Tsutomu Mitsuzuka

Low-resistance tunnel magnetoresistive head

A tunnel magnetoresistive (TMR) head with a low resistance of about 30 /spl Omega/ and effective track width of 1.4 /spl mu/m was fabricated using an in situ natural oxidation (ISNO) technique. Its read-output was almost the same as that expected from test elements at the wafer level. We found no large difference in noise voltages between TMR head and GMR head when their resistance was about 30 /spl Omega/. A very low-resistivity TMR element with a resistance-area product of 14 /spl Omega//spl middot//spl mu/m/sup 2/ and a fairly high /spl Delta/R/R of 14% was also developed using ISNO. A signal-to-noise ratio consideration suggests that such low resistance is a key to TMR heads for high recording densities.

Interface structures and magnetoresistance in magnetic tunnel junctions

The interface structures of magnetic tunnel junctions were studied using x-ray photoelectron spectroscopy (XPS). The structures were correlated with magnetoresistance (MR) characteristics. For MR measurements, Fe(50 nm)/AlOx/CoFe(30 nm) junctions with an in situ naturally oxidized Al tunnel barrier were fabricated. The thickness of the Al layer, an important parameter in MR characteristics, was varied from 0 to 5 nm. MR curves showed that the largest MR ratio occurred when the Al layers were 2–3 nm in thickness. XPS analysis showed that an Al layer greater than 1 nm thick covers the entire surface of the Fe underlayer. However, if the Al layer is more than 1 nm thick, the unoxidized Al remaining after the oxidation process increases as the thickness is increased. For Al layers that are greater than 3 nm thick, the MR ratio is strongly affected by unoxidized Al, probably due to the decrease in spin polarization at the surface of an Fe/Al electrode. On the other hand, the hysteresis loops indicate that the ...

A highly oriented Al[111] texture developed on ultrathin metal underlayers

A highly oriented [111] texture is developed in ion beam sputtered Al films on metal underlayers of Ti, V, Cr, Co, Ni, Cu, or Y. The textured Al films show an extremely smooth surface. Deposition of highly textured Al films depends on the presence of this underlayer, the thickness of which must lie within a specific range that varies with the metal being used. We discuss here the mechanisms of texturing in terms of phenomenological surface‐interface energy balance considerations. The great tolerance for high‐power operations of Al films with a highly oriented [111] texture makes them particularly suitable for use as electrodes in surface acoustic wave devices.

Exchange-biased magnetic tunnel junctions fabricated with in situ natural oxidation

Exchange-biased magnetic tunnel junctions with a Ta/NiFe/FeMn/NiFe/Al–oxide/NiFe/Ta structure have been fabricated. The tunnel barrier was formed by the in situ natural oxidation of an Al metal layer under controlled oxygen pressure. Photolithography and ion milling were used to pattern the multilayer into junction structures of 2×2 μm2–20×20 μm2 dimensions. Magnetoresistance (MR) curves show spin-valve-like characteristics, in which an antiparallel configuration of magnetizations in both ferromagnetic layers is observed between 50 and 240 Oe, and the hysteresis loops for both the free and pinned layers exhibit sufficient separation. An evaluation of the MR curves shows the exchange-bias field to be 340 Oe and coercivity levels in the free layer to become as low as 13 Oe. At room temperature normalized junction resistance is 2×10−5 Ω cm2, with MR ratios still being maintained at 13%. This resistance value is much lower than previously reported values for junctions produced either with plasma oxidation or ...

Structure and magnetic properties of Co/Al multilayered films

We report on an investigation of Co/Al multilayered films (MLFs). The samples had periodic layered structures and had in‐plane easy axes. Nonmagnetic CoAl compound was formed at the Co/Al interfaces. Co/Al MLFs had a perpendicular interface anisotropy. This interface anisotropy energy (Ks) was estimated to be 0.25 erg/cm2. Taking account the volume contribution of Co layers, it was suggested that perpendicular magnetism would appear when the remaining unmixed Co layer thickness was under 6 A. However, this surface anisotropy energy vanished when the Co layers were thinner than 9 A. In Co/Al MLFs with thin Co layers, the island growth of Co on the initial stage was considered to be the reason for Ks=0.

Thermal asperity of TMR heads for removable disk drives

The thermal asperity of the tunneling magnetoresistive (TMR) head was studied using Zip-type flexible media, and compared with that of the anisotropic magnetoresistive (AMR) head. The examined head had a shielded structure with the TMR element close to the air bearing surface. Nevertheless, it generated relatively small thermal asperity even when the mechanical spacing between the head and medium was less than 20 nm, at which large and frequent thermal asperity was observed when the AMR head was used. Such relatively small thermal asperity of the TMR head Is attributed mainly to the small low-temperature coefficient of the electrical resistivity of the TMR element.

X-Band Mixing Performance of Y1Ba2Cu3O7-x Step-Edge Junction

The X-band mixing performance of some step-edge junctions using Y1Ba2Cu3O7-x films has been evaluated. The mixing conversion efficiency (η) depends predominantly on normal resistance (R n) of a junction, which determines impedance matching for the microstrip signal line. Under constant impedance conditions obtained from temperature dependence of R n, conversion efficiency (η) increases with increase of the I cR n product. In the range of 12 GHz, however, the efficiency is saturated above the I cR n product of 1 mV. This tendency agrees with our simulation based on the resistively shunted junction (RSJ) model.

Application of ion-beam-sputtered Al films to ultrathin surface acoustic wave devices

Ion-beam sputtering technique has been applied to Al film deposition for electrodes in high-frequency surface acoustic wave devices. Al films having low resistivity and a smooth surface have been obtained, even in the ultrathin thickness range. It was shown that the ion-beam sputtering technique provided excellent thickness uniformity and controllability. This method was also applied to the deposition of highly preferred [111]-textured Al films.

Structure and electric properties of YBa2Cu3O7−δ/SrRuO3/PtSi on Si substrate

We have fabricated superconducting YBa2Cu3O7-δ thin films on a Si substrate with metallic buffer layers, SrRuO3/PtSi. The T c on is 90 K and the T c0 is 35 K. The interface shows electrical conductivity with contact resistance 3×102 Ω cm2 at 293 K. Cross-sectional transmission electron microscopy and Auger electron depth profile show that YBa2Cu3O7-δ is protected from reaction with Si. However, SrRuO3 reacts with PtSi and forms an amorphous layer which has high resistance. The SrRuO3 and YBa2Cu3O7-δ are polycrystalline.