Recent Progress of Ferroelectric-Gate Field-Effect Transistors and Applications to Nonvolatile Logic and FeNAND Flash Memory

We have investigated ferroelectric-gate field-effect transistors (FeFETs) with Pt/SrBi2Ta2O9/(HfO2)(x)(Al2O3)(1-x) (Hf-Al-O) and Pt/SrBi2Ta2O9/HfO2 gate stacks. The fabricated FeFETs have excellent data retention characteristics: The drain current ratio between the on- and off-states of a FeFET was more than 2 x 10(6) after 12 days, and the decreasing rate of this ratio was so small that the extrapolated drain current ratio after 10 years is larger than 1 x 10(5). A fabricated self-aligned gate Pt/SrBi2Ta2O9/Hf-Al-O/Si FET revealed a sufficiently large drain current ratio of 2.4 x 10(5) after 33.5 day, which is 6.5 x 10(4) after 10 years by extrapolation. The developed FeFETs also revealed stable retention characteristics at an elevated temperature up to 120 degrees C and had small transistor threshold voltage (V-th) distribution. The V-th can be adjusted by controlling channel impurity densities for both n-channel and p-channel FeFETs. These performances are now suitable to integrated circuit application with nonvolatile functions. Fundamental properties for the applications to ferroelectric-CMOS nonvolatile logic-circuits and to ferroelectric-NAND flash memories are demonstrated.