Carl A. Kotecki

Fabrication of microshutter arrays for space application

Two-dimensional microshutter arrays are being developed at NASA Goddard Space Flight Center for the Next Generation Space Telescope (NGST) for use in the near-infrared region. Functioning as object selection devices, the microshutter arrays are designed for the transmission of light with high efficiency and high contrast. The NGST environment requires cryogenic operation at 45K. Arrays are close-packed silicon nitride membranes with a pixel size of 100 X 100 micrometers . 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 with MEMS technologies. The processing includes a RIE front-etch to form shutters out of the nitride membrane, an anisotropic back-etch for wafer thinning, and a deep RIE (DRIE) back-etch down to the nitride shutter membrane to form frames and to relieve shutters from the silicon substrate. Two approaches for shutter actuation have been developed. Shutters are actuated using either a combined mechanical and electrostatic force or a combined magnetic and electrostatic force. A CMOS circuit embedded in the frame between shutters allows programmable shutter selection for the first approach. A control of row and column electrodes fulfills shutter selection for the second approach.

Volatile Analysis by Pyrolysis of Regolith for planetary resource exploration

The extraction and identification of volatile resources that could be utilized by humans including water, oxygen, noble gases, and hydrocarbons on the Moon, Mars, and small planetary bodies will be critical for future long-term human exploration of these objects. Vacuum pyrolysis at elevated temperatures has been shown to be an efficient way to release volatiles trapped inside solid samples. In order to maximize the extraction of volatiles, including oxygen and noble gases from the breakdown of minerals, a pyrolysis temperature of 1400°C or higher is required, which greatly exceeds the maximum temperatures of current state-of-the-art flight pyrolysis instruments. Here we report on the recent optimization and field testing results of a high temperature pyrolysis oven and sample manipulation system coupled to a mass spectrometer instrument called Volatile Analysis by Pyrolysis of Regolith (VAPoR). VAPoR is capable of heating solid samples under vacuum to temperatures above 1300°C and determining the composition of volatiles released as a function of temperature.

Planarization for the integration of CMOS and micromirror arrays

A large format individually addressable Micro-Mirror-Array (MMA) has been developed at NASA, GSFC for possible application in the Next Generation Space Telescope (NGST). The 100micron X100micron aluminum micro-mirrors are built on top of CMOS driven address and driver circuit for individual addressing. The high voltage CMOS fabrication process produces about 2.8microns surface roughness on the silicon wafer. The wafer surface is planarized before integration of the MMA. Three different planarization materials were evaluated; polyimide, spin-on glass and BCB. BCB showed the best results for our application. A single layer of BCB coating reduced the surface topology from 2.8micron to less than 1,700Angstroms and two layers of BCB coating reduced the surface topology to about 600Angstroms. Since the MMA has to operate at 30K for the NGST application, a wafer coated with cured BCB was dunk tested in liquid nitrogen at 77K and no cracks were found after thermal cycling. For specific application in NGST, the optical reflectance of BCB was measured at 40K over 1-5micron wavelength range and the results showed that BCB could absorb 30-40 percent of infrared light over this range. Details of coating, curing and etching properties of BCB are discussed along with its low temperature optical properties.

Organics Analyzer for Sampling Icy Surfaces: A liquid chromatograph-mass spectrometer for future in situ small body missions

Liquid chromatography mass spectrometry (LC-MS) is an important laboratory technique for the detection and analysis of organic molecules with high sensitivity and selectivity. This approach has been especially fruitful in the analysis of nucleobases, amino acids, and measuring amino acid enantiomeric ratios in extraterrestrial materials. We are developing OASIS, Organics Analyzer for Sampling Icy Surfaces, for in situ analysis on future landed missions to astrochemically important icy bodies, such as asteroids, comets, and icy moons. The OASIS design employs a microfabricated, on-chip analytical column to chromatographically separate liquid analytes using known LC stationary phase chemistries. The elution products are then interfaced through spray ionization and analyzed by a time-of-flight mass spectrometer (TOF-MS). A particular advantage of our design is its suitability for microgravity environments, such as for a primitive small body.

Liquid chromatography-mass spectrometry interface for detection of extraterrestrial organics

The OASIS (Organics Analyzer for Sampling Icy surfaces) microchip enables electrospray or thermospray of analyte for subsequent analysis by the OASIS time-of-flight mass spectrometer. Electrospray of buffer solution containing the nucleobase adenine was performed using the microchip and detected by a commercial time-of-flight mass spectrometer. Future testing of thermospray and electrospray capability will be performed using a test fixture and vacuum chamber developed especially for optimization of ion spray at atmosphere and in low pressure environments.

