JPH0610349Y2 - Liquid crystal display element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION "Industrial field of application" This invention is used, for example, to display an image, in which a plurality of display electrodes are formed in a liquid crystal cell, and the plurality of display electrodes are selectively formed by thin film transistors. The present invention relates to a liquid crystal display device adapted to display.

"Prior Art" In a conventional liquid crystal display element of this type, as shown in FIG. 1, transparent substrates 11 and 12 such as glass are provided in close proximity to each other, and a spacer 13 is interposed at a peripheral portion thereof. A liquid crystal 14 is sealed between the transparent substrates 11 and 12. A plurality of display electrodes 15 are formed on the inner surface of one transparent substrate 11, thin film transistors 16 are formed as switching elements in contact with the respective display electrodes 15, and the drains of the thin film transistors 16 are connected to the display electrodes 15. A transparent common electrode 17 is formed on the inner surface of the other transparent substrate 12 so as to face the plurality of display electrodes 15.

The display electrode 15 is, for example, a pixel electrode, and the square display electrodes 15 are arranged in rows and columns on the transparent substrate 11 as shown in FIG. Gate buses 18 are formed along the respective lines, and source buses 19 are formed along and adjacent to the respective column arrays of the display electrodes 15. The thin film transistors 16 are provided at the intersections of the gate buses 18 and the source buses 19, the gates of the thin film transistors 16 are connected to the gate buses 18 at the intersections of the buses, and the sources are connected to the source buses 19 respectively. The drain is connected to the display electrode 15.

Each of the gate bus 18 and the source bus 19 is selected and a voltage is applied between them, and only the thin film transistor 16 to which the voltage is applied becomes conductive, and the display connected to the drain of the conductive thin film transistor 16 is displayed. Electrode 15
By accumulating electric charges in the liquid crystal display device and applying a voltage only to the portion of the liquid crystal 14 between the display electrode 15 and the common electrode 17, the portion of the display electrode 15 is transparent or light-shielded. Display selectively. The display can be erased by discharging the charges accumulated in the display electrode 15.

Conventionally, the thin film transistor 16 is configured as shown in FIGS. 3 and 4, for example. That is, the transparent substrate 1
The display electrode 15 and the source bus 19 are formed on the display substrate 1 by a transparent conductive film such as ITO. The display electrode 15 and the source bus 19 are formed of amorphous silicon such that they are parallel and close to each other. A semiconductor layer 21 is formed, and a gate insulating film 22 made of silicon nitride or the like is further formed thereon. The semiconductor layer 21 is formed on the gate insulating film 22.
The gate electrode 23 is formed so as to partially overlap the display electrode 15 and the source bus 19 via the gate electrode 23. Gate electrode 2
One end of 3 is connected to the gate bus 18. In this way, the display electrode 15 and the source bus 19 which face the gate electrode 23 respectively form the drain electrode 15a and the source electrode 19a, and these electrodes 15a and 19a, the semiconductor layer 21, the gate insulating film 22, and the gate electrode 23 are formed. Therefore, the thin film transistor 16 is configured. The gate electrode 23 and the gate bus 18 are formed at the same time and are made of, for example, aluminum.

In each thin film transistor 16 thus formed, the source electrode 19a and the gate electrode 23 thereof are connected to the source bus 19 and the gate bus 18, respectively. The buses 19 and 18 are, for example, as shown in FIGS. 6 Figure A,
As shown in B, they are separately connected to a source terminal T _S and a gate terminal T _G formed integrally with the buses 19 and 18, respectively. An external drive circuit is connected to each of the terminals T _S and T _G , and a drive signal from the external drive circuit is input, and each thin film transistor 16 of the liquid crystal display element is selectively driven by this drive signal.

[Problems to be Solved by the Invention] As described above, in the conventional liquid crystal display device, the source terminal of the source bus and the gate terminal of the gate bus are made of the same material as the source electrode and the gate electrode, respectively. The source terminal is made of ITO and the gate terminal is made of different materials such as aluminum. Therefore, in order to connect each of these terminals to the external drive circuit, it is necessary to make connection under the condition suitable for each material, and it is troublesome to make the connection under different conditions.

