When we talk about planetary exploration missions most people think spontaneously about fascinating images from other planets or close-up pictures of small planetary bodies such as asteroids and comets. Such images come in most cases from VIS/NIR- imaging- systems, simply called ‘cameras’, which were typically built by institutes in collaboration with industry. Until now, they have nearly all been based on silicon CCD sensors, they have filter wheels and have often high power-consuming electronics.
The question is, what are the challenges for future missions and what can be done to improve performance and scientific output. The exploration of Mars is ongoing. NASA and ESA are planning future missions to the outer planets like to the icy Jovian moons. Exploration of asteroids and comets are in focus of several recent and future missions. Furthermore, the detection and characterization of exo-planets will keep us busy for next generations.
The paper is discussing the challenges and visions of imaging sensors for future planetary exploration missions. The focus of the talk is monolithic VIS/NIR- detectors.
The One Degree Imager (ODI) was deployed during the summer of 2012 at the WIYN 3.5m telescope, located on Kitt Peak near Tucson, AZ (USA). ODI is an optical imager designed to deliver atmosphere-limited image quality (≤ 0.4” FWHM) over a one degree field of view, and uses Orthogonal Transfer Array (OTA) detectors to also allow for on-chip tip/tilt image motion compensation. At this time, the focal plane is partially populated (”pODI”) with 13 out of 64 OTA detectors, providing a central scientifically usable field of view of about 24′ x 24′; four of the thirteen detectors are installed at outlying positions to probe image quality at all field angles. The image quality has been verified to be indeed better than 0.4′′ FWHM over the full field when atmospheric conditions allow. Based on over one year of operations, we summarize pODIs performance and lessons learned. As pODI has proven the viability of the ODI instrument, the WIYN consortium is engaging in an upgrade project to add 12 more detectors to the focal plane enlarging the scientifically usable field of view to about 40′ x 40′. A design change in the new detectors has successfully addressed a low light level charge transfer inefficiency.
The Geostationary Lightning Mapper (GLM) instrument selected to fly on the National Oceanic and Atmospheric
Administration (NOAA) GOES-R Series environmental satellites has very unique requirements as compared to an
imaging array. GLM's requirements to monitor lightning on a continental scale will provide new insight into the
formation, distribution, morphology and evolution of storms.
A 500 frame per second backside illuminated frame transfer CCD imager (STA3900A) with variable pixel size has
been developed to meet these requirements. A variable pixel architecture provides a near uniform mapping of the curved
surface of the earth, while 56 outputs running at 20 MHz yield greater than a 1.1 Gigapixel per second data rate with low
RMS noise and high MTF. This paper will provide detailed information on design trades required. We will report CCD
read noise, dark current, full well capacity, and quantum efficiency (QE).
The demand from the astronomical community for high resolution low noise CCDs has led to the development of the
STA1600LN, a 10560 × 10560 pixel, 95mm × 95mm, full-frame CCD imager with 9×9 μ2 pixels. The device
improvements include noise reduction to below 3ē at 100kHz, improved quantum efficiency, as well as packaging
developments for improved fill factor in mosaic systems. We provide test results from production devices, along with
updates on scientific systems utilizing the STA1600 for astronomy.
The WIYN One Degree Imager (ODI) will provide a one degree field of view for the WIYN 3.5 m telescope located on
Kitt Peak near Tucson, Arizona. Its focal plane consists of an 8x8 grid of Orthogonal Transfer Array (OTA) CCD
detectors. These detectors are the STA2200 OTA CCDs designed and fabricated by Semiconductor Technology
Associates, Inc. and backside processed at the University of Arizona Imaging Technology Laboratory. Several lot runs
of the STA2200 detectors have been fabricated. We have backside processed devices from these different lots and
provide detector performance characterization, including noise, CTE, cosmetics, quantum efficiency, and some
orthogonal transfer characteristics. We discuss the performance differences for the devices with different silicon
thickness and resistivity. A fully buttable custom detector package has been developed for this project which allows
hybridization of the silicon detectors directly onto an aluminum nitride substrate with an embedded pin grid array. This
package is mounted on a silicon-aluminum alloy which provides a flat imaging surface of less than 20 microns peakvalley
at the -100 C operating temperature. Characterization of the package performance, including low temperature
profilometry, is described in this paper.
