Single-walled Carbon Nanotube Transistors Research Articles

Enhanced charge transport behaviors of single-walled carbon nanotube transistors by phenylphosphonic acid doping

Inkjet printing technology holds promise as a cost-effective method for fabricating large-area electronics, with high compatibility with various substrates. In this paper, we investigate the electrical doping behaviors of p-type transistors based on single-walled carbon nanotubes (SWCNTs), where semiconducting channels and electrodes are patterned using inkjet printing. We demonstrate improved charge transport properties by encapsulating SWCNTs with phenylphosphonic acid (PPA) without annealing. The PPA-coated SWCNT transistors exhibit significantly enhanced hole mobility, reaching approximately 8.25 cm2 V−1 s−1. The presence of the benzene ring in PPA facilitates hole injection and induces a p-doping effect, resulting in a 4.3-fold increase in the on-current level of the transistors.

Poly(ionic liquid) dielectric for high performing P- and N-type single walled carbon nanotube transistors

There is an increasing demand for low-cost and high-performance electronics which has stimulated a need for new high-performance dielectric materials. We have developed a facile synthesis of poly(2-(methacryloyloxy)ethyl trimethylammonium bis(trifluoromethylsulfonyl)azanide-ran-methyl methacrylate) (P(METATFSI-MMA)), a polymeric ionic liquid that can be used as a high-performance dielectric for semiconducting single walled carbon nanotube (SWCNTs) thin film transistors (TFTs). The P(METATFSI-MMA) polymer was synthesized at both 35 and 62 mol% of 2-(methacryloyloxy)ethyl trimethylammonium bis(trifluoromethylsulfonyl)azanide and produced p- and n-type devices that functioned under ambient conditions. These TFTs were then used to study the impact of electrochemical doping on the performance of SWCNT TFTs when switching from n-type, where an electrical double layer is formed, to p-type, where the TFSI− anions are free to interact with the SWCNTs. The TFTs operating in p-type had higher current on/off ratios and a larger transconductance than those operating in n-type, which is characteristic of electrochemically doped transistors. Furthermore, we tested the impact of operating frequency on device performance and discovered that decreasing the operating frequency of the TFTs resulted in a decreased hysteresis. The decrease in hysteresis was also observed to be more significant for the 35 mol% polymer.

I-V Characteristics Modeling of the Carbon Nanotube Field Effect Transistor (CNTFET)

Abstract: A simulation model of a zig-zag type (10.0) single-walled carbon-nanotube (SW-CNT) transistor based on virtual source (VS-CNTFET) approach is presented in this paper. This semi-empirical physics-based model allowed the study of current-voltage (I-V) characteristics of the transistor. Additionally, analytical modeling of reflection coefficient, electron mobility in the CNT with low and high electric field and parasitic resistances (Rs and Rd) were presented as well in this model. Then, the obtained I-V characteristics of this SW-CNTFET were explored and compared with literature data obtained experimentally. Results showed that this model was a different approach which is significant compared to the silicon model in terms of the carrier mobility, where µCNT = 104 cm2/Vs. Moreover, the impacts of some geometric parameters, such as CNT length and diameter as well as oxide permittivity on the I-V characteristics, were proved. Keywords: Carbon nanotube, Virtual source, CNTFET, Electron mobility, I-V characteristics.

(Invited) DNA Sequencing with Carbon Nanotube Electronics

Nanoscale materials and devices provide new opportunities to monitor and understand biomolecules. This presentation will review novel devices in which single molecules of DNA polymerase have been joined to single-walled carbon nanotube (SWNT) transistors.DNA polymerases are the enzymes that convert single-stranded DNA into double-stranded helices. This biochemical process is the primary step in DNA replication, amplification, and most sequencing technologies. When one of these polymerases is attached to a SWNT transistor, the enzyme’s native activity is simultaneously transduced into a high-resolution electrical signal [1]. Each time the enzyme works its way down a DNA strand, it generates a nucleotide-by-nucleotide signal that encodes the DNA sequence.This hybrid, biofunctional device is the key element for developing a new, electronic DNA sequencing technology. As a solid-state, manufacturable element, the SWNT transistors provide exciting possibilities for high-density, high-throughput, and low cost sequencing solutions. In addition, the technique is easily generalized to DNA polymerases with specialized properties. Proof-of-principle measurements have been accomplished with DNA polymerases from five different organisms, including the highly processive polymerase of φ29 phage and the high-temperature polymerase Thermus aquaticus (Taq), which is the foundation of the polymerase chain reaction (PCR) and commercial DNA amplification. The SWNT transistor technique operates equally well at room temperature and the elevated PCR temperature of 72 °C, which opens opportunities for novel, high-temperature sequencing strategies with Taq or similar thermostable polymerases.[1] T. J. Olsen et. al., JACS 135, 7855 (2013); O. T. Gul et. al., Biosensors 6, 29 (2016)

