Non-galvanic Interconnects for Millimeter-wave Systems

Licentiate thesis, 2018

Fueled by the increasing demand for higher data rates, millimeter-wave (mmW) systems emerged as a candidate that can provide multi-gigabit per second (Gb/s) transmission. This demand is mainly driven by modern communication systems and several other wireless and sensing applications such as production quality inspection and imaging systems. The full realization of such systems has been always challenged by the lack of low-loss low-cost interconnects and high-level integration. This challenge is more critical in systems operating beyond 100 GHz where conventional packaging techniques would not be suitable from performance perspective.

D-band offers a wide spectrum ranging from 110 to 170 GHz and hence providing wide bandwidth that makes it suitable for high data rate systems. In this thesis, several interconnects that operate at D-band are presented. Different technologies were used to realize the interconnects. Two interconnects are realized in Embedded Wafer Level Ball Grid Array (eWLB) packaging technology. The technology has been widely used for low frequency applications. The proposed interconnects are based on slot antennas radiating to a standard air-filled waveguides. The interconnects achieve an average insertion loss of 3 dB and 3.4 dB across the frequency ranges 110-138 GHz and 116-151 GHz respectively. The proposed interconnects are generic and do not require any galvanic contacts. The utilized eWLB packaging technology is suitable for low-cost high-volume production and allows heterogeneous integration with other technologies as well.

A chip-to-waveguide transition based on unilateral finline structure is also demonstrated. The interconnect consists of a microstrip line implemented on a 75 um-thick substrate. The line then couples to a unilateral finline taper that is mounted in the E-plane of a standard D-band waveguide. The transition achieves a very low loss of only 0.7 dB and covers a very wide band ranging from 110 to 170 GHz.

A chip-to-waveguide transition in a commercial MMIC technology is also presented. The transition is based on Linearly Tapered Slot antenna (LTSA) structure. The antenna is implemented on a 50 um-thick Gallium Arsenide (GaAs) substrate. The transition exhibits an insertion loss of 1 dB across the frequency range 110-170 GHz.

This work presents low-cost high-performance mmW interconnects and addresses integration challenges facing systems operating beyond 100 GHz paving the way for high-volume commercialization of such systems in the future.