JP2006003809A - Liquid crystal apparatus and electronic device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To optimize transmittance characteristics and the like of a liquid crystal and to obtain a display image of desired brightness. <P>SOLUTION: A plurality of scanning lines are formed on a color filter substrate, a plurality of data lines, pixel electrodes, TFD elements and the like are formed on an element substrate and a liquid crystal is encapsulated in between the both substrates. In this liquid crystal display, distance D1 between the pixel electrode and the data line connected to the pixel electrode is made longer than the distance D5 between the pixel electrode and the adjacent data line which is not connected to the pixel electrode to reduce a parasitic capacitance Cp. Thereby, voltage V1c given to the pixel electrode from the data line side during a retention period by division of a capacity ratio can be made low and the display image wherein the transmittance characteristics and the like of the liquid crystal are optimized and which has desired brightness can be obtained. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a liquid crystal device and an electronic apparatus suitable for use in displaying various information.

  Currently, liquid crystal devices are widely used in electronic devices such as mobile phones, personal digital assistants, PDAs (Personal Digital Assistants), and the like. For example, a liquid crystal device is used as a display unit for displaying various information related to electronic devices. The liquid crystal device includes an active matrix type liquid crystal device using a three-terminal type switching element such as a TFT (Thin Film Transistor) element and an active matrix type liquid crystal device using a two-terminal type switching element such as a TFD element. There are various types such as a liquid crystal device and a passive matrix type liquid crystal device that does not use a switching element.

  In an active matrix liquid crystal device using a TFD element, for example, a dot electrode and a strip electrode are opposed to each other and a liquid crystal layer is interposed between the electrodes. In addition, a TFD element is connected to the dot electrode (see, for example, Patent Document 1). In this liquid crystal device, a plurality of display dot areas are individually lit by transmitting a scanning signal to one of the dot-shaped electrode and the band-shaped electrode and transmitting a data signal to the other. Further, white display (transmission), black display (non-transmission), and intermediate color display are selected by adjusting the relationship between the pulse width of the scanning signal and the pulse width of the data signal. However, in the conventional liquid crystal device using the TFD element, the brightness of the obtained display may be insufficient.

JP 2002-328627 A (pages 3 to 4, FIG. 1)

  The present invention provides a liquid crystal device capable of optimizing the transmittance characteristics and the like of liquid crystal by appropriately setting the liquid crystal capacity and the VT characteristic, and obtaining a display image having a desired brightness, and an electronic apparatus using the same. The issue is to provide.

The present inventor conducted various considerations and experiments in order to solve the above problems. As a result, it was found that the brightness of the obtained display is greatly influenced by the liquid crystal capacitances Clc and C ′ _TFD in the liquid crystal device. Here, C ′ _TFD is an element capacitance C _TFD of the two-terminal switching element, and a parasitic capacitance Cp generated between the pixel electrode and the data line Vd connected to the pixel electrode via the two-terminal switching element. Is the sum of Furthermore, it has been found that the relationship between the capacitance characteristics and the VT characteristics (voltage-transmittance characteristics) greatly affects display brightness. Based on this, the present invention makes it possible to optimize the transmittance characteristics of the liquid crystal by appropriately setting the liquid crystal capacitance Clc, C ′ _TFD and VT characteristics, respectively, and to obtain a display image having a desired brightness. .

In one aspect of the present invention, a liquid crystal device in which liquid crystal is sealed between a first substrate having a data line, a two-terminal element and a pixel electrode, and a second substrate having a scanning line is provided on the two-terminal element. The element capacitance is C _TFD , the liquid crystal capacitance of the liquid crystal sandwiched between the scanning line and the pixel electrode is Clc, and the data line and the pixel electrode connected to the pixel electrode via the two-terminal element Cp is a parasitic capacitance generated between Vd, the amplitude voltage of the data line is Vd, the sum of the element capacitance C _TFD of the two-terminal element and the parasitic capacitance Cp is C ′ _TFD , and transmission in the voltage-transmittance characteristics of the liquid crystal When the voltage corresponding to 50% is V (T50), the parasitic capacitance Cp is the distance between the pixel electrode and the data line connected to the pixel electrode via the two-terminal element. Inversely proportional to the liquid crystal Voltage Vlc applied is set so as to satisfy the _{Vlc = {C 'TFD / (} Clc + C' TFD)} × Vd <V (T50).

  According to the above liquid crystal device, a data line, a two-terminal element such as a thin film diode, and a pixel electrode are formed on the first substrate, while a scanning line is formed on the second substrate. In this liquid crystal device, in order to display a desired image, a desired voltage is applied from the data line to the pixel electrode via the two-terminal element in the line selection period. However, since a parasitic capacitance Cp exists between the pixel electrode and the data line connected to the pixel electrode via the two-terminal element, the liquid crystal sandwiched between the pixel electrode and the scanning line facing the pixel electrode is parasitic from the data line. A voltage corresponding to the capacitance Cp is applied, and as a result, the voltage of the liquid crystal changes from a desired potential. In particular, when this liquid crystal device is a liquid crystal device having a normally white display mode, the voltage applied from the data line to the pixel electrode by the capacitance ratio division increases due to the parasitic capacitance Cp during the holding period Th. The liquid crystal transmittance is reduced.

Therefore, in this liquid crystal device, the element capacitance of the two-terminal element is C _TFD , the liquid crystal capacitance of the liquid crystal sandwiched between the scanning line facing the pixel electrode is Clc, and the data line connected to the pixel electrode via the two-terminal element Cp is a parasitic capacitance generated between the pixel electrode and the pixel electrode, Vd is the amplitude voltage of the data line, C ′ _TFD is the sum of the element capacitance C _TFD and the parasitic capacitance Cp of the two-terminal element, and the voltage-transmittance characteristics of the liquid crystal When the voltage corresponding to the transmittance of 50% is V (T50), the parasitic capacitance Cp is inversely proportional to the distance between the pixel electrode and the data line connected to the pixel electrode via a two-terminal element. The voltage Vlc applied to the liquid crystal is set so as to satisfy Vlc = {C ′ _TFD / (Clc + C ′ _TFD )} × Vd <V (T50).

  Thereby, the voltage Vlc applied to the liquid crystal during the holding period can be accurately suppressed to an allowable value or less. Therefore, the transmittance of the liquid crystal can be optimized, and a display image with a desired brightness can be obtained. In particular, when a low voltage (a voltage corresponding to white) is applied to the pixel electrode through the data line during the selection period, it is possible to suppress application of a high voltage to the liquid crystal during the holding period. The white display image having a desired brightness can be obtained.

  In one aspect of the liquid crystal device, the first substrate includes a transparent substrate having translucency, and the data line, the two-terminal element, and the pixel electrode are each formed on the transparent substrate, and the pixel The distance between the electrode and the data line connected to the pixel electrode via the two-terminal element is greater than the distance between the pixel electrode and the adjacent data line not connected to the pixel electrode. Yes.

According to this aspect, the first substrate includes the transparent substrate having translucency. In this liquid crystal device, the data line, the two-terminal element, and the pixel electrode are each formed on a transparent substrate. Further, the distance between the pixel electrode and the data line connected to the pixel electrode via the two-terminal element is larger than the distance between the pixel electrode and the adjacent data line not connected to the pixel electrode. Yes. For this reason, the parasitic capacitance Cp becomes small. As a result, in the above formula Vlc = {C ′ _TFD / (Clc + C ′ _TFD )} × Vd <V (T50), C ′ _TFD can be reduced, so that the voltage Vlc applied to the liquid crystal can be reduced. Can do. Therefore, the transmittance of the liquid crystal can be optimized, and a display image with a desired brightness can be obtained.

  In another aspect of the liquid crystal device, the first substrate includes a transparent substrate having translucency and an insulating film having a contact hole and formed on the transparent substrate, and the data line and the second substrate are provided. The terminal element is formed on the transparent substrate so as to be covered with the insulating film, and the pixel electrode is formed on the insulating film at a position overlapping the data line. The parasitic capacitance Cp is defined based on the thickness of the insulating film.

