Roadmap on ferroelectric hafnia- and zirconia-based materials and devices

Abstract

Ferroelectric hafnium and zirconium oxides have undergone rapid scientific development over the last decade, pushing them to the forefront of ultralow-power electronic systems. Maximizing the potential application in memory devices or supercapacitors of these materials requires a combined effort by the scientific community to address technical limitations, which still hinder their application. Besides their favorable intrinsic material properties, HfO2–ZrO2 materials face challenges regarding their endurance, retention, wake-up effect, and high switching voltages. In this Roadmap, we intend to combine the expertise of chemistry, physics, material, and device engineers from leading experts in the ferroelectrics research community to set the direction of travel for these binary ferroelectric oxides. Here, we present a comprehensive overview of the current state of the art and offer readers an informed perspective of where this field is heading, what challenges need to be addressed, and possible applications and prospects for further development.

Growth of emergent simple pseudo-binary ferroelectrics and their potential in neuromorphic computing devices

“…Considering the aforementioned challenges of perovskites, the discovery of ferroelectricity in Si-doped hafnium oxide (Si:HfO 2 ) thin films has provided a promising alternative to resolve these problems. 15,16 Following this exciting discovery, ferroelectricity in the nano-regime in Si:HfO 2 has attracted significant attention from the ferroelectrics community due to its compatibility with the complementary metal–oxide–semiconductor (CMOS) technology. Inducing ferroelectricity at the nanoscale is the current trend in non-volatile memories to realize applications such as high-density memory, storage class memory, neuromorphic computing, hardware security, etc.…”

“…Perovskite-based ferroelectric materials such as lead zirconate titanate (PZT) and strontium bismuth tantalate (SBT) are promising materials for achieving the performance required for memory applications such as logic-in memory (LiM) and non-volatile logic devices. [9][10][11][12][13][14][15][16][17] For instance, different companies (such as Cypress Semiconductor, Texas Instruments, and Fujitsu) installed a PZTbased FeRAM in applications, including wearable medical gadgets, smart cards, energy meters, airplane black boxes, radio frequency tags, and code storage in microcontrollers. 11 SBT-based FeFETs with a huge memory window and almost infinite cycling endurance (410 12 ) were demonstrated by Sakai et al, 12 which later exhibited adequate operation in non-volatile logic (NVL) circuits 12 and 64 kbit NAND memory arrays.…”

Internal Photoemission Spectroscopy Measurements of Interfacial Energy Barriers in Operating TaN/Hf0.5Zr0.5O2/TaN Metal/Ferroelectric/Metal (MFM) Devices

“…Ferroelectric materials have long attracted interest for applications in ferroelectric random access memory (FeRAM), negative capacitance field effect transistors (NC-FETs), ferroelectric tunnel junctions (FTJs), and high- k capacitors. − These applications are of particular interest for lowering the energy cost associated with computing. Since the first report in 2011 of ferroelectric behavior in thin-film-doped HfO 2 , Zr-substituted HfO 2 (Hf 1– x Zr x O 2 or HZO) has become a leading candidate ferroelectric material for Si complementary metal oxide semiconductor (CMOS) technology. − This is primarily due to the potential ease of HZO integration, as HfO 2 -based materials are already widely used as the gate dielectrics. To fully understand the operation of electronic devices constructed with HZO, knowledge of the electron energy barriers or band offsets between HZO and adjacent metal electrodes in operating devices is required.…”

Highly Stable Epitaxially Crystallized Ferroelectric Hf0.5Zr0.5O2 Films

“…12 The intense research on the effects of annealing conditions and kinetics has permitted the understanding of the mechanisms of polymorph formation in polycrystalline-doped hafnia films and the optimization of their ferroelectric properties. However, despite the progress made on epitaxial films in recent years, 2,13 the impact of cooling conditions after epitaxial growth at high temperature remains unknown. Determining this impact is critical since a strong influence of cooling conditions after epitaxy at high temperatures could challenge achieving optimal properties and would limit the repeatability of properties among different laboratories.…”

“…Doped HfO 2 films exhibit robust ferroelectricity at room temperature when the metastable orthorhombic phase is stabilized rather than the stable monoclinic (paraelectric) phase. , Various thermodynamic factors, such as surface and interface energy, lattice strain, defects (particularly oxygen vacancies), and doping, contribute to the stabilization of a metastable phase of a material affecting the relative energy of competing polymorphs. − The relative energy also depends on the crystal size and temperature and can therefore change during crystal growth or cooling procedures. Besides, kinetics may be an important factor since phase transformations involve crossing energy barriers, and transformations between polymorphs can be suppressed.…”