JP2007033575A - Liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display device capable of surely setting the alignment direction of a liquid crystal. <P>SOLUTION: The liquid crystal 20 is disposed between a display electrode 12 and a counter electrode 32, and alignment control electrodes 36 are mounted on the counter electrode 32 via an insulating layer 34. The alignment control electrodes 36 are formed one by one, on respective pixels with a predetermined pattern and are maintained at a voltage different from that of the counter electrode 32. In particular, polarity of the voltage applied to the alignment control electrode 36, with respect to the counter electrode 32, is preferably controlled corresponding to polarity of the voltage applied to the display electrode 12. In this way, a suitable electric field is formed between the alignment control electrode 36 and the counter electrode 32, and with this electric field the aligning direction of the liquid crystal 20 is controlled. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a liquid crystal display device having an alignment control electrode for controlling the alignment of liquid crystal.

  Conventionally, a liquid crystal display (LCD) has been widely used as a typical flat panel display. The liquid crystal used in this liquid crystal display device includes various types such as a TN (twisted nematic) type, an STN (super twisted nematic) type, and a VA (vertical alignment) type.

  Here, some liquid crystal display devices using VA type liquid crystal have alignment control means for dividing the alignment direction of the liquid crystal. This alignment control means is provided with an alignment control window formed by opening a counter electrode that faces the display electrode and drives the liquid crystal together with the display electrode, and at least one of the display electrode or the counter electrode is provided with a bulge. There is an alignment control inclined portion formed by the above-mentioned method, and a combination of these alignment control windows and an alignment control inclination portion, which are disclosed in Patent Documents 1 and 2, for example. These alignment control means divide the electric field formed by each display electrode and the counter electrode to divide the alignment direction of the liquid crystal in each display electrode, thereby realizing a wide viewing angle display.

  The vertical alignment type liquid crystal display device having the alignment control means as described above has an advantage that it is not necessary to perform a rubbing process on the vertical alignment film and a manufacturing process can be omitted. However, generally, such a liquid crystal display device has a problem that the force for controlling the alignment direction of the liquid crystal is weaker than other liquid crystal display devices that control the alignment direction of the liquid crystal by rubbing the alignment film. There is.

  In addition, since the alignment control window and the alignment control inclined portion require a relatively large area, there is also a problem that the aperture ratio becomes small.

  Patent Document 3 describes the provision of an alignment control electrode on a display electrode.

JP-A-12-214464 Japanese Patent No. 3005418 Japanese Patent Laid-Open No. 7-13164

  The present invention relates to a display electrode, a counter electrode disposed opposite to the display electrode, a liquid crystal disposed between the display electrode and the counter electrode, the optical characteristics of which are controlled, and the display electrode and the counter electrode. And an alignment control electrode for independently controlling the potential and controlling the alignment of the liquid crystal.

  Further, it is preferable that the following relations (i) and (ii) are satisfied, where Va is the potential of the alignment control electrode, Vc is the potential of the counter electrode, and Vp is the potential of the display electrode. Here, (i) (Vp−Vc) and (Vp−Va) have the same sign (ii) | (Vp−Vc) |> | (Vp−Va) |.

  Further, it is preferable that the control voltage is a voltage equal to or lower than a threshold voltage of change in optical characteristics of the liquid crystal.

  It is preferable that the relationship (i) below is satisfied, where Va is the potential of the alignment control electrode, Vc is the potential of the counter electrode, and Vp is the potential of the display electrode. Here, the signs of (i) (Vp−Vc) and (Vp−Va) are opposite.

  In addition, an alignment film for aligning the liquid crystal in the vertical direction without rubbing is provided on the surface side of the display electrode and the counter electrode that contacts the liquid crystal, and the liquid crystal is VA (Virtical Alignment) liquid crystal. Is preferred.

  The alignment control electrode is preferably formed on the liquid crystal surface of the counter electrode via an insulating film.

  The alignment control electrode is preferably formed on the surface of the counter electrode opposite to the liquid crystal via an insulating film.

