Nanocrystalline ZnO based MEMS Gas Sensors with CMOS ASIC for Mining Applications

In this paper a nanocrystalline (nc) zinc oxide based hybrid gas sensor with signal conditioning ASIC has been reported for sensing and transmitting the information about methane concentration from the underground coalmine environment. A low power, low temperature nc zinc oxide MEMS based gas sensor has been designed, fabricated and tested for the purpose with a power consumption of ~70mW and sensitivity of 76.6 % at 1.0% methane concentration at a sensor operating temperature of 150C. For transmitting the output of the gas sensor, a voltage controlled oscillator (VCO) chip integrated with a low noise amplifier has been fabricated in 0.35μm CMOS technology to convert the voltage output of the gas sensor to desirable frequency. The power consumption of the chip has been obtained to be around 3mW. The amplifier gain is set suitably ~13 to apply the desirable control voltage (~1.2V-3.2V)to the VCO. The noise of the amplifier has been obtained to be around 2μV/Hz. The output frequency of the VCO varies from 20kHz to 100kHz for the change in methane concentration from 0 to 1%. The output of the VCO chip can be applied as a modulating signal to a commercially available transceiver, which transmits the signal to the control room.