{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,2,1]],"date-time":"2026-02-01T10:49:55Z","timestamp":1769942995892,"version":"3.49.0"},"reference-count":33,"publisher":"MDPI AG","issue":"5","license":[{"start":{"date-parts":[[2014,5,16]],"date-time":"2014-05-16T00:00:00Z","timestamp":1400198400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/3.0\/"}],"content-domain":{"domain":["www.mdpi.com"],"crossmark-restriction":true},"short-container-title":["Sensors"],"abstract":"<jats:p>This paper presents a low-cost low-power CMOS humidity sensor for passive RFID sensing applications. The humidity sensing element is implemented in standard CMOS technology without any further post-processing, which results in low fabrication costs. The interface of this humidity sensor employs a PLL-based architecture transferring sensor signal processing from the voltage domain to the frequency domain. Therefore this architecture allows the use of a fully digital circuit, which can operate on ultra-low supply voltage and thus achieves low-power consumption. The proposed humidity sensor has been fabricated in the TSMC 0.18 \u03bcm CMOS process. The measurements show this humidity sensor exhibits excellent linearity and stability within the relative humidity range. The sensor interface circuit consumes only 1.05 \u00b5W at 0.5 V supply voltage and reduces it at least by an order of magnitude compared to previous designs.<\/jats:p>","DOI":"10.3390\/s140508728","type":"journal-article","created":{"date-parts":[[2014,5,16]],"date-time":"2014-05-16T12:09:04Z","timestamp":1400242144000},"page":"8728-8739","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":28,"title":["A CMOS Humidity Sensor for Passive RFID  Sensing Applications"],"prefix":"10.3390","volume":"14","author":[{"given":"Fangming","family":"Deng","sequence":"first","affiliation":[{"name":"School of Electrical Engineering and Automation, Hefei University of Technology, Hefei 230009, China"},{"name":"School of Electrical and Electronic Engineering, East China JiaoTong University,  Nanchang 330013, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Yigang","family":"He","sequence":"additional","affiliation":[{"name":"School of Electrical Engineering and Automation, Hefei University of Technology, Hefei 230009, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Chaolong","family":"Zhang","sequence":"additional","affiliation":[{"name":"School of Electrical Engineering and Automation, Hefei University of Technology, Hefei 230009, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-3023-5225","authenticated-orcid":false,"given":"Wei","family":"Feng","sequence":"additional","affiliation":[{"name":"School of Electrical Engineering and Automation, Hefei University of Technology, Hefei 230009, China"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2014,5,16]]},"reference":[{"key":"ref_1","first-page":"4101","article-title":"Analysis and measurments of path loss effects for ultra high frequency radio-frequency identification in real environments","volume":"62","author":"Zuo","year":"2013","journal-title":"Acta Phys. Sinica"},{"key":"ref_2","first-page":"4103","article-title":"Analysis and improvement for UHF RFID reading region in real enviorments","volume":"61","author":"Zuo","year":"2012","journal-title":"Acta Phys. Sinica"},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"394","DOI":"10.1016\/j.jfoodeng.2009.02.004","article-title":"RFID smart tag for traceability and cold chain monitoring of foods: Demonstration in an intercontinental fresh fish logistic chain","volume":"93","author":"Abad","year":"2009","journal-title":"J. Food Eng."},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"227","DOI":"10.1016\/j.snb.2009.04.019","article-title":"Temperature, humidity and gas sensors integrated on plastic foil for low power applications","volume":"140","author":"Oprea","year":"2009","journal-title":"Sens. Actuators B Chem."