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NASA NTRS2003

Characterization of Pixelated Cadmium-Zinc-Telluride Detectors for Astrophysical Applications

Comparisons of charge sharing and charge loss measurements between two pixelated Cadmium-Zinc-Telluride (CdZnTe) detectors are discussed. These properties along with the detector geometry help to define the limiting energy resolution and spatial resolution of the detector in question. The first detector consists of a 1-mm-thick piece of CdZnTe sputtered with a 4x4 array of pixels with pixel pitch of 750 microns (inter-pixel gap is 100 microns). Signal readout is via discrete ultra-low-noise preamplifiers, one for each of the 16 pixels. The second detector consists of a 2-mm-thick piece of CdZnTe sputtered with a 16x16 array of pixels with a pixel pitch of 300 microns (inter-pixel gap is 50 microns). This crystal is bonded to a custom-built readout chip (ASIC) providing all front-end electronics to each of the 256 independent pixels. These detectors act as precursors to that which will be used at the focal plane of the High Energy Replicated Optics (HERO) telescope currently being developed at Marshall Space Flight Center. With a telescope focal length of 6 meters, the detector needs to have a spatial resolution of around 200 microns in order to take full advantage of the HERO angular resolution. We discuss to what degree charge sharing will degrade energy resolution but will improve our spatial resolution through position interpolation.

Gaskin, Jessica↗

NASA NTRS2003

Development of a 1K x 1K GaAs QWIP Far IR Imaging Array

In the on-going evolution of GaAs Quantum Well Infrared Photodetectors (QWIPs) we have developed a 1,024 x 1,024 (1K x1K), 8.4-9 microns infrared focal plane array (FPA). This 1 megapixel detector array is a hybrid using the Rockwell TCM 8050 silicon readout integrated circuit (ROIC) bump bonded to a GaAs QWIP array fabricated jointly by engineers at the Goddard Space Flight Center (GSFC) and the Army Research Laboratory (ARL). The finished hybrid is thinned at the Jet Propulsion Lab. Prior to this development the largest format array was a 512 x 640 FPA. We have integrated the 1K x 1K array into an imaging camera system and performed tests over the 40K-90K temperature range achieving BLIP performance at an operating temperature of 76K (f/2 camera system). The GaAs array is relatively easy to fabricate once the superlattice structure of the quantum wells has been defined and grown. The overall arrays costs are currently dominated by the costs associated with the silicon readout since the GaAs array fabrication is based on high yield, well-established GaAs processing capabilities. In this paper we will present the first results of our 1K x 1K QWIP array development including fabrication methodology, test data and our imaging results.

Jhabvala, M.↗

NASA NTRS2003

High-Sensitivity X-ray Polarimetry with Amorphous Silicon Active-Matrix Pixel Proportional Counters

Photoelectric X-ray polarimeters based on pixel micropattern gas detectors (MPGDs) offer order-of-magnitude improvement in sensitivity over more traditional techniques based on X-ray scattering. This new technique places some of the most interesting astronomical observations within reach of even a small, dedicated mission. The most sensitive instrument would be a photoelectric polarimeter at the focus of 2 a very large mirror, such as the planned XEUS. Our efforts are focused on a smaller pathfinder mission, which would achieve its greatest sensitivity with large-area, low-background, collimated polarimeters. We have recently demonstrated a MPGD polarimeter using amorphous silicon thin-film transistor (TFT) readout suitable for the focal plane of an X-ray telescope. All the technologies used in the demonstration polarimeter are scalable to the areas required for a high-sensitivity collimated polarimeter. Leywords: X-ray polarimetry, particle tracking, proportional counter, GEM, pixel readout

Black, J. K.↗

NASA NTRS2003

X-ray Polarimetry with an Active-Matrix Pixel Proportional Counter

We report the first results from an X-ray polarimeter with a micropattern gas proportional counter using an amorphous silicon active matrix readout. With 100% polarized X-rays at 4.5 keV, we obtain a modulation factor of 0.33+/- 0.03, confirming previous reports of the high polarization sensitivity of a finely segmented pixel proportional counter. The detector described here has a geometry suitable for the focal plane of an astronomical X-ray telescope. Amorphous silicon readout technology will enable additional extensions and improvements.

