Decent Mobility Research Articles

Surface engineering of Al2O3 dielectric layer for all-sputtered-oxide transparent and flexible a-IGZO thin film transistor

Transparent flexible display devices have attracted massive attention in recent years owing to their practical applications that can be compatibly adapted to human demand and technological development. Worldwide researchers have studied flexible transparent thin film transistors (TFTs) to qualify them for the backplane component of future transparent and flexible displays. Simplifying the fabrication process of a TFT can be considered a critical need for reducing consumed cost, time, toxic chemicals. In this study, sputtering was utilized as a major fabrication method for manufacturing a transparent oxide TFT device, which demonstrated good mechanical flexibility. A simple surface treatment process was applied to enhance the susceptibility of the sputtered Al2O3 dielectric through multiple coatings of solution processed Al2O3. It is noteworthy that the transparent oxide TFT device exhibits a high optical transparency of 81.12% and good electrical switchability at low operating voltage (3 V) with a decent mobility of 4.37 cm2 V−1 s−1 and proven mechanical durability.

Development of MnxCo0.015Zn1-xO electron transport layer for perovskite solar cells: Experimental and simulation study

The electron transport layer (ETL) plays an important role in the performance and stability enhancement of perovskite solar cells (PSCs). Zinc oxide is considered a cost-effective and low-temperature processed ETL for PSCs, which offers decent mobility. However, the interface reaction occurs via a reaction of zinc oxide with the organic-inorganic metal hybrid halide perovskite absorber, which results in the degradation of the PSCs. To overcome this issue, metal doping was carried out. However, metal doping causes a reduction in the transmittance of the zinc oxide ETL layer because of high absorption. Thus, the overall performance of the PSCs was reduced due to the lessening of the photogenerated current. In this regard metal co-doping (Mn and Co) was done to improve the electrical as well as electronic properties. Furthermore, the influence of Mn doping on the structural, optical, and photoluminescence properties of MnxCo0.015Zn1-xO (x = 0, 0.002, 0.008, and 0.012) hexagonal nanosheets was investigated. X-ray diffraction results revealed that the inter-planar spacing, cell parameters, unit cell volume, lattice strain, and dislocation density were maximum for the Mn content of 0.2%. The acquired values of the optical band gap (Eg) are 3.39, 3.52, 3.58, and 3.18 eV for x = 0, 0.2%, 0.8%, and 1.2%, respectively. The corresponding absorption coefficient is reduced with increasing Mn content. The obtained refractive indices are 1.437, 1.402, 1.428, and 1.426 for x = 0, 0.2, 0.8, and 1.2%, respectively. The above results confirm that the MnxCo0.015Zn1-xO with x = 0.8% provides the lowest absorption and the highest value of bandgap. Thus, it can be the most suitable ETL for high-performance PSCs. The simulation results reveal that via applying MCZO ETL, the efficiency can be achieved over 23%.

Non‐symmetric Half‐Fused B←N Coordinated Diketopyrrolopyrrole Building Block for n‐type Semiconducting Polymers

AbstractThe development of conjugated polymers with high semiconducting performance and high reliability is of great significance for flexible electronics. Herein, we developed a new type of electron‐accepting building block; i.e., non‐symmetric half‐fused B←N coordinated diketopyrrolopyrrole (DPP) (HBNDPP), for amorphous conjugated polymers toward flexible electronics. The rigid B←N fusion part of HBNDPP endows the resulting polymers with decent electron transport, while its non‐symmetric structure causes the polymer to exhibit multiple conformation isomers with flat torsional potential energies. Thus, it gets packed in an amorphous manner in solid state, ensuring good resistance to bending strain. Combined with hardness and softness, the flexible organic field‐effect transistor devices exhibit n‐type charge properties with decent mobility, good bending resistance, and good ambient stability. The preliminary study makes this building block a potential candidate for future design of conjugated materials for flexible electronic devices.

Non-symmetric Half-Fused B←N Coordinated Diketopyrrolopyrrole Building Block for n-type Semiconducting Polymers.

