{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,8,18]],"date-time":"2026-08-18T04:54:13Z","timestamp":1787028853452,"version":"build-2736575974"},"reference-count":34,"publisher":"MDPI AG","issue":"7","license":[{"start":{"date-parts":[[2025,3,22]],"date-time":"2025-03-22T00:00:00Z","timestamp":1742601600000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"Korea Technology and Information Promotion Agency","award":["RS-2024-00467765"],"award-info":[{"award-number":["RS-2024-00467765"]}]},{"name":"Korea Technology and Information Promotion Agency","award":["RS-2024-00456813"],"award-info":[{"award-number":["RS-2024-00456813"]}]},{"name":"Commercialization Promotion Agency for R&amp;D Outcomes of Korea","award":["RS-2024-00467765"],"award-info":[{"award-number":["RS-2024-00467765"]}]},{"name":"Commercialization Promotion Agency for R&amp;D Outcomes of Korea","award":["RS-2024-00456813"],"award-info":[{"award-number":["RS-2024-00456813"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Materials"],"abstract":"<jats:p>Silk fibroin, a biocompatible and flexible biopolymer derived from Bombyx mori silkworms, has shown promise in bioelectronics, due to its adjustable dielectric properties. This study investigates the influence of spin coating parameters on the optical, electrical, and dielectric properties of thin silk fibroin films. Silk fibroin solutions were spin coated onto indium tin oxide (ITO)\/glass substrates at speeds ranging from 1000 to 7000 revolutions per minute (RPM), resulting in films with thicknesses that varied from 264.8 nm to 81.9 nm. Atomic force microscopy analysis revealed that the surface roughness remained consistent at approximately 1.5 nm across all the spin coating speeds, while the film thickness decreased with the increasing spin speed. Ultraviolet (UV)\u2013visible spectroscopy showed that the transmittance at 550 nm increased from 81.2% at 1000 RPM to 93.8% at 7000 RPM, and the optical bandgap widened from 3.82 eV at 1000 RPM to 3.92 eV at 7000 RPM, which was attributed to reduced molecular packing and quantum confinement effects. Electrical characterization showed that thinner films (a spin speed of 5000\u20137000 RPM) exhibited a 15-fold increase in the leakage current, rising from 2.99 pA at 1000 RPM to 44.9 pA at 7000 RPM, and a decrease in resistance from 334 G\u03a9 at 1000 RPM to 22.2 G\u03a9 at 7000 RPM. The capacitance\u2013voltage measurements indicated a 4-fold increase in voltage-dependent capacitance for thinner films, with capacitance values increasing from 36 pF at 1000 RPM to 176 pF at 7000 RPM. Dielectric loss analysis revealed that thinner films experienced higher energy dissipation at low frequencies (tan \u03b4 of 0.041 at 0.01 MHz for 7000 RPM), but lower losses at high frequencies (tan \u03b4 of 0.123 at 1 MHz for 7000 RPM). These findings emphasize the importance of film thickness control in optimizing the performance of silk fibroin-based bioelectronic devices.<\/jats:p>","DOI":"10.3390\/ma18071408","type":"journal-article","created":{"date-parts":[[2025,3,24]],"date-time":"2025-03-24T04:48:18Z","timestamp":1742791698000},"page":"1408","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":8,"title":["Capacitance and Dielectric Properties of Spin-Coated Silk Fibroin Thin Films for Bioelectronic Capacitors"],"prefix":"10.3390","volume":"18","author":[{"given":"Jongyun","family":"Choi","sequence":"first","affiliation":[{"name":"Department of IT Semiconductor Convergence Engineering, Tech University of Korea, Siheung 15073, Republic of Korea"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Seung Hun","family":"Lee","sequence":"additional","affiliation":[{"name":"Department of IT Semiconductor Convergence Engineering, Tech University of Korea, Siheung 15073, Republic of Korea"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0009-0007-9666-5945","authenticated-orcid":false,"given":"Taehun","family":"Kim","sequence":"additional","affiliation":[{"name":"Department