The Challenge of Realising Low Power Logic from Thin Film Semiconductors: from Circuit and Material Optimisation to the Physics of Disordered Semiconductors
Abstract:
Thin film transistors (TFTs) have enabled the active matrix displays that are a ubiquitous part of everyday life, from mobile phones and tablets through to desktop monitors and home televisions. These pixel circuits only require either n-channel or p-channel enhancement mode TFTs. More recently, there has been an increasing interest in producing other logic circuits using TFTs on glass and plastic substrates as this could enable a new generation of products with embedded electronics if we can produce low power circuits. CMOS is an inherently low power technology, but it requires both n-channel and p-channel transistors. Whilst this can be realised in silicon CMOS FETs, it has not yet been achieved using TFTs because it has proved difficult to realise both n-channel and p-channel devices using one material system at low cost. Thin film oxide semiconductors such as amorphous indium gallium zinc oxide have been successfully commercialised and there is therefore a lot of interest in finding a suitable complementary p-type metal oxide thin film material to allow CMOS-type logic to be realised using this material system. Whilst the material development is important, we need to first appreciate how the circuit design rules for TFTs are different to those for MOSFETs before looking at the development of the p-type thin film oxides themselves. This reveals the importance of band tails in such disordered semiconductors and we will look again at the physical significance of these states.
Bio:
Professor Andrew Flewitt is Professor of Electronic Engineering in Cambridge University Engineering Department and is currently head of the Electrical Engineering Division. He is also a Fellow in Engineering at Sidney Sussex College. He graduated in Physics from the University of Birmingham in 1994 before moving to Cambridge to carry out a PhD in Engineering investigating the growth of hydrogenated amorphous silicon thin films using scanning tunnelling microscopy which he completed in 1998. He stayed in Cambridge as a Research Associate sponsored by Philips Research Laboratories working on the low temperature fabrication of thin film transistors. He was first appointed to a Lectureship in 2002 and was promoted to Professor in 2015. Current research interests encompass both large-area electronics, with a particular focus on thin film oxide materials, and microelectromechanical systems. He is a co-Founder of Sorex Sensors Limited which is commercialising film bulk acoustic wave sensors. He published a new textbook on ‘Electromagnetism for Engineers’ in 2022 with the aim of making this subject, which underpins so much of the technology we take for granted today, more accessible to undergraduate students, based over 20 years of supervising Cambridge students in this area. He currently serves on the University of Cambridge HR Committee. He is a Member of the Institute of Physics, a Member of the Institution of Engineering and Technology and is a Chartered Engineer.
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