According to this aspect, the first substrate includes the transparent substrate having translucency and the insulating film having the contact hole and formed on the transparent substrate. In this liquid crystal device, the data line and the two-terminal element are formed on the transparent substrate while being covered with the insulating film, while the pixel electrode is formed on the insulating film and at a position overlapping the data line. In the state, it is connected to a two-terminal element through a contact hole. Thus, this liquid crystal device has a so-called overlayer structure. The parasitic capacitance Cp is defined based on the thickness of the insulating film. In a preferred example, the parasitic capacitance Cp can be reduced by increasing the thickness of the insulating film formed on the transparent substrate and increasing the distance between the pixel electrode and the data line connected thereto as much as possible. As a result, in the above formula Vlc = {C ′ _TFD / (Clc + C ′ _TFD )} × Vd <V (T50), C ′ _TFD can be reduced, so that the voltage Vlc applied to the liquid crystal can be reduced. Can do. Therefore, the transmittance of the liquid crystal can be optimized, and a display image with a desired brightness can be obtained.

  In another aspect of the liquid crystal device, the first substrate includes a transparent substrate having translucency and an insulating film having a contact hole and formed on the transparent substrate, and the data line and the second substrate are provided. The terminal element is formed on the transparent substrate while being covered with the insulating film, and the pixel electrode is formed on the insulating film and between the data lines. It is connected to the two-terminal element through a hole, and the parasitic capacitance Cp is defined based on the thickness of the insulating film.

According to this aspect, the first substrate includes the transparent substrate having translucency and the insulating film having the contact hole and formed on the transparent substrate. In this liquid crystal device, the data lines and the two-terminal elements are formed on the transparent substrate while being covered with the insulating film, and the pixel electrodes are formed on the insulating film and between the data lines. In this state, it is connected to a two-terminal element through a contact hole. Thus, this liquid crystal device has a so-called overlayer structure. The parasitic capacitance Cp is defined based on the thickness of the insulating film. In a preferred example, the parasitic capacitance Cp can be reduced by increasing the thickness of the insulating film formed on the transparent substrate and increasing the distance between the pixel electrode and the data line connected thereto as much as possible. In particular, in this liquid crystal device, data lines are formed at positions on both sides of the pixel electrode. For this reason, when comparing the liquid crystal device with a liquid crystal device having a structure in which the pixel electrode and the data line connected thereto overlap with each other through an insulating film, the former has a thinner insulating film than the latter, The parasitic capacitance Cp can be made as small as the latter. As a result, in the above formula Vlc = {C ′ _TFD / (Clc + C ′ _TFD )} × Vd <V (T50), C ′ _TFD can be reduced, so that the voltage Vlc applied to the liquid crystal can be reduced. Can do. Therefore, the transmittance of the liquid crystal can be optimized, and a display image with a desired brightness can be obtained.

  In addition, an electronic device including the above-described liquid crystal display device can be configured.

The best mode for carrying out the present invention will be described below with reference to the drawings. In the following embodiments, the present invention is applied to a liquid crystal display device. In each of the embodiments of the present invention, the liquid crystal capacitance Clc, C ′ _TFD, and VT characteristics are appropriately set to optimize the liquid crystal transmittance characteristics and obtain a display image having a desired brightness.

[First embodiment]
(Configuration of the liquid crystal display device 100)
First, the configuration of the liquid crystal display device according to the first embodiment of the present invention will be described. FIG. 1 is a plan view schematically showing a schematic configuration of the liquid crystal display device 100 according to the first embodiment. In FIG. 1, the configuration of electrodes and wirings of the liquid crystal display device 100 is mainly shown as a plan view. Here, the liquid crystal display device 100 according to the first embodiment is an active matrix driving method using a TFD element, and is a transflective liquid crystal display device. The liquid crystal display device 100 according to the first embodiment is also a liquid crystal display device having a normally white display mode. FIG. 2 is a schematic cross-sectional view along the cutting line AA ′ in the liquid crystal display device 100 of FIG.

  First, the cross-sectional configuration of the liquid crystal display device 100 taken along the cutting line A-A ′ will be described with reference to FIG.

  In FIG. 2, the liquid crystal display device 100 includes an element substrate 92 and a color filter substrate 91 disposed so as to face the element substrate 92 with a frame-shaped seal member 3 interposed therebetween, and liquid crystal is sealed inside. Thus, the liquid crystal layer 4 is formed. A conductive member 7 such as a plurality of gold particles is mixed in the frame-shaped seal member 3. The element substrate 92 includes a transparent substrate 1 such as glass (hereinafter also referred to as “upper substrate”), and the color filter substrate 91 includes a transparent substrate 2 such as glass (hereinafter also referred to as “lower substrate”). .

  On the inner surface of the lower substrate 2, a scattering layer 9 having fine irregularities formed on the surface is formed. On the inner surface of the scattering layer 9, a reflective layer 5 having a predetermined thickness is formed for each subpixel SG. A plurality of rectangular openings 20 (hereinafter also referred to as “transparent areas”) are formed in each reflective layer 5. Each reflective layer 5 can be formed of a thin film such as aluminum, an aluminum alloy, or a silver alloy. The opening 20 is formed so as to have an area of a predetermined ratio with respect to the total area of the sub-pixel SG for each sub-pixel SG arranged in a matrix in the vertical and horizontal directions on the inner surface of the color filter substrate 91.

  On the reflective layer 5 and between the sub-pixels SG, a black light-shielding layer BM is provided between the adjacent sub-pixels SG to prevent light from entering from one sub-pixel to the other sub-pixel. Is formed. The black light shielding layer BM can be made of a black resin material, for example, a black pigment dispersed in a resin. Instead of this, an overlapping light shielding layer (not shown) formed by overlapping R, G, and B colored layers may be used.

  On the reflective layer 5 and the opening 20, colored layers 6R, 6G, and 6B made of any of the three colors R, G, and B are formed for each subpixel SG. A color filter is constituted by the colored layers 6R, 6G, and 6B. A pixel G indicates a region for one color pixel composed of R, G, and B sub-pixels SG. In the following description, when referring to a colored layer regardless of color, it is simply referred to as “colored layer 6”, and when referring to a colored layer by distinguishing colors, it is referred to as “colored layer 6R” or the like. Further, as shown in FIG. 2, the thickness of the colored layer 6 formed on the opening 20 is formed to be thicker than the thickness of the colored layer 6 formed on the reflective layer 5. Thus, the colored layer 6 is designed to exhibit a desired hue and brightness in the reflective display mode and the transmissive display mode, respectively.

  A protective layer 18 made of a transparent resin or the like is formed on the colored layer 6 and the black light shielding layer BM. The protective layer 18 has a function of protecting the colored layer 6 from corrosion and contamination caused by chemicals used during the manufacturing process of the color filter substrate 91 and the liquid crystal display device 100. On the surface of the protective layer 18, a transparent electrode (scanning electrode) 8 (hereinafter also referred to as “scanning line of the lower substrate 2”) such as striped ITO (Indium-Tin Oxide) is formed. One end of the transparent electrode 8 extends into the seal member 3 and is electrically connected to the conducting member 7 in the seal member 3.

  On the other hand, the TFD element 21 and the pixel electrode 10 are formed on the inner surface of the upper substrate 1 for each subpixel. A protective layer 17 made of transparent resin or the like is formed on the inner surfaces of the TFD element 21 and the pixel electrode 10. Scan lines 31 are formed on the left and right peripheral edge portions on the inner surfaces of the upper substrate 1 and the protective layer 17. One end of the scanning line 31 extends into the seal member 3, and the scanning line 31 is electrically connected to the conduction member 7 in the seal member 3.

  An alignment film (not shown) is formed on the inner surface of the transparent electrode 8 of the lower substrate 2 and the inner surface of the protective layer 17 of the upper substrate 1. In order to keep the thickness of the liquid crystal layer 4 uniform between these alignment films, particulate spacers (not shown) are randomly arranged. As a material for the spacer, a material mainly composed of silica or resin is preferable.

  A retardation plate (¼ wavelength plate) 11 and a polarizing plate 12 are arranged on the outer surface of the lower substrate 2, and a retardation plate (¼ wavelength plate) on the outer surface of the upper substrate 1. 13 and a polarizing plate 14 are arranged. A backlight 15 is disposed below the polarizing plate 12. The backlight 15 is preferably a point light source such as an LED (Light Emitting Diode) or a linear light source such as a cold cathode fluorescent tube.

