Earl C. Johns

Influence of Additive Adsorption on Properties of Pulse Deposited CoFeNi Alloys

In this paper, we investigated the conditions at the electrochemical interface for additive adsorption during the pulse current deposition of a CoFeNi alloy. Depending on the magnitude of the pulse currents used, different potentials and the corresponding additive coverage of CoFeNi surface are established affecting the CoFeNi alloy composition, concentration of incorporated C, S, and O inclusions, crystal structure, magnetic properties, and the surface quality of the deposit. The maximum content of S, O, and C in the CoFeNi deposit is found for the pulse current where the electrode potential is in the range where the maximum additive coverage is observed, indicating a close correlation between additive adsorption and additive incorporation phenomena. The anomalous codeposition effect was moderate in the potential range where maximum surface coverage of additives occurs, causing the composition of the CoFeNi films and their crystal structure to have a relatively mild change for a broad range of pulse current densities. The surface quality and the coercivity of the CoFeNi alloy have a strong correlation to the additive coverage during the pulse stage, and practical aspects of these findings are discussed. Organic additives have been commonly used in the electrodeposition of magnetic alloys for many years. 1 Besides the commonly seen action of leveling and brightening of the deposit, the benefit of using additives in the plating bath for ferromagnetic alloys is usually attributed to improvement in the crystal structure of the deposit, 2,3 smaller grain size, and reduction of the residual stress in the deposit. 4 These improvements usually reflect positively on the overall magnetic properties of these alloys as compared to the ones produced without any additives in the bath. Additional benefits of additives in the plating solution are also seen through the suppression of hydrogen evolution and impediment of FesOHd3 4 precipitation at the electrochemical interface, and in some instances, a relative improvement of corrosion resistance of the deposit. 5 More recently, it was demonstrated that an appropriate choice of the additives and bath chemistry could substantially improve the magnetic properties of CoFeNi films. 2,3,6-9

Optimization of neutron scattering instrumentation using neutron spin echo: Application to the discrimination of diffuse scattering in neutron reflectivity experiments

We describe a method, based on the neutron spin-echo technique, to achieve good resolution in many neutron-scattering experiments, without sacrificing signal intensity. By “good resolution” we do not mean the ∼10−6 energy resolution usually associated with neutron spin-echo spectrometers, but rather the level of resolution traditionally obtained by collimation or monochromatization of neutron beams, often on specialized instruments, and almost always at some penalty in measured intensity. The method we discuss allows good resolution to be achieved in any chosen direction in the vector space defined by the neutron scattering wave vector, Q, and the energy transfer, E. Although the method has general applicability to many neutron scattering measurements, we discuss in detail its application to the problem of separating diffuse scattering from specular reflection in neutron reflectometry. The technological basis of the method is the availability of thin films of magnetic or easily magnetizable material that ...

A perpendicular write head design for high-density recording

In this paper, we discuss a single-pole perpendicular head design and process that is suitable for densities of the order of 100 Gb/in/sup 2/. The single-pole write head was integrated with a narrow-track bottom spin valve reader. The design uses a single-turn coil to generate magnetomotive force in the head. Because of the very short yoke length that is achieved by using a single-coil turn, this writer design has a very low head inductance. Low magnetic impedance of the head makes it suitable for high data rate writing. Using the finite element model (FEM), the head geometry was optimized to write on media with coercivity (H/sub c/) of 5000 Oe. Because of the very efficient head structure, a write current below 100 mA was sufficient. As trackwidths are reduced, the field contours at the media show significant curvature, resulting in written-in transition curvature. Because of the very small yoke structure, no degradation of low-frequency amplitude up to /spl plusmn/90 Oe of external field is observed.

Fabrication of FePt nanoparticles for self-organized magnetic array

A self-organized array of magnetic nanoparticles can be potentially used to increase the storage density in magnetic recording. One challenge in this approach is to obtain long-range order assemblies of the nanoparticles. One method to solve this problem is to pattern a substrate having circumferential patterns, whose dimensions are within the coherent length of the self-organized array. By patterning the disk into topographically confined circumferential patterns with such dimensions, thermally stable magnetic nanoparticles may be used to fabricate magnetic recording disks. The circumferential patterns in this case are formed on the disk substrate with dimensions of 100–500 nm and depths of 5–20 nm, prepared by electron beam lithography and reactive ion etching techniques. The monodispersed FePt nanoparticles were synthesized by thermal decomposition of iron pentacarbonyl and reduction of platinum salt simultaneously in the presence of surfactant molecules, achieving a size distribution of 3.15±0.20 nm. ...

Charge-based scanning probe readback of nanometer-scale ferroelectric domain patterns at megahertz rates

We present a method for data storage in continuous ferroelectric (FE) media, applicable to storage systems based on one or more scanning probes. Written FE domains are read back in a destructive fashion by applying a constant voltage of magnitude greater than the coercive voltage, as is done in FE random access memory (FeRAM). The resulting flow of screening charges through the readback amplifier provides sufficient signal to allow readback of domains of minimum dimension of the order of 10 nm at MHz rates, orders of magnitude faster than previously demonstrated techniques for readback of domains in continuous FE media.

