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 (~& nbsp;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.& nbsp;Published under an exclusive license by AIP Publishing.