Single-molecule Taq DNA polymerase dynamics.

Taq DNA polymerase functions at elevated temperatures with fast conformational dynamics—regimes previously inaccessible to mechanistic, single-molecule studies. Here, single-walled carbon nanotube transistors recorded the motions of Taq molecules processing matched or mismatched template–deoxynucleotide triphosphate pairs from 22° to 85°C. By using four enzyme orientations, the whole-enzyme closures of nucleotide incorporations were distinguished from more rapid, 20-μs closures of Taq’s fingers domain testing complementarity and orientation. On average, one transient closure was observed for every nucleotide binding event; even complementary substrate pairs averaged five transient closures between each catalytic incorporation at 72°C. The rate and duration of the transient closures and the catalytic events had almost no temperature dependence, leaving all of Taq’s temperature sensitivity to its rate-determining open state.

Reactivity of an air-stable dihydrobenzoimidazole n-dopant with organic semiconductor molecules

Summary 1,3-Dimethyl-2-(4-(dimethylamino)phenyl)-2,4-dihydro-1H-benzoimidazole, N-DMBI-H, is widely used as an air-stable n-dopant for organic semiconductors. Here, its reactivity is investigated with a variety of imide- and amide-containing semiconductor molecules that have reduction potentials in the range −0.54 to −1.10 V versus ferrocene. Reaction rates correlate poorly with these potentials. The more reactive of the imides form the corresponding radical anions cleanly, but kinetic isotope studies using N-DMBI-D indicate that the reaction proceeds via an initial hydride- or hydrogen-transfer step. For an amide- and ester-rigidified bis(styryl)benzene derivative the hydride-reduced product is stable under an inert atmosphere and can be observed directly; the radical anion can only be obtained in sub-stoichiometric yield and under certain reaction conditions. On the other hand, (N-DMBI)2 rapidly reduces all the imides and amides examined to the corresponding radical anions. The implications of these findings for dopant selection and use are discussed.

Individual SWCNT Transistor with Photosensitive Planar Junction Induced by Two‐Photon Oxidation

AbstractThe fabrication of planar junctions in carbon nanomaterials is a promising way to increase the optical sensitivity of optoelectronic nanometer‐scale devices in photonic connections, sensors, and photovoltaics. Utilizing a unique lithography approach based on direct femtosecond laser processing, a fast and easy technique for modification of single‐walled carbon nanotube (SWCNT) optoelectronic properties through localized two‐photon oxidation is developed. It results in a novel approach of quasimetallic to semiconducting nanotube conversion so that metal/semiconductor planar junction is formed via local laser patterning. The fabricated planar junction in the field‐effect transistors based on individual SWCNT drastically increases the photoresponse of such devices. The broadband photoresponsivity of the two‐photon oxidized structures reaches the value of 2 × 107 A W−1 per single SWCNT at 1 V bias voltage. The SWCNT‐based transistors with induced metal/semiconductor planar junction can be applied to detect extremely small light intensities with high spatial resolution in photovoltaics, integrated circuits, and telecommunication applications.

