Hisao Matsutera

Reactive ion etching of Fe-Si-Al alloy for thin film head

Elevated-temperature reactive ion etching (ET-RIE) in CCI/sub 4/ containing a gas plasma was investigated on Fe-Si-Al alloy by using an infrared lamp. A high etching rate, 200 nm/min, is obtained at 378 degrees C. Etching residues containing chloride are easily removed by an after-treatment process. Applying this ET-RIE to Fe-Si-Al alloy, a 1.7 mu m*3 mu m cross section pattern is achieved. No permeability deterioration is detected after ET-RIE. The ET-RIE method is very promising for patterning Fe-based alloy as thin-film head pole material. >

Design and characteristics for vertical bloch line memory using a ring-shaped domain

A vertical Bloch line (VBL) memory test chip which attains complete operation has been developed. The test chip is composed of a ring-shaped domain, stabilized in a garnet groove as a VBL pair circulation track which forms the data storage register, a current access major track for a data access read/write channel and a read/write gate between the ring-shaped domain and the major track for transforming a VBL information into bubble information or the inverse operation. The VBL propagation on the straight wall of the ring-shaped domain is found to have the reasonable operation bias margin of approximately 10 Oe. The VBL circulation around the outer domain wall of the domain is confirmed in high bias field range. Bubble propagation bias margins for major track are about 13 Oe, sufficient for overlapping the VBL circulation margins. Quasi-static ring-shaped domain head stretching and the stretched domain chopping for read/write gate operations have been successfully operated, while the dynamic domain head stretching permits VBL injection. VBL memory devices with large capacity may clearly be constructed with ring-shaped domain arrays and the other functional elements mentioned above.

Analysis of track-edge noise in thin-film recording media

Track-edge noise has been analyzed to clarify track-edge noise mechanisms. Edge noise arises from two different regions: the bit edge where the magnetization direction is opposite to the previously dc-erased direction and the magnetic transition edge. The edge noise at low density is mainly due to the magnetic distribution at the bit edge. The transition edge noise increases with increasing recording density, and it becomes dominant at high-recording density for an oriented medium. On the other hand, the transition edge noise is almost constant with increasing recording density for an isotropic medium.

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. >

Characteristics of Bloch line memory with major/minor-loop structure

The characteristics of the functions of a vertical Bloch line memory (VBL) with major/minor-loop structure and field access scheme, except for the detector, were investigated. The memory is composed of a major line with two-level conductor patterns, minor loops utilizing stabilized ring-shaped domains, and read/write gates with three-level conductor patterns. Bubbles generated at the bubble generator are propagated on the major line with greater than 4-mA drive current at 500-kHz frequency. Stretching of the ring-shaped domain head is well controlled by the presence or absence of a bubble in the major line. The round propagation for a VBL pair is achieved quasi-statically by a pulsed bias field with 6.5-Oe potential barrier for a 4.0- mu m-period track. Bias-field margins of 8.5 Oe for the minor loop and 13 Oe for the major line were obtained, verifying the feasibility of this device. >

Vertical Bloch line pair operation by in-plane field for Bloch line memory

Operation of a vertical Bloch lines (VBLs) pair by local in-plane field has been investigated. It has been confirmed that a VBLs pair is propagated by in-plane fields generated by conductor currents. A VBLs pair separation to two isolated VBLs and their recombination by in-plane fields were also confirmed to be successfully carried out. An in-plane field access VBL memory test chip configuration, including read/write function parts as well as propagation track, is presented.

Instability evaluation for permanent magnet biased magnetoresistive heads

We have used micromagnetic modeling to study instability of permanent magnet biased magnetoresistive heads. A new approach based on the dependence of reproducing characteristics on initial magnetization is proposed to examine the instability of both AMR and spin-valve heads. When the permanent magnet strength is smaller than a critical value, the output voltage of an AMR head depends on the initial magnetization, which results in instability. The critical permanent magnet strength gradually increases as shield-to-shield separation decreases. The critical value for spin-valve heads is smaller than that for AMR heads, because the pinned layer under a large exchange field does not change its magnetization at all.

A self-biased spin valve sensor with a longitudinally pinned layer

We have developed a novel self-biased spin valve sensor in which a free layer is magnetostatically coupled to a longitudinally and moderately pinned layer. Such spin-valve sensors are more appropriate for GMR/inductive head processes than conventional spin-valve sensors because the direction of pinning is parallel to the desired magnetic anisotropy for the free layer and shields. To fabricate the spin valves, we deposited Ta(3 nm)/NiFe(3 nm)/Cu(2.5 nm)/NiFe(8 nm)/NiMn(15 nm)/Ta(3 nm) films, patterned the spin valve, and attached an Au lead to each of its sides. The transfer curve of this spin valve sensor exhibits excellent linearity without Barkhausen noise. Dynamic range is great in proportion to the sense current, while sensitivity is slightly less than that of conventional spin valve sensors at high sense current levels.

Offtrack characteristics on media noise for Co-Cr-Ta films

The effect of remanent magnetic flux density (B/sub r/) and magnetic layer thickness (/spl delta/) on offtrack noise characteristics in Co-Cr-Ta alloy thin films is investigated. It has been found that decreasing the value of B/sub r/ is a more effective method of improving offtrack noise characteristics than decreasing the value of /spl delta/. Offtrack noise is shown to be due to the fluctuations in the amplitude of readback waveforms, fluctuations which are caused by fluctuations in magnetic transition amplitude. It was observed, using a magnetic force microscope, that lower B/sub r/ media had sharp boundaries at the track edge regions and the magnetization was more uniform, compared with those of higher B/sub r/ media.

Characteristics for Bloch line memory with field access scheme

The characteristics of functions such as read/write gate operation and vertical Bloch line (VBL) propagation have been investigated for a VBL memory with a field access scheme. The memory is compared of a minor loop utilizing a stabilized ring-shaped domain and a read/write gate with three-level conductor patterns. Potential wells that define the VBL bit position are formed by an in-plane field from a zigzag conductor for evaluation of VBL propagation. The read/write gate and VBL pair propagation operations are confirmed. A bias field margin of 7 Oe (10%) is obtained, verifying the feasibility of this device. >