Multilayer Resistance Research Articles

Inversion of Resistivity and Permittivity Using Phase Induction Logging Data

AbstractAn inverse method is presented to estimate the permittivity and resistivity profile of formation in a two‐dimensional axisymmetric inhomogeneous medium, the measured data of phase induction logging are the phase difference and amplitude ratio of the two receiving coils. The initial value of formation geometrical parameter is taken by using phase difference and amplitude ratio logging curves. The inverse equation is derived from the logging response equation and the variation principle, the conjugate gradient (CG) method is used to solve this inverse equation. The simultaneous inversion of multi‐layer formation resistivity, permittivity and geometrical parameter is obtained, the numerical results show the validity of this method.

RF sputtering deposition of alternate TiN/ZrN multilayer hard coatings

TiN/ZrN multilayers have been deposited on (100) silicon and glass substrates using a reactive RF magnetron sputtering process. These combined coatings are known to possess high wear resistance and high-grade hardness, good chemical and thermal stability. We have investigated the influence of the bilayer period ( Λ) on the morphological and structural properties of the multilayers at a given nitrogen partial pressure and RF power. Nano-indentation test showed that mechanical properties of the coatings varied with the bilayer period. In fact, the indentation depth reaches the minimum when bilayer period Λ was 9 nm; XRD analyses detected a superlattice structure at this Λ value. The individual layers, TiN and ZrN, show (111) or (200) orientation perpendicular to the plane of the film according to the deposition conditions. In order to optimize the structural properties of the superlattice, we stacked nitride layers having different preferential orientations. When both layers grew (111) or (100) texture, superlattice structure showed (111) or (100) preferred orientation, respectively, but in the first case the structure is more ordered, while alternate (111) ZrN/(100) TiN lead to (111) superlattice preferred orientation. Corrosion test in saline ambient showed a higher multilayer corrosion resistance than that of single layers. This result can be attributed to the interface effect providing better resistance to diffusion of saline vapors into the film.

The influence of the period size on the corrosion and the wear abrasion resistance of TiN/Ti multilayers

Metal-ceramic multilayers were deposited by reactive magnetron sputtering with the aim to simultaneously improve the corrosion and wear resistance of metallic substrates. In this paper we report the results of studies of the influence of the period size on the corrosion and the wear abrasion resistance of TiN/Ti multilayers deposited on H13 steel substrates. The Ti layers were deposited with thickness between 19 and 150 nm and TiN deposited with 22–150 nm; the number of periods was from 1 to 60. The wear was studied using a commercial ball cratering system and the corrosion with potentiodynamic polarizations in an electrolyte of NaCl 0.5 M. It was found that reducing the period also decreased the grain size and that the wear resistance of multilayer was improved; however the results of the corrosion testing were somewhat mixed. The results obtained for the periodic multilayers are compared with monolithic films. XRD analysis was used to study the influence of the period on the grain size and texture of the multilayers. Ion beam methods (RBS) were used to obtain the atomic composition profiles and the TiN/Ti multilayer thickness.

The influence of interface roughness on electrical transport in nanoscale metallic multilayers

We study the effects of annealing on the electrical resistivity of thin metallic multilayers of nickel and aluminum. Resistivity is seen to rise with anneal temperature. Above a specific temperature the resistivity decreases. We model this behavior based on the interface evolution due to the formation of intermetallic nanocrystals. The rise is attributed to interface roughening and to constraints placed on the electron mean-free paths by the nanocrystals. At high temperatures, the lateral coalescence preserves the smooth stratification producing the observed drop in film resistivity.

Changing Behavior of Residue during Dry Etching in Multilayer Resist Process

Changing Behavior of Residue during Dry Etching in Multilayer Resist Process

Multi-layer Resist Process Using Top-layer Resist as Phase Shifters

A new resolution enhancement method named SPLIT (Superimposition of Phase-shifting Layer for Image Transformation) is proposed. In the new method, top-layer resist patterns act as clear phase shifters for bottom-layer exposure. Since the phase shifters are closely contacted on the bottom-layer resist, very fine patterns are printed just under edges of top-layer shifter patterns. Theoretical resolution limit is infinitely small if the bottom-layer resist is infinitely thin. Using THMR iP3300 and KRF-M60G as the top- and the bottom-layer resists, feasibility of the new method is investigated. The top-layer shifter patterns are printed by projection exposure using blue light with a wavelength of 480 nm. The bottom layer is exposed to flood UV light with a wavelength of and 254 nm. As a result, 130-nm line pairs with a pitch of 240 nm are successfully printed.

