Robert E. Mills

488 x 640-element hybrid platinum silicide Schottky focal-plane array

A medium wavelength infrared (MWIR) staring focal plane array (FPA) technology using Schottky barrier detectors with arrays consisting of 20-micron pixel spacings in a 488 x 640 array format is described. The new 488 x 640 hybrid FPA is a result of an ongoing developmental process that has evolved from a 62 x 58 array to a 488 x 640 array over the past nine years. Reported are the performance goals, design, fabrication, and test results of this high-density hybrid FPA based on PtSi infrared detector technology. The advantages of the hybrid approach include the ease of fabrication, high optical fill factor, compatibility with existing multiplexer technology, and excellent imaging performance. We review past Schottky FPA development and discuss the technical trade-offs of our approach. Also discussed are the design, fabrication, and test results of our most recent Schottky FPA.

Evolution of large format impurity band conductor focal plane arrays for astronomy applications

Raytheon Vision Systems (RVS) has developed a family of high performance large format infrared (IR) detector arrays whose detectors are most effective for the detection of long and very long wavelength IR energy. This paper describes the evolution of the present state of the art one mega-pixel Si: As Impurity Band Conduction (IBC) arrays toward a four mega-pixel array that is desired by the astronomy community. Raytheons Aquarius-1k, developed in collaboration with ESO, is a 1024 × 1024 pixel high performance array with a 30 μm pitch that features high quantum efficiency IBC detectors, low noise, low dark current, and on-chip clocking for ease of operation. Since the Aquarius-1k array was designed primarily for ground-based astronomy applications, it incorporates selectable gains and a large well capacity among its other features. Raytheon, in collaboration with JAXA (Japan Aerospace Exploration Agency), is also designing a 2048 × 2048 pixel high performance array with a 25 μm pitch. This 2k × 2k readout circuit will be based on the successful design used for the on the Mid-Infrared Instrument (MIRI) aboard the James Webb Space Telescope (JWST). It will feature high quantum efficiency IBC detectors, low noise, low dark current, and on-chip clocking for ease of operation. This version will also incorporate flight qualified packaging to support space-based astronomy applications. Previous generations of RVS IBC detectors have flown on several platforms, including NASAs Spitzer Space Telescope and Japans Akari Space Telescope.

Megapixel and larger readouts and FPAs for visible and infrared astronomy

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.

Methodology for testing infrared focal-plane arrays in simulated nuclear radiation environments

Santa Barbara Research Center (SBRC) and Hughes Technology Center (HTC) have developed nuclear radiation testing methodology to measure performance of infrared (IR) focal plane arrays (FPAs) in simulated total ionizing dose, transient dose rate (and flux), and neutron fluence environments. Test methodology for FPAs requires that temperature, background, bias, and vacuum conditions be maintained and controlled during in-situ measurements of performance parameters, which are accomplished with specially fabricated dewars, configurable test sets, and a new FPA portable test set. Radiation sources, dewars and test-set configurations allow measurements of functionality, responsivity, noise, pulse-height distributions, and response/recovery time under operational conditions for the selected radiation environment. This paper summarizes test methodology for EPA testing that can be used for benign (clear) and radiation environments, and describes the use of custom dewars and integrated test equipment in an example environment. The test methodology, consistent with American Society for Testing Materials (ASTM) standards, is presented for the total accumulated gamma dose, transient dose rate, gamma flux, and neutron fluence environments. The merits and limitations of using Cobalt 60 for gamma environment simulations and of using various fast-neutron reactors and neutron sources for neutron simulations are presented. Test result examples are presented to demonstrate test data acquisition and FPA parameter performance under different measurement conditions and environmental simulations.

