(Invited) Ferroelectric Hafnium Oxide for Non-Volatile Memory Applications: From Single Capacitors to Memory Arrays

Abstract

This year marks the 10th anniversary of the public announcement of the discovery of ferroelectricity in HfO2-based thin films. Tremendous strides have been made in both the physical understanding and the technological use of ferroelectric HfO2. These unique fluorite-structured ferroelectrics have outstanding potential for commercial applications due to their scalability, CMOS-compatibility, and facile manufacturability. Such advantages make ferroelectric HfO2 particularly attractive for nonvolatile memories technologies such as ferroelectric random access memory (FRAM) and ferroelectric field effect transistors. Due to the wide variety of conditions in which ferroelectricity can emerge in HfO2 thin films, there has been a vast effort by the international scientific community to enhance and optimize the ferroelectric properties using a wide variety of approaches. Advancements in thin film ferroelectric capacitor and memory array technologies are therefore progressing rapidly.The structural properties of HfO2 are a major focal point for technology development because the competition between several crystalline phases in HfO2 thin films can have a major impact on device performance. For thin film memory capacitors, stabilizing the polar orthorhombic phase and eliminating secondary paraelectric phases is paramount in achieving robust polycrystalline HfO2 ferroelectrics. Doping and the presence of a capping electrode during crystallization have been extensively demonstrated to influence the emergence and stability of the ferroelectric orthorhombic phase. Greater attention has been placed recently on the thin film growth conditions in atomic layer deposition and physical vapor deposition, especially with regard to the oxidation conditions that have been shown to have a substantial impact on the device performance of ferroelectric HfO2 and Hf0.5Zr0.5O2 capacitors. Composition, film growth, and the crystallization processes are critical aspects for thin film ferroelectric capacitor development and the latest developments will be comprehensively reviewed in the context of how the material properties relate to nonvolatile memory performance.Developments in thin film HfO2 ferroelectric capacitors are now coming to fruition with the emergence of ferroelectric random access memory arrays and demonstrators. Thin film ferroelectric HfO2 based capacitors are successfully being demonstrated in back-end-of-line (BEOL) processes at the 130nm CMOS technology. The performance of these early demonstrator memory arrays show very promising long term data retention, large memory windows with good statistical distributions, and projections for area scaling to nanoscale dimensions. The transition from large-scale micron-sized laboratory devices to smaller scale integrated capacitors has proven to be a major step forward in endurance cycling with >1011 cycles being reported in memory arrays. The most recent integration of thin film ferroelectric HfO2 capacitors into FRAM memory arrays and what future developments are expected for HfO2 ferroelectric random access memories will be presented. Figure 1