Carbon Nanotube Thin-film Transistors Research Articles

Enhancement-Mode Carbon Nanotube Optoelectronic Synaptic Transistors with Large and Controllable Threshold Voltage Modulation Window for Broadband Flexible Vision Systems.

The development of large-scale integration of optoelectronic neuromorphic devices with ultralow power consumption and broadband responses is essential for high-performance bionics vision systems. In this work, we developed a strategy to construct large-scale (40 × 30) enhancement-mode carbon nanotube optoelectronic synaptic transistors with ultralow power consumption (33.9 aJ per pulse) and broadband responses (from 365 to 620 nm) using low-work function yttrium (Y)-gate electrodes and the mixture of eco-friendly photosensitive Ag2S quantum dots (QDs) and ionic liquids (ILs)-cross-linking-poly(4-vinylphenol) (PVP) (ILs-c-PVP) as the dielectric layers. Solution-processable carbon nanotube thin-film transistors (TFTs) showed enhancement-mode characteristics with the wide and controllable threshold voltage window (-1 V∼0 V) owing to use of the low-work-function Y-gate electrodes. It is noted that carbon nanotube optoelectronic synaptic transistors exhibited high on/off ratios (>106), small hysteresis and low operating voltage (≤2 V), and enhancement mode even under the illumination of ultraviolet (UV, 365 nm), blue (450 nm), and green (550 nm) to red (620 nm) pulse lights when introducing eco-friendly Ag2S QDs in dielectric layers, demonstrating that they have the strong fault-tolerant ability for the threshold voltage drifts caused by various manufacturing scenarios. Furthermore, some important bionic functions including a high paired pulse facilitation index (PPF index, up to 290%), learning and memory function with the long duration (200 s), and rapid recovery (2 s). Pavlov's dog experiment (retention time up to 20 min) and visual memory forgetting experiments (the duration of high current for 180 s) are also demonstrated. Significantly, the optoelectronic synaptic transistors can be used to simulate the adaptive process of vision in varying light conditions, and we demonstrated the dynamic transition of light adaptation to dark adaptation based on light-induced conditional behavior. This work undoubtedly provides valuable insights for the future development of artificial vision systems.

High-sensitivity and energy-efficient chloride ion sensors based on flexible printed carbon nanotube thin-film transistors for wearable electronics

The advent of flexible single-walled carbon nanotube thin-film transistors (SWCNT-TFTs) has transformed electronics, providing significant benefits like low operating voltage, reduced power consumption, cost-effectiveness, and improved signal amplification. This study focuses on leveraging these attributes to develop a novel flexible high-sensitivity and energy-efficient chloride ion sensors based on printed flexible SWCNT-TFTs utilizing polymers-sorted semiconducting SWCNTs (sc-SWCNTs) as the active layers and ion liquids-poly(4-vinylphenol as dielectric layers along with the evaporated deposition of aluminum electrodes and printed silver electrodes as the gate and source-drain electrodes, respectively. The sensors exhibit several operational advantages, including low voltage requirements (≤1 V), rapid response speed (5.32 s), significant signal amplification (Up to 702.6%), low power consumption (0.31 μJ at 1 mmol chloride ion), good repeatability, high sensitivity for both low and high concentrations of chloride ion (up to 100 mmol/L) and excellent mechanical flexibility (No obvious changes after bending for 10,000 times with a 5 mm radius). The detection mechanism of chloride ions was analyzed using X-ray Photoelectron Spectroscopy (XPS). It was found that chloride ions react with silver nanoparticles (AgNPs) to form silver chloride (AgCl) on printed electrodes, impeding carrier transport and reducing the currents in SWCNT TFTs. Importantly, our sensors' compatibility with smart devices allows for real-time monitoring of chloride ion levels in human sweat, offering significant potential for daily health monitoring.

