Electrolyte-Solution-Gate FETs Using Diamond Surface for Biocompatible Ion Sensors

Diamond field effect transistors have operated in electrolyte solution for the first time. Since the hydrogen-terminated diamond surfaces are stable enough for the use as an electrochemical electrode, the diamond surface channels are exposed to the electrolyte in the transistor structure. A perfect pinch-off and saturated current-voltage characteristics have been obtained for bias voltages within the potential window. The threshold voltages are almost constant in electrolytes with different pH values of 7-13, indicating pH insensitiveness of the hydrogen-terminated diamond surface. Based on this pH insensitive surface, ion selective regions can be fabricated to form transistor-based biosensors.