Francis Picard

Vanadium oxide films for optical switching and detection

Structural, electrical, and optical properties of the polycrystalline films of VO2, V2O5, and mixtures of these two oxides are presented. Resistivity change by a factor larger than 103 accompanying the semiconductor-metal phase transition in the VO2 films is reported. A significant contrast in optical transmittance for the two phases of VO2 is observed. High temperature resistivity and optical transmittance of the V2O5 films are shown. Values of the temperature coefficient of resistance in some of the VO2 films in their semiconducting phase and in some of the V2O5 films are as high as 5.2 and 4% per degree Celsius, respectively. Phase switching properties of the VO2-V2O5 films are described. Applications of the fabricated films include optical switches and bobmetric-type light detectors.

Micromachined, uncooled, VO2-based, IR bolometer arrays

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.

128 x 128 pixel uncooled bolometric FPA for IR detection and imaging

An uncooled IR camera making use of a 128 X 128 pixel bolometric FPA is presented. The reconfigurable bolometric focal plane array consist of 50 micrometer X 50 micrometer pixels and simple on-chip CMOS readout electronics which can be operated in random access, independent row and column clocking, and self-scanning modes. Depending on the selected pixel format and frame rate, the FPAs NETD varies from 0.52 degrees Celsius down to 0.10 degrees Celsius. The modular IR camera is software configured and provides RS170A analog video and 12-bit TTL format digital outputs.

Micromachined VO2-based uncooled IR bolometric detector arrays with integrated CMOS readout electronics

Uncooled IR bolometric detectors fabricated using surface silicon micromachining are presented. The detector fabrication process employs a polyamide sacrificial layer, and a VO2 thermistor layer exhibiting a thermal coefficient of resistance on the order of -3 percent/degrees C. Detector sizes are 100 micrometers X 100 micrometers and 50 micrometers X 50 micrometers , and 64 X 64 and 128 X 128 pixel arrays are fabricate. The detectors exhibit responsivities of up to 15 000 VW-1, normalized detectivities typically exceeding 108 cm Hz1/2W-1, and response times below 20 ms. Three integrated readout circuit designs for 64 X 64 and 128 X 128 pixel detector arrays, fabricated using a standard 1.5 micrometers CMOS process,a re described. These circuits include several test and detector nonuniformity correction features and can operate in either self scanning mode at a rate of 30 frames per second, or in the random access mode in which column and row addresses are input directly.

Commercial and custom 160x120, 256x1, and 512x3 pixel bolometric FPAs

INO has been active in microbolometer and FPA technology development since the early 1990s. Microbolometer detectors based on VO2 films with TCR above 3% are typically fabricated. VOx films with TCR above 2% have been developed for applications where FPA temperature is not stabilized. INO is continuing its development of high fill factor pixels with sizes down to 25 micrometers and new macro- and micro-packaging technology. All fabrication is done on six inch wafers in INOs newly expanded clean room facility. INO currently offers as standard products 256x1 and 160x120 pixel FPAs with 52 micrometers pixel pitch. Both arrays have simple, robust, and versatile CMOS readout integrated circuits (ROICs) that may be accessed in self-scanning or random access mode, and reference detectors for on-chip coarse offset and temperature drift compensation. Single frame NETDs (f/1, 300 K, 8-12 micrometers ) are on the order of 150 - 250 mK and may be reduced by frame averaging. Prototyping boards have been developed for both arrays, and the 160x120 FPA has been integrated in a number of thermal cameras and instruments. In collaboration with its clients, INO has developed several FPAs for specific space and terrestrial applications. Custom ROICs fabricated in several different CMOS processes from multiple foundries have been used. A 512x3 pixel microbolometer FPA with 39 micrometers pitch is being developed for the European Space Agency. The array is designed for multi-spectral pushbroom imaging applications and features a novel ROIC with very low 1/f noise, pixel by pixel offset and drift compensation, variable integration time, and digital output. Its single frame NETD (f/1, 300 K, 8-12 micrometers ) is nominally 80 mK.

