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Title: Materials, device, and system integration of amorphous oxide semiconductor TFTs
Author: Yao, Guangyu
ISNI:       0000 0004 7972 9645
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2019
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Amorphous oxide semiconductor (AOS) thin-film transistors (TFTs) have great potential for use in the next-generation of electronics. AOS TFTs can be used to fabricate circuits and sensors on various substrates, due to unique properties, including high mobility, excellent uniformity, and it requiring a low-temperature process. Currently, indium gallium zinc oxide (IGZO) is the predominant AOS used in the display industry as a TFT semiconductor. Although the IGZO technology is very mature, the development of AOS continues. Additional AOSs are being investigated to reduce cost and improve stability. Considering availability and the potential of materials, indium silicon oxide (ISO) was selected for this project. ISO uses silicon to suppress the instability originating from the oxygen vacancy. The silicon-oxygen bond has a higher dissociation energy, which improves retention of oxygen atoms in the film, and thus, increases the transistor's stability. This detailed study follows a bottom-up approach. It starts with the fabrication and characterisation of materials. Basic material properties of the ISO film are discussed within, including amorphicity, bandgap, stoichiometry, and Hall-effect parameters. Based on the characterisation results, different deposition recipes for the TFT were developed and tested. The interface quality and etching selectivity were investigated. Uniformity and stability data were extracted from a TFT array using the developed photo-lithography process, which was used to verify and quantitate the capability of the process in system integration and circuit design. A Monte-Carlo simulation environment was established based on the extracted data. The two urgent challenges in all-TFT analogue circuit design, the lack of proper active load and the large parasitic capacitance, were investigated. In-depth analysis on these two issues and applicable solutions were presented. Investigation on system integration of TFT circuits and sensors were conducted, since the device demonstrated the required performance and uniformity. An all-TFT differential-input amplifier was designed and verified, as the first mixed signal all-TFT circuit.
Supervisor: Sambandan, Sanjiv Sponsor: China Scholarship Council ; Cambridge Trust
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
Keywords: TFT ; AOS ; Circuit ; Fabrication