A design procedure for an acoustic mirror providing dual reflection of longitudinal and shear waves in Solidly Mounted BAW Resonators (SMRs)

Abstract

Abstract-The quality factor of the traditional Solidly Mounted Resonator (SMR) is limited by substrate losses, as the traditionally employed acoustic mirror reflects longitudinal waves but not shear waves. Modern mirrors do reflect both waves, but design rules for such mirrors have not been published so far. We propose a systematic design procedure derived from optics leading to a novel embodiment for the acoustic mirror which effectively reflects both longitudinal and shear waves. This method can be applied for the acoustic mirror design for any given material combination. An analytical model is presented; its agreement with FEM simulations is good. With the optimized design, we can obtain a minimum transmission for longitudinal and shear waves of −25 dB and −20 dB at resonance frequencies for longitudinal and shear waves, respectively, for various reflector material combinations.

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“…On the other hand, the Q factor measures the damping of the resonators. Following the study of S. Jose et al [7], the losses are minimized when the number of layers is odd. In Fig.…”

“…Bulk Acoustic Wave (BAW) resonators have gained traction due their ability to be aggressively miniaturized and their frequency tuning capabilities. They can also operate at ultra-high frequencies, extending up to 20 GHz and beyond, in contrast to the performance of Surface Acoustic Wave (SAW) resonators, which exhibit decaying efficiency beyond 2 GHz [7]. Despite the presence of a high-quality factor (Qfactor) in BAWs resonators, degradation in device performance is observed due to energy losses.…”

“…The main loss factor at BAWs is caused by the contact between the piezoelectric material and the substrate. To reduce the wave propagation between them, the main structures that have been proposed are FBARs (thin-film bulk acoustic wave resonators) and SMRs (solidly mounted resonators) [7], [8].…”