An active matrix display device, a method of manufacturing the same and a method to treat defective pixels

Abstract: An active matrix display device comprising scanning branch lines ( 22 ) each branching from the scanning line ( 21 ), and switching elements ( 31 ) each formed on an end portion of the scanning branch line, wherein the distance between the scanning line side of the switching element ( 31 ) and the scanning line ( 21 ) is so provided as to enable the scanning branch line ( 22 ) to be cut off by irradiation with light energy ( 26,27 ).

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention: The present invention relates to a display device which performs its display function by applying driving signals to pixel electrodes via switching elements, and more particularly to an active matrix driving type display device which performs high-density display by using pixel electrodes arranged in a matrix pattern. 2. Description of the Prior Art: In liquid crystal display devices, EL display devices, plasma display devices and the like, it is known how to produce a display pattern on a screen by selectively driving pixel electrodes arranged in a matrix pattern. In such display devices, voltage is applied between each selected pixel electrode and a counter electrode disposed facing it, to optically modulate a display medium such as liquid crystal or the like interposed between these electrodes. This optical modulation is recognized as a display pattern. As a method for driving pixel electrodes, an active matrix driving method is known in which independent pixel electrodes are arrayed and are driven via switching elements connected to the respective pixel electrodes. As the switching elements used to selectively drive the pixel electrodes, TFT (thin film transistor) elements, MIM (metal-insulator-metal) elements, MOS transistors, diodes, varistors, etc. are generally known. Because the active matrix driving method is capable of performing high contrast display, it has been put to practical use in liquid crystal televisions, word processors, computer terminal displays and the like. Figures 11 and 12 are plan views of active matrix substrates used in active matrix display devices according to a prior art. On the substrate shown in Figure 11, source bus lines 23 are disposed in parallel and intersecting at right angles with gate bus lines 21 which are arranged parallel with each other. A pixel electrode 41 is disposed in each rectangular area surrounded by two gate bus lines 21 and two source bus lines 23. On each gate bus line 21 and adjacent to the intersection of the gate bus line 21 and the source bus line 23, there is formed a TFT 31 which functions as a switching element, a portion of the gate bus line 21 functioning as the gate electrode of the TFT 31. The drain electrode of the TFT 31 is electrically connected to the pixel electrode 41, while a branch line branching from the source bus line 23 is connected to the source electrode of the TFT 31. The active matrix substrate of Figure 12 is the same as that of Figure 11 except that the construction around the TFT 31 is different. In Figure 12, the TFT 31 is formed on a gate bus branch line 22 branching from the gate bus line 21, a portion of the gate bus branch line 22 functioning as the gate electrode of the TFT 31. To achieve high-density display using such display devices, it is necessary to array a great number of pixel electrodes 41 and TFTs 31. However, there may be cases in which some TFTs 31 have been already formed as defective TFTs when they are formed on a substrate. The pixel electrodes connected to such a defective TFT cause defective pixel elements that do not contribute to the display. Such defective pixel elements result in substantial damage to the image quality of the display device, and therefore, greatly reduce the product yield. Display devices having constructions to correct the defective TFTs are disclosed in Japanese Laid-Open Patent Publications Nos. 2-153324, 2-294623 and 2-254423. These display devices comprise spare TFTs which are connected to a pixel element electrode connected to the defective TFT. There are two major cases of causes for the defective pixel elements. One is the failure to sufficiently charge the pixel electrode during the period in which the pixel electrode is selected by a scanning signal (hereinafter referred to as the "on-failure"). The other is a failure that causes the charge in the charged pixel electrode to leak during the period in which the pixel electrode is not selected (hereinafter referred to as the "off-failure"). The on-failure is attributable to a defective TFT. The off-failure is caused either by electrical leakage via the TFT or by electrical leakage between the pixel electrode and the bus line. In either causes of failure, since necessary voltage