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Proceedings of the Eurosensors XXIII conference
Novel Fabrication Process Using Nanoporous Anodic Aluminum
Oxidation And MEMS Technologies For Gas Detection
Jun-Wei Huang, Kevin Chih-Cheng Lu*, Yon-Sheng Huang and Sen-Po Wu
Graduate Institute of Mechtronic Engineering, National Taipei University of Technology, Taipei, Taiwanti
Prof.：Yi-Chu Hsu
Student：Kuo-Wei Yen
Date：2012.06.07
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Outlet
•Introduction
•Device and fabrication
•Verification of nanoporous TiO2 thin films
•Experimental results
•Conclusion
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Introduction
Chemoresistive gas sensors have been most developed and widely used in
industrial applications and environmental control.
Recently , along with widespread applications of nano-structural materials,
corroborated smaller materials dimension and extensive surface area could improve
sensitivity and response time.
This paper to present a novel approach to produce nano-porous gas sensors
which combine thin film AAO process with MEMS micromachining.
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Device and fabrication
The sensor can be made by standard MEMS technologies and our revised AAO
process, followed by a bulk back-etch with KOH or TMAH etchants to form the membrane
in which a thick oxide layer of 1.5 μm is applied as an etch stop.
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A perspective illustration of the sensor device and Cross-section of sensor
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Device and fabrication
Wafer deposited 1.5μm of
PECVD silicon dioxide.
Masking and
Etching
3 % of phosphoric acid for 4 hours
at room temperature
Lift-off 1μm of aluminium thin film
sputtering onto silicon dioxide
AAO process was performed by using 0.3 M oxalic acid
solution at 4°C for 90 minutes
AAO process DC 55~60V
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Device and fabrication
The aluminum oxide nanotubes acted as an dry-etch mask (see figure (a)), and RIE
process etched through Al2O3 to form nanoporous pores ranging 500~750 μm on silicon or
silicon dioxide (see figure (b)).
(a)
(b)
SEM images of nanoporous gmeoetry by TiO2 thin film:(a) aluminum oxide etching mask;(b) nanoporous Si surface.
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Verification of nanoporous TiO2 thin films
To characterize the surface geometry of as-deposited TiO2 layer, scanning
electron microscopy (SEM) image.
XRD result confirmed a prominent intensity peak at 2-theta degree of 24.97°
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The SEM image of nanoporous geometry
of the active sensing area, covered by 260
nm TiO2 thin film. (Left)
The XRD result of ananoporous TiO2 thin
film.(Right)
Experimental results
Experimental results corresponding gas response to different oxygen concentrations
were successfully
Gas detection resistance to different oxygen concentrations at 500 ℃ with non-porous TiO2 active film. (Left)
Gas detection resistance to different oxygen concentrations at 500 ℃ with nanoporous TiO2 active film.(Right)
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Comparisons of sensor sensitivity of nanoporous and non-porous TiO2 active films at 500 ℃.
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Conclusion
A new way to fabricate nano-porous anodic aluminum oxide structure.
This new method is highly porous surface that is believed to enhance sensor sensitivity.
TiO2 thin film of gas response in terms of less noise, fast response time and improved
sensitivity.
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