JP2503266B2 - Thin film transistor matrix - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Outline] A thin film transistor (TFT) matrix used in an active matrix liquid crystal display device, a complete AC drive without complicating the manufacturing process and eliminating the voltage shift applied to the liquid crystal. In order to realize the above, a plurality of pixel electrodes and a plurality of thin film transistors associated with the pixel electrodes are arranged in a matrix on one insulating substrate, and a first controlled target of the thin film transistors is provided. A counter electrode having an electrode connected to the pixel electrode, a second controlled electrode connected to a data signal line, a control electrode connected to a scanning signal line, and connected to a common potential facing the pixel electrode on the other insulating substrate. In the structure of the thin film transistor matrix in which the above-mentioned one is disposed, the one thin film transistor has the same structure and the same connection relationship as the thin film transistor on the one insulating substrate. Compensation element is provided corresponding to the transistor matrix, a scanning line is provided adjacent to the scanning signal line, the control electrode of the compensation element is connected to the additional scanning line, and scanning is applied to the scanning signal line. The configuration is such that an inverted signal of the signal is applied.

[Industrial applications]

The present invention relates to a thin film transistor (TFT) matrix used in an active matrix type liquid crystal display device.

In an active matrix liquid crystal display device in which a large number of display cells are arranged in a matrix and each display cell is driven by a thin film transistor (TFT), the voltage applied to the liquid crystal layer in order to stabilize the liquid crystal and obtain a good display. It is necessary to completely remove the DC component from the DC voltage and apply only the AC voltage.

[Conventional technology]

FIG. 4 shows an equivalent circuit of one pixel of the conventional active matrix type liquid crystal display device, and FIG. 5 shows a driving waveform of the TFT and a voltage waveform applied to the liquid crystal.

As shown in FIG. 5, when the gate voltage V _G is turned off,
There is a phenomenon that the source (pixel) voltage V ₅ changes by ΔV, but the direction of this change is the same in both the positive frame and the negative frame, and both shift in the negative direction. Further, this shift amount ΔV is expressed by the following equation.

ΔV = (C _GS / C _LC + C _GS ) × V _G ...... where C _GS is the gate capacitance and C _LC is the liquid crystal cell capacitance.

In the figure, 1 is a thin film transistor, G, S and D are gate electrodes, source electrodes and drain electrodes, V _C is a common potential, V _G is a scanning signal, V _D is a display data voltage, and V _S is a source electrode potential.

Conventionally, in order to compensate the direct current component due to this voltage shift to drive the alternating current, a method of shifting the common electrode potential V _C by ΔV has been adopted. In this method, the common potential V _C is shifted for all pixels regardless of whether the pixel is on or off, so that the direct current component cannot be completely compensated and complete alternating current drive cannot be achieved. Therefore, the problem that the display characteristics are deteriorated cannot be solved.

The reason is that the liquid crystal cell capacitance C _LC of the formula is different between the on-state and the off-state of the liquid crystal, and the change rate is very large in the normal liquid crystal. As an example, the capacitance C _{LC of} a liquid crystal cell with a pixel size of 250 μm □ and a cell gap of 5 μm
Is 1pF in the off state, but 0.5pF in the off state
There is a difference of about 2 times.

As one of methods for eliminating such inconvenience, conventionally, as shown in FIG. 6, a method of adding a storage capacitor C _S in parallel with a liquid crystal cell capacitor C _LC has been proposed.

However, in order to make the influence of the fluctuation of the liquid crystal cell capacitance C _LC negligible, the capacitance of the storage capacitance C _S is set to the liquid crystal cell capacitance C _LC.
It should be about 10 times, that is, 5 to 10 pF. Creating such a large capacity requires a large area, and
There is a problem that the manufacturing process is complicated and the manufacturing yield is reduced.

[Problems to be Solved by the Invention]

As described above, conventionally, the DC component cannot be completely removed from the voltage applied to the liquid crystal layer.