  The transparent electrode 8 of the lower substrate 2, that is, the scanning line of the lower substrate 2, and the scanning line 31 of the upper substrate 1 are vertically connected via the conductive member 7 mixed in the seal member 3.

  When the reflective display is performed in the liquid crystal display device 100 of the present embodiment, the external light incident on the liquid crystal display device 100 travels along the path R shown in FIG. That is, the external light incident on the liquid crystal display device 100 is reflected by the reflective layer 5 and reaches the observer. In this case, the external light passes through the region where the colored layer 6 is formed, is reflected by the reflective layer 5 below the colored layer 6, and passes through the colored layer 6 again to have a predetermined hue. And brightness. Thus, a desired color display image is visually recognized by the observer.

  On the other hand, when transmissive display is performed, the illumination light emitted from the backlight 15 travels along the path T shown in FIG. 1 and is observed through the transparent region, that is, the colored layer 6 on the opening 20. To the person. In this case, the illumination light has a predetermined hue and brightness by passing through the colored layer 6. Thus, a desired color display image is visually recognized by the observer.

  Next, with reference to FIG. 1, FIG. 3, and FIG. 4, the configuration of the electrodes and wirings of the element substrate 92 and the color filter substrate 91 of the present invention will be described. FIG. 3 is a plan view showing a configuration of electrodes, wirings, and the like of the element substrate 92 when the element substrate 92 is observed from the back direction (ie, the lower side in FIG. 2). FIG. 4 is a plan view showing the configuration of the electrodes of the color filter substrate 91 when the color filter substrate 91 is observed from the front direction (that is, the upper side in FIG. 2). In FIG. 3, the electrodes and wirings are formed on the back side in the observation direction, but are represented by solid lines for convenience of explanation. 3 and 4, other elements other than the electrodes and wiring are not shown for convenience of explanation.

  In FIG. 1, a region where the pixel electrode 10 of the element substrate 92 and the transparent electrode 8 of the color filter substrate 91 intersect constitute a sub-pixel SG which is the minimum unit of display. A region in which a plurality of the sub-pixels SG are arranged in a matrix in the vertical direction and the horizontal direction in the drawing is a display region V (region surrounded by a two-dot chain line). In the display area V, images such as letters, numbers, and figures are displayed. In FIG. 1, an area defined by the outer shape of the liquid crystal display device 100 and the display area V is a frame area 38 that does not contribute to image display.

  First, with reference to FIG. 3, the structure of the electrode and wiring of the element substrate 92 will be described. The element substrate 92 includes a TFD element 21, a pixel electrode 10, a plurality of scanning lines 31, a plurality of data lines 32, a Y driver IC 33, an X driver IC 34, and a plurality of external connection terminals 35.

  On the projecting region 36 of the element substrate 92, a Y driver IC 33 and an X driver IC 34 are mounted, for example, via an ACF (Anisotropic Conductive Film). In FIG. 3, the direction from the side 92a on the projecting region 36 side of the element substrate 92 to the side 92c on the opposite side is defined as the X direction, and the direction from the side 92d to the side 92b is defined as the Y direction.

  A plurality of external connection terminals 35 are formed on the overhang region 36. Each input terminal (not shown) of the Y driver IC 33 and the X driver IC 34 is connected to the plurality of external connection terminals 35 through conductive bumps. The external connection terminal 35 is connected to a wiring board (not shown) such as a flexible printed board via ACF or solder. Thereby, for example, signals and power are supplied to the liquid crystal display device 100 from an electronic device such as a mobile phone or an information terminal.

  The output terminal (not shown) of the X driver IC 34 is connected to the plurality of data lines 32 through conductive bumps. On the other hand, the output terminal (not shown) of each Y driver IC 33 is connected to the plurality of scanning lines 31 via conductive bumps. Accordingly, each Y driver IC 33 outputs a scanning signal to the plurality of scanning lines 31, and the X driver IC 34 outputs a data signal to the plurality of data lines 32.

  The plurality of data lines 32 are linear wirings extending in the vertical direction on the paper surface, and are formed in the X direction from the overhanging region 36 to the display region V. Each data line 32 is formed at a constant interval. Each data line 32 is connected to a plurality of TFD elements 21 at appropriate intervals, and each TFD element 21 is connected to a corresponding pixel electrode 10.

  The plurality of scanning lines 31 includes a main line portion 31a and a bent portion 31b that bends at substantially right angles to the main line portion 31a. Each main line portion 31 a is formed in the X direction from the overhanging region 36 in the frame region 38. Each main line portion 31a is formed substantially parallel to each data line 32 and at a predetermined interval. Each bent portion 31b extends in the Y direction to the inside of the seal member 3 located on the left and right in the frame region 38. The end portion of the bent portion 31 b is connected to the conductive member 7 in the seal member 3.

  Next, the configuration of the electrodes of the color filter substrate 91 will be described. The color filter substrate 91 has stripe-shaped transparent electrodes (scanning electrodes) 8 formed in the Y direction. As shown in FIGS. 1 and 4, the left end portion or the right end portion of each transparent electrode 8 extends into the seal member 3 and is connected to the conduction member 7 in the seal member 3.

  FIG. 1 shows a state where the color filter substrate 91 and the element substrate 92 are bonded together via the seal member 3 as described above. As shown in the figure, each transparent electrode 8 of the color filter substrate 91 is orthogonal to each data line 32 of the element substrate 92 and overlaps the plurality of pixel electrodes 10 in a row in a plane. Thus, the region where the transparent electrode 8 and the pixel electrode 10 overlap constitutes the sub-pixel SG.

  Further, the transparent electrode 8 (that is, the scanning line on the color filter substrate 91 side) of the color filter substrate 91 and the scanning line 31 of the element substrate 92 alternately overlap between the left side and the right side as shown in the figure. The transparent electrode 8 and the scanning line 31 are vertically connected via the conductive member 7 in the seal member 3. That is, conduction between each scanning line of the color filter substrate 91 as the transparent electrode 8 and each scanning line 31 of the element substrate 92 is alternately realized between the left side and the right side as shown in the figure. Thereby, the transparent electrode 8 of the color filter substrate 91 is electrically connected to the Y driver ICs 33 located on the left and right sides of the paper via the scanning lines 31 of the element substrate 92.

  Next, a gradation display method in the liquid crystal display device 100 will be described with reference to FIG. FIG. 5A shows a driving waveform of the scanning potential VA applied to the scanning electrode 8 from the Y driver IC 33 via the scanning line 31. FIG. 5B shows a drive waveform of the signal potential VB applied from the X driver IC 34 to the data line 32. FIG. 5C shows a driving waveform of the interelectrode voltage VAB of the scanning electrode 8 and the data line 32.

  The Y driver IC 33 applies a scanning potential VA to the scanning electrode 8 through the scanning line 31. On the other hand, the X driver IC 34 applies the signal potential VB to the data line 32. The potentials VA and VB will be described. First, a scanning potential VA as shown in FIG. 5A is applied to the scanning electrode 8. For each line selection period T, each scanning electrode 8 is sequentially selected via each scanning line 31, and a potential difference of ± Vsel with respect to a certain common potential VGND, that is, any potential having a voltage is applied. This voltage Vsel is called a selection voltage. Then, after the line selection period T, any potential having a voltage of ± Vhld with respect to the common potential VGND is applied. In the holding period Th, when the potential at the time of selection is VGND + Vsel, the potential of VGND + Vhld is applied, and when the potential at the time of selection is VGND-Vsel, the potential of VGND-Vhld is applied. This voltage Vhld is called a holding voltage. A period in which all the scan electrodes 8 are selected in a round is called a field period. In the next field period, the scan electrodes are sequentially selected using a selection voltage having a characteristic opposite to that of the previous field period. .

