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1.
The dielectric dispersion of a material holds significant importance for the understanding of basic material characteristics and the design parameters of a functional device. Here, the dielectric dispersion characteristics of multilayer hexagonal boron nitride (hBN) using time domain reflectometry under an extended device operating frequency range up to 100 MHz are studied. Contrary to what is previously reported, the capacitance, hence the effective dielectric constant, of hBN decreases with the increase of frequency above the MHz range, indicating heat dissipation in lossy hBN dielectric. Furthermore, hBN shows stubborn dielectric characteristics with temperature changes that confirm its thermal stability in extreme operating conditions. The charge carriers in hBN are transported by Fowler–Nordhiem tunneling with increasing the electrical field. Lastly, hBN endures electrical field of 7.8 MV cm?1 that implies its potential use as a promising dielectric material. These results will benefit the research and development of hBN supported high‐speed electronics operated at high‐frequency conditions for energy‐efficient device applications.  相似文献   

2.
Heat transport across vertical interfaces of heterogeneous 2D materials is usually governed by the weak Van der Waals interactions of the surface‐terminating atoms. Such interactions play a significant role in thermal transport across transition metal carbide and nitride (MXene) atomic layers due to their hydrophilic nature and variations in surface terminations. Here, the metallicity of atomically thin Ti3C2Tz MXene, which is also verified by scanning tunneling spectroscopy for the first time, is exploited to develop a self‐heating/self‐sensing platform to carry out direct‐current annealing experiments in high (<10?8 bar) vacuum, while simultaneously evaluating the interfacial heat transport across a Ti3C2Tz/SiO2 interface. At room temperature, the thermal boundary conductance (TBC) of this interface is found, on average, to increase from 10 to 27 MW m?2 K?1 upon current annealing up to the breakdown limit. In situ heating X‐ray diffraction and X‐ray photo‐electron spectroscopy reveal that the TBC values are mainly affected by interlayer and interface spacing due to the removal of absorbents, while the effect of surface termination is negligible. This study provides key insights into understanding energy transport in MXene nanostructures and other 2D material systems.  相似文献   

3.
Polymer dielectrics find applications in modern electronic and electrical technologies due to their low density, durability, high dielectric breakdown strength, and design flexibility. However, they are not reliable at high temperatures due to their low mechanical integrity and thermal stability. Herein, a self‐assembled dielectric nanocomposite is reported, which integrates 1D polyaramid nanofibers and 2D boron nitride nanosheets through a vacuum‐assisted layer‐by‐layer infiltration process. The resulting nanocomposite exhibits hierarchical stacking between the 2D nanosheets and 1D nanofibers. Specifically, the 2D nanosheets provide a thermally conductive network while the 1D nanofibers provide mechanical flexibility and robustness through entangled nanofiber–nanosheet morphologies. Experiments and density functional theory show that the nanocomposites through thickness heat transfer processes are nearly identical to that of boron nitride due to synergistic stacking of polyaramid units onto boron nitride nanosheets through van der Waals interactions. The nanocomposite sheets outperform conventional dielectric polymers in terms of mechanical properties (about 4–20‐fold increase of stiffness), light weight (density ≈1.01 g cm?3), dielectric stability over a broad range of temperature (25–200 °C) and frequencies (103–106 Hz), good dielectric breakdown strength (≈292 MV m?1), and excellent thermal management capability (about 5–24 times higher thermal conductivity) such as fast heat dissipation.  相似文献   

