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van der Waals Epitaxial Growth of Atomically Thin 2D Metals on Dangling-Bond-Free WSe <sub/>2</sub> and WS <sub/>2</sub>
摘要： 2D metals have attracted considerable recent attention for their special physical properties, such as charge density waves, magnetism, and superconductivity. However, despite some recent efforts, the synthesis of ultrathin 2D metals nanosheets down to monolayer thickness remains a significant challenge. Herein, by using atomically flat 2D WSe2 or WS2 as the growth substrate, the synthesis of atomically thin 2D metallic MTe2 (M = V, Nb, Ta) single crystals with the thickness down to the monolayer regime and the creation of atomically thin MTe2/WSe2 (WS2) vertical heterojunctions is reported. Comparison with the growth on the SiO2/Si substrate under the same conditions reveals that the utilization of the dangling-bond-free WSe2 or WS2 as the van der Waals epitaxy substrates is crucial for the successful realization of atomically thin MTe2 (M = V, Nb, Ta) nanosheets. It is further shown that the epitaxial grown 2D metals can function as van der Waals contacts for 2D semiconductors with little interface damage and improved electronic performance. This study defines a robust van der Waals epitaxy pathway to ultrathin 2D metals, which is essential for fundamental studies and potential technological applications of this new class of materials at the 2D limit.
关键词： van der Waals epitaxy,field-effect transistors,2D materials,chemical vapor deposition,transition metal dichalcogenides
更新于2025-09-19 17:15:36
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Textured Poling of the Ferroelectric Dielectric Layer for Improved Organic Field-Effect Transistors
摘要： Polymer ferroelectrics are playing an increasingly active role in flexible memory application and wearable electronics. The relaxor ferroelectric dielectric, poly(vinylidene fluoride trifluorethylene (PVDF-TrFE), although vastly used in organic field-effect transistors (FETs), has issues with gate leakage current especially when the film thickness is below 500 nm. This work demonstrates a novel method of selective poling the dielectric layer. By using solution-processed 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-pentacene) as the organic semiconductor, it is shown that textured poling of the PVDF-TrFE layer dramatically improves FET properties compared to unpoled or uniformly poled ferroelectric films. The texturing is achieved by first vertically poling the PVDF-TrFE film and then laterally poling the dielectric layer close to the gate electrode. TIPS-pentacene FETs show on/off ratios of 105 and hole mobilities of 1 cm2 Vs?1 under ambient conditions with operating voltages well below ?5 V. The electric field distribution in the dielectric layer is simulated by using finite difference time domain methods.
关键词： poling,organic semiconductor,ferroelectric dielectric,field-effect transistors,transport
更新于2025-09-19 17:15:36
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Scalable fabrication of a complementary logic inverter based on MoS <sub/>2</sub> fin-shaped field effect transistors
摘要： Integration of high performance n-type and p-type field-effect transistors with complementary device operation in the same kind of layered materials is highly desirable for pursuing low power and flexible next-generation electronics. In this work, we have shown a well-mannered growth of MoS2 on a fin-shaped oxide structure and integration of both n-type and p-type MoS2 by using a traditional implantation technique. With the advance of the fin-shaped structure, the maxima and the effective ON current density for the MoS2 fin-shaped field-effect transistors are respectively obtained to be about 50 μA μm?1 (normalized by the circumference of the fin) and around 500 μA μm?1 (only normalized by the fin size), while its ON/OFF ratio is more than 10? with low OFF current of a few pA. Based on our n-type and p-type MoS2 fin-shaped field-effect transistors, the complementary MoS2 inverter with a high DC voltage gain of more than 20 is acquired. Our results provide evidence for complementary 2D material operation in the same materials, a promising avenue for the development of high performance and high-density complementary 2D electronic devices.
关键词： ion implantation,2D materials,fin-shaped field-effect transistors,MoS2,complementary logic inverter
更新于2025-09-19 17:15:36
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Carbon Nanotube Complementary Gigahertz Integrated Circuits and Their Applications on Wireless Sensor Interface Systems
摘要： Along with ultralow-energy delay products and symmetric complementary polarities, carbon nanotube field-effect transistors (CNT FETs) are expected to be promising building blocks for energy-efficient computing technology. However, the work frequencies of the existing CNT-based complementary metal-oxide-semiconductor (CMOS) integrated circuits (ICs) are far below the requirement (850 MHz) in state-of-art wireless communication applications. In this work, we fabricated deep submicron CMOS FETs with considerably improved performance of n-type CNT FETs and hence significantly promoted the work frequency of CNT CMOS ICs to 1.98 GHz. Based on these high-speed and sensitive voltage-controlled oscillators, we then presented a wireless sensor interface circuit with working frequency up to 1.5 GHz spectrum. As a preliminary demonstration, an energy-efficient wireless temperature sensing interface system was realized combining a 150 mAh flexible Li-ion battery and a flexible antenna (center frequency of 915 MHz). In general, the CMOS-logic high-speed CNT ICs showed outstanding energy efficiency and thus may potentially advance the application of CNT-based electronics.
