The ULTRA (Uncooled, Low cost, Technology Reinvestment Alliance) Consortium, consisting of the Honeywell Technology Center of Honeywell Incorporated, the Autonetics Missile Systems Division of Rockwell International Corporation, Inframetrics Incorporated, and the New Jersey Institute of Technology, has been formally working together over the past year in an effort to develop, manufacture and sell industrial and military sensors and components incorporating silicon microbolometer uncooled focal plane array (UFPA) technology. Towards that end, Rockwell has been actively engaged in developing the UFPA component, with assistance from Honeywell, with the intention of being a merchant supplier of the UFPA. Inframetrics has been developing subsystems required to construct and characterize a prototype sensor, and NJIT is designing a Multi-Wavelength Imaging Pyrometry system around the performance of the uncooled prototype sensor. TRP Office funding administered by ARPA has been key to the significant advances made over the course of the year in this program. This paper will describe both the UFPA component specification and the prototype sensor. It will give a architectural overview of the detector array, with the anticipated performance characteristics. Multiplexer design and simulation, and array processing, will be addressed. A description of the array packaging, interface requirements, and unique design considerations will be provided. Anticipated and actual component performance will be explained and contrasted. The background of the sensor development will be presented. An overview of the camera architecture will be given, with some discussion of trade-offs in subsystem design of the sensor. Specific emphasis is placed on the radiometric evaluation of the sensor.
A cooperative research project between the Defense Science and Technology Organization, Australia, and the National Defense Research Establishment, Sweden, seeks to investigate concepts for smart IR focal plane detector arrays, whereby a monolithic Semiconductor Film Bolometer detector array is integrated with a CMOS signal conditioning circuit, analog- to-digital conversion and signal processing functions on the same silicon chip. Novel signal conditioning and on-chip digital readout techniques have been successfully demonstrated, and the supporting signal processing electronic design is being developed. This paper discusses the status of detector materials research and staring focal plane array development. The first experimental array has been delivered and is undergoing evaluation.
Uncooled microbolometer detector development has made significant progress within the past two years. Starting in June 1994, Amber fabricated a custom readout IC, and began the concurrent development of a hand held LWIR camera. This paper reviews the camera design, camera electronics, and packaging considerations. In addition system performance including NETD, MRTD, and corrected nonuniformity data will be presented.
Systems enabling uncooled infrared arrays capable of imaging room temperature scenes employ thermal detection mechanisms such as the resistive bolometric, pyroelectric/field enhanced pyroelectric and thermoelectric. All such approaches are subject to the fundamental limits of temperature fluctuation noise and background fluctuation noise. The thermal isolation structure is the most important item in optimizing the pixel design. Although it is possible to attain the limits with mechanisms which do not require bias, such as the thermoelectric or pyroelectric, it is probably easier to do so with mechanisms which require bias, such as the resistive bolometric and the field enhanced pyroelectric.
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.
This paper reviews the latest developments in pyroelectric devices for IR detection based on sol-gel derived ferroelectric thin films, highlighted by recent results from our laboratories. The optimization of sol-gel processing has led to ferroelectric films with pyroelectric coefficients as high as 200 nC/cm2-K. Some modeling results of the thin film devices, which aid in device design, are also discussed. At the film level, various factors such as chemistries, microstructures and processing conditions all affect the final pyroelectric properties of the films. At the device level, processing compatibility and device layout need to be taken into account to optimize fully the device performance.
Pyroelectric infrared detectors have among other things the known advantages of being able to be used at room temperature and of being provided with a sufficient signal- to-noise ratio for a number of applications, a spectral responsivity of a relative homogeneity within the infrared range, and properties of a very long-term stability. For extending their range of application both extensive and intensive efforts were made, during the last few years, to considerably improve responsivity, noise equivalent power (NEP) and modulation transfer function of linear arrays. The paper describes the structure and the main properties of newly developed line sensors based on lithium tantalate and containing 128 sensitive elements (size of element: 90 X 100 micrometers 2, pitch 100 micrometers ). It is shown that the thickness of the responsive elements has a strong influence on responsivity. Special techniques for structuring the pyroelectric chip and using a low-noise CMOS read-out circuit made it possible to achieve NEP values below 0.5 nW at a chopper frequency of 40 Hz. Illustrated by the examples of a line scanner and a 2D camera, the paper proves that noise equivalent temperature difference values around 0.1 K are possible.
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.
