Fabrication of a Tunable RF MEMS Inductor on Silicon in a sub-150°C Process

One of the major challenges of successfully integrating radio frequency integrated circuits (RFIC) on silicon (Si) continues to be the poor performance of inductors. The low resistivity Si substrate is a cost-effective solution, however it is a major source of energy loss and limits the quality factor (Q) of inductors at high frequency. Conventional oxides introduce considerable stress due to the difference in thermal expansion coefficient (TEC) with Si and stoichiometric SiO2 requires high temperature processing. Plasma enhanced chemical vapor deposition (PECVD) amorphous Si (a-Si) is a low temperature candidate for improving the isolation of RF devices on Si [1]. It has been explored as an alternative to polysilicon due to comparable mechanical properties at a considerably lower deposition temperature for the potential of microelectromechanical system (MEMS) integration [2].