Ultraviolet-Assisted Low-Thermal-Budget-Driven α-InGaZnO Thin Films for High-Performance Transistors and Logic Circuits

Low-Frequency Noise Related to the Scattering Effect in p-Type Copper(I) Oxide Thin-Film Transistors

In this study, we investigate the origins of low-frequency noise (LFN) and 1/f noise in Cu2O thin-film transistors (TFTs). The static direct current (DC) I-V characterization demonstrates that the channel resistance (Rch) contributes significantly to mobility degradation in the TFTs, with channel thickness (tch) controlled through the plasma-enhanced atomic layer deposition (PEALD) process. The 1/f noise followed the Hooge mobility fluctuation (HMF) model, and it was observed that both Coulomb and phonon scattering within the channel, which increased with a decrease in tch, contributed simultaneously. Increased Rch contributed more significantly to the 1/f noise than to the contact resistance (RC), as evidenced by the RC configuration of the measurements, which also revealed that RC depends upon tch. This study demonstrates that tch is a major noise source in Cu2O TFTs and presents guidelines for the development of Cu2O TFTs and potential high-mobility p-type oxide semiconductors.

High-Performance Tin Oxide Thin-Film Transistors Realized by Codoping and Their Application in Logic Circuits

Tin oxide is a promising channel material, offering the advantages of being low-cost and environmentally friendly and having a wide band gap. However, despite the high electron mobility of SnO2 in bulk, the corresponding thin-film transistors (TFTs) generally exhibit moderate performance, hindering their widespread application. Herein, we proposed a codoping strategy to improve both the electrical property and the stability of SnO2 TFTs. A comparative analysis between doped and undoped SnO2 was conducted. It is observed that taking advantage of the difference in ionic radii between two dopants (indium and gallium) and the tin ions in the host lattice can effectively reduce impurity-induced strain. Additionally, we investigated the effect of codoping content on SnO2 TFTs. The optimal codoped SnO2 (TIGO) TFTs demonstrate high performance, featuring a field-effect mobility of 15.9 cm2/V·s, a threshold voltage of 0.2 V, a subthreshold swing of 0.5 V/decade, and an on-to-off current ratio of 2.2 × 107. Furthermore, the devices show high stability under both positive and negative bias stress conditions with a small threshold voltage shift of 1.8 and -1.2 V, respectively. Utilizing the TIGO TFTs, we successfully constructed a resistor-loaded unipolar inverter with a high gain of 10.76. This study highlights the potential of codoped SnO2 TFTs for advanced applications in electronic devices.

Dependence of a Hydrogen Buffer Layer on the Properties of Top-Gate IGZO TFT

In this paper, the effect of a buffer layer created using different hydrogen-containing ratios of reactive gas on the electrical properties of a top-gate In-Ga-Zn-O thin-film transistor was thoroughly investigated. The interface roughness between the buffer layer and active layer was characterized using atomic force microscopy and X-ray reflection. The results obtained using Fourier transform infrared spectroscopy show that the hydrogen content of the buffer layer increases with the increase in the hydrogen content of the reaction gas. With the increase in the hydrogen-containing materials in the reactive gas, field effect mobility and negative bias illumination stress stability improve nearly twofold. The reasons for these results are explained using technical computer-aided design simulations.

Gate-bias stability of triple-gated feedback field-effect transistors with silicon nanosheet channels

In this study, we investigate the gate-bias stability of triple-gated feedback field-effect transistors (FBFETs) with Si nanosheet channels. The subthreshold swing (SS) of FBFETs increases from 0.3 mV dec-1to 60 and 80 mV dec-1inp- andn-channel modes, respectively, when a positive bias stress (PBS) is applied for 1000 s. In contrast, the SS value does not change even after a negative bias stress (NBS) is applied for 1000 s. The difference in the switching characteristics under PBS and NBS is attributed to the ability of the interface traps to readily gain electrons from the inversion layer. The switching characteristics deteriorated by PBS are completely recovered after annealing at 300 °C for 10 min, and the characteristics remain stable even after PBS is applied again for 1000 s.

