Increased Insulation Thickness Research Articles

Design of the winding–bushing interconnections in large power transformers

The paper presents the improvement in design of the conductor connecting the windings and bushings in oil power transformers. This is a sensitive part of large transformers and there is a need to optimise its manufacturing time and costs. The thermal problem of the heating of this conductor with increased insulation thickness on a part of it is treated using a non-linear two-dimensional thermal model. The experiments performed made determining of some problematic parameters (heat resistance of oil-paper insulation and the paper to oil convection heat transfer coefficient) of the thermal model feasible. The results obtained are of practical interest in the design practice of interconnections, but also affect the important parameters of heat transfer by devices with oil immersed paper insulation.

Calibrated scanning capacitance microscopy investigations on p-doped Si multilayers

Using Si samples with 400-nm-wide alternately high and low doped p-type layers on p-type substrate, we investigate the dependence of the scanning capacitance microscope (SCM) signal amplitude as a function of oxide thickness and dopant concentration. The oxide layers were created by a standard industrial high temperature oxidation process. Together with the implementation of the newly developed conductive diamond tips, good and quantitatively reproducible contrast for differently doped domains is obtained on all samples. A comparison with conventional metal-oxide-semiconductor theory shows good correlation for the decrease of the capacitance signal with increasing insulator thickness and increasing dopant concentration. Furthermore, geometry effects, such as the influence of the domain width on the SCM signal, are discussed.

Microstructure and electrical properties of magnetic tunneling junctions: Ta/NiFe/IrMn/M/Al-oxide/M/NiFe (M=Co, NiFe, CoFe)

The microstructure and electrical properties of the Ta/NiFe/IrMn/M/Al-oxide/M/NiFe (M=Co, NiFe, CoFe) ferromagnetic tunnel junctions with different Al-oxide thickness were investigated. The CoFe junction showed the highest magnetoresistance (MR) ratio of 32% at room temperature with the insulation layer of Al (15 Å)-oxide, but also had the highest junction resistance of 34 kΩ (junction area of 200×200 μm) out of the three electrodes. The Co junction had the lowest resistance with reasonably high MR ratio of 24%. Cross-sectional transmission electron microscopy of the junctions showed that the increasing insulation thickness resulted in the rapid increased roughness at the top electrode/Al-oxide interface and the subsequent reduction of the MR ratio for all three electrodes materials. We have demonstrated that the MR effect is not only dictated by the intrinsic properties of the FM electrode materials, but also by the thickness and the microstructure of the oxide layer, which could be utilized to optimize the electrical properties of the ferromagnetic tunneling junction.

Nonequilibrium superconductivity under spin-polarized quasiparticle currents in perovskite ferromagnet-insulator-superconductor heterostructures

We report phenomena manifesting nonequilibrium superconductivity induced by spin-polarized quasiparticles in perovskite ferromagnet-insulator-superconductor (F-I-S) heterostructures. Measurements of the critical current ${J}_{c},$ using a pulsed current technique to minimize Joule heating, reveal a monotonic increase with increasing insulator thickness; and for F-I-S with thin insulating barriers, a slight increase in ${J}_{c}$ is observed under small injection currents ${I}_{m}$ from the ferromagnet, followed by a strong suppression of ${J}_{c}$ under large ${I}_{m}.$ In contrast, no effect of injection on ${J}_{c}$ can be detected in the N-I-S control sample (N: nonmagnetic metal). The spin diffusion time and length in cuprate superconductors are also estimated and compared with our experimental results.

Structural performance of modern roofs with thick over-purlin insulation—Experimental investigation

In conventional roof and purlin systems, it is generally known that the roof cladding; restrains the purlins from lateral buckling. However, during the past recent years, the requirement of increased insulation thickness for energy saving has led to a proliferation of roof systems and fixing methods for industrial-type buildings in the UK. The modern roofs are likely to behave differently in their interaction with the purlins compared to conventional trapezoidal sheeting with relatively thin insulation. At worst, the restraint provided to the purlins by the modern roofs may not be sufficient, and the purlins may fail under heavy snow load or wind suction (negative pressure). This paper presents an experimental investigation (Chung, K. F., Final technical report to ECSC Project 7210/SA/834, Steel Construction Insitute, Report No. SCI-RT-398, 1994 1) on the structural performance of five modern roof systems with thick over-purlin insulation. Three full-scale test series with a Total of 12 single and five double span roofs supported by purlins of zed and sigma sections were carried out under both gravity and uplift loading conditions. Comparison on the structural performance of the modern roof systems are presented in detail and the implication of thick over purlin insulation is fully discussed.

Ionizing radiation effects on ULSI device yield and reliability

In terms of initial device yield, and long-term reliability, process-induced radiation damage represents an area of considerable concern. The processes that need to be examined include ion implantation, X-ray, E-beam and ion beam lithography, electron beam metal evaporation, sputtering, reactive ion etching, and even SEM examination. The paper discusses the effects of synchrotron X-radiation in the energy range 300–1000eV, as well as Al Kα exposures which simulate X-ray lithographic procedures. It describes such effects in the context of preliminary studies dealing with varying rad (SiO2) exposure levels at a constant gate insulator thickness, as well as the behavior at several rad exposure levels, as a function of gate insulator thickness. Data are presented showing that despite prevailing beliefs, damage in the synchrotron range follows a linear relationship over the thickness range form less than 10nm to 50nm, indicating strongly that damage resides near the interface and is constant with increasing insulator thickness. It is shown that such behavior is consistent with a simple model. Even if such damage can be annealed completely using normal techniques, which is questionable, there are wide-ranging implications concerning the rad hardness of scaled devices.

