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Palladium and Aluminum Gate Metals/Aluminum Nitride/Silicon Balanced Capacitors for Selective Hydrogen Sensing H. E. Prakasam, F. Serina,1 C. Huang, G. W. Auner, L. Rimai, S. Ng1, and R. Naik2 Department of Electrical and Computer Engineering, Wayne State University, MI 1 Department of Chemical Engineering and Material Science, Wayne State University, MI 2 Department of Physics and Astronomy, Wayne State University, MI ABSTRACT An alternate array of Pd/AlN/Si and Al/AlN/Si metal-insulator-semiconductor (MIS) devices has been developed using plasma source molecular beam epitaxy (PSMBE) method for deposition of AlN on Si and magnetron sputtering for deposition of Pd and Al electrodes (via mask) on AlN. Both devices show essentially identical capacitance (C) versus voltage (V) characteristics of the typical MIS capacitor. However, the C-V characteristic of a Pd-device shows a clear shift in the presence hydrogen, while that of an Al-device shows no shift. These sensors were characterized using C(V) and C(time) measurements under varying hydrogen concentration. The effects of oxygen and hydrocarbon gases on the sensors were also studied. The Pd-device responds selectively to hydrogen. These results suggest the possibility of fabricating a balanced sensor structure, which might have significant practical importance, as it would cancel all thermal and material sources of drift in the electrical component of the sensor response. INTRODUCTION The Hydrogen sensing property of a Si based metal/oxide/semiconductor (MOS) device structure, with a Pd gate, was demonstrated by Lundström et al in 1975 [1]. Further development of these devices, over the next 10 to 12 years, has also been reviewed by Lundström et al. [2]. The MOS structures using SiC as the semiconductor, but with Pt gates, have been extensively investigated for their application as hydrocarbon sensors [3,4,5]. The most important electrical characteristic of MOS devices is the non-linear dependence of the small signal ac capacitance on the applied biasing voltage. The sensor response to the gases consists of a shift of the C-V characteristic along the bias axis, which seems to be caused by an increase in the charge on the capacitor device induced by the gases. Recently it has been demonstrated that a Pd/AlN/SiC structure had a response, selective to H2, when used with a Pd gate at temperatures up to 300 oC [6]. However, this response was obtained by measuring the change in the forward current versus voltage profile in the presence of H2 gas. The electrical nature of this response is similar to that of the non-selective response to all types of combustibles of a Pt/AlN/SiC structure [7]. The response was not only dominated by a change in the barrier voltage with combustible concentration, but also affected the forward resistance of the diode. Considering that the thickness of the AlN film (~ 150 nm) was relatively large, the observed results indicated that the metal/AlN/SiC behaved as a hetero-junction device. However, if AlN film is used in conjunction with Si in a M