Carbon-silicon based hybrid quantum dot short wave infrared photodetector

Recently infrared photodetectors based on low-dimensional semiconductors have developed rapidly. However, due to its poor light absorption and incompatibility with traditional silicon-based readout circuit processes, the sensitivity and integration of such photodetectors are limited. In this work, we proposes a 64 × 64 quantum dot short-wavelength infrared (SWIR) photodetector composed of carbon nanotube thin film transistor (CNT TFT) and silicon-based ROIC. CNT TFT's gate is constructed by PbS colloidal quantum dots (PbS CQDs) which improve the absorption rate of infrared light. The generated photovoltage is amplified and converted in situ by CNT TFT. Notably, under infrared radiation of 1300 nm, the noise equivalent current reach up to 1.25*10−13A/Hz1/2. At a drain-source bias (Vds)= -0.1 V. The device exhibits detectivity of 5.6*1013 Jones and a fast response of 0.57 ms. The silicon-based ROIC is implemented by CMOS 0.18um process, with a power supply voltage of 1.8 V. It mainly includes a programmable integrator, a sampling and holding circuit, and a 10bit/2.5 MHz successive approximation analog-to-digital converter (SAR ADC). The programmable integrator has four levels of integral gain to meet the application requirements of different infrared light intensities. The experiment results show that the imaging function of the overall photodetector is correct, laying the foundation for the development of carbon-silicon based heterojunction integrated photodetector in the future.

Nozzle-Free Printing of CNT Electronics Using Laser-Generated Focused Ultrasound.

Printed electronics have made remarkable progress in recent years and inkjet printing (IJP) has emerged as one of the leading methods for fabricating printed electronic devices. However, challenges such as nozzle clogging, and strict ink formulation constraints have limited their widespread use. To address this issue, a novel nozzle-free printing technology is explored, which is enabled by laser-generated focused ultrasound, as a potential alternative printing modality called Shock-wave Jet Printing (SJP). Specifically, the performance of SJP-printed and IJP-printed bottom-gated carbon nanotube (CNT) thin film transistors (TFTs) is compared. While IJP required ten print passes to achieve fully functional devices with channel dimensions ranging from tens to hundreds of micrometers, SJP achieved comparable performance with just a single pass. For optimized devices, SJP demonstrated six times higher maximum mobility than IJP-printed devices. Furthermore, the advantages of nozzle-free printing are evident, as SJP successfully printed stored and unsonicated inks, delivering moderate electrical performance, whereas IJP suffered from nozzle clogging due to CNT agglomeration. Moreover, SJP can print significantly longer CNTs, spanning the entire range of tube lengths of commercially available CNT ink. The findings from this study contribute to the advancement of nanomaterial printing, ink formulation, and the development of cost-effective printable electronics.

Gate Capacitance Coupling of Double-Gate Carbon Nanotube Network Transistors.

Carbon nanotube (CNT) network channels constructed using a high-purity CNT solution for use in CNT thin-film transistors have the advantages of the possibility of requiring a low-temperature process and needing no special equipment. However, there are empty spaces between individual CNTs, resulting in unexpected effects. In this study, double-gate (DG) CNT network transistors were fabricated and measured in four different configurations to observe the capacitive coupling effects between the top gate (TG) and bottom gate (BG) in the DG structure. As a result, the electrical characteristics measured with the BG with a thicker gate oxide while floating the TG were similar to those measured with the TG with a thinner gate oxide. A comparison of the measured transfer curves showed that TG and BG were strongly coupled through the empty spaces in the channels. In addition, we evaluated the capacitance coupling effect due to changes in the CNT density, which is closely related to the empty space of the network channel. Finally, we proposed a method to determine the effective gate capacitance by considering the empty spaces between CNTs, which enabled the accurate evaluation of mobility. The effects of these materials were demonstrated by fabricating transistors using Al2O3, HfO2, and ZrO2 as TG oxide materials. By focusing on considerations based on the properties of CNT materials, our study provides valuable insights into accurate electrical modeling and potential advancements in CNT-based devices.

