Performance Analysis of BG-ZnO-ISFETs: Effects of Oxide Degradation on Electrical Characteristics

This chapter examines the electrical characteristics of a bottom-gated ZnO-based ion-sensitive field-effect transistor (BG-ZnO-ISFET), focusing on the effects of oxide degradation. The chapter evaluates shifts in threshold voltage ( \(\mathrm {V}_{\mathrm {th}}\) ) and drain current ( \(\mathrm {I}_{\mathrm {DS}}\) ) across a range of pH levels (1–10) by examining device behavior under varying thicknesses of oxide layer degradation. Device simulations were conducted using TCAD Silvaco, considering three cases of dielectric degradation with degraded oxide thicknesses ( \(\mathrm {t}_{\mathrm {ox1}}\) ) of 1 nm, 2 nm, and 3 nm. Results indicate that as oxide degradation increases, the \(\mathrm {V}_{\mathrm {th}}\) value rises, while the \(\mathrm {I}_{\mathrm {DS}}\) value decreases. This results in an increase in the drift in \(\mathrm {V}_{\mathrm {th}}\) and drift in \(\mathrm {I}_{\mathrm {DS}}\) with respect to the no degradation condition. Compared to reference electrode-based ISFETs, the BG-ZnO-ISFET shows a minimal decrease in these values due to degradation, attributed to its bottom-gate operation, which reduces the impact of oxide-electrolyte interface degradation.