KR20080073953A - Liquid crystal panel - Google Patents

Abstract

A liquid crystal panel is provided to reduce defects due to a stepped portion in a channel region even though a plurality of switching elements is formed in an upper region of a capacitor. A liquid crystal panel includes a upper substrate, a lower substrate(200), and a liquid crystal. The lower substrate includes at least one switching element, a pixel electrode, a maintenance capacitance capacitor(210), and an auxiliary capacitor(220). The pixel electrode applies a voltage to the liquid crystal. The maintenance capacitance capacitor temporarily stores an applied video. The auxiliary capacitor sufficiently maintains capacitance of a liquid crystal capacitor generated by the upper substrate, the lower substrate, and the liquid crystal during irradiation of light. One selected from the maintenance capacitance capacitor and the auxiliary capacitor is formed in a lower region of the switching element.

Description

Liquid crystal panel {LIQUID CRYSTAL PANEL}

1 is a schematic diagram of a liquid crystal projector using a conventional field sequential driving method.

2 is an operation timing diagram of a liquid crystal display device of a conventional field sequential driving method.

3 is an equivalent circuit diagram of an embodiment of a liquid crystal cell (C) provided in a field sequential driving liquid crystal display device disclosed in Korean Patent Application No. 10-2005-126548 filed by the applicant of the present application.

4 is an operation timing diagram of a liquid crystal display of a field sequential driving method shown in Korean Patent Application No. 10-2005-126548 filed by the present applicant.

5 is a layout view of a liquid crystal cell having two or more capacitors.

6 is a simplified cross-sectional view of the liquid crystal cell of FIG. 5.

7 is a simplified cross-sectional view of a liquid crystal cell of one embodiment according to the present invention.

The present invention relates to a liquid crystal panel, and more particularly, to a liquid crystal panel having two or more capacitors suitable for a field sequential driving method.

The liquid crystal display device has a configuration in which a TFT substrate on which a thin film transistor (TFT), which is a switching element, and a color filter substrate on which a color filter is formed are maintained at regular intervals, and a liquid crystal panel in which liquid crystal is injected therebetween. . In such a liquid crystal display, since the light is lost while passing through the color filter, there is a disadvantage that the brightness is low. In addition, in the case of a liquid crystal projector that does not use a color filter, a liquid crystal panel corresponding to R, G, and B light must be separately provided, thereby increasing the manufacturing cost. In order to solve such a decrease in optical efficiency and a rise in manufacturing cost, a liquid crystal display device having a field sequential driving method has been proposed.

The liquid crystal display of the field sequential driving method has no color filter and has a sequential light source that sequentially emits colors of red (R), green (G), and blue (B). The conventional field sequential driving type liquid crystal display device time-divides one field frame into three sub-frames, and sequentially displays red, green and blue light in each sub-frame to display colors. Will be displayed. 1 is a schematic diagram of a liquid crystal projector using a conventional field sequential driving method. The light emitted from the reflector and the illumination 110 is selected by R, G, B using the color filter 120 and then incident to the light collector. Light incident on the integrator 130 is collected at a uniform illuminance and then incident to the liquid crystal display 140. Light incident on the liquid crystal display device 140 is selectively transmitted or blocked to implement an image. The image generated by the liquid crystal display device 140 is enlarged through the projection lens 150 and then irradiated to the screen 160. Field sequential driving type liquid crystal display devices are used in various applications as reflective liquid crystal devices or transmissive liquid crystal devices in addition to liquid crystal projectors.

2 is an operation timing diagram of a liquid crystal display of a conventional field sequential driving method. One frame (FRAME) is composed of a sub-frame (SUB FRAME) for turning on the R optical backlight, a sub-frame (SUB FRAME) for turning on the G optical backlight, and a sub-frame (SUB FRAME) for turning on the B optical backlight. One subframe includes an addressing time t1 for addressing each liquid crystal cell array 30, a liquid crystal setting time t2 for charging a liquid crystal cell with an applied image signal, an irradiation time t3 for irradiating a light source, and a liquid crystal. It consists of the reset time t4 which resets a cell. The field sequential driving type liquid crystal display has a structure in which the corresponding light source can be irradiated only after the input of the image signal to all cells (particularly, the last liquid crystal cell) (t2). Due to such a structural problem, in the conventional field sequential driving method, as shown in FIG. 2, since the time required for transmitting video data to all pixels in a state in which one frame is divided into three subframes is required, real brightness can be expressed. Time is subject to many limitations.

