High Field-effect Mobility Research Articles

Enhanced electrical performance of InGaSnO thin-film transistors by designing a dual-active-layer structure

In this study, dual-active-layer InGaSnO (IGTO) thin-film transistors (TFTs) were designed, and their electrical properties were investigated. Consequently, compared with the single-layer IGTO (pure Ar) TFTs, the dual-layer IGTO TFTs exhibited improved electrical properties, including a high field-effect mobility of 25.1 cm2 V−1 s−1, a low threshold voltage of 0.8 V, a high on/off current ratio of 1 × 108, a small subthreshold slope of 300 mV/decade, and a low off current. Additionally, the dual-layer IGTO TFTs showed superior stability for small Vth shifts of −1.9 V and 1.8 V under gate bias stress test conditions. Band structure analysis indicated that a thin front layer of IGTO (pure Ar) can provide an appropriate carrier concentration (Ne) near the IGTO (pure Ar)/IGTO (Ar/O2) interface, whereas a thick layer of IGTO (Ar/O2) can control the channel conductance and threshold voltage of IGTO TFTs. Moreover, atomic force microscopy, X-ray photoelectron spectroscopy, and Hall effect measurement results showed that the surface roughness, oxygen vacancies, Ne, and total trap density of IGTO (Ar/O2) films and TFTs were reduced by increasing the oxygen flow rate. Over all, the high performance dual-active-layer IGTO TFTs provides insights that can contribute to developing a new generation of transparent oxide thin-film electronics.

Achieving High Field-Effect Mobility Exceeding 90 cm2/Vs in a-IGZTO Transistors With Excellent Reliability

Achieving High Field-Effect Mobility Exceeding 90 cm²/Vs in <i>a</i>-IGZTO Transistors With Excellent Reliability

Comparative Study on Indium Precursors for Plasma-Enhanced Atomic Layer Deposition of In2O3 and Application to High-Performance Field-Effect Transistors.

Indium oxide (In2O3) is a transparent wide-bandgap semiconductor suitable for use in the back-end-of-line-compatible channel layers of heterogeneous monolithic three-dimensional (M3D) devices. The structural, chemical, and electrical properties of In2O3 films deposited by plasma-enhanced atomic layer deposition (PEALD) were examined using two different liquid-based precursors: (3-(dimethylamino)propyl)-dimethyl indium (DADI) and (N,N-dimethylbutylamine)trimethylindium (DATI). DATI-derived In2O3 films had higher growth per cycle (GPC), superior crystallinity, and low defect density compared with DADI-derived In2O3 films. Density functional theory calculations revealed that the structure of DATI can exhibit less steric hindrance compared with that of DADI, explaining the superior physical and electrical properties of the DATI-derived In2O3 film. DATI-derived In2O3 field-effect transistors (FETs) exhibited unprecedented performance, showcasing a high field-effect mobility of 115.8 cm2/(V s), a threshold voltage of -0.12 V, and a low subthreshold gate swing value of <70 mV/decade. These results were achieved by employing a 10-nm-thick HfO2 gate dielectric layer with an effective oxide thickness of 3.9 nm. Both DADI and DATI-derived In2O3 FET devices exhibited remarkable stability under bias stress conditions due to a high-quality In2O3 channel layer, good gate dielectric/channel interface matching, and a suitable passivation layer. These findings underscore the potential of ALD In2O3 films as promising materials for upper-layer channels in the next generation of M3D devices.

High-Mobility and Bias-Stable Field-Effect Transistors Based on Lead-Free Formamidinium Tin Iodide Perovskites.

