KR100628258B1 - MI LCD Liquid Crystal Display Compensating Signal Delay - Google Patents

Abstract

The metal insulator metal (MIM) liquid crystal display device according to the present invention is to reduce distortion of a signal due to signal delay, and includes at least one scan line for transmitting a signal voltage from a scan line pad and a signal line pad. At least one signal line for transmitting a bias voltage, and a metal film positioned closest to each of the scan line pads and each of the signal line pads is formed to have the smallest size so as to reach the end of each scan line and the end of each signal line. It characterized in that it comprises at least one MIM element formed to increase the size of the metal film.

Line delay, MIM liquid crystal display, charging

Description

Line Delay Effect Compensated MIM LCD

1 is a cross-sectional view showing a conventional MIM liquid crystal display device.
2 is an equivalent circuit diagram showing pixels of a MIM liquid crystal display device.
3 is a waveform diagram showing a driving waveform of the MIM liquid crystal display device;
4 is a waveform diagram showing waveforms of voltages applied to an ON pixel and an OFF pixel;
5 is a waveform diagram illustrating a signal waveform of a MIM liquid crystal display device implementing gray scales.
6 is a block diagram showing a module of the MIM liquid crystal display device.
7 is an equivalent circuit diagram of scan lines and pixels.
8 is an equivalent circuit diagram of scan lines and pixels.
9 is a waveform diagram showing a voltage waveform of a scan line according to a pixel position;
10 is a plan view showing a metal film of the MIM device according to an embodiment of the present invention.
Fig. 11 is a waveform diagram showing a waveform of an external bias voltage.
12 is a graph showing the change of the electro-optical transmission according to the signal delay of the selection waveform.
※ Explanation of code for main part of drawing

delete

delete

delete

delete

delete

delete

delete

delete

delete

delete

delete

delete

1: upper glass substrate 2: lower glass substrate
3: liquid crystal 4: pixel electrode

5 scanning line 6 insulating film
7: metal film 9: signal line

The metal insulator metal (MIM) liquid crystal display device according to the present invention is to reduce distortion of a signal due to a line delay.
1 is a cross-sectional view showing a conventional MIM liquid crystal display device.
The metal insulator metal (MIM) liquid crystal display shown in FIG. 1 includes a signal line 9 made of ITO on the upper glass substrate 1, and a scan line 5 and Ta ₂ formed of Ta on the lower glass substrate _2. An insulating film 6 of O ₃ , a metal film 7 made of Cr, and a pixel electrode 4 are included. Here, the signal line 9 is formed of a transparent electrode, and the pixel electrode 4 is formed of a transparent electrode in the case of a transmissive type, Cr or Al in the case of a reflective type. In the case of the reflective type, the metal film 7 and the pixel electrode 4 are formed integrally with the same material.
Currently, the most widely used MIM device is a stacked structure of Ta, Ta ₂ O ₃ and Cr. Here, the Ta ₂ O ₃ film is formed by anodizing the Ta film.
The upper glass substrate 1 of the MIM liquid crystal display device has the same structure as a passive matrix LCD, and is mainly driven in the TN mode. A typical process sequence of the MIM device is as follows. Here, three to four exposure masks are required in the process.
(1) Ta is deposited on the lower glass substrate and annealed in 400 ° C. air to form a Ta ₂ O ₃ film. Here, the Ta ₂ O ₃ film prevents the glass substrate from being etched.
(2) Ta is deposited to a thickness of about 2000 GPa and an etching process is performed in a CF ₄ / O ₂ state.
(3) Anodic oxide films are formed from 1% glycol and 0.01% citric acid.
(4) Anneal in vacuum.
(5) Cr is deposited and an ITO film is formed.
The current flowing through the MIM device can be expressed as a function of the voltage applied to the anode oxide film and the ITO film (Poole-Frenkel conduction equation). As the voltage increases, the current increases algebraically.
3 is a waveform diagram showing a driving waveform of the MIM liquid crystal display device.
As shown in Fig. 3, the voltage applied to the scan line 5 during the non-selection period is based on 0V. The voltage applied to the scan line 5 during the selection period is V _P , and the polarity is changed every frame.
In the case of letters, a voltage of + V _d or -V _d is applied to the signal line 9, whereas a signal voltage opposite to the polarity of the scan line 5 is applied to the ON (selection) pixel, and an OFF (non-selection) pixel. The signal voltage having the same polarity as that of the scan line 5 is applied to the same. Here, the n-1 th and n th pixels are ON pixels, and the n + 1 th pixel is an OFF pixel.
4 is a waveform diagram illustrating waveforms of voltages applied to an ON pixel and an OFF pixel.
The absolute voltage applied to the ON pixel of the selection period shown in FIG. 4 is V _P + V _d , and the absolute voltage applied to the OFF pixel of the selection period is V _P −V _d . The selection period is a period in which ± V _P is applied to the scan line, and the non-selection period is a period in which a voltage of 0 V is applied to the scan line. The ON pixels and the OFF pixels in the non-selection period depend on the voltage of the signal line 9. -V _d or + V _d .
During the selection period, since the MIM element of the ON pixel has a smaller resistance than the MIM element of the OFF pixel, much current flows. The MIM liquid crystal display device varies the driving voltage of the liquid crystal by controlling the charge charged in the pixel during the selection period.
5 is a waveform diagram illustrating a signal waveform of a MIM liquid crystal display device implementing gray scales.
As shown in Fig. 5, the gray level is represented by adjusting the ratio of + V _d and -V _d applied to the signal during the selection period. That is, the gray scales are displayed by adjusting the time ratio at which the ON voltage and the OFF voltage are applied while the scan line 5 is selected.
6 is a configuration diagram showing a module of the MIM liquid crystal display device.
The module of the MIM liquid crystal display element shown in FIG. 6 includes a signal line driver IC, a scan line driver IC, and a controller.
The controller adjusts the signal from the external system to match the MIM LCD panel. The controller receives R, G, B pixel signals and system clock vertical and horizontal synchronization signals that are the basis of control. The timing controller inside the controller generates time-related signals to fit the MIM LCD panel.