In this report, a general analysis for optimal sensitivity of microbolometers with constant-current operation is described. Using a linear approximation of bolometer resistance with respect to temperature variation, close-form solution of the optimal condition can be obtained among a set of operational variables and device parameters, including the sensor resistance, TCR, thermal conductance and bias current or voltage. The solution is close to that calculated by the exact numerical method. It is found that, under constant-current operation, a stable (relative) maximum of the sensor responsivity can only be obtained for NTCR, bolometers. The maximum sensitivity may reach 106 V/W with practical parameters considered for uncooled FPA bolometers working in vacuum. At such conditions, a thermal detector may perform a D* value close to the BLIP condition, if it has a radiation-loss-limited feature. Also, a large-area single bolometer operated in the atmosphere may have a performance comparable to that of the present commercial pyroelectric detectors.
In this paper, we discuss the development of very sensitive long wavelength infrared GaAs/AlxGa1-xAs quantum well infrared photodetectors (QWIPs), fabrication of random reflectors for efficient light coupling, and the demonstration of first hand-held long-wavelength 256 X 256 QWIP focal plane array camera. Excellent imagery, with a noise equivalent differential temperature of 25 mK has been achieved.
We report on the experimental results of the effect of proton radiation on the performance of quantum well infrared photodetectors. A range of energies from 0.8 to 10 MeV and a range of fluences from 1012 to 1016 cm-2 were used. The detector performance are characterized by its responsivity becomes progressively worse with increasing fluence. For the same fluence, lower energy causes more damage to the detector.
A new method of infrared detection without any preamplifiers is presented. The method is based on well studied multiquantum well (MQW) structures and the injection mode integrate-and-fire infrared detectors using p+-n- n+ structures. A brief introduction to injection mode IR detectors (with p+-n-n+ diodes) is given. A model based on device physics to describe spontaneous pulsing in GaAs/AlGaAs quantum well structures is presented. The model includes space charge generation/recombination mechanisms such as tunneling and impact of injected hot electrons with cold well electrons, with current voltage relations leading to spontaneous pulsing in MQW structures. It is shown with the correct parameters, spontaneous pulsing could be observed in MQW structures at 300 K. The IR photoionization contribution to space charge generation is added to the model to obtain the infrared response. This response can take the form of a change in the pulse rate or pulses being generated for a subthreshold bias conditions. This gives rise to novel IR detectors operating above 77 K up to near room temperature.
Performance of a SWIR FPA targeting LANDSAT S/N levels in the near room temperature (> 220 K) is presented. The FPA consists of a 96 X 25 element InGaAs array with 48 (mu) X 48 (mu) photo-voltaic pixels bump-bonded to a Si multiplexer. Cutoff wavelength of an array is tailored from 1.68 (mu) to 2.4 (mu) . The longer cutoff is required for Band 7. The multiplexer design incorporates a CMOS CCD process and is a 96 channel X 25 TDI scanning array with pixel pitch of 48 (mu) cross track by 96 (mu) intrack. Each unit cell uses a Capacitive Trans-Impedance Amplifier) with Correlated Double Sampling. Other notable chip features include electrically selectable TDI modes (0, 1, 8, 16, and 25), forward and reverse scan, and 1 X 1 and 2 X 2 aggregation modes. Timing and biases are self generated by the multiplexer.
GaAs/AlxGa1-xAs quantum well infrared photodetectors grown by molecular-beam epitaxy with x varied from 0.26 up to 0.43 are investigated. The huge increase of dark current (by 2 - 3 orders) in photodetectors with x approximately equals 0.4 after illumination of samples by optical radiation ((lambda) < 1.3 micrometers ) at lowered temperatures and the subsequent slow dark current relaxation are observed. The model of barriers with a local sag potential increasing tunnel current is proposed. The value of the sag potential is increased at optical ionization of unintentional deep levels in the barrier and is decreased at the subsequent capture of electrons from conduction band on deep levels. Analysis of the dark current kinetics allowed to determine some parameters of these deep levels.
