High performance terahertz resonant tunnelling diode sources and broadband antenna for air-side radiation

Resonant tunnelling diode (RTD) is known to be the fastest electronics device that can be fabricated in compact form and operate at room temperature with potential oscillation frequency up to 2.5 THz. The RTD device consists of a narrow band gap quantum well layer sandwiched between two thin wide band gap barriers layers. It exhibits negative differential resistance (NDR) region in its current-voltage (I-V) characteristics which is utilised in making oscillators. Up to date, the main challenge is producing high output power at high frequencies in particular. Although oscillation frequencies of ~ 2 THz have been already reported, the output power is in the range of micro-Watts. This thesis describes the systematic work on the design, fabrication, and characterisation of RTD-based oscillators in microwave/millimetre-wave monolithic integrated circuits (MMIC) form that can produce high output power and high oscillation frequency at the same time. Different MMIC RTD oscillator topologies were designed, fabricated, and characterised in this project which include: single RTD oscillator which employs one RTD device, double RTDs oscillator which employs two RTD devices connected in parallel, and coupled RTD oscillators which combine the powers of two oscillators over a single load, based on mutual coupling and which can employ up to four RTD devices. All oscillators employed relatively large size RTD devices for high power operation. The main challenge was to realise high oscillation frequency (~ 300 GHz) in MMIC form with the employed large sized RTD devices. To achieve this aim, proper designs of passive structures that can provide small values of resonating inductances were essential. These resonating inductance structures included shorted coplanar wave guide (CPW) and shorted microstrip transmission lines of low characteristics impedances Zo. Shorted transmission line of lower Zo has lower inductance per unit length. Thus, the geometrical dimensions would be relatively large and facilitate fabrication by low cost photolithography. A series of oscillators with oscillation frequencies in the J-band (220 – 325 GHz) range and output powers from 0.2 – 1.1 mW have been achieved in this project, and all were fabricated using photolithography. Theoretical estimation showed that higher oscillation frequencies (> 1 THz) can be achieved with the proposed MMIC RTD oscillators design in this project using photolithography with expected high power operation. Besides MMIC RTD oscillators, reported planar antennas for RTD-based oscillators were critically reviewed and the main challenges in designing high performance integrated antennas on large dielectric constant substrates are discussed in this thesis. A novel antenna was designed, simulated, fabricated, and characterised in this project. It was a bow-tie antenna with a tuning stub that has very wide bandwidth across the J-band. The antenna was diced and mounted on a reflector ground plane to alleviate the effect of the large dielectric constant substrate (InP) and radiates upwards to the air-side direction. The antenna was also investigated for integration with the all types of oscillators realised in this project. One port and two port antennas were designed, simulated, fabricated, and characterised and showed the suitability of integration with the single/double oscillator layout and the coupled oscillator layout, respectively.

Devotional reading and dissolving the self: a critical reading of the late medieval Scottish Legendary using Kristevan theory

The Scottish Legendary is a fourteenth century collection of saints’ lives in Older Scots. The prologue describes the lives as ‘merroure’ (mirror) to readers from which ‘men ma ensample ta’ (people may take example). Thus, the Legendary sets out to reveal how the reader is (mirror) thereby moving her to wish to become how she should be (exemplarity). This dissertation argues that, rather than encouraging devotion to saints along purely dogmatic lines, the Legendary transforms the reader’s selfhood by engaging her affectively, i.e. on an emotional and somatic level. By provoking the reader affectively, the text puts the reader into what Julia Kristeva has described as a ‘semiotic state’ which harks back to the reader’s or listener’s pre-cultural, pre-subjective self (Kristeva, 1984). Thus, the text disrupts the reader’s conception of herself as a complete, hermetic subjectivity, thereby dissolving the boundaries of the reader’s self. The Legendary most powerfully infiltrates the reader’s sense of self along these lines in the moments in which female saints’ bodies are tortured and dismembered. These scenes foreground the permeability of human flesh as well as its powerful influence over selfhood. Such images of abjection are, in Kristeva’s words, ‘opposed to I’; by confronting the reader with the disintegration of subjectivity in abjection, the text incites the reader to likewise experience herself as abject, i.e. disintegrable and permeable (Kristeva 1982). As I shall demonstrate, Kristeva’s psychoanalytic theory of the formation of the self offers a fruitful framework for understanding the processes of self-knowledge through reading that these saints’ lives inspire.