Unique Characteristics of Vertical Carbon Nanotube Field-effect Transistors on Silicon

A vertical carbon nanotube field-effect transistor(CNTFET) based on silicon(Si) substrate has been proposed and simulated using a semi-classical theory. A single-walled carbon nanotube(SWNT) and an n-type Si nanowire in series construct the channel of the transistor. The CNTFET presents ambipolar characteristics at positive drain voltage(Vd) and n-type characteristics at negative Vd. The current is significantly influenced by the doping level of n-Si and the SWNT band gap. The n-branch current of the ambipolar characteristics increases with increasing doping level of the n-Si while the p-branch current decreases. The SWNT band gap has the same influence on the p-branch current at a positive Vd and n-type characteristics at negative Vd. The lower the SWNT band gap, the higher the current. However, it has no impact on the n-branch current in the ambipolar characteristics. Thick oxide is found to significantly degrade the current and the subthreshold slope of the CNTFETs.

Impacts of Parameter Scaling for Low-Power Applications Using CNTFET （Carbon Nanotube Field Effect Transistor） Models： A Comparative Assessment

This paper provides an extension to the earlier work wherein a comparison between different models that had studied the effects of several parameters scaling on the performance of carbon nano tube field-effect transistors was presented. The evaluation for the studied models, with regard to the scaling effects, was to determine those which best reflect the very essence of carbon nano-tube technologies. Whereas the models subject this comparison （Fettoy, Roy, Stanford, and Southampton） were affected to varying degrees due to such parametric variations, the Stanford model was shown as still being valid for a wide range of chiralities and diameter sizes; a model that is also applicable for circuit simulations. In this paper, we present a comparative assessment of the various models subject to the study with regard to the effect of incorporating multiple carbon nanotubes in the channel region. We also assess the effect of oxide thickness on transistor performance in terms of the supply voltage threshold effects. Results leveraging our findings in this ongoing research endeavor reveal that many research efforts were not efficient to high degree due to high delay and not valid for circuit simulations.

Study on the Carbon Nanotube Separative Structure for the Extended Gate H^+-Ion Sensitive Field Effect Transistor

We use the carbon nanotube (CNT) as the material of the pH sensing layer of the separative structure for the extended gate H^+-ion sensitive field effect transistor (EGFET) device.The CNT paste was prepared with CNT powder,Ag powder,silicagel,the di-n-butyl phthalate and the toluene solvents by appropriate ratio,then immobilized on the silicon substrate to form the carbon nanotube sensing layer.We measured theⅠ_(DS)-Ⅴ_G curves of the carbon nanotube separative structure EGFET device in the different pH buffer solutions by the Keithley 236Ⅰ-Ⅴmeasurement system.According to the experimental results,we can obtain the pH sensitivities of the carbon nanotube separative structure EGFET device,which is 62.54mV/pH from pH1 to pH13.

Designing a Carbon Nanotube Field-Effect Transistor with High Transition Frequency for Ultra-Wideband Application

Theoretical calculations predict transition frequencies in the terahertz range for the field-effect transistors based on carbon nanotubes, and this shows their suitability for being used in high frequency applications. In this paper, we have designed a field-effect transistor based on carbon nanotube with high transition frequency suitable for ultra-wide band applications. We did this by optimizing nanotube diameter, gate insulator thickness and dielectric constant. As a result, we achieved the transition frequency about 7.45 THz. The environment of open source software FETToy is used to simulate the device. Also a suitable model for calculating the transition frequency is presented.

A voltage-controlled chaotic oscillator based on carbon nanotube field-effect transistor for low-power embedded systems

This paper presents a compact and low-power-based discrete-time chaotic oscillator based on a carbon nanotube field-effect transistor implemented using Wong and Deng＇s well-known model. The chaotic circuit is composed of a nonlinear circuit that creates an adjustable chaos map, two sample and hold cells for capture and delay functions, and a voltage shifter that works as a buffer and adjusts the output voltage for feedback. The operation of the chaotic circuit is verified with the SPICE software package, which uses a supply voltage of 0.9 V at a frequency of 20 kHz. The time series, frequency spectra, transitions in phase space, sensitivity with the initial condition diagrams, and bifurcation phenomena are presented. The main advantage of this circuit is that its chaotic signal can be generated while dissipating approximately 7.8 μW of power, making it suitable for embedded systems where many chaos-signal generators are required on a single chip.