An object of the present invention is to realize a complete AC drive without complicating the manufacturing process and eliminating the shift of the voltage applied to the liquid crystal.

[Means for solving the problem]

The present invention provides a compensating element having substantially the same configuration as a pixel driving thin film transistor, which is connected back to back with the thin film transistor, and one of the controlled terminals of the compensating element is connected to one of the controlled terminals of the thin film transistor. It is commonly connected to the pixel electrodes, and an inverted signal of the scanning signal applied to the control electrode of the thin film transistor is applied to the control electrode.

[Work]

In the thin film transistor and the gate electrode of the compensation element,
Since the scanning signals having the same magnitude and the opposite polarity and the inverted signals thereof are applied, the two gate capacitors that have accumulated the same amount of charge are
It is connected to the pixel electrode in the opposite direction. When the scanning signal and its inversion signal are turned off, the electric charges in the two gate capacitors flow out to shift the pixel electrode potentials respectively, but since the magnitudes are the same and the directions are opposite, they cancel each other out, The pixel electrode potential shift ΔV becomes zero.

Since this compensation is performed independently for each pixel without being affected by other pixels, complete compensation is possible, and the common potential V _C may be set to 0 [V], and the additional capacitance is also set. It becomes unnecessary.

Since the compensating element according to the present invention has substantially the same structure as the pixel driving thin film transistor, it is only necessary to partially change the photomask to be used when manufacturing the thin film transistor.
Since the manufacturing method itself is not different, it does not complicate the manufacturing process.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 (a) and 1 (b).

In the figure, 1 is a thin film transistor (TFT), 1 '
Is a compensating element, G, S, D are the gate electrode (control electrode), source electrode (first controlled electrode), drain electrode (second controlled electrode), G ′, S ′, D ′ of the TFT 1, respectively. Are the gate electrode, source electrode, drain electrode, and DB of the compensating element 1 ', respectively.
Is a data signal line for supplying display data, SB is a scanning signal line for supplying a scanning signal to the gate electrode G, SB 'is an additional scanning line for supplying an inverted signal of the scanning signal, C _LC is a liquid crystal cell capacitance, C _{LC GS} and C _GS ′ are the gate capacitances of the TFT 1 and the compensation element 1 ′, V _G is a scanning signal, and _G ′ is an inverted signal of the scanning signal (hereinafter simply referred to as an inverted signal).

The TFT1 is driven by a positive voltage and operates as an electronic accumulation type TFT, and the compensating element 1'has the same structure as the TFT1, and the negative accumulation voltage is applied to the gate electrode G'to drive the hole accumulation type TFT. Operates as a TFT.

The gate electrodes G and G'of the TFT1 and the compensating element 1'are respectively to the scanning signal line SB and the additional scanning line SB ', and the source electrodes S and S'are both to one end (pixel electrode E) of the liquid crystal cell capacitance C _LC , The drain electrodes D and D ′ are both connected to the data line DB, and the other end (counter electrode) of the liquid crystal cell capacitance C _LC is kept at a common potential.

When driving the present embodiment configured as described above,
A voltage having the opposite polarity to the voltage of the scanning signal line SB is applied to the additional scanning line SB '.

The operation will be described below with reference to FIGS.

This figure shows the potential change of each part when the liquid crystal cell having the above structure is driven. The operation of the TFT1 is the same as the conventional one, and when the scanning signal V _G is applied (when selected), the source voltage V _S , that is, the voltage of the pixel electrode E rises to the voltage of the display data V _D , and V _G
Is turned off (when not selected), negative voltage shift Δ
V ₁ is generated [see (a) in the figure].

The scanning signal V _{G of the} TFT1 is applied to the gate electrode G'of the compensating element 1 '.
Since an inversion signal _G of this is applied, its source voltage V _S ′
Shifts in the positive direction by ΔV ₁ ′ (see FIG. 7B).

