Device Performance Improvement of Transparent Thin-Film Transistors With a Ti-Doped GaZnO/InGaZnO/Ti-Doped GaZnO Sandwich Composite-Channel Structure

In this paper, two transparent thin-film transistors (TFTs) with distinct channel designs were fabricated. The first was a single-channel TFT (SC-TFT) with a typical 50-nm-thick amorphous indium–gallium–zinc oxide (a-IGZO) layer, and the second was a sandwich composite-channel TFT (CC-TFT) comprising three layers of 10-/30-/10-nm-thick Ti-doped GaZnO (GTZO)/a-IGZO/GTZO. In the CC-TFT, the bottom GTZO thin film in the composite channel exhibited a highly smooth surface, serving as a buffer template for superior IGZO channel layer thin-film growth. The top GTZO thin film had a high carrier concentration and served as both a carrier supplement and passivation layer for reducing the adsorption of moisture and oxygen molecules. The studies of material quality indicated that the CC-TFT exhibited improved a-IGZO thin-film quality; relative to the SC-TFT, the oxygen vacancy concentration of the composite structure was reduced from 25.1% to 18.2%. The CC-TFT demonstrated a high level of device performance, exhibiting an excellent field-effect mobility of 14.1 cm2/ $\text{V}\,\cdot \, \text{s}$ , subthreshold swing of 0.33 V/decade, off current of $2.92 \times 10^{-12}$ A, threshold voltage of 1.7 V, and on–off current ratio of $3.95 \times 10^{7}$ . Stable device operation with nearly unaltered device characteristics was observed following a bias-stress test.