CHARACTERIZATION OF SILICON TRANSDUCERS WITH SI3N4 SENSING SURFACES BY AN AFM AND A PAB SYSTEM

Silicon nitride is normally used as a sensitive surface for silicon-ba sed transducers like ISFETs or light-addressable potentiometric sensor s (LAPS), because of its capability to sense preferentially H+ ions. W e have investigated Si/SiO2/Si3N4 heterostructures and studied the sur face layers via an atomic force microscope (AFM) and a PAB (potentiome tric alternating biosensor) system; in particular, the latter method a llows the investigation of the temporal behaviour after input pH steps . A suitable experimental set-up has been installed in order to optimi ze the pH changes in the measuring chamber; data have been acquired co rresponding to unit pH steps. The resulting time constants are calcula ted and the data related to the surface layer images acquired by the A FM. A correlation between different observed responses and the corresp onding surface characteristics has been established.