RF MEMS and NEMS components and adsorption-desorption induced phase noise

Radio frequency micro- and nanoelectro-mechanical systems (RF MEMS and RF NEMS) and technologies have a great potential to overcome the constraints of conventional IC technologies in realization of fully integrated transceivers of next generation wireless communications systems. During the last two decades a considerable effort has been made to develop RF MEMS/NEMS resonators so that they could replace conventional bulky off-chip resonators in wireless transceivers. In MEMS, and especially in NEMS resonators, additional noise generating mechanisms exist that are characteristic for structures of small dimensions and mass, and high surface to volume ratio. One such mechanism is the adsorption-desorption (AD) process that generates the resonator frequency (phase) noise. In the first part of this paper a short overview of RF MEMS resonators is given, including comments on the necessary improvements and the direction of future research in this field (especially having in mind the need for NEMS resonators), with the intention to optimize RF MEMS and NEMS components according to requirements of both current and future systems. The main part of the paper presents a comprehensive theory of AD noise in MEMS/NEMS resonators. Apart from having a theoretical significance, the derived models of AD noise in multiple different cases of adsorption are also a useful tool for the design of optimal performance RF MEMS and NEMS resonators. The model of the MEMS/NEMS oscillator phase noise that takes into account the influence of AD noise is presented for the first time.