A 52-M pixel, 71mm x 54mm, full-frame CCD imager with 8.6 um x 8.6 um pixel size has been
developed for use in high speed scanning applications. On-going interest for ultra-high resolution, high
speed imagers for electronic imaging OEM customers in various scientific markets including spectroscopy
and digital photography has led to the development of the STA2500A. Innovative design techniques were
utilized in the production of this device. 32 outputs running at 40 Mhz yield a 20Hz frame rate with low
RMS noise and high MTF. This paper will provide detailed information on design trades developed for
high-speed imagers leading to the design and performance capabilities of the STA2500A, as well as a
description of the electronics required for its use.
The WIYN One Degree Imager (ODI) will provide a one degree field of view for the WIYN 3.5 m telescope located on Kitt Peak near Tucson, Arizona. Its focal plane will consist of an 8x8 grid of Orthogonal Transfer Array (OTA) CCD detectors with nearly one billion pixels. The implementation of these detectors into the focal plane has required the development of several novel packaging and characterization techniques, which are the subject of this paper. We describe a new packaging/hybridization method in which the CCD die are directly bonded to aluminum nitride ceramic substrates which have indium bump on one side and brazed pins on the other. These custom packages allow good thermal conductivity, a flat imaging surface, four side buttability, and in situ testing of the devices during backside processing. We describe these carriers and the backside processing techniques used with them. We have also modified our cold probing system to screen these OTA die at wafer level to select the best candidates for backside processing. We describe these modifications and characterization results from several wafer lots.
A full-wafer, 10,580 × 10,560 pixel (95 × 95 mm) CCD was designed and tested at Semiconductor Technology
Associates (STA) with 9 μm square pixels and 16 outputs. The chip was successfully fabricated in 2006 at DALSA
and some performance results are presented here. This program was funded by the Office of Naval Research
through a Small Business Innovation in Research (SBIR) program requested by the U.S. Naval Observatory for
its next generation astrometric sky survey programs. Using Leach electronics, low read-noise output of the 111
million pixels requires 16 seconds at 0.9 MHz. Alternative electronics developed at STA allow readout at 20
MHz. Some modifications of the design to include anti-blooming features, a larger number of outputs, and use
of p-channel material for space applications are discussed.
A 111-Mega pixel, 92x92 mm2, full-frame CCD imager with 9x9 um2 pixel size has been developed for use in scientific
applications. Recent interest for ultra-high resolution imagers for electronic imaging OEM customers in various
scientific markets, including biotechnology, microscopy, crystallography, astronomy, spectroscopy, and aerial
reconnaissance markets has lead to the development of the STA1600A 111-Mega pixel monochromatic charge-coupled
device. Innovative design techniques were utilized in the early development of this device, yielding low RMS noise and
high MTF for readout speeds ranging from 1 Mpixel/s to 25 Mpixel/sec. This paper will provide detailed information on
the design and performance capabilities of the STA1600A, as well as background information on the commercial uses of
this device.
Due to aggressive scientific specifications, Semiconductor Technology Associates and
the University of Arizona's Imaging Technology Laboratory have collaborated to
develop a fully depleted back illuminated CCD for scientific imaging. These devices are
designed to target increased quantum efficiency into the near-infrared, without reduction
in the modulation transfer function, charge transfer efficiency, or rms noise. The
STA1700 series imagers are back illuminated 100 micron thick devices with a 10 micron
pixel pitch targeted to meet the requirements of the Large Synoptic Survey Telescope
(LSST). Recent characterization results will be presented including the point spread
function of a 2 micron spot. Also discussed will be the thinning and packaging
developments for the STA1700. These efforts include the addition of a backside bias
contact, invar package design with high density connectors, as well as etching and
backside coating optimization for high resistivity silicon.
A 111-Mega pixel, 92×92 mm2, full-frame CCD imager with 9×9 um2 pixel size has been developed for use in scientific
applications. Recent interest for ultra-high resolution imagers for electronic imaging OEM customers in various
scientific markets, including biotechnology, microscopy, crystallography, astronomy, spectroscopy, and digital
photography markets has lead to the development of the STA1600A 111-Mega pixel monochromatic charge-coupled
device. Innovative design techniques were utilized in the early development of this device, yielding low RMS noise and
high MTF for readout speeds ranging from 1 Mpixel/s to 10 Mpixel/sec. This paper will provide detailed information on
the design and performance capabilities of the STA1600A, as well as background information on the commercial uses of
this device.
