Performance Enhancement Of High Frequency MEMS Resonators Through Anchor Loss Reduction Using Phononic Crystals

Performance enhancement of MEMS resonators is one of critical problems in designing of MEMS resonators.To evaluate the performance of a MEMS resonators,a set of parameters including the resonant frequency,quality factor,motional resistance,nonlinearity,power handling,and frequency stability are used to measure the quality of the design.Among these,quality factor is a key parameter which can boost the resonator performance and it is presented by many researchers in several years.Anchor loss is kind of energy dissipation caused by the attachment of resonator body and a substrate,which is due to the propagation of elastic/acoustic wave from the resonant body to the substrate through the device support tethers.This propagation of acoustic wave through the tethers leads to decrease the store energy on the resonator and then decreases the resonator quality factor.It is a common and critical parameter in designing MEMS resonators.Anchor loss reduction leads to the high performance of the resonators resulting from the quality factor improvement.Many methods can be applied to reduce the anchor loss and enhance quality factor such as optimization of support tethers but provide low quality factor,concentration of the vibrational energy at resonant body through the pattering of resonator geometry also result in low quality factor,reflection of the elastic wave back to the resonator also low quality factor and isolation of the elastic/acoustic wave propagation between the resonant body and the substrate by using 1D Phononic crystals provide high quality factor but the device be sensitive to the mechanical shocks and 2D Phononic crystals provide high quality factor,etc.Among these the use of phononic crystals(PnCs)that have been widely used in MEMS resonators to reduce the anchor loss of the resonators.This thesis presents an approach to reduce the anchor loss of thin-film-piezoelectric-on-silicon(TPoS)high frequency MEMS resonator.By using 2D Phononic crystals(PnCs)positioned externally on anchors.The PnCs prevents acoustic wave to propagate through the support tethers,which leads to increase the store energy,and then enhances the quality factor(Q).This thesis discuss the effect of the tether width,tether length,and impact of the design geometry on band gap and the quality factor.The results shows that a band gap up to 380MHz with BG%of 83%and enhances the quality factor from 21,180 to 221,544.T-shape phononic crystals is also introduced in this thesis as another shape of the PnC which produce wide band gap and rise up the frequency level to 860 MHz below 1 GHz and two band gaps over 1 GHz.The technique provide a high quality factor and wide band gap than the previous works.