A field sequential driving type liquid crystal display device having increased light irradiation time has been proposed. The newly proposed field sequential driving type liquid crystal display device has a large number of capacitors and transistors provided in one cell. A rescue was needed.

An object of the present invention is to provide a liquid crystal panel suitable for the field sequential driving method, which has been developed by the necessity as described above.

The object of the present invention is to provide a liquid crystal panel including a liquid crystal injected between an upper substrate and a lower substrate and both substrates, the lower substrate comprising at least one switching element, a pixel electrode for applying a voltage to the liquid crystal, A storage capacitor for temporarily storing a video signal, and an auxiliary capacitor for sufficiently maintaining the capacity of the liquid crystal capacitor formed by the upper substrate / lower substrate / liquid crystal while light is irradiated, the storage capacitor and the auxiliary capacitor Any one selected from the capacitors may be formed in the lower region of the switching element, and the remaining non-selected capacitors may be formed in the upper region of the switching element.

Hereinafter, with reference to the accompanying drawings will be described in detail the advantages, features and preferred embodiments of the present invention.

FIG. 3 shows an equivalent circuit diagram of a liquid crystal cell (C) according to an embodiment provided in a field sequential driving liquid crystal display device disclosed in Korean Patent Application No. 10-2005-126548 filed by the present applicant. As shown in FIG. 3, the liquid crystal cell of the liquid crystal display device disclosed in Korean Patent Application No. 10-2005-126548 has a gate electrode electrically connected to a gate control signal line 21 and a source electrode of the source control signal line 11. And a first switching element TR1 electrically connected to the fixed power supply line 71, a storage capacitor Cs at which one electrode is electrically connected to the drain electrode of the first switching element TR1, and a source. A second switching element TR2 in which the electrode is electrically connected to the other end of the storage capacitor Cs and the gate electrode is electrically connected to the write control signal line 51, and the gate electrode is electrically connected to the reset control signal line 61. A third switching element TR3 connected to the source electrode of the second switching element and electrically connected to the source electrode of the second switching element, and a second common voltage Vcom2 applied to the drain electrode; And a display capacitor capacitor (CL + Ca) electrically connected between the drain electrode of TR2 and the first common voltage Vcom1. While an auxiliary capacitor (Ca) is the time as being formed on a lower substrate is small, the capacity of the liquid crystal capacitor (C _L) only by the charge stored in the liquid crystal capacitor (C _L) to turn on during the hold time for a long time, that is, light of the corresponding color, In order to compensate for the problem that the voltage cannot be maintained, the capacitor is installed in parallel with the liquid crystal capacitor. Here, the same potential may be applied to the first common voltage Vcom1 and the second common voltage Vcom2.

4 is an operation timing diagram of a liquid crystal display of a field sequential driving method shown in Korean Patent Application No. 10-2005-126548 filed by the present applicant. The timing for irradiating R light will be described, and the remaining G light and B light are also irradiated at the same timing. Image data corresponding to R light is input to the storage capacitor Cs of the liquid crystal cell electrically connected to each gate line while sequentially addressing each gate line during the 't1' addressing time. The image data (video signal) is stored in the storage capacitor Cs from the source control signal line 11 through the first switching element TR1 in the 'on' state. The 't2' hold time is sufficient for the time when the image data is written in the storage capacity of the liquid crystal cell electrically connected to the last gate line and the light of the previous stage (B light when irradiated in the order of R / G / B light). The time interval for turning on the light source for irradiation. The minimum interval of the 't2' hold time will be the time at which the image data is written in the storage capacity of the liquid crystal cell electrically connected to the last gate line, and the maximum time may vary depending on the design. At this time, since the charge amount of the display capacitor is not affected, it can be confirmed from the timing diagram of FIG. 4 that the B light is irradiated for a sufficient time even during the 't2' hold time of the R light.

After a sufficient 't2' hold time has elapsed, all liquid crystal cells of the liquid crystal cell array are reset during the 't3' reset time. At this time, irradiation of the B light ends before the 't3' reset starts. The reset operation may be applied to the reset line 61 to simultaneously perform all the display capacitors of the liquid crystal cell array, or may be performed line by line or sector by sector. Thereafter, all liquid crystal cells of the liquid crystal cell array are written as R optical image data for a 't4' write time. At this time, the charge accumulated in the storage capacitor Cs of each liquid crystal cell is transferred to the display capacitor. The write operation may be performed simultaneously with all display capacitors of the liquid crystal cell array, or may be performed line by line or sector by sector, but it is preferable to simultaneously perform the write operation in order to secure more irradiation time of the backlight. After the 't4' write time, the irradiation of the R light is started by irradiating the light source corresponding to the R light. As shown in FIG. 4, while the image data for R light is recorded in the storage capacitor Cs of the liquid crystal cell, image data corresponding to the light of the previous stage remains in the display capacitor, which corresponds to the previous light. It can be seen that the light source of the color can be irradiated.