  On the other hand, as shown in FIG. 5B, any potential having a voltage of ± Vsig with respect to the common potential VGND is applied to the data line 32. Here, when the potential applied to the scan electrode 8 selected in a certain selection period is VGND + Vsel, VGND−Vsig is used as the ON potential Von, and VGND + Vsig is used as the OFF potential Voff. Further, when the potential applied to the scan electrode 8 selected in a certain selection period is VGND−Vsel, VGND + Vsig is used as the on potential Von and VGND−Vsig is used as the off potential Voff.

  That is, the waveform of the signal potential VB in each line selection period T is set according to the gradation of each pixel in the column related to the data line 32. First, the signal potential VB is set for each line selection period T. Are divided into an ON section and an OFF section, and are set to the ON potential Von in the ON section and to the OFF potential Voff in the OFF section. That is, the signal potential VB is pulse width modulated according to the gradation value. Then, the higher the gradation to be given to the pixel (the darker the normally white mode), the larger the proportion occupied by the ON section.

  Next, the interelectrode voltage VAB of the scan electrode 8 and the data line 32 is indicated by a solid line in FIG. This interelectrode potential VAB is applied to the liquid crystal layer 4. As shown in the figure, it can be seen that the absolute value of the interelectrode voltage VAB increases during the selection period of the pixel. Further, the liquid crystal layer voltage VLC applied to the liquid crystal layer 4 is indicated by hatching in FIG. When the liquid layer voltage VLC changes, the capacity formed by the liquid crystal layer 4 must be charged and discharged, so the liquid crystal layer voltage VLC changes in a transient response to the interelectrode voltage VAB. In FIG. 5C, the voltage VNL is the difference between the interelectrode voltage VAB and the liquid layer voltage VLC, that is, the terminal voltage of the TFD element 21. As described above, in the liquid crystal display device 100, gradation display is performed by pulse width modulation of the driving voltage applied to the liquid crystal layer 4.

(Optimization method for transmittance characteristics of liquid crystal)
Next, with reference to FIGS. 6 to 8, a method for optimizing the transmittance characteristics of the liquid crystal in the liquid crystal display device 100 will be described. FIG. 6 shows a partially enlarged plan view in which one pixel (RGB three subpixels) in the liquid crystal display device 100 is enlarged. FIG. 7A shows, as an example, a layer cross-sectional view in which a local portion of a general transmissive liquid crystal panel is enlarged. FIG. 7B shows an example of a graph of voltage-transmittance characteristics of the liquid crystal panel.

  The pixel electrode 10 is formed between the pair of data lines 32. In particular, in the liquid crystal display device 100, the distance D1 between the pixel electrode 10 and the data line 32 connected thereto via the TFD element 21 is the distance between the pixel electrode 10 and the adjacent data line 32 not connected thereto. Although formed so as to be larger than D5, this point will be described later. The data lines 32a, 32b, and 32c are connected to the pixel electrodes 10a, 10b, and 10c via the TFD element 21. A parasitic capacitance Cp exists between the pixel electrode 10 and the data line 32 connected to the pixel electrode 10 via the TFD element 21.

  In the liquid crystal display device 100, in order to display a desired image, a desired voltage is applied to each of the pixel electrodes 10a to 10c in the line selection period T. In the example of FIG. 6, a desired voltage Vc is applied from the data line 32b to the pixel electrode 10b via the TFD element 21.

  However, since a parasitic capacitance Cp exists between the pixel electrode 10b and the data line 32b connected to the pixel electrode 10b via the TFD element 21, the liquid crystal sandwiched between the scan electrode 8 facing the pixel electrode 10b is not included in the liquid crystal. A voltage corresponding to the parasitic capacitance Cp is applied from the data line 32b, and as a result, the potential Vc of the liquid crystal changes from a desired potential.

Specifically, during the holding period Th, the voltage applied to the liquid crystal sandwiched from the data line 32b to the scanning electrode 8 facing the pixel electrode 10b, that is, the voltage Vlc caused by the parasitic capacitance Cp is:
Vlc = {C ′ _TFD / (Clc + C ′ _TFD )} × Vd (Formula 1)
It can be expressed as Here, C ′ _TFD is the sum of the element capacitance C _TFD and the parasitic capacitance Cp of one TFD element, Clc is the liquid crystal capacitance of one pixel electrode, and Vd is the data amplitude voltage applied to the data line. is there.

  As described above, the liquid crystal display device 100 is a liquid crystal panel having a normally white display mode. Therefore, as the voltage Vlc in Equation 1 increases, the voltage applied from the data line 32b to the pixel electrode 10b by the capacity ratio division during the holding period Th increases, and the transmittance of the liquid crystal decreases. In particular, when a low voltage (a voltage corresponding to white) is applied to the data line 32b during the line selection period T and the high voltage Vlc is applied to the pixel electrode 10b during the holding period Th, the effective voltage of the liquid crystal increases. Therefore, the transmittance of the liquid crystal is reduced. This makes it difficult to obtain a display image having a desired brightness. Therefore, in order to obtain a display image having a desired brightness, due to the parasitic capacitance Cp, the liquid crystal sandwiched between the scanning electrode 8 facing the pixel electrode 10 from the data line 32 connected to the pixel electrode 10 is applied. It is necessary to suppress the applied voltage Vlc to a certain level.

  Therefore, in the first embodiment, the voltage Vlc is regulated to a certain level. Specifically, it is desirable to determine the upper limit value of the voltage Vlc in relation to the applied voltage value in the voltage-transmittance characteristics as shown in FIG. Here, voltage-transmittance characteristics of a general transmissive liquid crystal panel will be described with reference to FIGS.

  The voltage-transmittance characteristics (so-called VT characteristics) of the liquid crystal layer 503 are expressed as in the graph of FIG. 7B, for example. In the graph shown in FIG. 7B, as shown in FIG. 7A, the light T1 is transmitted through the liquid crystal layer 503 sandwiched between the transparent electrodes 501 and 502, and the voltage V applied between the electrodes is changed. In this case, how the transmittance of the liquid crystal layer 503 changes is shown by way of an example of a normally white display mode. From this graph, it can be seen that the transmittance of the liquid crystal decreases as the voltage V applied to the liquid crystal layer 503 increases. In the graph, V (T10) indicates a voltage when the transmittance is 10%, and V (T50) indicates a voltage when the transmittance is 50%.

  In particular, in the liquid crystal display device 100 of the first embodiment, as shown in the following equation, the upper limit value of the voltage Vlc is set to be smaller than V (T50).

That is, the voltage Vlc is
Vlc = {C ′ _TFD / (Clc + C ′ _TFD )} × Vd <V (T50) (Formula 2).

Here, as a method of reducing the voltage Vlc in order to satisfy the above-described Expression 2, a method of increasing the liquid crystal capacitance Clc and / or decreasing C ′ _TFD can be considered.

Here, the general capacitance equation is
C = ε0 × ε × (S / d) (Formula 3)
It is represented by “C” is a capacitance, “ε0” is a vacuum dielectric constant, “ε” is a relative dielectric constant, “S” is an area, and “d” is an interval.

Considering the above equation 3, the method of increasing the liquid crystal capacitance Clc is as follows: (1) decrease the distance between the upper substrate 1 and the lower substrate 2, that is, the cell gap “d”; (2) dielectric of the liquid crystal layer 4 A method of increasing the rate “ε” and (3) increasing the area “S” of the pixel electrode 10 can be considered. However, since the area “S” of the pixel electrode 10 is determined to some extent for design reasons, in the present invention, the above (1) and (2) are applied rather than the above (3). preferable. As a method of reducing C ′ _TFD , a method of reducing the element capacitance C _TFD of the TFD element 21 and / or reducing the parasitic capacitance Cp is conceivable.

As a method of reducing the element capacitance C _TFD of the former TFD element 21, (1) the area “S” of the insulating film of the TFD element 21 is reduced, and (2) the film thickness “d” of the insulating film of the TFD element 21. (3) The dielectric constant “ε” of the insulating film of the TFD element 21 may be lowered. However, since the outer dimensions and the like of the TFD element 21 are determined to some extent due to process reasons and the like, there is a certain limit to reducing the element capacitance C _TFD of the TFD element 21. On the other hand, as a method of reducing the latter parasitic capacitance Cp, a method of increasing the distance between the pixel electrode 10 and the data line 32 connected to the pixel electrode 10 via the TFD element 21 can be considered.

