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

Abstract

Abstract: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 150 0 C. 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 1/2 . 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.

Development of integrated microsystem for hydrogen gas detection

“…The portable gas sensor as reported in this paper was manufactured using standard MEMS technology as already reported by many researchers [5][6][7][8][9]. The sensitive element consists of a semiconducting MO layer [zinc oxide (ZnO)] to detect various gases by changing its electrical conductivity [6,8,[10][11][12][13][14][15][16]. It can be envisaged from the below-mentioned set of publications that many of the combustible gases (such as methane, ethanol, methanol, acetone etc.)…”

“…There are some reports on such integrated MEMS sensor with Application Specific Integrated Circuit design of the signal conditioning unit [16]. Some of them also reported on the development of integrated gas sensor systems with log‐invertor circuits for linearising the output voltage [20].…”

Microcontroller based Power Efficient Signal Conditioning Unit for Detection of a Single Gas using MEMS based Sensor

“…Conventional signal processing techniques can be used for this purpose, for instance the various responses of the sensing electrodes may be digitized and subsequently processed, or combined in analogue form. For integrated sensor application, for hazardous environments like underground coalmines where continuous monitoring of hazardous gas concentration is required it is extremely desirable that the entire signal-processing unit capable of amplifying low signal level output from the sensor as well as transmitting the modified signal to remote control station, should be integrated along with the sensor platform [11,12].In our earlier work we reported on such integrated MEMS sensor with ASIC design of the signal conditioning unit [13]. There are also some reports on the development of integrated gas sensor systems with log-invertor circuits for linearising the output voltage [14].…”

The Effect of Catalytic Metal Contact on Methane Sensing Performance of Nanoporous ZnO -Si Heterojunction

“…These heterostructures are very effective in gas sensing applications [5]. Many works have already been reported on the fabrication of ZnO thin film via several routes such as sputtering [6], spray pyrolysis [7], CVD [8], sol-gel [9] and galvanic deposition technique [10] etc. Among all the techniques sol gel gives good control over the morphology, particle size and thickness of the ZnO.…”