High Sensitivity of Dual Gate ISFETs Using HfO₂ and HfO₂/Y₂O₃ Gate Dielectrics

Hafnium oxide gate dielectrics have elicited interest in dual gate ion-sensitive field-effect transistors because of their high dielectric constant, high band gap, and a good interface with amorphous indium gallium zinc oxide semiconductors. In this work, we have studied the pH sensing of double-gate ion-sensitive field-effect transistors with hafnium oxide and a stack of hafnium oxide/yttrium oxide as the top gate dielectric, and such a study has not been conducted earlier. Sputter deposition and postannealing of hafnium oxide and hafnium oxide/yttrium oxide were studied for reduction of defects at the interface of the semiconductor and the gate dielectric. A high pH sensitivity of 718 mV/pH was obtained with the stack of hafnium oxide/yttrium oxide, while with only hafnium oxide as the gate dielectric resulted in a pH sensitivity of 917 mV/pH but with lower mobility. The experimental results of pH sensitivity were benchmarked with the simulation and theoretical results. The highlights of the work include identification of diffusion of hafnium and yttrium into gallium to improve the sensitivity of the pH sensor by modification of the gate dielectric–semiconductor interface. High pH sensing of such devices makes them promising for various analytical and biomedical applications.