The development of conjugated polymers with high semiconducting performance and high reliability is of great significance for flexible electronics. Herein, we develop a new type of electron-accepting building block; ie., non-symmetric half-fused B←N coordinated diketopyrrolopyrrole (DPP) (HBNDPP),for amorphous conjugated polymers towards flexible electronics. The rigid B←N fusion part of HBNDPP endows the resulting polymers with decent electron transport, while the non-symmetric structure of HBNDPP causes the polymer to exhibit multiple conformation isomers with flat torsional potential energies.Thus, it gets packed in anamorphous mannerin solid state, ensuring good resistance to bending strain. Combined with hardness and softness, the flexible OFET devices exhibit n-type charge properties with decent mobility, good bending resistance, and good ambient stability. The preliminary study makes this building block a potential candidate for future design of conjugated materials for flexible electronic devices.

Transport properties of crystallized antiferromagnetic MnBi2Te4 thin films grown by magnetron sputtering

The intrinsic magnetic topological insulator MnBi2Te4 has drawn great attention due to its novel quantum states, among which the most promising one is the quantum anomalous Hall effect. However, MnBi2Te4 is a metastable phase with a narrow temperature range for synthesis, which remains a challenge to grow uniform and high quality MnBi2Te4 sample. Large-area MnBi2Te4 thin films are mainly prepared by molecular beam epitaxy so far. Here, we report a highly versatile method for growing crystallized MnBi2Te4 films on amorphous SiO2/Si substrates by magnetron sputtering at room temperature and post-annealing. High-quality MnBi2Te4 films with a c-axis perpendicular to the substrate and low surface roughness are realized. MnBi2Te4 films have an antiferromagnetic Néel temperature of 21 K, with low carrier concentration (2.5 × 1019 cm−3) and decent mobility (34 cm2 V−1s−1). The films reveal ferromagnetic at ground state and a typical spin-flop transition at 2–3 T. This work provides a pathway toward the fabrication of sputtered-MnBi2Te4 devices for electronic and spintronic applications.

How much infrastructure is required to support decent mobility for all? An exploratory assessment

Decarbonizing transport is crucial for achieving climate targets, which is challenging because mobility is growing rapidly. Personal mobility is a key societal service and basic need, but currently not available to everyone with sufficient quality and quantity. The basis for mobility and accessibility of desired destinations is infrastructure, but its build-up and maintenance require a substantial fraction of global resource use. The question arises, how much mobility and how much infrastructure are required to deliver decent, sustainable mobility.We explore the relations between mobility levels, mobility infrastructure and well-being. We synthesize definitions of decent mobility and assess mobility measurements and provide a novel estimate of mobility infrastructure stocks for 172 countries in the year ~2021. We then explore the relations between infrastructure, travelled distances, accessibility, economic activity and several ‘beyond GDP’ well-being indicators.We find that travelled distances and mobility infrastructure levels are significantly correlated. Above levels of ~92–207 t/cap of mobility infrastructure no further significant gains in well-being can be expected from a further increase of infrastructure. We conclude that high mobility in terms of distances travelled as well as building up mobility infrastructure is only beneficial for well-being up to a certain point.

Eliminating Leakage Current in Thin‐Film Transistor of Solution‐Processed Organic Material Stack for Large‐Scale Low‐Power Integration

AbstractFor organic thin‐film transistors (OTFTs) made of solution processed stacks of organic semiconductor and dielectric materials, it is a grand challenge to eliminate the leakage current paths. With a top‐gate bottom‐contact structure, this work introduces a strong dipole interfacial layer made of self‐assembled monolayer (SAM) molecules at metal‐semiconductor contacts to suppress minority carrier injection for low leakage and stable operation, while not affecting majority carrier injection. Both gate insulator (GI) leakage and parasitic leakage in the device architecture are also effectively suppressed with a sputtering‐resistant polymer GI layer and photolith patterned OSC islands, respectively. The devices present a decent mobility with a typical value of 1.98 cm2 V–1 s–1, record‐low leakage current at 10–18 A µm−1 and large ON/OFF ratio (>1010) in a wide gate voltage range (100 V), reaching the theoretical limit and also the best level of inorganic counterparts despite much lower processing temperature (120 °C). Manufacturability of the material stack is verified on a 200 mm × 200 mm substrate and the fabricated 4.7 in. active‐matrix organic light‐emitting diode display, integrating more than 150 000 OTFTs, can be operated at ultra‐low frame‐rate (0.1 Hz) for power saving.

