Browsing by Author "Singh, Ranjodh"

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A new biodegradable gate dielectric material based on keratin protein for organic thin film transistors
(2017-05-01)
Singh, Ranjodh
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Lin, Yen-Ting
;
Chuang, Whae-Ling
;
Ko, Fu-Hsiang
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材料科學與工程學系
By virtue of the biocompatibility, environmental benignity, and sustainability, as well as low cost of keratin protein's source herein, we report its application as a gate dielectric material for organic electronic devices. Keratin protein, which is a biodegradable material was directly extracted from poultry chicken feathers (CFs). Solution-processed regioregular poly(3-hexylthiophene) (P3HT) organic thin film transistors (OTFTs) with keratin dielectric thin film exhibited enhanced charge mobility of 2.293-10(-3) cm(2) V-1 s(-1) (saturation regime), high on-off current ratio of 105 and low threshold voltage, -1V as compared to conventional SiO2 dielectric. All the fabrication processes were performed below 100 degrees C. A detailed semiconductor-dielectric interface study has revealed that the high content of beta-sheet structure in keratin protein has guided the P3HT polymer chains, through supramolecular forces of interaction to form 2D nanoribbons of large crystallite size (150 nm) over keratin thin film. This has led to the reduced trapping sites at the semiconductor/dielectric interface and hence the enhanced electrical performance of OTFTs was observed. Atomic force microscopy (AFM) and Grazing Incidence X-ray diffraction (GI-XRD) study was further employed to explore the mechanism of formation of 2D nanoribbons of P3HT. The primary and secondary structure of keratin protein as analyzed by AFM, Transmission electron microscopy (TEM) and Fourier transform spectroscopy (FTIR) is also provided in this study. The water compatible nature of keratin has helped to overcome the common issue of dielectric layer washing that occurs mostly during fabrication of OTFTs by sol-gel method. The biodegradable nature of keratin protein has also been demonstrated here by providing it as feed to fishes in an aquarium. (C) 2017 Elsevier B. V. All rights reserved.
Aqueous Solution-Processable, Flexible Thin-Film Transistors Based on Crosslinked Chitosan Dielectric Thin Films
(2018-03-01)
Singh, Ranjodh
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Lin, Yen-Ting
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Ko, Fu-Hsiang
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材料科學與工程學系
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Department of Materials Science and Engineering
The hydrophilic character of chitosan (CS) limits its use as a gate dielectric material in thin-film transistors (TFTs) based on aqueous solution-processable semiconductor materials. In this study, this drawback is overcome through controlled crosslinking of CS and report, for the first time, its application to aqueous solution-processable TFTs. In comparison to natural CS thin films, crosslinked chitosan (Cr-CS) thin films are hydrophobic. The dielectric properties of Cr-CS thin films are explored through fabrication of metal-insulator-metal devices on a flexible substrate. Compared to natural CS, the Cr-CS dielectric thin films show enhanced environmental and water stabilities, with a high breakdown voltage (10 V) and low leakage current (0.02 nA). The compatibility of Cr-CS dielectric thin films with aqueous solution-processable semiconductors is demonstrated by growing ZnO nanorods via a hydrothermal method to fabricate flexible TFT devices. The ZnO nanorod-based TFTs show a high field-effect mobility (linear regime) of 10.48 cm(2) V-1 s(-1). Low temperature processing conditions (below 100 degrees C) and water as the solvent are utilized to ensure the process is environmental friendly to address the e-waste problem.
