Acoustic properties of carbon nanotube electrodes in BAW resonators

In this paper the acoustic characterization of a layer of carbon nanotubes (CNT) deposited on AlN solidly mounted resonators is described. The structure of the CNT layer is analyzed by scanning electron microscopy and Raman spectroscopy. The electrical sheet resistance is derived from 4 point probe measurements and from the fitting of the electrical response of the resonators. Values of sheet resistance around 100 Ω/□ are measured. The longitudinal acoustic velocity is derived from the fitting of the electrical response of the resonators using Mason´s model, by adjusting the overtones produced in the CNT layer. A mean value of 62000 m·s^-1 is obtained, although some devices show values around 90000 m·s^-1, close to the theoretical value of 100000 m·s^-1. Some results on the deposition of CNT layers on metallic top electrodes and their influence on the performance of the resonator are also presented.