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Organic Field Effect Transistor | Printed Electronics | Sensors | Polymer Thin Film

Organic Field Effect Transistor

1. Dielectric surface Control

Physical or chemical properties characterizing a surface of gate dielectric have a huge impact on the electrical properties of organic field-effect transistors. Here, we applied various organic interlayers between an organic semiconductor and a gate dielectric to describe field-effect mobilities being a function of a certain macroscopic parameter associated with the surface energy of gate dielectric.
The organic interlayers with various chemical moieties, that is, hydroxyl, methyl, octadecyl, polystyrene, and polymethylmetacrylate, are obtained using diverse organosilane compounds and hydroxyl-end-terminated polymer brushes. Two prototypical vapor-deposited p-type organic small molecules, dinaphtho[2,3-b:2โ€ฒ,3โ€ฒ-f]thieno[3,2-b]thiophene and pentacene, are used as semiconducting layers.
We separate the surface energy of the organic interlayers into two terms, that is polar and dispersive terms, and define three parameters consisting of these two terms, so-called surface energy ratio, polar ratio, and polarity. The three parameters are plotted with the field-effect mobilities and it becomes apparent that the field-effect mobility is a function of polar ratio and polarity regardless of the semiconducting material as well as its morphology and crystallinity. In particular, the polarity that is the polar energy term divided by the total surface energy showed a clear exponential relationship, allowing a reliable prediction of field-effect mobilities.
OFET์˜ ์ „๊ธฐ์  ์„ฑ๋Šฅ์„ ํ–ฅ์ƒ์‹œํ‚ค๊ธฐ ์œ„ํ•œ ์ฃผ์š” ์ ‘๊ทผ ๋ฐฉ์‹ ์ค‘ ํ•˜๋‚˜๋Š” ์„œ๋กœ ๋‹ค๋ฅธ ๊ตฌ์„ฑ ์š”์†Œ์˜ ๊ณ„๋ฉด, ํŠนํžˆ ๊ฒŒ์ดํŠธ ์œ ์ „์ฒด์™€ ์œ ๊ธฐ ๋ฐ˜๋„์ฒด ์‚ฌ์ด์˜ ๊ณ„๋ฉด์˜ ํŠน์„ฑ์„ ์กฐ์ ˆ ํ•˜๋Š” ๊ฒƒ์ด๋‹ค. ์œ ์ „์ฒด ํ‘œ๋ฉด์ด ์œ ๊ธฐ ๋ฐ˜๋„์ฒด ์ฆ์ฐฉ ๋™์•ˆ ๋ถ„์ž ์กฐ๋ฆฝ์„ ๋‹ด๋‹นํ•  ๋ฟ๋งŒ ์•„๋‹ˆ๋ผ ๊ณ„๋ฉด์—์„œ์˜ ํšจ์œจ์ ์ธ ์ „ํ•˜ ์ˆ˜์†ก์„ ๋‹ด๋‹นํ•˜๊ธฐ ๋•Œ๋ฌธ์— ์ด ๊ณ„๋ฉด์€ OFET์˜ ์ „ํ•˜ ์ˆ˜์†ก ๋ฐ ์ „๊ธฐ์  ํŠน์„ฑ์„ ๊ฒฐ์ •ํ•˜๋Š”๋ฐ ์ค‘์š”ํ•œ ์—ญํ• ์„ ํ•œ๋‹ค. ์ผ๋ฐ˜์ ์œผ๋กœ ์œ ๊ธฐ ๋ฐ˜๋„์ฒด์™€ ๊ฒŒ์ดํŠธ ์œ ์ „์ฒด ์‚ฌ์ด์˜ ํ‘œ๋ฉด ์—๋„ˆ์ง€๋Š” ๋ถˆ์ผ์น˜ํ•˜๋ฏ€๋กœ ์œ ์ „์ฒด ํ‘œ๋ฉด์˜ ๋ฌผ๋ฆฌ์  ๋˜๋Š” ํ™”ํ•™์  ํŠน์„ฑ์„ ์กฐ์ ˆํ•˜์—ฌ ์ด๋Ÿฌํ•œ ํ‘œ๋ฉด ์—๋„ˆ์ง€์˜ ๋ถˆ์ผ์น˜๋ฅผ ์กฐ์ •ํ•˜๊ธฐ ์œ„ํ•œ ๋…ธ๋ ฅ์„ ํ•ด์™”๋‹ค. ๋ณธ ์—ฐ๊ตฌ์ง„์€ ๊ฒŒ์ดํŠธ ์œ ์ „์ฒด์˜ ํ‘œ๋ฉด ์—๋„ˆ์ง€์™€ ๊ด€๋ จ๋œ ํŠน์ • ๊ฑฐ์‹œ์  ๋งค๊ฐœ๋ณ€์ˆ˜์˜ ํ•จ์ˆ˜์ธ ์ „๊ณ„ ํšจ๊ณผ ์ด๋™๋„๋ฅผ ์„ค๋ช…ํ•˜๊ธฐ ์œ„ํ•ด ์œ ๊ธฐ ๋ฐ˜๋„์ฒด์™€ ๊ฒŒ์ดํŠธ ์œ ์ „์ฒด ์‚ฌ์ด์— ๋‹ค์–‘ํ•œ ์œ ๊ธฐ ์ค‘๊ฐ„์ธต์„ ์ ์šฉํ•˜์˜€๋‹ค. ํžˆ๋“œ๋ก์‹ค, ๋ฉ”ํ‹ธ, ์˜ฅํƒ€๋ฐ์‹ค, ํด๋ฆฌ์Šคํ‹ฐ๋ Œ ๋ฐ ํด๋ฆฌ๋ฉ”ํ‹ธ๋ฉ”ํƒ€ํฌ๋ฆด๋ ˆ์ดํŠธ๋ฅผ ๊ฐ–๋Š” ๋‹ค์–‘ํ•œ ์œ ๊ธฐ์‹ค๋ž€ ํ™”ํ•ฉ๋ฌผ ๋ฐ ํžˆ๋“œ๋ก์‹ค ๋ง๋‹จ ์ค‘ํ•ฉ์ฒด ๋ธŒ๋Ÿฌ์‹œ๋ฅผ ์‚ฌ์šฉํ•˜์—ฌ ์œ ๊ธฐ ์ค‘๊ฐ„์ธต์„ ๋„์ž…ํ•˜์—ฌ ๋‹ค์–‘ํ•œ ํ™”ํ•™์  ํŠน์„ฑ์„ ์ œ๊ณตํ•˜์˜€๋‹ค. ๋‘๊ฐœ์˜ ํ”„๋กœํ† ํƒ€์ž… ์ฆ์ฐฉ pํ˜• ์œ ๊ธฐ ์†Œ๋ถ„์ž์ธ DNTT์™€ Pentacene์ด ๋ฐ˜๋„์ฒด ์ธต์œผ๋กœ ์‚ฌ์šฉ๋˜์—ˆ์œผ๋ฉฐ, ์œ ๊ธฐ ์ค‘๊ฐ„์ธต์˜ SE๋ฅผ ๊ทน์„ฑ ๋ฐ ๋ถ„์‚ฐ term์ด๋ผ๋Š” ๋‘๊ฐ€์ง€ term์œผ๋กœ ๋ถ„๋ฆฌํ•˜๊ณ  OFET ์žฅ์น˜์—์„œ ์ „ํ•˜ ์ด๋™์„ฑ๊ณผ ๊ฐ•ํ•œ ๊ด€๊ณ„๋ฅผ ๊ฐ™๋Š” SE ๊ด€๋ จ ์œ„ํ•œ ์„ธ ๊ฐ€์ง€ ๋งค๊ฐœ๋ณ€์ˆ˜์ธ ํ‘œ๋ฉด์—๋„ˆ์ง€ ๋น„์œจ, ๊ทน์„ฑ ๋น„์œจ ๋ฐ ๊ทน์„ฑ์„ ์ •์˜ํ•˜์˜€๋‹ค. ๊ฒฐ๊ณผ์ ์œผ๋กœ ๋ฐ˜๋„์ฒด ๋ฌผ์งˆ์— ๊ด€๊ณ„์—†์ด ๊ทน์„ฑ๋น„์™€ ๊ทน์„ฑ์˜ ํ•จ์ˆ˜์ธ ์ „๊ณ„ ํšจ๊ณผ ์ด๋™๋„๋ฅผ ํ™•์ธํ•  ์ˆ˜ ์žˆ์—ˆ์œผ๋ฉฐ, ๊ฒŒ์ดํŠธ ์œ ์ „์ฒด์˜ ํ‘œ๋ฉด ํŠน์„ฑ์„ ๊ธฐ๋ฐ˜์œผ๋กœ OFET ์„ฑ๋Šฅ์„ ์˜ˆ์ธกํ•˜๊ธฐ ์œ„ํ•œ ๊ฐ„๋‹จํ•œ ๊ธฐ์ค€์„ ์ œ๊ณตํ•  ์ˆ˜ ์žˆ์—ˆ๋‹ค.

