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This Thesis Has Been Submitted in Fulfilment of the Requirements for a Postgraduate Degree (E.G This thesis has been submitted in fulfilment of the requirements for a postgraduate degree (e.g. PhD, MPhil, DClinPsychol) at the University of Edinburgh. Please note the following terms and conditions of use: This work is protected by copyright and other intellectual property rights, which are retained by the thesis author, unless otherwise stated. A copy can be downloaded for personal non-commercial research or study, without prior permission or charge. This thesis cannot be reproduced or quoted extensively from without first obtaining permission in writing from the author. The content must not be changed in any way or sold commercially in any format or medium without the formal permission of the author. When referring to this work, full bibliographic details including the author, title, awarding institution and date of the thesis must be given. Development of a High Temperature Sensor Suitable for Post-Processed Integration with Electronics Aleksandr Tabasnikov A thesis submitted for the degree of Doctor of Philosophy The University of Edinburgh 2016 Declaration of originality I declare that this thesis has been composed by me, the work is my own, and it has not been submitted for any other degree or professional qualification. Research recorded was carried out by me except as specified below: X-ray diffraction measurement results obtained using X-ray diffractometer Siemens D5000 were collected by Richard Yongqing Fu and his students Jimmy Zhou and Chao Zhao at the University of West of Scotland. Measurement results are analysed in section 4.4.6 of Chapter 4 and have been jointly published in 2014 (DOIs: 10.1109/ICMTS.2014.6841491). Aleksandr Tabasnikov ___________________________ II Abstract Integration of sensors and silicon-based electronics for harsh environment applications is driven by the automotive industry and the maturity of semiconductor processes that allow embedding sensitive elements onto the same chip without sacrificing the performance and integrity of the electronics. Sensor devices post- processed on top of electronics by surface micromachining allow the addition of extra functionality to the fabricated ICs and creating a sensor system without significant compromise of performance. Smart sensors comprised of sensing structures integrated with silicon carbide-based electronics are receiving attention from more industries, such as aerospace, defense and energy, due to their ability to operate in very demanding conditions. This thesis describes the design and implementation of a novel, integrated thin film temperature sensor that uses a half-bridge arrangement to measure thin film platinum sensitive elements. Processes have been developed to fabricate temperature insensitive thin film tantalum nitride resistors which can be combined with the platinum elements to form the temperature transducing bridge. This circuit was designed to be integrated with an existing silicon carbide-based instrumentation amplifier by post-CMOS processing and to be initially connected to the bond pads of the amplifier input and output ports. Thin films fabricated using the developed TaN and Pt processes have been characterized using resistive test structures and crystallographic measurements of blanket thin film layer samples, and the relationship between the measurement results obtained has been analyzed. An initial demonstration of temperature sensing was performed using tantalum nitride and platinum thin film resistor element chips which were fabricated on passivated silicon substrates and bonded into high temperature packages. The bridge circuit was implemented by external connections through a printed circuit board and the bridge output was connected to a discrete instrumentation amplifier to mimic the integrated amplifier. The temperature response of the circuit measured at the output III of the amplifier was found to have sensitivity of 844 µV·°C–1 over the temperature range of 25 to 100 °C. Two integrated microfabrication process flows were evaluated in this work. The initial process provided a very low yield for contact resistance structures between TaN and Pt layers, which highlighted problems with the thin film platinum deposition process. Multiple improvement options have been identified among which removal of the dielectric layer separating TaN and Pt layers and thicker Pt film were considered and a redesign of both layout and the process flow has resulted in improved yield of platinum features produced directly on top of TaN features. Temperature sensitivity of the integrated sensor devices was found to depend significantly on parasitic elements produced by thin film platinum step coverage, the values of which were measured by a set of resistive test structures. A new microfabrication design has enabled the production of a group of integrated temperature sensors that had a sensitivity of 150.84 µV·°C–1 in the temperature range between 25 and 200 °C on one of the fabricated wafers while the best fabricated batch of sensors had a sensitivity of 1079.2 µV·°C–1. IV Lay summary Producing sensors on silicon-based integrated circuits enables additional sensing functions on the same chip without reduction in the performance of the electronics. Silicon carbide (SiC) dramatically lifts the fundamental temperature limitation of silicon electronics (125 °C) to at least 300 °C and producing sensors with electronics based on this new material is a challenge as well as a new research area. Sensor devices fabricated on top of SiC electronics would create a sensor system able to perform in extreme conditions, and this perspective was the key motivation behind this work. This thesis describes the design and implementation of an integrated, thin film temperature sensor based on temperature insensitive, thin film tantalum nitride (TaN) resistors and thin film platinum (Pt) temperature sensitive elements. These films as well as the insulating layers separating them were produced using production processes that would be safe to perform on SiC integrated circuits. Electrical resistance parameters, physical structure and stability of thin film Pt and TaN have been measured, and fabrication processes have been developed step by step to form a temperature transducing circuit. The temperature sensor was demonstrated in two implementations, both of which produced sufficiently high sensitivity to temperature. The first implementation used external connections between separate TaN and Pt resistor chips, and a commercial instrumentation amplifier that was not exposed to high temperatures. An integrated bridge implementation was later produced by a microfabrication process flow that potentially enabled the sensor to be integrated with a SiC instrumentation amplifier and was measured up to 200 °C. This points the way towards future integration of sensors for extreme environments such as wind turbines, gas turbines, oil drills, geothermal wells and other demanding industrial applications. V Acknowledgments I gratefully acknowledge the financial support by UK EPSRC through the FS/01/02/10 IeMRC Flagship Project on Smart Microsystems. I would like to thank my supervisor Dr. Stewart Smith for supporting and guiding me through my PhD, spending days of his time on discussions of my work and initiating me to many insights of microfabrication and test. I am extremely grateful to my second supervisor Professor Anthony Walton for his advice, help and direction throughout the project and thesis write-up stages, and also for the opportunity given to me to work at the facilities and with specialists of Scottish Microelectronics Centre. My major thanks go to Stewart Ramsay, Ewan MacDonald, Richard Blair, Brian Neilson and Hugh Frizell as well as Andrew Bunting and Tom Stevenson for their immense technical help and assistance for the duration of this work. I also want to thank Jonathan Terry, Gerard Cummins, Jeremy Murray, Atif Syed, Yifan Li, Peter Lomax, Ross Walker, Evgeny Sirotkin, Ewan Blair and Ilka Schmueser for their assistance and groundwork that influenced this research. I gladly appreciate help and communication from Richard YongQing Fu, Khelil Sefiane and their PhD students who provided the required measurement setups in critical times. I would also like to express my gratitude to the staff of electronic and mechanical workshops, School of Biological Sciences and School of Physics for their support in building parts of different experimental setups, producing experimental samples and other deliverables. I am especially grateful to my friends and relatives for their encouragement and most importantly I would not go far without love and support from my mother, father and my wife Irina who never lost faith in me. VI Table of contents Declaration of originality........................................................................................... II Abstract ..................................................................................................................... III Lay summary ............................................................................................................. V Acknowledgments .................................................................................................... VI Table of contents ..................................................................................................... VII List of figures ............................................................................................................ XI List of tables ..........................................................................................................
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