No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Short Channel Field-Effect-Transistors with Inkjet-Printed Semiconducting Carbon Nanotubes
Abstract
For short-channel field-effect transistors with inkjet-printed semiconducting carbon nanotubes, a novel fabrication strategy is developed by M. C. Hersam, A. Dodabalapur, and co-workers to minimize material consumption. On page 5505 they show how a single droplet of 10 pL ink containing 0.5 pg of nanotubes can be used, confining the inkjet droplet into the active channel area. This fabrication approach is compatible with roll-to-roll processing and enables the formation of high-performance short channel device arrays based on inkjet printing.
... In recent work, we have shown that inkjet printed short channel length SWCNT FETs, where the average nanotube length (∼1.4 microns) is greater than the source/drain (S/D) spacing, exhibit high hole mobilities in excess of 100 cm 2 V −1 s −1 [12]. The SWCNTs were deposited by inkjet printing, which is a highthroughput and cost-effective method for fabricating FETs and circuits. ...
... As shown in figure 1(a), a single 10 pl drop of semiconducting SWCNT ink (>98% semiconducting SWCNTs sorted by density gradient ultracentrifugation [15,16]) was printed onto the prepatterned S/D area followed by top gate dielectric and top-gate electrode deposition processes. Experimental details and device dimensions for our conventional top-gate/bottom-contact devices can be found in [12]. The bottom-contact structure is advantageous to inkjet printing and also avoids potential SWCNT damage during the electron beam lithography (EBL) process. ...
We report on the effects of mechanical distortion and gate insulator-semiconductor interface modification on the electronic transport characteristics of inkjet printed short channel length single walled carbon nanotube (SWCNT) transistors with Al2O3 top gate insulators. In these transistors, which are typically ambipolar, the average nanotube length is greater than the source-drain (S/D) spacing resulting in individual SWCNTs spanning the entire channel length. Mechanical distortion of the nanotubes due to bending near source and drain contacts when they are not recessed is found to suppress electron transport and transform the ambipolar transistors into p-type devices. Inclusion of printed interfacial polymer layers such as poly(vinylidene fluoride-trifluoroethylene) (PVDF-TrFE) between the SWCNTs and Al2O3 also results in p-type doping and reductions in electron transport. We discuss mechanisms responsible for these effects.
... Since carbon nanotubes (CNTs) have excellent properties, such as high strong mechanical stability, electrical conductivity, and good compatibility with polymer films, micronthickness CNT-based electronics consisting of polymer films and CNT micropatterns have wide applications in supercapacitors [1,2], sensors [3][4][5][6], solar cells [7], and other functional devices [8][9][10]. With the growing demand for device performance enhancement, the design of polymer substrates and CNT micropatterns has become more complex [11,12] and tends to be multi-layered [13,14]. ...
The direct fabrication of micron-thickness patterned electronics consisting of patterned PVA films and CNT micropatterns still faces considerable challenges. Here, we demonstrated the integrated fabrication of PVA films of micron-thickness and CNT-based patterns by utilising micro-pen writing and drop-on-demand printing in sequence. Patterned PVA films of 1–5 μm in thickness were written first using proper micro-pen writing parameters, including the writing gap, the substrate moving velocity, and the working pressure. Then, CNT droplets were printed on PVA films that were cured at 55–65 °C for 3–15 min, resulting in neat CNT patterns. In addition, an inertia-pseudopartial wetting spreading model was established to release the dynamics of the droplet spreading process over thin viscoelastic films. Uniform and dense CNT lines with a porosity of 2.2% were printed on PVA substrates that were preprocessed at 55 °C for 9 min using a staggered overwriting method with the proper number of layers. Finally, we demonstrated the feasibility of this hybrid printing method by printing a patterned PVA-CNT film and a micro-ribbon. This study provides a valid method for directly fabricating micron-thickness PVA-CNT electronics. The proposed method can also provide guidance on the direct writing of other high-molecular polymer materials and printing inks of other nanosuspensions.
... They also showed that CNT inks with densities higher than 0.2 mg/L clog nozzles, so an upper density limit for printable inks is set. Remarkably, a single drop of inkjetdeposited CNT ink has been used as an active channel material in multiple studies [78,79], which demonstrates the material cost-effectiveness of the inkjet printing method. ...
Active-matrices serve as the backplane circuitry for large-area display technologies and distributed sensors. Recently, there has been significant interest in developing flexible, additively manufactured active matrices for the burgeoning flexible electronics industry. Carbon nanotubes (CNTs) are prime candidate materials for semiconducting elements of transistors due to their solution processability, carrier mobility, and mechanical flexibility. There have been many recent accomplishments in the development of CNT inks and in their deposition via printing that enable their use in thin-film transistors (TFTs), and their appropriate performance make them suitable for use in large-area active matrices. In this review, we provide an overview of the field, with a specific focus on recent advancements in CNT sorting, ink preparation, and printing techniques. We also provide a benchmarking study of printed CNT devices presented in literature after 2017. Next, we discuss printable CNT-TFTs used for active-matrix applications. Finally, we provide a concluding perspective on the outlook and challenges for printed CNT-TFT active matrices.
