Silicon-based Microwave Coplanar Waveguide Transmission Characteristics In The Microwave Phase Shifter Applications Research

Monolithic microwave integrated circuit (MMIC) designs on Si substrates have become an important topic in recent years. With constantly increasing frequencies in communications and integrated circuits, there are great demands for low-cost, miniature microwave transmission lines. Another increasingly important (actor is to be integrated with analog and digital circuits. For this reason, it is highly advantageous for the microwave components to be fabricated through a commercial CMOS process. So we research the microwave transmission lines and apply it into phase shift. Several results have obtained.1. First several kinds of implementation of Si-micromachined transmission line have been investigated. With different fabricating process, each transmission line has its different structure, and the insertion loss and operating frequency range are different. Then we determined our objective.2. A new similarity method in FEM is presented for researching of the problems about the nonuniform and irregular region, such as micromachined microwave coplanar waveguide. By using this method, we calculate the characteristic impedances of MEMS waveguide and analyse the change with its different dimensions. With the use of a recurrence relation, this new method not only use much less computer's memory than the conventional FEM, but also simplify the post-process..5. The samples with characteristic impedances of 120 and 50 have been fabricated through the surface micromachining and bulk micromachining. Stress relaxation has been considered carefully through designing and fabricating, to obtain the structures with the lowest stress.4. The multiline method is applied in measuring the effective dielectric constant of micromachined microwave transmission lines. This multiline method does not need a network analyzer calibration.5. Other technologies have been researched. One is the transmission lines on p-type high-resistivity silicon. The other is the transmission line on low-resistivity silicon covered polyimide. The initial experiment results indicate that the inserter loss has been greatly reduced.These two kinds of processes can be compatible with commercial CMOS process and easily integrated the transmission line with microwave circuits. The design and fabrication of low-loss distributed MEMS phase shifter has also been researched. Its MEMS capacitors and control voltage are discussed in detail. Among several different membranes, Al0.98 S0.4 Alloy exposed the best performance and the pulling-down voltage of the MEMS phaseshifter was no more than 20V. We also describe the principle and design of Bragg frequency, and present the limit to the bandwidth of the MEMS phase shifters. In addition, the Bragg frequencies of the phase shifters using the different dimensions have been calculated. Insert loss of the MEMS shatter will be no more than 3dB in the whole frequency and the phase shifter is 25. Lifetime of the MEMS membrane is more than 3+10.In conclusion, we have proposed the application of silicon to microwave devices as a low-loss material. These all show the prospect of monolithic microwave integrated circuit (MMIC) on Si substrate.