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All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Future directions for NICMOS arrays

The Near Infrared Camera and Multi-Object Spectrometer (NICMOS) for the Hubble Space Telescope (HST) requires focal plane arrays of 256x256 pixels for both its cameras and its spectrometers. The new arrays, developed by the Rockwell Corporation for NICMOS, have 40 microns pixels of HgCdTe bump bonded to a switched MOSFET readout. Expected read noise and dark current for the arrays at 60 K are 30 e and 1 e/sec. respectively. The basis for these numbers is previous experience with 128x128 arrays.

Thompson, R.↗
NASA NTRS2009

Delta-Doped Back-Illuminated CMOS Imaging Arrays: Progress and Prospects

In this paper, we report the latest results on our development of delta-doped, thinned, back-illuminated CMOS imaging arrays. As with charge-coupled devices, thinning and back-illumination are essential to the development of high performance CMOS imaging arrays. Problems with back surface passivation have emerged as critical to the prospects for incorporating CMOS imaging arrays into high performance scientific instruments, just as they did for CCDs over twenty years ago. In the early 1990's, JPL developed delta-doped CCDs, in which low temperature molecular beam epitaxy was used to form an ideal passivation layer on the silicon back surface. Comprising only a few nanometers of highly-doped epitaxial silicon, delta-doping achieves the stability and uniformity that are essential for high performance imaging and spectroscopy. Delta-doped CCDs were shown to have high, stable, and uniform quantum efficiency across the entire spectral range from the extreme ultraviolet through the near infrared. JPL has recently bump-bonded thinned, delta-doped CMOS imaging arrays to a CMOS readout, and demonstrated imaging. Delta-doped CMOS devices exhibit the high quantum efficiency that has become the standard for scientific-grade CCDs. Together with new circuit designs for low-noise readout currently under development, delta-doping expands the potential scientific applications of CMOS imaging arrays, and brings within reach important new capabilities, such as fast, high-sensitivity imaging with parallel readout and real-time signal processing. It remains to demonstrate manufacturability of delta-doped CMOS imaging arrays. To that end, JPL has acquired a new silicon MBE and ancillary equipment for delta-doping wafers up to 200mm in diameter, and is now developing processes for high-throughput, high yield delta-doping of fully-processed wafers with CCD and CMOS imaging devices.

imagers↗
NASA NTRS2018

Fabrication of a Hybrid Transition Edge Sensor Array for Lynx

Lynx is a proposed NASA X-Ray telescope flight mission aimed at achieving state-of-the-art angular and energy resolution with a 100 kilopixel array to probe the hot energetic young universe in unprecedented detail. To achieve these goals, our team plans on leveraging our current work in development of the focal plane for the Athena X-Ray Integral Field Unit (X-IFU) while advancing the state-of-the-art in transition edge sensor (TES) X-ray detector technology. The TES is an optimal technology for achieving both high energy and fine angular resolution at the same time because pixel features can be made extremely small and the absorber which dominates the heat capacity can be tuned to meet resolution requirements. Specifically, the proposed mission concept calls for a hybrid detector of three different arrays fabricated in the same planar process in one focal plane and optimized for different science goals. The main arrays consist of 5x5 hydras, 25 pixels of 4 micron thick Au absorbers each with a different thermal link to one common TES. The outer array has absorbers on a 50-micron pitch for most of the 5 arc-minute field-of-view, and the inner array has 25-micron absorbers for the central 1 arc-minute region. A high resolution array consisting of single pixel 1 micron thick Au absorbers on 50-micron pitch will lie off to the side. Reading out an array of this magnitude will likely require improvements in indium bump bonding to superconducting flexible wiring. Fabrication of absorbers of two different sizes requires electroplating through a photoresist mold by careful tuning of the current density to achieve uniform flat absorbers on a fine pitch scale, followed by ion milling to yield narrow streets separating the pixels while preserving high quantum efficiency. We report on progress made at fabricating the hybrid array with different absorber sizes and thicknesses. Further, we also report on ongoing work to adequately heat sink the pixels with backside wire bonding and copper coating. We also report on work to improve detector pixel yield and top side indium bump bonding to flexible wiring.

