{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,6,19]],"date-time":"2026-06-19T16:12:27Z","timestamp":1781885547238,"version":"3.54.5"},"reference-count":35,"publisher":"MDPI AG","issue":"7","license":[{"start":{"date-parts":[[2015,7,10]],"date-time":"2015-07-10T00:00:00Z","timestamp":1436486400000},"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>This paper reports on the fabrication and characterization of a Complementary Metal Oxide Semiconductor-Microelectromechanical System (CMOS-MEMS) device with embedded microheater operated at relatively elevated temperatures (40 \u00b0C to 80 \u00b0C) for the purpose of relative humidity measurement. The sensing principle is based on the change in amplitude of the device due to adsorption or desorption of humidity on the active material layer of titanium dioxide (TiO2) nanoparticles deposited on the moving plate, which results in changes in the mass of the device. The sensor has been designed and fabricated through a standard 0.35 \u00b5m CMOS process technology and post-CMOS micromachining technique has been successfully implemented to release the MEMS structures. The sensor is operated in the dynamic mode using electrothermal actuation and the output signal measured using a piezoresistive (PZR) sensor connected in a Wheatstone bridge circuit. The output voltage of the humidity sensor increases from 0.585 mV to 30.580 mV as the humidity increases from 35% RH to 95% RH. The output voltage is found to be linear from 0.585 mV to 3.250 mV as the humidity increased from 35% RH to 60% RH, with sensitivity of 0.107 mV\/% RH; and again linear from 3.250 mV to 30.580 mV as the humidity level increases from 60% RH to 95% RH, with higher sensitivity of 0.781 mV\/% RH. On the other hand, the sensitivity of the humidity sensor increases linearly from 0.102 mV\/% RH to 0.501 mV\/% RH with increase in the temperature from 40 \u00b0C to 80 \u00b0C and a maximum hysteresis of 0.87% RH is found at a relative humidity of 80%. The sensitivity is also frequency dependent, increasing from 0.500 mV\/% RH at 2 Hz to reach a maximum value of 1.634 mV\/% RH at a frequency of 12 Hz, then decreasing to 1.110 mV\/% RH at a frequency of 20 Hz. Finally, the CMOS-MEMS humidity sensor showed comparable response, recovery, and repeatability of measurements in three cycles as compared to a standard sensor that directly measures humidity in % RH.<\/jats:p>","DOI":"10.3390\/s150716674","type":"journal-article","created":{"date-parts":[[2015,7,13]],"date-time":"2015-07-13T03:49:22Z","timestamp":1436759362000},"page":"16674-16687","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":42,"title":["Fabrication and Characterization of a CMOS-MEMS  Humidity Sensor"],"prefix":"10.3390","volume":"15","author":[{"given":"John-Ojur","family":"Dennis","sequence":"first","affiliation":[{"name":"Department of Fundamental and Applied Sciences, Universiti Teknologi PETRONAS,  Bandar Seri Iskandar, Perak Darul Ridzuan 32610, Malaysia"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Abdelaziz-Yousif","family":"Ahmed","sequence":"additional","affiliation":[{"name":"Department of Electrical and Electronic Engineering, Universiti Teknologi PETRONAS,  Bandar Seri Iskandar, Perak Darul Ridzuan 32610, Malaysia"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Mohd-Haris","family":"Khir","sequence":"additional","affiliation":[{"name":"Department of Electrical and Electronic Engineering, Universiti Teknologi PETRONAS,  Bandar Seri Iskandar, Perak Darul Ridzuan 32610, Malaysia"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2015,7,10]]},"reference":[{"key":"ref_1","unstructured":"Atta, N.F. (2013). Nanosensors: Materials and Technologies, International Frequency Sensor Association Publishing."},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"309","DOI":"10.1109\/7361.983470","article-title":"Micromachined Water Vapor Sensors: A Review of Sensing Technologies","volume":"1","author":"Fenner","year":"2001","journal-title":"IEEE Sens. J."},{"key":"ref_3","first-page":"2361","article-title":"Room Temperature Synthesized Nano Metal Oxide Humidity Sensor","volume":"8","author":"Sreelekshmi","year":"2013","journal-title":"Inter. J. Appl. Eng. Res."},{"key":"ref_4","unstructured":"Lee, D.H., Hong, H.K., Park, C.K., Kim, G.H., Jeon, Y.S., and Bu, J.U. (2001, January 25). A Micromachined Robust Humidity Sensor for Harsh Environment Applications. Proceedings of the 14th IEEE International Conference on Micro Electro Mechanical Systems (MEMS), Interlaken, Switzerland."