Dose-Dependent Performance of Boron-Implanted Self-Aligned Bottom-Gate IGZO TFTs

This work provides an interpretation of donor activation in self-aligned bottom-gate (SA-BG) Indium-Gallium-Zinc Oxide (IGZO) TFTs with ion-implantation of boron ( 11 B + ) species as the source/drain treatment. The effect of implant dose on device operation was investigated. Transfer characteristics appeared similar with a boron dose of 1 and 2×10 15 cm -2 however, a 45% decrease in max current was observed for devices implanted with a 4×10 15 cm -2 dose. Van der Pauw measurements displayed a similar trend; an increase in boron dose resulted in an increase in sheet resistance. A left-shift in transfer characteristics was observed with a greater shift in the 4×10 15 cm -2 dose devices, following thermal stability treatments. The existence of two separate boron species is hypothesized, (1) an electrically active donor species involving a relatively small fraction of the total boron concentration and (2) additional boron interstitials and/or other associated defects. A detailed discussion on developed arguments arrived at through analysis of TFT electrical characteristics is presented.