Ultra-high sensitivity infrared imaging array developed

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The French research and technology organisation, CEA-Leti, has developed the first infrared imaging array in the 8-10µm band capable of returning an image with a minimum temperature difference, or thermal resolution, of 1 to 2mK at ambient temperature and with traditional image cadences of 25-50Hz.

Leti has also created an infrared detection array by linking an innovative reading circuit, manufactured using CMOS-silicon technology, to an array of HgCdTe infrared detectors.

Designed for defence and security applications, the HgCdTe array has a format of 320 x 256 and a pitch of 25µm. The array achieved ultimate sensitivity of close to one-thousandth of a degree Kelvin at an operating temperature of 77K. It represents 10-20 times increase in sensitivity compared with what is normally possible under the same observation conditions with conventional components.

To obtain this extremely high sensitivity, CEA-Leti designed and produced a special silicon reading circuit with a 0.18µm CMOS die, involving an analogue-to-digital conversion at each elementary detection point with a pitch of 25µm.

The analogue-to-digital conversion is based on the counting of charge packets given off by the detector. An equivalent stored charge of 3 Giga-electrons can be obtained. This reading circuit, which is noise-optimised, thus makes it possible to achieve an extremely high level of sensitivity.

CEA-Leti presented these results at the international Defense, Security and Sensing conference Orlando, Florida, US, and as part of an invited paper at the international SPIE Defense and Security conference in Toulouse, France, this year.

These results are the fruit of research carried out in a joint Sofradir-CEA (DEFIR) laboratory, with support from CEA, Sofradir, DGA and Onera. Sofradir is producing the HgCdTe infrared detector technology developed by CEA-Leti under exclusive license from CEA.

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