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Al2O3 ultra-thin films were deposited by PEALD to improve the rubidium optically pumped atomic magnetometers\u2019 (OPMs) cell lifetime. This requirement is due to the consumption of the alkali metal (rubidium) inside the vapor cells. Moreover, as a silicon wafer was used, an on-chip photodiode was already integrated into the fabrication of the OPM. The ALD parameters were achieved with a GPC close to 1.2 \u00c5\/cycle and the ALD window threshold at 250 \u00b0C. The PEALD Al2O3 ultra-thin films showed a refractive index of 1.55 at 795 nm (tuned to the D1 transition of rubidium for spin-polarization of the atoms). The EDS chemical elemental analysis showed an atomic percentage of 58.65% for oxygen (O) and 41.35% for aluminum (Al), with a mass percentage of 45.69% for O and 54.31% for Al. A sensitive XPS surface elemental composition confirmed the formation of the PEALD Al2O3 ultra-thin film with an Al 2s peak at 119.2 eV, Al 2p peak at 74.4 eV, and was oxygen rich. The SEM analysis presented a non-uniformity of around 3%. Finally, the rubidium consumption in the coated OPM was monitored. Therefore, PEALD Al2O3 ultra-thin films were deposited while controlling their optical refractive index, crystalline properties, void fraction, surface roughness and thickness uniformity (on OPM volume 1 mm \u00d7 1 mm \u00d7 0.180 mm cavity etched by RIE), as well as the chemical composition for improving the rubidium OPM lifetime.<\/jats:p>","DOI":"10.3390\/coatings13030638","type":"journal-article","created":{"date-parts":[[2023,3,20]],"date-time":"2023-03-20T05:46:42Z","timestamp":1679291202000},"page":"638","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":9,"title":["Al2O3 Ultra-Thin Films Deposited by PEALD for Rubidium Optically Pumped Atomic Magnetometers with On-Chip Photodiode"],"prefix":"10.3390","volume":"13","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-2633-1233","authenticated-orcid":false,"given":"Florival M.","family":"Cunha","sequence":"first","affiliation":[{"name":"Center for Microelectromechanical Systems\u2014CMEMS-UMinho, Department of Industrial Electronics, University of Minho, 4800-058 Guimar\u00e3es, Portugal"},{"name":"LABBELS\u2014Associate Laboratory, 4800-122 Braga, Portugal"}]},{"given":"Manuel F.","family":"Silva","sequence":"additional","affiliation":[{"name":"Center for Microelectromechanical Systems\u2014CMEMS-UMinho, Department of Industrial Electronics, University of Minho, 4800-058 Guimar\u00e3es, Portugal"},{"name":"LABBELS\u2014Associate Laboratory, 4800-122 Braga, Portugal"}]},{"given":"Nuno M.","family":"Gomes","sequence":"additional","affiliation":[{"name":"Center for Microelectromechanical Systems\u2014CMEMS-UMinho, Department of Industrial Electronics, University of Minho, 4800-058 Guimar\u00e3es, Portugal"},{"name":"LABBELS\u2014Associate Laboratory, 4800-122 Braga, Portugal"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-5991-1069","authenticated-orcid":false,"given":"Jos\u00e9 H.","family":"Correia","sequence":"additional","affiliation":[{"name":"Center for Microelectromechanical Systems\u2014CMEMS-UMinho, Department of Industrial Electronics, University of Minho, 4800-058 Guimar\u00e3es, Portugal"},{"name":"LABBELS\u2014Associate Laboratory, 4800-122 Braga, Portugal"}]}],"member":"1968","published-online":{"date-parts":[[2023,3,17]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"598","DOI":"10.1016\/j.neuroimage.2019.05.063","article-title":"Optically Pumped Magnetometers: From Quantum Origins to Multi-Channel Magnetoencephalography","volume":"199","author":"Tierney","year":"2019","journal-title":"Neuroimage"},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"025013","DOI":"10.1088\/0960-1317\/22\/2\/025013","article-title":"Microfabricated Rubidium Vapour Cell with a Thick Glass Core for Small-Scale Atomic Clock Applications","volume":"22","author":"Affolderbach","year":"2012","journal-title":"J. Micromech. Microeng."},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"8153","DOI":"10.1088\/0031-9155\/58\/22\/8153","article-title":"A Compact, High Performance Atomic Magnetometer for Biomedical Applications","volume":"58","author":"Shah","year":"2013","journal-title":"Phys. Med. Biol."