Adam M. Kennedy

320 x 240 silicon microbolometer uncooled IR FPAs with on-chip offset correction

SBRC has developed a high-quality 320 X 240 room- temperature infrared FPA that operates in the 8 - 14 micrometers spectral band. The FPA is based upon the silicon microbolometer technology that has been licensed from Honeywell. This monolithic uncooled FPA utilizes a novel BiCMOS readout circuit that provides high sensitivity and excellent output uniformity. The 320 X 240 FPA operates at frame rates up to 60 Hz with a single output. The microbolometers were fabricated monolithically on the silicon readout circuits at SBRC using VOx as the bolometer material. As advanced microbridge structure design was used that achieves an optical fill-factor greater than 65% in the 48 micrometers X 48 micrometers pixels. The structure also provides excellent thermal isolation for high responsivity and sensitivity. Initial measurements indicate the FPAs are operating with an NETD sensitivity of about 100 mK for an f/1 aperture. This FPA is ultimately expected to operate at sensitivities of less than 20 mK. The FPA also demonstrates peak-to-peak output nonuniformities of less than 100 mV. The FPAs have been mounted in permanently-sealed vacuum packages with single-stage thermoelectric temperature stabilizers. These vacuum packages have been integrated into a camera system that has produced high-quality infrared imagery.

Sensitivity improvements in uncooled microbolometer FPAs

Raytheon IRCOE has developed a family of uncooled, microbolometer FPAs. These FPAs have been designed to address commercial and high-performance military applications. The SB-151 is a high-sensitivity 320 X 240 FPA with 50 micrometers pixels. The SB-151 FPA has been fabricated with several microbolometer pixel designs that allow optimization of either sensitivity or response time. Noise equivalent temperature difference (NETD) values as low as 8.6 mK have been measured for the SB-151 FPAs with f/1 optics. NETD values less than 25 mK have been measured for FPAs with thermal time constants of approximately 18 msec.

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.

Microbolometer uncooled infrared camera with 20-mK NETD

Raytheon Systems Company has developed a prototype infrared imaging rifle-sight using an uncooled, microbolometer FPA. The high-sensitivity FPA (SBRC-151) used in the Long-wavelength Staring Sensor (LWSS) was developed by Raytheon Infrared Center of Excellence (IR COE). The NETD (noise equivalent temperature difference) sensitivity of the camera has been measured at 14 mK with f/1 optics and at 74 mK with an f/2.1 aperture stop. Excellent imagery has been demonstrated with the f/2.1 aperture. The 320 X 240 FPA utilizes a high-yield CMOS readout integrated circuit (ROIC) that achieves high sensitivity, low output nonuniformity, and large scene dynamic range. The ROIC provides multi-level, on-chip nonuniformity correction and on-chip temperature compensation. The FPA has 50 micrometer X 50 micrometer pixels and operates at frame rates up to 60 Hz with a single output. The LWSS was characterized by the U.S. Armys NVESD in 1997 using an earlier version of the SBRC-151 FPA. The NVESD measurements validated the Raytheon NETD data. The NVESD evaluation also demonstrated outstanding MRT and spatial noise characteristics. The VOx microbolometer detectors are produced at the Raytheon IR COE facility in Santa Barbara, CA using an advanced dry-etch fabrication process. In addition to the LWSS project, the IR COE has initiated production of the microbolometer FPAs (AE-189) for commercial applications. Over 600 FPAs have been produced on this project, and data is presented for the first 250 FPAs that have been packaged and tested. The pixel operability of the production radiometer FPAs (AE-189) is typically greater than 99.9%.

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.

High sensitivity 640 × 512 (20 μm pitch) microbolometer FPAs

RVS has made a significant breakthrough in the development of a 640 × 512 array with a unit cell size of 20μm × 20 μm and performance equivalent to that of the 25μm arrays. The successful development of this array is the first step in achieving mega-pixel formats. This FPA is designed to ultimately achieve performance near the temperature fluctuation limited NETD (<20mK, f/1, 30 Hz). The SB-300 is a highly productized readout and is designed to achieve very good sensitivity (low NETD and low spatial noise) and good dynamic range. The improved performance is through bolometer structure improvements and an innovative ROIC design. It also has a simple and flexible electrical interface which allows external electronics to be small, light, low-cost, and low-power. Almost all adjustments can be made through the serial interface; hence there is no need for external adjustable (DAC) circuitry. The improved power supply rejection helps maintain highly stable detector and strip resistor bias voltages which helps reduce spatial noise and image artifacts. We will show updated performance and imagery on these arrays, which is currently being measured at <30mK, f/1,555 30 Hz. Pixel operability is greater than 99.5% on most FPAs, where the uncorrected responsivity nonuniformity is less than 4% (sigma/mean), and time constant for these arrays was measured at <8msec. We will report detailed FPA performance results including responsivity, noise, uniformity and pixel operability. We also plan to present video imagery from the most recent FPAs. The reduction in pixel size offers several potential benefits for IR systems. For a given system resolution (IFOV) requirement, the 20 μm pixel will allow an optical volume that is 50 % the size of a 25 μm based system! We will also provide an update on the enhanced performance and yield producibility of our NVESD ManTech 640 × 480 25 μm arrays, and also show data on 25 μm arrays that have been designed for faster time constants (5 ms), while maintaining high performance. We will also show the improvement in our uncooled 320 × 240 and 640 × 480 sensor electronics in terms of reduced power and size for helmet and rifle mounted sensors.

Expanded applications for high performance VOx microbolometer FPAs

RVS is producing high-quality microbolometer FPAs with 25 μm pixels. We have developed formats in both 320 x 240 and 640 x 480 array formats. These FPAs have demonstrated sensitivities that are comparable to microbolometer FPAs with 50 μm pixels with the best measured NETD value for these FPAs now <25mK 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 3% (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 systems. We will report on our latest performance data and IR captive flight test imagery. We will also show data on 25μm arrays that have been designed for faster time constants (5 msec), while maintaining high performance. RVS is also developing a 320 x 240 50μm mid-wave responding FPA. We will review the MWIR sensitivity improvements with this array and provide IR imagery. RVS is developing a 640 x 480 25μm uncooled FPA for a countermine detection application using a two-band assembly designed to be sensitive in both the Restrahlen and Thermal spectral bands. We will provide IR image data on these arrays. RVS has made a significant breakthrough in the development of a 640 x 512 array with a unit cell size of 20 μm x 20 μm, and performance approaching that of the 25μm arrays. The successful development of this array is the first step in achieving mega-pixel formats. This FPA is designed to ultimately achieve performance near the temperature fluxuation limited NETD (<20mK, f/1, 30 Hz). We will show updated performance and imagery on these arrays, which is currently being measured at <45mK, f/1, 30 Hz.

Low-cost microsensors program

The objectives of the Low Cost Microsensors (LCMS) Program are twofold. The first is to develop and deliver a long-range infrared (IR) sensor built upon an uncooled vanadium oxide (VOx) 640 X 512 format focal plane array (FPA) engine. The second is to develop an expendable microsensor built upon a VOx 160 X 128 format FPA engine. The 640 X 480 sensor is applicable to long-range surveillance and targeting missions and is a reusable asset. The 160 X 120 sensor is designed for applications where miniaturization is required as well as low cost and low power. The 160 X 120 is also intended for expendable military applications. The intent of this DUS&T effort is to further reduce the cost, weight, and power of uncooled IR sensors, and to increase the capability of these sensors, thereby expanding their applicability to military and commercial markets never before addressed by thermal imaging.