2. Organic Semiconductor Structural Control

A thermal gradient distribution was applied to a substrate during the growth of a vacuum-deposited n-type organic semiconductor (OSC) film prepared fromย N,Nโ€ฒ-bis(2-ethylhexyl)-1,7-dicyanoperylene-3,4:9,10-bis(dicarboxyimide) (PDI-CN2), and the electrical performances of the films deployed in organic field-effect transistors (OFETs) were characterized. The temperature gradient at the surface was controlled by tilting the substrate, which varied the temperature one-dimensionally between the heated bottom substrate and the cooled upper substrate.
The vacuum-deposited OSC molecules diffused and rearranged on the surface according to the substrate temperature gradient, producing directional crystalline and grain structures in the PDI-CN2 film. The morphological and crystalline structures of the PDI-CN2 thin films grown under a vertical temperature gradient were dramatically enhanced, comparing with the structures obtained from either uniformly heated films or films prepared under a horizontally applied temperature gradient.
The field effect mobilities of the PDI-CN2-FETs prepared using the vertically applied temperature gradient were as high as 0.59 cm2ย Vโ€“1ย sโ€“1, more than a factor of 2 higher than the mobility of 0.25 cm2ย Vโ€“1ย sโ€“1ย submitted to conventional thermal annealing and the mobility of 0.29 cm2ย Vโ€“1ย sโ€“1from the horizontally applied temperature gradient.
OSC ๋ฐ•๋ง‰์˜ ํ˜•ํƒœ ๋ฐ ๊ฒฐ์ • ๊ตฌ์กฐ๋Š” ์—ด ๋˜๋Š” ์šฉ๋งค ์–ด๋‹๋ง ๋ฐ ์šฉ๋งค soaking์„ ํฌํ•จํ•œ ๋‹ค์–‘ํ•œ ๊ณต์ • ๋ฐฉ๋ฒ•์„ ์‚ฌ์šฉํ•˜์—ฌ OSC ๋ถ„์ž์˜ ์ž๊ธฐ ์กฐ์งํ™” ํŠน์„ฑ์„ ์กฐ์ ˆํ•จ์œผ๋กœ์จ ๊ฐœ์„ ๋  ์ˆ˜ ์žˆ๋‹ค. ์—ด์ฒ˜๋ฆฌ๋Š” ๊ณต์ • ์˜จ๋„์™€ ์‹œ๊ฐ„์„ ์กฐ์ •ํ•˜์—ฌ OSC ํ•„๋ฆ„์˜ ์ „๊ธฐ์  ํŠน์„ฑ์„ ํšจ์œจ์ ์œผ๋กœ ํ–ฅ์ƒ์‹œํ‚ค๊ธฐ ๋•Œ๋ฌธ์— ์ง„๊ณต์ฆ์ฐฉ์ด๋‚˜ ์šฉ์•ก ๊ณต์ •์— ์˜ํ•ด OSC ๋ถ„์ž ์žฌ๋ฐฐ์—ด ๋ฐ ๊ฒฐ์ •ํ™”๋ฅผ ์ œ์–ดํ•˜๋Š”๋ฐ ๋„๋ฆฌ ์‚ฌ์šฉ๋œ๋‹ค. ๊ทธ๋Ÿฌ๋‚˜ OFET์˜ ์„ฑ๋Šฅ์€ ์—ด ์—๋„ˆ์ง€๊ฐ€ ๊ธฐํŒ ์ „์ฒด์— ๋ฌด์ž‘์œ„๋กœ ์ ์šฉ๋˜๊ธฐ ๋•Œ๋ฌธ์— ๋‹จ์ˆœํžˆ ์—ด ์–ด๋‹๋ง ๊ณผ์ •์„ ์‚ฌ์šฉํ•˜์—ฌ ๊ฐœ์„ ํ•˜๊ธฐ ์–ด๋ ต๋‹ค. ๊ณ ์„ฑ๋Šฅ OFET ์žฅ์น˜๋Š” OSC ํ•„๋ฆ„์˜ ๋ฐฉํ–ฅ์„ฑ ์„ ํƒ ์„ฑ์žฅ์„ ํ†ตํ•ด ์ž˜ ์ œ์–ด๋œ ํ•„๋ฆ„ ํ˜•ํƒœ์™€ ์กฐ์งํ™”๋œ ๊ฒฐ์ • ๊ตฌ์กฐ๋ฅผ ๊ฒฐํ•ฉํ•˜์—ฌ ์–ป์„ ์ˆ˜ ์žˆ๋‹ค. ํŠน์ • ๊ตฌ์—ญ์˜ ์–ด๋‹๋ง ๋ฐฉ๋ฒ•์€ ๊ตญ๋ถ€์ ์ธ ์šฉ์œต ๋ฐ ๋ƒ‰๊ฐ์„ ํ†ตํ•ด ๋ฐฉํ–ฅ์„ฑ ์žฌ๊ฒฐ์ •ํ™”๋ฅผ ๋‹ฌ์„ฑํ•˜๋Š” ๋Œ€ํ‘œ์ ์ธ ๋ฐฉ๋ฒ•์œผ๋กœ, ์—ฌ๋Ÿฌ ์—ฐ๊ตฌ ๊ทธ๋ฃน์€ OFET์— ๊ตฌ์—ญ ์–ด๋‹๋ง ๊ณผ์ •์„ ์ ์šฉํ•˜์—ฌ ๊ณ ์„ฑ๋Šฅ OFET ์žฅ์น˜๋ฅผ ๋‹ฌ์„ฑํ•˜์˜€๋‹ค. ๊ทธ๋Ÿฌ๋‚˜ ๊ตฌ์—ญ ์–ด๋‹๋ง ๊ณผ์ •์€ ์ตœ์ ์˜ ๋ฐฉํ–ฅ, ์†๋„ ๋ฐ ์ง€์—ฐ ์‹œ๊ฐ„์„ ๋ณด์žฅํ•˜๊ธฐ ์œ„ํ•ด ์กฐ๊ฑด์„ ์„ธ์‹ฌํ•˜๊ฒŒ ์ œ์–ดํ•ด์•ผํ•˜๋ฏ€๋กœ ๋น„ํšจ์œจ์ ์ด๋‹ค. ๋ฟ๋งŒ ์•„๋‹ˆ๋ผ ํŽœํƒ€์„ผ๊ณผ ๊ฐ™์€ ์ง„๊ณต ์ฆ์ฐฉ๋œ ์†Œ๋ถ„์ž OSC์— ๋Œ€ํ•œ ๊ตฌ์—ญ ์–ด๋‹๋ง์˜ ํšจ๊ณผ๋Š” ํƒ์›”ํ•˜์ง€ ์•Š์•˜์œผ๋ฉฐ, ๊ตฌ์—ญ ์–ด๋‹๋ง์€ ์šฉ์œต ์˜จ๋„์— ๊ทผ์ ‘ํ•˜๋Š” ๋งค์šฐ ๋†’์€ ์˜จ๋„๋ฅผ ์š”๊ตฌํ•œ๋‹ค.
๋ณธ ์—ฐ๊ตฌ์ง„์€ ๊ธฐํŒ์— ์—ด ๊ตฌ๋ฐฐ๋ฅผ ์ ์šฉํ•˜์—ฌ ์—ด์ฆ์ฐฉ OSC์˜ ๋ฐ•๋ง‰ ์„ฑ์žฅ์„ ์กฐ์ ˆํ•˜๊ธฐ ์œ„ํ•œ ํšจ์œจ์ ์ธ ์ „๋žต์„ ์‹œ์—ฐํ•˜์˜€๋‹ค. ์˜จ๋„ ๊ตฌ๋ฐฐ๋Š” ๊ฐ€์—ดํŒ์—์„œ ๊ธฐํŒ์„ ์ˆ˜์ง์œผ๋กœ ๊ธฐ์šธ์—ฌ์„œ ๋ฐ”๋‹ฅ๊ณผ ์œ„์ชฝ์— ๊ฐ๊ฐ ๋†’์€ ๊ธฐํŒ ์˜จ๋„์™€ ๋‚ฎ์€ ๊ธฐํŒ ์˜จ๋„๋ฅผ ์œ ๋„ํ•˜์—ฌ ํ˜•์„ฑ์‹œ์ผฐ๋‹ค. ๊ธฐ์šธ์–ด์ง„ ๊ธฐํŒ์€ OSC ๋ถ„์ž์˜ ์ฆ์ฐฉ ๋™์•ˆ ์‚ฌ์šฉ๋˜์–ด ์ˆ˜์ง ๋ฐฉํ–ฅ์„ ๋”ฐ๋ผ ๋” ๋†’์€ ๊ฒฐ์ •๋„์™€ ์šฐ์ˆ˜ํ•œ ์ „๊ธฐ์  ํŠน์„ฑ์„ ๊ฐ€์ง„ ํ•„๋ฆ„์„ ์ƒ์„ฑํ•˜์˜€๋‹ค. nํ˜• OSC ๋ฌผ์งˆ์ธ PDI-CN2๋ฅผ ์‚ฌ์šฉํ•˜์—ฌ ์ด ์˜จ๋„ ๊ตฌ๋ฐฐ ๋ฐฉ์‹์„ ์ ์šฉํ•˜์—ฌ FET์˜ ์ „๊ณ„ ํšจ๊ณผ ์ด๋™๋„๋Š” 0.59cm2 V-1 s-1๋ฅผ ๊ธฐ๋กํ•˜์˜€๋‹ค. ์ด๋Š” 0.25cm2 V-1 s-1์˜ ๊ธฐ์กด ์—ด ์–ด๋‹๋ง์„ ์‚ฌ์šฉํ•˜์—ฌ ์ œ์ž‘๋œ OFET ์žฅ์น˜์—์„œ ์–ป์€ ๊ฐ’์„ ํ›จ์”ฌ ์ดˆ๊ณผํ•˜๋Š” ๊ฐ’์„ ๋‹ฌ์„ฑํ•˜์˜€๋‹ค(๊ทธ๋ฆผ 3c).

