Technical Description
A sensor is the result of a process to prepare a sensible layer
based on semiconductor oxides. The basic phenomena for is
functioning is the absorption on its surface of ions-oxygen
which react with the gases present in the atmosphere.
When a semiconductor based on type
n
metal oxides
(conduction by electrons) is burned at a certain
temperature, the oxygen present in the atmosphere is
adsorbed as a ionic form on its surface.
The electrons in the conduction area of the above
semiconductors are transferred from the surface area to
the oxygen adsorbed, with the result of creating an empty
area around the surface. It is generated a surface
potential which acts as a barrier able to hinder the
electrons flow among the granes.
.
In presence of reducing gases, the density on the surface
of the negative charged oxygen decreases; in that way
the hight of the barrier in contact with the granes gets
lower, as evidenced in the Fig. 1.3.
The reduced barrier decreases the resistance of the
sensor (always for a semiconductor type n) which, at a
microscopic level, is detected and measured by specific
circuital elements.
On the other hand, in presence of oxydant gases the
reaction leads to a decreasing number of free electrons
and to an increase of the potential barrier and therefore
of the sensor resistance .
In the case of semiconductor type
p
the behaviour could
be described similarly taking into account that those
with more charge are the gaps.
Fig 1.2 –Adsorbtion of Oxygen on the
surface and its effect on the border granes
Fig. 1.3 – Example of reaction with a
reducing gas (carbon monoxide)
ORION S.r.l.
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