Oxygen sensor

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


• 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


• What’s new?

– Measuring procedure:

3

Interaction between oxygen and n-type semiconductor

Ec

Ev

NOMO(O2-)


• 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


• 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


• What’s new?– Hypothetical image:

Although SrTiO3 is

paraelectric,

near the surface of STO

adsorbed oxygen can (?)

induce the

ferroelectric-like

Ionic displacement.

6

O

Sr

Sr

O

O

Sr

Sr

O

Sr

Sr

O

O

O e

Ti

O

Ti

O


• What’s new?

– Only paraelectric perovskites can show oxygen-concentration-sensitive electrical resistance.

7


• Performance:

8

1.0E+08

1.0E+10

1.0E+12

1.0E+14

1.E-15 1.E-10 1.E-05 1.E+00

Res

ista

nce

(Ω)

Oxygen concentration ( PO2 / (PO2 + PHe) )

108

10010-15

1014

1012

1010

10-10 10-5


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http://toruhara.page.tl/2-.--Solid_Gas-Interface.htm

http://toruhara.page.tl/2-.--Solid_Gas-Interface.htm

Education

Oxygen sensor