(Keynote) Nanomaterials for Printable Electronics

The National Research Council (NRC) is Canada’s premier organization for research and technology development. NRC’s Printable Electronics (PE) program develops materials and inks for additive manufacturing in order to enable a sustainable PE sector in Canada. Progress has been made over the last 20 years, yet many challenges remain at the materials, fabrication and integration level, limiting performance and commercialization. This presentation covers our progress in high purity semiconducting single-walled carbon nanotube (sc-SWCNT) enrichment and transistor fabrication via solution based processes as well as conductive molecular ink development [1-11]. I will highlight our recent progress in understanding sc-SWCNT enrichment using conjugated polymers (isolation of high purity sc-SWCNT), with special consideration given to the effects of solvent parameters and doping on the mechanism and yield/purity of the final product [2-4]. Removal of the wrapping polymer using a dry process on-wafer will also be described [5]. Challenges and advances associated with using polymer-based dielectrics and encapsulants will be discussed as well [6-7]. Such transistor packages have enabled the realization of fully inkjet-printed transistors as a result of the excellent electrical properties of sc-SWCNTs [8]. A demonstration of a fully additive process to make TFT backplanes via R2R printing will also be highlighted. Developments in conductive molecular inks and progress towards the commercialization of new applications such as in-mold electronicswill also be described [9-11]. The development of new functional nanomaterials and their successful integration into devices will enable additive manufacturing of TFT arrays and in-mold electronics.[1] J. Lefebvre et al. Acc. Chem. Res. 50, 2479 (2017).[2] J. Ouyang et al. ACS Nano 12, 1910 (2018).[3] J. Ding et al. J. Phys. Chem. C 120, 21946 (2016).[4] Z. Li et al. ACS Omega 3, 3413 (2018).[5] Z. Li et al. Adv. Funct. Mater. 28, 1705568 (2018).[6] J. Lefebvre et al. Appl. Phys. Lett. 107, 243301 (2015).[7] F. Lapointe et al. Appl. Mater. Interfaces 11, 36027 (2019).[8] C. Homenick et al. ACS Appl. Mater. Interfaces 8, 27900, (2016)[9] A. J. Kell et al. ACS Appl. Mater. Interfaces 9, 17226 (2017).[10] C. Paquet et al. Nanoscale 10, 17226 (2018).[11] B. Deore et al. ACS Appl. Mater. Interfaces 11, 38880 (2019).

Improved electrical performance and transparency of bottom-gate, bottom-contact single-walled carbon nanotube transistors using graphene source/drain electrodes

A highly transparent and high-performance random-network single-walled carbon nanotubes (r-SWCNTs) transistor was successfully fabricated by using chemical vapor deposition-grown graphene source/drain (S/D) electrodes. The bottom-gate, bottom-contact geometry was selected for the graphene S/D contact r-SWCNT (Gr-SWCNT) transistor because of its enhanced gate modulation and good sustainability. A palladium S/D contact r-SWCNT (Pd-SWCNT) transistor with the same device geometry was also fabricated for a comparative study. The transmission line method demonstrated that the resistivity of graphene was small enough (∼0.95Ωμm) to be used as S/D electrodes in a single transistor device, and the contact resistance of Gr-SWCNTs was much lower than that of Pd-SWCNTs. Particularly, the correlation between the applied gate voltage and the sheet resistance is strongly dependent on the r-SWCNT film density. The resulting Gr-SWCNT transistor exhibits high mobility and good on/off current ratio compared to the Pd-SWCNT transistor. The high charge injection originated from the ohmic contact behavior and dense r-SWCNT channel formation by the enhancement of selective wetting due to the surface energy matching between the r-SWCNT semiconductor and graphene S/D electrodes. Thus, this approach can encourage creating highly transparent and high-performance carbon-based field effect transistor.

Nanoscale Sensor-Based Tunneling Carbon Nanotube Transistor for Toxic Gases Detection: A First-Principle Study

Carbon nanotube transistor is a spotlight components for toxic gas monitoring. In this regard, we present a new toxic gas molecules sensor base on a single-walled carbon nanotube transistor and use the Poisson and Schrodinger equations in a self-consistent manner and is modeled using non-equilibrium Green’s function. The reaction between gaseous molecules and single-walled carbon nanotubes can harness the charge and potential level inside the channel, which changes the electrical characteristics of the device. Investigations carried out over a 20-nm channel and at a temperature range between 200 and 400 K shows that the conductivity and current–voltage characteristic of the proposed Nano-sensor depend on temperature and gas conditions. According to the simulation results, the decrease in the temperature decreases the OFF-state current of the tunneling carbon nanotube field-effect transistor which leads to a decrease in the leakage current and the band-to-band tunneling. In addition, due to the temperature rise, the sensitivity is increased, and by increasing the dielectric constant of the gas, the on-state current of the device will also increase significantly. The maximum sensitivity for Carbonyl Chloride is 630 (nm/RIU).

