Electrical conductivity of zinc oxide films to be used in an oxygen partial pressure sensor is measured as a function of temperature, oxygen partial pressure, and other atmospheric constituents. Time response following partial pressure changes is studied as a function of temperature and environmental changes

Canady, K. S.

Wortman, J. J.

English

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September 1970	 Brief 70-10419 
NASA TECH BRIEF 
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be directed to the Technology Utilization Division, NASA, Code UT, Washington, D.C. 20546. 
Thin Film Devices Used as Oxygen Partial Pressure Sensors 
The use of thin films of zinc oxide to measure the 
oxygen pressure of specific environments as a function 
of conductance is relatively new. The method is useful 
in that the simplicity, low power, and large dynamic 
range will allow improved pressure sensing. This 
information should prove interesting to industries 
involved in monitoring or detecting oxygen levels 
at high temperatures. 
The research effort centered in two major areas: 
preparing and characterizing zinc oxide and tin oxide 
films to be used for oxygen sensing elements; and 
designing and constructing a laboratory model suit-
able for evaluating thin films for sensing oxygen 
partial pressure. 
Zinc oxide films were successfully prepared at ele-
vated temperatures and studied experimentally and 
theoretically. Their electrical conductivity was meas-
ured as a function of temperature, oxygen partial 
pressure, and other atmospheric constituents. The 
time response following partial pressure changes was 
also studied as a function of temperature and environ-
mental changes. Using the results, an oxygen partial 
pressure sensor was fabricated utilizing zinc oxide 
films. 
Tin oxide doped with zinc wasalso investigated and 
found to be sensitive to oxygen partial pressures 
at temperatures less than 300 C C. The tin oxide films 
exhibited more instability than films of zinc oxide, 
but had much shorter response times. Due to the dif-
ficulty in preparing the zinc doped tin oxide films and 
their instability, further effort in this area was dis-
continued in favor of the more promising zinc oxide 
films. 
To illustrate the feasibility of using thin films as 
oxygen sensing elements, a laboratory model was fab-
ricated and evaluated. The oxygen partial pressure sen-
sor consisted of a heater, electrical readout, and tem-
perature controller. The entire unit required approx-
imately seven watts of power. 
In testing the laboratory model, no failures were 
observed indicating a sensor lifetime of several 
months. The use of thin films as oxygen sensors made 
it feasible for the sensing head to be very small and 
lightweight. The sensing head for the laboratory model 
weighed approximately 30 grams and occupied 30cm3. 
Additional laboratory models proved to be rugged, 
stable, and capable of a wide sensing range of oxygen 
partial pressures from less than 1 mm Hg to greater 
than one atmosphere. Time constants of approxi-
mately one minute were possible, and a 63 percent 
value of the oxygen partial pressure was obtained. 
Note: 
The following documentation may be obtained 
from:
Clearinghouse for Federal Scientific 
and Technical Information 
Springfield, Virginia 22151 
Single document price $3.00 
(or microfiche $0.65) 
Reference: 
NASA-CR-I 182(N68-35 149), An Investi-
gation of Thin Film Oxygen Partial Pres-
sure Sensors 
Patent status: 
No patent action is contemplated by NASA. 
Source: K.S. Canady and J.J. Wortman of 
Research Triangle Institute 
under contract to 
Langley Research Center 
(XLA-06473) 
Category 04 
This document was prepared under the sponsorship of the National	 Government assumes any liability resulting from the use of the 
Aeronautics and Space Administration. Neither the United States	 information contained in this document, or warrants that such use 
Government nor any person acting on behalf of the United States	 will be free from privately owned rights.
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Thin film devices used as oxygen partial pressure sensors

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