Two-Mode MoS2 Filament Transistor with Extremely Low Subthreshold Swing and Record High On/Off Ratio

Ultralow-Power Circuit and Sensing Applications Based on Subthermionic Threshold Switching Transistors

The most recent breakthrough in state-of-the-art electronics and optoelectronics involves the adoption of steep-slope field-effect transistors (FETs), promoting sub-60 mV/dec subthreshold swing (SS) at ambient temperature, effectively overcoming "Boltzmann limit" to minimize power consumption. Here, a series integration of nanoscale copper-based resistive-filamentary threshold switch (TS) with the IGZO channel-based FET is used to develop a TS-FET, in which the turn-on characteristics exhibit an abrupt transition over five decades, with an extremely low SS of 7 mV/dec, a high on/off ratio (>109), and ultralow leakage current (40-fold decrease), ensuring excellent repeatability and device yield. Unlike previous device-centric studies, this work highlights potential circuit applications (logic-inverter, pulse-sensor amplification, and photodetector) based on TS-FET. The sharp transition behavior of TS-FET enables the establishment of logic inverters with a high voltage gain of ≈800, with a circuit-level demonstration achieving a bias-independent record-high intrinsic gain (>1000). A wearable pulse sensor integrated with an amplifier circuit ensured the precise amplification of electrophysical signals by 450 times. In addition, the application of a TS-FET-based photodetector features high responsivity (1.08 × 104 mA/W) and detectivity (1.03 × 1020 Jones). The low-power strategy of TS-FETs is promising for the development of energy-efficient integrated circuits alongside sensor-interconnected biomedical applications in wearable technology.

Evaluation of Cellulose–MXene Composite Hydrogel Based Bio-Resistive Random Access Memory Material as Mimics for Biological Synapses

We report a memory device based on organic-inorganic hybrid cellulose-Ti₃C₂T_X MXene composite hydrogel (CMCH) as a switching layer sandwiched between Ag top and FTO bottom electrodes. The device (Ag/CMCH/FTO) was fabricated by a simple, solution-processed route and exhibits reliable and reproducible bipolar resistive switching. Multilevel switching behavior was observed at low operating voltages (±0.5 to ±1 V). Furthermore, the capacitive-coupled memristive characteristics of the device were corroborated with electrochemical impedance spectroscopy and this affirmed the filamentary conduction switching mechanism (LRS-HRS). The synaptic functions of the CMCH-based memory device were evaluated, wherein potentiation/depression properties over 8 × 10³ electric pulses were observed. The device also exhibited spike time-dependent plasticity-based symmetric Hebbian learning rule of a biological synapse. This hybrid hydrogel is expected to be a potential switching material for low-cost, sustainable, and biocompatible memory storage devices and artificial synaptic applications.

Improved Performance of NbOx Resistive Switching Memory by In-Situ N Doping

Valence change memory (VCM) attracts numerous attention in memory applications, due to its high stability and low energy consumption. However, owing to the low on/off ratio of VCM, increasing the difficulty of information identification hinders the development of memory applications. We prepared N-doped NbO_x:N films (thickness = approximately 15 nm) by pulsed laser deposition at 200 °C. N-doping significantly improved the on/off ratio, retention time, and stability of the Pt/NbO_x:N/Pt devices, thus improving the stability of data storage. The Pt/NbO_x:N/Pt devices also achieved lower and centralized switching voltage distribution. The improved performance was mainly attributed to the formation of oxygen vacancy (V_O) + 2N clusters, which greatly reduced the ionic conductivity and total energy of the system, thus increasing the on/off ratio and stability. Moreover, because of the presence of Vo + 2N clusters, the conductive filaments grew in more localized directions, which led to a concentrated distribution of SET and RESET voltages. Thus, in situ N-doping is a novel and effective approach to optimize device performances for better information storage and logic circuit applications.

