Improved polarization and endurance in ferroelectric Hf0.5Zr0.5O2 films on SrTiO3(110)

Symmetry Engineering of Epitaxial Hf0.5Zr0.5O2 Ultrathin Films

Robust ferroelectricity in HfO2-based ultrathin films has the potential to revolutionize nonvolatile memory applications in nanoscale electronic devices because of their compatibility with the existing Si technology. However, to fully exploit the potential of ferroelectric HfO2-based thin films, it is crucial to develop strategies for the controlled stabilization of various HfO2-based polymorphs in nanoscale heterostructures. This study demonstrates how substrate-orientation-induced anisotropic strain can engineer the crystal symmetry, structural domain morphology, and growth orientation of ultrathin Hf0.5Zr0.5O2 (HZO) films. Epitaxial ultrathin HZO films were grown on the heterostructures of (001)- and (110)-oriented La2/3Sr1/3MnO3/SrTiO3 (LSMO/STO) substrate. Various structural analyses revealed that the (110)-oriented substrate promotes a higher degree of structural order (crystallinity) with improved stability of the (111)-oriented orthorhombic phase (Pca21) of HZO. Conversely, the (001)-oriented substrate not only induces a distorted orthorhombic structure but also facilitates the partial stabilization of nonpolar phases. Electrical measurements revealed robust ferroelectric properties in epitaxial thin films without any wake-up effect, where the well-ordered crystal symmetry stabilized by STO(110) facilitated better ferroelectric characteristics. This study suggests that tuning the epitaxial growth of ferroelectric HZO through substrate orientation can improve the stability of the metastable ferroelectric orthorhombic phase and thereby offer a better understanding of device applications.

Metal-Induced Trap States: The Roles of Interface and Border Traps in HfO2/InGaAs

By combining capacitance-voltage measurements, TCAD simulations, and X-ray photoelectron spectroscopy, the impact of the work function of the gate metals Ti, Mo, Pd, and Ni on the defects in bulk HfO2 and at the HfO2/InGaAs interfaces are studied. The oxidation at Ti/HfO2 is found to create the highest density of interface and border traps, while a stable interface at the Mo/HfO2 interface leads to the smallest density of traps in our sample. The extracted values of Dit of 1.27 × 1011 eV-1cm-2 for acceptor-like traps and 3.81 × 1011 eV-1cm-2 for donor-like traps are the lowest reported to date. The density and lifetimes of border traps in HfO2 are examined using the Heiman function and strongly affect the hysteresis of capacitance-voltage curves. The results help systematically guide the choice of gate metal for InGaAs.

HfO2-based ferroelectric thin film and memory device applications in the post-Moore era: A review

The rapid development of 5G, big data, and Internet of Things (IoT) technologies is urgently required for novel non-volatile memory devices with low power consumption, fast read/write speed, and high reliability, which are crucial for high-performance computing. Ferroelectric memory has undergone extensive investigation as a viable alternative for commercial applications since the post-Moore era. However, conventional perovskite-structure ferroelectrics (e.g., PbZr x Ti1- x O3) encounter severe limitations for high-density integration owing to the size effect of ferroelectricity and incompatibility with complementary metal-oxide-semiconductor technology. Since 2011, the ferroelectric field has been primarily focused on HfO2-based ferroelectric thin films owing to their exceptional scalability. Several reviews discussing the control of ferroelectricity and device applications exist. It is believed that a comprehensive understanding of mechanisms based on industrial requirements and concerns is necessary, such as the wake-up effect and fatigue mechanism. These mechanisms reflect the atomic structures of the materials as well as the device physics. Herein, a review focusing on phase stability and domain structure is presented. In addition, the recent progress in related ferroelectric memory devices and their challenges is briefly discussed.

Hafnium-doped zirconia ferroelectric thin films with excellent endurance at high polarization

Using thermal atomic layer deposition and subsequent rapid thermal annealing without the need for metal clamping atop, a remanent polarization (P_r) of 25.5 μC cm^-2 was achieved in a 10 nm-thick ZrO₂ film deposited on a W bottom electrode. Hafnium doping was further explored to improve the ferroelectric properties in P_r as well as the endurance of zirconia-based thin films. A significantly enhanced P_r reaching 41 μC cm^-2 was obtained for 10 nm-thick hafnium-doped ZrO₂ with an optimal Zr : Hf ratio of 3 : 1. Importantly, owing to the greatly reduced leakage, the optimal hafnium-doped ZrO₂ thin films exhibited superior retention and outstanding endurance performances at relatively high polarizations, free of serious degradation for up to 2.3 × 10⁹-6.8 × 10⁹ field cycles at an initial P_r of 27 μC cm^-2 and were even capable of over 10⁷ cycles at a maximum P_r of 41 μC cm^-2. The superb ferroelectricities were demonstrated on big-sized capacitors as well as sub-micrometer ones, isolated or in array. This would empower zirconia-based ferroelectric thin films as a competitive front-runner for practical applications in ferroelectric-related nanoelectronics.

In-Memory Computation Based Mapping of Keccak-f Hash Function

Cryptographic hash functions play a central role in data security for applications such as message authentication, data verification, and detecting malicious or illegal modification of data. However, such functions typically require intensive computations with high volume of memory accesses. Novel computing architectures such as logic-in-memory (LIM)/in-memory computing (IMC) have been investigated in the literature to address the limitations of intense compute and memory bottleneck. In this work, we present an implementation of Keccak-f (a state-of-the-art secure hash algorithm) using a variant of simultaneous logic-in-memory (SLIM) that utilizes emerging non-volatile memory (NVM) devices. Detailed operation and instruction mapping on SLIM-based digital gates is presented. Through simulations, we benchmark the proposed approach using LIM cells based on four different emerging NVM devices (OxRAM, CBRAM, PCM, and FeRAM). The proposed mapping strategy when used with state-of-the-art emerging NVM devices offers EDP savings of up to 300× compared to conventional methods.