Abstract
A solution processed top-contact bottom-gated SnO2 thin-film transistor (TFT) has been fabricated using a TiO2/Li–Al2O3 bilayer stacked gate dielectric that show operating voltage of this TFT within 2.0 V. It is observed that the bilayer dielectric has much higher areal capacitance with lower leakage current density that significantly improve the overall device performance of TFT. The TFT with bilayer gate dielectric shows an effective carrier mobility (μsat) of 9.2 cm2 V−1 s−1 with an on/off ratio of 7.1 × 103 which are significantly higher with respect to the TFT with a single layer Li–Al2O3 gate dielectric. The origin of this improvement is due to the Schottky junction between the highly doped silicon (p++-Si) and TiO2 of bilayer stacked dielectric that induced electrons to the channel which reduces the dielectric/semiconductor interface trap-state. This investigation opens a new path to develop TFT device performance using a suitable bilayer stack of gate dielectric.
Highlights
The charge carrier conduction of the channel of a thin film transistor (TFT) normally occurs within < 10 nm thickness of the semiconductor film next to the gate-dielectric.[1]
To analyse the structural properties of spin coated TiO2, Li-Al2O3 and SnO2 thin film, individually all these thin films were deposited on p-doped Si wafer (p++-Si) substrate under the same condition of TFT fabrication
The surface morphologies of single layer Li-Al2O3 and bilayer TiO2/Li-Al2O3 dielectrics were studied by atomic force microscopy (AFM)
Summary
The charge carrier conduction of the channel of a thin film transistor (TFT) normally occurs within < 10 nm thickness of the semiconductor film next to the gate-dielectric.[1]. To reduce the operating voltage of a TFT below 2 V for portable electronics application, it requires very low thickness of SiO2 (< 10 nm) which sometime becomes very licky.[2,3] Employment of high-k dielectric materials insead of SiO2 is the best alternative which allow us to deposit thicker dielectric film by maitaining the advantage of low operating voltage TFT fabrication.[4,5,6,7,8] ionic bonds in high-k dielectrics results in high defect concentrations with oxygen vacancies (VO) being the primary source of traps These can be source of fixed charges or act as electron traps, scattering carriers in channel (decreasing mobility), changing the threshold voltage (VT) and assisting dielectric breakdown and gateleakage mechanism,[9] decreasing device performance, and affects the stability and reliability of devices. A schematic presentation of energy band gap of multilayer thin films and related charge transfer of p++Si/TiO2 Schottky junction explain the probable reason for enhancing device performance
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