N. Kordas et al., A CMOS-COMPATIBLE MONOLITHIC CONDUCTIVITY SENSOR WITH INTEGRATED ELECTRODES, Sensors and actuators. A, Physical, 43(1-3), 1994, pp. 31-37
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 circui
try on a single silicon substrate. A standard CMOS process has been us
ed 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 thei
r macroscopic counterparts. The polarization impedance of the electrod
es, their noise performance and influences of the planar arrangement o
n the field distribution have been investigated. A four-electrode meth
od using a square-wave current has been developed to avoid errors resu
lting from parasitic polarization voltages. The chip size is 1 x 5 mm
and the measuring current is 10 muA. Measurements with a prototype ver
sion of the chip in KCl solution show a linearity of +/- 1 %. The syst
em can be easily adapted to the desired conductivity range by changing
the current or the amplification factor.