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Owing to their switchable spontaneous polarization, ferroelectric materials have been applied in various fields, such as information technologies, actuators, and sensors. In the last decade, as the characteristic sizes of both devices and materials have decreased significantly below the nanoscale, the development of appropriate characterization tools became essential. Recently, a technique based on conductive atomic force microscopy (AFM), called AFM‐positive‐up‐negative‐down (PUND), is employed for the direct measurement of ferroelectric polarization under the AFM tip. However, the main limitation of AFM‐PUND is the low frequency (i.e., on the order of a few hertz) that is used to initiate ferroelectric hysteresis. A significantly higher frequency is required to increase the signal‐to‐noise ratio and the measurement efficiency. In this study, a novel method based on high‐frequency AFM‐PUND using continuous waveform and simultaneous signal acquisition of the switching current is presented, in which polarization–voltage hysteresis loops are obtained on a high‐polarization BiFeO3 nanocapacitor at frequencies up to 100 kHz. The proposed method is comprehensively evaluated by measuring nanoscale polarization values of the emerging ferroelectric Hf0.5Zr0.5O2 under the AFM tip.

HfO2-based ferroelectrics are highly expected to lead the new paradigm of nanoelectronic devices owing to their unexpected ability to enhance ferroelectricity in the ultimate thickness scaling limit (≤2 nm). However, an understanding of its physical origin remains uncertain because its direct microstructural and chemical characterization in such a thickness regime is extremely challenging. Herein, we solve the mystery for the continuous retention of high ferroelectricity in an ultrathin hafnium zirconium oxide (HZO) film (∼2 nm) by unveiling the evolution of microstructures and crystallographic orientations using a combination of state-of-the-art structural analysis techniques beyond analytical limits and theoretical approaches. We demonstrate that the enhancement of ferroelectricity in ultrathin HZO films originates from textured grains with a preferred orientation along an unusual out-of-plane direction of (112). In principle, (112)-oriented grains can exhibit 62% greater net polarization than the randomly oriented grains observed in thicker samples (>4 nm). Our first-principles calculations prove that the hydroxyl adsorption during the deposition process can significantly reduce the surface energy of (112)-oriented films, thereby stabilizing the high-index facet of (112). This work provides new insights into the ultimate scaling of HfO2-based ferroelectrics, which may facilitate the design of future extremely small-scale logic and memory devices.

In this work, we report sub-ns polarization switching in highly scaled 25 nm ferroelectric (FE) FinFET with Hf 0.5 Zr 0.5 O 2 (HZO) ferroelectric (FE)/SiO 2 dielectric (DE) gate stack for high performance CPU application for the first time. Observed limited endurance was attributed to the increase of trap density in the stack, which was quantitatively analyzed upon program/erase cycles by various methods including newly adopted low-frequency noise (LFN) characteristics for resolving spatial and energetic distribution of traps. In particular, we identified three different types of traps at FE/DE interface (D it_2 ) and SiO 2 /Si channel interface (D it_1 ) as well as in the bulk oxide (N ot ) of the HZO/SiO 2 gate stack of FE FinFETs. In addition, with the developed trap analysis, we investigated radiation-induced degradation of HZO/SiO 2 gate stack for application under harsh environments. Highly scaled and high performance FE FinFETs with enhanced endurance would provide a viable solution for future platform of low-power computing.

Each atomic layer in van der Waals heterostructures possesses a distinct electronic band structure that can be manipulated for unique device operations. In the precise device architecture, the subtle but critical band splits by the giant Stark effect between atomic layers, varied by the momentum of electrons and external electric fields in device operation, has not yet been demonstrated or applied to design original devices with the full potential of atomically thin materials. Here, resonant tunneling spectroscopy based on the negligible quantum capacitance of 2D semiconductors in resonant tunneling transistors is reported. The bandgaps and sub-band structures of various channel materials could be demonstrated by the new conceptual spectroscopy at the device scale without debatable quasiparticle effects. Moreover, the band splits by the giant Stark effect in the channel materials could be probed, overcoming the limitations of conventional optical, photoemission, and tunneling spectroscopy. The resonant tunneling spectroscopy reveals essential and practical information for novel device applications.

