably with experimental data.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The effect of rise time and field gradient on nonlinear bit shift in thin film heads

We present a discussion of nonlinear bit shift in thin film inductive heads. A three dimensional finite element model and two dimensional dynamic and self consistent model were used to calculate the nonlinear bit shift as a function of rise time, write current waveform and pole tip saturation. The analysis shows a strong dependency of nonlinear bit shift on rise time and write pole magnetic image. A comparison of experimental data with the theoretical model is presented.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Write induced track misregistration due to magnetic center shifts in thin film inductive heads

The effect of writing on track misregistration in thin film heads for hard disk drives is discussed. An experimental technique is presented which shows that writing causes changes in the magnetic state of the head. These magnetic changes are interpreted by the servo channel as shifts in the position of the head. Real track misregistration occurs as the servo tries to compensate. Typical variations in head position have a standard deviation of 2 to 4 microinches. From ontrack testing of a known unstable head it is concluded that unstable waveforms do not necessarily indicate a magnetic center shift. The opposite behavior has also been seen: magnetic center shifts occur with no noticeable change in waveform.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Wear Behavior of Thin Film Heads for VCR in Sliding with Metal Evaporated Tapes

In order to apply thin film heads to digital video cassette recorders, wear behavior, machinability of head materials, and level difference of the heads were evaluated. The tests, performed with metal evaporated tapes, were divided into two stages. First, wear rate and machinability of individual materials were evaluated. It was found that adhesive wear was dominant for every material. Wear damage was especially-severe for metal magnetic films. Machinability was satisfactory for most bulk materials except for those with a hardness of more than 1000 kgf/mm2, ZrO2 ceramics and devitalized glass. Secondly, wear damage and level difference were evaluated using model heads. After the test, a number of flows were formed on sliding surfaces, mainly on the film surfaces, indicating that abrasive wear occurred. With bulk material of larger wear rate, the level difference reached the final value faster and its deviation was smaller. With Co-Zr-Nb magnetic metal and an Al2O3 protective layer, the level difference wa...

Stress effects of water sorption in cure baked photoresist underlayers on the magnetic easy axis of Permalloy film overlayers

Variations in the uniaxial mechanical stress of Permalloy films can change the magnetic easy axis of the Permalloy films through the magnetostrictive effect. Conventional inductive film heads are fabricated with the use of cure baked photoresist (CBP). We show that water absorption in the CBP can produce significant changes in the magnetic properties of Permalloy films similar to those used in recording head yokes. The diffusion coefficient of water in 3 /spl mu/m thick CBP films was measured with a quartz crystal microbalance and found to be 2.2/spl times/10/sup -9/ cm/sup 2//s at 25 degrees C. A large and reversible change in the magnetic easy axis is observed in 1 /spl mu/m thick Permalloy films that overlay a mound of CBP when it is exposed to water vapor. We infer from the observed magnetic easy axis changes that uniaxial stresses of greater than 5/spl times/10/sup 8/ dynes/cm/sup 2/ are produced due to the swelling and contraction of the underlaying CBP. >

Mechanical Properties and Wear Resistance of High Moment thin Film Head Materials

AbstractMechanical and tribological properties of soft magnetic thin films with high permeability and low coercivity are very important for the application of these films in high-density recording heads. This paper reports our experimental observations on these important properties of FeTaN thin film head materials. Hardness(H) and Young’s modulus(E) for FeTaN sputtered films were determined by nanoindentation. Wear resistance of these films against commercial magnetic tapes was measured with a sphere-on-flat wear tester. The experimental results indicate that the FeTa films can be hardened when nitrogen is introduced. It was found in this study that the thermal stability of the mechanical properties such as hardness of thin films containing nitrogen is better than that of the film without nitrogen. However, our experiments also revealed that the wear resistance of FeTaN films decreases when the concentration of nitrogen increases and the hardness of the worn surface at a wear scar is lower than that of the unworn surface.

