Display device having island-shaped conductor for repairing line disconnection

A liquid crystal display device has a gate line formed on a substrate, and a gate insulating film deposited thereon. On the gate insulating film are provided a source line, and a conductive layer above the gate line. An insulating layer is formed thereon, and a pixel electrode is then provided. The conductive layer does not contact the source line, and at least two portions of the conductive layer are electrically connected with the gate line.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for repairing line disconnection of a display device and a display device capable of repairing line disconnection, which are particularly suitable for application to a liquid crystal display device.

2. Related Background Art

A liquid crystal display device is provided with a matrix of number of signal lines and pixel electrodes. As the number of signal lines is on the increase because of the recent trend of larger and higher resolution liquid crystal display devices, the problem of line disconnection can occur more often. Line disconnection occurs due to pinholes and dust in the manufacturing process. In the event of disconnection, a proper voltage is not applied to a pixel electrode corresponding to a disconnected line, causing line defects and other display problems to produce a defective product. Therefore, a method for repairing line disconnection using a laser is now under research and development.

FIG. 7shows a configuration of a conventional active matrix liquid crystal display device.FIG. 7is a plan view showing a structure of one pixel area of the liquid crystal display device. Reference numeral12designates a pixel electrode,13a thin film transistor (TFT),15a gate line,16a storage capacitor line,17a source line, and28a disconnected portion.

The active matrix liquid crystal display device shown inFIG. 7is provided with a matrix of plurality of the pixel electrodes12, each of which is connected with the TFT13that is a switching element. The gate electrode of the TFT13is connected with the gate line15, and gate signals input to the gate electrode control and drive the TFT13. The source electrode of the TFT13is connected with the source line17, and data (display) signals are input to the pixel electrode12through the TFT13when the TFT13is selected. The gate line15and the source line17cross each other at right angles, surrounding the pixel electrode12. The drain electrode of the TFT13is connected with the pixel electrode12.

A method for repairing signal line disconnection is described in Japanese Patent Application Laid-Open No. H09-113930, for example. The method according to the first embodiment of the above prior art will be explained hereinbelow.FIG. 8Ashows a structure of a cross-section of a disconnected portion of a gate line. The same reference numerals as those inFIG. 7designate the same elements, and redundant description will be omitted. Reference numeral11designates a substrate,22a gate insulating film, and29a molten metal.

As shown inFIG. 7, the pixel electrode12is arranged to partially overlap the-gate line15. They are electrically isolated by the gate insulating film22to enlarge the area of the pixel electrode12, that is, to increase the aperture ratio. Also, an additional capacitor is formed by placing the gate insulation film22between the pixel electrode12and the gate line15.

As shown inFIG. 7, there are cross marks on both outsides of the disconnected portion28of the gate line15. A laser is applied to the marks. The gate line15or the pixel electrode12is molten to produce the molten metal29as shown inFIG. 8B. Abypass route through the gate line15, the molten metal29, the pixel electrode12, the molten metal29, and the gate line15is thereby created; therefore, the disconnection is repaired. Disconnection of the source line17and the storage capacitor line16is also repaired in the same way.

FIGS. 9 and 10show a structure of one pixel area of the liquid crystal display device where disconnection is repaired according to the second embodiment of the invention disclosed in Japanese Patent Application Laid-Open No. H09-113930.FIG. 9is a plan view of a structure of one pixel area where disconnection is repaired, andFIG. 10is a sectional view thereof. The same reference numerals as those inFIGS. 7 and 8designate the same elements, and redundant description will be omitted. Reference numeral41designates a conductive layer for repairing gate line disconnection,42a conductive layer for repairing storage capacitor line disconnection, and43a conductive layer for repairing source line disconnection.

