Radiant energy – Invisible radiant energy responsive electric signalling – Infrared responsive
Reexamination Certificate
1999-07-13
2001-11-20
Hannaher, Constantine (Department: 2878)
Radiant energy
Invisible radiant energy responsive electric signalling
Infrared responsive
C250S332000, C250S330000
Reexamination Certificate
active
06320189
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a device for detecting multispectral infrared/visible radiation with a space coherence or even a space-time coherence in certain embodiments.
It is used in the field of the recognition of objects or persons and in the surveillance field.
PRIOR ART
In the recognition and surveillance fields, numerous detector types can be used as a function of the radiation type to be detected.
In particular, for the detection of visible radiation, it is standard practice to use photoelectric detectors produced from semiconductor materials, whose photoelectric properties make it possible to convert visible radiation into electrical signals. Thus, the illumination by a visible radiation generates, within the semiconductor materials, a number of carriers proportional to the absorbed light energy. The most widely used visible detectors are of the photovoltaic type and are e.g. pn, pin, avalanche or SCHOTTKY photodiodes or alternatively phototransistors. The electric charges from these detectors are then collected, stored and processed by multiplexing devices, or reading devices of the CCD or CMOS type.
Moreover, for the detection of infrared (IR) radiation, it is standard practice to use uncooled, thermal detectors. These detectors generally comprise one or more sensitive elements, which can be heated by an infrared radiation in the III band (8 to 12 &mgr;m), characteristic of the temperature and the emissivity of the bodies observed.
Thus, the temperature rise of a sensitive element produces a variation of one of the electrical properties of the sensitive material: appearance of electric charges by the pyroelectric effect or variation of the capacitance by a change of the dielectric constant or a variation of the resistance of a semiconductor or metallic material.
However, for such detectors to have good performance characteristics, it is necessary for the sensitive material to have a low calorific mass, a good thermal insulation of the active layer relative to its support, which requires the formation of a microbridge and a high sensitivity of the effect of converting the heating into an electrical signal.
Only thin film detectors satisfy these conditions and in particular bolometric thermal detectors, such as those described in patent application FR-A-2 752 299 and the patent application filed under No. 97 16791. Metallic bolometric detectors are generally made from nickel (Ni), titanium (Ti), titanium nitride (TiN) or platinum (Pt).
Such detectors can be connected in array form to a silicon multiplexing circuit of the CMOS or CCD type (also known as a reading circuit) in order to implement monolithic infrared imagers operating at ambient temperature.
An example of a microbridge bolometric detector (reference
28
) on a multiplexing circuit is shown in FIG.
1
. The CMOS or CCD-type multiplexing circuit carries the reference
1
and the microbridge the reference
4
. Said microbridge
4
comprises supports
5
supporting active elements of the microbridge and the connections of said active elements to the multiplexing circuit
1
by metal connections
6
incorporated into an insulating material layer
2
covering the multiplexing circuit
1
. The active elements of the microbridge
4
are a layer of material sensitive to IR radiation designated
9
and electrodes
7
extended by thermal insulation arms
8
. A reflector
3
is placed beneath the microbridge for reflecting the IR radiation towards the sensitive material
9
.
For the detection of multispectral radiation detection devices exist which are combined or grouped in the form of strips or mosaics. In such devices, detectors of a first radiation type are associated with detectors of a second radiation type, being juxtaposed or adjacent to one another in the same plane or in different planes, or are strictly superimposed.
The most widespread superimposed multispectral systems in the infrared detection field are implemented from a stack of epitaxial layers of Cd
x
Hg
1−x
Te having different compositions, which are themselves epitaxied on an infrared radiation-transparent substrate. The spectral absorption bands are determined by the composition x of the detecting layers. These detectors are of the photovoltaic type and operate at low temperature in a wavelength range between 1 and 12 &mgr;m, i.e. outside the visible radiation spectrum. Thus, such systems do not permit the simultaneous detection of IR and visible radiation.
In the infrared/visible radiation field, the most widespread multispectral detection systems are implemented on the basis of two cameras, which scan the spectral bands, respectively of the infrared and the visible, as described in the article “IR/VIS Light Surveillance System Finds—Applications in Defense, Security”, EUROPHOTONICS, Dec./Jan. 1998. In such a system, the infrared camera is constituted by cooled detectors, made from InSb or Cd
x
Hg
1−x
Te and operating in bands II and III. The visible camera is e.g. implemented on the basis of a CCD-type component.
Other multispectral detection systems consist of a juxtaposing of Cd
x
Hg
1−x
Te, cooled, infrared (IR) detectors and silicon, visible (VIS) detectors. The radiation from the scene observed is then split by an external device into two beams, which are then focussed onto each type of detector.
In such a system, the visible detectors operate at ambient temperature and the infrared detectors operate in the cold. Therefore, such systems are costly and complex.
DESCRIPTION OF THE INVENTION
The invention aims at obviating the disadvantages of the procedures described hereinbefore.
To this end, it proposes a multispectral infrared/visible detection device using simple, uncooled, thermal, photoelectric detectors, which are approximately superimposed and which can have one or more electrodes and/or a common active layer, which ensures a space (or in certain cases a space-time) coherence of the detection and prevents a complex, costly detector cooling.
More specifically, the invention relates to a multispectral infrared/visible radiation detection device comprising:
at least one bolometric detector having at least one active layer and two control electrodes and ensuring the detection of IR and visible radiation and
at least one photoelectric detector having at least two active layers and two control electrodes and solely ensuring the detection of visible radiation. An electronic processing of the results of the two detections then makes it possible to access the infrared component of the incident radiation.
The bolometric detector and the photoelectric detector are characterized in that they are of the uncooled type and are superimposed and combined with one another in order to constitute the same sensitive element.
In the device according to the invention, the sensitive element has a microbridge connected to a multiplexing circuit via supporting and connecting means.
According to a first embodiment, the microbridge incorporates the active layers of the bolometric detector and photoelectric detector, as well as their control electrodes.
In this embodiment, the bolometric detector and the photoelectric detector can have at least one common control electrode.
According to a variant of the invention, the active layers of the photoelectric detector form a photodiode having a lower electrode and an upper electrode, the latter also constituting one of the electrodes of the bolometric detector. In this case, the device has a type P
+
a-Si:H layer common to the two detectors, the photoelectric detector also having an intrinsic a-Si:H layer and a type N
+
a-Si:H layer.
According to another variant of the invention, the active layers of the photoelectric detector form an insulated photodiode. In this case, the bolometric detector active layer is of type P
+
/N
+
a-Si:H or of VOx/metal and the photoelectric detector active layers are of type P
+
a-Si:H, intrinsic a-Si:H and type N
+
a-Si:H.
According to yet another variant, the active layers of the photoelectric detector form a phototr
Beccia Chantal
Ouvrier-Buffet Jean-Louis
Vilain Michel
Commissariat A l'Energie Atomique
Hannaher Constantine
Israel Andrew
Pearne & Gordon LLP
LandOfFree
Device for the detection of multispectral infrared/visible... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Device for the detection of multispectral infrared/visible..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Device for the detection of multispectral infrared/visible... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2586773