Total effective surface area principle for enhancement of capacitive humidity sensor of thick-film nanoporous alumina

C. K. Chung, O. K. Khor, E. H. Kuo, C. A. Ku

Research output: Contribution to journalArticle

Abstract

Total effective surface area is an important factor for environmentally sensing performance. The porous anodic aluminum oxide (AAO) film with a high density of nanopores leads to a tremendous surface area for absorbing water molecules. But such an AAO humidity sensor formed in oxalic acid exhibits a low response of capacitance, especially under the low relative humidity (RH). Here, we demonstrate total effective surface area principle to greatly enhance the performance of AAO capacitive humidity sensor using small anodizing potential in oxalic acid. For pore-dependent surface area, the AAO pore wall would directly affect the absorbance of water molecules and the response of capacitive sensor. Decreasing the anodizing potential reduces both of the pore diameter and interpore distance proportionally but increases the surface area inversely. Therefore, the AAO sensor formed at small 20 V can greatly increase the amount of water molecules absorbed on the wall for enhancing 2–3 times response under low-to-high RH compared to those at 40 and 50 V. The good stability and reliable response/recovery time are also obtained for the AAO sensor synthesized at 20 V in oxalic acid.

Original languageEnglish
Article number126921
JournalMaterials Letters
Volume260
DOIs
Publication statusPublished - 2020 Feb 1

Fingerprint

Capacitive sensors
Humidity sensors
Aluminum Oxide
Thick films
thick films
humidity
Alumina
aluminum oxides
Aluminum
Oxalic Acid
oxalic acid
Oxalic acid
augmentation
sensors
Oxides
anodizing
Anodic oxidation
porosity
Molecules
Water

All Science Journal Classification (ASJC) codes

  • Materials Science(all)
  • Condensed Matter Physics
  • Mechanics of Materials
  • Mechanical Engineering

Cite this

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abstract = "Total effective surface area is an important factor for environmentally sensing performance. The porous anodic aluminum oxide (AAO) film with a high density of nanopores leads to a tremendous surface area for absorbing water molecules. But such an AAO humidity sensor formed in oxalic acid exhibits a low response of capacitance, especially under the low relative humidity (RH). Here, we demonstrate total effective surface area principle to greatly enhance the performance of AAO capacitive humidity sensor using small anodizing potential in oxalic acid. For pore-dependent surface area, the AAO pore wall would directly affect the absorbance of water molecules and the response of capacitive sensor. Decreasing the anodizing potential reduces both of the pore diameter and interpore distance proportionally but increases the surface area inversely. Therefore, the AAO sensor formed at small 20 V can greatly increase the amount of water molecules absorbed on the wall for enhancing 2–3 times response under low-to-high RH compared to those at 40 and 50 V. The good stability and reliable response/recovery time are also obtained for the AAO sensor synthesized at 20 V in oxalic acid.",
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Total effective surface area principle for enhancement of capacitive humidity sensor of thick-film nanoporous alumina. / Chung, C. K.; Khor, O. K.; Kuo, E. H.; Ku, C. A.

In: Materials Letters, Vol. 260, 126921, 01.02.2020.

Research output: Contribution to journalArticle

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