is not applied between the pixel electrode and the counter electrode, a defective pixel element is produced. When such failures occur, the defective pixel element appears as a bright spot in the normally white mode in which light transmittance is the highest when the voltage applied between the pixel electrode and the counter electrode is 0 V, and as a black spot in the normally black mode in which light transmittance is the lowest when the voltage is 0 V. Such a defective pixel element can be corrected by performing laser trimming, etc. However, correction of the defective pixel element must be done on an active matrix substrate before the substrate is assembled into a display device. It is easy to detect pixel defects after the display device has been assembled, but it is extremely difficult to detect pixel defects in an active matrix substrate before assembly, particularly in the case of a large-size display device having 100,000 to 500,000 pixels. Even if the detection and the correction of the defective pixel electrode can be achieved, it requires a high precision measuring instrument as disclosed in Japanese Laid-Open Patent Publication No. 1-144092. It involves a complicated inspection process and is detrimental to mass production efficiency to examine the electrical characteristics of all pixel electrodes and detect the defective TFTs. It therefore causes an increase in costs. For these reasons, as the situation stands now, it is not possible to correct defective pixels in an active matrix substrate before being assembled by the above-mentioned method using a laser beam in the case of large-size display devices having a great number of pixels. JP 58184758 discloses a technique for dealing with a defective picture element in a matrix array. A laser beam is used to isolate a gate electrode of a switching transistor from a gate line. Also the gate electrode, source electrode and drain electrode of the transistor are short-circuited. JP 1186916 discloses a technique for repairing a line defect in a display matrix array by passing a large fusing current through a connection between the gate of a switching transistor and a scanning line in the event of a short-circuit between the gate and source or drain. SUMMARY OF THE INVENTION According to one aspect of the invention, there is provided an active matrix display device comprising: a pair of insulating substrates at least one of which is light transmitting; scanning lines arranged on one of said pair of substrates; scanning branch lines each branching from a said scanning line; switching elements each formed on an end portion of a said scanning branch line and each connected between a pixel electrode and a signal line; and at least one defective pixel wherein at the site of the defective pixel the scanning branch line is cut off by irradiation with light energy in a portion lying between the scanning line side of said switching element and said scanning line, and wherein a permanent electrical connection between the pixel electrode and the signal line via said switching element is established by irradiation of said switching element with light energy at said site. In a preferred embodiment, the active matrix display device further comprises a pixel electrode connected to said switching element and a supplemental capacitor electrode disposed opposite to said pixel electrode with an insulating film interposed therebetween, a supplemental capacitor being formed between said pixel electrode and said supplemental capacitor electrode. In a preferred embodiment, the active matrix display device further comprises a pixel electrode connected to said switching element and disposed opposite to a scanning line adjacent to the scanning line from which the branch line branches with an insulating film interposed therebetween, a supplemental capacitor being formed at the superimposing portion of said pixel electrode and said adjacent scanning line. In a preferred embodiment the portion where said scanning branch line is cut off is narrower than the portion thereof where said switching element is formed. In a preferred embodiment, said narrower width portion is formed by cutting one or the other side of a portion of said scanning branch line other than the portion thereof where said switching element is formed. In a preferred embodiment, the distance (Y) between a pixel electrode side of the narrower portion of said scanning branch line and said pixel electrode is at least 10 µm. In a preferred embodiment, the distance (X) between a scanning line side of said switching element and said scanning line is at least 10 µm. According to another aspect of the invention, there is provided a method of manufacturing an active matrix display device, comprising: forming an active matrix substrate which comprises an insulating substrate, scanning