Enhancing sensitivity of graphene gas sensors using molecular doping
Physical Sciences : Materials and Compounds
Available for licensing
- Deji Akinwande, Ph.D. , Electrical and Computer Engineering
- Seyedeh Maryam Mortazavi Zanjani , University of Texas at Austin
- Mir Sadeghi, M.S. , Nascent
- Milo Holt, B.S. , Microelectronics Research Center
Detecting the presence of gas molecules is of prominent importance for controlling chemical processes, safety systems, and industrial and medical applications. Despite enormous progress in developing and improving various types of gas sensors, sensors with higher sensitivity, lower sensing limit, and lower cost that can perform at room temperature remain desirable. Graphene is a promising candidate for gas sensing applications due to its unique transport properties, exceptionally high surface-to-volume ratio, and low electrical noise.
Researchers at The University of Texas at Austin have demonstrated that the sensitivity of a graphene sensor to a gas molecule can be significantly enhanced using molecular doping, which was found to be as effective as substitutional doping and more effective than electric-field doping.
The room temperature sensitivity of NO2-doped graphene to NH3 was measured to be comparable to sensitivity of graphene doped with substitutional boron atoms and superior to that of as-fabricated graphene by an order of magnitude. The detection limit for doped graphene sensors was estimated to be ~200 ppb, which can potentially be improved with extended exposure to NO2, compared to ~1.4 ppm before doping. While the stability analysis of NO2-doped graphene sensors indicates that this doping method is not completely stable, this study nevertheless presents molecular doping as a candidate technique for sensitivity improvement by enhancing the initial carrier concentration.
Such high levels of doping cannot be readily obtained via the electric field effect in real applications due to restrictions on power consumption and maximum supply voltage, especially for the case of CMOS-compatible integrated sensors. Electrical characterization and Raman spectroscopy results proved that the observed sensitivity enhancement was due to localized hole doping of graphene via adsorption of NO2 molecules.
- The device offers an order of magnitude improvement in sensitivity and response time over existing electrochemical sensors.
- The invention takes advantage of the low cost and miniaturization potential of existing CMOS fabrication infrastructures.
- Direct integration of the sensor material with a back-end MOS ring oscillator makes for an inherently wireless solution.
- No heating is required for device operation (operates at room temperature).
- The graphene sensor element contains no finite exhaustible electrolyte, as is the case for electrochemical sensors.
The gas sensor market is projected to reach $2.7B by the year 2020, with toxic gas sensing for environmental safety in the auto industry and industrial manufacturing applications accounting for a significant percentage of that growth [Gas Sensors Market Analysis by Product and Segment Forecasts to 2020, Grand View Research, 2014].
- 1 U.S. patent issued: 9,869,651