New concepts of miniaturised reference electrodes in silicon technology for potentiometric sensor systems

Abstract

Different types of reference electrodes have been realised by means of thin-film technique (electron-beam evaporation/pulsed laser deposition (PLD) or electron-beam evaporation/chlorination) and thick-film technique. As inner electrolyte, KCl-containing membranes have been deposited and different coatings have been used to protect the reference electrode from a fast leaching out of KCl. The potential stability of the “quasi-reference electrodes”—that means reference electrodes without KCl-containing membrane—in a 3M KCl solution was up to 7h (thin-film technique) and about 500h (thick-film technique). The reference electrodes with KCl-containing membrane were stable during a period of more than 2 months (measured in Titrisol buffer, pH 7). The averaged drift during a typical measurement time of 10h was less than 0.1mV/h for the thick-film reference electrodes with cellulose nitrate (CN) as protective coating. The averaged drift rate of the thin-film reference electrodes was about 0.4mV/h. The thick-film reference electrode was combined with a thin-film pH sensor together on one chip. The characteristics of this “one-chip” sensor were investigated in the capacitance/voltage (C/V) and constant capacitance (ConCap) mode.