Focal plane array↗
NASA NTRS2008

Instrument Performance of GISMO, a 2 Millimeter TES Bolometer Camera used at the IRAM 30 m Telescope

In November of 2007 we demonstrated a monolithic Backshort-Under-Grid (BUG) 8x16 array in the field using our 2 mm wavelength imager GISMO (Goddard IRAM Superconducting 2 Millimeter Observer) at the IRAM 30 m telescope in Spain for astronomical observations. The 2 mm spectral range provides a unique terrestrial window enabling ground-based observations of the earliest active dusty galaxies in the universe and thereby allowing a better constraint on the star formation rate in these objects. The optical design incorporates a 100 mm diameter silicon lens cooled to 4 K, which provides the required fast beam yielding 0.9 lambda/D pixels. With this spatial sampling, GISMO will be very efficient at detecting sources serendipitously in large sky surveys, while the capability for diffraction limited imaging is preserved. The camera provides significantly greater detection sensitivity and mapping speed at this wavelength than has previously been possible. The instrument will fill in the spectral energy distribution of high redshift galaxies at the Rayleigh-Jeans part of the dust emission spectrum, even at the highest redshifts. Here1 will we present early results from our observing run with the first fielded BUG bolometer array. We have developed key technologies to enable highly versatile, kilopixel, infrared through millimeter wavelength bolometer arrays. The Backshort-Under-Grid (BUG) array consists of three components: 1) a transition-edge-sensor (TES) based bolometer array with background-limited sensitivity and high filling factor, 2) a quarter-wave reflective backshort grid providing high optical efficiency, and 3) a superconducting bump-bonded large format Superconducting Quantum Interference Device (SQUID) multiplexer readout. The array is described in more detail elsewhere (Allen et al., this conference). In November of 2007 we demonstrated a monolithic 8x 16 array with 2 mm-pitch detectors in the field using our 2 mm wavelength imager GISMO (Goddard IRAM Superconducting 2 Millimeter Observer) at the IRAM 30 m telescope in Spain for astronomical observations. The 2 mm spectral range provides a unique terrestrial window enabling ground-based observations of the earliest active dusty galaxies in the universe and thereby allowing a better constraint on the star formation rate in these objects. The optical design incorporates a 100 mm diameter silicon lens cooled to 4 K, which provides the required fast beam yielding 0.9 lambda1D pixels. With this spatial sampling, GISMO will be very efficient at detecting sources serendipitously in large sky surveys, while the capability for diffraction limited imaging is preserved. The camera provides significantly greater detection sensitivity and mapping speed at this wavelength than has previously been possible. The instrument will fill in the spectral energy distribution of high redshift galaxies at the Rayleigh-Jeans part of the dust emission spectrum, even at the highest redshifts. Here I will we present early results from our observing run with the first fielded BUG bolometer array.

Staguhn, Johannes↗
NASA NTRS1989

Hybrid Infrared Imager

Experimental device has low noise and high uniformity. Infrared imaging device combines array of InSb photodetectors with array of silicon field-effect-transistor switches. InSb chip forms roof over Si chip, each InSb detector cell engaging indium bump on corresponding Si switch cell below it. FET switches in 128-by-128 array turn on in sequence, read out charges on 128-by-128 array of photodetectors and multiplex them in serial output that represents pattern of light on array of photodetectors. Useful in sensitive infrared cameras for astronomy, medicine, inspection, and military surveillance. Reads out image data at rates up to 10 MHz and expands to 256-by-256 array.

Bailey, Gary C.↗
NASA NTRS1995

Solid-state image sensor with focal-plane digital photon-counting pixel array

A photosensitive layer such as a-Si for a UV/visible wavelength band is provided for low light level imaging with at least a separate CMOS amplifier directly connected to each PIN photodetector diode to provide a focal-plane array of NxN pixels, and preferably a separate photon-counting CMOS circuit directly connected to each CMOS amplifier, although one row of counters may be time shared for reading out the photon flux rate of each diode in the array, together with a buffer memory for storing all rows of the NxN image frame before transfer to suitable storage. All CMOS circuitry is preferably fabricated in the same silicon layer as the PIN photodetector diode for a monolithic structure, but when the wavelength band of interest requires photosensitive material different from silicon, the focal-plane array may be fabricated separately on a different semiconductor layer bump-bonded or otherwise bonded for a virtually monolithic structure with one free terminal of each diode directly connected to the input terminal of its CMOS amplifier and digital counter for integration of the photon flux rate at each photodetector of the array.

