Caroline MAYE

Sujet de thèse : « Validation of a telecommunication system in the frequency range 71-77 and 81-86 GHz »

The 55nm BiCMOS technology, manufactured by STMicroelectronics, shows great potential for applications in the millimeter and sub-millimeter frequency ranges. It features a heterojunction bipolar transistor (HBT) with characteristic frequencies, ft and fmax of 320 and 370 GHz respectively. The development of the test bench involves lengthy fabrication and validation processes. Therefore, it is important to develop a load-pull characterization bench at frequencies above 140 GHz in order to validate the model of such a transistor. The realization of this bench is still limited by the power performance of the sources, detectors and impedance synthesizers available on the market. Thus, a hybrid solution is proposed. The source, similar to the architecture of a VNA extension head, as well as the detectors are kept off-wafer for a perennial use of the measurement bench. Particular attention is paid to the calibration steps, during which the difficulty of scalar measurement at millimeter frequencies is highlighted. Moreover, the impedance tuner is integrated on-chip with the HBT in order to avoid the losses of the RF probe which reduce the reflexion coefficient presented at the output of the device under test. The design of the tuner still appears as a huge challenge and is under development. In parallel, an automation program is implemented to improve the measurement accuracy, to perform the calculation of the component parameters and to reduce the measurement time. Finally, the first load-pull measurements are performed at 185 GHz on the heterojunction bipolar transistor and for several dimensions.