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Electrode for conductivity measurement

Conductivity measurement     Picture

In conducting polymer film having a high resistance (R>10k), a conductivity

measurement commonly performed by simple 2 terminal method. In a film with low

resistance (R<10k), a simple 2 terminal method will be affected by surface leak

current. Therefore must provide a guard ring electrode to measure inner current


Measurement using simple 2 terminal method to measure low resistance sample

(high conductivity) will greatly affected by the resistance of lead wire used in

measurement and joint resistance between lead wire and sample. Measurement using

4 terminal method can be carry out without gaining this problem. A principle of

simple 4 terminal method shown at the right figure. Attach four electrodes on

sample, add constant current I from constant current source S through current

electrode C and C' into sample. Measure potential difference UPP' between two

point P and P' on sample using high input impedance potentiometer (POT). At this

time, UPP' and ZPP' (impedance between P and P') have a relation as UPP' =

IZPP'. If distance of potential terminal is d and cross section area is S then

the conductivity is a function described below.

Usually AC current source are used in measurement so this measurement called by

AC 4 terminal method. 4 terminal measurement method using combination of AC

source, amplifier and phase detector also applicable using this electrode.

Electrode for conductivity measurement

For current electrode and potential measuring electrode are using Pt vacuum

evaporated on Quartz. Potential terminal are printed with distance as figure

below, therefore distance are exchangeable by changing connection terminal. In

in-situ measurement of doped conducting polymer generating insulator-metal

transition is performed by 2 terminal method on insulator phase low dopant area

and with 4 terminal method on metal phase high dopant area.