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High-Performance Flexible Bottom-Gate Organic Field-Effect Transistors with Gravure Printed Thin Organic Dielectric.

Vaklev NL, Müller R, Muir BV, James DT, Pretot R, van der Schaaf P, Genoe J, Kim JS, Steinke JH, Campbell AJ - Adv Mater Interfaces (2014)

View Article: PubMed Central - PubMed

Affiliation: Experimental Solid State Group and the Centre for Plastic Electronics, Department of Physics, Blackett Laboratory, South Kensington Campus, Imperial College London London, SW7 2AZ, UK E-mail: alasdair.campbell@imperial.ac.uk.

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One of the key advantages of organic field-effect transistors (OFETs) is their ability to form flexible, conformable and lightweight electronic devices, e.g. radio frequency identification (RFID) tags, microprocessors and flexible displays... While high performance source, drain and gate electrodes and interconnects require metal evaporation under vacuum, ideally the dielectric and organic semiconductor (OSC) should be processed from solution under ambient conditions to reduce fabrication costs... These can be processed by techniques such as spin-casting, gravure printing and ink-jet printing at room temperature in ambient conditions... To avoid significant gate leakage current these polymer dielectrics have typically been deposited with film thicknesses ≥ 500 nm, resulting in high OFET operating voltages ≥20 V... To fabricate the BG BC OFETs, non-birefringent plastic substrates coated with a transparent conducting oxide (TCO) were used as required for flexible display applications... Breakdown voltages of the spin-cast and printed films were typically >2.4 MV cm (Figure S4)... Therefore, we conclude that gravure printing can produce dielectric films with comparable surface properties and homogeneity as spin-casting... Semiconductor crystallinity and charge-carrier mobility in BG BC OFETs is known to be affected by the dielectric surface energy, increasing with increasing water contact angle... The water contact angle of the dielectric surface with and without PαMS was found to be 90 ± 2° and 69 ± 2°, respectively... The SSV can be associated with the ratio between mobile and trapped charge-carriers at the semiconductor–dielectric interface as carriers first enter the channel when the OFET is switched from off- to on-state... The presence of PαMS therefore reduces the density of interfacial traps responsible for the SSV in TIPS-pentacene... Therefore, the triacrylate based dielectric can be processed using large-area compatible coating techniques such as gravure to give equally high performance devices as when it is spin-cast... In conclusion, we have demonstrated that it is possible to fabricate state-of-the-art flexible small molecule BG BC OFETs on plastic foil using a large-area scalable platform... Evaporated pentacene OFETs achieved an average mobility of 0.6 cm V s, which is state-of-the-art for this device geometry for flexible transistors on plastic... We also demonstrated that zone-casting can be used to fabricate small molecule OFETs on plastic with a polymer dielectric, TIPS-pentacene achieving an average mobility of 0.3 cm V s, which is state-of-the-art for this device geometry for flexible devices.

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Leakage current characteristics of capacitors with (a) gravure printed and (b) spin-cast dielectric. (c) Saturation mobility, onset voltage, sub-threshold swing voltage (SSV) and On/Off ratio of OFETs with and without PαMS on gravure printed and spin-cast dielectric. The data was extracted from the saturation regime at Vds = −10 V. Error bars are ±1 standard deviation. Numerical values for this figure are tabulated in Table S1. ODTS = octadecyltrichlorosilane; PPA = phenylphosphonic acid.
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fig02: Leakage current characteristics of capacitors with (a) gravure printed and (b) spin-cast dielectric. (c) Saturation mobility, onset voltage, sub-threshold swing voltage (SSV) and On/Off ratio of OFETs with and without PαMS on gravure printed and spin-cast dielectric. The data was extracted from the saturation regime at Vds = −10 V. Error bars are ±1 standard deviation. Numerical values for this figure are tabulated in Table S1. ODTS = octadecyltrichlorosilane; PPA = phenylphosphonic acid.

Mentions: The dielectric was deposited by gravure contact printing, a high volume, reel-to-reel compatible, large-area coating technique;[12,17] this gave ca. 110 nm thick films which are the thinnest printed dielectric films reported to date.[11] The dielectric formulation was based on a triacrylate cross-linker blended with high molecular weight PMMA as a viscosity modifier.[18] A radical photoinitiator for photopatterning, whose absorption band overlapped with the UV wavelength of the mask aligner at 365 nm, was added to the dielectric formulation. The dielectric gravure formulation had a high boiling point component (ca. 150 °C) to improve ink levelling on the substrate after printing.[19] After printing, the dielectric was photopatterned in ambient on top of the TCO gate electrodes. After a washing step to remove unexposed material, crosslinking was completed in a UV chamber filled with nitrogen. This formulation was also spin-cast, at 130 nm thickness, onto the substrate and then processed as per the gravure-printed films, to allow comparison between the two deposition methods. The spin-cast and gravure printed dielectric had a similar root-mean-square (RMS) surface roughness of 2 nm as measured by AFM (Figure S1). Optical interferometry and microscopy confirmed print homogeneity over large areas (Figure S2). Electrical testing of the films in capacitors gave a similar dielectric constant εr of 2.9 and similarly low leakage currents, <10–7 A mm−2, in parallel capacitors (Figure2a, b and Figure S3). Breakdown voltages of the spin-cast and printed films were typically >2.4 MV cm−1 (Figure S4). Therefore, we conclude that gravure printing can produce dielectric films with comparable surface properties and homogeneity as spin-casting.


High-Performance Flexible Bottom-Gate Organic Field-Effect Transistors with Gravure Printed Thin Organic Dielectric.

