Haruo Urai

Soft magnetism of high‐nitrogen‐concentration FeTaN films

High‐nitrogen‐concentration FeTaN films have been newly developed as a high performance magnetic head core material. 10.5–14.5 (at. %) N, 8–13 Ta, and balance Fe composition films, prepared by a nitrogen reactive sputtering method followed by appropriate annealing (500–550 °C), have high saturation flux density (14–17 kG) and excellent soft magnetic properties: such as low coercivity (∼0.1 Oe), high relative permeability (3000 at 20 MHz), and small saturation magnetostriction ( < 0.5 × 10−6). Fine crystal structure is one of the most essential origins for the soft magnetism of FeTaN films. The FeTaN films are expected to realize recording density increases and rubbing noise reduction with high durability and high reliability due to their high Vickers hardness (1000) and their higher corrosion resistance than Sendust film.

FeN phase generation effects for high moment FeTaN films

FeN phase generation has been observed by x‐ray analysis in FeTaN films, which normally show α‐Fe, TaN phase, and no FeN phases. With a rise in substrate temperature Ts above 200 °C, FeN phases are generated in nitrogen reactive sputtering process with columnar structure formation, and remain after annealing. With FeN phase generation, coercivity Hc and magnetostriction λ values increase markedly. Moreover, internal stress σ for the films increases drastically. The FeTaN films, sputtered on low temperature substrate, generate no FeN phases, and show low Hc, about 0.1 Oe, and low λ. Consequently, FeN phase generation with columnar structure formation has negative effects for FeTaN films to be used as magnetic head core materials. For preparation of FeTaN films, the substrate temperature has to be controlled to a sufficiently low value for suppression of FeN phase generation.

CoZrMo amorphous films as a soft adjacent layer for biasing magnetoresistive elements with a current shunt layer

Sputtered Co94−xZr6Mox (4.4≤x≤17 at. %) films have been investigated as a soft‐adjacent‐layer (SAL) material for trilayered magnetoresistive (MR) sensors with a MR element layer, a current shunt layer, and a SAL for biasing layer. The saturation magnetization 4πMs linearly decreases from 14 to 3 kG with an increase in Mo content. The magnetic anisotropy field Hk decreases to a low value, equivalent to that for NiFe MR films, as the Mo content is increased. The magnetoresistance ratio Δρ/ρ is negative, but sufficiently small, namely one‐hundredth of that for NiFe films, while the electrical resistivity ρ, about 140 μΩ cm, is 5.6 times greater than that for NiFe films. The films also have a small magnetostriction coefficient λs on the order of 10−7. A 500‐A‐thick CoZrMo film with 12 at. % Mo content is selected as the SAL, because a lesser thickness causes an extreme increase in Hk. Higher Mo content degrades the temperature characteristics of the magnetic properties, due to the lower Curie temperature. Tri...

Shielded magnetoresistive head for high density recording

The fabrication process and the head material properties for shielded magnetoresistive heads with planarized lower shields using a tri-layered MR element are described in detail. Applying the etch-back process with low molecular weight polystyrene and CF/sub 4//O/sub 2/ reactive ion etching, the residual step height for a lower shield is dramatically decreased to less than 5% of the initial step height. The tri-layered MR element consists of an MR layer, a magnetic separation layer (MSL), and a soft adjacent layer (SAL). 40-nm thick Ni/sub 81/Fe/sub 19/ (wt.%) films were deposited by evaporation for use as an MR layer. Evaporated Ti MSL thickness was experimentally determined to be 20 nm. Amorphous Co/sub 82/Zr/sub 6/Mo/sub 12/ SAL films exhibited preferable magnetic properties as an SAL material. The fabricated shielded MR heads, using the tri-layered MR element with these NiFe, Ti, and CoZrMo films, provide superior capability to realize high recording density. >

Soft-adjacent-layer optimization for self-biased MR elements with current shunt layers

A soft adjacent layer (SAL) for a self-biased magnetoresistive (MR) element has been optimized experimentally by the aid of simple computer simulation. In the element, a Ti current shunt layer is placed between an NiFe MR layer and an amorphous CoZrMo SAL. The maximum sensitivity and the minimum nonlinearity are calculated under the condition that the product of the thickness and the saturation magnetization M/sub s/ for the SAL is 75% of that for the MR layer. MR elements have been prepared with various combinations of thickness and M/sub s/ for the SAL. The thickness of both the NiFe and Ti films was 40 nm. The MR response of an element with a 100- mu m-long, 10- mu m-wide stripe pattern has been measured. The best biasing condition was achieved with 50-nm thickness and 480 emu/cm/sup 3/ M/sub s/ for the SAL. A 0.028/Oe sensitivity value was measured. No Barkhausen jump was observed in the MR response. >

4Mb on-chip-cache bubble memory chips with 4 &#181;m period ion-implanted propagation patterns

