Integration of RF switches based on chalcogenide phase change materials: application to millimeter wave imaging
In order to satisfy the requirements of a millimeter (30-300GHz) or sub-THz (300GHz-1THz) medical imaging, it is necessary to develop more efficient millimeter systems, whose electrical properties can be modified according to the need. Millimeter switches, or RF switches, are one of the essential components of these systems and are used, for example, for filter switching, for the reconfiguration of multi-mode and multi-band antenna beams, for impedance matching, or for the realization of switching matrices, allowing complex routing of the transmitted or received signal. Beyond millimeter or sub-THz imaging, radar, backhaul, and 5G-6G telecom applications are also envisaged. For almost a decade, RF switches based on chalcogenide phase change materials (PCM RF switches) have attracted considerable attention because they have the potential to achieve figures of merit (FoM = RON*COFF) in the order of 10fs, which is a factor of 10 improvements over today's best solid-state switches. Recently, CEA-Léti has produced an RF switch based on a PCM alloy, GeTe, with state-of-the-art performance. Preliminary design laws have been defined, demonstrating the very high potential of these switches. However, a great deal of work remains to be done before obtaining a component that provides the necessary performance for the targeted applications. In particular, the resistive transition of the PCM material enabling switching is achieved thermally via Joule heating. Thus, the energy efficiency of the switch, as well as its performance, reliability, and endurance, will strongly depend on the phase change material used, the technological stacking achieved, the geometry of the switch, and the means of applying the thermal pulse. The proposed thesis work will define the main specifications of the switches for the targeted applications and seek to identify the key properties required of the phase change material. The aim will be to evaluate different chalcogenide material alloys and to develop a technological integration path for switches that will optimize the reliability and electrical and energy performance of the component. Finally, innovative circuits will have to be designed, including the SP4T required for the IMHOTEP project, which must operate between 50 and 75GHz. The impact of design parameters on the overall performance of the system, within an application demonstrator, will need to be studied.