of IT Semiconductor Convergence Engineering, Tech University of Korea, Siheung 15073, Republic of Korea"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-7626-043X","authenticated-orcid":false,"given":"Kyungtaek","family":"Min","sequence":"additional","affiliation":[{"name":"Department of IT Semiconductor Convergence Engineering, Tech University of Korea, Siheung 15073, Republic of Korea"},{"name":"Department of Semiconductor Engineering, Tech University of Korea, Siheung 15073, Republic of Korea"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-4800-5199","authenticated-orcid":false,"given":"Sung-Nam","family":"Lee","sequence":"additional","affiliation":[{"name":"Department of IT Semiconductor Convergence Engineering, Tech University of Korea, Siheung 15073, Republic of Korea"},{"name":"Department of Semiconductor Engineering, Tech University of Korea, Siheung 15073, Republic of Korea"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2025,3,22]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"86","DOI":"10.1016\/j.progpolymsci.2015.02.001","article-title":"Structure, mechanical properties and applications of silk fibroin materials","volume":"46","author":"Koh","year":"2015","journal-title":"Prog. Polym. Sci."},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"2210764","DOI":"10.1002\/adfm.202210764","article-title":"Silk fibroin as sustainable advanced materials: Mterial properties and characteristics, processing and applications","volume":"33","author":"Reizabal","year":"2022","journal-title":"Adv. Funct. Mater."},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"1238","DOI":"10.1039\/D0TB02099K","article-title":"Functional silk fibroin hydrogels; preparation, properties, and applications","volume":"9","author":"Zheng","year":"2021","journal-title":"J. Mater. Chem. B"},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"4250","DOI":"10.1002\/adma.201504276","article-title":"Silk fibroin for flexible electronic devices","volume":"28","author":"Zhu","year":"2016","journal-title":"Adv. Mater."},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"2301924","DOI":"10.1002\/adfm.202301924","article-title":"Eco-friendly transparent silk fibroin radiative cooling film for thermal management of optoelectronics","volume":"33","author":"Chen","year":"2023","journal-title":"Adv. Funct. Mater."},{"key":"ref_6","doi-asserted-by":"crossref","unstructured":"Santhosh Kumar Gunapu, D.V., Bhavani Prasad, Y., Sushma Mudigunda, V., Yasam, P., Rengan, A.K., Korla, R., and Vanjari, S.R.K. (2021). Development of robust, ultra-smooth, flexible and transparent regenerated silk composite films for bio-integrated electronic device applications. Int. J. Biol. Macromol., 176.","DOI":"10.1016\/j.ijbiomac.2021.02.051"},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"2300176","DOI":"10.1002\/admi.202300176","article-title":"High-efficiency ZnO-based ultraviolet photodetector with integrated single-walled carbon nanotube thin-film heater","volume":"10","author":"Kim","year":"2023","journal-title":"Adv. Mater. Interfaces"},{"key":"ref_8","doi-asserted-by":"crossref","unstructured":"Lee, S.H., Lee, H.J., Jeon, D.B., Kim, H.J., and Lee, S.N. (2024). Enhancing long-term memory in carbon-nanotube-based optoelectronic synaptic devices for neuromorphic computing. Nanomaterials, 14.","DOI":"10.3390\/nano14181501"},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"26381","DOI":"10.1021\/acsami.5b08786","article-title":"Antiferroelectric thin-film capacitors with high energy-storage densities, low energy losses, and fast discharge times","volume":"7","author":"Ahn","year":"2015","journal-title":"ACS Appl. Mater. Interfaces"},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"1974","DOI":"10.1007\/s11664-022-09485-y","article-title":"Review of thin film transistor gas sensors: Comparison with resistive and capacitive sensors","volume":"51","author":"Singh","year":"2022","journal-title":"J. Electron. Mater."