Optronics detector technologies

The outcome should contribute to:

• improved situational awareness and decision-making thanks to sensors with better detection, recognition and identification performance;
• improved characteristics of infrared detectors, including SWAP-C, available to the armed forces of EU Member States and EDF associated countries (Norway);
• preparation of technologies necessary for a sovereign European supply chain for substrates, epitaxial wafer and ROIC processing for infrared imaging based on T2SL;
• preparation of technologies necessary for a sovereign European supply chain for cryo-coolers adapted to new high performance infrared image sensors based on T2SL technology with improved characteristics;
• improving the competitiveness and innovation capacity of the EDTIB in the field of infrared detectors by providing complementary technological know-how to ongoing efforts and established solutions.

The domain of infrared (IR) detectors encompasses a variety of technologies that operate in different spectral bands for a variety of applications. IR detectors are key elements to increase detection/recognition/identification (DRI) ranges of sensors and thus improve the global efficiency of the system with respect to situational awareness and targeting. Passive systems based on high-performance electro-optical (EO) thermal imaging are mandatory for realising these advantages under stealth conditions. IR thermal detectors usually operate either in the mid-wavelength (3-5µm, MWIR) or in the long-wavelength (8-12 µm¹, LWIR) atmospheric window.

For armed forces, sensor systems with maximised detection, recognition and identification ranges are key to prevail on the battlefield. In the naval domain, typical applications like surveillance against non-conventional threats require several sensors (active and passive) and visual confirmation is required in many cases. In the land domain, situational awareness in armoured vehicles requires sophisticated IR sensors. Soldiers greatly benefit from IR sensors that are robust and comply with size, weight, power consumption and cost requirements (SWAP-C), especially in low visibility conditions. SWAP is also an important requirement for payloads of observation satellites. In the air domain, Missile Warning System (MWS) will also benefit from progress in IR technology. Similarly, for airborne surveillance, new generation of IR sensors will improve the trade-off between range and field of view.

The specific requirements of demanding military applications often require adapting existing products or developing specific products within the defence community. Several IR detector materials are particularly interesting for defence applications, amongst which II-VI compounds, where European manufacturers are currently able to offer state-of-the-art IR detectors and III-V compounds, which are regarded as possible cost-efficient and performant alternatives. One particular type of detectors are the Type-II superlattice materials, which are made of periodic structures of two III-V compounds (e.g. InAs and GaSb or other combinations). Additionally to the semiconductor material, most infrared sensors necessitate a Read-Out Integrated Circuit (ROIC) to convert the collected infrared light into a corresponding electrical signal. Finally, many IR sensors need cooling technology as, depending on the materials used and the wavelength of the radiation to be detected, high performance IR detectors must commonly operate at low temperatures to cope with the relatively small characteristic infrared energy and in order to achieve an adequate signal-to-noise ratio.

Infrared technology is an important element of Europe’s technological sovereignty in key value chains. In this regard, the European defence industrial and technological base faces a threefold challenge in the field of optronic detectors: achieving high performance, maintaining international competitiveness and securing non-dependency of supply chains.

Specific objective

Currently, three domains in European cooled infrared sensors supply chain need further investment in cooperative R&D to answer to those challenges: detector materials, ROIC bumping technology and cryocoolers.

Concerning detector material, Type-II superlattice (T2SL) materials have been identified as a potential alternative to current technologies (like InSb and CMT) in the mid wave infrared (MWIR) range and may also be a viable alternative in the long wave infrared (LWIR) range. They may be usable for bi-spectral / multispectral applications and High Operating Temperature focal plane arrays, be more cost-effective, and also provide for very compact solutions. T2SL based technology may offer very fine pitch and process flexibility needed for future defence applications. T2SL have been under intensive development and promotion in the U.S., Israel and in some European countries. South Korea and China are also becoming very active in this field. T2SL offer in terms of supply chain and eco system remains for the time being poor in the EU and EDF associated countries, despite some already existing competitive fielded products in relevant military programmes. For example, European providers are facing today dependency on non-European suppliers of Gallium Antimonide material substrates (GaSb) and lack an industrial III-V epitaxy source, only available in the U.S.

Concerning the ROIC, critical steps to manufacture such circuits were addressed by the EDF-2021-SENS-R-IRD topic. Complementary activities are necessary on ROIC bumping technology in order to prepare for hybridisation of detection circuits on the ROICs. As defence applications require lower volumes of infrared detectors compared with civil applications, these activities need to be shared by IR manufacturers in Europe.