},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"8143","DOI":"10.3390\/s110808143","article-title":"Fabrication and Characterization of Polyaniline\/PVA Humidity Microsensors","volume":"11","author":"Yang","year":"2011","journal-title":"Sensors"},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"322","DOI":"10.1007\/BF03218371","article-title":"Resistive Humidity Sensor Using Phosphonium Salt-Containing Polyelectrolytes Based on the Mutually Cross-Linkable Copolymers","volume":"11","author":"Lee","year":"2003","journal-title":"Macromol. Res."},{"key":"ref_7","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_8","doi-asserted-by":"crossref","unstructured":"Lee, M.J., Lee, C.J., Singh, V., Yoo, K.P., and Min, N.K. (2008, January 26\u201329). Humidity Sensing Characteristics of Plasma Functionalized Multiwall Carbon Nanotube-polyimide Composite Films. Proceedings of the IEEE Sensors, Lecce, Italy.","DOI":"10.1109\/ICSENS.2008.4716470"},{"key":"ref_9","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. Proceedings of the 4th IEEE International Conference on Nano\/Micro Engineered and Molecular Systems (NEMS), Shenzhen, China.","DOI":"10.1109\/NEMS.2009.5068676"},{"key":"ref_10","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_11","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_12","doi-asserted-by":"crossref","first-page":"2017","DOI":"10.1007\/s00542-010-1139-0","article-title":"High-Performance Capacitive Humidity Sensor with Novel Electrode and Polyimide Layer Based on MEMS Technology","volume":"16","author":"Kim","year":"2010","journal-title":"Microsys. Technol."},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"31","DOI":"10.1007\/s00542-011-1373-0","article-title":"Capacitive Humidity Sensors Based on a Newly Designed Interdigitated Electrode Structure","volume":"18","author":"Kim","year":"2012","journal-title":"Microsys. Technol."},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"4177","DOI":"10.3390\/s140304177","article-title":"Titanium Dioxide Nanoparticle Humidity Microsensors Integrated with Circuitry on-a-Chip","volume":"14","author":"Hu","year":"2014","journal-title":"Sensors"},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"365","DOI":"10.5185\/amlett.2012.5350","article-title":"Fabrication of ultra-sensitive optical fiber based humidity sensor using TiO2 thin film","volume":"3","author":"Shukla","year":"2012","journal-title":"Adv. Mater. Lett."},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"197","DOI":"10.1109\/84.925735","article-title":"A high-sensitivity polyimide capacitive relative humidity sensor for monitoring anodically bonded hermetic micropackages","volume":"10","author":"Dokmeci","year":"2001","journal-title":"J. Microelectromech. Syst."},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"183","DOI":"10.1109\/JMEMS.2009.2036584","article-title":"CMOS-MEMS Capacitive Humidity Sensor","volume":"19","author":"Lazarus","year":"2010","journal-title":"J. Microelectromech. Syst."},{"key":"ref_18","doi-asserted-by":"crossref","unstructured":"Bedair, S.S., and Fedder, G.K. (2007, January 28\u201331). Polymer Mass Loading of CMOS\/MEMS Microslot Cantilever for Gravimetric Sensing. Proceedings of the IEEE Sensors, Atlanta, GA, USA.","DOI":"10.1109\/ICSENS.2007.4388614"},{"key":"ref_19","unstructured":"Bedair, S.S., and Fedder, G.K. (2005, January 5\u20139). Polymer Wicking to Mass Load Cantilevers for Chemical Gravimetric Sensors. Proceedings of the 13th International Conference on Solid-State Sensors, Actuators and Microsystems, Seoul, Korea."},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"8728","DOI":"10.3390\/s140508728","article-title":"A CMOS Humidity Sensor for Passive RFID Sensing Applications","volume":"14","author":"Deng","year":"2014","journal-title":"Sensors"},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"6197","DOI":"10.3390\/s110606197","article-title":"A Standard CMOS Humidity Sensor without Post-Processing","volume":"11","author":"Nizhnik","year":"2011","journal-title":"Sensors"},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"807","DOI":"10.1109\/JMEMS.2010.2049194","article-title":"CMOS-Integrated RF MEMS Resonators","volume":"19","author":"Zalalutdinov","year":"2010","journal-title":"J. Microelectromech. Sys."