Teledyne Imaging Sensors develops and produces high performance infrared sensors, electronics and packaging for
astronomy and civil space. These IR sensors are hybrid CMOS arrays, with HgCdTe used for light detection and a
silicon integrated circuit for signal readout. Teledyne manufactures IR sensors in a variety of sizes and formats.
Currently, the most advanced sensors are based on the Hawaii-2RG (H2RG), 2K×2K array with 18 μm pixel pitch. The
HgCdTe detector achieves very low dark current (<0.01 e-/pixel/sec) and high quantum efficiency (80-90%) over a wide
bandpass. Substrate-removed HgCdTe can simultaneously detect visible and infrared light, enabling spectrographs to
use a single focal plane array (FPA) for Visible-IR sensitivity. The SIDECARTM ASIC provides focal plane electronics
on a chip, operating in cryogenic environments with very low power (<11 mW). The H2RG and SIDECAR<sup>TM</sup> have been
qualified to NASA Technology Readiness Level 6 (TRL-6). Teledyne continues to advance the state-of-the-art and is
producing a high speed, low noise array designed for IR wavefront sensing. Teledyne is also developing a 4K×4K, 15
µm pixel infrared array that will be a cost effective module for the large focal planes of the Extremely Large Telescopes
and future generation space astronomy missions.
The Universe appears to be expanding at an accelerating rate, driven by a mechanism called Dark Energy. The nature of Dark Energy is largely unknown and needs to be derived from observation of its effects. JEDI (Joint Efficient Dark-energy Investigation) is a candidate implementation of the NASA-DOE Joint Dark Energy Mission (JDEM). It will probe the effects of Dark Energy in three independent ways: (1) using Type Ia supernovae as cosmological standard candles over a range of distances, (2) using baryon acoustic oscillations as a cosmological standard ruler over a range of cosmic epochs, and (3) mapping the weak gravitational lensing distortion by foreground galaxies of the images of background galaxies at different distances. JEDI provides crucial systematic error checks by simultaneously applying these three independent observational methods to derive the Dark Energy parameters. The concordance of the results from these methods will not only provide an unprecedented understanding of Dark Energy, but also indicate the reliability of such an understanding. JEDI will unravel the nature of Dark Energy by obtaining observations only possible from a vantage point in space, coupled with a unique instrument design and observational strategy. Using a 2 meter-class space telescope with simultaneous wide-field imaging (~ 1 deg<sup>2</sup>, 0.8 to 4.2 μm in five bands) and multi-slit spectroscopy (minimum wavelength coverage 1 to 2 μm), JEDI will efficiently execute the surveys needed to solve the mystery of Dark Energy.
Advancements in space and ground-based astronomy focal plane array (FPA) technology at Rockwell Scientific
Company (RSC) are presented. The review covers the broad base of astronomy work at RSC for both present and
next generation FPAs, and details recent achievements in detector, readout, and packaging technologies. RSC
astronomy FPA progress includes: RSC FPA delivery for NASA's successful Deep Impact mission, progress on
RSC's programs supplying H-2RG FPAs for James Webb Space Telescope (JWST) instruments JWST NIRCam,
NIRSpec and FGS; selection of RSC's SIDECAR Application Specific Integrated Circuit (ASIC) for use on JWST
instruments NIRCam, NIRSpec and FGS and the development of the JWST SIDECAR space flight package; first
silicon on the 16 million pixel HAWAII-4RG (4Kx4K); optimization of NIR FPAs for space telescope missions;
construction of multiple 16 million pixel 2x2 mosaic FPAs using the HAWAII-2RG readouts, and the development
of the Microlensing Planet Finder (MPF) very large, 150 million pixel FPA.
The demand for large-format near infrared arrays has grown for both ground-based and space-based applications. These arrays are required for maintaining high resolution over very large fields of view for survey work. We describe results of the development of a new 2048 × 2048 HgCdTe/CdZnTe array with 20-micron pixels that responds with high quantum efficiency over the wavelength range 0.85 to 2.5 microns. With a single-layer anti-reflection coating, the responsive quantum efficiency is greater than 70% from 0.9 micron to 2.4 microns. Dark current is typically less than 4 e-/sec at 80 K. The modular package for this array, dubbed the VIRGO array, allows 3-side butting to form larger mosaic arrays of 4K × 2nK format. The VIRGO ROIC utilizes a PMOS Source Follower per Detector input circuit with a well capacity of about 2 × 10<sup>5</sup> electrons and with a read noise of less than 20 e- rms with off-chip Correlated Double Sampling. Other features of the VIRGO array include 4 or 16 outputs (programmable), and a frame rate of up to 1.5 Hz in 16-output mode. Power dissipation is about 7 mW at a 1 Hz frame rate. Reset modes include both global reset and reset by row (ripple mode). Reference pixels are built-in to the output data stream. The first major application of the VIRGO array will be for VISTA, the United Kingdom’s Visible and Infrared Survey Telescope for Astronomy. The VISTA focal plane array will operate near 80 K. The cutoff wavelength of the HgCdTe detector can be adjusted for other applications such as SNAP, the Supernova/Acceleration Probe, which requires a shorter detector cutoff wavelength of about 1.7 microns. For applications which require both visible and near infrared response, the detector CdZnTe substrate can be removed after hybridization, allowing the thinned detector to respond to visible wavelengths as short as 0.4 microns.
