K. Shimazawa

Low resistance and high thermal stability of spin-dependent tunnel junctions with synthetic antiferromagnetic CoFe/Ru/CoFe pinned layers

In this work, submicron-size (down to 0.273 μm2) spin–dependent tunnel junctions with resistance as low as ∼30 Ω μm2 have been fabricated, where the tunneling barrier of AlOx was formed by in situ natural oxidation. These junctions annealed at 250 °C for 5 h showed tunneling magnetoresistance (TMR) of 14.3% and 25.8% for the pinned layers of CoFe/RuRhMn and CoFe/PtMn, respectively, while the TMR is further increased to 31.6% for a synthetic antiferromagnetic pinned layer of CoFe/Ru/CoFe/PtMn due to less interdiffusion at CoFe/Ru interface. The investigation has indicated that the growth of ultrathin Al layer is very sensitive to the surface roughness of bottom ferromagnetic electrode, and large surface roughness leads to small junction resistance.

Magnetic tunnel junctions on magnetic shield smoothed by gas cluster ion beam

In this work, a technique, gas cluster ion beam (GCIB), was introduced to smooth the bottom NiFe magnetic shield for magnetic tunnel junction (MTJ) read heads. The GCIB treatment can bring the surface roughness of the shield from 15 to 20 A to around 5 A, and the most of scratch marks can be removed. The efficiency of the GCIB process is dependent on the initial surface morphology. The MTJs grown on the magnetic shield smoothed by the GCIB show that the resistance area product RA is increased from 60 to ∼100 Ω μm2 with the GCIB dose up to 1×1016 ions/cm2, arising from a smooth insulating layer, meanwhile, the tunneling magnetoresistance (TMR) is almost constant or slightly decreases. This GCIB process can also improve breakdown voltage (approximately 0.019 V per 1015 ions/cm2) of the MTJs, and slightly increase the ferromagnetic coupling mainly due to the change of the surface morphology. Using this technology, an RA as low as 3.5–6.5 Ω μm2 together with a TMR of 14%–18% can be obtained for MTJs grown on ...

Electrical breakdown of the magnetic tunneling junction with an AlOx barrier formed by radical oxidation

In this work, the dielectric breakdown in magnetic tunnel junctions (MTJs) was studied. The MTJ structure is Ta50/NiFe100/Co20/AlOx/Co30/RuRhMn100/Ta50 with the bottom lead of Ta50/Cu500/Ta50 and the top lead of Cu2000/Ta50 (in A), where the tunneling barrier was formed by 2–20 min radical oxygen oxidation of a 10 A-thick Al layer. The junctions with area from 2×2 to 20×20 μm2 were patterned using the photolithography process, leading to tunneling magnetoresistance up to 17.2% and resistance-area product ranging from 350 Ω μm2 to 200 kΩ μm2. The junctions studied show dc breakdown voltage from 0.7 to 1.3 V, depending on the junction area and the oxidation time. Long oxidation time up to 14 min and a small junction area results in a large dc breakdown voltage. The electrostatic discharge (ESD) of MTJs was tested by using a human body model. The ESD breakdown voltage increases with decreasing junction resistance. These results are discussed in terms of the E-model based on the field-induced distortion of at...

Evaluation of front flux guide-type magnetic tunnel junction heads

Magnetic tunnel junction (MTJ) heads have been successfully fabricated using the free layer as flux guide to prevent electrical short during the definition of the air bearing surface (ABS). For a 6 Gbits/in/sup 2/ design, an output as high as 5740 /spl mu/Vpp was achieved for 3 mA sense current, and the output waveform was stable and noise free. Noise analysis confirmed that shot noise is prevailing in these MTJ heads, suggesting that the junction resistance has to be further reduced to challenge spin-valve heads in terms of signal to noise ratio. Landau-Lifshitz-Gilbert simulations showed that for 20 Gbits/in/sup 2/ application, the flux guide height should not exceed 0.1 /spl mu/m.

