Triple Gate Polycrystalline-Silicon-Based Ion-Sensitive Field-Effect Transistor for High-Performance Aqueous Chemical Application

In this paper, we developed a polycrystalline-silicon (poly-Si) thin-film transistor (TFT)-based high-performance ion-sensitive field-effect transistor (ISFET) pH sensor that far surpasses the sensitivity of dual-gate (DG) pH sensors. A triple gate (TG) structure on the same plane as the channel of the ISFET has been proposed to enhance the pH sensitivity. In a poly-Si TFT-based ISFET, a TG is more advantageous than a bottom-gate for increasing the capacitive coupling with the top-gate. As a result, the pH sensitivity by TG mode detection using the TG is much greater than the single-gate (SG) mode detection using the top-gate, or the DG mode detection using the bottom-gate. The sensitivity of the TG mode increased greatly compared with the sensitivity of the conventional SG mode or DG mode. The measured pH sensitivity was 57.75 ± 0.77 mV/pH in the SG mode and 467.08 ± 9.92 mV/pH in the DG mode. In particular, the TG mode gives a maximum sensitivity of 1283.56 ± 45.54 mV/pH for sensing membranes having a theoretical Nernstian pH response (59.15 mV/pH at 25 °C). Furthermore, we measured the hysteresis and drift characteristics, and found that the TG mode has improved non-ideal behavior compared with the SG and DG modes. Therefore, the poly-Si TFT-based TG ISFET pH sensor has the potential to become a promising biosensor application platform, with excellent sensitivity and stability.