ISFET pH sensor characterization: towards biosensor microchip application

The ion-sensitive field effect transistor (ISFET) based pH sensor has the advantages of smaller size, fast response time and fabrication compatible with standard MOS technology. Beside that, the functionality of pH ISFETs is various especially in biomedical areas. In the design and characterization of an ISFET pH sensor, the ISFET model was characterized and a final design has been evolved with the assistance of the Tanner tools software. To provide a better understanding´ of pH ISFET as a biosensor, the C-V characteristics, temperature dependence of the ISFET and pH sensitivity of electrolyte-insulator-semiconductor in response to different pH are examined. The insulator, aluminium oxide (AI₂O₃) has been applied as a pH sensitive layer. The ISFET is matched with a metal oxide field effect transistor (MOSFET) at the differential input stage of a CMOS operational amplifier and realized in a 0.8 um CMOS technology. From the output of ISFET operational amplifier, the pH sensitivity is approximately 54.8 mV per pH.