4.
A simple catalysis‐free approach that utilises a gas–solid reaction for the synthesis of large‐scale single‐crystalline PrB6 nanorods using Pr and BCl3 as starting materials is demonstrated. The nanorods exhibit a low turn‐on electric field (2.80 V µ‐b;m?1 at 10 µ‐b;A cm?2), a low threshold electric field (6.99 V µ‐b;m?1 at 1 mA cm?2), and a high current density (1.2 mA cm?2 at 7.35 V µ‐b;m?1) at room temperature (RT). The turn‐on and threshold electric field are found to decrease clearly from 2.80 to 0.95 and 6.99 to 3.55 V µ‐b;m?1, respectively, while the emission current density increases significantly from 1.2 to 13.8 mA cm?2 (at 7.35 V µ‐b;m?1) with an increase in the ambient temperature from RT to 623 K. The field enhancement factor, emission current density, and the dependence of the effective work function with temperature are investigated. The possible mechanism of the temperature‐dependent emission from PrB6 nanorods is discussed.  相似文献   

5.
Low‐voltage self‐assembled monolayer field‐effect transistors (SAMFETs) that operate under an applied bias of less than ?3 V and a high hole mobility of 10?2 cm2 V?1 s?1 are reported. A self‐assembled monolayer (SAM) with a quaterthiophene semiconducting core and a phosphonic acid binding group is used to fabricate SAMFETs on both high‐voltage (AlOx/300 nm SiO2) and low‐voltage (HfO2) dielectric platforms. High performance is achieved through enhanced SAM packing density via a heated assembly process and through improved electrical contact between SAM semiconductor and metal electrodes. Enhanced electrical contact is obtained by utilizing a functional methylthio head group combined with thermal annealing post gold source/drain electrode deposition to facilitate the interaction between SAM and electrode.  相似文献   

6.
Carbon nanoparticles (CNPs) are grown on flexible carbon fabric via a simple and low‐cost flame synthesis process. The entire struture of the carbon fabric substrate retains its high flexibility after the growth of CNPs and can even be rolled‐up and twisted to a large degree without affecting the electric characteristics. No appreciable changes in the conductance can be observed under different bending curvatures after hundreds of bending cycles. The thermal conductivity of the carbon fabric with CNPs is about 2.34 W m?1 K?1, about one order of magnitude higher than that of most polymer substrates. The field emitter fabricated using the structure has a low threshold electric field of around 2.8 V μm?1, and a high field emission current density of 108 mA cm?2, which is about two to four orders of magnitude higher than that of most polymer substrate‐based flexible CNT field emitters. These results indicate that CNPs on carbon fabric have potential applications in flexible electronics devices and displays.  相似文献   

7.
A 3‐aminopropyltrimethoxysilane‐derived self‐assembled monolayer (NH2SAM) is investigated as a barrier against copper diffusion for application in back‐end‐of‐line (BEOL) technology. The essential characteristics studied include thermal stability to BEOL processing, inhibition of copper diffusion, and adhesion to both the underlying SiO2 dielectric substrate and the Cu over‐layer. Time‐of‐flight secondary ion mass spectrometry and X‐ray spectroscopy (XPS) analysis reveal that the copper over‐layer closes at 1–2‐nm thickness, comparable with the 1.3‐nm closure of state‐of‐the‐art Ta/TaN Cu diffusion barriers. That the NH2SAM remains intact upon Cu deposition and subsequent annealing is unambiguously revealed by energy‐filtered transmission electron microscopy supported by XPS. The SAM forms a well‐defined carbon‐rich interface with the Cu over‐layer and electron energy loss spectroscopy shows no evidence of Cu penetration into the SAM. Interestingly, the adhesion of the Cu/NH2SAM/SiO2 system increases with annealing temperature up to 7.2 J m?2 at 400 °C, comparable to Ta/TaN (7.5 J m?2 at room temperature). The corresponding fracture analysis shows that when failure does occur it is located at the Cu/SAM interface. Overall, these results demonstrate that NH2SAM is a suitable candidate for subnanometer‐scale diffusion barrier application in a selective coating for copper advanced interconnects.  相似文献   