Electronic devices based on tin halide perovskites often exhibit a poor operational stability. Here, we report an additive engineering strategy to realize high-performance and stable field-effect transistors (FETs) based on 3D formamidinium tin iodide (FASnI3) films. By comparatively studying the modification effects of two additives, i.e., phenethylammonium iodide and 4-fluorophenylethylammonium iodide via combined experimental and theoretical investigations, we unambiguously point out the general effects of phenethylammonium (PEA) and its fluorinated derivative (FPEA) in enhancing crystallization of FASnI3 films and the unique role of fluorination in reducing structural defects, suppressing oxidation of Sn2+ and blocking oxygen and water involved defect reactions. The optimized FPEA-modified FASnI3 FETs reach a record high field-effect mobility of 15.1 cm2/(V·s) while showing negligible hysteresis. The devices exhibit less than 10% and 3% current variation during over 2 h continuous bias stressing and 4200-cycle switching test, respectively, representing the best stability achieved so far for all Sn-based FETs.

Atomically Thin Amorphous Indium-Oxide Semiconductor Film Developed Using a Solution Process for High-Performance Oxide Transistors.

High-performance oxide transistors have recently attracted significant attention for use in various electronic applications, such as displays, sensors, and back-end-of-line transistors. In this study, we demonstrate atomically thin indium-oxide (InOx) semiconductors using a solution process for high-performance thin-film transistors (TFTs). To achieve superior field-effect mobility and switching characteristics in TFTs, the bandgap and thickness of the InOx were tuned by controlling the InOx solution molarity. As a result, a high field-effect mobility and on/off-current ratio of 13.95 cm2 V-1 s-1 and 1.42 × 1010, respectively, were achieved using 3.12-nanometer-thick InOx. Our results showed that the charge transport of optimized InOx with a thickness of 3.12 nm is dominated by percolation conduction due to its low surface roughness and appropriate carrier concentration. Furthermore, the atomically thin InOx TFTs showed superior positive and negative gate bias stress stabilities, which are important in electronic applications. The proposed oxide TFTs could provide an effective means of the fabrication of scalable, high-throughput, and high-performance transistors for next-generation electronic applications.

Low-Temperature Solution-Processed HfZrO Gate Insulator for High-Performance of Flexible LaZnO Thin-Film Transistor.

Metal-oxide-semiconductor (MOS)-based thin-film transistors (TFTs) are gaining significant attention in the field of flexible electronics due to their desirable electrical properties, such as high field-effect mobility (μFE), lower IOFF, and excellent stability under bias stress. TFTs have widespread applications, such as printed electronics, flexible displays, smart cards, image sensors, virtual reality (VR) and augmented reality (AR), and the Internet of Things (IoT) devices. In this study, we approach using a low-temperature solution-processed hafnium zirconium oxide (HfZrOx) gate insulator (GI) to improve the performance of lanthanum zinc oxide (LaZnO) TFTs. For the optimization of HfZrO GI, HfZrO films were annealed at 200, 250, and 300 °C. The optimized HfZrO-250 °C GI-based LaZnO TFT shows the μFE of 19.06 cm2V-1s-1, threshold voltage (VTH) of 1.98 V, hysteresis voltage (VH) of 0 V, subthreshold swing (SS) of 256 mV/dec, and ION/IOFF of ~108. The flexible LaZnO TFT with HfZrO-250 °C GI exhibits negligible ΔVTH of 0.25 V under positive-bias-temperature stress (PBTS). The flexible hysteresis-free LaZnO TFTs with HfZrO-250 °C can be widely used for flexible electronics. These enhancements were attributed to the smooth surface morphology and reduced defect density achieved with the HfZrO gate insulator. Therefore, the HfZrO/LaZnO approach holds great promise for next-generation MOS TFTs for flexible electronics.

