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Doctoral Training Network in Terahertz Technologies for Imaging, Radar and Communication Applications

Periodic Reporting for period 1 - TeraApps (Doctoral Training Network in Terahertz Technologies for Imaging, Radar and Communication Applications)

Reporting period: 2018-01-01 to 2019-12-31

Research into terahertz (THz) radiation, with frequencies between 0.3 THz and 3 THz, has burgeoned in the last decade. The interest has been stimulated by the unique properties of THz waves: they offer wider bandwidths, i.e. higher data rates, and improved spatial resolution compared with RF (radio frequency) electronics and they can penetrate materials such as plastics, paper and many organic compounds, including human tissue, without the hazards or potential dangers associated with ionising radiation such as X-rays. Furthermore, THz may be used to identify specific materials via their characteristic spectra, including explosives, hazardous chemicals, drugs and DNA, as molecular rotations and vibrations occur in this frequency range. Broadband THz transceivers, e.g. for future 5G systems, intra-chip communications, etc. are being researched, while THz imaging is finding applications in areas such as security, healthcare, pharmaceuticals, automotive, materials science and non-destructive testing. THz waves are also offering new sensing opportunities including medical diagnostics, inspection of sealed packages and the detection of concealed weapons, chemicals and biological agents.

The aim of the TeraApps project is to train the pool of young early-stage researchers (ESR) in the design, fabrication, characterization and systems utilization of THz sources and detectors based mainly on resonant tunnelling diode (RTD) semiconductor technology, but also on emerging novel technologies including 2D materials, and their deployment in typical applications areas such as imaging, short range wireless communications, radar and sensing.

Considering that this semiconductor approach to THz electronics/photonics is relatively new, with only a few players world-wide, and the potentially huge societal and commercial gains possible, TeraApps provides a concerted effort to simultaneously crystallise European efforts in this area, training the next generation of research leaders to push forward the field in future years.
The project has achieved success right across its broad and ambitious work programme, including the following highlights:
• Training, networking, and supervision
o Recruitment of all 15 early stage researchers (ESRs) was completed
o A transferable skills course covering creative thinking, presenting with impact, research integrity, data management was completed 23-24 January 2019 at the University of Glasgow (UGLA)
o All ESRs completed an introductory course to terahertz (THz) technology and applications held at the National Physical Laboratory, 11-12 April 2019
o ESRs successfully completed the progression viva for year 1
o The first summer school was organised jointly with CELTA ITN and held 13-19 July 2019 at the Goethe University in Frankfurt, Germany
o To date 12 ESRs have completed their first-year progression webinars

• RTD Design – Achieve uniform and reproducible technology
o First RTD device designs have been completed by ESRs at UGLA and UWUE
o Wafers have been grown and some assessed using non-destructive techniques while others are being processed into devices for experimental evaluation
o The physics-based simulation of triple barrier RTDs has achieved device results which match experimental measurements, providing a basis for advanced CAD-based device design.

• THz Sources – Achieve THz sources with milli-Watt output powers.
o Various RTD epitaxial designs have been completed; wafers have been grown and devices are being fabricated for evaluation.
o Existing optically controllable RTDs were assessed experimentally as optical to wireless interfaces to establish current performance levels; New epitaxial wafers designs targeting expected/higher performance specifications have been completed
o Design and simulation of sub-harmonically injection locked RTD oscillators operating at 300 GHz has been completed

• THz Detectors – Realise high sensitivity THz detectors.
o First design, fabrication and characterisation cycles of detectors have been completed
o Triple barrier RTD detectors, nanowire field effect transistors, 1D and 2D materials including graphene, mercury cadmium telluride and indium arsenide quantum dots have been designed, fabricated and evaluated

• THz Instruments – Demonstrator systems.
o Design of a compact metamaterial-based THz optical lens has been completed; first experimental results are very promising with regards to realising very compact imagers for non-destructive testing applications.
o Evaluation of pharmaceutical tablets using THz time domain spectroscopy is underway
o The study of biomolecules using THz excitation is also underway with first results showing clustering of atoms for excitation at 260 GHz.
o The design of an on-wafer S-parameter characterisation setup for THz electronic devices such as RTDs for up to 260 GHz has been completed and prototypes for evaluation are being fabricated.

• Objective 6: Build a high-impact structure ensuring multi-level dissemination and exploitation of all results.
o Each ESRs will create a short YouTube video about their individual research projects for the public. These are accessible via the project’s website.
o A number of ESRs have presented their results at national and international conferences, and some journal papers have started to appear
o There is a strong interaction between ESRs and our industrial partners, with some secondments already underway and others planned
With some minor exceptions, mainly related to recruitment period which took 6 months longer than anticipated, the project has achieved all its objectives for the first year.
Systems operating in the THz band will offer new and efficient solutions for imaging, radar, communications and sensing applications. TeraApps is expected to significantly impact these application areas. Moreover, the project offers all beneficiaries an opportunity to complement their research expertise with methodologies and tools not available at their institutions. It will provide pivotal aspects needed for the development of a new generation of scientific and technological leaders predisposed to inter-disciplinarity and with an open and constructive attitude toward technological innovation. Specifically, the impact of the TeraApps consortium will be:
• Improved awareness of semiconductor THz technology and applications.
• Increased attention to the education and training of researchers in semiconductor THz technologies.
• Increased industrial focus on semiconductor research and development for THz systems, which may lead to compact and energy efficient systems with new functionality in both the short- and long-term.
• State-of-the-art interdisciplinary doctoral training at the intersection of experimental research, semiconductor technologies, and system design & implementation among other disciplines, making these individuals ideally suited for future careers in associated industries.

The project highlights to date include:
• Demonstration of a novel metal-material based THz lens which could lead to very compact and higher performance imaging systems
• Demonstration of the use of THz in the pharmaceutical industry for the assessment of the quality of medicines which are in tablet form
• Successful completion by the cohort of ESRs of key project milestones/events incl. transferable skills training courses
TeraApps Consortium at NPL in April 2019