Classical IR detectors used for tactical or space missions are mainly linear arrays or two dimensions Focal Plane Arrays (FPA) which designs are compatible with the scene to observe. For defense applications, the typical scenes to observe include vehicles, humans and buildings. For Earth observation missions from satellites, the scenes to observe are landscapes, ground, sea and atmosphere. These applications require detectors compatible with IR flux from Near IR (NIR), ShortWave IR (SWIR), MidWave IR (MWIR) and LongWave IR (LWIR). The fluxes coming from these scenes are in the range of 1000 to 1e6 photons/seconds/pixel. Moreover, the sizes of the classical detector used for these applications are XGA format at maximum (range 1000x1000 pixels).
However, for science and astronomy, specific infrared (IR) detectors are required. These types of detectors have their own specificities. These focal plane arrays (FPA) need to be very large (> four million pixels) and compatible with very high performances. Today large dimension infrared focal plane arrays (IR FPA) are only available from US Company Teledyne. Its Hawaii-2RG FPA (2048x2048 pixels, 18 µm pitch) is installed on all major ground based observatories. Europe is thus until today dependent on US for large format arrays in NIR and SWIR.
To be able to manufacture very large FPA, 4 key constraints exist. Indeed large FPA require:
- Very large dimension Read Out Integrated Circuits (ROIC)
- Very large substrates (mono-crystalline CdZnTe alloy);
- The capacity to epitaxy high quality HgCdTe material on these substrates;
- A manufacturing line fully compatible with large substrate dimensions.
Thus the whole industrial chain must be adapted especially if the number of detectors to produce is important.
The main objective of the ASTEROID project is thus to extend the dimension of high performance infrared FPA that can be manufactured in Europe to dimensions equivalent to that of the HAWAII FPA, overturning all constraints mentioned above. This will allow Europe to become independent for the procurement of this type of detectors. The targeted format is 2k² 15µm pitch FPA (2048x2048 pixels).
It has here to be noted that synergies with ALFA ESA program and ASTEROID exists. ESA has launched for years development of Astronomy IR detector. Today, ALFA (Astronomy Large Focal Array) is dealing with the development of 2048x2048 15µm pitch IR detector. This program runs with CEA-LETI and CEA-IRFU in France and is funded by ESA and Labex FOCUS.
At the end of the project the Consortium results are really enthousiastic. The technologies developped demonstrates that both industrial capability demonstration for large detector manufacturing is accessible. In terms of performances, the prototypes developped reached utmost performances comparable to state of the art.
Thanks to CEA-LETI and Lynred efforts, large MCT materials and Silicum wafers are available at Lynred and will be used for futur programs were very large infrared detectors are requested. EVG has developped tools methods and process that can be usefull for that purpose. On modeling parts, ADDL computed a thermo-mechanical simulator for infrared detectors, validated with internal measurements on real detectors at Lynred. CEA-IRFU tested very low dark current comparable to state of the art, with TV format detectors p/n SWIR, achieved in the frame of that program. IFAE laboratory increase its testing and charaterization skills in the infrared domain and demonstrates that the 2K² structure is really reliable after numbers of thermal cylcling at cold temperature.