8.
Thermal conductivity of free‐standing reduced graphene oxide films subjected to a high‐temperature treatment of up to 1000 °C is investigated. It is found that the high‐temperature annealing dramatically increases the in‐plane thermal conductivity, K, of the films from ≈3 to ≈61 W m?1 K?1 at room temperature. The cross‐plane thermal conductivity, K, reveals an interesting opposite trend of decreasing to a very small value of ≈0.09 W m?1 K?1 in the reduced graphene oxide films annealed at 1000 °C. The obtained films demonstrate an exceptionally strong anisotropy of the thermal conductivity, K/K ≈ 675, which is substantially larger even than in the high‐quality graphite. The electrical resistivity of the annealed films reduces to 1–19 Ω □?1. The observed modifications of the in‐plane and cross‐plane thermal conductivity components resulting in an unusual K/K anisotropy are explained theoretically. The theoretical analysis suggests that K can reach as high as ≈500 W m?1 K?1 with the increase in the sp2 domain size and further reduction of the oxygen content. The strongly anisotropic heat conduction properties of these films can be useful for applications in thermal management.  相似文献   

9.
A donor–acceptor (D–A) semiconducting copolymer, PDPP‐TVT‐29, comprising a diketopyrrolopyrrole (DPP) derivative with long, linear, space‐separated alkyl side‐chains and thiophene vinylene thiophene (TVT) for organic field‐effect transistors (OFETs) can form highly π‐conjugated structures with an edge‐on molecular orientation in an as‐spun film. In particular, the layer‐like conjugated film morphologies can be developed via short‐term thermal annealing above 150 °C for 10 min. The strong intermolecular interaction, originating from the fused DPP and D–A interaction, leads to the spontaneous self‐assembly of polymer chains within close proximity (with π‐overlap distance of 3.55 Å) and forms unexpectedly long‐range π‐conjugation, which is favorable for both intra‐ and intermolecular charge transport. Unlike intergranular nanorods in the as‐spun film, well‐conjugated layers in the 200 °C‐annealed film can yield more efficient charge‐transport pathways. The granular morphology of the as‐spun PDPP‐TVT‐29 film produces a field‐effect mobility (μ FET) of 1.39 cm2 V?1 s?1 in an OFET based on a polymer‐treated SiO2 dielectric, while the 27‐Å‐step layered morphology in the 200 °C‐annealed films shows high μ FET values of up to 3.7 cm2 V?1 s?1.  相似文献   

10.
A novel application of ethylene‐norbornene cyclic olefin copolymers (COC) as gate dielectric layers in organic field‐effect transistors (OFETs) that require thermal annealing as a strategy for improving the OFET performance and stability is reported. The thermally‐treated N,N′‐ditridecyl perylene diimide (PTCDI‐C13)‐based n‐type FETs using a COC/SiO2 gate dielectric show remarkably enhanced atmospheric performance and stability. The COC gate dielectric layer displays a hydrophobic surface (water contact angle = 95° ± 1°) and high thermal stability (glass transition temperature = 181 °C) without producing crosslinking. After thermal annealing, the crystallinity improves and the grain size of PTCDI‐C13 domains grown on the COC/SiO2 gate dielectric increases significantly. The resulting n‐type FETs exhibit high atmospheric field‐effect mobilities, up to 0.90 cm2 V?1 s?1 in the 20 V saturation regime and long‐term stability with respect to H2O/O2 degradation, hysteresis, or sweep‐stress over 110 days. By integrating the n‐type FETs with p‐type pentacene‐based FETs in a single device, high performance organic complementary inverters that exhibit high gain (exceeding 45 in ambient air) are realized.  相似文献   

