MEMS-based high performance tunable passive components for RF applications

Abstract

In the recent wireless communication environment, large number of communication standards is coexist in a wide frequency range and they are needed to be accessible easily and independently. With the great demand on an effective frequency management spreading in the wide frequency range, reconfigurable systems using tunable passive components have gained great attentions. There have been tremendous research activities in the tunable passive components, but they have focused on either a tunable capacitor or a tunable inductor because their tuning mechanisms were quite different. As a result, the designs and technologies proposed in previous researches were incompatible with each other. The main research objective in this thesis is the development on universal integrated tunable components to realize the reconfigurable RF systems. For the realization on universal integrated tunable components with high RF performances, I will introduce the concept of a floating metal plate to tune capacitance and inductance continuously and simultaneously. In chapter 2, new MEMS tunable capacitor actuated with the electrically floating metal plate has been proposed and successfully demonstrated. The proposed tunable capacitor showed better quality factor $(\varrho -factor)$ performance than that of the conventional tunable-gap capacitor by means of eliminating the electrical series resistance of mechanical spring in the RF signal pathway. The fabricated tunable capacitor showed almost 200 % increment (i.e. 3 times higher) in $\varrho$ -factor from the conventional tunable-gap capacitor. In addition, an array of tunable capacitors connected in parallel with four capacitors for larger capacitance was fabricated and measured. A continuous tuning ratio of 41 % with $\varrho$ -factor of 300 at 1 GHz and 34.9 at 5 GHz for the single capacitor and the continuous tuning ratio of 29 % with Q-factor of 39.8 at 1 GHz for the capacitor array were obtained. In chapter 3, novel MEMS-bas...