A CMOS-compatible monolithic conductivity sensor with integrated electrodes

A CMOS compatible monolithic single chip system for the measurement of the electrolytic conductivity of human blood has been developed. The chip combines electrodes, current source, amplifier and digital circuits on a single silicon substrate. A standard CMOS-process has been used with only one additional step for the fabrication of the electrodes, which are made of a thin platinum layer. Due to the small size, the behaviour of the integrated microelectrodes differs strongly from their macroscopic counterparts . The polarization impedance of the electrodes, their noise performance and influences of the planar arrangement on the field distribution have been investigated. A four-electrode-method using a square-wave-current has been developed to avoid errors resulting from parasitic polarization voltages. The chip size is 1 x 5 mm and the measuring current is 10 fA. Measurements with a prototype version of the chip in KCI solution show a linearity of +/- 1%.