Felix Cayer

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.

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.

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.

Novel beam-steering micromirror device

A novel type of light modulating micromirror device has been designed and fabricated. A unique hinge structure provides the device with the potential for modulating both the phase and amplitude of light signals, while its high thermal conductivity makes the device amenable to high power laser applications. An extremely high fill factor can be attained since the hinges lie entirely beneath the mirror surface. This hidden hinge structure is comprised of a single level and therefore involves a simple fabrication process. Micromirrors with dimensions ranging from 100 micrometers X 100 micrometers to 300 micrometers X 300 micrometers with maximum deflection angles from 2 degree(s) to 4 degree(s) were fabricated. The devices were characterized in terms of the reflecting surface optical quality, the operational modes attainable, the critical voltages (as low as 15 volts), and the response time (as short as 125 microsecond(s) ).

Linear microbolometer arrays for space and terrestrial imaging

Linear detector array formats are suitable for applications where relative motion between the detector and scene provides an intrinsic scanning mechanism, such as industrial inspection systems and satellite-based earth and planetary observation. The linear array format facilitates the introduction readout features not available in 2-D formats and when combined with low cost packaging approaches reduces sensor cost. We present two linear uncooled detector arrays based on VOx microbolometer technology and integrated CMOS readout electronics. The IRL256B is a linear array of 256 detectors on a 52 μm pitch. It includes a parallel array of 256 reference detectors to provide coarse offset correction and substrate temperature drift compensation. The IRL512A consists of 3 parallel lines of 512 pixels on a 39 μm pitch. It is particularly well suited to multi-spectral pushbroom imaging applications. Each pixel includes active and reference detectors to reduce pixel offset, eliminate common mode power supply noise and increase immunity to chip temperature drift. All pixels are integrated in parallel and the data are output in 14-bit digital format on three parallel output buses. The microbolometer detector design can be customized for selected wavelength ranges from NIR to VLWIR. The IRL256B has been integrated in industrial thermal line-scan imagers and spectrometers and may also be employed in uncooled airborne imaging and scanned surveillance or inspection systems. The IRL512A has been selected as the baseline detector for a number of future earth observation satellite missions.

Latest developments in active remote sensing at INO

Remote sensing or stand-off detection using controlled light sources is a well known and often used technique for atmospheric and surface spatial mapping. Today, ground based, vehicle-borne and airborne systems are able to cover large areas with high accuracy and good reliability. This kind of detection based on LiDAR (Light Detection and Ranging) or active Differential Optical Absorption Spectroscopy (DOAS) technologies, measures optical responses from controlled illumination of targets. Properties that can be recorded include volume back-scattering, surface reflectivity, molecular absorption, induced fluorescence and Raman scattering. The various elastic and inelastic backscattering responses allow the identification or characterization of content of the target volumes or surfaces. INO has developed instrumentations to measure distance to solid targets and monitor particles suspended in the air or in water in real time. Our full waveform LiDAR system is designed for use in numerous applications in environmental or process monitoring such as dust detection systems, aerosol (pesticide) drift monitoring, liquid level sensing or underwater bathymetric LiDARs. Our gated imaging developments are used as aids in visibility enhancement or in remote sensing spectroscopy. Furthermore, when coupled with a spectrograph having a large number of channels, the technique becomes active multispectral/hyperspectral detection or imaging allowing measurement of ultra-violet laser induced fluorescence (UV LIF), time resolved fluorescence (in the ns to ms range) as well as gated Raman spectroscopy. These latter techniques make possible the stand-off detection of bio-aerosols, drugs, explosives as well as the identification of mineral content for geological survey. This paper reviews the latest technology developments in active remote sensing at INO and presents on-going projects conducted to address future applications in environmental monitoring.

Novel applications of an affordable short-range digital lidar

The design and application results of an affordable short range (less than 100 m) digital LIDAR (LIght Detection And Ranging) system will be presented. This work was initiated because many short-range standoff detection applications would benefit from such a system. The lidar features a fiber-based component integrated in the optical module, which allows for hardware partial compensation of the backscattered signal losses observed at short distances due to a biaxial configuration of the lidar optics. This is an important advantage for particle density computations. The digitized backscattered laser signals are available for signal processing. A dedicated FPGA (Field Programmable Gate Array) allows for real-time averaging of the signal waveforms captured at the maximum 50-kHz pulse repetition frequency of the laser. Several application-specific tests have been performed. The first of these was real-time onboard monitoring of pesticide drift in agricultural spraying applications. The signal levels were sufficient for control of the spraying operations and prevention of pesticide drift into sensitive areas. The second was a dust monitoring application. The lidar was installed in a quarry and signals from dust clouds were recorded. Real-time monitoring capabilities were shown to be promising. Other applications involving detection of solid targets in degraded visibility conditions caused by fog or snowfalls were also tested and are discussed.

On-chip replication of high-sag micro-optical components fabricated by direct laser writing

This paper describes the fabrication of very high-sag (up to 42 μm) microlenses by direct laser writing and their integration onto a simple microoptical bench processed by conventional microfabrication technologies pertaining to MOEMS. At the heart of such a work is INOs laser writer. It is based on a He-Cd laser operating at 442 nm whose intensity can be modulated up to 1024 levels, and on a 40 nm accuracy X-Y translation stage. Laser writing into thick photoresist layers introduces however particular problems in terms of the roughness achievable. Simulations show that the writing beam diameter, the line-to-line spacing and the translation stage accuracy contribute to some unavoidable residual roughness. By applying optimized laser writing parameters, arrays of 1 x 5 aspherical microlenses were fabricated in a thick positive photoresist, along with alignment marks concurrently generated for on-chip alignment purposes. The microlenses were successfully integrated with a microoptical bench by first generating a UV-transparent mold from the photoresist laser written master. The microlenses imprinted in the mold were then replicated in a layer of hybrid glass material cast on the microoptical bench by UV-embossing with a modified MA6 mask aligner. The uniformity of focal lengths was approximately 3% as determined from best fits of profilometric traces. The replication with alignment of this array in a hybrid glass material was demonstrated on a 12 mm x 12 mm microoptical bench chip. An alignment accuracy of less than 5 μm was obtained. The replication error was less than about 4%. The measured surface roughness was 50-60 nm RMS, in good agreement with simulation results.

Microfabrication services at INO

MEMS (Micro Electro Mechanical Systems) technology has expanded widely over the last decade in terms of its use in devices and instrumentation for diverse applications. However, access to versatile foundry services for MEMS fabrication is still limited. At INO, the presence of a multidisciplinary team and a complete tool set allow us to offer unique MEMS foundry-type services. These services include: design, prototyping, fabrication, packaging and testing of various MEMS and MOEMS devices. The design of a device starts with the evaluation of different structures adapted to a given application. Computer simulation tools, like IntelliSuite, ANSYS or custom software are used to evaluate the mechanical, optical, thermal and electromechanical performances. Standard IC manufacturing techniques such as metal, dielectric and semiconductor film deposition and etching as well as photolithographic pattern transfer are available. In addition, some unique techniques such as on-wafer lithography by laser writing, gray-scale mask lithography, thick photoresist lithography, selective electroplating, injection moulding and UV-assisted moulding are available to customers. The hermetic packaging and a novel patented wafer-level micropackaging are also applied. This multifaceted expertise has been utilized to manufacturing of several types of MEMS devices as well as complex instruments including micromirror-type devices, microfilters, IR microbolometric detector arrays, complete cameras and multipurpose sensors.