P. Arnett

White-noise magnetization fluctuations in magnetoresistive heads

Thermal magnetization fluctuations in magnetoresistive (MR) heads for magnetic hard-disk storage are a fundamental limit on their signal-to-noise ratio. The resultant noise is essentially frequency flat (white), scales with head sensitivity as signal does, but increases inversely with sensor volume. It will impact the present course of industrial R&D efforts toward geometric scaling and increasing raw head sensitivity to achieve increased areal storage densities and data rates. Magnetization noise is shown to exceed Johnson noise in 0.4 μm sensor size, giant-MR spin-valve heads designed for ∼20 Gbit/in.2 areal storage density. The basic physics underlying the experimental results is shown to be consistent with predictions from the fluctuation–dissipation theorem.

Silicon nitride trap properties as revealed by charge−centroid measurements on MNOS devices

Previous charge−centroid studies of MNOS devices have shown that electrons injected into the insulator structure from the silicon are trapped not solely at the dielectric interface, but can be distributed over nearly the entire nitride thickness. In this paper, results of charge−centroid measurements on thin−oxide MNOS devices are interpreted with a charge trapping model, leading to values for the nitride trap density, capture cross section, and average trapping distance of 6×1018/cm3, 5×10−13 cm2, and 35 A, respectively.

Hole injection into silicon nitride: Interface barrier energies by internal photoemission

Energy barrier heights at the interfaces of metal–silicon nitride–silicon structures have been measured by internal photoemission as a function of metal electrode material and substrate doping. These measurements have been interpreted in terms of a dominant hole internal photoemission mechanism. Hole energy barriers from the Au, Al, or Mg Fermi level and the Si valence band to the Si3N4 valence band were found to be 1.9±0.1, 3.0±0.1, 4.0±0.1, and 2.1±0.1 eV, respectively.

5 Gb/in/sup 2/ recording demonstration with conventional AMR dual element heads and thin film disks

We have successfully demonstrated magnetic recording at an areal density of 5 Gb/in/sup 2/ and a data rate of 10 MB/s using narrow track dual element heads with conventional AMR sensors and low noise Co alloy thin film disks. In this work, the target densities of 240 K bpi/spl times/21 K tpi were achieved by a combination of narrow track and low-flying technologies. The write and read head trackwidths were reduced to submicron dimensions, with high moment pole-tips to maintain good writability. At the same time, magnetic spacing was substantially reduced by using low-flying airbearing surface designs. Finally, significant signal-to-noise improvements were attained with the development of high sensitivity AMR read heads and very low noise thin film media. Recording tests showed satisfactory writability in terms of overwrite and hard-transitions from the submicron width write heads. Readback yielded symmetrical signals close to 1 mV//spl mu/m and rolloff measurements yielded 50% densities as high as 7000 fc/mm. Track profile and microprofile measurements showed write and read trackwidths to be around 1.2 /spl mu/m and 0.7 /spl mu/m respectively, with tight side-writing and sidereading characteristics. An overall assessment of the parametric recording results suggested an areal density feasibility of around 5 Gb/in2. This projection was confirmed by error rate testing at 10 MB/s using a PRML channel with digital filter and write precompensation. At low ontrack errors of 10/sup -10/-10/sup -9/ without error correction codes, linear densities of /spl sim/240 K bpi and optimized track pitches of /spl sim/1.2 /spl mu/m were achieved, corresponding to areal densities of /spl ges/5 Gb/in/sup /2.