As shown inFIGS. 9 and 10A, the pixel electrode12partially overlaps the gate line15with the insulating film interposed therebetween. On the part of the pixel electrode12overlapping the gate line15is formed a conductive metal layer. The conductive metal layer provided for repairing disconnection of the gate line15will be referred to hereinafter as a conductive layer41. Similarly, conductive metal layers for repairing disconnection of the source line17and the storage capacitor line16will be referred to as a conductive layer42and a conductive layer43, respectively.

In the following, a description will be given on the case where the gate line15is disconnected. As shown inFIGS. 9 and 10A, on the insulating substrate11are formed the gate line15and the storage capacitor line16. The gate insulating film22is formed thereon. Next, the source line17, the TFT13, and an insulating layer are formed. Then, the pixel electrode12is formed. Further, the conductive layer41for repairing gate line disconnection is formed. The conductive layer41is provided on the area where the pixel electrode12overlaps the gate line15with the gate insulating film22interposed therebetween. The conductive layer41is formed in an island shape above the gate line15except the crossing with the source line17.

Disconnection of the gate line15, the storage capacitor line16, and the source line17occurs due to pinholes and dust in the manufacturing process. If the disconnection occurs, no drive signal is given to the pixel, thus disabling display.

The case where disconnection occurs at the disconnected portion28of the gate line15of an active matrix liquid crystal display device will be explained hereinbelow. A laser is applied to the positions at both outsides of the disconnected portion28(the positions shown by the cross marks inFIG. 9) through the conductive layer41. The molten metal29produced by the laser application electrically connects the conductive layer41and the gate line15. The disconnected gate line15regains continuity by a bypass line through the molten metal29, the conductive layer41, and the molten metal29. It is therefore possible to apply drive signals to the gate line where no signal has been given.

Disconnection of the source line17can be also repaired in the same way as shown in FIG.11. Further, the storage capacitor line16can be repaired in the same manner.

The above conventional technique, however, has the following problems. In the first embodiment of the invention disclosed in Japanese Patent Application Laid-Open No. H09-113930, the connection resistance of the pixel electrode12and the molten metal29can be high. The pixel electrode12is formed by Indium Tin Oxide (ITO), and the connection resistance with chromium, tantalum, titanium, and molybdenum used for the gate line15and the storage capacitor line16significantly differs depending on conditions of film deposition and film surface. There is a case where the connection resistance reaches several megohms, which results in decrease in the rate of successful repair. Use of aluminum for the gate line15is especially problematic since the connection resistance of an aluminum element and ITO used for the pixel electrode12is extremely high. Therefore, when a laser is applied to connect them, the connection electrical resistance almost reaches one megohm, which is above the limit of the connection resistance for repairing disconnection. Besides, the application of a laser to the pixel electrode12causes the ITO to be peeled off and a fragment of the ITO is stuck in between a counter electrode and the pixel electrode to trigger unexpected short-circuit.

The repair method described in the second embodiment of the invention disclosed in Japanese Patent Application Laid-Open No. H09-113930 also has problems. According to the method, the conductive layer for repairing line disconnection is additionally provided on the pixel electrode12. Therefore, the manufacturing process requires an additional step of forming the conductive layer. Also, the conductive layer is placed on the pixel electrode applying an electric field to liquid crystals. Therefore, after the repair, an electric potential of a source signal, gate signal, or common signal is directly applied to the liquid crystals through the conductive layer. It causes noise to have an adverse effect on operations of the liquid crystals, resulting in poor display quality.

As described above, the conventional method for repairing line disconnection has the problems of a reduced rate of successful repair and deteriorated display quality caused by an expected short-circuit and noise.

SUMMARY OF THE INVENTION

The present invention has been accomplished to solve the above problems and an object of the present invention is thus to provide a display device capable of repairing line disconnection without decreasing display quality, and the repair method.

