Miniaturization of Electrical Conductivity Sensors for a Multimodal Smart Microchip

A new electrical conductivity (EC) sensor with Pt electrodes on a Si substrate was proposed for use in agricultural applications. The complementary metal oxide semiconductor (CMOS) logic technology-compatible sensor was successfully fabricated with a small chip (area, 25 mm2). This sensor was used for an alternating voltage, owing to the polarization of the Pt electrode and its best operation at 10 kHz frequency. Measurements were conducted on water with electrical conductivities ranging from 10-2 to 101 S/m, which shows sufficient linearity for use as a sensor for agriculture applications. It was also possible to be miniaturized. In an agricultural application, measurements were carried out with the sensor inserted in the rock wools, which was confirmed by the linearity of the values obtained using the sensor. In addition, successful real-time measurements using the sensor were conducted by inserting the sensor into the compost in the vicinity of the roots of a tomato seedling. This sensor provides a promising solution for an EC sensor for broad fields of agricultural applications.