},{"key":"ref_5","doi-asserted-by":"crossref","unstructured":"Beriain, A., Rebollo, I., Fernandez, I., Sevillano, J.F., and Berenguer, R. (2012, January 17\u201322). A passive UHF RFID pressure sensor tag with a 7.27 bit and 5.47 pj capacitive sensor interface. Montreal, Quebec, Canada.","DOI":"10.1109\/MWSYM.2012.6258415"},{"key":"ref_6","doi-asserted-by":"crossref","unstructured":"Cartasegna, D., Conso, F., Donida, A., Grassi, M., Picolli, L., Rescio, G., and Regnicoli, G.F. (2011, January 28\u201331). Integrated microsystem with humidity, temperature and light sensors for monitoring the preservation conditions of food. Limerick, Ireland.","DOI":"10.1109\/ICSENS.2011.6127283"},{"key":"ref_7","unstructured":"Okada, C.T. (2011). Humidity Sensor: Types, Nanomaterials and Environmental Monitoring, Nova Science."},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"702","DOI":"10.1109\/16.830983","article-title":"A high-speed capacitive humidity sensor with on-chip thermal reset","volume":"47","author":"Kang","year":"2000","journal-title":"IEEE Trans. Electron Devices"},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"84","DOI":"10.1049\/mnl.2009.0005","article-title":"Miniature humidity micro-sensor based on organic conductive polymer-poly (3, 4-ethylenedioxythiophene)","volume":"4","author":"Li","year":"2009","journal-title":"Micro Nano Lett. IET"},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"274","DOI":"10.1166\/sl.2005.045","article-title":"Humidity sensors: A review of materials and mechanisms","volume":"3","author":"Chen","year":"2005","journal-title":"Sens. Lett."},{"key":"ref_11","doi-asserted-by":"crossref","unstructured":"Kim, J.H., Hong, S.M., Lee, J.S., Moon, B.M., and Kim, K. (2009, January 5\u20138). High sensitivity capacitive humidity sensor with a novel polyimide design fabricated by MEMS technology. Kyoto, Japan.","DOI":"10.1109\/NEMS.2009.5068676"},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"6197","DOI":"10.3390\/s110606197","article-title":"A StandardCMOS HumiditySensor without Post-Processing","volume":"11","author":"Nizhnik","year":"2011","journal-title":"Sensors"},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"3071","DOI":"10.1109\/TED.2007.907165","article-title":"A low-power robust humidity sensor in a standard CMOS process","volume":"54","author":"Okcan","year":"2007","journal-title":"IEEE Trans. Electron Devices"},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"75","DOI":"10.1016\/0925-4005(93)85030-E","article-title":"High sensitivity CMOS humidity sensors with on-chip absolute capacitance measurement system","volume":"15","author":"Boltshauser","year":"1993","journal-title":"Sens. Actuators B Chem."},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"491","DOI":"10.1016\/j.snb.2003.12.060","article-title":"A novel capacitive-type humidity sensor using CMOS fabrication technology","volume":"99","author":"Gu","year":"2004","journal-title":"Sens. Actuators B Chem."},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"2986","DOI":"10.1109\/JSEN.2011.2154325","article-title":"A fully packaged CMOS interdigital capacitive humidity sensor with polysilicon heaters","volume":"11","author":"Zhao","year":"2011","journal-title":"IEEE Sens."},{"key":"ref_17","unstructured":"Zhao, C.L., Qin, M., Li, W.H., and Huang, Q.A. (2011, January 5\u20139). Enhanced performance of a CMOS interdigital capacitive humidity sensor by graphene oxide. Kyoto, Japan."},{"key":"ref_18","unstructured":"Dai, C.L., and Lu, D.H. (2010, January 20\u201323). Fabrication of a micro humidity sensor with polypyrrole using the CMOS process. Nice, France."},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"226","DOI":"10.3390\/s120100226","article-title":"Self-calibrated humidity sensor in CMOS without post-processing","volume":"12","author":"Nizhnik","year":"2012","journal-title":"Sensors"},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"2373","DOI":"10.1109\/JSSC.2005.856280","article-title":"0.5 V analog circuit techniques and their application in OTA and filter design","volume":"40","author":"Chatterjee","year":"2005","journal-title":"IEEE J. Solid-State Circuits"},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"220","DOI":"10.1016\/j.sna.2011.04.047","article-title":"A novel PLL-based frequency-to-digital conversion mechanism for sensor interfaces","volume":"172","author":"Danneels","year":"2011","journal-title":"Sens. Actuators A Phys."