Expérimental
Silicon Germanium (SiGe) Heterojunction Bipolar Transistors (HBTs) achieve the best performances of Si-based technologies and are now enabling low-noise and high-speed applications in our daily life. They rely on a graded content of Ge introduced in the epitaxial growth of the HBT base. By doing so, a true bandgap engineering is achieved and allows to optimize the transistor characteristics far beyond the limits of pure materials like Si. Our laboratory in PHELIQS at CEA-Grenoble studies spin quantum bits made with Si MOSFETs from CEA-Leti or homemade Ge heterostructures. Even though it is not always widely known, all such qubits experiments include a HEMT or a SiGe HBT in the first front-end cryogenic low noise amplifier (LNA) of the readout chain. Recently we have designed and fabricated our own LNAs, using a commercially available BiCMOS technology, which exhibits low performances than more recent technologies. In this internship we will investigate advanced BiCMOS devices from the B55 technology of STMicroelectronics, for applications in quantum bits experiments. We will measure their characteristics down to 3.2K or 0.45K in homemade pulse-tube based cryostats. This work will be carried in close collaboration with STMicroelectronics which not only provides advanced BiCMOS chips but also shares its deep knowledge of SiGe HBT devices, including previous cryogenic characterizations at high frequency and above 4K.