Nanocrystalline Diamond-Based Field-Effect Capacitive pH Sensor

The pH-sensitive properties of field-effect capacitive electrolyte-diamond-insulator- semiconductor (EDIS) sensors with undoped nanocrystalline diamond (NCD) thin films (100-500 nm) having hydrogen (H)- and oxygen (O)-terminated surfaces have been investigated. The NCD films were grown on p-Si-SiO₂ substrates by a microwave plasma-enhanced chemical vapour deposition from a mixture of methane and hydrogen. The EDIS sensors have been characterised by means of capacitance- voltage spectroscopy, constant-capacitance and impedance-spectroscopy method. The developed EDIS sensors with O-terminated and H-terminated NCD surfaces show an average pH sensitivity of 38 mV/pH and 34-36 mV/pH, respectively. A possible mechanism of the pH sensitivity is discussed.