JPH0434412A - Method for driving active matrix type liquid crystal display element and active matrix type liquid crystal display element - Google Patents

Abstract

PURPOSE:To eliminate defective modes, such as deterioration and seizure of a liquid crystal and flickering, and to drop a driving voltage by forming a source signal voltage as the AC voltage which has substantially no DC components with respect to a com mon potential and is symmetrical in positive and negative and as the polarity reverse from the polarity of a gate pulse voltage. CONSTITUTION:An amorphous silicon layer is formed on a glass substrate and plural TFTs each consisting of one set of N channel and P channel are formed to obtain the active matrix substrate. On the other hand, color filters and a protective film are formed on another glass substrate and ITO is used as a counter substrate. Two kinds of the substrates are subjected to an orientation treatment and are stuck to each other via a spacer to form a cell. A liquid crystal is packed into this cell. Gate pulses having the positive and negative polarities are generated and are impressed to this cell. The voltage of the polarity reverse from the polarity of the gate pulse is impressed as the source signal voltage to the source electrode. The defective modes, such as deterioration of the liquid crystal and the deterioration of the electrodes, are eliminated in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method of driving an active matrix liquid crystal display element.

[Prior Art] An active matrix type liquid crystal display device in which active elements are arranged near the intersections of scanning electrodes and signal electrodes in a matrix has characteristics of good contrast and viewing angle dependence, and fast response speed. When a color filter is placed on the opposing substrate, the color reproducibility is excellent, so it is considered to be the best choice for a flat display as an alternative to a CRT.

Conventionally, active elements include MIM, varistor,
Two-terminal elements such as diodes and thin film transistors (TP)
Three-terminal devices such as T) are used, but three-terminal devices are generally superior in display quality.

In the case of this TPT, conventionally, one TFT 56 is basically arranged for one pixel as shown in FIG. In FIG. 7, 5] is a gate pass line, 52 is a source pass line, 53 is a liquid crystal display section, 54 is a common electrode, 55 is a storage capacitor, and 57i is a parasitic capacitor, and this T P T 5
6 is N channel TPT or P channel TP
Which of T is used. In order to improve the yield of active matrix substrates, two or three or more TPTs are sometimes arranged for one pixel, but the type of TPT is N-channel or P-channel, whichever is the element configuration. there were.

When driving such a TPT, for example, N
In the case of channel TPT, a positive gate pulse 61 is applied to the gate electrode as shown in Figure 8, and the positive and negative polarity is reversed every frame so that the voltage applied to the liquid crystal becomes alternating current to the source electrode. It was common to apply a signal 62 that

Furthermore, as shown in FIG. 10, one or more sets of N
In the method of arranging channel TPT and P-channel TPT, positive and negative gate pulses 77 are applied as shown in FIG.
It has been common practice to apply a voltage 78 to the gate electrode, and to apply a voltage 78 of the same polarity as the polarity of the pulse applied to the gate electrode to the source electrode.

In FIG. 10, 71 is a gate pass line, 72 is a source pass line, 73 is a liquid crystal display section, 74 is a common electrode, 75 is a storage capacitor, and 76 is a set of NPP channels P.
In FIG. 11, 79 is a common potential.

[Problems to be Solved by the Invention] When a unipolar gate pulse and an AC source voltage as shown in FIG. 8 are applied to a TPT as shown in FIG. Since there is a parasitic capacitance between the gate and the drain, the drain voltage 64 of the TPT becomes asymmetrical due to the voltage 66 caused by this parasitic capacitance, as shown in FIG. 9, and a DC component is present. This voltage asymmetry can be alleviated to some extent by shifting the common potential, but as can be seen from the voltage waveform in FIG. 9, it is currently not possible to completely compensate for it. If the voltage applied to the liquid crystal becomes asymmetrical in this way, the DC component may cause the liquid crystal to deteriorate, or a type of memory phenomenon called burn-in may occur, or it may cause flickering. Various inconveniences occur, and C.
This has been one of the obstacles to display images that can replace RT.

