Graded Crystalline HfO₂ Gate Dielectric Layer for High-k/Ge MOS Gate Stack

Germanium (Ge) has gained great attention not only for future nanoelectronics but for back-end of line (BEOL) compatible monolithic three-dimensional (M3D) integration recently. For high performance and low power devices, various high-k oxide/Ge gate stacks including ferroelectric oxides have been investigated. Here, we demonstrate atomic layer deposited (ALD) polycrystalline (p-) HfO
₂
/GeO
_x
/Ge stack with an amorphous (a-) HfO
₂
capping layer. The consecutively deposited a-HfO
₂
capping layer improves hysteretic behaviors (ΔV) and interface state density (D
_it
) of the p-HfO
₂
/GeO
_x
/Ge stack. Furthermore, leakage current density (J) is significantly reduced (×100) by passivating leakage paths through grain boundaries of p-HfO
₂
. The proposed HfO
₂
layer with the graded crystallinity suggests possible high-k/Ge stacks for further optimized Ge MOS structures.