Low TCF Lithium Tantalate contour mode resonators

Abstract

This paper presents for the first time thin-film contour mode resonators (CMR) using Lithium Tantalate (LT). Exploiting the inherent low temperature coefficient of frequency (TCF) of certain acoustic modes in LT, we demonstrate low TCF S <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</inf> lamb wave mode CMRs in rotated Y-cut LT thin films. With an electrode configuration using a top interdigitated transducer (IDT) and bottom ground electrode, we fabricated 1-port resonators at 501MHz and 870MHz, and 2-port resonator at 849MHz. These devices exhibit low motional impedance (10-20 Ω), with quality factors as high as 3200. More significantly, a TCF of −20ppm/K is demonstrated from the 1-port devices, while the 2-port device exhibits −16.7ppm/K. These are the lowest TCFs demonstrated to date from an uncompensated thin-film contour mode resonators, making LT thin-film technology a promising candidate for oscillator applications.