Mikio Matsuzaki

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.

ESD induced pinned layer reversal in spin-valve GMR heads

Magnetization direction of the pinned layer in the Spin-Valve giant magnetoresistive (SV) heads has been found to be reversed easily by electrostatic discharge (ESD). Thermal stress and magnetic field from ESD cause this phenomenon. This phenomenon happens only when the bias field direction by ESD current Is opposite to the magnetization of the pinned layer. The energy of magnetization reversal of the pinned layer from ESD is found to be a quarter of the ESD breakdown energy. For SV heads which consist of an AF film with higher blocking temperature, the energy becomes higher.

Fabrication of discrete track perpendicular media for high recording density

The feasibility of discrete track media with perpendicular anisotropy for high track density has been studied. The discrete tracks are separated physically and magnetically by grooves. The discrete track media were fabricated by using an e-beam lithography and dry etching process. In particular, the recording layer was etched using reactive ion etching with CO-NH3 mixed gas. With this process, we obtained a discrete track medium with a track pitch of 90 nm without causing damage to the magnetic recording film or degradation of its magnetic properties. To solve the flying instability issue due to the grooved surface roughness, a smooth surface like continuous layer media was obtained by using only dry processes. The surface roughness (Ra) was below 1 nm. Flying stability of a head-slider on the smooth surface of the discrete track media similar to the continuous layer media has been achieved.

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.

The distribution of blocking temperature in NiFe-Ru/sub x/Rh/sub y/Mn bilayers

We report the distribution profiles of blocking temperature (T/sub b/) in Ru/sub x/Rh/sub y/Mn-NiFe interfaces with comparisons of FeMn, NiMn, and PtMn. The distribution of T/sub b/ at the temperature around 120/spl sim/150/spl deg/C decreased with increasing Rh content. The FWHM of the distribution profile in Ru/sub 4/Rh/sub 14/Mn is one half of that in ordered phase NiMn and PtMn. The unblocked ratio at 125/spl deg/C decreases with increasing Rh content, and becomes a minimum in Ru/sub 4/Rh/sub 14/Mn, which is one half of FeMn.

Edge eliminated head

The authors report that the extra pulses observed in the readback signal of an inductive thin film head can be eliminated by modification of pole tip geometry. The pole surfaces of inductive film head were partially etched by ion milling to reduce the pole length to 0.7 mu m. The etched depth was adjusted to 1 mu m from the pole surface (Type I edge eliminated head). Another modification of the pole tip geometry was also performed. The pole edges were shaped canted to the read/write gap by the same ion mill etching. The angle between the gap and the pole edges was set to 27 deg (Type II edge eliminated head). In both cases of Type I and Type II edge eliminated head, the amplitude of the extra pulses in the readback signal is significantly decreased without reduction of overwrite or any other performance degradation of the head. >

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.

New antiferromagnetic RuRhMn film and its application for spin-valves

We have successfully developed new RuRhMn antiferromagnetic (AF) films for spin-valves. The spin-valves with RuRhMn exhibit larger unidirectional anisotropy (Hua), higher blocking temperature (Tb), higher thermal stability and higher corrosion resistance than those with FeMn films. The MR ratio of 7.4% and Tb of 250/spl deg/C are obtained for glass/Ta(5)-NiFe(7)-Co(0.5)-Cu(3)-Co(2.5)-RuRhMn(10)-Ta(5), unit nm, spin-valve with Hua of 350 Oe. The rest potential of RuRhMn films is listed between one of NiFe and Co films and is much better than that of FeMn films.