JP3254731B2 - Driving method of liquid crystal panel - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to improving the quality of an MIM liquid crystal display panel, and more particularly to measures for preventing afterimages and image sticking.

[0002]

2. Description of the Related Art In recent years, various video-related devices, measuring devices, information devices, personal computer displays, etc.
Large capacity matrix liquid crystal panels are beginning to be used. When these liquid crystal panels are classified by an address method, they are classified into a simple matrix method, an active matrix method, an optical address method, a thermal address method, and the like. Among these, the active matrix system has come to be marketed as a high-quality and large-capacity display. A typical active matrix liquid crystal panel is a TFT liquid crystal panel using amorphous silicon or polysilicon. Also, MIM liquid crystal panels whose manufacturing process is simpler than those of TFT liquid crystal panels have been manufactured. On the other hand, in the simple matrix system, the display capacity can be increased by increasing the twist as in STN and FTN, and a large number of products are sent to the market. Although the display quality, particularly the contrast, of the MIM liquid crystal panel according to the present invention has been remarkably improved, there is a phenomenon called image sticking or image sticking remaining when a fixed pattern is displayed, which is a serious problem.

FIG. 2 is a diagram showing an example of a driving waveform of a conventional MIM liquid crystal panel.

The signal applied to the Yj line (horizontal line) is denoted by 21, the signal applied to the Xi line (vertical line) is denoted by 22, and the signal applied to the intersection of the Yj line and the Xi line is denoted by 22.
The Xi composite signal is shown at 24. The composite signal 24 can be divided into a selection period 25 and a non-selection period 26. A pulse set to write a signal to a pixel during the selection period is referred to as a composite selection pulse 27, and is used to turn on / off the pixel or to select a pixel. The key has been determined. The non-selection period is a period for storing a signal written during the selection period. A broken line 28 shows a signal voltage written in the liquid crystal layer in the pixel. An alternate long and short dash line 29 is referred to as a bias voltage and represents a time average of voltages in one non-selection period. The bias voltage 29 is set to 0 as shown in this example.
When the voltage is set to several volts instead of volts, the current that the signal voltage 28 written in the liquid crystal leaks through the MIM element decreases, and the contrast is easily secured.

FIG. 3 is a diagram showing another example of a driving waveform of a conventional MIM liquid crystal panel.

The signal applied to the Yj line (horizontal line) is set to 31, the signal applied to the Xi line (vertical line) is set to 32, and the signal applied to the intersection of the Yj line and the Xi line is set to 32.
The Xi composite signal is shown at 34. The composite signal 34 can be divided into a selection period 35 and a non-selection period 36, and a pulse set for writing a signal to a pixel during the selection period is referred to as a composite selection pulse 37, and is used to turn on / off the pixel or to select a level. The key has been determined. The non-selection period is a period for storing a signal written during the selection period. The broken line 38 shows the signal voltage written in the liquid crystal layer in the pixel. Combination selection pulse 37
A high-voltage pulse 39 whose amplitude is equal to or greater than the crest value of the combined selection pulse is set before.

FIG. 4 is an equivalent circuit diagram showing a configuration of a pixel portion of the MIM liquid crystal panel.

An MIM element is formed on the Xi line 41. The resistance component is shown at 42 and the capacitance component is shown at 43. MI
Since the resistance 42 of the M element changes according to the applied voltage, it is depicted as a variable resistance. 44 is a pixel electrode. 45,
46 is a resistance component and a capacitance component of the liquid crystal layer, respectively. 4
Reference numeral 7 denotes a line capacitance between the Yj line and the Xi line.

[0009]

However, the conventional driving method has the following problems.

When the insulating film of the MIM element uses a tantalum oxide or an insulating film containing tantalum oxide as a main component, the insulating film has a very small relative ferroelectric constant, but has a small but ferroelectric property. are doing. Therefore, once a large electric field is applied, the effect remains after the electric field is removed. This means that polarization occurs in the film even when no voltage is applied (this is called remanent polarization). Since the polarization also changes the conductive characteristics of the element, the MIM panel cannot avoid image quality defects such as image sticking and burn-in.