Further, in the above-mentioned conventional example, the source bus 19 is formed of ITO, but ITO has a relatively poor electric conductivity, and the source bus 19 has a relatively large resistance as a whole bus line. A potential that is not negligible is generated between the start end and the end of the source bus 19 line, and a potential gradient is formed in the bus line 19. Therefore, the source electrode 19a and the drain electrode 1 applied to each thin film transistor 16 are
The voltage between 5a and 5a is not constant but depends on the potential frequency of the bus line 19, that is, there is a luminance gradient between the thin film transistors 16. Therefore, there is a disadvantage that one side of the liquid crystal display element becomes dark.

One possible solution to this is to increase the thickness of the ITO film forming the source bus. But ITO
Film and (I _n fold-out in P-CVD process) When too thick ITO film is deteriorated, not a complete solution has the disadvantage that the characteristics of the TFT are deteriorated. Further, since the ITO film is a transparent conductive film, the light L leaks from the bus line portion as shown in FIG. 4, and accordingly, the light L not controlled by the thin film transistor 16 always appears on the liquid crystal display surface to improve the contrast of pixel display. Make it worse.

According to the present invention, one of a gate bus and a gate terminal connected to the gate bus, a source bus and a source terminal connected to the gate bus is made of the same transparent material as the pixel electrode. The other has a metal layer, the other has a second metal layer of the same material as the electrode of the thin film transistor to which the bus is connected, and a third metal layer of the same material as the second metal layer is laminated on most of the first metal layer. The second metal layer and the third metal layer are located on the surface side of the source terminal and the gate terminal. That is, the surface of the terminal connected to the external circuit is made of the same metal material. Therefore, the source terminal and the gate terminal can be connected to the external circuit under the same condition.

[Embodiment] An embodiment of the liquid crystal display device according to the present invention will be described below with reference to the drawings starting from FIG. In this embodiment, as described with reference to FIG. 2, the pixel electrodes are formed on the rows and columns as the display electrodes, and the portions corresponding to those of FIGS. 1 to 4 are designated by the same reference numerals. There is. Further, although amorphous silicon is used as the semiconductor layer in this example, when the amorphous silicon is exposed to light, its conductivity increases, so that the ratio of ON and OFF in the switching characteristics of the thin film transistor becomes small. In order to avoid such a problem, a case will be described as an example where a light-shielding layer that does not allow light to be incident is formed on a semiconductor layer of amorphous silicon.

FIG. 7 is a plan view corresponding to FIG. 3, and FIG. 8 is a plan view.
It is sectional drawing corresponding to a figure, ie, thin film transistor 1
FIG. 6 is a sectional view of a portion 6; Further, FIG. 9 shows the gate bus 18.
10 is a cross-sectional view of the channel portion of the thin film transistor 16 along this line, and FIG. 11 is a cross-sectional view of the gate bus portion thereof. The examples shown in FIGS. 7 to 11 will be described below in the order of their manufacturing methods.

In the case where the light shielding layer is formed as described above,
As shown in FIGS. 13A and 13A, a region 15 ′ on which the display electrode 15 is to be formed and the source bus 19 on the transparent substrate 11.
The light-shielding layer 25 is formed between the regions 19 'in which the holes are to be formed. The light-shielding layer 25 is the portion 1 that should become the drain electrode 15a.
5a 'and a portion 19a' to be the source electrode 19a partially overlap each other. The light shielding layer 25 is made of, for example, chrome. The light-shielding layer 25 is arranged so as to completely face the so-called channel forming portion of the thin film transistor 16.