As in the embodiment shown in Korean Patent Application No. 10-2005-126548, a liquid crystal cell constituting a newly proposed field sequential driving type liquid crystal display device includes a plurality of capacitors Cs and Ca and three switching elements TR1 on a lower substrate. And TR2 and TR3, and the liquid crystal capacitor C _L formed by the liquid crystal injected between the lower substrate and the upper substrate. Conventionally, a liquid crystal cell constituting a liquid crystal display device is usually composed of one switching element, a storage capacitor (Cs) and a liquid crystal capacitor (C _L ), whereas the liquid crystal cell of the newly proposed field sequential driving liquid crystal display device has a complicated structure. Able to know.

Three switching elements TR1, TR2, and TR3 provided on the lower substrate are preferably formed on the same layer in order to process the active layer forming the channel in one process. However, when two or more capacitors (Cs, Ca) are formed on the lower substrate and three switching elements (TR1, TR2, TR3) are formed on the lower substrate without reducing the effective area of the liquid crystal cell, the channel of the switching element is There is a problem formed in the stepped area. FIG. 5 is a layout diagram of a liquid crystal cell having two or more capacitors. FIG. 5 will be described as an example.

The liquid crystal cell may be divided into a light transmission region through which a pixel electrode is formed to transmit incident light, and a light blocking region except for the light transmission region. Since a part of the region where the pixel electrode is formed includes a region through which light cannot transmit due to overlapping with an area where the upper BM is formed, not all regions where the pixel electrode is formed are light transmissive regions.

Since the capacitor and the switching element are formed of a material that does not transmit light, they should be formed in the light shielding area. As shown in the embodiment of FIG. 5, the storage capacitor Cs is formed in the light shielding region 210, the auxiliary capacitor Ca is formed in the light shielding region 220, and the first switching element TR1 is shielded on the light shielding region 210. When the second switching element TR2 is formed in the region 241 and the light blocking region 242 and the third switching element TR3 are formed in the light blocking region 243, the active layer forming region of the switching element has a step difference. Problems are formed on top of the layer. The first switching element TR1 is formed at the intersection of the gate line 251 and the data line, and the data line has a straight line connected vertically to the gate line 251. In FIG. 5, the data line is segmented for convenience of description. Shown in form.

FIG. 6 is a simplified cross-sectional view of the liquid crystal cell of FIG. 5, and the problem will be described in more detail with reference to FIG. 6. 6 is to be understood as a simplified cross-sectional view that does not indicate a cross-sectional view of a substantially necessary contact hole. In addition, as shown in FIG. 5, since the upper BM is formed in an area where the pixel electrode 290 is not formed, the pixel electrode is not shown when the cross section is displayed based on the area where the upper BM is formed. In order to explain the vertical position relationship between the electrode 290 and the upper BM, the pixel electrode 290 is illustrated as being applied on the upper BM 270.

The storage capacitor 210 and the auxiliary capacitor 220 are stacked on the lower substrate 200. The interlayer insulating film 230 is laminated on the upper portion, and the active layers 241, 242, and 243 are patterned simultaneously. In the case of the polysilicon liquid crystal display, the polysilicon process is performed after the amorphous active layers 241, 242, and 243 are formed. Next, the first gate insulating layer 245 is laminated and formed on the gate line 247 for the second switching element TR2 and the gate line 248 for the third switching element TR3. The second gate insulating layer 250 is stacked again, and a gate line 251 for the first switching element TR1 is formed thereon. Next, after forming the interlayer film 260 including the data electrode, the upper BM layer 270 is formed. An insulating layer 280 is formed on the upper BM layer 270, and a pixel electrode 290 is formed on the insulating layer 280.

As shown in FIG. 6, when the storage capacitor capacitor 210 and the auxiliary capacitor 220 are formed under the active layer forming layer constituting the switching element, the second switching element TR2 is formed due to the stepped region formed therebetween. It can be seen that a step occurs in the active layer region of.

