# Patent

## Title
Electrostatic discharge guide and liquid crystal display utilizing same

## Abstract

An electrostatic discharge guide comprises a ground wire isolated from a data line. The ground wire has a main ground segment and at least one electrostatic discharge triggering segment connected to the main ground segment.

## Background
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates in general to a liquid crystal display with an electrostatic discharge guide, and more particularly to a liquid crystal display with a structure guiding electrostatic discharge to occur at a specific location.
2. Description of the Related Art
Electrostatic discharge, abbreviated as ESD in the following description, may occur during measurement, assembly, installation, and use in integrated circuits and liquid crystal displays and may damage the circuits or devices therein. Furthermore, function of the entire system may be affected. The three models often explain the causes of ESD stress. The first ESD stress model of the Human Body Model (HBM) refers to ESD stress caused by discharge when a charged human body touches a device under test (DUT). The second ESD stress model of the Machine Model (MM) refers to ESD stress caused by discharge when a charged machine contacts a device under test (DUT). The third ESD stress model of the Charged Device Model (CDM) refers to ESD stress caused by discharge when a charged DUT contacts a conductor which is at a different voltage potential.
In the fabrication process of a thin film transistor liquid crystal display (TFT-LCD), a panel is processed by many machines and operators. Inevitably, electrostatic charge builds up. Electrostatic charge that is not released in some way is harmful to the TFT-LCD. Typically, the Joule heat generated during discharge causes ESD damage to a TFT-LCD. Joule heat may result in a short circuit between two isolated conductors or an open circuit caused by melted conductive wire. Both types of damage may cause the TFT LCD to malfunction.
Damage can be detected by electrical testing subsequent to fabrication of a liquid crystal display. However, TFT-LCD is large devices measured in inches while the physical dimensions of ESD damage is measured in micrometers. Thus rapid determination of location of ESD damage in a large size display and rapid repair thereof are important issues. Overcoming either or both issues can enhance the repair rate and improve yield.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a structure for guiding electrostatic discharge to a specific location.
Thus, the present invention provides an ESD guide comprising a ground wire, isolated from a data line, with at least one main ground segment and at least one electrostatic discharge triggering segment connected to the main ground segment.
According to an embodiment of the present invention, the electrostatic discharge triggering segment comprises two ends connected with the main ground segment respectively.
In another embodiment of the present invention, the ground wire further comprises an opening substantially surrounded by the main ground segment and the electrostatic discharge triggering segment and intersecting the data line.
According to another embodiment of the present invention, the electrostatic discharge triggering segment has a first line width and the main ground segment has a second line width. The first line width is smaller than the second line width.
The present invention provides another liquid crystal display with an electrostatic discharge guide. The liquid crystal display comprises a substrate, a plurality of data lines arranged substantially in parallel thereon, and at least one ground wire isolated from and intersecting the data lines to form a plurality of intersecting regions. In each intersecting region, the ground wire comprises at least one main ground segment isolated from and intersecting a corresponding data line and at least an ESD triggering segment, connected to the main ground segment, isolated from a corresponding data line.
In the liquid crystal display with an ESD guide, the ground wires are located between the substrate and each data line or each data line is located between the substrate and the ground wire.



BRIEF DESCRIPTION OF THE DRAWINGS
The present invention can be more fully understood by reading the subsequent detailed description in conjunction with the examples and references made to the accompanying drawings, wherein:
FIG. 1 illustrates the electrostatic discharge guide with the data line located under the ground wire;
FIG. 2 illustrates a short circuit between a data line and a ground wire when ESD occurs in the electrostatic discharge guide shown in FIG. 1;
FIG. 3 illustrates the method for repairing the short circuit shown in FIG. 2;
FIG. 4 illustrates an open circuit of a data line when ESD occurs in the electrostatic discharge guide shown in FIG. 1;
FIG. 5A illustrates a repairing method wherein a repair wire circumvents a defect;
FIG. 5B illustrates a repairing method wherein a repair wire crosses a defect;
FIG. 6 is a liquid crystal display according to the present invention; and
FIG. 7 illustrates an electrostatic discharge guide with two electrostatic discharge triggering segments.