A display device according to the present invention is a display device having a plurality of pixels, including a substrate; a conductive line provided on the substrate; a first insulating layer provided on the conductive line; an island-shaped conductor for repairing line disconnection, provided above the conductive line with the first insulating layer interposed therebetween; a switching element controlling a signal to a pixel; a second insulating layer with a through hole, provided on the switching element and the island-shaped conductor; and a pixel electrode provided above the switching element with the second insulating layer interposed therebetween and connected with the switching element via the through hole. In this configuration, the display device is capable of repairing line disconnection without decreasing display quality.

In the above display device, the conductive line can be a gate line transmitting a control signal to the switching element.

The above display device can also include a source line provided in the same layer as the island-shaped conductor.

In the display device, the conductive line can be a storage capacitor line forming a storage capacitor with the pixel electrode.

The above display device can also include a source line provided in the same layer as the island-shaped conductor.

It is also possible in the display device that a plurality of island-shaped conductors are provided above the conductive line.

It is preferable in the display device that at least two portions of the island-shaped conductor are connected to the conductive line.

In the display device, the island-shaped conductor and the conductive line can be connected by laser application.

Another display device according to the present invention is a display device having a plurality of pixels, including a substrate; a first insulating layer provided on the substrate; a conductive line provided on the first insulating layer; an island-shaped conductor for repairing line disconnection, provided below the conductive line with the first insulating layer interposed therebetween; a switching element controlling a signal to a pixel; a second insulating layer with a through hole, provided on the switching element and the conductive line; and a pixel electrode provided above the switching element with the second insulating layer interposed therebetween and connected with the switching element via the through hole. In this configuration, the display device is capable of repairing line disconnection without decreasing display quality.

In the above display device, the conductive line can be a source line transmitting a display signal to the switching element.

It is also possible in the display device that a plurality of island-shaped conductors are provided above the conductive line.

It is preferable in the display device that at least two portions of the island-shaped conductor are connected to the conductive line.

The display device can also include a gate line provided in the same layer as the island-shaped conductor, the gate line transmitting a control signal to the switching element.

The above display device can also include an island-shaped conductor for repairing gate line disconnection provided in the same layer as the source line, above the gate line.

The display device can also include a gate line and a storage capacitor line provided in the same layer as the island-shaped conductor, the gate line transmitting a control signal to the switching element, and the storage capacitor line forming a storage capacitor with the pixel electrode.

The above display device can also include an island-shaped conductor for repairing gate line disconnection provided in the same layer as the source line, above the gate line; and an island-shaped conductor for repairing storage capacitor line disconnection provided in the same layer as the source line, above the storage capacitor line.

A method for repairing a display device having a plurality of pixels according to the present invention is a method including a step of preparing a display device, the display device having a substrate, a conductive line layer provided on the substrate, an island-shaped conductor for repairing line disconnection, the island-shaped conductor overlapping with the conductive line layer, a first insulating layer provided between the island-shaped conductor and the conductive line layer, a switching element controlling a signal to a pixel, a second insulating layer with a through hole, provided on the switching element, and a pixel electrode provided above the switching element and the island-shaped conductor with the second insulating layer interposed therebetween and connected with the switching element via the through hole; a step of applying a laser to two points across a disconnected portion of the conductive line layer; and a step of connecting the island-shaped conductor and the conductive line layer at the two points by applying a laser. This method is capable of repairing line disconnection of the display device without decreasing display quality.

In the above method, the island-shaped conductor can be provided above the conductive line layer.

In the method, on the other hand, the island-shaped conductor can be provided below the conductive line layer.

In the step of applying a laser in the above method, the laser can be applied from the side of the substrate.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

First Embodiment

A method for repairing line disconnection according to the present invention will be explained hereinafter with reference toFIGS. 1to4.FIG. 1is a plan view showing a structure of one pixel area of an active matrix liquid crystal display device according to the present invention.FIG. 2is a plan view showing a structure of the pixel area where each of a gate line, source line, and storage capacitor line has a disconnected portion28.FIG. 3Ais a sectional view showing a structure of the disconnected portion of the gate line.FIG. 4is a sectional view showing a structure of a TFT area of the active matrix liquid crystal display device. Reference numeral11designates a substrate,12a pixel electrode,13a thin film transistor (TFT),14a drain electrode,15a gate line,16a storage capacitor line,17a source line,21a gate electrode,22a gate insulating film,23a silicon semiconductor layer,24an etching stopper,25the first n+silicon layer,26the second n+silicon layer,27a source electrode,28a disconnected portion,29a molten metal,30a contact hole,41a conductive layer for repairing gate line disconnection,42a conductive layer for repairing storage capacitor line disconnection, and43a conductive layer for repairing source line disconnection.

