MEMS-based gas sensors being miniaturised have various advantages such as low power consumption, robust and stable electrical properties. These gas sensors have three main components namely micro-heater, interdigitated electrodes and sensing film. Micro-heater as the important part of the gas sensor device decides the power consumption of the gas sensor.
Metal oxide based gas sensing platform for Ammonia (NH3), Carbon monoxide (CO), Ethanol (C2H5OH), Propanol (C3H7OH) and Hydrogen sulphide (H2S) was developed and demonstrated (Fig.1). Gas sensors could be integrated with electronics to make a portable as well as fixed kind of gas detection/analysis system. Gas sensors were characterised in controlled environment chamber to observe the sensor response at various gas concentrations (Fig.2). Operating temperature for different gases was adjusted by the platinum micro-heater. Platinum being a noble metal exhibits stable electrical and mechanical properties even at higher temperatures.
Fig. 1: (a) Devices at wafer level, (b&c) packaged devices
- Gases: NH3, CO, H2S, C2H5OH and C3H7OH (other useful gases can be explored based on requirement
- Response time: Sensor responds to gases in lessthan 1-2 minutes (depends on gas concentration)
- Recovery time: Sensor can achieve the base line (upto 95%) in less than 3 minutes
- Power: Varies with target-gas as the temperature consumption requirements are different. MEMS based gas sensor can be operated for less than 100 mW, whereas non MEMS (without cavity) gas sensor can be used for rugged applications for power less than 600 mW.
- Minimum: 10 PPM (NH3), 100 PPM (CO), 25 detectable PPM (H2S), 250 PPM (C2H5OH) and limits 250 PPM (C3H7OH).
Fig. 2: Gas concentration vs sensitivity plots for NH3, CO, H2S, C2H5OH and C3H7OH
The gas sensors were developed under a project on ‘Development of MEMS-based integrated micro gas sensor for volatile organic compounds and polluted gases’ sponsored by Department of Electronics and Communication Technology (DeitY), Government of India. The prototype devices were handed over by Dr. Chandra Shekhar, director CSIR-CEERI to Dr. S.C. Gadkari, Chairman Review Committee (Fig. 3).
Fig. 3: Dr. Chandra Shekhar, director CSIR-CEERI handing over prototypes of the Gas sensor to Dr. S.C. Gadkari, chairman, Review Committee