The above contents will be described in detail. FIG. 5 is a diagram illustrating the principle of polarization, and FIG. 6 is a graph illustrating how the conductivity-voltage characteristics of the element change due to polarization. In FIG. 5, the horizontal axis indicates the electric field strength E, and the vertical axis indicates the polarization P. For a substance having a large dielectric constant, such as tantalum oxide, the relationship between the electric field intensity E and the polarization P draws a hysteresis curve 51. It is considered that this is because tantalum atoms (ions) and oxygen atoms (ions) are shifted in a certain direction by applying an electric field. In a substance having such characteristics, even when the electric field is set to 0, the polarization remains as shown by 53. Therefore, in order to make the polarization zero, it is necessary to apply an electric field 52 in the opposite direction.

FIG. 6 is a graph in which the conductivity of the MIM element is measured and plotted while changing the applied voltage. Since the conduction of the MIM element is considered to be centered on a conduction mechanism called Pool-Frenkel conduction, the horizontal axis is the square root of voltage and the vertical axis is the ratio of current to voltage, that is, the logarithm of conductivity. When the same element is repeatedly measured, its characteristic becomes 6
It moves to the right as soon as it is 1, 62, 63 and saturates. This characteristic shift can be well explained by assuming that the insulating film of the element is polarized by several volts.

The afterimage of the MIM liquid crystal panel is caused by the characteristic shift of the element and the direct current component applied to the panel causes impurity ions or strongly polar molecules to be adsorbed at the interface between the liquid crystal layer and the alignment film. There are things that arise. If these two are not removed, the afterimage cannot be erased. As mentioned earlier, the afterimage is due to the properties of the device's insulating film, so the relative dielectric constant of the device itself is reduced to reduce the ferroelectric properties, or the residual polarization is compensated during driving. There is a need to continue to.

As shown in the example of FIG. 3, when a high-voltage pulse 39 is provided immediately before the composite selection pulse 37, the polarization of the MIM element is almost determined by the high-voltage pulse 39.
Although the effect of 7 appears to be small, the afterimage appears to be improved, but in fact it does not. This is because the potential in the pixel immediately before the application of the composite selection pulse 37 is opposite to the polarity of the composite selection pulse due to the application of the high-voltage pulse 39, and the composite selection pulse 37 is applied there. The voltage applied to the MIM element is increased by the combined selection pulse 37, and the influence of the polarization is greatly increased. Since the peak value of the combined selection pulse 37 changes according to the ON / OFF signal of the pixel, it is considered that the polarization amount of the MIM element also changes according to the ON / OFF signal. In other words, the influence of the previously applied ON / OFF signal affects the next display, so that it tends to remain as an afterimage.

An object of the present invention is to provide a MIM in view of the above points.
An object of the present invention is to provide a method for eliminating the afterimage of a panel.

[0016]

The driving method of the liquid crystal panel according to the present invention has the following features.

According to the method of driving a liquid crystal panel of the present invention, the MIM element using the insulating layer containing tantalum oxide or an insulating material containing tantalum oxide as a main component and the liquid crystal layer between the first line and the second line. A driving method for driving a liquid crystal panel, wherein a synthesized signal corresponding to a difference voltage between a signal applied to the first line and a signal applied to the second line is applied to the liquid crystal panel. Is a reverse polarity pulse having a polarity different from that of the composite selection pulse before the composite selection pulse for writing a signal to the liquid crystal layer, and a maximum peak value of the composite selection pulse provided before the reverse polarity pulse. A high voltage pulse having a larger peak value is provided, wherein the peak value of the opposite polarity pulse is smaller than the peak value of the high voltage pulse.

