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.

Impact of Temperature Variation on Performance of Carbon Nanotube Field-Effect Transistor-Based on Chaotic Oscillator:A Quantum Simulation Study

We evaluate the impact of temperature on the output behavior of a carbon nanotube field effect transistor （CNFET） based chaotic generator. The sources cause the variations in both current-voltage characteristics of the CNFET device and an overall chaotic circuit is pointed out. To verify the effect of temperature variation on the output dynamics of the chaotic circuit, a simulation is performed by employing the CNFET compact model of Wong et al. in HSPICE with a temperature range from -100℃ to 100℃. The obtained results with time series, frequency spectra, and bifurcation diagram from the simulation demonstrate that temperature plays a significant role in the output dynamics of the CNFET-based chaotic circuit. Thus, temperature-related issues should be taken into account while designing a high-quality chaotic generator with high stability.

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.

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.

Suppression of leakage current in carbon nanotube field-effect transistors

Carbon nanotube field-effect transistor(CNT FET)has been considered as a promising candidate for future high-performance and low-power integrated circuits(ICs)applications owing to its ballistic transport and excellent immunity to short channel effects(SCEs).Still,it easily suffers from the ambipolar property,and severe leakage current at off-state originated from gate-induced drain leakage(GIDL)in CNT FETs with small bandgap.Although some modifications on device structure have been experimentally demonstrated to suppress the leakage current in CNT FETs,there is still a lack of the structure with excellent scalability,which will hamper the development of CNT FETs toward a competitive technology node.Here,we explore how the device geometry design affects the leakage current in CNT FETs,and then propose the possible device structures to suppress off-state current and check their availability through the two-dimensional(2D)TCAD simulations.Among all the proposed structures,the L-shaped-spacer CNT FET exhibits significantly suppressed leakage current and excellent scalability down to sub-50 nm with a simple self-aligned gate process.According to the simulation results,the 50 nm gate-length L-shaped-spacer CNT FET exhibits an off-state current as low as approximately 1 nA/μm and an on-current as high as about 2.1 mA/μm at a supply voltage of-1 V and then can be extended as a universal device structure to suppress leakage current for all the narrow-bandgap semiconductors based FETs.

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.

Carbon nanotube integrated circuit technology:purification,assembly and integration

As the manufacturing process of silicon-based integrated circuits(ICs)approaches its physical limit,the quantum effect of silicon-based field-effect transistors(FETs)has become increasingly evident.And the burgeoning carbon-based semiconductor technology has become one of the most disruptive technologies in the post-Moore era.As one-dimensional nanomaterials,carbon nanotubes(CNTs)are far superior to silicon at the same technology nodes of FETs because of their excellent electrical transport and scaling properties,rendering them the most competitive material in the next-generation ICs technology.However,certain challenges impede the industrialization of CNTs,particularly in terms of material preparation,which significantly hinders the development of CNT-based ICs.Focusing on CNT-based ICs technology,this review summarizes its main technical status,development trends,existing challenges,and future development directions.

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.

Observation of Van Hove Singularities and Temperature Dependence of Electrical Characteristics in Suspended Carbon Nanotube Schottky Barrier Transistors

A Van Hove singularity(VHS) is a singularity in the phonon or electronic density of states of a crystalline solid. When the Fermi energy is close to the VHS, instabilities will occur, which can give rise to new phases of matter with desirable properties. However, the position of the VHS in the band structure cannot be changed in most materials. In this work, we demonstrate that the carrier densities required to approach the VHS are reached by gating in a suspended carbon nanotube Schottky barrier transistor. Critical saddle points were observed in regions of both positive and negative gate voltage, and the conductance flattened out when the gate voltage exceeded the critical value. These novel physical phenomena were evident when the temperature is below 100 K. Further, the temperature dependence of the electrical characteristics was also investigated in this type of Schottky barrier transistor.