Electrical properties of a low-temperature fabricated Ge-based top-gate MOSFET structure with epitaxial ferromagnetic Heusler-alloy Schottky-tunnel source and drain

We show electrical properties of a Ge-based top-gate metal-oxide-semiconductor field-effect transistor (MOSFET) structure with epitaxial ferromagnetic Heusler alloy/Ge Schottky-tunnel contacts, fabricated with a low-temperature gate-stack process. For shaping the Ge-MOSFET with the ferromagnetic source and drain (S/D) contacts, we use a combination process of Ar+ ion milling and reactive ion etching (RIE). As a consequence of the formation of a gate stack (SiO2/GeO2) using a process temperature of 240 °C, we demonstrate inversion channel MOSFETs with a low gate-voltage operation (VG ∼5 V). Furthermore, we achieve a relatively high field-effect mobility (μFE) of ∼300 cm2/Vs compared to those in a Si-based back-gate spin-MOSFET reported previously [Phys. Rev. B 102, 035305 (2020).]. This study will open a way for developing a Ge-based top-gate spin-MOSFET on the Si platform.

The influence of annealing atmosphere on sputtered indium oxide thin-film transistors

Indium oxide (In2O3) thin films sputtered at room temperature were annealed under different atmospheres and examined for thin-film transistor (TFT) active channel applications. The annealing process was performed in a rapid thermal annealing system at 350 °C under O2, Ar, forming gas (FG, 96% N2/4% H2), and N2. It was found that the annealed In2O3 TFTs exhibited high field-effect mobility (μ FE > 40 cm2 V−1s−1), high on/off current ratio (I on/off∼ 108), and controlled threshold voltage (V TH) for the enhancement- and depletion-mode operations. Note that the annealing atmosphere has a significant effect on the electrical performance of the In2O3 TFTs by inducing changes in oxygen-related species, particularly oxygen vacancies (VO) and hydroxyl/carbonate species (O–H/C–O). For the O2-, Ar-, FG-, and N2-annealed TFTs, μ FE was in increasing order accompanied by a negative shift in V TH, which is a result attributed to the larger VO in the In2O3 thin films. Furthermore, the ΔV TH of the FG-, and N2-annealed TFTs in a positive bias stress test was greater than that of the O2-, Ar-annealed devices, attributing to their lower density of O–H/C–O groups in the In2O3 thin films. Our results suggest that the annealing atmosphere contributes to the internal modifications of the In2O3 structure and in turn altered the electrical characteristics of TFTs. These annealed In2O3 TFTs with high performance are promising candidates for realizing large-area, transparent, and high-resolution displays.

Effect of Single Spinel Phase Crystallization on Drain-Induced-Barrier-Lowering in Submicron Length IZTO Thin-Film Transistors

This study shows the effect of single spinel phase crystallization on drain-induced barrier lowering (DIBL) of indium-zinc-tin-oxide (IZTO) thin-film transistors (TFTs) with submicron channel length. The 0.9-μm-long amorphous IZTO (a-IZTO) TFT shows a poor DIBL of 318 mV/V. In contrast, a significant improvement in the DIBL is achieved in the single spinel phase IZTO (s-IZTO) TFT, which could be attributed to the suppression of lateral diffusion of oxygen vacancy (VO) and low VO defects through crystallization-induced enforcement of metal-oxygen bonds. Consequently, 0.9-μm-long s-IZTO TFT reveals a small DIBL of 92 mV/V as well as a high field-effect mobility of 90.1 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /Vs and a low subthreshold swing of 0.1 V/dec. In addition, reliability against external bias temperature stress is considerably improved through single-phase crystallization, leading to an insignificant threshold voltage shift of +0.4 (–0.4) V under positive (negative) bias stress with electric field of 2 (–2) MV/cm at 60 °C for 10,000 s, respectively, in the 0.9-μm-long s-IZTO TFT.

In-plane gate graphene transistor with epitaxially grown molybdenum disulfide passivation layers

We demonstrate in-plane gate transistors based on the molybdenum disulfide (MoS2)/graphene hetero-structure. The graphene works as channels while MoS2 functions as passivation layers. The weak hysteresis of the device suggests that the MoS2 layer can effectively passivate the graphene channel. The characteristics of devices with and without removal of MoS2 between electrodes and graphene are also compared. The device with direct electrode/graphene contact shows a reduced contact resistance, increased drain current, and enhanced field-effect mobility. The higher field-effect mobility than that obtained through Hall measurement indicates that more carriers are present in the channel, rendering it more conductive.