Global Photocurrent Generation in Phototransistors Based on Single‐Walled Carbon Nanotubes toward Highly Sensitive Infrared Detection

AbstractBecause of their cost‐effective synthesis and appropriate bandgap opening by various mechanisms, single‐walled carbon nanotubes (SWCNTs) exhibit significant promise for highly efficient near‐infrared photodetection. In this work, the first investigation of manipulating the electrode contact and exciton effect is performed on photocurrent generation of SWCNT transistors by separately depositing Cr or Pd as symmetric source/drain electrodes. Two different photoconducting behaviors of the devices, namely localized and global photocurrent generations, are then observed, where these effects are attributed to thermally assisted tunneling at the 1D‐SWCNTs/3D‐metal contact. A phototransistor with global photocurrent generation is demonstrated having a typical photoconductive effect with a responsivity of 2 A W−1 at λ = 785 nm and a fast rise (decay) time of ≈7.35 µs (11.8 µs). However, the corresponding optical response at 2000 nm is still weak due to low incident photon energy and large exciton binding energy. By further spin coating PbS quantum dots onto the SWCNTs channel, the optical response can be greatly enhanced for 2000 nm irradiation. All these results can not only illustrate the photoresponse of SWCNTs but also indicate that photogating plays a crucial role in these devices, providing valuable insights for the performance enhancement.

Improved Device Performance of Solution-Processed Single-Wall Carbon Nanotube Transistors by a Patterning Technique Using a Selective Surface Treatment.

During the fabrication processes for single-wall carbon nanotube thin-film transistors (SWCNT-TFTs), the impurities of organic residues such as photoresist and developer can be induced, which affects the charge transport. As a result, solution-processed SWCNT-TFTs exhibit poor and non-uniform device performance regardless of the intrinsic electrical characteristics. Here, we demonstrate a patterning technique using a selective surface treatment with solution-processed hydrophobic fluorocarbon copolymer in SWCNT-TFTs. By using the difference of wettability in a selective area, a channel region in SWCNT-TFTs can be patterned without the conventional photolithography and etching process. Furthermore, the optimized surface treatment results in denser random networks of SWCNTs in the channel patterned by such technique, compared to the dropcasted SWCNT. The statistical results of the key device metrics such as mobility and threshold voltage extracted from 30 SWCNT-TFTs conclusively prove the improved device performance of SWCNT-TFTs fabricated by such pattering technique. We believe that this work can provide a promising route to stimulate the process innovation of fabrication for high performance solution-processed electronics based on SWCNT random networks.

Ultraclean individual suspended single-walled carbon nanotube field effect transistor

In this work, we report an effective technique of fabricating ultraclean individual suspended single-walled carbon nanotube (SWNT) transistors. The surface tension of molten silver is utilized to suspend an individual SWNT between a pair of Pd electrodes during annealing treatment. This approach avoids the usage and the residues of organic resist attached to SWNTs, resulting ultraclean SWNT devices. And the resistance per micrometer of suspended SWNTs is found to be smaller than that of non-suspended SWNTs, indicating the effect of the substrate on the electrical properties of SWNTs. The ON-state resistance (∼50 kΩ), mobility of 8600 cm2 V–1 s–1 and large on/off ratio (∼105) of semiconducting suspended SWNT devices indicate its advantages and potential applications.