Applications of Carbon Nanotubes in the Internet of Things Era

The post-Moore's era has boosted the progress in carbon nanotube-based transistors.Indeed,the 5 G communication and cloud computing stimulate the research in applications of carbon nanotubes in electronic devices.In this perspective,we deliver the readers with the latest trends in carbon nanotube research,including high-frequency transistors,biomedical sensors and actuators,brain–machine interfaces,and flexible logic devices and energy storages.Future opportunities are given for calling on scientists and engineers into the emerging topics.

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.

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.

Drain-engineered carbon-nanotube-film field-effect transistors with high performance and ultra-low current leakage

A small bandgap and light carrier effective mass(mo)lead to obv ous ambipolar transport behavior in carbon nanotube(CNT)fild-effect transistors(FE Ts),including a high off-state current and severe degradation of the subthreshold swing(SS)with increasing drain bias voltage.We demonstrate a drain-engineered method to cope with this common problem in CNT-film FETs with a sub-μum channel length,i.e.,suppressing the ambipolar behavion while maintaining high on-state performance by adopting a feedback gate(FBG)structure to extend the drain region from the CNT/metal contact to the proximate CNT channels to suppress the tunneling current.Sub-400-nm-channel-length FETs with a FBG structure statistially present a high on/off ratio of up to 10*and a sub-200 mV/dec SS under a high drain bias of up to-2 V whle maintaining a high on-state current of 0.2 mA/μm or a peak transconductance of 0.2 mS/um.By lowering the supply voltage to 1.5 V,FBG CNT-fim FETs can meet the requirement of standard-pertormance ultra large scale integrated circuits(ULSICs).Therefore,the introduction of the drain engineering structure enables applications of CNT-film-based FETs in ULSICs and could also be widely extended to other small-bandgap semiconductor-based FETs for an improvement in their off-state property.

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.

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.

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.

Large-area and highly uniform carbon nanotube film for nigh-performance thin film transistors

Carbon nanotube thin film transistors （CNT-TFTs） are a potential TFT technology for future high-performance macroelectronics. Practical application of CNT-TFTs requires the production of large-area, highly uniform, density-controllable, repeatable, and high-throughput CNT thin films. In this stud35 CNT films were fabricated on 4-inch Si wafers and 2.5th generation （G2.5） backplane glasses （370 mm×470 ram） by dip coating using a chloroform-dispersed high-purity semiconducting CNT solution. The CNT density was controlled by the solution concentration and coating times, but was almost independent of the substrate lifting speed （1-450 mm.min-1）, which enables high-throughput CNT thin film production. We developed an image processing software to efficiently characterize the density and uniformity of the large-area CNT films. Using the software, we confirmed that the CNT films are highly uniform with coefficients of variance （Cv） 〈 10% on 4-inch Si wafers and - 13.8% on G2.5 backplane glasses. High-performance CNT-TFTs with a mobility of 45-55 cm2-V-l.s-1 were obtained using the fabricated CNT films with a high-performance uniformity （Cv =11%-13%） on a 4-inch wafer. To our knowledge, this is the first fabrication and detailed characterization of such large-area, high-purity, semiconducting CNT films for TFT applications, which is a significant step toward manufacturing CNT-TFTs.

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.

Carbon nanotube transistor technology for More-Moore scaling

Scaling of silicon field-effect transistors has fueled the exponential development of microelectronics in the past 60 years,but is now close to its physical limits with the critical dimensions of state-of-the-art silicon devices approaching the sub-10 nm regime.Carbon nanotubes have been suggested to hold great promise of replacing the central role of silicon in the next-generation logic switches with their unique geometrical and electrical properties.In this article,I firstly examine the scaling advantages of carbon nanotubes compared to silicon from technology-development perspective,and then review the latest progress on addressing the manufacturability issues for scaled carbon-nanotube transistors,from materials to device-integration levels.Finally,the possible pathways for nanotube transistors to transition into commercial applications are discussed.