Laser-based Techniques and Applications - LATA
Electrical mesurements
Conductivity measurements (I-V measurements) at RT

Principle of the method

We apply the van der Pauw technique to deduce the sheet resistance RS. The principle of the measurement is shown below:


RA and RB are related to the sheet resistance through the van der Pauw equation:

 exp(-πRA/RS) + exp(-πRB/RS) = 1

To obtain the two characteristic resistances, one applies a dc current I into contact 1 and out of contact 2 and measures the voltage V43 from contact 4 to contact 3 as shown above. Next, one applies the current I into contact 2 and out of contact 3 while measuring the voltage V14 from contact 1 to contact 4. RA and RB are then

RA = V43/I12 and RB = V14/I23


This equation can be solved numerically for RS. The bulk electrical resistivity can be calculated using

ρ = RS d

where d is the film thickness.

  B.  Experimental setup

The experimental setup is shown in the figure below:


The electronic circuit consists of a Keithley M. 6220 DC current source and a Keithley Mo. 2182 Nanovoltmeter. Both instruments are connected to a pC via an IEEE-488 interface.

The home-made sample holder consists of 4 spring probes that are mechanically pressed of the thin film sample. The probes form a quadrant with side length 10 mm (minimum sample dimensions).

  C.  Example

The I-V measurement is presented for a PLD grown NiO thin film with the following deposition parameters:

Glass substrate temperature 200 oC

 Oxygen pressure 10 Pa.



MO thin film development
Gas sensor testing
Electrical mesurements
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