Matched printed carbon nanotube complementary metal-oxide-semiconductor (CMOS) devices for flexible circuits

The development of matched carbon nanotube (CNT) complementary metal-oxide-semiconductor (CMOS) devices still remains a challenge for flexible and low-power-dissipation circuits. In this study, we found a reliable technique to achieve matched CNT CMOS thin-film transistors (TFTs) for integrated circuits (IC) with low power consumption. The enhancement-mode p-type CNT TFTs were obtained using the low-work-function Al gate electrodes and ultrathin (10 nm) Al2O3 dielectrics, which exhibit the average field-effect mobility(μ) of 6.5 cm2V−1s−1, subthreshold swing (SS) down to 70–85 mV/dec and on/off ratio up to 106 at the low working voltages between −1.5 V and 0.5 V, as well the outstanding stability and mechanical flexibility after 10,000 cycles of bending. Then, by adjusting the aspect ratios of the TFT channels and selectively dropping the electron-doping inks into p-type CNT TFTs’ channels, matched n-type and p-type CNT TFTs were obtained. Finally, flexible printed CMOS inverters with high noise tolerance (84% of 1/2 VDD), high voltage gain (over 32), and low power consumption (down to 32.9 pW) were successfully constructed, owing to the work style of CMOS circuits and electrically symmetrical n-type and p-type TFTs. Furthermore, good-performance NAND and NOR gates have been demonstrated. This work can effectively resolve the leakage current issue of flexible carbon-based electronics with the ultra-thin dielectrics by optimizing the conductive ink formula and printing technology.

35‐4: Carbon Nanotube Thin‐Film Transistors for Active‐Matrix Micro‐LED Display – Device Performances, Bias Stress Stability and Compact Modeling

Carbon nanotube thin‐film transistor (CNT‐TFT) is expected to be a promising candidate for backplane technologies for emerging displays including micro‐LED, due to its extraordinary driving capability. In this work, CNT‐TFTs are characterized, which exhibit excellent on‐state current, high carrier mobility, and low subthreshold swing. Different from conventional TFTs, a positive threshold voltage shift under negative bias stress is observed in these devices. The mechanism is explored and explained, and an improved stretched‐exponential model is developed for such phenomenon. To predict the driving capability of CNT‐TFT backplane technology, compact models for CNT‐TFTs and micro‐LEDs are built based on experimental data, and SPICE simulation of a 3T1C pixel circuit is carried out. The results indicate that CNT‐TFTs enables high driving current in active‐matrix micro‐LED display with relative ease, paving the way for practical applications of CNT‐TFTs.

P‐153: Late‐News Poster: Temporal Photo‐Response Analysis of Inkjet‐Printed Transparent Single‐Walled Carbon Nanotube Thin‐Film Transistors

We demonstrated the temporal photo‐response of transparent and flexible carbon nanotube thin‐film transistors. Fabricated carbon nanotube thin film transistors showed exponential degradation with light illumination and linear recovery after light off. The result indicates that the principal mechanism of photo‐response in carbon nanotube transistors is photo‐desorption of oxygen molecules.

Control of the coffee ring effect during R2R gravure printing for minimizing threshold voltage variation in printed carbon nanotube-based thin film transistors

Devising a high-throughput additive manufacturing method (HTAM) could aid in fabricating flexible electronic devices with marginal greenhouse gas (GG) emissions and net zero by-products. A roll-to-roll (R2R) gravure printing method is considered a typical platform of HTAM to fabricate carbon nanotube-based flexible electronic devices. However, the large variation in threshold voltage (Vth) in the printed carbon nanotube devices restricts device yield, thereby limiting their practical applications. In this study, the authors would like to show a way of minimizing the variation of Vth in the R2R gravure printed carbon nanotube thin-film transistors (TFTs) by understanding how the morphology of the printed dielectric layer can be controlled during ink drying. Since the formation of an uneven morphology after drying with higher edge thickness, also known as the coffee ring effect (CRE), is one of the key factors causing the variation in Vth, regulating the morphology of the dielectric ink is vital in minimizing the Vth variation of the TFTs printed via R2R gravure. By optimizing the rheological characteristics of the dielectric ink, a homogeneous morphology was attained without CRE, consequently minimizing the Vth variation from 19.6% to 6.9%. Furthermore, the printed device stability was improved by removing the CRE and avoiding the localized bias stress during device operation. Based on this work, the yield, and the stability of R2R gravure printed devices could be improved, enabling the rapid commercialization of additively manufactured flexible devices without the emission of GG or any harmful by-products.

