JP4361104B2 - Liquid crystal display - Google Patents

Description

  The present invention relates to a liquid crystal display device, and more particularly to a low power consumption liquid crystal display device capable of display using reflected light.

  Currently, with the widespread use of mobile devices such as mobile phones and PDAs, it is desired to reduce the power consumption of liquid crystal display devices mounted on these mobile devices. In addition, the amount of information to be displayed is increasing, and improvement in display quality is also desired.

For example, Patent Document 1 discloses a method of driving a liquid crystal display device at a low frequency in order to reduce power consumption.
JP 2002-14321 A

  The present inventor has developed a method of driving a TFT type liquid crystal display device capable of performing display using reflected light at a low frequency in order to realize a liquid crystal display device capable of high-quality display with low power consumption. As a result of the examination, it has been found that when the frequency at which the image is rewritten is lowered, flicker (luminance change) that cannot be prevented by adjusting the so-called “opposite deviation” occurs. Hereinafter, the relationship between the flicker and the counter deviation will be described.

  In the TFT liquid crystal display device, the voltage of the pixel electrode is drawn by the parasitic capacitance in the TFT and the switching operation of the TFT from on to off. In order to compensate for this pull-in voltage, an offset voltage corresponding to the pull-in voltage is applied to the counter electrode arranged to face the pixel electrode through the liquid crystal layer.

  However, when the pull-in voltage and the offset voltage do not match (the difference between the pull-in voltage and the offset voltage may be referred to as “opposing deviation”), every time the polarity of the voltage applied to the liquid crystal layer is reversed. In addition, a difference occurs in the effective voltage applied to the liquid crystal layer, which is visually recognized as flicker.

  Even in a general liquid crystal display device driven at a rewrite frequency of 60 Hz, so-called gate line inversion (also referred to as “1H inversion”) driving in which the polarity is inverted for each scanning line in order to reduce the visibility of the flicker. However, if the counter deviation amount is still large, the flicker may be visually recognized as a moving stripe pattern.

  As a result of investigating the amount of opposite deviation in which flicker is not visually recognized in a state where a halftone is displayed in a reflection type liquid crystal display device having a pixel pitch of 60 μm × RGB × 180 μm, the present inventor is about It has been found that when a counter deviation of 250 mV occurs, flicker is visually recognized even with gate line inversion driving.

  When low-frequency driving is performed to reduce power consumption, the flicker due to this opposing deviation becomes more visible. For example, when driven at 5 Hz, even if the opposing deviation is only 30 mV, one scanning line Each shade will be visually recognized. Moreover, since the rewrite cycle (vertical scanning cycle) is relatively slow at 200 ms, it is not practically used because the state in which the light and shade lines are alternately replaced in the vertical scanning cycle is visually recognized.

  For example, the above-mentioned counter deviation of about 30 mV easily occurs due to variations in the production process of the thickness of the liquid crystal layer, slight temperature changes of the liquid crystal layer in the usage environment, and changes in electrical properties such as liquid crystal materials and alignment films over time. It is very difficult to suppress the counter deviation amount to 30 mV or less by adjusting the offset voltage of the counter electrode, and the adjustable counter deviation amount is about 100 mV.

  According to an experiment by the present inventor, it has been found that the above flicker problem becomes apparent in a low-frequency drive with a rewrite frequency of 45 Hz or less, and this flicker cannot be sufficiently prevented by adjusting the amount of facing deviation as much as possible. .

  Further, it has been found that flicker is particularly visible in a reflection / transmission liquid crystal display device having a reflection portion for displaying in the reflection mode and a transmission portion for displaying in the transmission mode for each pixel. Flicker in this dual-use liquid crystal display device is also particularly noticeable when driving at a low frequency of 45 Hz or less. However, since flicker is more visible than the reflective type and transmissive type, it is not limited to low frequency driving, and countermeasures are required.

  The present invention has been made in view of the above-described points, and provides a liquid crystal display device with low power consumption and in which flicker is difficult to be visually recognized. In particular, flicker is difficult to be visually recognized even when driving at a low frequency of 45 Hz or less, and An object of the present invention is to provide a liquid crystal display device capable of high-quality display.

  The liquid crystal display device of the present invention is arranged in a matrix having a plurality of rows and a plurality of columns, each of which has a plurality of pixel electrodes each having a reflective electrode region, a plurality of scanning lines extending in the row direction, and a column direction. A plurality of signal lines, and a plurality of switching elements provided corresponding to the plurality of pixel electrodes, respectively, each of the plurality of pixel electrodes, the plurality of scanning lines, and the plurality of the plurality of scanning lines. A plurality of switching elements connected to the signal lines, a liquid crystal layer, and at least one counter electrode facing the plurality of pixel electrodes via the liquid crystal layer, and scanning the plurality of scanning lines. By sequentially supplying a signal voltage, a group of pixel electrodes connected to the same scanning line is sequentially selected from the plurality of pixel electrodes, and the plurality of pixel electrodes are connected to the plurality of pixel electrodes. A liquid crystal display device that performs display by supplying a display signal voltage via a signal line, wherein the plurality of pixel electrodes are applied to the liquid crystal layer in each of the plurality of rows and in each of the plurality of columns. The display signal voltage supplied to each of the plurality of pixel electrodes is rewritten at a frequency of 45 Hz or less.

  In a preferred embodiment, among the plurality of switching elements, a switching element connected to any one of the plurality of scanning lines or a switching element connected to any one of the plurality of signal lines. Is connected to the switching element connected to one of a pair of rows adjacent to the arbitrary one scanning line or a pixel electrode belonging to a pair of columns adjacent to the arbitrary one signal line and the other. Switching elements for each of the predetermined number, and the polarity of the voltage applied to the liquid crystal layer is set for each pixel electrode connected to the predetermined number of scanning lines or to the pixels connected to the predetermined number of signal lines. Inverted for each electrode.

  In a preferred embodiment, among the plurality of switching elements, a switching element connected to any one of the plurality of scanning lines is a pixel belonging to a pair of rows adjacent to the one scanning line. Each of the electrodes has a switching element connected to one of the electrodes and a switching element connected to the other.

  In a preferred embodiment, each of the plurality of pixel electrodes is a reflective electrode, the plurality of pixel electrodes have a congruent shape, substantially overlap each other by the translation operation in the row direction, and It arrange | positions so that it may mutually overlap substantially by the translation operation to a row direction.

  Each of the plurality of pixel electrodes may include a reflective electrode region and a transmissive electrode region.

  It is preferable that the variation width along the row direction and the column direction of the geometric center of gravity of the transmissive electrode region included in each of the plurality of pixel electrodes is equal to or less than half of the pitch in each direction.

  The transmissive electrode regions of each of the plurality of pixel electrodes have a congruent shape, substantially overlap each other by the translation operation in the row direction, and substantially by the translation operation in the column direction. It is preferable that they are arranged so as to overlap each other.

