Advances in the application of high TcT_{\rm c} superconductors to microwave devices for analog signal processing

During the last five years, the surface resistance $R_{\rm s}$ (10 GHs, 77 K) of YBCO thin films has decreased from a value of about 10 to 20 milliohms — i.e. the same as cooled pure copper or as bulk YBCO — down to values lower than 200 micro-ohms, close to the theoretical value of 100 micro-ohms obtained by a straightforward calculation from BCS theory. This improvement of $R_{\rm s}$ is due to a better quality of the material from random grain ceramics to quasi epitaxial films. These highly textured films can be obtained by many deposition methods : sputtering, laser ablation, co-evaporation, molecular beam epitaxy, MOCVD, using heating sample holders in order to obtain in situ crystal oriented layers. The value of the surface resistance is about one hundred times lower than that of usual metallizations, which can be used either to improve the specifications of some components by two order of magnitude such as high $Q$ 3D resonators ($Q > 10^6$ for low phase noise oscillators) and high $Q$ inductances ($Q > 10^4$ for circuit matching of antennae in the MHz range) or to reduce the size of voluminous devices such as filter banks for multiplexing or spectral analysis

Temperature measurement by micro-Raman scattering spectroscopy in the active zone of AlGaN/GaN high-electron-mobility transistors

The high power RF device performance decreases as the operation temperature increases (e.g. fall of electron mobility impacting the cut-off frequencies and degradation of device reliability). Therefore the determination of device temperature is a key issue for device topology optimisation. In this work the temperature variation of AlGaN/GaN high-electron-mobility transistors grown either on silicon or sapphire substrates under bias operation was measured by micro Raman scattering spectroscopy. The differences in thermal resistance for similar devices grown on the two different substrates were assessed. The thermal resistances of different device topologies were compared in order to optimise the component design. The temperature measurement across the gate and along the component fingers were made to quantify the thermal gradient of the device. Temperature measurement up to a power dissipation of 16 W for a 4 mm development device was carried out and the peak temperature of 650 K was determined

Temperature measurement in AlGaN/GaN High-Electron-Mobility Transistors using micro-Raman scattering spectroscopy

High power RF device performance decreases as operation temperature increases (e.g. decreasing electron mobility affects cut-off frequencies and degrades device reliability). Therefore determination of device temperature is a key issue for device topology optimisation. In this work the temperature variation of AlGaN/GaN high-electron-mobility transistors grown either on silicon or sapphire substrate under bias operation was measured by micro Raman scattering spectroscopy. Temperature measurements up to power dissipation of 16 W for 4 mm development devices were carried out and a peak temperature of 650 K was determined. The difference of thermal resistance for similar devices grown on the two different substrates was assessed. The thermal resistances of different device topologies were compared to optimise the component design