Vaklev NL, Müller R, Muir BV, James DT, Pretot R, van der Schaaf P, Genoe J, Kim JS, Steinke JH, Campbell AJ - Adv Mater Interfaces (2014)

Leakage current characteristics of capacitors with (a) gravure printed and (b) spin-cast dielectric. (c) Saturation mobility, onset voltage, sub-threshold swing voltage (SSV) and On/Off ratio of OFETs with and without PαMS on gravure printed and spin-cast dielectric. The data was extracted from the saturation regime at Vds = −10 V. Error bars are ±1 standard deviation. Numerical values for this figure are tabulated in Table S1. ODTS = octadecyltrichlorosilane; PPA = phenylphosphonic acid.
© Copyright Policy - open-access
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC4493673&req=5

fig02: Leakage current characteristics of capacitors with (a) gravure printed and (b) spin-cast dielectric. (c) Saturation mobility, onset voltage, sub-threshold swing voltage (SSV) and On/Off ratio of OFETs with and without PαMS on gravure printed and spin-cast dielectric. The data was extracted from the saturation regime at Vds = −10 V. Error bars are ±1 standard deviation. Numerical values for this figure are tabulated in Table S1. ODTS = octadecyltrichlorosilane; PPA = phenylphosphonic acid.
Mentions: The dielectric was deposited by gravure contact printing, a high volume, reel-to-reel compatible, large-area coating technique;[12,17] this gave ca. 110 nm thick films which are the thinnest printed dielectric films reported to date.[11] The dielectric formulation was based on a triacrylate cross-linker blended with high molecular weight PMMA as a viscosity modifier.[18] A radical photoinitiator for photopatterning, whose absorption band overlapped with the UV wavelength of the mask aligner at 365 nm, was added to the dielectric formulation. The dielectric gravure formulation had a high boiling point component (ca. 150 °C) to improve ink levelling on the substrate after printing.[19] After printing, the dielectric was photopatterned in ambient on top of the TCO gate electrodes. After a washing step to remove unexposed material, crosslinking was completed in a UV chamber filled with nitrogen. This formulation was also spin-cast, at 130 nm thickness, onto the substrate and then processed as per the gravure-printed films, to allow comparison between the two deposition methods. The spin-cast and gravure printed dielectric had a similar root-mean-square (RMS) surface roughness of 2 nm as measured by AFM (Figure S1). Optical interferometry and microscopy confirmed print homogeneity over large areas (Figure S2). Electrical testing of the films in capacitors gave a similar dielectric constant εr of 2.9 and similarly low leakage currents, <10–7 A mm−2, in parallel capacitors (Figure2a, b and Figure S3). Breakdown voltages of the spin-cast and printed films were typically >2.4 MV cm−1 (Figure S4). Therefore, we conclude that gravure printing can produce dielectric films with comparable surface properties and homogeneity as spin-casting.

View Article: PubMed Central - PubMed

Affiliation: Experimental Solid State Group and the Centre for Plastic Electronics, Department of Physics, Blackett Laboratory, South Kensington Campus, Imperial College London London, SW7 2AZ, UK E-mail: alasdair.campbell@imperial.ac.uk.

AUTOMATICALLY GENERATED EXCERPT
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One of the key advantages of organic field-effect transistors (OFETs) is their ability to form flexible, conformable and lightweight electronic devices, e.g. radio frequency identification (RFID) tags, microprocessors and flexible displays... While high performance source, drain and gate electrodes and interconnects require metal evaporation under vacuum, ideally the dielectric and organic semiconductor (OSC) should be processed from solution under ambient conditions to reduce fabrication costs... These can be processed by techniques such as spin-casting, gravure printing and ink-jet printing at room temperature in ambient conditions... To avoid significant gate leakage current these polymer dielectrics have typically been deposited with film thicknesses ≥ 500 nm, resulting in high OFET operating voltages ≥20 V... To fabricate the BG BC OFETs, non-birefringent plastic substrates coated with a transparent conducting oxide (TCO) were used as required for flexible display applications... Breakdown voltages of the spin-cast and printed films were typically >2.4 MV cm (Figure S4)... Therefore, we conclude that gravure printing can produce dielectric films with comparable surface properties and homogeneity as spin-casting... Semiconductor crystallinity and charge-carrier mobility in BG BC OFETs is known to be affected by the dielectric surface energy, increasing with increasing water contact angle... The water contact angle of the dielectric surface with and without PαMS was found to be 90 ± 2° and 69 ± 2°, respectively... The SSV can be associated with the ratio between mobile and trapped charge-carriers at the semiconductor–dielectric interface as carriers first enter the channel when the OFET is switched from off- to on-state... The presence of PαMS therefore reduces the density of interfacial traps responsible for the SSV in TIPS-pentacene... Therefore, the triacrylate based dielectric can be processed using large-area compatible coating techniques such as gravure to give equally high performance devices as when it is spin-cast... In conclusion, we have demonstrated that it is possible to fabricate state-of-the-art flexible small molecule BG BC OFETs on plastic foil using a large-area scalable platform... Evaporated pentacene OFETs achieved an average mobility of 0.6 cm V s, which is state-of-the-art for this device geometry for flexible transistors on plastic... We also demonstrated that zone-casting can be used to fabricate small molecule OFETs on plastic with a polymer dielectric, TIPS-pentacene achieving an average mobility of 0.3 cm V s, which is state-of-the-art for this device geometry for flexible devices.

No MeSH data available.


Related in: MedlinePlus