We present a novel method for fabricating large-area field-effect transistors (FETs) based on densely packed multichannel graphene nanoribbon (GNR) arrays using advanced direct self-assembly (DSA) nanolithography. The design of our strategy focused on the efficient integration of the FET channel and using fab-compatible processes such as thermal annealing and chemical vapor deposition. We achieved linearly stacked DSA nanopattern arrays with sub-10 nm half-pitch critical dimensions (CD) by controlling the thickness of topographic Au confinement patterns. Excellent roughness values (∼10% of CD) were obtained, demonstrating the feasibility of integrating sub-10 nm GNRs into commercial semiconductor processes. Based on this facile process, FETs with such densely packed multichannel GNR arrays were successfully fabricated on 6 in. silicon wafers. With these high-quality GNR arrays, we achieved FETs showing the highest performance reported to date (an on-to-off ratio larger than 10(2)) for similar devices produced using conventional photolithography and block-copolymer lithography.

Recent discovery of ferroelectricity from non-centrosymmetric orthorhombic phase (Pca21) of Hf/Zr oxides [1] has brought enormous research interests and activities because the material compatibility with CMOS process and its scalability to a few nm thickness, which have been critical issues for introducing perovskites ferroelectric (FE) materials in nanoscale devices. Physical concept of “negative capacitance” in FE materials when stacked with dielectrics (DE) has been proposed to enhance the total capacitance larger than that of DE only [2,3] and has been demonstrated in DE-FE stacks such as Al2O3/Hf0.5Zr0.5O2 or Ta2O5/Hf0.5Zr0.5O2 via transient measurement [4,5]. However, stacks with amorphous Al2O3 DE layer having relatively low dielectric constant were vulnerable to irreversible charge injection from electrodes into the DE-FE interface and thus hysteresis-free operation of the capacitor was only limited to short pulse condition below 1μs. Also Ta2O5 DE layer is often found to be defective and the film easily becomes leaky with repeated cycles. Here we propose novel DE-FE stack based on all crystallized Hf/Zr oxides where polymorphic Hf/Zr oxides have three dominant phases, monoclinic (P21/c), orthorhombic (Pca21), and tetragonal (P42/nmc) and by varying parameters such as Zr composition and thickness in initial amorphous film, the oxides can be crystallized in phase-selective way. We employ the tetragonal phase of Hf/Zr oxide for DE layer which possesses high-k value above 30 and wide bandgap about 5.4 eV ensuring low leakage current and further enabling thickness scaling. All crystallized DE-FE stacks were fabricated on bottom electrodes via atomic layer deposition of Hf/Zr oxides with compositional variation and subsequent metal deposition and post-metallization-annealing. Electrical data from capacitance vs. voltage and polarization vs. voltage measurements manifests an intermediate characteristic between ferroelectric and anti-ferroelectric ones due to multi-phase layers. Pulsed voltage measurements and structural analyses with XRD and selective area electron diffraction will be presented to assess the proposed stack for devices with enhanced capacitance. References [1] T. S. Boske, J.Muller, D. Brauhaus, U. Schroder, and U. Bottger, Applied Physics Letters 99, 102903 (2011). [2] S. Salahuddin, and S. Datta, Nano Letters 8, 2, 405-410 (2008). [3] H. W. Park, J. Roh, Y. B. Lee, and C. S. Hwang, Advanced Materials 31, 32, 1805266 (2019). [4] K. D. Kim, Y. J. Kim, M. H. Park, H. W. Park, Y. J. Kwon, Y. B. Lee, H. J. Kim, T. Moon, Y. H. Lee, S. D. Hyun, B. S. Kim, and C. S. Hwang, Advanced Functional Materials 29, 17, 1808228 (2019). [5] M. Hoffmann, F. P. G. Fengler, M. Herzig, T. Mittmann, B. Max, U. Schroeder, R. Negrea, P. Lucian, S. Slesazeck, and T. Micholajick, Nature 565, 464-467 (2019). Figure 1