  Therefore, in the liquid crystal display device 100, in order to satisfy the above formula 2, the cell gap “d” is decreased and the dielectric constant “ε” of the liquid crystal layer 4 is increased to increase the liquid crystal capacitance Clc. The parasitic capacitance Cp is reduced by this method. As a specific method for reducing the parasitic capacitance Cp, as shown in FIG. 6, the pixel electrode 10 is connected to the pixel electrode 10 via the TFD element 21 within a range where the design specifications can be satisfied. The distance D1 from the data line 32 is as far as possible. That is, as shown in FIG. 6, the distance D1 between the pixel electrode 10 and the data line 32 connected to the pixel electrode 10 via the TFD element 21 is within a range where the design specifications can be satisfied. The pixel electrode 10, the data line 32, and the like are formed on the inner surface of the upper substrate 1 so as to be larger than the distance D5 between the data line 32 and the adjacent data line 32 not connected thereto. As a result, as can be understood with reference to Equation 3, the distance “d” between the pixel electrode 10 and the data line 32 connected to the pixel electrode 10 via the TFD element 21 is increased, and the parasitic capacitance Cp is decreased. . Therefore, the voltage Vlc can be reduced in Equation 2 above.

  Thereby, in the liquid crystal display device 100, the voltage Vlc applied to the liquid crystal during the holding period Th can be accurately suppressed to an allowable value or less. Therefore, in the liquid crystal display device 100, the transmittance of the liquid crystal can be optimized, and a display image with a desired brightness can be obtained. In particular, when a low voltage (a voltage corresponding to white) is applied to the pixel electrode 10 through the data line 32 during the selection period Th, it is possible to suppress a high voltage from being applied to the liquid crystal during the holding period Th. Can be optimized, and a white display image with a desired brightness can be obtained.

In the above description, the case where the voltage-transmittance characteristic of the liquid crystal layer 4 is used as a reference for defining the voltage Vlc to a certain level is described. It is considered that the characteristic (so-called VR characteristic) is included. For example, as shown in FIG. 8, the voltage-reflectance characteristic supplies light R <b> 1 reflected by the reflective film 504 to the liquid crystal layer 503 sandwiched between the transparent electrodes 501 and 502, and a voltage V applied between the electrodes. It shows how the reflectance of the reflected light changes when it is changed. For example, if the voltage corresponding to the reflectance of 50% is V (R50), the voltage Vlc is
Vlc = {C ′ _TFD / (Clc + C ′ _TFD )} × Vd <V (R50) (Formula 4)
Can be set to Note that V (R50) and V (T50) are not necessarily the same value. Thereby, in the liquid crystal display device 100, the reflectance of the liquid crystal can be optimized as described above, and a display image having a desired brightness can be obtained.
[Second Embodiment]
In the first embodiment, the method for optimizing the transmittance characteristics of the liquid crystal according to the present invention is applied to the liquid crystal display device 100 having no so-called overlayer structure. On the other hand, in the second embodiment, the liquid crystal display device has an overlayer structure, and the pixel electrode 10 and the data line 32 connected to the pixel electrode 10 via the TFD element 21 overlap through the overlayer. The method for optimizing the transmittance characteristics of the liquid crystal according to the present invention is applied to the liquid crystal display device having the above.

  Hereinafter, with reference to FIGS. 9 to 11, a configuration of the liquid crystal display device 200 according to the second embodiment and a method for optimizing the transmittance characteristics of the liquid crystal will be described. When the liquid crystal display device 100 of the first embodiment and the liquid crystal display device 200 of the second embodiment are compared, only the configuration of the element substrate is different between the former and the latter. Therefore, hereinafter, a configuration of the element substrate 93 and a method for optimizing the transmittance characteristics of the liquid crystal in the liquid crystal display device 200 will be described. In the following description, the same components as those of the liquid crystal display device 100 of the first embodiment are denoted by the same reference numerals, and the description thereof is simplified or omitted.

(Configuration of the liquid crystal display device 200)
First, the configuration of the liquid crystal display device according to the second embodiment of the present invention will be described. FIG. 9 shows a cross-sectional view of the liquid crystal display device 200 corresponding to the cross-sectional view of the liquid crystal display device 100 of FIG. Here, the liquid crystal display device 200 of the present invention is a liquid crystal display device having an overlayer structure. The liquid crystal display device 200 of the present invention is an active matrix driving method using a TFD element as in the first embodiment, and is a transflective liquid crystal display device. The liquid crystal display device 200 of the present invention is also a liquid crystal display device having a normally white display mode, as in the first embodiment.

  In FIG. 9, the liquid crystal display device 200 includes an element substrate 93 and a color filter substrate 91 disposed so as to be opposed to the element substrate 93 with a frame-shaped seal member 3, and a TN liquid crystal inside. Is formed to form the liquid crystal layer 4.

  A TFD element 21 and a data line 32 are formed on the inner surface of the upper substrate 1. On the inner surface of the upper substrate 1, a TFD element 21 is formed for each sub-pixel, and a plurality of TFD elements 21 arranged in the vertical direction are commonly connected to each data line 32. On the inner surface of the upper substrate 1, an insulating film made of transparent resin or the like and having an insulating property, that is, an overlayer 25 is formed. The TFD element 21 and the data line 32 are covered with the overlayer 25. The overlayer 25 has an opening, that is, a contact hole 25a for each subpixel. Each pixel electrode 10 is connected to each corresponding TFD element 21 and each data line 32 through each contact hole 25a. A protective layer 17 made of a transparent resin or the like is formed on each inner surface of the overlayer 25 and the pixel electrode 10. Scanning lines 31 are formed on the left and right peripheral edges on the inner surface of the upper substrate 1. One end of the scanning line 31 extends into the seal member 3, and the scanning line 31 is electrically connected to the conduction member 7 in the seal member 3. An alignment film (not shown) is formed on the inner surface of the protective layer 17 of the upper substrate 1. On the other hand, a phase difference plate (¼ wavelength plate) 13 and a polarizing plate 14 are arranged on the outer surface of the upper substrate 1.

  When the reflective display is performed in the liquid crystal display device 200 of the second embodiment, the external light that has entered the liquid crystal display device 200 travels along the path R shown in FIG. That is, external light incident on the liquid crystal display device 200 is reflected by the reflective layer 5 and reaches the observer. In this case, the external light passes through the region where the colored layer 6 is formed, is reflected by the reflective layer 5 below the colored layer 6, and passes through the colored layer 6 again to have a predetermined hue. And brightness. Thus, a desired color display image is visually recognized by the observer.

  On the other hand, when transmissive display is performed, the illumination light emitted from the backlight 15 travels along the path T shown in FIG. To the person. In this case, the illumination light has a predetermined hue and brightness by passing through the colored layer 6. Thus, a desired color display image is visually recognized by the observer.

(Overlayer structure)
First, an overlayer structure according to the liquid crystal display device 200 of the present invention will be described in detail with reference to FIGS. FIG. 10 is a plan view showing a layout of the plurality of pixel electrodes 10 and the like on the element substrate 93. FIG. 11A shows a cross-sectional view along the cutting line BB ′ of FIG. FIG. 11B shows an enlarged cross-sectional view of the area E1 in FIG. 11A, that is, the vicinity of the connection portion between the pixel electrode 10 and the TFD element 21 and the data line 32. Since FIG. 10 shows a configuration when the observation side is viewed from the back side, the front side in FIG. 10 and the upper side in FIG.

  The structure of the element substrate 93 in the liquid crystal display device 200 of the present invention, that is, the overlayer structure will be described. In the liquid crystal display device 200, the protective layer 17 is originally formed so as to cover the pixel electrode 10 and the overlayer 25 (see FIG. 9), but in FIG. 10 and FIG. Yes.

  A phase difference plate 13 and a polarizing plate 14 are disposed on the outer surface of the upper substrate 1. On the other hand, a TFD element 21 and a data line 32 are formed on the inner surface of the upper substrate 1.

