The bio-organic thin film transistor (BiOTFT) with the DNA and DNA-surfactant complex as a dielectric layer shows memory function. In order to investigate the effect of surfactant structure on the OTFT memory device performance, different kinds of surfactant were introduced. Cetyltrimethylammonium chloride (CTMA), Lauroylcholine chloride (Lau) or Octadecyltrimethylammonium chloride (OTMA) as the cationic surfactant was mixed with DNA to prepare the DNA complex through the electrostatic interaction. In addition, the different molecular weight DNA also has been studied to analyze the effect of DNA chain length on the performance of the physical property. Many kinds of methods including UV-vis, Circular dichiroism (CD) and I-V characteristic have been applied to analyze the property of DNA complex. In conclusion, all of DNA complex with CTMA, OTMA and Lau were revealed to work as the bio-organic thin film transistor memory, and the device fabricated by Lau has the highest ON current and showed better device performance.
The bio-organic thin film transistor (BiOTFT) with the DNA and DNA-surfactant complex as a dielectric layer shows
memory function. In order to investigate the effect of surfactant structure on the OTFT memory device performance,
different kinds of surfactant were introduced. Cetyltrimethylammonium chloride (CTMA), Lauroylcholine chloride
(Lau) or Octadecyltrimethylammonium chloride (OTMA) as the cationic surfactant was mixed with DNA to prepare the
DNA complex through the electrostatic interaction. In addition, the different molecular weight DNA also has been
studied to analyze the effect of DNA chain length on the performance of the physical property. Many kinds of methods
including UV-vis, Circular dichiroism (CD), I-V characteristic and atomic force microscope (AFM) have been applied to
analyze the property of DNA complex. In conclusion, all of DNA complex with CTMA, OTMA and Lau were revealed
to work as the bio-organic thin film transistor memory, and the device fabricated by Lau has the highest ON current and showed better device performance.
We fabricated a novel type photo-FET using poly(N-vinylcarbazole) (PVK) as a photosensitive gate dielectric. For the
photo-FET, photo-illumination to the PVK insulator layer makes the field-effect mobility μFET two orders of magnitude
higher than dark condition. In particular, under blue-light illumination condition the on-off ratio was also a few ten times
higher than dark condition. Furthermore, by introducing blocking layer between semiconductor layer and insulator layer lead.
We concluded that the improvement of the transistor properties resulted from effective charge accumulation at the conductive
channel by photo illuminations.
In this paper, we introduce our recent results on organic thin-film transistor (TFT) technologies; self-aligned self-assembly process and a high-resolution color active-matrix LCD panel driven by organic TFT. First, a novel process for fabricating alignment-free, printable, organic thin-film transistors is presented. This process exploits a self-assembly phenomenon in which soluble nanomaterials such as metal nanoparticles and organic molecules are self-assembled into a device structure. Solution-processed source and drain electrodes were self-aligned to a gate electrode by using a hydrophobic self-assembled monolayer optically patterned onto the gate electrode with a back-substrate exposure technique. An organic semiconductor film deposited on the patterned SAM was selectively ordered and substantially self-aligned to the gate electrode. A field-effect mobility of 0.15 cm2/Vs and on/off current ratio of 105 were experimentally demonstrated when pentacene molecules were used as the semiconductor and silver nanoparticles were used as electrode materials. Second, a full-color twisted-nematic type liquid crystal display (TN-LCD) of 1.4-inch diagonal size driven by organic TFT has been fabricated. This TN-LCD has 80 x 80 x 3 (RGB) pixel arrays addressed by pentacene TFT with a channel width of 50 μm. The contact resistance between the pentacene film and the source/drain electrodes has been reduced by steepening the side slope of the electrodes. In addition, a solution-processed passivation film with a novel structure, consisting of organic and inorganic stacked layers, has been developed to protect the TFT against degradation induced by integration with TN-LCD devices. Consequently, the organic-TFT-driven TN-LCD is capable of displaying full-color moving images at a resolution of 80 pixels per inch.
