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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)/Δε, 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.

We investigate the enhancement of the signal-to-noise ratio (SNR) of spintronic micro-electro mechanical-system (Spin-MEMS) microphones in which spintronic strain-gauge sensors (Spin-SGSs) are integrated on a micro-electro mechanical-system (MEMS) diaphragm by using a large array of N Spin-SGSs connected in series similar to that in a previous report on magnetic tunnel junction magnetic sensors. Since the strain-gauge properties of Spin-SGSs strongly depend on the angle between the applied uniaxial strain and the magnetization direction of the reference layer, in order to obtain the same signals from each Spin-SGS in an array, it is necessary to locate the Spin-SGS array in a region where the uniaxial strain occurs uniformly on the MEMS diaphragm. We theoretically and experimentally investigate the effect of the diaphragm shape on uniaxial strain on the diaphragm surface. As a result, it is found that a rectangular-shaped diaphragm provides a larger region in which a uniform uniaxial strain is applied to the Spin-SGS array compared with the generic circular diaphragm. Finally, an SNR enhancement of 18 dB by connecting N = 62 Spin-SGSs in series is successfully confirmed in a Spin-MEMS microphone with a rectangular diaphragm.

The fabrication of an etching template for 5 Td/in.2 bit patterned media using a self-organization material, namely, poly(styrene)-poly(dimethylsiloxane) (PS-PDMS), was investigated. The molecular weight of the PS-PDMS for forming the areal density of 5 Td/in.2 dot pattern was estimated from the polymerization index related to the Flory–Huggins interaction parameter. Annealing was carried out to obtain a fine-order dot pattern. PS-PDMS films were subjected to thermal treatment or solvent annealing. The ordering of the dot array in these films was evaluated by using Voronoi diagrams. The results indicate that the film annealed in N-methylpyrrolidone (NMP) vapor showed finer ordering than did the thermally treated film. This seemed to be attributable to the high solubility parameter of NMP. The soaking of NMP into the PS phase slightly shifted the phase separation energy of the polymer matrix. The lattice spacing of the obtained hexagonal pattern was 11 nm. By using low-molecular-weight PS-PDMS with solvent annealing, a dot-array template for 5 Td/in.2 bit patterned media was formed.

We demonstrate the mold fabrication and replication process for the production of 0.8 and 2.5 Tbit/in. 2 directed self-assembly bit patterned media (DSA-BPM). These devices are fabricated with 33 and 17 nm dot pitch patterns using the microphase segregation structure of polystyrenepoly(dimethylsiloxane) as an etching mask template. The self-assembled dot arrays are simultaneously ordered on both the circular tracks for the data area and the arbitrary marks for the servo area by DSA using groove guides. We fabricated the Si mold with dot pillars of 19.3 nm height for the 2.5 Tbit/in. 2 DSA-BPM from the poly(dimethylsiloxane) dot mask. We also demonstrated the nickel mold replication of the 0.8 Tbit/in. 2 DSA-BPM by electroforming from the Si mold. #