... 161 Hersam's group developed a low-consumption inkjet printing of high-performance short channel (150 nm-250 nm) SWCNT FETs with only 0.5 pg material consumption in a single ink droplet of 10 pL. 162 Vertical OFETs (VOFETs) have recently been explored to shorten the channel length by utilizing the vertical thickness of the active layer, rather than the line width in the plane. Compared with conventional lateral-channel OFETs, vertical architectures of VOFETs break the accuracy limitation of the inkjet printer system and thus promote the output current density as well as the switching speed. ...
Flexible and wearable electronic devices are emerging as the novel platform for portable health monitoring, human–machine interaction, and some other electronic/optic applications. Future development of human-friendly smart electronics relies on efficient manufacturing and processing of advanced functional materials on flexible/stretchable substrates with effective device integration. Inkjet printing, known as a highly efficient solution-based printing and patterning technology with low-cost, high-quality, and high-throughput advantages, suits large-scale fabrication of flexible and wearable electronics. Over the years, researchers focused on high pattern resolution and uniformity on flexible substrates for advanced electrical/optical performances by various inkjet printing techniques. Different ink materials that can realize multiple functions have been fully investigated for achieving favorable printability and desired interactions with the substrates. Here, the most recently reported inkjet printing strategies, functional ink materials, and diverse inkjet-printed wearable electronic devices for practical applications (e.g., sensors, displays, transistors, and energy storage devices) are summarized. An outlook on future challenges as well as opportunities of inkjet-printed flexible and wearable electronics for research development and industrial commercialization is also presented.
... Recently, the fabrication of SWCNT-TFTs by ink-printing SWCNT solution at a well-defined position on a substrate was reported, which dramatically simplified the fabrication process [11][12][13][14]. The performance of the ink-printed SWCNT-TFTs is strongly dependent on the electronic purity of the semiconducting nanotube ink. ...
The electrical characteristics of carbon nanotube (CNT) thin-film transistors (TFTs) strongly depend on the properties of the gate dielectric that is in direct contact with the semiconducting CNT channel materials. Here, we systematically investigated the dielectric effects on the electrical characteristics of fully printed semiconducting CNT-TFTs by introducing the organic dielectrics of poly(methyl methacrylate) (PMMA) and Octadecyltrichlorosilane (OTS) to modify SiO2 dielectric. The results showed that the organic-modified SiO2 dielectric formed a favorable interface for the efficient charge transport in s-SWCNT-TFTs. Compared to single-layer SiO2 dielectric, the use of organic-inorganic hybrid bilayer dielectrics dramatically improved the performances of SWCNT-TFTs such as mobility, threshold voltage, hysteresis and On/Off ratio due to the suppress of charge scattering, gate leakage current and charge trapping. The transport mechanism is related that the dielectric with few charge trapping provided efficient percolation pathways for charge carriers, while reduced the charge scattering. High density of charge traps which could directly act as physical transport barriers and significantly restrict the charge carrier transport and, thus, result in decreased mobile carriers and low device performance. Moreover, the gate leakage phenomenon is caused by conduction through charge traps. So, as a component of TFTs, the gate dielectric is of crucial importance to the manufacture of high quality TFTs from the aspects of affecting the gate leakage current and device operation voltage, as well as the charge carrier transport. Interestingly, the OTS-modified SiO2 allows to directly print horizontally aligned CNT film, and the corresponding devices exhibited a higher mobility than that of the devices with the hybrid PMMA/SiO2 dielectric although the thickness of OTS layer is only ~2.5 nm. Our present result may provide key guidance for the further development of printed nanomaterial electronics.
... In theory this yields a gap where the width is limited by the resolution of the printer. Given that a printer like the Dimatix has a resolution of 10-30 µm depending on drop volume 13 , this provides a small gap, but by no means a short channel compared to photolithographic methods in a CMOS foundry 4,5 . ...
This paper reports a 100% inkjet printed transistor with a short channel of approximately 1 µm with an operating speed up to 18.21 GHz. Printed electronics are a burgeoning area in electronics development, but are often stymied by the large minimum feature size. To combat this, techniques were developed to allow for the printings of much shorter transistor channels. The small gap size is achieved through the use of silver inks with different chemical properties to prevent mixing. The combination of the short channel and semiconducting carbon nanotubes (CNT) allows for an exceptional experimentally measured on/off ratio of 106. This all inkjet printed transistor allows for the fabrication of devices using roll-to-roll methodologies with no additional overhead compared to current state of the art production methods.
In recent years, electronic products have continued to develop rapidly toward the trend of thinness, personalization, flexibility, high performance, high density, and multi-functional integration, and the development and research of new semiconductor materials and field-effect transistors (FETs) have become a hot topic of research today. With its excellent electrical, mechanical, and chemical properties, carbon nanotubes can be combined with printed electronics to become one of the most ideal channel materials for next-generation chips and flexible electronics. This paper outlines the separation methods of semiconductor carbon nanotubes and the research progress of printed carbon nanotube thin-film transistors in the fields of Internet of Things, artificial intelligence, and wearable electronics, and summarizes the challenges and opportunities for printed carbon nanotube thin-film transistor devices.
