Single-layer Channel Research Articles

Chiral Diketopyrrolopyrrole-Based Conjugated Polymers with Intramolecular Rotation-Isomeric Conformation Asymmetry for Near-Infrared Circularly Polarized Light-Sensing Organic Phototransistors.

Recent advances in chiral nanomaterials interacting with circularly polarized (CP) light open new expectations for optoelectronics in various research fields such as quantum- and biology-related technology. To fully utilize the great potential of chiral optoelectronic devices, the development of chiral optoelectronic devices that function in the near-infrared (NIR) region is required. Herein, we demonstrate a NIR-absorbing, chiroptical, low-band-gap polymer semiconductor for high-performance NIR CP light phototransistors. A newly synthesized diketopyrrolopyrrole-based donor-acceptor-type chiral π-conjugated polymer with an asymmetric alkyl side chain exhibits strong chiroptical activity in a wavelength range of 700-1000 nm. We found that the attachment of an enantiomerically pure stereogenic alkyl substituent to the π-conjugated chromophore backbone led to strong chiroptical activity through symmetry breaking of the π-conjugation of the backbone in a molecular rotational motion while maintaining the coplanar backbone conformation for efficient charge transport. The NIR CP light-sensing phototransistors based on a chiral π-conjugated polymer photoactive single channel layer exhibit a high photoresponsivity of 26 A W-1 under NIR CP light irradiation at 920 nm, leading to excellent NIR CP light distinguishability. This study will provide a rationale and strategy for designing chiral π-conjugated polymers for high-performance NIR chiral optoelectronics.

Performance optimization of tri-gate junctionless FinFET using channel stack engineering for digital and analog/RF design

This manuscript explores the behavior of a junctionless tri-gate FinFET at the nano-scale region using SiGe material for the channel. For the analysis, three different channel structures are used: (a) tri-layer stack channel (TLSC) (Si–SiGe–Si), (b) double layer stack channel (DLSC) (SiGe–Si), (c) single layer channel (SLC) (Si). The I−V characteristics, subthreshold swing (SS), drain-induced barrier lowering (DIBL), threshold voltage (V t), drain current (I ON), OFF current (I OFF), and ON-OFF current ratio (I ON/I OFF) are observed for the structures at a 20 nm gate length. It is seen that TLSC provides 21.3% and 14.3% more ON current than DLSC and SLC, respectively. The paper also explores the analog and RF factors such as input transconductance (g m), output transconductance (g ds), gain (g m/g ds), transconductance generation factor (TGF), cut-off frequency (f T), maximum oscillation frequency (f max), gain frequency product (GFP) and linearity performance parameters such as second and third-order harmonics (g m2, g m3), voltage intercept points (VIP2, VIP3) and 1-dB compression points for the three structures. The results show that the TLSC has a high analog performance due to more g m and provides 16.3%, 48.4% more gain than SLC and DLSC, respectively and it also provides better linearity. All the results are obtained using the VisualTCAD tool.

Flow and heat transfer of hydrocarbon fuel in the double-layer regenerative cooling channels

Hypersonic air-breathing propulsion (>Mach 5) based on scramjet offers new solutions to both the military strike platform and the civil transportation. However, the hypersonic flight seriously challenges the engine thermal protection. One of the key problems is the tricky flow and thermal behaviors of hydrocarbon fuel in regenerative cooling channels under the complex thermal boundaries and channel geometry, which may cause heat transfer deterioration and structure over-temperature. To improve the cooling design, the double-layer regenerative cooling channels are focused and compared with the traditional single-layer channels. The flow and thermal behaviors of hydrocarbon fuel under different cooling configurations are numerically studied. Cooling performance of double-layer channels is superior than single-layer channels. Tw ,max falls by 295.2 K/17.7%. Gravity direction and magnitude show negligible influence on the heat transfer. Regarding channel height ratio, H 1/H 2 = 1.1/1 achieves optimal cooling performance in present conditions. Double-layer-channel scheme presents high practicability in scramjet cooling.

