Design of solid state array for simultaneous potentiometric and impedance sensing in gas phase

A general sensing platform consisting of eight modules has bean designed an d fabricated in silicon. The operating function of this platform has been d ivided between a chemical sensing chip (CSC) and an electronic service chip (ESC). The CSC uses a gold metallization and a high temperature silicon ni tride as the passivation layer. The smallest feature size on the CSC is 20 mu m. It houses eight sensing modules each consisting of a pair of gold ele ctrodes for measurement of impedance of the conducting polymer and a field- effect transistor for measurement of chemical modulation of the work functi on of the same polymer. The modules are separated from each other by a patt erned 25 mu m thick polyimide. Fhe ESC was fabricated by a standard CMOS te chnology with 1.25 mu m feature size. The CSC and ESC chips are connected b y flip-chip bonding which greatly simplifies the packaging. The operation o f the combined impedance and work function sensing has been verified by exp osure to ammonia in ppm range.