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ASTronomy EuROpean Infrared Detection

Periodic Reporting for period 2 - ASTEROID (ASTronomy EuROpean Infrared Detection)

Reporting period: 2018-05-01 to 2019-06-30

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. These requirements are mandatory for observation where the objects to observe are very far from Earth and deliver a very small signal to detect. In this case, the infrared flux is of the order of 1 to a few hundreds of photons per second per pixel. 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.
The main work achieved during the period 05/2017-05/2018 is summarized as followed:
• WP1 : Evaluation of new method for Silicon wafers processing compatible with large 8’’ ROIC wafers
• WP2 : Preparation, design and validation of all the tooling necessary to manufacture the objects during the second period of the program (06/2018-05/2019). Tools and equipment have been validated thanks to manufacturing of CdZnTe ingots, substrate slicing and polishing and manufacturing of very large 4’’ diameter LPE wafer
• WP3 : Preparation of the test plan for the test vehicle (2K² n/p, TV format p/n)
• WP3 : Specification of the modeling tool that will bring important information about the thermos-mechanical behavior of the large 2048x2048 15µm pitch focal plane array detector
• WP3 : Simulation of the impact of the CdZnTe substrate thinning onto the HgCdTe epilayer, in terms of electro-optical performance

A public brochure and a website have been issued during this period also.

The main work achieved during the period 1/05/2018-30/06/2019 is summarized as followed:
Important results have been obtained regarding all the different technologies involved in the program. Relevant examples are:
• ASTEROID will use as expected ALFA ROIC, indeed the probe test at 300K are OK.
• Innovated processes developed at EVG are under interest for Lynred manufacturing line for both bonding and photolithography process and equipments
• CEA-LETI and Lynred have demonstrated the feasibility to manufacture very large CdZnTe ingots, HgCdTe 73x72mm size LPE and PV processes with quality and critical parameters comparable to internal standards
• Lynred has obtained the very first ALFA 2048x2048 hybridized circuit and analyzes that the connectivity of the diode is very promising
• ADDL is developing a full model of the 2048x2048 15µm pitch able to simulate this very large detector during its manufacturing and also at operating temperature
• IFAE and CEA-IRFU have started to prepare their tests facilities and equipments to be ready to test TV test vehicles and 2K² test vehicle.
At the end of the project we want to demonstrate that the manufacturing of very large MCT wafer is possible and that it can be used in an industrial way. In detail, we want to achieve the main objectives:
- WP1 : ROIC 8’’ process compatible with Sofradir standards showing equivalent results as the current industrial line
- WP2 : MCT wafer (at LETI and/or Sofradir) showing good characteristics (mechanical, material quality, cosmetics) and also electro-optical results equivalent to the one obtained on the previous n/p TV format detector for ESA with low dark current and high quantum efficiency
- WP3 : hybridized circuit 2K² will be manufactured. We want to assess the reliability of the hybridized process showing that even after thermal cycling, the operability is still correct
The impacts of such results are described hereafter:
• Reduce the dependence on critical technologies and capabilities from outside Europe for future space applications, as identified in the list of Actions for 2015/2017 as part of the Joint EC-ESA-EDA task force on Critical Technologies. All technologies required for manufacturing of large IR FPA will come from European sources.
• Develop, or regain in the mid-term, the European capacity to operate independently in space, e.g. by developing in a timely manner reliable and affordable space technologies that in some cases may already exist outside Europe or in European terrestrial applications. One of the focus of the project will be to define the industrial manufacturing line for the fabrication of components for Space applications and other applications requiring such components and in particular astronomy applications.
• Enhance the technical capabilities and overall competitiveness of European space industry satellite vendors on the worldwide market. Europe will be in position to sale large IR detectors outside Europe.
• Open new competition opportunities for European manufacturers by reducing the dependency on export restricted technologies that are of strategic importance to future European space efforts. Competition with US vendor will become possible.
• Enable the European industry to get non-restricted access to high performance technologies that will allow increasing its competitiveness and expertise in the space domain. None of the technologies and parts used in ASTEROID is subject to ITAR restriction.
• Improve the overall European space technology landscape and complement the activities of European and national space programs.