Resistance of multilayers with long length scale interfacial roughness

The resistance of multilayers with interface roughness on a length scale which is large compared to the atomic spacing is computed in several cases via the Boltzmann equation. When the electronic mean free paths are small compared to the layer thicknesses, the current flow is non-uniform, and the resistance decreases in the current-perpendicular-to-plane (CPP) configuration and increases in the current-in-plane (CIP) configuration. For mean free paths much longer than the layer thicknesses, the current flow is uniform, and the resistance increases in both the CPP and CIP configurations due to enhanced surface scattering. In both the CPP and CIP geometries, the giant magnetoresistance can be either enhanced or reduced by the presence of long length scale interface roughness depending on the parameters.

Resistance of multilayers with long length scale interfacial roughness

The resistance of multilayers with interfacial roughness on a length scale large compared to the layer spacing is obtained using the Boltzmann equation. Both the current-perpendicular-to-plane (CPP) and current-in-plane (CIP) geometries are considered in the limits where the mean-free paths are short and long compared to the atomic spacing. In the short mean-free path limit, the resistance decreases in the CPP geometry and increases in the CIP geometry. In the long mean-free path limit, the resistance increases in both configurations due to enhanced surface scattering. The giant magnetoresistance can either be enhanced or reduced by roughness depending on the sample parameters. Estimates of the short and long mean-free path effects in Fe/Cr multilayers are obtained using experimentally determined parameters.

Spinelectronics and its applications

AbstractThe discovery of antiferromagnetic coupling in metallic Fe/Cr multilayers by Grünberg has triggered enormous research activities in the area of magnetic thin films. Additionally, the resistance of multilayers in the antiferromagnetic state is higher than in the parallel state at magnetic saturation. This Giant Magneto Resistance is caused by spin‐dependent scattering of the conduction electrons in the magnetic layers. For applications, however, moderate saturation fields, tailorable resistance characteristics and good temperature stability are required. Additional opportunities are opened by a similar effect in magnetic tunnel junctions. Here, the tunneling probability depends on the relative orientation of the magnetizations of the electrodes and thus a large dependence of the tunneling current on an external magnetic field can be found. This effect is usually called Tunneling Magneto Resistance and can again be used both for detecting external fields as well as for information storage. Much more possible applications are still ahead, especially after the finding of magnetoelectronic effects in semiconductors. In this contribution, we will sketch basic physics of these effects and give examples for current developments.

Magnetic and transport properties of discontinuous metal-oxides multilayers

We report on structural, magnetic and transport properties of Al 2O 3/CoFe discontinuous multilayers deposited by RF sputtering at room temperature on silicon substrate. Transmission electron microscopy observations show that these multilayers consist of discontinuous layers of CoFe particles embedded in an insulating Al 2O 3 matrix. This is further supported by magnetization measurements showing the presence at room temperature of both superparamagnetic and ferromagnetic components. The current-in-plane resistivity of the discontinuous multilayers has shown a negative magnetoresistance due to a spin-dependent tunneling between the CoFe magnetic particles through the insulating Al 2O 3 barrier. The magnetoresistance response gives rise to two spin-dependent tunneling contributions. A contribution at small applied fields due to ferromagnetic particles and a contribution at larger magnetic applied fields due to a superparamagnetic particles.

Improved reflectance and stability of Mo-Si multilayers

Commercial EUV lithographic systems require multilayers with higher reflectance and better stability than those published to date. This work represents our effort to meet these specifications. Interface-engineered Mo-Si multilayers with 70% reflectance and 0.545-nm bandwidth at 13.5-nm wavelength and 71% reflectance with 0.49-nm bandwidth at 12.7-nm wavelength were developed. These results were achieved with 50 bilayers. These new multilayers consist of alternating Mo and Si layers separated by thin boron carbide layers. Depositing boron carbide on the interfaces leads to reduction in molybdenum silicide formation of the Mo-on-Si interfaces. Bilayer contraction is reduced by 30%, implying that there is less intermixing of Mo and Si to form silicide. As a result, the Mo-on-Si interfaces are sharper in interface-engineered multilayers than in standard Mo-Si multilayers. The optimum boron carbide thicknesses have been determined and appear to be different for the Mo-on-Si and Si-on-Mo interfaces. The best results were obtained with 0.4-nm-thick boron carbide layers for the Mo-on-Si interfaces and 0.25-nm-thick boron carbide layers for the Si-on-Mo interfaces. The increase in reflectance is consistent with multilayers having sharper and smoother interfaces. A significant improvement in oxidation resistance of EUV multilayers has been achieved with ruthenium-terminated Mo-Si multilayers. The best capping-layer design consists of a Ru layer separated from the top Si layer by a boron carbide diffusion barrier. This design achieves high reflectance and the best oxidation resistance during EUV exposure in a water-vapor (oxidizing) environment. Electron-beam exposures of 4.5 h (in an effort to simulate EUV exposure perturbation of the top layers) in the presence of 5×10 - 7 -Torr water-vapor partial pressure show no measurable reflectance loss and no increase in the oxide thickness of Ru-terminated multilayers.