lines and signal lines arranged in vertical and horizontal directions on said substrate, scanning branch lines each branching from said scanning line, switching elements each formed on an end portion of a said scanning branch line, and pixel electrodes each connected to a said switching element wherein at least one pixel is defective, and attaching an opposing substrate to said active matrix substrate with a display medium sandwiched between said active matrix substrate and said opposing substrate; detecting the pixel defect by applying a driving voltage to said pixel electrodes from said scanning lines and said signal lines via said switching elements, said pixel defect caused by a defective pixel electrode; and irradiating light energy through one of said active matrix and opposing substrates onto said scanning branch line so as to electrically disconnect said scanning branch line from said scanning line; characterised by the step of irradiating light energy through one of said active matrix and opposing substrates onto the switching element connected to a defective pixel electrode to form a permanent electrical connection between said defective pixel electrode and said signal line via said switching element. According to a further aspect of the invention, there is provided a method of treating a pixel defect in an active matrix display device in which scanning lines, transverse signal lines, and pixel electrodes are supported on an insulating substrate together with switching elements controlled by signals on the scanning lines for connecting respective pixel electrodes to adjacent said signal lines, characterised in that the method comprises making a permanent electrical connection through the switching element between the pixel electrode of the defective pixel and the adjacent signal line using light energy irradiated onto the switching element through said substrate or through an opposed substrate carrying counter electrode means. In the active matrix display device of the present invention, when an on-failure or off-failure occurs because of a defective switching element, occurrence of a weak leakage current between a signal line and a pixel electrode, or the other reasons, the defective pixel can be corrected in an assembled display device. First, the scanning branch line concerned is cut off by irradiating a laser beam. The distance between the scanning line side of a switching element and the scanning line is so provided as to allow the scanning branch line to be cut off by irradiation of light energy such as a laser beam or the like. Also, in an embodiment of the present invention, the scanning branch line is provided with a portion having a reduced width so as to facilitate the cutting thereof by laser beam irradiation. Therefore, the scanning branch line can be reliably cut off. Next, light energy is irradiated to electrically interconnect the electrode of the switching element connected to the pixel electrode and the electrode thereof connected to the signal line. When the switching element is a TFT, the electrical interconnection is made by irradiating light energy onto the superimposed portion of the source electrode and the gate electrode and also onto the superimposed portion of the drain electrode and the gate electrode. When a laser beam is used as the light energy, a spot-like hole is made in each of the superimposed portions. Around these holes, the source electrode is electrically connected to the gate electrode and the drain electrode is electrically connected to the gate electrode. Thus, the source electrode and the drain electrode are electrically interconnected via the gate electrode. Referring now to Figure 13, it will be explained how the voltage is applied to the pixel electrode which has been directly connected to the signal line in the above manner (hereinafter referred to as the "corrected pixel electrode"). In Figure 13, G n represents the relationship of the signal voltage (plotted along the ordinate) on the n-th scanning line with respect to the time (plotted along the abscissa) while S m illustrates the relationship of the signal voltage (plotted along the ordinate) on the m-th signal line with respect to the time (plotted along the abscissa). P n,m indicates the voltage applied to a normal pixel electrode connected to the n-th scanning line and the m-th signal line. P' n,m indicates the voltage applied to a corrected pixel electrode connected to the n-th scanning line and the m-th signal line. As shown in G n and G n+1 , a signal (V gh ) for sequentially selecting the switching elements is output on the scanning line during a selection time T on . Corresponding to the selection time T on on the scanning line, a video signal voltage V 0 is output on the signal line, and in the case of a normal pixel electrode, the video signal