Materials exhibiting high energy/power density are currently needed to meet the growing demand of portable electronics, electric vehicles and large-scale energy storage devices. The highest energy densities are achieved for fuel cells, batteries, and supercapacitors, but conventional dielectric capacitors are receiving increased attention for pulsed power applications due to their high power density and their fast charge-discharge speed. The key to high energy density in dielectric capacitors is a large maximum but small remanent (zero in the case of linear dielectrics) polarization and a high electric breakdown strength. Polymer dielectric capacitors offer high power/energy density for applications at room temperature, but above 100 °C they are unreliable and suffer from dielectric breakdown. For high-temperature applications, therefore, dielectric ceramics are the only feasible alternative. Lead-based ceramics such as La-doped lead zirconate titanate exhibit good energy storage properties, but their toxicity raises concern over their use in consumer applications, where capacitors are exclusively lead free. Lead-free compositions with superior power density are thus required. In this paper, we introduce the fundamental principles of energy storage in dielectrics. We discuss key factors to improve energy storage properties such as the control of local structure, phase assemblage, dielectric layer thickness, microstructure, conductivity, and electrical homogeneity through the choice of base systems, dopants, and alloying additions, followed by a comprehensive review of the state-of-the-art. Finally, we comment on the future requirements for new materials in high power/energy density capacitor applications.

Electroceramics for High-Energy Density Capacitors: Current Status and Future Perspectives

The discovery of ferroelectricity in oxides that are compatible with modern semiconductor manufacturing processes, such as hafnium oxide, has led to a re-emergence of the ferroelectric field-effect transistor in advanced microelectronics. A ferroelectric field-effect transistor combines a ferroelectric material with a semiconductor in a transistor structure. In doing so, it merges logic and memory functionalities at the single-device level, delivering some of the most pressing hardware-level demands for emerging computing paradigms. Here, we examine the potential of the ferroelectric field-effect transistor technologies in current embedded non-volatile memory applications and future in-memory, biomimetic and alternative computing models. We highlight the material- and device-level challenges involved in high-volume manufacturing in advanced technology nodes (≤10 nm), which are reminiscent of those encountered in the early days of high-K-metal-gate transistor development. We argue that the ferroelectric field-effect transistors can be a key hardware component in the future of computing, providing a new approach to electronics that we term ferroelectronics. This Perspective examines the use of ferroelectric field-effect transistor technologies in current embedded non-volatile memory applications and future in-memory, biomimetic and alternative computing models, arguing that the devices will be a key component in the development of data-centric computing.

The future of ferroelectric field-effect transistor technology

Ferroelectrics are a class of materials that possess a variety of interactions between electrical, mechanical, and thermal properties that have enabled a wealth of functionalities. To realize integrated systems, the integration of these functionalities into semiconductor processes is necessary. To this end, the complexity of well-known ferroelectric materials, e.g., the perovskite class, causes severe issues that limit its applications in integrated systems. The discovery of ferroelectricity in hafnium oxide-based materials brought a renewed interest into this field during the last decade. Very recently, ferroelectricity was also verified in aluminum scandium nitride extending the potential of seeing a wealth of ferroelectric functions in integrated electronics in the future. This paper discusses the prospects of both material systems in various applications.

Next generation ferroelectric materials for semiconductor process integration and their applications

The local crystal phase and orientation of ferroelectric grains inside TiN/Hf0.5Zr0.5O2/TiN have been studied by the analysis of the local electron beam scattering Kikuchi patterns, recorded in transmission. Evidence was found that the ferroelectric phase of the layers is derived from an orthorhombic phase, most likely of space group Pca21. The orientation analysis reveals a strong out-of-plane texture of the polycrystalline film which is in accordance with a high remanent polarization Pr observed for P-V measurements. The results of this analysis help us to further optimize the ratio of ferroelectric grains and their orientation for many applications, e.g., in the field of emerging memory or infrared sensors.

