Neal R. Butler

Performance limits of uncooled VOx microbolometer focal plane arrays

Uncooled microbolometer technology has shown dramatic improvements in recent years as tens of thousands of imaging systems have been delivered. This paper outlines the performance limits that must be overcome to continue to achieve performance improvements.

Uncooled infrared sensors with digital focal plane array

Loral Infrared & Imaging Systems is developing low cost, high performance, uncooled infrared imaging products for both military and commercial applications. These products are based on the microbolometer technology, a silicon micromachined sensor which combines the wafer level silicon processing with a device structure capable of yielding excellent infrared imaging performance. Here, we report on the development of an uncooled sensor, the LTC500, which incorporates an all digital focal plane array and has a measured NETD of less than 70 mK. The focal plane array and the electronics within the LTC500 have been designed as an integrated unit to meet a broad range of end user applications by providing features such as nonuniformity correction, autogain and level, NTSC video, and digital outputs. The 327 X 245 element focal plane array has a 46.25 micrometers pixel pitch and an on focal plane array 14 bit to analog to digital converter (ADC). The ADC has a measured instantaneous dynamic range of more than 76 dB at a 6.1 MHz output data rate and 60 Hz frame rate. The focal plane array consumes less than 500 mW of power, of which less than 250 mW is used in the ADC. An additional 36 dB of digital coarse offset correction in front of the ADC on the focal plane array results in a total electronic dynamic range of 112 dB. The MRT of the LTC500 camera has been measured at less 0.2 C at fo.

Low-cost uncooled microbolometer imaging system for dual use

Loral Infrared & Imaging Systems is developing low cost, high performance uncooled infrared imaging products for both military and commercial applications. These products are based on the microbolometer technology, a silicon micromachined sensor which combines the wafer level silicon processing with a device structure capable of yielding NETD performance of better than 40 mK. To achieve a low cost sensor, Loral is proceeding with an integrated approach to the design and manufacturing processes associated with each major element of the uncooled sensor: focal plane array, electronics, optics and housings. Lorals 327 by 245 focal plane array has a 46.25 micrometer pixel pitch and incorporates a CMOS readout integrated circuit (ROIC). The ROIC has been designed to greatly simplify the external electronics, and features a single output which can operate at both 60 Hz (NTSC) and 50 Hz (PAL) video rates. The sensor electronics have been designed to meet a broad range of end user applications by providing both analog video and digital outputs with a large selection of user definable options and operating modes. To achieve low manufacturing costs across multiple end user applications, common optical interfaces, structural components, and manufacturing processes are being utilized. Sensor NETD is projected to be 40 mK normalized to f/1 and a 30 Hz frame rate. MRT is projected to be better than 0.1 degree Celsius at f0.

More applications of uncooled microbolometer sensors

Lockheed Martin IR Imaging Systems is developing low cost, high performance, uncooled infrared imaging products for both military and commercial applications. These products are based on microbolometer technology, a silicon micromachined sensor that combines wafer level silicon processing with a device structure capable of yielding excellent imaging performance. Here, in the first of a series of papers, we report on several applications that are utilizing the Lockheed Martin microbolometer sensor. The performance of our basic uncooled sensor has been measured (and reported in multiple papers) to determine sensor capabilities for insertion into both military and commercial products. Non-linearity of the sensor over a scene temperature range of 95 degrees Celsius is less than 0.5%. Our sensors typically have temporal NETDs of less than 70 mK as well as spatial NETDs of less than 50 mK. MRTD performance is less than 0.4 degrees Celsius at spatial frequencies more than 20% beyond Nyquist. Spatial noise variation over time has been measured and found to meet both commercial and military requirements with excellent spatial noise over wide scene and ambient temperature ranges. Some of the multiple applications in which our uncooled sensors have been used have just recently been described in one report demonstrating the varied and unique uses of this product. Our sensor is now used by dozens of partners and customers for applications ranging from hand-held radiometric cameras to driving aids; from drivers aids to miniature cameras from rifle sights to radiometers. These applications will be discussed along with their unique system level performance parameters. Video will be used to demonstrate the various applications discussed.

Recent improvements and developments in uncooled systems at BAE SYSTEMS North America

BAE SYSTEMS has designed and developed MicroIR microbolometer focal plane arrays (FPAs) in three formats (160x120, 320x240, and 640x480) and with two different pixel sizes (46micrometers and 28micrometers ). In addition to successfully demonstrating these FPA technologies, BAE SYSTEMS has produced and delivered thousands of 320x240 (46micrometers pixel) imaging modules and camera cores for military, thermography, firefighting, security and numerous other applications throughout the world. Recently, BAE SYSTEMS has started production deliveries of 160x120 (46micrometers ) systems, demonstrated 320x240 and 640x480 second-generation (28micrometers ) imaging, and demonstrated second-generation thermoelectric cooler-less operation. This paper discusses these recent accomplishments and, when possible, provides quantitative NETD and performance data for our newly developed FPAs and systems. Video will be shown to demonstrate sensor performance capabilities.

