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Title: Enhanced spectroscopic gas sensors using in-situ grown carbon nanotubes

In this letter, we present a fully complementary-metal-oxide-semiconductor (CMOS) compatible microelectromechanical system thermopile infrared (IR) detector employing vertically aligned multi-walled carbon nanotubes (CNT) as an advanced nano-engineered radiation absorbing material. The detector was fabricated using a commercial silicon-on-insulator (SOI) process with tungsten metallization, comprising a silicon thermopile and a tungsten resistive micro-heater, both embedded within a dielectric membrane formed by a deep-reactive ion etch following CMOS processing. In-situ CNT growth on the device was achieved by direct thermal chemical vapour deposition using the integrated micro-heater as a micro-reactor. The growth of the CNT absorption layer was verified through scanning electron microscopy, transmission electron microscopy, and Raman spectroscopy. The functional effects of the nanostructured ad-layer were assessed by comparing CNT-coated thermopiles to uncoated thermopiles. Fourier transform IR spectroscopy showed that the radiation absorbing properties of the CNT adlayer significantly enhanced the absorptivity, compared with the uncoated thermopile, across the IR spectrum (3 μm–15.5 μm). This led to a four-fold amplification of the detected infrared signal (4.26 μm) in a CO{sub 2} non-dispersive-IR gas sensor system. The presence of the CNT layer was shown not to degrade the robustness of the uncoated devices, whilst the 50% modulation depth of the detector was only marginally reducedmore » by 1.5 Hz. Moreover, we find that the 50% normalized absorption angular profile is subsequently more collimated by 8°. Our results demonstrate the viability of a CNT-based SOI CMOS IR sensor for low cost air quality monitoring.« less
Authors:
; ;  [1] ; ; ;  [2] ; ;  [3] ;  [1] ;  [4] ;  [5]
  1. Department of Engineering, University of Cambridge, Cambridge CB3 0FA (United Kingdom)
  2. Cambridge CMOS Sensors Ltd., Deanland House, 160 Cowley Road, Cambridge CB4 0DL (United Kingdom)
  3. Department of Materials, University of Oxford, Oxford OX1 3PH (United Kingdom)
  4. (United Kingdom)
  5. School of Engineering, University of Warwick, Coventry CV4 7AL (United Kingdom)
Publication Date:
OSTI Identifier:
22399070
Resource Type:
Journal Article
Resource Relation:
Journal Name: Applied Physics Letters; Journal Volume: 106; Journal Issue: 19; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; ABSORPTION; ABSORPTIVITY; CARBON DIOXIDE; CARBON NANOTUBES; CHEMICAL VAPOR DEPOSITION; COMPARATIVE EVALUATIONS; DIELECTRIC MATERIALS; FOURIER TRANSFORMATION; INFRARED SPECTRA; LAYERS; MEMS; RAMAN SPECTROSCOPY; SCANNING ELECTRON MICROSCOPY; SEMICONDUCTOR MATERIALS; SENSORS; SILICON; THERMOCOUPLES; TRANSMISSION ELECTRON MICROSCOPY; TUNGSTEN