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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.


(a) Schematic of the top view; (b) Cross-sectional view along AA’ showing CMOS layers and the SCS substrate.
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sensors-15-16674-f001: (a) Schematic of the top view; (b) Cross-sectional view along AA’ showing CMOS layers and the SCS substrate.

Mentions: The sensor device is fabricated using standard 0.35 µm CMOS process technology and post-CMOS micromachining through a multiple project wafer (MPW). The CMOS process technology consists of two polysilicon, three metal, several dielectric layers, and two vias. All metal layers are aluminum (Al), whereas silicon dioxide (SiO2) is used as the dielectric layer and tungsten is used for the vias. Figure 1a shows a schematic of the top view of the device and consists of a plate supported by four beams with each beam having two sections of different widths of 7 µm and 19 µm but the same length of 240 µm each. The stator comb-fingers are anchored to the substrate while the rotor comb-fingers are attached to the 400 µm × 400 µm plate and also to the thick 19 µm beam (beam 2). Figure 1b shows a schematic cross-sectional view of the device viewed along AA’ to show the CMOS layers and the single crystal silicon (SCS) substrate.


Fabrication and Characterization of a CMOS-MEMS Humidity Sensor.

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

(a) Schematic of the top view; (b) Cross-sectional view along AA’ showing CMOS layers and the SCS substrate.
© Copyright Policy
Related In: Results  -  Collection

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

sensors-15-16674-f001: (a) Schematic of the top view; (b) Cross-sectional view along AA’ showing CMOS layers and the SCS substrate.
Mentions: The sensor device is fabricated using standard 0.35 µm CMOS process technology and post-CMOS micromachining through a multiple project wafer (MPW). The CMOS process technology consists of two polysilicon, three metal, several dielectric layers, and two vias. All metal layers are aluminum (Al), whereas silicon dioxide (SiO2) is used as the dielectric layer and tungsten is used for the vias. Figure 1a shows a schematic of the top view of the device and consists of a plate supported by four beams with each beam having two sections of different widths of 7 µm and 19 µm but the same length of 240 µm each. The stator comb-fingers are anchored to the substrate while the rotor comb-fingers are attached to the 400 µm × 400 µm plate and also to the thick 19 µm beam (beam 2). Figure 1b shows a schematic cross-sectional view of the device viewed along AA’ to show the CMOS layers and the single crystal silicon (SCS) substrate.

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.