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When voltage is applied
to zirconia solid electrolyte electric current flows
in it and gaseous oxygen is pumped out from one
side to the other by oxygen ion conduction. If the
oxygen amount supplid to the electrolyte is restricted
by a small hole or porous material, the electric
current is saturated at a constant level. The saturated
current is called limiting current and proportional
to the ambient oxygen concentration. Therefore,
the oxygen concentration can be detected from the
current by applying a fixed voltage to the electrolyte.
An oxygen sensor on
the basis of the above principle was fabricated
by utilizing thin-film micro-machining technology.
In the fabrication process, thin-films of platinum
cathode, zirconia electrolyte and platinum anode
were successively laminated on a porous alumina
substrate.
Features of the oxygen
sensor include small size (1.8mm square), wide measuring
range for oxygen content (0 to 90% O2),
high-speed response (200ms for 90% response). Other
features of the sensor are long maintenance free
use, small heater power consumption by heater (approximate
1W), suitable fabrication proceses for mass production,
excellent heat resistance, and high reliability
under severe conditions.
The sensor can be
utilized as a monitoring device to control fuel
combustion efficiencies, acceleration or retardation
of chemical reactions, oxidation states of sealed
products, medical treatments, and many other applications
where ambient oxygen content plays an important
role.
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