The thin dielectric film capacitive displacement transducer to nanometer

Abstract

The paper deals with the new capacitive transducer for small displacements (from a few micrometers to a few millimeters), denoted the Thin Dielectric Film Capacitive Displacement Transducer (TFCDT). This principle is based on the properties of a very thin dielectric film between the faced electrodes. The film may be applied by a dielectric, such as alumina. The transducers are designed in a differential form. Their electrodes have to be constructed by either photo-chemical- or laser etching. A few implementation prototypes (IPs) of the TFCDT have been designed and constructed. The first of the IPs (TO IF) has been constructed in two forms, for linear and rotary displacement by a dielectric spray varnish with thickness of about 2 /spl mu/m. The second of the IPs (II/spl deg/IP) has been designed and constructed only in the form for linear displacement, with different techniques for achieving lower thickness of the alumina dielectric film. The test results on both the I/spl deg/IP and II/spl deg/IP are critically analyzed. The sensitivity and linearity obtained, respectively, are about: 5 pF/mm, 0.6 pF//spl deg/, 25/spl times/10/sup -6/, 2 nF/mm, and 7 nm//spl mu/V, nearly in the absence of nonlinearities. A feature for improving the sensitivity and linearity, respectively, to about 40 /spl mu/V/nm and to a few/spl times/10/sup -8/ is also illustrated. A variable absolute scale of capacitance and capacitive voltage divider based on the TFCDT is also proposed.