Improvement in current drivability and stability in nanoscale vertical channel thin-film transistors via band-gap engineering in In–Ga–Zn–O bilayer channel configuration

Vertical channel thin film transistors (VTFTs) have been expected to be exploited as one of the promising three-dimensional devices demanding a higher integration density owing to their structural advantages such as small device footprints. However, the VTFTs have suffered from the back-channel effects induced by the pattering process of vertical sidewalls, which critically deteriorate the device reliability. Therefore, to reduce the detrimental back-channel effects has been one of the most urgent issues for enhancing the device performance of VTFTs. Here we show a novel strategy to introduce an In–Ga–Zn–O (IGZO) bilayer channel configuration, which was prepared by atomic-layer deposition (ALD), in terms of structural and electrical passivation against the back-channel effects. Two-dimensional electron gas was effectively employed for improving the operational reliability of the VTFTs by inducing strong confinement of conduction electrons at heterojunction interfaces. The IGZO bilayer channel structure was composed of 3 nm-thick In-rich prompt (In/Ga = 4.1) and 12 nm-thick prime (In/Ga = 0.7) layers. The VTFTs using bilayer IGZO channel showed high on/off ratio (4.8 × 109), low SS value (180 mV dec−1), and high current drivability (13.6 μA μm−1). Interestingly, the strategic employment of bilayer channel configurations has secured excellent device operational stability representing the immunity against the bias-dependent hysteretic drain current and the threshold voltage instability of the fabricated VTFTs. Moreover, the threshold voltage shifts of the VTFTs could be suppressed from +5.3 to +2.6 V under a gate bias stress of +3 MV cm−1 for 104 s at 60 °C, when the single layer channel was replaced with the bilayer channel. As a result, ALD IGZO bilayer configuration could be suggested as a useful strategy to improve the device characteristics and operational reliability of VTFTs.

Integration of bandgap-engineered double-stacked channel layers with nitrogen doping for high-performance InGaO TFTs

High-performance indium-gallium oxide (IGO) thin film transistors (TFTs) with a double-stacked channel layer (DSCL) were obtained by the in-situ nitrogen doping technique. By means of their distinctive feature of bandgap narrowing, devices with an IGO/IGO:N double-stacked channel showed superior electrical characteristics (μFE = 25 cm2/V s and ION/IOFF > 108) than those with a single channel layer. Moreover, owing to the reduced oxygen vacancies, the bias stability was significantly improved. Through X-ray photoelectron spectroscopy analysis, we optimized the model of bandgap engineering. It not only provides an explicit principle for the design of the DSCL configuration but also facilitates the manufacture of high-quality passivation-free TFTs for practical applications.

Secondary bonding of PMMA micromixer with high-pressure

This paper studies the process to fabricate a micromixer by bonding the PMMA sheets after CO2 laser processing microchannel. It has been widely used in analysis chemical and detection as its low cost. Chemical analysis chips are commonly produced using low-pressure bonding. The bonding strength of the micromixer is improved by secondary bonding with high-pressure, which can meet the requirements of the chemical analysis with higher flowing rate and higher pressure. The effects on the single-layer and multi-layer microchannels are compared with high-pressure and low-pressure bonding. The deformation of the width and height at low pressure and high pressure of the single-layer channel are 12.4 μm, 23.5 μm and 17.1 μm, 54.1 μm, respectively. The multi-layer channels are 43.44 μm, 23.7 μm and 78.1 μm, 27.7 μm. The influence on the height of the V-shaped microchannel is greater when the single-layer micromixer is performed with high-pressure bonding, and when multi-layer bonding with high-pressure, the effect on the width of the rectangular microchannel is obvious. In the process of secondary bonding and pressurization, the chip position can be appropriately adjusted to avoid deformation caused by uneven force on the chip during manual operation. Since high-pressure bonding has an effect on the shape of the microchannel, different bonding methods can be selected according to different requirements of the chemical analysis chips on microchannel quality and bonding strength.

FeIn2S4 Nanocrystals: A Ternary Metal Chalcogenide Material for Ambipolar Field-Effect Transistors.

An ambipolar channel layer material is required to realize the potential benefits of ambipolar complementary metal–oxide–semiconductor field‐effect transistors, namely their compact and efficient nature, reduced reverse power dissipation, and possible applicability to highly integrated circuits. Here, a ternary metal chalcogenide nanocrystal material, FeIn2S4, is introduced as a solution‐processable ambipolar channel material for field‐effect transistors (FETs). The highest occupied molecular orbital and the lowest unoccupied molecular orbital of the FeIn2S4 nanocrystals are determined to be −5.2 and −3.75 eV, respectively, based upon cyclic voltammetry, X‐ray photoelectron spectroscopy, and diffraction reflectance spectroscopy analyses. An ambipolar FeIn2S4 FET is successfully fabricated with Au electrodes (E F = −5.1 eV), showing both electron mobility (14.96 cm2 V−1 s−1) and hole mobility (9.15 cm2 V−1 s−1) in a single channel layer, with an on/off current ratio of 105. This suggests that FeIn2S4 nanocrystals may be a promising alternative semiconducting material for next‐generation integrated circuit development.

