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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.


Schematic cross-sectional view of (a) Back grind; (b) PR layer deposited; (c) Anisotropic etching of Si from backside; (d) Anisotropic etching of SiO2 from front side; (e) Isotropic etching of Si from front side; (f) Released device with photoresist mask removed.
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sensors-15-16674-f002: Schematic cross-sectional view of (a) Back grind; (b) PR layer deposited; (c) Anisotropic etching of Si from backside; (d) Anisotropic etching of SiO2 from front side; (e) Isotropic etching of Si from front side; (f) Released device with photoresist mask removed.

Mentions: After completion of the CMOS process, before the dry etching step, the eight-inch wafer is back-grinded to a thickness of 350 µm from the initial thickness of 750 µm, as shown in the cross section view in Figure 2a. A thick photoresist (PR) layer is then coated on the backside of the eight-inch wafer and patterned as shown in Figure 2b to expose the regions of the sensor devices that need to be exposed while protecting the bonding pads and other regions of the CMOS-MEMS devices that do not need to be released. Anisotropic Deep Reactive Ion Etching (DRIE) is then used to partially etch the SCS substrate from the backside, leaving a layer of 15 µm thick SCS under the CMOS layers to define the MEMS structures as shown in Figure 2c. After SCS etching from backside, the wafer is diced into individual chips and the chips are then mounted on a carrier wafer for front side etching. Figure 2d shows the appearance of trenches after front side etching of SiO2 using Reactive Ion Etching (RIE), while Figure 2e shows a released MEMS structure after using isotropic DRIE to etch through Si from front side. Finally, the photoresist mask is removed to complete the post-CMOS micromachining process as shown in Figure 2f.


Fabrication and Characterization of a CMOS-MEMS Humidity Sensor.

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

Schematic cross-sectional view of (a) Back grind; (b) PR layer deposited; (c) Anisotropic etching of Si from backside; (d) Anisotropic etching of SiO2 from front side; (e) Isotropic etching of Si from front side; (f) Released device with photoresist mask removed.
© Copyright Policy
Related In: Results  -  Collection

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

sensors-15-16674-f002: Schematic cross-sectional view of (a) Back grind; (b) PR layer deposited; (c) Anisotropic etching of Si from backside; (d) Anisotropic etching of SiO2 from front side; (e) Isotropic etching of Si from front side; (f) Released device with photoresist mask removed.
Mentions: After completion of the CMOS process, before the dry etching step, the eight-inch wafer is back-grinded to a thickness of 350 µm from the initial thickness of 750 µm, as shown in the cross section view in Figure 2a. A thick photoresist (PR) layer is then coated on the backside of the eight-inch wafer and patterned as shown in Figure 2b to expose the regions of the sensor devices that need to be exposed while protecting the bonding pads and other regions of the CMOS-MEMS devices that do not need to be released. Anisotropic Deep Reactive Ion Etching (DRIE) is then used to partially etch the SCS substrate from the backside, leaving a layer of 15 µm thick SCS under the CMOS layers to define the MEMS structures as shown in Figure 2c. After SCS etching from backside, the wafer is diced into individual chips and the chips are then mounted on a carrier wafer for front side etching. Figure 2d shows the appearance of trenches after front side etching of SiO2 using Reactive Ion Etching (RIE), while Figure 2e shows a released MEMS structure after using isotropic DRIE to etch through Si from front side. Finally, the photoresist mask is removed to complete the post-CMOS micromachining process as shown in Figure 2f.

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.