The electrolytic capacitive displacement transducer for nano-technologies

The paper deals with the basic principle of a new capacitive displacement transducer, the “electrolytic capacitive transducer” (ECT), for small displacements (from a few micrometers to a few millimeters with nanometer resolution). The principle of the ECT is based on the use of both a very thin dielectric film between the faced electrodes and the enlargement of the effective equivalent faced electrodes surface by etching the dielectric film both obtained by the electrolytic capacitor construction technique. The transducer is designed in a differential form. Its electrodes are constructed by photochemical-etching. A first implementation prototype, a linear displacement form transducer, has been designed and constructed using a dielectric etched film of alumina, 0.35 μm thick. The test results obtained on this prototype are critically analyzed. Its sensitivity and resolution are respectively 0.5 μF/mm or 0.5 nF/μm and, by a 61/2 digit DMM, 2 nm nearly in absence of nonlinearities. On the basis of the present test results, a proposal for a variable absolute scale of capacitance and capacitive voltage divider is illustrated