High-performance large format impurity band conductor focal plane arrays for astronomy applications

Raytheon Vision Systems (RVS) has developed a family of high performance large format infrared detector arrays whose detectors are most effective for the detection of long and very long wavelength infrared energy. This paper describes the state of the art in mega-pixel Si:As Impurity Band Conduction (IBC) arrays and relevant system applications that offers unique off-the-shelf solutions to the astronomy community. Raytheons Aquarius-1k, developed in collaboration with ESO, is a 1024 × 1024 pixel high performance array with a 30μm pitch that features high quantum efficiency IBC detectors, low noise, low dark current, and on-chip clocking for ease of operation. This large format array was designed for ground-based astronomy applications but lends itself for space based platforms too. The detector has excellent sensitivity out to 27μm wavelength. The readout circuit has several programmable features such as low gain for a well capacity of 11 × 106e-, high gain for a well capacity of 106e- and a programmable number of outputs (16 or 64). Programmable integration time and integration modes, like snapshot, rolling and non-destructive integrations, allow the Aquarius to be used for a wide variety of applications and performance. A very fast full frame rate of 120Hz is achieved with 64 outputs (32 outputs per side) and a programmable centered windowing will accommodate a wide range of readout rates. The multiplexer and packaging design utilizes two alignment edges on the SCA which can be butted on two sides for expansion to 2k × 1k and wider focal planes. Data is shown on several focal plane arrays to demonstrate that very low noise and high quantum efficiency performance has been achieved. This array leverages over thirty years of experience in both ground and space based astronomy sensor applications. The technology has been successfully demonstrated on programs such as NASAs Spitzer Space Telescope and Japans Akari Space Telescope, and will be used on the Mid-Infrared Instrument (MIRI) aboard the James Webb Space Telescope (JWST).

Novel methods for cryogenic testing of infrared focal-plane arrays in a Co60 radiation environment

Co60 sources and test equipment have successfully been integrated to provide total, accumulated gamma dose and debris (delayed) gamma flux testing on a routine basis. Three Co60 sources provide a wide range of testing capabilities and dose rates: (1) one-curie source mated to a custom dewar and blackbody specifically designed for debris gamma testing, (2) a 2200-curie internal irradiator primarily used for discrete component testing, and (3) an 8000-curie Shepherd Cell internal irradiator with custom dewars utilizing graybody IR sources which is capable of complete radiometric characterizations of IR FPAs while being exposed to a wide range of position-selectable gamma fluxes and accommodates both total dose and debris gamma testing. Any of these sources and dewars can be interfaced with customer-specific test equipment, allowing the same test set to be used for clear environment and in-situ radiation testing. This paper describes the radiation sources and their associated dewars, the uses, and the test methodology utilized for testing IR focal plane arrays (FPAs) in the total gamma dose and the debris gamma environments. Examples of test data acquisition and reduction are presented.

Evolution of long wavelength astronomy sensors

Astronomers have been interested in performing observations in the very long wavelength infrared band (5–28 m) for decades. IR telescopes are useful to detect very cold or distant objects, so they are important for studying star formation regions, cold stars and extragalactic objects, among others. To this purpose, both groundand space-based observatories have to be equipped with specific sensors that can collect infrared radiation. These so-called impurity band conductor (IBC) sensors have a sensitivity adequate to detect light in the desired spectral range (see Figure 1). They use impurities in the semiconductor to convert long-wavelength photons into an electrical current. We have been manufacturing IBC detectors for many decades.1 These arrays, in multiple formats, can be found in numerous space and ground-based instruments. For example, NASA’s Spitzer Space Telescope’s Infrared Array Camera, for example, uses two IBC detectors and two InSb (Indium antimonide) detectors. Observers used this early instrument for a wide range of astronomical research programs and produced images such as those in Figure 2. The success of Spitzer encouraged the use of large format (wider field of view) IBC arrays. With these devices, astronomers benefit from increased sky coverage and improved sensitivity, thereby decreasing observation time. For instance, we recently delivered 1k 1k IBC mid-infrared detectors to the Jet Propulsion Laboratory (JPL) for the Mid-Infrared Instrument. This device is expected to be on board the planned James Webb space telescope (JWST), successor of the famous Hubble telescope. JPL performed qualification testing and characterization of dark current (the excess current present when a detector has no incoming photons) and noise on these detectors, and both should be minimal for higher performance. While the results delivered by these new IBC arrays will have to wait until the launch of the JWST mission (now delayed by several years), tests showed that Figure 1. Spectral sensitivity of impurity band conductor (IBC) focal planes is well suited for space and ground based astronomy (the photon response to infrared light from 5 to 28 m is excellent).