Ferroelectric Pb(Zr0.52Ti0.48)O3 (PZT) (001) and (Mn,Sn) doped-PZT (PMSZT) (001) thin films have been integrated to high Tc superconducting c-oriented YBa2Cu3O7-x (YBCO) films for use as infrared detectors. The films were grown on LaAlO3(100) substrates by the pulsed laser deposition technique. The photocurrent responses of the PZT/YBCO and PMSZT/YBCO heterostructures fabricated as infrared (IR) detector have been measured from room temperature up to the ferroelectric phase transition temperatures. A stable photocurrent was observed to increase with increasing temperature throughout the temperature range. It was observed that the photocurrent of PMSZT/YBCO IR detector was significantly higher than that of the PZT/YBCO IR detectors in the temperature range of 20 - 170 degree(s)C. The current enhancement with temperature was found to be strongly polarization dependent and is due to the change of the pyroelectric coefficient of the PZT and PMSZT thin films with temperature. The YBCO thin films in the heterostructure were not used for their superconducting properties, but for their IR reflector-conductive electrode properties and as an atomic template for PZT/PMSZT epitaxial growth. With the high dielectric constants of PZT (600 - 800) and PMSZT (300 - 450) measured in this work, and the stable photocurrent in the infrared region (above 1 micrometers ), the PZT/YBCO and PMSZT/YBCO heterostructures are believed to be suitable materials for use in infrared detectors applicable at temperatures higher than room temperature.
Experimental Multi-wavelength Imaging Pyrometer (M-WIP) is presented for remote sensing of temperature profiles of targets with unknown spectrally varying emissivity. A software package was developed for calibration and real-time M-WIP measurements. An experimental 7-filter line-sensing M- WIP system was implemented with a 320 X 122-element PtSi IR-CCD imager and an assembly of narrow-band striped IR filters in the spectral range from 1797 nm through 4512 nm. The M-WIP system was calibrated against a commercial blackbody source over temperature range from 450 degree(s)C to 950 degree(s)C. The signal processing included background subtraction, compensation for variation of dark current with detected signal and correction for non-linearities of IR imager response. Initial M-WIP measurements demonstrated real-time temperature resolution (Delta) T of +/- 1 degree(s)C for blackbody target over temperature range from 600 degree(s)C to 900 degree(s)C. Temperature resolution of +/- 4 degree(s)C was demonstrated for the blackbody source viewed through the double polished silicon wafer with unknown spectral transmissivity in the temperature range from 500 degree(s)C to 950 degree(s)C.
The results of MBE growth of CdHgTe epilayers and fabrication of photosensitive in 8 - 10 mkm region small p-n junctions using planar technology are presented. During MBE epitaxy the growing dynamic, composition and surface roughness were controlled in situ using build in high energy electron diffractometer and ellipsometer. Small area photosensitive diodes (50 X 70 mkm) were fabricated using planar technology and annealing under anodic oxide film. The measurements of V-I, spectral response and noise characteristics showed that the photodiodes on MCT epilayers grown by MBE have an acceptable parameters for fabrication of the linear and 2D photodiode arrays.
The cooling of infrared sensors and electro-optical devices by Joule-Thomson cryostats has been a viable systems option for electro optical systems since the 1960's. Currently, other options such as thermal electric coolers, closed cycle coolers and non-cooled detector technology are available and present alternatives for the system designer. In specific applications, Joule-Thomson cryostats still prove to be the option of choice. This paper will discuss the current and projected applications for Joule-Thomson cryostats as well as define and discuss the advantages of Joule-Thomson cooling technology. The importance of contamination control, reliability, and `Total Quality Management' in the manufacturing of Joule-Thomson cryostats will be emphasized.
To give an answer to the potential demand of low cost integrated dewar cooler assembly (IDCA) devoted to CMT Infra Red detectors with a cut-off wavelength in a 3 - 5 micrometers bandwidth cooled at intermediate cooling temperature (i.e. 140 - 200 K), small, efficient and reliable coolers with affordable price are required. A comparison between different cooling concept like lightweight IDCA Stirling and Pulse Tube, active Joule Thomson and thermoelectric is done. This comparison is made with respect to the efficiency, reliability and cost for a cooling power objective of 500 mW at 140 K and 23 degree(s)C ambient.
Novel integrated intelligent videosensor and its possible application using on-FPA real-time parallel processing are discussed. This solid-state single-chip sensor is photoelectric structure with memory (PESM), which consists of semiconductor, insulator and metal layers, wherein optical information are detected, recorded and stored in the form of 2D charge and potential patterns, and then processed due to internal interaction of these patterns in a normal direction to the input plane. Thus, such Z-plane technology allows the PESM to operate as multifunctional device utilizing massively parallel processing with high effective operational speed (up to 1014 operation/bit/s) without additional electronic and computing units. Except reading, writing and storing, PESM performs such parallel image processing as summation, subtraction, contouring, convolution and correlation, which may be effectively applied to numerous tasks of diverse optoelectronic systems. Two image operations--subtraction and correlation, which seems to us of high importance, are demonstrated as an example of the PESM performance. It allows one to solve in a real time the main problems concerned with background subtraction, moving object selection, target tracking and pointing, recognition of extended objects and so on. As we suppose, the possible applications of the PESM as an intellectual `supersensor', which combines a high-quality imager and a high-capacity multifunctional processor, would provide substantially lower prime cost of the designed systems in comparison with the now-existing ones and may be widely extended.
