James F. Asbrock

High-sensitivity 25-μm microbolometer FPAs

Raytheon Infrared Operations (RIO) has achieved a significant technical breakthrough in uncooled FPAs by reducing the pixel size by a factor of two while maintaining state-of-the-art sensitivity. Raytheon has produced the first high-quality 320x240 microbolometer FPAs with 25 micrometers pitch pixels. The 320 x240 FPAs have a sensitivity that is comparable to microbolometer FPAs with 50 micrometers pixels. The average NETD value for these FPAs is about 35 mK with an f/1 aperture and operating at 30 Hz frame rates. Good pixel operability and excellent image quality have been demonstrated. Pixel operability is greater than 99% on some FPAs, and uncorrected responsivity nonuniformity is less than 4% (sigma/mean). The microbolometer detectors also have a relatively fast thermal time constant of approximately 10 msec. This state-of-the-art performance has been achieved as a result of an advanced micromachining fabrication process. The process allows maximization of both the thermal isolation and the optical fill-factor. The reduction in pixel size offers several potential benefits for IR systems. For a given system resolution (IFOV) requirement, the 25 micrometers pixels allow a factor of two reduction in both the focal length and aperture size of the sensor optics. The pixel size reduction facilitates a significant FPA cost reduction since the number of die printed on a wafer can be increased. The pixel size reduction has enabled the development of a large-format 640x480 FPA array. Raytheon has produced arrays with very good sensitivity, operability, and excellent image quality. These FPAs are applicable to wide-field-of-view, long range surveillance and targeting missions. Raytheon is also developing a high performance 160x128 FPA that is designed for applications where miniaturization and temperature invariance are required as well as low cost and low power.

Performance improvements for VOx microbolometer FPAs

Raytheon is producing high-quality 320 x 240 microbolometer FPAs with 25 μm pitch pixels. The 320 x 240 FPAs have a sensitivity that is comparable to microbolometer FPAs with 50 μm pixels. Typical NETD values for these FPAs are <50mK with an f/1 aperture and operating at 30 Hz frame rates. Pixel operability is greater than 99.9% on most FPAs, and uncorrected responsivity nonuniformity is less than 4% (sigma/mean). These 25 μm microbolometer detectors also have a relatively fast thermal time constant of approximately 10 msec. These arrays have produced excellent image quality, and are currently fielded in a variety of demonstration systems. The pixel size reduction facilitates a significant FPA cost reduction since the number of die printed on a wafer can be increased, and also has enabled the development of a large-format 640 x 480 FPA array. Raytheon is producing these arrays with excellent sensitivity and typical NETD values of <50mK with an f/1 aperture and operating at 30 Hz frame rates. These arrays have excellent operability and image quality. Several dual FOV prototype 640 x 480 systems have been delivered under the LCMS and UAV programs. RVS has developed a flexible uncooled front end (UFE) electronics that will serve as the basis for the camera engine systems using 320 x 240 arrays. RVS has developed a 640 x 480 Common Uncooled Engine (CUE) which is intended for small pixel, high performance applications. The CUE is the ideal cornerstone for ground and airborne systems, multi-mode sensor, weapon sight or seeker architectures, and commercial surveillance.

High-sensitivity (25-μm pitch) microbolometer FPAs and application development

Raytheon Infrared Operations (RIO) has achieved a significant technical breakthrough in uncooled FPAs by reducing the pixel size by a factor of two while maintaining state-of-the-art sensitivity. Raytheon has produced high-quality 320 X 240 microbolometer FPAs with 25 μm pitch pixels. The 320 X 240 FPAs have a sensitivity that is comparable to microbolometer FPAs with 50 micrometers pixels. The average NETD value for these FPAs is about 35 mK with an f/1 aperture and operating at 30 Hz frame rates. Good pixel operability and excellent image quality have been demonstrated. Pixel operability is greater than 99% on some FPAs, and uncorrected responsivity nonuniformity is less than 4% (sigma/mean). The microbolometer detectors also have a relatively fast thermal time constant of approximately 10 msec. This state-of-the-art performance has been achieved as a result of an advanced micromachining fabrication process. The process allows maximization of both the thermal isolation and the optical fill-factor. The reduction in pixel size offers several potential benefits for IR systems. For a given system resolution (IFOV) requirement, the 25 μm pixels allow a factor of two reduction in both the focal length and aperture size of the sensor optics. The pixel size reduction facilitates a significant FPA cost reduction since the number of die printed on a wafer can be increased. The pixel size reduction has enabled the development of a large-format 640 X 512 FPA array applicable to wide-field-of-view, long range surveillance and targeting missions, and a 160 X 128 array where applications for miniaturization and temperature invariance are required as well as low cost and low power.