A 111-Mega pixel, 92x92 mm2, full-frame CCD imager with 9x9 um2 pixel size has been developed for use in scientific
applications. Recent interest for ultra-high resolution imagers for electronic imaging OEM customers in various
scientific markets, including biotechnology, microscopy, crystallography, astronomy, spectroscopy, and digital
photography markets has lead to the development of the STA1600A 111-Mega pixel monochromatic charge-coupled
device. Innovative design techniques were utilized in the early development of this device, yielding low RMS noise and
high MTF for readout speeds ranging from 1 Mpixel/s to 10 Mpixel/sec. This paper will provide detailed information on
the design and performance capabilities of the STA1600A, as well as background information on the commercial uses of
this device.
Recent discoveries show new promise for a formerly assumed extinct technology, CCDs. A primary limitation to the implementation of new ground-based astronomy measurement techniques is the inaccuracy of navigation and targeting due to error in the celestial frame of reference. This celestial frame of reference is relied upon for satellite attitude determination, payload calibration, in-course missile adjustments, space surveillance, and accurate star positions used as fiducial points. STA will describe the development of an ultrahigh resolution CCD (up to the maximum limit of a 150 mm wafer) that integrates high dynamic range and fast readout that will substantially decrease the error in the celestial reference frame. STA will also discuss prior and ongoing experience with large area CCD focal-plane arrays which include innovative design and fabrication techniques that ensure performance and yield.
There is little doubt that the Hubble Space Telescope is one of the most important astronomical instruments of the late 20th and early 21st centuries. Spectacular imagery has been sent back to earth-bound observers leading to a much greater understanding and appreciation of the universe around us. Much of this ability to image has been due to an extraordinary detector: the charge-coupled device (CCD). The intent of this paper is to review the history of the CCDs that have been employed on Hubble and consider some of the lessons learned.
The orthogonal-transfer array (OTA) is a new CCD architecture designed to provide wide-field tip-tilt correction of astronomical images. The device consists of an 8x8 array of small (~500x500 pixels) orthogonal-transfer CCDs (OTCCD) with independent addressing and readout of each OTCCD. This approach enables an optimum tip-tilt correction to be applied independently to each OTCCD across the focal plane. The first design of this device has been carried out at MIT Lincoln Laboratory in support of the Pan-STARRS program with a collaborative parallel effort at Semiconductor Technology Associates (STA) for the WIYN Observatory. The two versions of this device are functionally compatible and share a common pinout and package. The first wafer lots are complete at Lincoln and at Dalsa and are undergoing wafer probing.
The Stratospheric Aerosol and Gas Experiment (SAGE) III requires a detector that provides spectral coverage from 280 - 1050 nm. In order to achieve higher responsivity at the ultra-violet wavelengths a backside-thinned silicon CCD technology was chosen. For strength, the backside-thinned detector was bonded to a soda glass substrate. The device thinness allowed the long near infrared wavelengths to pass through the silicon, scatter off the soda glass, and cause cross talk into nearby pixels. Reflections from the soda glass caused etalon-like effects and gave the thinned CCD a highly temperature dependent response. These difficulties led the project manager to examine different options for a replacement detector. Photodiode/CCD technology based on the Moderate- Resolution Imaging Spectrometer-Tilt (MODIS-T) and Gas and Aerosol Monitoring Sensorcraft (GAMS) detectors systems was combined and used to design and fabricate a backup detector for the SAGE III program. The device design and characterization are presented. The design focused on elimination of the scattering due to the soda glass and the temperature dependent etalon effect, increasing charge storage capacity. The detector was designed to allow a retrofit with the existing SAGE III spectrometer. The primary disadvantage of the new detector is its loss of responsivity at the shorter wavelengths.
We describe the design of an ultra-format, 8192 x 8192 pixel CCD mosaic imager under construction for the Mauna Kea Observatory. The mosaic will be built from a 4 x 2 array of 3-edge-buttable 2048 x 4096 15 micrometers pixel CCDs fabricated by Loral Fairchild. We outline the scientific justification for such a mosaic and the technical details of the 3-edge-buttable 2048 x 4096 CCD design. We also present our strategy for imager packaging and subsequent mosaic construction which will result in a mosaic with individual elements that can easily be installed and removed. This particular CCD mosaic is intended for two existing MKO telescopes: the UH 2.2 m and the CFHT 3.6m. In either configuration, the imager will offer an enormous field of view with excellent spatial sampling.