High field-effect mobility in oriented thin films of D-A type semiconducting polymers by engineering stable interfacial system

Conjugated polymers (CPs) have emerged as excellent organic semiconducting materials for flexible electronic applications. CPs exhibit a notably fast carrier transport along their main π-conjugated backbone followed by inter-chain hopping compelling the need to form large and ordered domains in thin films. Therefore, the formation of larger domains, along with their orientation, is critical in controlling the electrical properties of CP-based organic electronic devices. However, controlling the molecular ordering along with the formation of large aggregates is a challenge. In this work, the unidirectional floating film transfer method (UFTM) has been utilized to prepare oriented thin films of CPs, which is a highly facile, cost-effective and material utilization efficient technique. We have demonstrated that extent and direction of molecular orientation in the fabricated thin films can be tuned along with the higher degree of aggregation. The rheological aspects, especially viscosity, play a significant role in determining molecular ordering along with the formation of these large aggregates. Active control of viscosity to achieve a stable interfacial viscous system is paramount to achieving this, resulting in a very high mobility of 12.4 cm2V−1s−1.

The Discovery of a High-Mobility Two-Dimensional Bismuth Oxyselenide Semiconductor and Its Application in Nonvolatile Neuromorphic Devices.

The development of two-dimensional (2D) electronics is always accompanied by the discovery of 2D semiconductors with high mobility and specific crystal structures, which may bring revolutionary breakthrough on proof-of-concept devices and physics. Here, Bi3O2.5Se2, a 2D bismuth oxyselenide semiconductor with non-neutral layered crystal structure is discovered. Ultrathin Bi3O2.5Se2 films are readily synthesized by chemical vapor deposition, displaying tunable band gaps and high room-temperature field-effect mobility of >220 cm2 V-1 s-1. Moreover, the as-synthesized Bi3O2.5Se2 nanoplates were fabricated into top-gated transistors with a simple device configuration, whose carrier density can be reversibly regulated in the range of 1014 cm-2 just by a facile method of electrostatic doping at room temperature. These features enable it to be functionalized into nonvolatile synaptic transistors with ultralow operating energy consumption (∼0.5 fJ), high repeatability, low operating voltage (0.1 V), and long retention time. Our work extends the family of bismuth oxyselenide 2D semicondutors.

Hf-doped ZnO transistor with high bias stability and high field-effect mobility by modulation of oxygen vacancies and interfaces

ZnO-based thin film transistors (TFTs) with high bias stability are challenging due to the intrinsic defects and overhigh interface trap density. In this work, we fabricated Hf-doped ZnO films with different cycle ratio of Zn/Hf via atomic layer deposition and subsequent annealing treatment. The results show that the cycle ratio of Zn/Hf is optimized to be 10:1, and the corresponding atomic ratio is 2.24%. The threshold voltage and subthreshold swing of the devices are improved as the annealing temperature increases, owning to the decrease of the oxygen vacancies and interface trap density. Furthermore, we developed Hf-doped ZnO TFT with high bias stability by introducing HfO2 intermediate layer between the active layer and SiO2 dielectric layer, and the shift of threshold voltage is as low as -0.273 V, showing high bias stability. Also, the device has the high field-effective mobility of 52.4 cm2/Vs, low subthreshold swing of 0.68 V/dec and high Ion/Ioff of 3.6 × 108. The results indicate a promising fabrication method for high-performance ZnO-based TFTs, which may be applied in logic circuits, radio frequency identification and so on.

Direct C-H Arylation of Dithiophene-Tetrathiafulvalene: Tuneable Electronic Properties and 2D Self-Assembled Molecular Networks at the Solid/Liquid Interface.

