JPH036668B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a thin film transistor (hereinafter abbreviated as
It is related to the substrate (written as TFT). Furthermore, the present invention relates to the electrical properties of TFT matrix substrates.

In recent years, new displays have been actively developed to replace conventional CRT displays. Among these, liquid crystal displays are thin and can operate with low voltage power, so they are attracting attention as displays for personal information devices and portable information devices, and have a large market as displays for calculators, watches, home appliances, and automobiles. is expected. Among these, the characteristics that will be required of liquid crystal displays in the future will be large capacity display capabilities. That is, at first static driving was changed to time-division driving, and with the development of liquid crystal materials, it has now become possible to display up to about 60 horizontal scanning lines. However, the development of liquid crystal materials has reached its limit, and it will be difficult to further increase the number of display scanning lines without adopting an active matrix method. Against this background, liquid crystal display devices using the active matrix method have recently been actively developed. Among active matrix methods, those using MOS (metal-oxide-semiconductor element) arrays,
Some use TFT arrays. The former is suitable for small-area, high-density display devices because the peripheral drivers can be on-chip, and the latter is suitable for large-area, high-density display devices. In addition, from the viewpoint of display quality, in the latter case, the TFT array can be formed on a transparent insulating substrate, so it is not suitable for liquid crystal display mode.
TN mode is possible and the contrast is high.

FIG. 1 shows a plan view, a sectional structure diagram, and a circuit diagram of a conventional TFT active matrix substrate. FIG. 1a is a plan view of one pixel which is a constituent unit of an image display area of a TFT active matrix substrate. In the figure, 1 is a data signal line, 2 is a gate signal line, and 3 is an image display electrode. This image display electrode may normally be a metal electrode or a transparent conductive film electrode. 4 is a contact hole between the TFT source region and the data line, and a contact hole between the TFT drain region and the image display electrode. 5 is TFT. Reference numeral 6 denotes a crossover portion between the data signal line and the gate signal line, and the data signal line and gate signal line are usually electrically separated by a thin insulating film such as an oxide film or a nitride film. The area surrounded by the dashed line in the figure is a one-pixel area. Figure 1a
A sectional view taken along line A-A inside is shown in FIG. 1b. 7 in the diagram is
A gate oxide film of the TFT, 8 a source and drain diffusion region of the TFT, and 9 an insulating plate. FIG. 1c is a circuit diagram of one pixel. In such a conventional TFT active matrix board, as shown in Fig. 2, the gate line and data line are provided with terminal extraction pads on the outer periphery of the board, and these are connected to the driver circuit. There is.
At least one pad for taking out the terminal may be provided for one gate line or one data line. This TFT active matrix substrate has TFTs on an insulating substrate as shown in Figure 1.
Since it is formed in an array, it has the disadvantage of being extremely susceptible to static electricity. For example, if static electricity enters from the terminal extraction pad on the outer periphery of a TFT active matrix substrate, the static electricity will destroy either the gate insulating film of the TFT or the insulating film at the crossover area between the gate line and the data line. Since the voltage of static electricity is usually from several thousand volts to tens of thousands of volts, if static electricity were to enter, these insulating films would be destroyed, resulting in a short connection with low resistance. Therefore, in the manufacturing process of TFT active matrix substrates, it is necessary to take sufficient measures against static electricity. Also
It would be nice if an electrostatic protection circuit with resistors and diode circuits could be installed on the TFT active matrix substrate, as is done on MOS substrates, but for now, due to the characteristics, these electrostatic protection circuits cannot be installed on the TFT active matrix substrate. Difficult to form. Therefore, consider designing a TFT active matrix board so that if static electricity is applied, it will break at a specific location, and then repair that location later by cutting the wiring using a laser, etc. There is a need.

The present invention is based on the idea that if static electricity were to occur in a TFT active matrix substrate that is sensitive to static electricity, it would be destroyed at a specific location, and this location would be repaired later.
The present invention relates to a TFT active matrix substrate, and will be explained below using specific examples.

FIG. 3a shows a case where the insulating film at the crossover portion 6 between the gate line 2 and the data line 1 is broken when static electricity enters the TFT active matrix substrate. This crossover portion breaks down when the dielectric breakdown voltage of the insulating film of this crossover portion is smaller than the dielectric breakdown voltage of the gate insulating film of the TFT 5. In this case, since the gate line and the data line are shorted at this crossover portion, when applied to a liquid crystal display device or the like, line defects appear as a serious problem. Therefore, as shown at 10 in FIG. 3b and 11 in FIG. 3c, it is necessary to perform laser correction on both sides of the gate line or data line across this crossover portion. For example, as shown in FIG. 3B, the gate line may be cut at two places with a laser, and the gate signal may be input from terminal extraction pads provided on both sides of the gate line. However, in this case, two series of gate driver circuits are required in order to input the same gate signal to the terminal extraction pads on both sides. Since it is difficult to insert two lines of gate driver circuits from a cost standpoint, signals from adjacent gate lines are usually input. In this case, adjacent gate lines have the same display, resulting in a display defect. The same applies to the case of FIG. 3c.

