Semiconductor oxide for gas sensing applications

• Main Author: Phuan, Ying Sin.
• Other Authors: Tan Ooi Kiang
• Format: Final Year Project
• Language: English
• Published: 2009
• Subjects: DRNTU::Engineering::Electrical and electronic engineering::Semiconductors
• Online Access: http://hdl.handle.net/10356/17052
• Institution: Nanyang Technological University

The semiconductor gas sensors have been the subject of increasing interest during the past few years. In this project, uniform and dense SrTi1−x FexO3−δ (STFx) composite film was developed. Optimization on the sensing performance and electrical characterization of the optimized composite film devices serve as key importance in research and development of STF02 composite film gas sensor. High energy ball milling technology was used to synthesize STF02 powder. The STF02 sol-gel recipe was fine tuned and effect of pH on sol-gel stability was investigated. Higher amount of DI water can eliminate precipitation at higher pH condition. From Zeta potential test, better dispersion of STF02 powder in medium with pH 3 to pH 4. Slurry preparation procedures were revised to obtain stable and well dispersed STF02 slurry. The slurry was spin coated onto wafer substrate with gold bottom electrodes and annealed. To optimize the STF02 composite film, the effect of deposition parameters and number of composite film layering were investigated. The powder to sol-gel mole ratio (10:1), strontium to DI water ratio (1:108) and composite layering Sol-Composite-Composite-Sol-Sol-Sol structure (SCCSSS) have comparative uniform and dense surface. The pure sol-gel precursor layer on substrate and final capping layer can increase the adhesion of film. Stability of STF02 sol-gel was studied and reasonable solution was proposed. Spin-coated STF02 composite film was fabricated into gas sensing device using photolithography technique. Gas sensing characterization was carried out by using home-designed gas sensor characterization system (GSCS). The STF02 composite sensing device exhibits predominant p-type electronic conductivity and shows optimal sensitivity to oxygen (557), obtained at operating temperature of 300 °C. In addition, the device shows low sensitivity to other four types of test gases (H2, CO, CH4 and NH3), with no significant selectivity to any of the gases.