The ever-increasing combined carbon footprint of information and communications technology (ICT) is unsustainable - more efficient devices must be developed. Thermal characterisation, which feeds into design optimisation, is one of the key steps for ensuring the efficiency and reliable operation of the new electronic devices being developed. However, accurately measuring the temperature of leading-edge electronic devices is becoming increasingly difficult or impossible because of their small size, and that is the challenge addressed in this proposal. Wide bandgap electronic devices including GaN have great proven potential for the next generation of sustainable ICT and power electronics, contributing to the needed carbon emissions reduction. Miniaturization is one of the routes to further increase the efficiency and performance of wide bandgap electronic devices, decreasing the active region size to <200 nm, similar to the technology pathway that silicon (Si) electronics has taken, using concepts such as the FinFET. Thermal management, which is the efficient extraction of waste heat from the active part of the device, is especially important for achieving efficient reliable nanoscale electronic devices; thermal resistance increases as they are "scaled" to nanometre dimensions because of a thermal conductivity reduction and heat confinement in 3-D device structures, e.g. in a fin shape. While self-heating can be mitigated reasonably easily for lower power density Si FinFETs, it is potentially a significant roadblock for "scaled" wide bandgap devices which operate at enormous power densities. However there is currently no thermal imaging technique with a sufficiently high spatial resolution (e.g. Raman thermography has a diffraction limited resolution of about 0.5 micrometer, >10x the hotspot size) to be able to accurately measure the hotspot temperature of these novel nanoscale wide bandgap electronic devices. Instead we currently rely on complex electrothermal models to estimate the temperature of nanoscale devices, with inherent uncertainties - measurement is needed.

A step change is required, namely a sub diffraction limit (super resolution) thermal imaging technique, which is addressed by the Future thermal Imaging with Nanometre Enhanced Resolution (FINER) project. We will develop a transformative nano quantum dot based thermal imaging (nQTI) technique to deliver nanometre resolution thermal imaging for the first time. To demonstrate the newly developed technique our application focus is on scaled wide bandgap electronic devices supplied by our national and international partners, however this technique will be widely applicable. Quantum dots are ideal for this application: They can be deposited as a nm-thickness film on the surface of the device being tested, and the emission colour is temperature dependent, which is what we exploit for thermal imaging. Structured Illumination Microscopy (SIM) and Stimulated Emission Depletion (STED) super-resolution techniques which were originally developed for fluorescence microscopy, but are presently unsuitable for thermal imaging, will be exploited to achieve a resolution as small as 50nm for nQTI.

nQTI will enable nano-scale electrothermal models to be developed and experimentally verified. Accurate models will further our understanding of nano-scale self-heating and heat diffusion, feeding back into improved device designs and novel thermal management solutions. This work will be done at the Centre for Device Thermography and Reliability (CDTR) which has an international reputation for being at the forefront of high spatial and temporal resolution thermal imaging, pioneering Raman thermography. This expertise makes the CDTR ideally placed to deliver this project successfully. The generous industrial support for this programme demonstrates that there is a great need for this and their belief in our ability to successfully deliver it.