Interactive Design of MEMS Varactors With High Accuracy and Application in an Ultralow Noise MEMS-Based RF VCO

Abstract

The monolithic integration of microelectromechanical systems (MEMS) varactors into the backend of line metal stack of a state of the art semiconductor process is an attractive alternative to the field effect transistor or bipolar transistor varactors for continuous frequency tuning of ultralow phase noise voltage-controlled oscillators (VCOs). An efficient design of MEMS varactors according to application-specific demands requires a deep insight into the electromechanical and electromagnetic (EM) device properties and an accurate prediction of the varactor phase noise contribution to the overall phase noise of the MEMS-based VCO. Generally, MEMS varactors are designed using a combination of finite-element method and EM softwares. Due to the large computational and time effort, the required deep insight into the MEMS device is hard to achieve. This paper presents interactive design methodologies to predict the electromechanical, EM, and the phase noise properties of a MEMS varactor with high accuracy. These methodologies are verified by fabricated MEMS varactors and an experimental MEMS-based VCO with continuous frequency tuning.