Jongill Hong

cw laser anneal of polycrystalline silicon: Crystalline structure, electrical properties

0.4‐μm‐thick polycrystalline silicon deposited in a low‐pressure CVD reactor was implanted with B to a dose of 5×1014/cm2 and then irradiated in a cw laser scanning apparatus. The laser annealing produced an increase in grain size from ∼500 A to long narrow crystals of the order of ∼25×2 μ, as observed by TEM. Each grain was found to be defect free and extended all the way to the underlying Si3N4. Electrical measurements show 100% doping activity with a Hall mobility of about 45 cm2/V sec, which is close to single‐crystal mobility at the same carrier concentration. Thermal annealing produces material with an average grain size of 1000 A and a resistivity higher by a factor of 2.2 than that obtained with the laser anneal. Laser annealing performed after a thermal anneal reduces the resistivity to approximately the same value obtained by laser annealing only.

Solid solubility of As in Si as determined by ion implantation and cw laser annealing

Complete electrical activity was obtained by cw laser annealing of 7×1015 As/cm2 implanted into (100) Si at 100 keV. The peak concentration for these implantation conditions is 1.4×1021/cm3, both theoretically and experimentally. However, this peak concentration was found to be thermally unstable, relaxing to a value of 3×1020/cm3 in a period of less than 2 min at 900 °C. If the peak implanted concentration is below 3×1020/cm3, the electrical activation and crystal structure are unaffected by similar thermal processing. We conclude from these data that the solid solubility of As in Si at 900 °C is approximately 3×1020/cm3, which is almost an order of magnitude below the published value.

Nanoscale patterning of complex magnetic nanostructures by reduction with low-energy protons

Techniques that can produce patterns with nanoscale details on surfaces have a central role in the development of new electronic, optical and magnetic devices and systems. High-energy ion irradiation can produce nanoscale patterns on ferromagnetic films by destroying the structure of layers or interfaces, but this approach can damage the film and introduce unwanted defects. Moreover, ferromagnetic nanostructures that have been patterned by ion irradiation often interfere with unpatterned regions through exchange interactions, which results in a loss of control over magnetization switching. Here, we demonstrate that low-energy proton irradiation can pattern an array of 100-nm-wide single ferromagnetic domains by reducing [Co(3)O(4)/Pd](10) (a paramagnetic oxide) to produce [Co/Pd](10) (a ferromagnetic metal). Moreover, there are no exchange interactions in the final superlattice, and the ions have a minimal impact on the overall structure, so the interfaces between alternate layers of cobalt (which are 0.6 nm thick) and palladium (1.0 nm) remain intact. This allows the reduced [Co/Pd](10) superlattice to produce a perpendicular magnetic anisotropy that is stronger than that observed in the metallic [Co/Pd](10) superlattices we prepared for reference. We also demonstrate that our non-destructive approach can reduce CoFe(2)O(4) to metallic CoFe.

Fabrication of metallic nano-stamper and replication of nano-patterned substrate for patterned media

With an increasing demand for ultra-high-density information storage, patterned media have received much attention as a solution to overcome the limits of conventional continuous magnetic media. One of the current methods to fabricate the patterned media is to use direct patterning and etching. However, those procedures are very costly and are not suitable for mass production. In this study, we investigate the possibility of mass production of patterned media by nano-moulding technology with a metallic nano-stamper. The physically and chemically resistant metallic nano-stamper was fabricated using an electroforming process, and then the nano-patterned substrate was replicated using a nano-moulding process without additional etching. For evaluation of the replication quality, a magnetic layer was deposited on the substrate. We finally confirmed that the magnetic islands were successfully formed as a single magnetic domain on the nano-patterned substrate.

Spin-valve head with specularly reflective oxide layers for over 100 Gb/in/sup 2/

We have developed spin valves with thin oxide reflective layers, which exhibit a greatly improved magnetoresistance (MR) performance while keeping other good properties, such as an exchange bias field of over 1000 Oe and a coercivity and an interlayer coupling field of less than 10 Oe. The giant magnetoresistance (GMR) values reached over 12% for the spin valve with a single specular layer and over 15% for the spin valve with double specular layers. The oxide reflective layers helped improve MR performance due to enhanced specularity at the oxide interfaces. Evidence of enhanced specularity was provided by the observed reduced sheet resistance and oscillatory interlayer exchange coupling between the free layer and the spacer in the spin valve. The observation of the oscillation was possible due to amplified Ruderman-Kittel-Kasuya-Yoshida (RKKY) coupling, as seen in a multilayered superlattice composed of ferromagnetic layers with nonmagnetic spacers. We successfully fabricated read heads by incorporating such spin valves. In particular, very narrow read track width was achieved in the head with double reflective layers. The read track width was estimated to be less than 0.14 /spl mu/m. The head was tested on a low noise CoCrPt-based alloy disk with a coercivity of 3170 Oe and an areal moment of 0.36 memu/cm/sup 2/. The head showed a normalized output of 8.6 mV//spl mu/m with an asymmetry of 0.5% at 2 mA sense current, a /spl sim/40% increase over that of the head with a single reflective layer that was used in the demonstration of 56.1 Gb/in/sup 2/. We have therefore demonstrated that our head with the specular layers can be used for an areal density of over 100 Gb/in/sup 2/ in magnetic recording with the help of advanced media and integration techniques.