When the storage capacitors 210 and the auxiliary capacitors 220 are formed at the same time under the region forming the switching element, a problem occurs in that the capacitance of the capacitor is reduced, and the channel region of the switching element TR2 is formed in the stepped region. This causes a defect in which a short circuit occurs.

Therefore, in the present invention, either the storage capacitor or the auxiliary capacitor is formed in the upper BM region. Figure 7 shows a simplified cross-sectional view of a liquid crystal cell of one embodiment according to the present invention. 7 is also shown in a simplified state in which the indication of the required contact holes is omitted. In addition, as shown in FIG. 5, since the upper BM is formed in a region where the pixel electrode 290 is not formed, the pixel electrode is not shown when the cross section is displayed based on the region where the upper BM is formed. In order to explain the vertical position relationship between the electrode 290 and the upper BM, the pixel electrode is illustrated as being coated on the upper BM.

As shown in FIG. 7, in the liquid crystal cell of the present invention, a storage capacitor 210 is formed in the lower region of the switching elements TR1, TR2, and TR3, and the auxiliary capacitor 220 is formed of the switching elements TR1, TR2, and TR3. Formed in the upper region.

A storage capacitor capacitor 210 is formed on the lower substrate 200. The storage capacitor 210 is formed by depositing a doped polysilicon having a high electrical conductivity by injecting a dopant into the storage capacitor first electrode 211 and patterning the insulating film thereon. The dielectric film 215 is deposited by thermal oxidation or low pressure chemical vapor deposition (LPCVD), and the polysilicon and tungsten doped with the storage capacitor second electrode 213 thereon. Silicide (WSix) is continuously deposited and patterned to form a double film. In this case, at least one of the storage capacitor first electrode 211 or the storage capacitor second electrode 213 is formed of a light blocking material so that the storage capacitor 210 performs the function of the lower BM at the same time. Preferably, the storage capacitor capacitor second electrode 213 is preferably formed of a light blocking material. The reason why the double layer is formed is that the cracks caused by the internal stress of the tungsten silicide thin film can be suppressed to relieve stress, and the interfacial properties of SiO 2 and silicide (Six) are improved. The storage capacitor second electrode 213 may be formed of a single layer film such as titanium silicide (TiSix) or tungsten silicide (WSix), or may be formed of titanium silicide instead of tungsten silicide. . When the first electrode 211 of the storage capacitor 210 is formed larger than the second electrode 213, the first electrode 211 is the drain electrode of the first switching element TR1 or the second switching element TR2. It was made to be easy to contact with the source electrode of.

The interlayer insulating film 230 is laminated on the upper portion, and the active layers 241, 242, and 243 are simultaneously formed. In the case of the polysilicon liquid crystal display, the polysilicon process is performed after the amorphous active layers 241, 242, and 243 are formed. Next, the first gate insulating layer 245 is laminated and formed on the gate line 247 for the second switching element TR2 and the gate line 248 for the third switching element TR3. The second gate insulating layer 250 is stacked again, and a gate line 251 for the first switching element TR1 is formed thereon.

In the cross-sectional view of FIG. 7, the gate line 247 for the second switching element TR2 and the gate line 248 for the third switching element TR3 are formed under the gate line 251 for the first switching element TR1. As described above, the positions of the two may be interchanged.

Next, the data electrode is included Interlayer 260  After forming, the auxiliary capacitor 220 is formed. What is the interlayer film 260 , Data electrodes, switching elements contact  Commonly referred to as a film in which an electrode or the like is formed, and usually Stacked  It is formed in the form of a film. assistant Capacitor  The first electrode 271 is TiN - Al With a double layer By pattern  Form an insulating film thereon. plasma  Vapor deposition PECVD , Plasma Enhanced  Chemical Vapor Deposition ) Has a thickness of less than 1000Å The dielectric film 275  Deposition formed, and on top of that Capacitor  The second electrode 273 TiN - Al With a double layer  Form. assistant Capacitor  Electrode With a double layer  The reason for forming Al This is because the step coverage is poor in the case of using only the breakage failure. therefore Al At the top of the membrane TiN Reapplied With a double layer  Forming or TiN - Al - TiN Triple film  Form in the form. Thus the secondary Capacitor  First electrode 271 or auxiliary Capacitor  The second electrode 273 Metal  Formed by light blocking material Capacitor 220  Top BM Will function as.

assistant Capacitor  Make up The dielectric film 275  1000Å Thicker than  When the thickness is formed, the amount of charge induced by the same potential difference becomes small Capacitor  Capacity is reduced, secondary cap Sitter Difficulty in using it. Also, secondary Capacitor  Electrode Al Is formed using The dielectric film 275  If forming Al Melting point (660 ℃) lower  At temperature Possible to deposit  Process temperature is 400 ℃ plasma  Evaporation method was used. BM To form Dielectric film  The LPCVD method of process temperature 680 degreeC was used.