The above ΔV ₁ and ΔV ₁ ′ are equal in magnitude only with the opposite polarities of V _G seen in the equation, and therefore cancel each other out. Therefore, the waveform obtained by superimposing these is completely zero in voltage shift as shown in FIG.

FIG. 1 (c) is a diagram summarizing FIGS. 2 (a) to 2 (c). As can be seen in FIG. 1, the voltage shift itself can be set to 0 in the present embodiment. The components are removed, complete AC driving is realized, and good display is stably obtained.

 Next, a modified example of the present invention will be described with reference to FIG.

In the above embodiment, the drain electrode D'of the compensating element 1'is
Is connected to the data line DB, the amount of charge accumulated in the gate capacitance C _GS ′ is determined by the source voltage V _S ′ and the gate voltage _G, so the drain electrode D ′ of the compensating element 1 ′ is strongly connected. There is no need to keep it.

Therefore, in this modification, the gate electrode G'of the compensating element 1'is
And only the source electrode S ′ are connected in the same manner as in the above-mentioned embodiment,
The drain electrode D'is left free.

Further, in this case, since it is not necessary to perform the TFT operation and it may operate as a capacitor, the blocking layer for the source / drain may be made of the same material as the TFT1.

As described above, the manufacturing process of this embodiment is exactly the same as the conventional one.

〔The invention's effect〕

As described above, according to the present invention, since the voltage shift itself can be eliminated, the liquid crystal can be completely AC-driven and a good display can be stably obtained.

[Brief description of drawings]

1 (a) and 1 (b) are explanatory views of an embodiment of the present invention, FIG. 2 is a drive waveform diagram of the above embodiment, FIG. 3 is an equivalent circuit diagram of a modified example of the present invention, and FIG. Is an equivalent circuit diagram of one pixel of a conventional thin film transistor matrix, FIG. 5 is a drive waveform diagram of a conventional thin film transistor matrix, and FIG. 6 is an equivalent circuit diagram of one pixel of a thin film transistor matrix to which a conventional storage capacitor is added. In the figure, 1 is a TFT (thin film transistor), 1'is a compensating element, G and G'are gate electrodes (control electrodes), S and S'are source electrodes (first controlled electrodes), and D and D'are drains. Electrode (second controlled electrode), DB is a data signal line, SB is a scanning signal line, SB 'is an additional scanning line, V _G is a scanning signal, _G is an inversion signal of the scanning signal, V _S and V _S ′ are Source voltage, V _D is display data, V _C is common potential, C _LC is liquid crystal cell capacitance, and C _GS and C _GS ′ are gate capacitances.

(72) Inventor Jun Inoue 1015 Kamiodanaka, Nakahara-ku, Kawasaki City, Kanagawa Prefecture, Fujitsu Limited (72) Inventor Norio Nagahiro, 1015, Kamedotachu, Nakahara-ku, Kawasaki City, Kanagawa Prefecture, Fujitsu Limited

Claims (1)

(57) [Claims] 1. A plurality of pixel electrodes (E) and a plurality of thin film transistors (1) associated with the pixel electrodes are arranged in a matrix on one insulating substrate, and the thin film transistors (1) are arranged. Of the first controlled electrode (S) of the pixel electrode (E) and the second controlled electrode (D) of the data signal line (D).
B), a structure of a thin film transistor matrix in which a control electrode (G) is connected to a scanning signal line (SB) and an opposite electrode connected to a common potential facing the pixel electrode is provided on the other insulating substrate. In the above-mentioned one insulative substrate, a compensating element (1 ′) having the same configuration and the same connection relationship as the thin film transistor (1) is further provided corresponding to the transistor matrix and adjacent to the scanning signal line (SB). Then scan line (SB ')
Annexed to, and connect the additional scan lines (SB ') the compensating element (1') the control electrode of the (G '), and the inverse of the scanning signal applied to the scanning signal lines (SB) (V _G) A thin film transistor matrix, wherein a signal ( _G ) is applied.