A Research On Crosstalk In TFT-LCDs

As the high development of thin film transistor liquid crystal display(TFT-LCD), the demands of high resolution, wide viewing angle, high response speed and high aperture ratio require the display devices with better qualities. And as the pixel size becoming smaller and smaller, the space between lines becoming narrower and narrower, the interference of induced electric field between lines which current signal passed by, become particularly outstanding, and the coupling between pixels become stronger. All these can lead to the crosstalk phenomenon occurs, which greatly affecting the product yield and benefits. So crosstalk in TFT-LCD, is a serious problem to be solved.First of all, this article started with the basic structure, working principle and technology process of TFT-LCDs. By analyzing the waveform of common electrode, pixel electrode, and data line, and the coupling effect between them under the condition of different polarity inversion, I found out the causes of vertical and horizontal crosstalk phenomenon. The cause of horizontal crosstalk is mainly for a delay of common electrode, and the causes of vertical crosstalk including the coupling between pixel electrode and data line, and the TFT leakage.Secondly,(1) Against the cause of horizontal crosstalk, I simulated the ITO resistance of different thickness, studied the ITO thickness’s influence on common electrode delay. And then I carried out some methods to decrease the common electrode delay:On the aspect of design, we should increase the width of Vcom ITO lines and reduce the width of data lines. On the aspect of process, we should increased the thickness of ITO electrode and passivated layer, or use new electrode materials with smaller square resistance and new passivated materials smaller dielectric constant.(2) Against the cause of vertical crosstalk, I simulated the coupling capacitance Cpd between pixel electrode and data line under the condition of right alignment and mis-alignment, studied its influence to the crosstalk value. I explored the best VGL to shut off TFT, and did some experiments to find out the influence of light and temperature to the leakage current. Through thees studies I took out:②To reduce the coupling capacitance Cpd:On the aspect of design, the distance between pixel ITO and data line should be guaranteed to above6μm (which includes the process fluctuation of2.5μm), and the distance between Vcom ITO and data line should be guaranteed to above3.5μm (which includes the process fluctuation of2.5μm). Also we can use new pixel structures, those are above data line, add a integrated shield bar (suit for TN mode TFT-LCD),or a resin layer (suit for IPS mode TFT-LCD). And add a metallic Vcom line on the opposite side of scanning line in the pixel. On the aspect of process, we should strictly control the alignment among pixel ITO, data line and common line.②To minish TFT leakage:On the aspect of design, we should reduce the area of the active layer to make it covered by gate station, set the cut off voltage to about-10.5V, or use double active layer structure and double gate structure to improve the TFT standoff features. On the aspect of process, we must strictly control the alignment of active layer.