Monolithic Wafer-Level Rectangular Waveguide and Its Transition to Coplanar Waveguide Line Using a Simplified 3-D Fabrication Process

In this paper, we are introducing a new category of wafer-level micromachined rectangular waveguide devices and illustrate a new transition of these devices to Coplanar Waveguide (CPW) lines for millimeter-wave applications. The 3-D fabrication process used in this paper utilizes a combination of thin film and thick film processes and produces a simple three-mask fabrication process. As a result, all the on-wafer elements such as the waveguide, the CPW lines, and their transition are simultaneously fabricated, which eliminates the ever-existing requirement of hybrid assembly of the waveguide parts. A metalized post is employed to couple the signal from the CPW line to the waveguide. Unlike the previous designs that are mostly based on capacitive coupling, the proposed CPW to waveguide transition is based on inductive coupling, which simplifies the fabrication requirements and improves the performance. Here, the entire back-to-back structure is designed, fabricated, and measured on a 10 mm² wafer area. A wide-band RF performance is measured for the proposed waveguide structure. Our measured results show an insertion loss of as low as 1 dB at 72 GHz range. The proposed technique to realize wafer-level waveguides has great potential to include a variety of waveguide topologies including bends and arcs. Besides, this method allows for further expansion of the topic to integrate MEMS components inside the waveguide.