LWIR camera sets new standard for sensitivity

29 Nov 2010

French project develops long-wavelength infrared mercury cadmium telluride camera with milli-Kelvin thermal resolution.

A team headed by CEA-Leti in France has developed an imaging array with record-breaking thermal resolution. The mercury cadmium telluride (MCT) detector, designed for defense and security applications, operates in the long-infrared range at 8-10 µm.

The key attribute of the 320 x 256 pixel camera is its remarkable sensitivity – offering a resolution of just 1-2 mK at ambient temperature and a typical 25-50 Hz frame-rate.

To achieve those operating characteristics, CEA-Leti researchers came up with a new reading circuit based on a 0.18 µm CMOS die that provides analog-to-digital conversion at each pixel in the MCT array.

“This reading circuit, which is noise-optimised, makes it possible to achieve a level of sensitivity never before obtained on a component of this class,” said CEA-Leti.

With a pixel pitch of 25 µm and an operating temperature of 77 K, that level of sensitivity represents an improvement of more than an order of magnitude on what is normally possible under the same conditions while using conventional components, claims the team.

The array will enable highly sensitive applications of thermography in security and defense applications, such as stand-off detection of explosives. The LWIR region is very important spectroscopically, with industrial chemicals such as ethanol, ammonia and sulfur hexafluoride all absorbing in or close to the 8-10 µm band. The nerve agent sarin and the explosive triacetone triperoxide (TATP) also absorb in this region, hinting at the potential security applications of the new imaging array.

TATP is relatively easy to make and was reportedly the trigger explosive used in many notorious terrorist incidents, including the July 2005 bombings in London, and the failed Northwest Airlines Christmas Day 2009 plot.

Details of the new camera technology were presented at the SPIE Security + Defence conference, held in Toulouse, France, in September 2010. The development is a collaboration between CEA-Leti, MCT detector manufacturer Sofradir, France’s defense procurement agency, the Direction Générale pour l'Armement (DGA), and the aerospace company Onera. Sofradir produces MCT detectors using a molecular beam epitaxy (MBE) technique under an exclusive licensing agreement with CEA.

Main photo credit: Sofradir