Transistor Applications Research Articles

Side-Chain Engineering of Conjugated Polymers for High-Performance Organic Field-Effect Transistors.

Past decades have witnessed the rapid development of conjugated polymers because of their promising semiconducting properties and applications in organic field-effect transistors (OFETs). Recent studies have shown that side-chain engineering of conjugated polymers is an efficient strategy to increase semiconducting performance. This Perspective focuses on the side-chain modulation of conjugated polymers and evaluating their effects on the performance of OFETs. The challenges and potential applications of functional high-performance OFETs through side-chain engineering are also discussed.

Hybrid density functional theory study on zinc blende GaN and diamond surfaces and interfaces: Effects of size, hydrogen passivation, and dipole corrections

GaN-diamond heterojunctions show promise in high electron mobility transistor applications. This prompts the need for accurate models of structural and electronic properties. We detail here a hybrid density functional theory study of zinc blende (ZB) GaN and diamond heterostructures using slab supercell models. The dependence of electronic properties on supercell size, pseudo-hydrogen passivation, and dipole corrections is detailed. The larger bulk modulus of diamond is shown to provide a templating structure for GaN to grow upon, where the large lattice mismatch is accounted for through the inclusion of a cationic Ga adlayer. Looking at both type I and II surfaces and interfaces of GaN shows the instability of zb GaN without an adlayer (type II), where increased size, pseudo-hydrogen passivation and dipole corrections do not remove the spurious interaction between the top and bottom layers in type II GaN. Layer dependent density of states, local potential differences, and charge density differences show that the type I interface (with a Ga adlayer) is stable with an adhesion energy of 0.704 eV/Å2 (4.346 J/m2); interestingly, the diamond charge density intercalates into the first layer of GaN, which was seen experimentally for wurtzite GaN grown over diamond. The type II interface is shown to be unstable which implies that, to form a stable, thin-film zb interface between GaN and diamond, the partial pressure of trimethylgallium must be controlled to ensure a Ga layer exists both on the top and bottom layer of the GaN thin film atop the diamond. We believe our results lead to a better understanding of the GaN/diamond multifaceted interface present in the GaN overgrowth on diamond heterojunction used in electronic device applications.

Impact of Furan Substitution on the Optoelectronic Properties of Biphenylyl/Thiophene Derivatives for Light-Emitting Transistors.

Biphenylyl/thiophene systems are known for their ambipolar behavior and good optical emissivity. However, often these systems alone are not enough to fabricate the commercial-grade light-emitting devices. In particular, our recent experimental and theoretical analyses on the three-ring-constituting thiophenes end capped with biphenylyl have shown good electrical properties but lack of good optical properties. From a materials science perspective, one way to improve the properties is to modify their structure and integrate it with additional moieties. In recent years, furan moieties have proven to be a potential substitution for thiophene to improve the organic semiconductive materials properties. In the present work, we systematically substituted different proportions of furan rings in the biphenylyl/thiophene core and studied their optoelectronic properties, aiming toward organic light-emitting transistor applications. We have found that the molecular planarity plays a vital role on the optoelectronic properties of the system. The lower electronegativity of the O atom offers better optical properties in the furan-substituted systems. Further, the furan substitution significantly affects the molecular planarity, which in turn affects the system mobility. As a result, we observed drastic changes in the optoelectronic properties of two furan-substituted systems. Interestingly, addition of furan has reduced the electron mobility by one fold compared to the pristine thiophene-based derivative. Such a variation is interpreted to be due to the low average electronic coupling in furan systems. Overall, systems with all furan and one ring of furan in the center end capped with thiophene have shown better optoelectronic properties. This molecular architecture favors more planarity in the system with good electrical properties and transition dipole moments, which would both play a vital role in the construction of an organic light-emitting transistor.

Thermal Rectifier and Thermal Transistor of 1T/2H MoS2 for Heat Flow Management.

