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A new nanoscale electric field sensor was developed for studying triboelectric charging in terrestrial and Martian dust devils. The sensor was fabricated using MEMS techniques, integrated at the system level, and deployed during a dust devil field campaign. The two-terminal piezoresistive sensor consists of a micron-scale network of suspended singlewalled carbon nanotubes (SWCNTs) that are mechanically coupled to a free-standing electrically conductor. Electrostatic coupling of the conductor to the electric field is expected to produce a deflection of the conductor and a corresponding change in nanotube device resistance, based on the known piezoresistive properties of SWCNTs. The projected device performance will allow measurement of the large electric fields for large dust devils without saturation. With dimensions on the 100 μm scale and power consumption of only tens of nW, the sensor features dramatically reduced mass, power, and footprint. Recent field testing of the sensor demonstrated the robustness of suspended SWCNT devices to temperature fluctuations, mechanical shock, dust, and other environmental factors.

The lifetime of a patterned carbon nanotube film is evaluated for use as the cold cathode field emission ionization source of a miniaturized mass spectrometer. Emitted current is measured as a function of time for varying partial pressures of nitrogen gas to explore the robustness and lifetime of carbon nanotube cathodes near the expected operational voltages (70-100 eV) for efficient ionization in mass spectrometry. As expected, cathode lifetime scales inversely with partial pressure of nitrogen. Results are presented within the context of previous carbon nanotube investigations, and implications for planetary science mass spectrometry applications are discussed.

The microshutter array (MSA) is a key component in the James Webb Space Telescope Near Infrared Spectrometer (NIRSpec) instrument. The James Webb Space Telescope is the next generation of a space-borne astronomy platform that is scheduled to be launched in 2013. However, in order to effectively operate the array and meet the severe operational requirements associated with a space flight mission has placed enormous constraints on the microshutter array subsystem. This paper will present an overview and description of the entire microshutter subsystem including the microshutter array, the hybridized array assembly, the integrated CMOS electronics, mechanical mounting module and the test methodology and performance of the fully assembled microshutter subsystem. The NIRSpec is a European Space Agency (ESA) instrument requiring four fully assembled microshutter arrays, or quads, which are independently addressed to allow for the imaging of selected celestial objects onto the two 4 mega pixel IR detectors. Each microshutter array must have no more than ~8 shutters which are failed in the open mode (depending on how many are failed closed) out of the 62,415 (365x171) total number of shutters per array. The driving science requirement is to be able to select up to 100 objects at a time to be spectrally imaged at the focal plane. The spectrum is dispersed in the direction of the 171 shutters so if there is an unwanted open shutter in that row the light from an object passing through that failed open shutter will corrupt the spectrum from the intended object.

We are implementing nano- and micro-technologies to develop a miniaturized electron impact ionization mass spectrometer for planetary science. Microfabrication technology is used to fabricate the ion and electron optics, and a carbon nanotube (CNT) cathode is used to generate the ionizing electron beam. Future NASA planetary science missions demand miniaturized, low power mass spectrometers that exhibit high resolution and sensitivity to search for evidence of past and present habitability on the surface and in the atmosphere of priority targets such as Mars, Titan, Enceladus, Venus, Europa, and short-period comets. Toward this objective, we are developing a miniature, high resolution reflectron time-of-flight mass spectrometer (Mini TOF-MS) that features a low-power CNT field emission electron impact ionization source and microfabricated ion optics and reflectron mass analyzer in a parallel-plate geometry that is scalable. Charged particle electrodynamic modeling (SIMION 8.0.4) is employed to guide the iterative design of electron and ion optic components and to characterize the overall performance of the Mini TOF-MS device via simulation. Miniature (< 1000 cm3) TOF-MS designs (ion source, mass analyzer, detector only) demonstrate simulated mass resolutions > 600 at sensitivity levels on the order of 10-3 cps/molecule N2/cc while consuming 1.3 W of power and are comparable to current spaceflight mass spectrometers. Higher performance designs have also been simulated and indicate mass resolutions ~1000, though at the expense of sensitivity and instrument volume.

