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A CMOS-compatible monolithic conductivity sensor with integrated electrodes

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

Transducers '93. 7th International Conference on Solid-State Sensors and Actuators. Digest of technical papers
ISBN: 4-9900247-2-9
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 monolithic single chip system for the measurement of the electrolytic conductivity of human blood has been developed. It was designed for medical applications within a heart catheter containing several chips for the invasive measurement of various blood parameters (pressure, temperature,...). However, the system can be used well in other applications, where extreme miniaturization is required. 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 microelectrodes have a very high polarization impedance. A 4-electrode-method using a square-wave-current has therefore been developed to avoid errors resulting from parasitic polarization voltages. The chip size is 1 by 5 mmü and the measuring current is 10fA.