},{"key":"ref_23","doi-asserted-by":"crossref","unstructured":"Yusof, N.B., Soin, N., and Dawal, S.Z.M. (2009, January 14\u201315). Capacitive Interfacing for MEMS Humidity and Accelerometer Sensors. Proceedings of the International Conference for Technical Postgraduates (TECHPOS), Kuala Lumpur, Malaysia.","DOI":"10.1109\/TECHPOS.2009.5412067"},{"key":"ref_24","doi-asserted-by":"crossref","first-page":"7892","DOI":"10.3390\/s110807892","article-title":"A Low-Cost CMOS-MEMS Piezoresistive Accelerometer with Large Proof Mass","volume":"11","author":"Khir","year":"2011","journal-title":"Sensors"},{"key":"ref_25","unstructured":"Yang, T.Y., Huang, J.J., Liu, C.Y., and Wang, H.Y. (2011, January 28\u201329). A CMOS-MEMS Humidity Sensor. Proceedings of the International Conference on Circuits, System and Simulation (ICCSS), Bangkk, Thailand."},{"key":"ref_26","unstructured":"Saha, T. (2012). Design, Fabrication, and CMOS Integration of MEMS Humidity Sensors. [Master\u2019s Thesis, Engineering, Department of Electrical and Computer Engineering, McGill University]."},{"key":"ref_27","doi-asserted-by":"crossref","first-page":"839","DOI":"10.1109\/JPROC.2003.813583","article-title":"Microfabrication Techniques for Chemical\/Biosensors","volume":"91","author":"Hierlemann","year":"2003","journal-title":"IEEE Proc."},{"key":"ref_28","unstructured":"Lei, S., Chen, Y., and Li, Y. (2011, January 6\u20137). A Novel SAW Humidity Sensor Based on Electrosprayed Polymerized Electrolyte Film. Proceedings of the 2011 Third International Conference on Measuring Technology and Mechatronics Automation (ICMTMA), Shanghai, China."},{"key":"ref_29","doi-asserted-by":"crossref","first-page":"285","DOI":"10.1016\/S0924-4247(00)00391-5","article-title":"Quartz Crystal Microbalance (QCM) Used as Humidity Sensor","volume":"84","author":"Sorli","year":"2000","journal-title":"Sens. Actuators A Phys."},{"key":"ref_30","doi-asserted-by":"crossref","first-page":"305","DOI":"10.1088\/1742-6596\/10\/1\/075","article-title":"Simulation of Capacitive Type Bimorph Humidity Sensors","volume":"10","author":"Fragakis","year":"2005","journal-title":"J. Phys. Conf. Ser."},{"key":"ref_31","doi-asserted-by":"crossref","first-page":"176","DOI":"10.4028\/www.scientific.net\/MSF.737.176","article-title":"Resonance Frequency Change in Microcantilever-Based Sensor due to Humidity Variation","volume":"737","author":"Nuryadi","year":"2013","journal-title":"Mater. Sci. Forum"},{"key":"ref_32","doi-asserted-by":"crossref","unstructured":"Sappat, A., Wisitsoraat, A., Sriprachuabwong, C., Jaruwongrungsee, K., Lomas, T., and Tuantranont, A. (2011, January 17\u201319). Humidity Sensor Based on Piezoresistive Microcantilever with Inkjet Printed PEDOT\/PSS Sensing Layers. Proceedings of the 8th International Conference on Electrical Engineering\/Electronics, Computer, Telecommunications and Information Technology (ECTI-CON), Khon Kaen, Thailand.","DOI":"10.1109\/ECTICON.2011.5947764"},{"key":"ref_33","doi-asserted-by":"crossref","first-page":"12","DOI":"10.1016\/S0925-4005(01)00785-7","article-title":"Multicomponent Analysis and Prediction with a Cantilever Array Based Gas Sensor","volume":"78","author":"Kima","year":"2001","journal-title":"Sens. Actuators B Chem."},{"key":"ref_34","doi-asserted-by":"crossref","unstructured":"Ahmed, A.Y., Dennis, J.O., Khir, M.H.M., and Saad, M.N.M. (2014, January 3\u20135). Design and Characterization of Embedded Microheater on CMOS-MEMS Resonator for Application in Mass-Sensitive Gas Sensors. Proceedings of the 2014 5th International Conference on Intelligent and Advanced Systems: Technological Convergence for Sustainable Future (ICIAS), Kuala Lumpur, Malaysia.","DOI":"10.1109\/ICIAS.2014.6869462"},{"key":"ref_35","first-page":"729","article-title":"Modelling and Simulation of the Effect of Air Damping on the Frequency and Quality factor of a CMOS-MEMS Resonator","volume":"9","author":"Dennis","year":"2015","journal-title":"Appl. Math. Infor. Sci. (AMIS)"}],"container-title":["Sensors"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/1424-8220\/15\/7\/16674\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T20:49:00Z","timestamp":1760215740000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/1424-8220\/15\/7\/16674"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2015,7,10]]},"references-count":35,"journal-issue":{"issue":"7","published-online":{"date-parts":[[2015,7]]}},"alternative-id":["s150716674"],"URL":"https:\/\/doi.org\/10.3390\/s150716674","relation":{},"ISSN":["1424-8220"],"issn-type":[{"value":"1424-8220","type":"electronic"}],"subject":[],"published":{"date-parts":[[2015,7,10]]}}}