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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.

This study investigates the stability of the (Hf,Zr)O2 (HZO) and AlScN thin films against the depolarization effect. In order to adversely interfere with the polarization screening of ferroelectric (FE) film and induce the depolarization effect, an Al2O3 film was inserted between the TiN bottom electrode and the FE film. Subsequently, to minimize charge injection through Al2O3 films, the double remanent polarization–voltage (2Pr–V) curve was measured employing voltage pulses with 1 μs-length. As the thickness of the Al2O3 film increased, the charge injection through the Al2O3 film decreased, leading to a decrease in the slope of the 2Pr–V curve. The magnitude of the depolarization field applied to the FE film was determined by simulating the 2Pr–V curve using an equivalent circuit model. Subsequently, the proportion of reversed domains during the delay period due to the depolarization effect was measured. It was revealed that HZO films exhibited vulnerability to the depolarization effect, with 16% of domains being reversed. On the other hand, AlScN films demonstrated superior stability, with polarization loss of less than 1%. Ultimately, it was revealed that AlScN films demonstrated superior stability against the depolarization effect compared to HZO films due to their higher coercive field and more uniform polarization distribution across the film area. [ABSTRACT FROM AUTHOR]

Grazing incidence x-ray diffraction reveals that conventional post-deposition-annealed ZrO2 and in situ crystallized (by local epitaxy) ZrO2 thin films (<15 nm) have different internal strain states. A comparison between single- and two-step grown films enables the diverse strain components to be discretely identified. In particular, thickness-dependent intrinsic growth strain is unevenly distributed within the film according to the Volmer–Weber growth. Furthermore, extrinsic thermal strain, locally present in the annealed seed layer, does not spread over the in situ crystallized upper main layer of the two-step film. Post-deposition annealing of the two-step film renders the strain state identical to the single-step films by imposing thermal strain on the in situ crystallized main layer. Local strains created by diffused aluminum and yttrium dopants are also examined. Since each stress factor plays a vital role in the phase formation and electrical behaviors of ZrO2 and other fluorite-structure films, this method will pave the way for understanding the film's internal strain distribution and accompanying performance engineering. [ABSTRACT FROM AUTHOR]

The effects of in-plane strain on the dielectric constant of the Be0.25Mg0.75O rock salt superlattice are investigated through ab initio thermodynamics calculations. Based on a previous report that the long apical Be–O bond increased the dielectric constant, the in-plane compressive strain dielectric constant is expected to increase the dielectric constant. Unlike the zero-strain case, the apical Mg–O bonds also contribute to the increase in the dielectric constant under compressive strain. However, small Be ions tend to occupy narrow spaces in the MgO-based rock salt structure, which can lead to an increase in dielectric constant even under in-plane tensile strain, depending on the local position of Be ions and its interaction with O ions. At higher temperatures, several configurations under strain showed a significant increase in the dielectric constant due to the elongation of the apical Be–O bond. Considering temperature and strain comprehensively, this study suggests that the Be0.25MgO0.75O superlattice under −2% in-plane compressive strain could be a promising candidate structure for achieving a high-κ value of approximately 30. [ABSTRACT FROM AUTHOR]

In this paper, we present a unique resistive switching (RS) mechanism study of Pt/TiO2/Pt cell, one of the most widely studied RS system, by focusing on the role of interfacial bonding at the active TiO2-Pt interface, as opposed to a physico-chemical change within the RS film. This study was enabled by the use of a non-conventional scanning probe-based setup. The nanoscale cell is formed by bringing a Pt/TiO2-coated atomic force microscope tip into contact with a flat substrate coated with Pt. The study reveals that electrical resistance and interfacial bonding status are highly coupled together. An oxygen-mediated chemical bonding at the active interface between TiO2 and Pt is a necessary condition for a non-polar low-resistance state, and a reset switching process disconnects the chemical bonding. Bipolar switching mode did not involve the chemical bonding. The nature of chemical bonding at the TiO2-metal interface is further studied by density functional theory calculations.

This study investigates the insertion traits of the Al2O3 and Y2O3 insertion layers (ILs) and their effects on the phase evolution and electrical characteristics of polycrystalline Hf0.5Zr0.5O2 (HZO) thin films grown by atomic layer deposition (ALD). The Al2O3 and Y2O3 ILs are located at the middle position along the HZO film. The thick Al2O3 IL, above 2–3 ALD cycles, forms a continuous layer, physically separating the upper and lower regions of the film. Conversely, the thin Al2O3 IL, below 2–3 ALD cycles, and all the Y2O3 IL diffuse into the nearby HZO layers, making a single Al- or Y-doped HZO layer. The most crucial finding is that the diffused trivalent Al and Y ions substitute the tetravalent Hf and Zr ions, creating oxygen vacancies for charge neutrality and changing the phase evolutions. The substituted Al and Y suppress the monoclinic phase and enhance the tetragonal phase. Ultimately, the study suggests a new perspective on doped HfO2-based thin films, highlighting the crucial role of substitutional diffusion of dopants and charge neutrality in determining the formation of the tetragonal phase. [ABSTRACT FROM AUTHOR]

This research explores the high-k dielectric behavior of ultra-thin BeMgO (BMO) films (≪5 nm) using the super-cycle atomic layer deposition (ALD) technique. The fabricated metal–insulator–metal devices, utilizing sputtered TiN as both bottom and top electrodes, demonstrate low leakage current and high capacitance characteristics with a minimum equivalent oxide thickness of 1.30 nm. The dielectric constants of the films are significantly higher than those of pure MgO or BeO films, reaching a maximum value of 14.2 at a film composition of Be0.29Mg0.71O, indicating the realization of the cubic rocksalt configuration of Be–O bonds. The rocksalt phase remains dominant even in Be-rich BMO films due to the structural coherence with the TiN electrodes, revealing the intricate interplay between composition and interface engineering. BMO films showed exceptional electrical stability even at a film thickness of 2.5 nm, demonstrating their strong dielectric strength. The trap-assisted tunneling mechanism governed the leakage current at this thickness. Such attributes make BMO films highly appealing in dynamic random-access memory capacitors, where the industry's relentless drive toward miniaturization necessitates ultra-thin dielectric films with uncompromising performance. [ABSTRACT FROM AUTHOR]

Analog and digital switching performances in a Ta/HfO2/RuO2 (THR) memristor are studied to implement a density‐based spatial clustering of applications with noise (DBSCAN) algorithm in a low‐power, parallel‐computing memristor crossbar structure. In the analog mode THR memristor, more than 256 states can be stored through a fine‐tuning process with a denoising scheme. The analog mode crossbar array facilitates Euclidean distance calculation between any points in the given graphic dataset. In the digital mode, the on/off ratio of more than three orders of magnitude between the binary states is achieved, providing functionality to cluster the data points with a reduced number of operations. The parallel computing capacity of the adopted crossbar decreases the time complexity of the original DBSCAN from O(n2) to O(n). Through array‐level simulations, the effectiveness of hardware functionality is validated using representative synthetic datasets and single‐cell RNA sequences datasets. [ABSTRACT FROM AUTHOR]