[0018]

Embodiments of the present invention will be described below. FIG.
4 is a graph showing one embodiment of the present invention. The signal applied to the Yj line (horizontal line) is indicated by 11, the signal applied to the Xi line (vertical line) is indicated by 12, and the Yj-Xi combined signal applied to the intersection of the Yj line and the Xi line is indicated by 13. .
The composite signal 13 can be divided into a selection period 14 and a non-selection period 15, and a pulse set to write a signal to a pixel in the selection period 14 is referred to as a composite selection pulse 18,
The on / off and gradation of the pixel are determined. The selection period is further divided into two periods 111 and 112. A low-voltage reverse-polarity pulse 113 is applied in the first half period, and a combined selection pulse 18 is applied in the second half period to turn on / off the pixel. The gradation is controlled. A high-voltage pulse 114 is provided before the low-voltage reverse-polarity pulse 113, and this signal almost saturates the polarization of the MIM element. The low voltage reverse polarity pulse 113 is the composite selection pulse 1
8 is applied to prevent a large voltage from being applied to the MIM element when the voltage 8 is applied. Since the voltage of the composite selection pulse can be set low by reducing the voltage of the pulse of the opposite polarity, the polarization by the composite selection pulse 18 is performed. The afterimage does not appear remarkably under the influence of. The broken line 19 indicates the voltage applied to the liquid crystal layer in the pixel.

FIG. 7 shows another embodiment of the present invention, in which a plurality of low voltage pulses 78 and 710 (78 is a low voltage reverse polarity pulse) and a plurality of high voltage pulses 79 are provided in a non-selection period. In the example, the point that the combined selection pulse is set in the first half of the selection period and the gradation of the signal of the combined selection pulse are performed by pulse width modulation in FIG. 1 whereas amplitude modulation is performed in the present invention. The points are different. .

[0020]

According to the present invention, there is provided a MIM using a tantalum oxide or an insulating film containing tantalum oxide as a main component.
This has the effect of eliminating the afterimage and image sticking of the panel.

In the present invention, the example of the X line signal and the Y line signal is also shown, but the Y line signal shown in the claims of the present invention is shown.
-X-line signals and Y-line signals capable of realizing an X combined waveform are included in the contents of the present patent. Further, the case where the pulse of the opposite polarity is not adjacent to the composite selection pulse is also included in the present invention.

[Brief description of the drawings]

FIG. 1 is a graph showing one embodiment of the present invention.

FIG. 2 is a diagram showing an example of a driving waveform of a conventional MIM liquid crystal panel.

FIG. 3 is a diagram showing another example of a driving waveform of a conventional MIM liquid crystal panel.

FIG. 4 is an equivalent circuit diagram showing a configuration of a pixel portion of the MIM liquid crystal panel.

FIG. 5 is a diagram illustrating the principle of polarization.

FIG. 6 is a diagram showing a state in which the conductivity-voltage characteristics of the element change due to polarization.

FIG. 7 is a diagram showing another embodiment of the present invention.

[Explanation of symbols]

 18: Composite selection pulse 113: Low-voltage reverse polarity pulse 114: High-voltage pulse 77: Composite selection pulse 78: Low-voltage reverse polarity pulse 79: High-voltage pulse 710 ... Low-voltage pulses

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G02F 1/133 550 G02F 1/1365 G09G 3/36 H01L 27/12 H01L 49/02

Claims (1)

(57) [Claims] 1. A liquid crystal layer and a MIM element using an insulating layer containing tantalum oxide or an insulating material containing tantalum oxide as a main component are connected in series between a first line and a second line. In a method for driving a liquid crystal panel, a composite signal corresponding to a voltage of a difference between a signal applied to the second line and a signal applied to the second line is applied. Before the composite selection pulse for writing a signal, a reverse polarity pulse having a polarity different from that of the composite selection pulse, and a high voltage provided before the reverse polarity pulse and having a peak value larger than the maximum peak value of the composite selection pulse. And a peak value of the reverse polarity pulse is smaller than a peak value of the high voltage pulse.