Tetrathiafulvalene is among the best known building blocks in molecular electronics due to its outstanding electron-donating and redox properties. Among its derivatives, dithiophene-tetrathiafulvalene (DT-TTF) has attracted considerable interest in organic electronics, owing to its high field-effect mobility. Herein, we report the direct C-H arylation of DT-TTF to synthesise mono- and tetraarylated derivatives functionalised with electron-withdrawing and electron-donating groups in order to evaluate their influence on the electronic properties by cyclic voltammetry, UV-vis spectroscopy and theoretical calculations. Self-assembly of the DT-TTF-tetrabenzoic acid derivative was studied by using scanning tunnelling microscopy (STM) which revealed the formation of ordered, densely packed 2D hydrogen-bonded networks at the graphite/liquid interface. The tetrabenzoic acid derivative can attain a planar geometry on the graphite surface due to van der Waals interactions with the surface and H-bonding with neighbouring molecules. This study demonstrates a simple method for the synthesis of arylated DT-TTF derivatives towards the design and construction of novel π-extended electroactive frameworks.

Influence of indium doping on electrical performance of gallium oxide thin-film transistors

In the field of oxide semiconductor thin-film transistors (TFTs), the occurrence of charge trapping in the gate dielectric and interfaces presents significant challenges to their operational stability and reliability. In this study, we present high-performing amorphous Ga2O3 TFTs created using atomic layer deposition with varying indium doping concentrations. The channel length (Lch) and channel width (Wch) are 50 and 200 μm, respectively. As the Indium concentration increases from 0% to 60%, the charge trap density (Nit) decreases, resulting in a smaller hysteresis window. The TFTs with a doping concentration of 20% are particularly noteworthy, exhibiting high field-effect mobility (22.6 cm2 V−1 s−1), lower subthreshold swing (160 mV/dec) than amorphous Ga2O3 channel devices, a high on-off current ratio (109), an appropriate threshold voltage (−1 V), and a substantial output current (26 mA/mm at VGS = 16 V).

Homojunction structure amorphous oxide thin film transistors with ultra-high mobility

Amorphous oxide semiconductors (AOS) have unique advantages in transparent and flexible thin film transistors (TFTs) applications, compared to low-temperature polycrystalline-Si (LTPS). However, intrinsic AOS TFTs are difficult to obtain field-effect mobility (μ FE) higher than LTPS (100 cm2/(V·s)). Here, we design ZnAlSnO (ZATO) homojunction structure TFTs to obtain μ FE = 113.8 cm2/(V·s). The device demonstrates optimized comprehensive electrical properties with an off-current of about 1.5 × 10–11 A, a threshold voltage of –1.71 V, and a subthreshold swing of 0.372 V/dec. There are two kinds of gradient coupled in the homojunction active layer, which are micro-crystallization and carrier suppressor concentration gradient distribution so that the device can reduce off-current and shift the threshold voltage positively while maintaining high field-effect mobility. Our research in the homojunction active layer points to a promising direction for obtaining excellent-performance AOS TFTs.

Fully Printed Low-Voltage Field-Effect Transistor Biosensor Array for One-Drop Detection of Shewanella onedensis MR-1 Bacteria

Fast and simple bacterial detection using an in situ measurement technique is indispensable for medical diagnosis, public hygiene, and environmental monitoring. However, current bacterial detection techniques still require large measurement apparatus with complicated analysis. In this work, we propose the use of a full printing process for the fabrication of field-effect-transistor (FET) biosensors using π-junction gold nanoparticle (AuNP) ink and semiconducting single-wall carbon nanotube (sc-SWCNT) ink, which show a low voltage (<1 V) and high field-effect mobility (70 cm2 V–1 s–1), allowing for highly efficient and accurate bacterial detection from a minimal size of the target analyte droplet. This method provides a fully printed sensing platform for the determination of Shewanella onedensis MR-1 bacteria with a linear range of 10–1000 CFU in one drop of bacterial suspension (0.1 μL) (i.e., 105 to 107 CFU/mL), which is promising for the practical application of low-cost and disposable biosensors, especially in the regions with restricted medical conditions.