voltage V 0 is held during a non-selection time T off as shown in P n,m . Then, when the next selection signal voltage V gh is applied, a video signal -V 0 is applied to the signal line. On the other hand, in the case of a corrected pixel electrode, since the video signal from the signal line is applied all the time as shown in P' n,m , the corrected pixel electrode is unable to function properly. However, when the entire cycle is viewed, the pixel driven by the corrected pixel electrode produces a display corresponding to the root-mean-square value of the video signal applied to the signal line during that one cycle. Therefore, the pixel does not appear as a complete bright spot or black spot but produces a display having the average brightness of the pixels arrayed along the signal line. Thus, the defect of the pixel is made extremely difficult to discern. It is required that the connections made in the above manner have an electrical resistance lower than the resistance of the switching element in a selected condition (hereinafter referred to as the "on-state resistance"). The reason is believed to be as follows. The on-state resistance of the switching element is determined so that a current enough to charge the pixel electrode flows during the time in which the switching element is selected. Therefore, if the resistance at the above connection is higher than the on-state resistance, the signal voltage varying at every selection time of the switching element will not be completely written in the corrected pixel electrode, reducing the root-mean-square value of the voltage applied to the corrected pixel electrode. In such a condition, the difference in brightness increases between the pixel driven by the corrected pixel electrode and the normally operating pixels, so that the pixel defect becomes visually discernible. Thus, it is an object of the present invention to provide an active matrix display device in which any pixel defect can be corrected to an undiscernible level within the assembled display device itself. It is another object of the present invention to provide a method of manufacturing an active matrix display device in which any pixel defect can be corrected to an undiscernible level in an assembled display device. In the active matrix display device of the present invention, any pixel defect can be corrected to an undiscernible level with the display device in an assembled condition under which the pixel defect is easy to detect. Therefore, according to the present invention, the display device can be manufactured at a high yield ratio, thus contributing to a reduction of the cost of the display device. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a plan view of an active matrix substrate used in an active matrix display device of the present invention. Figure 2 is an enlarged plan view of a TFT and its adjacent portions as shown in Figure 1. Figure 3 is a cross sectional view of a display device using the substrate of Figure 1, taken along line S-S in Figure 1. Figures 4 and 5 are plan views of other embodiments each having a supplemental capacitor. Figure 6 is a plan view showing an embodiment with a gate bus branch line having a reduced width portion. Figure 7 is an enlarged plan view of the TFT and its adjacent portions shown in Figure 6. Figure 8A and Figure 8B are plan views of gate bus branch lines in other embodiments of the present invention. Figures 9 and 10 are plan views of other embodiments each having a supplemental capacitor. Figures 11 and 12 respectively are plan views of active matrix substrates used in prior art active matrix display devices. Figure 13 is a diagram showing the relationship of the signal applied to a scanning line and a signal line with respect to the voltage applied to a pixel electrode. DESCRIPTION OF THE PREFERRED EMBODIMENTS Figure 1 shows a plan view of an active matrix substrate used in one embodiment of the display device of the present invention. Figure 3 shows a cross sectional view of a display device using the substrate of Figure 1, taken along line S-S in Figure 1. The following describes the active matrix display device of this embodiment in the sequence of its manufacturing steps. In this embodiment, a transparent glass substrate is used as the insulating substrate. There are formed on the glass substrate 1 a gate bus line 21 which functions as a scanning line and a gate bus branch line 22 which branches from the gate bus line 21. Generally, the gate bus line 21 and the gate bus branch line 22 are formed from a single or multiple layer of such metals as Ta, Ti, Al, Cr, etc. In this embodiment, Ta is used as the material. The gate bus line 21 and the gate bus branch line 22 are formed by patterning the Ta metal layer deposited by using a sputtering method. A base coat film formed from Ta 2 O 5 , etc. may