The lower substrate of the liquid crystal display for field sequential driving is completed by forming an insulating layer 280 on the auxiliary capacitor second electrode 273 and forming a pixel electrode 290 thereon.

In this case, one electrode of the storage capacitor 210 is connected to a contact electrode connected to the drain electrode of the first switching element TR1, and the other electrode is connected to a source electrode of the second switching element TR1. To be connected. Similarly, a contact electrode applying a common voltage is connected to one electrode of the auxiliary capacitor 220, and the contact electrode connected to the pixel electrode is connected to the other electrode. More preferably, a contact electrode for applying a common voltage is connected to the first electrode 271 of the auxiliary capacitor 220, and a contact electrode connected to the pixel electrode is connected to the second electrode 273 of the auxiliary capacitor 220. Be sure to This is because having such a contact electrode structure can simplify the wiring structure. In FIG. 7, the second electrode of the auxiliary capacitor 220 is electrically connected by the pixel electrode 290 and the contact electrode 320, and is electrically connected by the drain of the second switching element TR2 and the contact electrode 310. Shows connection to. The contact electrodes 310 and 320 of FIG. 7 are merely exemplary diagrams for explaining the electrical connection, and differ from the actual positive wiring.

In the embodiment of FIG. 7, a structure in which the storage capacitor 210 is formed in the lower region of the switching element and the auxiliary capacitor 220 is formed in the upper region of the switching element is proposed. It is readily possible for those skilled in the art related to the present invention. However, preferably provided in the position as shown in Figure 7 it is possible to stabilize the circuit more.

In the present invention, the storage capacitor is provided in the lower region of the switching element, and the auxiliary capacitor is provided in the upper region of the switching element, thereby reducing the capacitance of the capacitor.

In addition, since the stepped region is not generated by the capacitor provided under the switching element, even if a plurality of switching elements are formed in the upper region of the capacitor, defects due to the step generated in the channel region can be reduced.

Due to the liquid crystal cell structure according to the present invention, it is possible to easily commercialize a field sequential driving type liquid crystal display device having a complex cell structure.

While the preferred embodiments of the present invention have been described using specific terms, such descriptions are for illustrative purposes only, and it is understood that various changes and modifications may be made without departing from the spirit and scope of the following claims. Should be done.

Claims (10)

In the liquid crystal panel comprising a liquid crystal injected between the upper substrate and the lower substrate and both substrates, The lower substrate is At least one switching element, A pixel electrode for applying a voltage to the liquid crystal; A storage capacitor which temporarily stores the applied video signal; An auxiliary capacitor for sufficiently maintaining the capacity of the liquid crystal capacitor formed by the upper substrate, the lower substrate, and the liquid crystal while light is irradiated; Wherein any one selected from the storage capacitor and the auxiliary capacitor is formed in the lower region of the switching element, and the remaining unselected capacitor is formed in the upper region of the switching element. The method of claim 1, And the storage capacitor is provided in the lower region of the switching element, and the auxiliary capacitor is provided in the upper region of the switching element. The method according to claim 1 or 2, The switching element includes a first switching element for applying an external image signal to the storage capacitor, and a second switching element for switching the charge accumulated in the storage capacitor to the liquid crystal capacitor. . The method of claim 3, wherein The channel of the first switching element and the channel of the second switching element are formed on the same layer formed on the one of the capacitor electrode selected from the storage capacitor and the auxiliary capacitor formed below them. Liquid crystal panel. The method according to claim 1 or 2, At least one of the electrodes forming the storage capacitor is formed of a light blocking material. The method according to claim 1 or 2, At least one of the electrodes forming the auxiliary capacitor is formed of a light blocking material. The method according to claim 1 or 2, Any one of the electrodes forming the auxiliary capacitor is electrically connected to the pixel electrode. The method according to claim 1 or 2, And the dielectric material forming the auxiliary capacitor has a thickness of 1000 mW or less. The method according to claim 1 or 2, The dielectric material forming the auxiliary capacitor is formed by a plasma deposition method. The method of claim 7, wherein And the remaining electrodes forming the auxiliary capacitor are electrically connected to the electrodes applying the common potential.

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