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A CMOS-compatible monolithic conductivity sensor with integrated electrodes

: Kordas, N.; Manoli, Y.; Mokwa, W.; Rospert, M.


Sensors and Actuators. A 43 (1994), Nr.1-3, S.31-37
ISSN: 0924-4247
International Conference on Solid-State Sensors and Actuators <7, 1993, Yokohama>
Fraunhofer IMS ()
CMOS-Technik; CMOS technology; conductivity measurement; integrated electrode; integrated sensor; Leitfähigkeit

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%.