Solar system exploration and the anticipated discovery of biomarker molecules is driving the development of a new miniature time-of-flight (TOF) mass spectrometer (MS). Space flight science investigations become more feasible through instrument miniaturization, which reduces size, mass, and power consumption. However, miniaturization of space flight mass spectrometers is increasingly difficult using current component technology. Micro electro mechanical systems (MEMS) and nano electro mechanical systems (NEMS) technologies offer the potential of reducing size by orders of magnitude, providing significant system requirement benefits as well. Historically, TOF mass spectrometry has been limited to large separation distances as ion mass analysis depends upon the ion flight path. Increased TOF MS system miniaturization may be realized employing newly available high speed computing electronics, coupled with MEMS and NEMS components. Recent efforts at NASA Goddard Space Flight Center in the development of a miniaturized TOF mass spectrometer with integral MEMS and NEMS components are presented. A systems overview, design and prototype, MEMS silicon ion lenses, a carbon nanotube electron gun, ionization methods, as well as performance data and relevant applications are discussed.

We have developed microshutter array systems at NASA Goddard Space Flight Center for use as multi-object aperture arrays for a Near-Infrared Spectrometer (NIRSpec) instrument. The instrument will be carried on the James Webb Space Telescope (JWST), the next generation of space telescope, after the Hubble Space Telescope retires. The microshutter arrays (MSAs) are designed for the selective transmission of light from objected galaxies in space with high efficiency and high contrast. Arrays are close-packed silicon nitride membranes with a pixel size close to 100x200 μm. Individual shutters are patterned with a torsion flexure permitting shutters to open 90 degrees with minimized stress concentration. In order to enhance optical contrast, light shields are made on each shutter to prevent light leak. Shutters are actuated magnetically, latched and addressed electrostatically. The shutter arrays are fabricated using MEMS bulk-micromachining and packaged utilizing a novel single-sided indium flip-chip bonding technology. The MSA flight system consists of a mosaic of 2 x 2 format of four fully addressable 365 x 171 arrays. The system will be placed in the JWST optical path at the focal plane of NIRSpec detectors. MSAs that we fabricated passed a series of qualification tests for flight capabilities. We are in the process of making final flight-qualified MSA systems for the JWST mission.

A cold cathode field emission electron gun (e-gun) based on a patterned carbon nanotube (CNT) film has been fabricated for use in a miniaturized reflectron time-of-flight mass spectrometer (RTOF MS), with future applications in other charged particle spectrometers, and performance of the CNT e-gun has been evaluated. A thermionic electron gun has also been fabricated and evaluated in parallel and its performance is used as a benchmark in the evaluation of our CNT e-gun. Implications for future improvements and integration into the RTOF MS are discussed.

A complex MEMS device, microshutter array system, is being developed at NASA Goddard Space Flight Center for use as an aperture array for a Near-Infrared Spectrometer (NirSpec). The instrument will be carried on the James Webb Space Telescope (JWST), the next generation of space telescope after Hubble Space Telescope retires. The microshutter arrays (MSAs) are designed for the selective transmission of light with high efficiency and high contrast. Arrays are close-packed silicon nitride membranes with a pixel size close to 100x200 mm. Individual shutters are patterned with a torsion flexure permitting shutters to open 90 degrees with a minimized mechanical stress concentration. Light shields are made on to each shutter for light leak prevention so to enhance optical contrast. Shutters are actuated magnetically, latched and addressed electrostatically. The shutter arrays are fabricated using MEMS bulk-micromachining technologies and packaged using single-sided indium flip-chip bonding technology. The MSA flight concept consists of a mosaic of 2 x 2 format of four fully addressable 365 x 171 arrays placed in the JWST optical path at the focal plane.

Two-dimensional MEMS microshutter arrays are being developed at NASA Goddard Space Flight Center for use in the near-infrared region on the James Webb Space Telescope (JWST). The microshutter arrays are designed for the selective transmission of light with high efficiency and high contrast. The JWST environment requires cryogenic operation at 35K. Microshutter arrays are fabricated out of silicon-oxide-insulated (SOI) silicon wafers. Arrays are close-packed silicon nitride membranes with a pixel size of 100x200 p. Individual shutters are patterned with a torsion flexure permitting shutters to open 90 degrees with a minimized mechanical stress concentration. The mechanical shutter arrays are fabricated using MEMS technologies. The processing includes a multi- layer metal deposition and patterning of shutter electrodes and magnetic pads, reactive ion etching (NE) of the front side to form shutters out of the nitride membrane, an anisotropic back-etch for wafer thinning, followed by a deep RIE (DRIE) back-etch down to the nitride shutter membrane to form W e s and relieve shutters from the silicon substrate. An additional metal deposition and patterning is used to form back electrodes. Shutters are actuated using a magnetic force and latched using an electrostatic force. . . . KEYWORDS: microshutter, MEMS, RIE, DRIE, micro-optics, near inbred, space telescope

