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Hydrogen sensor application of Pd doped anodic TiO 2  film 

Workshop on Atomic-Scale Challenges in Advanced Materials Defects in Materials ASCAM VI. Hydrogen sensor application of Pd doped anodic TiO 2  film . 23. Aug. 2013 Jongyun Moon, Hannu-Pekka Hedman, Risto Punkkinen Department of Information Technology. Introduction.

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Hydrogen sensor application of Pd doped anodic TiO 2  film 

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  1. Workshop on Atomic-Scale Challenges in Advanced Materials Defects in Materials ASCAM VI Hydrogen sensor application of Pd doped anodic TiO2 film  23. Aug. 2013 Jongyun Moon, Hannu-Pekka Hedman, Risto Punkkinen Department of Information Technology

  2. Introduction

  3. Hydrogen sensor based on semiconductor Semiconducting oxides that can be used for hydrogen detection SnO2, ZnO, TiO2, FeO, Fe2O3, NiO, Ga2O3, In2O3, MoO3 and WO3 Hydrogen is detected by the change of the electrical properties when the metal oxide are exposed to target gases. Advantages: High sensitivity, feasibility of miniaturization, low production cost Shortcoming: low selectivity toward carbon monoxide, methane, alcohols, humidity etc. Decoration with catalytic materials can achieve improvements in selectivity and sensitivity

  4. Hydrogen sensor using TiO2 thin film via anodization • TiO2 has a large electric band gap of 3.0 eV. • Crystallized TiO2 nanostructures prepared by anodization has shown a remarkable hydrogen sensing performance • (TiO2 nanotube arrays:to 1000 ppm H2 a resistance variation of 107). • O.K. Varghese, Mater. Res. Soc. Symp. Proc. 835 (2005) • Low production cost due to an easy synthesis method • Shortcoming: • Ti foil which underlines TiO2 film, limit the usage of the material in various applications. • i) metal electrode atop the oxide layer may diffuse into the Ti metal layer and cause an electrical short circuit • Ii) vulnerable to mechanical shock or vibrations. Figure 1. Schematic of a gas sensor using TiO2 nanotube arrays on Ti metal sheet

  5. Research objective Synthesis of TiO2 thin film on foreign substrate with metal electrodes by using anodization → Reliable sensor structure. Decoration of the sensor material with catalyric material (ex. Pd) Improvement of gas sensor performance → Sensitivity, response/recovery time and selectivity to other gases

  6. Materials and Methods

  7. Anodization of Ti on SiO2/Si wafer Figure 2. An image of the anodization experiment instrument • Substrate: SiO2 (1 µm)/Si ( 2 cm × 2.5 cm) • Anode : Ti film (500 nm) by DC sputtering in argon (Ar) at a pressure of 0.02 mbar at 150°C • Cathode : Platinum sheet (99.98%) • Electric potential : 30 - 60 V (Voltage ramping rage: 0.5 V/s) • Electrolyte : NH4F 0.25wt % in Ethylene Glycol • Anodization bath temperature : 5 °C

  8. Schematic of the sensor preparation Pt Al Ti film (500 nm) deposition by DC sputtering at 150°C Heat treatment at 300 °C for 10 min Au/Al metal electrode deposition by DC sputtering Anodization Pd thin film depostion Formation of Porous TiO2 film Heat treatment for crystallization at 500°C

  9. Analysis • Material characteristics i) Observation of current behavior during the andization ii) FESEM (Field Emission Scanning Electron Microscope) analysis iii) EDS (Energy-dispersive X-ray spectroscopy) • Gas sensor measurement i) Sensor Temperature control: Heater plate (15 mm × 15 mm × 10 mm, Ultramic 600, Watlow) ii) Measurement chamber: 56 l glass test chamber with continuous air circulation iii) Desired volume of hydrogen was inserted to chamber. * Concentration was verified by a commercial sensor (SX-917, Sensorex, Finland)

  10. Results

  11. Current plot during anodization Voltage: 60V Voltage increase 0-60V

  12. FESEM (Field Emission Scanning Electron Microscope) • Thickness : ≈ 20nm • Diameter : ≈ 15-20 nm FESEM image of TiO2 layer prepared by anodization using 30V

  13. EDS (Energy-dispersive X-ray spectroscopy) TiO2 area Metal electrode area

  14. Gas sensor measurement 180°C 160°C 140°C Low concentration of H2 : 1 – 50 ppm

  15. Sensor response Operating temperature: 160°C Y (Trend line equation) = 1.3219x0.8914 R² (correlation coefficient) = 0.9652

  16. Conclusion Porous TiO2 film with Pd thin film was synthesized on SiO2/Si substrate with metal electrodes without loss of Ti/TiO2 layer Its morphology modification is feasible by the control of the anodization experimental parameters, such as the voltage. The formation of TiO2 nanostructure can be interpreted by monitoring the anodic current variation The sensor exhibited a three order magnitude drop in resistance on exposing to 10,000 ppm hydrogen gas at 160°C

  17. Future work Since the study is still ongoing, more material characteristics are required. Selectivity measurement to various gases Modification of the nanostructure to improve sensor’s performance Material decoration using various doping methods Miniaturization for the mass production Integration of the sensor into a practical electric device

  18. Thank you for your attention

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