Fabrication of Silicon Nitride Ion Sensitive Field-Effect Transistor for pH Measurement and DNA Immobilization/Hybridization

The fabrication of ion sensitive field-effect transistor (ISFET) using silicon nitride (Si3N4) as the sensing membrane for pH measurement and DNA is reported. For the pH measurement, the Ag/AgCl electrode was used as the reference electrode, and different pH values of buffer solution were used in the ISFET analysis. The ISFET device was tested with pH buffer solutions of pH2, pH3, pH7, pH8, and pH9. The results show that the IV characteristic of ISFET devices is directly proportional and the device's sensitivity was 43.13mV/pH. The ISFET is modified chemically to allow the integration with biological element to form a biologically active field- effect transistor (BIOFET). It was found that the DNA immobilization activities which occurred on the sensing membrane caused the drain current to drop due to the negatively charged backbones of the DNA probes repelled electrons from accumulating at the conducting channel. The drain current was further decreased when the DNA hybridization took place.