02 May 2023
New detectors can work at 130 K; with applications in defense, astronomy, and weather forecasting.
Now scientists at French nuclear research center CEA-Leti say they have “overcome unprecedented technical challenges” to enable the transfer of this small pixel, high-sensitivity technology to industry.”
CEA-Leti, which is based in Grenoble, France, is thus transferring its “record-breaking” infrared sensing technology to Lynred, based in Palaiseau, France, which provides infrared detectors for a broad range of markets. Lynred’s detector lineup covers the entire infrared spectrum, from SWIR to VLWIR.
The key advantage of this new technology, says CEA Leti, is its image sharpness. In an infrared detector, photons are absorbed by the semiconductor material and generate an electric charge, which is then diffused throughout the material for a few microseconds. This phenomenon is acceptable as long as the diffusion area is smaller than the size of the pixel.
However, if a charge can travel up to 20 µm and the pixel measures only 7.5 µm, the result is reduced image sharpness. In addition, Lynred wants its detectors to have a high operating temperature (130 K or more as compared to current 110 K operating levels) as this reduces the size and cost of the cryogenic cooling system.
Unfortunately, higher temperatures also mean that charges travel further. Therefore CEA-Leti's researchers came up with an innovative solution to this challenge. The 7.5µm pixels are designed in such a way that electrical charges never reach the neighboring pixel. The innovation resides not in the material (a mercury-cadmium-tellurium alloy common in infrared vision solutions), but in the pixel architecture itself.
The resulting performance is remarkable in terms of sharpness, which is measured as a percentage of the modulation transfer function or MTF. While a theoretical detector made up of perfect pixels cannot exceed 64 % MTF, CEA-Leti's detectors achieve 55 %.
“We devised a new method for measuring MTF sharpness,” commented Olivier Gravrand, research director at CEA-Leti. “Instead of injecting photons locally to excite the pixels, we use a scanning electron microscope to inject electrons. This ‘electron brush’ is much finer than the conventional optical beam and allows for a more accurate measurement of MTF.”
These high-performance infrared detectors are primarily intended for use by the defense sector as they provide improved visibility at greater distances thanks to their high resolution and record sharpness. To date, no other published technology demonstrates an MTF of 55% or more, assert the partners.
These infrared detectors can also be used on weather satellites to better monitor temperature, humidity and CO2 content in the atmosphere. Finally, they are of interest to astrophysicists to help them observe very distant stars.
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