Cryocooling components needed for cooled infrared sensors must face both high requirements and strong competition from other continents, on a wide spectrum of products (handheld, embedded, airborne high-end). Fundamental technological improvements are necessary for the European cryocooling supply chain in order to remain competitive, both economically and performance-wise. Cryogenics technologies adapted for temperatures higher than 150K, are expected to bring significant gains in power consumption and volume, and will most likely require more efficient cryogenic solutions contributing to SWAP-C improvement.

This topic aims at consolidating a fully sovereign common supply chain of some critical technology building blocks for the next generation of high performance infrared detectors for defence applications in all battlespace dimensions.

The proposals must address IR detector technologies based on Type-II Superlattice (T2SL) materials, including the necessary competences and know-how to supply large-diameter high-quality substrates to the infrared sensor providers, as well as a corresponding epitaxy process.

The proposals should also address advanced silicon ROIC technology with the objective to develop a common post-processing of future ROICs to prepare them for bumping and bumping technology.

Finally, the proposals must aim to improve the fundamental knowledge of cryocoolers and find innovative solutions in order to improve the performances of European cryocoolers solutions for IR sensors.

Types of activities

The following table lists the types of activities which are eligible for this topic, and whether they are mandatory or optional (see Article 10(3) EDF Regulation):

The proposals must cover at least the following tasks as part of the mandatory activities:

• Integrating knowledge:
  • acquire necessary knowledge on substrate production processes, suitable for T2SL detectors;
  • acquire necessary knowledge on epitaxy for T2SL detectors, including epitaxial structure modelling activities, epitaxial structure growth, validation through test chip processing and electrical characterisations.

In addition, the proposals should cover the following tasks:

• Generating knowledge:
  • concerning the aspect of cryocoolers, create a complete thermodynamical model of cryocoolers based on an innovative principle;
• Integrating knowledge:
  • concerning the aspect of ROIC technology, improve the technology of common ROIC bumping process steps (e.g. Under Bump Metallisation and indium bumps) and process flow;
  • concerning the aspect of cryocooler technologies, investigate characteristics of cryocoolers with improved performances with respect to cost, size, weight and efficiency, low vibrations and acoustic noise of cryocoolers;
  • concerning the aspect of cryocooler technologies, investigate new materials, concepts, manufacturing technics to improve the thermal transfer internal to the cooler and its interfaces;
• Studies:
  • identify physical parameters and sensors allowing to predict the time-to-failure of coolers and of solutions to provide efficient Health monitoring of cryocoolers;
• Design:
  • design of innovative and improved cryocoolers adequate for T2SL applications and demonstration by partial testing of the designed solutions in a relevant environment.

The proposals may also cover the following tasks:

• Design:
  • validation of substrate and epitaxy processes using sample focal plane arrays;
  • implementation of an IR T2SL detector with high-resolution / small pitch based on the substrate and epitaxy processes investigated;
  • complete testing of the designed solutions in a relevant environment.

In addition, the proposals should substantiate synergies and complementarity with foreseen, ongoing or completed activities in the field of infrared technologies, notably those performed or foreseen in the context of the call topic EDF-2021-SENS-R-IRD.

Functional requirements

The proposed technologies should meet the following functional requirements:

• reduction of size, weight, power, and cost;
• the solutions of substrates for T2SL detectors should:
  • be suited for all IR detector providers in the EU and EDF associated countries;
  • be suited for at least MWIR and LWIR wavelengths;
  • address large diameter (≥3’’), cost-effective bulk crystal growth;
  • ensure an epi-ready surface preparation that is compatible with imagery requirements (e.g. low dislocation density, high homogeneity, low bow, low warp, adequate doping…);
• the epitaxy solutions for T2SL should:
  • be suited for all IR detector providers in the EU and EDF associated countries;
  • ensure a material quality in accordance with IR detectors requirements (operating temperature for defence applications, suited for at least MWIR and LWIR wavelength bands, high homogeneity and low defectivity on large wafers (≥3’’) …);
  • ensure an epitaxial stack in accordance with the detector design;
• the ROIC post processing should:
  • be compatible with 300mm Silicon wafers;
  • be compatible with the common bumping process with low defectivity (< 0.05% defects) and high homogeneity;
• the proposed cryo-coolers solutions should:
  • be compliant with SWAP-C requirements;
  • exhibit vibration and noise reduction for stealthiness;
  • be based on innovative cryocooler models valid for temperatures ranging from 120K to 200K.