enabling © 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) Copyright © 2009-2013