Pt/SrBi2Ta2O9/Hf-Al-O/Si Field-Effect-Transistor with Long Retention Using Unsaturated Ferroelectric Polarization Switching

A metal-ferroelectric-insulator-semiconductor (MFIS) field-effect-transistor (FET) composed of a Pt/SrBi 2 Ta 2 O 9 (SBT)/Hf-Al-O/Si stack with a long data retention over 10 6 s was fabricated. The poling voltages to obtain the long data retention were ±6 V. The memory window in the drain current vs gate voltage ( I d – V g ) curve increased monotonically with increasing gate scan-voltage amplitude ( V scan ) up to V scan =6 V. This behavior indicates that the device operation is based on unsaturated ferroelectric polarization switching. A direct cross-sectional transmission electron microscopy image of the Pt/SBT/Hf-Al-O/Si stack and the electrical properties of a Pt/Hf-Al-O/Si metal-insulator-semiconductor (MIS) FET used as a reference showed the existence of a 4.4-nm-thick interfacial layer between the Hf-Al-O layer and the Si substrate, which can explain the device operation with the unsaturated ferroelectric polarization. The results thus concluded that saturation of ferroelectric polarization is not essential for obtaining the long data retention.