Sub-10-nm ferroelectric Gd-doped HfO2 layers

Sub-10 nm thick gadolinium-doped hafnia (Gd:HfO2) layers were grown in metal-insulator-metal (TiN/Gd:HfO2/TiN) stacks using a plasma-enhanced atomic layer deposition process. Thermally annealed Gd:HfO2 layers with a thickness of 8.8, 6.6, and 4.4 nm exhibited orthorhombic crystalline structure and showed ferroelectric properties. Indeed, polarization vs electric field hysteresis loops were recorded with 2P(r) polarization ranging from 2 to 20 mu C/cm(2). The studied layers showed the same coercive electric field (similar to 2 MV/cm). Consequently, polarization switching voltage between +P-r and -P-r decreased down to 0.9 V for the thinnest layer. Remanent polarization cycling showed a strong wake-up effect, with no fatigue, up to 10(9), followed by a stabilization up to 10(10) cycles, where 2P(r) reached 33 mu C/cm(2) for 8.8 nm Gd:HfO2. This endurance result and the absence of noticeable remanent polarization fatigue can be attributed to the optimal chemical composition of the TiN/Gd:HfO2 interface, which is supposed to be at the origin of defect generation, mostly oxygen vacancies, that leads to ferroelectric polarization fatigue. Published under an exclusive license by AIP Publishing.

Automated summary

Sub-10 nm thick gadolinium-doped hafnia layers were grown in metal-insulator-metal stacks using a plasma-enhanced atomic layer deposition process, exhibiting ferroelectric properties with lower polarization switching voltage. Cycling tests on the thinnest Gd:HfO2 layer showed excellent endurance and stable ferroelectric performance without noticeable deterioration.