Thermal rectifiers and thermal transistors are expected to be widely used for efficient thermal management and energy cascade utilization due to their excellent directional thermal management. Two-dimensional micro/nano materials have huge potential in the applications of thermal transistors, thermal logic circuits, and thermal rectifiers owing to the phase transition and thermal rectification phenomenon. Herein, a lithium intercalation method was used to transform 2H-MoS2 into the 1T phase with a purity of 76%, and a suspended microelectrode was applied to measure the thermal conductivity and thermal rectification coefficient of the same MoS2 film with 1T and 2H phases in suit. The thermal conductivity and thermal rectification effect of two-phase MoS2 couple with its phase state and structure were also obtained. The results demonstrate that the thermal conductivities of MoS2 in both 1T and 2H phases decrease with increasing temperature. It is also found that the thermal rectification coefficient has no obvious dependence on the temperature and phase change but the asymmetric structure. Furthermore, a thermal rectifier and transistor with a high thermal rectification effect are designed. The direction and magnitude of heat flow through the samples can be effectively controlled and managed by adjusting the phase, size, and structural asymmetry of the different samples. The maximum thermal rectification coefficient of the thermal rectifiers is up to 0.8.

Remarkably High-Performance Nanosheet GeSn Thin-Film Transistor.

High-performance p-type thin-film transistors (pTFTs) are crucial for realizing low-power display-on-panel and monolithic three-dimensional integrated circuits. Unfortunately, it is difficult to achieve a high hole mobility of greater than 10 cm2/V·s, even for SnO TFTs with a unique single-hole band and a small hole effective mass. In this paper, we demonstrate a high-performance GeSn pTFT with a high field-effect hole mobility (μFE), of 41.8 cm2/V·s; a sharp turn-on subthreshold slope (SS), of 311 mV/dec, for low-voltage operation; and a large on-current/off-current (ION/IOFF) value, of 8.9 × 106. This remarkably high ION/IOFF is achieved using an ultra-thin nanosheet GeSn, with a thickness of only 7 nm. Although an even higher hole mobility (103.8 cm2/V·s) was obtained with a thicker GeSn channel, the IOFF increased rapidly and the poor ION/IOFF (75) was unsuitable for transistor applications. The high mobility is due to the small hole effective mass of GeSn, which is supported by first-principles electronic structure calculations.

High-yield production of mono- or few-layer transition metal dichalcogenide nanosheets by an electrochemical lithium ion intercalation-based exfoliation method.

Transition metal dichalcogenide (TMD) nanomaterials, especially the mono- or few-layer ones, have received extensive research interest owing to their versatile properties, ranging from true metals (e.g., NbS2 and VSe2) and semimetals (e.g., WTe2 and TiSe2) to semiconductors (e.g., MoS2 and We2) and insulators (e.g., HfS2). Therefore, the reliable production of these nanomaterials with atomically thin thickness and laterally uniform dimension is essential for their promising applications in transistors, photodetectors, electroluminescent devices, catalysis, energy conversion, environment remediation, biosensing, bioimaging, and so on. Recently, the electrochemical lithium ion intercalation-based exfoliation method has emerged as a mature, efficient and promising strategy for the high-yield production of mono- or few-layer TMD nanosheets; monolayer MoS2 (yield of 92%), monolayer TaS2 (yield of 93%) and bilayer TiS2 (yield of 93%) with lateral dimensions of ~1 µm (refs. 1-3). This Protocol describes the details of experimental procedures for the high-yield synthesis of mono- or few-layer TMDs and other inorganic nanosheets such as MoS2, WS2, TiS2, TaS2, ZrS2, graphene, h-BN, NbSe2, WSe2, Sb2Se3 and Bi2Te3 by using the electrochemical lithium ion intercalation-based exfoliation method, which involves the electrochemical intercalation of lithium ions into layered inorganic crystals and a mild sonication process. The whole protocol takes 26-38 h for the successful production of ultrathin inorganic nanosheets.

