JPH05323385A - Driving waveform - Google Patents

Abstract

(57) [Summary] [Objective] The object of the present invention is to use M containing tantalum oxide.
It is to reduce the afterimage of the IM panel. A reverse polarity pulse having a large voltage and a large polarity is set before the composite selection pulse in the composite drive waveform of the Y line-X line of the MIM panel, and the bias voltage also has a polarity different from that of the composite selection pulse. To set. According to the present invention, there is an effect that the afterimage of the MIM panel is significantly reduced.

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, MIMs have been manufactured that are easier to manufacture than TFTs. 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, especially the contrast, of the MIM liquid crystal panel according to the present patent is remarkably improved, but there is a phenomenon called afterimage or image sticking which 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. The signal voltage written in the liquid crystal layer in the pixel is shown at 28. Reference numeral 29 is called a bias voltage and represents the time average of the voltage in one non-selected period. When the bias voltage 29 is set to several volts instead of 0 volt as shown in this example, the signal voltage 28 written in the liquid crystal leaks less current through the MIM element, and it is easier to secure the contrast.

FIG. 3 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 31, and its resistance component is indicated by 32 and its capacitance component is indicated by 33. MI
Since the resistance 32 of the M element changes depending on the applied voltage, it is drawn as a variable resistance. 34 is a pixel electrode. 35,
36 are the resistance component and the capacitance component of the liquid crystal layer, respectively. Three
7 is a Yj line, and 38 is a line-to-line capacitance with the Xi line.

[0007]

However, the conventional driving method has the following problems.

When the insulating film of the MIM element is made of tantalum oxide or an insulating film containing tantalum oxide as a main component, the insulating film has a very large 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. 4 is a diagram explaining the principle of polarization, and FIG. 5 is a graph showing how the conductivity-voltage characteristics of the element change due to polarization. In FIG. 4, 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 strength E and the polarization P draws a hysteresis curve 41. 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 43 even when the electric field is 0. Therefore, in order to make the polarization zero, it is necessary to apply the electric field 42 in the opposite direction.

FIG. 5 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 5
After 1, 52, 53, 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.

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.

[0013]

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

A driving 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 pulse having a polarity opposite to that of the composite selection pulse is set before the composite selection pulse for writing the ON / OFF signal to the pixel. , Or a plurality of pulses applied intermittently, and the pulse width of the opposite polarity pulse (in the case of a plurality of pulses, the total width of each pulse) is equal to the width of the composite selection pulse. Alternatively, it is characterized by being wider than that. In the drive waveform described above, a value obtained by time-averaging the voltage in a period excluding the period in which the pulse of the opposite polarity is present in the non-selection period, which is a period for holding the signal written by the composite selection pulse, When referred to as a bias voltage, the polarity of the composite selection pulse is different from the polarity of the bias voltage.

In the drive waveform described above, the peak value of the pulse having the opposite polarity is equal to or higher than the peak value of the composite selection pulse.

[0016]

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. In the first half period, the high voltage pulse 113 having the opposite polarity is applied, and in the latter half period, the composite selection pulse 18 is applied to turn on / off the pixel. It controls the gradation. The non-selection period is a period for storing the signal written in the selection period. A signal voltage waveform written in the liquid crystal layer in the pixel is shown at 16. The polarization of the MIM element can be completely saturated by increasing the voltage of the pulse 113 of the opposite polarity as high as possible. In order to set the pulse 113 of reverse polarity high,
It is necessary to set the voltage 114 on the Yj line high and set the signal 115 on the Xi line to the ON waveform (the ON waveform has the greatest effect, but other waveforms may be used). Next, the applied voltage of the composite selection pulse 18 is set as small as possible and applied. This is to suppress the polarization of the MIM element due to the combined selection pulse 18 as much as possible, and to prevent the polarization amount from being different due to the on / off signal difference. The panel in which the amount of polarization of the MIM element is not affected by the ON / OFF signal in this way means a panel in which the previously displayed image has no effect after the display is changed, that is, there is no afterimage. FIG. 6 shows another embodiment of the present invention, which is an example of a drive waveform in which a pulse 63 having a reverse polarity is provided in the non-selection period 62, and the reverse polarity as shown in the example of FIG. Pulse 64 is installed. In this example, the pulse 66 of the same polarity is also installed, so that the polarization of the MIM element can be sufficiently saturated. When the bias voltage 67 is defined as the time average value of the voltage of the period 68 in which the reverse polarity pulse 63 does not exist in the non-selection period 62, the composite selection pulse 65 is set to the reverse polarity of the bias voltage 67 and its set value is small. Since it is suppressed, M is generated by the on / off signal waveform of the composite selection pulse 65.
The polarization amount of the IM element is not influenced. With such a driving waveform, it is possible to realize an MIM panel without an afterimage.

FIG. 7 shows an example of a driving waveform in which a plurality of pulses of opposite polarities are provided in the non-selection period according to another embodiment of the present invention, in which the composite selection pulse is set in the first half of the selection period and the non-selection. The signal potential at the rear of the period is different from that in FIG. Further, the gradation of the signal is modulated by the pulse width modulation in FIG. 6, but is modulated by the amplitude modulation in the present invention.

[0018]

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, an example of the X line signal and the Y line signal is shown, but Y shown in the claims of the present invention.
-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 an equivalent circuit diagram showing a configuration of a pixel portion of an MIM liquid crystal panel.

FIG. 4 is a diagram explaining the principle of polarization.

FIG. 5 is a diagram showing how the conductivity-voltage characteristics of an element change due to polarization.

FIG. 6 is a diagram showing another embodiment of the present invention.

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

[Explanation of symbols]

16 ... Signal voltage written in the liquid crystal layer. 17 ... Bias voltage 18 ... Composite selection pulse when ON 113 ... Reverse polarity pulse 63 ... Reverse polarity pulse within non-selection period 64 ... Reverse polarity pulse during selection period 65 ... Synthetic selection pulse 66 ... Pulse of the same polarity 67 ... Bias voltage 68 ... Period excluding a period having a pulse of opposite polarity in the non-selection period 69 ... Writing to liquid crystal layer Signal voltage 71 ... Selection period 72 ... Non-selection period 73 ... Reverse polarity pulse 74 ... Bias voltage 75 ... Composite selection pulse 76 ... Reverse polarity in non-selection period Of the signal voltage written in the liquid crystal layer

Claims (3)

[Claims] 1. A drive waveform (composite waveform of Y line applied signal-X line applied signal) of a MIM 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. Therefore, a pulse having a polarity opposite to that of the composite selection pulse is set before the composite selection pulse for writing the ON / OFF signal to the pixel, and the pulse of the reverse polarity is applied as one pulse or intermittently. A plurality of pulses having the opposite polarity, the pulse width of the pulse of the opposite polarity (width of each pulse in the case of a plurality of pulses) is equal to or wider than the width of the composite selection pulse. Drive waveform of MIM LCD panel. 2. A bias voltage is a value obtained by time-averaging a voltage in a period excluding a period in which the pulse of the opposite polarity exists in a non-selection period in which a signal written by the combined selection pulse is held. The drive waveform according to claim 1, wherein the polarity of the composite selection pulse is different from the polarity of the bias voltage. 3. The drive waveform according to claim 2, wherein the peak value of the pulse of the opposite polarity is equal to or higher than the peak value of the composite selection pulse.