  In a preferred embodiment, among the plurality of switching elements, a switching element connected to any one of the plurality of scanning lines is connected to a pixel electrode belonging to an upper row of the one scanning line. The first switching elements connected to each other and the second switching elements connected to the pixel electrodes belonging to the lower row of the arbitrary one scanning line for each of the predetermined number, and the first switching elements and the The distance from the geometric center of gravity of the transmissive electrode region of the pixel electrode connected to the first switching element is the geometry of the transmissive electrode region of the pixel electrode connected to the second switching element and the second switching element. The distance from the target center of gravity is different.

  Each of the plurality of pixel electrodes may have a unique transmissive electrode region surrounded by the reflective electrode region.

  It is preferable that an auxiliary capacitor is formed below the reflective electrode region.

  Each of the plurality of pixel electrodes defines each of a plurality of pixels, and each of the plurality of pixels has a reflective portion defined by the reflective electrode region and a transmissive portion defined by the transmissive electrode region. And it is preferable that the electrode potential difference of the said reflection part and the electrode potential difference of the said transmission part are substantially equal.

  In a preferred embodiment, the reflective electrode region includes a reflective conductive layer and a transparent conductive layer provided on the liquid crystal layer side of the reflective conductive layer.

  In a preferred embodiment, the transparent conductive layer is amorphous.

  The difference between the work function of the transparent conductive layer and the work function of the transmissive electrode region is preferably within 0.3 eV.

  In a preferred embodiment, the transmissive electrode region is formed of an ITO layer, the reflective conductive layer includes an Al layer, and the transparent conductive layer includes an oxide layer mainly composed of indium oxide and zinc oxide. Is formed.

  The transparent conductive layer preferably has a thickness of 1 nm to 20 nm.

  In a preferred embodiment, each of the plurality of pixel electrodes defines a plurality of pixels, and each of the plurality of pixels is defined by a reflective portion defined by the reflective electrode region and the transmissive electrode region. The liquid crystal layer of the reflective portion and the liquid crystal layer of the transmissive portion so as to substantially compensate for the difference between the electrode potential difference of the reflective portion and the electrode potential difference of the transmissive portion. An AC signal voltage having a different center level is applied.

  In a preferred embodiment, the at least one counter electrode includes a first counter electrode facing the reflective electrode region of the plurality of pixel electrodes, and a second counter electrode facing the transmissive electrode region of the plurality of pixel electrodes. The first counter electrode and the second counter electrode are electrically independent of each other.

  In a preferred embodiment, the first counter electrode and the second counter electrode have a comb shape having a plurality of branch portions extending in the row direction.

  In a preferred embodiment, the counter signal voltages applied to the first counter electrode and the second counter electrode are AC signal voltages having the same polarity, period, and amplitude, but different center levels.

  In a preferred embodiment, the reflective portion is electrically connected in parallel to the reflective portion liquid crystal capacitor including the reflective electrode region, the first counter electrode, and the liquid crystal layer therebetween, and the reflective portion liquid crystal capacitor. The transmissive portion includes the transmissive electrode region, the second counter electrode, and the liquid crystal layer therebetween, and the transmissive portion liquid crystal capacitance. And the second auxiliary capacitor electrically connected in parallel to the first auxiliary capacitor counter electrode of the first auxiliary capacitor is applied with the same AC signal voltage as the first counter electrode, The same AC signal voltage as that of the second counter electrode is applied to the second auxiliary capacitor counter electrode of the auxiliary capacitor.

  Another liquid crystal display device according to the present invention includes a plurality of pixel electrodes arranged in a matrix having a plurality of rows and a plurality of columns, each having a reflective electrode region and a transmissive electrode region, and a plurality of scanning lines extending in the row direction. A plurality of signal lines extending in the column direction, and a plurality of switching elements provided corresponding to the plurality of pixel electrodes, respectively, each of the plurality of pixel electrodes and the plurality of pixel electrodes A plurality of switching elements connected to the scanning lines and the plurality of signal lines, a liquid crystal layer, and at least one counter electrode facing the plurality of pixel electrodes via the liquid crystal layer, By sequentially supplying scanning signal voltages to a plurality of scanning lines, a group of pixel electrodes connected to the same scanning line is sequentially selected from the plurality of pixel electrodes, and the selected A display device that performs display by supplying a display signal voltage to the pixel electrode via the plurality of signal lines, wherein the plurality of pixel electrodes are respectively in the plurality of rows and in the plurality of columns. In the liquid crystal layer, the polarity of the voltage applied to the liquid crystal layer is different for each of a certain number of pixel electrodes, and the geometric center of gravity of the transmissive electrode region of each of the plurality of pixel electrodes is arranged. The variation width along the row direction and the column direction is less than half of the pitch in each direction.

  In a preferred embodiment, among the plurality of switching elements, a switching element connected to any one of the plurality of scanning lines or a switching element connected to any one of the plurality of signal lines. Is connected to the switching element connected to one of a pair of rows adjacent to the arbitrary one scanning line or a pixel electrode belonging to a pair of columns adjacent to the arbitrary one signal line and the other. Switching elements for each of the predetermined number, and the polarity of the voltage applied to the liquid crystal layer is set for each pixel electrode connected to the predetermined number of scanning lines or to the pixels connected to the predetermined number of signal lines. Inverted for each electrode.

  In a preferred embodiment, among the plurality of switching elements, a switching element connected to any one of the plurality of scanning lines is a pixel belonging to a pair of rows adjacent to the one scanning line. Each of the electrodes has a switching element connected to one of the electrodes and a switching element connected to the other.

  In a preferred embodiment, the transmissive electrode regions of each of the plurality of pixel electrodes have a congruent shape with each other, substantially overlap each other by the translation operation in the row direction, and translate in the column direction. It arrange | positions so that it may mutually overlap substantially by operation.

  In a preferred embodiment, among the plurality of switching elements, a switching element connected to any one of the plurality of scanning lines is connected to a pixel electrode belonging to an upper row of the one scanning line. The first switching elements connected to each other and the second switching elements connected to the pixel electrodes belonging to the lower row of the arbitrary one scanning line for each of the predetermined number, and the first switching elements and the The distance from the geometric center of gravity of the transmissive electrode region of the pixel electrode connected to the first switching element is the geometry of the transmissive electrode region of the pixel electrode connected to the second switching element and the second switching element. The distance from the target center of gravity is different.

  In a preferred embodiment, each of the plurality of pixel electrodes has a unique transmissive electrode region surrounded by the reflective electrode region.

  It is preferable that an auxiliary capacitor is formed below the reflective electrode region.

  Each of the plurality of pixel electrodes defines each of a plurality of pixels, and each of the plurality of pixels has a reflective portion defined by the reflective electrode region and a transmissive portion defined by the transmissive electrode region. And it is preferable that the electrode potential difference of the said reflection part and the electrode potential difference of the said transmission part are substantially equal.

