MEMS composite structures for tunable capacitors and IC-package nano interconnects

This paper presents novel low-temperature processes that combine high-aspect-ratio polymer structures with electroless copper plating to create laterally compliant MEMS structures. This low-cost processing was developed for two applications: 1) low-voltage comb-drive actuators for tunable capacitors to reduce the tuning voltage in MEMS structures to less than 5 V and simultaneously increase the capacitance in between the electrode fingers; 2) compliant IC-package interconnects for reliable, low-cost and high-performance nano wafer-level packaging. In both situations, metallic structures show limited electrical performance and create severe reliability issues. Analytical modeling was used to show the advantages of novel composite structures. High-aspect ratio structures were fabricated from lithography and plasma etching. Processing of metal-coated polymers is limited by side-wall adhesion of metal to the polymer and polymer adhesion to underlying substrates. While photodefinable polymers can simplify the processing cost, a dry plasma etching process can give more flexibility in the selection of polymers.