JPH07140489A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To prevent reduction in an opening ratio and to reduce the wiring resistance. CONSTITUTION:A liquid crystal display device, wherein an electrode opposed to a storage capacity part 11 connected in parallel to a liquid crystal is constituted of two layers of metal wirings 4b formed on a part of a transparent electrode 3b and the gate electrode of a thin film transistor 10 has a two layer structure constituted of opposing electrodes 3b and 4b, common transparent electrode 3a and an electrode by the metal wiring 4a. In this way, while a high opening ratio is maintained, a storage capacity is formed and further, the wiring resistance of a gate line is reduced.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a thin film transistor (T
The present invention relates to a liquid crystal display device using FT).

[0002]

2. Description of the Related Art Conventionally, as a high-definition large-sized liquid crystal display device, a so-called active type liquid crystal display device using a thin film transistor (hereinafter referred to as a TFT) using non-single crystal silicon as a switching element has been proposed and put into practical use. Has been done.

In the active type liquid crystal display device,
In order to hold the applied voltage written through the data line until the next writing, it is necessary to build a capacitor in parallel with the liquid crystal.

As a method of forming a capacitor connected in parallel with the liquid crystal, an additional capacity method and a storage capacity method have already been proposed.

FIG. 4 shows these two methods.

FIG. 4A shows an additional capacitance system in which the overlap between the gate line and the pixel electrode is used as a capacitance.

On the other hand, FIG. 4 (b) shows a storage capacitance method in which a counter electrode for the capacitance is separately formed.

In FIG. 4, 6 is a semiconductor layer and 19 is a TF.
T gate electrode, 20 pixel electrode, 11 'additional capacitance,
Reference numeral 11 is a storage capacity.

The storage capacitance method is advantageous for suppressing the increase in the gate line capacitance and increasing the aperture ratio.

In this storage capacity method, the counter electrode of the capacity is drawn out as a terminal different from the gate line, and there are two methods: a method of forming the storage capacity forming electrode with the same material as the gate electrode and a method of forming it with a transparent electrode. There is.

[0011]

However, the two conventional methods of forming the counter electrode of the storage capacitance system have the following drawbacks.

(1) When the counter electrode and the gate electrode are made of the same material Since the gate electrode of the TFT is made of a metal such as Al, Cr, Ta, and Ti, if the counter electrode is made of the same material as the gate electrode, The counter electrode serves as a light shielding layer, and the aperture ratio of the pixel electrode decreases.

(2) When the counter electrode is a transparent electrode Since the transparent electrode is used, the aperture ratio does not decrease, but the transparent electrode has a large specific resistance (sputtered ITO is used).

[0014]

[Outer 1] On the other hand, Al is 3 × 10 ⁻⁶ Ω · cm, Cr is 5 × 10
^-5 Ω · cm) Since the counter electrode is held at a constant potential, metal wiring with low resistance is further required.

On the other hand, in the active type liquid crystal display device,
The resistance of the gate wiring affects the delay of the gate line as a CR component. In particular, as the number of pixels increases and the number of gate lines increases, the gate writing time becomes shorter and the resistance of the gate wiring becomes a problem.

However, if the thickness of the wiring is simply increased to reduce the sheet resistance, a step of the wiring portion causes a problem of coverage failure.

[0017]

According to another aspect of the present invention, there is provided a liquid crystal display device using a thin film transistor as a switching element, wherein a counter electrode of a storage capacitor portion connected in parallel with liquid crystal is a transparent electrode, and the transparent electrode is a transparent electrode. It has a two-layer structure of metal wiring formed in a part of the upper part, and the gate electrode of the thin film transistor has a two-layer structure of a transparent electrode common to the counter electrode and an electrode made of metal wiring. Is.

According to the liquid crystal display device of the present invention, it is possible to form a storage capacitor while maintaining a high aperture ratio, and it is also possible to reduce the wiring resistance of the gate line.

[0019]

【Example】

(Embodiment 1) 1 of the liquid crystal display device of the first embodiment of the present invention
A plan view of pixels is shown in FIG. 1, and a cross-sectional view of the AA 'portion in FIG. 1 is shown in FIG.

In FIGS. 1 and 2, a glass substrate 1 having a polarizing plate 2 on the back side has a thickness of 100 mm, which is a transparent electrode such as ITO, a first gate electrode 3 (a), and a first counter electrode 3.
(B) is formed, and a second gate electrode 4 made of a metal such as Al or Cr and having a thickness of 100 mm is further formed on the upper side.
(A), 2nd counter electrode 4 (b) is formed. First
The gate electrode 3 (a), the first counter electrode 3 (b), and the second
The gate electrode 4 (a) and the second counter electrode 4 (b) are made of a common material.

