NANO2021-Nanoteknologi og nye materiale

The evolution of nuclear science and increased awareness of the effect of radiation exposure on humans, have led to the need of new methods and instrumentation in radiation detection. The use of advanced radiation detectors is of vital importance for our society and their application expands from the medical field, radiation protection, environmental monitoring, renewable energy to security and counter terrorism. Out of the many sources of radiation, Neutrons are proving to be the most challenging to detect. Neutron detection still heavily relies on early sensor technologies based on gas detectors. These devices are bulky and operate with high power consumption. They also make use of scarce, expensive and toxic gases as medium of neutron conversion. It is therefore crucial to find new ways of neutron detection with a positive environmental impact as well as the preservation of natural resources. The obvious next step for the detection of neutrons is to exploit the many advancements in silicon manufacturing of the past decades to produce modern silicon detectors for neutrons that will offer increased spatial resolution, lower power consumption, increased radiation hardness and ease of operation through the interfacing of the detector with modern readout systems. The INDET project had the ambitious goal of exploiting the advancements in silicon micro-machining and modern material science to produce novel silicon sensors featuring 3D micro-structures filled with neutron converting materials, that would deliver increased neutron detection efficiency. This technology has the potential to revolutionize neutron detection and will allow the development of new scientific instruments and techniques for neutron imaging, neutron scattering, neutron tomography, radiation monitoring and medical application. The INDET project involved several Norwegian and international research groups in the fields of radiation detection, material science, and nuclear science. The development of highly efficient silicon detector for neutrons, required considerable R&D in many fields. New processes had to be developed and optimized and finally implemented into the production process for silicon radiation detectors. The main objectives of the projects can be summarized as follows: (i) development of new techniques for the electrical passivation of silicon, (ii) development and optimization of a highly conformal neutron converter deposition, (iii) accurate numerical modelling of silicon detectors using modern simulation tools, (iv) fabrication of advanced silicon neutron detectors. Novel techniques for the passivation of silicon were studied at UiO. Aluminium Oxide (Al2O3) deposited by means of Atomic Layer Deposition (ALD) was the material of choice. It was demonstrated that excellent passivation can be achieved with good electrical characteristics, also after heavy radiation damage with irradiation campaign performed by IEAP (Czech Republic). The groups at LiU and ESS (Sweden), developed new techniques for the deposition of neutron converting materials directly onto silicon sensors. The process now available at LiU has shown world-leading conformality and was able to properly coat also the most challenging 3D micro-structures. Advanced sensors numerical modelling was performed at UiB and SINTEF, for prediction of the electrical sensor characteristics and their interaction with neutrons. The numerical models developed in the INDET project will be used as a starting point for any future development of this technology. The sensor fabrication was carried out successfully at SINTEF MiNaLab, by integrating all the knowledge generated in the project. The deposition of the neutron converter was carried out at LiU and ESS and final assembly of the detectors was carried out at SINTEF in preparation for testing. The detectors were tested at the Paul Scherrer Institute (PSI, Switzerland) and at the Budapest Neutron Centre (BND, Hungary). Access to the facilities was granted through application for public beam time successfully submitted by UiB in collaboration with IFE. The project was successful in demonstrating that the chosen approach is feasible and can yield silicon neutron detectors exhibiting good performance. It was also demonstrated that further development is necessary to increase the maturity of some of fabrication steps. The results of the INDET project contributed to an important investment at SINTEF with the purchase of an ALD tool that will allow better process control. The deposition of the neutron converter will need to be further developed to make it available at wafer level and ease the sensor production. The INDET project resulted in several publications in scientific journals and presentations at international conferences, increasing the visibility of the Norwegian contribution in the field of nuclear science and establishing a strong international collaboration that will prove fruitful in many other research activities.

Project outcomes. The INDET project had important outcomes for all project partners: theoretical modelling, novel fabrication technology, and analysis techniques, forming a strong foundation of competences required in nuclear science, micro- and nano- technology. Advanced numerical modelling techniques have now provided a vital tool for the design, development, and in-depth physical understanding of the next generation radiation detectors. The investigation of Atomic Layer Deposition (ALD) demonstrated many advantages over the current state-of-the-art and established the basis of a brand-new approach in radiation detector technology. This success led to an important investment decision to acquire an ALD tool at SINTEF MiNaLab. The integration of new processing steps into a well-established sensor technology has proven very challenging and required the development of new procedures for sensor handling and assembly. New strategies for sensor characterization and data analysis had to be investigated. The testing performed in neutron beam facilities in Europe required the careful preparation and verification of dedicated testing setup to be re-used in future experiments. Project impact. Solid-state radiation detectors offer numerous advantages in many applications. Neutron science is an important tool in many fields, including the development of safer and longer lasting batteries, strength analysis in materials, novel cancer therapy, security, and many more. The most direct and immediate impact of the INDET project is generating higher contribution by Norwegian institutes and universities at the European Spallation Source (ESS) in Sweden. The numerical modeling performed in INDET is the starting point for the design of the next generation of radiation detectors. The techniques used and developed in INDET and its related activities, can be utilized to deliver novel semiconductors sensors for applications in many fields ranging from material science, medical, aerospace to fundamental scientific research. The introduction of ALD passivation in standard detector technology can deliver sensors with enhanced energy resolution for the next generations of material science analysis tools. It can also offer enhanced sensitivity for photodiodes in the ultra-violet range. A high interest for ALD is also shown in the solar energy field, with its applications in novel solar cells. The conformal CVD deposition of neutron converting material utilized in INDET, opens the door for enhancement in neutron sensitivity intended for applications beyond fundamental neutron science. Combined with another sensor technology being developed at SINTEF, enhanced neutron detection can extend the capability of today's dosimetry systems in novel radiation therapy. Enhanced neutron sensitivity is also crucial in space applications to monitor the radiation dose received by the astronauts over long-haul missions.

This research project targets an innovative approach for integrating neutron converting materials into novel silicon detectors to obtain devices exhibiting extreme neutron detection efficiency. The innovation will be pursued through a combination of Micro-Electro-Mechanical-System (MEMS) and Very-Large-Scale Integration (VLSI) technologies, and state of the art Thin Film deposition methods. Fabrication activities will be carried out in the framework of the Norfab infrastructures available at SINTEF MiNaLab and UiO with contribution from UiB and IFE on design and characterisation at the JEEP II neutron reactor. The key Norwegian partners will collaborate with a team of international experts in thin-film deposition and neutron/radiation science from the European Spallation Source (ESS, Sweden), Linköping University (LiU, Sweden), and the Institute for Experimental and Applied Physics (IEAP) at the Czech Technical University in Prague (Czech Republic). Record neutron detection efficiencies will be sought by investigating enhanced coupling between converting films and novel silicon detectors, with advanced numerical simulation tools and deposition methods. The outcomes of the project will guarantee the development new instrumentation in modern radiation/neutron based investigation techniques in the fields of medical imaging and radiotherapy, cultural heritage, material analysis for future renewable energy sources, radiation protection and environmental monitoring, thus contributing to improved health, and environment and knowledge preservation. The highly inter-disciplinary and international environment will contribute to the creation of new knowledge in the field of semiconductor neutron detectors through experimental characterisation and numerical modelling and will make use of many of the Norwegian research infrastructures.