JPH05341264A - Driving waveform of liquid crystal panel - Google Patents

Abstract

PURPOSE:To obviate a residual image and seizure of an MIM panel using a tantalum oxide or an insulating film whose main component is a tantalum oxide by setting a crest value of an opposite polarity pulse so as to become smaller than a crest value of a high voltage pulse. CONSTITUTION:A selection period is divided into two periods 111, 112, and in the first half period, a pulse 113 of opposite polarity of a low voltage is applied, and in the latter half period, a composite selection pulse 18 is applied, and ON/OFF/gradation of a picture element are controlled. In front of the pulse 113 of opposite polarity of the low voltage, a high voltage pulse 114 is installed, and by this signal, polarization of an MIM element is almost saturated. The opposite polarity pulse 113 of the low voltage is installed in order that a large voltage is not applied to the MIM element at the time of applying the composite selection pulse 18. Accordingly, by lowering the voltage of the pulse of opposite polarity, the voltage of the composite selection pulse 18 can also be set lowly, therefore, it does not occur that a residual image appears remarkably by the influence of polarization by the pulse 18.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to quality improvement of MIM liquid crystal display panels, and more particularly to measures for preventing afterimages and burn-in.

[0002]

2. Description of the Related Art In recent years, various video-related devices, measuring instruments, information devices, displays of personal computers, etc.
Large-capacity matrix liquid crystal panels are beginning to be used. When these liquid crystal panels are classified by the address system, they can be classified into a simple matrix system, an active matrix system, an optical address system, a thermal address system and the like. In view of the above, the active matrix system has come into the market as a display with high image quality and large capacity. A typical active matrix liquid crystal panel is a TFT liquid crystal panel using amorphous silicon or polysilicon. In addition, MIM liquid crystal panels, which are easier to manufacture than TFT liquid crystal panels, have been manufactured. On the other hand, in the simple matrix system, the display capacity can be expanded by increasing the twist like STN and FTN, and a large amount has been sent to the market. The display quality, particularly the contrast, of the MIM liquid crystal panel according to the present patent has been remarkably improved, but there is a phenomenon called afterimage or burn-in that remains when a fixed pattern is displayed, which is a serious problem.

FIG. 2 is a diagram showing an example of drive waveforms of a conventional MIM liquid crystal panel.

The signal applied to the Yj line (horizontal line) is 21, the signal applied to the Xi line (vertical line) is 22, and the signal Yj applied to the intersection of the Yj line and the Xi line.
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. The key is decided. The non-selection period is a period for storing the signal written in the selection period. A broken line 28 shows the signal voltage written in the liquid crystal layer in the pixel. The alternate long and short dash line 29 is called a bias voltage and represents the time average of the voltage in one non-selected period. The bias voltage 29 is 0 as shown in this example.
When the voltage is set to several volts instead of the voltage, the signal voltage 28 written in the liquid crystal leaks less current through the MIM element, and the contrast is easily secured.

FIG. 3 is a diagram showing another example of drive waveforms of a conventional MIM liquid crystal panel.

The signal applied to the Yj line (horizontal line) is 31, the signal applied to the Xi line (vertical line) is 32, and the signal Yj applied to the intersection of the Yj line and the Xi line.
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. A pulse set to write a signal to a pixel during the selection period is referred to as a composite selection pulse 37. The key is decided. The non-selection period is a period for storing the signal written in the selection period. A broken line 38 shows the signal voltage written in the liquid crystal layer in the pixel. Composite selection pulse 37
In front of, a high voltage pulse 39 having a peak value of the composite selection pulse equal to or larger than the peak value is set.

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

An MIM element is formed on the Xi line 41, and its resistance component is indicated by 42 and its capacitance component is indicated by 43. MI
The resistance 42 of the M element is drawn as a variable resistance because it changes depending on the applied voltage. 44 is a pixel electrode. 45,
46 is a resistance component and a capacitance component of the liquid crystal layer, respectively. Four
7 is a Yj line and 48 is a line-to-line capacitance with the Xi line.

[0009]

However, the conventional driving method has the following problems.

When a tantalum oxide or an insulating film containing tantalum oxide as a main component is used as the insulating film of the MIM element, the insulating film has a very small relative dielectric constant and thus has a slight ferroelectric property. is doing. Therefore, once a large electric field is applied, the effect remains even 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 this polarization also changes the conductivity characteristics of the element, the MIM panel cannot avoid the image quality defects such as afterimage and image sticking.

The above contents will be described in detail. FIG. 5 is a diagram explaining the principle of polarization, and FIG. 6 is a graph showing how the conductivity-voltage characteristic of the element changes due to polarization. In FIG. 5, the horizontal axis represents the electric field strength E and the vertical axis represents 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 displaced in a certain direction by applying an electric field. In a substance having such characteristics, the polarization remains as shown by 53 even when the electric field is 0. Therefore, in order to reduce the polarization to 0, it is necessary to apply the electric field 52 in the opposite direction.