Recent progress and perspectives on atomic‐layer‐deposited semiconducting oxides for transistor applications

AbstractThis paper reviews recent developments in the fabrication of high‐performance n‐channel metal‐oxide thin‐film transistors (TFTs) through atomic‐layer deposition (ALD), which are now attracting attention due to their potential for use in augmented and virtual reality, ultra‐high‐definition organic light‐emitting diodes, and flexible electronics. Recent trends in research on TFT backplanes for display applications are provided in the introduction. In the main section, ALD‐derived n‐type oxides serving as active layers are classified into binary, ternary, and quaternary systems, and recent developments and critical issues in n‐channel oxide TFTs are described. The performance of n‐channel oxide TFTs can be boosted through advanced architectures, including stacked heterojunction channels using two‐dimensional electron gases, and the introduction of high‐k dielectric such as ALD‐derived hafnium oxide, which is highlighted in this review. Finally, progress in p‐channel ALD‐derived oxide TFTs is briefly addressed with respect to complementary metal–oxide‐semiconductor applications.

Electro-Magneto-Optically Active Polyaniline/Hydroxypropyl Cellulose Composite

A polyaniline (PANI) composite was prepared through chemical polymerization of aniline in the cholesteric liquid crystal (CLC) state of hydroxypropyl cellulose (HPC). Polymerization and composite formation were simultaneously performed. Polarizing optical microscopy, scanning electron microscopy, electrochemistry, and optical spectroscopy were used to characterize the composite. Electron spin resonance and a superconducting quantum-interference device were used to investigate the composite’s magnetic properties. PANI in the composite exhibited a helical structure of the main chain as a result of the main chain growing in the direction of the LC orientation. The main chains of PANI were secondarily doped, thus they exhibited moderate electrical conductivity as a conducting polymer (PANI)/insulating polymer composite. Polarons (radical cations) distributed along the main chain with a helical structure are responsible for the composite’s magnetic spins. Consequently, the spins, like the helical structure, are delocalized. Because of the doping–dedoping of the PANI component, the composite exhibits excellent redox properties. The PANI/HPC composite’s potential applications in capacitors, electrochemical transistors, thermistors, and optical fibers were investigated.

Functionalized D/A–A–D quinolines for application in solution-processable p-channel organic field-effect transistors

New functionalized quinolines with a D/A–A–D architecture and pi-end-groups at terminals were designed and synthesized. OFETs fabricated from compounds with a D–A–D architecture exhibited p-channel transistor characteristics with high hole mobilities.

DFT investigation on D-π-A structures for n type semiconducting material for the application in organic field effect transistors

Organic Field Effect Transistors have been widely researched since the first reported OFET in 1986 which was made of Polythiophene. The designed two molecular structures are based on D-π-A model and looked for their efficient use in Organic field effect transistors. The designed systems are named as system first (anthracene-pyrrole-propanoic acid) and system second (naphthalene-pyrrole-nitroethane) where anthracene and naphthalene are donors, pyrrole is spacer molecule, propanoic acid and nitroethane are acceptors. Both the structures were optimized under the framework of Density functional theory with B3LYP/6–31 + G(d,p) basis set on a Gaussian16W software package. The calculated charge transport parameters are hole reorganization energy λh, electron reorganization energy λe , HOMO-LUMO energy gap. Further, these have been looked upon their electric field dependence of the HOMO-LUMO energy gap and molecular electrostatic potential (MESP). The λh value for system first is 2.8 × 10-4 eV, and λe value is 4.08 × 10-5 eV. Similarly, the λh value for system second is 1.36 × 10-5 eV and λe value is 1.08 × 10-5 eV. In both the systems the electron reorganization energy λe is smaller as compared to the hole reorganization energy λh. Therefore, this is confirmed that the designed molecules can be utilized as n-type semiconductor for Organic Field Effect Transistors.

Electric field and strain engineering tuning Rashba spin splitting in quasi-one-dimensional organic-inorganic hybrid perovskites (MV)AI3Cl2 (MV = methylviologen, A = Bi, Sb).

We systematically study the Rashba spin texture of lead-free quasi-one-dimensional organic-inorganic hybrid perovskites (OIHP), (MV)AI3Cl2 (MV = methylviologen, A = Bi, Sb) with first-principles calculations. The kx-ky plane Rashba spin splitting was found to depend on the composition of Bi (Sb) and I atoms at band edges. Importantly, increasing ferroelectric polarization and the stretch along the z-direction can effectively enhance the amplitude of the Rashba spin splitting. This work provides an avenue for electric field and strain-controlled spin splitting and highlights the potential of quasi-one-dimensional OIHP for further applications in spin field effect transistors and photovoltaic cells.