  In addition, a display electrode and an alignment control electrode are provided for each pixel arranged in a matrix. With respect to the alignment control electrodes of two adjacent rows of pixels, the alignment control electrode of every other pixel in one row and the other row The alignment control electrodes of every other pixel shifted by one pixel in the row direction are connected, and this is connected to the first reference voltage source, and the first two adjacent rows shifted by one row in the column direction are connected to the first reference voltage source. An orientation control electrode of every other pixel not connected to the reference power source and an orientation control electrode of every other pixel shifted by one pixel in the row direction of the other row are connected, and this is connected to the second By connecting to the reference voltage source and repeating this, it is preferable that the alignment control electrodes of the pixels adjacent in the row direction and the column direction are sequentially connected to either the first or second reference voltage source. .

  The polarity of the voltage applied to the display electrode with respect to the counter electrode is preferably a dot inversion method in which the polarity is inverted for each pixel in the row direction.

  As described above, according to the present invention, the alignment control electrode is provided, and the voltage of the alignment control electrode is appropriately set, so that the alignment direction (azimuth) of the liquid crystal can be reliably controlled. Therefore, an appropriate orientation direction can be set in a VA type liquid crystal or the like. The orientation control electrode may be small. Therefore, the aperture ratio can be increased compared to the case where the alignment control window and the alignment control inclined portion are provided, and high-definition display is possible.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram illustrating a planar pattern of alignment control electrodes in the liquid crystal display device according to the embodiment, and FIG. 2 is a cross-sectional view taken along line AA in FIG. In addition, illustration is abbreviate | omitted about a polarizing plate.

  As shown in FIG. 2, a display electrode 12 is formed on the TFT substrate 10 for each pixel. The TFT substrate 10 has a pixel circuit that takes in a data voltage for the pixel supplied from the data line for each pixel, holds the data voltage in a capacitor, and applies the data voltage to the display electrode 12. For example, a switching TFT having an active layer made of low-temperature polysilicon or the like formed on a glass substrate is formed, and this switching TFT is used for control of taking in a data voltage from a data line. Then, the data voltage supplied from the data line is held in the capacitor via the switching TFT, and the held voltage is applied to the display electrode 12.

  The display electrode 12 is a transparent electrode made of, for example, ITO (Indium Tin Oxide) or the like. Light from a backlight disposed below the TFT substrate 10 can be emitted to the observation side.

  An alignment film 14 made of polyimide or the like is formed so as to cover the surface of the display electrode 12 and the surface of the TFT substrate 10. The alignment film 14 is rubbing-less and aligns the liquid crystal in the vertical direction.

  A counter substrate 30 is disposed on the TFT substrate 10 on which the display electrode 12 is formed via a VA type liquid crystal 20. A counter electrode 32 made of a transparent conductive material such as ITO is formed on the surface of the counter substrate 30 on the liquid crystal 20 side. The counter electrode 32 is formed on almost the entire surface of the counter substrate 30 in common to all pixels.

Further, an alignment control electrode 36 is formed on the counter electrode 32 via an insulating film 34. The insulating film 34 may be made of any insulating material such as inorganic SiO ₂ , SiN, or organic acrylic resin. The orientation control electrode may be a transparent conductive material such as ITO, but may be composed of a metal material such as aluminum. An alignment film 38 is formed to cover the alignment control electrode 36 and the counter electrode 32. This alignment film 38 is also a rubbing-less vertical alignment film similar to the alignment film 14 described above.

  Note that the liquid crystal display device may be any of a transmissive type, a reflective type, and a transflective type. In the case of a reflection type, the display electrode 12 may be formed of a metal such as aluminum, and light incident from the counter substrate side may be reflected by the display electrode 12. Further, a reflective film such as aluminum may be disposed on the back side of the display electrode to reflect light passing through the transparent display electrode 12. Further, in the case of the semi-transmissive type, a reflective film may be disposed only on the reflective portion.

