Excitation of high-frequency in-plane bulk acoustic resonance modes in geometrically engineered hafnium zirconium oxide nano-electro-mechanical membrane

Abstract

A nano-electro-mechanical membrane created from atomic-layered ferroelectric hafnium zirconium oxide (Hf0.5Zr0.5O2), titanium nitride (TiN), and silicon dioxide is engineered to localize high quality factor (Q) in-plane bulk acoustic resonance modes over 80–840 MHz. The in-plane geometry of the membrane, with an overall thickness of 50 nm and an aspect ratio exceeding 104:1, is optimized to simultaneously preserve the stress profile needed for sustaining ferroelectric polarization and enable propagation and constructive interaction of extensional and shear waves to create bulk acoustic modes. A ferroelectric polarization of 11.2 μC/cm2 is measured at the transduction ports, which is consistent after nano-membrane release. The first, third, and seventh order width extensional modes (WE1,3,7) and the third order of the width shear mode (WS3) are electrically measured at 109, 389, 766, and 267 MHz, respectively, showing Qs over 50–100 that are dominated by the large electrical resistance of TiN electrodes. High mechanical Qs of 538, 407, 781, and 594 are extracted for the WE1,3,7 and WS3 modes, respectively, after de-embedding the TiN electrode impedance, resulting in large resonance frequency (f0) × Q products as high as 6 × 1011. The measured characteristics, along with numerical simulations, are used to extract a Young's modulus of ∼340 GPa for the 10 nm-thick Hf0.5Zr0.5O2 film, which is in close agreement with the reported ab initio estimations.