Uncooled Technology Research Articles

Uncooled infrared detectors toward smaller pixel pitch with newly proposed pixel structure

An uncooled infrared (IR) focal plane array (FPA) with 23.5 μm pixel pitch has been successfully demonstrated and has found wide commercial applications in the areas of thermography, security cameras, and other applications. One of the key issues for uncooled IRFPA technology is to shrink the pixel pitch because the size of the pixel pitch determines the overall size of the FPA, which, in turn, determines the cost of the IR camera products. This paper proposes an innovative pixel structure with a diaphragm and beams placed in different levels to realize an uncooled IRFPA with smaller pixel pitch (≦17 μm ). The upper level consists of a diaphragm with VO x bolometer and IR absorber layers, while the lower level consists of the two beams, which are designed to be placed on the adjacent pixels. The test devices of this pixel design with 12, 15, and 17 μm pitch have been fabricated on the Si read-out integrated circuit (ROIC) of quarter video graphics array (QVGA) (320×240 ) with 23.5 μm pitch. Their performances are nearly equal to those of the IRFPA with 23.5 μm pitch. For example, a noise equivalent temperature difference of 12 μm pixel is 63.1 mK for F/1 optics with the thermal time constant of 14.5 ms. Then, the proposed structure is shown to be effective for the existing IRFPA with 23.5 μm pitch because of the improvements in IR sensitivity. Furthermore, the advanced pixel structure that has the beams composed of two levels are demonstrated to be realizable.

Polycrystalline lead selenide: the resurgence of an old infrared detector

AbstractThe existing technology for uncooled MWIR photon detectors based on polycrystalline lead salts is stigmatized for being a 50-year-old technology. It has been traditionally relegated to single-element detectors and relatively small linear arrays due to the limitations imposed by its standard manufacture process based on a chemical bath deposition technique (CBD) developed more than 40 years ago. Recently, an innovative method for processing detectors, based on a vapour phase deposition (VPD) technique, has allowed manufacturing the first 2D array of polycrystalline PbSe with good electro optical characteristics. The new method of processing PbSe is an all silicon technology and it is compatible with standard CMOS circuitry. In addition to its affordability, VPD PbSe constitutes a perfect candidate to fill the existing gap in the photonic and uncooled IR imaging detectors sensitive to the MWIR photons. The perspectives opened are numerous and very important, converting the old PbSe detector in a serious alternative to others uncooled technologies in the low cost IR detection market. The number of potential applications is huge, some of them with high commercial impact such as personal IR imagers, enhanced vision systems for automotive applications and other not less important in the security/defence domain such as sensors for active protection systems (APS) or low cost seekers.Despite the fact, unanimously accepted, that uncooled will dominate the majority of the future IR detection applications, today, thermal detectors are the unique plausible alternative. There is plenty of room for photonic uncooled and complementary alternatives are needed. This work allocates polycrystalline PbSe in the current panorama of the uncooled IR detectors, underlining its potentiality in two areas of interest, i.e., very low cost imaging IR detectors and MWIR fast uncooled detectors for security and defence applications. The new method of processing again converts PbSe into an emerging technology.

Continuous facesheet low voltage deformable mirrors

Litton/Itek Optical Systems has been a leader in the development of deformable mirrors for use in high quality optical systems since 1973. The monolithic piezoelectric mirror (MPM), which was introduced in 1974, has been the quality product against which all other visible wavelength compensators have been compared. The stacked actuator deformable mirror (SADM), first delivered in 1980, set new performance standards for infrared systems. These devices continue to maintain high quality large stroke performance in the field. In 1981 Itek began the development of a new concept in deformable mirrors, the low voltage electrodisplacive mirror (LVEM). Itek teamed with Bell Aerospace in 1984 to develop a cooled silicon electrodisplacive mirror (CSEM) technology. The CSEM development emphasized extending the LVEM technology to high energy laser systems applications by incorporating a silicon multiport pin-fin heat exchanger into the mirror structure. Recently, in 1988, Itek began developing a cost efficient cooled mirror technology compatible with moderate flux levels and quantity production. The LVEM uncooled technology has matured and represents the current state of the art in deformable mirror performance. Upon its maturity, the CSEM technology will provide both high performance and cost efficient cooled deformable mirrors for the needs of the high energy laser community.