Carbon nanotube forests as top electrodes for AlN-based electroacoustic resonators

High sensitive sensors are one of the goals of the modern society due to an increasing necessity for real-time monitoring. To achieve this, new devices and materials are being developed nowadays. In particular, electroacoustic resonators have gained importance in the chemical and biological sensors field owing to their promising performances. Although important advances have been made in the electroacoustic field, additional work is still required to improve the quality factor of the acoustic resonators and their sensing layer. Carbon nanotubes (CNTs) are good candidate materials to act as sensing layers but they can also be used as electrodes. Here we use CNT forests as top electrodes for solidly mounted resonators (SMR) based in AlN thin films and we study their influence on the latters. We prove that, under specific conditions, SMRs do not degrade during the high-temperature CNTs growth process. Also, CNT forests have a weak influence on the SMRs acoustic characteristics. The main drawback regarding their use is a large parasitic resistance presented by the devices. However, this can be solved by depositing denser CNT forests or by growing them on metallic top electrodes layers. SMRs with CNT top electrode can be used as high sensitive and high selective gas sensors due to their high performance and increased functionalized area that CNTs offer.