1. Field of the Invention
The present invention relates to a display device and a manufacturing method of the display device.
2. Description of the Related Art
Through holes are used in various electronic devices. As an example, in a display device, the through hole is used as a connecting portion between a source electrode of a TFT (Thin Film Transistor) and a pixel electrode. An insulation film of one layer or two or more layers is formed between the source electrode and the pixel electrode, and the pixel electrode and the source electrode are connected with each other via a through hole formed in the insulation film (see JP-A-11-326949, for example).
Above-mentioned JP-A-11-326949 discloses, in a state that the insulation film is formed of two layers, a case in which an opening formed in the upper-layer insulation film is smaller than an opening formed in the lower-layer insulation film at a through hole portion (see FIG. 8 in JP-A-11-326949) and a case in which the opening formed in the upper-layer insulation film is larger than the opening in the lower-layer insulation film at the through hole portion (see FIG. 3 in JP-A-11-326949) respectively.
By forming the insulation film in two layers, it is possible to obtain an advantage that the insulation properties of the lower layer and the upper layer of the insulation layer can be enhanced. And hence, the technique is effective for enhancing an image quality due to the reduction of a parasitic capacitance or the reduction of a short circuiting defect.
However, it has been found out that the constitution which includes the multi-layered insulation film in the through hole portion eventually may fail to enhance the yield rate. Inventors of the present invention have studied causes and have found out the followings.
(A) When the opening formed in the upper-layer insulation film is larger than the opening formed in the lower-layer insulation film in the through hole portion as shown in FIG. 3 of JP-A-11-326949, a stepped portion or an edge is formed on the side surface of the through hole structurally. Accordingly, it has been found that the above-mentioned pixel electrode is liable to be easily disconnected by the stepped portion or the edge thus bringing about the lowering of the yield rate.
(B) When the opening formed in the upper-layer insulation film is smaller than the opening formed in the lower-layer insulation film in the through hole portion as shown in FIG. 8 of JP-A-11-326949, only the upper-layer insulation film is exposed on the side surface of the through hole and hence, the stepped portion or the edge is reduced whereby the lowering of the yield rate can be suppressed. However, when the constitution shown in FIG. 8 of JP-A-11-326949 is adopted, it has been found out that in spite of the realization of contact between the source electrode and the pixel electrode structurally, the electrical connection becomes insufficient and point defects frequently occur.
Accordingly, the inventors of the present invention have found out that in either one of these constitutions, even when the short-circuiting defect is lowered, new causes which generate the lowering of the yield rate are newly generated.