A micromachining post-process module for RF silicon technology

A bulk-micromachining post-process module, based on two-level structuring of RF silicon substrates and a 4-/spl mu/m thick one-level sub-surface metal pattern, is presented. This allows for fabricating three-dimensional structures for novel RF components and has potential in more compact integration. Next to a concise description of the relevant aspects of the fabrication process, mechanical stability of the postprocessed wafers is analyzed. Sub-surface spiral inductors with good quality and low coupling to inductors built at the wafer surface are presented, thus demonstrating the feasibility of three-dimensional integration of RF components.