Resolution and sensitivity improvements for VOx microbolometer FPAs

Raytheon Vision Systems (RVS) has achieved a significant technical breakthrough in uncooled FPAs by reducing the pixel size by a factor of two while maintaining state-of-the-art sensitivity. Raytheon is producing high-quality 320 x 240 microbolometer FPAs with 25 μm pitch pixels. The 320 x 240 FPAs have a sensitivity that is comparable to microbolometer FPAs with 50 μm pixels. The array average NETD value for these FPAs is about 30 mK with an f/1 aperture and operating at 30 Hz frame rates. Pixel operability is greater than 99% on most FPAs, and uncorrected responsivity nonuniformity is less than 4% (sigma/mean). These 25 μm microbolometer detectors also have a relatively fast thermal time constant of approximately 10 msec. This state-of-the-art performance has been achieved as a result of an advanced micro machining fabrication process, which allows maximization of both the thermal isolation and the optical fill-factor. These arrays have produced excellent image quality, and are currently fielded in demonstration systems. The reduction in pixel size offers several potential benefits for IR systems. For a given system resolution (IFOV) requirement, the 25 μm pxiels allow a factor of two reduction in both the focal length and aperture size of the sensor optics. These FPAs are applicable to wide-field-of-view, long-range surveillance and targeting missions. The pixel size reduction facilitates a significant FPA cost reduction since the number of die printed on a wafer can be increased, and also has enabled the development of a large-format 640 x 480 FPA array. Raytheon is producing these arrays with very good sensitivity. These arrays have excellent operability and image quality. Several dual FOV prototype systems have been delivered under the LCMS and UAV programs, and are under evaluation at NVESD. Raytheon Vision Systems (RVS) has developed a flexible uncooled front end (UFE) electronics that will serve as the basis for camera engine systems using 320 x 240 and 640 x 480 FPAs. The focus has been to develop architecture suitable for a wide variety of systems from low cost modest performance to high performance military applications. This product has been designed with military environmental and shock and vibration conditions in mind. Intended for small pxiel, high performance applications, the UFE is the ideal cornerstone for ground and airborne UAV, multi-mode sneosr, weapon sight or seeker architectures.

Advances in linear and area HgCdTe APD arrays for eyesafe LADAR sensors

HgCdTe APDs and APD arrays offer unique advantages for high-performance eyesafe LADAR sensors. These include: operation at room temperature, low-excess noise, high gain, high-quantum efficiency at eyesafe wavelengths, GHz bandwidth, and high-packing density. The utility of these benefits for systems are being demonstrated for both linear and area array sensors. Raytheon has fabricated 32 element linear APD arrays utilizing liquid phase epitaxy (LPE), and packaged and integrating these arrays with low-noise amplifiers. Typical better APDs configured as 50-micron square pixels and fabricated utilizing RIE, have demonstrated high fill factors, low crosstalk, excellent uniformity, low dark currents, and noise equivalent power (NEP) from 1-2 nW. Two units have been delivered to NVESD, assembled with range extraction electronics, and integrated into the CELRAP laser radar system. Tests on these sensors in July and October 2000 have demonstrated excellent functionality, detection of 1-cm wires, and range imaging. Work is presently underway under DARPAs 3-D imaging Sensor Program to extend this excellent performance to area arrays. High-density arrays have been fabricated using LPE and molecular beam epitaxy (MBE). HgCdTe APD arrays have been made in 5 X 5, 10 X 10 and larger formats. Initial data shows excellent typical better APD performance with unmultiplied dark current < 10 nA; and NEP < 2.0 nW at a gain of 10.

Low-noise, low-temperature 256 x 256 Si:As IBC staring FPA

Cryogenic space telescopes such as the Space Infrared Telescope Facility (SIRTF) require large-area focal plane arrays (FPAs) with high sensitivity. Such applications set requirements for the readout arrays to simultaneously provide low noise and low power dissipation at very low temperatures. The Hughes Technology Center (HTC) has developed a low-noise 256 X 256-pixel hybrid FPA composed of a PMOS readout array hybridized to an arsenic- doped silicon (Si:As) impurity-band conduction (IBC) detector which is designed to operate below 10 K. The readout unit cell employs a switched source-follower-per-detector (SFD) design where in signals are multiplexed onto four outputs. The detector was processed using high-purity, multilayered epitaxial processing. The readout was processed using the p-channel subset of HTCs CryoCMOS process.

