Flexible substrate technology for millimeter wave applications

This thesis is part of research effort to develop a 3D heterogeneous integration of wireless sensor node on flexible substrate for the unlicensed 60GHz band. The System in Package (SiP) should have a very low power consumption and very low cost to meet the requirements of applications like Wireless Sensor Networks (WSNs) for Structure Health Monitoring (SHM). Using a flexible substrate for wireless sensor node integration can offer the advantage of being localized in areas with access difficulty especially in non-planar area. Each node is composed of nano-sensors, transceivers and TX/RX antenna. Nanotechnologies made it possible the development of ultra-sensitive nano-sensors based on nanoparticles deposition. Transceivers become more and more miniaturized and hence enable the possibility of postpone them onto flexible substrate. The antennas can be integrated on the flexible substrate along with the developed nano-sensors and miniaturized transceivers, which is the very innovative approach. In this work, we propose customized photolithography processes to manufacture the passive element circuits (resonators, antennas, rectennas, etc…) on flexible substrate. The technique of flip-chip was used for the integration of 60 GHz transceivers, a novel technique to form Au interconnection bump directly onto the flexible substrate by using electrodeposition process is also presented here for the first time. The concordance between the simulations and the measurements is observed, which proves the reliability and reproducibility of such process technique. Furthermore, for a high-volume application like the node deployment of WSNs, wafer cost reductions can significantly lower the total cost per node and became comparable to a low-cost inkjet printing process.