Gated four-probe technique

As depicted in Figure 2.4.10(b), contact resistance at the source and drain electrodes results in a smaller than expected slope of the potential versus channel position profile. The profile is estimated by linear extrapolation between Vi and V2. Individual source and drain contact resistances are calculated by dividing the voltage drops AVs and AV by the source-drain current, respectively. By isolating the source and drain contact contributions to the total contact resistance, the gated four-probe technique provides more information than the transmission line technique, and it is possible to determine in one device (vs. several). An important caveat for the gated four-probe technique is that the extrapolated channel potential profile wiU only be valid for strict linear regime OFET operation (Vq V, ), where the channel potential profile can be expected to be linear and uniform. 

The use of the gated four-probe technique has readily extended to the organic transistor [75-77]. The basic principle of the method is illustrated in Fig. 8. It consists of introducing two additional electrodes within the space separating the source and... 

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