Van der Waals nanomesh electronics on arbitrary surfaces

Chemical bonds, including covalent and ionic bonds, endow semiconductors with stable electronic configurations but also impose constraints on their synthesis and lattice-mismatched heteroepitaxy. Here, the unique multi-scale van der Waals (vdWs) interactions are explored in one-dimensional tellurium (Te) systems to overcome these restrictions, enabled by the vdWs bonds between Te atomic chains and the spontaneous misfit relaxation at quasi-vdWs interfaces. Wafer-scale Te vdWs nanomeshes composed of self-welding Te nanowires are laterally vapor grown on arbitrary surfaces at a low temperature of 100 °C, bringing greater integration freedoms for enhanced device functionality and broad applicability. The prepared Te vdWs nanomeshes can be patterned at the microscale and exhibit high field-effect hole mobility of 145 cm2/Vs, ultrafast photoresponse below 3 μs in paper-based infrared photodetectors, as well as controllable electronic structure in mixed-dimensional heterojunctions. All these device metrics of Te vdWs nanomesh electronics are promising to meet emerging technological demands.

Effects of Sn Doping on the Electrical Performance and Stability of Sub-V Operating Metal-Oxide Thin-Film Transistors Fabricated by Oxygen Annealing

The incorporation of Sn into a sol-gel-based indium-gallium-zinc oxide (IGZO) channel layer is investigated to improve the electrical characteristics and operational stability of amorphous metal-oxide thin-film transistors (oxide-TFTs). Sub-V operating Sn-doped IGZO-TFTs (IGZTO-TFTs) fabricated by solution-process under a high-pressure oxygen-enriched (O2) atmosphere exhibit significantly improved electrical properties such as a high linear field-effect mobility (11.5 cm2 V−1 s−1), high on/off ratio (up to 108), and low subthreshold swing (0.10 V/dec). The activation energy and density of states are determined to perform comparative analysis on the charge transport characteristics of the IGZTO-TFTs. Under both prolonged positive and negative bias illumination stresses, large shifts in threshold voltages of the IGZO-TFTs are reduced significantly after Sn doping. The suppressed formation of oxygen-related defect states affects the electrical characteristics and operational stability. This is verified by determining the proportional ratio of metal-oxygen bonding states in the O2-annealed IGZTO films.

High Mobility IZTO Thin-Film Transistors Based on Spinel Phase Formation at Low Temperature through a Catalytic Chemical Reaction.

In this paper, In0.22 Znδ Sn0.78- δ O1.89- δ (δ = 0.55) films with a single spinel phase are successfully grown at the low temperature of 300 °C through careful cation composition design and a catalytic chemical reaction. Thin-film transistors (TFTs) with amorphous In0 .22 Znδ Sn0.78- δ O1.89- δ (δ = 0.55) channel layers have a reasonable mobility of 41.0 cm2 V-1 s-1 due to the synergic intercalation of In and Sn ions. In contrast, TFTs with polycrystalline spinel In0 .22 Znδ Sn0.78- δ O1.89- δ (δ = 0.55) channel layers, achieved through a metal-induced crystallization at 300 °C, exhibit a remarkably high field-effect mobility of ≈83.2 cm2 V-1 s-1 and excellent stability against external gate bias stress, which is attributed to the uniform formation of the highly ordered spinel phase. The relationships between cation composition, microstructure, and performance for the In2 O3 -ZnO-SnO2 ternary component system are investigated rigorously to attain in-depth understanding of the roles of various crystalline phases, including spinel Zn2- y Sn1- y In2 y O4 (y = 0.45), bixbyite In2-2 x Znx Inx O4 (x = 0.4), rutile SnO2 , and a homologous compound of compound (ZnO)k (In2 O3 ) (k = 5). This work concludes that the cubic spinel phase of Zn2- y Sn1- y In2 y O4 (y = 0.45) film is a strong contender as a substitute for semiconducting polysilicon as a backplane channel ingredient for mobile active-matrix organic light-emitting diode displays.