Integrated Ion-Sensitive Field-Effect Transistor Using CMOS-Based Technology

Ion-sensitive field-effect transistors (ISFETs) for pH measurement have been extensively investigated for the past 50 years. However, the integration of a reference field-effect transistor (REFET) with an ISFET, where the REFET replaces a standard Ag/AgCl reference electrode and allows for device miniaturization, still remains a challenge. In this work, two separate n-wells in a p-EPI-Si wafer are used to integrate an ISFET and a REFET, with the EPI layer on a doped p-Si substrate. This allows for the ISFET and the REFET to be electrically insulated from one another, thus utilizing CMOS integration. Other configurations, such as arrays, would also be possible with this integration technology.