Laser Annealing for high-Q MEMS Resonators
NAVAL RESEARCH LAB WASHINGTON DC
Pagination or Media Count:
High frequency and high quality factor, Q, defined as a half-width of the resonant peak are the key factors that enable applications of microelectromechanical MEMS oscillators for supersensitive force detection or as elements for radio frequency signal processing. By shrinking the dimensions of MEMS resonators to the sub-micron range one increases the resonant frequency of the devices. Shrinking the devices, however, also increases the surface-to-volume ratio leading to a significant degradation of the quality factor to below 5,000 due to the increased contribution of surface-related losses11. We demonstrate that local annealing performed by focused low-power laser beams can improve the quality factor of MEMS resonators by more than an order of magnitude, which we attribute to the alteration of the surface state. Quality factors over 100,000 were achieved after laser annealing3.1 MHz disc-type oscillators radius R10 micrometers, thickness h0.25 micrometer compared with a Q6,000 for the as-fabricated device. The mushroom-type design of our resonator a single-crystal silicon disc supported by a thin silicon dioxide pillar at the center provides low heat loss. The combined power of a red HeNe laser Pred4mW and a blue Ar ion laser Pblue5mW focused on the periphery of the mushroom provides enough energy for surface modification. The post-treatment quality factor, exceeding 100,000 for MHz-range resonators, boosts the performance of MEMS to be comparable to that of lower frequency single-crystal quartz devices. The local nature of laser annealing, safe for surrounding electronics, is a crucial element for integration of MEMS resonators into a CMOS environment.
- Lasers and Masers
- Manufacturing and Industrial Engineering and Control of Production Systems