7 research outputs found

    Electric Field Guided Assembly of One-Dimensional Nanostructures for High Performance Sensors

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    Various nanowire or nanotube-based devices have been demonstrated to fulfill the anticipated future demands on sensors. To fabricate such devices, electric field-based methods have demonstrated a great potential to integrate one-dimensional nanostructures into various forms. This review paper discusses theoretical and experimental aspects of the working principles, the assembled structures, and the unique functions associated with electric field-based assembly. The challenges and opportunities of the assembly methods are addressed in conjunction with future directions toward high performance sensors

    Retinal Neural Stimulation Method Using Silicon Nanowire-based Photodetection Circuits for the Realization of High Resolution Retinal Prosthesis

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    ํ•™์œ„๋…ผ๋ฌธ (๋ฐ•์‚ฌ)-- ์„œ์šธ๋Œ€ํ•™๊ต ๋Œ€ํ•™์› : ์ „๊ธฐยท์ปดํ“จํ„ฐ๊ณตํ•™๋ถ€, 2015. 8. ์กฐ๋™์ผ.์ธ๊ฐ„์˜ ๋ˆˆ์— ๋“ค์–ด์˜จ ๋น› ์ •๋ณด๋Š” ๋ง๋ง‰์—์„œ ์ „๊ธฐ์‹ ํ˜ธ๋กœ ๋ณ€ํ™˜๋˜์–ด ์‹œ์‹ ๊ฒฝ์„ ํ†ตํ•ด ๋‡Œ๋กœ ์ „๋‹ฌ๋˜์–ด ์˜์ƒ์„ ์ธ์‹ํ•˜๊ฒŒ ๋œ๋‹ค. ๊ทธ๋Ÿฌ๋‚˜ ์‹œ์„ธํฌ๊ฐ€ ์†์ƒ๋œ ๊ฒฝ์šฐ์—๋Š” ๋‹ค๋ฅธ ์‹ ๊ฒฝ์„ธํฌ๋“ค์˜ ๊ธฐ๋Šฅ์ด ๋‚จ์•„์žˆ๋”๋ผ๋„ ๋น›์„ ์ธ์ง€ํ•  ์ˆ˜ ์—†์–ด ๊ฒฐ๊ตญ ๋ณผ ์ˆ˜ ์—†๊ฒŒ ๋œ๋‹ค. ์ธ๊ณต ๋ง๋ง‰ ์‹œ์Šคํ…œ(retinal prosthetic system)์€ ์ด๋Ÿฌํ•œ ๋ง๋ง‰ ์†์ƒ์œผ๋กœ ์ธํ•ด ์‹œ๊ฐ ์žฅ์• ๋ฅผ ๊ฒช๊ณ  ์žˆ๋Š” ์žฅ์• ์ธ์˜ ์‹œ๋ ฅ ํšŒ๋ณต์„ ์œ„ํ•ด ๋ง๋ง‰ ์„ธํฌ ๋‚ด์— ์ธ์œ„์ ์œผ๋กœ ๋ฏธ์„ธ ์ „๊ทน ์–ด๋ ˆ์ด(micro electrode array, MEA)๊ฐ€ ์ง‘์ ๋œ ๋ง๋ง‰ ์ž๊ทน๊ธฐ๋ฅผ ์ด์‹ํ•˜๊ณ  ์—ฌ๊ธฐ์— ์ „๊ธฐ ์ž๊ทน ์‹ ํ˜ธ๋ฅผ ์ธ๊ฐ€ํ•˜์—ฌ ๋ง๋ง‰ ์„ธํฌ์— ์ธ์œ„์ ์ธ ์ „๊ธฐ ์ž๊ทน์„ ์œ ๋ฐœ์‹œํ‚ด์œผ๋กœ์จ ๋ง๋ง‰ ์‹œ์„ธํฌ ์†์ƒ์œผ๋กœ ์‹œ๋ ฅ์„ ์žƒ์€ ์‚ฌ๋žŒ์—๊ฒŒ ์˜์ƒ์„ ์ธ์‹ํ•  ์ˆ˜ ์žˆ๋„๋ก ํ•ด์ฃผ๋Š” ์žฅ์น˜์ด๋‹ค. ๋ณธ ๋…ผ๋ฌธ์—์„œ๋Š” ์˜์ƒ์ธ์‹์„ ์œ„ํ•œ ๊ด‘ ๊ฒ€์ถœ๊ธฐ๊ฐ€ ๋‚ด์žฅ๋œ ์™„์ „ํ•œ ์•ˆ๊ตฌ ์ด์‹ํ˜•์˜ ๊ณ ํ•ด์ƒ๋„ ์ธ๊ณต ๋ง๋ง‰ ์‹œ์Šคํ…œ ๊ตฌํ˜„์„ ์œ„ํ•ด ์‹ค๋ฆฌ์ฝ˜ ๋‚˜๋…ธ์™€์ด์–ด ๊ธฐ๋ฐ˜์˜ ๊ด‘ ๊ฒ€์ถœ ๋ฐ ์ž๊ทน ์‹ ํ˜ธ ๋ณ€์กฐํšŒ๋กœ์™€ ๋ฏธ์„ธ ์ „๊ทน ์–ด๋ ˆ์ด๊ฐ€ ์ง‘์ ๋œ ๊ณ ํ•ด์ƒ๋„ ๋ง๋ง‰ ์ž๊ทน๊ธฐ์™€ ๊ด‘ ๊ฒ€์ถœ ๊ธฐ๋ฐ˜์˜ ๋ง๋ง‰ ์‹ ๊ฒฝ ์ž๊ทน ๊ธฐ๋ฒ•์„ ์ œ์•ˆํ•œ๋‹ค. ์ œ์•ˆํ•˜๋Š” ๋ง๋ง‰ ์ž๊ทน๊ธฐ๋Š” ์‹ค๋ฆฌ์ฝ˜ ๋‚˜๋…ธ์™€์ด์–ด ๊ธฐ๋ฐ˜์˜ ๊ด‘ ๊ฒ€์ถœ ๋ฐ ์ž๊ทน ์‹ ํ˜ธ ๋ณ€์กฐํšŒ๋กœ์™€ ๋ฏธ์„ธ ์ „๊ทน ์–ด๋ ˆ์ด๊ฐ€ Nร—N matrix ํ˜•ํƒœ๋กœ ์ง‘์ ๋˜์–ด ์žˆ์œผ๋ฉฐ, ๋ง๋ง‰ ์„ธํฌ์— ์ด์‹์ด ์šฉ์ดํ•˜๋„๋ก ์œ ์—ฐํ•œ ํ˜•ํƒœ๋กœ ์ œ์ž‘๋œ๋‹ค. ๊ฐ ํ”ฝ์…€์—๋Š” 1๊ฐœ์˜ ์‹ค๋ฆฌ์ฝ˜ ๋‚˜๋…ธ์™€์ด์–ด ๊ด‘ ๊ฒ€์ถœ๊ธฐ์™€ 2๊ฐœ์˜ ์‹ค๋ฆฌ์ฝ˜ ๋‚˜๋…ธ์™€์ด์–ด FET(field effect transistor)๋กœ ๊ตฌ์„ฑ๋˜๋Š” ๊ด‘ ๊ฒ€์ถœ ๋ฐ ์ž๊ทน ์‹ ํ˜ธ ๋ณ€์กฐ ํšŒ๋กœ๋ฅผ ๋‚ด์žฅํ•˜๊ณ  ์žˆ์œผ๋ฉฐ, ์‹ ํ˜ธ์ฒ˜๋ฆฌ ์นฉ์—์„œ ์ƒ์„ฑ๋œ ํŽ„์Šค ํ˜•ํƒœ์˜ ๊ธฐ์ค€ ์ž๊ทน ์‹ ํ˜ธ(reference stimulation signal)๊ฐ€ ๊ฐ ํ”ฝ์…€์— ์ „๋‹ฌ๋˜๊ณ , ๊ฐ ํ”ฝ์…€์—์„œ๋Š” ๊ธฐ์ค€ ์ž๊ทน ์‹ ํ˜ธ๋ฅผ ๋น›์˜ ์„ธ๊ธฐ์— ๋น„๋ก€ํ•˜๋Š” ์ง„ํญ์„ ๊ฐ€์ง€๋Š” ์ž๊ทน ์‹ ํ˜ธ๋กœ ๋ณ€์กฐํ•˜์—ฌ ๋ฏธ์„ธ ์ „๊ทน์— ์ „๋‹ฌํ•˜์—ฌ ๋ง๋ง‰ ์‹ ๊ฒฝ์„ ์ž๊ทนํ•œ๋‹ค. ์‹ค๋ฆฌ์ฝ˜ ๋‚˜๋…ธ์™€์ด์–ด ๊ธฐ๋ฐ˜์˜ ๊ด‘ ๊ฒ€์ถœ ๋ฐ ์ž๊ทน ์‹ ํ˜ธ ๋ณ€์กฐ ํšŒ๋กœ๋ฅผ ๊ตฌ์„ฑํ•˜๋Š” ์ „์•• ๋ถ„๋ฐฐ๊ธฐ ๋ฐ ์ „๋ฅ˜ ๊ตฌ๋™๊ธฐ ํšŒ๋กœ๋ฅผ ์ œ์ž‘ํ•˜๊ธฐ ์œ„ํ•œ ๊ธฐ๋ณธ ์†Œ์ž๋กœ์„œ ์‹ค๋ฆฌ์ฝ˜ ๋‚˜๋…ธ์™€์ด์–ด ๊ด‘ ๊ฒ€์ถœ๊ธฐ์™€ ์‹ค๋ฆฌ์ฝ˜ ๋‚˜๋…ธ์™€์ด์–ด FET, ๊ทธ๋ฆฌ๊ณ  ๋ฏธ์„ธ ์ „๊ทน์„ ์ œ์ž‘ํ•˜์—ฌ ํŠน์„ฑ์„ ํ‰๊ฐ€ํ•˜์˜€๋‹ค. ์ œ์ž‘๋œ ์‹ค๋ฆฌ์ฝ˜ ๋‚˜๋…ธ์™€์ด์–ด ๊ด‘ ๊ฒ€์ถœ๊ธฐ๋Š” ๋น›์— ๋Œ€ํ•œ ๊ฐ๋„๊ฐ€ ์ตœ๋Œ€ 1,936์— ์ด๋ฅด๊ณ , ์‘๋‹ต๋„์˜ ๊ฒฝ์šฐ 400 nm ~ 800 nm์˜ ํŒŒ์žฅ ๋ฒ”์œ„์—์„œ 104 ~ 105 A/W์— ์ด๋ฅผ ์ •๋„๋กœ ๋งค์šฐ ์šฐ์ˆ˜ํ•œ ๊ด‘ํ•™์  ์„ฑ๋Šฅ์„ ๋ณด์˜€๋‹ค. ๊ทธ๋ฆฌ๊ณ  ์‹ค๋ฆฌ์ฝ˜ ๋‚˜๋…ธ์™€์ด์–ด FET๋Š” ์‹ค๋ฆฌ์ฝ˜ ๋‚˜๋…ธ์™€์ด์–ด์˜ ๊ฐœ์ˆ˜, ์‹ค๋ฆฌ์ฝ˜ ๋‚˜๋…ธ์™€์ด์–ด์˜ ๊ธธ์ด, ๊ทธ๋ฆฌ๊ณ  FET ๊ตฌ๋™ ์ „์••์„ ์„ค๊ณ„ ํŒŒ๋ผ๋ฏธํ„ฐ๋กœ ํ•˜์—ฌ ์‹ค๋ฆฌ์ฝ˜ ๋‚˜๋…ธ์™€์ด์–ด FET์˜ ํŠน์„ฑ์„ ์กฐ์‚ฌํ•˜์˜€์œผ๋ฉฐ, 103 ์ด์ƒ์˜ on-off ratio์™€ 5 V ๊ตฌ๋™์ „์••์—์„œ ์ตœ๋Œ€ 225 ฮผA์˜ ์ „๋ฅ˜ ๋ ˆ๋ฒจ์„ ๋ณด์˜€๋‹ค. ๊ณ ๋ฐ€๋„ํ™”์— ๋”ฐ๋ฅธ ์ „๊ทน์˜ ์†Œํ˜•ํ™”์—๋„ ๋ถˆ๊ตฌํ•˜๊ณ  ์ถฉ๋ถ„ํ•œ ์ „๋ฅ˜ ์ฃผ์ž… ์šฉ๋Ÿ‰์„ ํ™•๋ณดํ•˜๊ธฐ ์œ„ํ•œ ๋ฐฉ๋ฒ•์œผ๋กœ ์›ํ†ตํ˜•์˜ Au ์ „๊ทน์˜ ํ‘œ๋ฉด์— ์ „์ฃผ๋„๊ธˆ๊ณต์ •์œผ๋กœ 5,000 โ„ซ ๋‘๊ป˜์˜ nano-porousํ•œ Pt-black์ธต์„ ํ˜•์„ฑํ•จ์œผ๋กœ์จ ๋„“์€ ํ‘œ๋ฉด์ ์„ ๊ฐ€์ง„ ๊ณ ๋ฐ€๋„ ๋ฏธ์„ธ ์ „๊ทน ์ œ์ž‘์ด ๊ฐ€๋Šฅํ•œ ๋‚˜๋…ธ 3D ๋ฏธ์„ธ ์ „๊ทน์„ ์ œ์ž‘ํ•˜์˜€๋‹ค. ์‹ค๋ฆฌ์ฝ˜ ๋‚˜๋…ธ์™€์ด์–ด ๊ด‘ ๊ฒ€์ถœ๊ธฐ์™€ ์‹ค๋ฆฌ์ฝ˜ ๋‚˜๋…ธ์™€์ด์–ด FET ์†Œ์ž๋ฅผ ์ œ์ž‘ํ•˜์—ฌ ๋ง๋ง‰ ์ž๊ทน๊ธฐ์˜ ์ „์•• ๋ถ„๋ฐฐ๊ธฐ ๋ฐ ์ „๋ฅ˜ ๊ตฌ๋™๊ธฐ ํšŒ๋กœ๋ฅผ ๊ตฌ์„ฑํ•˜๊ณ  ๊ฐ๊ฐ์˜ ํšŒ๋กœ์˜ ๋™์ž‘์„ ์กฐ์‚ฌํ•จ์œผ๋กœ์จ ๋ณธ ๋…ผ๋ฌธ์—์„œ ์ œ์•ˆํ•˜๋Š” ๊ด‘ ๊ฒ€์ถœ ๋ฐ ์ž๊ทน ์‹ ํ˜ธ ๋ณ€์กฐ์˜ ์›๋ฆฌ๊ฐ€ ์ž˜ ์ ์šฉ๋จ์„ ํ™•์ธํ•˜์˜€๋‹ค. ์ œ์•ˆํ•˜๋Š” ๋ง๋ง‰ ์ž๊ทน๊ธฐ์˜ ๊ณ ํ•ด์ƒ๋„ ๋ง๋ง‰ ์‹œ์Šคํ…œ์œผ๋กœ์˜ ์ ์šฉ ๊ฐ€๋Šฅ์„ฑ ๊ฒ€ํ† ๋ฅผ ์œ„ํ•ด 32ร—32์˜ ๊ณ ํ•ด์ƒ๋„ ๋ง๋ง‰ ์ž๊ทน๊ธฐ๋ฅผ ์„ค๊ณ„, ์ œ์ž‘ํ•˜์˜€๋‹ค. ์ œ์ž‘๋œ ๋ง๋ง‰ ์ž๊ทน๊ธฐ์—๋Š” ์•ฝ 40 ฮผm ๋‘๊ป˜์˜ ๋งค์šฐ ์–‡์€ flexibleํ•œ ํด๋ฆฌ์ด๋ฏธ๋“œ ํ•„๋ฆ„ ๋‚ด์— ๋‹จ์œ„ ํ”ฝ์…€์˜ ํฌ๊ธฐ๊ฐ€ 110 ฮผm ร— 110 ฮผm์ธ ์‹ค๋ฆฌ์ฝ˜ ๋‚˜๋…ธ์™€์ด์–ด ๊ธฐ๋ฐ˜์˜ ๊ด‘ ๊ฒ€์ถœ ๋ฐ ์ž๊ทน ์‹ ํ˜ธ ๋ณ€์กฐ ํšŒ๋กœ๊ฐ€ ์ง‘์ ๋˜์—ˆ๋‹ค. ์ œ์•ˆํ•˜๋Š” ๋ง๋ง‰ ์ž๊ทน๊ธฐ ๋ฐ ๋ง๋ง‰ ์‹ ๊ฒฝ ์ž๊ทน ๊ธฐ๋ฒ•์˜ ์œ ํšจ์„ฑ์„ ํ‰๊ฐ€ํ•˜๊ธฐ ์œ„ํ•ด in-vitro ๋™๋ฌผ ์‹คํ—˜์„ ์‹ค์‹œํ•˜์˜€๋‹ค. In-vitro ๋™๋ฌผ์‹คํ—˜์—์„œ๋Š” ๋น›์˜ ์„ธ๊ธฐ์— ๋”ฐ๋ฅธ ์ž๊ทน ์‹ ํ˜ธ์˜ ๋ณ€์กฐ๋ฅผ ํ†ตํ•ด ๋ง๋ง‰ ์‹ ๊ฒฝ์œผ๋กœ ์˜ ์ฃผ์ž… ์ „ํ•˜๋Ÿ‰์˜ ์กฐ์ ˆ์ด ๊ฐ€๋Šฅํ•˜๋ฉฐ, ์‹คํ—˜ ๊ฒฐ๊ณผ ์•ฝ 10 nC ์ด์ƒ์˜ ์ฃผ์ž… ์ „ํ•˜๋Ÿ‰์—์„œ ๋ง๋ง‰ ์‹ ๊ฒฝ์˜ ์œ ํšจ ์ž๊ทน์ด ์ผ์–ด๋‚จ์„ ๊ด€์ฐฐํ•  ์ˆ˜ ์žˆ์—ˆ์œผ๋ฉฐ, ์ด๋ฅผ ํ†ตํ•ด ๋น›์˜ ๊ฒ€์ถœ ๋ฐ ์ž๊ทน ์‹ ํ˜ธ ๋ณ€์กฐ๋ฅผ ํ†ตํ•œ ๋ง๋ง‰ ์‹ ๊ฒฝ์˜ ์ž๊ทน์ด ํšจ๊ณผ์ ์œผ๋กœ ์ž˜ ์ด๋ฃจ์–ด์ง์„ ํ™•์ธํ•  ์ˆ˜ ์žˆ์—ˆ๋‹ค.์ œ 1 ์žฅ ์„œ๋ก  ์ œ 1 ์ ˆ ์—ฐ๊ตฌ ๋ฐฐ๊ฒฝ ์ œ 2 ์ ˆ ๊ณ ํ•ด์ƒ๋„ ์ธ๊ณต๋ง๋ง‰ ์‹œ์Šคํ…œ์˜ ๊ตฌํ˜„ ์ œ 3 ์ ˆ ์—ฐ๊ตฌ ๋™๊ธฐ ์ œ 4 ์ ˆ ๋…ผ๋ฌธ ๋‚ด์šฉ ์š”์•ฝ ๋ฐ ๋…ผ๋ฌธ์˜ ๊ตฌ์„ฑ ์ œ 2 ์žฅ ๋ณธ๋ก  ์ œ 1 ์ ˆ ์‹ค๋ฆฌ์ฝ˜ ๋‚˜๋…ธ์™€์ด์–ด ๊ด‘ ๊ฒ€์ถœ๊ธฐ๊ฐ€ ๋‚ด์žฅ๋œ ๊ณ ํ•ด์ƒ๋„ ๋ง๋ง‰ ์ž๊ทน๊ธฐ 1. ๊ด‘ ๊ฒ€์ถœ๊ธฐ๊ฐ€ ๋‚ด์žฅ๋œ ๊ณ ํ•ด์ƒ๋„ ์ธ๊ณต ๋ง๋ง‰ ์‹œ์Šคํ…œ์˜ ๊ตฌ์„ฑ 2. ์‹ค๋ฆฌ์ฝ˜ ๋‚˜๋…ธ์™€์ด์–ด ๊ธฐ๋ฐ˜์˜ ๊ด‘ ๊ฒ€์ถœ ๋ฐ ์ž๊ทน ์‹ ํ˜ธ ๋ณ€์กฐ ํšŒ๋กœ์˜ ๋™์ž‘ ์›๋ฆฌ ๋ฐ ๋ง๋ง‰ ์‹ ๊ฒฝ ์ž๊ทน ๊ธฐ๋ฒ• ์ œ 2 ์ ˆ ์‹ค๋ฆฌ์ฝ˜ ๋‚˜๋…ธ์™€์ด์–ด ๊ธฐ๋ฐ˜์˜ ๊ด‘ ๊ฒ€์ถœ ํšŒ๋กœ๊ฐ€ ๋‚ด์žฅ๋œ ๋ง๋ง‰ ์ž๊ทน๊ธฐ์˜ ์„ค๊ณ„ 1. ๋‚ด๋ถ€ ๊ด‘ ๊ฒ€์ถœ๊ธฐ๋ฅผ ์ด์šฉํ•˜๋Š” ๋ฐฉ์‹์˜ ๋ง๋ง‰ ์ž๊ทน๊ธฐ์˜ ์„ค๊ณ„ 2. ๋‚ด๋ถ€ ๊ด‘ ๊ฒ€์ถœ๊ธฐ์™€ ์™ธ๋ถ€ ์นด๋ฉ”๋ผ๋ฅผ ์„ ํƒ์ ์œผ๋กœ ์ด์šฉํ•  ์ˆ˜ ์žˆ๋Š” ๋ฐฉ์‹์˜ ๋ง๋ง‰ ์ž๊ทน๊ธฐ์˜ ์„ค๊ณ„ ์ œ 3 ์ ˆ ๋ง๋ง‰ ์ž๊ทน๊ธฐ ๊ฐ ๊ตฌ์„ฑ ์š”์†Œ๋ณ„ ์†Œ์ž ์ œ์ž‘ ๋ฐ ํŠน์„ฑ ํ‰๊ฐ€ 1. ์‹ค๋ฆฌ์ฝ˜ ๋‚˜๋…ธ์™€์ด์–ด์˜ ์ œ์ž‘ 2. ์‹ค๋ฆฌ์ฝ˜ ๋‚˜๋…ธ์™€์ด์–ด ๊ด‘ ๊ฒ€์ถœ๊ธฐ ์ œ์ž‘ ๋ฐ ํŠน์„ฑ ํ‰๊ฐ€ 3. ์‹ค๋ฆฌ์ฝ˜ ๋‚˜๋…ธ์™€์ด์–ด FET ์ œ์ž‘ ๋ฐ ํŠน์„ฑ ํ‰๊ฐ€ 4. ๊ณ ๋ฐ€๋„ ๋ฏธ์„ธ ์ „๊ทน์„ ์œ„ํ•œ ๋‚˜๋…ธ 3D ์ „๊ทน ์ œ์ž‘ ์ œ 4 ์ ˆ ์‹ค๋ฆฌ์ฝ˜ ๋‚˜๋…ธ์™€์ด์–ด ๊ธฐ๋ฐ˜์˜ ๊ด‘ ๊ฒ€์ถœ ๋ฐ ์ž๊ทน ์‹ ํ˜ธ ๋ณ€์กฐ ํšŒ๋กœ ์ œ์ž‘ ๋ฐ ํŠน์„ฑ ํ‰๊ฐ€ 1. ์ „์•• ๋ถ„๋ฐฐ๊ธฐ ๋™์ž‘ ์‹œํ—˜ 2. ์ „๋ฅ˜ ๊ตฌ๋™๊ธฐ ๋™์ž‘ ์‹œํ—˜ ์ œ 5 ์ ˆ ์‹ค๋ฆฌ์ฝ˜ ๋‚˜๋…ธ์™€์ด์–ด ๊ด‘ ๊ฒ€์ถœ๊ธฐ๊ฐ€ ๋‚ด์žฅ๋œ 32ร—32 ๊ณ ํ•ด์ƒ๋„ ๋ง๋ง‰ ์ž๊ทน๊ธฐ์˜ ์„ค๊ณ„ ๋ฐ ์ œ์ž‘ 1. 32x32 ๊ณ ํ•ด์ƒ๋„ ๋ง๋ง‰ ์ž๊ทน๊ธฐ์˜ ์„ค๊ณ„ 2. 32x32 ๊ณ ํ•ด์ƒ๋„ ๋ง๋ง‰ ์ž๊ทน๊ธฐ์˜ ์ œ์ž‘ ์ œ 6 ์ ˆ In-vitro ๋™๋ฌผ ์‹คํ—˜์„ ํ†ตํ•œ ๋ง๋ง‰ ์ž๊ทน๊ธฐ์˜ ์œ ํšจ์„ฑ ํ‰๊ฐ€ 1. In-vitro ๋™๋ฌผ ์‹คํ—˜ ์žฅ์น˜ ์…‹์—… ๋ฐ ๋ง๋ง‰ ์‹ ๊ฒฝ ์ž๊ทน ์‹คํ—˜ 2. ์ž๊ทน ์‹ ํ˜ธ์˜ ๋ถ„์„ ๋ฐ ๋ง๋ง‰ ์ž๊ทน์˜ ์œ ํšจ์„ฑ ํ‰๊ฐ€ ์ œ 3 ์žฅ ๊ฒฐ๋ก  ์ œ 1 ์ ˆ ๊ฒฐ๊ณผ ์š”์•ฝ ์ œ 2 ์ ˆ ํ–ฅํ›„ ๊ณ„ํš ์ฐธ๊ณ ๋ฌธํ—Œ AbstractDocto