High-performance silicon transistors support computational function for digital technologies that profoundly impact modern lives. The scaling of silicon transistors, following Moore’s law for almost 6 decades, has slowed and will eventually run out of steam as the fundamental limits are approaching, and nanomaterials offer an auspicious path towards future generations of transistors beyond silicon. Meanwhile, larger size thin-film transistors (TFTs) enable a large variety of applications including displays, and printable nanomaterials present a potentially cost-effective approach for the mass production and customization of TFT devices. This article includes a review of the use of nanomaterials (e.g., carbon nanotubes, 2D materials, and nanostructured bulk materials) in high-performance and thin-film transistors, with an emphasis on the relevant technical achievements and remaining challenges.
The growing demand for ubiquitous data collection has driven the development of sensing technologies with local data processing. As a result, solution-processed semiconductors are widely employed due to their compatibility with low-cost additive manufacturing on a wide range of substrates. However, to fully realize their potential in sensing applications, high-performance scalable analog amplifiers must be realized. Here, ohmic-contact-gated transistors (OCGTs) based on solution-processed semiconducting single-walled carbon nanotubes are introduced to address this unmet need. This new device concept enables output current saturation in the short-channel limit without compromising output current drive. The resulting OCGTs are used in common-source amplifiers to achieve the highest width-normalized output current (≈30 µA µm–1) and length-scaled signal gain (≈230 µm–1) to date for solution-processed semiconductors. The utility of these amplifiers for emerging sensing technologies is demonstrated by the amplification of complex millivolt-scale analog biological signals including the outputs of electromyography, photoplethysmogram, and accelerometer sensors. Since the OCGT design is compatible with other solution-processed semiconducting materials, this work establishes a general route to high-performance, solution-processed analog electronics.
The economical, agile, customizable manufacturing, and integration of multifunctional device modules into networked systems with mechanical compliance and robustness enable unprecedented human‐integrated smart wearables and usher in exciting opportunities in emerging technologies. The additive manufacturing (AM) processes have emerged as potential candidates for rapid prototyping printed devices with diversified functionalities, e.g., energy harvesting/storage, sensing, actuation, and computation. However, there are few review reports about the ink‐based additive nanomanufacturing of functional materials for human‐integrated smart wearables. To fill this gap, herein, the recent progress in ink‐based additive nanomanufacturing technologies, focusing on their capability and potential for producing wearable human‐integrated devices, is reviewed. The manufacturing process integration, functional materials, device implementation, and application performance issues in designing and implementing the ink‐based additively nanomanufactured wearable systems are thoroughly discussed. The recent printed devices focusing on the processing conditions and performance metrics are comprehensively reviewed. Finally, the vision and outlook for the challenges and opportunities associated with related topics are provided. The rapid progress achieved in related disciplines enables more capable smart human‐integrated wearable systems that can be fully printed with rapid, agile, reconfigurable, and smart AM platforms. The recent progress in ink‐based additive nanomanufacturing is reviewed, focusing on its capability and potential for producing human‐integrated devices. The manufacturing process integration, functional materials, device implementation, and application performance are discussed. The rapid progress achieved in related areas enables smart human‐integrated wearable systems that are fully printed with agile, reconfigurable, and smart additive manufacturing platforms.
Semiconducting single-walled carbon nanotubes (s-SWCNTs) have been used in electrical transducers for environmental and health monitoring due to their quasi ballistic electronic transport, efficient transconductance, high carrier mobility, high On/Off ratio, excellent mechanical properties etc. Herein, we have prepared a non-enzymatic pesticide sensor to selectively detect methyl parathion (MP, which is a restricted use pesticide by EPA) using silver-zinc oxide (Ag-ZnO) composite decorated s-SWCNTs based field-effect transistor (FET). Ag/ZnO/s-SWCNTs film is also characterized by field-emission scanning electron microscopy (FE-SEM), Energy-dispersive spectrometry (EDS), X-ray diffraction (XRD) spectroscopy, Fourier-transform infrared (FT-IR) spectroscopy, Ultraviolet visible (UV-Vis) spectroscopy, Raman spectroscopy and photoluminescence (PL) spectroscopy. The response of the Ag-ZnO/s-SWCNTs-FET was measured under ambient condition in the presence and absences of MP. Hydrolysis of MP is taken place due to the potent catalytic activity of Ag-ZnO, which led to changes in transistor conductance. Based on this, detection of different concentrations of MP was demonstrated by Ag-ZnO-s-SWCNTs-FET. The Ag-ZnO-s-SWCNTs/FET device showed a linear response from 1×10-16 M to 1×10-4 M MP with a limit of detection (LOD) of 0.45×10-16 M in 100 mM PBS. In addition, Ag-ZnO/s-SWCNT-FET exhibited acceptable reproducibility and repeatability when employed for MP detection. Moreover, the proposed MP sensor was highly stable in ambient condition. Finally, detection of MP is demonstrated in soil and rice samples with good recovery.
For the past half century, silicon has served as the primary material platform for integrated circuit technology. However, the recent proliferation of nontraditional electronics, such as wearables, embedded systems, and low‐power portable devices, has led to increasingly complex mechanical and electrical performance requirements. Among emerging electronic materials, single‐walled carbon nanotubes (SWCNTs) are promising candidates for next‐generation computing as a result of their superlative electrical, optical, and mechanical properties. Moreover, their chirality‐dependent properties enable a wide range of emerging electronic applications including sub‐10 nm complementary field‐effect transistors, optoelectronic integrated circuits, and enantiomer‐recognition sensors. Here, recent progress in SWCNT‐based computing devices is reviewed, with an emphasis on the relationship between chirality enrichment and electronic functionality. In particular, after highlighting chirality‐dependent SWCNT properties and chirality enrichment methods, the range of computing applications that have been demonstrated using chirality‐enriched SWCNTs are summarized. By identifying remaining challenges and opportunities, this work provides a roadmap for next‐generation SWCNT‐based computing.
Ultrashort channel of electrodes is essential for the construction of advanced functional devices with high-level integration and high operation speed. However, the channel length of the fabricated electrodes is limited to 20 μm in inkjet printing. Although lots of methods have been previously proposed to obtain short channel, they require extra processing steps. In this paper, channel self-aligning phenomenon was found in directly patterned electrodes on unmodified substrate by inkjet printing, when using an interspace defects growing method. Further exploring the underlying mechanism reveals that the capillary force induced air film prevents droplets coalescence even on the same substrate with no temperature difference. The wetting region, which is generated during the retracting process of droplets impingement, will draw droplets closer at a larger drop space, thus demanding smaller air pressure for coalescence inhibition and contributing to the self-aligning phenomenon of micro-sized droplets released by inkjet printing. Accordingly, an ultrashort channel of 2.38 μm is obtained with relative smooth boundary, when electrodes are printed on a slightly heated substrate, which reduces the air pressure between two neighboring droplets. This work will provide referential significance for high resolution applications of inkjet printing technology.
Single-walled carbon nanotubes (SWCNTs) have attracted great attention on account of their superior and tunable electrical properties for promising applications in low-cost and high-performance nano-electronics and thin film devices. However, SWCNTs are usually produced as a mixture of m-/s- nanotubes with small diameters and long aspect ratios, tend to form bundles or entangled ropes owing to high Van der Waals attraction and π-π interactions among inter-tubes. Therefore, the dispersion and sorting of SWCNTs with both high-yield and desirable electronic structures has been a great challenge but a long-term motivation to achieve practical utility since its discovery. This review provides a comprehensive summary of strategies for surface modification and dispersion of SWCNTs, and surveys the up-to-date development of SWCNTs enrichment via mainly non-covalent interactions with molecular species. The effect of molecular architecture of selective dispersion and sorting of SWCNTs by surfactants, bio-macromolecules and conjugated polymers has been discussed with respect to the structure-property relationship and interaction mechanism
Improved thin-film microbatteries are needed to provide appropriate energy-storage options to power the multitude of devices that will bring the proposed "Internet of Things" network to fruition (e.g., active radio-frequency identification tags and microcontrollers for wearable and implantable devices). Although impressive efforts have been made to improve the energy density of 3D microbatteries, they have all used low energy-density lithium-ion chemistries, which present a fundamental barrier to miniaturization. In addition, they require complicated microfabrication processes that hinder cost-competitiveness. Here, inkjet-printed lithium-sulfur (Li-S) cathodes for integrated nanomanufacturing are reported. Single-wall carbon nanotubes infused with electronically conductive straight-chain sulfur (S@SWNT) are adopted as an integrated current-collector/active-material composite, and inkjet printing as a top-down approach to achieve thin-film shape control over printed electrode dimensions is used. The novel Li-S cathodes may be directly printed on traditional microelectronic semicoductor substrates (e.g., SiO2 ) or on flexible aluminum foil. Profilometry indicates that these microelectrodes are less than 10 µm thick, while cyclic voltammetry analyses show that the S@SWNT possesses pseudocapacitive characteristics and corroborates a previous study suggesting the S@SWNT discharge via a purely solid-state mechanism. The printed electrodes produce ≈800 mAh g(-1) S initially and ≈700 mAh g(-1) after 100 charge/discharge cycles at C/2 rate.
We report on the marked improvements in key device characteristics of single walled carbon nanotube (SWCNT) field-effect transistors (FETs) by coating the active semiconductor with a fluoropolymer layer such as poly(vinylidene fluoride-trifluoroethylene) (PVDF-TrFE). The observed improvements include: (i) A reduction in off-current by about an order of magnitude, (ii) a significant reduction in the variation of threshold voltage, and (iii) a reduction in bias stress-related instability and hysteresis present in device characteristics. These favorable changes in device characteristics also enhance circuit performance and the oscillation amplitude, oscillation frequency, and increase the yield of printed complementary 5-stage ring oscillators. The origins of these improvements are explored by exposing SWCNT FETs to a number of vapor phase polar molecules which produce similar effects on the FET characteristics as the PVDF-TrFE. Coating of the active SWCNT semiconductor layer with a fluoropolymer will be advantageous for the adoption of SWCNT FETs in a variety of printed electronics applications.
We fabricated single-walled carbon nanotube (SWNT) field-effect transistor (FET) devices on flattened electrodes, in which there are no height difference between metal electrodes and the substrate. SWNT-FET fabricated using bottom contact technique have some advantages, such that the SWNTs are free from electron irradiation, have direct contact with the desired metal electrodes, and can be functionalized before or after deposition. However, the SWNTs can be bent at the contact point with the metal electrodes leading to a different electrical characteristic of the devices. The number of SWNT direct junctions in short channel length devices is drastically increased by the use of flattened electrodes due to strong attractive interaction between SWNT and the substrate. The flattened electrodes show a better balance between their hole and electron mobility compared to that of the non-flattened electrodes, that is, ambipolar FET characteristic. It is considered that bending of the SWNTs in the non-flattened electrode devices results in a higher Schottky barrier for the electrons.