Black, J. K.↗

NASA NTRS2003

Development of a Cryogen-Free Continuous ADR for the Constellation-X Mission

Constellation-X is a multi-satellite x-ray astronomy mission presently being planned for launch in the 2010 time frame. Each of 4 identical satellites will contain a telescope and instruments for imaging and spectroscopic analysis of both hard and soft x-rays. The X- ray Microcalorimeter Spectrometer (XMS) instrument will use arrays of microcalorimeters to detect X-rays with energies from 0.2 to 6 keV. The technologies under development for this instrument include Transition-Edge Sensors (TES) with multiplexed SQUID readouts and NTD-Ge detectors with JFET readouts. Both will be operated at temperatures in the 50-60 mK range and both have a projected cooling power requirement of approximately 5 microwatts. In addition, in order to meet the lifetime requirement of 6 years (with a goal of 10 years), a mechanical cryocooler will be used to provide a heat sink for the low temperature cooler. The required performance is 20 mW at 6 K, with a goal of 4 K operation. In this paper we present the development status of an adiabatic demagnetization refigerator (ADR) that meets the cooling requirements of the X M S instrument. At present we have demonstrated a 4-stage ADR that operates continuously at 50 mK using a 4.2 K helium bath as a heat sink. The cooling power is 21 microwatts at 100 mK and 6 microwatts at 50 mK. Its efficiency when operating at 50 mK is 1 1 % of Carnot (accounting for all dissipation at 4.2 K and below, but not including power dissipation in the room temperature electronics), but this is expected to rise to 25% in the next generation system in which active gas-gap heat switches are replaced with passive devices. This will reduce the peak heat rejection rate of the ADR to less than 7 mW at 6 K. Details of the ADR s design and operation, as well as the development program leading up to a flight-qualified instrument, will be discussed.

Shirron, Peter↗

NASA NTRS2004

Thermopile Detector Arrays for Space Science Applications

Thermopile detectors are widely used in uncooled applications where small numbers of detectors are required, particularly in low-cost commercial applications or applications requiring accurate radiometry. Arrays of thermopile detectors, however, have not been developed to the extent of uncooled bolometer and pyroelectric/ferroelectric arrays. Efforts at JPL seek to remedy this deficiency by developing high performance thin-film thermopile detectors in both linear and two-dimensional formats. The linear thermopile arrays are produced by bulk micromachining and wire bonded to separate CMOS readout electronic chips. Such arrays are currently being fabricated for the Mars Climate Sounder instrument, scheduled for launch in 2005. Progress is also described towards realizing a two-dimensional thermopile array built over CMOS readout circuitry in the substrate.

Foote, M. C.↗

NASA NTRS2004

Ideal Integrating Bolometer

We describe a new "ideal integrator" bolometer as a prototype for a new generation of sensitive, flexible far-IR detectors suitable for use in large arrays. The combination of a non-dissipative sensor coupled with a fast heat switch provides breakthrough capabilities in both sensitivity and operation. The bolometer temperature varies linearly with the integrated infrared power incident on the detector, and may be sampled intermittently without loss of information between samples. The sample speed and consequent dynamic range depend only on the heat switch reset cycle and can be selected in software. Between samples, the device acts as an ideal integrator with noise significantly lower than resistive bolometers. Since there is no loss of information between samples, the device is well-suited for large arrays. A single SQUID readout could process an entire column of detectors, greatly reducing the complexity, power requirements, and cost of readout electronics for large pixel arrays.

Kogut, A.↗

NASA NTRS2004

A Program to Detect and Characterize Extra-Solar Giant Planets

The upgrade to the AFOE spectrograph at the 1.5-m Tillinghast telescope at FLWO Observatory, described in detail in the previous progress report, was completed. Work included installing a new CCD detector (using SA0 internal funds) to replace the previous detector, which had failed after many thermal cyclings during the previous nearly ten years of operation. The new detector (a back-illuminated Marconi 2K x 2K detector) shows excellent quantum efficiency, and employs dual readout channels to keep the readout time as short as 20 seconds. Tests of the attainable radial velocity precision of the upgraded spectrograph with the new detector show an improvement in radial velocity detection efficiency by a factor of about 10 over the previous AFOE configuration, allowing us to push the photon-noise-limited doppler precision of 7 m/s to correspondingly fainter stars. This work was carried out by Co-investigator Sylvain Korzennik, along with the late Peter Nisenson.

