The effect of metallization contact resistance on the measurement of the field effect mobility of long-channel unannealed amorphous In-Zn-O thin film transistors

The effect of contact resistance on the measurement of the field effect mobility of compositionally homogeneous channel indium zinc oxide (IZO)/IZO metallization thin film transistors (TFTs) is reported. The TFTs studied in this work operate in depletion mode as n-channel field effect devices with a field effect mobility calculated in the linear regime (μ _FE) of 20 ± 1.9 cm ²/Vs and similar of 18 ± 1.3 cm ²/Vs when calculated in the saturation regime (μ _FE ^sat). These values, however, significantly underestimate the channel mobility since a large part of the applied drain voltage is dropped across the source/drain contact interface. The transmission line method was employed to characterize the contact resistance and it was found that the conducting-IZO/semiconducting-IZO channel contact is highly resistive (specific contact resistance, ρ _C > 100 Ωcm ²) and, further, this contact resistance is modulated with applied gate voltage. Accounting for the contact resistance (which is large and modulated by gate voltage), the corrected μ _FE is shown to be 39 ± 2.6 cm ²/Vs which is consistent with Hall mobility measurements of high carrier density IZO.