Temperature dependent leakage currents in polycrystalline silicon thin film transistors

Abstract

We have studied the origins of the leakage current in polycrystalline silicon (poly-Si) thin film transistors. Temperature dependent transfer characteristics were measured as a function of drain voltage. Three kinds of leakage current were introduced to explain the experimental results. The leakage current may arise from the generation current at very low drain voltage, and may result in the same activation energy between leakage current and conductivity of undoped poly-Si. The leakage current may be due to the thermionic field emission via grain boundary defects in the intermediate drain voltage region. At high drain voltage and high negative gate voltage, the leakage current may result from the field enhanced tunneling of electrons in the valence band to the conduction band via grain boundary traps.

Improving Switching Performance of Thin-Film Transistors in Disordered Silicon

“…Quantum confinement increases E g and can thereby effectively reduce I sub . For transistors in disordered silicon, it has been found that the anomalously high leakage current arises by electron-hole pairs generated via traps near the midgap at drain junction through thermal emission or thermionic field emission [10], as shown in Fig. 1, and the junction leakage (I jun ) can be given as I jun ∝ exp(− (qE g /2kT )).…”

“…1. Schematic band diagram of the thin-film transistor in disordered silicon, showing the discrete energy levels originating from carrier confinement in the thin channel, the subthreshold leakage current (I sub ) generated by carriers traversing the barrier between the source and the channel, and the junction leakage (I jun ) arising by electron-hole pairs generated via traps near the midgap at drain junction through thermal emission or thermionic field emission [10].…”

“…Second, the presence of defects in the semiconductor layers leads to a decreasing effect of gate voltage on the surface potential, which in turn induces large S value [9]. Third, the trap states in the bandgap may assist the generation of carriers at the drain junction via thermionic emission or thermionic field emission of carriers, thus causing anomalous large leakage current [10]. In a previous work, the ultrathin channel transistor was demonstrated as an excellent candidate for ultralow power memory design [11].…”

Down-scaling of Thin-Film Transistors: Opportunities and Design Challenges

“…For disordered silicon transistors, the performance is compromised by an anomalously high leakage current due to defect states that are present in the bandgap, which is exponentially dependent on the bandgap of the material (E g ) (17). When the transistor channel becomes shorter, the influence of the drain on the channel grows, resulting in an increased subthreshold leakage current when the gate voltage is below the threshold voltage.…”

High Quality Vertical Silicon Channel by Laser-Induced Epitaxial Growth for Nanoscale Memory Integration

“…Moreover, negligible temperature dependence in leakage currents of VSC transistor with LEG Si indicates high quality crystalline nature (inset graph of Fig. 3(a)) [13,14]. The drain current of VSC transistor is a function of the potential of VSC, and the potential at VSC is variable according to the charge density in VSC.…”