CMOS-MEMS Capacitive Humidity Sensor

Abstract

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 mask-less post-processing followed by inkjet deposition of sensitive polymer. This technique is demonstrated with a humidity sensor but could be used for other types of analytes. The measured sensitivity is 0.18% change in capacitance per percent relative humidity, a factor of four improvement over previous integrated capacitive sensors.

CMOS-MEMS technologies for the applications of environment sensors and environment sensing hubs

“…Therefore, various MEMS technologies have also been investigated and developed to design and fabricate micro humidity sensors. The sensing mechanisms include resistive type [111][112][113], capacitive type [88,109,[114][115][116][117][118][119][120][121][122][123][124], piezo-resistive type [125] and resonance type [126,127], etc. This section will review the CMOS-MEMS humidity sensors and their monolithic integration with thermometer as well.…”

“…The basic structure of a CMOS-MEMS humidity sensor includes the water vapor sensitive materials that absorb external water vapor combined with a specially designed sensing structure. Various CMOS process platforms combined with appropriate post-CMOS fabrication techniques have been exploited to realize resistive type [113], capacitive type [116][117][118][119][120][121][122][123][124], and resonant type [126,127] humidity sensors. Due to the advantages of multi-layer stacking and submicron level linewidths of CMOS processes, the CMOS-MEMS approach has been most commonly utilized to fabricate capacitive type humidity sensors.…”

“…Additionally, a more comprehensive measurement of relative humidity sensor by integrating the humidity sensor with temperature sensor on a single chip can be achieved by the CMOS-MEMS technologies [88,117,122]. The following sub-sections will focus on capacitive humidity sensors of different sensing materials and structures design [116][117][118][119][120][121][122][123][124], and also provide a brief review for the CMOS-MEMS resistive [113] and resonant [126,127] type humidity sensors.…”

“…By exploiting the existing BEOL thin film layers of the CMOS processes and design rules of the CMOS processes, different sensing electrodes can be designed and fabricated using post-CMOS processes, and then the water vapor sensing materials can be filled into the sensing electrodes. Generally speaking, the design concerns for humidity sensors may include the response time, and sensitivity [109,[111][112][113][114][115][116][117][118][119][120][121][122][123][124][125][126][127], etc. The response time indicates how fast the sensor can detect two different humidity levels.…”

“…Since polyimide is a compatible material for the CMOS process, it is one of most common sensing material for CMOS-MEMS capacitive humidity sensors [88,116,117,[120][121][122][123]. Polyimide can absorb water vapor due to its morphological structure [128].…”