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Bolometric detector with thermal isolation by constriction and device for detecting infrared radiation that uses such a bolometric detectorRelated Patent Categories: Radiant Energy, Invisible Radiant Energy Responsive Electric Signalling, Infrared ResponsiveBolometric detector with thermal isolation by constriction and device for detecting infrared radiation that uses such a bolometric detector description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070205364, Bolometric detector with thermal isolation by constriction and device for detecting infrared radiation that uses such a bolometric detector. Brief Patent Description - Full Patent Description - Patent Application Claims
TECHNICAL FIELD [0001] The present invention relates to a bolometric detector as well as the device for detecting infrared radiation that uses such detectors. [0002] The invention has application areas in the field of infrared imaging in particular. DESCRIPTION OF THE PRIOR ART [0003] In infrared detectors, the use of devices configured in the form of an array and capable of operating at ambient temperatures, i.e. not requiring cooling to extremely low temperatures is known,--in contrast to detecting devices called "quantum detectors" which can only operate at extremely low temperature, typically that of liquid nitrogen. [0004] These uncooled detectors traditionally use the variation in a physical unit of an appropriate material as a function of temperature at around 300 K. [0005] In the case of bolometric detectors, this physical unit is electrical resistivity. [0006] Such an uncooled detector generally consists of: [0007] means of absorbing the infrared radiation and converting it into heat, [0008] means of thermally isolating the detector so that its temperature can rise due to the effect of the infrared radiation, [0009] thermometric means which, in the context of a bolometric detector, use a resistance element, [0010] and means of reading electrical signals provided by the thermometric means. [0011] Detecting devices intended for infrared imaging are produced as a one- or two-dimensional array of elementary detectors mounted on a substrate generally made of silicon which incorporates means of electrically exciting said elementary detectors and means of pre-processing the electrical signals generated by these elementary detectors. [0012] These means of electrical excitation and pre-processing are thus produced on the substrate and constitute a read-out circuit. [0013] A device comprising such an array of elementary detectors and an associated read-out circuit is generally placed in a package and is connected, especially electrically, to its external environment using classic technologies. The pressure inside such a package is reduced in order to limit thermal losses. The package also has a window that is transparent to the radiation to be detected. [0014] In order to observe a scene using this detector, the scene is projected through suitable optics onto the array of elementary detectors and clocked electrical stimuli are applied via the read-out circuit (also provided for this purpose) to each of the elementary detectors or to each row of such detectors in order to obtain an electrical signal that constitutes an image of the temperature reached by each elementary detector. [0015] This signal is then processed to a greater or lesser extent by the read-out circuit and then, if applicable, by an electronic device outside the package in order to generate the thermal image of the observed scene. FIGS. 1 and 2 show, respectively, a simplified perspective and top view of a bolometric detector according to the prior art. These Figures show the silicon substrate, referred to as (1), which accommodates, in particular, the read-out circuit. [0016] This substrate accommodates an integrated electronic circuit which comprises, on the one hand, the devices that generate the stimuli for said detector and the devices to read out the signals output by the latter and, on the other hand, multiplexing components that make it possible to convert the signals output by the various detectors into serial form and send them to a reduced number of outputs so that they can be analysed by a processing system, especially an imaging system of traditional style. [0017] The detector itself consists of a suspended membrane (2), above the substrate (1), most of which is intended to absorb incident radiation and convert it into heat, then into an electrical signal. [0018] Said-membrane (2) is suspended above the read-out circuit and therefore, in particular, substrate (1) by means of studs, posts or anchor points (3), more generically referred to as support areas or structures. [0019] In this way, an empty space that extends to a height typically of 1 to 5 .mu.m is defined between the substrate (1) and membrane (2). [0020] These support structures (3) are essentially vertical. They conduct electricity, thus making it possible to apply the excitation potentials to the conductive parts or electrodes that are among the components of the actual bolometric detector itself via flat stretched structures (4) that also conduct electricity but are thermally resistant. These flat, stretched structures (4) are conventionally referred to as arms. [0021] The suspended membrane (2) essentially comprises a layer (5) that absorbs incident thermal radiation. [0022] This absorption of radiation causes heating of this layer which transfers the temperature thus accumulated to a layer (6) deposited on the membrane that acts as a thermometer and is made of a bolometric material. [0023] This bolometric material traditionally consists of slightly or highly resistive p or n type polycrystalline or amorphous silicon but may also be made of vanadium oxide (V.sub.2O.sub.5 or VO.sub.2) made in a semiconducting phase or even ferrites with a spinel structure. [0024] As already stated, electrodes, conventionally located in the same plane as the detector, are used in order to define the electrical signal in the bolometric detector and these are referred to as coplanar electrodes or stacked electrodes or a sandwich structure as disclosed, for example, in American Patent U.S. Pat. No. 5,021,663. [0025] The various parameters that affect the level of performance of an uncooled bolometric detector include, in particular, mastering the design and construction of the elementary detectors and, especially, the micro bridges and posts, especially thermal isolation between the read-out circuit (1) and the suspended membrane (2). [0026] As already indicated, the space between the active part of the bolometer and the substrate comprising the read-out circuit, possibly coated with a layer that reflects infrared radiation, is a void apart from the posts or support areas (3) in order to prevent thermal losses due to solid conduction. Continue reading about Bolometric detector with thermal isolation by constriction and device for detecting infrared radiation that uses such a bolometric detector... 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