text: There are four typically Organic field-effect transistor architectures: Top-gate, bottom-contacts; bottom-gate, top-contacts; bottom-gate, bottom-contacts; top-gate, top-contact.
  In order to create the accumulation charge layer, a positive/negative direct current voltage is applied to the gate of the organic field-effect transistor (positive for the P type transistor, negative for the N type transistor). In order to modulate the charge, an AC voltage is given between the gate and source. It is important to notice that only mobile charge can follow the modulation and that the modulation frequency given to lock-in amplifier has to be synchronous.