A III-V channel field effect transistor for non-classical CMOS: process optimisation for improved gate stack function

This thesis describes a collection of studies into the electrical response of a III-V MOS stack comprising metal/GaGdO/GaAs layers as a function of fabrication process variables and the findings of those studies. As a result of this work, areas of improvement in the gate process module of a III-V heterostructure MOSFET were identified. Compared to traditional bulk silicon MOSFET design, one featuring a III-V channel heterostructure with a high-dielectric-constant oxide as the gate insulator provides numerous benefits, for example: the insulator can be made thicker for the same capacitance, the operating voltage can be made lower for the same current output, and improved output characteristics can be achieved without reducing the channel length further. It is known that transistors composed of III-V materials are most susceptible to damage induced by radiation and plasma processing. These devices utilise sub-10 nm gate dielectric films, which are prone to contamination, degradation and damage. Therefore, throughout the course of this work, process damage and contamination issues, as well as various techniques to mitigate or prevent those have been investigated through comparative studies of III-V MOS capacitors and transistors comprising various forms of metal gates, various thicknesses of GaGdO dielectric, and a number of GaAs-based semiconductor layer structures. Transistors which were fabricated before this work commenced, showed problems with threshold voltage control. Specifically, MOSFETs designed for normally-off (VTH > 0) operation exhibited below-zero threshold voltages. With the results obtained during this work, it was possible to gain an understanding of why the transistor threshold voltage shifts as the gate length decreases and of what pulls the threshold voltage downwards preventing normally-off device operation. Two main culprits for the negative VTH shift were found. The first was radiation damage induced by the gate metal deposition process, which can be prevented by slowing down the deposition rate. The second was the layer of gold added on top of platinum in the gate metal stack which reduces the effective work function of the whole gate due to its electronegativity properties. Since the device was designed for a platinum-only gate, this could explain the below zero VTH. This could be prevented either by using a platinum-only gate, or by matching the layer structure design and the actual gate metal used for the future devices. Post-metallisation thermal anneal was shown to mitigate both these effects. However, if post-metallisation annealing is used, care should be taken to ensure it is performed before the ohmic contacts are formed as the thermal treatment was shown to degrade the source/drain contacts. In addition, the programme of studies this thesis describes, also found that if the gate contact is deposited before the source/drain contacts, it causes a shift in threshold voltage towards negative values as the gate length decreases, because the ohmic contact anneal process affects the properties of the underlying material differently depending on whether it is covered with the gate metal or not. In terms of surface contamination; this work found that it causes device-to-device parameter variation, and a plasma clean is therefore essential. This work also demonstrated that the parasitic capacitances in the system, namely the contact periphery dependent gate-ohmic capacitance, plays a significant role in the total gate capacitance. This is true to such an extent that reducing the distance between the gate and the source/drain ohmic contacts in the device would help with shifting the threshold voltages closely towards the designed values. The findings made available by the collection of experiments performed for this work have two major applications. Firstly, these findings provide useful data in the study of the possible phenomena taking place inside the metal/GaGdO/GaAs layers and interfaces as the result of chemical processes applied to it. In addition, these findings allow recommendations as to how to best approach fabrication of devices utilising these layers.

Is the legal protection for the foetus adequate in clinical trials?

In 2009 and 2010, the major drug regulatory bodies, the European Medicines Agency and the Food and Drug Administration in the USA, issued requests for the generation of information relating to the absorption, distribution, metabolism, excretion, efficacy and safety of investigational drugs in pregnant women prior to approval. In the wake of thalidomide, research involving pregnant women other than for obstetric or gynaecologic purposes became rare, and studies of investigational drugs practically unknown. Consequently, none of the legislation applicable in the UK and few of the guidelines introduced in the last 40 years properly addresses the conduct of clinical trials of investigational drugs in this population. This thesis questions whether the legal protection for the foetus is adequate in clinical trials. The answer appears to be a qualified “no”. Arguments persist regarding the moral standing of the foetus, particularly regarding abortion. That will not be the intent of such trials, and a moral case is made for the conduct of clinical trials in this population by analogy with the neonate, and the pregnant woman’s autonomy. Legally, we already recognise the foetus has ‘interests’ which crystallise upon live birth, and that compensation is recoverable for harm inflicted in utero manifesting as congenital injury. The essence of research is quite different from medical practice, and the extent to which this is understood by trial participants is unclear. The approvals processes contain a number of inadequacies which have the potential to expose the foetus to harm and affect the consent of the pregnant woman. The recovery of compensation in the event of children born injured following clinical trials during pregnancy in many ways may be more complex than other personal injury cases.. The conclusions of this thesis are that the existence of a foetus does merit recognition by the law in this setting and that morally such studies are justifiable. However, the present legislation and approval processes potentially expose the foetus to avoidable risk and may not be appropriate to enable the recovery of compensation, thereby creating potential to deter future trial participants. A proposal is made regarding an approach to simplify the process for recovery of compensation, and thereby strengthen the approval and consent processes.

Solidarity, the network and the history of workers' self-management from the Gdańsk Agreement to shock therapy

This PhD thesis is an empirical research project in the field of modern Polish history. The thesis focuses on Solidarity, the Network and the idea of workers’ self-management. In addition, the thesis is based on an in-depth analysis of Solidarity archival material. The Solidarity trade union was born in August 1980 after talks between the communist government and strike leaders at the Gdansk Lenin Shipyards. In 1981 a group called the Network rose up, due to cooperation between Poland’s great industrial factory plants. The Network grew out of Solidarity; it was made up of Solidarity activists, and the group acted as an economic partner to the union. The Network was the base of a grass-roots, nationwide workers’ self-management movement. Solidarity and the self-management movement were crushed by the imposition of Martial Law in December 1981. Solidarity revived itself immediately, and the union created an underground society. The Network also revived in the underground, and it continued to promote self-management activity where this was possible. When Solidarity regained its legal status in April 1989, workers’ self-management no longer had the same importance in the union. Solidarity’s new politico-economic strategy focused on free markets, foreign investment and privatization. This research project ends in July 1990, when the new Solidarity-backed government enacted a privatization law. The government decided to transform the property ownership structure through a centralized privatization process, which was a blow for supporters of workers’ self-management. This PhD thesis provides new insight into the evolution of the Solidarity union from 1980-1990 by analyzing the fate of workers’ self-management. This project also examines the role of the Network throughout the 1980s. There is analysis of the important link between workers’ self-management and the core ideas of Solidarity. In addition, the link between political and economic reform is an important theme in this research project. The Network was aware that authentic workers’ self-management required reforms to the authoritarian political system. Workers’ self-management competed against other politico-economic ideas during the 1980s in Poland. The outcome of this competition between different reform concepts has shaped modern-day Polish politics, economics and society.