Hubert Jerominek

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.

Noise-equivalent power characterization of an uncooled microbolometer-based THz imaging camera

A THz camera based on an uncooled microbolometer 160X120 pixel array with nominal pitch of 52 μm has been developed at INO and initial transmission and reflection images showed promise. In the present paper, the characterization of both standard infrared and THz-optimized uncooled microbolometer pixel arrays are presented at both infrared and THz wavelengths. Measurements in the THz region has been performed using non-uniform low-power quantum-cascade laser (QCL) and uniform high-power far-infrared laser (FIR laser) beams at 3 THz and 4.25 and 2.54 THz, respectively. A measurement comparison has been achieved in the infrared using a blackbody radiation. Different methods for noise-equivalent power (NEP) measurements have been investigated. These characterization methods are promising especially for non-uniform laser beams irradiated on pixel arrays. The NEP results obtained from the different methods are in good agreement independent of the method used in the experiments. The results show a high sensitivity of the THz-optimized pixel array in the THz region. Large beam area reflection imaging of obscured materials at 2.54 THz have been performed at video rates of 30 frames per second using the THz-optimized pixel array equipped with a semi-custom fast THz objective, proving that the INO THz camera provides a promising solution for stand-alone imaging systems.

A microbolometer-based THz imager

THz imaging is a very promising field rapidly growing in importance. This expanding field is at its early stage of development but already a large number of applications are foreseen. THz imaging promises to be a key technology in various fields, such as defense & security where it can be used to defeat camouflage. Based on its many years of experience in uncooled bolometers technology, INO has developed, assembled and characterized a prototype THz imager. The cameras 160 × 120 pixel array consists of pixels with a 52 μm pitch that have been optimized for the THz region. Custom camera electronics and an F/1 THz lens barrel complete the imager design. Real-time imaging at video rate of 30 frame/sec has been performed with a 3 THz quantum cascade laser set-up. THz images of numerous object-obscurant combinations are presented, proving the feasibility of video imaging in security screening applications.

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.

Resolution capability comparison of infrared and terahertz imagers

Infrared and terahertz are two imaging technologies that differ fundamentally in numerous aspects. Infrared imaging is an efficient passive technology whereas terahertz technology is an active technology requiring some kind of illumination to be efficient. Whats more, the detectors are also different and yield differences in the fundamental physics when integrated in a complete system. One of these differences lies in the size of the detectors. Infrared detectors are typically larger than the infrared wavelengths whereas terahertz detectors are typically smaller than the wavelength of illumination. This results in different constraints when designing these systems, constraints that are imposed by the resolution capabilities of the system. In the past INO has developed an infrared imaging camera core of 1024×768 pixels and tested some microscanning devices to improve its sampling frequency and ultimately its resolution. INO has also engineered detectors and camera cores specifically designed for active terahertz imaging with smaller dimensions (160×120 pixels). In this paper the evaluation of the resolution capabilities of a terahertz imager at the pixel level is performed. The resolution capabilities for the THz are evaluated in the sub-wavelength range, which is not actually possible in the infrared wavebands. Based on this evaluation, the comparison between the resolution limits of infrared detectors and the terahertz detectors at the pixel level is performed highlighting the differences between the wavebands and their impact on system design.

Video-rate THz imaging using a microbolometer-based camera

A THz 160×120 pixel array camera has been developed at INO. Real-time transmission and reflectance imaging at video rates of 30 frames/s were performed with a low-power 3 THz quantum cascade laser. Various hidden objects were imaged, proving feasibility of real-time THz imaging for security screening applications.

Hybrid wafer-level vacuum hermetic micropackaging technology for MOEMS-MEMS

Packaging constitutes one of the most costly steps of MEMS/MOEMS manufacturing. The package protects the MEMS devices and, in the case of MOEMS, it also provides light access to the device. In many cases, MEMS require a specific atmosphere for their proper functioning. The atmosphere should be kept invariable during the lifetime of the package in order to not degrade the performance of the device. Maintaining a constant atmosphere inside the package becomes more challenging as the cavity volume is decreased to the microliter and nanoliter range. Other packaging requirements are compatibility with wafer-level microfabrication techniques (cost reduction) and low temperature assembly in cases where temperature sensitive devices are to be packaged. In recent years, INO has performed a great amount of work towards the development of uncooled IR microbolometer detectors using VOx technology. Different pixel designs have been optimized for different applications. The bolometer pixels require a vacuum atmosphere below 10 mTorr to be maintained during the lifetime of the device in order to operate at their highest sensitivity. INOs micropackaging technology has been demonstrated to provide base pressures below 5 mTorr. An equivalent flow rate of 2.5×10-14 Torr.l/sec has been obtained for a device packaged without any getter. The advantages of INOs micropackaging technology are the possibility of achieving very low base pressures, the low temperatures required for the assembly (the package device is never exposed to a temperature above 150 °C) and its compatibility with hybrid wafer-level packaging. The technology has been developed for the micropackaging of INOs 160×120 pixel uncooled microbolometer FPA, but it is compatible with any other kinds of MOEMS-MEMS devices requiring vacuum hermetic packaging. In order to increase the lifetime of the package, knowledge of the gases outgassing inside the package is crucial. A hybrid approach has been chosen as it permits packaging only known-good dies and saving considerable quantities of IR window material. In INOs hybrid wafer-level packaging, dicing is performed only through one of the wafers, therefore reducing the risk of perturbing the vacuum during the separation of the different dies.