Bio-Inspired Supramolecular Chemistry Provides Highly Concentrated Dispersions of Carbon Nanotubes in Polythiophene
(2016-06-01)
Lin, Yen-Ting
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Singh, Ranjodh
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Kuo, Shiao-Wei
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Ko, Fu-Hsiang
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材料科學與工程學系
In this paper we report the first observation, through X-ray diffraction, of noncovalent uracil-uracil (U-U) dimeric 7r-stacking interactions in carbon nanotube (CNT)-based supramolecular assemblies. The directionally oriented morphology determined using atomic force microscopy revealed highly organized behavior through pi-stacking of U moieties in a U-functionalized CNT derivative (CNT-U). We developed a dispersion system to investigate the bio-inspired interactions between an adenine (A)-terminated poly(3-adeninehexyl thiophene) (PAT) and CNT-U. These hybrid CNT-U/PAT materials interacted through pi-stacking and multiple hydrogen bonding between the U moieties of CNT-U and the A moieties of PAT. Most importantly, the U center dot center dot center dot A multiple hydrogen bonding interactions between CNT-U and PAT enhanced the dispersion of CNT-U in a high-polarity solvent (DMSO). The morphology of these hybrids, determined using transmission electron microscopy, featured grape-like PAT bundles wrapped around the CNT-U surface; this tight connection was responsible for the enhanced dispersion of CNT-U in DMSO.
Control of active semiconducting layer packing in organic thin film transistors through synthetic tailoring of dielectric materials
(2014-01-01)
Singh, Ranjodh
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Meena, Jagan Singh
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Chang, Yu-Cheng
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Wua, Chung-Shu
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Ko, Fu-Hsiang
Apart from the development of new dielectric and semiconductor materials, the semiconductor-dielectric interface study is also very important for the optimum performance of organic thin film transistors (OTFTs). Herein, we have reported the detailed synthesis of a whole new family of dielectric materials which are 1,3,5,7-tetrabromoadamantane; 1,3,5,7-tetrachloroadamanatane; 1,3,5,7-tetraiodoadamantane and 1,3,5,7-tetrauraciladamantane (AdUr(4)). The unique ability of these molecules to undergo supramolecular thin film formation at low temperature, was analysed for their potential use as an insulator in organic electronic devices. Owing to the good leakage current density property shown by AdUr4 dielectric material it was further employed as a gate dielectric in regioregular poly(3-hexylthiophene), (P3HT) based OTFT. This OTFT device which was fabricated on a flexible PI plastic substrate has shown a good on/off current ratio (e.g., 2.18 x 10(4)) and high mobility (e.g., 0.15 cm(2) V-1 s(-1)). The semiconductor-dielectric interface study, has revealed that the AdUr(4) gate dielectric layer has guided the P3HT molecular chain domains to undergo edge-on orientation, which is the charge transport direction in OTFTs. In this process, the grazing incidence X-ray diffraction (GI-XRD) analysis and AFM study was also employed.
Control of active semiconducting layer packing in organic thin film transistors through synthetic tailoring of dielectric materials
(2014-01-01)
Singh, Ranjodh
;
Meena, Jagan Singh
;
Chang, Yu-Cheng
;
Wua, Chung-Shu
;
Ko, Fu-Hsiang
Apart from the development of new dielectric and semiconductor materials, the semiconductor-dielectric interface study is also very important for the optimum performance of organic thin film transistors (OTFTs). Herein, we have reported the detailed synthesis of a whole new family of dielectric materials which are 1,3,5,7-tetrabromoadamantane; 1,3,5,7-tetrachloroadamanatane; 1,3,5,7-tetraiodoadamantane and 1,3,5,7-tetrauraciladamantane (AdUr(4)). The unique ability of these molecules to undergo supramolecular thin film formation at low temperature, was analysed for their potential use as an insulator in organic electronic devices. Owing to the good leakage current density property shown by AdUr4 dielectric material it was further employed as a gate dielectric in regioregular poly(3-hexylthiophene), (P3HT) based OTFT. This OTFT device which was fabricated on a flexible PI plastic substrate has shown a good on/off current ratio (e.g., 2.18 x 10(4)) and high mobility (e.g., 0.15 cm(2) V-1 s(-1)). The semiconductor-dielectric interface study, has revealed that the AdUr(4) gate dielectric layer has guided the P3HT molecular chain domains to undergo edge-on orientation, which is the charge transport direction in OTFTs. In this process, the grazing incidence X-ray diffraction (GI-XRD) analysis and AFM study was also employed.
