Abstract
In this work, two stacked gate dielectrics of Al2O3/tetraethyl-orthosilicate (TEOS) oxide were deposited by using the equivalent capacitance with 100-nm thick TEOS oxide on the patterned InGaZnO layers to evaluate the electrical characteristics and stability improvement of amorphous indium gallium zinc oxide (a-IGZO) thin-film transistors (TFTs) devices, including positive bias stress (PBS) and negative bias stress (NBS) tests. Three different kinds of gate dielectrics (Al2O3, TEOS, Al2O3/TEOS) were used to fabricate four types of devices, differing by the gate dielectric, as well as its thickness. As the Al2O3 thickness of Al2O3/TEOS oxide dielectric stacks increased, both the on-current and off-current decreased, and the transfer curves shifted to larger voltages. The lowest ∆Vth of 0.68 V and ∆S.S. of −0.03 V/decade from hysteresis characteristics indicate that the increase of interface traps and charge trapping between the IGZO channel and gate dielectrics is effectively inhibited by using two stacked dielectrics with 10-nm thick Al2O3 and 96-nm thick TEOS oxide. The lowest ∆Vth and ∆S.S. values of a-IGZO TFTs with 10-nm thick Al2O3 and 96-nm thick TEOS oxide gate dielectrics according to the PBS and NBS tests were shown to have the best electrical stability in comparison to those with the Al2O3 or TEOS oxide single-layer dielectrics.
Highlights
Amorphous oxide semiconductors (AOSs) are promising for channel materials of thin-film transistors [1,2] (TFTs) and are feasible for driving TFTs in organic light-emitting diode displays due to their large carrier mobility (>10 cm2 V−1 s−1 ) and low process temperatures
The S.S. values of top-gate amorphous indium gallium zinc oxide (a-IGZO) TFTs with two stacked Al2 O3 /TEOS oxide gate dielectrics are larger than the values of the Al2 O3 or TEOS oxide single-layer dielectric
The results obviously indicate that the electrical characteristics of a-IGZO TFTs had more positive Vth, less S.S., and μFE corresponding to the increasing Al2 O3 thickness
Summary
Amorphous oxide semiconductors (AOSs) are promising for channel materials of thin-film transistors [1,2] (TFTs) and are feasible for driving TFTs in organic light-emitting diode displays due to their large carrier mobility (>10 cm V−1 s−1 ) and low process temperatures. The conventional bottom-gate structure has been widely studied for amorphous indium gallium zinc oxide (a-IGZO). TFTs [3,4] This structure is unsuitable for integration onto the glass of peripheral circuits for the system and for the realization of high-resolution, high-quality active-matrix organic light-emitting diode (AMOLED) displays due to the high parasitic capacitance and poor scalability. The development of self-aligned top-gate oxide TFTs with good performance and high stability is necessary for AMOLED display applications [5,6]. The voltage shift is attributed to the trapping of carriers (electrons) at the active-layer/gate-insulator interface and/or in Coatings 2020, 10, 1146; doi:10.3390/coatings10121146 www.mdpi.com/journal/coatings
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