Yan Desroches

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.

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.

Design, manufacturing, and qualification of an uncooled microbolometer focal plane array–based radiometric package for space applications

Uncooled microbolometer detectors are well suited for space applications due to their low power consumption while still exhibiting adequate performance. Furthermore, the spectral range of their response could be tuned from the mid- to the far-infrared to meet different mission requirements. If radiometric measurements are required, the radiometric error induced by variation of the temperature of the detector environment must be minimized. In a radiometric package, the detector environment is thermally stabilized by means of a temperature-controlled radiation shield. The radiation shield must be designed to prevent stray radiation from reaching the detector. A radiometric packaging technology for uncooled microbolometer FPAs is presented. The selection of materials is discussed and the final choices presented based on thermal simulations and experimental data. The radiometric stability with respect to stray light and variation of the temperature of the environment as well as the different noise components studied by means of the Allan variance are presented. It is also shown that the device successfully passed the prescribed environmental tests without degradation of performance.

Introducing a 384x288 pixel terahertz camera core

Terahertz is a field in expansion with the emergence of various security needs such as parcel inspection and through-camouflage vision. Terahertz wavebands are characterized by long wavelengths compared to the traditional infrared and visible spectra. However, it has recently been demonstrated that a 52 μm pixel pitch microscanned down to an efficient sampling pitch of 26 μm could provide useful information even using a 118.83 μm wavelength. With this in mind, INO has developed a terahertz camera core based on a 384x288 pixel 35 μm pixel pitch uncooled bolometric terahertz detector. The camera core provides full 16-bit output video rate.

Influence of ceramic package internal components on the performance of vacuum sealed uncooled bolometric detectors

INO has developed a hermetic vacuum packaging technology for uncooled bolometric detectors based on ceramic leadless chip carriers (LCC). Cavity pressures less than 3 mTorr are obtained. Processes are performed in a state-of-the art semi-automated vacuum furnace that allows for independent activation of non-evaporable thin film getters. The getter activation temperature is limited by both the anti-reflection coated silicon or germanium window and the MEMS device built on CMOS circuits. Temperature profiles used to achieve getter activation and vacuum sealing were optimized to meet lifetime and reliability requirements of packaged devices. Internal package components were carefully selected with respect to their outgassing behavior so that a good vacuum performance was obtained. In this paper, INO’s packaging process is described. The influence of various package internal components, in particular the CMOS circuits, on vacuum performance is presented. The package cavity pressure was monitored using INO’s pressure microsensors and the gas composition was determined by internal vapor analysis. Lifetime was derived from accelerated testing after storage of packaged detectors at various temperatures from room temperature to 120°C. A hermeticity yield over 80% was obtained for batches of twelve devices packaged simultaneously. Packaged FPAs submitted to standard MIL-STD-810 reliability testing (vibration, shock and temperature cycling) exhibited no change in IR response. Results show that vacuum performance strongly depends on CMOS circuit chips. Detectors packaged using a thin film getter show no change in cavity pressure after storage for more than 30 days at 120°C. Moreover, INO’s vacuum sealing process is such that even without a thin film getter, a base pressure of less than 10 mTorr is obtained and no pressure change is observed after 40 days at 85°C.

Pressure sensing in vacuum hermetic micropackaging for MOEMS-MEMS

Packaging constitutes one of the most costly steps of MEMS/MOEMS manufacturing. Uncooled IR bolometers require a vacuum atmosphere of 1 mTorr and can be integrated with the IR bolometers in a die-level packaging process or microfabricated simultaneously on the same die. We present the typical performance and measurement uncertainty of these pressure sensors along with a reading method that provides a pressure measurement with a dependence on the package temperature as low as 0.7%/°C. A complex reading circuit or temperature control of the packages are not required, making the pressure sensor well adapted for low-cost high-volume production and integration with IR bolometer arrays.

Novel spot size converter for coupling standard single mode fibers to SOI waveguides

We have designed and numerically simulated a novel spot size converter for coupling standard single mode fibers with 10.4μm mode field diameter to 500nm × 220nm SOI waveguides. Simulations based on the eigenmode expansion method show a coupling loss of 0.4dB at 1550nm for the TE mode at perfect alignment. The alignment tolerance on the plane normal to the fiber axis is evaluated at ±2.2μm for ≤1dB excess loss, which is comparable to the alignment tolerance between two butt-coupled standard single mode fibers. The converter is based on a cross-like arrangement of SiOxNy waveguides immersed in a 12μm-thick SiO2 cladding region deposited on top of the SOI chip. The waveguides are designed to collectively support a single degenerate mode for TE and TM polarizations. This guided mode features a large overlap to the LP01 mode of standard telecom fibers. Along the spot size converter length (450μm), the mode is first gradually confined in a single SiOxNy waveguide by tapering its width. Then, the mode is adiabatically coupled to a SOI waveguide underneath the structure through a SOI inverted taper. The shapes of SiOxNy and SOI tapers are optimized to minimize coupling loss and structure length, and to ensure adiabatic mode evolution along the structure, thus improving the design robustness to fabrication process errors. A tolerance analysis based on conservative microfabrication capabilities suggests that coupling loss penalty from fabrication errors can be maintained below 0.3dB. The proposed spot size converter is fully compliant to industry standard microfabrication processes available at INO.

Small uncooled bolometers with a broad spectral response

This paper reports the infrared spectral responses of 17 and 35 μm uncooled bolometers fabricated at INO. They are measured by making use of an external readout circuit along with a monochromator. As expected, the spectral absorption strongly depends on the bolometer stack as well as the pixel layout. By proper selection of design parameters, the spectral response can be made flat from 3 to 14 μm without significant deterioration of the detector figure of merit.

Customized packaged bolometers in niche applications at INO

This paper reviews recent developments in customized packaged bolometers at INO with an emphasis on their applications. The evolution of INOs bolometer packages is also presented. Fully packaged focal plane arrays of broadband microbolometers with expanded absorbing range are shown, for applications in spectroscopic and THz imaging. This paper also reports on the development of customized packaged bolometer focal plane arrays (FPAs) for space applications such as a multispectral imaging radiometer for fire diagnosis, a far infrared radiometer for in-situ measurements of ice clouds and a net flux radiometer for Mars exploration.

Wideband response of a terahertz-millimeter imager based on a 384x288 pixel uncooled bolometric detector

In the past, bolometer-based imagers have been used for earth observation. Uncooled-bolometer based imagers are especially well suited for this due to their low power consumption. NIRST (New Infra-Red Sensor Technology), an example of an imager based on uncooled bolometers, monitors high temperature events on the ground related to fires and volcanic events, and will measure their physical parameters and takes measurements of sea surface temperatures mainly off the coast of South America as well as other targeted opportunities. NIRST has one band in the mid-wave infrared centered at 3.8 um with a bandwidth of 0.8 um, and two bands in the thermal infrared, centered respectively at 10.85 and 11.85 um with a bandwidth of 0.9 um.