While large area scientific CCD imagers have high resolution and sensitivity in the visible region, the UV and near IR wavelength regions typically have a decreased response. Therefore, modified designs and advanced techniques are used to broaden the range for high quantum efficiency. For the UV band, deposition of a very thin polysilicon gate allows transmittance of shorter wavelength photons, and frontside coating a completed device with lumogen absorbs lower wavelength photons and re-emits them near the peak sensitivity of the CCD. For the near IR band, high-resisitivity, thick epitaxial material is used for collection of longer wavelength photons. Overall broad spectral band QE is enhanced with backside thinning and antireflective coatings of various dielectric layers. QE has been predicted by calculating the transmission, reflection, and absorption over a cross section of the CCD. Data is presented to confirm the QE increase from 120 to 1000 nm. Design and fabrication are discussed for each improvement technique, as well as trade-offs in cost, device performance, and yield.
We are demonstrating a high-speed video camera and recorder system that captures 8-bit image data at 500 frames per second and stores 500 frames of 640 x 480 pixel image data in solid-state digital memory. The base configuration contains 160 MBytes of dynamic RAM and can be expanded to 2.5 GBytes for 8000 frames of storage. The camcorder synthesizes an RS-170 output from the digital store. This standard video output can drive a monitor for viewing or drive a video cassette recorder for archiving the stored event. The camcorder is designed for enhancement to 2000 frames per second.
A large-format CCD imager to be used in a 2 X 2 mosaic array has been designed and fabricated. Each quadrant is an independent imager of 2048 X 2048 15 micrometers pixels, designed to be edge-butted on two sides. After sawing and mounting the individual dice in custom, buttable packages, the authors assembled a 4096 X 4096 mosaic array measuring more than 61 mm on a side with just 400 microns dead space between imaging areas. With this buttable package design, each quadrant of the mosaic can be separately tested, optimized, and, if necessary, replaced. Also described are smaller 2688 X 512 15 micrometers pixel CCD imagers designed for spectrographic applications that were fabricated using space in the chords of the same 100 mm silicon wafer containing the 2048 X 2048 edge-buttable devices.
A technique for improving the performance oflarge area high resolution Charge-Coupled Device (CCD) imagers will be described. Adding an additional doped channel down the center of a CCD register provides for charge confinement. This leads to improved charge transfer efficiency and resistance to radiation damage. Two dimenslonal theoretical analysis will be shown along with measured device performance.
A large-format CCD imager is described and tested. The CCD imager incorporates floating diffusion as well as floating gate amplifiers on a 2048 by 2048 format which was employed as the design base. The amplifiers are intended to allow repeated nondestructive read operations on individual pixels in the array. The serial register was separated into two independently clocked halves to permit simultaneous readout of all four quadrants of the imager. Extensive schematic layouts of the base model and modification are given. The results of a performance test are presented, showing good results in the cooling curve for average dark current, and for charge transfer characteristics. The amplifiers are intended to reduce net readout noise, and the simultaneous readout capability is intended to reduce total read time, although neither was fully tested. The large-format CCD imager is of interest for astronomical photography and spectroscopic applications.
A charge coupled device designed for celestial spectroscopy has achieved readout noise as low as 0.6 electrons rms. A nondestructive output circuit was operated in a special manner to read a single pixel multiple times. Off-chip electronics averaged the multiple values, reducing the random noise by the square root of the number of readouts. Charge capacity was measured to be 500,000 electrons. The device format is 1600 pixels horizontal by 64 pixels vertical. Pixel size is 28 microns square. Two output circuits are located at opposite ends of the 1600 bit CCD register. The device was thinned and operated backside illuminated at -110 degrees C. Output circuit design, layout, and operation are described. Presented data includes the photon transfer curve, noise histograms, and bar-target images down to 3 electrons signal. The test electronics are described, and future improvements are discussed.
This paper reports on two new advancements in CCD technology. The first area of development has produced a special purpose CCD designed for ultra low-signal level imaging and spectroscopy applications that require sub-electron read noise floors. A nondestructive output circuit operating near its 1/f noise regime is clocked in a special manner to read a single pixel multiple times. Off-chip electronics average the multiple values, reducing the random noise by the square-root of the number of samples taken. Noise floors below 0.5 electrons rms are reported. The second development involves the design and performance of a high resolution imager of 4096 x 4096 pixels, the largest CCD manufactured in terms of pixel count. The device utilizes a 7.5-micron pixel fabricated with three-level poly-silicon to achieve high yield.
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