On the other hand, as shown in Fig. 10, one or more sets of N
In the method of arranging channel TPT and P-channel TPT, as shown in Figure 11, a pulse with both positive and negative polarity is applied to the gate electrode, and a pulse with the same polarity as the pulse applied to the gate electrode is applied to the source electrode. As shown in Figure 12, by applying a voltage of Further, since the punching is a direct current component due to the influence of voltage, there is a drawback that the voltage applied to the liquid crystal decreases. In FIG. 12, 79 is a common potential.

1. Means for Solving the Problems] The present invention has been made to solve the above problems, and consists of arranging electrodes in rows and columns in an intersecting manner on an insulating substrate, and placing active electrodes in the vicinity of the intersecting portions of the electrodes. In an active matrix type liquid crystal display element in which liquid crystal is filled between an active matrix substrate on which the elements are arranged and a counter substrate having a transparent electrode, the active element part includes at least one set of N-channel transistors and P-channel transistors connected in parallel. The source signal voltage applied to the source electrodes of these transistors is an alternating voltage that has almost no DC component with respect to the common potential and is symmetrical in positive and negative, and the source signal voltage has a polarity opposite to that of the gate pulse voltage. The present invention provides a method for driving an active matrix liquid crystal display element characterized by the following.

The present invention will be explained in detail below with reference to the drawings.

FIG. 1 shows one of the drive waveforms according to the present invention. 1 is a gate pulse voltage, 2 is a source signal voltage, and 3 is a common potential.

FIG. 2 shows the voltage waveform applied to the liquid crystal display section 73 when the driving waveform shown in FIG. 1 is applied to a set of N and P channel TPTs as shown in FIG. 10 according to the present invention. show.

In FIG. 2, 4 indicates a drain voltage, and this train voltage 4 becomes the voltage waveform applied to the liquid crystal. The drain voltage 4 is almost symmetrical with respect to the common potential 3, so no DC component is applied to the liquid crystal display section 73.

In this way, the driving waveform shown in FIG. 1 enables proper driving of the liquid crystal. The drive waveform according to the present invention is not limited to the waveform shown in FIG. 1, and as shown in FIG. It can be used if the signal voltage 2 has almost no direct current component and is an alternating voltage with positive and negative symmetry, and if the source signal voltage 2 has the opposite polarity to the gate pulse voltage.

Note that it is necessary to use a TPT having such characteristics that both the P-channel and N-channel TFTs are turned off in a portion where there is no gate pulse.

The present invention is effective when a pair of N-channel TPT and P-channel TPT are connected in parallel between the gate, source, and drain 6942 for one display pixel electrode as shown in FIG. Although it is a driving method, the fourth
As shown in the figure, redundancy is provided to improve the yield of TF'r substrates, and it is also effective for panels composed of two or more sets of N-channel TPTs and P-channel TPTs.

In FIG. 4, 11 is a gate pass line, 12 is a source pass line, 16 (a) and 16 (b) are a pair of N and P channel TPTs, 13 is a liquid crystal display section, 14 is a common electrode, and 15 is a storage capacitor. It is.

Further, as shown in FIG. 5, for one display pixel electrode, N channel T F T 26 (a) and P channel T P
Connect T 26(b) and connect N channel T P T 2
Even in the method of driving the gate voltages of 6(a) and P channel T P T 26(b) separately, it is sufficient to apply a signal voltage of the opposite polarity to the polarity of each gate pulse as shown in FIG. .

Here, FIG. 5 21(a) is a gate pass line for N-channel TFT, 21(b) is a gate pass line for P-channel TFT, 22 is a source pass line, 23 is a liquid crystal display section, 24 is a common electrode, and 25 is an accumulation capacity, and the sixth
In the figure, (a) is a drive waveform for N-channel TFT, (b) is a drive waveform for P-channel TFT, and 2
7(a) is a positive gate pulse, z7(b) is a negative gate pulse, and 28 is a source signal voltage.

The present invention is also effective for element configurations in which one pixel is divided into a plurality of parts and one or more sets of N-channel TPT and P-channel TPT are connected to each of them, and the driving method of the present invention can be applied to each of them. A similar effect can be obtained. In this case, a driving waveform as shown in FIG. 3 can also be used.

Furthermore, the present invention is not only applicable to active matrices made of TPT, but also silicon wafers may be used as semiconductor substrates, and active matrices made of semiconductors other than silicon or compound semiconductors as semiconductor materials. It is possible.

