Achieving High Carrier Mobility Exceeding 70 cm2/Vs in Amorphous Zinc Tin Oxide Thin-Film Transistors

This paper proposes a new defect engineering concept for low-cost In-and Ga-free zinc tin oxide (ZTO) thin-film transistors (TFTs). This concept is comprised of capping ZTO films with tantalum (Ta) and a subsequent modest thermal annealing treatment at 200 degrees C. The Ta-capped ZTO TFTs exhibited a remarkably high carrier mobility of 70.8 cm(2)/Vs, low subthreshold gate swing of 0.18 V/decade, threshold voltage of -1.3 V, and excellent I-ON/OFF ratio of 2 x 10(8). The improvement (> two-fold) in the carrier mobility compared to the uncapped ZTO TFT can be attributed to the effective reduction of the number of adverse tailing trap states, such as hydroxyl groups or oxygen interstitial defects, which stems from the scavenging effect of the Ta capping layer on the ZTO channel layer. Furthermore, the Ta-capped ZTO TFTs showed excellent positive and negative gate bias stress stabilities.