Local crystallographic phase detection and texture mapping in ferroelectric Zr doped HfO 2 films by transmission-EBSD

Negative capacitance in ferroelectric materials has been suggested as a solution to reduce the power dissipation of electronics beyond fundamental limits. The discovery of ferroelectricity and negative capacitance in the widely used class of HfO2-based materials has since sparked large research efforts to utilize these effects in ultra-low power transistors. While significant progress has been made in the basic understanding of ferroelectric negative capacitance in recent years, the development of practical devices has seen limited success so far. Here, we present a unique view of the field of negative capacitance electronics from the ferroelectric materials perspective. Starting from the basic principles of ferroelectric negative capacitance, we discuss the desirable characteristics of a negative capacitance material, concluding that HfO2-based ferroelectrics are currently most promising for applications in electronics. However, we emphasize that material non-idealities can complicate and in some cases even inhibit the design and fabrication of practical negative capacitance devices using HfO2-based ferroelectrics. Finally, we review the recent progress on experimental devices and give an outlook on the future direction of the field. In particular, further investigations of the microscopic structure of HfO2-based ferroelectrics are needed to provide an insight into the origin of negative capacitance in this material system and to enable predictive device design.

Progress and future prospects of negative capacitance electronics: A materials perspective

https://www.onlinelibrary.wiley.com/doi/pdf/10.1002/pssa.201900840

Back‐End‐of‐Line Compatible Low‐Temperature Furnace Anneal for Ferroelectric Hafnium Zirconium Oxide Formation

The pyroelectric response of polycrystalline, Si-doped HfO2 layers in a thickness range of 10 nm to 50 nm is investigated employing the temperature oscillation method. The largest value of the pyroelectric coefficient is obtained for the 20 nm layer with p = 84 μC m−2 K−1, which is similar to that of lithium niobate. Furthermore, the pyroelectric coefficient is analyzed with respect to field cycling and is found to increase proportionally with the remanent polarization during wake-up, providing further evidence that the hysteresis of the material is truly ferroelectric. However, for different material thicknesses, the switchable polarization and pyroelectric coefficient are not proportional, indicating that only part of the domains is pyroelectrically active, which suggests potential for further improvement of the pyroelectric response. Due to its CMOS compatibility and conformal deposition using atomic layer deposition (ALD), Si-doped HfO2 is a promising candidate for future energy harvesting and sensor applications.

Layer thickness scaling and wake-up effect of pyroelectric response in Si-doped HfO2

Lanthanum has been identified as a promising dopant to achieve ferroelectricity in HfO2 thin films in recent theoretical and experimental studies. In this work, the pyroelectric properties of 10 nm thick polycrystalline La-doped HfO2 layers manufactured by thermal atomic layer deposition are assessed employing a sinusoidal temperature profile. Compared to Si doping, La offers a broader dopant range in which ferroelectric behavior is obtained, making the material interesting for large-scale integration and deposition on area-enhanced substrates. Pyroelectric coefficients of up to −80 μC/m2 K are obtained using an optimized stoichiometry, which is comparable to earlier measurements with Si-doped HfO2 samples. Phase-sensitive evaluation of the measured current confirms the pyroelectric origin with minimal spurious contributions. The results are discussed with respect to the ferroelectric switching behavior, which is analyzed employing first-order reversal curve measurements. It is found that there is no simple linear relationship between the remanent polarization and the pyroelectric coefficient. Experimental evidence indicates that the pyroelectric response in polycrystalline thin films is modulated by internal bias fields, which can arise from charged defects. This illustrates the need for careful tuning of the manufacturing conditions and the film phase composition in future applications such as pyroelectric sensors, energy harvesting, or solid-state cooling.

Ferroelectric and pyroelectric properties of polycrystalline La-doped HfO2 thin films

https://onlinelibrary.wiley.com/doi/pdf/10.1002/pssr.202100086

C. Mart

Papers

Local crystallographic phase detection and texture mapping in ferroelectric Zr doped HfO 2 films by transmission-EBSD

Back‐End‐of‐Line Compatible Low‐Temperature Furnace Anneal for Ferroelectric Hafnium Zirconium Oxide Formation

Layer thickness scaling and wake-up effect of pyroelectric response in Si-doped HfO2

Ferroelectric and pyroelectric properties of polycrystalline La-doped HfO2 thin films

On the Origin of Wake-Up and Antiferroelectric-Like Behavior in Ferroelectric Hafnium Oxide