Improving the pH sensitivity of ISFET arrays with reactive ion etching

In this paper, we report a method to improve sensitivity for CMOS ISFET arrays using Reactive Ion Etching (RIE) as a post-processing technique. The process etches away the passivation layers of the commercial CMOS process, using an oxygen (O
₂
) and sulfur hexafluoride (SF
₆
) plasma. The resulting attenuation and pH sensitivity are characterised for five dies etched for 0 to 15 minutes, and we demonstrate that capacitive attenuation is reduced by 196% and pH sensitivity increased by 260% compared to the non-etched equivalent. The spread of trapped charge is also reduced which relaxes requirements on the analogue front-end. The technique significantly improves the performance of the fully-integrated sensing system for applications such as DNA detection.