CMOS compatible fabrication methods for submicron Josephson junction qubits

The authors have developed two distinct processes for the fabrication of mesoscopic Josephson junction qubits that are compatible with conventional CMOS processing. These devices, based on superconducting Al/Al/sub 2/O/sub 3//Al tunnel junctions, are fabricated by electron beam lithography using single-layer and multilayer resists. The new single-layer resist process is found to have significant advantages over conventional fabrication methods using suspended tri-layer shadow masks. It is simpler and more accurate to implement, and avoids the significant areas of redundant metallisation that are an unavoidable by-product of the tri-layer shadow mask method.

A comparison of models to estimate in-canopy photosynthetically active radiation and their influence on canopy stomatal resistance

The models for photosynthetically active radiation (PAR) used in a multi-layer canopy stomatal resistance (CSR) model developed by Baldocchi et al. (Atmospheric Environment 21 (1987) 91–101) and in a two-big-leaf CSR model developed by Hicks et al. (Water, Air and Soil Pollution 36 (1987) 311) are investigated in this study. The PAR received by shaded leaves in Baldocchi et al. (1987) is found to be larger than that predicted by a canopy radiative-transfer model developed by Norman (in: Barfield, Gerber, (Eds.), Modification of the Aerial Environment of Crops. ASAE Monograph No. 2. American Society for Agricultural. Engineering, St. Joseph, MI, 1979, p. 249) by as much as 50% even though the Baldocchi et al. (1987) model is indirectly based on Norman's model. This larger value of PAR results in turn in a smaller CSR by as much as 30% for canopies with larger leaf area indexes. A new formula to predict vertical profiles for PAR received by shaded leaves inside a canopy is suggested in the present study based on Norman (1979) and agrees well with the original model of Norman (1979). The simple treatment used in Hicks et al. (1987) for canopy-average PAR received by shaded leaves is found to diverge for canopies with leaf area indexes not close to two A new empirical formula for canopy-average PAR is then suggested for use in a two-big-leaf model, and it is shown that under most conditions the modified two-big-leaf CSR model can predict reasonable values when compared with the more complex multi-layer CSR model. Both the modified multi-layer CSR model and the modified two-big-leaf CSR model are also shown to predict reasonable dry deposition velocities for O 3 when compared to several sets of measurements.

Novel fabrication methods for submicrometer Josephson junction qubits

Novel processes for the fabrication of mesoscopic Josephson junction qubits have been developed, based on superconducting Al/Al2O3/Al tunnel junctions. These are fabricated by electron beam lithography using single-layer and multi-layer resists, and standard processes that are compatible with conventional CMOS processing. The new single-layer resist process is found to have significant advantages over conventional fabrication methods using suspended tri-layer shadow masks.

