Design and Fabrication of Integrated Terahertz Oscillator Circuits

This project focuses on micro-fabrication of novel oscillators at terahertz frequencies with full integration of a semiconductor device and a resonant circuit. The terahertz frequency range is located between the microwave and mid-infrared regions of the electromagnetic spectrum. It has long resisted full-scale commercial exploitation because of significant difficulties in fabricating compact and convenient sources (or transmitters) and detectors (or receivers) in large, cost-effective numbers. State-of-the-art results were achieved with superlattice electronic devices (SLEDs) in resonant waveguide circuits for high reliablity at current densities much lower than those of heterojunction bipolar transistors or high electron mobility transistors at similar frequencies. However, these results depended on well-established, but extensive manual assembly of oscillators. Integration of resonant circuits and SLEDs greatly facilitates portable commercial applications such as medical diagnostics and ultra-wideband wireless communications far beyond current 5G technology. It also provides a clear path to further integration of oscillators, mixers, and frequency multipliers. The PhD project will develop and study various types of integrated structures and hence greatly enhance the performance boundaries of SLEDs. The developed technologies not only apply to SLEDs, but also greatly accelerate the evaluation of other active semiconductor devices for terahertz frequency generation. The project will involve device and high-frequency circuit simulations, a range of micro-fabrication techniques in cleanroom facilities, and precision high-frequency measurements.

<p style="margin-bottom:11px">The terahertz frequency range offers unique and now well-known opportunities for scientific and commercial applications, but was many decades ago largely known for its crucial benefits to radio-astronomy. It is located between the microwave and mid-infrared regions of the electromagnetic spectrum. This frequency range has long resisted full commercial exploitation compared to that of other wireless devices such as mobile phones at microwave frequencies. This has been the consequence of difficulties in fabricating convenient and compact sources and detectors in large, cost-effective numbers; terahertz radiation is too high in frequency to be generated easily by the electronic techniques employed in, for example, mobile telephones and their base stations, but too low in frequency to be produced by the optical techniques exploited in, for example, lasers for CD players or optical fibre communications.</p> <p>However, the last twenty years have witnessed a remarkable growth in the field of terahertz technologies owing to the development of innovative sources, detectors, and imaging systems. One of the innovative sources uses a semiconductor superlattice to produce a negative differential resistance (NDR) at the frequencies of interest. Such a negative differential resistance eliminates any damping from inevitable losses in a resonant LC circuit and thus yields clean terahertz oscillations at the resonance frequency of this circuit. State-of-the-art results were achieved in the School of Electronic & Electrical Engineering with these superlattice electronic devices in resonant waveguide circuits. These results required well-established, but extensive manual assembly.</p> <p>Integration of resonant circuits with these superlattice electronic devices greatly facilitates portable commercial applications such as medical diagnostics (see V. Vaks et al., Sci. Rep., vol. 12, Oct. 2022, Art. no. 18117. doi: 10.1038/s41598-022-22783-z) and ultra-wideband wireless communications far beyond current 5G technology. These integrated structures will either be employed inside suitable metallic waveguide structures mainly for precision high-frequency measurements or include antenna structures for radiating the terahertz signals into free space. Such antenna structures then lend themselves to efficient quasi-optical power-combining of several if not many oscillators, then to be used as powerful transmitters in wireless communications.</p> <p>The PhD project will develop and study various types of integrated structures and hence greatly enhance the performance boundaries of superlattice electronic devices from the current state-of-the-art results. The project will involve device and high-frequency circuit simulations, device and circuit micro-fabrication in the University’s superb cleanroom facilities, and precision high-frequency measurements. It envisaged that such integration techniques can be easily adopted for other material systems such as GaN/AlGaN or other types of NDR devices. Therefore, integration techniques will greatly help with the exploration of such devices as their frequencies of operation increase. These integrated terahertz oscillator circuits will also provide a clear path to further integration of oscillators with mixers and / or frequency multipliers, all based on superlattice device structures.</p>

