SEARCH WITHIN CONTENT
Citation Information : International Journal on Smart Sensing and Intelligent Systems. Volume 3, Issue 4, Pages 605-620, DOI: https://doi.org/10.21307/ijssis-2017-411
License : (CC BY-NC-ND 4.0)
Published Online: 13-December-2017
Nanocrystalline n-ZnO thin films were deposited on SiO2-coated (0.45 μm) p type Si substrates (10-20Ω-cm) by a low cost chemical deposition technique to fabricate ZnO-based resistive sensors for methane detection. The nanocrystalline ZnO needle like structures were grown on RCA cleaned p-Si<100> substrates by successive immersion (100-200 times) into a Sodium Zincate bath (0.125M) kept at room temperature and DI water maintained at 90 oC . The Sodium Zincate was prepared by reacting Zinc Sulphate and excess Sodium Hydroxide in aqueous solution. The film thickness of 1.5 μm (approx.) for 75 dippings was obtained. The dipping time is 1 second. The annealing was done at a lower temperature (150 oC) for 30 minutes in air. Structural characteristics were studied by FESEM and EDAX to indicate the formation of ZnO with vertical orientation. The hexagonal needle like structures of 0.3-0.5μm diameter and 1-1.5μm length were formed. The resistance of the ZnO films in ambient air (zero level for gas sensing) was found to be stable and reproducible after several thermal cyclings. Surface modification with palladium (0.01% PdCl2 for 5 seconds) was done to enhance sensitivity; so that the ZnO thin films can give significant response to target gases at the operating temperature of as low as 130oC, compared to the normal operating temperature range of 200–400oC for zinc oxide resistive gas sensors. The planar gold contacts were deposited by vacuum evaporation technique. The device was then tested for its methane sensing property at different operating temperatures (150,175,200,250,300,350oC) and at 5 different methane concentrations (0.01,0.05,0.1,0.5,1%) taking N2 as a carrier gas. The response magnitude, response time and recovery time were studied in detail for both Pd modified and unmodified ZnO film. The maximum response of 99.76% and the lowest response time of 39 seconds were obtained at 200oC for Pd modified sensor. A high sensitivity to methane even at low temperature (130oC) was observed comparable to those obtained by more sophisticated and expensive deposition process e.g. MOCVD.
 C. Baratto, G.Sberveglieri, A.Onischuk, B.Caruso and S. D. Stasi , “Low temperature selective NO2 sensors by nano structured fibres of ZnO”, Sensors Actuators B, Vol.100 February 2004, pp.261-265.
 P.K.Basu, P.Bhattacharyya, N.Saha, H.Saha and S.Basu, Sensor Letters, Vol.6, February 2008, pp. 219-225.
 J. F. Chang, H. H. Kuo, I. C. Leu and M. H. Hon, “The effect of thickness on ZnO thin film CO gas sensor”, Sensors Actuators B, Vol.84, May 2002, 258-264.
 S.Basu, A.Dutta, “Modified heterojunction based on zinc oxide thin film for hydrogen gas-sensor application”. Sens. &Actuators B, Vol. 22 , April 1994, pp.83-87.
 K.Maeda, M. Sato, I.Niikura, T.Fukuda, “Growth of 2 inch ZnO bulk single crystal by the hydrothermal method”, Semicond. Sci. Technol., Vol.20, October 2005, pp. 49-54.
 L.C. Chao, P.C. Chiang, S.H. Yang, J.W. Huang, C.C. Liau, J.S. Chen, and C.Y. Su, “Zinc oxide nanodonut prepared by vapor-phase transport process” Appl. Phys. Lett.,Vol.88, June 2006, pp. 251111-13.
 P. Bhattacharyya, P.K. Basu, C. Lang, H. Saha, S. Basu, “Noble metal catalytic contacts to sol–gel nanocrystalline zinc oxide thin films for sensing methane”, Sensors and Actuators B, Vol.129 September 2007, pp. 551–557.
 A.Sengupta, S.Maji, H.Saha, “CBD Grown aligned ZnO nanorods based methane sensor and the effect of Pd sensitization” , Advanced Sci.Lett., Vol.3, December 2010, pp. 385-392.
 P.K.Basu, S.K.Jana, H.Saha, “Low temperature methane sensing by electrochemically grown and surface modified ZnO thin films”.S.Basu, Sensors and Actuators B, Vol.135, July 2008, pp.81-88.
 V. R. Shinde, T.P. Gujar, C.D.Lokhande, “Enhanced response of porous ZnO nanobeads towards LPG : Effect of Pd sensitization”, Sensors and Actuators B,Vol.123, September 2007, pp.701-706.
 T. J. Hsueh, S.J.Chang,“Highly sensitive ZnO nanowire ethanol sensor with Pd adsorption”, Appl.Phys.Lett. Vol.91, July 2007, pp.053111-13.
 A.P.Chatterjee,P.Mitra,A.K.Mukhopadhyay, “Chemical deposition of ZnO films for gas sensors”, J. of Mat. Science, Vol.34, March 1999,pp.4225-4231.
 P.Mitra, A.P.Chatterjee,H.S.Maiti, “chemically deposited zinc oxide thin film
gas sensor”,J. of Mat. Science , Vol.9, June 1998, pp. 441-445.
 H.Yoshiki,K.Hashimoto,A.Fujishima, Met. Finish Vol.94,1996, pp. 28-29.
 P. Mitra and H. S. Maiti, “A wet-chemical process to form palladium oxide sensitiser layer on thin film zinc oxide based LPG sensor”Sens. Actuators B. ,Vol.97,June 2003, pp.49-58.
 P. Bhattacharyya, S. Maji, S. Biswas, A. Sengupta, T. Maji, H. Saha, “Palladium Surface Modification of Nanocrystalline Sol-Gel derived Zinc Oxide Thin Films and its Effect on Methane Sensing”, Sensors & Transducers, Vol.110, November 2009, pp. 38-46.
 M. J. Hudson, J.A. Knowles, “Preparation and Characterisation of Mesoporous, High Surface Area Zirconium(IV) Oxide.”, J. Mater. Chem., Vol.6, January 1996, 89-95.
 H.Ogawa, M. Nishikawa, A. Abe, “Hall measurement studies and an electrical conduction model of tin oxide ultrafine particle films”,J. Appl. Phys., Vol.53, June1982, pp. 4448-4455.
 C. Wang, L.Yin, L. Zhang, D. Xiang, R. Gao, “Metal Oxide Gas Sensors: Sensitivity and Influencing Factors.”,Sensors, Vol. 10, March 2010, pp.2088-2106.