Fossum, Eric R.↗
NASA NTRS1987

IRAC test report. Gallium doped silicon band 2: Read noise and dark current

A direct readout infrared detector array, a candidate for the Space Infrared Telescope Facility (SIRTF) Infrared Array Camera (IRAC), has been tested. The array has a detector surface of gallium doped silicon, bump bonded to a 58x62 pixel MOSFET multiplexer on a separate chip. Although this chip and system do not meet all the SIRTF requirements, the critically important read noise is within a factor of 3 of the requirement. Significant accomplishments of this study include: (1) development of a low noise correlated double sampling readout system with a readout noise of 127 to 164 electrons (based on the detector integrator capacitance of 0.1 pF); (2) measurement of the readout noise of the detector itself, ranging from 123 to 214 electrons with bias only (best to worst pixel), and 256 to 424 electrons with full clocking in normal operation at 5.4 K where dark current is small. Thirty percent smaller read noises are obtained at a temperature of 15K; (3) measurement of the detector response versus integration time, showing significant nonlinear behavior for large signals, well below the saturation level; and (4) development of a custom computer interface and suitable software for collection, analysis and display of data.

Lamb, Gerald↗
NASA NTRS1991

Gallium arsenide quantum well-based far infrared array radiometric imager

We have built an array-based camera (FIRARI) for thermal imaging (lambda = 8 to 12 microns). FIRARI uses a square format 128 by 128 element array of aluminum gallium arsenide quantum well detectors that are indium bump bonded to a high capacity silicon multiplexer. The quantum well detectors offer good responsivity along with high response and noise uniformity, resulting in excellent thermal images without compensation for variation in pixel response. A noise equivalent temperature difference of 0.02 K at a scene temperature of 290 K was achieved with the array operating at 60 K. FIRARI demonstrated that AlGaAS quantum well detector technology can provide large format arrays with performance superior to mercury cadmium telluride at far less cost.

Forrest, Kathrine A.↗
NASA NTRS2005

Hybrid UV Imager Containing Face-Up AlGaN/GaN Photodiodes

A proposed hybrid ultraviolet (UV) image sensor would comprise a planar membrane array of face-up AlGaN/GaN photodiodes integrated with a complementary metal oxide/semiconductor (CMOS) readout-circuit chip. Each pixel in the hybrid image sensor would contain a UV photodiode on the AlGaN/GaN membrane, metal oxide/semiconductor field-effect transistor (MOSFET) readout circuitry on the CMOS chip underneath the photodiode, and a metal via connection between the photodiode and the readout circuitry (see figure). The proposed sensor design would offer all the advantages of comparable prior CMOS active-pixel sensors and AlGaN UV detectors while overcoming some of the limitations of prior (AlGaN/sapphire)/CMOS hybrid image sensors that have been designed and fabricated according to the methodology of flip-chip integration. AlGaN is a nearly ideal UV-detector material because its bandgap is wide and adjustable and it offers the potential to attain extremely low dark current. Integration of AlGaN with CMOS is necessary because at present there are no practical means of realizing readout circuitry in the AlGaN/GaN material system, whereas the means of realizing readout circuitry in CMOS are well established. In one variant of the flip-chip approach to integration, an AlGaN chip on a sapphire substrate is inverted (flipped) and then bump-bonded to a CMOS readout circuit chip; this variant results in poor quantum efficiency. In another variant of the flip-chip approach, an AlGaN chip on a crystalline AlN substrate would be bonded to a CMOS readout circuit chip; this variant is expected to result in narrow spectral response, which would be undesirable in many applications. Two other major disadvantages of flip-chip integration are large pixel size (a consequence of the need to devote sufficient area to each bump bond) and severe restriction on the photodetector structure. The membrane array of AlGaN/GaN photodiodes and the CMOS readout circuit for the proposed image sensor would be fabricated separately.

Zheng, Xinyu↗
NASA NTRS2009

Silicon Wafer-Scale Substrate for Microshutters and Detector Arrays

The silicon substrate carrier was created so that a large-area array (in this case 62,000+ elements of a microshutter array) and a variety of discrete passive and active devices could be mounted on a single board, similar to a printed circuit board. However, the density and number of interconnects far exceeds the capabilities of printed circuit board technology. To overcome this hurdle, a method was developed to fabricate this carrier out of silicon and implement silicon integrated circuit (IC) technology. This method achieves a large number of high-density metal interconnects; a 100-percent yield over a 6-in. (approximately equal to 15-cm) diameter wafer (one unit per wafer); a rigid, thermally compatible structure (all components and operating conditions) to cryogenic temperatures; re-workability and component replaceability, if required; and the ability to precisely cut large-area holes through the substrate. A method that would employ indium bump technology along with wafer-scale integration onto a silicon carrier was also developed. By establishing a silicon-based version of a printed circuit board, the objectives could be met with one solution. The silicon substrate would be 2 mm thick to survive the environmental loads of a launch. More than 2,300 metal traces and over 1,500 individual wire bonds are required. To mate the microshutter array to the silicon substrate, more than 10,000 indium bumps are required. A window was cut in the substrate to allow the light signal to pass through the substrate and reach the microshutter array. The substrate was also the receptacle for multiple unpackaged IC die wire-bonded directly to the substrate (thus conserving space over conventionally packaged die). Unique features of this technology include the implementation of a 2-mmthick silicon wafer to withstand extreme mechanical loads (from a rocket launch); integrated polysilicon resistor heaters directly on the substrate; the precise formation of an open aperture (approximately equal to 3x3cm) without any crack propagation; implementation of IR transmission blocking techniques; and compatibility with indium bump bonding. Although designed for the microshutter arrays for the NIRSpec instrument on the James Webb Space Telescope, these substrates can be linked to microshutter applications in the photomask generation and stepper equipment used to make ICs and microelectromechanical system (MEMS) devices.

