Highly sensitive and system integrable gas sensors play a significant role in industry and daily life, and MoS2 has emerged as one of the most promising two-dimensional nanomaterials for gas sensor technology. In this study, we demonstrate a scalable and monolithically integrated active-matrix gas sensor array based on large-area bilayer MoS2 films synthesized via two-successive steps: radio-frequency magnetron sputtering and thermal sulfurization. The fabricated thin-film transistors exhibit consistent electrical performance over a few centimeters area and resulting gas sensors detect NO2 with ultra-high sensitivity across a wide detection range, from 1 to 256 ppm. This is due to the abundant grain boundaries of the sputtered MoS2 channel, which perform as active sites for absorption of NO2 gas molecules. The demonstrated active-matrix gas sensor arrays display good switching capabilities and are anticipated to be readily integrated with additional circuitry for different gas sensing and monitoring applications.

The wireless communication and power transmission environment varies widely depending on time and place, and thus reconfigurable devices and circuits are in high demand due to the significant increase in complexity of the power stage and chip size required for current non‐reconfigurable device‐based systems. Reconfigurable radio‐frequency (RF) devices, however, are difficult to demonstrate due to the lack of suitable materials with desirable material properties that can also be integrated with conventional high‐power materials. Here, reconfigurable gallium nitride (GaN) high‐electron mobility transistors (HEMTs) that are heterointegrated with 2D van der Waals‐interfaced α‐In2Se3 semiconductor are demonstrated. The switchable ferroelectric polarization of the 2D α‐In2Se3 layer is exploited to control the 2D electron gas charge density in the GaN channel. Further, a native interfacial indium oxide layer between the gate dielectric and α‐In2Se3 functions as a charge trapping layer, boosting the effect of the ferroelectric α‐In2Se3 layer. The fabricated HEMTs exhibit the sharpest subthreshold slope with tunable threshold voltage, transconductance, and maximum frequency in the range of several GHz under the application of a fast pulsed gate‐voltage signal without sacrificing the performance. The results clearly demonstrate the immense potential of ferroelectric‐based mixed‐dimensional heterostructures as a viable pathway toward simple and compact reconfigurable RF systems.

No abstract

Indium selenide (α‐In2Se3), which is a recently emerging ferroelectric semiconductor, can solve a major hindrance to applications of an ultra‐wide bandgap beta‐gallium oxide (β‐Ga2O3) semiconductor. Here, ferroelectric α‐In2Se3 wrapped‐gate β‐Ga2O3 field‐effect transistors (FETs) for dynamic threshold voltage (VTH) control is demonstrated. The dry‐transferred α‐In2Se3 layer is wrapped around β‐Ga2O3 channel, which allows efficient electrostatic gate modulation. Thus, the ferroelectricity of α‐In2Se3 and a thin native oxide interlayer formed at the interface between β‐Ga2O3 and α‐In2Se3 can provide effective VTH control. Applying a positive voltage pulse to the gate electrode induces positive VTH shift; hence, the device can be even changed from depletion to enhancement (E‐) mode. The E‐mode β‐Ga2O3 FET exhibits steep‐subthreshold slope with a negligible hysteresis. The VTH of E‐mode can be further modulated by applying back‐gate bias, and electrical performance can be enhanced via dual‐gate operation. The approach demonstrates an energy efficient β‐Ga2O3‐based switching device architecture integrated with ferroelectric van der Waals 2D materials.

Germanium (Ge) has gained great attention not only for future nanoelectronics but for back-end of line (BEOL) compatible monolithic three-dimensional (M3D) integration recently. For high performance and low power devices, various high-k oxide/Ge gate stacks including ferroelectric oxides have been investigated. Here, we demonstrate atomic layer deposited (ALD) polycrystalline (p-) HfO2/GeOX/Ge stack with an amorphous (a-) HfO2 capping layer. The consecutively deposited a-HfO2 capping layer improves hysteretic behaviors (ΔV) and interface state density (Dit) of the p-HfO2/GeOX/Ge stack. Furthermore, leakage current density (J) is significantly reduced (x 100) by passivating leakage paths through grain boundaries of p-HfO2. The proposed HfO2 layer with the graded crystallinity suggests possible high-k/Ge stacks for further optimized Ge MOS structures.

Significant effort for demonstrating a gallium nitride (GaN)-based ferroelectric metal–oxide–semiconductor (MOS)-high-electron-mobility transistor (HEMT) for reconfigurable operation via simple pulse operation has been hindered by the lack of suitable materials, gate structures, and intrinsic depolarization effects. In this study, we have demonstrated artificial synapses using a GaN-based MOS-HEMT integrated with an α-In2Se3 ferroelectric semiconductor. The van der Waals heterostructure of GaN/α-In2Se3 provides a potential to achieve high-frequency operation driven by a ferroelectrically coupled two-dimensional electron gas (2DEG). Moreover, the semiconducting α-In2Se3 features a steep subthreshold slope with a high ON/OFF ratio (∼1010). The self-aligned α-In2Se3 layer with the gate electrode suppresses the in-plane polarization while promoting the out-of-plane (OOP) polarization of α-In2Se3, resulting in a steep subthreshold slope (10 mV/dec) and creating a large hysteresis (2 V). Furthermore, based on the short-term plasticity (STP) characteristics of the fabricated ferroelectric HEMT, we demonstrated reservoir computing (RC) for image classification. We believe that the ferroelectric GaN/α-In2Se3 HEMT can provide a viable pathway toward ultrafast neuromorphic computing.

No abstract

No abstract