Halide Perovskites: Thermal Transport and Prospects for Thermoelectricity.

The recent re‐emergence of halide perovskites has received escalating interest for optoelectronic applications. In addition to photovoltaics, the multifunctional nature of halide perovskites has led to diverse applications. The ultralow thermal conductivity coupled with decent mobility and charge carrier tunability led to the prediction of halide perovskites as a possible contender for future thermoelectrics. Herein, recent advances in thermal transport of halide perovskites and their potentials and challenges for thermoelectrics are reviewed. An overview of the phonon behavior in halide perovskites, as well as the compositional dependency is analyzed. Understanding thermal transport and knowing the thermal conductivity value is crucial for creating effective heat dissipation schemes and determining other thermal‐related properties like thermo‐optic coefficients, hot‐carrier cooling, and thermoelectric efficiency. Recent works on halide perovskite‐based thermoelectrics together with theoretical predictions for their future viability are highlighted. Also, progress on modulating halide perovskite‐based thermoelectric properties using light and chemical doping is discussed. Finally, strategies to overcome the limiting factors in halide perovskite thermoelectrics and their prospects are emphasized.

Progress on Crystal Growth of Two-Dimensional Semiconductors for Optoelectronic Applications

Two-dimensional (2D) semiconductors are thought to belong to the most promising candidates for future nanoelectronic applications, due to their unique advantages and capability in continuing the downscaling of complementary metal–oxide–semiconductor (CMOS) devices while retaining decent mobility. Recently, optoelectronic devices based on novel synthetic 2D semiconductors have been reported, exhibiting comparable performance to the traditional solid-state devices. This review briefly describes the development of the growth of 2D crystals for applications in optoelectronics, including photodetectors, light-emitting diodes (LEDs), and solar cells. Such atomically thin materials with promising optoelectronic properties are very attractive for future advanced transparent optoelectronics as well as flexible and wearable/portable electronic devices.

Novel antimonene tunneling field-effect transistors using an abrupt transition from semiconductor to metal in monolayer and multilayer antimonene heterostructures.

Recently, a mono-elemental two-dimensional (2-D) material, namely antimonene, with a large band gap, decent mobility and ambient stability has been extensively researched. Interestingly, although antimonene is a semiconductor with a sizable band gap in the monolayer, it is transformed to a metal in the multilayer. Inspired by this thickness dependent semiconductor to metal transition, we propose novel antimonene tunneling field-effect transistors (TFETs) based on the lateral monolayer (semiconducting)/multilayer (metallic)/monolayer (semiconducting) heterostructure. Our antimonene TFETs consist of a semiconducting monolayer source, channel and a drain and a small metallic multilayer region between the source and the channel. The local multilayer region introduces gapless metallic states which dramatically enhance the tunneling probability and hence result in a large current. To investigate the effect of a metallic multilayer on device performances, we carried out ab-initio electronic structure and quantum transport calculations for several antimonene TFETs based on different monolayer/multilayer/monolayer heterostructures. Simulation shows that even ∼1 nm scale nanostructured multilayer significantly boosts the current and enables abrupt device switching. More extensive evaluation is performed through benchmarking with phosphorene TFETs which have been identified as the best 2-D material based TFETs so far. In terms of the main figures of merit for FETs such as the intrinsic delay time and the power delay product, antimonene heterostructure TFETs outperform phosphorene TFETs, primarily due to the elimination of the tunneling barrier by the locally constructed multilayer antimonene.

Giant Rashba Splitting in CH_{3}NH_{3}PbBr_{3} Organic-Inorganic Perovskite.