Frequency response of common lead and shield type magnetic tunneling junction head

In this work, the frequency response in magnetic tunnel junction (MTJ) heads was studied. Both stray capacitance and junction resistance, forming a low-pass-filter, have to be reduced to improve the cutoff frequency in MTJ heads. By employing an Ar gas cluster ion beam (GCIB) process, junctions grown on the magnetic shield show a resistance area product as low as 3.6 /spl Omega//spl mu/m/sup 2/ and tunneling magneto-resistance over 14%. The dominant capacitance in common lead and shield MTJ heads was found mainly resulting from the shield-to-shield spacing, whose capacitance can be reduced by using an SiO/sub 2/ gap layer instead of Al/sub 2/O/sub 3/ layer and thus leading to an improved frequency response. Simple analysis indicates that a read amplifier design with low impedance could be helpful to realize a high data transfer rate, and a rate of around 800 Mbps for 100 Gbits/in/sup 2/ recording system can be thus expected.

Transport and Magnetic Properties of CPP-GMR Sensor With CoMnSi Heusler Alloy

We investigated structural and magnetic properties of CoMnSi (CMS) Heusler alloy films and giant magneto-resistance (GMR) ratio of current-perpendicular-to-plane (CPP) GMR sensor elements. The films were deposited with magnetron sputtering method and annealed at 673 K and 773 K. The CMS films were identified as B2 structure by using X-ray diffraction and the magnetization of the films were evaluated as 0.95 T. We fabricated the CPP-GMR sensors varying the composition of the CMS films, Co48 Mn21 Si31 (at. %) as Si-rich CMS and Co51Mn25Si24 (at. %) as CMS-ref, having a FeCo layer between the CMS and Cu spacer. It was found that the element with Si-rich CMS exhibited higher GMR ratio of 9.0% than that with CMS-ref. Our calculations indicate that larger spin polarization of contact region between the CMS film and the FeCo film relates to larger GMR ratio.

Enhanced GMR ratio of dual spin valve with monolayer pinned structure

A new type of dual spin valve (DSV) structure with enhanced giant magnetoresistance (GMR) ratio is proposed, and the performance is characterized by the prototype read heads. The bottom part of DSV is kept as a synthetic pinned structure and only the top part adopts a monolayer pinned structure. The top monolayer pin DSV (TM-DSV) showed three percentage points higher GMR ratio and 20% higher /spl Delta/R value. After the mechanical lapping process, the monolayer pinned layer can be stabilized by not only sense current but also large stress induced anisotropy due to Villari effect. After the quantitative analysis, the induced stress is measured to be about 4.2/spl times/10/sup 9/ N/m/sup 2/. The bias point was tuned by adjustment of Cu spacer layer thickness using the RKKY interaction between pinned layer and free layer. There is no reliability concern related to the monolayer pinned structure. In a perpendicular magnetic recording system, TM-DSV technology could successfully demonstrate the output of 35.5 mV//spl mu/m and /spl sim/170 Gbits/in/sup 2/ density feasibility.

Extra current channels in longitudinally biased magnetic tunnel junctions

Experiments on the longitudinal biasing of microsized magnetic tunnel junctions have been conducted using permanent magnets partially overlapping the junction area. The tunneling magnetoresistance ratio showed a strong dependency on the overlap length, since even a 10% overlap of the sensor length resulted in a 25% drop from its initial value without overlap. Analytical and micromagnetic analyses have demonstrated that this decrease comes from extra current channels, located in the regions below the permanent magnets, that shorted a large amount of the sense current from the central active region in the antiparallel magnetization state. The high uniaxial anisotropy field, induced by the permanent magnets in the overlapped regions, created particular magnetic configurations responsible for these low resistance paths. Several alternatives, using antiferromagnetic material in place of the permanent magnets or a modified design of the magnetic tunnel junction structure, are presented and discussed to prevent ...