The Navy faces an ever evolving threat scenario, ranging from sub-sonic sea skimming cruise missiles to newer, unconventional threats such as that experienced by the USS Cole. Next generation naval technology development programs are developing “stealthy” ships by reducing a ships radar cross section and controlling electromagnetic emissions. To meet these threat challenges in an evolving platform environment, ONR has initiated the “Wide Aspect MWIR Array” program. In support of this program, Raytheon Vision Systems (RVS) is developing a 2560 X 512 element focal plane array, utilizing Molecular Beam Epitaxially grown HgCdTe on silicon detector technology. RVS will package this array in a sealed Dewar with a long-life cryogenic cooler, electronics, on-gimbal power conditioning and a thermal reference source. The resulting sub system will be a component in a multi camera distributed aperture situation awareness sensor, which will provide continuous surveillance of the horizon. We will report on the utilization of MWIR Molecular Beam Epitaxial HgCdTe on Silicon material for fabrication of the detector arrays. Detector arrays fabricated on HgCdTe/Si have no thermal expansion mismatch relative to the readout integrated circuits. Therefore large-area focal plane arrays (FPAs) can be developed without concern for thermal cycle reliability. In addition these devices do not require thinning or reticulation like InSb FPAs to yield the high levels of Modulation Transfer Function (MTF) required by a missile warning sensor. HgCdTe/Si wafers can be scaled up to much larger sizes than the HgCdTe/CdZnTe wafers. Four-inch-diameter HgCdTe/Si wafers are currently being produced and are significantly larger than the standard 1.7 inch x 2.6 inch HgCdTe/CdTe wafers. The use of Si substrates also enables the use of automated semiconductor fabrication equipment.
The demand for large-format NIR arrays has grown for both ground-based and space-based applications. These arrays are required for maintaining high resolution over very large fields of view for survey work. We describe results of the development of a new 2048 x 2048 HgCdTe/CdZnTe array with 20-micron pixels that responds with high quantum efficiency over the wavelength range 0.85 to 2.5 microns. With a single-layer anti-reflection (AR) coating, the responsive quantum efficiency is expected to be greater than 85% from 0.9 micron to 2.4 microns. The modular package for this array, dubbed the VIRGO array, allows three-side butting to form large mosaic arrays of 4K x 2nK format. The VIRGO readout integrated circuit (ROIC) utilizes a Source Follower per Detector (SFD) input circuit with a well capacity of about 2 x 10<sup>5</sup> electrons and with a read noise of less than 20 e-rms with off-chip Correlated Double Sampling (CDS). Other features of the VIRGO array include 4 or 16 outputs (programmable), and a frame rate of up to 1.5 Hz in 16-output mode. Power dissipation is about 7 mW at a 1 Hz frame rate. Reset modes include both global
reset and reset by row (ripple mode). Reference pixels are built-in to the output data stream.
The first major application of the VIRGO array will be for VISTA, the United Kingdom’s Visible and Infrared Survey Telescope for Astronomy. The VISTA FPA will operate near 80K. Dark current is less than 0.1e-/sec at 80K. The cutoff wavelength of the HgCdTe detector can be adjusted for other applications. Space applications might include
SNAP, the Supernova/Acceleration Probe, which requires a shorter detector cutoff wavelength of about 1.7 microns. For applications which require both visible and NIR response, the detector CdZnTe substrate can be removed after hybridization, allowing the thinned detector to respond to visible wavelengths as short as 0.4 microns.
The desire for larger and larger format arrays for astronomical observatories -- both ground and space based -- has fueled the development of detector, readout, and hybrid Focal Plane Array (FPA) technology that has paved the way for later development of tactical and strategic arrays for military applications. Since 1994, Raytheon has produced megapixel readouts and FPAs for Infrared Astronomy. In 1999 Raytheon demonstrated a revolutionary approach to photolithography called Reticle Image Composition Lithography (RICL) that opened the door to very large format FPAs in state of the art sub-micron CMOS processes. The first readout processed using the patented RICL technique was a 4.2 megapixel readout for astronomy.
We present the design and performance of several 4.2 megapixel (2048 x 2048) readout arrays for visible and infrared astronomy applications. The first of these arrays are fabricated in a workhorse 2 μm CMOS process that is optimized for low temperature operation (down to as low as 6 Kelvin). Most recently Raytheon has developed a scaleable 2,048 x 2,048 high density array for several ground based astronomical applications. This array can be manufactured in any m x n multiple of a basic 1024 (V) x 512 (H) pixel array core. The primary design is a 2 x 4 array to yield a 2,048 x 2,048 format array. This same design can be extended to at least a 4,096 x 4,096 format array -- an incredible 16.7 megapixel array!