As shown inFIG. 1, the pixel electrode12is connected with the TFT13that is a switching element. The gate electrode21of the TFT13is connected with the gate line15, and gate signals input to the gate electrode21drives and controls the TFT13. The source electrode27of the TFT13is connected with the source line17, and data (display) signals are input to the drain electrode14shown in FIG.4through the TFT13when the TFT13is selected. From the drain electrode14, the data signals are input to the pixel electrode12through the contact hole30. The gate line15and the source line17cross each other at right angles, surrounding the pixel electrode12. The drain electrode14of the TFT13is connected with the pixel electrode12. The conductive layer41, the conductive layer43, and the conductive layer42are provided for the gate line15, the source line17, and the storage capacitor line16, respectively. The conductive layers are island shaped or electrically floating.

FIG. 2shows the case where each of the three lines has the disconnected portion28. Repair of the disconnection will be explained hereinafter with reference to FIG.3. The explanation will be given on the repair of the gate line15.FIG. 3Ashows a structure of a cross-section of the disconnected portion of the gate line in one pixel area of an active matrix liquid crystal display device. On the substrate11as the bottom layer are provided the gate line15, the gate insulating film22, the conductive layer41, the insulating film45, and the pixel electrode12as the top layer. For example, on the insulating substrate11such as a glass substrate, aluminum of approximately 0.3 μm thick is formed as the gate line15. Next, silicon nitride of approximately 0.3 to 0.5 μm thick is formed as the gate insulating film22. Then, a conductive metal is provided as the conductive layer41. The conductive layer41melts by laser application. A laser device is a YAG laser, for example. The conductive metal is formed by chromium, tantalum, titanium, aluminum, molybdenum, and the like. Its thickness is approximately 0.1 to 0.2 μm. Further, silicon nitride of approximately 0.1 μm is formed as the insulating film45. Finally, the top layer of the pixel electrode12is formed by ITO of approximately 0.05 to 0.1 μm thick.

FIG. 4shows a sectional view of the TFT area of the active matrix liquid crystal display device. As shown inFIG. 4, on the insulating substrate11such as a glass is formed the gate electrode21. Then, the gate insulating film22is formed to cover the gate electrode21. The silicon semiconductor layer23is formed thereon; then, on the middle thereof, the etching stopper24as a protective layer of a channel layer, and the insulating layer45are successively formed. The gate electrode21is formed by patterning a conductive film deposited by spattering in a photolithography process. The gate insulating film22, the silicon semiconductor layer23, and the etching stopper24are successively deposited by chemical vapor deposition (CVD), and patterned by the photolithography process.

Next, the first n+silicon film25and the second n+silicon film26are formed in isolation from each other. On the second n+silicon film26is formed the source electrode27, the two electrically connected. On the first n+silicon film25is the drain electrode14, electrically connected. The first n+silicon film25and the second n+silicon film26are formed by doping the silicon semiconductor layer23with impurities such as P and As. It is therefore possible to form the first n+silicon film25and the second n+silicon film26in the same step. The drain electrode14and the source electrode27are deposited by sputtering, and patterned by the photolithography process.