Solid state pyroelectric imager

A long wavelength infrared imaging system is under development at Loral Infrared & Imaging Systems. The imager features a solid state pyroelectric focal plane array sensitive to 8 - 14 micrometers radiation operating at ambient temperature; it needs no cooling or temperature control to obtain performance comparable to conventional cooled FLIR systems. The focal plane array is fabricated as a hybrid structure with a fully reticulated lithium tantalate detector array bump mounted to a CMOS multiplexer. The optical, thermal, and electrical design of the focal plane array is described in detail. The prototype imaging system uses a focal plane array of 192 X 128 pixels on 50 micrometers centers. The next version will use a focal plane with approximately 330 X 240 pixels for full NTSC (U.S. standard television) compatibility. The design of the prototype imaging system is described. The predicted noise equivalent temperature difference (NETD) for these systems is less than 0.1 degree(s)C with f/1 optics at a 30 Hz display rate.

Recent developments in uncooled IR technology

Sanders IR Imaging Systems (IRIS), a Lockheed Martin Company, has made recent improvements in high performance uncooled IR focal plane arrays and systems. This paper provides performance results for three of these new FPAs and systems. First we discuss a new 320 X 240, 46 micrometer pitch FPA, which when put into a system with a transmission of 74%, will provide a system NETD of < 26 mK (F/0.8, 60 Hz). This FPA has a power of < 250 mW (which includes on-chip 14 bit analog to digital conversion), and virtually no crosstalk from saturation. Second, we discuss the first ever 640 X 480 element uncooled IR camera. This camera, which is based on a 28 micrometer pitch microbolometer staring FPA, produces a system sensitivity of < 150 mK, (F/1, 30 Hz) and has a Minimum Resolvable Temperature Difference of < 0.4 degrees Celsius at the Nyquist frequency. Finally, we have developed a new lightweight thermal weapons sight (TWS). Our TWS, which weighs < 3 lbs. (with battery) and operates over the -37 degrees Celsius to +49 degrees Celsius temperature range, has demonstrated a boresight retention of < 0.2 mrad after 1000s of rounds were fired.

Developments in uncooled IR technology at BAE SYSTEMS

Uncooled microbolometer thermal imaging sensor technology has begun to successfully address military, government and commercial applications in the real world. BAE SYSTEMS, located in Lexington MA, has been involved in the design and development of uncooled IR technology since the early 1980s. Our current MicroIRTM products are based on vanadium oxide (VOx) microbolometers. Thousands of uncooled microbolometer thermal imaging sensors are now being produced and sold annually. A the same time, applied research and development on the technology continues to improve the basic products and make them suitable for new applications. In this paper we report on the status and improvements achieved in the MicroIRTM product line, based on 320 X 240 element and 160 X 120 element FPAs with 46 μm pixel pitch. Other near term MicroIRTM products include 320 X 240 and 640 X 480 FPAs with 28 micrometers pixel pitch and measured sensitivities below 50 mK. In the systems area we discuss development and testing of a Light Thermal Weapon Sight (LTWS) for the U.S. Army, being developed by BAE SYSTEMS in partnership with Thales, based upon our uncooled MicroIRTM focal plane arrays (FPA) and systems. The LTWS prototypes were based upon our Standard Imaging Module SIM200, which employs our LAM2C, 320 X 240 element, microbolometer FPA. Finally we discuss the 480 X 640 element FPA and its application to the Heavy Thermal Weapon Sight application.

Quantitative and imaging performance of uncooled microbolometer sensors

Lockheed Martin IR Imaging Systems is developing low cost, high performance, uncooled infrared imaging products for both military and commercial applications. These products are based on the microbolometer technology, a silicon micromachined sensor that combines wafer level silicon processing with a device structure capable of yielding excellent imaging performance. Here we report on the latest technical improvements and performance of an uncooled sensor as measured through laboratory and field testing. The performance of our uncooled sensor has been measured to determine sensor capabilities for insertion into both military and commercial products. Linearity of the sensor over a scene temperature range of 95 degrees Celsius is less than 0.5%. Our sensors typically have temporal NETDs of less than 70 mK as well as spatial NETDs of less than 50 mK. MRTD performance is less than 0.4 degrees Celsius at spatial frequencies more than 20% beyond Nyquist. Sensor stability over time has been measured and found to meet both commercial and military requirements. Spatial noise over a wide scene temperature range is reported as well as other test results. Video is used to demonstrate sensor performance capabilities in a variety of applications.

Ambient temperature IR focal plane arrays

The advent of modern photolithography and micromachining techniques has led to the development of many kinds of infrared sensitive focal plane arrays. This paper outlines the history of the development of modern uncooled thermal detector arrays, considerations for reading out those arrays, scaling laws for array design parameters, and ways to improve sensitivity and dynamic range. Future arrays will have smaller pitch (15 micrometer), higher sensitivity (10 - 20 mK, F/1), wider dynamic range (> 100 degrees Celsius, 10,000:1), and better resolution (1280 X 1024). These improvements will come about with better photolithographic resolution, thinner structures, and reduced noise.