(Invited) Correlating Device Physics with Material Chemistry in Hafnia-Based Ferroelectric Memory Systems
Authors: Park Min Hyuk 
Published: December 2024

The discovery of ferroelectricity in (Hf,Zr)O2 (HZO) thin films in 2011 [1] ignited renewed exploration into ferroelectric memory technologies, such as ferroelectric random-access-memory (FeRAM) and ferroelectric field-effect-transistor (FeFET), which offer promising avenues for next-generation memory solutions.[2-5] Despite the commercialization of FeRAM using traditional materials like Pb(Zr,Ti)O3 and SrBi2Ta2O9, its niche presence indicates a gap in mainstream adoption for high-density information storage.[3-5] Conversely, HfO2 and ZrO2, integrated into mainstream semiconductor devices like metal-oxide-semiconductor field-effect-transistor (MOSFET) and dynamic random-access-memory (DRAM), suggest compatibility with established fabrication processes, hinting at the potential of ferroelectric HZO for next-gen memory. Unlike electron-stored DRAM and Flash, ferroelectric memories store data based on material polarization, underlining the substantial impact of material properties on device performance. Thus, understanding the physics and chemistry of ferroelectric HZO is paramount for enhancing memory performance, given the intricate interplay of intrinsic and extrinsic factors such as thermodynamics, polymorphism, doping effects, and surface energy. [2,6-8]

This presentation provides a comprehensive examination of hafnia-based ferroelectrics and their applications in semiconductor devices, underscoring the intrinsic link between device physics and material chemistry.[9] Specifically, the integration into next-gen memory devices like DRAM and Flash is explored. Managing trade-offs between remanent polarization (Pr) and endurance, crucial for demanding DRAM applications, requires reducing coercive field (Ec), which directly impacts operational voltage. Recent advancements in depositing metal-rich HZO film via sputtering show promise, with potential implications for FeRAM implementation through ALD. [10]

Regarding flash operation, read disturbance poses a significant challenge to FeFET NAND functionality, necessitating optimal Pr and Ec ratios in ferroelectric materials. While achieving high Pr is a focus, excessive Pr can be detrimental to gate insulators, requiring a balance to avoid charge trapping and fatigue. Uniformly attaining suitable Pr and Ec values in hafnia-based ferroelectrics remains a considerable challenge without significant breakthroughs. Evaluation of FeFET performance reveals notable advancements in material chemistry control, enabling endurance up to 1010 cycles and write times as low as 300 ps, indicating a promising trajectory for FeFET technology.

While substantial progress has been made in understanding material properties and exploring device applications in the first decade of ferroelectric HZO research, ongoing assessment and future directions are critical. Addressing device issues and material property challenges are urgent for practical applications in mainstream memory devices. Furthermore, concerns regarding circuitry and system integration in large-scale ferroelectric memory arrays necessitate continued research and development efforts. Despite these challenges, the benefits of ferroelectric materials and devices in semiconductor applications justify sustained exploration and innovation.

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