  As shown in FIG. 11B, the TFD element 21 includes a first TFD element 21a and a second TFD element 21b. The first TFD element 21a and the second TFD element 21b include an island-shaped first metal film 322 made of tantalum tungsten or the like, and an insulating film 323 formed by anodizing the surface of the first metal film 322. And second metal films 316 and 336 formed on the surface and spaced apart from each other. Among these, the second metal films 316 and 336 are formed by patterning the same conductive film such as chromium, and the former second metal film 316 is branched from the data line 21 in a T shape, The latter second metal film 336 is used for connection to the connection portion 10z of the pixel electrode 10 such as ITO.

  Here, among the TFD elements 21, the first TFD element 21 a becomes the second metal film 316 / insulating film 323 / first metal film 322 in order when viewed from the data line 32 side. Due to the body / metal structure, the current-voltage characteristics are nonlinear in both positive and negative directions. On the other hand, when viewed from the data line 32 side, the second TFD element 21b becomes a first metal film 322 / insulating film 323 / second metal film 336 in the order opposite to the first TFD element 21a. The structure of For this reason, the current-voltage characteristics of the second TFD element 21b are obtained by making the current-voltage characteristics of the first TFD element 21a point-symmetric with respect to the origin. As a result, the TFD element 21 has a shape in which two TFDs are connected in series in opposite directions. Therefore, the current-voltage nonlinear characteristic is symmetric in both positive and negative directions compared to the case of using one element. become.

  Further, as shown in FIG. 11B, a first metal film 312 and an insulating film 313 are formed from the upper substrate 1 below the data line 32. As shown in FIG. 10, the data lines 32a, 32b, and 32c are disposed at positions overlapping the pixel electrode 10 below the pixel electrodes 10a, 10b, and 10c, respectively.

  Further, an overlayer 25 is formed on the inner surface of the upper substrate 1, and the TFD element 21 and the data line 32 are covered with the overlayer 25. The overlayer 25 has a substantially circular opening, that is, a contact hole 25a in plan view.

  The pixel electrodes 10 are arranged in a matrix on the inner surface of the overlayer 25. The pixel electrodes 10a, 10b, and 10c are opposed to the colored layers 6 corresponding to B (blue), R (red), and G (green) colors, respectively. Each pixel electrode 10 has a connection portion 10 z that extends into the contact hole 25 a and is electrically connected to the TFD element 21. The connection portion 10z of each pixel electrode 10 is connected to the second metal film 336 of the corresponding TFD element 21 through the contact hole 25a. The pixel electrodes 10 belonging to the same column are commonly connected to one data line 32 via the TFD elements 21. In addition, the pixel electrodes 10 belonging to the same row face one transparent electrode 8 (scanning line).

(Optimization method for transmittance characteristics of liquid crystal)
The method for optimizing the transmittance characteristics of the liquid crystal in the liquid crystal display device 200 is basically the same as in the first embodiment. That is, in the liquid crystal display device 200, by satisfying the above formula 2, the voltage Vlc applied to the liquid crystal during the holding period Th is accurately suppressed to an allowable value or less, and the transmittance characteristics and the like of the liquid crystal are optimized. A display image having a desired brightness is obtained.

Therefore, in order to satisfy the above equation 2, it is necessary to reduce the voltage Vlc. For this purpose, the liquid crystal capacitance Clc must be increased and / or C ′ _TFD must be decreased.

  In the liquid crystal display device 200, the cell gap “d” is decreased and / or the dielectric constant “ε” of the liquid crystal is increased, as in the liquid crystal display device 100 of the first embodiment, in order to increase the liquid crystal capacitance Clc. Further, in the liquid crystal display device 200, the data line 32 and the pixel electrode 10 are not provided on the same plane, so that the area “S” of the pixel electrode 10 is increased to some extent as compared with the liquid crystal display device 100 of the first embodiment. can do. As a result, as understood with reference to Equation 3 above, the liquid crystal capacitance Clc of the liquid crystal display device 200 of the second embodiment may be made larger than the liquid crystal capacitance Clc of the liquid crystal display device 100 of the first embodiment. it can.

In order to reduce C ′ _TFD , as described above, it is necessary to reduce the capacitance C _{TFD of the} TFD element and / or to reduce the parasitic capacitance Cp. As with the first embodiment, the outer dimensions and the like of the TFD element 21 are determined to some extent due to process reasons and the like, so there is a certain limit to reducing the capacitance C _{TFD of the} TFD element. Therefore, in the liquid crystal display device 200, the parasitic capacitance Cp is reduced as in the first embodiment. However, since the liquid crystal display device 200 has an overlayer structure, the realization method is different from that of the first embodiment.

  In the liquid crystal display device 200, as a method of reducing the parasitic capacitance Cp, as will be understood with reference to the above equation 3, (1) the pixel electrode 10 and the data line 32 connected to the pixel electrode 10 via the TFD element 21. (2) Increasing the film thickness “D2” of the overlayer 25 and (3) increasing the dielectric constant “ε” of the overlayer 25. However, since the width of the data line 32 is determined to some extent due to design reasons, the area “S1” cannot be increased too much.

Therefore, in the liquid crystal display device 200, in order to reduce the parasitic capacitance Cp, the film thickness “D2” of the overlayer 25 is increased as much as possible within the range satisfying the design specifications, and the dielectric of the overlayer 25 is also increased. Increase the rate “ε”. By the former, the distance D100 between the pixel electrode 10 and the data line 32 connected to the pixel electrode 10 via the TFD element 21 can be separated as much as possible. Therefore, since the interval “d” in Equation 3 can be increased, the parasitic capacitance Cp can be reduced as much as possible. Therefore, since C ′ _TFD can be reduced in Equation 2 above, the voltage Vlc can be reduced.

  Thereby, in the liquid crystal display device 200, the voltage Vlc applied to the liquid crystal during the holding period Th can be accurately suppressed to an allowable value or less. Therefore, in the liquid crystal display device 200, the transmittance of the liquid crystal can be optimized, and a display image with a desired brightness can be obtained. In particular, when a low voltage (a voltage corresponding to white) is applied to the pixel electrode 10 through the data line 32 during the selection period Th, it is possible to suppress a high voltage from being applied to the liquid crystal during the holding period Th. Can be optimized, and a white display image with a desired brightness can be obtained.

  In the above description, the case where the voltage-transmittance characteristic of the liquid crystal layer 4 is used as a reference for defining the voltage Vlc to a certain magnitude has been described. The voltage-transmittance characteristic referred to here is the first embodiment. It is considered that the voltage-reflectance characteristic (so-called VR characteristic) is included as well as the form. For example, if the voltage corresponding to the reflectance of 50% is V (R50), the voltage Vlc can be defined as shown in Equation 4 above. Thereby, in the liquid crystal display device 200, the reflectance of the liquid crystal can be optimized as described above, and a display image with a desired brightness can be obtained.

[Third embodiment]
In the second embodiment, the liquid crystal display device has an overlayer structure, and the pixel electrode 10 and the data line 32 connected to the pixel electrode 10 via the TFD element 21 overlap each other through the overlayer. The method for optimizing the transmittance characteristics of the liquid crystal according to the present invention is applied to the liquid crystal display device. On the other hand, the third embodiment relates to a liquid crystal display device having an overlayer structure, and further having a structure in which the pixel electrode 10 and the data line 32 do not overlap with each other. Apply optimization methods such as the transmittance characteristics of liquid crystals. Here, the liquid crystal display device 300 of the present invention is an active matrix driving method using a TFD element as in the first and second embodiments, and is a transflective liquid crystal display device. The liquid crystal display device 300 of the present invention is also a liquid crystal display device having a normally white display mode, as in the first and second embodiments.

(Overlayer structure)
Hereinafter, a configuration of the liquid crystal display device 300 according to the third embodiment and a method for optimizing the transmittance characteristics of the liquid crystal will be described with reference to FIGS. Note that the liquid crystal display device 300 of the third embodiment has substantially the same configuration as the liquid crystal display device 200 of the second embodiment, and the former only differs in the configuration of the element substrate from the latter. Therefore, in the following, a method for optimizing the configuration of the element substrate 94 and the transmittance characteristics of the liquid crystal in the liquid crystal display device 300 will be described. In FIG. 12 and FIG. 13, the same components as those in the second embodiment are denoted by the same reference numerals, and the description thereof is omitted. Moreover, in FIG.12 and FIG.13, the code | symbol of the liquid crystal display device 300 which concerns on 3rd Embodiment is abbreviate | omitted and demonstrated for convenience.

