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Ferroelectric Hafnium Oxide Material Enhanced Reliability

Subject Area Electronic Semiconductors, Components and Circuits, Integrated Systems, Sensor Technology, Theoretical Electrical Engineering
Synthesis and Properties of Functional Materials
Term from 2020 to 2024
Project identifier Deutsche Forschungsgemeinschaft (DFG) - Project number 430054035
 
Final Report Year 2025

Final Report Abstract

Device reliability is a significant criterion determining whether or not the relatively new class of fluorite ferroelectrics can be used in commercial non-volatile memories. Recognizing the significant importance of ferroelectric device reliability, the HOMER project investigated a wide range of reliability criteria that are either intrinsic to fluorite ferroelectrics or the result of material and physical interactions arising from the device structure. Although doping and film processing conditions have been generally documented to influence the ferroelectric properties of HfO2-based thin films in recent years, investigations from the HOMER project established new insights that set it apart from previous studies. For example, incorporating different amounts of Si dopants into thick ZrO2 showed that more Si resulted in a greater in-plane tensile strain, resulting in antiferroelectric behavior. In addition, it was demonstrated that modifying the ozone dose time during atomic layer deposition dramatically affects the electric field cycling behavior. This was found to be in direct correlation to the change in film strain induced by the oxygen processing conditions during film growth. Both studies demonstrated for the first time that doping and oxygen film processing change the internal film strains, which has significant implications for stabilizing the ferroelectric properties of fluorite films. The influence of film strain was further studied in ZrO2 films over a wide thickness range (4–390 nm), where it was demonstrated that the key predictor of generating ferroelectric behavior was the internal film strains, independent of thickness. Furthermore, the influence of the ALD growth temperature of ZrO2 on TiN electrodes was studied, showing that competing effects between in-plane tensile strains and interfacial layers can deteriorate the films' propensity to display ferroelectric instead of antiferroelectric behavior. These significant findings offer a clear route to optimizing ferroelectricity in fluorites by demonstrating that adjusting in-plane film strains (such as via ALD temperature, doping, and oxygen processing) and minimizing interfacial layers can yield improved ferroelectric hysteresis loops and less wake-up. The two last reliability criteria the HOMER project looked at were the influence of interfacial dead layers and the impact of the electrode materials. Through the project, it was shown how to optimize the operating conditions to retain more ferroelectric polarization when interfacial layers are present. Furthermore, better data retention and read/write cycling were strongly correlated with the electrode materials' chemical reactivity and oxygen scavenging potential with respect to the HfO2 or ZrO2 layer. Despite the cessation of the collaboration between German and Russian teams after the invasion of Ukraine, the HOMER project significantly contributed to the current knowledge of ferroelectric fluorite reliability.

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