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.
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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.
2e.g., 1 sec
3. Oxygen sensor (2006-2012)
• What’s new?
– Measuring procedure:
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Interaction between oxygen and n-type semiconductor
Ec
Ev
NOMO(O2
-)
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 )
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5. Oxygen sensor (2006-2012)
• What’s new?
– To use ultrathin film with the thickness being
comparable with polaron diameter:
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Polaron diameter
Larger polaron diameter:
Higher conductance
(Lower resistance)
Smaller polaron diameter:
Lower conductance
(Higher resistance)
Film
thickness
TiO6 unit cell
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.
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O
Sr
Sr
O
O
Sr
Sr
O
Sr
Sr
O
O
O e
Ti
O
Ti
O
7. Oxygen sensor (2006-2012)
• What’s new?
– Only paraelectric perovskites can show oxygen-
concentration-sensitive electrical resistance.
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