Thin Film Ruthenium Oxide - Iridium Oxide Thermocouples

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THIN FILM RUTHENIUM OXIDE - IRIDIUM OXIDE THERMOCOUPLES

KENNETH G. KREIDER National Institute of Standards and Technology,

Gaithersburg, MD

20899

ABSTRACT Ruthenium

oxide and iridium oxide have outstanding resistance

to

corrosion.

These oxides are also excellent electrical conductors and have

been used

as

electrical

biochemical

and

charge

electrochemical

injection properties

electrodes. have

consideration as high temperature pH electrodes. useful form for these applications

also

Their led

unique

to

their

Thin films are the most

as they permit the miniaturization of

fast response sensors and electrodes. This study was used to characterize the thermoelectric and electrical conductance parameters of ruthenium and iridium oxide sputtered thin films. The electric and thermoelectric properties of the thin films were found to be sensitive to the annealing temperature of the sputtered oxides. properties of the film are related to the microstructure, crystal structure as determined by x-ray diffraction. used to stabilize

The

stoichiometry and

Heat treatments were

the thermoelectric response and the thermal coefficient

of resistivity.

INTRODUCTION Thin film thermocouples hold great promise for measuring temperature in unique applications and at very low cost.

Their simplicity, small size,

fast response, and minimal disturbance to the solid surface being monitored have led to numerous applications.

Early reports on sputtered bismuth and

antimony [1] led to their use in controlling the temperature in electronic circuits

[2] and vacuum guages

[3].

Further developments of their high

temperature stability and utilizing their fast response led to applications in turbine engines [4,5] and diesel engines [6,7].

The very fast response

characteristics were measured using pulsed laser irradiation [8,9]

which

established the microsecond capabilities of the one micrometer thick sensor. Experimental

[1,10]

and theoretical

define the size effect in

[11]

investigations

thin film thermocouples, however,

have helped

to

the output of

individual thermocouples appears to be quite sensitive to size, composition, and other structural properties. Mat. Res. Soc. Symp. Proc. Vol. 234. ©1991 Materials Research Society

206

This

investigation was

initiated to find a thermocouple pair less

sensitive to corrosion than the type S (Pt + PtlO%Rh)

thermocouple.

The

chemical

thermocouples

are

sensitive

environments

in

which

the

platinum

alloy

to corrosion include halogen releasing solutions such as aqua

regia and cyanide containing solutions.

This corrosion sensitivity has led

to the use of ruthenium oxide and iridium oxide for electrodes in the Cl. [12] and as charge injection electrodes in vitro [13].

production process With the success

of these two highly conductive

demanding outstanding appeared logical. oxides

corrosion

We have,

[14,15,16]

resistance

oxides

their

for several years,

use

in

applications

as thermoelements

been investigating

for use as pH sensors at el

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