Synthesis and characterization of combinatorial libraries of semiconductor gas sensors.
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JJ9.14.1
Synthesis and characterization of combinatorial libraries of semiconductor gas sensors. M. A. Aronova, K. S. Chang, I. Takeuchi Small Smart Systems Center, Department of Material Science and Engineering, and Center for Superconductivity Research, Department of Physics, University of Maryland, College Park, Maryland 20742 H. Jabs, D. Westerheim, A. Gonzalez-Martin, J. Kim, B. Lewis Lynntech, Inc., College Station, Texas 77840 ABSTRACT We have fabricated thin-film combinatorial gas sensor libraries based on doped semiconducting SnO2 thin films. The utility of combinatorial libraries is two-fold: one is to search and optimize the compositions for high sensitivity and selectivity of gases, and the other is to make use of the natural array geometry of the libraries with different sensor elements for electronic noses. Combinatorial pulsed-laser ablation was used to deposit compositionally varying arrays of sensor elements onto a pre-patterned device electrode configuration. Using a multiplexing electronics, we have demonstrated detection of chloroform, formaldehyde, and benzene gases at concentrations down to 12.5 ppm through pattern recognition of signals from the arrays of sensors. INTRODUCTION Electrical properties of some semiconductive metal oxides are sensitive to the surrounding gas atmosphere. In particular, SnO21-5 based semiconductors are commonly used for commercial gas sensors. Their low manufacturing cost, low operation power consumption, and high compatibility with microelectronic processing make semiconductive gas sensors ideal in a variety of settings including environmental monitoring, military applications, chemical industrial processes, food processing and biomedical applications. 6-9 The gas sensing mechanism of semiconducting metal oxide thin films involves interaction between surface adsorbates such as O-, O2-, and O2 and gas molecules of reactive chemical species. The reaction results in a change in the depletion layer thickness, which in turn changes the resistance of the film. Because the reaction takes place at the surface, microstructural details, such as grain size, grain boundaries and the film thickness of the semiconductors are known to strongly affect their sensing properties.10-14 The chemical composition of the semiconductor is also a key parameter that influences their sensing performance. In fact, composition by itself can affect the microstructure and, thus determine the sensing properties. It is known that a small amount of dopants such as Pt and Pd can boost the sensitivity of SnO2 gas sensors by increasing the thickness of the space charge layer, which enhances the consumption of oxygen adsorbates on the metal in addition to those on the SnO2 surface. Gas sensing characteristics of a number of other metal oxides including In2O3, ZnO, and WO3 have also been previously reported.15-18
JJ9.14.2
There is a continuing need to improve the sensitivity19 and selectivity19, 20 of inorganic gas sensors. In particular, selectivity is a critical figure of merit, and ideal sensors wo
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