Monolithically Integrated Reconfigurable RF MEMS Based Impedance Tuner on SOI Substrate

This paper presents the design and implementation of a MEMS-based impedance tuner realized on a Silicon-on-Insulator (SOI) substrate. Contactless lateral MEMS varactors were realized using laterally moving capacitive thick plates whose motion was precisely controlled using Chevron actuators. The voltage required for the maximum displacement is under 12 V. These varactors are monolithically integrated with CPW lines using a single mask fabrication process on SOI substrate. The implemented MEMS capacitive varactors exhibit a capacitance range of 0.19 pf to 0.8 pf. The improvement of the Smith chart coverage is achieved by proper choice of the electrical lengths of the CPW lines and precise control of the lateral motion of the capacitive plates. The measured results demonstrate a good impedance matching coverage with an insertion loss of 2.9 dB. Details of the SOI-based fabrication process are presented along with discussions on techniques to improve the insertion loss of the device. The proposed design does not suffer from the dielectric charging, micro-welding and stiction problems associated with RF MEMS devices realized using surface micromachining processes. In addition, the device promises to be useful in high power applications, since it is constructed from lateral thick structures.