FIG. 6 is a graph in which the conductivity of the MIM element is measured and plotted by 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 is 6
After 1, 62, 63, it gradually moves to the right and becomes saturated. This characteristic shift can be well explained by assuming that the insulating film of the device is polarized by several volts.

The afterimage of the MIM liquid crystal panel is caused by the characteristic shift of the device as described above, and impurity ions or molecules with strong polarity are adsorbed at the interface between the liquid crystal layer and the alignment film due to the direct current component applied to the panel. There are things that arise. The afterimage cannot be erased unless both are removed. Since the afterimage of the former is due to the property of the insulating film of the element as described above, the relative dielectric constant of the element itself is reduced to reduce the ferroelectric property, 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 placed immediately before the composite selection pulse 37, the polarization of the MIM element is almost determined by the high voltage pulse 39 and the composite selection pulse 3
Although the effect of 7 seems to be small, the afterimage seems to be improved, but this is not the case. The potential in the pixel immediately before the application of the composite selection pulse 37 is the potential 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 thereto, so that it is actually In addition, 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 depending on the ON / OFF signal of the pixel, it is considered that the polarization amount of the MIM element also changes depending on the ON / OFF signal. That is, the influence of the ON and OFF signals applied before affects the next display, and thus it tends to remain as an afterimage.

The object of the present invention is to solve the above-mentioned problems.
It is to provide a method of eliminating the afterimage of the panel.

[0016]

The panel drive waveform of the MIM liquid crystal panel of the present invention has the following features.

A drive waveform of a MIM liquid crystal panel using a tantalum oxide or an insulating material containing tantalum oxide as a main component (Y line applied signal-X).
In the composite waveform of the line applied signal), a reverse polarity pulse having a polarity different from that of the composite selection pulse is placed before the composite selection pulse for writing a signal such as ON / OFF to the pixel. A high voltage pulse having a peak value larger than the maximum peak value (absolute value) of the selection pulse is set before, and the peak value of the reverse polarity pulse is set smaller than the peak value of the high voltage pulse. It is characterized by

[0018]

EXAMPLES Examples of the present invention will be described below. Figure 1
It is a graph which shows one Example of this invention. The signal applied to the Yj line (horizontal line) is shown in 11, the signal applied to the Xi line (vertical line) is shown in 12, and the Yj-Xi composite signal applied to the intersection of the Yj line and the Xi line is shown in 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.
It determines on / off and gradation of pixels. 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 synthetic selection pulse 18 is applied in the latter half period to turn on / off the pixel. It controls the gradation. A high-voltage pulse 114 is placed before the low-voltage reverse-polarity pulse 113, and the polarization of the MIM element is almost saturated by this signal. The low-voltage reverse polarity pulse 113 is the composite selection pulse 1
This is installed in order to prevent a large voltage from being applied to the MIM element when the voltage of 8 is applied. Since the voltage of the composite selection pulse can be set low by lowering the voltage of the pulse of the opposite polarity, the polarization by the composite selection pulse 18 can be set. The afterimage does not appear remarkably due to the effect 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, which is a drive waveform 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 during the non-selection period. In the example, the point at which the composite selection pulse is set in the first half of the selection period and the gradation of the signal of the composite selection pulse are pulse width modulation in FIG. 1, whereas they are amplitude modulation in the present invention. The points are different. ..

[0020]

According to the present invention, MIM using tantalum oxide or an insulating film containing tantalum oxide as a main component.
It has the effect of eliminating afterimages and image sticking on the panel.

In the present invention, examples of the X line signal and the Y line signal are also shown, but Y shown in the claims of the present invention is used.
-The X line signal and the Y line signal that can realize the X synthesized waveform are included in the contents of this patent. The present patent also covers the case where the reverse polarity pulse and the composite selection pulse are not adjacent to each other.

[Brief description of drawings]

FIG. 1 is a graph showing an example of the present invention.

FIG. 2 is a diagram showing an example of drive waveforms of a conventional MIM liquid crystal panel.

FIG. 3 is a diagram showing another example of drive waveforms of a conventional MIM liquid crystal panel.

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

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

FIG. 6 is a diagram showing how the conductivity-voltage characteristics of an 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 pulse

Claims (1)

[Claims] 1. A driving waveform (composite waveform of Y line applied signal-X line applied signal) of a liquid crystal panel using tantalum oxide or an insulating material containing tantalum oxide as a main component in an insulating layer of an MIM element. , A reverse polarity pulse having a polarity different from that of the composite selection pulse is installed before the composite selection pulse for writing a signal such as ON / OFF to the pixel, and the maximum peak value of the selection pulse is further provided before the reverse polarity pulse. A high-voltage pulse having a peak value larger than (absolute value) is installed, and the peak value of the reverse polarity pulse is set smaller than the peak value of the high-voltage pulse. ..