Fluxes of ammonia over oilseed rape: Overview of the EXAMINE experiment

An integrated field experiment was organized as part of the EC EXAMINE project to quantify surface–atmosphere fluxes of ammonia (NH 3). Fluxes of NH 3, NH 4 + aerosol, HNO 3 and HCl were measured using the gradient method with several continuous and batch sampling systems. Within-canopy NH 3 was determined to quantify the contribution of leaf cuticles, sub-stomatal apoplastic (intercellular) fluids and other sources and sinks to net fluxes. The campaign included the first field measurements of apoplastic pH and [NH 4 +], providing independent estimates of the stomatal compensation point ( χ s) for comparison with micrometeorological results. The latter also compared fluxes before and after cutting. Under the clean conditions of the experiment, [NH 3][HNO 3] and [NH 3][HCl] were much less than values required for aerosol formation, while the NH 4 + aerosol size distribution indicated that aerosol evaporation would be much slower than the time-scale of turbulent exchange. Nevertheless, the measurements suggest that aerosol production/growth as well as formation of HCl may have occurred within the canopy. Apoplastic [NH 4 +] and pH of leaves showed no diurnal patterns, with the main control on χ s being the temperature dependence of the solubility equilibria. Fluxes of NH 3 were bi-directional (−200 to 620 ng m −2 s −1), with deposition generally occurring when the canopy was wet and emission when it was dry, particularly during the day. Nocturnal emissions indicated a non-stomatal NH 3 source, while daytime emissions were larger than indicated by the apoplastic estimates of χ s. The within-canopy data, together with an inverse Lagrangian source–sink analysis, showed decomposing litter to be a significant NH 3 source, explaining nocturnal NH 3 emissions and larger emissions following cutting. Daytime net fluxes were controlled by the top part of the canopy, due to χ s for siliques apparently being larger than for leaves. The measurements have been used to develop multi-layer resistance models of NH 3 exchange. A 3-layer ‘foliage–litter–silique model’ provides a detailed mechanistic treatment of the component fluxes, while a 2-layer ‘foliage–litter model’ is better suited to generalization in atmospheric transport models. Application of the new models should help improve estimates of regional atmospheric ammonia budgets.

Characterisation of combined positive-negative photoresists by excimer laser ablation

Novel photopolymers containing side groups based on o-methoxycinnamylidenemalonic acid, which undergo selective photo-crosslinking without destruction of the polymer backbone upon irradiation at λ>395 nm, have been developed for potential applications as combined positive-negative resists and multilayer resists. An XeCl excimer laser (λ=308 nm, τ=20 ns) was used as the irradiation source to study the ablation and microstructuring characteristics of the polymers. The materials were structured before and after crosslinking. The ablation rate was analysed by varying the fluence (0.01–10 J/cm2) and the number of pulses for a given irradiation area. Etch rates of about 2 μm per pulse at a fluence of 9 J/cm2 could be achieved for all polymers. The polymer with triazene groups reveals a higher etch rate at low fluences (less than 300 mJ/cm2) than the polymer without a triazene group. The experimentally observed threshold fluence for the triazene-containing polymer is about 30 mJ/cm2. Using a Schwarzschild-type reflection objective (15×), microstructures with a resolution in the micron range were produced on both polymer films. The quality of the structures was evaluated by scanning electron microscopy. The results indicate that the new polymers could be used as resists for excimer laser ablation lithography.

Transport properties of multilayers with nano-scale structures

We have investigated the Hall effect of the multilayers prepared on substrates with submicron V-grooves; for both the current-at-an-angle-to-plane (CAP) geometry and the current-perpendicular-to-plane (CPP)-like geometry. No difference was found in the Hall resistivity, when only the current direction was changed with respect to the V-grooves on a single sample. By a comparison of the results on an ordinary multilayer made on a flat substrate, we found an enhanced extraordinary Hall resistivity of the CAP-type multilayers, which supports the theoretical prediction reported previously.

Superconducting transition temperatures and structure of MBE-grown Nb/Pd multilayers

We have studied the structure and superconducting properties of molecular-beam-epitaxy-grown Nb/Pd multilayers. The resistivity of each layer was calculated from the multilayer resistivity by including size effect and bulk imperfection terms. The superconducting transition temperatures obtained using these resistivities together with the de Gennes--Werthamer theory showed good agreement with the experimental results.

A superlattice effect in the resistivity of multilayers

Calculations are presented of a superlattice effect, observable in samples where most of the scattering is at sharp interfaces. As the layer thicknesses change, oscillations in the resistivity of up to 100% are found. These oscillations are due to interface disorder breaking the degeneracy of certain states, causing them to have nodes at the interfaces. The states with nodes have high conductivities, leading to a short-circuit effect. Only for special thicknesses is it possible for a state to have nodes at all the interfaces. Hence, the oscillations occur as a function of layer thickness. Spreading the width of the interfaces or increasing the ratio of bulk disorder to interface disorder reduces the effect.

Analysis of high frequency properties of multilayer structures for multichip modules

Abstract The microwave surface resistance and reactance of YBa2Cu3O7 multilayers for MCMs have been studied as a function of thickness and relative permittivity of dielectric layers at 500 MHz and 10 GHz propagation frequency. Additionally, frequency properties of a YBCO/CeO2/SrTiO3/YBCO/LaAlO3 multilayer have been analyzed and results compared with measurement results. Performed simulations have shown that a dielectric layer of high relative permittivity, necessary for good isolation between superconducting ground planes and power planes in the multichip modules, has negligible influence on the effective surface resistance and reactance up to 0.5 μm dielectric thickness.