DETAILED DESCRIPTION OF THE INVENTION
Electrostatic discharge typically occurs at a location where current density is higher and results in an open or short circuit of a data line. To prevent open or short circuits caused by electrostatic discharge at the intersection of a data line and a ground wire, the present invention provides a structure for guiding electrostatic discharge to occur at a specific location. The structure is useful for the repair of data lines and ground wires.
FIG. 6 shows a TFT-LCD according to one embodiment of the present invention. The TFT-LCD comprises a substrate 60, a ground wire GND and data lines DL0 ̃DLN−1. Data lines DL0 ̃DLN−1 are implemented substantially in parallel on the substrate 60. A ground wire GND is also implemented on the substrate 60. From the three dimensional viewpoint, the sequence of the layers are substrate 60, ground wire GND, and data lines DL0 ̃DLN−1. The sequence may alternately be substrate 60, data lines DL0 ̃DLN−1, and ground wire GND.
Ground wire GND and data lines DL0 ̃DLN−1 are isolated and intersected to form a plurality of intersections 620 ̃62N−1. All intersections are identical. To simplify the description, the structure of the intersection 620 is given as an example. The scope of the invention, however, is not limited by the following explanation.
Referring to FIG. 1, a data line DL0 is located under a ground wire GND and they are electrically isolated from each other. The ground wire GND has a main ground segment 72 and one electrostatic discharge triggering segment 70 at the intersection of the ground wire GND and the data line DL0. Both ends of the electrostatic discharge triggering segment 70 are connected with the main ground segment 72. Both ends of the electrostatic discharge triggering segment 70 are connected with the main ground segment 72 and are therefore regarded as part of the ground wire GND. The electrostatic discharge triggering segment 70, the main ground segment 72 and the surrounding area form an opening 10 at the intersection of the ground wire GND and the data line DL0.
It is noted that in FIG. 1, the line width of the electrostatic discharge triggering segment 70 is smaller than that of the main ground segment 72. The main advantage of such design is that the ESD current flows through the electrostatic discharge triggering segment 70 instead of the main ground segment 72 when an ESD event discharges through the data line DL0 and the ground wire GND. The method is described in the following.
It is well known that at the equal potential surface of a conductor, the intensity of electric field is directly proportional to the curvature of the surface. Put simply, on the same conductor, the electric field increases with the curvature. Once ESD stress occurs across the data line DL0 and the ground wire GND, breakdown starts from the electrostatic discharge triggering segment 70 because the electric field is higher at the electrostatic discharge triggering segment 70 than at the main ground segment 72. In other words, if there is a first ESD triggering voltage at the electrostatic discharge triggering segment 70 and a second ESD triggering voltage at the main ground segment 72 in FIG. 1, the first ESD triggering voltage is obviously lower than the second ESD triggering voltage. Therefore, the electrostatic discharge is guided to occur at the intersection of the narrower electrostatic discharge triggering segment 70 and the data line DL0. Thus, the ESD current flows through electrostatic discharge triggering segment 70 instead of the main ground segment 72. When ESD damage to the data line DL0 is discovered, the damage can be verified by observing the intersection of the electrostatic discharge triggering segment 70 and the data line DL0.
An ESD event occurring across the data line DL0 and the ground line GND, wherein heat is definitely generated at the intersection of the electrostatic discharge triggering segment 70 and the data line DL0, has three potential results. The first result may be a short between the electrostatic discharge triggering segment 70 and the data line DL0, the second possible result may be meltdown of the electrostatic discharge triggering segment 70, and the third result may be meltdown of the data line DL0 at the intersection. Meltdown of the electrostatic discharge triggering segment 70, however, does not result in circuit malfunction and as such is not addressed. The repairing methods for repairing a short circuit and a melted data line DL0 are described in the following.
FIG. 2 shows a short between the electrostatic discharge triggering segment 70 and the data line DL0 caused by ESD. The method for repairing the short is illustrated in FIG. 3. The repair is accomplished by disconnecting the ends B and C of the electrostatic discharge triggering segment 70 and the electrostatic discharge triggering segment 70 is thereby disconnected from the ground wire GND. As a result, the data line DL0 is isolated from the ground wire GND. A laser cut can then be utilized to cut a thinner electrostatic discharge triggering segment 70. Further, to ensure that the data line DL0 remains normal, a repair wire can be formed to cross over the defect A to connect both ends of the data line. The repairing method is illustrated in detail in FIGS. 5A and 5B.
FIG. 4 shows a meltdown of data line DL0 at the intersection and an open circuit formed at location A caused by ESD. In FIG. 4, the ground wire GND is located under the data line DL0 and disconnected. The repairing method is illustrated in FIG. 5A or 5B. The method forms an additional repair wire 20 across the open circuit A to re-connect the data line DL0. Generally, two contacts 30a and 30b across the defect A on the data line DL0 are formed by a laser, i.e. contact windows 30a and 30b are formed in the dielectric layer on the data line DL0. Subsequently, a repair wire 20 is formed by laser CVD. The repair wire 20 electrically contacts the data line DL0 via contacts 30a and 30b. Since the-use of a laser to form contacts 30a and 30b may result in melting between the two layers, locations of the contacts 30a and 30b should not overlap the ground wire GND. As shown in FIGS. 5A and 5B, the contact 30b corresponds to the opening 10 of the ground wire GND. The formed repair wire can circumvent the defect A, as shown in FIG. 5A or directly cross over the defect A, as shown in FIG. 5B. If the data line DL0 should contact with the ground wire GND when it is broken, the repair can be accomplished by cutting the ends B and C of the electrostatic discharge triggering segment 70. Again, a laser can be utilized to cut a narrower electrostatic discharge triggering segment 70.
Moreover, the number of the electrostatic discharge triggering segments of the ground wire intersecting the data line DL0 can be one, two, or more. As shown in FIG. 7, if two electrostatic discharge triggering segments 70 and a main ground segment 72 are desired, two openings 10, perpendicular to the data line DL0, in the ground wire GND at the intersection are required.
The present invention provides an electrostatic discharge guide, which directs ESD damage to occur at specific locations. Therefore, damage can be rapidly identified. Furthermore, the electrostatic discharge triggering segments simplify the repair process.
While the invention has been described by way of example and in terms of the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.