  In a preferred embodiment, the reflective electrode region includes a reflective conductive layer and a transparent conductive layer provided on the liquid crystal layer side of the reflective conductive layer.

  In a preferred embodiment, the transparent conductive layer is amorphous.

  The difference between the work function of the transparent conductive layer and the work function of the transmissive electrode region is preferably within 0.3 eV.

  In a preferred embodiment, the transmissive electrode region is formed of an ITO layer, the reflective conductive layer includes an Al layer, and the transparent conductive layer includes an oxide layer mainly composed of indium oxide and zinc oxide. Is formed.

  The transparent conductive layer preferably has a thickness of 1 nm to 20 nm.

  In a preferred embodiment, each of the plurality of pixel electrodes defines a plurality of pixels, and each of the plurality of pixels is defined by a reflective portion defined by the reflective electrode region and the transmissive electrode region. The liquid crystal layer of the reflective portion and the liquid crystal layer of the transmissive portion so as to substantially compensate for the difference between the electrode potential difference of the reflective portion and the electrode potential difference of the transmissive portion. An AC signal voltage having a different center level is applied.

  In a preferred embodiment, the at least one counter electrode includes a first counter electrode facing the reflective electrode region of the plurality of pixel electrodes, and a second counter electrode facing the transmissive electrode region of the plurality of pixel electrodes. The first counter electrode and the second counter electrode are electrically independent of each other.

  In a preferred embodiment, the first counter electrode and the second counter electrode have a comb shape having a plurality of branch portions extending in the row direction.

    In a preferred embodiment, the counter signal voltages applied to the first counter electrode and the second counter electrode are AC signal voltages having the same polarity, period, and amplitude, but different center levels.

  In a preferred embodiment, the reflective portion is electrically connected in parallel to the reflective portion liquid crystal capacitor including the reflective electrode region, the first counter electrode, and the liquid crystal layer therebetween, and the reflective portion liquid crystal capacitor. The transmissive portion includes the transmissive electrode region, the second counter electrode, and the liquid crystal layer therebetween, and the transmissive portion liquid crystal capacitance. And the second auxiliary capacitor electrically connected in parallel to the first auxiliary capacitor counter electrode of the first auxiliary capacitor is applied with the same AC signal voltage as the first counter electrode, The second auxiliary capacitor counter electrode of the auxiliary capacitor has a configuration in which the same AC signal voltage as that of the second counter electrode is applied.

  Another liquid crystal display device according to the present invention includes a plurality of pixel electrodes each having a reflective electrode region and a transmissive electrode region, a liquid crystal layer, and at least one counter facing the plurality of pixel electrodes through the liquid crystal layer. Each of the plurality of pixel electrodes defines a plurality of pixels, and each of the plurality of pixels is defined by a reflective portion defined by the reflective electrode region and the transmissive electrode region. The electrode potential difference of the reflection part and the electrode potential difference of the transmission part are substantially equal.

  In a preferred embodiment, the reflective electrode region includes a reflective conductive layer and a transparent conductive layer provided on the liquid crystal layer side of the reflective conductive layer.

  In a preferred embodiment, the transparent conductive layer is amorphous.

  The difference between the work function of the transparent conductive layer and the work function of the transmissive electrode region is preferably within 0.3 eV.

  In a preferred embodiment, the transmissive electrode region is formed of an ITO layer, the reflective conductive layer includes an Al layer, and the transparent conductive layer includes an oxide layer mainly composed of indium oxide and zinc oxide. Is formed.

  The transparent conductive layer preferably has a thickness of 1 nm to 20 nm.

  In a preferred embodiment, each of the plurality of pixel electrodes defines a plurality of pixels, and each of the plurality of pixels is defined by a reflective portion defined by the reflective electrode region and the transmissive electrode region. The liquid crystal layer of the reflective portion and the liquid crystal layer of the transmissive portion so as to substantially compensate for the difference between the electrode potential difference of the reflective portion and the electrode potential difference of the transmissive portion. An AC signal voltage having a different center level is applied.

  In a preferred embodiment, the at least one counter electrode includes a first counter electrode facing the reflective electrode region of the plurality of pixel electrodes, and a second counter electrode facing the transmissive electrode region of the plurality of pixel electrodes. The first counter electrode and the second counter electrode are electrically independent of each other.

  In a preferred embodiment, the first counter electrode and the second counter electrode have a comb shape having a plurality of branch portions extending in the row direction.

  In a preferred embodiment, the counter signal voltages applied to the first counter electrode and the second counter electrode are AC signal voltages having the same polarity, period, and amplitude, but different center levels.

  In a preferred embodiment, the reflective portion is electrically connected in parallel to the reflective portion liquid crystal capacitor including the reflective electrode region, the first counter electrode, and the liquid crystal layer therebetween, and the reflective portion liquid crystal capacitor. The transmissive portion includes the transmissive electrode region, the second counter electrode, and the liquid crystal layer therebetween, and the transmissive portion liquid crystal capacitance. And the second auxiliary capacitor electrically connected in parallel to the first auxiliary capacitor counter electrode of the first auxiliary capacitor is applied with the same AC signal voltage as the first counter electrode, The second auxiliary capacitor counter electrode of the auxiliary capacitor has a configuration in which the same AC signal voltage as that of the second counter electrode is applied.

  According to the present invention, there is provided a liquid crystal display device capable of displaying high quality with low power consumption, in which flicker is not visually recognized even when driving at a low frequency of 45 Hz or less. Further, the dual-use liquid crystal display device according to the present invention can perform high-quality display at least with no jaggedness in the transmissive electrode region in a configuration employing a staggered arrangement of switching elements.

  In addition, according to the present invention, it is possible to suppress the occurrence of flicker due to the difference in electrode potential between the reflective portion and the transmissive portion in a liquid crystal display device having a reflective portion and a transmissive portion for each pixel, thereby improving display quality. can do.

  The liquid crystal display device according to the present invention is applied to various electronic devices such as mobile devices such as mobile phones, pocket game machines, PDAs (Personal Digital Assistants), mobile TVs, remote controls, notebook personal computers, and other mobile terminals. Preferably used. In particular, when mounted on a battery-driven electronic device, low power consumption can be achieved while maintaining good display quality, and long-time driving is possible.

  Hereinafter, embodiments of the liquid crystal display device according to the present invention will be described with reference to the drawings. The liquid crystal display device according to the present invention is a display device that can perform display using at least reflected light. In addition to a general reflective liquid crystal display device, a reflective electrode region and a transmissive electrode region are formed on a pixel electrode. The liquid crystal display device of a type called a transflective type or a dual-use type is included.