Oxide Semiconductor Heterojunction Transistor with Negative Differential Transconductance for Multivalued Logic Circuits

Multivalued logic (MVL) technology is a promising solution for improving data density and reducing power consumption in comparison to complementary metal-oxide-semiconductor (CMOS) technology. Currently, heterojunction transistors (TRs) with negative differential transconductance (NDT) characteristics, which play an important role in the function of MVL circuits, adopt organic or 2D semiconductors as active layers, but it is still difficult to apply conventional CMOS processes. Herein, we demonstrate an oxide semiconductor (OS) heterojunction TR with NDT characteristics composed of p-type copper(I) oxide (Cu2O) and n-type indium gallium zinc oxide (IGZO) using the conventional CMOS manufacturing processes. The electrical characteristics of the fabricated device exhibit a high Ion/Ioff ratio (∼3 × 103), wide NDT ranges (∼29 V), and high peak-to-valley current ratios (PVCR ≈ 25). The electrical properties of 15 devices were measured, confirming uniform performance in the PVCR, NDT range, and Ion/Ioff ratio. We analyze the device operation by varying the source/drain (S/D) position and changing the device geometry and the thickness of the Cu2O layer. Additionally, we demonstrate heterojunction ambipolar TR to elucidate the transport mechanism of NDT devices at a high gate voltage (VGS). To confirm the feasibility of the MVL circuit, we present a ternary inverter with three clearly expressed logic states that have a long intermediate state and greater margin of error induced by wide NDT regions and high PVCR.

Wearable Nano-Based Gas Sensors for Environmental Monitoring and Encountered Challenges in Optimization

With a rising emphasis on public safety and quality of life, there is an urgent need to ensure optimal air quality, both indoors and outdoors. Detecting toxic gaseous compounds plays a pivotal role in shaping our sustainable future. This review aims to elucidate the advancements in smart wearable (nano)sensors for monitoring harmful gaseous pollutants, such as ammonia (NH3), nitric oxide (NO), nitrous oxide (N2O), nitrogen dioxide (NO2), carbon monoxide (CO), carbon dioxide (CO2), hydrogen sulfide (H2S), sulfur dioxide (SO2), ozone (O3), hydrocarbons (CxHy), and hydrogen fluoride (HF). Differentiating this review from its predecessors, we shed light on the challenges faced in enhancing sensor performance and offer a deep dive into the evolution of sensing materials, wearable substrates, electrodes, and types of sensors. Noteworthy materials for robust detection systems encompass 2D nanostructures, carbon nanomaterials, conducting polymers, nanohybrids, and metal oxide semiconductors. A dedicated section dissects the significance of circuit integration, miniaturization, real-time sensing, repeatability, reusability, power efficiency, gas-sensitive material deposition, selectivity, sensitivity, stability, and response/recovery time, pinpointing gaps in the current knowledge and offering avenues for further research. To conclude, we provide insights and suggestions for the prospective trajectory of smart wearable nanosensors in addressing the extant challenges.

Integration of microbattery with thin-film electronics for constructing an integrated transparent microsystem based on InGaZnO

A full integration of miniaturized transparent energy device (lithium-ion battery), electronic device (thin-film transistor) and sensing device (photodetector) to form a monolithic integrated microsystem greatly enhances the functions of transparent electronics. Here, InGaZnO is explored to prepare the above devices and microsystem due to its multifunctional properties. A transparent lithium-ion battery with InGaZnO as anode (capacity~9.8 μAh cm-2) is proposed as the on-chip power source. Then, thin-film transistor with InGaZnO as channel (mobility~23.3 cm2 V-1 s-1) and photodetector with InGaZnO as photosensitive layer (responsivity~0.35 A W-1) are also prepared on the substrate for constructing an fully integrated transparent microsystem. Each device displays acceptable performance. Moreover, alternating-current signals can be successfully charged into the lithium-ion battery by using the thin-film transistor as the on-chip rectifier and also the photodetector works well by using the charged battery as the on-chip power, demonstrating collaborative capabilities of each device to achieve systematic functions.

