Editing Electron mobility (section)

====Using saturation mode====
In this technique,<ref name=Rost/> for each fixed gate voltage V<sub>GS</sub>, the drain-source voltage V<sub>DS</sub> is increased until the current I<sub>D</sub> saturates. Next, the square root of this saturated current is plotted against the gate voltage, and the slope ''m''<sub>sat</sub> is measured. Then the mobility is:
<math display="block">\mu = m_\text{sat}^2 \frac{2L}{W} \frac{1}{C_i}</math>
where ''L'' and ''W'' are the length and width of the channel and ''C''<sub>''i''</sub> is the gate insulator capacitance per unit area. This equation comes from the approximate equation for a MOSFET in saturation mode:
<math display="block">I_D = \frac{\mu C_i}{2}\frac{W}{L}(V_{GS}-V_{th})^2.</math>
where ''V''<sub>th</sub> is the threshold voltage. This approximation ignores the [[Early effect]] (channel length modulation), among other things. In practice, this technique may underestimate the true mobility.<ref name=Rost2>{{cite book|author=Constance Rost-Bietsch|title=Ambipolar and Light-Emitting Organic Field-Effect Transistors|url=https://books.google.com/books?id=Xxvt0CkVKaIC&pg=PA19|access-date=20 April 2011|date=August 2005|publisher=Cuvillier Verlag|isbn=978-3-86537-535-3 |pages=19–}} "Extracting the field-effect mobility directly from the linear region of the output characteristic may yield larger values for the field-effect mobility than the actual one, since the drain current is linear only for very small VDS and large VG. In contrast, extracting the field-effect mobility from the saturated region might yield rather conservative values for the field-effect mobility, since the drain-current dependence from the gate-voltage becomes sub-quadratic for large VG as well as for small VDS."</ref>