  FIG. 12 is a partial plan view of the element substrate corresponding to FIG. 10, and is a plan view in which the configuration of the element substrate 92 of the liquid crystal display device 200 is slightly changed. FIG. 13A is a cross-sectional view of the element substrate corresponding to FIG. 11A, and is a cross-sectional view taken along the cutting line CC ′ of FIG. FIG. 13B is an enlarged cross-sectional view of the vicinity of a connection portion between the pixel electrode 10 and the TFD element 21 and the data line 32 corresponding to FIG. 11B, and is a cross-sectional view of a region E2. . Since FIG. 12 shows a configuration when the observation side is viewed from the back side, the front side in FIG. 12 and the upper side in FIG.

  The structure of the element substrate 94 in the third embodiment, that is, the overlayer structure will be described. In addition, although the protective layer 17 is normally formed on each inner surface of the pixel electrode 10 and the overlayer 25, in FIG.12 and FIG.13, it is abbreviate | omitting for convenience.

  A phase difference plate 13 and a polarizing plate 14 are disposed on the outer surface of the upper substrate 1. On the other hand, a TFD element 21 and a data line 32 are formed on the inner surface of the upper substrate 1.

  In the third embodiment, the arrangement of the TFD elements 21 on the upper substrate 1 is the same as in the second embodiment. Since the configuration of the TFD element 21 is the same as that of the second embodiment, the description thereof is omitted.

  In the third embodiment, the arrangement of the data lines 32 on the upper substrate 1 is different from that in the second embodiment. That is, in the second embodiment, the data lines 32a, 32b, and 32c are arranged at positions below and overlapping the pixel electrodes 10a, 10b, and 10c, respectively, as shown in FIGS. 11 and 12A. It was. On the other hand, in the third embodiment, the data lines 32a, 32b, and 32c do not overlap with the lower positions of the pixel electrodes 10a, 10b, and 10c, respectively, as shown in FIGS. It is arrange | positioned in the position, ie, the position of both sides. In particular, one data line 32 is arranged between the pixel electrode 10 connected thereto via the TFD element 21 and the adjacent pixel electrode 10 not connected to the one data line 32. . This point is greatly different from the second embodiment in structure. Since the configuration of the data line 32 is the same as that of the second embodiment, description thereof is omitted.

  Further, an overlayer 25 is formed on the inner surface of the upper substrate 1, and the TFD element 21 and the data line 32 are covered with the overlayer 25. The overlayer 25 has a substantially circular opening, that is, a contact hole 25a in plan view. Further, the pixel electrode 10 is formed on the inner surface of the overlayer 25 with the same layout as in the second embodiment.

(Optimization method for transmittance characteristics of liquid crystal)
The method for optimizing the transmittance characteristics of the liquid crystal in the liquid crystal display device 300 is basically the same as in the second embodiment. In other words, in the liquid crystal display device 300, the voltage Vlc applied to the liquid crystal during the holding period Th is accurately suppressed below the allowable value by satisfying the above-described Expression 2, and the transmittance characteristics of the liquid crystal are optimized. A display image having a desired brightness is obtained.

Therefore, in order to satisfy the above equation 2, it is necessary to reduce the voltage Vlc. For this purpose, the liquid crystal capacitance Clc must be increased and / or C ′ _TFD must be decreased.

In the liquid crystal display device 300, the liquid crystal capacitance Clc is increased by the same method as in the second embodiment described above. In order to reduce C ′ _TFD , it is necessary to reduce the capacitance C _TFD of the TFD element 21 and / or to reduce the parasitic capacitance Cp as described above. Since the external dimensions and the like of the TFD element 21 are determined to some extent due to process reasons as in the second embodiment, there is a certain limit in reducing the capacitance C _TFD of the TFD element 21. Therefore, in the liquid crystal display device 300, the parasitic capacitance Cp is reduced as in the first and second embodiments.

  Specifically, in the liquid crystal display device 300 according to the third embodiment, the parasitic capacitance Cp is reduced by two of the three methods described in the second embodiment. That is, in the liquid crystal display device 300, as shown in FIG. 12 and FIG. 13A, the data line 32 and the pixel electrode 10 do not overlap, so one of the three methods, that is, the pixel electrode 10 and In addition, the method of increasing the overlapping area with the data line 32 connected via the TFD element 21 cannot be applied. Therefore, in the liquid crystal display device 300 according to the third embodiment, the remaining two methods out of the three methods, that is, the dielectric constant “ε” of the overlayer 25 is increased and / or the film thickness “D3 of the overlayer 25 is increased. The parasitic capacitance Cp is reduced by applying the method of increasing the thickness of the capacitor.

In particular, in the liquid crystal display device 300 according to the third embodiment, as shown in FIGS. 12 and 13A, the data line 32 is formed at a position that does not overlap the pixel electrode 10. Therefore, in the third embodiment, the distance between the pixel electrode 10b and the data line 32b connected to the pixel electrode 10b via the TFD element 21 is longer than that in the second embodiment. For example, in the third embodiment, as shown in FIG. 13A, the distance between the pixel electrode 10b and the data line 32b connected thereto is D101. In the second embodiment, as shown in FIG. 11A, the distance between the pixel electrode 10b and the data line 32b is D100. Therefore, D100 <D101. For this reason, when the liquid crystal display device 300 according to the third embodiment is compared with the liquid crystal display device 200 according to the second embodiment, the former has the thickness of the overlayer 25 made thinner than the latter, and the parasitic capacitance Cp is changed to the latter. Can be as small as Therefore, since C ′ _TFD can be reduced in Equation 2 above, the voltage Vlc can be reduced.

  Thereby, in the liquid crystal display device 300, the voltage Vlc applied to the liquid crystal during the holding period Th can be accurately suppressed to an allowable value or less. Therefore, in the liquid crystal display device 300, the transmittance of the liquid crystal can be optimized, and a display image with a desired brightness can be obtained. In particular, when a low voltage (a voltage corresponding to white) is applied to the pixel electrode 10 through the data line 32 during the selection period Th, it is possible to suppress a high voltage from being applied to the liquid crystal during the holding period Th. Can be optimized, and a white display image with a desired brightness can be obtained.

  In the above description, the case where the voltage-transmittance characteristic of the liquid crystal layer 4 is used as a reference for defining the voltage Vlc to be a certain magnitude has been described. Similar to the second embodiment, it is considered to include voltage-reflectance characteristics (so-called VR characteristics). For example, if the voltage corresponding to the reflectance of 50% is V (R50), the voltage Vlc can be defined as shown in Equation 4 above. Thereby, in the liquid crystal display device 300, the reflectance of the liquid crystal can be optimized as described above, and a display image having a desired brightness can be obtained.

[Example (Example of design value)]
An example of design values applicable to the liquid crystal display devices 100 to 300 according to the first to third embodiments will be described.

In this example, the liquid crystal display devices 100 to 300 were manufactured under the following conditions, respectively. This condition is determined in consideration of the above-described optimization method for the transmittance characteristics of the liquid crystal according to the present invention. Under such conditions,
(1) The distance between the upper substrate 1 and the lower substrate 2, that is, the cell gap is 3 μm.
(2) The liquid crystal capacitance Clc of one pixel electrode is 123 (F)
(3) The element capacitance C _TFD of one TFD element is 38 (F)
(4) The parasitic capacitance Cp generated between the data line connected to the pixel electrode via the TFD element and the pixel electrode is 20 (F).
(5) The data amplitude voltage Vd applied to the data line is 4 (V).
(6) The voltage V _{(T50) at} which the transmittance is 50% in the voltage-transmittance characteristics of the liquid crystal is 2.3 (V).

Here, since C ′ _TFD is the sum of the capacitance C _TFD of one TFD element and the parasitic capacitance Cp, C ′ _TFD is 58 (F) from the above (3) and (4). Substituting these values into Equation 1 above, the voltage Vlc is
Vlc = {C ′ _TFD / (Clc + C ′ _TFD )} × Vd = 1.28 (V)
Is calculated. It is understood that the calculated voltage value Vlc is sufficiently smaller than V _(T50) = 2.3V. In other words, the calculated voltage value Vlc satisfies the above formula 2.

