0.6/spl mu/m CMOS pH sensor IC with Si/sub 3/N/sub 4/ island structure

The design and research of an integrated monolithic pH sensor IC using an unmodified commercial 0.6 mum CMOS process offered by Shanghua is introduced. Si₃N₄ passivation layer in isolated island structure designed compatibly with standard CMOS process is used as pH sensitive layer, and pH-ISFET with multi-layer floating electrode structure is used as the sensing unit. The output of the circuit is proportional with the value of pH by the use of constant source-drain current constant source-drain voltage control module. Differential measurement of pH-ISFET and REFET is adapted to reduce the fixed pattern noise existed in solution and circuits. The total die area is 4mm². The test result shows the pH sensor has an average sensitivity of 35.8mV/pH from pH I to pH 13, and its linearity is better than 5%. Hence, this integrated pH sensor offers the possibility for the intelligent measurement required in various chemical, biochemical applications