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QWIP for Infra-Red Imager (contact : eric.costard@3-5lab.fr)
Sensitive arrays are fabricated using QWIP technology based on GaAs materials. This technology allows the fabrication of large staring arrays for thermal imagers working in the LWIR band, used for instance in Thales cameras.
QWIP arrays are presently fabricated on 3” wafers. This SEM picture shows a detail of a classical 25 µm pitch array before hybridization.
A systematic use of plasma etching makes possible very high filling factors (> 85 %) and an accurate control of dimensions maintaining the intrinsic epitaxial uniformity. Fabrication yields obtained today on a GaAs wafer are above 80 % for full TV format arrays, with a pixel yield better than 99.95 %
QWIP arrays are designed to operate in the medium to long wavelength infra-red wavelength range (typically 4 to 12 µm), and delivered to integrators whose task is hybridization with the Read Out IC and integration into a Dewar Cooler.Arrays with both Half TV format (wafer in the background) and Full TV format (front wafer) are available.
Owing to a high quality epitaxial structure and associated process, excellent characteristics are obtained, as illustrated below for a new compact product with a 20 µm pitch (characteristics are given for the full Integrated Detector Dewar Cooler Assembly) :
Pixels number 640 x 512
NETD < 50 mK
Integration time < 5 ms
Operating temperature > 73 K
The stacked pixel architecture suitable for dual band imagery is based on a two-stack quantum well structure. Each stack is clad between heavily doped GaAs thick layers. An optical coupling pattern, optimized for the longer wavelength is implemented on top of the mesa in order to increase the operating temperature.
QWIP arrays can be designed for operation at 9µm / 11µm or 4.5µm / 9µm. On full half TV format (384 x 388 pixels) pixel operability is higher than 99.5 %.
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