  In the present embodiment, as described above, the liquid crystal 20 is of the VA type and is used as normally black. The liquid crystal 20 is basically aligned in the vertical direction by the alignment films 14 and 38, but the alignment direction is controlled by the alignment control electrode 36.

  As shown in FIG. 1, the insulating film 34 and the orientation control electrode 36 have a shape in which a bifurcated leg extends in both the upper and lower directions, in which a Y shape and an inverted Y shape are connected in the vertical direction. The alignment control electrodes 36 are divided into two groups by connection wiring, one group being connected to the reference voltage line 40a and the other group being connected to the reference voltage line 40b.

  For example, in FIG. 1, for the sake of convenience, a total of 44 pixels of 11 horizontal and 4 vertical are shown. If the upper left pixel is (1, 1) and the lower right pixel is (11, 4), the alignment control electrode 36 in the pixel (1, 1) is connected to the reference voltage line 40a at the lower left corner, and the lower right corner. Is connected to the upper left corner of the orientation control electrode 36 of the pixel (2, 2). The upper right corner of the orientation control electrode 36 of the pixel (2, 2) is connected to the lower left corner of the orientation control electrode 36 of the pixel (1, 3). In this way, the alignment control electrodes 36 of the odd-numbered pixels in the pixels in the first row are connected to the alignment control electrodes 36 of the even-numbered pixels in the pixels in the second row. The alignment control electrodes 36 of the odd-numbered pixels in the pixels in the second row are connected to the alignment control electrodes 36 of the even-numbered pixels in the pixels in the third row, and such connection is repeated.

  Here, the reason why the alignment control electrodes 36 are grouped is that the dot inversion method is adopted as the polarity inversion method.

  For example, the voltage of the counter electrode 32 is set to a constant voltage Vc, and the polarity of the data voltage supplied to each pixel in the row direction is reversed with respect to Vc. For example, as shown in FIG. 4, the voltage (Vp−Vc) of each pixel in the row direction is alternately made positive and negative. On the other hand, the voltage (Va−Vc) of the alignment control electrode 36 is positive for pixels in which (Vp−Vc) is written to the display electrode 12 as positive, and for pixels in which (Vp−Vc) is written to the display electrode 12 as negative. Is negative. This is achieved by setting (Va−Vc) positive for the first reference voltage line 40a and negative (Va−Vc) for the second reference voltage line 40b.

  As described above, for the reference voltage lines 40a and 40b, for example, (Va−Vc) is set to be positive and negative in an odd-numbered frame, and inverted for each even-numbered frame. As a result, the polarity of the data voltage is inverted for each dot in a plan view, and dot inversion display control can be performed for one dot in which the polarity of the data voltage is inverted for each frame.

For example, the voltage is set so as to satisfy the following relationship.
[Equation 1]
(I) The signs of (Vp−Vc) and (Vp−Va) are the same.
(Ii) | (Vp−Vc) |> | (Vp−Va) |

  For example, (Vp−Vc) is a black display of 1.5V and a white display of 4.5V, and varies depending on the image to be displayed. When (Vp−Vc) is positive, (Va−Vc) is + 1V and (Vp−Vc) ) Is negative, (Va−Vc) is −1V. Thereby, the liquid crystal 20 can control the alignment of the liquid crystal 20 according to the electric field generated from the edge of the alignment control electrode 36. That is, an electric field is generated from the edge of the alignment control electrode 36 toward the counter electrode 32, and the liquid crystal 20 is aligned according to the electric field. In the case of VA liquid crystal, liquid crystal molecules are aligned in a direction perpendicular to the lines of electric force. FIG. 9 shows this state obtained by simulation. Here, the lines in the figure are equipotential surfaces and orthogonal to the electric field. That is, the liquid crystal is parallel to the same potential surface. In this example, since it is a simulation, the voltage of a part of the counter electrode 32 is changed to be the alignment control electrode 36. 9A shows a state where the voltage Vp of the central display electrode 12 is −4.5V, and FIG. 9B shows a state where the voltage Vp of the central display electrode 12 is + 4.5V. ing.

