DEVELOPMENT OF NA-SENSITIVE MEMBRANES BASED ON SPUTTERED NA-AL-SI GLASSES()

Na+-sensitive microdevices are of increasing interest for integration in microanalytical systems e.g. for biomedical applications or for ind ustrial process control. In order to produce ultra thin Na+-sensitive layers with fixed and reproducible composition and, in particular, def ined Na concentration by means of RF sputtering, an off-axis geometry of a magnetron with cylindrical target was chosen for minimizing back- sputtering effects from the already deposited material. With this inve rted cylindrical magnetron (ICM) it was possible to obtain reproducibl e and controllable sodium aluminosilicate glass layers on semiconducto r substrates. Several surface and thin layer analytical techniques wer e applied for characterization of the membranes and for stoichiometry control. Especially by the non-destructive nuclear reaction analysis m ethod a constant Na profile throughout the glass layer and - together with AES depth profiles the diffusion barrier effect of an Si3N4 inter face layer could be verified. Electrochemical measurements proved Nern stian sensitivity down to 10(-4) M Na+ in solutions of pH 7, supportin g sufficient stability and reproducibility of the sputtered Na+-sensit ive layers.