High frequency capacitive single crystal silicon resonators and coupled resonator systems

High frequency mechanical resonators such as quartz crystals, surface acoustic wave (SAW) and film bulk acoustic wave resonators (FBAR) and filters are widely used in electronic systems as highly stable frequency references for oscillators and bandpass filters. Recent developments in silicon micromachining technologies has enabled implementation of high frequency silicon capacitive resonators with close to one order of magnitude higher quality factors (Q) compared to the SAW resonators and FBARs. Such devices are gradually entering the market opening up new opportunities for more advanced highly integrated electronic systems. Due to their lithographically-defined resonant frequencies, in-plane capacitive resonators with operating frequencies in a wide range from tens of kHz up to GHz can be implemented on the same substrate simultaneously, providing higher levels of integration. In addition, due to their much high Q values and tunability compared to piezoelectric resonators, capacitive resonators can provide higher performance e.g. lower phase noise for tunable oscillators or ultra-narrow bandwidth for bandpass filters. High-Q micro and nanomechanical resonators also have tremendous potential for precision chemical and biomedical sensing applications.;The objective of the presented research is to implement high-Q silicon capacitive micromechanical resonators operating in the HF, VHF and UHF frequency bands. Several variations of a fully silicon-based bulk micromachining fabrication process referred to as HARPSS have been developed, characterized and optimized to overcome most of the challenges facing application of such devices as manufacturable electronic components. Several micromechanical structures for implementation of high performance capacitive silicon resonators covering various frequency ranges have been developed. Design criteria and electromechanical modeling of such devices is presented.;Under this work, HF and VHF resonators with quality factors in the tens of thousands and RF-compatible equivalent electrical impedances have been implemented successfully. Resonance frequencies in the GHz range with quality factors of a few thousands and lowest motional impedances reported for capacitive resonators to date have been achieved. Several resonator coupling techniques for implementation of higher order resonant systems with possibility of extension to highly selective bandpass filters have been investigated and practically demonstrated. Finally, a wafer-level vacuum sealing technique applicable to such resonators has been developed and its reliability and hermeticity is characterized.