High-performance five-ring-fused organic semiconductors for field-effect transistors.

Organic molecular semiconductors have been paid great attention due to their advantages of low-temperature processability, low fabrication cost, good flexibility, and excellent electronic properties. As a typical example of five-ring-fused organic semiconductors, a single crystal of pentacene shows a high mobility of up to 40 cm2 V-1 s-1, indicating its potential application in organic electronics. However, the photo- and optical instabilities of pentacene make it unsuitable for commercial applications. But, molecular engineering, for both the five-ring-fused building block and side chains, has been performed to improve the stability of materials as well as maintain high mobility. Here, several groups (thiophenes, pyrroles, furans, etc.) are introduced to design and replace one or more benzene rings of pentacene and construct novel five-ring-fused organic semiconductors. In this review article, ∼500 five-ring-fused organic prototype molecules and their derivatives are summarized to provide a general understanding of this catalogue material for application in organic field-effect transistors. The results indicate that many five-ring-fused organic semiconductors can achieve high mobilities of more than 1 cm2 V-1 s-1, and a hole mobility of up to 18.9 cm2 V-1 s-1 can be obtained, while an electron mobility of 27.8 cm2 V-1 s-1 can be achieved in five-ring-fused organic semiconductors. The HOMO-LUMO levels, the synthesis process, the molecular packing, and the side-chain engineering of five-ring-fused organic semiconductors are analyzed. The current problems, conclusions, and perspectives are also provided.

Flexible neuromorphic transistors and their biomimetric sensing application

Biological perception system has the unique advantages of high parallelism, high error tolerance, self-adaptation and low power consumption. Using neuromorphic devices to emulate biological perceptual system can effectively promote the development of brain-computer interfaces, intelligent perception, biological prosthesis and so on. Compared with other neuromorphic devices, multi-terminal neuromorphic transistors can not only realize signal transmission and training learning at the same time, but also carry out nonlinear spatio-temporal integration and collaborative regulation of multi-channel signals. However, the traditional rigid neuromorphic transistor is difficult to achieve bending deformation and close fit with the human body, which limits the application range of neuromorphic devices. Therefore, the research of flexible neuromorphic transistor with good bending characteristics has become the focus of recent research. Firstly, this review introduces the research progress of many kinds of flexible neuromorphic transistors, including device structure, working principle and basic functions. In addition, the application of the flexible neuromorphic transistor in the field of bionic perception is also introduced. Finally, this review also gives a summary and simple prospect of the above research fields.

Benzobisthiazole Polymer with Resonance-assisted Hydrogen Bonds for High-performance Transistor and Solar Cell Applications

Benzobisthiazole Polymer with Resonance-assisted Hydrogen Bonds for High-performance Transistor and Solar Cell Applications

Effect of ZnO buffer layer on the structural and electrical properties of Bi1.5Zn1Nb1.5O7 thin films grown by pulsed laser ablation

The effect of ZnO buffer layer on the growth and dielectric properties of Bi1.5Zn1Nb1.5O7 (BZN) thin films deposited on Pt-Si substrate using pulsed laser ablation was studied in detail. An intermediate ZnO buffer greatly enhanced the crystalline quality as well as the dielectric properties of BZN thin films. Variation of Raman spectra with oxygen partial pressure was studied in detail. The presence of the ZnO buffer layer has increased the dielectric constant as well as tunability. This enhancement in dielectric properties may be attributed to the increased crystallinity and oxygenation of the BZN thin films in the presence of a semiconducting buffer layer. The directly stacked structure of the fabricated device with the top dielectric oxide thin films as a gate oxide and the semiconducting buffer layer as the channel layer can be used as a potential candidate for thin film field effect transistor applications.

