C.FALCONI, F.LO CASTRO, L.FUSARO, M.SCOCCIA, C.DI NATALE, A.D AMICO
Department of Electronic Engineering, University of Tor Vergata, Via Politecnico 1, 00133, Roma, Italy
e-mail: falconi@eln.uniroma2.it
In this paper, first, we theoretically investigate the sensitivity of vibrating capacitors, concluding that significant improvements are possible if the mean distance is reduced; this and other issues make very attractive, for chemical sensors applications, full integration of work function gas sensors; a main obstacle to such systems is the complexity of existing electronic interfaces for Kelvin Probe systems. We propose a new electronic interface which may, in principle, be integrated; simulations and preliminary experimental results, obtained with a discrete prototype, are shown.
The most convenient approach to the work function measurement is often the Kelvin method, which guarantees surface integrity and can be used for a wider range of materials, temperatures and pressures than any one of the others [1]. In Kelvin Probe systems, a voltage V X is applied across a capacitor whose plates are constituted, respectively, by a reference material, A, and by the sample material, B, whose work function is unknown. The charge Q stored in the capacitor is
where ? ? AB is the contact potential difference (corresponding to the work function difference q ? ? AB ) and C is the capacitance. In general, if the capacitance is time-dependent, C(t), the current through the capacitor may be expressed as the sum of the Kelvin current i K (t)
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