Carbon nanotube isolation layer enhancing in-liquid quality-factors of thin film bulk acoustic wave resonators for gravimetric sensing

Girish Rughoobur, Hisashi Sugime, Mario DeMiguel-Ramos, Teona Mirea, Shan Zheng, John Robertson, Enrique Iborra, Andrew John Flewitt

Research output: Contribution to journalArticle

6 Citations (Scopus)


A thickness longitudinal mode (TLM) thin film bulk acoustic resonator biosensor is demonstrated to operate in water with a high quality-factor, Q. This is achieved using a layer of carbon nanotubes (CNTs) on top of the resonator which has a significantly different acoustic impedance to either the resonator or liquid whilst being susceptible to the binding of biological molecules. This allows the resonance to be decoupled from direct energy loss into the liquid, although still retaining mass sensitivity. AlN solidly mounted resonators (SMRs) having a thickness shear mode (TSM) at 1.1 GHz and TLM at 1.9 GHz are fabricated. CNTs with different forest densities are grown by chemical vapor deposition on the active area with Fe as the catalyst and resulting devices are compared. High forest density CNTs are shown to acoustically decouple the SMRs from the water and in-liquid TLM Q values higher than 150 are recorded even exceeding TSM SMRs without CNTs. The TLM Q in water is remarkably improved from 3 to 160 for the first time by dense CNT forests, rendering the large-scale fabrication of TLM SMRs for liquid-phase sensing applications possible. Despite this partial isolation, SMRs with CNT forests ∼15 μm tall can still detect binding of bovine serum albumin.

Original languageEnglish
Pages (from-to)398-407
Number of pages10
JournalSensors and Actuators, B: Chemical
Publication statusPublished - 2018 May 15



  • Acoustic wave decoupling
  • Bulk wave resonators
  • Carbon nanotubes
  • Gravimetric sensing
  • In-liquid sensors

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Instrumentation
  • Condensed Matter Physics
  • Surfaces, Coatings and Films
  • Metals and Alloys
  • Electrical and Electronic Engineering
  • Materials Chemistry

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