Flexible micromirror linear array for high-resolution projection display

The visual displays of contemporary military flight simulators lack adequate definition to represent scenes in basic fast-jet fighter tasks. For example, air-to-air and air-to-ground targets are not projected with sufficient contrast and resolution for a pilot to perceive aspect, aspect rate and object detail at real world slant ranges. Simulator display geometries require the development of ultra-high resolution projectors with greater than 20 megapixel resolution at 60 Hz frame rate. A new micromirror device has been developed to address this requirement; it is able to modulate light intensity in an analog fashion with switching times shorter than 5 μs. When combined with a scanner, a microlaser and Schlieren optics, a linear array of these flexible micromirrors can display images composed of thousands of lines at a frame rate of 60 Hz. The approach selected for light modulation and the micromirror fabrication process flow are reviewed. Static and dynamic performances of these electrostatic MOEMS are described. Preliminary results following the integration of the described modulator into a projector prototype are reported. Developments toward a fully addressable 2000 × 1 flexible micromirror array are presented. The specifications and design of the CMOS circuit required to control this micromirror array are described. Packaging issues related to these large arrays are discussed.

Miniature VO2-based bolometric detectors for high-resolution uncooled FPAs

Prototypes of VO2-based bolometric detectors with lateral dimensions of 25 X 25, 30 X 30, 35 X 35, 40 X 40 and finally 50 X 50 micrometers2 and fill factors approaching 90% are presented. These detectors are grouped in hardwired linear arrays as large as 512 X 1 pixels. Under DC biasing, the fabricated detectors, even the smallest ones, exhibit responsivities from 48,000 to 120,000 VW-1, detectivities in the range of 1.5 X 108 cm Hz1/2W-1 and response times in the range of 5 ms. These new bolometric detector structures contain hidden-legs placed completely underneath the bolometer platform. Results of simulations of the mechanical, optical and electrical properties of these new detector structures are presented. A complete detector fabrication process flow is described.

256 x 1 and 256 x 40 pixel bolometer arrays for space and industrial applications

Three types of uncooled IR bolometric detector arrays equipped with 256 X 1 and 256 X 40 VO2 thermistor pixels and on-chip readout electronics are presented. These reconfigurable arrays consist of 50 micrometer X 50 micrometer pixels and CMOS readout electronics that can be operated either in random access mode or in self-scanning mode. Depending on the operational conditions, the NETD of the arrays can be as low as 20 mK.

Operation modes for a linear array of optical flexible reflective analog modulators

A unique MEMS based spatial light modulator has been developed by INO and its partners for projection display applications. This unique device incorporates a linear array of micromirrors. Each micromirror is a 25 μm x 25 μm microbridge. Electrostatic actuation allows the control of the curvature of each micromirror independently. Combined with appropriate optics, this allows display of images with well over a thousands columns at a frame rate of 60 Hz. Operation and performance of this modulator have already been reported in the literature (SPIE Proceeding, Vol. 4985, p. 44-55; SPIE Proceeding, Vol. 5289, p. 284-293). In the latter paper, a brief description of various possible operation modes of this modulator has been presented. The objective of the present article is to provide an in-depth study of these operation modes. The study is done using numerical simulations. Several methods are employed to propagate the laser beam illuminating the micromirrors through the optical system. The gaussian beam superposition method is used to propagate the laser beam from the system input to the micromirrors. The reflexion on the micromirrors is computed by ray tracing. Finally, the angular spectrum of plane waves method is used to propagate the reflected coherent beam through Schlieren optics which converts the curvature of the micromirror into gray levels. The simulated optical response of the system as a function of the micromirror curvature is provided for various operation modes.

64 x 64, 128 x 128, 240 x 320 pixel uncooled IR bolometric detector arrays

Several prototypes of individual VO2-based bolometric detectors and their arrays consisting of 64 by 64, 128 by 128 and 240 by 320 pixels are presented. The fabrication method and the device characterization results are described. Three types of readout integrated circuits for the arrays are also presented. A custom vacuum package for the IR bolometric detector arrays is descried.