be formed on the glass substrate 1 prior to the formation of the gate bus line 21 and the gate bus branch line 22. The length of the gate bus branch line will be described later. A base insulating film 11 made of SiN x is formed all over the surface covering the gate bus line 21 and the gate bus branch line 22. The gate insulating film 11 is deposited to a thickness of 3000 Å using the plasma CVD technique. Next, a TFT 31 which functions as a switching element is formed at an end portion of the gate bus branch line 22. A portion of the gate bus branch line 22 functions as the gate electrode 25 of the TFT 31. After forming the gate insulating film 11 as described above, an amorphous silicon (a-Si) layer which is later formed as a channel layer 12 and an SiN x layer which is later formed as an etching stopper layer 13 are deposited. The thickness of the a-Si layer is 300 Å, and that of the SiN x layer is 2000 Å. Next, the SiN x layer is patterned to form the etching stopper layer 13. Furthermore, over the entire surfaces of the a-Si layer and the etching stopper layer 13, an n + -a-Si layer doped with P (phosphorus) which is later formed as contact layers 14 and 14 is deposited to a thickness of 800 Å using the plasma CVD technique. After that, the a-Si layer and the n + -a-Si layer are simultaneously patterned to form the channel layer 12 and the contact layers 14 and 14. Next, a Ti metal layer is formed which is later formed as a source electrode 32, a source bus line 23 to function as a signal line, and a drain electrode 33. Generally, the source bus line 23 and others are formed from a single or multiple layers of such metals as Ti, Al, Mo, Cr, etc. In this embodiment, Ti is used as the material. The Ti metal layer is deposited by sputtering. The Ti metal layer is patterned to form the source electrode 32, the source bus line 23, and the drain electrode 33. The source bus line 23 and the gate bus line 21 intersect each other with the gate insulating film 11 interposed therebetween. Next, a pixel electrode 41 made of ITO (indium tin oxide) is formed in a rectangular area surrounded by the gate bus line 21 and the source bus line 23, as shown in Figure 1. The pixel electrode 41 is superimposed on an end portion of the drain electrode 33 of the TFT 31 for electrical connection to the drain electrode 33. Further, over the entire surface of the substrate on which the TFT 31 and the pixel electrode 41 are formed, a protective film 17 made of SiN x is deposited. The protective film 17 may be formed in the shape of a window opened above the central portion of the pixel electrode 41. An orientation film 19 is formed over the protective film 17. On a glass substrate 2 disposed opposite to the glass substrate 1, there are formed a counter electrode 3 and an orientation film 9. A liquid crystal layer 18 is sandwiched between the substrates 1 and 2 to complete the active matrix display device. The construction around the TFT 31 will now be explained. Figure 2 shows an enlarged view of the TFT 31 and its adjacent portions. As previously described, the TFT 31 is formed on the gate bus branch line 22 branching from the gate bus line 21. The drain electrode 33 of the TFT 31 is electrically connected to the pixel electrode 41 while the source electrode 32 thereof is electrically connected to the source bus line 23. The distance X between the side of the TFT 31 nearer to the gate bus line 21 and the gate bus line 21 is greater than that in the prior art previously described in connection with Figure 12, so as to allow the gate bus branch line 22 to be cut off using light energy such as a laser beam or the like. It has been confirmed that the line can be cut off reliably if the distance X is 10 µm or more. If the distance X is smaller than 10 µm, it not only makes it impossible to cut off the gate bus branch line 22 without damaging the TFT 31 but also gives rise to a possibility that the irradiation by a laser beam may adversely affect the intersection of the gate bus line 21 and the source bus line 23 and may cause insulation failure between the bus lines 21 and 23. In the active matrix display device of the above construction, when the TFT 31 becomes defective or when a weak leakage current flows between the source bus line 23 and the pixel electrode 41, a pixel defect occurs. If this happens, correction is made in the following manner. First, light energy is irradiated onto an area 51 indicated by a broken line in Figure 2 to cut off the gate bus branch line 22. The gate bus branch line 22 is thus electrically isolated from the gate bus line 21. In this embodiment, a YAG laser beam is used as the light energy. As described, since the distance X is sufficiently large, the gate bus branch line 22 can be cut off reliably. The laser beam may be irradiated either through the substrate 