Buffer effects of two functional groups against pH variation at aminosilanized Electrolyte-Oxide-Semiconductor (EOS) capacitor

The pH sensitivity variations of Electrolyte-Oxide-Semiconductor (EOS) capacitor with both silanol and amine groups are analyzed in terms of their functional group ratio theoretically and experimentally. The phenomena causing the pH sensitivity variations are explained by the buffer effect of each functional group by using Henderson-Hasselbalch equation to compare the state ratio of the acid and the conjugate base of silanol and amine groups. When p is defined as the amine group fraction among the total functional groups, the theoretical pH sensitivity is relatively high around p = 0.3 or 0.7, but low at p = 0, 0.5 or 1. In addition, EOS capacitors with four types of surface treatments for various p are fabricated and characterized by C-V measurements. The pH sensitivity values of the fabricated EOS capacitors corresponding to all p values fit well with the theoretical results. This work allows to explain the reactions on the surface membrane and the characteristics of the pH sensitivity depending on the functional group ratio.