},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"62","DOI":"10.1016\/j.proeng.2010.09.048","article-title":"A novel PLL-based sensor interface for resistive pressure sensors","volume":"5","author":"Danneels","year":"2010","journal-title":"Procedia Eng."},{"key":"ref_23","unstructured":"Laconte, J., Wilmart, V., Raskin, J.P., and Flandre, D. (2003, January 25\u201327). Capacitive humidity sensor using a polyimide sensing film. Cannes, France."},{"key":"ref_24","doi-asserted-by":"crossref","first-page":"401","DOI":"10.1016\/0031-8914(65)90045-5","article-title":"Dielectric constants of heterogeneous mixtures","volume":"31","author":"Looyenga","year":"1965","journal-title":"Physica"},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"1220","DOI":"10.1109\/T-ED.1985.22104","article-title":"A polyimide-based capacitive humidity sensor","volume":"32","author":"Schubert","year":"1985","journal-title":"IEEE Trans. Electron Devices"},{"key":"ref_26","doi-asserted-by":"crossref","first-page":"896","DOI":"10.1109\/22.506449","article-title":"CAD models for multilayered substrate interdigital capacitors","volume":"44","author":"Gevorgian","year":"1996","journal-title":"IEEE Trans. Microw. Theory Tech."},{"key":"ref_27","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\u2013MEMS technique","volume":"122","author":"Dai","year":"2007","journal-title":"Sens. Actuators B: Chem."},{"key":"ref_28","doi-asserted-by":"crossref","first-page":"21","DOI":"10.1109\/TCSI.2004.840089","article-title":"A design-oriented study of the nonlinear dynamics of digital bang-bang PLLs","volume":"52","year":"2005","journal-title":"IEEE Trans. Circuits Syst. I Regul. Pap."},{"key":"ref_29","first-page":"1881","article-title":"Performance Analysis of Energy-Efficient BBPLL-Based Sensor-to-Digital Converters","volume":"11","author":"Danneels","year":"2013","journal-title":"IEEE Trans. Circuits Syst. I Regul. Pap."},{"key":"ref_30","doi-asserted-by":"crossref","first-page":"130","DOI":"10.1109\/TCSI.2006.887978","article-title":"Ultra-low-power interface chip for autonomous capacitive sensor systems","volume":"54","author":"Bracke","year":"2007","journal-title":"IEEE Trans. Circuits Syst. I Regul. Pap."},{"key":"ref_31","first-page":"90","article-title":"A delta-sigma interface circuit for capacitive sensors with an automatically calibrated zero point","volume":"58","author":"Shin","year":"2011","journal-title":"IEEE Trans. Circuits Syst. II Express Briefs"},{"key":"ref_32","doi-asserted-by":"crossref","first-page":"2469","DOI":"10.1109\/JSSC.2013.2275661","article-title":"A 1.2-V 8.3-nJ CMOS Humidity Sensor for RFID Applications","volume":"48","author":"Tan","year":"2013","journal-title":"IEEE J. Solid State Circuits"},{"key":"ref_33","doi-asserted-by":"crossref","first-page":"1419","DOI":"10.1109\/TCSI.2012.2220461","article-title":"A low-power interface for capacitive sensors with PWM output and intrinsic low pass characteristic","volume":"60","author":"Nizza","year":"2013","journal-title":"IEEE Trans. Circuits Syst. I Regul. Pap."}],"updated-by":[{"DOI":"10.3390\/s140713171","type":"correction","label":"Correction","source":"publisher","updated":{"date-parts":[[2014,5,16]],"date-time":"2014-05-16T00:00:00Z","timestamp":1400198400000}}],"container-title":["Sensors"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/1424-8220\/14\/5\/8728\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,8,4]],"date-time":"2025-08-04T07:49:22Z","timestamp":1754293762000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/1424-8220\/14\/5\/8728"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2014,5,16]]},"references-count":33,"journal-issue":{"issue":"5","published-online":{"date-parts":[[2014,5]]}},"alternative-id":["s140508728"],"URL":"https:\/\/doi.org\/10.3390\/s140508728","relation":{"correction":[{"id-type":"doi","id":"10.3390\/s140713171","asserted-by":"object"}]},"ISSN":["1424-8220"],"issn-type":[{"value":"1424-8220","type":"electronic"}],"subject":[],"published":{"date-parts":[[2014,5,16]]}}}