12 Gb/in/sup 2/ recording demonstration with SV read heads and conventional narrow pole-tip write heads

We have successfully demonstrated magnetic recording at areal densities as high as 12 Gb/in/sup 2/ at a data rate of 14/spl sim/15 MB/s using separate spin-valve read heads and narrow pole-tip inductive write heads on low noise Co alloy thin film disks. In this work, the nominal target densities were 350 Kbpi/spl times/34 Ktpi. To make these densities possible, large signal-to-noise gains were attained with the use of high performance spin-valve read heads and low noise thin film media. At the same time, very narrow track write heads were designed and fabricated by extending conventional photolithographic techniques. Finally, small magnetic spacings between the head and the disk were attained with low flying ABS designs and improved head and disk surfaces. Recording tests showed satisfactory writability and large readback signal of around 2 mV//spl mu/m. The 50% rolloff densities were as high as 10 Kfc/mm, while the write and read trackwidths were as narrow as 0.7 and 0.5 /spl mu/m respectively. An overall assessment of the parametric recording results indicated an areal density capability of at least 10 Gb/in/sup 2/. This projection was confirmed by error rate testing with an EPR-4 channel, where very low ontrack errors of 10/sup -10//spl sim/10/sup -9/ were achieved at 315/spl sim/380 Kbpi. Furthermore, squeeze measurements revealed well-defined 747 behavior with offtrack maxima at 0.7/spl sim/0.8 /spl mu/m trackpitch. The product of linear and track densities for the write and read head combinations tested indeed showed that an areal density of 11/spl sim/12 Gb/in/sup 2/ has been achieved.

Noise in a thin metallic medium: the connection with nonlinear behaviour

At high transition densities the noise in thin metallic films with longitudinal orientation shows an anomalous increase. At the same time, the medium becomes nonlinear, that is superposition of isolated pulses no longer applies. Measurements of both effects suggest that they are related. The anomalous increase in the noise is seen to be the consequence of the increase in nonlinearity as transition spacing is reduced. Nonlinear behavior is also responsible for the significant dependence of the noise on the recorded data pattern. >

Thermal magnetization noise in spin valves

Thermal magnetization fluctuations (mag-noise) in giant magnetoresistive (GMR) spin valve (or any MR) heads will serve as a fundamental limit on their signal-to-noise-ratio (SNR). Measured mag-noise in several varied spin-valve read sensors is shown to be in good quantitative agreement with predictions based on the fluctuation-dissipation theorem. The dependence of mag-noise and head-SNR on sensor geometry and other device parametrics is discussed.

Optical data storage media

Optical data storage media for bit-wise recording of a microhologram using an incident radiation at a wavelength of about 405 nm are provided. The optical storage medium includes (a) a non-photopolymer polymer matrix; (b) a non-linear sensitizer comprising a phenylethynyl platinum complex, wherein the non-linear sensitizer is capable of triplet-triplet energy transfer from an upper triplet state (Tn) of the non-linear sensitizer to a lower triplet state (T1) of a reactant, wherein “n” is an integer greater than 1; and (c) a reactant capable of undergoing a chemical change upon the triplet-triplet energy transfer from the non-linear sensitizer, thereby causing a refractive index change in the medium to record the microhologram.

Hole injection into silicon nitride: Dark current dependence on electrode materials and insulator thickness

Dark currents in MNS capacitors are studied as a function of metal electrode material and insulator thickness. Dark currents sensitively reflect different electrode materials for thin (∼200 A) nitride films. Thus, it is found that high‐work‐function metals increase conduction under metal positive bias by enhanced hole injection and low‐work‐function metals increase conduction under metal negative bias by enhanced electron injection. Similar polarity differences are observed betwen n‐type and p‐type degenerate Si substrates. These contact differences disappear as the nitride becomes thicker and the thickness of trapped space‐charge layers near the contacts becomes small compared to the nitride thickness.

Study of magnetic tunnel junction read sensors

Unshielded magnetic tunnel junction (MTJ) sensors stabilized by insulating hard magnetic tails have been fabricated. Testing results showed that the control of oxidation condition was important for obtaining MTJ with low junction resistances and high TMR coefficients. The results also showed that the thickness of insulating spacer between hard magnet and MTJ stack had a significant influence on sensor stability. Finally, recording tests of stabilized MTJ read heads demonstrated linear densities of 420 Kbpi at 10/sup -9/ ontrack error.