关键词： complementary metal-oxide semiconductor,sensor interface,voltage-controlled oscillators,field-effect transistors,carbon nanotube film
更新于2025-09-19 17:15:36
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[IEEE 2018 International Flexible Electronics Technology Conference (IFETC) - Ottawa, ON (2018.8.7-2018.8.9)] 2018 International Flexible Electronics Technology Conference (IFETC) - 3D Printed Ion-Selective Field Effect Transistors
摘要： This report describes 3D printed ion-selective field effect transistors (IS-FET), which contains electro-chemical working electrodes for selective ion detection. For the comparison of behaviors, two different types of field effect transistors are fabricated by 3D printing and vacuum deposition. And both types of FETs are integrated with the 3D printed ion-selective electrodes. Then, the sensing performance of these two types of IS-FET has been investigated. The source-drain current for the whole 3D printed IS-FET is in the scale of 10-8 A, which can be compared with current scale of deposited IS-FET with 10-6 A.
关键词： ion-selective field effect transistors,3D printing,oxide FET
更新于2025-09-19 17:15:36
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NIR polymers and phototransistors
摘要： A novel bisthiophene-fused diketopyrrolopyrrole unit (4,11-bis(2-octyldodecyl)-7H,14H-thieno[30,20:7,8]indolizino[2,1-a]thieno[3,2-g]indolizine-7,14-dione, BTI) has been designed as an electron acceptor and used to copolymerize with thiophene and bithiophene as electron donors to construct two D–A conjugated polymers, P1 and P2 via Stille coupling, respectively. The two polymers showed excellent thermal stability, broad light absorption and a narrow energy band gap. P1 and P2 were used to fabricate organic field-effect transistors (OFETs) to evaluate their charge transport characteristics. P2 showed much better hole transport performance with a mobility of 0.1 cm2 V?1 s?1. Near-infrared (NIR) phototransistors were also fabricated by using the two polymers blended with PC71BM as the active layer. With illumination of 35 mW cm?2 at a wavelength of 850 nm, the photocurrent/dark-current ratio (P) and photoresponsivity (R) of the phototransistor based on P1/PC71BM were 3.6 × 104 and 270 A W?1, respectively. For P2/PC71BM, P was 2.5 × 104 and R reached 2420 A W?1.
关键词： phototransistors,photoresponsivity,organic field-effect transistors,diketopyrrolopyrrole,NIR polymers,charge transport
更新于2025-09-19 17:15:36
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Optically Tunable Field Effect Transistors with Conjugated Polymer Entailing Azobenzene Groups in the Side Chains
摘要： Semiconducting conjugated polymers with photoswitching behavior are highly demanded for field-effect transistors (FETs) with tunable electronic properties. Herein a new design strategy is established for photoresponsive conjugated polymers by incorporating photochromic units (azobenzene) into the flexible side alkyl chains. It is shown that azobenzene groups in the side chains of the DPP (diketopyrrolopyrrole)-quaterthiophene polymer (PDAZO) can undergo trans/cis photoisomerization in fully reversible and fast manner. Optically tunable FETs with bistable states are successfully fabricated with thin films of PDAZO. The drain-source currents are reduced by 80.1% after UV light irradiation for ≈28 s, which are easily restored after further visible light irradiation for ≈33 s. Such fast optically tunable FETs are not reported before. Moreover, such current photomodulation can be implemented for multiple light irradiation cycles with good photofatigue resistance. Additionally, thin film charge mobility of PDAZO can be reversibly modulated by alternating UV and visible light irradiations. On the basis of theoretical calculations and GIWAXS data, it is hypothesized that the dipole moment and configuration changes associated with the trans-/cis-photoisomerization of azobenzene groups in PDAZO can affect the respective intra-chain and inter-chain charge transporting, which is responsible for the optically tunable behavior for FETs with thin films of PDAZO.