1 or through the substrate 2. When a light shield film is formed on the substrate 2, which is often the case, the laser beam is irradiated through the substrate 1. In this embodiment also, the laser beam is irradiated through the substrate 1. Next, the laser beam is irradiated onto areas 52 and 53 indicated by broken lines in Figure 2, that is, onto the portions indicated by arrows 26 and 27 in Figure 3. As a result, the source electrode 32 and the gate electrode 25 are electrically interconnected at the area 52, while at the area 53 the drain electrode 33 and the gate electrode 25 are electrically interconnected. Thus, the source electrode 32 and the drain electrode 33 are electrically interconnected via the gate electrode 25. Since the signal from the source bus line 23 is applied at all times to the pixel electrode 41 (corrected pixel electrode) connected to the TFT 31 corrected in the above manner, the corrected pixel electrode is unable to function properly. However, since the pixel driven by the corrected pixel electrode performs a display corresponding to the root-mean-square value of the signal applied to the source bus line 23, the pixel does not appear as a complete bright spot or black spot but performs display having the average brightness of the pixels arrayed along the source bus line 23. Thus, the defect of the pixel is made extremely difficult to discern. Even if the laser beam irradiates as described above, since the protective film 17 is formed over the gate bus branch line 22 and the TFT 31, molten metals or other foreign matter are prevented from entering the display medium, i.e. the liquid crystal layer 18, and therefore, no detrimental effects are caused to the display. Also, it has been found that by changing the irradiating conditions of the laser beam, the same laser beam can be used for melting and interconnecting the metal layers as well as for cutting the metal layers. Also, in the above correction work, interconnections between the gate electrode 25, source electrode 32, and drain electrode 33 of the TFT 31 may be made prior to the cutting of the gate bus branch line 22. The above-described construction may also be applied to an active matrix display device having a supplemental capacitor 42 as shown in Figure 4. The display device of Figure 4 is identical to the foregoing embodiment illustrated in Figures 1 to 3, except that the supplemental capacitor 42 is provided. The supplemental capacitor 42 is formed on the superimposed portion (shaded portion) of the pixel electrode 41 and a supplemental capacitor electrode 24 disposed on the substrate 1 in parallel with the gate bus line 21. In the display device of Figure 4 also, pixel defects can be corrected in the same manner as in the foregoing embodiment illustrated in Figures 1 to 3. Furthermore, the above-described features can be applied to an active matrix display device having a construction like that shown in Figure 5. The display device shown is so constructed as to prevent the opening area from being reduced by the provision of the supplemental capacitor 42 which is the case with the display device of Figure 4. That is, in the display device of Figure 5, the gate bus line 21 is enlarged in width so as to be superimposed on a portion of the pixel electrode 41. According to this construction, the adjacent gate bus line 21 which is in a non-selected condition can be used as the supplemental capacitor electrode. Further, since no gap is created between the gate bus line 21 and the supplemental capacitor electrode 24 unlike the construction of Figure 4, the opening area is prevented from being reduced. In this display device also, pixel defects can be corrected in the same manner as in the foregoing embodiment illustrated in Figures 1 to 3. Figure 6 shows a plan view of an active matrix substrate used in another embodiment of the display device of the present invention. This embodiment has the same construction as that of the embodiment illustrated in Figure 1, except that the shape of the gate bus branch line 22 is different when viewed from the top. The cross sectional view of a display device using the substrate of Figure 6, taken along line R-R in Figure 6, is the same as shown in Figure 3 previously described. Referring to Figure 7, the construction around the TFT 31 of this embodiment will be now explained. As previously described, the TFT 31 is formed on the gate bus branch line 22 branching from the gate bus line 21. The drain electrode 33 of the TFT 31 is electrically connected to the pixel electrode 41 while the source electrode 32 thereof is electrically connected to the source bus line 23. A portion of the gate bus branch line 22 other than the portion thereof where the TFT 31 is formed has a width narrower than that of the portion thereof where the TFT 31 is formed. By providing