  Therefore, in any of the liquid crystal display devices 100 to 300, the transmittance characteristic of the liquid crystal can be optimized, and a display image having a desired brightness can be obtained. More specifically, when the transmittance of the liquid crystal in a non-lighting (that is, non-energized) state is 100%, the liquid crystal display devices 100 to 300 each have a lighting transmittance of 80% or more during white display. I was able to secure it.

[Modification]
In each of the above embodiments, the present invention is applied to the transflective liquid crystal display device 100. However, the present invention is not limited to this, and the present invention can also be applied to a reflective or transmissive liquid crystal display device. In the above embodiment, the TN liquid crystal is applied to the liquid crystal display device 100. However, the liquid crystal display device 100 is not limited thereto, and the liquid crystal having negative dielectric anisotropy is applied to the liquid crystal display device 100. Also good.

[Electronics]
Next, embodiments in which the liquid crystal display devices 100 to 300 according to the first to third embodiments of the present invention are used as display devices for electronic devices will be described.

  FIG. 14 is a schematic configuration diagram showing the overall configuration of the present embodiment. The electronic apparatus shown here includes any one of the liquid crystal display devices 100 to 300 and a control unit 410 that controls the liquid crystal display devices. Here, any one of the liquid crystal display devices 100 to 300 is conceptually divided into a panel structure 403 and a drive circuit 402 including a semiconductor IC or the like. Further, the control means 410 includes a display information output source 411, a display information processing circuit 412, a power supply circuit 413, and a timing generator 414.

  The display information output source 411 includes a memory such as a ROM (Read Only Memory) or a RAM (Random Access Memory), a storage unit such as a magnetic recording disk or an optical recording disk, and a tuning circuit that tunes and outputs a digital image signal. The display information is supplied to the display information processing circuit 412 in the form of an image signal of a predetermined format based on various clock signals generated by the timing generator 414.

  The display information processing circuit 412 includes various well-known circuits such as a serial-parallel conversion circuit, an amplification / inversion circuit, a rotation circuit, a gamma correction circuit, and a clamp circuit, and executes processing of input display information to obtain image information. Are supplied to the drive circuit 402 together with the clock signal CLK. The driving circuit 402 includes a scanning line driving circuit, a data line driving circuit, and an inspection circuit. The power supply circuit 413 supplies a predetermined voltage to each of the above-described components.

  Next, specific examples of electronic devices to which the liquid crystal display devices 100 to 300 according to the present invention can be applied will be described with reference to FIG.

  First, an example in which any one of the liquid crystal display devices 100 to 300 according to the present invention is applied to a display unit of a portable personal computer (so-called notebook personal computer) will be described. FIG. 15A is a perspective view showing the configuration of this personal computer. As shown in the figure, the personal computer 710 includes a main body 712 having a keyboard 711 and a display 713 to which the liquid crystal display panel according to the present invention is applied.

  Next, an example in which any one of the liquid crystal display devices 100 to 300 according to the present invention is applied to a display unit of a mobile phone will be described. FIG. 15B is a perspective view showing the configuration of this mobile phone. As shown in the figure, a mobile phone 720 includes a plurality of operation buttons 721, a receiver 722, a transmitter 723, and a display unit 724 to which any one of the liquid crystal display devices 100 to 300 according to the present invention is applied. Prepare.

  Note that electronic devices to which any of the liquid crystal display devices 100 to 300 according to the present invention can be applied include the personal computer shown in FIG. 15A and the mobile phone shown in FIG. Examples include a liquid crystal television, a viewfinder type / monitor direct view type video tape recorder, a car navigation device, a pager, an electronic notebook, a calculator, a word processor, a workstation, a video phone, a POS terminal, and a digital still camera.

FIG. 3 is a plan view showing a configuration of electrodes and wirings of the liquid crystal display device according to the first embodiment. 1 shows a cross-sectional configuration of a liquid crystal display device according to a first embodiment. The top view which shows the structure of the electrode, wiring, etc. of the element substrate which concern on 1st Embodiment. 1 shows a configuration of electrodes of a color filter substrate according to a first embodiment. It is a wave form diagram of signal potential VA, VB, and VAB concerning a 1st embodiment. It is a figure explaining the optimization method etc. of the transmittance | permeability characteristic of the liquid crystal which concern on 1st Embodiment. It is a figure explaining the optimization method of the transmittance | permeability characteristic of the liquid crystal which concerns on 1st Embodiment. It is a figure explaining the optimization method of the reflectance characteristic of the liquid crystal concerning a 1st embodiment. The cross-sectional structure of the liquid crystal display device which concerns on 2nd Embodiment is shown. It is a figure explaining the optimization method etc. of the transmittance | permeability characteristic of the liquid crystal which concern on 2nd Embodiment. It is a figure explaining the optimization method etc. of the transmittance | permeability characteristic of the liquid crystal concerning 2nd Embodiment. It is a figure explaining the optimization method etc. of the transmittance | permeability characteristic of the liquid crystal which concern on 3rd Embodiment. It is a figure explaining the optimization method etc. of the transmittance | permeability characteristic of the liquid crystal which concern on 3rd Embodiment. 1 is a circuit block diagram of an electronic apparatus to which a liquid crystal display device of the present invention is applied. 6 shows examples of electronic devices to which the liquid crystal display device of the present invention is applied.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Upper substrate, 2 Lower substrate, 3 Seal member, 6 Colored layer, 7 Conductive member, 8 Scan electrode, 10 Pixel electrode, 31 Scan line, 32 Data line, 21 TFD element, 25 Overlayer, 25a Contact hole, 91 Color filter substrate, 92, 93, 94 Element substrate, 100, 200, 300 Liquid crystal display device

Claims (5)

A liquid crystal device in which liquid crystal is sealed between a first substrate having a data line, a two-terminal element and a pixel electrode, and a second substrate having a scanning line,
The element capacitance of the two-terminal element is C _TFD , the liquid crystal capacitance of the liquid crystal sandwiched between the scanning lines facing the pixel electrode is Clc, and the data line is connected to the pixel electrode via the two-terminal element Cp is the parasitic capacitance generated between the pixel electrode and the pixel electrode, the amplitude voltage of the data line is Vd, the element capacitance C _TFD of the two-terminal element and the parasitic capacitance Cp is C ′ _TFD , and the voltage of the liquid crystal − When the voltage corresponding to the transmittance of 50% in the transmittance characteristic is V (T50),
The parasitic capacitance Cp is inversely proportional to the distance between the pixel electrode and the data line connected to the pixel electrode via the two-terminal element,
The voltage Vlc applied to the liquid crystal is
Vlc = {C ′ _TFD / (Clc + C ′ _TFD )} × Vd <V (T50)
A liquid crystal device set to satisfy the above. The first substrate includes a transparent substrate having translucency,
The data line, the two-terminal element, and the pixel electrode are each formed on the transparent substrate,
A distance between the pixel electrode and the data line connected to the pixel electrode via the two-terminal element is larger than a distance between the pixel electrode and the adjacent data line not connected to the pixel electrode. The liquid crystal device according to claim 1, wherein: The first substrate includes a transparent substrate having translucency, and an insulating film having a contact hole and formed on the transparent substrate.
The data line and the two-terminal element are formed on the transparent substrate while being covered with the insulating film, and the pixel electrode is formed on the insulating film and at a position overlapping the data line. Connected to the two-terminal element through the contact hole
The liquid crystal device according to claim 1, wherein the parasitic capacitance Cp is defined based on a thickness of the insulating film. The first substrate includes a transparent substrate having translucency, and an insulating film having a contact hole and formed on the transparent substrate.
The data line and the two-terminal element are formed on the transparent substrate while being covered with the insulating film, and the pixel electrode is formed on the insulating film and between the data lines. Connected to the two-terminal element through the contact hole in the state
The liquid crystal device according to claim 1, wherein the parasitic capacitance Cp is defined based on a thickness of the insulating film. An electronic apparatus comprising the liquid crystal device according to claim 1.

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