Tapping Mode MEMS Gas Sensor

Micro gas sensors are widely used as chemical and biological sensors. Those sensors have detection limit to the order of few atto grams. Developing high resolution gas sensors is of great importance in many fields such as biological applications and hazardous environments. MEMS sensors are generally categorized according to their actuation state into static and dynamic sensors. Static sensors measure the deflection of the sensor as a means of detecting a specific gas concentration, whereas dynamic sensors measure changes in natural frequency due to added mass as a means of gas detection. The sensor is equipped with a polymeric sensing material that has high selectivity to ethanol. A novel tapping-mode region was found and proposed to measure the target mass in an analog mode. Unlike the conventional analog sensors that measure the shift in its natural frequency, measuring induced current from the contact area of the beam-tip and bottom electrode will be used as a detection mechanism to measure the sorbed mass. The main focus of this study is to design a novel electrostatic gas sensor based on tapping mode actuation and used to detect ethanol. The sensor consists of cantilever beam functionalized with a detector material, poly2,5-dimethylaniline (P25DMA), that has high selectivity to the target gas in its vicinity. A simple readout circuit is designed to simply detect the sorbed mass electrically. An efficient mathematical model for the sensor due to electrostatic actuation will be developed. The fabrication process of the sensor and the experimental setup and procedure are introduced. It is worth noting that depending on the added sensing material, the sensor could also be functionalized with a specific polymeric material capable of detecting toxic gases in petrochemical industry such as nitrogen dioxide, NO2, and sulfur dioxide, SO2. Development of such advanced MEMS sensors holds a great potential for industry in Saudi Arabia, especially for oil and gas industries.