  Note that an opening may be provided in the counter electrode 32 and the orientation control electrode 36 may be disposed in the opening so as to correspond to this simulation. In this case, the alignment control electrode 36 and the counter electrode 32 need to be insulated.

  Thus, by providing the alignment control electrode 36, the equipotential surface (lines of electric force) can be reliably controlled and the alignment of the liquid crystal can be aligned.

  In particular, the display area is basically divided into four areas by the orientation control electrode 36 having a shape as shown in FIG. 1, and the orientation of the liquid crystal 20 is controlled in different directions to achieve a wide viewing angle display. it can.

Each voltage can also be set as follows.
[Equation 2]
(I) The signs of (Vp−Vc) and (Vp−Va) are opposite.

  For example, when (Vp−Vc) is + 4.5V, (Vp−Va) is −1V. According to this setting, an electric field from the display electrode 12 to the alignment control electrode 36 is generated, and the alignment of the liquid crystal is controlled.

  FIG. 5 shows another configuration example. In this example, the counter electrode 32 is patterned and has an opening similar to the alignment control electrode 36 of FIG. 1 described above. That is, each pixel has an opening having a shape in which a Y-shape and an inverted Y-shape are connected in the vertical direction. An alignment control electrode 36 is formed on the back side of the opening of the counter electrode 32 via an insulating film 34. In this example, the insulating film 34 is formed over the entire surface of the alignment control electrode 36, and an acrylic resin-based organic film having a high leveling ability is suitable.

  According to such a configuration, an electric field from the edge of the opening of the counter electrode 32 to the alignment control electrode 36 is generated. This makes it possible to positively control the alignment of the liquid crystal 20 rather than simply providing an opening.

  Here, it is preferable to provide two capacitor lines for one row and invert the voltages of the two capacitor lines for each frame with opposite polarities. This configuration will be described below.

  FIG. 6 shows a schematic configuration of an embodiment in which two capacity lines are provided. The pixel circuit 1 is arranged in a matrix over the entire display area. The matrix arrangement may be a zigzag shape instead of a perfect lattice shape. The display may be monochrome or full color, and in the case of full color, the normal pixels are three colors of RGB, but it is also preferable to add pixels of a specific color including white as necessary.

  As shown in the drawing, one pixel circuit 1 includes an n-channel pixel TFT 110 having a drain connected to the data line DL, a liquid crystal element 112 connected to the source of the pixel TFT 110, and a storage capacitor 114. . A gate line GL arranged for each horizontal scanning line is connected to the gate of the pixel TFT 110.

  The liquid crystal element 112 is configured such that a pixel electrode provided individually for each pixel is connected to the source of the pixel TFT 110, and a common electrode common to all the pixels is disposed opposite to the pixel electrode with the liquid crystal interposed therebetween. The common electrode is connected to the common electrode power source Vc.

  In the storage capacitor 114, the extended portion of the semiconductor layer that constitutes the source of the pixel TFT 110 is directly used as one electrode, and a part of the capacitor line SC that is formed to face the oxide film via the oxide film serves as a counter electrode. Note that the portion that becomes the electrode of the storage capacitor 114 may be separated from the portion of the pixel TFT 110 as another semiconductor layer, and both may be connected by metal wiring.

  Here, there are two capacitance lines SC, SC-A and SC-B, for one row (horizontal scanning line), and the storage capacitance of each pixel circuit is SC-A and SC-B in the horizontal scanning direction. Are connected alternately. In the pixel circuit shown in this figure, the storage capacitor 114 is connected to the capacitor line SC-A, and the storage capacitor 114 of the adjacent pixel is connected to the capacitor line SC-B.

  A vertical driver 120 is connected to the gate line GL, and the vertical driver 120 sequentially selects the gate lines GL one by one for each horizontal period and sets them to the H level. The vertical driver 120 has a shift register, receives a signal STV indicating the start of one vertical scanning period, sets the first stage of the shift register to the H level, and then shifts the H level one by one by a clock signal, for example. Thus, the gate lines GL of each horizontal scanning line are sequentially selected one by one and set to the H level. Here, for example, the H level of the gate line GL is the VDD potential, the L level is the VSS potential, and these power supply voltages VDD and VSS are supplied to the vertical driver 120, thereby the gate line GL as the output of the vertical driver. H level and L level are set.