Then, the contact hole30is formed on the insulating film45to electrically connect the pixel electrode12and the drain electrode14. The contact hole30is formed in the process of resist coating, exposure, development, etching, resist stripping, and so on. The pixel electrode12is formed thereon by depositing ITO by sputtering to have electrical connection with the drain electrode14. The conductive layer41according to the present embodiment can be formed in the same layer as the drain electrode shown in FIG.4. That is, in patterning the conductive layer to form the drain electrode14and the source electrode27, the conductive layer is also left on the gate line15as the conductive layer41. No additional step is therefore required to form the conductive layer41. Similarly, the insulating layer45can be formed at the same time as forming the TFT13.

FIG. 3Bshows a cross-section of the gate line15when a laser is applied to the square marks on both outsides of the disconnected portion28of the gate line15shown in FIG.2. The laser is applied from the side of the gate line which is the side of the substrate11where the TFT13is not formed. The application of the laser to the marks melts the conductive layer41and the gate line15to produce the molten metal29. A bypass route through the gate line15, the molten metal29, the conductive layer41, the molten metal29and the gate line15is thereby created to let gate signals go through it, avoiding the disconnected portion28. The disconnection is thereby repaired. Since the bypass route has no contact with the pixel electrode12, the pixel electrode12serves as a shield so that gate signals going through the conductive layer41have no adverse effect on liquid crystals arranged on the pixel electrode12. No error voltage is thereby applied to the pixel electrode12to be free from deterioration of display quality.

If a laser is applied from the side of the pixel electrode12, on the other hand, electrical continuity is provided between the pixel electrode12and the gate line15as shown in FIG.3C. Gate signals go through a bypass route through the gate line15, the molten metal29, the conductive layer41, the molten metal29, and the gate line15, or through the gate line15, the molten metal29, the pixel electrode12, the molten metal29, and the gate line15. The laser is applied to a cut line50shown inFIG. 2to separate the pixel from the TFT13. Though a point defect occurs at the subject pixel, the disconnection of the gate line15is repaired. No error voltage is thereby applied to the pixel electrode12to prevent deterioration of display quality.

The connection resistance of the molten metal29and the pixel electrode12is substantially the same as the connection resistance of the pixel electrode12and the drain electrode14through the contact hole30composed of the same material. Further, the electrical resistance can be kept within 100kΩ that is sufficient value for the repair, thus increasing the repair rate. The conductive layer41can be formed and patterned in the same layer as the source line17and the drain electrode14. Therefore, the conductive layer41is formed by sputtering chromium, tantalum, titanium, aluminum, molybdenum, and the like. The conductive layer41has to lie over the disconnected portion28, and therefore it is preferably as large as possible without contacting the source line17for a larger repairable area.

Second Embodiment

A method for repairing line disconnection according to the second embodiment of the present invention will be explained hereinbelow with reference toFIGS. 5 and 6. LikeFIG. 1,FIG. 5is a plan view showing a structure of one pixel area of an active matrix liquid crystal display device.FIG. 6is a sectional view showing a structure of the portion where line disconnected is repaired. The same reference numerals as those inFIGS. 1to4designate the same elements, and redundant description will be omitted. The description of the manufacturing process will be also omitted since it is the same as in the first embodiment.

Below the pixel electrode12, a pair of the conductive layers41, a pair of the conductive layers42, and a pair of the conductive layers43are formed in an island shape above the gate line15, the storage capacitor line16, and the source line17, respectively. The conductive layers are electrically floating. In the first embodiment, the conductive layer is provided in a possibly larger area on each of the three lines surrounding one pixel. In the second embodiment, on the other hand, each of the pair of the conductive layers is provided at each end of the three lines. The conductive layers above the gate line15and the storage capacitor line16can be formed in the same layer as the drain electrode14shown inFIG. 4as with the case with the first embodiment. The conductive layers41and42have to avoid contact with the source line17. The conductive layers on one line are preferably separated as far as possible to obtain a larger repairable area.

