Effect of Doping Fluorine in Offset Region on Performance of Coplanar a-IGZO TFTs

We report the effect of doping fluorine in the offset region on the performance of coplanar amorphous indium–gallium–zinc oxide (a-IGZO) thin-film transistors (TFTs). The TFTs with 4- $\mu \text{m}$ offset length at both sides of the gate were fabricated. Hall mobility of the offset region a-IGZO increases, and its resistivity ( $\rho $ ) decreases with increasing F doping concentration. The TFTs with $\textsf {7}\times \textsf {10}^{\textsf {19}}$ cm −3 carrier concentration in the offset region exhibit the field-effect mobility of 27.17 cm $^{\textsf {2}}/\text {V}\,{\cdot }\,\text {s}$ . The fabricated 23-stage ring oscillator (RO) shows an oscillation frequency of 2.27 MHz at the supply voltage of 20 V with a propagation delay of 9.5 ns/stage, which is the lowest value for the oxide TFT ROs ever reported.