Influence of the Grain Boundaries and Intragrain Defects on the Performance of Poly‐Si Thin Film Transistors

Abstract

The influence of grain boundaries and intragrain defects on poly‐Si thin‐film transistors (TFTs) was investigated by examining the crystallinity of poly‐Si films formed by solid phase crystallization (SPC) and excimer laser annealing (ELA), and the electrical characteristics of transistors fabricated on the poly‐Si films were examined. The increase in grain size by SPC improves field effect mobility (μFE) due to the increase in the emission current over the potential barrier height at the grain boundary. The decrease in intragrain defect densities by an oxide thinning process improves the μFE, threshold voltage (V th) and subthreshold voltage swing (S). On the contrary, in spite of the small grain size of 800 Å, poly‐Si TFTs fabricated by ELA exhibit good characteristics with a high μFE, low V th and low S, and good uniformity. It is found that since the realization of excellent performance and good uniformity in poly‐Si TFTs depends on a low trap state density at the grain boundaries and a low intragrain defect density, poly‐Si films formed by ELA are well suited for the application to poly‐Si TFT liquid crystal display with peripheral integrated circuits.

Effects of the single and double (overlap) scanned excimer laser annealing on solid phase crystallized silicon films

“…Previous reports have connected the TFT field-effect mobility to the density of trap states close to the conduction and valence bands (tail states), whereas the threshold voltage and the sub-threshold slope seem to be more sensitive to the deep states near midgap [9,10]. Tail states are believed to emanate mostly from the defects within the grains of the poly-Si [11] while deep states are typically related to grain-boundary defects, especially dangling bonds [9,12]. If the overlapped irradiation does not change the TFT characteristics, it is very useful because the length of the beam will not limit the available panel size.…”

Development of rapid thermal processor for large‐glass LTPS production

“…17 Therefore, SPC poly-Si combined with thermal oxidation can result in high-performance TFTs, similarly to that of high-temperature poly-Si TFTs (HTPS). 18…”

Individual analysis of inter and intragrain defects in electrically characterized polycrystalline silicon nanowire TFTs by multicomponent dark-field imaging based on nanobeam electron diffraction two-dimensional mapping

“…6,[8][9][10][11][12] In addition, it has been reported that intragrain defects, such as dislocations and lattice distortions, degrade the characteristics of TFTs as well as GBs. 7,13) To elucidate the factor of characteristic variations, we investigate the channel crystallinities of the electrically characterized individual NW TFTs.…”