A magnetic head for 150 MHz, high density recording

A multilayered magnetic head that can read and write at 150 MHz on metal particle tape with a coercivity of 120 kA/m (1500 Oe) has been developed. Ten 2-μm layers of Fe₆₈Ru₈Ga₇ Si₁₇ alloy, with 100 nm of SiO₂ used as spacer, form the magnetic-core thickness and the track width. The head was tested in a rotary recording system at a relative head-to-tape speed of 73 m/s. At a linear density of 4000 fc/mm (100 kfc) and 150 MHz, the measured single frequency signal to 300-kHz-slot noise was 33 dB (RMS-RMS). The measured frequency response curve agrees with theory and indicates a head-to-tape spacing of 70 nm at high speed. The read efficiency of the head decreases from 37% at low frequency to 15% at 150 MHz     

Design of a manufacturable discrete track recording medium

The potential benefits of patterning discrete tracks onto a disk for magnetic data storage have long been investigated. A practical process for manufacturing a cost-effective discrete track recording (DTR) medium has prevented such a disk from being introduced into a product. In this paper, a process utilizing nano-imprint lithography techniques to create a land and groove structure on the surface of a disk substrate will be described. Design considerations for the geometry of the structure, as well as of the magnetic write and read widths of the head, are discussed. Data showing the magnetic characteristics and recording performance of a DTR medium are also presented.     

Recording performance characteristics of granular perpendicular media

The recording performance of CoCrPtO granular-type perpendicular media was examined with two types of perpendicular heads to demonstrate the importance of matching head and media designs in perpendicular recording. Shielded-pole heads with high write field gradients, field angles, and sufficient write field magnitude yielded superior writability and signal-to-noise ratio as compared to mono-pole heads. The recording performance dependences on head-to-medium spacing, interlayer thickness, and soft-underlayer (SUL) thickness were also weaker with the shielded-pole heads. In addition, the effect of stray fields on the SUL domain noise was investigated for a synthetic antiferromagnetically-coupled (SAF) SUL. A radial field close to the exchange field of the SAF SUL was found to induce domain noises that could potentially cause errors in recording systems.     

Overwrite as a function of record gap length

In disk recorders, a common head is used for both recording and reproducing. Old data are not erased but are simply recorded over. The partially erased old data signal appears in the new data as error-producing interference. The amount of erasure of the old data signal is called "overwrite", and 30 dB is typically required. To avoid the reproduce gap null, the head gap is usually chosen to be less than half of the 2F (or bandedge) flux change length. To achieve adequate overwrite using a gap this small, it is necessary to use a very thin recording layer. A simple explanation for this, involving greater depth of penetration for low density signals, is at best incomplete. The data below show that the overwrite phenomenon is complex. Overwrite spectra measured using a thick medium show large resonance peaks whose amplitude and position depend on the record gap, record current, and the densities of the overwriting signal and the signal being overwritten.     

Simulation of the head disk interface for discrete track media

This paper investigates the effect of discrete tracks on the steady state flying behavior of sub ambient proximity sliders. A finite element based air bearing simulator is used to simulate the flying characteristics of sliders over a grooved disk surface. Sliders flying over discrete track disks “see” a disk surface that consists of ridges and grooves. The air bearing pressure build-up for sliders flying over discrete track disks is different from that for sliders flying over plane disks. Low air bearing pressure can be expected for those regions of the slider that are positioned over grooves, while high air bearing pressure exists over ridges. The air bearing characteristics are determined for several pico and femto-type air bearing sliders flying over discrete track disks. An empirical equation is obtained describing the loss of flying height of a slider flying over discrete track disks.     

A measurement of signal-to-noise ratio versus trackwidth from 128 µm to 4 µm

Bulk-erased tape noise will vary as the square root of the reproduce head trackwidth if the noise signal is uncorrelated across the track. Recent models of erased noise involve clusters of interacting particles that could be as large as a few microns. As the trackwidth (TW) approaches the cluster size, the noise should become correlated across the track and the tape-noise-limited signal-to-noise ratio (SNR) should become constant as TW is further reduced. A check of this idea using inductive heads is impractical. Magnetoresistive (MR) heads have very high signal and low noise and so are well suited for this task, but precautions must be taken to minimize thermal and Barkhausen noise. A multichannel MR head having TW from 128 μM to 4 μM was built to explore the areal reproduce density limits of MR heads and measure the bulk-erased SNR versus TW for 3M 5198 tape. Tape-noise-limited performance was achieved with the narrowest 4μM TW channel at a wavelength as short as 1μM. A wideband-equalized SNR of 20 dB was demonstrated with this channel at a wavelength of 1.27 μm or 40 kilo flux changes per inch (40 kFCI), at a tape speed of 38.2 cm/sec. With a 100% guard band, or an 8-μm track-to-track pitch, this corresponds to the very high areal storage density of 127 MFC/in². The SNR was found to vary assqrt{TW}down to TW = 4 μm, which indicates that the expected particle cluster size must be smaller than 4 μm in the crosstrack direction.     

Ohmic contacts on n- and p-layers of GaAs using laser-induced diffusion

Thin surface layers of GaAs have been heavily doped by laser-assisted diffusion from the gas phase using H₂Se and Diethylzinc (DEZ) in H₂. The dependence of sheet carrier concentration and contact resistance of evaporated metal contacts on laser pulse energy, duration and substrate temperature is given. Specific contact resistances of 3·10^?5 ω cm² and 5·10^?5 ω cm² for nonalloyed n- and p-contacts, respectively, are obtained. After alloying they improve to values of 3·10^?6 ω cm². This process can be used to produce local ohmic contacts at low temperature.