  Note that the pixel electrode in this specification is not limited to a single electrode layer, and may include a plurality of electrode layers that are provided for each pixel and to which a corresponding display signal voltage is supplied. That is, the reflective electrode region may be configured with the reflective electrode layer and the transmissive electrode region may be configured with the transparent electrode layer, as in the dual-use liquid crystal display device exemplified below. Furthermore, for example, the reflective electrode region may be configured by a combination of a transparent electrode and a reflective film. Further, the pixel electrode may be a pixel electrode (that is, an electrode formed from a semi-transmissive conductive film) in which a hole (translucent portion) is provided in a single metal film. In this configuration, there is no electrode layer in the translucent part of the metal film, but when the hole is sufficiently small, the electric field from the metal film (electrode layer) around the translucent part is sufficiently applied. Since the hole of the metal layer does not substantially affect the voltage applied to the liquid crystal layer, the pixel electrode formed from this metal film also has a reflective electrode region and a transmissive electrode region (corresponding to the hole).

  Compared with a reflective liquid crystal display device, a liquid crystal display device having a transmissive electrode region and a reflective electrode region has an advantage that high-quality display can be performed even in an environment where the ambient light is dark. In addition, there are some that can select the use of display in the transmissive mode by turning on / off the backlight according to the use environment.

(Embodiment 1)
First, a pixel arrangement and a driving method of a liquid crystal display device in which flicker is difficult to be visually recognized even when low frequency driving of 45 Hz or less is performed will be described.

  First, the structure of a reflective liquid crystal display device 100 according to Embodiment 1 of the present invention will be described with reference to FIG. The reflective liquid crystal display device 100 includes a low frequency drive circuit (not shown). A preferred embodiment of the low frequency drive circuit will be described later.

  The reflective liquid crystal display device 100 includes a plurality of reflective pixel electrodes (hereinafter referred to as “reflective electrodes” for simplicity) 10 arranged in a matrix having a plurality of rows and a plurality of columns, and extends in the row direction. A plurality of scanning lines (gate lines) 32, a plurality of signal lines (source lines) 34 extending in the column direction, and a plurality of TFTs 20 provided corresponding to each of the reflective electrodes 10 are provided. The reflective electrode 10 is connected to the scanning line 32 and the signal line 34 via the TFT 20.

  The liquid crystal display device 100 sequentially selects a group of pixel electrodes 10 connected to the same scanning line 32 from among the plurality of reflective electrodes 10 by sequentially supplying scanning signal voltages to the plurality of scanning lines 32. Display is performed by supplying a display signal voltage to the selected group of reflective electrodes 10 via the signal line 34. That is, the liquid crystal display device 100 is driven line-sequentially.

  In this specification, a period in which individual scanning lines are selected is referred to as a horizontal scanning period, and a period required to scan a predetermined group of scanning lines over the entire display surface is referred to as a vertical scanning period. When all scanning lines are scanned every frame (that is, when the rewrite cycle is 60 Hz), one frame cycle corresponds to one vertical scanning period, and one frame is divided into a plurality of fields for driving. 1 field period required to scan all the scanning lines corresponding to each field corresponds to one vertical scanning period. In the liquid crystal display device according to the present invention, the display signal voltage supplied to each pixel electrode is rewritten at a frequency of 45 Hz or less. That is, the liquid crystal display device 100 is driven at a low frequency so that the vertical scanning period is 1/45 seconds or longer.

  Further, the plurality of pixel electrodes are arranged so that the polarity of the voltage applied to the liquid crystal layer is different for each of a certain number of pixel electrodes in each of the plurality of rows and the plurality of columns. Is done. In the following embodiments, a configuration in which inversion driving is performed for each pixel (the fixed number is equivalent to 1) is exemplified. For example, for every three consecutive pixels of R, G, and B (the fixed number is 3).

  In the reflective liquid crystal display device 100, the reflective electrodes 10 are arranged in a staggered manner with respect to the TFT 20 as shown in FIG. That is, the TFT 20 connected to a certain scanning line 32 is connected to the reflecting electrode 10 belonging to one row (for example, the upper row in FIG. 1) of the reflecting electrodes 10 belonging to a pair of rows adjacent to the scanning line 32. The connected TFTs 20 and the TFTs 20 connected to the reflective electrodes 10 belonging to the other row (for example, the lower row in FIG. 1) are alternately provided.

  With this arrangement, the polarity of the display signal voltage applied to all the signal lines 34 is inverted every time the scanning line 32 is selected, and further, the display signal applied to the same reflective electrode 10 in the next vertical scanning period. By inverting the polarity of the voltage, it is possible to realize dot inversion driving. That is, a substantial dot inversion drive is realized by combining the staggered arrangement of TFTs 20 and the gate line inversion drive. That is, the liquid crystal display device 100 according to the first embodiment can perform dot inversion driving with a conventional circuit configuration for gate line inversion driving.

  Here, for the sake of simplicity, the expression “polarity of the display signal voltage applied to the signal line 34” is used, but what is actually inverted is “driven by the pixel electrode 10 connected to the signal line 34”. This is “the polarity of the voltage applied to the liquid crystal layer” and “the polarity of the potential of the pixel electrode with respect to the potential of the counter electrode”. Hereinafter, for the sake of simplicity, the “display signal voltage applied to the pixel electrode 10” may be used in the same manner as the “voltage applied to the liquid crystal layer”.

  Table 1 shows the results of examining the amount of facing deviation in which flicker is not visually recognized in a state where halftone is displayed in the liquid crystal display device 100 of the first embodiment having a staggered arrangement of TFTs and the liquid crystal display device of the conventional TFT arrangement. . The pixel pitch was 60 μm × RGB × 180 μm in all cases.

  In the conventional liquid crystal display device, even when driven at 70 Hz, flicker was visually recognized when a counter deviation of about 250 mV occurred. Further, when the rewriting frequency is lowered to about 5 Hz, the shading for each scanning line is visually recognized even when the facing deviation amount is about 30 mV. Moreover, since the rewrite cycle (vertical scanning cycle) is relatively slow at 200 ms, it is visually recognized that the light and shade lines are alternately switched in the vertical scanning cycle.

  On the other hand, in the liquid crystal display device 100 of the present invention that adopts the staggered arrangement, flicker is visually recognized when a reversal of more than 150 mV occurs when rewriting is performed at a cycle of 5 Hz, for example. Due to the difference in polarity, it did not appear as a striped pattern, but only as a slight periodic repetition of roughness and brightness of the entire screen. As described above, the amount of opposite deviation that affects the display quality is about 150 mV, so that it is within the adjustable range even at the mass production level, and the occurrence of display defects can be avoided by adjusting the offset voltage.

  In this manner, by combining the staggered arrangement of TFTs and the gate line inversion drive, a liquid crystal display device capable of high-quality display with low power consumption in which flicker is not visually recognized even when low-frequency drive is performed can be obtained.

