- [Show abstract] [Hide abstract] ABSTRACT: We have systematically investigated the real-time IDS responses and electrical characteristics of pentacene OTFTs exposed to six volatile compound vapor flows of acetone, ethanol, methanol, water, chloroform, and toluene, which could be classified into two group according to the influence on the electric performance of OTFTs. The first three compounds caused remarkable and irreversible degradation of electric performance of OTFTs. However, the latter three compounds caused slight and reversible changes of their electric performance. Moreover, the good linearity existed in plot of changes of the normalized IDS as a function of their concentrations in N2 flow.
- [Show abstract] [Hide abstract] ABSTRACT: This paper describes a sheet-type scanner and its circuits. The three-dimensional-stacked sheets comprise of two organic-transistor sheets and one organic-photodiode sheet, which enable double-wordline and double-bitline structure. The operation was compared with the conventional single-wordline and single-bitline scheme, and confirmed by measurement. The double-wordline and double-bitline structure reduces the line delay and power by a factor of five and seven, respectively. A new dynamic decoder reduces active leakage current, to which the cut-and-paste customization can be applied
- [Show abstract] [Hide abstract] ABSTRACT: We have successfully fabricated ultra-flexible pentacene field-effect transistors (FETs) with a mobility of 0.5 cm2/V s and an on/off ratio of 105, which are functional even at a bending radius (R) smaller than 1 mm. The FETs are manufactured on a 13-μm-thick plastic substrate and encapsulated by a 13-μm-thick parylene passivation layer, thus placing the FET in the neutral plane. We measured the electrical properties of FETs under varying compressive and tensile strains, by changing the bending radius of the substrate. If the bending radius is larger than 2 mm, the mobility changes less than 3%. Further decrease in bending radius causes larger change in mobility. At R = 0.5 mm, the mobility increases by 20% in compression or decreases by 30% in tension.
- [Show abstract] [Hide abstract] ABSTRACT: Inverter circuits have been made by connecting two high-quality pentacene field-effect transistors. A uniform and pinhole-free 900 nm thick polyimide gate-insulating layer was formed on a flexible polyimide film with gold gate electrodes and partially removed by using a CO2 laser drilling machine to make via holes and contact holes. Subsequent evaporation of the gold layer results in good electrical connection with a gold gate layer underneath the gate-insulating layer. By optimization of the settings of the CO2 laser drilling machine, contact resistance can be reduced to as low as 3 ohms for 180 microm square electrodes. No degradation of the transport properties of the organic transistors was observed after the laser-drilling process. This study demonstrates the feasibility of using the laser drilling process for implementation of organic transistors in integrated circuits on flexible polymer films.
- [Show abstract] [Hide abstract] ABSTRACT: It is believed that skin sensitivity will be important for future robots working in our daily life for home-care and entertainment purposes. However, relatively little progress has been made in the field of pressure recognition compared to the areas of sight and voice recognition, mainly because good artificial ''electronic skin'' with a large area and mechanical flexibility is not yet available. The fabrication of a sensitive skin consisting of thousands of pressure sensors would require a flexible switching matrix that cannot be realized with present silicon-based electronics. Organic field-effect transistors can be used complimentary to such conventional electronics because organic circuits are inherently flexible and potentially ultra-low in cost even for large area. In this paper, we describe that integration of organic transistors and rubber pressure sensors provides an ideal solution to rea-lize a practical artificial skin. The authors thank Professors Yasuhiko Arakawa, Hiroyuki Sakaki, Makoto Kuwata-Gonokami, University of Tokyo, and Mr. Tadashi Kobayashi, for fruitful discussions. Those projects are partly supported by the IT Program, MEXT of Japan, NEDO, and MPHPT. Address correspondence to T.
