Damage mitigation as a strategy to achieve high ferroelectricity and reliability in hafnia for random-access-memory†

Abstract

Ferroelectric materials, characterized by their polarization switching capabilities, have emerged as promising candidates for non-volatile memory applications due to their fast operation speeds, low switching energies, and remarkable scalability. Among these, hafnia-based ferroelectrics are particularly noted for their compatibility with complementary metal-oxide-semiconductor (CMOS) technology. However, the development of high-quality ferroelectricity in ultra-thin films, essential for low-voltage operations and high-density integrations, remains challenging. This study introduces a novel low-damage metallization process designed to fabricate ultra-thin (sub-5 nm) ferroelectric films exhibiting exceptional ferroelectric properties and reliability. The process, compatible with standard CMOS techniques, achieves a significant remnant polarization (P_r) of 40 µC cm⁻² and low leakage currents, alongside enhanced retention characteristics. Crucially, it substantially mitigates the wake-up effect, often attributed to oxygen vacancy redistribution at the interface. Through comprehensive analyses utilizing electron energy loss spectroscopy (EELS), geometric phase analysis (GPA) and X-ray photoelectron spectroscopy (XPS), we demonstrate that our process effectively reduces oxygen vacancies and dislocations at the top interface of the ferroelectric film. The enhanced reliability of ferroelectric random-access memory (FeRAM), evidenced by improved sensing margins and consistency in ferroelectric properties, marks a substantial improvement over the conventional method. To precisely measure reliability characteristics, we propose a new retention model that considers charge screening over time. Moreover, circuit-level simulations via non-volatile memory simulator (NVSim) validate the process's integration potential with existing CMOS technologies, affirming its suitability for advanced, high-density memory configurations without compromising performance or energy efficiency. The findings from this study pave the way for broader applications of nanoscale high-quality dielectric thin films, extending beyond ferroelectric materials to various technological domains requiring advanced material solutions.