A micromachined gold–palladium Kelvin probe for hydrogen sensing

In this paper we discuss the fundamental principles of the Kelvin probe apparatus; in particular, first, we find an analytical relation for the sensitivity of vibrating capacitors, so that the advantages of integration can be quantitatively estimated; second, we describe an equivalent electric circuit for vibrating capacitors, thus allowing to simulate a complete Kelvin probe with a standard electronic circuit simulator; third, we illustrate the most important issues of the electronic interface. A fundamental part of the research and technological work reported by this paper deals with the fabrication process of micromachined gold–palladium vibrating capacitors fully integrated on silicon, for hydrogen sensing applications. The relevant technological fabrication steps are explained. Preliminary experimental results of the first capacitor prototypes testing are reported as static C– V (capacitance–voltage) curves and as measurement in air of the gold–palladium work–function difference.