The present invention relates to a display device, and more particularly, to a liquid crystal display device with a minor reduction in transmittance and a small amount of pixel defects even in a high definition screen.
A display device includes a TFT substrate in which pixels each having a pixel electrode, a thin film transistor (TFT), and the like are arranged in a matrix form. Further, a counter substrate is disposed opposite the TFT substrate, in which color filters and the like are formed at locations corresponding to the pixel electrodes of the TFT substrate. A liquid crystal is interposed between the TFT substrate and the counter substrate. Then, an image is formed by controlling the transmittance of light through each pixel by the liquid crystal molecules.
Liquid crystal display devices are flat and lightweight and have been applied in various fields. Small liquid crystal display devices are widely used in mobile phones, digital still cameras (DSC), or other portable devices. The viewing angle property is a problem for the liquid crystal display device. The viewing angle property is a phenomenon that the brightness changes or the chromaticity changes between when the screen is viewed from the front, and when it is viewed in an oblique direction. The viewing angle property is excellent in the In Plane Switching (IPS) mode for driving liquid crystal molecules by an electric field in the horizontal direction.
Among various types in the IPS mode, for example, there is a mode in which a common electrode is formed in a matted manner and a comb-shaped pixel electrode is provided on the common electrode with an insulating film interposed therebetween, to rotate liquid crystal molecules by the electric field generated between the pixel electrode and the common electrode. This type of mode can increase the transmittance and is now mainstream. The common electrode and the interlayer insulating film are formed on an organic passivation film that also functions as a flattening film.
Meanwhile in the liquid crystal display device, when the size of the pixel is reduced for a high definition screen, the ratio of the diameter of a through hole for connecting the pixel electrode and the source electrode of the TFT is increased.
In the IPS mode liquid crystal display device described above, when the ratio of the through hole to the pixel is increased, the bonding strength between an organic passivation film and an interlayer insulating film formed on the organic passivation film is reduced, resulting in a problem that the interlayer insulating film is removed. Patent Document 1 (Japanese Patent Application Laid-Open No. 2011-59314) describes a configuration in which the interlayer insulating film is formed only on the organic passivation film and not within the through hole, in order to reduce the stress on the interlayer film to prevent the interlayer film from removing.
The pixel becomes smaller as the screen is high definition. Along with this, in order to reduce the diameter of the through hole, it is necessary to increase the taper angle of the wall part of the through hole (hereinafter also referred to as the taper angle). Meanwhile, the alignment film is used for the initial alignment of the liquid crystal molecules. The alignment film material is initially liquid and is applied by flexographic or inkjet printing, or other printing processes.
When the taper angle of the through hole is increased, there is a phenomenon that the applied alignment film material does not enter the through hole due to the surface tension. In this case, display defects occur around the through hole, such as light leakage due to the poor initial alignment of the liquid crystal molecules, and uneven brightness due to the irregularity of the film thickness. Patent Document 2 (Japanese Patent Application Laid-Open No. 2007-322563) describes a configuration in which the alignment film can easily flow into the through hole by changing the height around the upper side of the through hole.