Low power integrated pH sensor in a ISFET
The Fraunhofer Institute for Photonic Microsystems in Germany has developed a sensing layer for chip-based pH measurement has and successfully integrated it into an ion-sensitive field-effect transistor (ISFET).
An ISFET with a novel sensor layer developed by Fraunhofer IPMS, in combination with a conventional reference electrode, enables highly precise pH measurement in the range from pH 1 to pH 13.
The compact, unbreakable sensor chip measures 5 x 5 mm and has a minimal drift of < 20 µV/h as well as low hysteresis while being easy to integrate. A significant improvement has also been achieved in the reduction of light sensitivity.
The team at IPMS, led by Dr Olaf R. Hild, Head of the Chemical Sensor Technology Business Unit, developed the ISFET to improve the measurement of pH for chemical and biochemical analysis systems.
The chip can be easily stored, and the electrical operating point of the sensor can be flexibly adjusted via the design and the operating parameters as an operating voltage (VDS) of below 1V is possible.
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“With these properties, the new ISFET is particularly suitable for on-site environmental analysis,” said Hild.
The operation of the pH sensor in the ISFET
The ISFET 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. Hydronium or hydroxide ions from the medium are reversibly adsorbed on this sensing layer, allowing for the pH of the medium to be measured. The gate-to-source voltage (VGS) response versus a reference electrode (Ag/AgCl in 3 M KCl) is then used as the measurement signal.
The next goal is to develop a sensor layer that enables a purely chip-based pH measurement that eliminates the need for conventional reference electrodes. This would then have the potential to continuously collect environmental data over long time periods without the need for intervention by operating personnel.
www.ipms.fraunhofer.de
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