},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"3935","DOI":"10.1111\/j.1551-2916.2010.04211.x","article-title":"Processing technologies for high-permittivity thin films in capacitor applications","volume":"93","author":"Brennecka","year":"2010","journal-title":"J. Am. Ceram. Soc."},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"061605","DOI":"10.1063\/1.3055416","article-title":"Leakage current evolution versus dielectric thickness in lead zirconate titanate thin film capacitors","volume":"105","author":"Chentir","year":"2009","journal-title":"J. Appl. Phys."},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"074102","DOI":"10.1063\/1.2713934","article-title":"Thickness dependence of intrinsic dielectric response and apparent interfacial capacitance in ferroelectric thin films","volume":"101","author":"Pertsev","year":"2007","journal-title":"J. Appl. Phys."},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"2721","DOI":"10.1103\/PhysRevB.32.2721","article-title":"Dipole-dipole-interaction-induced line narrowing in thin-film vibrational-mode spectra","volume":"32","author":"Schlesinger","year":"1985","journal-title":"Phys. Rev. B"},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"15913","DOI":"10.1039\/D0RA02634D","article-title":"Influence of alcohol treatment on properties of silk-fibroin-based films for highly optically transparent coating applications","volume":"10","author":"Kaewpirom","year":"2020","journal-title":"RSC Adv."},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"40792","DOI":"10.1039\/C9RA07391D","article-title":"Nanopatterned silk fibroin films with high transparency and high hazy for optical applications","volume":"9","author":"Malinowski","year":"2019","journal-title":"RSC Adv."},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"248","DOI":"10.1063\/1.1534411","article-title":"Polarization dynamics and retention loss in fatigued PbZr0.4Ti0.6O3 ferroelectric capacitors","volume":"82","author":"Kang","year":"2003","journal-title":"Appl. Phys. Lett."},{"key":"ref_18","doi-asserted-by":"crossref","first-page":"3380","DOI":"10.1063\/1.121610","article-title":"Built-in voltages and asymmetric polarization switching in Pb(Zr,Ti)O3 thin film capacitors","volume":"72","author":"Lee","year":"1998","journal-title":"Appl. Phys. Lett."},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"1901","DOI":"10.1021\/acsaelm.2c00100","article-title":"Silk fibroin nanocomposites with indium thin oxide toward sustainable capacitive touch sensing applications","volume":"4","author":"Reizabai","year":"2022","journal-title":"ACS Appl. Electron. Mater."},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"108927","DOI":"10.1016\/j.compscitech.2021.108927","article-title":"Broadband dielectric response of silk fibroin\/BaTiO3 composite: Influence of nanoparticles size and concentration","volume":"213","author":"Costa","year":"2021","journal-title":"Compos. Sci. Technol."},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"1172","DOI":"10.3103\/S1062873820090087","article-title":"Frequency management of the capacitance and conductivity of a dielectric upon relaxation polarization","volume":"84","author":"Bogatin","year":"2020","journal-title":"Bull. Russ. Acad. Sci. Phys."},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"1062","DOI":"10.1109\/TMTT.2003.809693","article-title":"Measurement of the dielectric constant and loss tangent of high dielectric-constant materials at terahertz frequencies","volume":"51","author":"Bolivar","year":"2003","journal-title":"IEEE Trans. Microw. Theory Tech."},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"2100199","DOI":"10.1002\/adhm.202100199","article-title":"Recent advances of energy solutions for implantable bioelectronics","volume":"10","author":"Sheng","year":"2021","journal-title":"Adv. Healthc. Mater."