Printed Electronics

1. Spray Coating

The ultrasonic nozzle (US) spray method was investigated for its utility in fabricating organic electrodes composed of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), a standard conductiveย polymerย material used to produce large-area low-cost OFETs. The US spray technique involves generating a solution spray by first passing the solution through a head and nozzle subjected to ultrasonic vibrations that induce atomization. This method is advantageous in that the resulting spray comprises extremely small solution droplets a few micrometers in diameter, unlike the spray produced using conventional air spray methods. The PEDOT:PSS US solution spraying process was optimized by controlling the flow rate of the N2ย carrier gas and the substrate temperature while monitoring the quality of the resulting PEDOT:PSS electrode films. Theย pentacenefield-effectย transistors prepared using the US spray method displayed a maximum field-effect mobility of 0.47ย cm2Vโˆ’1sโˆ’1ย (with an average value of 0.31ย cm2Vโˆ’1sโˆ’1), 35% better than the mobilities achieved using the conventional air spray method. In addition, the device-to-device reproducibility was improved, as indicated by a decrease in the standard deviation of the mobility values from 30% for the air spray devices to 24% for the US spray devices. These results indicated that the US spray technique is efficient and superior to the conventional air spray method for the development of low-cost large-areaย organic electronics.
์—์–ด ์Šคํ”„๋ ˆ์ด ํ”„๋ฆฐํŒ… ๋ฐฉ๋ฒ•์€ ๋„“์€ ๋ฉด์ ์—์„œ ๊ท ์ผํ•œ ์ฝ”ํŒ… ํ’ˆ์งˆ์„ ์ œ๊ณตํ•  ์ˆ˜ ์žˆ์–ด ์ €๊ฐ€์˜ ์œ ๊ธฐ ๋ฐ•๋ง‰์„ ์ œ์กฐํ•˜๊ธฐ ์œ„ํ•ด ์ผ๋ฐ˜์ ์œผ๋กœ ์‚ฌ์šฉ๋˜๋Š” ์šฉ์•ก ๊ณต์ • ๊ธฐ์ˆ ์ด๋‹ค. ํ•˜์ง€๋งŒ ์—์–ด ์Šคํ”„๋ ˆ์ด ํ”„๋ฆฐํŒ… ๊ธฐ์ˆ ์€ ๋…ธ์ฆ์—์„œ ํ† ์ถœ๋˜๋Š” ์šฉ์•ก ๋ฐฉ์šธ์˜ ์ง๊ฒฝ์ด 50~1000um ๋ฒ”์œ„์ด๊ธฐ ๋•Œ๋ฌธ์— ๊ณ ์ •๋ฐ€๋„์™€ ๊ท ์ผํ•œ ํ‘œ๋ฉด ์ฝ”ํŒ…์„ ๋‹ฌ์„ฑํ•˜๋Š”๋ฐ ์–ด๋ ค์›€์ด ์žˆ๋‹ค. ๋”ฐ๋ผ์„œ ์ตœ๊ทผ์—๋Š” ์ด๋Ÿฌํ•œ ์—์–ด ์Šคํ”„๋ ˆ์ด ํ”„๋ฆฐํŒ… ๋ฐฉ์‹์„ ๋ณด์™„ํ•˜๊ธฐ ์œ„ํ•ด ์ดˆ์ŒํŒŒ ๋…ธ์ฆ ์Šคํ”„๋ ˆ์ด ๋ฐฉ์‹์ด ๋„์ž…๋˜์—ˆ๋‹ค. ์ดˆ์ŒํŒŒ ๋…ธ์ฆ ์Šคํ”„๋ ˆ์ด ๊ธฐ์ˆ ์€ ์šฉ์•ก์ด ๋ถ„์‚ฌ๋˜๋Š” ๋…ธ์ฆ์— ์ดˆ์ŒํŒŒ ์ง„๋™์„ ๊ฐ€ํ•˜๋„๋ก ์„ค๊ณ„๋œ ์ฝ”ํŒ… ์žฅ๋น„์ด๋ฉฐ, ์šฉ์•ก์€ 2~5um์˜ ๋งค์šฐ ์ž‘์€ ์•ก์ ์œผ๋กœ ํ† ์ถœ๋˜๋ฏ€๋กœ ๊ธฐ์กด์˜ ์Šคํ”„๋ ˆ์ด ์ฝ”ํŒ… ๋ฐฉ๋ฒ•์— ๋น„ํ•ด ๋ฏธ์„ธํ•˜๊ณ  ๊ท ์ผํ•œ ์œ ๊ธฐ ํ•„๋ฆ„์„ ์ œ์ž‘ํ•  ์ˆ˜ ์žˆ๋‹ค.
๋ณธ ์—ฐ๊ตฌ์ง„์€ ์ €๋น„์šฉ ๋Œ€๋ฉด์  OFET ์ œ์ž‘์— ์ผ๋ฐ˜์ ์œผ๋กœ ์‚ฌ์šฉ๋˜๋Š” ์ „๋„์„ฑ ๊ณ ๋ถ„์ž ์žฌ๋ฃŒ์ธ PEDOT:PSS๋กœ ์ดˆ์ŒํŒŒ ๋…ธ์ฆ ์Šคํ”„๋ ˆ์ด ๋ฐฉ์‹์„ ์ด์šฉํ•œ ์œ ๊ธฐ ์ „๊ทน์„ ์ œ์ž‘ํ•˜์˜€๋‹ค. ์ตœ์ ์˜ ์ดˆ์ŒํŒŒ ๋…ธ์ฆ ์Šคํ”„๋ ˆ์ด ์กฐ๊ฑด์„ ์กฐ์‚ฌํ•˜๊ธฐ ์œ„ํ•ด N2 ๊ฐ€์Šค์˜ ์œ ๋Ÿ‰๊ณผ ๊ธฐํŒ ์˜จ๋„๋ฅผ ์กฐ์ ˆํ•˜์˜€์œผ๋ฉฐ, OFET ์†Œ์ž์˜ ํ™œ์„ฑ์ธต์€ ํ‘œ์ค€ ์œ ๊ธฐ ๋ฐ˜๋„์ฒด ์žฌ๋ฃŒ์ธ ํŽœํƒ€์„ผ์„ ์‚ฌ์šฉํ•˜์˜€๋‹ค. PEDOT:PSS ์ „๊ทน์˜ ๋ฌผ์„ฑ์„ ๊ธฐ์กด ์—์–ด ์Šคํ”„๋ ˆ์ด ๋ฐฉ์‹๊ณผ ๋น„๊ตํ•˜์˜€์„ ๋•Œ ์ดˆ์ŒํŒŒ ๋…ธ์ฆ ์Šคํ”„๋ ˆ์ด ๊ณต์ •์„ ์ด์šฉํ•˜์—ฌ ์ œ์กฐ๋œ ํŽœํƒ€์„ผ-FET๋Š” ๊ฐ๊ฐ 0.47 ๋ฐ 0.31์˜ ์ตœ๋Œ€ ๋ฐ ํ‰๊ท  ์ „๊ณ„ ํšจ๊ณผ ์ด๋™๋„๋ฅผ ๋ณด์˜€๊ณ , ํ‰๊ท  Vth๋Š” 3.7V๋ฅผ ๋‚˜ํƒ€๋‚ด์—ˆ๋‹ค. ์ด๋Š” ์—์–ด ์Šคํ”„๋ ˆ์ด ๊ณต์ •์„ ์‚ฌ์šฉํ•˜์—ฌ ์–ป์€ ์„ฑ๋Šฅ์— ๋น„ํ•ด ์•ฝ 35%๊ฐ€ ํ–ฅ์ƒ๋˜์—ˆ๋‹ค. ๋˜ํ•œ, ์ด๋™๋„ ๊ฐ’์˜ ํ‘œ์ค€ํŽธ์ฐจ ๋˜ํ•œ 30%์—์„œ ์ดˆ์ŒํŒŒ ๋…ธ์ฆ ์Šคํ”„๋ ˆ์ด ๊ณต์ •์„ ์ ์šฉ ํ›„ 24%๋กœ ๊ฐ์†Œํ•˜์—ฌ ์žฅ์น˜๊ฐ„ ์žฌํ˜„์„ฑ์ด ํ–ฅ์ƒ๋˜์—ˆ๋‹ค. ์ด๋ฅผ ํ†ตํ•˜์—ฌ ์ดˆ์ŒํŒŒ ๋…ธ์ฆ ์Šคํ”„๋ ˆ์ด ๊ธฐ์ˆ ์ด ํ•„๋ฆ„์˜ ํ’ˆ์งˆ์— ๋”ฐ๋ผ ์ „๊ธฐ์  ์„ฑ๋Šฅ์— ํฌ๊ฒŒ ์˜ํ–ฅ ๋ฐ›๋Š” ๊ท ์ผํ•œ ์œ ๊ธฐ ํ™œ์„ฑ์ธต, ์ „๊ทน ๋˜๋Š” ์œ ์ „์ธต์„ ํšจ์œจ์ ์œผ๋กœ ์ œ์ž‘ํ•  ์ˆ˜ ์žˆ์Œ์„ ํ™•์ธํ•˜์˜€๋‹ค.