Improved Monolayer MoS Performance With Two-Step Atomic Layer Deposited High- Dielectrics

Gate dielectric engineering is crucial to enable two-dimensional (2D) transition metal dichalcogenides (TMDs) for logic transistor applications. In this work, we demonstrate a uniform and pinhole-free bilayer high-K fabricated on monolayer (1L) molybdenum disulfide (MoS2) through thermal atomic layer deposition (ALD) without surface pretreatment. A thin low-temperature (75∘C) AlOx film deposited directly on 1L-MoS2 mitigates 2D channel damage and serves as a nucleation and protection layer for high-temperature (250∘aC) HfOx high-K layer. The 1L-MoS2 back-gate (BG) devices with low-temperature ALD capping show minor mobility degradation, less threshold voltage shift, smooth surface topography, and lower device variability compared to those with high-temperature ALD capping. These electrical differences are closely related to the coverage of the AlOx film at the initial ALD stage and the resultant quality of the AlOx -MoS2 interface after HfOx deposition. The underlying mechanism of ALD on the TMDs is proposed in terms of physical analysis and electrical findings. This work provides a practical and scalable ALD approach in gate dielectrics toward high performance 2D electronics.

Indium-free GZO thin films prepared using plasma-enhanced atomic layer deposition: toward thin film transistor application

Indium-free GZO thin films have been prepared using PEALD and employed as a channel layer of TFTs.

First-principles study of metal-semiconductor contact OF CS and X2CO2 (X=Ti, Zr, Hf) monolayers

Using first principles calculations, we have investigated the structural and electronic properties of Carbon Sulfide (CS) and X2CO2 (X=Ti, Zr, Hf) MXenes monolayers and their CS-X2CO2 (X=Ti, Zr, Hf) metal-semiconductor (MS) contacts. The energetic stability of MS contacts is confirmed by minimum binding energy. The intrinsic electronic properties of CS-X2CO2 are well preserved due to weak van der Waals (vdWs) contact. An indirect band gap semiconductor behavior is found for Ti2CO2, Zr2CO2, Hf2CO2, while CS and all MS contacts are metals. Our results show that the interface CS-X2CO2formed p-type Schottky contact with a SBH of 0.69 eV. Furthermore, we also compute the electrostatic potential for CS-X2CO2 MS contacts, where the CS layer have deeper potential than X2CO2 layer and the electrons/charges of CS-X2CO2 MS contacts transfer from CS layer to X2CO2 monolayer. Also, we calculate the work function of CS-X2CO2 (X=Ti, Zr, Hf) MS contacts, which corresponds to minimum amount of energy required to remove an electron from the metal. These results will be useful for promising applications in field-effect transistors (FET) and photodetectors devices.

Advances in organic micro/nanocrystals with tunable physicochemical properties

Organic micro/nanocrystals based on small organic molecules have drawn extensive attention due to their potential application in organic field-effect transistors, electrochemical sensors, solar cells, etc. Herein, the recent advances for organic micro/nanocrystals from the perspective of molecule aggregation mode, morphology modulation, and optical property modulation are reviewed. The stacking mode and the intermolecular interaction depend on the molecular structure, which eventually determines the morphology of organic micro/nanocrystals. The morphologies of the organic micro/nanocrystals make the aggregates exhibit photon confinement or light-guiding properties as organic miniaturized optoelectronic devices. In this review, we conclude with a summary and put forward our perspective on the current challenges and the future development of morphology and optical tunable direction for the organic micro/nanocrystals.

Long-Wavelength Instabilities Impact Alignment during Blade Coating of a Stretchable Organic Transistor Blend.

The use of polymer-polymer blends to tailor mechanical properties and improve electrical performance is becoming widespread in the field of printed electronics. Similarly, meniscus-guided coating can be used to tailor electrical properties through alignment of the semiconducting material. We report on a long-wavelength instability during blade coating of a semiconducting polymer/elastomer blend for organic transistor applications that results in significant variation of the semiconducting polymer nanofibril alignment across the instability period. By correlating measurements over diverse (nm to mm) length scales, we can directly relate the charge transport in top-gate transistors to the local polymer nanofibril alignment. Hole mobility is directly correlated to the local alignment and shows an ≈2 × variation across the instability for devices aligned with the coating direction. The potential for long-wavelength instabilities to create device-relevant morphology variations should be considered when optimizing coating conditions. These results reveal considerable potential for error in assuming that smooth films are necessarily structurally uniform; material structure may spatially vary for some coating methods, leading to a correlated, spatially varying device performance.