  In the liquid crystal display device 100, the case where the TFTs are arranged in a staggered manner with respect to the scanning lines 32 and the gate lines are inverted is illustrated, but the TFTs 20 are staggered with respect to the signal lines 34 as in the liquid crystal display device 200 shown in FIG. Even if they are arranged and source line inversion driving is performed, substantial dot inversion driving can be realized. In the liquid crystal display device 200 shown in FIG. 2, the TFT 20 connected to a certain signal line 34 has one column (for example, the left side in FIG. 2) of the reflective electrodes 10 belonging to a pair of columns adjacent to the signal line 34. TFTs 20 connected to the reflective electrode 10 belonging to the other column (in FIG. 2), for example, and TFTs 20 connected to the reflective electrode 10 belonging to the other column (eg, the right column in FIG. 2) are alternately provided.

  With this arrangement, the polarities of the display signal voltages applied to the adjacent signal lines 34 are reversed in each vertical scanning period, and are applied to the respective signal lines 34 in the next vertical scanning period. By driving so as to invert the polarity of the display signal voltage, dot inversion driving can be realized. In other words, substantial dot inversion driving is realized by combining the staggered arrangement of TFTs 20 and source line inversion driving. That is, the liquid crystal display device 200 of Embodiment 1 can perform dot inversion driving with a conventional circuit configuration for source line inversion driving.

  However, in the source line inversion drive, since the counter electrode is DC driven, the amplitude of the drive voltage applied to the liquid crystal layer must be given by the amplitude of the display signal voltage supplied from the signal line 34. It is necessary to increase the amplitude of the display signal voltage as compared with the gate line inversion driving in which the difference between the voltage of the electrode and the display signal voltage of the signal line 34 is the amplitude of the driving voltage applied to the liquid crystal layer. That is, since a high breakdown voltage is required for the source driver drive circuit, the source line inversion drive consumes more power than the gate line inversion drive, and the gate line inversion drive is preferable.

  As described above, by combining the staggered arrangement of TFTs with the line inversion drive, a high-quality display in which flicker is not visually recognized even when low-frequency drive is performed can be realized.

  However, as shown in FIGS. 1 and 2, when the staggered arrangement is formed while the arrangement relationship between the reflection electrode (pixel electrode) 10 and the TFT 20 is kept constant, the arrangement of the two adjacent reflection electrodes 10 is different from each other. . For example, in the case of FIG. 1 described above, one of the two adjacent reflective electrodes 10 is arranged by rotating the other by 180 °. In the case of FIG. 2, one of the two reflective electrodes 10 is mirrored with the other signal line 34 as a mirroring axis. Therefore, as shown in FIG. 1 and FIG. 2, the arrangement of the reflective electrodes 10 is constant along with the staggered arrangement of the TFTs 20 if there is no symmetry with respect to the 180 ° rotation and the mirroring operation. It will deviate from the arrangement. As a result, an irregular arrangement of the reflective electrodes 10 (that is, an irregular arrangement of pixels) may be visually recognized as a jagged line. This becomes remarkable when the rewrite frequency is 45 Hz or less.

  In order to prevent this, it is possible to solve the problem by arranging the reflective electrodes 10 having congruent shapes substantially in a straight line in the row direction and the column direction. That is, all the reflective electrodes 10 may be congruent with each other, and may be disposed so as to substantially overlap each other by a translation operation in the row direction and substantially overlap each other by a translation operation in the column direction. Even when the reflective electrode 10 is not completely arranged in a straight line, it is difficult to be visually recognized as jagged if the geometric center of gravity of the reflective electrode 10 is arranged substantially in a straight line in the row and column directions.

  In the liquid crystal display devices 100 and 200 shown in FIGS. 1 and 2, the reflective electrode 10 has a shape in which a part of the rectangle is missing so as not to cover the TFT 20. By doing so, it is possible to prevent jaggedness from being visually recognized even when low frequency driving of 45 Hz or less is performed.

  Here, the reflective liquid crystal display device is illustrated, but the transflective liquid crystal display device having the transflective electrode in which the pixel electrode 10 is formed of a transflective conductive film (for example, an Al film having a plurality of pinholes) is also applicable. It can be applied in the same manner, and the same effect can be obtained.

(Transmission / reflection liquid crystal display device)
Next, a preferred example of the arrangement of the pixel electrodes 10 in the case where a staggered arrangement of TFTs is employed will be described for a transflective liquid crystal display device (hereinafter referred to as “a dual-use liquid crystal display device”). In the dual-use liquid crystal display device exemplified below, each pixel electrode has a reflective electrode region and a transmissive electrode region, and each pixel displays in a reflective mode using light reflected by the reflective electrode region. And a transmissive portion that performs display in a transmissive mode using light transmitted through the transmissive electrode region. That is, in a transflective liquid crystal display device in which a pixel electrode is formed using a metal film having a pinhole, the light that has passed through the pinhole and the light reflected by the metal film are not separately viewed. On the other hand, in the dual-use liquid crystal display device, the transmissive portion and the reflective portion are separated and visually recognized.

  The dual-use liquid crystal display device 300 according to the present invention shown in FIG. 3A has a configuration in which the TFTs 20 are arranged in a staggered manner with respect to the scanning lines 32, and is similar to the liquid crystal display device 100 shown in FIG. The dot inversion drive is substantially performed by the gate line inversion drive. The pixel electrode 10 of the dual-use liquid crystal display device 300 has a reflective electrode region 10a and a transmissive electrode region 10b, and the transmissive electrode region 10b has a congruent shape with respect to the row direction (pitch Px). It arrange | positions so that it may mutually overlap substantially by translation operation, and may mutually overlap substantially by translation operation to a row direction (pitch Py). That is, the transmissive electrode regions 10b are arranged in a straight line in the row direction and the column direction.

  FIG. 3B shows a liquid crystal display device 300 ′ having a staggered arrangement obtained according to a conventional general design procedure, and the positional relationship between the TFT 20 and the pixel electrode 10 is kept constant. In the liquid crystal display device 300 ′, the transmissive electrode regions 10b are irregularly arranged in the row direction, and the shift of the center of gravity between the transmissive electrode regions 10b adjacent to each other is about Py / 2, which is larger than the row direction pitch Px. Therefore, it is visually recognized as jagged in the transmission mode display. In the illustrated example, since the pixel electrode 10 has the only transmissive electrode region 10b surrounded by the reflective electrode region 10a, an irregular change in the geometric center of gravity of the transmissive electrode region 10b is caused by the reflective electrode region 10a. This causes a change in the geometric center of gravity, so that the jaggedness is visually recognized even in the reflection mode display.

  On the other hand, in the liquid crystal display device 300 shown in FIG. 3A, since the transmissive electrode region 10b is arranged in a straight line along the row direction, the display of the transmissive mode is not visually recognized. Note that if the fluctuation range of the center of gravity along the row direction (the fluctuation direction is the column direction) is half or less of the pitch in the row direction, it can be made difficult to see. Of course, it is preferable that the geometric centers of gravity of the transmissive electrode region 10b are arranged in a straight line, and as illustrated, the transmissive electrode regions 10b having congruent shapes are arranged in a straight line. Of course, it is preferable.