We report on methods to minimize thermally-induced deformation in a MEMS-based reconfigurable aperture. The device is an enabling component of the Near-Infrared Spectrometer, a principle instrument on NASA’s James Webb Space Telescope. The Microshutter Array consists of 384x175 individually addressable shutters which can be magnetically rotated 90° into the plane of the array and electrostatically latched open. Each shutter is a 100x200 μm rectangular membrane suspended by a small neck region and torsion flexure. The primary materials in the shutter are a 5000a Si3N4 layer for mechanical rigidity, 2000a Al for opacity and electrostatic latching, and 2200a Co90Fe10 for magnetic actuation. This multi-layer stack presents a challenge due to the operating temperatures required for the device: both room temperature (300K) and cryogenic temperature (30K). Thermal expansion of the materials causes the shutters to bow out of plane excessively, which can prevent actuation of the shutters, cause damage to portions of the array, and allow light leakage around closed shutters. Here we present our investigation of several methods to prevent microshutter bowing including deposition of additional materials on the shutters to create a symmetrical layer stack and replacing the current stack with low-coefficient of thermal expansion materials. Using shutter-size suspended cantilever beams as a rapid-development test bed, we have reduced out-of-plane bowing between 300K and 30K to 10% or better. We are currently applying these results to microshutter arrays to develop shutters that remain flat from room temperature to cryogenic temperature while retaining the required mechanical, optical, and magnetic properties.

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 35 K. Microshutter arrays are fabricated out of silicon-on-insulator (SOI) silicon wafers. Arrays are close-packed silicon nitride membranes with a pixel size of 100 x 200 μm. 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.

The Near Infrared Spectrograph (NIRSpec) for the James Webb Space Telescope (JWST) is a multi-object spectrograph operating in the 0.6-5.0 μm spectral range. One of the primary scientific objectives of this instrument is to measure the number and density evolution of galaxies following the epoch of initial formation. NIRSpec is designed to allow simultaneous observation of a large number of sources, vastly increasing the capability of JWST to carry out its objectives. A critical element of the instrument is the programmable field selector, the Microshutter Array. The system consists of four 175 x 384 close packed arrays of individually operable shutters, each element subtending 0.2” x 0.4”on the sky. This device allows simultaneous selection of over 200 candidates for study over the 3.6’ x 3.6’ field of the NIRSpec, dramatically increasing its efficiency for a wide range of investigations. Here, we describe the development, production, and test of this critical element of the NIRSpec.

Magnetically actuated MEMS microshutter arrays are being developed at the NASA Goddard Space Flight Center for use in a multi-object spectrometer on the James Webb Space Telescope (JWST), formerly Next Generation Space Telescope (NGST). The microshutter arrays are designed for the selective transmission of light with high efficiency and high contrast. The JWST environment requires cryogenic operation at 45K. Microshutter arrays are fabricated out of silicon-on-insulator (SOI) wafers. Arrays consist of close-packed shutters made on silicon nitride (nitride) membranes with a pixel size of 100 × 100 m. Individual shutters are patterned with a torsion flexure permitting shutters to open 90°, with a minimized mechanical stress concentration. Shutters operated this way have survived fatigue life test. The mechanical shutter arrays are fabricated using MEMS technologies. The processing includes a multi-layer metal deposition, patterning of shutter electrodes and magnetic pads, reactive ion etching (RIE) of the front side to form shutters in a nitride film, an anisotropic back-etch for wafer thinning, and a deep RIE (DRIE) back-etch, down to the nitride shutter layer, to form support frames and relieve shutters from the silicon substrate. An additional metal deposition and patterning has recently been developed to form electrodes on the vertical walls of the frame. Shutters are actuated using a magnetic force, and latched electrostatically. One-dimensional addressing has been demonstrated.