Microwave Electronic Devices
Semiconductor microwave electronic devices have a major impact on how the world ticks, and ultimately on how each of us lives. For example, microwave devices are used in collision avoidance systems and radars in cars and commercial aircrafts, and in 4G - and soon 5G - communication. For the past 50 years, microwave technology used mostly traditional semiconductor materials, such as Silicon (Si) and Gallium Arsenide (GaAs), however these materials now have reached their limits. GaN devices, typically grown on SiC substrates, are presently superseding these traditional devices, delivering greater power and efficiency by, for example, offering a greater range in a radar. However, power comes at a price: Heat.
Device performance and lifetime are critically impacted by any resulting device temperature rise; the high electrical fields present in these devices can also have an impact on performance and reliability. No-one wishes to have an electronic component to fail on an airplane, or during a space mission on a satellite; therefore whilst GaN-based HEMTs already reach RF power levels 10x that of GaAs devices, and power densities as high as 40 W/mm and frequencies exceeding 300 GHz have been demonstrated, problems arising from self-heating means devices can only be reliably operated to power densities of 10 W/mm.
There are two opposite drivers in this field, and the CDTR is active in both: (i) lower cost GaN devices on Si substrates and (ii) ultra-high power GaN devices replacing the currently used SiC substrate with diamond. Integrating devices with heterogeneous materials - benefiting from the most optimal properties - offers a huge potential for new technology. This is at the core of our research.
Our research focuses on developing new experimental techniques to understand heat transport in devices, to design optimal heat sinking solutions and new devices with integrated heat sinking. Equally, we aim to understand how devices fail, which includes developing electrical testing techniques that detect the generation of unwanted electronic traps in these devices, and to develop device design concepts with electronic traps in the ‘right’ locations, to mitigate these effects.
Figure 1. GaN-on-Diamond microwave technology