4Mb ion-implanted bubble devices (IIBD) with on-chip-cache organization (OCCO) have been designed for 1μm bubbles, and characterized for all functional elements in the devices. The 4Mb memory chip with 9.5×11.8 mm chip size consists of the same two 2Mb units, each of which is divided into 1Mb even and odd sites with 300 strorage loops (s-loops) and cache loops (c-loops), whose bit lengths are 4160 bits and 130 bits, repectively. Basic bit cell size is 4 × 4 μm. The 4Mb chip has an OCCO structure with the following distinguishing functional elements: (1) Bidirectional N-shape transfer gates. (2) A major line replicator with 2 crossed hairpin conductors. (3) DRO detector with folded thin NiFe elements. (4) A hairpin nucleation generator in a 240° super track. (5) Even bit minor loops. Operating margins for the 4Mb IIBD fabricated on (YSmLuBiCa) 3 (FeGe) 5 O 12 are well balanced in all functional elements, and obtained as 25 Oe, sufficient for practical use. It has been found that in-plane holding field applied to stop/start (s/s) direction is necessary for s/s stabilization, and that anisotropy along pattern edges due to stress relief acts a significant role for bit instability and for c-s gate operation. LPE film thickness has been optimized as 1.1 μm for 100-120 keV He+ implantation.

Design and characterization of 3 μm bubble memory chips utilizing Y‐Y patterns

Major‐minor organized bubble memory chips have been developed utilizing 14 μm period Y‐Y propagation circuits. First type is a 75 kbit memory chip consisting of four major‐minor units for high performance demands. Designed access time and data rate for 300 kHz drive are 0.3 nsec and 2×600 kbits/sec, respectively. Second type is a single unit major‐minor 78 kbit memory chip for medium access time use. Main chip design features are as follows: (1) 14 μm Y shaped Permalloy circuits are used throughout the chip, except for the 18 μm chevron stretcher. (2) Y‐Y transfer gates have been tailored in order to adapt to Y patterns. (3) A thin film Permalloy detector is used for the sake of large output (15 mV/2 mA) amd O‐π phase detection. The 3 μm bubble chips are fabricated on (YSmTmCa)3(FeGe)5O12 garnet films. Wafers are processed through 3 evaporation steps and 5 masks. Total 20 Oe operating bias margin is obtained at 300 kHz for 50 Oe drive field.

Shielded MR head for high‐density magnetic recording (invited)

A narrow‐gap shielded magnetoresistive (MR) head with a 8‐μm track width has been constructed for high‐density magnetic recording. The head consists of a pair of NiFe shields and a trilayered MR element between the shields. In the MR element NiFe, Ti, and amorphous CoZrMo films are used. The thickness of the three layers and the shields, as well as the shield gap length, are optimized with a one‐dimensional self‐consistent calculation. The shielded MR head has been fabricated using calculated thickness parameters for individual layers: 60 nm for CoZrMo with 40 nm NiFe and 20 nm Ti, 1‐μm shields, and 0.5 μm for the total shield gap. The reproduced characteristics from the MR head are evaluated with a plated disk. Neither Barkhausen noise nor distortion is observed in the output waveform. The output voltage is 600 μVpp at a 4 mA/μm sense current with 30 kFCI transition density. The D50 transition density is 40 kFCI. These values are in good agreement with the calculated values. Assuming a 12‐μm track pitch,...

Fabrication process for high track density yoke MR heads

A fabrication process was developed for a high track density yoke MR (magnetoresistive) head whose track width is determined by its front yoke thickness. The fabrication process, involving planarized front yoke formation, consists of the deposition process for a grooved yoke pattern with vertical side wall and a subsequent etch-back process with polystyrene polymer. Extraordinary recessed patterns, 3.5- mu m deep, were almost completely planarized to less than 0.1 mu m using these processes. Fabricated pattern-evaluation results indicate that CoZr system films are more suitable for use as a yoke material than NiFe films. Microstructure analyses reveal that the degradation in fabricated NiFe patterns is related to the structural change at the region near the grooved pattern side wall. >

Bidirectionally propagating fast access bubble memory chips

Bidirectional propagation bubble memory chips have been successfully realized as 78 kb memory chips with 3μm bubbles and 14μm period symmetrical Y-Y propagation patterns. The chips are markedly characterized with the following functional patterns: (1) Transfer gate Ni-Fe patterns with complete symmetry. (2) Operation with no guard rail pattern around the memory area. (3) Collapsing type bubble annihilator. Chips are mainly fabricated in dry etching processes on an (YSmLuCa) 3 (FeGe) 5 O 12 LPE garnet film. Bias field operation margins greater than 18 Oe have been obtained for all functions, including bidirectional bubble propagation in minor loops in a 50 Oe rotating field at 300 kHz within a 0-100°C temperature range. Operation with no guard rail at all is guaranteed by the employment of a thin Ni-Fe detector, set in a major loop, and the collapsing annihilator. The detector, gives an output voltage of 14 mV/2mA at 25°C and -0.29%/°C temperature coefficient. A 64 kB memory system, capable of bidirectional accessing, has been developed using the 8 chips in four 128 kb modules. An average access time of 0.4 msec has been obtained.