The transition metal oxides ZrO(2) and HfO(2) as well as their solid solution are widely researched and, like most binary oxides, are expected to exhibit centrosymmetric crystal structure and therewith linear dielectric characteristics. For this reason, those oxides, even though successfully introduced into microelectronics, were never considered to be more than simple dielectrics possessing limited functionality. Here we report the discovery of a field-driven ferroelectric phase transition in pure, sub 10 nm ZrO(2) thin films and a composition- and temperature-dependent transition to a stable ferroelectric phase in the HfO(2)-ZrO(2) mixed oxide. These unusual findings are attributed to a size-driven tetragonal to orthorhombic phase transition that in thin films, similar to the anticipated tetragonal to monoclinic transition, is lowered to room temperature. A structural investigation revealed the orthorhombic phase to be of space group Pbc2(1), whose noncentrosymmetric nature is deemed responsible for the spontaneous polarization in this novel, nanoscale ferroelectrics.

Incipient ferroelectricity is known to occur in perovskites such as SrTiO3, KTaO3, and CaTiO3. For the first time it is shown that the intensively researched HfO2 thin films (16 nm) also possess ferroelectric properties when aluminium is incorporated into the host lattice. Polarization measurements on Al:HfO2 based metal–insulator–metal capacitors show an antiferroelectric‐to‐ferroelectric phase transition depending on annealing conditions and aluminium content. Structural investigation of the electrically characterized capacitors by grazing incidence X‐ray diffraction is presented in order to gain further insight on the potential origin of ferroelectricity. The non‐centrosymmetry of the elementary cell, which is essential for ferroelectricity, is assumed to originate from an orthorhombic phase of space group Pbc21 stabilized for low Al doping in HfO2. The ferroelectric properties of the modified HfO2 thin films yield high potential for various ferroelectric, piezoelectric, and pyroelectric applications. Furthermore, due to the extensive knowledge accumulated by various research groups regarding the HfO2 dielectric, an immediate relevance of ferroelectric hafnium oxide thin films is anticipated by the authors.

Bound to complex perovskite systems, ferroelectric random access memory (FRAM) suffers from limited CMOS-compatibility and faces severe scaling issues in today's and future technology nodes. Nevertheless, compared to its current-driven non-volatile memory contenders, the field-driven FRAM excels in terms of low voltage operation and power consumption and therewith has managed to claim embedded as well as stand-alone niche markets. However, in order to overcome this restricted field of application, a material innovation is needed. With the ability to engineer ferroelectricity in HfO 2 , a high-k dielectric well established in memory and logic devices, a new material choice for improved manufacturability and scalability of future 1T and 1T-1C ferroelectric memories has emerged. This paper reviews the recent progress in this emerging field and critically assesses its current and future potential. Suitable memory concepts as well as new applications will be proposed accordingly. Moreover, an empirical description of the ferroelectric stabilization in HfO 2 will be given, from which additional dopants as well as alternative stabilization mechanism for this phenomenon can be derived. The recent success of smartphones and tablet computers has accelerated the R&D of fast and energy efficient non-volatile semiconductor memories, capable of replacing the conventional SRAM-DRAM-Flash memory hierarchy. These so called emerging memories usually leverage on the fact that certain materials possess the capacity for remembering their electric, magnetic or caloric history. For the extensively investigated ferroelectrics this ability to memorize manifests in atomic dipoles switchable in an external electric field. This unique property renders them the perfect electric switch for semiconductor memories. Consequently, only a few years after the realization of a working transistor the first ferroelectric memory concepts were proposed. 1 However, more than 60 years and several iterations later it is now clear that the success or failure of FRAM is mainly determined by the proper choice and engineering of the ferroelectric material. Perovskite ferroelectrics and related electrode systems underwent an extensive optimization process to meet the requirements of CMOS integration and are now considered the front up solution in FRAM manufacturing. Nevertheless, those perovskite systems require complex integration schemes and pose scaling limitations on 1T and 1T-1C memory cells that until now remain unsolved. This creates an unbalance between memory performance on the one side and manufacturing and R&D costs on the other side. This dilemma has ever since restricted FRAM to niche markets.With the recent demonstration of ferroelectricity in HfO 2 -based systems (FE-HfO 2 ) a CMOS-compatible, highly scalable and manufacturable contender has emerged, that significantly expands the material choice for 1T and 1T-1C ferroelectric memory solutions (Reference 2 and references therein) as well as nanoscale ferroelectric devices.In this paper we will r...

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The incorporation of Gd into HfO2 thin films is shown to induce ferroelectricity. A significant influence of electric field cycling on both polarization as well as small-signal capacitance-voltage measurements can be observed. X-ray diffraction measurements are supported by infrared absorption analysis and give further evidence of the previously proposed non-centrosymmetric transition phase of space group Pbc21.