Next, as shown in FIGS. 8 to 11 and 13B, an insulating layer 2 such as silicon dioxide is formed on the entire surface of the transparent substrate 11.
7 is formed. As shown in FIG. 13C, the display electrode 15 and the source bus 19 are formed on the entire surface of the insulating layer 27.
A transparent conductive film 28 such as ITO which should be
Further, as shown in FIG. 13D, an ohmic contact layer 29 of, for example, N ⁺ amorphous silicon for facilitating ohmic contact with the semiconductor layer is formed on the entire surface of the transparent conductive film 28. Then, FIGS.
As shown in FIG. 14 and FIG. 14, the display electrode 15, the drain electrode 15a, the source bus 19 and the source electrode 19a,
The transparent conductive film 28 and the ohmic contact layer 29 are formed by photo etching. In this case, as shown in FIG. 13E, ohmic contact layers 29 still remain on the display electrodes 15 and the source buses 19, respectively.

Next, as shown in FIG. 13F, a semiconductor layer 21 such as amorphous silicon is formed over the entire surface, and a gate insulating film 22 such as a silicon nitride film is further formed thereon. After that, by photo-etching with respect to the semiconductor layer 21 and the gate insulating film 22, a portion forming the thin film transistor 16 as shown in FIGS. 8 to 11 and 15, that is, between the display electrode 15 and the source bus 19. Of the semiconductor layer 21 and the gate insulating film 22 are removed, leaving the region 26 and a region 26 slightly wider than the region where the gate bus is to be formed. This gate insulating film 22
When forming a pattern on the semiconductor layer 21, the ohmic contact layer 2 on the display electrode 15 and the source bus 19 is formed.
9 is removed except the portions on the drain electrode 15a and the source electrode 19a. At this time, the semiconductor layer 21 and the gate insulating film 22 are formed in exactly the same pattern and are completely overlapped. Further, the semiconductor layer 21 makes ohmic contact with the drain electrode 15a and the source electrode 19a through the ohmic contact layer 29.

Next, as shown in FIG. 13H, a metal to be a gate electrode, for example, a chrome layer 31 is formed, and then photoetching is performed on the metal to form the gate electrode 23 and the gate electrode 23 as shown in FIGS. The gate bus 18 is formed.

Thus, in this embodiment, as shown in FIGS. 16A and 16B, the source bus terminal, that is, the metal layer 19 extending from the source bus 19 as the source terminal T _S and the metal 32 of the same material as the gate electrode 23 are provided. It is constructed by overlapping. The gate terminal T _G of the gate bus 18 is also formed by the chrome layer 31. As shown in FIGS. 7 and 8, the source bus 19
It is preferable to leave the chrome layer 31 on the top and use it as the auxiliary conductive layer 33. That is, it is preferable that the source bus 19 has a two-layer structure.

In the above description, the light shielding layer 25 may be omitted depending on the case. Further, as the thin film transistor 16, the gate electrode 23
The present invention can also be applied to a device provided with the transparent substrate 11 side. This example is shown in FIG. 17 with the same numbers assigned to the parts corresponding to those in FIG. 4, and description thereof will be omitted. In this case, although not shown in the drawing, when the gate electrode 23 is formed of the same material as the display electrode 15, the gate terminal T _G is also formed of a transparent conductive film, but when the source bus 19 is formed thereon. , The same metal layer is formed and the gate terminal T _G has a two-layer structure, and the source terminal is
T _S is formed only of the source bus 19, that is, the same metal layer as the source electrode 19a. In addition, this device has a display electrode 15
Not limited to the example of arranging in a matrix, the present invention is also applied to a liquid crystal display device in which seven rod-shaped segments are arranged in a figure of eight for numeric display, or display electrodes of various shapes are provided to selectively display. it can.

[Advantage of Device] As described above, according to the liquid crystal display device of the present invention, for example, the source terminal T _S has the metal layer 19 made of the same material as the source bus (source electrode) and the gate electrode as described with reference to FIG. 23 and the metal layer 32 made of the same material, the surface of the connection portion of the source terminal T _{S with} the outside is made of the same material as the gate terminal T _G of the gate bus, and is subjected to thermocompression bonding or soldering. When connecting to an external drive circuit such as attachment, these source terminals and gate terminals can be connected simultaneously under the same conditions, which is very convenient. Moreover, the metal layer 32 is the gate electrode 23.
Since it can be performed at the same time as the formation, the number of manufacturing steps does not increase.