  In a dual-use liquid crystal display device, particularly a liquid crystal display device having a single transmissive electrode region 10b surrounded by the reflective electrode region 10a, the arrangement of the transmissive electrode region 10b tends to affect the display quality. It is preferable to satisfy the above relationship. Of course, it is needless to say that the reflective electrode region 10a preferably satisfies the above relationship.

  The problem that the irregular arrangement of the transmissive electrode region 10b and / or the reflective electrode region 10a is visible as jagged is noticeable in low frequency driving with a rewrite frequency of 45 Hz or lower, but the display quality is lowered in driving at 60 Hz or higher. Therefore, the above-described effects can be obtained for a dual-use liquid crystal display device having a staggered arrangement of TFTs, not limited to a liquid crystal display device driven at a low frequency. Further, similarly to the above-described liquid crystal display device 100, even when low frequency driving is performed, flicker is hardly visible and a high-quality display can be provided.

  Next, the structure of the dual-use liquid crystal display device 300 will be further described with reference to FIGS. 4 and 5. A schematic cross-sectional view of the liquid crystal display device 300 is shown in FIG. 4, and a top view thereof is shown in FIG. 4 corresponds to a cross-sectional view taken along line IV-IV in FIG.

  The liquid crystal display device 300 includes two insulating substrates (for example, glass substrates) 11 and 12 and a liquid crystal layer 42 provided therebetween.

  A color filter 18 and a counter electrode (common electrode) 19 are formed on the liquid crystal layer 42 side of the insulating substrate 11. Furthermore, on the upper surface of the insulating substrate 11, a phase difference plate 15, a polarizing plate 16, and an antireflection film 17 for controlling the state of incident light are provided in this order. The antireflection film 17 may be omitted. An alignment film (not shown) is provided on the outermost surface of the insulating substrate 11 on the liquid crystal layer 42 side. A retardation plate, a polarizing plate, and a backlight (both not shown) are also provided outside the insulating substrate 12.

  On the liquid crystal layer 42 side on the insulating substrate 12, the TFT 20, the scanning line 32, the signal line 34, and the pixel electrode 10 connected to the scanning line 32 and the signal line 34 via the TFT 20 are formed. The pixel electrode 10 has a reflective electrode region 10a and a transmissive electrode region 10b.

  The TFT 20 includes a gate electrode 32a formed as a part of the scanning line 32, a gate insulating film 21 formed so as to cover the gate electrode 32a, a semiconductor layer (for example, an amorphous silicon layer) 22 formed thereon, and these A source electrode 24 and a drain electrode 25 formed thereon. A contact layer 23 is formed between the semiconductor layer 22 and the source electrode 24 and the drain electrode 25. The source electrode 24 has a two-layer structure of an ITO layer 24 a and a Ta layer 24 b, which is formed integrally with the signal line 34. Similarly, the drain electrode 25 has a two-layer structure of an ITO layer 25a and a Ta layer 25b, and an extended portion of the ITO layer 25a forms a transmissive electrode region 10b and an auxiliary capacitance electrode 35.

  An insulating film (for example, SiN film) 26 and an interlayer insulating film (photosensitive resin film) 27 are formed so as to cover the TFT 20, and fine irregularities are formed on a part of the surface of the interlayer insulating film 27. A reflective electrode (corresponding to the reflective electrode region 10a) 29 formed on the interlayer insulating film 27 has a surface shape reflecting the unevenness of the interlayer insulating film 27, and diffusely reflects incident light appropriately. The reflective electrode 29 has a two-layer structure in which an Al film 29b is formed on a Mo film 29a. The reflective electrode 29 is in contact with the ITO layer 25a in the opening 27a and the contact hole 27b formed in the insulating film 26 and the interlayer insulating film 27. A region in the opening 27a where the reflective electrode 29 is not formed functions as the transmissive electrode region 10b.

  As shown in FIG. 5, the TFT 20 connected to one arbitrary scanning line 32 includes the TFT 20 connected to the pixel electrode 10 belonging to the upper row of the scanning line 32 and the lower portion of the scanning line 32. The TFTs 20 are alternately connected to the pixel electrodes 10 belonging to the row. Therefore, the distances between the TFT 20 and the geometric center of gravity of the transmissive electrode region 10b of the pixel electrode 10 are alternately arranged. With this configuration, the transmissive electrode region 10b satisfies the above condition along the row direction. Arranged regularly to satisfy.

  The reflection mode display is performed by the liquid crystal layer 42 between the reflection electrode 29 (reflection electrode region 10 a) and the counter electrode 19, and the transmission mode display is performed by the liquid crystal layer between the transmission electrode region 10 b and the counter electrode 19. Is called. The thickness of the liquid crystal layer 42 in the transmissive part (transmission region) that performs display in the transmissive mode is substantially greater than the thickness of the liquid crystal layer 42 in the reflective part (reflective region) that performs display in the reflective mode. Bigger than that. By having such a structure, it is possible to optimize the display in the transmission mode and the reflection mode, respectively. Of course, it is preferable that the thickness of the liquid crystal layer 42 in the transmission part is twice the thickness of the liquid crystal layer 42 in the reflection part.

  The liquid crystal display device 300 has an auxiliary capacitor CCS electrically connected in parallel with a liquid crystal capacitor CLC formed by the pixel electrode 10, the counter electrode 19, and the liquid crystal layer 42 therebetween. The auxiliary capacitance includes an auxiliary capacitance wiring 33 formed in the same process as the scanning line 32, a gate insulating film 21, and an ITO layer 25a (at the position facing the auxiliary capacitance wiring 33 via the gate insulating film 21). Auxiliary capacitance electrode). The auxiliary capacitor CCS is preferably formed below the reflective electrode 29 so as not to substantially reduce the pixel aperture ratio.

  Further, by providing the auxiliary capacitor, the shift of the counter voltage can be reduced, so that the occurrence of flicker can be further suppressed. From the viewpoint of forming an auxiliary capacitor having a large capacity and suppressing the occurrence of flicker, a larger value of the auxiliary capacitor CCS is preferable. Here, in order to obtain 99% as the charge rate (voltage holding rate) of the pixel when the area of the reflective electrode region 10a is 60% of the area of the pixel electrode 10 and the rewrite frequency is 5 Hz, the value of the auxiliary capacitor CCS is 0.96 pF. The ratio of the auxiliary capacitance CCS value to the liquid crystal capacitance CLC value 0.48 pF is 2.00. Similarly, the above-described liquid crystal display devices 100 and 200 are preferably provided with an auxiliary capacitor CCS.