Development of individually addressable micromirror arrays for space applications

A 2D array of individually addressable micro-mirrors with 100 micrometers by 100 micrometers pixel size, capable of tilting +/- 100 by electrostatic actuation is being developed and fabricated at the Detector Development Laboratory of NASA, GSFC. The development requires integration of CMOS and MEMS fabrication processes. We have competed extensive analytical studies and performed laboratory test to compare model predictions with actual performance of a 3 by 3 array. We are testing the address and driver circuit for a 32 by 32 array and also developing the process integration of the CMOS and MEMS fabrication of the larger arrays. The mirrors are capable of operating at cryogenic temperature for astronomical applications. Our goal is to extend the development to a 25 6by 256 array for a wide variety of space applications including the multi-object-spectrometer in the next generation space telescope.

HgCdTe detector technology and performance for the Composite Infrared Spectrometer (CIRS)/Cassini mission

The composite infrared spectrometer (CIRS) instrument, an important component of the Cassini mission, consists of 3 focal plane arrays for sensing IR radiation of the Saturnian planetary system. Goddard Space Flight Center has fabricated, tested, and delivered high performance, 10- element HgCdTe photoconductive (PC) arrays for use on CIRS FP3, the focal plane responsible for detection of radiation in the 9.1 to 16.7 micrometers spectral band. The delivered flight array has peak responsivity 100 percent above CIRS specification, detectivity 30 percent or more above specification, and a cutoff wavelength of 17.3 micrometers at the operating temperature of 80 K. In order to achieve high performance at low frequency while maintaining limited power dissipation, we adopted a split-geometry detector structure. This design also ensured the buttability of the PC arrays to photovoltaic arrays supplied by CE-Saclay-France for detection of radiation in the 7.1 to 9.1 micrometers range. The detector structure is also noteworthy for its use of 0.05 micrometers Alumina powder-loaded epoxy to minimize reflection at the epoxy/HgCdTe interface, thus spoiling undesired optical resonance. This was done in order to meet the CIRS spectral uniformity requirement, which would have been difficult at these long wavelengths without this feature.

High-performance HgCdTe infrared detectors for the GOES long-wave sounder

GOES long wave sounder (LWS) detector requirements have always pushed the state-of-the-art for longwave detectors operating in the vicinity of 102 K. Performance and yield of acceptable detectors have always been problems and continue to be important issues affecting the performance of instruments of both present and future design. GSFC has been examining new device and operational concepts aimed at producing significant improvements in performance and yield. Our approach has been directed towards mitigating the deleterious effects of operating small geometry HgCdTe PC devices under heavy bias, that is, under minority carrier sweepout, as is typical in conventional LWS detector operation. Specifically, theory indicates that detectors of the new design operating under optimal bias conditions have significantly higher responsivity, lower power dissipation,and lower 1/f noise knees than conventional LWS detectors. In this paper we will describe the new LWS detectors fabricated at GSFC, present detector data, and review the theory of operation of these devices.

In situ instrument to detect prebiotic compounds in planetary ices

Understanding the distribution of organic molecules in Solar System materials is a high priority goal of NASA’s Astrobiology Program. To this end, our team at NASA Goddard Space Flight Center is now developing a compact instrument prototype, the Organics Analyzer for Sampling Icy Surfaces (OASIS), that will be compatible with a flight mission to the surface of an icy planetary body. The technique of liquid chromatography-mass spectrometry (LC-MS) has revealed important new understanding in Earthbased investigations of the inventory of prebiotic organics in extraterrestrial materials, and we are demonstrating that LC-MS is compatible with instrument miniaturization (Figure 1) through the use of microfluidic components and a compact time-of-flight mass spectrometer (TOF-MS) [Getty 2011, Glavin 2012].

Split-geometry detectors, our eyes in space

Infrared detectors have projected our ability to explore our planet and our solar system far beyond the spatial, temporal, and spectral limitations of our natural vision. As such, they are our eyes in space, constantly searching the heavens, and sending back information about the origin, constitution, and dynamics of planetary atmospheres, and other processes of interest. Their ability to do this effectively depends on their sensitivity. Today, long wave PC (photoconductive) HgCdTe detectors are the detectors of choice for applications requiring high sensitivity at long wavelengths and elevated temperature. However, planetary exploration and space surveillance of the earth’s climatic condition are presently still limited by the sensitivity of available detectors. This paper will describe detectors developed at Goddard to provide enhanced performance for applications such as the CIRS/Cassini mission to Saturn and Titan, and the GOES weather satellite. Specifically, this paper will show theoretically and experimentally how detectors of split-geometry design can be exploited to increase detector resistance, responsivity, and detectivity, while decreasing 1/f noise and power dissipation. Photomicrographs of split-geometry detectors will be shown, and data demonstrating theoretical split-geometry design advantages will be presented for flight arrays built for the CIRS/Cassini mission, and for advanced detectors for GOES.