2 is an equivalent circuit diagram illustrating pixels of a MIM liquid crystal display device.
The MIM liquid crystal display device has a structure in which a liquid crystal and a MIM device are connected in series. Since the specific resistance of the liquid crystal is as high as 10 ¹³ Ω-cm, it can be ignored. During the selection period, the capacitance of the MIM element is ignored because the resistance of the MIM element is usually about 10 ⁶ Ω, which is lower than the impedance of the capacitance of the MIM element.
7 is an equivalent circuit diagram of scan lines and pixels.
A plurality of resistors (R _{scan lines} ) are connected in series to the _{scan line} shown in FIG. 7. The capacitance C _LC of the liquid crystal and the MIM resistor R _MIM are connected in parallel to the plurality of resistors R _{scan line} to form a pixel.
Due to the capacitance C _LC and the MIM resistance R _MIM of the liquid crystal connected to the resistance R _{scan line} of the scan line, the voltage waveform applied to the scan line is different depending on the position of the pixel.
9 is a waveform diagram illustrating voltage waveforms of scan lines according to pixel positions.
The first waveform A shown in Fig. 9 is a drive waveform of a scan line applied to a pixel at a position close to the scan line pad, and a second waveform B is a drive waveform of a scan line applied to a pixel in the middle of the scan line. The third waveform C is a driving waveform applied to the pixel farthest from the pad of the scanning line. That is, the waveform is distorted due to signal delay as the distance from the scanning line pad increases.