  Although the dual-use liquid crystal display device 300 shows an example in which the TFTs 20 are arranged in a staggered manner with respect to the scanning lines 32, the TFTs 20 may be arranged in a staggered manner with respect to the signal lines 34 as in the liquid crystal display device 200. Good. The arrangement of the pixel electrodes in the dual-use liquid crystal display device is not limited to the above example. For example, as shown in FIG. 6, the transmissive electrode region 10b of the pixel electrode 10 is divided into transmissive electrode regions 10b ′ and 10b ″. Of course, the number of dividing the transmissive electrode region 10b may be three or more. In this case, it is preferable that the transmissive electrode region 10b including the transmissive electrode regions 10b ′ and 10b ″ satisfies the above conditions as a whole. More preferably, the regions 10b ′ and 10b ″ are arranged so as to satisfy the above-described conditions.

  The structure and material of each component in the dual-use liquid crystal display device 300 are not limited to the above example, and various known structures and materials can be used. Further, another three-terminal element such as an FET can be used as a switching element instead of the TFT 20. In addition, a method for manufacturing the dual-use liquid crystal display device 300 can also be performed by a known process (see, for example, Japanese Patent Laid-Open No. 2000-305110).

(Low frequency drive circuit)
Next, a preferred embodiment of a circuit configuration for performing low frequency driving will be described.

  FIG. 7 shows a system block diagram of the liquid crystal display device 1 of the first embodiment. The liquid crystal display device 1 represents the liquid crystal display devices 100, 200, and 300 described above.

  The liquid crystal display device 1 includes a liquid crystal panel 2 and a low frequency drive circuit 8. The liquid crystal panel 2 has the configuration described by exemplifying the liquid crystal display devices 100, 200, and 300 described above. The low frequency drive circuit 8 includes a gate driver 3, a source driver 4, a control IC 5, an image memory 6, and a synchronous clock generation circuit 7.

  The gate driver 3 as a scanning signal driver outputs a scanning signal having a voltage corresponding to each of the selection period and the non-selection period to each scanning line 32 of the liquid crystal panel 2. The source driver 4 as a data signal driver outputs the image data supplied to each of the pixel electrodes on the selected scanning line 32 to each signal line 34 of the liquid crystal panel 2 as a display signal by AC driving. The control IC 5 receives the image data stored in the image memory 6 inside the computer or the like, delivers the gate start pulse signal GSP and the gate clock signal GCK to the gate driver 3, and RGB gradation data to the source driver 4. The source start pulse signal SP and the source clock signal SCK are distributed.

  The synchronous clock generation circuit 7 as frequency setting means includes a synchronous clock for the control IC 5 to read out image data from the image memory 6, a gate start pulse signal GSP, a gate clock signal GCK, a source start pulse signal SP, and a source A synchronous clock for generating the clock signal SCK is generated. In the present embodiment, the frequency setting of the synchronous clock for adjusting each signal to the rewriting frequency of the screen of the liquid crystal panel 2 is performed here. The frequency of the gate start pulse signal GSP corresponds to the above-described rewriting frequency, and the synchronous clock generation circuit 7 can set at least one rewriting frequency to 30 Hz or less, and any number of rewritings including 30 Hz or more. The frequency can be set.

  In the figure, the synchronous clock generation circuit 7 changes the setting of the rewrite frequency according to the frequency setting signals M1 and M2 inputted from the outside. The number of frequency setting signals may be arbitrary. For example, if there are two types of frequency setting signals M1 and M2 as described above, the rewriting frequency can be set in four ways as shown in Table 2.

  The rewriting frequency may be set such that a plurality of frequency setting signals are input to the synchronous clock generating circuit 7 as in this example, or the rewriting frequency adjusting volume or selection is selected in the synchronous clock generating circuit 7. For example, a switch may be provided. Of course, a volume for rewriting frequency adjustment, a switch for selection, and the like may be provided on the outer peripheral surface of the liquid crystal display device 1 so that the user can easily set. The synchronous clock generation circuit 7 may be configured to change the setting of the rewriting frequency in accordance with at least an external instruction. Alternatively, it is possible to set so that the rewriting frequency is automatically switched according to the image to be displayed.

  The gate driver 3 starts scanning the liquid crystal panel 2 in response to the gate start pulse signal GSP received from the control IC 5, and sequentially applies a selection voltage to each scanning line 32 in accordance with the gate clock signal GCK. Based on the source start pulse signal SP received from the control IC 5, the source driver 4 stores the received gradation data of each pixel in a register according to the source clock signal SCK, and according to the next source start pulse signal SP, the liquid crystal panel 2 The gradation data is written to each signal line 34.

  FIGS. 8A and 8B show equivalent circuits for one pixel in the liquid crystal panel 2 (for example, the liquid crystal panel of the liquid crystal display device 300) having the above-described auxiliary capacitor CCS. In FIG. 8A, the gate insulating film 21 is sandwiched between the liquid crystal capacitor CLC formed by sandwiching the liquid crystal layer 42 between the counter electrode 19 and the pixel electrode 10, the storage capacitor electrode pad, and the storage capacitor wiring 33. This is an equivalent circuit in which the auxiliary capacitor CCS formed thereby is connected to the TFT 20 and the counter electrode 19 and the auxiliary capacitor wiring 33 are set to a constant DC potential. In FIG. 8B, an AC voltage Va is applied to the counter electrode 19 of the liquid crystal capacitor CLC via a buffer, and an AC voltage Vb is applied to the auxiliary capacitor wiring 33 of the auxiliary capacitor CCS via a buffer. It is an equivalent circuit. The AC voltage Va and the AC voltage Vb have the same voltage amplitude and the same phase. Therefore, in this case, the potential of the counter electrode 19 and the potential of the auxiliary capacitance wiring 33 vibrate in the same phase. Further, as shown in FIG. 8A, the liquid crystal capacitor CLC and the auxiliary capacitor CCS are connected in parallel, and a common AC voltage may be applied through a buffer instead of a constant DC potential.

  In these equivalent circuits, a selection voltage is applied to the scanning line 32 to turn on the TFT 20, and a display signal is applied from the signal line 34 to the liquid crystal capacitor CLC and the auxiliary capacitor CCS. Next, by applying a non-selection voltage to the scanning line 32 to turn off the TFT 20, the pixel holds the charge written in the liquid crystal capacitor CLC and the auxiliary capacitor CCS. Here, since the auxiliary capacitance line 33 for forming the auxiliary capacitance CCS of the pixel is provided at a position where no capacitive coupling is generated between the scanning line 32 and the scanning line 32 (see, for example, FIG. 5), the equivalent circuit is ignored by ignoring the capacitive coupling. Is illustrated. If the setting of rewriting the charge of the liquid crystal capacitor CLC, that is, the screen of the liquid crystal panel 2 at a rewrite frequency of 45 Hz or less is performed by the synchronous clock generation circuit 7 in this state, unlike the case where the auxiliary capacitor CCS is formed with an on-gate structure, scanning is performed. The potential fluctuation of the pixel electrode 10 which is the electrode of the liquid crystal capacitance CLC due to the potential fluctuation of the line 32 is suppressed.