Furthermore, in the present invention, in order to simplify the explanation, the common potential is assumed to be at a constant level in FIG. Can be applied to engraving.

Also, various types of TPT configurations have been proposed, such as staggered, reverse staggered, and coplanar structures, but the present invention can be applied to TPTs of all configurations, and the semiconductor material may be amorphous silicon or polysilicon. It may also be a TPT. In particular, in the case of polysilicon, the peripheral drive circuit can also be created using TPT due to its high mobility, but it is difficult to use TPT as an element for the drive circuit because of the drive margin.
- MOS is advantageous, in which case N-channel T
Since PT and P channel TPT can be created at the same time,
The driving method of the present invention can be effectively utilized.

The present invention can also be used for black-and-white TPT panels,
It can also be used for TPT panels for color display using color filters, etc.

[Function] The drive waveform as shown in FIG. 1 according to the present invention is applied to N-channel TPT and P for one display pixel electrode as shown in FIG.
Apply the drive waveform as shown in Figure 6 to a TPT element configured by connecting channel TPTs in parallel, or apply the drive waveform as shown in Figure 6 to N-channel and P-channel TPT elements driven by separate gate lines as shown in Figure 5. When applied, the N-channel TPT is turned on by a positive gate pulse, and a negative signal enters the drain electrode from the source line. Then the gate closes
At the moment the PT is turned OFF, a voltage is generated due to the parasitic capacitance between the gate and drain of the N-channel TPT, but since the direction of the gate pulse and the polarity of the source signal are opposite, the voltage is generated as shown in Figure 2. A larger negative voltage is applied to the liquid crystal. After that, during the period when the TPT is OFF, the voltage is constant or gradually decreases depending on the voltage holding characteristics of the TPT panel. At this time, since the P channel TPT has a sufficiently large negative threshold value, it remains OFF and has no effect on driving.

Next, when a negative gate pulse is applied in the next frame, the P-channel TPT is turned ON and a positive signal enters the drain electrode from the source line. After that, at the moment when the gate closes and the TPT turns OFF, a punch-through voltage is generated due to the parasitic capacitance between the gate and drain of the P-channel TPT, but its direction is symmetrical to that of the positive gate pulse, and the liquid crystal As shown in FIG. 2, a larger positive voltage is applied. After that, TPT is O
During the FF period, the voltage is constant or gradually decreases depending on the voltage holding characteristics of the TPT panel.

At this time, since the N-channel TPT has a sufficiently large positive threshold value, it remains OFF and has no effect on the speed drive.

When such driving is performed, no DC component is generated in the voltage applied to the liquid crystal, as can be seen from FIG. Furthermore, in the conventional driving method in which a signal voltage of the same polarity as the gate pulse is applied to the source electrode, no direct current voltage is applied, but the voltage applied to the liquid crystal decreases as shown in Figure 12. On the other hand, in the present invention, the voltage is not only not reduced but can even be increased.

[Example] Example 1 An amorphous silicon layer was formed on a glass substrate (rAN glass J manufactured by Asahi Glass Co., Ltd., and a set of N-channel and P-channels as shown in FIG. 10 was formed using the self-line method using ion implantation.
Multiple channel TPTs were created to complete the active matrix substrate.

A color filter and a protective film were formed on different glass substrates, and ITO was deposited by sputtering to serve as a counter substrate.

The above-mentioned two types of substrates were subjected to an alignment treatment and pasted together with a spacer interposed therebetween to form a cell, and this cell was filled with liquid crystal. The cell gap was 5 μm.

Next, a gate pulse with positive and negative polarities as shown in FIG. 1 was generated using a pulse generator and applied to this cell. The absolute value of each gate pulse centered on the common potential was 20 V, and as shown in FIG. 1, a voltage with the opposite polarity to the gate pulse was applied to the source electrode as the source signal voltage.

Next, the electro-optical characteristics were measured and reliability tests were conducted. First of all, regarding the deterioration of the liquid crystal, even after 1000 hours of continuous current testing, the threshold voltage for writing to the liquid crystal hardly changed from the value before the current testing, and it was also visually observed that there was no electrode deterioration. No failure mode was recognized.

