高性能氢气传感器

Polymer-assisted Deposition of Co-doped Zinc Oxide Thin Film for the Detection ofAromatic Organic CompoundsWei Li, Dojin Kim*Abstract-Cobalt-doped Zinc oxide thin film was deposited onto SiO2/Si substrate using polymer-assisted deposition method. The surface morpholog y, phase structure and chemical state of the thin film were characterized by SEM, XRD, and XPS. The g as-sensing characteristics of the thin film upon exposure to aromatic org anic compound vapors were investig ated with a home-made sensor measurement system. The current results show that the film morphology is influenced by the doping of Co, and the sensor behavior was quite different between undoped and Co-doped ZnO thin films.B ACKGROUNDZnO has been widely used as a low cost sensing element for detection and monitoring of hazardous gases and vapors. Their advantages are high sensitivity, fast response, and long-time stability. Of the family of ZnO sensor, thin film type may be more favorable structure since the gas sensing properties are determined by the gases absorbing on the materials surfaces leading to a change of charge carriers and thus, of the materials resistances [1]. In the past several years, a large number of papers about ZnO sensor have been published. However, only a few ZnO sensors could be found for detection of aromatic organic compounds (AOC) [2-4]. Considering adverse effect of AOC on environment and human, developing reliable sensors to monitor the AOCs from the surrounding atmosphere becomes more and more important.The conventional methods for preparation of zinc oxide thin films can be divided into two categories: one is the vacuum techniques and the other is wet chemical solution methods. Recently, an alternative method named polymer-assisted deposition (PAD) was developed, and was successfully implemented to deposition of metal oxide thin film [5]. This method does not suffer from either the high cost for device fabrication, or complex operation and rigorous conditioning in the processing in comparison to conventional methods.In the current work, ZnO thin films are prepared by the PAD method. Furthermore, Co-doped ZnO thin films are also prepared. We compared the gas sensing properties of the ZnOC URRENT R ESULTSThe deposition of Co-doped ZnO thin films were carried out as the following. A certain amount of cobalt sultanate, zinc acetate and polyethylenimine (PEI, branched, Aldrich) were dissolved in 30 ml water with assistance of sonication. The solution was then spin-coated (2000 rpm for 30 s) onto SiO2/Si substrates followed by annealing in a quartz tube furnace of air environment. Gas sensor device structure was completed by sputter deposition of platinum electrodes onto the films through a metal shadow mask of interdigitated pattern. For the gas sensing property measurements, a bubbler is used to deliver the AOC vapors because they are in liquid form at room temperature (Fig. 1).The SEM images of the thin films shown in Fig.2 suggest slight change in the surface morphology due to the doping of Co. The XRD patterns of the thin film shown in Fig.3 showed that only pure wurtzite structures of ZnO are detected both in the undoped and doped ZnO thin films. The chemical state of the thin film is identified by XPS (Fig.4), and the results show that Co is doped as intended. The response to m-xylene is shown in Fig. 5. Shown is that the resistance change of doped ZnO is opposite to undoped ZnO because of different carrier types. The recovery was poor in p-type ZnO:Co thin film. The related mechanism and other sensor properties will be further presented in detail.R EFERENCES[1] P.P.Sahay, R.K. Nath, “Al-doped ZnO thin film as methanol sensors”, Sens.Actuators B 134 (2008) pp.654-659.[2] B.L.Zhu, C.S.Xie, J.Wu, D.W. Zeng, A.H.Wang,X.Z.Zhao, “ Influence ofSb, In and Bi dopants on the response of ZnO thick films to VOCs”, Mater.Chem. Phys. 96 (2006) pp. 459-465.[3] B.L.Zhu, C.S.Xie, D.W. Zeng, W.L.Song, A.H.Wang, “Investigation of gassensitivity of Sb-doped ZnO nanoparticles”, Mater. Chem. Phys. 89 (2005) pp. 148-153.[4] S. Morandi, F. Prinetto, M. Di Martino, G. Ghiotti,O. Lorret, D. Tichit, C.Malagù, B. Vendemiati, M.C. Carotta, “Synthesis and characterization of gas sensor materials obtained from Pt/Zn/Al layered double hydroxides”, Sens. Actuators B 118 (2006) pp.215-220.Lin, G. E. Collis, H.Wang,A.D. Q. Li, S. R. Foltyn, “Polymer-assisted deposition of metal-oxidefilms”, Nature Mater. 3 (2004) pp. 529-532.978-1-4244-3544-9/10/$25.00 ©2010 IEEEFig. 1. Diagram of sensor measurement systemFig. 2. SEM images of typical Co-doped ZnO thin film. (a) undoped, (b)0.08 at. % Co, (c) 8.53 at. % Co, and (d) 18.91 at. % Co.Fig. 3. XRD pattern of Co-doped ZnO thin films.Fig. 4. XPS spectra of Co-doped ZnO thin film in (a) a wideenergy range and (b) the Co region.Fig.5. The sensor response to 1000 ppm m -xylene at 200 ć.( a) undoped ZnO and (b) 8.53 at.% Co doped ZnO.。