2. Pen Printing

The molecular orientation and crystallinity of polymers are one of the most important factors in the performance of organic electronic devices. Depending on the crystallinity, the mobility of the OTFT may vary several orders of magnitude.
Polymer arrangements that are advantageous for performance enhancement include edge on structure, large grain size, and spherulite formation in low molecular weight materials.
We are studying to produce high performance electronic devices through favorable molecular alignment and high crystalline arrangement of polymers.

Sensors

1. Strain Sensors

Flexible strain sensors are a key component of electronic skin (e-skin), a technology that is currently receiving considerable research attention with a view to future applications ranging from human healthcare monitoring to robotic skins and environmental risk detection. Here, we developed a highly sensitive, simple, and low-cost piezoresistive strain sensor, which acted as a flexible reactive resistor with a cracked microtectonic architecture that could be fabricated over a large area. In particular, our strain sensor recognizes the direction of tensile stimulation through its rational crisscross electrode design, allowing it to overcome some of the shortcomings of traditional flexible strain sensors. Under a given stress, the strain sensor developed here showed a variation in the relative resistance (ฮ”R/R0) of up to 24-fold depending on the direction of the applied stress. For example, application of a 1% strain changed ฮ”R/R0ย by 0.11 when the strain was applied parallel to the direction of current flow, but by only 0.012 when the strain was applied perpendicular to that direction. Similarly, a 5% strain changed ฮ”R/R0ย by 0.85 and 0.062, and a 20% strain changed ฮ”R/R0ย by 2.37 and 0.098, depending on whether the strain was applied parallel or perpendicular to the current flow, respectively. In addition, ฮ”R/R0ย varied approximately linearly as a function of the strain over the operational range. The results thus show that the proposed sensor is sensitive to the direction in which an external stress is applied. Finally, we demonstrated that our sensor could be used to detect the bending of a human finger.