Further, in this embodiment, in order to secure the aperture ratio, the metal second counter electrode 4 (b) is replaced by the first counter electrode 3
It is formed on a part of (b).

In the TFT section 10, a thickness of 300 nm is formed on the TFT section 10.
A gate insulating film 5 made of SiN film formed by plasma CVD in common with the insulating layer of the counter electrode, on which a semiconductor layer 6 made of amorphous Si having a thickness of 300 nm, an amorphous semiconductor having a thickness of 100 nm, Alternatively, the ohmic contact layer 7 made of microcrystalline n ⁺ Si, the drain electrode 8 (a) and the source electrode 8 made of Al.
(B) is formed. On the other hand, in the storage capacitor portion 11, the pixel electrode 9 made of a transparent electrode is formed on the counter electrode via the gate insulating layer 5. In this embodiment, as shown in FIGS. 1 and 2, the storage capacitor portion 11 is provided at a part of the pixel electrode.
Is formed. The pixel electrode 11 is connected to the source electrode 8 (b) of the TFT. A passivation layer 12 made of a SiN _x film or the like is formed on top of it.

At this time, the second gate electrode 4 (a) forming the gate electrode of the TFT section 10 is the first gate electrode 3
In the TFT portion which is wider than (a) and has the semiconductor layer at least in the upper portion, since it is formed so as to cover the entire surface of the first gate electrode, the step of the gate electrode is equal to the step of the total of two layers. However, a step difference based on the film thickness of each layer is sufficient.

In this embodiment, the step difference in the wiring portion is 1000
Since it was Å, no occurrence of poor coverage was seen.

As shown in FIG. 2, the liquid crystal display device of this embodiment has a polarizing plate 18 on the back surface (outside), a color filter 15 on the liquid crystal side, a TFT 10 and a drain, and a black matrix 16 above the bus line of the gate, and further above it. To IT
Common electrode 14 made of transparent electrode such as O, glass substrate 17
And the liquid crystal 13 are arranged.

(Embodiment 2) FIG. 3 shows a schematic view of a part of the cell of the second embodiment. Here, a cross-sectional view from the glass substrate to the passivation film is shown.

The same parts as in FIG. 2 are assigned the same numbers as in FIG.

In FIG. 3, the gate wiring of the TFT section 10 is formed such that the width of the second gate electrode 4 (a) made of metal is smaller than that of the first gate electrode 3 (a) made of a transparent electrode. ing. However, the channel portion of the TFT is formed entirely on the metal second gate electrode, and there is substantially no deviation in the threshold voltage Vth of the TFT.

The other structure is similar to that shown in FIG.

[0030]

As described above, the counter electrode for the pixel electrode of the storage capacitor connected in parallel with the liquid crystal has a two-layer structure of the transparent electrode and the metal wiring formed on a part of the transparent electrode, and the counter electrode By forming the gate electrode of the TFT with the same two-layer electrode material as the above (one of the two-layer gate electrode material is arranged inside the other electrode), a high pixel aperture ratio is maintained. However, a storage capacitor can be formed. Further, the wiring resistance of the gate electrode can be reduced without increasing the step of the gate electrode, and a liquid crystal display device having a large area and high definition and having a bright response can be provided.

[Brief description of drawings]

FIG. 1 is a schematic view showing an example of a liquid crystal display device of the present invention.

FIG. 2 is a view showing a cross section taken along the line AA ′ of FIG.

FIG. 3 is a schematic diagram showing another example of the present invention.

FIG. 4 is a schematic diagram showing a conventional liquid crystal display device.

[Explanation of symbols]

 1,17 glass 3 (a) first gate electrode 3 (b) first counter electrode 4 (a) second gate electrode 4 (b) second counter electrode 10 TFT section 11 storage capacitor section 9 pixel electrode

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location G09G 3/36 H01L 29/786

Claims (3)

[Claims] 1. A liquid crystal display device using a thin film transistor as a switching element, wherein a counter electrode of a storage capacitor portion connected in parallel with liquid crystal is a transparent electrode, and a metal wiring formed on a part of the transparent electrode. A liquid crystal display device having a layered structure, wherein the gate electrode of the thin film transistor has a two-layered structure including a counter electrode, a common transparent electrode, and an electrode formed of metal wiring. 2. The liquid crystal display device according to claim 1, wherein the gate electrodes of the two-layer structure of the thin film transistor have different widths, and one electrode is formed inside the other electrode. 3. The liquid crystal display device according to claim 1, wherein an insulating film common to the gate insulating film is formed between the counter electrode of the storage capacitor section and the pixel electrode.