Zero-Level Packaged RF-MEMS Switched Capacitors on Glass Substrates

This article presents the design, realization and measurement of thin-film packaged RF-MEMS switched capacitors for millimeter-wave applications. Packaging is included in the MEMS fabrication process, with silicon nitride thin film shell above MEMS structure. Thin-film packaging is done using a combination of electron beam evaporated metal and silicon nitride PECVD deposition. The package hermeticity has been evaluated after the first metal sealing layer deposition, indicating that the protective nitride shells are hermetic enough before the final PECVD passivation. The devices have been fabricated on glass substrates, allowing for further combination with low loss, millimeter-wave passive circuits. The MEMS capacitors are actuated by deflecting thin gold metal membrane towards the package dielectric layer, increasing the capacitance by a factor 3, from 25 fF to 75 fF. The device size, including its hermetic packaging, is 70×50 μm2. Reliability has been evaluated, through 12-hour hold-down test measurements.