2006

Alastalo, Ari

Starting in the early 1960's, when the integrated-circuit (IC) technology was developed, micromachining and microelectromechanical systems (MEMS) have grown into a broad research field with several commercial successes. Typical applications of MEMS are in physical, chemical and biochemical sensors, as well as in optical systems such as the digital micromirror device of Texas Instruments. From the 1990's, the advances in the processing technologies and the tremendous growth of the wireless-communication market have drawn much interest into radio-frequency MEMS devices (RF MEMS) such as filters, oscillators, switches and tunable capacitors. These are now beginning to penetrate the market.<br/>This thesis considers electrostatically-actuated RF-MEMS filters and delay lines. For filters, the work concentrates on nonlinear distortion and filter design. The intermodulation properties of capacitively-coupled MEMS filters are analytically solved in closed form and the theory is verified in numerical simulations as well as in measurements with MEMS resonators. The analysis is more generally valid than the previously published results. The theory is utilized to formulate a design procedure for MEMS filters that, for the first time, takes systems speci-fications for tolerable intermodulation distortion and insertion-loss into account. For delay lines, capacitive actuation of bulk-acoustic waves in a solid rod is analyzed. In particular, challenges in impedance matching due to the weakness of the electrostatic coupling are quantified. Finally, a new kind of resonator-chain delay line for high-frequency (HF) signals is introduced. This delay line is characterized by extremely slow signal group velocity (? 10-100 m/s), narrow-band response, and much lower characteristic impedance than found for the solid-rod waveguide enabling efficient signal coupling. Properties of the resonator-chain waveguide are theoretically analyzed and the results are verified in measurements of fabricated devices.