Enhanced performance of a-IGZO thin-film transistors by forming AZO/IGZO heterojunction source/drain contacts

A low-cost Al-doped ZnO (AZO) thin film was deposited by radio-frequency magnetron sputtering with different Ar/O-2 flow ratios. The optical and electrical properties of an AZO film were investigated. A highly conductive AZO film was inserted between the amorphous InGaZnO (a-IGZO) channel and the metal Al electrode to form a heterojunction source/drain contact, and bottom-gate amorphous a-IGZO thin-film transistors (TFTs) with a high kappa HfON gate dielectric were fabricated. The AZO film reduced the source/drain contact resistivity down to 79 Omega cm. Enhanced device performance of a-IGZO TFT with Al/AZO bi-layer S/D electrodes (W/L = 500/40 mu m) was achieved with a saturation mobility of 13.7 cm(2) V-1 s(-1), a threshold voltage of 0.6 V, an on-off current ratio of 4.7 x 10(6), and a subthreshold gate voltage swing of 0.25 V dec(-1). It demonstrated the potential application of the AZO film as a promising S/D contact material for the fabrication of the high performance TFTs.