Strategies of miniaturised reference electrodes integrated in a silicon based "one chip" pH sensor

Different types of Ag/AgCl reference electrodes have been realised by means of thin- and thick-film technique. For inner electrolyte, KCl-containing membranes have been deposited and different coatings have been used to protect the reference electrode from a fast leaching out of KCl. The stability of the potential of the reference electrodes without KCl-containing membranes in 3 M KCl was about 7 hours for thin- film electrodes and up to 90 hours for thick-film electrodes. The reference electrodes with membrane were stable for more than two months. The thick-film reference electrode was integrated with a thin- film pH sensor onto one chip and the system pH sensor/reference electrode was investigated by means of capacitance/voltage (C/V) and constant capacitance (ConCap) mode.