Atomic switches, also known as conductive bridging random access memory devices, are resistive-switching devices that utilize the electrochemical reactions within a solid electrolyte between metal electrodes, and are considered essential components of future information storage and logic building blocks. In spite of their advantages as next generation switching components such as high density, large scalability, and low power consumption, the large deviations in their electrical properties and the instability of their switching behaviors hinder their application in information processing systems. Here, we report the fabrication of a uniform, low-power atomic switch with a bi-layer structure consisting of TaO as the main switching layer (SL) and a relatively oxygen-deficient TaO as an oxygen vacancy control layer (VCL). The depth profiles of the filaments in the bi-layer device were obtained by performing conductive atomic force microscopy to assess the improvements in uniformity, reliability, and electrical performance that result from the insertion of the VCL. The coefficient of variation of the high resistance state of the bi-layer device was found to be drastically reduced from 60.92% to 2.77% in the cycle-to-cycle measurements and from 82.73% to 4.85% in the device-to-device measurements when compared with the values obtained for a single-layer device. The bi-layer device also exhibits a forming-free low operation voltage of ∼0.4 V, a high on/off ratio of ∼10, and high reliability with 10 years data retention at 85 °C.

Recently, for overcoming the fundamental limits of conventional silicon technology, multivalued logic (MVL) circuits based on two-dimensional (2D) materials have received significant attention for reducing the power consumption and the complexity of integrated circuits. Compared with the conventional silicon complementary metal oxide semiconductor technology, new functional heterostructures comprising 2D materials can be readily implemented, owing to their unique inherent electrical properties. Furthermore, their process integration does not pose issues of lattice mismatch at junction interfaces. This facilitates the realization of new functional logic gate circuit configurations. However, the reported three-valued NOT gates (ternary inverters) based on 2D materials require stringent operating conditions and complex fabrication processes to obtain three distinct logic states. Herein, a general structure of MVL devices based on a simple series connection of 2D materials with partial surface functionalization is demonstrated. By arranging three 2D materials exhibiting p-type, ambipolar, and n-type conductivities, ternary inverter circuits can be established based on the complementary driving between 2D heterotransistors. This ternary inverter circuit can be further improved for quaternary inverter circuits by controlling the charge neutral point of partial ambipolar 2D materials using surface functionalization, which is an effective and nondestructive doping method for 2D materials.

The Fermi-Dirac distribution of carriers and the drift-diffusion mode of transport represent two fundamental barriers towards the reduction of the subthreshold slope (SS) and the optimization of the energy consumption of field-effect transistors. In this study, we report the realization of steep-slope impact ionization field-effect transistors (I2FETs) based on a gate-controlled homogeneous WSe2 lateral junction. The devices showed average SS down to 2.73 mV/dec over three decades of source-drain current and an on/off ratio of ~106 at room temperature and low bias voltages (<1 V). We determined that the lucky-drift mechanism of carriers is valid in WSe2, allowing our I2FETs to have high impact ionization coefficients and low SS at room temperature. Moreover, we fabricated a logic inverter based on a WSe2 I2FET and a MoS2 FET, exhibiting an inverter gain of 73 and almost ideal noise margin for high- and low-logic states. Our results provide a promising approach for developing functional devices as front runners for energy-efficient electronic device technology.

No abstract

High‐sensitivity broad‐spectrum photodetectors with detection capabilities ranging from ultraviolet to infrared have attracted significant attention for their application as photodetectors. They can be used as a receiver for all applications in optical communication for covering a wide spectral range with a single photodetector, which can significantly lower the overall system cost. In this study, by constructing an avalanche photodetector (APD) fabricated with 2D WSe2, a high photoresponsivity of over 107 A W−1 for a broad spectrum of 405–1310 nm is achieved under an electric field higher than the critical field for the avalanche multiplication of 35 kV cm−1, overcoming the limitation of the detectable wavelength induced by the energy bandgap of the material. The benchmark in terms of the photocurrent‐to‐dark current ratio and responsivity over a wide wavelength range demonstrates that the fabricated WSe2 APD outperforms the reported 2D layered material‐based APDs and reported WSe2 photodetectors. The obtained results can be attributed to the high‐gain mechanism via avalanche multiplication and phonon‐assisted photogeneration in WSe2, enabling efficient photodetection beyond sub‐bandgap wavelengths. This result provides a promising general approach for developing a single photodetector that can cover a broad spectral range with a high sensitivity for future optical communication.