Dielectrics - Digest of literature, volume 28, 1964
Dielectric constants, dipole moments, relaxation times, conduction phenomena, insulating films, breakdown, materials, and applications of dielectrics - annotated bibliography
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The radar cross section of dielectric disks
A solution is presented for the backscatter (monostatic) radar cross section of dielectric disks of arbitrary shape, thickness, and dielectric constant. The result is obtained by employing a Kirchhoff-type approximation to obtain the fields inside the disk. The internal fields induce polarization and conduction currents from which the scattered fields and the radar cross section can be computed. The solution for the radar cross section obtained in this manner will be shown to agree with known results in the special cases of normal incidence, thin disks, and perfect conductivity. It will also be shown that the solution can be written as a product of the reflection coefficient of an identically oriented slab times the physical optics solution for the backscatter cross section of a perfectly conducting disk of the same shape. This result follows directly from the Kirchhoff-type approximation without additional assumptions.
Radar cross section↗
Designing Dielectric Grating Filters with PGAPACK
The chapter is concerned with the design of planar dielectric layer diffraction gratings, which exhibit sharp resonances due to the coupling of exterior evanescent diffractive fields to the leaky modes of dielectric waveguides.
genetic algorithms↗
(abstract) Characterization of Tree Water Status and Dielectric Constant Changes of North American Boreal Forests in Combination with Synthetic Aperture Radar Remote Sensing
The occurrence and magnitude of temporal and spatial tree water status changes in the boreal environment were studied in a floodplain forest in Alaska and in four forest types of Central Canada. Under limited water supply conditions from the rooted soil zone in early spring (freeze/thaw transition) and during summer, trees show declining water potentials. Coincidental change in tree water potential, tree transpiration and tree dielectric constant had been observed in previous studies performed in Mediterranean ecotones. If radar is sensitive to chances in tree water status as reflected through changes in dielectric constant, then radar remote sensing could be used to monitor the water status of forests. The SAR imagery is examined to determine the response of the radar backscatter to the ground based observations of the water status of forest canopies. Comparisons are made between stands and also along the large North-South gradient between sites. Data from SAR are used to examine the radar response to canopy physiological state as related to vegetation freeze/thaw and growing season length.
remote sensing imaging↗
Microclimate, Water Potential, Transpiration, and Bole Dielectric Constant of Coniferous and Deciduous Tree Species in the Continental Boreal Ecotone of Central Alaska
Tree canopy microclimate, xylem water flux and xylem dielectric constant have been monitored in situ since June 1993 in two adjacent natural forest stands in central Alaska. The deciduous stand represents a mature balsam poplar site on the Tanana River floodplain, while the coniferous stand consists of mature white spruce with some black spruce mixed in. During solstice in June and later in summer, diurnal changes of xylem water potential were measured to investigate the occurrence and magnitude of tree transpiration and dielectric constant changes in stems.
bole dielectric constant coniferous trees deciduou↗
Thin Ribbon Tapered Coupler for Dielectric Waveguide/Optical Fiber
This paper presents a new way to design a low-loss couipler for high- or low-dielectric constant, dielectric waveguide for optical or millimeter/submillimeter waves.
coupler dielectric waveguide↗
Infrared Dielectric Properties of Low-stress Silicon Nitride
Silicon nitride thin films play an important role in the realization of sensors, filters, and high-performance circuits. Estimates of the dielectric function in the far- and mid-IR regime are derived from the observed transmittance spectra for a commonly employed low-stress silicon nitride formulation. The experimental, modeling, and numerical methods used to extract the dielectric parameters with an accuracy of approximately 4% are presented.