Electronic Detection of Escherichia coli O157︰H7 Using Single-Walled Carbon Nanotubes Field-Effect Transistor Biosensor

Field effect transistors (FET) based on Single-Walled Carbon Nanotubes (SWNTs) become the hot topic in fields of nano-electronic, clinical diagnostics, environmental testing etc. in recent years. In this paper, we reported a simple, scalable way to enrich semiconducting SWNTs by using HNO3/H2SO4. Then carbon nanotube field-effect transistors (CNTFET) biosensor was fabricated with the enrichment SWNTs for Escherichia coli O157︰H7 detection. The response of each CNTFET was monitored in real time before and after introduction of the Escherichia coli O157︰H7 at various concentrations. The results show that CNT-FET biosensors we fabricated are sensitive to change of concentration of solution and response time is really short.

Combined Effect of Uniaxial Strain and Magnetic Field on the Exciton States in Semiconducting Single-Walled Carbon Nanotubes

The exciton states of semiconducting carbon nanotubes are calculated by a tight-binding model supplemented by Coulomb interactions under the combined effect of uniaxial strain and magnetic field. It is found that the excitation energies and absorption spectra of zigzag tubes（11,0） and（10,0） show opposite trends with the strain under the action of the magnetic field. For the（11,0） tube, the excitation energy decreases with the increasing uniaxial strain, with a splitting appearing in the absorption spectra. For the（10,0） tube, the variation trend firstly increases and then decreases, with a reversal point appearing in the absorption spectra. More interesting,at the reversal point the intensity of optical absorption is the largest because of the degeneracy of the two bands nearest to the Fermi Level, which is expected to be observed in the future experiment. The similar variation trend is also exhibited in the binding energy for the two kinds of semiconducting tubes.

Design of Multi-Valued Logic Circuit Using Carbon Nano Tube Field Transistors

The design of a three-input logic circuit using carbon nanotube field effect transistors(CNTFETs)is presented.Ternary logic must be an exact replacement for dual logic since it performs straightforwardly in digital devices,which is why this design is so popular,and it also reduces chip area,both of which are examples of circuit overheads.The proposed module we have investigated is a triple-logic-based one,based on advanced technology CNTFETs and an emphasis on minimizing delay times at various values,as well as comparisons of the design working with various load capacitances.Comparing the proposed design with the existing design,the delay times was reduced from 66.32 to 16.41 ps,i.e.,a 75.26%reduction.However,the power dissipation was not optimized,and increased by 1.44%compared to the existing adder.The number of transistors was also reduced,and the product of power and delay(P∗D)achieved a value of 0.0498053 fJ.An improvement at 1 V was also achieved.A load capacitance(fF)was measured at different values,and the average delay measured for different values of capacitance had a maximum of 83.60 ps and a minimum of 22.54 ps,with a range of 61.06 ps.The power dissipations ranged from a minimum of 3.38μW to a maximum of 6.49μW.Based on these results,the use of this CNTFET half-adder design in multiple Boolean circuits will be a useful addition to circuit design.

Alignment of Nanoscale Single-Walled Carbon Nanotubes Strands

Depositing single-walled carbon nanotubes(SWNTs) with controllable density, pattern and orientation on electrodes presents a challenge in today's research. Here, we report a novel solvent evaporation method to align SWNTs in patterns having nanoscale width and micronscale length. SWNTs suspension has been introduced dropwise onto photoresist resin microchannels; and the capillary force can stretch and align SWNTs into strands with nanoscale width in the microchannels. Then these narrow and long aligned SWNTs patterns were successfully transferred to a pair of gold electrodes with different gaps to fabricate carbon nanotube field-effect transistor(CNTFET). Moreover, the electrical performance of the CNTFET show that the SWNTs strands can bridge different gaps and fabricate good electrical performance CNTFET with ON/OFF ratio around 106. This result suggests a promising and simple strategy for assembling well-aligned SWNTs into CNTFET device with good electrical performance.

Electrochemical potential at the interface between carbon nanotubes and electrolyte

The dependences of electrochemical potential at the interface between carbon nanotubes and electrolyte upon temperature and electrolyte concentration are studied. Carbon nanotubes were synthesized by hot filament chemical vapor deposition with Si as the substrate. Four substances were tested: NaCl solution, KCl solution, water and alcohol. It is found that for NaCl and KCl solutions, at the interface, there is a large electrochemical potential which increases with temperature and is larger for an electrolyte of higher concentration. There is a significant field effect of carbon nanotubes with electrolyte as the gate, and the effect depends on the ionizability of the electrolyte. Such physicochemical property invests carbon nanotube a potential application in nanoelectronics.

