DRIE of high Q-factor length-extensional mode quartz micro-resonator

A two dimensional (2D) length-extensional mode quartz micro-resonator has been designed and patented by ONERA. Thanks to a specific decoupling, this resonator is expected to show a very high Quality factor x Frequency product (Q.f) near the theoretical limit of 3.10(13). This design offers a range of frequencies between 1 MHz up to 10 MHz, thanks to homothetic geometries with thickness ranging from 210 to 30 mu m. These very good characteristics and the small dimensions (final package is foreseen to be less than 10 mm(3)) as well as the intrinsic qualities of quartz (high quality factor, piezoelectricity and good thermal stability) make this resonator capable of outperforming the MEMS silicon resonators of comparable size with performances comparable to Ultra Stable Oscillators. Nevertheless, the small dimensions at stake to achieve higher frequencies devices require specific manufacturing processes, such as Deep Reactive ion Etching of Quartz (DRIE). This paper focuses on the presentation of two proposed fabrication processes using Deep Reactive Ion Etching of quartz. It brings out critical factors for practical realizations and highlights the design adaptations necessary to enable the etching for depth comprised between 30 and 210 mu m and to promote vertical etching walls. First realizations and characterizations are also reported.