When forming the auxiliary conductive layer 33 on the source bus 19, the thickness of the source bus becomes thicker, there is no fear of disconnection, and the electric resistance becomes smaller. Therefore, it is necessary to thicken the source bus 19 of the transparent conductive film. Easy to manufacture,
In addition, light is blocked by the auxiliary conductive layer 33, and display with good contrast can be obtained. Moreover, since the auxiliary conductive layer 33 is formed at the same time as the formation of the gate electrode 23, there is no fear of increasing the number of manufacturing steps.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a part of a general structure of a liquid crystal display element, FIG. 2 is a circuit diagram showing an electric circuit of its display electrode and thin film transistor, and FIG. 3 is a display electrode in FIG. A plan view, FIG. 4 is a cross-sectional view taken along line AA of FIG. 3, FIGS. 5A and 5B are plan views and cross-sectional views of a source bus bus terminal, and FIGS. 6A and 6B are plan views of a gate bus bus terminal. And a sectional view, FIG. 7 is a plan view corresponding to FIG. 3 showing a liquid crystal display device according to the present invention, FIG. 8 is a sectional view taken along the line AA of FIG. 7 showing an essential part of the present invention, and FIG. 7 BB
FIG. 10 is a sectional view taken along line CC of FIG. 7, FIG. 11 is a sectional view taken along line DD of FIG. 7, and FIG. 12 is a plan view showing a state in which a light shielding layer is formed on a transparent substrate. 13 is a cross-sectional view showing the manufacturing process of the display electrode and the thin film transistor shown in FIG. 7, FIG. 14 is a plan view with the display electrode and the source bus formed, and FIG. 15 is a plan view with the semiconductor layer formed. Figure,
16A and 16B are plan views and cross-sectional views of the source terminal portion, respectively, showing the main part of the present invention, and FIG. 17 is a cross-sectional view showing another example of the thin film transistor 16. 11, 12: transparent substrate, 13: spacer, 14: liquid crystal, 15: display electrode, 15a: drain electrode, 16: thin film transistor, 17: common electrode, 18: gate bus,
19: source bus, 19a: source electrode, 21: semiconductor layer, 22: gate insulating film, 23: gate electrode, 25: light-shielding layer, 25a: blocking region, 27: insulating layer, 28: transparent conductive film, 29: oh Mic contact layer, 31: aluminum layer, 32: metal layer, 33: auxiliary conductive layer, 35: passivation film, T _S : bus terminal of source bus, T _G : bus terminal of gate bus.

Claims (1)

[Scope of utility model registration request] 1. Two transparent substrates are arranged in close proximity to each other, liquid crystal is sealed between these transparent substrates, and pixel electrodes made of a transparent material are arrayed in a matrix on the inner surface of the one transparent substrate. A gate bus and a source bus are formed along and adjacent to each row and column array of pixel electrodes, and a thin film transistor is formed at the intersection of the gate bus and the source bus. Connected to the gate bus at the bus intersection position, the source is connected to the source bus,
In a liquid crystal display element in which a common electrode made of a transparent material is formed on the inner surface of the other transparent substrate facing the plurality of pixel electrodes, and the thin film transistors are selectively switching-controlled to selectively display the pixel electrodes, One of the gate bus and the gate terminal connected thereto and the source bus and the source terminal connected thereto has a first metal layer made of the same transparent material as the pixel electrode, and the other is connected to the bus. A second metal layer made of the same material as the electrode of the thin film transistor, a third metal layer made of the same material as the second metal layer is laminated on most of the first metal layer, and the source terminal and the gate are formed. A liquid crystal display element, wherein the second metal layer and the third metal layer are located on the surface side of the terminal.