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organic electronics
Calculating Capacitance
The capacitance of a parallel plate capacitor is given by:
Where Ɛ0 is the permittivity of a vacuum and has a value of Ɛ0 = 8.85 x 10-12 farads per meter (F·m−1)
and Ɛr is the relative permittivity for a given dielectric material. The area of the capacitor is given by A
and the thickness of the dielectric is given by d.
Therefore the capacitance per unit area ( ) is given by:
Calculate for the below typical gate dielectrics in S.I Units.
Material
Ɛr
Thickness (nm)
Thickness (m)
PMMA
2.6
1200 nm
Silicon Oxide
3.7
300 nm
(Fm-2)
However, since OFET mobility is usually measured in cm2/Vs it is useful to calculate capacitance in
these units too. Therefore, recalculate the capacitance calculate for the below typical gate
dielectrics in F/cm2.
First calculate the value of Ɛ0 in farads per cm (F.cm−1) then recalculate Ci in F.cm−2
Ɛ0 = ..................... F.cm-1
Material
Ɛr
Thickness (nm)
Thickness (cm)
PMMA
2.6
1200 nm
Silicon Oxide
3.7
300 nm
(F.cm-2)
If the area of a 300 nm thick silicon drain contact pad is 4mmx2mm then calculate what the actual
capacitance should be:
Material
(from above) (F.cm-2)
300 nm Silicon Oxide
Now measure on the probe station - what do you get...
Ossila Limited
Area (cm2)
Capacitance (F)
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