We provide an overview of the design and capabilities of the near-infrared spectrograph (NIRSpec) onboard the James Webb Space Telescope. NIRSpec is designed to be capable of carrying out low-resolution (R = 30− 330) prism spectroscopy over the wavelength range 0.6 − 5.3µm and higher resolution (R = 500− 1340 or R = 1320− 3600) grating spectroscopy over 0.7 − 5.2µm, both in singleobject mode employing any one of five fixed slits, or a 3.1×3.2 arcsec 2 integral field unit, or in multiobject mode employing a novel programmable micro-shutter device covering a 3.6×3.4 arcmin 2 field of view. The all-reflective optical chain of NIRSpec and the performance of its different components are described, and some of the trade-offs made in designing the instrument are touched upon. The faint-end spectrophotometric sensitivity expected of NIRSpec, as well as its dependency on the energetic particle environment that its two detector arrays are likely to be subjected to in orbit are also discussed.

A major limitation in the fabrication of microstructures as a postCMOS (complimentary metal oxide semiconductor) process has been overcome by the development of a hybrid processing technique, which combines both an isotropic and anisotropic etch step. Using this hybrid technique, microelectromechanical structures with sizes ranging from 0.05 to 1 mm in width and up to 6 mm in length were fabricated in CMOS technology. The mechanical robustness of the microstructures determines the limit on their dimensions. Examples of an application of this hybrid technique to produce microwave coplanar transmission lines are presented. The performance of the micromachined microwave coplanar waveguides meets the design specifications of low loss, high phase velocity, and 50characteristic impedance. Various commonly used etchants were investigated for topside maskless postmicromachining of h100i silicon wafers to obtain the microstructures. The isotropic etchant used is gas-phase xenon difluoride (XeF2), while the wet anisotropic etchants are either ethylenediamine-pyrocatechol (EDP) or tetramethylammonium hydroxide (TMAH). The advantages and disadvantages of these etchants with respect to selectivity, reproducibility, handling, and process compatibility are also described. [258] Index Terms-CMOS microwave elements, isotropic and anisotropic silicon etching, maskless etching, microelectromechanical systems (MEMS), micromachining, suspended transmission lines.

Micromachined power sensors with operation up to 50 GHz were recently achieved in CMOS technology [1]. To improve their sensitivity and signal-to-noise ratio, while maintaining microwave performance, several design parameters must be considered, such as the number and placement of thermocouples. This paper presents experimental and analytical thermal characterization of the sensors, which provides insight into the proper adjustment of the layout parameters. Experimental results were obtained by indirect measurements of the sensor temperature distribution under various applied power conditions. A simple and approximate model was developed, and adjusted based on experimental results, which was then used to show the effects of the variations in layout parameters on the overall device sensitivity. The model includes thermoelectric Peltier and Thomson effects. V. Hvyhvüà và vuà urà 7rxryrà Trà hqà 6phà 8rr

Micro Electromechanical System (MEMS) microshutter arrays are being developed at NASA Goddard Space Flight Center for use as a field selector of the Near Infrared Spectrograph (NIRSpec) on the James Webb Space Telescope (JWST). The microshutter arrays are designed for the spontaneous selection of a large number of objects in the sky and the transmission of light to the NIRSpec detector with high contrast. The JWST environment requires cryogenic operation at 35K. Microshutter arrays are fabricated out of silicon-on-insulator (SOI) silicon wafers. Arrays are closepacked silicon nitride membranes with a pixel size of 100x200 m. Individual shutters are patterned with a torsion flexure permitting shutters to open 90 degrees with a minimized mechanical stress concentration. Light shields are processed for blocking light from gaps between shutters and frames. The mechanical shutter arrays are fabricated using MEMS technologies. The processing includes multi-layer metal depositions, the patterning of magnetic stripes and shutter electrodes, a reactive ion etching (RIE) to form shutters out of the nitride membrane, an anisotropic back-etch for wafer thinning, followed by a deep RIE (DRIE) back-etch to form mechanical supporting grids and release shutters from the silicon substrate. An additional metal deposition is used to form back electrodes. Shutters are actuated by a magnetic force and latched using an electrostatic force. Optical tests, addressing tests, and life tests are conducted to evaluate the performance and the reliability of microshutter arrays.

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