<p>Formal applications for research degree study should be made online through the <a href="https://www.leeds.ac.uk/research-applying/doc/applying-research-degrees">University's website</a>. Please state clearly in the Planned Course of Study section that you are applying to <em><strong>PhD Electronic & Electrical Engineering FT</strong></em> and in the research information section that the research degree you wish to be considered for is <em><strong>Design and Fabrication of Integrated Terahertz Oscillator Circuits</strong></em> as well as <a href="https://eps.leeds.ac.uk/electronic-engineering/staff/297/dr-heribert-eisele">Dr Heribert Eisele</a> as your proposed supervisor. Please state in the Finance section that the funding source you are applying for is <em><strong>School of Electronic & Electrical Engineering Studentship 2025/26</strong></em>.</p> <p>If English is not your first language, you must provide evidence that you meet the University's minimum English language requirements (below).</p> <p><em>As an international research-intensive university, we welcome students from all walks of life and from across the world. We foster an inclusive environment where all can flourish and prosper, and we are proud of our strong commitment to student education. Across all Faculties we are dedicated to diversifying our community and we welcome the unique contributions that individuals can bring, and particularly encourage applications from, but not limited to Black, Asian, people who belong to a minority ethnic community, people who identify as LGBT+ and people with disabilities. Applicants will always be selected based on merit and ability.</em></p> <p>Applications will be considered after the deadline. Potential applicants are strongly encouraged to contact the supervisors for an informal discussion before making a formal application. We also advise that you apply at the earliest opportunity as the application and selection process may close early, should we receive a sufficient number of applications or that a suitable candidate is appointed.</p> <p><strong>Please note that you must provide the following documents in support of your application by the closing date of 31 January 2025:</strong><br /> <strong>•</strong>    Full Transcripts of all degree study or if in final year of study, full transcripts to date<br /> <strong>•</strong>    Personal Statement outlining your interest in the project<br /> <strong>•</strong>    CV</p>

Applicants to research degree programmes should normally have at least a first class or an upper second class British Bachelors Honours degree (or equivalent) in an appropriate discipline. The criteria for entry for some research degrees may be higher, for example, several faculties, also require a Masters degree. Applicants are advised to check with the relevant School prior to making an application. Applicants who are uncertain about the requirements for a particular research degree are advised to contact the School or Graduate School prior to making an application.

The minimum English language entry requirement for research postgraduate research study is an IELTS of 6.0 overall with at least 5.5 in each component (reading, writing, listening and speaking) or equivalent. The test must be dated within two years of the start date of the course in order to be valid. Some schools and faculties have a higher requirement.

<p style="margin-bottom:11px">A highly competitive School of Electronic & Electrical Engineering Studentship providing the award of full academic fees, together with a tax-free maintenance grant at the standard UKRI rate (£19,237 in academic session 2024/25) for 3.5 years. There are no additional allowances for travel, research expenses, conference attendance or any other costs.</p> <p>This funding opportunity is open to all applicants. All candidates will be placed into the School of Electronic & Electrical Engineering Studentship Competition, and selection will be based on academic merit.</p> <p>You will be responsible for paying the overtime fee in full in your writing up/overtime year (£320 in Session 2024/25), but the scholarship maintenance allowance will continue to be paid for up to 6 months in the final year of award.</p> <p><strong>Important:</strong> Please note that that the award does <em><strong>not</strong></em> cover the costs associated with moving to the UK.  All such costs (<a href="https://www.leeds.ac.uk/international-visas-immigration/doc/applying-student-visa">visa, Immigration Health Surcharge</a>, flights etc) would have to be met by yourself, or you will need to find an alternative funding source. </p> <p>Please refer to the <a href="https://www.ukcisa.org.uk/">UKCISA</a> website for information regarding Fee Status for Non-UK Nationals.</p>

<p style="margin-bottom:11px">For further information about this project, please contact Dr Heribert Eisele by email to <a href="mailto:h.eisele@leeds.ac.uk">h.eisele@leeds.ac.uk</a></p> <p>For further information about your application, please contact PGR Admissions by email to <a href="mailto:EMAIL@leeds.ac.uk">phd@engineering.leeds.ac.uk</a></p>