A reliable and rapid manufacturing process of molybdenum disulfide (MoS2 ) with atomic-scale thicknesses remains a fundamental challenge toward its successful incorporation into high-performance nanoelectronics. It is imperative to achieve rapid and scalable production of MoS2 exhibiting high carrier mobility and excellent on/off current ratios simultaneously. Herein, inhibitor-utilizing atomic layer deposition (iALD) is presented as a novel method to meet these requirements at the wafer scale. The kinetics of the chemisorption of Mo precursors in iALD is governed by the reaction energy and the steric hindrance of inhibitor molecules. By optimizing the inhibition of Mo precursor absorption, the nucleation on the substrate in the initial stage can be spontaneously tailored to produce iALD-MoS2 thin films with a significantly increased grain size and surface coverage (>620%). Moreover, highly crystalline iALD-MoS2 thin films, with thicknesses of only a few layers, excellent room temperature mobility (13.9 cm2 V-1 s-1 ), and on/off ratios (>108 ), employed as the channel material in field effect transistors on 6″ wafers, are successfully prepared.

Organic semiconducting polymer thin-films of 3-hexylthiophene, 3-octylthiophene, 3-decylthiophene, containing highly oriented crystal were fabricated by gas-phase polymerization using the CVD technique. These poly(3-alkylthiophene) films had a crystallinity up to 80%, and possessed a Hall mobility up to 10 cm2/Vs. The degree of crystalinity and the mobility values increased as the alkyl chain length increased. The crystal structure of the polymers was composed of stacked layers constructed by a side-by-side arrangement of alkyl chains and in-plane pi-pi stacking. These thin films are capable of being applied to organic electronics as the active materials used in thin-film transistors and organic photovoltaic cells.

A spin injection is achieved in a direct-contact cobalt$\ensuremath{-}$single-layer graphene nonlocal spin-valve system, overlaid with a top gate. The spin signal is retained even in bipolar configurations of graphene. Hanle spin-precession analysis demonstrates that proportionality between spin and momentum relaxation times, which supports the Elliot-Yafet-type spin relaxation, holds consistently only when the carrier-density dependence of the density of states is taken into account. The corresponding strong spin-orbit coupling ($\ensuremath{\sim}$10 meV) suggests that covalently bonded adsorbates, rather than charged impurities, govern the spin relaxation in diffusive graphene.

Improved conductive poly(3,4-ethylenedioxy thiophene) (PEDOT) electrode films were made through hybridization with charged gold nanoparticles. The conductivity of these hybrid films increased more than seven times than the value for the PEDOT alone. The optimized films show a sheet resistance value down to 85 ohm·sq−1 at 85% transparency when PEDOT was hybridized with gold particles of 12 nm diameter, and the organic light-emitting diode devices deposited on these electrodes show a performance equivalent to that of devices based on a conventional indium tin oxide electrode.

We investigate transport through ionic liquid gated field effect transistors (FETs) based on exfoliated crystals of semiconducting WS$_2$. Upon electron accumulation, at surface densities close to -or just larger than- 10$^{14}$ cm$^{-2}$, transport exhibits metallic behavior, with the surface resistivity decreasing pronouncedly upon cooling. A detailed characterization as a function of temperature and magnetic field clearly shows the occurrence of a gate-induced superconducting transition below a critical temperature $T_c \approx 4$ K, a finding that represents the first demonstration of superconductivity in tungsten-based semiconducting transition metal dichalcogenides. We investigate the nature of superconductivity and find significant inhomogeneity, originating from the local detaching of the frozen ionic liquid from the WS$_2$ surface. Despite the inhomogeneity, we find that in all cases where a fully developed zero resistance state is observed, different properties of the devices exhibit a behavior characteristic of a Berezinskii-Kosterlitz-Thouless transition, as it could be expected in view of the two-dimensional nature of the electrostatically accumulated electron system., 18 pages, 4 figures; Nano Letters (2015)