11.
A novel application of ethylene‐norbornene cyclic olefin copolymers (COC) as gate dielectric layers in organic field‐effect transistors (OFETs) that require thermal annealing as a strategy for improving the OFET performance and stability is reported. The thermally‐treated N,N′‐ditridecyl perylene diimide (PTCDI‐C13)‐based n‐type FETs using a COC/SiO2 gate dielectric show remarkably enhanced atmospheric performance and stability. The COC gate dielectric layer displays a hydrophobic surface (water contact angle = 95° ± 1°) and high thermal stability (glass transition temperature = 181 °C) without producing crosslinking. After thermal annealing, the crystallinity improves and the grain size of PTCDI‐C13 domains grown on the COC/SiO2 gate dielectric increases significantly. The resulting n‐type FETs exhibit high atmospheric field‐effect mobilities, up to 0.90 cm2 V?1 s?1 in the 20 V saturation regime and long‐term stability with respect to H2O/O2 degradation, hysteresis, or sweep‐stress over 110 days. By integrating the n‐type FETs with p‐type pentacene‐based FETs in a single device, high performance organic complementary inverters that exhibit high gain (exceeding 45 in ambient air) are realized.  相似文献   

12.
The development of advanced dielectric materials with high electric energy densities is of crucial importance in modern electronics and electric power systems. Here, a new class of multilayer‐structured polymer nanocomposites with high energy and power densities is presented. The outer layers of the trilayered structure are composed of boron nitride nanosheets dispersed in poly(vinylidene fluoride) (PVDF) matrix to provide high breakdown strength, while PVDF with barium strontium titanate nanowires forms the central layer to offer high dielectric constant of the resulting composites. The influence of the filler contents on the electrical polarization, breakdown strength, and energy density is examined. Simulations are carried out to model the electrical tree formation in the layered nanocomposites and to verify the experimental breakdown results. The trilayered polymer nanocomposite with an optimized filler content displays a discharged energy density of 20.5 J cm?3 at Weibull breakdown strength of 588 MV m?1, which is among the highest discharged energy densities reported so far. Moreover, the nanocomposite exhibits a superior power density of 0.91 MW cm?3, more than nine times that of the commercially available biaxially oriented polypropylene. The findings of this research provide a new design paradigm for high‐performance dielectric polymer nanocomposites.  相似文献   

13.
For the first time, the feasibility of ultrathin oxides grown by high pressure oxidation (HIPOX) technology in O2 ambient and nitrided in N2O ambient with rapid thermal processing has been investigated in order for them to be used as a gate oxide of ULSI devices. The dielectric breakdown electric field (E BR) and the midgap interface trap density (D itm) of the nitrided-HIPOX oxide are ?13:9MVcm?1 and 2 × 1010cm?2eV?1 respectively which are almost the same as those of the control oxide and the nitrided-control oxide. The time-tobreakdown (tBD) of the nitrided-HIPOX oxide is longer than that of the control oxide at low electric field (<10?4 A cm?2) owing to the combination of nitrogen and defects near the Si?SiO2 interface during nitridation. The lifetimes of the nitrided-HIPOX oxides increase initially, reaching a maximum value of 1:2 × 109 s at a stress current density of 1 × 10?6 A cm?2,corresponding to over 10 years, and then decrease as nitridation proceeds.  相似文献   

14.
The stability of a field‐emission event, i.e., the stability of the emission current over a long period of time, against thermal effects, etc., is one of the key factors for its application in real devices. Although nanostructures have the advantages of high aspect ratios and faster device turn‐on times, the small masses and large surface areas make them vulnerable to both chemical and physical damages and they have a lower melting point compared to bulk materials of same compositions. SnO2, one of the most attractive oxide semiconductors, which has with a relatively low work function of 4.7 eV, has been a perspective candidate for field emitters. A highly stable field emitter based on thin and quasi‐aligned SnO2 nanowire ensembles with uniform diameter is shown. Field‐emission measurements of these SnO2 nanowire ensembles show low turn‐on and threshold voltages of 3.5 V μm?1 and 4.63 V μm?1, respectively, at an anode–sample distance of 200 μm and very long term scale stability of more than 2400 min, acquired at the electric field of 4.65 V μm?1. Such values are not only better than those of the recently developed SnO2 nanostructures with different morphologies and of randomly oriented SnO2 nanowire ensembles with a similar diameter distribution, but also comparable with the most widely studied field‐emission materials, such as carbon nanotubes and ZnO nanostructures. The potential for using these thin SnO2 nanowire ensembles with uniform diameter in field emitters is shown, with particular promise in those operated for long‐term real device applications.  相似文献   