2. Pressure Sensors

Flexible pressure sensors are a key component of electronic skin (e-skin) for use in future applications ranging from human healthcare monitoring to robotic skins and environmental risk detection. Here, we demonstrated the development of a highly sensitive, simple, and low-cost capacitive pressure sensor, which acted as a flexible capacitive dielectric, based on a microstructured elastomeric template that could be fabricated over a large area. To achieve this goal, the dielectric template was prepared simply by stretching and releasing a flexible Ecoflex film to produce wrinkled surface microstructures with a feature size on the order of tens of micrometers. The effects of the wrinkled surface microstructure on the sensing performance were systematically investigated by comparing the nonwrinkled film, one-side wrinkled film, and double-side wrinkled film. The response and release times of the double-side wrinkled pressure sensor were improved by 42% and 25% in comparison with the values obtained from the unwrinkled case, respectively. These results showed that the introduction of wrinkled surface microstructures to the elastomeric template efficiently enhanced the pressure sensor performance. We also demonstrated that our sensor could be used to detect a variety of changes in the surroundings, such as variations in the angle of a stimulus, object loading/unloading, or an exhaled breath.
๋ณธ ์—ฐ๊ตฌ์ง„์€ ์œ ์—ฐํ•œ ์ •์ „์šฉ๋Ÿ‰์‹ ์••๋ ฅ ์„ผ์„œ ์—ญํ• ์„ ํ•˜๋Š” ๋Œ€๋ฉด์  ๋ฏธ์„ธ๊ตฌ์กฐ ์—˜๋ผ์Šคํ† ๋จธ ํ…œํ”Œ๋ฆฟ์„ ์ œ์ž‘ํ•˜๊ธฐ ์œ„ํ•œ ๊ฐ„๋‹จํ•˜๊ณ  ์ €๋ ดํ•œ ๊ณต์ •์„ ์„ค๊ณ„ํ•˜์˜€๋‹ค. Ecoflex ์œ ์ „์ฒด ๋ฐ•๋ง‰์„ ์–‘์ชฝ์œผ๋กœ ๋Š˜๋ฆฐ ํ›„ UVO ์ฒ˜๋ฆฌ๋ฅผ ํ†ตํ•ด ๊ทœ์‚ฐ์—ผ ์ธต์„ ํ˜•์„ฑ์‹œ์ผฐ๊ณ , Ecoflex ํ•„๋ฆ„์˜ ๋ณ€ํ˜•์ด ์™„ํ™”๋˜๋ฉด์„œ ์ˆ˜์‹ญ ๋งˆ์ดํฌ๋กœ๋ฏธํ„ฐ ์ •๋„์˜ ์ฃผ๋ฆ„์ง„ ๋ฏธ์„ธ๊ตฌ์กฐ๊ฐ€ ํ˜•์„ฑ๋˜์—ˆ๋‹ค(๊ทธ๋ฆผ 7a). ์—ฌ๊ธฐ์— Au๊ฐ€ ์ฝ”ํŒ…๋œ ์‹ค๋ฆฌ์ฝ˜ ์›จ์ดํผ์™€ PDMS๋ฅผ ๊ฐ๊ฐ Ecoflex template ์ƒ๋‹จ๊ณผ ํ•˜๋‹จ์— ๋ฐฐ์น˜ํ•˜์—ฌ ์ „๊ทน์„ ํ˜•์„ฑ์‹œ์ผœ ์ฃผ๋ฆ„์ง„ ๊ตฌ์กฐ๋ฅผ ๊ฐ–๋Š” ์œ ์—ฐ ์••๋ ฅ์„ผ์„œ๋ฅผ ์ œ์ž‘ํ•˜์˜€๋‹ค. ์ฃผ๋ฆ„์ด ์—†๋Š” ํ•„๋ฆ„, ๋‹จ๋ฉด ์ฃผ๋ฆ„ ํ•„๋ฆ„, ์–‘๋ฉด ์ฃผ๋ฆ„ ํ•„๋ฆ„์„ ๋น„๊ตํ•˜์—ฌ ์ฃผ๋ฆ„์ง„ ํ‘œ๋ฉด ๋ฏธ์„ธ๊ตฌ์กฐ๊ฐ€ ๊ฐ์ง€ ์„ฑ๋Šฅ์— ๋ฏธ์น˜๋Š” ์˜ํ–ฅ์„ ์ฒด๊ณ„์ ์œผ๋กœ ์กฐ์‚ฌํ•˜์˜€๋‹ค. ์–‘๋ฉด ์ฃผ๋ฆ„ํ˜• ์••๋ ฅ์„ผ์„œ์˜ ์‘๋‹ต์†๋„์™€ ํ•ด์ œ์‹œ๊ฐ„์€ ์ฃผ๋ฆ„์ด ์—†๋Š” ๊ฒฝ์šฐ์— ๋น„ํ•ด ๊ฐ๊ฐ 42%, 25% ๊ฐœ์„ ๋˜์—ˆ๋‹ค(๊ทธ๋ฆผ 7b). ์ด๋Ÿฌํ•œ ๊ฒฐ๊ณผ๋Š” ์—˜๋ผ์Šคํ† ๋จธ ํ…œํ”Œ๋ฆฟ์— ์ฃผ๋ฆ„์ง„ ํ‘œ๋ฉด ๋ฏธ์„ธ๊ตฌ์กฐ์˜ ๋„์ž…์ด ์••๋ ฅ ์„ผ์„œ ์„ฑ๋Šฅ์„ ํšจ์œจ์ ์œผ๋กœ ํ–ฅ์ƒ์‹œํ‚ด์„ ๋ณด์—ฌ์ฃผ์—ˆ๋‹ค. ๊ฐœ๋ฐœ๋œ ์••๋ ฅ์„ผ์„œ๋Š” ๋†’์€ ๊ฐ๋„, ๋น ๋ฅธ ์‘๋‹ต์„ฑ, ์šฐ์ˆ˜ํ•œ ๋‚ด๊ตฌ์„ฑ ๋ฐ ์„ฑ๋Šฅ ๋ฐ˜๋ณต์„ฑ์„ ๋ฐ”ํƒ•์œผ๋กœ ์ฑ…์„ ํŽผ์น˜๊ฑฐ๋‚˜ ๋ฌผ์ฒด์˜ ์œ ๋ฌด, ๊ทธ๋ฆฌ๊ณ  ๋‚ด์‰ฌ๋Š” ํ˜ธํก๊ณผ ๊ฐ™์€ ์ฃผ๋ณ€์˜ ๋‹ค์–‘ํ•œ ๋ณ€ํ™”๋ฅผ ๊ฐ์ง€ํ•˜๋Š” ๋ฐ ์‚ฌ์šฉ๋  ์ˆ˜ ์žˆ์Œ์„ ํ™•์ธํ•˜์˜€๋‹ค(๊ทธ๋ฆผ 7c-e).

