Liquid-phase chemical sensing using lateral mode resonant cantilevers

Area of Science:

• Micro/Nanoelectromechanical Systems (MEMS/NEMS)
• Chemical Sensing Technology
• Materials Science

Background:

• Liquid-phase operation of resonant cantilevers is hindered by fluid damping, leading to low quality factors (Q factors).
• Existing out-of-plane flexural modes suffer from significant damping in liquids, limiting sensor sensitivity and detection limits.

Purpose of the Study:

• To investigate and apply resonant cantilevers operating in an in-plane flexural mode for detecting volatile organic compounds (VOCs) in water.
• To overcome the limitations of fluid damping and improve the performance of liquid-phase chemical sensors.

Main Methods:

• Fabrication of resonant cantilevers using a CMOS-compatible bulk micromachining process.
• Excitation of cantilevers in an in-plane flexural mode to minimize fluid damping.
• Coating cantilevers with chemically sensitive polymers (Polyisobutylene and Poly(ethylene-co-propylene)) for analyte sorption.

Main Results:

• Achieved significantly higher Q factors in water for in-plane vibrating cantilevers compared to out-of-plane modes.
• Demonstrated detection of volatile organic compounds in water at concentrations ranging from 1-100 ppm.
• Estimated detection limits in the parts per billion (ppb) range for the developed sensors.

Conclusions:

• In-plane flexural mode cantilevers offer superior sensing properties in liquid environments.
• These cantilever-type mass-sensitive chemical sensors show great potential for sensitive and selective detection of VOCs in aqueous solutions.