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Oxygen sensor

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Oxygen sensor

  1. 1. Oxygen sensor (2006-2012) • Introduction – Before the extinction level event in Japanese vacuum-technology- based manufacturing industries in 200X, the detection of trace amounts (e.g., 10-9, 10-12, 10-15, …) of oxygen had been gaining increasing attention. – As the key device for in-situ monitoring trace levels of oxygen, one kind of sensor had been focused. – Our R&D project was subsidized by the government and the company. 1
  2. 2. Oxygen sensor (2006-2012) • What’s new? – Measuring procedure: • To desorb oxygen from an n-type semiconductor surface by ultraviolet(UV) light irradiation. • To adsorb oxygen onto the semiconductor surface after turning the UV-light off. • To measure electrical resistance of the n-type semiconductor surface. e.g., 1 sec 2
  3. 3. Oxygen sensor (2006-2012) • What’s new? – Measuring procedure: 3 Ec Ev NOMO(O2 -) Interaction between oxygen and n-type semiconductor
  4. 4. Oxygen sensor (2006-2012) • What’s new? – To use ultrathin film with the thickness being – comparable with polaron diameter: ( Large Low conc. O2 ) 6 TiO6 units at PO2=10-20 5 TiO6 units at PO2=10-9 ( Small High conc. O2 ) 4
  5. 5. Oxygen sensor (2006-2012) • What’s new? – To use ultrathin film with the thickness being comparable with polaron diameter: 5 Polaron diameter Larger polaron diameter: Higher conductance (Lower resistance) Smaller polaron diameter: Lower conductance (Higher resistance) Film thickness TiO6 unit cell
  6. 6. Oxygen sensor (2006-2012) • What’s new? – Hypothetical image: Although SrTiO3 is paraelectric, near the surface of STO adsorbed oxygen can (?) induce the ferroelectric-like Ionic displacement. 6 Sr O Sr O O Sr O Sr Sr O Sr O O e O Ti O Ti
  7. 7. Oxygen sensor (2006-2012) • What’s new? – Only paraelectric perovskites can show oxygen-concentration- sensitive electrical resistance. 7
  8. 8. Oxygen sensor (2006-2012) • Performance: 8 1.0E+14 1.0E+12 1.0E+10 1.0E+08 1.E-15 1.E-10 1.E-05 1.E+00 Resistance (Ω) Oxygen concentration ( PO2 / (PO2 + PHe) ) 108 10-15 100 1014 1012 1010 10-10 10-5
  9. 9. Oxygen sensor (2006-2012) 9 http://toruhara.page.tl/2-.--Solid_Gas-Interface.htm

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