Estimation of contact resistance in four terminal amorphous IGZO thin film transistor

Accurate electrical characterization of thin film transistor (TFT), requires measurement of its contact resistance. This work describes experimental extraction of contact resistance in top contact a-IGZO TFTs using a four-terminal structure. The auxiliary contact terminal is deposited adjacent to source away from the channel region and kept electrically floating leading to unperturbed device operation. A simplified transmission-line model of source contact relates the open-circuit voltage measured at the floating terminal with the total resistance of the transistor to directly give estimates of the contact resistance. Contact resistance corrected values of threshold voltage and field-effect mobility were extracted as 4 V and 3.2 cm2 V−1 s−1 respectively whereas the uncorrected values were 1 V and 2.4 cm2 V−1 s−1.