dielectric parameters↗
Inter-Comparison of SMOS and Aquarius Sea Surface Salinity: Effects of the Dielectric Constant and Vicarious Calibration
Two spaceborne instruments share the scientific objective of mapping the global Sea Surface Salinity (SSS). ESA's Soil Moisture and Ocean Salinity (SMOS) and NASA's Aquarius use L-band (1.4 GHz) radiometry to retrieve SSS. We find that SSS retrieved by SMOS is generally lower than SSS retrieved by Aquarius, except for very cold waters where SMOS SSS is higher overall. The spatial distribution of the differences in SSS is similar to the distribution of sea surface temperature. There are several differences in the retrieval algorithm that could explain the observed SSS differences. We assess the impact of the dielectric constant model and the ancillary sea surface salinity used by both missions for calibrating the radiometers and retrieving SSS. The differences in dielectric constant model produce differences in SSS of the order of 0.3 psu and exhibit a dependence on latitude and temperature. We use comparisons with the Argo in situ data to assess the performances of the model in various regions of the globe. Finally, the differences in the ancillary sea surface salinity products used to perform the vicarious calibration of both instruments are relatively small (0.1 psu), but not negligible considering the requirements for spaceborne remote sensing of SSS.
radiometry↗
Infrared Dielectric Properties of Low-Stress Silicon Oxide
Silicon oxide thin films play an important role in the realization of optical coatings and high-performance electrical circuits. Estimates of the dielectric function in the far- and mid-infrared regime are derived from the observed transmittance spectrum for a commonly employed low-stress silicon oxide formulation. The experimental, modeling, and numerical methods used to extract the dielectric function are presented.
Silicon oxide↗
500 C Electronic Packaging and Dielectric Materials for High Temperature Applications
High-temperature environment operable sensors and electronics are required for exploring the inner solar planets and distributed control of next generation aeronautical engines. Various silicon carbide (SiC) high temperature sensors, actuators, and electronics have been demonstrated at and above 500C. A compatible packaging system is essential for long-term testing and application of high temperature electronics and sensors. High temperature passive components are also necessary for high temperature electronic systems. This talk will discuss ceramic packaging systems developed for high temperature electronics, and related testing results of SiC circuits at 500C and silicon-on-insulator (SOI) integrated circuits at temperatures beyond commercial limit facilitated by these high temperature packaging technologies. Dielectric materials for high temperature multilayers capacitors will also be discussed. High-temperature environment operable sensors and electronics are required for probing the inner solar planets and distributed control of next generation aeronautical engines. Various silicon carbide (SiC) high temperature sensors, actuators, and electronics have been demonstrated at and above 500C. A compatible packaging system is essential for long-term testing and eventual applications of high temperature electronics and sensors. High temperature passive components are also necessary for high temperature electronic systems. This talk will discuss ceramic packaging systems developed for high electronics and related testing results of SiC circuits at 500C and silicon-on-insulator (SOI) integrated circuits at temperatures beyond commercial limit facilitated by high temperature packaging technologies. Dielectric materials for high temperature multilayers capacitors will also be discussed.
dielectric performance↗
Relationship of Cure Temperature to Mechanical, Physical, and Dielectric Performance of PDMS Glass Composite for Electric Motor Insulation
Achieving NASAs aggressive fuel burn and emission reduction for N-plus-3 aircraft will require hybrid electric propulsion system in which electric motors driven by either power generated from turbine or energy storage system will power the fan for propulsion. Motors designed for hybrid electric aircraft are expected to operate at medium to high voltages over long durations in a high altitude service environment. Such conditions have driven research toward the development of wire insulation with improved mechanical strength, thermal stability and increased breakdown voltage. The silicone class of materials has been considered for electric wire insulation due to its inherent thermal stability, dielectric strength and mechanical integrity. This paper evaluates the dependence of these properties on the cure conditions of a polydimethyl-siloxane (PDMS) elastomer; where both cure temperature and base-to-catalyst ratio were varied. The PDMS elastomer was evaluated as a bulk material and an impregnation matrix within a lightweight glass veil support. The E-glass support was selected for mechanical stiffness and dielectric strength. This work has shown a correlation between cure conditions and material physical properties. Tensile strength increased with cure temperature whereas breakdown voltage tended to be independent of process variations. The results will be used to direct material formulation based on specific insulation requirements.