Jhabvala, Murzy↗
NASA NTRSDate not supplied

Characterizations of Optimized Microshutter Arrays for Space Borne Observatory Applications

We report the latest design, fabrication, and characterization result of the Next-Generation Microshutter Arrays (NGMSA) for space borne observatory applications. Our improved blade design aims to reduce the counter torque induced by the potential on the opposing wall to eliminate the torque bump, and thus enables pure electrostatic actuation for more reliable and stable microshutter operations. This paper presents the experimental performances of micro-fabricated microshutter arrays with varying design parameters and compares the results with simulation predictions.

Electrostatic↗
NASA NTRS1992

Real-time processor for staring receivers

The design, fabrication, and testing of a state-of-the-art, high-throughput on-focal plane IR-image signal processor is described. The processing functions performed are frame differencing and thresholding. The final focal plane array will consist of a 128 x 128-pixel platinum-silicide detector bump-mounted to an on-chip CCD multiplexer. The processor is in a 128-channel parallel-pipeline format. Each channel consists of a pixel regenerator (charge differencer), 128-pixel frame store CCD memory, pixel differencer, second pixel regenerator, thresholder (analog comparator), and digital latch. Four parallel analog outputs and four parallel digital outputs are included. The digital outputs provide a bit map of the image. All analog clock signals (128 KHz, 256 KHz, and 5 MHz) are generated by on-chip TTL-input clock drivers. TTL clock driver inputs are generated off-chip. The technology is low-temperature surface and buried channel CCD/CMOS/indium bump. The design goal was 8-bit resolution at 77 K and 1000 frames/s. Applications include point- or extended-target motion detection with thresholding. Design trade-offs and enhancements (such as on-chip detector gain compensation and a simple window processor) are discussed.

Hanzal, Brian↗
NASA NTRS1992

An Analog Processor for Image Compression

This paper describes a novel analog Vector Array Processor (VAP) that was designed for use in real-time and ultra-low power image compression applications. This custom CMOS processor is based architectually on the Vector Quantization (VQ) algorithm in image coding, and the hardware implementation fully exploits the inherent parallelism built-in the VQ algorithm.

Vector Array Processor VAP analog processor image ↗
NASA NTRS2007

Indium Hybridization of Large Format TES Bolometer Arrays to Readout Multiplexers for Far-Infrared Astronomy

The advance of new detector technologies combined with enhanced fabrication methods has resulted in an increase in development of large format arrays. The next generation of scientific instruments will utilize detectors containing hundreds to thousands of elements providing a more efficient means to conduct large area sky surveys. Some notable detectors include a 32x32 x-ray microcalorimeter for Constellation-X, an infrared bolometer called SAFIRE to fly on the airborne observatory SOFIA, and the sub-millimeter bolometer SCUBA-2 to be deployed at the JCMT which will use more than 10,000 elements for two colors, each color using four 32x40 arrays. Of these detectors, SCUBA-2 is farthest along in development and uses indium hybridization to multiplexers for readout of the large number of elements, a technology that will be required to enable the next generation of large format arrays. Our current efforts in working toward large format arrays have produced GISMO, the Goddard IRAM Superconducting 2-Millimeter observer. GISMO is a far infrared instrument to be field tested later this year at the IRAM 30 meter telescope in Spain. GISMO utilizes transition edge sensor (TES) technology in an 8x16 filled array format that allows for typical fan-out wiring and wire-bonding to four 1x32 NIST multiplexers. GISMO'S electrical wiring is routed along the tops of 30 micron walls which also serve as the mechanical framework for the array. This architecture works well for the 128 element array, but is approaching the limit for routing the necessary wires along the surface while maintaining a high fill factor. Larger format arrays will benefit greatly from making electrical connections through the wafer to the backside, where they can be hybridized to a read-out substrate tailored to handling the wiring scheme. The next generation array we are developing is a 32x40 element array on a pitch of 1135 microns that conforms to the NIST multiplexer, already developed for the SCUBA-2 instrument This architecture will utilize electrical connections that route from the TES to the support frame and through the wafer. The detector chip will then be hybridized to the NIST multiplexer via indium bump bonding. In our development scheme we are using substrates that allow for diagnostic testing of electrical continuity across the entire array and we are testing our process to minimize or eliminate any contact resistance at metal interfaces. Our goal is hybridizing a fully functional 32x40 array of TES bolometers to a NIST multiplexer. The following work presents our current progress toward enabling this technology.