- [Show abstract] [Hide abstract] ABSTRACT: A flexible, shock-resistant, and lightweight Braille sheet display has been successfully manufactured on a plastic film by integrating a plastic sheet actuator array with a high-quality organic transistor active matrix. This is the first demonstration, to the best of our knowledge, to integrate plastic MEMS (microelectromechanical systems) actuators with organic transistor active matrices, which opens up new versatile possibilities for flexible, large-area electronic applications including tactile displays
- [Show abstract] [Hide abstract] ABSTRACT: A large-area, flexible, and lightweight sheet image scanner has been successfully manufactured on a plastic film by integrating high-quality organic transistors and organic photodetectors. The effective sensing area of the integrated device is 5×5 cm<sup>2</sup>; the resolution, 36 dots per inch (dpi); and the total number of sensor cells, 5184. The pentacene transistors with top contact geometry have a channel length of 18 μm and mobility of 0.7 cm<sup>2</sup>/Vs. Organic photodetectors composed of copper phthalocyanine and 3,4,9,10-perylene-tetracarboxylic-diimide distinguish between black and white parts on paper based on the difference in their reflectivity. Since this new area-type image-capturing device does not require any optics or mechanical scanning devices, the present sheet image scanners are mechanically flexible, lightweight, shock resistant, and potentially inexpensive to manufacture; therefore, they are suitable for human-friendly mobile electronics.
Conference Paper: Pocket scanner using organic transistors and detectors[Show abstract] [Hide abstract] ABSTRACT: A pocket scanner has been manufactured by integrating high-quality organic transistors with organic photodetectors. Because the pocket scanner requires no mechanical components, it is mechanically flexible, light to transport, shock-resistant and potentially inexpensive to manufacture.
- [Show abstract] [Hide abstract] ABSTRACT: We fabricated ultraflexible pentacene field-effect transistors (FETs) with a mobility of 0.5 cm2/V s and an on/off ratio of 105, which are functional at the bending radius less than 1 mm. The transistors are manufactured on a 13-mum-thick polyimide film and covered by a 13-mum-thick poly-chloro-para-xylylene encapsulation layer so that transistors can be embedded at a neutral position. This sandwiched structure can drastically suppress strain-induced changes in transistor characteristics. Furthermore, the FETs show no significant change after bending cycles of 60 000 times on inward and outward bending stresses.
- [Show abstract] [Hide abstract] ABSTRACT: Skin-like sensitivity, or the capability to recognize tactile information, will be an essential feature of future generations of robots, enabling them to operate in unstructured environments. Recently developed large-area pressure sensors made with organic transistors have been proposed for electronic artificial skin (E-skin) applications. These sensors are bendable down to a 2-mm radius, a size that is sufficiently small for the fabrication of human-sized robot fingers. Natural human skin, however, is far more complex than the transistor-based imitations demonstrated so far. It performs other functions, including thermal sensing. Furthermore, without conformability, the application of E-skin on three-dimensional surfaces is impossible. In this work, we have successfully developed conformable, flexible, large-area networks of thermal and pressure sensors based on an organic semiconductor. A plastic film with organic transistor-based electronic circuits is processed to form a net-shaped structure, which allows the E-skin films to be extended by 25%. The net-shaped pressure sensor matrix was attached to the surface of an egg, and pressure images were successfully obtained in this configuration. Then, a similar network of thermal sensors was developed with organic semiconductors. Next, the possible implementation of both pressure and thermal sensors on the surfaces is presented, and, by means of laminated sensor networks, the distributions of pressure and temperature are simultaneously obtained.
- [Show abstract] [Hide abstract] ABSTRACT: We fabricate pentacene field-effect transistors (FETs) showing a very small degradation in performance under a continuous DC bias stress. Pentacene FETs are manufactured on polyimide films with polyimide gate dielectric layers, and then encapsulated by poly-chloro-para-xylylene passivation layers, resulting in very flexible and heat-resistant devices. When such devices are annealed at 140 ° C for 12 h in a nitrogen environment, the change in their source-drain current is 3±1% even after the application of continuous DC voltage biases of V <sub> DS </sub>= V <sub> GS </sub>=-40 V for 11 h . Furthermore, their mobility is increased by postannealing effects from 0.27 cm <sup>2</sup>/ V s to 0.36 cm <sup>2</sup>/ V s and their on/off ratio is also increased from 10<sup>3</sup> to 10<sup>6</sup> .
- [Show abstract] [Hide abstract] ABSTRACT: We fabricated pentacene field-effect transistors with planar-type double-gate structures, where the top- and bottom-gate electrodes can independently apply voltage biases to channel layers. The threshold voltage of organic transistors is changed systematically in a wide range from -16 to -43 V when the voltage bias of the top-gate electrode is changed from 0 to +60 V . The mobility in the linear regime is almost constant (0.2 cm <sup>2</sup>/ V s ) at various voltage biases of the top-gate electrode and the on/off ratio is 10<sup>6</sup> .