关键词： side alkyl chains,semiconducting polymers,thin-film field-effect transistors,azobenzene,photoresponsiveness
更新于2025-09-19 17:15:36
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Bias-stress effects in diF-TES-ADT field-effect transistors
摘要： A systematic analysis of the bias-stress effects in solution-processed organic field-effect transistors is reported. Difluoro 5,11-bis(triethylsilylethynyl) anthradithiophene, a high-performance molecular semiconductor, forms a charge-transport channel and is coupled with injection contacts made of Au, Ag, or Cu. The electrode metal is found to not only greatly affect the switching performances but also drive the response of transistors to the extended applications of gate voltage. The observations are put into the framework of contact-limited transistor model, which holistically assesses the material, geometry, and stress-related contributions.
关键词： Bias stress,Device physics,Contact resistance,DiF-TES-ADT,Organic field-effect transistors
更新于2025-09-19 17:15:36
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Naphthalene Diimide-Based Terpolymers with Controlled Crystalline Properties for Producing High Electron Mobility and Optimal Blend Morphology in All-Polymer Solar Cells
摘要： We report a series of new n-type random copolymers (P(NDI2OD-Se-Th x) where x = 0, 0.5, 0.7, 0.8, 0.9, 1.0) consisting of naphthalene diimide (NDI), selenophene-2,2’-thiophene (Se-Th), and seleno[3,2-b]thiophene (SeTh) to demonstrate their use in producing efficient all-polymer solar cells (all-PSCs) and organic field-effect transistors (OFETs). To investigate the effect of polymer crystallinity on the performance of all-PSCs and OFETs, we tuned the composition of the Se-Th and SeTh moieties in the P(NDI2OD-Se-Th x) polymers, resulting in enhanced crystalline properties with higher Se-Th ratio. Thus, the OFET electron mobility was increased with higher Se-Th ratio, exhibiting the highest value of 1.38×10?1 cm2 V?1 s?1 with P(NDI2OD-Se-Th 1.0). However, the performance of all-PSCs based on PBDB-T:P(NDI2OD-Se-Th x) showed a non-linear trend relative to the Se-Th ratio and the performance was optimized with P(NDI2OD-Se-Th 0.8) exhibiting the highest power coversion efficiency of 8.30%. This is attributed to the stronger crystallization-driven phase separation in all-polymer blends for higher Se-Th ratio. At the optimal crystallinity of P(NDI2OD-Se-Th 0.8) in all-PSCs, the degree of phase separation, domain purity and the electron mobility were optimized, resulting in enhanced charge generation and transport. Our works describe structure-property-performance relationships to design effective n-type polymers in terms of crystalline and electrical properties suitable for both efficient OFETs and all-PSCs.
关键词： organic field-effect transistors,seleno[3,2-b]thiophene,polymer crystallinity,n-type random copolymers,selenophene-2,2’-thiophene,charge generation,all-polymer solar cells,charge transport,naphthalene diimide
更新于2025-09-19 17:13:59
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Describing broadband terahertz response of graphene FET detectors by a classical model
摘要： Direct power detectors based on field-effect transistors are becoming widely used for terahertz applications. However, accurate characterization at terahertz frequencies of such detectors is a challenging task. The high-frequency response is dominated by parasitic coupling and loss associated with contacts and overall layout of the component. Moreover, the performance of such detectors is complicated to predict since many different physical models are used to explain the high sensitivity at terahertz frequencies. This makes it hard to draw important conclusions about the underlying device physics for these detectors. For the first time, we demonstrate accurate and comprehensive characterization of graphene field-effect transistors from 1 GHz to 1.1 THz, simultaneously accessing the bias dependence, the scattering parameters, and the detector voltage responsivity. Within a frequency range of more than 1 THz, and over a wide bias range, we have shown that the voltage responsivity can be accurately described using a combination of a small-signal equivalent circuit model, and the second-order series expansion terms of the nonlinear dc I ? V characteristic. Without bias, the measured low-frequency responsivity was 0.3 kV/W with the input signal applied to the gate, and 2 kV/W with the input signal applied to the drain. The corresponding cut-off frequencies for the two cases were 140 GHz and 50 GHz, respectively. With a 300-GHz signal applied to the gate, a voltage responsivity of 1.8 kV/W was achieved at a drain-source current of 0.2 mA. The minimum noise equivalent power was below 30 pW/√Hz in cold mode. Our results show that detection of terahertz signals in graphene field-effect transistors can be described over a wide frequency range by the nonlinear carrier transport characteristic obtained at static electrical fields. This finding is important for explaining the mechanism of detection and for further development of terahertz detectors.
关键词： classical model,field-effect transistors,scattering parameters,graphene,broadband characterization,terahertz detectors
更新于2025-09-19 17:13:59