Miller, Timothy M.↗
NASA NTRS2007

Array of Bolometers for Submillimeter- Wavelength Operation

A feed-horn-coupled monolithic array of micromesh bolometers is undergoing development for use in a photometric camera. The array is designed for conducting astrophysical observations in a wavelength band centered at 350 m. The bolometers are improved versions of previously developed bolometers comprising metalized Si3N4 micromesh radiation absorbers coupled with neutron- transmutation-doped Ge thermistors. Incident radiation heats the absorbers above a base temperature, changing the electrical resistance of each thermistor. In the present array of improved bolometers (see figure), the thermistors are attached to the micromesh absorbers by indium bump bonds and are addressed by use of lithographed, vapor-deposited electrical leads. This architecture reduces the heat capacity and minimizes the thermal conductivity to 1/20 and 1/300, respectively, of earlier versions of these detectors, with consequent improvement in sensitivity and speed of response. The micromesh bolometers, intended to operate under an optical background set by thermal emission from an ambient-temperature space-borne telescope, are designed such that the random arrival of photons ("photon noise") dominates the noise sources arising from the detector and readout electronics. The micromesh is designed to be a highly thermally and optically efficient absorber with a limiting response time of about 100 s. The absorber and thermistor heat capacity are minimized in order to give rapid speed of response. Due to the minimization of the absorber volume, the dominant source of heat capacity arises from the thermistor.

Bock, James↗
NASA NTRS2011

Programmable Aperture with MEMS Microshutter Arrays

A microshutter array (MSA) has been developed for use as an aperture array for multi-object selections in James Webb Space Telescope (JWST) technology. Light shields, molybdenum nitride (MoN) coating on shutters, and aluminum/aluminum oxide coatings on interior walls are put on each shutter for light leak prevention, and to enhance optical contrast. Individual shutters are patterned with a torsion flexure that permits shutters to open 90 deg. with a minimized mechanical stress concentration. The shutters are actuated magnetically, latched, and addressed electrostatically. Also, micromechanical features are tailored onto individual shutters to prevent stiction. An individual shutter consists of a torsion hinge, a shutter blade, a front electrode that is coated on the shutter blade, a backside electrode that is coated on the interior walls, and a magnetic cobalt-iron coating. The magnetic coating is patterned into stripes on microshutters so that shutters can respond to an external magnetic field for the magnetic actuation. A set of column electrodes is placed on top of shutters, and a set of row electrodes on sidewalls is underneath the shutters so that they can be electrostatically latched open. A linear permanent magnet is aligned with the shutter rows and is positioned above a flipped upside-down array, and sweeps across the array in a direction parallel to shutter columns. As the magnet sweeps across the array, sequential rows of shutters are rotated from their natural horizontal orientation to a vertical open position, where they approach vertical electrodes on the sidewalls. When the electrodes are biased with a sufficient electrostatic force to overcome the mechanical restoring force of torsion bars, shutters remain latched to vertical electrodes in their open state. When the bias is removed, or is insufficient, the shutters return to their horizontal, closed positions. To release a shutter, both the electrode on the shutter and the one on the back wall where the shutter sits are grounded. The shutters with one or both ungrounded electrodes are held open. Sub-micron bumps underneath light shields and silicon ribs on back walls are the two features to prevent stiction. These features ensure that the microshutter array functions properly in mechanical motions. The MSA technology can be used primarily in multi-object imaging and spectroscopy, photomask generation, light switches, and in the stepper equipment used to make integrated circuits and MEMS (microelectromechanical systems) devices.

Moseley, Samuel↗
NASA NTRS1994

Reconfigurable Full-Page Braille Displays

Electrically actuated braille display cells of proposed type arrayed together to form full-page braille displays. Like other braille display cells, these provide changeable patterns of bumps driven by digitally recorded text stored on magnetic tapes or in solid-state electronic memories. Proposed cells contain electrorheological fluid. Viscosity of such fluid increases in strong electrostatic field.

Garner, H. Douglas↗