November 21, 2024 
Professional magazine and portal dedicated to electronics 
With groundbreaking developments in the field of chemical sensor technology, the Fraunhofer Institute for Photonic Microsystems IPMS is setting new standards in the assessment of water quality for humans and the environment.
In addition to key parameters such as conductivity and pH, nutrients such as nitrate, phosphate and potassium will also play an important role as key ions in the future. Their evaluation is particularly important in environmental analysis, agriculture and water management.
In the Chemical Sensors and Systems business unit, the Fraunhofer IPMS research team has been working intensively on the development of state-of-the-art ion-sensitive field-effect transistors (ISFET) and capacitive conductivity sensors that can be seamlessly integrated into environmental measurement systems. Innovative control electronics have now been developed for the successful and efficient use of the sensors, enabling extremely flexible and energy-efficient use of these sensors.
Demonstrator for pH and conductivity measurement (© Fraunhofer IPMS)
The outstanding properties of the pH sensors from Fraunhofer IPMS are particularly noteworthy, as Dr. Olaf Hild, Head of the Chemical Sensor Technology Business Unit at the institute, reports: "The low drift of less than 20 µV/h, the wide addressable pH range from pH 1 to pH 13 as well as the extremely small hysteresis and low light sensitivity make our pH sensors unique. Added to this is their impressive mechanical stability." In addition, the conductivity sensors with a measuring range from 10 µS/cm to 100 mS/cm offer versatile application possibilities for environmental analysis. The sensors can also be adapted to customer-specific requirements, both sensory and electrical.
These pioneering technologies from Fraunhofer IPMS help to significantly increase the efficiency and precision of environmental analysis and open up new possibilities for individual applications in various industries.
Exemplary measuring arrangement with ISFET, conductivity sensor and reference electrode (© Fraunhofer IPMS)
Physical principles of the ISFET from Fraunhofer IPMS
The capacitive conductivity sensor developed by Fraunhofer IPMS uses a metallic 4-electrode arrangement coated with a chemically and mechanically robust metal oxide. This design ensures that the measuring medium only contacts the oxide and not the electrode metal, preventing the release or contamination of metal ions during measurement. The sensors have a cell constant of 0.8 to 1.1 cm-1 and can be used at a measuring frequency in the range of 100 Hz to 1 MHz.
Conductivity sensor, with and without temperature sensor Pt1000 available (© Fraunhofer IPMS)
The novel ISFET from Fraunhofer IPMS is based on metal-oxide-semiconductor (MOS) field-effect transistor technology, whereby the sensor area in contact with the medium consists of an amphoteric metal oxide layer. This pH-sensitive layer reversibly adsorbs hydronium or hydroxide ions from the measuring medium based on the pH value. The voltage (VGS) measured between the source electrode and the gate or reference electrode (Ag/AgCl in 3M KCl) is then used as the measurement signal.
Multi-Sensor System: Sensor control for recording and displaying measurement data (© Fraunhofer IPMS)
Some of the research results were achieved in the "REISen" project, a project in the field of materials science, which was co-financed from tax funds on the basis of the budget approved by the Saxon State Parliament.