  The SC driver 122 outputs two voltage levels to the two storage capacitor lines SC-A and SC-B.

  Although not shown, the display device is also provided with, for example, a horizontal driver, and controls line-sequential supply of the input video signal to the data line DL. That is, in this example, the horizontal driver outputs a sampling clock for each pixel in accordance with the clock of the video signal for each pixel, and the video signal (data signal) for one horizontal scanning line is turned on / off by this sampling clock. Latch. Then, a data signal for each pixel of one latched horizontal scanning line is output to the data line DL over one horizontal scanning period.

  Actually, there are three types of video signals, RGB, and each pixel in the vertical direction is one of the same color pixels of R, G, and B. Therefore, a data signal of any one of RGB is set in the data line DL.

  In the apparatus of this embodiment, a dot inversion AC application method is employed. That is, in each pixel (dot) in the horizontal scanning direction, a voltage applied to the pixel electrode of the liquid crystal element 112 is applied as a data signal having a polarity opposite to the voltage Vc of the common electrode.

  The left side of FIG. 7 shows a data signal with the first polarity, and the hypotenuse of the triangle written as Vvideo indicates a data signal (write voltage) corresponding to the luminance. The data signal has a potential difference (dynamic range) of Vb from the black level to the white level, and the voltage applied to the pixel electrode after the voltage shift is white when the voltage is separated from Vc as the center and black when the voltage is close. It has become. Therefore, in this example, the black level is Vc−Vb / 2 and the white level is Vc + Vb / 2. Further, as shown on the right side of FIG. 7, the adjacent pixels have the second polarity opposite to the first polarity, and the black level is Vc + Vb / 2 and the white level is Vc−Vb / 2. ing.

  Then, as shown in FIG. 8, after the ON period to the pixel TFT 110 ends and data writing ends, the capacitance lines SC-A and SC-B shift by a predetermined voltage ΔVsc. In this example, a normally black vertical alignment (VA) type liquid crystal is used as the liquid crystal. For the pixel on the left side of FIG. 7, the capacitor line SC-A is connected, and Vsc is shifted in the higher voltage direction by ΔVsc. For the pixel on the right side of FIG. 7, the capacitor line SC-B is connected, and Vsc is shifted in the direction of decreasing the voltage by ΔVsc.

  As a result, as shown in FIG. 8, the data signal applied to the pixel electrode is shifted by a voltage corresponding to ΔVsc, and this is applied to Vc. Here, ΔVsc is set to a voltage corresponding to the threshold voltage Vath at which the change in transmittance according to the applied voltage of the liquid crystal starts, and display by the liquid crystal element 112 is possible by the voltage after the shift. Become. The dynamic range of the data signal is set so that the shifted dynamic range is a potential difference from the black level to the white level in the display.

  In FIG. 7, Va (W) is the shift amount of the white level data signal, and Va (B) is the shift amount of the black level data signal, and these shift amounts are determined by ΔVsc. Vb is the potential difference (dynamic range) between the black level and the white level of the data signal, and Vb 'is the dynamic range after the shift.

  In such a circuit, as shown in FIG. 8, the voltage of the orientation control electrode 36 is changed in synchronization with the waveforms of the capacitance lines SC-A and SC-B. Thereby, the voltage applied to the alignment control electrode 36 can be controlled according to the voltage of the display electrode 12.

  That is, when the capacitor line SC-A is specifically connected to an odd-numbered pixel in one row, the reference voltage line 40a is connected to that pixel, and the same polarity is applied to the counter electrode 32 voltage Vc. As a result, the control shown in the above equation 1 can be performed.