Low cost equipment is the universal motto with the decrease in military budgets. A large panoply exists to solve partially this problem, such as simplification of the process, industrialization and the use of a collective manufacturing concept; but this is not enough. In the field of IRFPA using Mercury Cadmium Telluride (MCT), Sofradir has spent a lot of time in order to develop a very simple process to ensure producibility which has been totally demonstrated today. The production of more than 25 complex IRFPA per month has also allowed us to industrialize the process. A key factor is quantities. Today the only solution to increase quantities is to standardize detectors but in the field of IRFPA it is not so easy because each imaging system is specific. One solution to decrease the cost is to obtain the best trade-off between the application and the technology. As an example, people focus on indium antimonide staring array detectors today as they consider them as less expensive than other cooled infrared detector technologies. This is just because people focus on the FPA only, not on the global cost of the equipment. It will be demonstrated in this paper that MCT is a material so flexible that it is possible to obtain InSb detector performance at a higher temperature which allows decreased cost, volume and weight of the infrared equipment.
The accurate form of image noise is helpful for noise- suppressing. The random process of 1/f noise is analyzed with wavelet functions and a Maximum Likelihood method is employed for finding the accurate power spectral density of 1/f noise. The signal is estimated effectively from noise image.
AEG has successfully developed a family of PtSi detection modules to cover various applications. The development was performed in a cooperation with Daimler Benz Research and Technology F2M and Telefunken Microelectronic TEMIC EZIS. The modules are designed around 2 staring PtSi focal plane arrays (FPA) having 256 X 256 pixels or 640 X 486 pixels, respectively. Both arrays are identical in their basic features like 24 micrometers pitch, > 60% fillfactor, variable integration time, optional interlaced and non interlaced rolling frame readout, subframe capability and excellent thermal resolution with measured values for the NETD < 70 mK (300 K, 20 ms, F/1.4). The FPA's are integrated either in integrated dewar cooler assemblies with a 1/3 W split linear compressor for the 256 X 256 FPA or a 1 W split linear compressor for the 640 X 486 FPA, respectively, or designed for the use in seeker applications with a Joule Thomson cryocooler (640 X 486 FPA only). The modules are completed by different miniaturized types of electronics, providing all DC and clock supplies to drive the FPA's and providing the customer with either a buffered analog or a 14 Bit resolution digital interface. Digital signal processor (DSP) based image correction units were developed for testing the units. The DSP boards provide the ability for freely programmable real-time functions like 2 point correction or other data manipulations in camera applications. The modules and their key features are reviewed together with their performance data.
Properties of n-epilayer InAs-SiO2 interface with various chemical treatments of InAs surface have been studied. Epilayer InAs films (Nd equals 1015 cm-3) of 5 - 7 micron thickness has been grown on n+-substrate with doping level 3.1018 cm-3. High quality properties of MIS-structures have been observed: surface state density < 1011 cm-2 eV-1, flat band voltage 2 - 5 V for SiO2 120 nm thickness. The array of photosensitive 128 X 128 MIS-structures with In2O3 gate has been mounted on silicon readout multiplexer by flip-chip method. The detectivity of InAs-cells in range of temperatures 80 - 100 K is more than 2(DOT)1012 cmHz1/2W-1.
We used the heterostructures of HgCdTe/CdZnTe/GaAs grown by molecular beam epitaxy for fabrication of photoconductor devices. The composition of MCT films throughout the thickness was controlled in situ by ellipsometry during the growth process. There were wide band gap layers at the interface and at the surface of the MCT films for decreasing the surface recombination which strongly influences on devices characteristics. The use of n-type material for LWIR photoconductors (77 K, the cutoff wavelength is more than 13 mkm) with good performance was demonstrated. The detectivity in maximum of wavelength dependence varies in interval (1.5 divided by 5)(DOT)1010 cmHz1/2 W-1. P-type material was used for MWIR photoconductors that operated at room and near room temperatures with the close to the theoretical value detectivity.