Lindstrim, David↗

NASA NTRS2004

International Space Station (ISS) Major Constituent Analyzer (MCA) On-Orbit Performance

The Major Constituent Analyzer (MCA) is an essential part of the International Space Station (ISS) environmental control and life support system. The analyzer provides continuous readout of the partial pressures of six gases, nitrogen (N2), oxygen (O2), hydrogen (H2), carbon dioxide (CO2), methane (CH4) and water vapor (H2O) in the various ISS US. on-orbit modules. Continuous readout of the partial pressures of these gases is critical to verifying safe operation of the Atmosphere Revitalization (AR) system, Atmosphere Control System (ACS), and crew safety for Airlock Extravehicular Activities (EVAs). The MCA encountered some operational interruptions since being launched to orbit on Flight 5A in February 2001. Electronic, software, and hardware modifications and on-orbit crew maintenance of the MCA were necessary to restore its capability. This paper describes the modifications and the on-orbit maintenance performed to return the MCA to operational status, including brief explanations of the MCA failures and the associated hardware and electronic modifications. Operational procedures that were required to return the MCA to operational status, and the more recent successes of supporting both Russian and U.S. ISS EVA preparations, are also discussed

Reysa, Richard↗

NASA NTRS2007

Radiometric and Radiation Response of Visible FPAs

The readout integrated circuit (ROIC) used in these devices was originally developed for use in space based infrared systems operating at deep cryogenic temperatures and was selected because of its proven tolerance to total ionizing radiation? The detectors are a 128 x 128 array of 60 pm x 60 pm pixel elements that have been anti-reflection (AR) coated to improve the response at very short wavelengths. These visible focal plane arrays were operated at -40 C (233 K). Two focal planes were characterized using cobalt-60 radiation to produce ionizing total dose damage in the VFPAs. Both operational and performance data were obtained as functions of total dose. The first device tested showed no appreciable change in responsivity or noise up to 300 krad(Si). However, at the next dose level of 600 krad(Si), the readout was non-operational due to failure in the digital circuitry. The second device was characterized to a total dose of 750 krad(Si) with no observed change in responsivity. An increase dark current was observed in both devices, and in the second device, the dark current caused an increase in noise at low irradiance at 400 krad(Si) and above. The increase in dark current was somewhat un-expected for visible PIN detectors. The median dark current increased more than two orders of magnitude at 300 krad(Si) for the first device and a factor of 350 at 750 krad(Si) for pixels near the edge for the second device. The dark current was found to be a strong function of detector bias, with pixels near the edge of the array showing a greater increase in dark current with bias than those near the center. Since the optical response was not a function of bias, it is hypothesized that the dark current is a surface effect and that the variation in dark current with location is due to a variation in pixel bias, caused by a voltage drop across the pixel common lead. As the total dose increased, the dark current and the voltage drop increased

Hubbs, John↗

NASA NTRS2000

Delta-doped hybrid advanced detector for low energy particle detection

A delta-doped hybrid advanced detector (HAD) is provided which combines at least four types of technologies to create a detector for energetic particles ranging in energy from hundreds of electron volts (eV) to beyond several million eV. The detector is sensitive to photons from visible light to X-rays. The detector is highly energy-sensitive from approximately 10 keV down to hundreds of eV. The detector operates with milliwatt power dissipation, and allows non-sequential readout of the array, enabling various advanced readout schemes.

Cunningham, Thomas J.↗

NASA NTRS2000

Active pixel sensor having intra-pixel charge transfer with analog-to-digital converter

An imaging device formed as a monolithic complementary metal oxide semiconductor Integrated circuit in an industry standard complementary metal oxide semiconductor process, the integrated circuit including a focal plane array of pixel cells, each one of the cells including a photogate overlying the substrate for accumulating photo-generated charge in an underlying portion of the substrate, a readout circuit including at least an output field effect transistor formed in the substrate, and a charge coupled device section formed on the substrate adjacent the photogate having a sensing node connected to the output transistor and at least one charge coupled device stage for transferring charge from the underlying portion of the substrate to the sensing node and an analog-to-digital converter formed in the substrate connected to the output of the readout circuit.