such a narrower width portion, it is possible to make the distance Y between the pixel electrode 41 and the gate bus branch line 22 larger than that in the prior art previously illustrated with reference to Figure 12. The provision of a sufficiently long distance Y allows the gate bus branch line 22 to be cut off more easily and reliably using light energy such as a laser beam or the like. It has been confirmed that the line can be cut off reliably if the distance Y is 10 µm or more. If the distance Y is smaller than 10 µm, it not only makes it impossible to cut off the gate bus branch line 22 without damaging the TFT 31 but also gives rise to a possibility that the irradiation by laser beam may adversely affect the intersection of the gate bus line 21 and the source bus line 23 and may cause insulation failure between the bus lines 21 and 23. In the active matrix display device of the above construction, when the TFT 31 becomes defective or when a weak leakage current flows between the source bus line 23 and the pixel electrode 41, a pixel defect occurs. If this happens, the defect is corrected in the same manner as in the foregoing embodiment illustrated in Figure 1. First, light energy is irradiated onto an area 51 indicated by a broken line in Figure 7, to cut off the gate bus branch line 22. As a result, the gate bus branch line 22 is electrically isolated from the gate bus line 21. As previously described, since the gate bus branch line 22 has a portion where the width is narrower than the portion thereof on which the TFT 31 is formed, the gate bus branch line 22 can be cut off easily and reliably. Next, the laser beam is irradiated onto areas 52 and 53 indicated by broken lines in Figure 7. As a result, the source electrode 32 and the drain electrode 33 are electrically interconnected via the gate electrode 25. The signal from the source bus line 23 is applied at all times to the pixel electrode 41 (corrected pixel electrode) connected to the TFT 31 corrected in the above manner. Therefore, the pixel defect is made extremely difficult to discern. The gate bus branch line 22, when viewed from the top, may be formed as shown in Figure 8A or Figure 8B. In the gate bus branch line 22 shown in Figure 8A, the portion having a reduced width is formed by removing a portion from the pixel electrode 41 side of the gate bus branch line 22. Likewise, in the gate bus branch line 22 shown in Figure 8B, the portion having a reduced width is formed by removing a portion from the source bus line 23 side of the gate bus branch line. The above-described features may also be applied to an active matrix display device having a supplemental capacitor 42 as shown in Figure 9. The display device of Figure 9 is identical to the foregoing embodiment illustrated in Figure 6, except that a supplemental capacitor 42 is provided. The supplemental capacitor 42 is formed on the superimposed portion (shaded portion) of the pixel electrode and a supplemental capacitor electrode 24 that is disposed on the substrate 1 in parallel with the gate bus line 21. In the display device of Figure 9 also, pixel defects can be corrected in the same manner as in the foregoing embodiment illustrated in Figure 6. Furthermore, the above-described features can be applied to an active matrix display device having a construction as shown in Figure 10. The display device shown is so constructed as to prevent the opening area from being reduced by the provision of the supplemental capacitor 42 which is the case with the display device of Figure 9. That is, in the display device of Figure 10, the gate bus line 21 is enlarged in width so as to be superimposed on a portion of the pixel electrode 41. According to this construction, the adjacent gate bus line 21 which is in a non-selected condition can be used as the supplemental capacitor electrode. Further, since no gap is created between the gate bus line 21 and the supplemental capacitor electrode 24 unlike the construction of Figure 9, the opening area is prevented from being reduced. In this display device also, pixel defects can be corrected in the same manner as in the foregoing embodiment illustrated in Figure 6. Any of the embodiments shown in Figures 1 to 10 uses a TFT as the switching element. For the embodiments of Figures 1 to 10, there can be used any switching element as long as the signal line side electrode and the pixel electrode side electrode thereof can be electrically interconnected by irradiating light energy such as a laser beam or the like. In any of the above embodiments, the TFT 31 shown has a gate electrode in the lower portion and a source electrode and a drain electrode in the upper portion, but alternatively, a TFT having a gate electrode in the upper portion and a source electrode and a drain electrode in the lower portion can be used.

