{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,3,24]],"date-time":"2026-03-24T01:07:54Z","timestamp":1774314474515,"version":"3.50.1"},"reference-count":22,"publisher":"MDPI AG","issue":"11","license":[{"start":{"date-parts":[[2014,10,28]],"date-time":"2014-10-28T00:00:00Z","timestamp":1414454400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>The study develops an integrated humidity microsensor fabricated using the commercial 0.18 \u03bcm complementary metal oxide semiconductor (CMOS) process. The integrated humidity sensor consists of a humidity sensor and a ring oscillator circuit  on-a-chip. The humidity sensor is composed of a sensitive film and branch interdigitated electrodes. The sensitive film is zinc oxide prepared by sol-gel method. After completion of the CMOS process, the sensor requires a post-process to remove the sacrificial oxide layer and to coat the zinc oxide film on the interdigitated electrodes. The capacitance of the sensor changes when the sensitive film adsorbs water vapor. The circuit is used to convert the capacitance of the humidity sensor into the oscillation frequency output. Experimental results show that the output frequency of the sensor changes from 84.3 to 73.4 MHz at  30 \u00b0C as the humidity increases 40 to 90%RH.<\/jats:p>","DOI":"10.3390\/s141120360","type":"journal-article","created":{"date-parts":[[2014,10,28]],"date-time":"2014-10-28T10:25:07Z","timestamp":1414491907000},"page":"20360-20371","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":28,"title":["Sol-Gel Zinc Oxide Humidity Sensors Integrated with a Ring Oscillator Circuit On-a-Chip"],"prefix":"10.3390","volume":"14","author":[{"given":"Ming-Zhi","family":"Yang","sequence":"first","affiliation":[{"name":"Department of Mechanical Engineering, National Chung Hsing University, Taichung 402, Taiwan"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Ching-Liang","family":"Dai","sequence":"additional","affiliation":[{"name":"Department of Mechanical Engineering, National Chung Hsing University, Taichung 402, Taiwan"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Chyan-Chyi","family":"Wu","sequence":"additional","affiliation":[{"name":"Department of Mechanical and Electro-Mechanical Engineering, Tamkang University, Tamsui 251,  Taiwan"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2014,10,28]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","unstructured":"Gardner, J.W., Varadan, V.K., and Awadelkarim, O.O. 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Actuators B Chem."},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"212","DOI":"10.1016\/j.apsusc.2004.08.013","article-title":"Zinc oxide nanorod and nanowire for humidity sensor","volume":"242","author":"Zhang","year":"2005","journal-title":"Appl. Surf. Sci."},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"772","DOI":"10.1016\/j.spmi.2010.03.006","article-title":"A ZnO nanowire-based humidity sensor","volume":"47","author":"Chang","year":"2010","journal-title":"Superlatt. Microstruct."},{"key":"ref_7","doi-asserted-by":"crossref","unstructured":"Hong, H.S., Phan, D.T., and Chung, G.S. (2012). High-sensitivity humidity sensors with ZnO nanorods based two-port surface acoustic wave delay line. Sens. Actuators B Chem., 1283\u20131287.","DOI":"10.1016\/j.snb.2012.06.026"},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"280","DOI":"10.1016\/j.snb.2013.11.069","article-title":"Enhanced sensing performance of relative humidity sensors using laterally grown ZnO nanosheets","volume":"193","author":"Tsai","year":"2014","journal-title":"Sens. Actuators B Chem."},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"101","DOI":"10.1016\/j.sna.2012.05.041","article-title":"Room temperature ultra-sensitive resistive humidity sensor based on single zinc oxide nanowire","volume":"182","author":"Kiasari","year":"2012","journal-title":"Sens. Actuators A Phys."},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"1143","DOI":"10.1007\/s00542-006-0243-7","article-title":"Low voltage actuated RF micromechanical switches fabricated using COMS-MEMS technique","volume":"12","author":"Dai","year":"2006","journal-title":"Microsyst. Technol."},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"612","DOI":"10.1088\/0960-1317\/11\/5\/326","article-title":"Fabrication of a micromachined optical modulator using the CMOS process","volume":"11","author":"Dai","year":"2001","journal-title":"J. Micromech. Microeng."},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"10158","DOI":"10.3390\/s91210158","article-title":"Capacitive micro pressure sensor integrated with a ring oscillator circuit on chip","volume":"9","author":"Dai","year":"2009","journal-title":"Sensors"},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"4177","DOI":"10.3390\/s140304177","article-title":"Titanium dioxide nanoparticle humidity microsensors integrated with circuitry on chip","volume":"14","author":"Hu","year":"2014","journal-title":"Sensors"},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"2366","DOI":"10.1088\/0960-1317\/15\/12\/019","article-title":"A maskless post-CMOS bulk micromachining process and its application","volume":"15","author":"Dai","year":"2005","journal-title":"J. Micromech. Microeng."},{"key":"ref_15","unstructured":"Kang, S.M., and Leblebici, Y. (1996). Digital Integrated Circuits, McGraw-Hill."},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"10095","DOI":"10.3390\/s101110095","article-title":"Polypyrrole porous micro humidity sensor integrated with a ring oscillator circuit on chip","volume":"10","author":"Yang","year":"2010","journal-title":"Sensors"},{"key":"ref_17","first-page":"620","article-title":"Synthesis of 1-dimensional ZnO and its sensing property for CO","volume":"143","author":"Chen","year":"2009","journal-title":"Sens. Actuators B Chem."},{"key":"ref_18","doi-asserted-by":"crossref","first-page":"6804","DOI":"10.1143\/JJAP.44.6804","article-title":"A micromachined microwave switch fabricated by the complementary metal oxide semiconductor post-process of etching silicon dioxide","volume":"44","author":"Dai","year":"2005","journal-title":"Jpn. J. Appl. Phys."},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"444","DOI":"10.1007\/s00542-004-0486-0","article-title":"A circular micromirror array fabricated by a maskless post-CMOS process","volume":"11","author":"Cheng","year":"2005","journal-title":"Microsyst. Technol."},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"2543","DOI":"10.1016\/j.mee.2006.06.006","article-title":"A maskless wet etching silicon dioxide post-CMOS process and its application","volume":"83","author":"Dai","year":"2006","journal-title":"Microelectron. Eng."},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"375","DOI":"10.1016\/j.snb.2006.05.042","article-title":"A capacitive humidity sensor integrated with micro heater and ring oscillator circuit fabricated by CMOS-MEMS technique","volume":"122","author":"Dai","year":"2007","journal-title":"Sens. Actuators B Chem."},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"67","DOI":"10.1016\/j.sna.2013.11.017","article-title":"Out-of-plane MEMS-based mechanical airflow sensor co-integrated in SOI CMOS technology","volume":"206","author":"Andre","year":"2014","journal-title":"Sens. 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