## Claims

1. An electrostatic discharge guide device, comprising:
a data line;
a ground wire, intersecting the data line, having at least one opening therein to form at least one main segment and at least one sub-segment such that the at least one main segment and the least one sub-segment substantially surrounds with the at least one opening;
a cutting line located at least one of two sides of the at least one sub-segment so as to disconnect from at least one of the at least one around wire and the at least one main segment; and
at least one repair wire, disposed on a portion of the at least one data line in the outside of the ground wire, a portion of the at least one date line in the at lest one opening, and connected with each other.

2. The electrostatic discharge guide device of claim 1, wherein the width of the ground wire is substantially equal to a sum of a width of the at least one main segment, at least one sub-segment, and the at least one opening.

3. The electrostatic discharge guide device of claim 1, wherein the at least one ground wire intersecting the data line has a region comprises a portion of the at least one opening, a portion of the at least one main segment, and a portion of the at least one sub-segment.

4. The electrostatic discharge guide device of claim 1, wherein an electric field intensity of the at least one sub-segment is substantially greater than an electric field intensity of the at least one main segment.

5. The electrostatic discharge guide device of claim 1, wherein a temperature of the at least one sub-segment is substantially greater than a temperature of the at least one main segment at the electrostatic discharge.

6. The electrostatic discharge guide device of claim 1, wherein the at least one opening is an open-up form.