Improving the capabilities of electrostatically transduced mems mass sensors and the influence of the parasitic current on their nonlinear response

• Autores: Gabriel Vidal Álvarez
• Directores de la Tesis: Francisco Torres Canals (dir. tes.)
• Lectura: En la Universitat Autònoma de Barcelona ( España ) en 2015
• Idioma: español
• Tribunal Calificador de la Tesis: José Antonio Plaza Plaza (presid.), Jérôme Juillard (secret.), Warner Venstra (voc.)
• Enlaces
  • Tesis en acceso abierto en: TESEO
• Resumen

  • Resonant micro- and nanoelectromechanical sensors are an excellent tool to study various properties of micro- and nanoparticles and to characterize different physical processes at the micro- and nanoscales. For this reason, this thesis focuses on new strategies to improve the capabilities of this kind of sensors for mass sensing applications. Additionally, it also deals with the influence of the parasitic current on the nonlinear response of this kind of sensors having electrostatic actuation and capacitive detection.

    In this thesis, we present two different devices for resonant mass sensing. The first one is a stepped cantilever composed of a bottom-up silicon nanowire coupled to a top-down silicon microcantilever. The underlying idea behind this device is to detect in the microcantilever the frequency shift produced by a mass deposited in the nanowire, achieving near the mass sensitivity of the nanowire while retaining the frequency resolution of the microcantilever. We validate this approach theoretically and experimentally, demonstrating that coupling nano- with microstructures improves the capabilities of micromechanical sensors.

    The second one is a suspended microbridge resonator with an embedded nanochannel monolithically integrated with complementary metal-oxide-semiconductor (CMOS) readout circuitry. We demonstrate the feasibility of this device and show that the combination of nanosize channel dimensions and integrated circuitry opens the possibility to attain unprecedented mass resolution in measuring the mass of analytes that need an aqueous environment.

    Finally, we show, theoretically and experimentally, that the nonlinear electrical frequency response of a capacitively sensed cantilever resonator can significantly change due to the parasitic feedthrough current. We show that in the electrical domain, the transitions from stable branches present jumps up or down depending on the parasitic current and independently of the mechanical response. This results in the occurrence of three different hysteretic cycle topologies in the electrical domain: counterclockwise, bow tie, and clockwise. Thus, the qualitatively different electrical frequency response of capacitively sensed cantilevers encountered experimentally can be readily explained by the influence of the parasitic current on the nonlinear electrical response.