We fabricated a novel type photo-FET using poly(N-vinylcarbazole) as a photosensitive gate dielectric. For the photo-FET, photo-illumination to the PVK insulator layer make the field-effect mobility μFET two order of magnitude higher than dark condition. In particular, under blue-light illumination condition the on-off ratio was also a few ten times higher than dark condition. We concluded that the improvement of the transistor properties resulted from effective charge accumulation at the conductive channel by photo illuminations.
We studied on the effect of nanoparticle dispersion on electrical properties of polymer field effect transistor (FET). Various kinds of powder materials were prepared and dispersed into P3HT films. In order to determine the electronic structures of particle-dispersed P3HT films, photoelectron emission spectra were measured. Using these spectra ionization potentials (IPs) of these films were determined. The shifts of IP originated from the particle dispersions were very small (from 4.69 to 4.72eV). Similarly, any differences were not observed between the electron absorption spectra of the particle-dispersed P3HT films and that of the pristine P3HT films. According to these results, no chemical reactions would occur between P3HT matrices and dispersed particles. On the other hand, Fermi levels of particle-dispersed P3HT films were obviously shifted from that of the pristine P3HT film. The shift was well correlated to the difference between the workfunction of P3HT and that of the dispersed material. Namely, the dispersion of the particles with the lower workfunction contributed to the decrease of workfunction of the P3HT film. Further, the decrease of workfunction of P3HT film resulted in the decrease of the off-current values of the P3HT-FET. This would be because the electrons transferred from the dispersed particles neutralized the excess holes in the P3HT film. Actually, the Ag particle dispersion remarkably improved on-off ratio of the P3HT-FET.
In order to develop a printable organic thin film transistor with high performance, it is required to develop not only printable materials and a printing process but also a suitable device structure for it. We have newly designed an organic field effect transistor with a diagonal configuration of source and drain electrode, named as the Top and bottom contact (TBC) configuration. It has several advantages due to its unique structure. For example, it can be prepared by a simple stacking process without any micro-machining process or related photolithography procedures. This is thus suitable for applying the simple printing technique such as a screen-printing. In the proposed structure, source and drain electrodes are arranged diagonally across the active layer. Therefore, the channel length can be controlled by the deposited active layer thickness. In this study, we have prepared the pentacene transistor with the TBC configuration. By inserting the extra insulator layer, leakage current between the top and bottom electrode was remarkably reduced. The output current
density was about two orders larger than the conventional organic transistor with a top contact configuration. These high performances are mainly due to the improvement of the carrier injection efficiency owing to the short channel length (ca.0.5μm).
The strong coupling between exciton and photon modes in a conjugated polymer-based semiconductor microcavity was observed. The σ-conjugated poly(bis(p-butylphenyl)silane) (PBPS) thin films were inserted between metal and dielectric stack mirrors to form the microcavity structure. Change of the PBPS film-thickness (from 80 to 140 nm) allowed the cavity photon resonance to be tuned in the free-exciton transition. The expected anti-crossing behavior was observed at room temperature in the reflection spectra and the vacuum Rabi-splitting energy was found to be about 430 meV. This giant value is almost the same as the expectations of transfer matrix reflectivity calculations performed with optical constants (refractive index: n, extinction coefficient: k) derived from a Kramers-Kronig analysis of the PBPS absorption spectrum. Angle-dependent photoluminescence measurements were performed in each PBPS-based microcavity. In the microcavity with a 120nm-PBPS layer, the polariton emission that displays almost no blueshifts with angle was observed, a desirable feature for potential display applications.
A method for quantitative evaluation of the molecular orientation in thin Langmuir-Blodgett (LB) films by FT-IR transmission and reflection-absorption (RA) spectroscopy is presented and applied to the study of the 11-monolayer LB film of barium salt of an azobenzene- containing long-chain fatty acid. This was also applied to the study of temperature dependence of the molecular orientation in alternate LB films consisting of a phenylpyrazine-containing long-chain fatty acid and deuterated stearic acid as well as in those consisting of their barium salts. At the same time, pyroelectricities of these films were measured in the temperature range from -30 to 60 degree(s)C, and the results were discussed in connection with changes in the molecular structure and orientation.
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