Electrical and structural effects on ionizing radiation in IGFETS

In terms of initial device yield, and long term reliability, process induced radiation damage represents an area of considerable concern. The processes that need to be examined include Ion Implantation, X-ray, E-Beam and Ion Beam lithography, Electron Beam metal evaporation, Sputtering, Reactive Ion Etching, and even SEM examination. The paper discusses the effects of synchrotron X-radiation in the energy range 300-100 eV, as well as Al Ka exposures which simulate the effective wavelength of storage rings planned for X-ray lithography. It will describe such effects in the context of preliminary studies dealing with varying rad exposure level at constant gate insulator thickness, as well as the behavior at several rad exposure levels as a function of gate insulator thickness. Data will be presented indicating that despite prevailing beliefs, damage in the synchrotron range follows a linear relationship over the thickness range from less than 10 nm to 50 nm, indicating strongly that damage resides near the interface and is constant with increasing insulator thickness. It will be shown that such behavior is consistent with a simple model. Even if such damage can be annealed completely using normal techniques, which is questionable, there are wide-ranging implications concerning the rad hardness of scaled devices.

Thermosyphons and foundation design in cold regions

Laboratory tests were conducted with two full-size, two-phase commercial thermosyphons in an atmospheric wind tunnel at the U.S. Army Cold Regions Research and Engineering Laboratory. The test variables were air velocity and evaporator slope angle. The air velocity ranged from 0 to 5.2 m/s. The evaporator angles were varied from 0 to 12°, measured from the horizontal. The effect of nearby walls on thermosyphon performance was also investigated. The air temperature for all tests was about − 18°C. Test results are presented with thermal conductance of the thermosyphon as a function of air velocity and evaporator slope angle. The heat transfer conductance was found to increase with increasing air velocity and increasing evaporator slope angle. The use of thermosyphons in a slab-on-grade foundation design on permafrost was modeled using the finite element technique. Depth of thaw within the fill decreases with increased thermosyphon conductance and increased insulation thickness. The simulations indicate that it is slightly better to place the thermosyphon evaporator vertically towards the fill base.

Insertion loss tests for fiberglass pipe insulation

Insertion loss tests were conducted for three different thicknesses of fiberglass pipe insulation and five different jacketings using a proposed test standard. Results indicate that the procedure is a feasible method for testing pipe lagging. The insertion loss increased with increasing thickness of insulation. A significant increase resulted at all test frequencies for the insulation without jacketing and with the aluminum jacketing. The increases at the higher frequencies due to increased insulation thickness diminished with the use of heavier jacketing. When the insulation thickness was held constant at 2 in., each doubling of the weight of the jacketing resulted in increases in insertion loss at all frequencies. For each thicker insulation, these increases due to heavier jacketings were restricted to fewer test frequencies. There was good agreement between the 100‐Hz and 1/3‐oct test data for the 2‐ and 3‐in. pipe insulation with a slight preference for the 100‐Hz data measured at the lower end of each 1/3 oct.

Deviation of freezing rate from translation rate in the Bridgman-Stockbarger technique I. Very low translation rates

An analytical solution is obtained for the deviations of freezing rate from translation rate in the Bridgman-Stockbarger technique. The equations include a finite length ampoule, differences in heat transfer coefficients between the two ends, insulation between the heater and cooler, and latent heat. The present result accounts for heat conduction only, and is valid for low travel rates, small ampoule diameters and/or high thermal conductivities. In all cases the freezing rate approaches the translation rate if the interface is sufficiently far from the ends of the ampoule. The length required to achieve this condition increases with increasing ampoule diameter, decreasing heat transfer coefficient, increasing thermal conductivity and increasing insulation thickness. This length shows a minimum versus the heater temperature for a fixed cooler temperature. The present results are in agreement with previously reported experimental data and numerical predictions.

A Comparison of Cw Laser and Electron-Beam Recrystallization of Polysilicon in Multilayer Structures

ABSTRACTA thermal model for beam-induced melting of polysilicon in polysilicon/insulator/silicon structures has been used to compare CW Ar+ laser and electron-beam melting processes. The laser melting process exhibits a decreasing recrystallization threshold power and an increasing substrate melting threshold power with increasing insulator thickness. The decrease in recrystallization threshold with increasing insulator thickness is generally smaller for electron beams because of their deep penetration. The substrate melting threshold is approximately independent of insulator thickness for e-beams since no change in the power absorption occurs on melting of the polysilicon. As a result, the process window between the onset of recrystallization and melting of the substrate is narrower for e-beams than for laser beams. Also, essentially no window will exist between the onset of melting over a seed and substrate melting under an oxide if lateral epitaxy is performed with an electron beam.

Fatigue Resistance of Large-Size Helically Corrugated Aluminum Sheathed Cables

Large-size corrugated aluminum sheathed cables are finding an increasing use in duct and manhole installations. The complex sheath geometry, relatively large conductors and increased insulation thickness, combined with restricted manholes, would lead to severe sheath strains, increasing the probability of sheath fatigue failure. The results of a program is presented for evaluating fatigue life of large-sized corrugated aluminum sheathed cables. A fatigue life curve is derived from axial fatigue tests on sine-type corrugated aluminum cable sheath specimens, the validity of which is checked by a fatigue test on a manhole model.

Effect of Deep Traps on the Barrier Heights of Metal-Insulator-Metal Tunnel Junctions

It is shown that the potential barrier ${\ensuremath{\phi}}_{max}$ in a thin-film metal-insulator-metal system increases rapidly with increasing insulator thickness when electrons are immobilized in deep traps in the insulator, and at low voltage biases $\frac{d{\ensuremath{\phi}}_{max}}{\mathrm{dV}}$ is independent of the insulator parameters. This effect may be an explanation of the observations of Lewicki and Mead.