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.
The VIS/NIR bands polarization sensitivity of Joint Polar Satellite Sensor 1 (JPSS1) Visible/Infrared Imaging Radiometer Suite (VIIRS) instrument was measured using a broadband source. While polarization sensitivity for bands M5-M7, I1, and I2 was less than 2.5%, the maximum polarization sensitivity for bands M1, M2, M3, and M4 was measured to be 6.4%, 4.4%, 3.1%, and 4.3%, respectively with a polarization characterization uncertainty of less than 0.3%. A detailed polarization model indicated that the large polarization sensitivity observed in the M1 to M4 bands was mainly due to the large polarization sensitivity introduced at the leading and trailing edges of the newly manufactured VISNIR bandpass focal plane filters installed in front of the VISNIR detectors. This was confirmed by polarization measurements of bands M1 and M4 bands using monochromatic light. Discussed are the activities leading up to and including the instruments two polarization tests, some discussion of the polarization model and the model results, the role of the focal plane filters, the polarization testing of the Aft-Optics-Assembly, the testing of the polarizers at Goddard and NIST and the use of NIST's T-SIRCUS for polarization testing and associated analyses and results.
The Climate Absolute Radiance and Refractivity Observatory (CLARREO) mission addresses the need to observe high-accuracy, long-term climate change trends and to use decadal change observations as the most critical method to determine the accuracy of climate change. One of the major objectives of CLARREO is to advance the accuracy of SI traceable absolute calibration at infrared and reflected solar wavelengths. This advance is required to reach the on-orbit absolute accuracy required to allow climate change observations to survive data gaps while remaining sufficiently accurate to observe climate change to within the uncertainty of the limit of natural variability. While these capabilities exist at NIST in the laboratory, there is a need to demonstrate that it can move successfully from NIST to NASA and/or instrument vendor capabilities for future spaceborne instruments.The current work describes the test plan for the Solar, Lunar for Absolute Reflectance Imaging Spectroradiometer (SOLARIS) which is the calibration demonstration system (CDS) for the reflected solar portion of CLARREO. The goal of the CDS is to allow the testing and evaluation of calibration approaches , alternate design and/or implementation approaches and components for the CLARREO mission. SOLARIS also provides a test-bed for detector technologies, non-linearity determination and uncertainties, and application of future technology developments and suggested spacecraft instrument design modifications. The end result of efforts with the SOLARIS CDS will be an SI-traceable error budget for reflectance retrieval using solar irradiance as a reference and methods for laboratory-based, absolute calibration suitable for climate-quality data collections.https://ntrs.nasa.gov/search.jsp?R=20120014254 2018-05-12T22:48:36+00:00Z
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 (SiO x ) is widely employed as a dielectric medium due to its low loss, insulating properties, and general compatibility with optical coating and micro-fabrication processing [1,2]. Thin silicon monoxide films have demonstrated acceptable dielectric performance for high-frequency applications, as a dielectric medium [3]; however, the achievable loss tangent is dependent on the deposition rate, annealing and trace elemental constituents (H, C, OH, etc.) incorporated during deposition, and subsequent use. From this perspective SiO 1.5 is a preferable stoichiometric composition in order to reduce the number of free bonds and minimize the dielectric medium's absorption [4]. The strength and details of the infrared bands are of particular importance in determining the behavior of amorphous solids such as silicate glasses. In the far-infrared the absorption coefficient of glasses is largely featureless, scales as the square of frequency, and typically exceeds that of crystalline solid counterparts by an order of magnitude due to optical coupling to Debye-like and lattice modes [5]. These general features arise in glasses from spatial and temporal disorder broadening of the lattice absorption bands into a continuum. Here, the infrared properties of low-stress silicon oxide films are characterized and compared to materials reported in the literature.The amorphous silicon oxide films were prepared by PECVD (plasma-enhanced chemical vapor deposition) on H-terminated 100-mm Si(001) substrates. A 1000-W microwave plasma with a 2:1 O 2 :SiH 4 gas ratio at 3.4 mT was used to grow the silicon oxide and a 50-W RF bias was used to densify it. This process enabled low-compressive-stress (< 200 MPa) films critical for yielding free-standing membranes. The resulting samples are consistent with the Fourier transform spectrometer (FTS) throughput requirements for optical characterization and use as a microwave dielectric substrate [6]. Each silicon oxide membrane is a square 6.45 mm on a side and has a 12.75-mm-diameter Si frame. Each wafer contains 19 samples. See insert in Fig. 1 for a photo of a representative sample.The silicon-oxide-coated side of the wafers was lithographically patterned with a street cut mask to define the perimeter of the samples and the silicon oxide was reactive ion etched in a CF 4 /CHF 3 /Ar plasma. The thickness, 1.020 µm, was determined with an α-SE spectroscopic ellipsometer using a calibrated SiO 2 thin-film reference standard. The wafers were then wax bonded to 100-mm Pyrex disks with Crystalbond-509. A photoresist mask and deep reactive ion etching were used to define ...
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