- [Show abstract] [Hide abstract] ABSTRACT: In this paper, we present recent advances of organic transistors and their applications to two kinds of large-area sensors, namely electronic artificial skins and sheet image scanners. Organic transistor integrated circuits are attracting much attention since they are expected to be complementary to the high-performance yet expensive silicon VLSI's. There are many attributes of organic transistors, which can't be easily achieved by silicon-based conventional electronics.
- [Show abstract] [Hide abstract] ABSTRACT: We manufactured markedly flexible pentacene field-effect transistors (FETs) on a polyethylenenaphthalate base film with polyimide gate dielectric layers, with a mobility of 0.3 cm2/Vs and an on/off ratio of 105. The electric performance of DC current-voltage characteristics was measured by applying compressive and tensile strains while reducing the bending radius down to 3 mm. It was found that the compressive strain leads to an increase in mobility of 10% induced by the change in strain of up to 1.4± 0.1%, although the tensile strain leads to a decrease in mobility of 10%. To elucidate the origin of the enhancement of mobility under the compressive strain, we also investigated the strain dependence of capacitance--voltage characteristics for a pentacene channel layer, and almost no change was observed. Our results suggest that the strains markedly affect the spacing between pentacene molecules rather than the number of induced carriers.
- [Show abstract] [Hide abstract] ABSTRACT: Double word-line and bit-line structure in an organic FET-based sheet-type scanner is described. This structure reduces the line delay by a factor of 5, and the power by a factor of 7. To realize the structure in a pixel array, 3D stacked organic FETs are manufactured. The active leakage is reduced by a dynamic serially connected decoder.
- [Show abstract] [Hide abstract] ABSTRACT: We have fabricated very flexible pentacene field-effect transistors with polyimide gate dielectric layers on plastic films with a mobility of 0.3 cm2/V s and an on/off ratio of 105, and have measured their electrical properties under various compressive and tensile strains while changing the bending radius of the base plastic films systematically. We have found that the change in source-drain current with bending radius is reproducible and reversible when the bending radius is above 4.6 mm, which corresponds to strains of ∼ 1.4±0.1%. Furthermore, the change in source-drain current does not depend on the direction of strain versus direction of current flow.
- [Show abstract] [Hide abstract] ABSTRACT: A large-area, flexible, and lightweight sheet image scanner has been successfully manufactured on a plastic film, for the first time, integrating high-quality organic transistors and organic photodetectors. Since this area-type image-capturing device does not require any optics or any mechanical scanning devices, it is innovatively light to carry, shock-resistant and potentially inexpensive to manufacture.
- [Show abstract] [Hide abstract] ABSTRACT: We have fabricated pentacene field-effect transistors (FETs) on polyimide-sheet films with polyimide gate dielectric layers and parylene encapsulation layer, and investigated the high-temperature performance. It is found that the mobility of encapsulated FETs is enhanced from 0.5 to 0.8 cm 2 /Vs when the device is heated from room temperature to 160°C under light-shielding nitrogen environment. Furthermore, after the removal of annealing temperatures up to 160°C, the transistor characteristic of mobility and on/off current ratio show no significant changes, demonstration the excellent thermal stability of the present organic FETs.
- [Show abstract] [Hide abstract] ABSTRACT: We have manufactured pentacene field-effect transistors (FETs) on polyimide base films with polyimide gate dielectric layers, and characterized electronic performance and surface morphology with application of heat in the temperature range from 30 to 210 ° C . It is found that mobility of pentacene FETs is enhanced from 0.27 to 0.71 cm <sup>2</sup>/ V s when measurement temperatures varies from 30 to 160 ° C under light-shielding nitrogen environment. To investigate postannealing effects, we have measured transfer curves at 30 ° C after many heat cycles at various temperatures. Mobility is almost constant even after annealing at 130 ° C , showing the excellent stability of the present device at high temperatures.
Nan-ching, Jiangsu Sheng, China
- Department of Chemical Engineering
The University of Tokyo
白山, Tōkyō, Japan
- Center for Quantum-Phase Electronics