Recent focal plane arrays for astronomy and remote sensing applications at RVS

Raytheon Vision Systems (RVS) arrays are being deployed world-wide in ground based and space based platforms. RVS has a family of high performance visible through far infrared detector arrays for astronomy and civil space applications. Unique and off-the-shelf product lines are readily available to the community. Large sensor chip assemblies using various detector materials like Si PIN, HgCdTe, InSb, and Si:As IBC, covering a detection range from visible (400nm) to mid-wave infrared (28μm, MWIR) have been demonstrated with excellent quantum efficiency, dark current, and uniformity. These focal plane arrays have been designed using state-of-the-art low noise, low power, and radiation hardened readout integrated circuits. Complete with optical filters, opto-mechanical packaging, active thermal cooling with matching thermal straps, and optional electronics, RVS provides complete solutions for a multitude of sensor types and mission objectives. This paper describes the recent developments of focal plane assemblies for upcoming missions and telescope platforms.

Advanced staring Si PIN visible sensor chip assembly for Bepi-Colombo mission to Mercury

The planet Mercury, by its near proximity to the sun, has always posed a formidable challenge to spacecraft. The Bepi-Colombo mission, coordinated by the European Space Agency, will be a pioneering effort in the investigation of this planet. Raytheon Vision Systems (RVS) has been given the opportunity to develop the radiation hardened, high operability, high SNR, advanced staring focal plane array (FPA) for the spacecraft destined (Fig. 1) to explore the planet Mercury. This mission will launch in 2013 on a journey lasting approximately 6 years. When it arrives at Mercury in August 2019, it will endure temperatures as high as 350°C as well as relatively high radiation environments during its 1 year data collection period from September 2019 until September 2020. To support this challenging goal, RVS has designed and produced a custom visible sensor based on a 2048 x 2048 (2k2) format with a 10 μm unit cell. This sensor will support both the High Resolution Imaging Camera (HRIC) and the Stereo Camera (STC) instruments. This dual purpose sensor was designed to achieve high sensitivity as well as low input noise (<100 e-) for space-based, low light conditions. It also must maintain performance parameters in a total ionizing dose environment up to 70 kRad (Si) as well as immunity to latch-up and singe event upset. This paper will show full sensor chip assembly data highlighting the performance parameters prior to irradiation. Radiation testing performance will be reported by an independent source in a subsequent paper.

Overview of Astronomy Arrays at Raytheon Infrared Operations (RIO)

We review the various types of astronomy arrays currently available from RIO for wide-field imaging and spectroscopy. Arrays for infrared astronomy became available from RIO (previously the Santa Barbara Research Center) with the introduction of the 58×62 InSb in 1984. Since the introduction of this first array, RIO has developed and produced increasingly larger format arrays, including the 256×256 InSb array for SIRTF (Space Infrared Telescope Facility) and the Aladdin 1K×1K array. Over 70 Aladdin arrays have been delivered and are currently deployed on a number of major telescopes throughout the world. RIO is currently developing the next generation of 2K×2K format arrays. These include the 2K×2K ORION InSb array, and the VIRGO 2K×K SWIR HgCdTe array for ground-based applications and the 2K×2K InSb array for the NGST program. In addition, RIO is currently developing the next generation large format 1K×1K Si:As Impurity Band Conduction (IBC) arrays for the NGST MIR instrument.