Performances of carbon nanotube field effect transistors with altered channel length

The influence of channel length on the performances of carbon nanotube field effect transistors(CNT-FETs) has been studied.Buffered oxide etching was used to remove approximately a 60 nm layer from the original 100 nm silicon dioxide layer,to thin the dielectric layer of the back gate.Channel length of the CNT-FETs was changed along with the etching process.The dependence of drain-source current on gate voltage was measured to analyze the performance of the CNT-FETs,including the transconductance,carrier mobility,current ON/OFF ratio,etc.The results indicate that the devices still keep good quality.

Sorting Semiconducting Single-Walled Carbon Nanotubes by Water-Soluble Polyfluorene Assisted Electrophoresis and Its Application in Field-effect Transistors

We report a considerably promising method based on agarose gel electrophoresis （AGE） to separate single-walled carbon nanotubes by adding a water-soluble polyfluorene （w-PFO） as surfactant into the agarose gel. In this effective method, the AGE/w-PFO gel network will trap more semiconducting single-walled carbon nanotubes （SWNTs） with the assistance ofw-PFO, for the strong interaction between w-PFO and semiconducting species. The optical absorbance, photoluminescence emission and resonant Raman scattering characterization were used to ver- ify the separation effect. The purity of separated semiconducting species is as high as （98±1）%. The demonstrated field effect transistors give the on/off ratio and mobility about 27000 and 10.2 cm^2·V^-1·s^-1, respectively.

High yield fabrication of semiconducting thin-film field-effect transistors based on chemically functionalized single-walled carbon nanotubes

Here we report a simple and scalable method to fabricate high performance thin-film field-effect transistors(FETs) with high yield based on chemically functionalized single-walled carbon nanotubes(SWNTs) by organic radical initiators.The UV-Vis-NIR spectra,Raman spectra and electrical characterization demonstrated that metallic species in CoMoCat 65 and HiPco SWNTs could be effectively eliminated after reaction with some organic radical initiators.The effects of the substrate properties on the electrical properties of FET devices were investigated,and the results showed that the electrical properties of FET devices fabricated on high hydrophobic substrates were better than those on low hydrophobic substrates.Furthermore,it was found that FET devices based on 1,1'-azobis(cyanocyclohexane)(ACN)-modified CoMoCat 65 SWNTs exhibited more excellent electrical performance with effective mobility of ～11.8 cm2/Vs and on/off ratio of ～2×105 as compared with benzoyl peroxide(BPO)-modified CoMoCat 65 SWNTs and lauoryl peroxideand(LPO)-modified HiPco SWNTs,likely due to the introduction of the electron-withdrawing groups(CN group) on the SWNT surface.This method does not require nontrivial reaction conditions or complicated purification after reaction,therefore promising low-cost production of high-performance devices for macroelectronics.

Field-effect transistors with multiple channels constructed by carbon nanotubes

Single-wall carbon nanotubes (SWNTs) pre-decorated with functional molecules are directly aligned in the AC electric field, which makes SWNTs parallelly bridge the source and drain electrodes and act as the multiple conduction channels of the field-effect transistor (FET). The method avoids the mutual tanglement of SWNTs and makes them align between the source and drain electrodes abreast and dispersedly. It is indicated that aligning SWNTs in the high-volatility solvents can decrease the contaminant around the electrodes and has a function to purify the raw SWNTs. The obtained multi-channel FET not only takes on a high transconductance, but also holds the good reliability and stability.

Reliability tests and improvements for Sc-contacted n-type carbon nanotube transistors

Scandium （Sc） contacted n-type carbon nanotube （CNT） field-effected transistors （FETs） with back and top-gate structure have been fabricated, and their stability in air were investigated. It was shown that oxygen and water molecules may affect both the nanotube channel and Scinanotube contacts, leading to deteriorated contact quality and device performance. These negative effects associated with the instability of n-type carbon nanotube FETs can be eliminated through passivating the CNT devices by a thin layer of atomic-layer-deposition grown A1203 insulator. After passivation, the n-type carbon nanotube FETs are shown to exhibit excellent atmosphere stability even after being tested and exposed to air for over 146 days, and then much smoother output characteristics and reduced gate voltage hysteresis from I to 0.1 V were demonstrated when compared with devices without passivation. Lasting power-on tests were also performed on the passivated CNT FETs under large gate stress and high drain current in air for at least 10 h, revealing null device degradation and sometimes even improved performance. These results promise that passivated CNT devices are reliable in air and may be used in practical applications.