FIG. 6shows a sectional view of the disconnected portion28of the gate line in the active matrix liquid crystal display device. The repair of the gate line15will be explained hereinbelow. Application of a laser to the conductive layer41from the pixel electrode12side or the insulating substrate11side produces the molten metal29. It creates a bypass route through the gate line15, the molten metal29, the conductive layer41, the molten metal29, the pixel electrode12, the molten metal29, the conductive layer41, the molten metal29, and the gate line15. Gate signals can thereby avoid the disconnected portion28and go through the bypass route. The line disconnection can be thus repaired.

The connection resistance of an aluminum element and ITO used for the pixel electrode12is extremely high. The repair of the gate line15in the conventional liquid crystal display device results in the cross-section structure shown inFIG. 8Bin which the pixel electrode12and the gate line15have the direct contact. Therefore, when a laser is applied to connect them, the connection electrical resistance almost reaches one megohm, which is above the limit of the connection resistance for repairing disconnection. For the above reason, when repairing the disconnection as inFIG. 6, the conductive layer to produce the molten metal29is preferably formed by the material other than aluminum, such as chromium. The conductive layer can be formed in the same layer as the drain electrode14shown in FIG.4. In order that the gate line15and ITO of the pixel electrode12are connected via the material such as chromium, tantalum, titanium, molybdenum to avoid direct contact, the source line17is formed by the above material, not aluminum. The connection resistance is thereby kept within 100KΩ that is substantially the same value as the connection resistance of the drain electrode14and the pixel electrode12through the contact hole30. Therefore, disconnection of the gate line15formed by aluminum can be also repaired.

Other Embodiments

The method for repairing line disconnection and the structure therefor described in the above first and second embodiments are also applicable to the repair of disconnection of the source line17and the storage capacitor line16. In the repair of disconnection of the source line17, the conductive layer43can be formed in the same layer as the gate line15; therefore, no extra manufacturing step is needed to maintain productivity. The conductive layer43is deposited by sputtering as with the case with the gate line15. A laser is applied from the backside of the substrate11(the side where the TFT is not provided) to avoid contact between the pixel electrode12and the molten metal29. The repair of the line disconnection is thereby attained without generating a point defect.

If the storage capacitor line16is provided between the gate lines15as shown inFIG. 1, the conductive layer43has to avoid electrical contact with the line16. The conductible layer43is preferably as large as possible to enlarge the area where line disconnection can be repaired. If the storage capacitor line16is not provided, on the other hand, the conductive layer43has to avoid electrical contact with the adjoining gate line15, while being as large as possible to obtain a larger repairable area. The conductive layer43can be formed between the source line17and the pixel electrode12with an insulating film interposed therebetween.

In the repair of the storage capacitor line16, the conductive layer42can be formed in the same layer as the source line17as with the case with the gate line15. No extra manufacturing step is therefore required. The conductive layer42has to avoid electrical contact with the adjoining source line17. The conductive layer42is preferably as large as possible to obtain a larger repairable area.

If the repair results in direct contact between the conductive layer and the pixel electrode12and signals are directly applied to the pixel electrode12, it is preferable to apply a laser to the cut line50on the TFT so as to separate the pixel from the TFT as shown in FIG.2. Though a point defect is generated, the line disconnection is repaired. No error voltage is thereby applied to the pixel electrode12allowing no deterioration of display quality.

The present invention is particularly effective when applied to an active matrix liquid crystal display device in which a gate line and a source line cross each other with a gate insulating film therebetween. The present invention is also applicable to a liquid crystal display device further having a storage capacitor line parallel to the gate line. Further, the present invention can be applied to a liquid crystal display device of In-Plane-Switching (IPS) mode having comb-shaped electrode pairs comprised of a plurality of electrodes to apply an electric field horizontally causing liquid crystal molecules to rotate parallel to a substrate. Furthermore, the present invention can be applied to a display device other than a liquid crystal display device, having two kinds of lines crossing each other with an insulating film therebetween.

As explained in the foregoing, the present invention provides a display device capable of repairing line disconnection without decreasing display quality, and the repair method.