Akio Hori

Highly sensitive spintronic strain-gauge sensor based on a MgO magnetic tunnel junction with an amorphous CoFeB sensing layer

We investigated spintronic strain-gauge sensors (Spin-SGSs) based on magnetic tunnel junctions (MTJs). To enhance the strain sensitivity of Spin-SGSs, which is defined as the gauge factor = (ΔR/R)/Δe, we investigated MgO-MTJs with an amorphous CoFeB sensing layer that exhibits high magnetostriction and soft magnetic properties. To maintain the amorphous structure of the CoFeB sensing layer even after post annealing, we applied a MgO capping layer (MgO-cap) to the CoFeB sensing layer and compared it with a Ta capping layer (Ta-cap). After post annealing at 320 °C, the CoFeB sensing layer with a MgO-cap maintained a low coercivity of 3 Oe, whereas that with a Ta-cap exhibited a high coercivity of 25 Oe. Microstructure analysis revealed that the CoFeB sensing layer with the MgO-cap has an amorphous structure because boron remains in the CoFeB sensing layer even after post annealing. The gauge factor for the Spin-SGS with the MgO-cap was 4016, which was four times larger than 942 for the Spin-SGS with the Ta-cap.

Narrow stripe fabrication of soft magnetic materials by trench filling process

Low-pressure collimation sputtering was applied to trench filling with soft magnetic materials. Collimation and substrate bias were found effective to fill the trenches with a uniform film. NiFe and CoZrNb were tested as soft magnetic materials, and it was found that NiFe was suitable for the process. Stripes of NiFe about two micron wide and one micron high, and with excellent morphology, were fabricated inside trenches by combining collimation sputtering with an etch-back process.

Preparation of terbium-cobalt thin films for erasable optical memory disk.

消去可能な光メモリーディスクの開発が非晶質希土類-遷移金属 (RE-TM) 合金膜を先頭として急ピッチで進められている.実用化には解決しなければならない諸点があり, 耐環境性改善もそのひとつである.これはRE-TM膜に含まれるFe成分の酸化 (さび) の防止でもある.筆者らは, さびないTbCo膜を選び, 垂直磁気異方性を持たせる成膜条件を探究した.Co系RE-TM膜にはバイアススパッタリング法が適しているとされるが, この方法では耐熱性の低い透明有機樹脂基板上に成膜できない.無バイアススパッタリング法での成膜条件を追究した結果, 膜のTbとCoの組成比を制約すれば充分であり, バイアススパッタの膜は緻密度が低下するため耐環境性が悪化した.また, スパッタで作製した透明下地膜には浮遊酸素が含まれており, これを除去すれば磁気特性が大幅に安定することが判明した.Feを含んだ膜よりも耐環境性の優れた光ディスクの作製技術を開発できたと思っている.