Air-stable n-type transistors based on assembled aligned carbon nanotube arrays and their application in complementary metal-oxide-semiconductor electronics

Carbon nanotubes(CNTs)are ideal candidates for beyond-silicon nano-electronics because of their high mobility and low-cost processing.Recently,assembled massively aligned CNTs have emerged as an important platform for semiconductor electronics.However,realizing sophisticated complementary nano-electronics has been challenging due to the p-type nature of carbon nanotubes in air.Fabrication of n-type behavior field effect transistors(FETs)based on assembled aligned CNT arrays is needed for advanced CNT electronics.Here in this paper,we report a scalable process to make n-type behavior FETs based on assembled aligned CNT arrays.Air-stable and high-performance n-type behavior CNT FETs are achieved with high yield by combining the atomic layer deposition dielectric and metal contact engineering.We also systematically studied the contribution of metal contacts and atomic layer deposition passivation in determining the transistor polarity.Based on these experimental results,we report the successful demonstration of complementary metal-oxide-semiconductor inverters with good performance,which paves the way for realizing the promising future of carbon nanotube nano-electronics.

Assessment of High-Frequency Performance Limits of Graphene Field-Effect Transistors

High frequency performance limits of graphene field-effect transistors （FETs） down to a channel length of 20 nm have been examined by using self-consistent quantum simulations. The results indicate that although Klein band-to-band tunneling is significant for sub-100 nm graphene FETs, it is possible to achieve a good transconductance and ballistic on-off ratio larger than 3 even at a channel length of 20 nm. At a channel length of 20 nm, the intrinsic cut-off frequency remains at a few THz for various gate insulator thickness values, but a thin gate insulator is necessary for a good transconductance and smaller degradation of cut-off frequency in the presence of parasitic capacitance. The intrinsic cut-off frequency is close to the LC characteristic frequency set by graphene kinetic inductance （L） and quantum capacitance （C）, which is about 100 GHz-um divided by the gate length.

Carbon nanomaterials： controlled growth and field-effect transistor biosensors

Carbon nanostructures, including carbon nanotubes （CNTs） and gra- phene, have been studied extensively due to their special structures, excellent electrical properties and high chemical stability. With the development of nanotechnology and nanoscience, various methods have been developed to synthesize CNTs/graphene and to assemble them into microelectroniclsensor devices. In this review, we mainly demon- strate the latest progress in synthesis of CNTs and graphene and their applications in field-effect transistors （FETs） for biological sensors.

微分求积法分析碳纳米管磁流体输送系统的稳定性

基于磁流体动力学方程及非局部欧拉-伯努利(Euler-Bernoulli)梁模型,建立了轴向磁场作用下单壁碳纳米管磁流体输送系统的振动微分方程.应用微分求积法(DQM),在固支边界条件下,求解此高阶偏微分方程,着重研究管内磁流体效应、轴向磁场、小尺度参数(磁流体克努森数Kn与碳纳米管小尺度系数)对该系统振动与失稳特性的影响.数值计算结果表明,轴向磁场提升系统刚度及系统稳定性,而小尺度参数降低系统稳定性.更重要的是,固支边界系统中磁流体在磁场作用下,降低输送系统的刚度,但能提升输送系统的稳定性.

碳纳米管场效应晶体管重离子单粒子效应研究

碳纳米管场效应晶体管(CNT FET)具备优良的电学性能和稳定的化学结构,表现出较强的恶劣环境耐受能力,但其抗辐射性能仍缺乏充足的试验验证。以超薄CNT为沟道材料、HfO2为栅介质层的CNT FET为对象,研究了209Bi重离子辐射引起的器件单粒子效应(SEE)。研究结果表明,在重离子辐射条件下,栅极单粒子瞬态电流大多处于10-11 A数量级,少数达10-10 A数量级;由于CNT FET具有纳米级超薄CNT沟道,漏极电流对单粒子辐射不敏感,漏极单粒子瞬态电流几乎可以忽略,无单粒子烧毁效应(SEB);得益于HfO2栅介质层,CNT FET未发生单粒子栅穿效应(SEGR),表现出较强的抗单粒子能力。