15.
The impact of the chemical structure and molecular order on the charge transport properties of two donor–acceptor copolymers in their neutral and doped states is investigated. Both polymers comprise 3,7‐bis((E)‐7‐fluoro‐1‐(2‐octyl‐dodecyl)‐2‐oxoindolin‐3‐ylidene)‐3,7‐dihydrobenzo[1,2‐b:4,5‐b′]difuran‐2,6‐dione (FBDOPV) as electron‐accepting unit, copolymerized with 9,9‐dioctyl‐fluorene (P(FBDOPV‐F)) or with 3‐dodecyl‐2,2′‐bithiophene (P(FBDOPV‐2T‐C12)). These copolymers possess an amorphous and semi‐crystalline nature, respectively, and exhibit remarkable electron mobilities of 0.065 and 0.25 cm2 V–1 s–1 in field effect transistors. However, after chemical n‐doping with 4‐(1,3‐dimethyl‐2,3‐dihydro‐1H‐benzoimidazol‐2‐yl)phenyl)dimethylamine (N‐DMBI), electrical conductivities four orders of magnitude higher can be achieved for P(FBDOPV‐2T‐C12) (σ = 0.042 S cm?1). More charge‐transfer complexes are formed between P(FBDOPV‐F) and N‐DMBI, but the highly localized polaronic states poorly contribute to the charge transport. Doped P(FBDOPV‐2T‐C12) exhibits a negative Seebeck coefficient of –265 µV K?1 and a thermoelectric power factor (PF) of 0.30 µW m?1 K?2 at 303 K which increases to 0.72 µW m?1 K?2 at 388 K. The in‐plane thermal conductivity (κ|| = 0.53 W m?1 K?1) on the same micrometer‐thick solution‐processed film is measured, resulting in a figure of merit (ZT) of 5.0 × 10?4 at 388 K. The results provide important design guidelines to improve the doping efficiency and thermoelectric properties of n‐type organic semiconductors.  相似文献   

16.
Barium titanate/polyimide (BaTiO3/PI) nanocomposite films with high dielectric permittivity (20), high breakdown strength (67 MV m?1), and high thermal stability are prepared by an in‐situ polymerization process. A very thin polymer layer (about 5 nm) is coated on the surface of nanosized BaTiO3 particles to form a core–shell‐like structure, which can guarantee homogeneous dispersion of the BaTiO3 particles in the PI matrix. It is confirmed that the core–shell‐like structure originates from both the electrostatic attraction between the precursor poly(amic acid) (PAA) and the BaTiO3 particles and the hydrogen bond interaction between PI and the BaTiO3 particles. Such a structure also has some influence on the dielectric properties and breakdown strength of films. After casting and degassing of the sticky film, the dielectric permittivity of the nanocomposite film is close to or even higher than that of submicrocomposite films, which is attributed to the advanced interfacial structure between the BaTiO3 and PI phases.  相似文献   

17.
The thermal conductivity of gas‐permeated single‐walled carbon nanotube (SWCNT) aerogel (8 kg m?3 density, 0.0061 volume fraction) is measured experimentally and modeled using mesoscale and atomistic simulations. Despite the high thermal conductivity of isolated SWCNTs, the thermal conductivity of the evacuated aerogel is 0.025 ± 0.010 W m?1 K?1 at a temperature of 300 K. This very low value is a result of the high porosity and the low interface thermal conductance at the tube–tube junctions (estimated as 12 pW K?1). Thermal conductivity measurements and analysis of the gas‐permeated aerogel (H2, He, Ne, N2, and Ar) show that gas molecules transport energy over length scales hundreds of times larger than the diameters of the pores in the aerogel. It is hypothesized that inefficient energy exchange between gas molecules and SWCNTs gives the permeating molecules a memory of their prior collisions. Low gas‐SWCNT accommodation coefficients predicted by molecular dynamics simulations support this hypothesis. Amplified energy transport length scales resulting from low gas accommodation are a general feature of CNT‐based nanoporous materials.  相似文献   