Heterostructured semiconductor single-walled carbon nanotube films for solution-processed high-performance field-effect transistors

In this paper, we report a simple and effective method to simultaneously achieve a high charge-carrier mobility and low off current in conjugated polymer-wrapped semiconducting single-walled carbon nanotube (s-SWNT) transistors by applying a SWNT bilayer. To achieve the high mobility and low off current, highly purified and less purified s-SWNTs are successively coated to form the semiconducting layer consisting of poly (3-dodecylthiophene-2,5-diyl) (P3DDT)-wrapped high-pressure carbon mono oxide (HiPCO) SWNT (P3DDT-HiPCO) and poly (9, 9-di-n-dodecylfluorene) (PFDD)-wrapped plasma discharge (PD) SWNT (PFDD-PD). The SWNT transistors with bilayer SWNT networked film showed highly improved hole field-effect mobility (6.18 ± 0.85 cm2V−1s−1 average), on/off current ratio (107), and off current (∼1 pA). Thus, the combination of less purified PFDD-PD (98%–99%) charge-injection layer and highly purified s-P3DDT-HiPCO (>99%) charge-transport layer as the bi-layered semiconducting film achieved high mobility and low off current simultaneously.

Ultrasensitive Detection of Oligonucleotides: Single-Walled Carbon Nanotube Transistor Assembled by DNA Block Copolymer

Biosensors, which harness the unique specific binding properties of biomaterials such as proteis, are increasingly recognized as a powerful tool for chemical sensing. In this context, the detection of nucleic acids DNA and RNA will take on ever more importance for screening as the fields of genomics and diagnostics advance. The same properties that allow molecular recognition-strong, specific non-covalent interactions-also enable bottom-up assembly of sensing architectures. Here, we take advantage of such interactions for the self-assembly of field-effect transistors from semi-conducting single-walled carbon nanotubes selectively dispersed by DNA-block-copolymers and anchored to the electrodes through DNA hybridization. These transistors can sensitively detect the hybridization of complementary target DNA strands through transduction of the chemical recognition event into electrical doping, achieving an analyte sensitivity of 10 fM. Such ultra-sensitive electrical-based detection removes the need for DNA amplification and offers a new route to nucleic acids diagnostics.

Efficient and Reversible Electron Doping of Semiconductor-Enriched Single-Walled Carbon Nanotubes by Using Decamethylcobaltocene

Single-walled carbon nanotubes (SWCNTs) offer great potential for field-effect transistors and integrated circuit applications due to their extraordinary electrical properties. To date, as-made SWCNT transistors are usually p-type in air, and it still remains challenging for realizing n-type devices. Herein, we present efficient and reversible electron doping of semiconductor-enriched single-walled carbon nanotubes (s-SWCNTs) by firstly utilizing decamethylcobaltocene (DMC) deposited by a simple spin-coating process at room temperature as an electron donor. A n-type transistor behavior with high on current, large Ion/Ioff ratio and excellent uniformity is obtained by surface charge transfer from the electron donor DMC to acceptor s-SWCNTs, which is further corroborated by the Raman spectra and the ab initio simulation results. The DMC dopant molecules could be reversibly removed by immersion in N, N-Dimethylformamide solvent, indicating its reversibility and providing another way to control the carrier concentration effectively as well as selective removal of surface dopants on demand. Furthermore, the n-type behaviors including threshold voltage, on current, field-effect mobility, contact resistances, etc. are well controllable by adjusting the surface doping concentration. This work paves the way to explore and obtain high-performance n-type nanotubes for future complementary CMOS circuit and system applications.

Thread-Like CMOS Logic Circuits Enabled by Reel-Processed Single-Walled Carbon Nanotube Transistors via Selective Doping.

The realization of large-area electronics with full integration of 1D thread-like devices may open up a new era for ultraflexible and human adaptable electronic systems because of their potential advantages in demonstrating scalable complex circuitry by a simply integrated weaving technology. More importantly, the thread-like fiber electronic devices can be achieved using a simple reel-to-reel process, which is strongly required for low-cost and scalable manufacturing technology. Here, high-performance reel-processed complementary metal-oxide-semiconductor (CMOS) integrated circuits are reported on 1D fiber substrates by using selectively chemical-doped single-walled carbon nanotube (SWCNT) transistors. With the introduction of selective n-type doping and a nonrelief photochemical patterning process, p- and n-type SWCNT transistors are successfully implemented on cylindrical fiber substrates under air ambient, enabling high-performance and reliable thread-like CMOS inverter circuits. In addition, it is noteworthy that the optimized reel-coating process can facilitate improvement in the arrangement of SWCNTs, building uniformly well-aligned SWCNT channels, and enhancement of the electrical performance of the devices. The p- and n-type SWCNT transistors exhibit field-effect mobility of 4.03 and 2.15 cm2 V-1 s-1 , respectively, with relatively narrow distribution. Moreover, the SWCNT CMOS inverter circuits demonstrate a gain of 6.76 and relatively good dynamic operation at a supply voltage of 5.0 V.