Fabrication of sub-50 nm critical feature for magnetic recording device using electron-beam lithography

We report an electron-beam lithography method for printing and plating sub-50 nm isolated trenches with a high aspect ratio (AR) for the nanofabrication of magnetic thin-film heads. To eliminate the issues of resist footing and resist residue in the narrow trench process, we coated a thin dissolution layer of polymethylglutarimide (PMGI) as an undercoat layer between a seed layer and a resist layer. The undercoat PMGI layer was easily and more quickly dissolved than the top resist layer, so it completely cleared the trench during the develop process. In addition, a vertical sidewall at the bottom of the narrow trench was achieved by controlling the processing conditions, e.g., bake temperature and thickness of the dissolution layer. All of these allowed us to facilitate plating the narrow trench with a high magnetic moment material. In this work, narrow trenches were electroplated with both 1.0 T NiFe and 1.8 T CoNiFe alloys. We demonstrated the capability of fabricating narrow electrodeposited magnetic w...

Sub-critical telephone cord delamination propagation and adhesion measurements

Thin film delamination can occur when the stored elastic energy per unit area in the film due to the residual stress exceeds the interfacial toughness. Telephone cord morphology is commonly observed in delaminating thin films under compressive stresses. Here, the biaxial film stress is partially relieved by film buckling in the direction perpendicular to the telephone cord propagation, and by “secondary” blister buckling in the direction of telephone cord propagation, which results in the sinusoidal fracture patterns. A superlayer indentation test, in which additional stress is supplied to the crack tip using a nanoindenter, can be used to measure the interfacial toughness. Estimates of the energy release rate for diamond-like carbon (DLC) films on magnetic media were obtained using the superlayer indentation test, as well as the delaminated buckling profiles. The results obtained by these two independent methods are in good agreement with each other. We find the average adhesion energy to be 6 J/m 2 for DLC films on magnetic media. Normally telephone cord blisters “run out of steam” and stop once the interfacial toughness exceeds the strain energy release rate. It is possible to make blisters propagate further by either putting mechanical energy into the system, or by introducing liquids at the crack tip, thus reducing the film interfacial toughness. Environmental species can assist cracking and contribute to thin film delamination, which is readily observed in vintage mirrors. Crack propagation rates on the order of microns per minute were measured for DLC films in different fluid environments. We identify how telephone cord buckling delamination can be used as a test vehicle for studying crack propagation rates and environmentally assisted cracking in thin films.

Sliding Contact Micro-Bearing for Nano-Precision Sensing and Positioning

Applications involving sub-nanometer, relative, in-plane motion between two substrates require precise control of gap-spacing between substrates for, both position-sensing as well as for signal transduction between the substrates. A method of passive gap-spacing control using MEMS-fabricated rigid spacers is proposed. A model to design a low-friction and low-wear interface between the sliding substrates is developed. Prototype parts with hard-coated interfaces and with and without lubrication were fabricated and tested. Sliding friction coefficients of 0.1-0.15 or less and wear life of millions of sliding cycles were achieved on prototype parts. Better results are predicted for MEMS-scale devices.

A MEMS read-write head for ferroelectric probe storage

We report a novel MEMS read-write head for probe data storage using ferroelectric (FE) media. In our FE storage approach, the minimum bit length is not dependent on the physical dimension of the writer electrode, which simplifies the writer fabrication. FE media has the advantages of high thermal stability, narrow domain walls, and low-voltage writability compared with magnetic storage. A read-write head based on MEMS technology is presented, along with process details. Preliminary test results on a scan stand show an obtainable areal density approaching 1 Tb/in2 with our prototype head and media.

Electron-beam lithography method for sub-50-nm isolated trench with high aspect ratio

An electron beam lithography method for printing and plating sub-50 nm isolated trenches with a high aspect ratio has been developed for the nanofabrication of magnetic thin film heads. To eliminate the issues of resist footing and resist residue in the narrow trench process, we put a thin dissolution layer of polymethylglutarimide (PMGI) as an undercoat layer between a seed layer and a resist layer. The undercoat dissolution layer competely cleared off the seed layer by the developer solution such that the sides of the narrow trench are vertical, particularly at the bottom of the narrow trench, thus facilitating plating the narrow trench with a high magnetic moment material. In this work, the narrow trenches were electroplated with both 1.0T NiFe and 1.8T CoNiFe. Three key issues in our trench process will be discussed here, including: 1) critieria for the selection of the undercoat dissolution layer materials; 2) processing conditions control , e.g. the thickness and the bake temperature of the dissolution layer to achieve vertical and smooth sidewalls; and 3) PEB delay on the narrow trench CD control, pattern degeneration, and the results from the resist top coat (RTC) experiments. With our new narrow trench process, we demonstrated the capability of fabricating narrow electrodeposited magnetic write structures with a CD of 35 nm in 0.35 μm resist (AR=10:1) and a CD of 30 nm in 0.25 μm resist (AR=8:1).