Tuning mechanical response in granular layers by adding rigid particle channel

The inhomogeneity of spatial packing by particles with different physical properties can significantly affect mechanical properties of granular packings. In this paper, a new approach by adding rigid particle channel is put forward to tune the mechanical response of granular layers induced by external loading. Based on the single-layer channel model, a phase diagram is firstly proposed to describe the crossover of mechanical response between a single-peaked and double-peaked feature, in which the tunable range of external loading and effective region of channel position are two key factors that reflect the tuning effect of this approach. Its tuning mechanism is further explored based on the variations of propagating feature of contact forces, and a linear function is proposed to predict the optimal position of the channel in systems with different sizes. Furthermore, the dependence of tuning effect on the spatial configuration and the number of rigid particle layers is also discussed in a double-layer and multi-layer rigid particle channel models, which can obviously improve the tunable effect but also undergo different tuning processes. By adding different rigid particle channels to actively change propagation paths of contact forces and weaken the anisotropy in vertical stress field within granular system, it has been verified that this approach is feasible to enhance the elasticity of whole system and tune its mechanical response.

Universally applicable three-dimensional hydrodynamic focusing in a single-layer channel for single cell analysis

A microfluidic cytometer which integrated 3D hydrodynamic focusing and integrated optical systems on a single-layer microfluidic structure was demonstrated.

Preparation of Amphotericin B-Ergosterol structures and molecular simulation of water adsorption and diffusion

In this study, molecular simulation was used to explore the structural characteristics and water transport performance of Amphotericin B-Brgosterol (AmBEr) channels. A molecular dynamics (MD) technique was used to construct two types of molecular models of AmBEr channels: single-layer channel (SLC) and double-layer channel (DLC). A MD simulation was used to illustrate the differences between SLC and DLC AmBEr models with respect to structure, channel diameter, interior affinity, and transportation behavior of water molecules. A Monte Carlo (MC) method was adopted to investigate the sorption behavior in these two types of AmBEr channels. The intramolecular properties and intermolecular interactions indicated the feasibility of the simple model construction method adopted in this study. The internal diameter and channel shape showed that the use of funnel-type AmBEr channels would lead to high levels of permeability and selectivity. The special tunnel shape was reflected in the diffusion calculation that resulted in a high displacement of water molecules in two types of channel models. The water molecule-channel hydrogen bond distribution and snapshot analyses of the adsorption site revealed an affinity between the amphotericin B monomer and water molecules. The novel chemical structure of the amphotericin B monomer features simultaneous hydrophilic and hydrophobic segments. This particular structural characteristic was reflected in the unique shape of the water adsorption isotherm curves, which show a unique three-step increase in equilibrated water pressure. In transport prediction, two AmBEr models had similar permeability values but different water transport mechanisms. Concisely, fabrication of the artificial water channel would help to enhance the water permeability in the water transport process. The results from the simulation provided valuable information for structural characterization and in estimating the transport behavior of the molecules in the AmBEr channels.

Computational optimization of counter-flow double-layered microchannel heat sinks subjected to thermal resistance and pumping power

Various microchannel heat sinks are widely used to cool electronic chips, but they are often designed to be single-layer channels. To a certain extent, single-layered microchannel heat sinks can solve the problem of high heat flux. However, due to the limitation of pumping power, only a small coolant flow rate can be adopted; and the temperature of the heated plate is non-uniform. In this paper, the structure of double-layered countercurrent microchannel heat sinks is designed. The NSGA-II optimization algorithm is used to optimize the height ratio of the two layers and the length of the upper layer. The corresponding Pareto frontier is obtained. After validation of the optimization Pareto front, some validated characteristic cases are investigated numerically. The results of the optimization show that despite a conflict between reducing the thermal resistance and lowering the pumping power, there is an appropriate structure of the double-layered countercurrent microchannel heat sink optimized by the NSGA-II optimization algorithm. For the selected cases, Case 4 has the best thermal performance, because Case 4 not only has a smaller pumping power than Case 0, but also has a smaller thermal resistance than Case 0. Therefore, it is indicated that better thermal performance of microchannel heat sinks can be achieved through the optimization algorithm.

Synthesis of integrated graphene films with self-assembled single-layer channels and multi-layer electrodes via a single process

Integrated graphene films (IGFs) with self-assembled single-layer graphene as a channel and multi-layer graphene as an electrode material were synthesized simultaneously using a one-step process by thermal chemical vapor deposition. The prominent difference in graphene growth rate between Ni and Cu catalytic substrates made enable to synthesize the IGFs with self-assembled single-layer and multi-layer graphene on a Cu foil with pre-patterned Ni films. The thickness of multi-layer graphene for IGFs was precisely controlled by optimizing conditions including the injection temperature of carbon feedstock and the surface concentration of Ni atoms affected by the inter-diffusion related to the growth temperature and time. The thickness and crystallinity of synthesized IGFs were evaluated by resonant Raman spectroscopy. We fabricated the IGFs-based field effect transistors (FETs) to examine electrical transport properties of the films. These results suggest that the synthesis technique for IGFs could lead to mass fabrication of wearable graphene-based FETs in the near future.

