Kanji Kawakami

Design and fabrication of thin‐film heads based on a dry process (invited)

High performance thin‐film heads for disk drive systems have been developed based on a dry process. Heads were computer simulated and optimal design was carried out. Relationships among Ni‐Fe composition, domain structure and wiggle of the read‐write waveform were obtained. Based on these results, optimum Ni‐Fe composition range was determined. A planarization procedure for an inbedding insulator of the conductor coil was developed. Also narrow track patterning and gap depth controlling procedures were developed. Using these procedures, a two‐layered seventeen‐turn thin‐film head for a large capacity disk drive system (23 Mb/in.2) has been developed. The head exhibited excellent read‐write characteristics.

A high frequency permeance meter for anisotropic films and its application in the determination of magneto striction constants

A new apparatus has been developed for the measurement of the permeance of thin magnetic film in the frequency range of 0.5 M to 100 MHz. The apparatus has a proportional accuracy of -10 to +20% and a low level resolution of 13 μm at 10 MHz. The accuracy of the new apparatus was confirmed and its frequency characteristics studied in experiments. The magneto striction constant determined with this meter is described in this report.

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.

Fabrication of 8 turn multi-track thin film heads

To obtain high bit and high track densities, fabrication of thin film magnetic recording heads has been studied by a number of companies.) This paper describes a newly developed method for fabricating layered type, multi-turn, multi-track thin film inductive heads with a central tap by using photolithographic and thin film deposition techniques.

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.

Permeability dependence of thin film head reproducing performance

Permeability of Ni-Fe thin film head yokes and its effect on the head sensitivity were studied by simulations and experiments. Examinations focused on head inductance with closed magnetic paths and reproducing performance. The reproduced output signal amplitude resulted from simulations had a larger permeability dependence around the pole tip than any other areas. The output was reduced approximately 2 % when the permeability around the tip was lowered from 3000 to 300. This permeability was estimated at between 50 and 300 in fabricated heads, while it was approximately 1000 elsewhere.

On magnetic path saturation in thin‐film heads

The distribution of magnetic field in the head gap and of flux density in in the magnetic path of thin‐film recording heads has been studied. It is shown that magnetic path saturation occurs first at the back end of the heads, which reduces efficiency. The relations which calculate the minimum current amplitude at magnetic path saturation are obtained. Results of the study are applied to thin‐film heads having two‐turn coils.