},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"158","DOI":"10.1016\/j.surfcoat.2013.01.044","article-title":"Lifetime Improvement of Micro-Fabricated Alkali Vapor Cells by Atomic Layer Deposited Wall Coatings","volume":"221","author":"Woetzel","year":"2013","journal-title":"Surf. Coat. Technol."},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"2187","DOI":"10.1364\/OE.25.002187","article-title":"Lifetime Assessment of RbN3-Filled MEMS Atomic Vapor Cells with Al2O3 Coating","volume":"25","author":"Karlen","year":"2017","journal-title":"Opt. 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B"},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"76","DOI":"10.1149\/1.3276040","article-title":"Influence of the Deposition Temperature on the C-Si Surface Passivation by Al2O3 Films Synthesized by ALD and PECVD","volume":"13","author":"Dingemans","year":"2010","journal-title":"Electrochem. Solid-State Lett."},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"G165","DOI":"10.1149\/1.2737629","article-title":"Plasma and Thermal ALD of Al2O3 in a Commercial 200 mm ALD Reactor","volume":"154","author":"Heil","year":"2007","journal-title":"J. Electrochem. Soc."},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"2846","DOI":"10.1016\/j.surfcoat.2010.10.052","article-title":"The influence of substrate on the adhesion behaviors of atomic layer deposited aluminum oxide films","volume":"205","author":"Ding","year":"2011","journal-title":"Surf. Coat. Technol."},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"216","DOI":"10.1016\/S0040-6090(02)01262-2","article-title":"Crystallization behavior of thin ALD-Al2O3 films","volume":"425","author":"Jakschik","year":"2003","journal-title":"Thin Solid Film."},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"600","DOI":"10.3390\/ma8020600","article-title":"Method for Aluminum Oxide Thin Films Prepared through Low Temperature Atomic Layer Deposition for Encapsulating Organic Electroluminescent Devices","volume":"8","author":"Li","year":"2015","journal-title":"Materials"},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"111","DOI":"10.1021\/cr900056b","article-title":"Atomic Layer Deposition: An Overview","volume":"110","author":"George","year":"2010","journal-title":"Chem. Rev."},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"639","DOI":"10.1021\/cm0304546","article-title":"Low-Temperature Al2O3 Atomic Layer Deposition","volume":"16","author":"Groner","year":"2004","journal-title":"Chem. Mater."},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"186","DOI":"10.1016\/S0040-6090(02)00438-8","article-title":"Electrical Characterization of Thin Al2O3 Films Grown by Atomic Layer Deposition on Silicon and Various Metal Substrates","volume":"413","author":"Groner","year":"2002","journal-title":"Thin Solid Film."},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"5625","DOI":"10.1021\/cm050704d","article-title":"Nucleation and Growth during Al2O3 Atomic Layer Deposition on Polymers","volume":"17","author":"Wilson","year":"2005","journal-title":"Chem. Mater."},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"1017","DOI":"10.1002\/adma.201104129","article-title":"Atomic Layer Deposition of Nanostructured Materials for Energy and Environmental Applications","volume":"24","author":"Marichy","year":"2012","journal-title":"Adv. Mater."},{"key":"ref_18","doi-asserted-by":"crossref","unstructured":"Zhu, W., Huang, X., Liu, T., Xie, Z., Wang, Y., Tian, K., Bu, L., Wang, H., Gao, L., and Zhao, J. (2019). Ultrathin Al2O3 Coating on LiNi0.8Co0.1Mn0.1O2 Cathode Material for Enhanced Cycleability at Extended Voltage Ranges. Coatings, 9.","DOI":"10.3390\/coatings9020092"},{"key":"ref_19","doi-asserted-by":"crossref","unstructured":"Li, C., Cauwe, M., Yang, Y., Schaubroeck, D., and Mader, L. (2019). Ultra-Long-Term Reliable Encapsulation Using an Atomic Layer Deposited HfO2\/Al2O3\/HfO2 Triple-Interlayer for Biomedical Implants. Coatings, 9.","DOI":"10.3390\/coatings9090579"},{"key":"ref_20","doi-asserted-by":"crossref","unstructured":"Huang, Y.C., and Chuang, R.W. (2021). Study on Annealing Process of Aluminum Oxide Passivation Layer for Perc Solar Cells. Coatings, 11.","DOI":"10.3390\/coatings11091052"},{"key":"ref_21","doi-asserted-by":"crossref","unstructured":"Xu, H., Ding, X., Qi, J., Yang, X., and