ZnO transparent electronics

Transparent electronics is a field gathering considerable interest in recent years, as it offers many new and useful applications in diverse sectors: automotive, aerospace, domestic, environmental

Professor S Hall

Some examples are: heads-up displays in car windscreens and airplanes, active matrix displays in windows, functional furniture with invisible electronics, windows in buildings for monitoring and local environmental control. The area of 'green buildings' is of great interest in the drive to reduce energy consumption. The transparent electronics global sector was nearly $76.4 billion in 2010, but is expected to increase to $123 billion in 2015, for a 5-year compound annual growth rate of 10.  Transparent conducting oxide (TCO) thin films are being increasingly exploited in a range of technological applications including architectural glazing, photovoltaic solar cells, flat panel displays, light emitting diodes and lasers.

The combination of high electrical conductivity (104Ω-1cm-1) and optical transparency (>80%) across the visible spectral range constitute enabling metrics for optoelectronic device in terms of reduced electrical power consumption and high optical power output.  Tin-doped indium oxide (ln2-xSnxO3, ITO) fulfils these requirements and has become a benchmark when qualifying the performances of other TCOs such as fluorine-doped tin oxide or doped zinc oxide [Edwards et al, Dalton Tran. 2995 (2004)]. Indium however is not an abundant element and is becoming increasingly expensive having experienced a more than tenfold increase in price since 2002.  The price of indium is also subject to large variations as it is susceptible to political decisions and policies. It is becoming clear therefore, that a technology based on indium is not viable for mass-production in this potentially massive global market.  Extensive research activity continues therefore, to be focused on the development of less expensive and non-toxic alternatives.

The central aim of this project is to embed circuits formed from simple devices, into glass windows for visual display, monitoring and control purposes. The project builds on recent UoL work whereby a scaleable ALD process for high quality zinc oxide (ZnO) transparent films has been demonstrated on glass. This technological breakthrough represents an excellent opportunity to replace indium based films in transparent electronics products. The device type, namely the metal-semiconductor field effect transistor (MESFET), is selected for implementation of electronics due to its relative ease of fabrication and low voltage operation.  

This device is further preferred over the metal-insulator field effect transistor MISFET (or MOSFET) because the need is avoided for the technologically changing development of a gate oxide technology.  The project is then concerned with the establishment of a MESFET fabrication process, device design for the intended circuitry and finally design and realisation of basic circuit blocks and gate arrays.  The project falls into the area of 'transparent electronics' where the market is dominated by expensive indium materials.

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