Miniaturized and Highly Integrated Humidity Sensor with Biocompatible Sensing Material for Smart Farming

Agriculture provides the base of our society. To enable sustainable processes, integrated pest management is an integral part in the future of agriculture. Novel biocompatible and miniaturized sensors allow a new base of data acquisition by direct measurement at the plant. In this work, a highly integrated, miniaturized and biocompatible humidity sensor is presented. Measurement vehicle are interdigitated copper electrodes on silicon substrate. The novel sensor uses the biocompatible material Parylene C not only as a sensing, but also as a passivation layer, against aggressive chemicals such as fertilizers, plant protection products as well as moisture. The interaction of the water, present in the environment, changes the capacitance of the sensing layer. The relative capacitance change is measured in a measurement bridge configuration. The capacitive humidity sensors are characterized by an inductance, capacitance and resistance (LCR) meter or an application specific integrated circuit (ASIC) and a humidity generator. The results are compared to a non-biocompatible Polyimide sensor. A linear correlation between the measured capacitance and relative humidity (RH) level is found in the range of 10 to 90%. Hence, the sensor is suitable for common climate conditions. The thickness of the Parylene C layer is identified to have no significant influence in the tested thickness range of 1.5 μm to 2.0 μm. Hysteresis is observed and described. Long-term stability in laboratory environment over 28 days is proven. This work proves the working principle of the developed miniaturized biocompatible RH sensor technology and paves the way for a scalable, highly miniaturized and inexpensive monitoring of single plants.