Anchor Loss Reduction of Lamb Wave Resonator by Pillar-Based Phononic Crystal

Abstract

Energy leakage via anchors in substrate plates impairs the quality factor (Q) in microelectromechanical system (MEMS) resonators. Most phononic crystals (PnCs) require complicated fabrication conditions and have difficulty generating a narrow bandgap at high frequency. This paper demonstrates a pillar-based PnC slab with broad bandgaps in the ultra high frequency (UHF) range. Due to Bragg interference and local resonances, the proposed PnC structure creates notably wide bandgaps and shows great advantages in the high frequency, large electromechanical coupling coefficient (k2) thin film aluminum nitride (AlN) lamb wave resonator (LWR). The dispersion relations and the transmission loss of the PnC structure are presented. To optimize the bandgap, the influence of the material mechanical properties, lattice type, pillar height and pillar radius are explored. These parameters are also available to adjust the center frequency of the bandgap to meet the desirable operating frequency. Resonators with uniform beam anchors and PnC slab anchors are characterized. The results illustrate that the Q of the resonator improves from 1551 to 2384, and the mechanical energy leakage via the anchors is significantly decreased using the proposed PnC slab anchors. Moreover, employment of the PNC slab anchors has little influence on resonant frequency and induces no spurious modes. Pillar-based PnCs are promising in suppressing the anchor loss and further improving the Q of the resonators.

H-Shaped Radial Phononic Crystal for High-Quality Factor on Lamb Wave Resonators

“…In particular, the ultra-wideband gap in the UHF range is achieved in . Compared with the 24.1% relative bandwidth of the cylindrical PCs proposed in the UHF range, the relative bandwidth of the band gap generated by the H-RPC structure proposed in this paper is as high as 80.2% [ 3 ]. Table 2 compares the band gaps of similar lattice constant structures in the relevant literature.…”

“…In recent years, with the rapid development of the fifth-generation mobile communication network (5G), microelectromechanical system (MEMS) technology has shown good application prospects in wireless communication systems and sensor networks [ 1 , 2 ]. The Lamb wave resonator (LWR) is considered by most researchers to be the preferred choice for miniaturized, high-performance, and low-power integrated resonators due to its high operating frequency, high electromechanical coupling coefficient, and low power consumption [ 3 , 4 ]. LWRs are considered to be highly desirable in the 300–800 MHz range commonly used in the field of wireless communications [ 2 , 5 , 6 ].…”

“…Pandey et al designed a mesa around the resonator to reflect the elastic energy back to the resonator [ 18 ]. Using the band gap characteristics of phononic crystals (PCs) to suppress the anchor loss has attracted the attention of researchers [ 3 , 11 , 15 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 ]. For example, Zhu et al used a two-dimensional stomatal PCs unit cell to increase the Q to twice the original [ 11 ].…”

“…Other shapes, such as rings [ 27 ], cross-like holes [ 13 ], fractals [ 14 ], Spider Web-Likes [ 15 ], cross-section connections [ 25 ], double “I” holes [ 26 ], and snowflakes [ 28 ] have also been reported. At present, Yinjie Tong has increased the Q of Pillar-Based PCs by 54% in the UHF range [ 3 ]. Although the Pillar-Based PCs improve the Q, they have a narrow band gap, a relatively low bandwidth, and a limited application frequency band.…”

Numerical Investigation of Phononic Crystal Based Film Bulk Acoustic Wave Resonators

“…[23,24]. Muhammad et al proved that the use of the acoustic bandgap generated by 2D PhC can effectively reduce the loss of acoustic waves through the anchor on the substrate for the Lamb wave resonators with frequencies in the range of 10-200 MHz, and significantly improve the Q factor of the resonators as compared with the traditional resonators [25][26][27][28]. Benchabance et al utilized the bandgap characteristics of PhC on piezoelectric materials to enhance the performance of surface acoustic wave (SAW) filters with an operating frequency of 100-300 MHz [29].…”