Fully solution-processed carbon nanotubes thin film transistors and PMOS inverters on glass substrate

We report fully solution-processed thin film transistors and PMOS inverters fabricated on glass substrates using single-walled carbon nanotubes (SWCNTs) as active semiconducting material. All the electrodes (gate, source, and drain) were inkjet-printed using silver (Ag) as conductive ink. Spin coated poly-4-vinylphenol dielectric was optimized in terms of thickness and heating conditions for solution-processed SWCNTs thin film transistors to achieve a mobility equal to 0.81 cm2 V−1s−1. We will show that, hole traps at the dielectric-semiconductor interface are responsible for the hysteresis in the transfer curve, and controlled by the different sweep rate of the gate field. Drain-current transients under different bias conditions were studied and the increase in current occurs due to slow polarizations of residual dipolar groups in the dielectric. The adopted technology has been exploited to fabricate a PMOS inverter and studied for high gain and noise margin values at the supply voltage, V DD = −40 V.

Study of gate induced sensitivity amplification in carbon nanotube thin film transistor based ammonia sensor

Gas sensors based on carbon nanotube thin film transistors (CNT TFT) have been widely investigated in the past. However, studies on the active sensing properties i.e. effects of gate induced variations in sensing of such devices are deficient. In this work the effects of gate voltage on the ammonia sensing properties of a single wall CNT TFT are investigated. It is observed that under the influence of a gate field, the device sensitivity and detection limit (LOD) can be improved by more than 11 and 6 times respectively. The amplification of sensor response is found to occur for both the gate polarities and this is attributed to a combination of two phenomena. Firstly, ab-initio Molecular dynamics (MD) based adsorption studies of ammonia molecules to a CNT device indicate that the introduction of a gate field leads to an increase in the adsorption energy of ammonia to the device especially for a positive gate which is directly relatable to the observed amplification in sensing. Additionally, in the negative gate regime, a reversible increase of the contact resistance induced by ammonia exposure is thought to be the primary contributing factor in increasing the responsivity of the sensor. This is also thought to contribute to improving the sensor selectivity at negative gate.

Photoresponse Analysis of All-Inkjet-Printed Single-Walled Carbon Nanotube Thin-Film Transistors for Flexible Light-Insensitive Transparent Circuit Applications

We report daylight-stable, transparent, and flexible single-walled carbon nanotube thin-film transistors (SWCNT TFTs) using an all-inkjet printing process. Although most of the previous reports classified SWCNT TFTs as photodetectors, we demonstrated that SWCNT films actually show two different types of photoresponses depending on the power levels of light sources. The electrical characteristics of SWCNT TFTs show no significant change under daily illumination conditions such as halogen lamps and sunlight, while under high-power laser illumination, they change as reported in the previous results. In addition, the low-temperature solution process of the SWCNT with its one-dimensional nature allows us to realize highly transparent and flexible TFTs and logic circuits on plastic substrates. Our result will provide new insights into utilizing SWCNT TFTs for light-insensitive transparent and flexible electronic applications.

Resolving the Unusual Gate Leakage Currents of Thin-Film Transistors with Single-Walled Carbon-Nanotube-Based Active Layers

Solution-processed single-walled carbon nanotube (SWCNT) thin-film transistors (TFTs) in the research stage often have large active areas. This results in unusual gate leakage currents with high magnitudes that vary with applied voltages. In this paper, we report an improved structure for solution-processed SWCNT-based TFTs. The unusual gate leakage current in the improved structure is resolved by patterning the SWCNT active layer to confine it to the channel region. For comparative purposes, this improved structure is compared to a traditional structure whose unpatterned SWCNT active layer expands well beyond the channel region. As TFT performance also varies with oxide layer thickness, 90 nm and 300 nm thick oxides were considered. The improved TFTs have gate leakage currents far lower than the traditional TFT with the same dimensions (aside from the unpatterned active area). Moreover, the unusual variation in gate leakage current with applied voltages is resolved. Patterning the SWCNT layer, increasing the oxide thickness, and reducing the top electrode length all help prevent a rapid dielectric breakdown. To take advantage of solution-based fabrication processes, the active layer and electrodes of our TFTs were fabricated with solution-based depositions. The performance of the TFT can be further improved in the future by increasing SWCNT solution incubation time and reducing channel size.