These readouts are compatible with a wide range of detector types including InSb, HgCdTe, and Si detectors. The use of hybrid technology -- even for the visible wavebands -- allows 100% optical fill factors to be achieved. The design and performance of these megapixel class detectors, readouts, and FPAs will be presented.
Proc. SPIE. 4028, Infrared Detectors and Focal Plane Arrays VI
KEYWORDS: Staring arrays, Readout integrated circuits, Spatial filters, Sensors, Signal processing, Analog electronics, Digital electronics, Signal detection, Filtering (signal processing), Standard readout integrated circuits
As 2nd and 3rd generation Focal Plane Arrays (FPA) become more complex, the readout integrated circuit (ROIC) has emerged as a major discriminator in system performance. The focus of development and advancement has traditionally involved the detector technology. Early ROICs were simple multiplexers that performed little if any signal processing on the detector diode signal. Advances in silicon fabrication processes for analog integrated circuits have opened a new era in IRFPAs where signal digital functions can be achieved on the focal plane. We present an overview of significant advances in the area of mixed mode ROIC designs that enable greater functionality and performance of the sensor chip assembly. Innovations, continuing progress in CMOS technology, and greater foundry access have allowed enhancements in practically every aspect of the ROIC, from sophisticated unit cells to lower noise and lower power signal paths to highly programmable digital support circuitry. Denser detector input circuits with active amplifiers (FEDI or CTIA) have been implemented in unit cells as small as 27 micrometer X 27 micrometer. In addition, multiple gain, temporal filtering, or spatial filtering capabilities have been incorporated into these small unit cells. Significant reductions in focal plane power have been fabricated and demonstrated enabling a factor of 2 increase in frame rates for very large staring FPAs and a factor of 4 increase in line rates for scanning FPAs. Other developments include, but are not limited to, alternative schemes for time-delayed integration (TDI) and breakthroughs for uncooled applications. As the chip designs increase in capability, greater systems on a chip are feasible, especially with more programmable features provided by the on-chip digital circuitry.
The development of the direct injection unit cell architecture with a direct readout has produced several varieties of high-performance large-area staring arrays. These arrays satisfy almost all foreseeable missile applications. The uniformity, noise, and linearity lend themselves to low-complexity, high-performance missile systems. These readout integrated circuits (ROICs) are demonstrated with InSb over a spectral band of 0.5 to 5.5 um with NE(Delta)T of 17 mK under ambient tactical and low-background space conditions. Hybridization of eighteen 128 x 128 ROICs with LWIR HgCdTe resulted in an average NE(Delta)T of 21 mK. The new EPIC substrates yielded high-performance 256 x 256 LWIR HgCdTe capable of withstanding 2000 thermal cycles. The simple interface requirements of the /ST ROIC coupled with the high yield and extremely high operability show promise for future low-cost commercial IR systems.
In the last two years, Hughes Aircraft Company and the Santa Barbara Research Center have demonstrated that LWIR PV HgCdTe staring focal plane arrays can be fabricated reproducibly with high performance and high yield. Record yields for detectors and readouts, in excess of 50%, have been achieved on 128 x 128 arrays with 40 x 40 gm pixels on 40 jam centers. Key to the successes are the development of p-on-n PV HgCdTe detector technology and high density CMOS readout circuitry. In 1988, Hughes Missile Systems Group established an inventory account whose goal was to fabricate 128 x 128 LWIR FPAs for a broad range of missile requirements. They range from high background tactical applications to low background SDI scenarios. The staring FPA chosen couples a high impedance p-on-n LWIR PV HgCdTe detector array to a CMOS high capacity direct injection readout array and is designated the DI-128. The detector arrays were fabricated with cutoff wavelengths ranging from 9.2 to 9.9 gm and with RoAo products ranging from 100 to 1000 S2-cm2. The excellent RoAo products allow a simple direct injection input circuit to be used while maintaining injection efficiencies in excess of 80% allowing near BLIP performance. The DI input circuit has a charge handling capacity in excess of 20 million carriers. A variable integration time capability is provided for dynamic range management and performance optimization. 39 LWIR HgCdTe FPAs have been fabricated by the inventory account to date with a yield of nearly 50 %. The arrays were tested at 77 Kelvin with an f/2.0 aperture at 295 Kelvin in the 8.0-9.0 gm spectral band resulting in a background flux of 6.0 x 1015 photons/cm2-sec. The array average NEAT achieved was typically in the range 0.025 to 0.020 Kelvin. Excellent dc and ac uniformities of 4-6% were universally observed. The yielded FPAs all had greater than 98.5% operability with many parts achieving greater than 99.5%. Additional tests were performed to determine if the LWIR detectors could be used in the MWIR. The NEAT achieved in these tests was approximately 0.025 Kelvin. the outstanding detector RoAo products achieved at SF RC reduce the leakage current sufficiently to achieve this performance level in the MWIR. The excellent MWIR performance opens the possibility of simultaneous MWIR and LWIR imagery using a single LWIR staring FPA.