Fully-Integrated CMOS Electrical Conductivity Sensor for Wet Media

This paper describes a fully-integrated CMOS electrical conductivity sensor for wet media that incorporates the sensing electrodes and the readout circuitry in the same die. The proposed sensor is realized using standard CMOS technology, where the top passivation layer is used to protect the sensing electrodes from corrosion. As a result, additional process steps for replacing the top metal layers with noble metals or creating protection layers for the sensing electrodes are not required. Furthermore, a harmonic oscillator with reconfigurable frequency is used for the sinusoidal stimulus generation, which can set the optimum detection frequency to maximize the sensitivity and accuracy of the sensor. The proposed electrical conductivity sensor is implemented using CMOS 0.18- $\mu {\mathrm{ m}}$ technology with core area of 2.1 mm2, which includes the four sensing electrodes and the readout circuitry. The detection range of the proposed sensor spans three orders of magnitude from 0.02 mS/cm to 10 mS/cm.