Fabrication and Modeling of Piezoelectric RF MEMS Resonators

Resonators serve as essential components in radio-frequency (RF) electronics, forming the backbone of filters and tuned amplifiers. However, traditional solid state or mechanic implementations of resonators and filters tend to be bulky and power hungry, limiting the versatility of communications, guidance, and avionics systems. Microelectro-mechanical systems (MEMS) are promising replacements for traditional RF circuit components. In particular Piazza, et al. has demonstrated high performance RF MEMS resonators utilizing thin film structures of piezoelectric aluminum-nitride (AlN) [2]. These AlN films have been previously patterned using chemical wet-etching techniques, whose isotropic nature results in mask undercutting and sidewall sloping. This paper demonstrates that inductively coupled plasma (ICP) etching results in a cleaner, straighter etch profile. Furthermore, the effects of sloped sidewalls are investigated through finite element simulations for ordinary and high-mode resonator structures. It is shown that sidewall sloping degrades resonator efficiency and performance.