insulation↗
BioLEAD: BioLogical Exploration via Autonomous Detection – Using Dielectric Spectroscopy to Monitor Biological Changes in Response to Deep Space Radiation
Leveraging the bio-fluidic hardware developed for BioSentinel, we propose a new payload for autonomous missions: BioLEAD – BioLogical Exploration via Autonomous Detection. With NASA's renewed focus to continue human exploration of the Moon (Artemis Program), the BioLEAD payload aims to investigate the effects of the lunar environment on biology, whether onboard a lunar lander, the Lunar Gateway, or as a free-flying CubeSat orbiting the Moon. In place of an optical detection system, BioLEAD will employ a miniaturized, non-invasive dielectric spectroscopy sensor to enable real-time monitoring of biological activity. The sensor operates by relating capacitance measurements to the dielectric properties of the cell, such as cell morphology, doubling time, and cell cycle stage. The implementation of this new sensor technology will address limitations of the optical measurement system used on BioSentinel. It will also advance the use of autonomous bioanalytical microsystems and reveal new information regarding biological responses to the Moon’s radiation environment. Most importantly, BioLEAD’s technology will be adaptable for a wide array of future missions.
Biosensor↗
A model for comprehensive studies of porosity in mesoporous low-k dielectrics
The successful integration of a porous low dielectric constant (k) material as an interlevel dielectric depends on the morphology of the embedded porosity.
porosity↗
Synthesis of Novel All-Dielectric Grating Filters using Genetic Algorithms
The feasibility of novel all-dielectric waveguide grating filters is demonstrated, using a genetic algorithm to solve for material dielectric constants and geometric boundaries separating homogeneous regions of the periodic cell.
all-dielectric↗
Effective Dielectric Passivation Scheme in Area-Selective Front/Back Poly-Si/SiOx Passivating Contact Solar Cells
Explored different dielectric passivation schemes on lifetime samples after removing poly-Si completely. Showed that SiNx/Al2O3 had the best passivation properties on SiOx/n+ c-Si in diffused surface. Applied SiNx/Al2O3 stack on poly-Si/SiOx passivating contact device and showed large improvement in Jsc, with best device efficiency of 21.8%. Future work: CV measurement of dielectric stacks to obtain Qf and Dit.
dielectric↗
Hydrogen Transport from Dielectrics to poly-Si/SiOx Passivating Contacts Measured by Mass Spectrometry and Vibrational Spectroscopy
We demonstrate the relationship between Si solar cell passivation and hydrogen content of various passivating films, including hydrogenated amorphous silicon (a-Si:H), aluminum oxide (Al2O3), silicon nitride (SiNx) and combinations thereof. Through isotopic studies using quadrupole mass spectrometry (QMS), Fourier transform infrared spectroscopy (FTIR), and Raman spectroscopy, we determine how hydrogen content and stability within each type of film relates to final passivation quality of solar cell test structures. Si solar cells using polycrystalline silicon on silicon oxide (poly-Si/SiOx) passivating contacts are at the forefront of Si solar cell research and emerging as top performers within industrial production. Performance of passivating contact Si solar cells is largely determined by a parameter known as the open-circuit voltage Voc, which directly relates to material quality within the bulk of the device and at surfaces. High Voc is achieved when defects within the bulk crystalline silicon (c-Si) and at interfaces are passivated, preventing them from acting as charge carrier recombination centers. One of the most important means of passivating defects within Si solar cells is via hydrogenation, injecting the cells with large amounts of H to satisfy dangling bonds in the bulk and at interfaces. Hydrogen is especially important in deactivating a prevalent defect in industrial p-type devices which leads to decreased device performance over long-term exposure to light, called light-induced degradation (LID). Some of the most common materials used to supply H to devices are a-Si:H, Al2O3, and SiNx, which can contain very large amounts of H. Upon annealing at elevated temperatures, the hydrogen becomes mobile enough to find and disable defect sites. However, too much hydrogen can also be problematic, sometimes leading to an effect called light and elevated temperature induced degradation (LeTID). It has been shown that these films passivate the interfaces of poly-Si passivating contacts differently, leading to differing performance. Though Al2O3 is a well-defined dielectric material, SiNx can have many different values of x depending on precursor gases and deposition conditions. We observe different FTIR and Raman spectra from different SiNx over a range of x values films to determine the bonding environments within them and further correlate the relative concentrations of Si, N, and H to the stability of H within SiNx and the passivation performance of each film. Because deuterium is chemically identical to hydrogen within these systems, but gives different signals in FTIR and Raman spectroscopy as well as in QMS, isotopic substitution can be used as an excellent tool to probe the H within films. In addition to measuring the H and D bonding within films using FTIR and Raman spectroscopy, we will use such isotopic experiments to observe H and D movement out of these hydrogenating films at elevated temperatures using QMS to determine the stability of H bonding within such systems. With these films characterized based on elemental composition, we will relate such measurements to passivation quality of these films and combinations thereof on poly-Si/SiOx contact structures using quasi-steady state photoconductance decay measurements to obtain implied open-circuit voltage (iVoc) and saturation current density J0 values. Such investigations into the performance of different passivating films and film stacks will lead to greater understanding of dielectrics in semiconductor devices, further improvements in passivated contact design, and eventually, greater proliferation of renewable solar energy worldwide.
