Hirotsugu Fukuoka

Investigation of 2 Gb/in/sup 2/ magnetic recording at a track density of 17 kTPI

Developments of magnetic head, recording medium, positioning, and signal processing technologies made it possible to perform magnetic recording at an areal density of 2 Gb/in/sup 2/ on a prototype 3.5-in diameter hard disk drive. A track density of 17 kTPI, which is comparable to or even greater than that used in optical storage systems, is used to minimize the reduction in the physical clearance between the medium and the head. The authors outline the system and its component technologies. The read/write characteristics of the 3.5-in prototype disk system are also reported. >

Submicron-trackwidth inductive/MR composite head

To explore the possibility for ultra-high areal density recording, submicron-trackwidth inductive-write/magnetoresistive-(MR)-read composite heads were fabricated. The focused ion beam etching technique was applied to fabricate a approximately 1- mu m-wide write-track completely aligned to the read-region of the MR sensor. The write head using multilayered Fe-based alloy pole pieces with a saturation magnetization of 2.0 T revealed sufficient writability and excellent frequency response. A shunt-biased MR sensor having a narrow gap-length operated at a high current density over 3*10/sup 7/ A/cm/sup 2/ is developed to reproduce a sufficient signal amplitude at high linear-density regions. Recording tests were carried out on a thin-film medium with a head-medium clearance of 0.05 mu m. The output voltage per micron of trackwidth over 400 mu V with symmetrical pulses, and a -6-dB rolloff density of around 90 kFCI were measured. The design procedure, fabrication method, and recording performances of the submicron-trackwidth inductive/MR composite heads which can attain 2 gigabits recording are discussed. >

Method for making a thin film magnetic head

DC bias currents are applied to a conducting wire of a thin film magnetic head to be inspected. When the DC bias currents (I0, I1, I2) are supplied to the conducting wire, the impedances (Z0, Z1, Z2) corresponding to the DC bias currents are measured. When a ratio (|Z1 -Z0 |/|Z2 -Z0 |) corresponding to an overwrite characteristic (OW) reaches to a predetermined value by lapping tip portions of an upper magnetic layer and a lower magnetic layer of the magnetic head, the lapping process of the magnetic head is finished.

Electrical detection of end point in polishing process of thin‐film heads (invited)

A novel method for detecting the polishing process end point was developed for thin‐film heads to achieve a gap depth (throat height) of smaller than 1.5 μm. Special thin‐film heads whose magnetic paths are closed at the front end of the gap films were used. As the throat height of these gap films are much the same as the maximum tolerable value of the gap depth, the end point can be detected by monitoring the opening of the magnetic paths of the thin‐film head themselves. Electrical detection of the opening was studied, utilizing the bias current dependence of the head inductance. Both inductance values of the head, with and without the bias current,L b and L n b , change when the magnetic path opens. The L n b and L b values at 3‐mA bias current are 250 and 95 nH for the head having a closed magnetic path, and 180 and 155 nH for an open one, respectively. The difference L n b −L b decreases to about 1/6 when the magnetic path is opened. An apparatus was developed to measure the amplitude of L n b −L b . It utilizes a Wheatstone bridge circuit, excited with a 10‐MHz sinusoidal signal for measuringinductance, and a 0.2‐Hz rectangular pulse train as a bias current, respectively. Experimental results indicate that polishing can be stopped within 0.6 μm of the front edge of the gap films.

Effect of magnetic saturation on reproducing characteristics of magnetoresistive heads

The reproducing characteristics of a magnetoresistive head were studied. Using a two-dimensional finite element method, recording density characteristics and peak shift characteristics of the MR head were estimated with a saturation effect. Recording density characteristics changed with the magnetic saturation of the MR element with a large remanent magnetization and thickness product of the recording medium, but peak shift was not affected by it. Compared with the gap length dependence of the inductive head, the MR head had a lower D/sub 50/ and smaller peak shift than did the inductive head. >

Surface equation of state for charged films on aqueous electrolyte substrate

Abstract The surface equation of state for charged films on an aqueous electrolyte substrate is studied on the basis of statistical mechanics. A modified Poisson—Boltzmann equation is formulated by including the electrical image force and ion-correlation energy. In the uniform density approximation to the film ions the results obtained are nearly identical with those of the existing theory. The effect of the fluctuation of film ions is also calculated. It is shown that the resultant surface pressure clears the disagreement of the existing theory with experiments on the oil-water interface of diluted film ions.