High performance carbon nanotubes thin film transistors by selective ferric chloride doping

Single wall carbon nanotubes (SWNT) have been a significant research topic as active layers for thin film transistors (TFTs) due to their high charge carrier mobility beyond that of crystalline silicon. In this study, we report an effective approach to achieve a very high field-effect mobility and on/off ratio for solution processed semiconducting SWNT TFTs, by selective doping through contact with a thin ferric chloride (FeCl3) dopant layer. The semiconducting layer is formed by a double spin coating of the highly purified (>99%) high pressure carbon mono oxide (HiPCO) SWNT sorted by wrapping of poly (3-dodecylthiophene-2,5-diyl) (P3DDT). In order to achieve effective hole injection from the top Au source electrode without increasing the off-state drain current, less purified (98-99%) SWNTs produced by the plasma discharge process sorted by wrapping of poly (9,9-di-n-dodecylfluorene) (PFDD) are formed on the top of HiPCO film. Significantly improved TFT performance is achieved by the insertion of a few nanometers of a FeCl3 dopant layer at the semiconductor-contact interface. A significant high hole field-effect of 48.35 ± 3.11 cm2V−1s−1 (bare: 6.18 ± 0.87 cm2V−1s−1) with a reasonable on/off current ratio of 105, and low off current of ∼80 pA, are obtained by controlling the concentration of FeCl3 dopant (thickness = 1.5 nm) at the contact. Mobility is improved further at 2.5 nm thickness of the FeCl3 dopant layer resulting in a hole mobility of 177 ± 13.2 cm2 V−1s−1, an on/off ratio of 7.4 × 103, and off state current of 1.2 × 10−9 A.

Passivation Strategies for Enhancing Solution-Gated Carbon Nanotube Field-Effect Transistor Biosensing Performance and Stability in Ionic Solutions.

Interest in point-of-care diagnostics has led to increasing demand for the development of nanomaterial-based electronic biosensors such as biosensor field-effect transistors (BioFETs) due to their inherent simplicity, sensitivity, and scalability. The utility of BioFETs, which use electrical transduction to detect biological signals, is directly dependent upon their electrical stability in detection-relevant environments. BioFET device structures vary substantially, especially in electrode passivation modalities. Improper passivation of electronic components in ionic solutions can lead to excessive leakage currents and signal drift, thus presenting a hinderance to signal detectability. Here, we harness the sensitivity of nanomaterials to study the effects of various passivation strategies on the performance and stability of a transistor-based biosensing platform based on aerosol-jet-printed carbon nanotube thin-film transistors. Specifically, non-passivated devices were compared to devices passivated with photoresist (SU-8), dielectric (HfO2), or photoresist + dielectric (SU-8 followed by HfO2) and were evaluated primarily by initial performance metrics, large-scale device yield, and stability throughout long-duration cycling in phosphate buffered saline. We find that all three passivation conditions result in improved device performance compared to non-passivated devices, with the photoresist + dielectric strategy providing the lowest average leakage current in solution (~2 nA). Notably, the photoresist + dielectric strategy also results in the greatest yield of BioFET devices meeting our selected performance criteria on a wafer scale (~90%), the highest long-term stability in solution (<0.01% change in on-current), and the best average on/off-current ratio (~104), hysteresis (~32 mV), and subthreshold swing (~192 mV/decade). This passivation schema has the potential to pave the path toward a truly high-yield, stable, and robust electrical biosensing platform.

Large-Scale Integrated Flexible Tactile Sensor Array for Sensitive Smart Robotic Touch.

In the long pursuit of smart robotics, it has been envisioned to empower robots with human-like senses, especially vision and touch. While tremendous progress has been made in image sensors and computer vision over the past decades, tactile sense abilities are lagging behind due to the lack of large-scale flexible tactile sensor array with high sensitivity, high spatial resolution, and fast response. In this work, we have demonstrated a 64 × 64 flexible tactile sensor array with a record-high spatial resolution of 0.9 mm (equivalently 28.2 pixels per inch) by integrating a high-performance piezoresistive film (PRF) with a large-area active matrix of carbon nanotube thin-film transistors. PRF with self-formed microstructures exhibited high pressure-sensitivity of ∼385 kPa-1 for multi-walled carbon nanotubes concentration of 6%, while the 14% one exhibited fast response time of ∼3 ms, good linearity, broad detection range beyond 1400 kPa, and excellent cyclability over 3000 cycles. Using this fully integrated tactile sensor array, the footprint maps of an artificial honeybee were clearly identified. Furthermore, we hardware-implemented a smart tactile system by integrating the PRF-based sensor array with a memristor-based computing-in-memory chip to record and recognize handwritten digits and Chinese calligraphy, achieving high classification accuracies of 98.8% and 97.3% in hardware, respectively. The integration of sensor networks with deep learning hardware may enable edge or near-sensor computing with significantly reduced power consumption and latency. Our work could empower the building of large-scale intelligent sensor networks for next-generation smart robotics.

