Hafnium Oxide (HfO₂) – A Multifunctional Oxide: A Review on the Prospect and Challenges of Hafnium Oxide in Resistive Switching and Ferroelectric Memories

Abstract

Hafnium oxide (HfO2) is one of the mature high‐k dielectrics that has been standing strong in the memory arena over the last two decades. Its dielectric properties have been researched rigorously for the development of flash memory devices. In this review, the application of HfO2 in two main emerging nonvolatile memory technologies is surveyed, namely resistive random access memory and ferroelectric memory. How the properties of HfO2 equip the former to achieve superlative performance with high‐speed reliable switching, excellent endurance, and retention is discussed. The parameters to control HfO2 domains are further discussed, which can unleash the ferroelectric properties in memory applications. Finally, the prospect of HfO2 materials in emerging applications, such as high‐density memory and neuromorphic devices are examined, and the various challenges of HfO2‐based resistive random access memory and ferroelectric memory devices are addressed with a future outlook.

In-Gap States of HfO2 Nanoislands Driven by Crystal Nucleation: Implications for Resistive Random-Access Memory Devices

“…The here-applied growth conditions for HfO 2 nanoislands on HOPG, resulting in carbide-type carbon (E a3 ) incorporation, can be transferred likewise to HfO 2 NCs on graphene, a substrate which is discussed for ReRAM devices. 17 On the other hand, oxidizable substrates used in ReRAM like, for example, Hf or Ti, 5 are expected to promote the creation of oxygen-deficient HfO 2 nanoclusters exhibiting E a1 and E d2 in-gap states. The here-presented methodology might be advantageously employed to identify which stoichiometric, oxygen-deficient, or oxygen-surplus HfO 2 nanoclusters will be the most stable under the respective growth conditions.…”

Moisture Effect on the Threshold Switching of TOPO-Stabilized Sub-10 nm HfO2 Nanocrystals in Nanoscale Devices

“…The presence of interstitial cations (Hf or other cations through doping) or oxygen vacancies, V o •• , is one requirement for the formation of conductive filaments in HfO 2 materials and thus for the enabling of resistive switching. , Here, we employ crystalline HfO 2 NC, which are not expected to have a high defect density, as an insulating material between two metal electrodes with a high work function. At these noble metal electrodes, no oxygen exchange reaction is possible, leading essentially to an electron transport through the Au/TOPO-HfO 2 NC interface.…”

“…The enduring aspiration to minimize electronic devices driven by the high request for non-volatile data storage as well as the demand for printed electronics on flexible supports promotes the application of ultrathin films or nanocrystals (NC) in future memory devices. − Consequently tracing this goal, that is, downscaling of the switching layer thickness as well as the effective electrode area, addressing an individual NC between two nanosized electrodes becomes the reasoned, technically feasible next step, like we have shown recently. − Today’s state-of-the-art hafnium oxide (HfO 2 ) exhibits qualitative advantages for a variety of applications in nanoelectronics and outperforms traditional oxide materials as it holds an outstanding chemical stability, high melting point, high dielectric constant, wide band gap, and transparency in the region from infrared to ultraviolet . HfO 2 is used in metal–oxide semiconductor field-effect transistors, ferroelectric field-effect transistors, highly scaled dynamic random access memories, and resistive random access memories (ReRAM).…”

“…HfO 2 is used in metal–oxide semiconductor field-effect transistors, ferroelectric field-effect transistors, highly scaled dynamic random access memories, and resistive random access memories (ReRAM). Especially, its proven CMOS compatibility and full scalability make it an advantageous material for future nanoelectronic devices. ,− It is known that in HfO 2 ReRAM, the resistive hysteresis is generated by an oxygen vacancy drift and linked redox reactions due to an applied electric field. ,, …”

Grain boundary passivation via balancing feedback of hole barrier modulation in HfO2-x for nanoscale flexible electronics

“…In the flexible electronics, grain boundary passivation is essential to prevent unintended grain boundary mediated-dielectric breakdown during bending. This is especially crucial in HfO 2 -based flexible neuromorphic devices, as oxygen deficiency variation of conductive channels is accountable for a gradual change of conductance [ 23 ]. For fabrication of the hafnia-based flexible electronics, deposition techniques for large-area growth such as atomic layer deposition and sputtering are commonly used [ 19 ].…”