High-performance single-walled carbon nanotube (SWCNT) thin-film transistors are fabricated by single-pass inkjet printing of SWCNTs on high-κ solution-processed ZrO2 gate dielectric. We demonstrate that an ultraviolet ozone treatment of the ZrO2 substrate is critical in achieving a uniform dispersion of sorted SWCNTs in the semiconducting channel. The resulting devices exhibit excellent performance with mobility and on/off current ratio exceeding 30 cm2 V−1 s−1 and 105, respectively, at low operating voltages (<5 V). The single-pass inkjet printing process demonstrated in this letter shows great promise as a reliable and scalable method for SWCNT based high performance electronics.
We report high-performance all-inkjet-printed organic thin-film transistors (OTFTs), where inkjet-printed silver electrodes, cross-linked poly(4-vinylphenol) (PVP) and 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS-pentacene) were used as gate/source/drain electrodes, a gate dielectric layer and an active semiconductor layer, respectively. To evaluate quality of the active semiconductor layer, we also fabricated OTFTs by using spin-coating and drop-casting methods for TIPS-pentacene layer on the inkjet-printed PVP gate dielectric layer. Comparable TFT electrical performances were obtained and well-crystallized TIPS-pentacene layer was formed for all cases. All TIPS-pentacene OTFTs show lower sub-threshold swing values than OTFTs with an evaporated pentacene active semiconductor layer on the inkjet-printed PVP gate dielectric layer. By using optimized inkjet-printing conditions, we obtained mobility of 0.06 cm2 V-1 s-1 and on/off ratio of 104 for all-inkjet-printed OTFT.
Thin-film transistors based on inkjet printed indium zinc tin oxide (IZTO) channel layers are reported in this paper. The printed IZTO transistor has a high field-effect mobility (µFE = 30 cm2V−1 s−1), excellent on-to-off current ratio (>1 × 106) and behaves as an enhancement mode device (turn-on voltage = 2 V). This mobility is an order magnitude higher than previously reported for inkjet printed oxide-based transistors. The printed films are highly transparent in the UV-Visible regime with a transmittance higher than 95%. A transparent thin film transistor using a printed IZTO channel was also demonstrated for the first time.
Some of the major application areas for organic and polymeric transistors are reviewed. Organic complementary devices are promising on account of their lower power dissipation and ease of circuit design. The first organic large-scale integrated circuits have been implemented with this circuit approach. Organic transistor backplanes are ideally suited for electronic paper applications and other display schemes. Low-cost and other processing advantages, as well as improving performance, have led to organic-based radio frequency identification tag development. The chemical interaction between various organic and polymer semiconductors can be exploited in chemical and biological sensors based upon organic transistors.
We report the radio-frequency performance of carbon nanotube array
transistors that have been realized through the aligned assembly of highly
separated, semiconducting carbon nanotubes on a fully scalable device platform.
At a gate length of 100 nm, we observe output current saturation and obtain
as-measured, extrinsic current gain and power gain cut-off frequencies,
respectively, of 7 GHz and 15 GHz. While the extrinsic current gain is
comparable to the state-of-the-art the extrinsic power gain is improved. The
de-embedded, intrinsic current gain and power gain cut-off frequencies of 153
GHz and 30 GHz are the highest values experimentally achieved to date. We
analyze the consistency of DC and AC performance parameters and discuss the
requirements for future applications of carbon nanotube array transistors in
high-frequency electronics.
The heterogeneity of as-synthesized single-walled carbon nanotubes (SWNTs) precludes their widespread application in electronics, optics and sensing. We report on the sorting of carbon nanotubes by diameter, bandgap and electronic type using structure-discriminating surfactants to engineer subtle differences in their buoyant densities. Using the scalable technique of density-gradient ultracentrifugation, we have isolated narrow distributions of SWNTs in which >97% are within a 0.02-nm-diameter range. Furthermore, using competing mixtures of surfactants, we have produced bulk quantities of SWNTs of predominantly a single electronic type. These materials were used to fabricate thin-film electrical devices of networked SWNTs characterized by either metallic or semiconducting behaviour.
Low-cost green manufacturing of singlewalled carbon nanotube films via precisely controlled inkjet printing is demonstrated. This type of transistor exceeds the performance of conventional organic transistors, both in mobility and the on/off ratio. The production of exclusively inkjet-printed SWCNT transistors with printable ionic-liquid gate dielectrics is also shown.
Extremely large-area roll-to-roll (R2R) manufacturing on flexible substrates is ubiquitous for applications such as paper and plastic processing. It combines the benefits of high speed and inexpensive substrates to deliver a commodity product at low cost. The challenge is to extend this approach to the realm of nanopatterning and realize similar benefits. In order to achieve low-cost nanopatterning, it is imperative to move toward high-speed imprinting, less complex tools, near zero waste of consumables, and low-cost substrates. We have developed a roll-based J-FIL process and applied it to a technology demonstrator tool, the LithoFlex 100, to fabricate large-area flexible bilayer wire-grid polarizers (WGPs)and high-performance WGPs on rigid glass substrates. Extinction ratios of better than 10,000 are obtained for the glass-based WGPs. Two simulation packages are also employed to understand the effects of pitch, aluminum thickness, and pattern defectivity on the optical performance of the WGP devices. It is determined that the WGPs can be influenced by both clear and opaque defects in the gratings; however, the defect densities are relaxed relative to the requirements of a high-density semiconductor device. (C) The Authors. Published by SPIE
Complementary metal oxide semiconductor (CMOS) technology with high transconductance and signal gain is mandatory for practicable digital/analog logic electronics. However, high performance all-oxide CMOS logics are scarcely reported in the literature; specifically, not at all for solution-processed/printed transistors. As a major step toward solution-processed all-oxide electronics, here it is shown that using a highly efficient electrolyte-gating approach one can obtain printed and low-voltage operated oxide CMOS logics with high signal gain (≈21 at a supply voltage of only 1.5 V) and low static power dissipation.
© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
This feature article provides an overview of several mechanical-based micro- and nanopatterning technologies that can achieve continuous and high-throughput fabrication of various sub-wavelength structures without resorting to the conventional optical lithography technique. These include a template-based and versatile roll-to-roll nanoimprint lithography technique, cost-effective dynamic mould sweeping patterning as well as mould-free patterning methods. Examples of demonstrated and potential applications in optoelectronics and photonics are also discussed.
The materials combination of inkjet printed single-walled carbon nanotubes (SWCNTs) and zinc tin oxide (ZTO) is very promising for large-area thin-film electronics. We compare the characteristics of conventional complementary inverters and ring oscillators measured in air - with SWCNT p-channel field effect transistors (FETs) and ZTO n-channel FETs - with those of ambilpolar inverters and ring oscillators with bilayer SWCNT/ZTO FETs. This is the first such comparison between the performance characteristics of ambipolar and conventional inverters and ring oscillators. The measured signal delay per stage of 140 ns, for complementary ring oscillators, is the fastest for any ring oscillator circuit with printed semiconductors to date.
Low-acceleration-voltage electron irradiation effects on single-walled
carbon nanotubes were studied by resonant Raman spectroscopy. The
irradiation at acceleration voltages of 0.5 to 25 kV was found to
extinguish the characteristic optical property of the nanotubes and
reduce their tolerance against annealing in air, indicating that the
nanotubes are inevitably damaged by ordinary scanning electron
microscope observation. The acceleration voltage of around 1 kV caused
the most extensive damage. Less defective SWNTs were found to have a
higher tolerance against the irradiation damage.
Solution-processed amorphous oxide semiconductors (AOSs) are emerging as important electronic materials for displays and transparent electronics. We report here on the fabrication, microstructure, and performance characteristics of inkjet-printed, low-temperature combustion-processed, amorphous indium gallium zinc oxide (a-IGZO) thin-film transistors (TFTs) grown on solution-processed hafnia self-assembled nanodielectrics (Hf-SANDs). TFT performance for devices processed below 300 °C includes > 4x enhancement in electron mobility (μFE) on Hf-SAND versus SiO2 or ALD-HfO2 gate dielectrics, while other metrics such as subthreshold swing (SS), current on:off ratio (ION:IOFF), threshold voltage (Vth), and gate leakage current (Ig) are unchanged or enhanced. Thus, low voltage IGZO/SAND TFT operation (< 2V) is possible with ION:IOFF = 107, SS = 125 mV/dec, near-zero Vth, and large electron mobility, μFE(avg) = 20.6 ± 4.3 cm2V-1s-1, μFE(max) = 50 cm2V-1s-1. Furthermore, X-ray diffraction analysis indicates that the 300 °C IGZO combustion processing leaves the underlying Hf-SAND microstructure and capacitance intact. This work establishes the compatibility and advantages of all-solution, low-temperature fabrication of inkjet-printed, combustion-derived high-mobility IGZO TFTs integrated with self-assembled hybrid organic-inorganic nanodielectrics.
We report a sol–gel method to deposit a high-k dielectric, zirconium oxide (ZrO2). This solution-based approach has advantages of easy processing and low fabrication cost. Effects of annealing temperatures on dielectric properties, such as tunneling current density and capacitance density, are reported. Morphological and chemical characterizations suggest that the process temperature can be kept at or below 300°C. We have employed the solution-processed ZrO2 dielectric in a zinc tin oxide thin-film transistor. Saturation mobility of 4.0 cm2/V s at operating voltage of 2 V has been observed. The measured subthreshold swing is 74 mV/decade, which is the result of the combination of an electronically clean dielectric/semiconductor interface and high insulator capacitance.
In this Letter, we demonstrate thin-film single-walled carbon nanotube (SWCNT) complementary metal-oxide-semiconductor (CMOS) logic devices with sub-nanowatt static power consumption and full rail-to-rail voltage transfer characteristics as is required for logic gate cascading. These results are enabled by a local metal gate structure that achieves enhancement-mode p-type and n-type SWCNT thin-film transistors (TFTs) with widely separated and symmetric threshold voltages. These complementary SWCNT TFTs are integrated to demonstrate CMOS inverter, NAND, and NOR logic gates at supply voltages as low as 0.8 V with ideal rail-to-rail operation, sub-nanowatt static power consumption, high gain, and excellent noise immunity. This work provides a direct pathway for solution processable, large area, power efficient SWCNT advanced logic circuits and systems.