Fossum, Eric R.↗

NASA NTRS2002

Delta-doped hybrid advanced detector for low energy particle detection

Cunningham, Thomas J.↗

NASA NTRS2005

Active pixel sensor pixel having a photodetector whose output is coupled to an output transistor gate

An imaging device formed as a monolithic complementary metal oxide semiconductor integrated circuit in an industry standard complementary metal oxide semiconductor process, the integrated circuit including a focal plane array of pixel cells, each one of the cells including a photogate overlying the substrate for accumulating photo-generated charge in an underlying portion of the substrate and a charge coupled device section formed on the substrate adjacent the photogate having a sensing node and at least one charge coupled device stage for transferring charge from the underlying portion of the substrate to the sensing node. There is also a readout circuit, part of which can be disposed at the bottom of each column of cells and be common to all the cells in the column. A Simple Floating Gate (SFG) pixel structure could also be employed in the imager to provide a non-destructive readout and smaller pixel sizes.

Fossum, Eric R.↗

NASA NTRS2003

Active pixel sensor having intra-pixel charge transfer with analog-to-digital converter

An imaging device formed as a monolithic complementary metal oxide semiconductor integrated circuit in an industry standard complementary metal oxide semiconductor process, the integrated circuit including a focal plane array of pixel cells, each one of the cells including a photogate overlying the substrate for accumulating photo-generated charge in an underlying portion of the substrate, a readout circuit including at least an output field effect transistor formed in the substrate, and a charge coupled device section formed on the substrate adjacent the photogate having a sensing node connected to the output transistor and at least one charge coupled device stage for transferring charge from the underlying portion of the substrate to the sensing node and an analog-to-digital converter formed in the substrate connected to the output of the readout circuit.

Fossum, Eric R.↗

NASA NTRS2006

Method and apparatus for optical encoding with compressible imaging

The present invention presents an optical encoder with increased conversion rates. Improvement in the conversion rate is a result of combining changes in the pattern recognition encoder's scale pattern with an image sensor readout technique which takes full advantage of those changes, and lends itself to operation by modern, high-speed, ultra-compact microprocessors and digital signal processors (DSP) or field programmable gate array (FPGA) logic elements which can process encoder scale images at the highest speeds. Through these improvements, all three components of conversion time (reciprocal conversion rate)--namely exposure time, image readout time, and image processing time--are minimized.

Leviton, Douglas B.↗

NASA NTRS1978

Semi-automatic aircraft control system

A flight control type system which provides a tactile readout to the hand of a pilot for directing elevator control during both approach to flare-out and departure maneuvers. For altitudes above flare-out, the system sums the instantaneous coefficient of lift signals of a lift transducer with a generated signal representing ideal coefficient of lift for approach to flare-out, i.e., a value of about 30% below stall. Error signals resulting from the summation are read out by the noted tactile device. Below flare altitude, an altitude responsive variation is summed with the signal representing ideal coefficient of lift to provide error signal readout.

Gilson, Richard D.↗

NASA NTRS2007

Kilopixel Pop-Up Bolometer Arrays for the Atacama Cosmology Telescope

The recently deployed Atacama Cosmology Telescope (ACT) anticipates first light on its kilopixel array of close-packed transition-edge-sensor bolometers in November of 2007. The instrument will represent a full implementation of the next-generation, large format arrays for millimeter wave astronomy that use superconducting electronics and detectors. Achieving the practical construction of such an array is a significant step toward producing advanced detector arrays for future SOFIA instruments. We review the design considerations for the detector array produced for the ACT instrument. The first light imager consists of 32 separately instrumented 32-channel pop-up bolometer arrays (to create a 32x32 filled array of mm-wave sensors). Each array is instrumented with a 32-channel bias resistor array, Nyquist filter array, and time-division SQUID multiplexer. Each component needed to be produced in relatively large quantities with suitable uniformity to meet tolerances for array operation. An optical design was chosen to maximize absorption at the focal plane while mitigating reflections and stray light. The pop-up geometry (previously implemented with semiconducting detectors and readout on the SHARC II and HAWC instruments) enabled straightforward interface of the superconducting bias and readout circuit with the 2D array of superconducting bolometers. The array construction program balanced fabrication challenges with assembly challenges to deliver the instrument in a timely fashion. We present some of the results of the array build and characterization of its performance.

Chervenak, J. A.↗