Low Voltage and Ferroelectric 2D Electron Devices Using Lead-Free Ba_xSr_1-xTiO₃ and MoS₂ Channel

Coupling between non-toxic lead-free high-k materials and 2D semiconductors is achieved to develop low voltage field effect transistors (FETs) and ferroelectric non-volatile memory transistors as well. In fact, low voltage switching ferroelectric memory devices are extremely rare in 2D electronics. Now, both low voltage operation and ferroelectric memory function have been successfully demonstrated in 2D-like thin MoS₂ channel FET with lead-free high-k dielectric Ba_xSr_1-xTiO₃ (BST) oxides. When the BST surface is coated with a 5.5-nm-ultrathin poly(methyl methacrylate) (PMMA)-brush for improved roughness, the MoS₂ FET with BST (x = 0.5) dielectric results in an extremely low voltage operation at 0.5 V. Moreover, the BST with an increased Ba composition (x = 0.8) induces quite good ferroelectric memory properties despite the existence of the ultrathin PMMA layer, well switching the MoS₂ FET channel states in a non-volatile manner with a ±3 V low voltage pulse. Since the employed high-k dielectric and ferroelectric oxides are lead-free in particular, the approaches for applying high-k BST gate oxide for 2D MoS₂ FET are not only novel but also practical towards future low voltage nanoelectronics and green technology.