Fabrication of a multi-modal sensor with PH, EC and temperature sensing areas for agriculture application

A multi-modal sensor, with which was possible to simultaneously measure pH, electrical conductivity (EC) and temperature, was fabricated. The pH sensor, EC sensor, and temperature sensor were integrated using compatible complementary metal-oxide semiconductor (CMOS) logic technology on a small Si chip (area, 25 mm
²
). Simultaneous measurements of pH, EC and temperature were demonstrated, and the sensor was used successfully to measure three different kinds of signal from the sensors with a pH 4.01 buffering solution. In another measurement, the sensor was possible to be inserted in soil, and used to successfully measure EC in real time for 6 days.