Boost up the electrical performance of InGaZnO thin film transistors by inserting an ultrathin InGaZnO:H layer

This study examined the electrical performance of bilayer channel InGaZnO:H/InGaZnO thin-film transistors (TFTs). The field-effect mobility and bias stress stability of the InGaZnO device were improved by inserting the hydrogenated InGaZnO ultrathin layer compared to the pure InGaZnO single channel layer device. As a consequence, a high field-effect mobility of 55.3 cm2/V s, a high on/off current ratio of 108, a threshold voltage of 0.7 V, and a small sub-threshold swing of 0.18 V/decade have been achieved. The X-ray photoelectron spectroscopy and low-frequency noise analysis suggest that these desirable properties should be attributed to the ultrathin InGaZnO:H layer, which could provide suitable carrier concentration and reduce the average trap density near the channel and insulator layer interface. Meanwhile, the channel conductance of the bilayer device is controlled by thick InGaZnO layer through formation barrier energy for electron transport at the interface of InGaZnO:H and InGaZnO layer. These improved electrical properties have represented a great step towards the achievement of transparent, high performances, and low-cost metal oxide TFTs.

Rational Design of ZnO:H/ZnO Bilayer Structure for High-Performance Thin-Film Transistors.

The intriguing properties of zinc oxide-based semiconductors are being extensively studied as they are attractive alternatives to current silicon-based semiconductors for applications in transparent and flexible electronics. Although they have promising properties, significant improvements on performance and electrical reliability of ZnO-based thin film transistors (TFTs) should be achieved before they can be applied widely in practical applications. This work demonstrates a rational and elegant design of TFT, composed of poly crystalline ZnO:H/ZnO bilayer structure without using other metal elements for doping. The field-effect mobility and gate bias stability of the bilayer structured devices have been improved. In this device structure, the hydrogenated ultrathin ZnO:H active layer (∼3 nm) could provide suitable carrier concentration and decrease the interface trap density, while thick pure-ZnO layer could control channel conductance. Based on this novel structure, a high field-effect mobility of 42.6 cm(2) V(-1) s(-1), a high on/off current ratio of 10(8) and a small subthreshold swing of 0.13 V dec(-1) have been achieved. Additionally, the bias stress stability of the bilayer structured devices is enhanced compared to the simple single channel layer ZnO device. These results suggest that the bilayer ZnO:H/ZnO TFTs have a great potential for low-cost thin-film electronics.

Influence of Double Channel Layers on the Performance of Nitrogen Doped Indium-zinc-oxide Thin Film Transistors

The nitrogen-doped amorphous indium-zinc-oxide thin film transistors with double channel layers (a-IZO/IZON-TFTs) were fabricated by RF magnetron sputtering of IZO target on the thermal oxidized p-type Si substrate. Influence of the double channel layers on the electrical performance and thermal stability of the devices were investigated. It is found that a-IZO/IZON-TFTs have high field effect mobility of 23.26 cm/(Vs) and more positively shifted threshold voltage than that of a-IZO-TFTs. This is ascribed to the doped nitrogen which can help reduce oxygen vacancy in the channel layer, suppress carrier concentration and make the devices have a better threshold voltage. Meanwhile, employing a-IZO thin film can avoid the sharp drop of field effect mobility and drain on current caused by nitrogen doping on a-IZON layer, leading to promoting Ion/Ioff ratio effectively. Besides, according to the transfer characteristics measured at temperatures from 298 K to 423 K, devices with a-IZO/IZON double layers have superior performance and thermal stability to TFTs of single channel layer, which can be ascribed to the protective effect of a-IZON thin film on the channel layers. The doped nitrogen can reduce the adsorption/desorption reaction of oxygen molecules on the back channel layer, leading to a significant improvement on thermal stability of the devices. 746 无 机 材 料 学 报 第 31卷

Bi-layer channel structure-based oxide thin-film transistors consisting of ZnO and Al-doped ZnO with different Al compositions and stacking sequences

