| As a major MEMS application, RF MEMS switches combine the advantages of traditional electromechanical switches (low insertion loss, high isolation, high linearity) with some major merits of solid-state switches (low power-consumption, integration). Single-pole single-throw (SPST) DC-contact switches have been demonstrated to frequencies as high as 90 GHz with isolation of 20 dB. However, the relatively large size of these switches results in the need for long stubs when using them for designing multi-throw switches and ultimately limits the upper frequency range of these switches. Previous work on compact MEMS switches has focused on cantilever based DC-contact designs. In order to make the cantilever beam insensitive to stress gradients from the fabrication process, relatively thick beams are used. However, such a thick beam is very stiff and difficult to be pulled down. With a new design and fabrication techniques, this research focused on the development of in-line DC-contact switches using thin-film cantilevers to achieve high isolation and reasonable actuation voltage simultaneously. It has shown promising results up to 50 GHz and can ultimately contribute to higher frequency performance in multi-throw switch designs.;This research has achieved three major technical advances: (1) modelling and fabrication of thin-film cantilever structures, the Au cantilever beams (thicknesses ranging from 0.4 mum to 1.2 mum, length ranging from 70 mum to 120 mum) are built on Al sacrificial layer(thicknesses range from 0.8 mum to 4 mum). The tip deflection can be controlled to well within 1 mum; (2) design and fabrication of RF MEMS single-pole-multi-throw switches up to 50 GHz with insertion loss lower than 2 dB and isolation better than 20 dB; (3) using these switches to build switched line phase shifters up to 50 GHz. Measurements of fabricated RF MEMS switches and phase shifters up to 50 GHz are presented. The 1.5 bit phase shifter (0°, 30°, 60°) demonstrates the capability of achieve desired phase change at 50 GHz. Design concepts, trade-offs, analysis and discussion are also investigated in this dissertation. |