Large format high-operability SWIR and MWIR focal plane array performance and capabilities

High-performance large-format detector arrays responsive to the 1-5μm wavelength range of the infrared spectrum fabricated using large area HgCdTe layers grown on 6-inch diameter (211) silicon substrates are available for advanced imaging applications. This paper reviews performance and capabilities of Raytheon Vision Systems (RVS) HgCdTe/Si Focal Plane Arrays (FPA) and shows 2k x 2k format MWIR HgCdTe/Si FPA performance with NEdT operabilities better than 99.9%. SWIR and MWIR detector performance for HgCdTe/Si is comparable to established performance of HgCdTe/CdZnTe wafers. HgCdTe devices fabricated on both types of substrates have demonstrated very low dark current, high quantum efficiency and full spectral band fill factor characteristic of HgCdTe. HgCdTe has the advantage of being able to precisely tune the detector cutoff via adjustment of the Cd composition in the MBE growth. The HgCdTe/Si detectors described in this paper are p-on-n mesa delineated architecture and fabricated using the same mature etch, passivation, and metallization processes as our HgCdTe/CdZnTe line. Uniform device quality HgCdTe epitaxial layers and application of detector fabrication processes across the full area of 6-inch wafers routinely produces high performing detector pixels from edge to edge of the photolithographic limits across the wafer, offering 5 times the printable area as costly 6×6cm CdZnTe substrates. This 6-inch HgCdTe detector wafer technology can provide applications demanding very wide FOV high resolution coverage the capability to produce a very large single piece infrared detector array, up to a continuous image plane 10×10 cm in size. Alternatively, significant detector cost reduction through allowing more die of a given size to be printed on each wafer is possible, with further cost reduction achieved through transition towards automated detector fabrication and photolithographic processes for both increased yields and reduced touch labor costs. RVS continues to improve its FPA manufacturing line towards achieving low cost infrared FPAs with the format, size, affordability, and performance required for current and future infrared applications.

Specification and design of the SBRC-190: a cryogenic multiplexer for far-infrared photoconductor detectors

We describe the development of a cryogenic multiplexer for far-infrared (FIR) photoconductor detectors operating at moderate backgrounds. The device is called the SBRC 190. Its architecture and basic functions are based on the 1×32-channel CRC 696 CMOS device used on SIRTF. The SBRC 190 is designed to accommodate the higher backgrounds to be encountered on SOFIA and Herschel, to tolerates a wider range of backgrounds, to permit faster sampling, and to facilitate synchronization of sampling with chopping. Major design differences relative to the CRC 696 which have been incorporated in the SBRC 190 design are: (a) an AC coupled, capacitive feedback transimpedence unit cell, which minimizes input offset effects, thereby enabling low detector biases, (b) selectable feedback capacitors to enable operation over a wide range of backgrounds, and (c) clamp and sample-and-hold output circuits to improve sampling efficiency, which can be a concern at the relatively high readout rates required. A relationship between sampling efficiency and noise performance needed to achieve background-limited instrument performance (BLIP) is derived. Requirements for use on SOFIA, the basic circuit design, fabrication, and operation are discussed.

High-sensitivity (25-μm pitch) microbolometer FPAs

RIO has achieved a significant technical breakthrough in uncooled FPAs by reducing the pixel size by a factor of two while maintaining state-of-the-art sensitivity. Raytheon has produced high-quality 320 by 240 micro bolometer FPAs with 25 micrometers pitch pixels. The 320 by 240 FPAs have a sensitivity that is comparable to micro bolometer FPAs with 50 micrometers pixels. The average NETD value for these FPAs is about 35 mK with an f/1 aperture and operating at 30 Hz frame rates. Good pixel operability and excellent image quality have been demonstrated. Pixel operability is greater than 99 percent on some FPAs, and uncorrected responsivity nonuniformity is less than 4 percent. The micro bolometer detectors also have a relatively fast thermal time constant of approximately 10 msec. This state-of-the-art performance has been achieved as a result of an advanced micromachining fabrication process. The process allows maximization of both the thermal isolation and the optical fill-factor. The reduction in pixel size offers several potential benefits for IR systems. For a given system resolution requirement, the 225 micrometers pixels allow a factor of two reduction in both the focal length and aperture size of the sensor optics. The pixel size reduction facilitates a significant FPA cost reduction since the number of die printed on a wafer can be increased. The pixel size reduction has enabled the development of a large-format 640 by 512 FPA array applicable to wide-field-of-view, long range surveillance and targeting missions, and a 160 by 128 array where applications for miniaturization and temperature invariance are required as well as low cost and low power.

Low-noise 256 x 256 10-kelvin staring FPA

Cryogenic spe telescopes such as the Space Infrared Telescope Faility (SIRTF) require large-area focal plane arrays (FPAs) with high sensitivity. This places large demands on readout arrays to simultaneously provide low noiseand high responsivity at low power dissipation. The Hughes Technology Center (HTC) has developed a low-noise 256x256-pixel readout array applicable to the SIRTF visible Fine Guidance Sensor (FGS), short-wavelength infrared array camera (IRAC), and Infrared Spectrometer (IRS). The readout is designed to operate at temperatures below 10 K. The unit cell employs a switched source follower-per-detector design wherein signals are multiplexed onto four outputs while row and column scanners can flexibly address small block portions of the array to conserve power. The readout has recently beenfabricated using the standard cryo-CMOS process developed at Hit specifically for low-temperawre, low-noise operation. The readout can be used with Si PIN, InSb, and Si impurity-band-conduction (IBC) detector arrays.