Performance evaluation of different pole geometries in thin film heads

To achieve higher areal density, inductive thin film recording heads require smaller track pitch. Pole trimming of conventional heads where P1 width is made equal to the P2 width is suggested in literature as a method for increasing the track density. A patented design called the bevel head where pole P1 of the conventional head is beveled to have the same width as P2 width at the gap, is shown to have equivalent offtrack performance as the pole trimmed heads. The bevel heads require a simpler process to manufacture compared to the pole trimmed heads. Three dimensional field maps are computed for conventional heads, pole trimmed heads and for the beveled heads at different values of write currents. Using these field maps, a simulation of the recording process is done to compute the erase width, write width, read width and isolated pulse response. Both pole trimmed heads and the bevel heads show improvement over the conventional heads in accomplishing a narrower erase width. An offtrack capability model is developed to fit the experimental 747 curve based on the microtrack profile, erase width and a SNR value. Using this model, track density is calculated for all the three heads. Pole trimmed heads and bevel heads show a similar improvement over conventional heads in accomplishing higher track density. >

Tribological and recording performance of carbon-coated thin film head sliders on unlubricated and lubricated thin film media

A significant improvement in wear performance of the head-disk interface has been obtained by coating thin film head sliders with a carbon thin film. Head sliders were coated with several thicknesses of diamond-like carbon sputtered by two methods: Facing Target Sputtering (FTS) and DC Magnetron Sputtering. The wear performance of standard 3.5" diameter disks with and without lubricant was evaluated by continuous drag testing (CDT). Comparison was made for each disk/head pair by the means of kinetic friction vs the number of revolutions and SEM image of wear features on the wear track. Finally, the signal output and S/N ratio were measured using 70% thin film head sliders uncoated and coated with various carbon thicknesses. The decrease of the output signal from carbon-coated head sliders followed the classical loss relationship fairly well.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Read Characteristics of Thin Film Head for VCR

Read Characteristics of Thin Film Head for VCR

Inductance fluctuation, domain instability and popcorn noise in thin film heads

The mechanisms of popcorn noise in thin film heads were studied by correlating the inductance fluctuations under DC bias current, domain instabilities after write and popcorn noise probabilities. Inductance fluctuations of heads were obtained by calculating the standard deviations of the inductance values measured from 20 traces by a HP network analyzer. Instantaneous domain patterns during and after write as well as popcorn noise probabilities of heads were observed by a 0.5-nsec exposure time wide-field Kerr effect microscope and a Barkhausen noise tester, respectively. A strong correlation was found among inductance fluctuations, domain instabilities and popcorn noise probabilities in a noisy head. This relationship was further confirmed by the quantitative correlation between the peak popcorn noise probabilities and peak inductance fluctuations of 12 different heads. Therefore, by measuring the inductance fluctuations of thin film heads under DC bias current, one can infer their susceptibilities to Barkhausen wall jumps, and thus popcorn noise probabilities. >

Topography studies of magnetic-head pole-tip areas using atomic-force microprobe

Atomic Force Microscopy (AFM) has made it possible to quantify an important phenomenon regarding magnetic head characterization, known as pole tip recession. The pole tip area of thin film magnetic heads, considered one of the critical regions in the head/disk interaction, became the subject of increasing concern within the past several years because of the rapid decrease of the flying heights (typical present values are ∽300 Å). The area of interest includes plated permalloy pole tips and the surrounding alumina matrix, sputter deposited onto a ceramic substrate. The complex topography of thearea is associated with the hardness differences between the materials in multiple layers compsiring the head.AFM analysis revealed significant variations in the topography of different thin film heads. Figure 1 presents a typical example of the pole tip area topography. In this AFM image the two pole tips are elevated above the surrounding matrix. A dark area above the upper pole (recessed by ∽190Å vs. the poles) and slightly brighter (elevated by ∽160Å) symmetrically positioned areas on both sides of the poles are clearly outlined.

Error Rate Measurement of Thin Film Heads through a PRML Read Channel

Error Rate Measurement of Thin Film Heads through a PRML Read Channel