  On the other hand, when the capacitor line SC-A is connected to an odd-numbered pixel in a specific row, the reference voltage line 40b is connected to the pixel, and the voltage of the counter electrode 32 is set to have a different polarity with respect to Vc. To do. As a result, the control shown in the above equation 2 can be performed.

It is a top view which shows arrangement | positioning of the orientation control electrode of the liquid crystal display device which concerns on embodiment. It is AA sectional drawing in FIG. It is a figure which shows the voltage etc. of a reference voltage line. It is a figure which shows the polarity for every pixel. It is sectional drawing which shows other embodiment. It is a figure which shows the structure of the pixel circuit which has two capacity lines SC-A and SC-B. It is a figure explaining operation | movement of the circuit of FIG. It is a figure which shows the timing of the voltage change in the circuit of FIG. It is a figure which shows the orientation state of a liquid crystal.

Explanation of symbols

  10 TFT substrate, 12 display electrode, 14, 38 alignment film, 20 liquid crystal, 30 counter substrate, 32 counter electrode, 34 insulating film, 36 alignment control electrode, 40a, 40b reference voltage line, 112 liquid crystal element, 114 storage capacitor, 120 Vertical driver, 122 SC driver.

Claims (9)

A display electrode;
A counter electrode disposed opposite to the display electrode;
A liquid crystal that is disposed between the display electrode and the counter electrode and whose optical characteristics are controlled by a voltage applied between the display electrode and the counter electrode;
The display electrode and the counter electrode are independently controlled in potential, and an alignment control electrode that controls the alignment of the liquid crystal;
A liquid crystal display device comprising: The liquid crystal display device according to claim 1.
A liquid crystal display device having the following relationships (i) and (ii), where Va is the potential of the alignment control electrode, Vc is the potential of the counter electrode, and Vp is the potential of the display electrode.
(I) The signs of (Vp−Vc) and (Vp−Va) are the same. (Ii) | (Vp−Vc) |> | (Vp−Va) | The liquid crystal display device according to claim 1 or 2,
The liquid crystal display device according to claim 1, wherein the control voltage is a voltage equal to or lower than a threshold voltage of change in optical characteristics of the liquid crystal. The liquid crystal display device according to claim 1.
A liquid crystal display device having the following relationship (i), where Va is the potential of the alignment control electrode, Vc is the potential of the counter electrode, and Vp is the potential of the display electrode.
(I) The signs of (Vp-Vc) and (Vp-Va) are opposite The liquid crystal display device according to claim 1,
An alignment film for aligning the liquid crystal in the vertical direction without rubbing is provided on the surface side of the display electrode and the counter electrode that contacts the liquid crystal, and the liquid crystal is VA (Virtical Alignment) liquid crystal. Liquid crystal display device. In the liquid crystal display device according to any one of claims 1 to 5,
The liquid crystal display device, wherein the alignment control electrode is formed on the liquid crystal surface of the counter electrode via an insulating film. In the liquid crystal display device according to any one of claims 1 to 5,
The liquid crystal display device, wherein the alignment control electrode is formed on an opposite surface of the counter electrode to the liquid crystal via an insulating film. In the liquid crystal display device according to any one of claims 1 to 7,
A display electrode and an alignment control electrode are provided for each pixel arranged in a matrix, and for the alignment control electrodes of adjacent two rows of pixels, the alignment control electrodes of every other pixel in one row and the row direction of the other row Are connected to the orientation control electrode of every other pixel shifted by one pixel, and this is connected to the first reference voltage source,
The alignment control electrodes of every other pixel not connected to the first reference power supply for every two adjacent rows shifted by one row in the column direction and every other pixel shifted by one pixel in the row direction of the other row Connected to the orientation control electrode of the pixel, and this to the second reference voltage source,
By repeating this, the alignment control electrodes of the pixels adjacent in the row direction and the column direction are sequentially connected to either one of the first or second reference voltage source. The liquid crystal display device according to claim 8.
The liquid crystal display device is characterized in that the polarity of the voltage applied to the display electrode with respect to the counter electrode is a dot inversion method in which the polarity is inverted for each pixel in the row direction.