Next, regarding the phenomenon of burn-in, even if the same pattern of electricity was applied continuously for 2 hours, 4 hours, 12 hours, 24 hours, and 72 hours, and then the display pattern was changed, the previous pattern did not remain at all.

Next, regarding flicker, even after 12- and 24-hour power tests, no visible flicker was observed, and even when analyzed using a spectrum analyzer, no frequency components that would cause flicker were observed. Ta.

Furthermore, in the case of the conventional driving method shown in FIG. 12, the magnitude of the signal voltage required a larger value because the voltage applied to the liquid crystal substantially decreases due to the effect of the punching voltage.
It has been found that the present invention allows driving with approximately the same voltage as in static driving.

Example 2 Next, as shown in Example 1, a TPT element in which one N-channel TPT and one P-channel T F r are driven per pixel with separate gate pulses is ionized in the same manner as in Example 1. It was created using the self-injection method.

Next, a sixth pulse generator is applied to this TPT element by a pulse generator.
As shown in the figure, gate pulses with positive and negative polarities were generated and applied. The absolute value of each gate pulse was 20 V, and a voltage with a polarity opposite to that of the gate pulse was applied to the source electrode as the source signal voltage.

Next, in the same manner as in Example 1, the electro-optical characteristics were measured and reliability tests were conducted, but as in Example 1, no failure modes such as liquid crystal deterioration, burn-in, or flicker occurred.

〔Effect of the invention〕

As described above, according to the present invention, when punching is caused by parasitic capacitance between the gate and drain, the voltage is symmetrical, so no direct current component is applied to the liquid crystal, and punching prevents the voltage from decreasing due to the voltage and prevents the parasitic In a TPT with a large capacity, a voltage larger than the signal voltage will be applied. As a result, it is possible to completely eliminate various failure modes such as liquid crystal deterioration, burn-in, and flicker that have conventionally occurred due to voltage asymmetry, and it has been recognized that the driving voltage can be reduced. It will be done.

[Brief explanation of the drawing]

FIG. 1 is a voltage waveform diagram showing a driving waveform according to the present invention. FIG. 2 is a voltage waveform diagram applied to the liquid crystal by a driving waveform according to the present invention. FIG. 3 is a voltage waveform diagram showing a driving waveform according to the present invention. FIG. 4 is a voltage waveform diagram of a different aspect from that shown in FIG. 1, in which two or more sets of N-channel TPT and P
A circuit configuration diagram according to the present invention configured with channel TPTs Figure 5 shows a circuit according to the present invention configured with one set of N-channel TPT and P-channel TPT per pixel, and each gate is driven with a separate pulse. 6 is a voltage waveform diagram according to the present invention of the gate pulse and source voltage that drive the TPT element shown in FIG. 5. FIG. 7 is a circuit diagram of a conventional TPT. FIG. 9 is a voltage waveform diagram for driving the conventional TPT shown in FIG. 7, and a voltage waveform diagram applied to the liquid crystal cell by the conventional circuit configuration shown in FIG. Figure 11 is a circuit diagram of a TFT consisting of one N-channel TPT and one P-channel TPT per pixel. Voltage waveform applied to the liquid crystal according to the conventional drive waveform shown in the figure.Figure 1: Gate voltage 2: Source signal voltage 3: Common potential

Claims (1)

[Scope of Claims] 1) An active matrix substrate in which electrodes are arranged in a cross-sectional manner in rows and columns on an insulating substrate, and active elements are arranged near the intersections of the electrodes, and a counter substrate having transparent electrodes. In an active matrix type liquid crystal display element filled with liquid crystal, the active element part consists of at least one set of N-channel transistor and P-channel transistor connected in parallel, and the source signal voltage applied to the source electrodes of these transistors is common. It is an alternating voltage with almost no direct current component relative to the potential, and is symmetrical in positive and negative.
A method for driving an active matrix liquid crystal display element, characterized in that the source signal voltage has a polarity opposite to that of the gate pulse voltage. 2) The method for driving an active matrix liquid crystal display element according to claim 1, wherein the transistor is a thin film transistor. 3) A liquid crystal display device using the driving method according to claim (1) or claim (2).