Zhang, J. (2021). A Study on Solution-Processed Y2O3 Films Modified by Atomic Layer Deposition Al2O3 as Dielectrics in Zno Thin Film Transistor. Coatings, 11.","DOI":"10.3390\/coatings11080969"},{"key":"ref_22","doi-asserted-by":"crossref","unstructured":"Mn, S.L., Co, O., and Atomic, A.O. (2022). Reduction of Surface Residual Lithium Compounds for Single-Crystal LiNi0.6Mn0.2Co0.2O2 via Al2O3 Atomic Layer Deposition and Post-Annealing. Coatings, 12.","DOI":"10.3390\/coatings12010084"},{"key":"ref_23","doi-asserted-by":"crossref","unstructured":"Ti, L., Cathode, M.O., Al, O., and Wang, R. (2022). Improved Cycling Performance of Cation-Disordered Rock-Salt Li1.2Ti0.4Mn0.4O2 Cathode through Mo-Doping and Al2O3-Coating. Coatings, 12.","DOI":"10.3390\/coatings12111613"},{"key":"ref_24","doi-asserted-by":"crossref","unstructured":"Huang, C., Liu, Y., Ma, D., Guo, Z., Yao, H., Lv, K., Tian, Z., Liang, L., Gao, J., and Ding, X. (2022). High Performance of InGaZnO TFTs Using HfxAlyOz Nanolaminates as Gate Insulators Prepared by ALD. Coatings, 12.","DOI":"10.3390\/coatings12121811"},{"key":"ref_25","doi-asserted-by":"crossref","unstructured":"Fern\u00e1ndez-Men\u00e9ndez, L.J., Gonz\u00e1lez, A.S., Vega, V., and de la Prida, V.M. (2018). Electrostatic Supercapacitors by Atomic Layer Deposition on Nanoporous Anodic Alumina Templates for Environmentally Sustainable Energy Storage. Coatings, 8.","DOI":"10.3390\/coatings8110403"},{"key":"ref_26","doi-asserted-by":"crossref","unstructured":"Pfeiffer, K., Schulz, U., T\u00fcnnermann, A., and Szeghalmi, A. (2017). Antireflection Coatings for Strongly Curved Glass Lenses by Atomic Layer Deposition. Coatings, 7.","DOI":"10.3390\/coatings7080118"},{"key":"ref_27","doi-asserted-by":"crossref","first-page":"641","DOI":"10.1149\/1.3207651","article-title":"Industrial Applications of Atomic Layer Deposition","volume":"25","author":"Ritala","year":"2009","journal-title":"ECS Trans."},{"key":"ref_28","doi-asserted-by":"crossref","first-page":"035301","DOI":"10.1088\/0957-4484\/21\/3\/035301","article-title":"Ta2O5-and TiO2-Based Nanostructures Made by Atomic Layer Deposition","volume":"21","author":"Kemell","year":"2010","journal-title":"Nanotechnology"},{"key":"ref_29","doi-asserted-by":"crossref","first-page":"N55","DOI":"10.1149\/2.0201903jss","article-title":"Review\u2014On Atomic Layer Deposition: Current Progress and Future Challenges","volume":"8","author":"Mallick","year":"2019","journal-title":"ECS J. Solid State Sci. Technol."},{"key":"ref_30","doi-asserted-by":"crossref","first-page":"03DA01","DOI":"10.7567\/JJAP.53.03DA01","article-title":"Review of Plasma-Enhanced Atomic Layer Deposition: Technical Enabler of Nanoscale Device Fabrication","volume":"53","author":"Kim","year":"2014","journal-title":"Jpn. J. Appl. Phys."},{"key":"ref_31","doi-asserted-by":"crossref","first-page":"050801","DOI":"10.1116\/1.3609974","article-title":"Plasma-Assisted Atomic Layer Deposition: Basics, Opportunities, and Challenges","volume":"29","author":"Profijt","year":"2011","journal-title":"J. Vac. Sci. Technol. A"},{"key":"ref_32","first-page":"975","article-title":"Plasma Enhanced Atomic Layer Deposition of Al2O3 and TiN","volume":"42","author":"Choi","year":"2003","journal-title":"J. Korean Phys. Soc."},{"key":"ref_33","doi-asserted-by":"crossref","first-page":"2","DOI":"10.1186\/s11671-015-0831-5","article-title":"Uniformity and Passivation Research of Al2O3 Film on Silicon Substrate Prepared by Plasma-Enhanced Atom Layer Deposition","volume":"10","author":"Jia","year":"2015","journal-title":"Nanoscale Res. Lett."}],"container-title":["Coatings"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/2079-6412\/13\/3\/638\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,10]],"date-time":"2025-10-10T18:57:57Z","timestamp":1760122677000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/2079-6412\/13\/3\/638"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2023,3,17]]},"references-count":33,"journal-issue":{"issue":"3","published-online":{"date-parts":[[2023,3]]}},"alternative-id":["coatings13030638"],"URL":"https:\/\/doi.org\/10.3390\/coatings13030638","relation":{},"ISSN":["2079-6412"],"issn-type":[{"value":"2079-6412","type":"electronic"}],"subject":[],"published":{"date-parts":[[2023,3,17]]}}}