Fully-printed transistors are a key component of ubiquitous flexible electronics. In this work, the advantages of an inverse gravure printing technique and the solution-processing of semiconductor-enriched single-walled carbon nanotubes (SWNTs) are combined to fabricate fully-printed thin-film transistors on mechanically flexible substrates. The fully-printed transistors are configured in a top-gate device geometry, and utilize silver metal electrodes and an inorganic/organic high-κ (~17) gate dielectric. The devices exhibit excellent performance for a fully-printed process, with mobility and on/off current ratio of up to ~9 cm2/Vs and 105, respectively. Extreme bendability is observed, without measurable change in the electrical performance down to a small radius of curvature of 1mm. Given the high performance of the transistors, our high-throughput printing process serves as an enabling nano-manufacturing scheme for a wide range of large-area electronic applications based on carbon nanotube networks.
Vertical organic thin-film transistors (VOTFTs) are promising devices to overcome the transconductance and cut-off frequency restrictions of horizontal organic thin-film transistors. The basic physical mechanisms of VOTFT operation, however, are not well understood and VOTFTs often require complex patterning techniques using self-assembly processes which impedes a future large-area production. In this contribution, high-performance vertical organic transistors comprising pentacene for p-type operation and C60 for n-type operation are presented. The static current-voltage behavior as well as the fundamental scaling laws of such transistors are studied, disclosing a remarkable transistor operation with a behavior limited by injection of charge carriers. The transistors are manufactured by photolithography, in contrast to other VOTFT concepts using self-assembled source electrodes. Fluorinated photoresist and solvent compounds allow for photolithographical patterning directly and strongly onto the organic materials, simplifying the fabrication protocol and making VOTFTs a prospective candidate for future high-performance applications of organic transistors.
Fullerene (C60) is a well-known n-channel organic semiconductor. We demonstrate that p-channel C60 field-effect transistors are possible by doping with molybdenum trioxide (MoO3). The device performance of the p-channel C60 field-effect transistors, such as mobility, threshold voltage, and on/off ratio is varied in a controlled manner by changing doping concentration. This work demonstrates the utility of charge transfer doping to obtain both n- and p-channel field-effect transistors with a single organic semiconductor.
The development of complex self-organizing molecular systems for future nanotechnology requires not only robust formation of molecular structures by self-assembly but also precise control over their temporal dynamics. As an exquisite example of such control, in this issue of ACS Nano, Fujii and Rondelez demonstrate a particularly compact realization of a molecular "predator-prey" ecosystem consisting of only three DNA species and three enzymes. The system displays pronounced oscillatory dynamics, in good agreement with the predictions of a simple theoretical model. Moreover, its considerable modularity also allows for ecological studies of competition and cooperation within molecular networks.
We develop short-channel transistors using solution-processed single-walled carbon nanotubes (SWNTs) to evaluate the feasibility of those SWNTs for high-performance applications. Our results show that even though the intrinsic field-effect mobility is lower than the mobility of CVD nanotubes, the electrical contact between the nanotube and metal electrodes is not significantly affected. It is this contact resistance which often limits the performance of ultra-scaled transistors. Moreover, we found that the contact resistance is lowered by the introduction of oxygen treatment. Therefore, high-performance solution-processed nanotube transistors with a 15 nm channel length were obtained by combining a top-gate structure and gate insulators made of a high-dielectric-constant ZrO2 film. The combination of these elements yields a performance comparable to that obtained with CVD nanotube transistors, which indicates the potential for using solution-processed SWNTs for future aggressively scaled transistor technology.
A new robust and exceptionally simple procedure for soft nano-imprint lithography (Soft-NIL) is described, which provides easy access to nanoscale patterns of a host of active materials on a Si/SiOx surface. Partial curing of a thiol-ene based UV cross-linkable resin (<1 μm) for 30−40 s prior to imprinting resulted in sufficient buildup of resin molecular weight to prevent its absorption into polydimethylsiloxane molds yet maintain a low enough viscosity to allow for rapid molding of nanoscale features during the subsequent imprint-and-cure stage of the process. Imprinted features were easily transferred to the underlying substrate by traditional reactive ion etching and lift-off processes. Easy soft imprint nano-lithography (ESINL) permitted the use of untreated PDMS molds for replicating patterns in gold, nickel, and complex aluminum capped silicon structures. ESINL was used to fabricate organic field effect transistors (poly(3,3′′′-didodecylquaterthiophene, W/L = 204, μsat = 6.0 × 10−3 cm2/(V·s)), demonstrating the first use of a soft imprint lithographic process to make such devices.
In the past decade, semiconducting carbon nanotube thin films have been recognized as contending materials for wide-ranging applications in electronics, energy, and sensing. In particular, improvements in large-area flexible electronics have been achieved through independent advances in postgrowth processing to resolve metallic versus semiconducting carbon nanotube heterogeneity, in improved gate dielectrics, and in self-assembly processes. Moreover, controlled tuning of specific device components has afforded fundamental probes of the trade-offs between materials properties and device performance metrics. Nevertheless, carbon nanotube transistor performance suitable for real-world applications awaits understanding-based progress in the integration of independently pioneered device components. We achieve this here by integrating high-purity semiconducting carbon nanotube films with a custom-designed hybrid inorganic-organic gate dielectric. This synergistic combination of materials circumvents conventional design trade-offs, resulting in concurrent advances in several transistor performance metrics such as transconductance (6.5 μS/μm), intrinsic field-effect mobility (147 cm(2)/(V s)), subthreshold swing (150 mV/decade), and on/off ratio (5 × 10(5)), while also achieving hysteresis-free operation in ambient conditions.