As shown in FIG. 9, since the driving waveform of the scan line is different for each pixel position, the amount of charge charged also varies greatly. The smaller the signal delay, the more time the high voltage is applied to the MIM element, so the more charge is charged in the pixel.
8 is an equivalent circuit diagram of scan lines and pixels.
As shown in FIG. 8, a plurality of MIM capacitances C _MIM and capacitances _LC of a plurality of liquid crystals are connected in parallel between a plurality of resistors (R _{signal lines} ) provided in the _{signal line} . It forms the pixel of a MIM liquid crystal display element.
At this time, since the resistance of the MIM element composed of the MIM capacitance C _MIM and the liquid crystal capacitance C _LC is high at about 10 ¹¹ Ω in the non-selection period of the signal line, the equivalent circuit of the MIM liquid crystal display element pixel is ignored. The MIM capacitance C _MIM and the liquid crystal capacitance C _LC are connected in series.
Among the plurality of pixels connected to the signal line, one pixel becomes a selection period, and the remaining pixels are all non-selection periods. The pixels in the selector are represented by the dotted dotted lines in FIG. 8. That is, in the selection period, the pixel has an equivalent structure in which the MIM resistor and the capacitance of the liquid crystal are connected in series, and in the non-selection period, the MIM capacitance (C _MIM ) and the capacitance of the liquid crystal (C _LC ) are connected in series. Structure.
Since signal lines mainly use ITO, which is a transparent conductive film, resistance is larger than that of scan lines. Since the signal delay of the signal line, like the scan line, reduces the charge rate of the pixel, the transmittance of the pixel in the part close to the signal line pad and in the part far away is different.
12 is a graph showing the change of electro-optic transmission according to the signal delay of the selection waveform.
As shown in FIG. 12, when the time constant RC is given to 3 kHz and the selection waveform is applied to the same pixel, the signal delay occurs in comparison with the electro-optic transmission curve of the pixel close to the signal line pad without signal delay. It can be seen that the optical transmission curve has shifted to the right by about 1V.
Conventional MIM liquid crystal display devices have been difficult to enlarge due to differences in transmittance due to signal delay.

The MIM liquid crystal display according to the present invention is to reduce distortion of a signal due to signal delay, and includes at least one scan line for transmitting a signal voltage from a scan line pad and at least one signal line for transferring a bias voltage from a signal line pad. And at least one metal film positioned closest to each of the scan line pads and the signal line pads so as to have the smallest size, so that the size of the metal film becomes larger as it reaches the end of each scan line and the end of each signal line. It characterized in that it comprises a MIM element.
In addition, in the method of driving the MIM liquid crystal display device according to the present invention, in the step of supplying a bias voltage from the outside to the metal film of the MIM device, the bias voltage is most close to the metal film located closest to the at least one signal line pad. It starts supplying at a low voltage and increases the size so that the highest voltage is applied to the metal film positioned at the end of at least one signal line.
In general, since the length of the scan line increases as the screen of the MIM liquid crystal display increases, the pixel delayed from the scan line pad increases. Accordingly, in the present invention, as the distance from the scanning line pad or the signal line pad to the pixel increases, the size of the metal film of the MIM element is increased. Therefore, the area of the portion where the metal film and the scan line or the signal line overlap is increased, thereby reducing the resistance, thereby increasing the amount of charge of the pixel which decreases due to signal delay.
10 is a plan view showing a metal film of the MIM device according to an embodiment of the present invention.
As shown in Fig. 10, the scanning line 5 and the plurality of metal films 7 are designed so that the area overlapping each other increases toward the right (the further away from the scan pad).
Specifically, as the metal film 7 of the MIM element moves away from the scan line pad, the area thereof becomes wider, and the area where the scan line and the metal film 7 overlap with each other is formed larger as the distance from the scan line pad increases.
As shown in FIGS. 9, 10 and 12, as the distance from the scanning line pad increases, the charge rate of the pixel decreases due to signal delay. The metal film of the MIM element closest to the scanning line pad has the smallest size and is located close to the end of the scanning line. The larger the MIM element, the larger the metal film is, thereby increasing the charge rate of the MIM element of the pixel. As a result, the light transmittance that appears smaller toward the end of the scan line at the closest portion of the scan line pad is compensated, thereby solving the problem due to signal delay.
The signal line of the MIM element is formed of a transparent conductive film, and since the resistance of the transparent conductive film is larger than that of the scan line, the distortion of the signal due to signal delay appears larger than that of the scan line. In this case, the pixel connected to the signal line, like the pixel connected to the scan line, may form a metal film of the MIM element closer to the end of the scan line from the closest portion of the scan line pad to compensate for the charge rate due to signal delay. That is, the smaller the metal film size of the MIM device closest to the signal line pad, such as the scan lines shown in FIGS. 9, 10, and 12, and the larger the MIM device positioned near the end of the signal line, the larger the metal film is. Increase the filling rate. As a result, the light transmittance that appears smaller toward the end of the signal line is compensated, thereby solving the problem due to signal delay.
In addition, the distortion of the signal due to the signal delay of the signal line can be compensated simply by adjusting the bias voltage. The signal line driver IC of the MIM device switches externally connected bias voltages V _d and −V _d to a gray level. The signal delay of the signal line can be compensated by driving the amplitudes of the externally connected bias voltages V _d and -V _d at different distances from the pads of the signal line.
Specifically, the signal voltage for the signal delay is prevented by increasing the magnitude of the bias voltage as the end of the signal line near the pad of the signal line increases.
11 is a waveform diagram showing a waveform of an external bias voltage.
Unlike using a fixed bias voltage in the related art, as shown in FIG. 11, a bias voltage having a different waveform is applied according to a frame. Specifically, the voltage across the pixel increases as the V _d (+) is constant and the V _d (−) is separated from the signal line pad during the + frame to which the + voltage is applied. In addition, during a frame in which a voltage is applied, V _d (−) is constant, and as the V _d (+) is separated from the signal line pad, the voltage applied to the pixel increases. Therefore, since the bias voltage is increased while being turned away from the signal line pad, i.e., closer to the end of the signal line, the signal voltage due to the signal delay of the signal line can be compensated for.