Analyzing Acceptor-like State Distribution of Solution-Processed Indium-Zinc-Oxide Semiconductor Depending on the In Concentration

Understanding the density of state (DOS) distribution in solution-processed indium-zinc-oxide (IZO) thin-film transistors (TFTs) is crucial for addressing electrical instability. This paper presents quantitative calculations of the acceptor-like state distribution of solution-processed IZO TFTs using thermal energy analysis. To extract the acceptor-like state distribution, the electrical characteristics of IZO TFTs with various In molarity ratios were analyzed with respect to temperature. An Arrhenius plot was used to determine electrical parameters such as the activation energy, flat band energy, and flat band voltage. Two calculation methods, the simplified charge approximation and the Meyer-Neldel (MN) rule-based carrier-surface potential field-effect analysis, were proposed to estimate the acceptor-like state distribution. The simplified charge approximation established the modeling of acceptor-like states using the charge-voltage relationship. The MN rule-based field-effect analysis validated the DOS distribution through the carrier-surface potential relationship. In addition, this study introduces practical and effective approaches for determining the DOS distribution of solution-processed IZO semiconductors based on the In molarity ratio. The profiles of the acceptor-like state distribution provide insights into the electrical behavior depending on the doping concentration of the solution-processed IZO semiconductors.

High-Performance Thin-Film Transistor with Atomic Layer Deposition (ALD)-Derived Indium-Gallium Oxide Channel for Back-End-of-Line Compatible Transistor Applications: Cation Combinatorial Approach

In this paper, the feasibility of an indium-gallium oxide (In_2(1-x)Ga_2xO_y) film through combinatorial atomic layer deposition (ALD) as an alternative channel material for back-end-of-line (BEOL) compatible transistor applications is studied. The microstructure of random polycrystalline In₂O_y with a bixbyite structure was converted to the amorphous phase of In_2(1-x)Ga_2xO_y film under thermal annealing at 400 °C when the fraction of Ga is ≥29 at. %. In contrast, the enhancement in the orientation of the (222) face and subsequent grain size was observed for the In_1.60Ga_0.40O_y film with the intermediate Ga fraction of 20 at. %. The suitability as a channel layer was tested on the 10-nm-thick HfO₂ gate oxide where the natural length was designed to meet the requirement of short channel devices with a smaller gate length (<100 nm). The In_1.60Ga_0.40O_y thin-film transistors (TFTs) exhibited the high field-effect mobility (μ_FE) of 71.27 ± 0.98 cm²/(V s), low subthreshold gate swing (SS) of 74.4 mV/decade, threshold voltage (V_TH) of -0.3 V, and I_ON/OFF ratio of >10⁸, which would be applicable to the logic devices such as peripheral circuit of heterogeneous DRAM. The in-depth origin for this promising performance was discussed in detail, based on physical, optical, and chemical analysis.

Water-Processed Ultrathin Crystalline Indium–Boron–Oxide Channel for High-Performance Thin-Film Transistor Applications

Thin-film transistors (TFTs) made of solution-processable transparent metal oxide semiconductors show great potential for use in emerging large-scale optoelectronics. However, current solution-processed metal oxide TFTs still suffer from relatively poor device performance, hindering their further advancement. In this work, we create a novel ultrathin crystalline indium–boron–oxide (In-B-O) channel layer for high-performance TFTs. We show that high-quality ultrathin (~10 nm) crystalline In-B-O with an atomically smooth nature (RMS: ~0.15 nm) could be grown from an aqueous solution via facile one-step spin-coating. The impacts of B doping on the physical, chemical and electrical properties of the In₂O₃ film are systematically investigated. The results show that B has large metal–oxide bond dissociation energy and high Lewis acid strength, which can suppress oxygen vacancy-/hydroxyl-related defects and alleviate dopant-induced carrier scattering, resulting in electrical performance improvement. The optimized In-B-O (10% B) TFTs based on SiO₂/Si substrate demonstrate a mobility of ~8 cm²/(V s), an on/off current ratio of ~10⁶ and a subthreshold swing of 0.86 V/dec. Furthermore, by introducing the water-processed high-K ZrO₂ dielectric, the fully aqueous solution-grown In-B-O/ZrO₂ TFTs exhibit excellent device performance, with a mobility of ~11 cm²/(V s), an on/off current of ~10⁵, a subthreshold swing of 0.19 V/dec, a low operating voltage of 5 V and superior bias stress stability. Our research opens up new avenues for low-cost, large-area green oxide electronic devices with superior performance.