3. Chemical Sensors

A person's sweat contains various ingredients, and the composition of sweat changes according to a person's health condition. Lactic acid, one of the components of sweat, is a chemical component that is an indicator of fatigue. Lactic acid is produced in cells during anaerobic exercise, which is accumulated in the muscles when fatigued, and causes fatigue in the body. In addition, lactic acid can be a good indicator of pathological disorders. Lack of oxygen in the blood, especially when the sweat gland cells produce lactic acid, the concentration of lactic acid in the sweat increases. This means that a disease that causes hypoxia can be diagnosed by detecting the concentration of lactic acid. Other studies have shown that lactic acid is a good indicator of reduced oxygen delivery in tissues from patients with peripheral arterial occlusive disease. Therefore, sensors that detect lactic acid may be required not only for personal health care, but also for specialized medical applications.
In the present study, we use transistors with a special structure called an interference gate. The interference gate is an electrode located on the dielectric. The sensing principle of this particular device acts as the sensing area of transistor-based sensors and is related to the threshold voltage shift by affecting the transfer characteristics of the transistor depending on the charge applied to the surface. This structure has the advantage of requiring a small amount of sample for detection without requiring a separate reference electrode. Carbon nanotube (CNT) was used as a sensing material in the interference gate sensing area. CNTs have functional groups that can chemically react with other materials such as carboxyl groups. Lactate oxidase (LOD) and peroxidase from horseradish were chemically combined with CNT-COOH to detect lactic acid. LOD oxidizes lactic acid to produce hydrogen peroxide (H2O2), and Peroxidase from horseradish (HRP) causes oxidation-reduction reaction while decomposing H2O2 to enable sensor detection.

Polymer Thin Film

1. Superhydrophobic Surface

A superhydrophobic surface with excellent chemical stability was fabricated using the spraying method, one of the most efficient technologies for producing large-area coatings at low cost. Poly(vinylidene fluoride) (PVDF) was used as a hydrophobic polymer material, and heptadecafluoro-1,1,2,2,-tetra-hydrodecyl)trichlorosilane (FTS), which reacts with moisture during curing, was used to improve the water repellency and durability. Spray coating of PVDF alone yielded PVDF nanostructures described by the Cassie-Baxter model. The water contact angle of a water droplet on this surface, however, was 128ยฐ, indicating that the surface was not superhydrophobic. On the other hand, spray-coating a mixed PVDF-FTS solution provided a complex and homogeneous nanostructured surface with excellent water repellency and a contact angle of up to 159ยฐ. Immersion of the PVDF-only film for 20 min inย N,N-dimethylformamide (DMF), a good solvent for PVDF, led to complete dissolution of the film. By contrast, the PVDF-FTS film maintained its superhydrophobicity with a water contact angle of 151ยฐ after 20 min of immersion in DMF, and still exhibited a high contact angle of 142ยฐ after 1 h. The PVDF-FTS film developed in the present work should enable the production of large-area superhydrophobic coatings at low cost using a simple spray process. Moreover, the PVDF-FTS film displayed excellent stability against solvents, thus increasing its suitability for robust superhydrophobic applications.

2. Polymer Coating

We developed a stable hydrophilic biocompatible hydrogel-forming coating for polypropylene (PP)-based disposal medical applications. Although PP has a variety of advantages, including good stability and inertness in medical applications, tissue damage and insertion resistance are observed upon insertion of PP-based devices into the human body due to the high hydrophobicity of the PP surface. These issues limit the utility of PP in medical applications. To address these problems, we sought to develop a stable hydrophilic and biocompatible hydrogel-forming layer using polyvinyl pyrrolidone (PVP) combined with a crosslinked polyethyleneglycolacrylate (PEGDA) matrix. Systematic studies of the blended hydrogel-forming PVP:PEGDA were conducted using a variety of blending ratios between the two polymers. The hydrophilicity and water-affinity of the hydrogel-forming layer improved significantly as the PEGDA-to-PVP blending ratio increased. Importantly, the tensile strain at the break point increased by a factor of more than 7, and the strength of adhesion to the PP surface for the 1:1 PVP:PEGDA (PVP(1):PEGDA(1)) blend ratio was 54 times that of the PVP film, determined using tensile strainโ€“stress and peel tests. The water stability of the PVP(1):PEGDA(1) improved significantly. This approach is potentially useful as a biocompatible hydrophilic polymer coating in a variety of low-priced consumable PP commercial medical applications.