Lowered operation voltage in Pt/SBi2Ta2O9/HfO2/Si ferroelectric-gate field-effect transistors by oxynitriding Si
Oxynitrided Si (SiON) surfaces show smaller subthreshold swings than do directly nitrided Si (SiN) surfaces when used in ferroelectric-gate field-effect transistors (FeFETs) having the following stacked-gate structure: Pt/SrBi2Ta2O9(SBT)/HfO2/Si. SiON/Si substrates for FeFETs were prepared by rapid thermal oxidation (RTO) in O2 at 1000 ?C and subsequent rapid thermal nitridation (RTN) in NH3 at various temperatures in the range 950?1150 ?C. The electrical properties of the Pt/SBT/HfO2/SiON/Si FeFET were compared with those of reference FETs, i.e. Pt/SBT/HfO2 gate stacks formed on Si substrates subjected to various treatments: SiNx/Si formed by RTN, SiO2/Si formed by RTO and untreated Si. The Pt/SBT/HfO2/SiON/Si FeFET had a larger memory window than all the other reference FeFETs, particularly at low operation voltages when the RTN temperature was 1050 ?C.