Advancement of a MEMS photoacoustic chemical sensor

Abstract

Photoacoustic spectroscopy is a useful monitoring technique that is well suited for trace gas detection. The technique also possesses favorable detection characteristics when the system dimensions are scaled to a micro-system design. The objective of present work is to incorporate two strengths of the Army Research Laboratory (ARL), piezoelectric microelectromechanical systems (MEMS) and chemical and biological sensing into a monolithic MEMS photoacoutic trace gas sensor. We initially miniaturized a macro-cell design as a means to examine performance and design issues as the photoacoustics is scaled to a dimension approaching the MEMS level. A miniature non-MEMS photoacoutic resonance cell was fabricated and tested with resonator dimensions: diam.=1.5 mm, length = 30mm. Knowledge gained in these initial tests provide the basic information required to fabricate a MEMS scale device while maintaining the sensor integrity. Initial MEMS work is centered on fabrication of a lead zirconate titanate (PZT) microphone subsystem to be incorporated in the full photoacoustic device. PZT membrane microphones have been designed, fabricated and acoustically tested. Presently, the piezoelectric microphone performance has revealed the possibility of using a PZT microphone as the passive acoustic detection mechanism of a photoacoustic resonant cavity. Preliminary designs of the MEMS photoacoustic resonator incorporate a three-wafer design to create a monolithic MEMS photoacoustic cavity. Results will be presented describing the miniature photoacoustic cell capabilities and initial MEMS microphone performance. Preliminary results concerning the MEMS photoacoustic cell design will also be discussed.