  In this paper, we investigated the performance of thin-film transistors
(TFTs) with different channel configurations including single-active-layer
(SAL) Sn-Zn-O (TZO), dual-active-layers (DAL) In-Sn-O (ITO)/TZO, and
triple-active-layers (TAL) TZO/ITO/TZO. The TAL TFTs were found to combine the
advantages of SAL TFTs (a low off-state current) and DAL TFTs (a high mobility
and a low threshold voltage). The proposed TAL TFTs exhibit superior electrical
performance, e.g. a high on-off state current ratio of 2*10^8, a low threshold
voltage of 0.52 V, a high saturation mobility of 145.2 cm2/Vs, and a low
off-state current of 3.3 pA. The surface morphology and characteristics of the
ITO and TZO films were investigated and the TZO film was found to be
C-axis-aligned crystalline (CAAC). A simplified resistance model was deduced to
explain the high channel resistance of TAL TFTs. At last, TAL TFTs with
different channel lengths were also discussed to show the stability and the
uniformity of our fabrication process. Owing to its low-processing temperature,
superior electrical performance, and low cost, TFTs with the proposed TAL
channel configuration are highly promising for flexible displays where the use
of heat-sensitive polymeric substrates is desirable.