    Dielectrophoresis Control of Semiconductor Nanowires for Sensing Technology

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    Semiconductor nanowires (NWs) synthesis successes have given keys to unprecedented nano-scale sensitivity opening up new opportunities in device applications. NWsโ€™ potential relies upon the possibility of engineering and modifying properties such as sensitivity and carrier transport, by tailoring the NWsโ€™ morphology and conductivity. New challenges have taken place with the downscaling of electronics for NWs integration and assembly techniques. Amongst a large variety of integration techniques, dielectrophoresis (DEP) is a powerful tool for the precise manipulation of NWs of different compositions and sizes. However, experimental implementation and analysis with DEP often lack depth regarding the optimisation of the technique and the effects of the parameters on the performances of the final devices, which is crucial for the understanding of NWsโ€™ electric transport properties and technology improvement. Consequently, this thesis presents a comprehensive study of the experimental implementation of DEP which is of paramount importance to obtaining optimum conditions for NWs alignment. With this aim in mind, the presented work demonstrates a detailed investigation of the electrical and optical properties of germanium (Ge) and gallium-arsenide-bismuth (GaAsBi) NWs-based devices by DEP as a function of the collection frequency. The Ge and GaAsBi NWs were obtained by MOVPE and MBE respectively as a collaborative work with the Institute of Material for Electronic and Magnet (Italy) for the Ge NWs, and with the research team of Dr Robert Richard at the University of Sheffield (Department of Electrical Engineering and Electronics) for the GaAsBi NWs. Firstly, to maximise NWs alignment precision, optimum DEP parameters are for the first time thoroughly extracted by testing the effects of different mediums (chemical inertia, volatility and contact angle) and electrode designs (gradients and electric field). Secondly, fabricated with a DEP frequency range of 500 kHz to 10 MHz the devices were electrically characterised using voltage-current response. An asymmetric diode-like behaviour was found to be originating from heterostructured Ge NWs specifically orientated by electrophoresis combined with DEP. This result is particularly promising for orientation control demonstrated for the first time, tuning and altering current response from chemically heterostructured nanowires. A particular focus was given to the effect of increasing frequency on the device performances such as carrier transport. Despite a decrease of aligned NWs corroborating theoretical analysis, increasing frequency collected higher conductivity Ge NWs with carrier mobility improving from 2ฮธ at 500 kHz to 4.38ฮธ at 10 MHz demonstrated using Mott-Gurney, and GaAsBi NWs with carrier mobility increasing from 5.29 ยฑ 0.027 to 100 ยฑ 0.70 cm2 Vโˆ’1.sโˆ’1 at 500 kHz and 10 MHz demonstrated using the Fermi-velocity law. Such selectivity is of great potential to improve sensing technology transduction. Using optimum parameters