A silicon micromechanical resonator with capacitive transduction for enhanced photoacoustic spectroscopy

Wioletta Trzpil (1, 2) , Julien Charensol (1, 2) , Diba Ayache (1, 2) , Nicolas Maurin (1, 2) , Roman Rousseau (1, 2) , Aurore Vicet (1, 2) , Michael Bahriz (1, 2)

1 IES - Institut d’Electronique et des Systèmes
2 NANOMIR - Composants à Nanostructure pour le moyen infrarouge

This paper presents the design of a silicon micromechanical resonator with capacitive transduction for a gas sensor based on photoacoustic spectroscopy. It overcomes problems imposed by opposite physical trends originating from the sensor's working principles. The capacitive transduction mechanism is considered incompatible with the photoacoustic gas detection as it reduces the mechanical displacement by a damping effect, thus decreasing the sensitivity. This occurs because the same part serves two functions: photoacoustic excitation and capacitive transduction. The suggested approach in this study focuses on the spatial separation of these two functions. We propose the first reported mechanical microresonator for photoacoustic gas sensing, which decouples photoacoustic excitation and capacitive transduction. The design has been modeled, fabricated, characterized, and compared with the on-beam Quartz-Enhanced Photoacoustic Spectroscopy (QEPAS) technique, a reference for compact and selective gas sensors. The performed photoacoustic measurement has been realized on calibrated concentrations of methane. For a 1 s integration time in first harmonic detection, we obtained a limit of detection (LOD) of 667 ppmv for silicon microresonator. In comparison to on-beam QEPAS technique, we obtained LOD of 163 ppmv, which constitutes a factor 4 between QEPAS and MEMS. The conditions for both experiments were the same.

Mots clés: Photo-acoustic; Gas sensor; MEMS; Capacitive transduction; Micro-mechanical resonator; Spectroscopy

Domaines: Optique / photonique; Micro et nanotechnologies/Microélectronique

Wioletta Trzpil, Julien Charensol, Diba Ayache, Nicolas Maurin, Roman Rousseau, et al.. A silicon micromechanical resonator with capacitive transduction for enhanced photoacoustic spectroscopy. Sensors and Actuators B: Chemical, In press, ⟨10.1016/j.snb.2021.131070⟩. ⟨hal-03444585⟩