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Haoshen ZHU TIMA Laboratory - MNS group visitor,

Theme: Thermodynamic Feedback and Nonlinearity Cancellation Effects in Longitudinal-mode Silicon MEMS Resonators : Modeling and Experimental Verification
Date: June 18th, 2014 (Wednesday) - 11:00, TIMA Laboratory - Room T202A

Biography

Haoshen Zhu received the B.E. degree in Electrical Engineering from Wuhan University of Technology, in 2009. Currently, he is a trainee in TIMA Laboratory and working toward the Ph.D. degree in the Department of Electronic Engineering, City University of Hong Kong. He is also affiliated with the State Key Laboratory of Millimeter Waves. His current research interests include design and modeling of silicon micromechancial resonators, particularly for high performance MEMS oscillator application. He is a student member of IEEE.

Abstract

Microelectromechanical systems (MEMS) oscillators have made significant progresses in the last decades and are regarded as an alternative to quartz crystal oscillators in the timing and frequency control market. Unlike quartz oscillators, MEMS oscillators are based on miniaturized micromechanical resonators (or MEMS resonators) that are fabricated in batch and CMOS-compatible processes. This makes them outperform quartz counterparts in size and cost. But in terms of phase noise (PN) performance, the MEMS oscillators are still inferior to quartz oscillators. According to Leeson's model, the larger achievable energy storage and higher quality factor (Q) are favorable for better PN performance. In this talk, we present two interesting phenomena found in the longitudinal-mode n-doped single-crystal-silicon MEMS resonator. First topic demonstrates the active Q boosting effect. A electro-thermo-mechanical coupled finite-element model is built to predict the thermodynamic feedback on the amplification of Q. Predictions by the model on the variation of Q with bias current are well validated against measurements. These results also provide an insight into design of devices capable of self-oscillation without the need for electronic amplification. In the second topic, we experimentally demonstrate the manipulation of nonlinear behaviors in this longitudinal-extension bulk-mode resonator. By controlling the bias dc current that locally heats up the device, reversed nonlinear features (turning from the spring hardening to softening) are observed and lead to the so-called "nonlinearity cancellation" at certain bias level. This is the first observation in any bulk-mode MEMS resonators. This scheme proofs that the material nonlinearity can be suppressed to extend the nonlinear limits of MEMS resonators so as to enhance the PN performance for future MEMS oscillators.