The present invention can reduce the distortion of the signal due to the signal delay, which has been an obstacle to the enlargement of the MIM liquid crystal display device, thereby opening the way for the MIM LCD to be enlarged in the future.
Conventionally, in order to reduce signal delay, signal lines and scan lines are mainly formed thick and wide to reduce resistance, thereby preventing deterioration in image quality due to signal delay. However, thickening the signal line and the scanning line takes a lot of processing time and decreases the aperture ratio, so that the screen is dark.
In the present invention, since the effect of signal delay is minimized by adjusting the area of the MIM device and the waveform of the bias voltage, a large sized MIM liquid crystal display device can be manufactured without changing the process and characteristics. The MIM liquid crystal display device of the present invention can be used for a very large TV or a monitor.

Claims (6)

At least one scan line for transmitting the signal voltage from the scan line pads; At least one signal line for transmitting a bias voltage from the signal line pad; And, At least one MIM element formed such that the size of the metal film positioned closest to each of the scan line pads and each of the signal line pads is the smallest so that the size of the metal film increases as the end of each scan line and the end of each signal line are increased. MIM liquid crystal display device comprising a. The method of claim 1, The signal line pad MIM liquid crystal display device for supplying a bias voltage input from the outside to the at least one signal line. The method of claim 2, The bias voltage starts to be applied at the lowest voltage to the metal films positioned closest to the respective signal line pads and increases in magnitude so that the highest voltage is applied to the metal films positioned at the ends of the signal line. MIM liquid crystal display device. The method of claim 1, The at least one MIM device The metal film positioned closest to the scan line pad has the smallest area of the overlapping portion of the scan line, and the closer the end of the scan line is, the larger the area of the overlapping portion of the scan line and the metal film is. MEM liquid crystal display device characterized in that the increased. The method of claim 1, The at least one MIM device The metal film positioned closest to the signal line pad has the smallest area of the overlapping portion of the signal line, and the closer the end of the signal line is, the larger the area of the overlapping portion of the signal line and the metal layer is. MEM liquid crystal display device characterized in that the increased. In the step of supplying a bias voltage from the outside to the metal film of the MIM element, Supplying the bias voltage at the lowest voltage to the metal film positioned closest to the at least one signal line pad and increasing the magnitude so that the highest voltage is applied to the metal film positioned at the end of the at least one signal line. A method for driving an MI liquid crystal display device, characterized in that.

Images