As they combine decent mobilities with extremely long carrier lifetimes, organic-inorganic perovskites open a whole new field in optoelectronics. Measurements of their underlying electronic structure, however, are still lacking. Using angle-resolved photoelectron spectroscopy, we measure the valence band dispersion of single-crystal CH_{3}NH_{3}PbBr_{3}. The dispersion of the highest energy band is extracted applying a modified leading edge method, which accounts for the particular density of states of organic-inorganic perovskites. The surface Brillouin zone is consistent with bulk-terminated surfaces both in the low-temperature orthorhombic and the high-temperature cubic phase. In the low-temperature phase, we find a ring-shaped valence band maximum with a radius of 0.043 Å^{-1}, centered around a 0.16eV deep local minimum in the dispersion of the valence band at the high-symmetry point. Intense circular dichroism is observed. This dispersion is the result of strong spin-orbit coupling. Spin-orbit coupling is also present in the room-temperature phase. The coupling strength is one of the largest ones reported so far.

Photo‐Stable Organic Thin‐Film Transistor Utilizing a New Indolocarbazole Derivative for Image Pixel and Logic Applications

Small molecule pentacene layer has been a representative among many organic thin‐film transistor (OTFT) channels with decent p‐type mobilities, but it is certainly light‐sensitive due to its relatively small highest occupied molecular orbital‐lowest unoccupied molecular orbital (HOMO‐LUMO) gap (1.85 eV). Although a few other small molecule‐based layers have been reported later, their photo‐stabilities or related device applications have hardly been addressed. Here, a new photostable organic layer is reported, heptazole (C26H16N2), which has almost the same HOMO level as that of pentacene but with a higher HOMO‐LUMO gap (≈2.95 eV). This heptazole OTFT displays a decent mobility comparable to that of conventional amorphous Si TFTs, showing good photostability unlike pentacene OTFTs. An image pixel driving the photostable heptazole OTFT connected to a pentacene/Al Schottky photodiode is demonstrated. This heptazole OTFT also conveniently forms a logic inverter coupled with a pentacene OTFT, sharing Au for source/drain.

High-Performance Flexible a-IGZO TFTs Adopting Stacked Electrodes and Transparent Polyimide-Based Nanocomposite Substrates

We demonstrated flexible amorphous In-Ga-Zn-O (a-IGZO) thin-film transistors (TFTs) on fully transparent and high-temperature polyimide-based nanocomposite substrates. The flexible nanocomposite substrates were coated on the carrier glass substrates and were debonded after the TFT microfabrication. The adoption of the Ti/IZO stacked electrodes as source/drain/ gain electrodes significantly improved the etching compatibility with other material layers, enabling successful implementation of flexible a-IGZO TFTs onto the transparent nanocomposite substrates by conventional lithographic and etching processes. The flexible a-IGZO TFTs exhibited decent mobility and mechanical bending capability. Field-effect mobility of up to 15.9 cm2/V · s, a subthreshold swing of 0.4 V/dec, a threshold voltage of 0.8 V, and an on/off ratio of >; 108 were extracted from the TFT characteristics. The devices could be bent down to a radius of curvature of 3 mm and yet remained normally functional. Such successful demonstration of flexible oxide TFTs on transparent flexible substrates using fully lithographic and etching processes that are compatible with existing TFT fabrication technologies shall broaden their uses in flexible displays and electronics.

Analysis of Elderly Mobility by Structural Equation Modeling

Mobility is a critical element of quality of life. This is as true for the elderly population as for the larger population. The elderly often have limited physical abilities and financial constraints that might reduce their mobility. Helping the growing elderly population to maintain decent mobility is a critical challenge for transportation planning and policy. For this, the factors that influence the mobility of the elderly population (elderly mobility) must be understood. Only a few systematic studies, however, have been published. Descriptive statistics of the potentially influential factors make it difficult to assess their effects on elderly mobility. The transportation mobility of retired people age 65 years or older in the Puget Sound region of Washington State was analyzed by using a structural equation model. The statistical significance and relative effects of various personal and household characteristics and urban form on elderly mobility were tested. The structural equation model finds statistically significant relationships between age, gender, transportation disability, possession of a driver's license, and education level and elderly mobility. Among these variables, age and education level show the strongest effects. Urban form, however, seems to be insignificant.