Engineering Reliability and Crystallographic Orientation by Al Doping of Ferroelectric Hafnium-Zirconium Oxide

Due to its scalability and CMOS compatibility, ferroelectric hafnium oxide (HfO₂) has attracted attention since its discovery in 2011 [1, 2]. Many elements can be used as dopant [3, 4] to stabilize the ferroelectric (FE) orthorhombic phase of HfO_2.Especially Zr doping of HfO₂(HZO) has some advantages for back-end-of-line (BEoL) integration, due to its low crystallization temperature [5].<br/>FE materials can be used in memories such as ferroelectric field-effect transistors (FeFETs) that are non-volatile and applicable in low-power systems. Good endurance and retention, high remanent polarization, and high-temperature resilience are required for embedded FE memories and the automotive industry requires high-temperature operation (up to 150 °C specifications given by the Automotive Electronics Council) which is not fulfilled by current HZO devices.<br/>Al can be co-doped into HZO (HZAO) to overcome the reliability challenges of HZO such as high-temperature, high-bias operation, endurance, and imprint limitations [6]. In this study, different Al concentrations (up to 3 at. % Al) were doped into HZO and various crystallization annealing conditions (400 °C, 650 °C, and 800 °C) were investigated.<br/>Increasing Al concentration and increasing annealing temperature in HZAO resulted in more antiferroelectric-like behavior. Additionally, endurance at high temperatures (up to 150 °C) and high-bias conditions (up to 5 MV/cm applied electric fields) were drastically improved in HZAO compared to HZO. A correlation between crystallographic phases and electrical results (coercive field E_c and remanent polarization P_r) was made. The ratio of (111)/(002) diffraction peak intensities increases with lower Al concentrations. Increase in P_r and E_c is observed with increasing ratio of (111)/(002) diffraction peak intensities. Consequently, this work will discuss the tuning of electrical properties (such as P_r, E_c, and endurance) depending on application requirements by controlling anneal conditions and Al doping concentration. It will investigate the impacts of Al concentration and anneal conditions on reliability aspects such as enhanced endurance, reduced leakage and high temperature resilience.<br/><br/>[1] T. S. Böscke, J. Müller, D. Bräuhaus, U. Schröder, U. Böttger. Appl. Phys. Lett. 2011; 99 (10): 102903.<br/>[2] T. S. Böscke, “Ferroelektrische Speicherzelle, Herstellungsverfahren und integrierte<br/>Schaltung mit der ferroelektrischen Speicherzelle.” DE102008024519B4.<br/>[3] T. S. Böscke, et al., Appl. Phys. Lett. 2011; 99 (11): 112904.<br/>[4] S. Mueller, et al, ECS J. Solid State Sci. Technol. 2012, 1, N123.<br/>[5] D. Lehninger, et al., Phys. Status Solidi A, 2020, 217: 1900840.<br/>[6] A. Sünbül, et al., Adv. Funct. Mater. 2023, Under Review.