MoS2transistors gated by ferroelectric HfZrO2with MoS2/mica heterojunction interface

Two-dimensional (2D) molybdenum disulfide (MoS₂) field-effect transistor (FET) gated by negative capacitance (NC) is a promising architecture to overcome the thermionic limit and thus reduce device consumption. Here, top-gated MoS₂NCFETs have been prepared by transferring a mica flake on MoS₂channel to form a van der Waals heterojunction interface, together with a ferroelectric HfZrO₂(HZO) deposited on mica. Stable NC effects are demonstrated for MoS₂NCFETs. The MoS₂NCFETs integrated with mica/HZO gate stack provide competitive electrical characteristics when they are applied with a gate voltage sweep-width in the range of 1-3 V and a sweep-rate from 0.01 to 0.2 V s^-1, including steep-slope of sub 60 mV dec^-1in four orders of magnitude of drain current, on/off current ratio over 10⁶, and small hysteresis-width less than 50 mV. Outstanding performance should be ascribed to damage-free properties of mica/MoS₂van der Waals interface and capacitance matching between the HZO ferroelectric and mica dielectric. The results confirm the promising nature of mica/HZO gate stack and potential applications for future electronics.

Metal chalcogenides for neuromorphic computing: emerging materials and mechanisms

The approaching end of Moore's law scaling has significantly accelerated multiple fields of research including neuromorphic-, quantum-, and photonic computing, each of which possesses unique benefits unobtained through conventional binary computers. One of the most compelling arguments for neuromorphic computing systems is power consumption, noting that computations made in the human brain are approximately 10⁶times more efficient than conventional CMOS logic. This review article focuses on the materials science and physical mechanisms found in metal chalcogenides that are currently being explored for use in neuromorphic applications. We begin by reviewing the key biological signal generation and transduction mechanisms within neuronal components of mammalian brains and subsequently compare with observed experimental measurements in chalcogenides. With robustness and energy efficiency in mind, we will focus on short-range mechanisms such as structural phase changes and correlated electron systems that can be driven by low-energy stimuli, such as temperature or electric field. We aim to highlight fundamental materials research and existing gaps that need to be overcome to enable further integration or advancement of metal chalcogenides for neuromorphic systems.

Atomic threshold-switching enabled MoS2 transistors towards ultralow-power electronics

Power dissipation is a fundamental issue for future chip-based electronics. As promising channel materials, two-dimensional semiconductors show excellent capabilities of scaling dimensions and reducing off-state currents. However, field-effect transistors based on two-dimensional materials are still confronted with the fundamental thermionic limitation of the subthreshold swing of 60 mV decade^-1 at room temperature. Here, we present an atomic threshold-switching field-effect transistor constructed by integrating a metal filamentary threshold switch with a two-dimensional MoS₂ channel, and obtain abrupt steepness in the turn-on characteristics and 4.5 mV decade^-1 subthreshold swing (over five decades). This is achieved by using the negative differential resistance effect from the threshold switch to induce an internal voltage amplification across the MoS₂ channel. Notably, in such devices, the simultaneous achievement of efficient electrostatics, very small sub-thermionic subthreshold swings, and ultralow leakage currents, would be highly desirable for next-generation energy-efficient integrated circuits and ultralow-power applications.

A Horizontal-Gate Monolayer MoS2 Transistor Based on Image Force Barrier Reduction

Transition metal dichalcogenides (TMDCs) have received wide attention as a new generation of semiconductor materials. However, there are still many problems to be solved, such as low carrier mobility, contact characteristics between metal and two-dimensional materials, and complicated fabrication processes. In order to overcome these problems, a large amount of research has been carried out so that the performance of the device has been greatly improved. However, most of these studies are based on complicated fabrication processes which are not conducive to the improvement of integration. In view of this problem, a horizontal-gate monolayer MoS₂ transistor based on image force barrier reduction is proposed, in which the gate is in the same plane as the source and drain and comparable to back-gated transistors on-off ratios up to 1 × 10⁴ have been obtained. Subsequently, by combining the Y-Function method (YFM) and the proposed diode equivalent model, it is verified that Schottky barrier height reduction is the main reason giving rise to the observed source-drain current variations. The proposed structure of the device not only provides a new idea for the high integration of two-dimensional devices, but also provides some help for the study of contact characteristics between two-dimensional materials and metals.