CMOS-MEMS Capacitive Humidity Sensor

• Published in: Journal of microelectromechanical systems Vol. 19; no. 1; pp. 183 - 191
• Main Authors: Lazarus, N., Bedair, S.S., Lo, C.-C., Fedder, G.K.
• Format: Journal Article
• Language: English
• Published: New York, NY IEEE 01.02.2010; Institute of Electrical and Electronics Engineers; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Applied sciences; Capacitance; Capacitance measurement; Capacitive sensors; Cartridges; Chemical sensing; Chemical sensors; CMOS microelectromechanical systems (MEMS); Coatings; Deposition; Electronic equipment testing; Electronics; Exact sciences and technology; Humidity; Humidity measurement; Instruments, apparatus, components and techniques common to several branches of physics and astronomy; Mechanical instruments, equipment and techniques; Microelectronic fabrication (materials and surfaces technology); Micromechanical devices and systems; permittivity; Physics; Polymer films; Relative humidity; Respirators; Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices; Sensor systems; Sensors; Solvents; Temperature sensors; Relative humidity; Chemical sensors; CMOS microelectromechanical systems (MEMS); Capacitive transducer; Measurement sensor; Experimental study; Capillary tube; Temperature sensors; Temperature measurement; Humidity measurement; High sensitivity; Complementary MOS technology; Chemical sensing; Capacitance; humidity; Maskless lithography; Embedded transducer; Permittivity; Microelectromechanical device
• ISSN: 1057-7157; 1941-0158
• DOI: 10.1109/JMEMS.2009.2036584

A high-sensitivity capacitive humidity sensor intended for use as part of a respirator end-of-service-life indicator system is presented. This paper reports a method for improving the sensitivity of integrated capacitive chemical sensors by removing the underlying substrate. The sensor is integrated with CMOS testing electronics using maskless postprocessing followed by ink-jet deposition of a sensitive polymer. Two different methods of depositing polymer, namely, capillary wicking and coating the top surface directly, were investigated. The sensors had measured sensitivities of 0.16% to 0.18% change in capacitance per percent relative humidity, which is the highest demonstrated for an integrated capacitive humidity sensor. Temperature sensitivity of the sensor, which is an important criterion for a sensor intended for a variety of different ambient conditions, was measured to be 0.07%/°C. The cross sensitivities to toluene and acetone, which are two common industrial solvents that are filtered by respirator cartridges, were measured to be 2.4 × 10 -4 and 9.0 × 10 -5 %/ppm, respectively.