High Q 2D-length extension mode resonators for potential time–frequency applications

This paper presents recent advances on two dimensional length-extension mode (2D-LEM) quartz resonators providing high quality ( Q ) factor on resonances at a few MHz. The resonators have been collectively manufactured using one or two steps quartz deep reactive-ion etching (DRIE) processes. These resonators combine the intrinsic qualities of quartz in comparison to silicon (i.e. high Q factor, low temperature sensitivity and piezoelectricity) and the advantages of microelectromechanical systems (MEMS) resonators: small dimensions, low power consumption and collective processes. Samples vibrating at frequencies f of 2.2, 3 and 4.5 MHz have shown promising results with very high Q factor. Q factor as high as 180,000 for fundamental mode vibrating at 2.2 MHz and 89,000 for harmonic mode at 8.9 MHz were measured which lead to quality factor and resonance frequency products ( Q·f ) figure of merit near 10 12 Hz at the state of the art for 2D-LEM quartz resonators and the higher Q factor measured for DRIE made quartz resonators. Two designs, several dimensions and two processes have been investigated. Two main limiting damping mechanisms were identified and one of them is strongly linked to the technological limits of the etching process.