II-VI and IV-VI compound semiconductors such as PbTe, CdTe and HgCdTe crystals were grown from melt with a special technique through Carbon Film formed on the wall of quartz tube by the process of Thermal Decomposition (CFTD). The efficiency of CFTD was investigated by means of X-ray Photoelectron Spectroscopy. The results show that the line of Carbon Film is 0.5 eV lower than the line of the graphite. The Carbon film can avoid the contamination and the sticking between the quartz tube and the crystal. The comparative study of the quartz tube wall with the CFTD and those without CFTD, the tube wall before crystallization and those after crystallization and the surface of the crystals grown in the tubes was conducted separately. The results agree with the measuring of the Auger electron spectrum.
We report significant improvements in the performance of short wavelength infrared 128 X 128 focal plane arrays at room temperature. Using InGaAs and HgCdTe detector materials coupled to readout multiplexers having gate modulated detector interface, sensitivity that is near the theoretical detector-limited levels has been achieved via both low detector dark current and self-adjusting readout current gain. Extrapolating to nocturnal imaging conditions, the uncooled FPA-level sensitivities of 1.68 micrometers InGaAs and 1.86 micrometers HgCdTe arrays are shown to be within 35% and 80% of theoretical, respectively.
Producibility and factory improvements continue to advance the state-of-the-art in hybrid uncooled infrared detector manufacturing. The emphasis has shifted from proof-of- principle experiments to implementation and refinement in the areas of facilities, statistical process control, wafer level processing, and in the resolution of several key yield problems. Improvements in yield, throughput, and consistency demonstrate the maturation of Texas Instruments' detector factory from a research and development oriented lab to a production facility. Reliability and field testing are also confirming detector suitability to the market. The present discussion addresses these recent developments and their impact on the evolution toward a low cost, infrared detector.
This paper presents the design and performance of Cincinnati Electronics newest portable infrared imaging system, the NightMaster. The system incorporates a number of advanced features to achieve low power, compact size, and high system magnification, while maintaining the exceptional thermal sensitivity of other Cincinnati Electronics focal plane array (FPA) based imager products. The sensor assembly is a 256 X 256 MWIR Imager Antimonide (InSb) staring FPA, integrated to a low power, high reliability microcooler. Some of the system features include: a lightweight, f/4 50 mm/250 mm dual field of view telescope assembly, low power analog electronics, `on demand' digital electronics for `field' calibration using internal thermal sources, 12-bit real time digital data output, and RS-422 serial interface for full remote control capability. These and other features and performance data will be described.
Bulk silicon micromachined IR bolometer detectors operating at room temperature are presented. These devices are based on VO2 films typically exhibiting a thermal coefficient of resistance of the order of -3%/ degree(s)C. Detector sizes are 50 micrometers X 50 micrometers and 100 micrometers X 100 micrometers , and they are arranged in 1 X 64, 1 X 128 and 1 X 256 pixel linear arrays. A test bench for detector performance evaluation is described. The fabricated detectors exhibit responsivities of up to approximately 20,000 V/W, normalized detectivities typically exceeding 108 cmHz1/2 W-1, and response times typically below 20 ms, At 300 K and a frequency of 30 Hz, the noise equivalent temperature difference for these detectors is of the order of 3 X 10-2 degree(s)C. A bolometer simulation tool is also briefly described.
An infrared detector system based on high-Tc superconducting (HTS) membrane bolometer is reported. Superconducting transition-edge bolometer has been manufactured by silicon micromachining using an epitaxial GdBa2Cu3O7-x film on an epitaxial yttria- stabilized zirconia buffer layer on silicon. The active area of the element is 0.85 X 0.85 mm2. The membrane thickness is 1 micrometers , those of the buffer layer and HTS films are 50 nm. The detectivity of bolometer, D*, is 3.8 X 109 cm Hz1/2 W-1 at 84.5 K and within the frequency regime 100 < f < 300 Hz. The optical response is 580 V/W at time constant 0.4 ms. This is one of the fastest composite type HTS-bolometer ever reported. The bolometer is mounted on a metal N2-liquid cryostat, which fits the preamplifier. With the volume of N2-reservoir being 0.1 liter, the cryostat holds nitrogen for about 8 hours. Using only wire heater with constant current, the temperature stability of about 0.03 K/h is achieved. The detector system can be used in IR- Fourier spectroscopy at wavelengths longer than the typical operating range of semiconductor detectors (wavelength greater than about 20 micrometers ).