3-D integration of RF circuits using Si micromachining

Micromachined silicon integrated circuits have the potential for providing an overarching circuit integration technology that can significantly reduce the size, weight, and cost of microwave and millimeter-wave components. The capability to integrate diverse substrate technologies opens the door for real multifunction chips, combining analog, digital, RF,and optoelectronic functions. This natural approach to three-dimensional (3-D) vertical integration not only can provide higher density circuits, but, by freeing RF circuit design from the tyranny of the two-dimensional (2-D) layout, can reach levels of performance not possible in a planar geometry. This article focuses on the concept of 3-D circuit integration using silicon (Si) bulk micromachining; however, similar techniques can be applied in any other III-V substrate material. Packaging issues prerequisite for the 3-D integration and component development that led to the capabilities for 3-D integration are discussed. The integration techniques are applied to a 3-D integrated W-band power cube, which provides a vehicle for successfully demonstrating the concept and basic techniques for 3-D integration. A concept study is presented of the use of micromachining to integrate Ka-band 2-D and 3-D corporate power combining architectures.