},{"key":"ref_24","doi-asserted-by":"crossref","unstructured":"Min, K., Kim, S., Kim, C.G., and Kim, S.H. (2017). Colored and fluorescent nanofibrous silk as a physically transient chemosensor and vitamin deliverer. Sci. Rep., 7.","DOI":"10.1038\/s41598-017-05842-8"},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"2229","DOI":"10.1002\/adfm.200601136","article-title":"Mechanical properties of robust ultrathin silk fibroin films","volume":"17","author":"Jiang","year":"2007","journal-title":"Adv. Funct. Mater."},{"key":"ref_26","doi-asserted-by":"crossref","first-page":"39268","DOI":"10.1039\/C4RA05873A","article-title":"Charge transport behaviors of end-capped narrow band gap polymers in bottom-contact organic field-effect transistor","volume":"4","author":"Kim","year":"2014","journal-title":"RSC Adv."},{"key":"ref_27","doi-asserted-by":"crossref","first-page":"5355","DOI":"10.1063\/1.1814429","article-title":"Quantum confinement effect of silicon nanocrystals in situ grown in silicon nitride films","volume":"85","author":"Kim","year":"2004","journal-title":"Appl. Phys. Lett."},{"key":"ref_28","doi-asserted-by":"crossref","first-page":"6351","DOI":"10.1039\/D4TB00112E","article-title":"Dry and wet wrinkle of a silk fibroin biopolymer by a shape-memory materials with insight into mechanical effects on secondary structures in the silk network","volume":"12","author":"Oguntade","year":"2024","journal-title":"J. Mater. Chem. B"},{"key":"ref_29","doi-asserted-by":"crossref","first-page":"251","DOI":"10.1063\/1.353897","article-title":"Capacitance-voltage profiling through graded heterojunctions: Theory and experiment","volume":"73","author":"Sundaram","year":"1993","journal-title":"J. Appl. Phys."},{"key":"ref_30","doi-asserted-by":"crossref","first-page":"688","DOI":"10.1016\/j.microrel.2016.07.027","article-title":"An in depth analysis of pull-up capacitance-voltage characteristics for dielectric charging assessment of MEMS capacitive switches","volume":"64","author":"Koutsoureli","year":"2016","journal-title":"Microelectron. Reliab."},{"key":"ref_31","doi-asserted-by":"crossref","first-page":"142906","DOI":"10.1063\/1.2719618","article-title":"Modeling of nonlinearities in the capacitance-voltage characteristics of high-k metal-insulator-metal capacitors","volume":"90","author":"Gonon","year":"2007","journal-title":"Appl. Phys. Lett."},{"key":"ref_32","doi-asserted-by":"crossref","first-page":"477","DOI":"10.1109\/95.311759","article-title":"Form and capacitance of parallel-plate capacitors","volume":"17","author":"Nishiyama","year":"1994","journal-title":"IEEE Trans. Compon. Packag. Manuf. Technol. A"},{"key":"ref_33","doi-asserted-by":"crossref","unstructured":"Liu, Q., Wang, F., Gu, Z., Ma, Q., and Hu, X. (2018). Exploring the structural transformation mechanism of Chinese and Thailand silk fibroin fibers and formic-acid fabricated silk films. Int. J. Mol. Sci., 19.","DOI":"10.3390\/ijms19113309"},{"key":"ref_34","doi-asserted-by":"crossref","unstructured":"Guan, J., Porter, D., and Vollrath, F. (2013). Thermally induced changes in dynamic mechanical properties of native silks. Biomacromolecules, 14.","DOI":"10.1021\/bm400012k"}],"container-title":["Materials"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/1996-1944\/18\/7\/1408\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,9]],"date-time":"2025-10-09T16:58:27Z","timestamp":1760029107000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/1996-1944\/18\/7\/1408"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2025,3,22]]},"references-count":34,"journal-issue":{"issue":"7","published-online":{"date-parts":[[2025,4]]}},"alternative-id":["ma18071408"],"URL":"https:\/\/doi.org\/10.3390\/ma18071408","relation":{},"ISSN":["1996-1944"],"issn-type":[{"value":"1996-1944","type":"electronic"}],"subject":[],"published":{"date-parts":[[2025,3,22]]}}}