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.

Highly sensitive SWIR photodetector using carbon nanotube thin film transistor gated by quantum dots heterojunction

Low-dimensional semiconductors have been considered excellent materials to construct photodetectors for infrared detection with an easy process and excellent compatibility but suffer from low detectivity mainly owing to the poor light absorption of the ultra-thin body. Here, we demonstrate a thin film transistor (TFT) based short-wave infrared photodetector consisting of a carbon nanotube (CNT) TFT gated by a PbS colloidal quantum dots (CQDs) based heterojunction. The thick PbS CQDs' film efficiently absorbs infrared light and then excites and separates electron–hole pairs to generate a photovoltage at the pn heterojunction of the PbS CQDs/ZnO film. The photovoltage is further amplified and transduced in situ by the CNT TFT under the heterojunction, and then the detector featured a specific detectivity of 5.6 × 1013 Jones under 1300 nm illumination and a fast response of the sub-ms level (0.57 ms). The CQDs based heterojunction gating TFT represents a universal architecture for highly sensitive low-dimensional semiconductor based infrared photodetectors, competitive with state-of-the-art epitaxial semiconductors and enabling monolithic integration technology.

Low-temperature supercritical activation enables high-performance detection of cell-free DNA by all-carbon-nanotube transistor

Biosensors based on carbon nanotube (CNT) thin-film transistors (TFTs) have drawn intense interests for their exhibiting great potential in ultrasensitive and label-free DNA detection. However, the inevitable defects in the dielectric and channel of CNT-based TFTs may induce noisy or unreliable output signals. Here, we propose a low-temperature supercritical carbon dioxide (SCCO2) fluid activation method to enhance the performance of transistor-based biosensors. An activation model of SCCO2 treatment is proposed to elaborate that the SCCO2 treatment can repair the dangling bonds of SiO2 dielectric facilely and passivate the hydroxyl groups effectively. Furthermore, a cell-free DNA detection platform is built up based on all-carbon-nanotube TFTs (AC-TFTs) modified by the CW-Peptide probe. By adopting the SCCO2 treatment, the response of AC-TFT biosensors to AKT2 gene related to triple-metastatic negative breast cancer can be enhanced by more than 114% with high uniformity, and a broad detection range of six orders of magnitude is yielded with a theoretical limit of detection of 42 fM. Additionally, the response has a linear correlation with the length of DNA targets. The nondestructive and eco-friendly SCCO2 activation method provides a promising and universal strategy for achieving highly accurate and sensitive transistor-based biosensors in future clinical applications.

Highly temperature-tolerant p-type carbon nanotube transistor doped with 1,4,5,8,9,11-hexaazatriphenylenehexacarbonitrile

The development of chemical doping methods for carbon nanotubes (CNTs) is essential for various electronic applications. However, typical p-doping methods for CNT thin-film transistors (TFTs), using oxygen and water from the atmosphere, are quite sensitive to changes in the surrounding environment, and thus, their poor temperature tolerance is a critical problem during device fabrication. As a p-dopant for CNT–TFTs, we used 1,4,5,8,9,11-hexaazatriphenylenehexacarbonitrile (HATCN), which is a strong electron acceptor aromatic compound. The HATCN-doped CNT–TFTs exhibited p-type characteristics after exposure to a high-temperature environment of 200 °C, and prolonged heating did not degrade the p-doping performance of HATCN. In addition, stable p-type characteristics even under ambient conditions were obtained by encapsulating the surface of the device with a Parylene–Al2O3 bilayer.