Al2O3↗
High-Performance Passivating Contacts for Si PV Based on Engineered, Doped Nanopinholes through Dielectric Layers
We present a novel, industrially relevant method to fabricate high-performance poly-Si passivating contacts for Si PV. Passivating contacts based on SiOx/poly-Si layer stacks have been implemented in record-efficiency homojunction Si solar cells. In this technology, the carrier transport through a surface-passivating SiOx is enabled either by quantum-tunneling or nanopinholes. The doped poly-Si layer provides charge-carrier selectivity. Previously, the ISFH research group demonstrated a record 26.1% efficient Si homojunction cell, where transport pinholes in ~2 nm SiOx were produced by thermal breakdown at > 1000 degrees C, which is hard to control and is surface morphology-dependent. At room temperature, our new process uses electroless plating of Ag nanoparticles, followed by metal-assisted chemical etching. Nanogalvanic corrosion yields < 20 nm-wide nanopinholes in an insulating > 2 nm SiOx layer. The nanopinholes are filled by a heavily doped a-Si:H overlayer. We drive in the dopants into the Si wafer with subsequent high-temperature annealing. Preferential incorporation of dopants at pinhole locations results in nanoscale p+/n or n+/n junctions near the wafer interface. Each heavily-doped nanoscale pinhole junction collects and transports photogenerated carriers to the cell metal contacts. The density of the engineered nanopinholes can be tuned over a wide range which is critical for optimization of device performance. The same nanogalvanic corrosion principles can be applied to produce doped transport pinholes in well-passivating thick dielectric SiOx/SiNy stacks. Importantly, our process does not rely on thermal breakdown of the dielectric layers and can be applied to textured wafers resulting in Si solar cells with > 20% conversion efficiency.
dielectric layer↗
Shaping the Infrared luminescence of Colloidal Nanocrystals Using a Dielectric Microcavity
As they have gained maturity, colloidal nanocrystals (NCs) have also expand the spectral range over of which they could be used for photonic and optoelectronic applications. In particular, the infrared use of NCs has become of utmost interest to develop cost-effective alternatives to current technologies. It is then critical not to let the material dictate the light–matter interaction, which is why the coupling of NCs to photonic cavities has been proposed. For infrared NCs, this approach has first been devoted to the control of absorption with in mind the increase of the signal magnitude for detectors. A Lot of efforts have been focused on the use of metallic metasurfaces. However, these generate significant optical losses and yield low quality factor. Here, this study rather focus on the coupling of infrared NCs to a dielectric mirror cavity. HgTe/CdS core-shell NCs are used and integrated into a cavity made of aperiodic dielectric mirrors. The effect of the substrate is systematically study on spectral linewidth, carrier dynamic, and emission directivity. The cavity is shown to narrow the PL by a factor 10, while focusing the emission over a 12° angle. Monitoring the power dependence of the emission, this study shows that the cavity leads to 250 K increase in the effective electronic temperature.
36 MATERIALS SCIENCE↗