| 초록 |
In order to fabricate homogeneous polycrystalline silicon thin film transistor (poly-Si TFT) array, we employed field aided lateral crystallization (FALC) method. It turned out that the current element in each pixel of TFT array must be provided uniformly to achieve a uniform crystallization. To determine the required optimal current density for the uniform crystallization and to design an optimal common electrode configuration, we carried out MathCAD simulation. In the previous study, it was observed that 2-inch poly-Si TFT array fabricated by FALC process shows a uniform electric characteristics and the simulation results of current density in TFT array are considerably correlated with the experimental results such as crystallinity and device parameters. Thus, it is suggested that the variations of the device parameters in an array can be controlled by the current density distribution in common electrode. However, the positional variation of current density in the prior common electrode is not still satisfactory to meet the requirements for larger area displays. We suggest a novel common electrode design using a revised simulation tool of current density, which demonstrated that the FALC process has a wide expandability in panel size. Using the novel common electrode design, the simulation result of current density shows zero positional variation in an array. A standard unit (1st unit) of the novel common electrode consists of four a-Si cells of parallel connection. Since the current density of each cell in the parallel-connected circuit consisting of less than four cells is same, the same current density of each a-Si cell in the 1st unit can be achieved. These four 1st units repeat to constitute the 2nd unit, and the current density of each 1st unit is also the same. We designed the novel common electrode consisting of the Nth unit which can provide completely uniform current density to individual 4N a-Si cell. By applying MathCAD simulation, the study to investigate whether the FALC process can be extended in a practical manner to a large panel was tested. According to the simulation result, it was demonstrated that 14-inch poly-Si TFT (1024×2048) array, which is almost equivalent to a XGA grade display, is possible using the novel common electrode design. We fabricated 2-inch poly-Si TFT array to confirm the size expandability using the revised common electrode. The device parameters of the poly-Si TFT array were observed to be uniform with the threshold voltage variations of ±0.3 V and the mobility variations of 10%. However, slight deviation between simulation results and profiles of device parameters seems to be associated with the influence of other process parameters. The detailed reason of this deviation will be reported in elsewhere near future. |