On the other hand, if the breakdown voltage of the crossover portion is made larger than the breakdown voltage of the gate insulating film as shown in FIG. 4a, the gate insulating film will definitely be broken down by the input of static electricity. If the gate electrode and source diffusion layer are shot at this time, a display defect (line defect) as shown in the above embodiment will occur. However, in this case, as shown in Figures 4b and 4c, 1
By cutting portions 2 and 13 with a laser, line defects can be easily converted to point defects. In other words, the breakdown voltage of the crossover section is
By setting the voltage to be higher than the gate dielectric breakdown voltage, the gate insulating film will always be destroyed if static electricity enters from the outside, and in this case it can be repaired more easily with a laser.

As explained in the above embodiments, the present invention provides a TFT active matrix substrate that is susceptible to static electricity by making the dielectric breakdown voltage of the crossover portion between the gate line and the data line larger than the dielectric breakdown voltage of the gate film. This relates to TFT active matrix substrates that can be easily repaired with a laser if they are damaged by static electricity, and improves the yield and reduces costs of TFT active matrix substrates for liquid crystal display devices and electroluminescent display devices. This will greatly contribute to the

For example, as in the present invention, there are many methods for making the dielectric breakdown voltage of the crossover section larger than the gate breakdown voltage. In other words, the insulating film in the crossover section and
When the gate insulating films of TFTs are made of the same film quality, the thickness of the insulating film in the crossover portion may be made thicker than the gate film thickness. For example, when the thickness of the gate insulating film is 1000 Å, the thickness of the insulating film at the crossover portion is preferably 1000 Å or more, about 2000 to 10000 Å. Further, it is desirable to design the process and pattern so that even if the thickness of the insulating film in the crossover part and the thickness of the gate insulating film are the same, the breakdown voltage is larger in the crossover part. For example, when using a SiO ₂ film as an insulating film, the breakdown voltage differs depending on the slight difference in phosphorus concentration. The breakdown voltage also differs depending on the annealing temperature after SiO ₂ formation.
Furthermore, the breakdown voltage differs depending on the shape of the step in the wiring section, so sufficient care must be taken in device and process design for TFT active matrix substrates.

FIG. 5 is a cross-sectional view of a TN mode (twisted nematic mode) liquid crystal display device using a TFT active matrix substrate 14 formed on a transparent insulating substrate. 15 is the upper glass substrate, 16
1 is a spacer, 17 is a liquid crystal layer, 18 is a polarizing layer plate, 1
9 is a reflecting plate. This TN mode liquid crystal display device provides a bright display with high contrast, making it ideal as a display for small pocket televisions.

[Brief explanation of the drawing]

1 and 2 are diagrams used to explain the structure and circuit of a conventional TFT active matrix substrate, and FIGS. 3 and 4 are diagrams used to explain the features of the TFT active matrix substrate according to the present invention. FIG. 5 is a structural diagram of a liquid crystal display device using a TFT active matrix substrate according to the present invention. 1...Data line, 2...Gate line, 3
...Liquid crystal drive electrode, 4...Contact hole, 5
...TFT, 6... Crossover section, 7... Gate insulating film, 8... Source, drain diffusion region,
9... Insulating substrate, 10... Laser fusing part of gate line, 11... Laser fusing part of data line, 12... Laser fusing part of gate electrode of TFT, 13... Laser fusing part of source scattering electrode,
14...TFT active matrix substrate, 1
5... Upper glass plate, 16... Spacer, 17...
...Liquid crystal layer, 18...Polarizing plate, 19...Reflecting plate.

Claims (1)

[Claims] 1 A liquid crystal is sealed in a pair of substrates, and one of the substrates has a plurality of gate lines, a plurality of data lines crossing the gate line, and the gate line and the data line. In an active matrix liquid crystal display device having a thin film transistor arranged at an intersection of the thin film transistor, the thickness of the gate insulating film of the thin film transistor and the insulating film at the intersection of the gate line and the data line are the same, and the gate of the thin film transistor An active matrix type liquid crystal display device, characterized in that the breakdown voltage of the insulating film is set lower than the breakdown voltage of the insulating film at the intersection of the gate line and the data line.