Investigation of Energy Trapping of the Lateral Field Excited Thickness Shear Mode in AT-Cut Quartz Crystal Microbalances

Abstract

Methods for improved energy trapping of the thickness shear mode (TSM) in quartz crystal microbalances (QCMs) under lateral field excitation (LFE) are presented. The dependencies of TSM resonant intensity and spurious mode presence on surface curvature and electrode geometry are analyzed for improved LFE QCM response. TSM resonance trend data are given for 6 MHz plano-convex uncoated wafers and electroded devices up to 6 diopters (D). The energy trapping concept is also extended to include electrical energy redistribution, which alters the active acoustic modes in LFE devices. Aspects of data on newly discovered metal-loaded LFE shear modes more intense than known LFE TSMs are presented. Variations of these metal-loaded device responses with surface curvature and metal layer thickness are reported. Butterworth-Van Dyke (BVD) equivalent circuit parameters are extracted for air- and metal-loaded response comparisons. The observed influences of acoustic and electrical energy trapping expand knowledge on the extent of LFE device capabilities and reveal implications for resonator applications.