Design of Solid State Array for Simultaneous Potentiometric and Impedance Sensing in Gas Phase

A general sensing platform consisting of eight modules has been designed and fabricated in silicon. The operating function of this platform has been divided between a chemical sensing chip (CSC) and an electronic service chip (ESC). The CSC uses a gold metallization and a high temperature silicon nitride as the passivation layer. The smallest feature size on the CSC is 20 µm. It houses eight sensing modules each consisting of a pair of gold electrodes for measurement of impedance of the conducting polymer and a field-effect transistor for measurement of chemical modulation of the work function of the same polymer. The modules are separated from each other by a patterned 25 µm thick polyimide. The ESC was fabricated by a standard CMOS technology with 1.25 µm feature size. The CSC and ESC chips are connected by flip-chip bonding which greatly simplifies the packaging. The operation of the combined impedance and work function sensing has been verified by exposure to ammonia in ppm range.