Al₂O₃/Silicon NanoISFET with Near Ideal Nernstian Response

Nanoscale ISFET (ion sensitive field-effect transistor) pH sensors are presented that produce the well-known sub-Nernstian pH-response for silicon dioxide (SiO2) surfaces and near ideal Nernstian sensitivity for alumina (Al2O3) surfaces. Titration experiments of SiO2 surfaces resulted in a varying pH sensitivity similar to 20 mV/pH for pH near 2 and >45 mV/pH for pH > 5. Measured pH responses from titrations of thin (15 nm) atomic layer deposited (ALD) alumina (Al2O3) surfaces on the nanoISFETs resulted in near ideal Nemstian pH sensitivity of 57.8 +/- 1.2 mV/pH (pH range: 2-10; T = 22 degrees C) and temperature sensitivity of 0.19 mV/pH degrees C (22 degrees C <= T <= 40 degrees C). A comprehensive analytical model of the nanoISFET sensor, which is based on the combined Gouy-Chapman-Stern and Site-Binding (GCS-SB) model, accompanies the experimental results and an extracted Delta pK approximate to 1.5 from the measured responses further supports the near ideal Nernstian pH sensitivity.