Gas Sensors Using CMOS MEMS

  Sarah Bedair

Gary Fedder
CMOS MEMS gas sensors

Micro-calorimeter gas exposure to toluene and isopropyl alcohol

Mass sensor frequency shifts due to acetone and 2-propanol exposures
Chemical sensing research has been an expanding field for the past twenty years. There are many applications for chemical sensors such as chemistry, quality control, process applications in the food industry, and medical applications. Such applications include "electronic noses", gas sensing arrays, and "electronic tongues", which are liquid sensing arrays. Full on-chip integration using CMOS/microelectromechanical systems (MEMS) technology provides for viable means for such chemical sensing applications because of its inherent qualities that lead to device miniaturization, low power consumption, and complete system on chip for biomedical and chemical applications. Commercial CMOS chips in conjunction with a few mask-less micromachining steps provides a platform for chemically sensitive polymer application on MEMS transducers using ink-jet printing. These transducers exploit the change in the physical properties such as mass, resistance, and heat transfer of the sensitive layer upon absorption of a gas species. The current research explores the fabrication and implementation of a mass and heat sensitive gas detectors.

Figures 1 (a) & (b) show a digital image of a micro-calorimeter and an SEM of the mass sensor, respectively. Polystyrene was deposited on these MEMS transducers and these sensors were tested under gas exposures. For the micro-calorimeter a voltage signal change proportional to heat exchange between the polymer and the transducer occurs upon gas absorption and desorption. This is shown in Figure 2. For the mass sensitive cantilever a negative resonance frequency shift occurs upon gas absorption. This is shown in Figure 3.



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