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Fabrication and Characterization of a CMOS-MEMS Humidity Sensor.

Dennis JO, Ahmed AY, Khir MH - Sensors (Basel) (2015)

Bottom Line: 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 °C to 80 °C and a maximum hysteresis of 0.87% RH is found at a relative humidity of 80%.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.

View Article: PubMed Central - PubMed

Affiliation: Department of Fundamental and Applied Sciences, Universiti Teknologi PETRONAS, Bandar Seri Iskandar, Perak Darul Ridzuan 32610, Malaysia. johndennis@petronas.com.my.

ABSTRACT
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 °C to 80 °C) 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 µm 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 °C to 80 °C 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.

No MeSH data available.


Sensitivity of the CMOS-MEMS humidity sensor vs. temperature.
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sensors-15-16674-f010: Sensitivity of the CMOS-MEMS humidity sensor vs. temperature.

Mentions: Figure 9 shows the measured results of output voltage of the device as a function of the relative humidity in the linear region from 60% RH to 95% RH when the device was operated at various applied voltages from 2 Vpp to 6 Vpp (corresponding to different operating temperatures from 40 °C to 80 °C) at a constant frequency of 2 Hz. It is observed that the output voltage of the device increases with increasing humidity for different operating temperatures. The slopes of the graph indicate that the sensitivity improves at higher temperatures, as indicated in Figure 10, where the sensitivity is seen to increase linearly from 0.102 mV/% RH to 0.501 mV/% RH with an increase in the temperature from 40 °C to 80 °C. This increase in sensitivity with temperature is expected as desorption of gaseous species such as H2O in humidity detection on the TiO2 surface is enhanced with increase in temperature. At higher temperatures more gaseous species desorb from the sensor surface, resulting in an overall decrease in the mass of the plate and TiO2 and thus an increase in the amplitude of the vibrating structure.


Fabrication and Characterization of a CMOS-MEMS Humidity Sensor.

Dennis JO, Ahmed AY, Khir MH - Sensors (Basel) (2015)

Sensitivity of the CMOS-MEMS humidity sensor vs. temperature.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4541900&req=5

sensors-15-16674-f010: Sensitivity of the CMOS-MEMS humidity sensor vs. temperature.
Mentions: Figure 9 shows the measured results of output voltage of the device as a function of the relative humidity in the linear region from 60% RH to 95% RH when the device was operated at various applied voltages from 2 Vpp to 6 Vpp (corresponding to different operating temperatures from 40 °C to 80 °C) at a constant frequency of 2 Hz. It is observed that the output voltage of the device increases with increasing humidity for different operating temperatures. The slopes of the graph indicate that the sensitivity improves at higher temperatures, as indicated in Figure 10, where the sensitivity is seen to increase linearly from 0.102 mV/% RH to 0.501 mV/% RH with an increase in the temperature from 40 °C to 80 °C. This increase in sensitivity with temperature is expected as desorption of gaseous species such as H2O in humidity detection on the TiO2 surface is enhanced with increase in temperature. At higher temperatures more gaseous species desorb from the sensor surface, resulting in an overall decrease in the mass of the plate and TiO2 and thus an increase in the amplitude of the vibrating structure.

Bottom Line: 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 °C to 80 °C and a maximum hysteresis of 0.87% RH is found at a relative humidity of 80%.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.

View Article: PubMed Central - PubMed

Affiliation: Department of Fundamental and Applied Sciences, Universiti Teknologi PETRONAS, Bandar Seri Iskandar, Perak Darul Ridzuan 32610, Malaysia. johndennis@petronas.com.my.

ABSTRACT
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 °C to 80 °C) 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 µm 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 °C to 80 °C 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.

No MeSH data available.