Selective Conversion from p-Type to n-Type of Printed Bottom-Gate Carbon Nanotube Thin-Film Transistors and Application in Complementary Metal-Oxide-Semiconductor Inverters.

The fabrication of printed high-performance and environmentally stable n-type single-walled carbon nanotube (SWCNT) transistors and their integration into complementary (i.e., complementary metal-oxide-semiconductor, CMOS) circuits are widely recognized as key to achieving the full potential of carbon nanotube electronics. Here, we report a simple, efficient, and robust method to convert the polarity of SWCNT thin-film transistors (TFTs) using cheap and readily available ethanolamine as an electron doping agent. Printed p-type bottom-gate SWCNT TFTs can be selectively converted into n-type by deposition of ethanolamine inks on the transistor active region via aerosol jet printing. Resulted n-type TFTs show excellent electrical properties with an on/off ratio of 106, effective mobility up to 30 cm2 V-1 s-1, small hysteresis, and small subthreshold swing (90-140 mV dec-1), which are superior compared to the original p-type SWCNT devices. The n-type SWCNT TFTs also show good stability in air, and any deterioration of performance due to shelf storage can be fully recovered by a short low-temperature annealing. The easy polarity conversion process allows construction of CMOS circuitry. As an example, CMOS inverters were fabricated using printed p-type and n-type TFTs and exhibited a large noise margin (50 and 103% of 1/2 Vdd = 1 V) and a voltage gain as high as 30 (at Vdd = 1 V). Additionally, the CMOS inverters show full rail-to-rail output voltage swing and low power dissipation (0.1 μW at Vdd = 1 V). The new method paves the way to construct fully functional complex CMOS circuitry by printed TFTs.

High-performance heterogeneous complementary inverters based on n-channel MoS2 and p-channel SWCNT transistors

Heterogeneous complementary inverters composed of bi-layer molybdenum disulfide (MoS2) and single-walled carbon-nanotube (SWCNT) networks are designed, and n-type MoS2/p-type SWCNT inverters are fabricated with a backgated structure. Field-effect transistors (FETs) based on the MoS2 and SWCNT networks show high electrical performance with large ON/OFF ratios up to 106 and 105 for MoS2 and SWCNT, respectively. The MoS2/SWCNT complementary inverters exhibit Vin-Vout signal matching and achieve excellent performances with a high peak voltage gain of 15, a low static-power consumption of a few nanowatts, and a high noise margin of 0.45VDD, which are suitable for future logic-circuit applications. The inverter performances are affected by the channel width-to-length ratios (W/L) of the MoS2-FETs and SWCNT-FETs. Therefore, W/L should be optimized to achieve a tradeoff between the gain and the power consumption.

Controlled n-Type Doping of Carbon Nanotube Transistors by an Organorhodium Dimer.

Single-walled carbon nanotube (SWCNT) transistors are among the most developed nanoelectronic devices for high-performance computing applications. While p-type SWCNT transistors are easily achieved through adventitious adsorption of atmospheric oxygen, n-type SWCNT transistors require extrinsic doping schemes. Existing n-type doping strategies for SWCNT transistors suffer from one or more issues including environmental instability, limited carrier concentration modulation, undesirable threshold voltage control, and/or poor morphology. In particular, commonly employed benzyl viologen n-type doping layers possess large thicknesses, which preclude top-gate transistor designs that underlie high-density integrated circuit layouts. To overcome these limitations, we report here the controlled n-type doping of SWCNT thin-film transistors with a solution-processed pentamethylrhodocene dimer. The charge transport properties of organorhodium-treated SWCNT thin films show consistent n-type behavior when characterized in both Hall effect and thin-film transistor geometries. Due to the molecular-scale thickness of the organorhodium adlayer, large-area arrays of top-gated, n-type SWCNT transistors are fabricated with high yield. This work will thus facilitate ongoing efforts to realize high-density SWCNT integrated circuits.