The decreasing feature sizes in complementary metal-oxide semiconductor (CMOS) transistor technology will require the replacement of SiO2 with gate dielectrics that have a high dielectric constant (high-k) because as the SiO2 gate thickness is reduced below 1.4 nm, electron tunnelling effects and high leakage currents occur in SiO2, which present serious obstacles to future device reliability. In recent years significant progress has been made on the screening and selection of high-k gate dielectrics, understanding their physical properties, and their integration into CMOS technology. Now the family of hafnium oxide-based materials has emerged as the leading candidate for high-k gate dielectrics due to their excellent physical properties. It is also realized that the high-k oxides must be implemented in conjunction with metal gate electrodes to get suffcient potential for CMOS continue scaling. In the advanced nanoscale Si-based CMOS devices, the composition and thickness of interfacial layers in the gate stacks determine the critical performance of devices. Therefore, detailed atomic-scale understandings of the microstructures and interfacial structures built in the advanced CMOS gate stacks, are highly required. In this paper, several high-resolution electron, ion, and photon-based techniques currently used to characterize the high-k gate dielectrics and interfaces at atomic-scale, are reviewed. Particularly, we critically review the research progress on the characterization of interface behavior and structural evolution in the high-k gate dielectrics by high-resolution transmission electron microscopy (HRTEM) and the related techniques based on scanning transmission electron microscopy (STEM), including high-angle annular dark-field (HAADF) imaging (also known as Z-contrast imaging), electron energy-loss spectroscopy (EELS), and energy dispersive X-ray spectroscopy (EDS), due to that HRTEM and STEM have become essential metrology tools for characterizing the dielectric gate stacks in the present and future gen
Xinhua Zhu Jian-min Zhu Aidong Li Zhiguo Liu Naiben Ming
Perovskite ferroelectric nanostructures offer a wide range of functional properties(e.g.,dielectric switchability,piezoelectricity,pyroelectricity,high permittivities and strong electro-optic effects),which have received much attention in theelds of microelectronic devices miniaturization over the last few years.Pronounced size effects of the functional properties have been demonstrated in the perovskite ferroelectric nanostructures.Besides its intrinsic scientic value,fundamental understanding of the size effects in perovskite ferroelectric nanostructures has become critical item for developing a new generation of revolutionary nanodevices.In this article,a comprehensive review of the state-of-the-art research progress on the size effects in perovskite ferroelectric nanostructures which have been achieved from both experiment and theory is provided.It begins with a historical perspective of the size effects in perovskite ferroelectrics,and then highlight the recent progress on the theoretical studies of the size effects in perovskite ferroelectric nanostructures which have been achieved by using different numerical approaches(e.g.,phenomenological approaches,rst-principle computations and the Ising model in a transverseeld).The current progress of the experimental testing of the size effects in perovskite ferroelectric nanostructures(e.g.,nanoparticles,nanowires,nanotubes and nanolms)is summarized.Finally,the perspectives toward the future challenges of the size effects in perovskite ferroelectric nanostructures is reviewed.