Controlled deposition of new organic ultrathin film as a gate dielectric layer for advanced flexible capacitor devices
(2013-06-01)
Meena, Jagan Singh
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Chu, Min-Ching
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Singh, Ranjodh
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Shieh, Han-Ping D.
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Liu, Po-Tsun
This letter describes a new organic (1-bromoadamantane) ultrathin film as gate dielectric, which was successfully deposited by sol-gel spin-coating process on a flexible polyimide substrate at room temperature. The metal-insulator-metal (MIM) device with organic (1-bromoadamantane) ultrathin (10 nm) film as gate dielectric layer operated at gate voltage of 5.0 V, showing a low leakage current density (5.63 x 10(-10) A cm(-2) at 5 V) and good capacitance (2.01 fF mu m(-2) at 1 MHz). The chemical structure of the 1-bromoadamantane layer was investigated by Fourier transform infrared spectrometer. The excellent leakage current density and better capacitance, probably due to the presence of polar, non-polar, low-polar groups, and bromine atoms in ultrathin film. Practical properties of the film in MIM capacitor such as dielectric constant as well as bending result of leakage current density and breakdown voltage have been better related to such fundamental adhesion nature over flexible substrate. This permits estimation of the properties of new dielectric in thin film form and short lists of the best materials for low loss and good capacitance flexible capacitors could be drawn up in future.
Eco-Friendly and Biodegradable Biopolymer Chitosan/Y2O3 Composite Materials in Flexible Organic Thin-Film Transistors
(2017-09-01)
Du, Bo-Wei
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Hu, Shao-Ying
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Singh, Ranjodh
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Tsai, Tsung-Tso
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Lin, Ching-Chang
The waste from semiconductor manufacturing processes causes serious pollution to the environment. In this work, a non-toxic material was developed under room temperature conditions for the fabrication of green electronics. Flexible organic thin-film transistors (OTFTs) on plastic substrates are increasingly in demand due to their high visible transmission and small size for use as displays and wearable devices. This work investigates and analyzes the structured formation of aqueous solutions of the non-toxic and biodegradable biopolymer, chitosan, blended with high-k-value, non-toxic, and biocompatible Y2O3 nanoparticles. Chitosan thin films blended with Y2O3 nanoparticles were adopted as the gate dielectric thin film in OTFTs, and an improvement in the dielectric properties and pinholes was observed. Meanwhile, the on/off current ratio was increased by 100 times, and a low leakage current was observed. In general, the blended chitosan/Y2O3 thin films used as the gate dielectric of OTFTs are non-toxic, environmentally friendly, and operate at low voltages. These OTFTs can be used on surfaces with different curvature radii because of their flexibility.
Effect of oxygen plasma on the surface states of ZnO films used to produce thin-film transistors on soft plastic sheets
(2013)
Meena, Jagan Singh
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Chu, Min-Ching
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Chang, Yu-Cheng
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You, Hsin-Chiang
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Singh, Ranjodh
Electronic displays and flexible electronics are poised to significantly impact emerging industries, including displays, energy products, sensors and medical devices, building a market that will significantly grow in the future. The implementation of transparent electronic devices requires the use of material components that could be formed using controlled deposition in the appropriate orientation onto a transparent flexible substrate. Here, we report a simple and efficient means of depositing onto a flexible polyimide (PI) substrate a highly ordered and highly aligned zinc oxide (ZnO) film for use as a carrier transporting and semiconducting layer with controlled surface charge density for thin-film transistor (TFT) applications. The deposition approach is based on the solution-coating of a zinc-acetate suspension under controlled conditions of the spread flow rate, droplet size of the drops, speed limit, and the oxygen (ca. O-2) plasma treatment of the coated film surface on the PI substrate. The plasma surface interactions on the surface states of the ZnO films for various times (ca. 1-5 min) were studied using X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. Moreover, the effects of O-2 plasma and the subsequent thermal annealing in an O-2 atmosphere at 250 degrees C on the properties of ZnO films were studied for its efficacy in TFT applications in terms of the charge carrier density and the change in the mobility. ZnO thin-film-based TFTs on PI exhibited a very high electron mobility of 22.8 cm(2) V-1 s(-1) at a drain bias of 5 V after treatment with O-2 plasma for 2 min. Furthermore, the plasma treatment for long durations of time caused a reduction in the charge carrier density from 1.58 x 10(19) cm(-3) for the 2 min treatment to 1.13 x 10(17) cm(-3) for the 5 min treatment, and the corresponding electron mobility was changed from 22.8 and 3.1 cm(2) V-1 s(-1) for the treatment times of 2 min and 5 min, respectively. The spin-coating technique used to deposit very thin ZnO films is currently used in microelectronics technology, which helps to ensure that the described ZnO thin-film deposition approach can be implemented in production lines with minimal changes in the fabrication design and in the auxiliary tools used in flexible electronics production.
