Ion-sensitive field-effect transistors (ISFET) Evaluation-Kit

We offer an evaluation kit for niobium pentoxide (Nb2O5) based ISFETs (Ion Sensitive Field Effect Transistors). The evaluation kit consists of a small box (54x50x18mm³), which controls our Nb₂O₅-ISFETs with fixed operating parameters. It is connected to the computer via USB-C. A socket for a conventional reference electrode is also included. Figure 2 shows the box wired and equipped with sensors. The ISFET parameters are selected so that the ISFET is operated at the isothermal intersection. This minimizes the temperature influence on the pH measurement.

The evaluation kit is suitable for the operation of individual ion-sensitive field effect transistors (ISFET) for measuring the pH value in liquids. Depending on the sensor module, the temperature can also be recorded. The connection and data readout are carried out via a USB-C connection. For the ISFETs, either connectors with a 1 mm pitch for ceramic modules or connectors with a 6-pin Molex “Microlock Plus” from sensors on FR4 boards are available as an assembly option. The electronics are automatically recognized by Windows as a serial USB device.

To read out the data, all you need is a serial terminal such as Terra Term or Putty.

For use in battery-operated systems, there is an analog control with particularly low power consumption, which is shown in Figure 3. The circuit board is only 20x12mm² in size. It operates at 2.7 to 5V and, together with the ISFET, only requires approx. 50 to 100µA. The voltage range of the analog output is 0.8 to 2.5V. Depending on the operating point, this voltage at pH7 is typically 1.5V to 2.2V. The IPMS Nb2O5 ISFETs have a slope of 58mV per pH at 20°C and therefore correspond to Nernst's equation.