Inkjet printing is used to fabricate CN-TFT devices on PET substrate with 70 nm HfO(2) gate dielectric. By varying the amount of printing, effective mobility can be raised to 43 cm(2) V(-1) s(-1) with on/off ratio ≥ 10(4) for devices with channel length 160 μm. This demonstrates that inkjet printing is promising for fabrication of high-performance devices in flexible electronics.
Solution-processed thin-films of semiconducting carbon nanotubes as the channel material for flexible electronics simultaneously offers high performance, low cost, and ambient stability, which significantly outruns the organic semiconductor materials. In this work, we report the use of semiconductor-enriched carbon nanotubes for high-performance integrated circuits on mechanically flexible substrates for digital, analog and radio frequency applications. The as-obtained thin-film transistors (TFTs) exhibit highly uniform device performance with on-current and transconductance up to 15 μA/μm and 4 μS/μm. By performing capacitance-voltage measurements, the gate capacitance of the nanotube TFT is precisely extracted and the corresponding peak effective device mobility is evaluated to be around 50 cm(2)V(-1)s(-1). Using such devices, digital logic gates including inverters, NAND, and NOR gates with superior bending stability have been demonstrated. Moreover, radio frequency measurements show that cutoff frequency of 170 MHz can be achieved in devices with a relatively long channel length of 4 μm, which is sufficient for certain wireless communication applications. This proof-of-concept demonstration indicates that our platform can serve as a foundation for scalable, low-cost, high-performance flexible electronics.
The large amount of hysteresis and threshold voltage variation in carbon nanotube transistors impedes their use in highly integrated digital applications. The origin of this variability is elucidated by employing a top-coated, hydrophobic monolayer to passivate bottom-gated devices. Compared to passivating only the supporting substrate, it is found that covering the nanotube channel proves highly effective and robust at improving device-to-device consistency-hysteresis and threshold voltage variation are reduced by an average of 84 and 53%, respectively. The effect of gate and drain-source bias on hysteresis is considered, showing strong dependence that must be accounted for when analyzing the effectiveness of a passivation layer. These results provide both key insight into the origin of variability in carbon nanotube transistors and a promising path for resolving this significant obstacle.
Although carbon nanotube (CNT) transistors have been promoted for years as a replacement for silicon technology, there is limited theoretical work and no experimental reports on how nanotubes will perform at sub-10 nm channel lengths. In this manuscript, we demonstrate the first sub-10 nm CNT transistor, which is shown to outperform the best competing silicon devices with more than four times the diameter-normalized current density (2.41 mA/μm) at a low operating voltage of 0.5 V. The nanotube transistor exhibits an impressively small inverse subthreshold slope of 94 mV/decade-nearly half of the value expected from a previous theoretical study. Numerical simulations show the critical role of the metal-CNT contacts in determining the performance of sub-10 nm channel length transistors, signifying the need for more accurate theoretical modeling of transport between the metal and nanotube. The superior low-voltage performance of the sub-10 nm CNT transistor proves the viability of nanotubes for consideration in future aggressively scaled transistor technologies.
To suppress undesirable short-channel effects in organic transistors with nanoscale lateral dimensions, aggressive gate-dielectric scaling (using an ultra-thin monolayer-based gate dielectric) and area-selective contact doping (using a strong organic dopant) are introduced into organic transistors with channel lengths and gate-to-contact overlaps of about 100 nm. These nanoscale organic transistors have off-state drain currents below 1 pA, on/off current ratios near 107, and clean linear and saturation characteristics.
We describe how iterative, orthogonal density gradient ultracentrifugation (DGU) separations can be used to produce nearly single-chirality (6,5) SWNTs. SWNT network transistors made from these highly pure, 98% semiconducting SWNTs simultaneously exhibit high on/off ratios, mobilities, and on-state conductances, suggesting their future application in integrated circuits and near-infrared optoelectronic light emitters and photodetectors.
A new, solution-processable, low-bandgap, diketopyrrolopyrrole- benzothiadiazole-based, donor-acceptor polymer semiconductor (PDPP-TBT) is reported. This polymer exhibits ambipolar charge transport when used as a single component active semiconductor in OTFTs with balanced hole and electron mobilities of 0.35 cm2 V-1s-1 and 0.40 cm 2 V-1s-1, respectively. This polymer has the potential for ambipolar transistor-based complementary circuits in printed electronics.
A simple and versatile method to fabricate micro- and nanoengineered organic field-effect transistors (OFET) from solution processable materials by additive lithographic techniques was reported. The OFETs were built in a bottom-gate, bottom-contact architecture, while heavily-doped Si wafers were used as substrates and gate terminals. The results show that the higher electrical resistivity of OFET electrodes with respect to submicrometric wires results from the size of the MIMIC channels used in a few orders of magnitude larger compared to the characteristic length scales of nucleation. The electrical characterization of OFETs processed by LCW from a 0.06 wt% chloroform solution, fabricated using standard Pd electrodes reveal a modest saturated mobility of 3 × 10-4 cm2 V-1 s -1.
- Chung