Efficiently controllable hybrid micelle of poly(3-adeninehexylthiophene)/[6,6]-phenyl-C61-butyric acid methyl ester for a flexible metal-insulator-semiconductor device
(2016-03-13)
Lin, Yen-Ting
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Singh, Ranjodh
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Ko, Fu-Hsiang
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Cheng, Chih-Chia
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材料科學與工程學系
Knitting up 2,7-disubstituted carbazole based oligomers through supramolecular interactions for their application in organic thin film transistors
(2015-01-01)
Singh, Ranjodh
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Meena, Jagan Singh
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Wu, Chung-Shu
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Ko, Fu-Hsiang
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材料科學與工程學系
For the design and development of organic electronic devices, the main focus is particularly on the synthesis of new organic semiconductors and dielectric materials. Molecular engineering is another effective strategy, in this direction which has been explored successfully in this study through synthesis of a p-conjugated oligomer CbzTPAU2, with M-w = 2169. This bow shaped oligomer has its core unit made of 2,7-disubstituted carbazole which further has been connected to its end-terminal unit TPAU2 by 1,4-bis(decyloxy)-2,5-diethynylbenzene. The presence of a uracil moiety on end terminals of CbzTPAU2 has triggered the self-assembly of CbzTPAU2 molecules through knitting up of each of these single units through four Uracil-Uracil intermolecular hydrogen bonds (U center dot center dot center dot U) per CbzTPAU2 unit. An Atomic Force Microscope (AFM) study was employed to explore the directionality of hydrogen bonding. Further, the effect of solvent polarity on the stability of U center dot center dot center dot U bonding in CbzTPAU2 oligomers has also been reported here in this study. The potential of these self-assembled CbzTPAU2 oligomers when explored as charge transporting layers in OTFTs has shown p-type behaviour. The OTFT device bottom-gate, top-contact when fabricated on the heavily doped n-type Si wafer with SiO2 as a gate dielectric (200 nm) has shown a good on/off ratio 3.43 x 10(3) and with an average hole mobility of 0.167 cm(2) V-1 s(-1).
Polystyrene-block-poly(methylmethacrylate) composite material film as a gate dielectric for plastic thin-film transistor applications
(2014)
Meena, Jagan Singh
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Chu, Min-Ching
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Singh, Ranjodh
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Wu, Chung-Shu
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Chand, Umesh
We report a simple approach to fabricate an organic-inorganic hybrid gate insulator based n-type thin-film transistor (TFT) on a plastic polyimide (PI) sheet at room temperature using an appropriate composition of commercially available polymers and block copolymer surfactant. The composite material film namely; polystyrene-block-poly(methylmethacrylate) (PS-b-PMMA) is readily deposited as a gate dielectric with zinc oxide (ZnO) as a semiconductor layer. This new dielectric material film exhibits high surface energy, high air stability, very low leakage current density and better dielectric constant as compared to the conventional polymer dielectrics. This plastic ZnO-TFT combines the advantages of a high-mobility transparent inorganic semiconductor with an ultrathin high-capacitance and low-leakage PS-b-PMMA composite gate dielectric. Fourier transform infrared (FT-IR) spectrum analysis is used for the PS-b-PMMA film to confirm the presence of functional components in this composite material film. The contact angle measurements for three test liquids (e.g., distilled water, ethylene glycol and diiodomethane) reveal that the composite dielectric materials film is nearly hydrophobic and the calculated surface energy is 35.05 mJ m(-2). The resulting TFT exhibits excellent operating characteristics at V-DS=10 V with a drain-source current on/off modulation ratio (I-on/I-off) of 3.12 x 10(6) and a carrier mobility of 2.48 cm(2) V-1 s(-1). Moreover in the bending mode and in a normal environment, the device remained undistorted and shows better reliability and performance, while the thickness of PS-b-PMMA is about 28 nm. The results have suggested a new and easy approach for achieving transparent and functionally bendable optoelectronics devices.
