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Fiasse_40001900_2024.pdf
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- With the advance in telecommunication technologies, the world needs better and better power amplifiers. To this end non-conventional transistors (HEMT) have been developed. However, as they shrink in size but increase in frequency and power output, they face more and more thermal-related problems. In this context, the goal of this thesis is to model the impact of different parameters, such as layer thicknesses, on the temperature distribution in the device. The temperature distri- bution is modeled using semi-analytical model using the thermal quadrupole theory and also finite element simulations. These results are then coupled to resistivity models to predict the apparition of a low resistivity parasitic channel at the bottom (AlN-Si) interface of the device. In parallel, the "3-omega" technique was investigated. This is a technique for the mea- surement of the thermal conductivity of a material in a multi-layered system. It consists in a oscillating current being applied to a heater, simple rectangular metal strip on top of the sample to analyse. This generate an heat wave at double the frequency in the specimen which is then send back to the heater. This leads to an increase of the temperature at the surface. The change in temperature then induces a change in resistance of the heater due to its temperature coefficient of resistance (TCR). This variation of resistance when multiplied with the input current generates a voltage across the heater which oscillates at thrice the initial frequency. This signal can then be picked-up by a device called a lock-in amplifier to get the thermal properties of the sample by sweeping in frequency. Measurement validated the setup for low thermal conductivity substrate (Quartz) but it showed inconsistent results with high thermal conductivity substrate (Si). More work needs to be done to fix current issues with the setup.