An additive micromolding approach for the development of micromachined ceramic substrates for RF applications

The selective removal of the substrate from under devices can help improve Q-factors, reduce losses and parasitics and can be applied to microwave components (transmission lines, spiral inductors, and capacitors) critical to high-frequency communications systems. A novel molding process has been developed to produce cavities in ceramic substrates over which gold transmission lines can be suspended. The "additive" method of fabricating cavities in ceramics was primarily based on the production of a substrate with preexisting cavities, as opposed to generation of cavities by the removal or the "subtraction" of material. The preexisting cavities were generated using a transfer mold technique based on photolithography, anisotropic silicon etching and nickel electroplating. The approach was demonstrated successfully using a commercial glass ceramic material (DuPont 951 Green Tape) to yield 100-μm-deep cavities that showed shape retention and dimensional stability.