Solution processable bilayered gate dielectric towards flexible organic thin film transistors
(2015-04-01)
Singh, Ranjodh
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Meena, Jagan Singh
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Tsai, I-Hsin
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Lin, Yen-Ting
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Wang, Cheng-Jyun
In this study, we have successfully explored the potential of a new bilayer gate dielectric material, composed of Polystyrene (PS), Pluronic P123 Block Copolymer Surfactant (P123) composite thin film and Polyacrylonitrile (PAN) through fabrication of metal insulator metal (MIM) capacitor devices and organic thin film transistors (OTFTs). The conditions for fabrication of PAN and PS-P123 as a bilayer dielectric material are optimized before employing it further as a gate dielectric in OTFTs. Simple solution processable techniques are applied to deposit PAN and PS-P123 as a bilayer dielectric layer on Polyimide (PI) substrates. Contact angle study is further performed to explore the surface property of this bilayer polymer gate dielectric material. This new bilayer dielectric having a k value of 3.7 intermediate to that of PS-P123 composite thin film dielectric (k similar to 2.8) and PAN dielectric (k similar to 5.5) has successfully acted as a buffer layer by preventing the direct contact between the organic semiconducting layer and high k PAN dielectric. The OTFT devices based on alpha,omega-dihexylquaterthiophene (DH4T) incorporated with this bilayer dielectric, has demonstrated a hole mobility of 1.37 x 10(-2) and on/off current ratio of 10(3) which is one of the good values as reported before. Several bending conditions are applied, to explore the charge carrier hopping mechanism involved in deterioration of electrical properties of these OTFTs. Additionally, the electrical performance of OTFTs, which are exposed to open atmosphere for five days, can be interestingly recovered by means of re-baking them respectively at 90 degrees C. (C) 2015 Elsevier B.V. All rights reserved.
Supramolecular control over the morphology of bio-inspired poly(3-hexylthiophene) for organic thin film transistors
(2017-02)
Lin, Yen-Ting
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Singh, Ranjodh
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Kuo, Shiao-Wei
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Ko, Fu-Hsiang
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材料科學與工程學系
We have developed a strategy for modifying the channel layer of organic thin film transistors (OTFTs) through side-chain induced self-organization into a well-ordered film. To obtain selectively self-patterned layers, we treated an adenine-functionalized poly(3-hexylthiophene) (PAT) with adenosine triphosphate (ATP). Using this strategy, interchain charge transport resulting from pi-conjugation was selected to control the polymer morphology, without the need of additional chemical synthetic processing. The side chain-induced self-organization can be understood in terms of supramolecular interactions. The pi-electrons were delocalized among the thiophene rings, thereby improving the interchain charge transport ability; the resulting planar pi-electron system in PAT: ATP resulted in closer intermolecular pep distances, facilitating enhanced charge carrier mobility within a fibrillar structure. The PAT: ATP-based OTFT device exhibited moderate to improved electronic characteristics, with an average field mobility of 3.2 x 10(-4) cm(2) V-1 s(-1) at -30 V and a threshold voltage (V-th) of 5 V, and an on/off current ratio of 10(6). This method has great potential for inducing selective intermolecular interactions in fully solution processed electronic devices. (C) 2016 Elsevier B.V. All rights reserved.