Zinc oxide (ZnO)-based bi-layers, consisting of ZnO and Al-doped ZnO (AZO) layers grown by atomic layer deposition, were utilized as the channels of oxide thin-film transistors (TFTs). Thin AZO layers (5 nm) with different Al compositions (5 and 14 at. %) were deposited on top of and beneath the ZnO layers in a bi-layer channel structure. All of the bi-layer channel TFTs that included the AZO layers showed enhanced stability (ΔV Th ≤ 3.2 V) under a positive bias stress compared to the ZnO single-layer channel TFT (ΔV Th = 4.0 V). However, the AZO/ZnO bi-layer channel TFTs with an AZO interlayer between the gate dielectric and the ZnO showed a degraded field effect mobility (0.3 cm2/V·s for 5 at. % and 1.8 cm2/V·s for 14 at. %) compared to the ZnO single-layer channel TFT (5.5 cm2/V·s) due to increased scattering caused by Al-related impurities near the gate dielectric/channel interface. In contrast, the ZnO/AZO bi-layer channel TFTs with an AZO layer on top of the ZnO layer exhibited an improved field effect mobility (7.8 cm2/V·s for 14 at. %) and better stability.

PLANAR SCHEMES TRACING IN THE SINGLE-LAYER CHANNEL

An algorithm for planar circuits tracing in a single layer channel, allowing more effective design solutions is proposed.

High-performance dual-layer channel indium gallium zinc oxide thin-film transistors fabricated in different oxygen contents at low temperature

In this work, fully transparent dual-layer channel amorphous indium gallium zinc oxide thin-film transistors (a-IGZO TFTs) are fabricated on glass substrates at low temperature. Dual-layer channel a-IGZO TFTs are studied by changing the partial pressure of oxygen while sputtering IGZO layers for comparison with single-layer channel TFTs which are fabricated with a constant oxygen content. All four types of dual-layer channel TFT sample demonstrate better performance, on-to-off ratios of ∼108 and low subthreshold swing (SS) of less than 200 mV/decade, than the single-layer ones. TFTs with two layers, a low-oxygen layer and a high-oxygen layer formed using oxygen partial pressures of 0.01 and 0.05 Pa, respectively demonstrate relatively better performance with a mobility of more than 60 cm2 V−1 s−1. Among them, the TFTs with a channel layer thickness ratio of 3 : 1 show the best transfer characteristics with a high on-to-off current ratio (Ion/off) of 1.8 × 108 and a low SS of 135 mV/decade.

Influence of channel layer and passivation layer on the stability of amorphous InGaZnO thin film transistors

The electrical stability of amorphous InGaZnO (a-IGZO) TFTs with three different channel layers was investigated. Compared with the single channel layer, the a-IGZO TFT with double stacked channel layer showed the lowest threshold voltage shift with slightly change in field effect mobility and sub-threshold swing under positive and negative gate bias stress tests. Moreover, sputtered SiNx thin film was served as passivation layer where the Vth shift in bias stress effect evidently became less. It was found that the passivated a-IGZO TFT with double stacked channel layer still exhibited the best stability. The results prove that the stability of a-IGZO TFTs can be effectively improved by using double stacked channel layer and passivation layer.

Computational Study and Optimization of Laminar Heat Transfer and Pressure Loss of Double-Layer Microchannels for Chip Liquid Cooling

The problem involved in the increase of the chip output power of high-performance integrated electronic devices is the failure of reliability because of excessive thermal loads. This requires advanced cooling methods to be incorporated to manage the increase of the dissipated heat. The traditional air-cooling can not meet the requirements of cooling heat fluxes as high as 100 W/cm2, or even higher, and the traditional liquid cooling is not sufficient either in cooling very high heat fluxes although the pressure drop is small. Therefore, a new generation of liquid cooling technology becomes necessary. Various microchannels are widely used to cool the electronic chips by a gas or liquid removing the heat, but these microchannels are often designed to be single-layer channels with high pressure drop. In this paper, the laminar heat transfer and pressure loss of a kind of double-layer microchannel have been investigated numerically. The layouts of parallel-flow and counter-flow for inlet/outlet flow directions are designed and then several sets of inlet flow rates are considered. The simulations show that such a double-layer microchannel can not only reduce the pressure drop effectively but also exhibits better thermal characteristics. Due to the negative heat flux effect, the parallel-flow layout is found to be better for heat dissipation when the flow rate is limited to a low value while the counter-flow layout is better when a high flow rate can be provided. In addition, the thermal performance of the single-layer microchannel is between those of parallel-flow layout and counter-flow layout of the double-layer microchannel at low flow rates. At last, the optimizations of geometry parameters of double-layer microchannel are carried out through changing the height of the upper-branch and lower-branch channels to investigate the influence on the thermal performance.