Hydrogenated monolayer graphene with reversible and tunable wide band gap and its field-effect transistor

Graphene is currently at the forefront of cutting-edge science and technology due to exceptional electronic, optical, mechanical, and thermal properties. However, the absence of a sizeable band gap in graphene has been a major obstacle for application. To open and control a band gap in functionalized graphene, several gapping strategies have been developed. In particular, hydrogen plasma treatment has triggered a great scientific interest, because it has been known to be an efficient way to modify the surface of single-layered graphene and to apply for standard wafer-scale fabrication. Here we show a monolayer chemical-vapour-deposited graphene hydrogenated by indirect hydrogen plasma without structural defect and we demonstrate that a band gap can be tuned as wide as 3.9 eV by varying hydrogen coverage. We also show a hydrogenated graphene field-effect transistor, showing that on/off ratio changes over three orders of magnitude at room temperature.

Effect of thin oxide capping on interlayer coupling in spin valves

We controlled interlayer coupling from ferromagnetic to antiferromagnetic by appropriately capping spin valves with thin oxides. The interlayer coupling field was -16.6 Oe at a Cu-spacer thickness of 30 /spl Aring/. The sign of coupling changed at a Cu-spacer thickness of 20 /spl Aring/. The antiferromagnetic coupling achieved in this way allowed a reduction of thickness of the Cu spacer down to 20 /spl Aring/ without loss of good magnetic and electrical properties, and this led to a significant improvement in the MR response of the spin valves. The interlayer coupling field was only +8.6 Oe even at a Cu-spacer thickness of 20 /spl Aring/. We attribute the improvement in MR response to less current shunting through the most conductive Cu layer and to enhanced specular scattering at the interface between the free and the oxide capping layer.

Back surface gettering and Cr out‐diffusion in VPE GaAs layers

Mechanical back surface damage gettering has been investigated for improving the quality of GaAs substrates and VPE layers on semi‐insulating GaAs. It has been shown that the pregettering of substrates reduces the interfacial defect density and alters the level of Cr out‐diffusion into the VPE layer during growth. At a postdeposition anneal temperature of 800 °C, Cr out‐diffusion into the VPE layer is relatively suppressed in the pregettered substrate, while the ungettered sample shows larger concentrations of Cr within the epitaxial layer.

Magnetic and electrical properties of spin valve with single and double specular oxide layers

Appropriate oxide capping on a spin valve significantly improved electrical and magnetic properties. The interlayer exchange coupling oscillated in the thickness range of a Cu spacer (between 20 and 30 A). The coupling was antiferromagnetic and it allowed us to reduce the Cu spacer down to 20 A without sacrificing the good properties of the spin valve. The improvement is due to enhanced specular reflection at the interface between the magnetic and the oxide layer and to less current shunting through the Cu spacer. In particular, the Cu in the capping acts as a filter controlling the diffusion of oxygen, which has led to the soft magnetic properties. Embedding an additional thin oxide layer into the pinned layer further improved the magnetoresistance response of the spin valve. Confinement of electrons between two oxides helps increase the occurrence of spin-dependent scattering. As a result, high giant magnetoresistance values resulted. The coupling oscillated from ferromagnetic to antiferromagnetic as a ...

Magnetic and microstructural characterization of FeTaN high saturation materials for recording heads

Magnetically soft FeTaN high saturation materials have been deposited on both sloping and planar surfaces by RF reactive sputtering with an appropriate high substrate bias. A perpendicular anisotropy component accompanying degrading soft magnetic properties is observed under low substrate bias. This undesirable perpendicular anisotropy in the FeTaN films arises from the magnetoelastic anisotropy due to in-plane compressive stress and positive magnetostriction constant and from the magnetocrystalline anisotropy due to out-of-plane [200] easy axes. This is supported by X-ray pole figures, temperature-dependent VSM measurements, and synchrotron radiation X-ray stress measurements. The absence of microshape perpendicular anisotropy is supported by SQUID measurements and high resolution TEM images. This work has identified the processing parameters and microstructures that are critical for successfully incorporating high saturation magnetic materials in recording heads.