Claims: An active matrix display device comprising: a pair of insulating substrates (1, 2) at least one (1) of which is light transmitting; scanning lines (21) arranged on one of said pair of substrates; scanning branch lines (22) each branching from a said scanning line; switching elements (31) each formed on an end portion of a said scanning branch line and each connected between a pixel electrode and a signal line; and at least one defective pixel wherein at the site of the defective pixel the scanning branch line is cut off by irradiation with light energy in a portion lying between the scanning line side of said switching element and said scanning line, and characterised in that a permanent electrical connection between the pixel electrode and the signal line via said switching element is established by irradiation of said switching element with light energy at said site. An active matrix display device according to claim 1, further comprising a pixel electrode (41) connected to said switching element and a supplemental capacitor electrode (24) disposed opposite to said pixel electrode (41) with an insulating film interposed therebetween, a supplemental capacitor (42) being formed between said pixel electrode and said supplemental capacitor electrode. An active matrix display device according to claim 1, further comprising a pixel electrode (41) connected to said switching element (31) and disposed opposite to a scanning line (21) adjacent to the scanning line from which the branch line branches with an insulating film interposed therebetween, a supplemental capacitor (42) being formed at the superimposing portion of said pixel electrode and said adjacent scanning line. An active matrix display device according to any preceding claim, wherein said portion where said scanning branch line (22) is cut off is narrower than the portion thereof where said switching element is formed. An active matrix display device according to claim 4, wherein said narrower width portion is formed by a cut-out in one or the other side of a portion of said scanning branch line other than the portion thereof where said switching element is formed. An active matrix display device according to claim 4 or claim 5, wherein the distance (Y) between a pixel electrode side of the narrower portion of said scanning branch line (22) and said pixel electrode is at least 10 µm. An active matrix display device according to any preceding claim wherein the distance (X) between a scanning line side of said switching element and said scanning line is at least 10 µm. A method of manufacturing an active matrix display device, comprising: forming an active matrix substrate which comprises an insulating substrate (1), scanning lines (21) and signal lines (23) arranged in vertical and horizontal directions on said substrate, scanning branch lines (22) each branching from said scanning line, switching elements (31) each formed on an end portion of a said scanning branch line, and pixel electrodes (41) each connected to a said switching element, wherein at least one pixel is defective and attaching an opposing substrate (2) to said active matrix substrate with a display medium (18) sandwiched between said active matrix substrate and said opposing substrate; detecting the pixel defect by applying a driving voltage to said pixel electrodes from said scanning lines and said signal lines via said switching elements, said pixel defect caused by a defective pixel electrode; and irradiating light energy through one of said active matrix and opposing substrates onto said scanning branch line so as to electrically disconnect said scanning branch line from said scanning line; characterised by the step of irradiating light energy through one of said active matrix and opposing substrates onto the switching element connected to a defective pixel electrode to form a permanent electrical connection between said defective pixel electrode and said signal line via said switching element. A method of treating a pixel defect in an active matrix display device in which scanning lines (21), transverse signal lines (23), and pixel electrodes (41) are supported on an insulating substrate (1) together with switching elements (31) controlled by signals on the scanning lines for connecting respective pixel electrodes to adjacent said signal lines, characterised in that the method comprises making a permanent electrical connection through the switching element between the pixel electrode of the defective pixel and the adjacent signal line using light energy irradiated onto the switching element and through said substrate or through an opposed substrate carrying counter electrode means.

Inventors: FUJIHARA TOSHIAKI, FUJIKI HIROSHI, KANEMORI YUZURU, KATAYAMA MIKIO, KATO HIROAKI, KONDO NAOFUMI, NAKAZAWA KIYOSHI, NEGOTO HIDENORI, TAKAHAMA MANABU, YANO KOZO, FUJIHARA, TOSHIAKI, FUJIKI, HIROSHI, KANEMORI, YUZURU, KATAYAMA, MIKIO, KATO, HIROAKI, KONDO, NAOFUMI, NAKAZAWA, KIYOSHI, NEGOTO, HIDENORI, TAKAHAMA, MANABU, YANO, KOZO
Applicants: SHARP KK, SHARP KABUSHIKI KAISHA
Application year: 1991
Main classification: G02F1
IPC codes: G02F1