A CMOS-Integrated MEMS Platform for Frequency Stable Resonators-Part I: Fabrication, Implementation, and Characterization

This paper introduces the comprehensive design concepts, procedure, and post-process flow of a robust manufacturing platform for complementary metal-oxide- semiconductor microelectromechanical systems (CMOS-MEMS) resonant transducers with enhanced frequency stability and capacitive-transduction efficiency. Thanks to a sandwich-stacking configuration of the interconnection metal line (TiN/AlCu/TiN) existing in standard CMOS technology, a deep-submicron TiN-to- TiN gap is successfully demonstrated by removing the central AlCu alloy layer through the proposed post-fabrication platform, thus realizing a novel titanium nitride composite (TiN-C) structure. Compared with the traditional release approaches utilized in the general post-CMOS fabrication, the proposed TiN composite transducer with TiN-to-TiN gap can simultaneously attain (i) a 400nm air gap for effective electrostatic transduction, (ii) adequate material selection and arrangement for near-zero frequencytemperature coefficient, and (iii) conductive electrodes to overcome frequency drift induced by dielectric charging during capacitive operation. In Part I of this study, the design guideline, layout rules, and detailed post-fabrication flow are addressed. The fabrication results of each post-process step are also exhibited. Numerical analysis, experiment results, and further discussions in terms of frequency stability for resonant transducers will be covered in Part II.