18.
The properties of metal oxides with high dielectric constant (k) are being extensively studied for use as gate dielectric alternatives to silicon dioxide (SiO2). Despite their attractive properties, these high‐k dielectrics are usually manufactured using costly vacuum‐based techniques. In that respect, recent research has been focused on the development of alternative deposition methods based on solution‐processable metal oxides. Here, the application of the spray pyrolysis (SP) technique for processing high‐quality hafnium oxide (HfO2) gate dielectrics and their implementation in thin film transistors employing spray‐coated zinc oxide (ZnO) semiconducting channels are reported. The films are studied by means of admittance spectroscopy, atomic force microscopy, X‐ray diffraction, UV–Visible absorption spectroscopy, FTIR, spectroscopic ellipsometry, and field‐effect measurements. Analyses reveal polycrystalline HfO2 layers of monoclinic structure that exhibit wide band gap (≈5.7 eV), low roughness (≈0.8 nm), high dielectric constant (k ≈ 18.8), and high breakdown voltage (≈2.7 MV/cm). Thin film transistors based on HfO2/ZnO stacks exhibit excellent electron transport characteristics with low operating voltages (≈6 V), high on/off current modulation ratio (~107) and electron mobility in excess of 40 cm2 V?1 s?1.  相似文献   

19.
To enhance the electrical performance of pentacene‐based field‐effect transistors (FETs) by tuning the surface‐induced ordering of pentacene crystals, we controlled the physical interactions at the semiconductor/gate dielectric (SiO2) interface by inserting a hydrophobic self‐assembled monolayer (SAM, CH3‐terminal) of organoalkyl‐silanes with an alkyl chain length of C8, C12, C16, or C18, as a complementary interlayer. We found that, depending on the physical structure of the dielectric surfaces, which was found to depend on the alkyl chain length of the SAM (ordered for C18 and disordered for C8), the pentacene nano‐layers in contact with the SAM could adopt two competing crystalline phases—a “thin‐film phase” and “bulk phase” – which affected the π‐conjugated nanostructures in the ultrathin and subsequently thick films. The field‐effect mobilities of the FET devices varied by more than a factor of 3 depending on the alkyl chain length of the SAM, reaching values as high as 0.6 cm2 V?1 s?1 for the disordered SAM‐treated SiO2 gate‐dielectric. This remarkable change in device performance can be explained by the production of well π‐conjugated and large crystal grains in the pentacene nanolayers formed on a disordered SAM surface. The enhanced electrical properties observed for systems with disordered SAMs can be attributed to the surfaces of these SAMs having fewer nucleation sites and a higher lateral diffusion rate of the first seeding pentacene molecules on the dielectric surfaces, due to the disordered and more mobile surface state of the short alkyl SAM.  相似文献   

20.
Despite the tremendous advancement of intelligent robots, it remains a great challenge to integrate living organisms‐like multistimuli responsive actuation and excellent self‐healing ability into one single material system, which will greatly benefit and broaden the development of smart biomimetic materials. Herein, a novel self‐healable multistimuli responsive actuator is developed based on hierarchical structural design and interfacial supramolecular crosslinking. The resulting biomimetic actuator shows a record high photothermal efficiency (ηPT = 79.1%) and thermal conductivity (31.92 W m?1 K?1), and presents a superfast actuating response (near‐infrared light: 0.44 s; magnetic field: 0.36 s). In addition, the supramolecular crosslinking endows excellent self‐healing performance in both mechanical and actuating properties to the material. This biomimetic actuator with its hierarchical structure design provides great potential for various applications, such as artificial muscles, soft robotics, and biomedical microdevices.  相似文献   

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