Haruya Okimoto

Tunable Carbon Nanotube Thin‐Film Transistors Produced Exclusively via Inkjet Printing

Inkjet printing in electronics production has attracted considerable attention for a wide-range of applications because it is an environmentally friendly and low-cost technique. [ 1–5 ] In addition to excellent charge-transport properties, materials for inkjet printing must meet other key requirements, such as high chemical stability, low-temperature processability, low hysteresis, and low-voltage operation. In the past, materials satisfying these criteria have not been available. Here, we demonstrate low-cost green manufacturing via precisely controlled inkjet printing of singlewalled carbon nanotube (SWCNT) fi lms. This transistor exceeds the performance of conventional organic transistors (a mobility of 1.6 to 4.2 cm 2 V − 1 s − 1 and an on/off ratio of 4 to 5 digits) and is fabricated at moderate temperatures (80 ° C). We also demonstrate the production of exclusively inkjetprinted SWCNT transistors with printable ionic-liquid gate dielectrics. Printable technology has the potential to drastically reduce ecological impact, energy consumption during manufacturing, and wasted materials by controlling the quantity and location of ink deposition. Inkjet technology is exceptionally promising because patterns can be generated without any material waste, leading to drastic reductions in production costs and in environmental impact. Materials for printable electronics must satisfy several requirements, such as high transport properties, chemical stability, and low-temperature processability. Research in this area has been focused largely on organic semiconductors [ 1–5 ] because carrier mobilities comparable to those of amorphous silicon ( ≤ 1 cm 2 V − 1 s − 1 ) are needed to create printable electronics. Although highly crystalline organic

Ink-jet printing of carbon nanotube thin-film transistors on flexible plastic substrates

Ink-jet printable thin-film transistors (TFTs) on flexible plastic substrates are an important focus of research because present silicon-based electronics cannot realize such devices. In the present study, we fabricated single-walled carbon nanotube (SWCNT) TFTs on plastic substrates using the ink-jet printing method, and realized high-on/off current ratio (~104) and flexibility, respectively. The present study therefore represents a major step towards flexible SWCNT electronics.

Ultrasensitive detection of DNA molecules with high on/off single-walled carbon nanotube network.

Single-walled carbon nanotubes (SWNTs) have recently attracted a great deal of attention due to their high potential for electronic and sensing applications. SWNT-based fi eld-effect transistor (FET) devices have been successfully used to perform electrical detection of various analytes. [ 1–12 ] For example, the electrical detection limit for DNA molecules with the devices based on SWNT networks has reached 100 fM, [ 9 ] which is already comparable to the methods based on electrochemical detection. [ 13 ] Several mechanisms have been proposed to explain the electrical detection, including charge-induced electrostatic gating, [ 1–3 ] changes in gate coupling, [ 4 ] impurity-induced carrier scattering, [ 5 , 7 ] and changes of the Schottky barrier. [ 3 , 8–10 , 14 ] For liquid-gated individual SWNT devices, Heller et al. [ 15 ] reported that the doping effect in the channel and the Schottky barrier between electrodes and SWNTs were the two competing mechanisms. Contrastly, the sensing mechanisms of network-based FETs are more complicated than those of individual-SWNT FETs due to the presence of nanotube–nanotube contact [ 7 , 16 ]

Ink-Jet Printing of a Single-Walled Carbon Nanotube Thin Film Transistor

Single-walled carbon nanotube (SWCNT) thin-film transistors (TFTs) were fabricated using ink-jet printing. We printed both thick source–drain electrodes and thin active semiconducting films using N,N-dimethylformamide (DMF)-based SWCNT dispersion. Despite the presence of metallic SWCNTs, the device exhibited field-effect behavior, with an effective mobility of 2.99 cm2 V-1 s-1 and an on/off current ratio of up to 75. The method used in this study is promising for the fabrication of large-scale high-performance SWCNT-TFTs.

Low-voltage operation of ink-jet-printed single-walled carbon nanotube thin film transistors

We demonstrate a low-voltage and less hysteresis operation of single-walled carbon nanotube thin film transistors (SWCNT-TFTs) using an ionic liquid gate dielectric layer. We fabricated the density controlled SWCNT-TFTs using the inkjet printing technique, where both source/drain electrodes and the semiconducting transistor channel were made from SWCNT films. As the gate dielectric, we have adopted a printable ionic liquid for future all-printable processes and achieved marked improvements in operating voltages and hysteretic response.

Thermally and environmentally stable carrier doping using a solution method in carbon nanotube films

In the present paper, we report the thermal stability of a single-walled carbon nanotube (SWCNT) film that was doped using tetrafluorotetracyano-p-quinodimethane (F4TCNQ). The SWCNTs were doped using a vapor method and a solution method, and their thermostabilities were characterized using a gas chromatography/mass spectrometer (GC/MS) and resistance measurements. These measurements clearly demonstrated the high thermal stability of F4TCNQ and the strong charge-transfer interaction between the SWCNTs and the dopants. As a result, we successfully observed an excellent long-term (longer than 500 h) thermal resistance up to 150 °C, which is a sufficient level of stability for the practical use of this dopant.