City Research Online

Abstract

The planar capacitors were prepared by depositing two co-planar electrodes of relatively thick aluminium films on one side of two different substrates, namely, Corning glass (7059) and "Melinex" which is the trade name of plastic sheets (polyethelene terephthalate). The length and width of the electrodes are 25mm and 4mm respectively while the width of the gap between them is 2mm. The capacitance of these capacitors was (i) calculated (ii) measured at different frequencies in the frequency range (1-lOO)Kc . The calculated values of the planar capacitance are slightly larger than the measured ones; but they could be considered in reasonable agreement if we allow, qualitatively, for the reduction in two of the contributions to the calculated capacitance, namely, the contribution from the medium above the electrodes and the contribution from the medium underneath the substrate. The reduction is due to the presence of the lid and the bottom of the shield boi which enclosed the capacitors during the measurements. The in situ monitoring of the changes in the planar capacitance and the dissipation factor of the capacitors, which used as sensing devices, as a consequence of depositing discontinuous gold and aluminium films across their gaps enabled us to (i) measure (deduce) the capacitance of the films (ii) see the factors which affect the dissipation factor after laying down the films. It was found that the capacitance of the films and the dissipation factor depends on the d.c. resistance of the films at the moment of halting the deposition , the operating frequency and time. Also the measured capacitance of our films was compared with (i) the calculated capacitance under certain conditions and not for the films themselves (ii) the reported values in the literature for the measured capacitance of discontinuous metal films and in this context it is very important to focus on the fact that the reported values were not the outcome of investigations conducted with the intention of measuring the capacitance of the films (Pd, Mn) but only mentioned as a by-product of the main enquiries. The comparison has revealed that the measured capacitance is larger than the calculated one and much smaller than those reported of Pd and Mn films.

Publication Type:	Thesis (Doctoral)
Subjects:	Q Science > QC Physics
Departments:	School of Science & Technology School of Science & Technology > School of Science & Technology Doctoral Theses Doctoral Theses

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