previously found, a low-cost and simple voltage divider system joined to DEP is demonstrated for the first time to improve the alignment technique of a single Ge nanowire. The resulting spectral response was consistent with optical characterisations found in the literature for a single Ge nanowire and demonstrated high sensitivity near-infrared and communication wavelength as confirmed with a high responsivity of 6.2 x 105 A/W at 1550 nm. Such high resistivity is amongst the highest ever obtained for NWs. Furthermore, a NWs-based biosensor for the spike protein of the SARS-CoV-2 was fabricated by multilayered surface functionalisation evidenced by Raman spectroscopy. Upon exposure to increasing concentration of the protein, the biosensors transduced increasing current response with a working range of at least 1 aM to 100 fM. Selectivity to the spike protein was testified using bovine serum albumin as a negative control reference. The GaAsBi NWs were for the first time fully characterised and implemented as devices by DEP. The NWs surface roughness showcased the importance of surface properties that influenced DEP collection and carrier transport. Spectral responses from the devices brought to light the different bismuth content at the origin of reduced band-gap energy shown by the cut-off energies of the spectrum. With a Bi content increase of roughly 1% in GaAs the photodetectors presented high responsivity from 1.3 x 104 A/W to 5.6 x 104 A/W. Effective NWs-based biosensors and photodetectors were proof of concept devices that corroborate NWs and dielectrophoresis functionality paving the way to future nanotechnology improvement
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