  By adopting a low frequency drive of 45 Hz or less, the frequency of the scanning signal is reduced and the power consumption of the scanning signal driver is sufficiently reduced, and the polarity inversion frequency of the display signal is reduced. In the case of the configuration, the power consumption of the source driver 4 is sufficiently reduced. Further, by suppressing the potential fluctuation of the pixel electrode 10, a stable display quality free from flicker can be obtained.

  9A to 9E show the scanning signal waveform, the display signal waveform, the potential of the pixel electrode 10, and the reflected light intensity by the reflective electrode 29 when the liquid crystal display device 1 having the above configuration is driven at a low frequency. Show. The screen rewriting frequency was set to 6 Hz, which is 1/10 of 60 Hz. Specifically, in the rewriting cycle 167 msec corresponding to 6 Hz, the selection period per scanning line 32 is set to 0.7 msec and the non-selection period is set to 166.3 msec. The display signal supplied to the signal line 34 is driven so that the polarity is inverted every scanning signal, and the display signal whose polarity is inverted every time rewriting is input to one pixel.

  9A shows the scanning signal waveform output to the scanning line 32 that is one line higher than the scanning line 32 of the pixel of interest, and FIG. 9B shows the pixel of the pixel of interest (own stage). 9C shows the scanning signal waveform output to the scanning line 32, FIG. 9C shows the display signal waveform output to the signal line 34 of the pixel of interest, and FIG. 9D shows the pixel electrode of the pixel of interest. A potential of 10 is shown. As can be seen from FIGS. 9A and 9D, when the selection voltage is applied to the scanning line 32 on one line, the potential of the pixel electrode 10 is stable. At this time, when the intensity of the reflected light from the reflective electrode 29 was measured, almost no change in the reflected light intensity was confirmed as shown in FIG. In addition, it was confirmed that a uniform and good display quality can be obtained with no flickering as a result of visual evaluation. Similar results were obtained for the transmission mode display using the transmission electrode region 10b of the pixel electrode 10.

  Next, when the power consumption of the liquid crystal display device 1 was further measured, it was 160 mW when driven with a screen rewrite cycle of 16.7 msec (rewrite frequency 60 Hz), whereas the screen rewrite cycle was 167 msec (rewrite). When driving at a frequency of 6 Hz), the power consumption was 40 mW, which was confirmed to be greatly reduced.

  As an example of setting the rewriting frequency to 45 Hz or less, 6 Hz is given in FIG. 9, but a preferable range of the rewriting frequency is 0.5 Hz to 45 Hz.

  The reason will be described with reference to FIGS. 10 (a) and 10 (b). 10A and 10B show the driving frequency of the liquid crystal voltage holding ratio Hr when the writing time is fixed (for example, 100 μsec) for the liquid crystal material (ZLI-4792 manufactured by Merck) used for the liquid crystal layer 42. FIG. It is the result of measuring the (rewrite frequency) dependency. FIG. 10B is an enlarged view of the region where the drive frequency is 0 Hz to 5 Hz in FIG.

  As can be seen from FIG. 10B, the liquid crystal voltage holding ratio Hr decreases from around 1 Hz, which is approximately 97%, and rapidly decreases when it is lower than 0.5 Hz, which is approximately 92%. When the liquid crystal voltage holding ratio Hr becomes too small, the potential of the pixel electrode 10 varies due to the leakage current of the liquid crystal layer 42 and the TFT 20, and the brightness changes, causing flicker. Further, the OFF resistance value of the TFT 20 does not fluctuate greatly in the time domain such as 1 sec to 2 sec after the writing discussed here. Therefore, the display flicker greatly depends on the liquid crystal voltage holding ratio Hr.

  Therefore, the potential fluctuation of the pixel electrode 10 is sufficiently suppressed by setting the lower limit to 0.5 Hz while setting the rewriting frequency to 45 Hz or less. Thereby, it is possible to achieve sufficiently low power consumption and reliable prevention of pixel flickering. More preferably, the rewrite frequency is set to 15 Hz or less and the power consumption is greatly reduced, while the lower limit is set to 1 Hz to suppress the potential fluctuation of the pixel electrode 10 to be extremely small. Accordingly, extremely low power consumption and more reliable prevention of pixel flickering can be achieved.

  As described above, the synchronous clock generation circuit 7 can set a plurality of rewrite frequencies. Therefore, for example, when displaying still images or images with little motion, the rewriting frequency is set to 45 Hz or less to reduce power consumption, and when displaying moving images, the rewriting frequency is set to 45 Hz or more for smoothness. The rewriting frequency suitable for the state of the image to be displayed can be set such as ensuring the display. If each of the plurality of rewrite frequencies is set to an integer multiple of the lowest rewrite frequency such as 15 Hz, 30 Hz, 45 Hz, and 60 Hz, a common reference synchronization signal may be used for all rewrite frequencies. In addition to this, it is possible to easily thin out or add display signals to be supplied when the rewriting frequency is switched. Further, as shown in this example, when the rewriting frequency is set to the integral multiplication of 2 of the lowest rewriting frequency such as 30 Hz which is twice 15 Hz and 60 Hz which is four times 15 Hz, the lowest frequency Each of the rewriting frequencies can be generated by using a normal simple frequency dividing circuit that performs frequency conversion by dividing the logic signal by 1 by an integer power of 2.

  Further, in the liquid crystal display device 1, a cycle for updating the display content of the liquid crystal panel 2 to a different image, that is, a cycle for supplying a display signal for supplying each pixel with different image data and updating the display state. The refresh frequency to be determined is set. By specifying the relationship between the rewrite frequency and the refresh frequency as follows, the characteristics of the liquid crystal panel 2 can be improved.

  For example, if at least the lowest one of a plurality of types of rewrite frequencies is set to an integer multiple of 2 or more of the refresh frequency, the rewritten frequencies set in such a manner can display the same display contents from the previous update to the next update. Thus, the number of times each pixel is selected based on the rewriting frequency is an integer number of 2 or more. If the refresh frequency is 3 Hz, the rewrite frequency of 6 Hz in the example of FIG. 9 is twice the refresh frequency. Therefore, a positive display signal and a negative display signal are applied to the same pixel from the previous update to the next update. Can be supplied once at a time. Therefore, the same display content can be displayed by reversing the polarity of the potential of the pixel electrode 10 by AC driving, and the reliability of the liquid crystal material used for the liquid crystal panel 2 is improved.

  If the synchronous clock generation circuit 7 can change at least the lowest rewrite frequency to an integer multiple of 2 or more of the refresh frequency after the change in accordance with the change of the refresh frequency, the refresh frequency is changed. Even so, at the rewriting frequency in which the setting is changed, the same display content on the liquid crystal panel 2 can be displayed with the polarity of the potential of the pixel electrode 10 reversed by AC driving. Therefore, the reliability of the liquid crystal used for the liquid crystal panel 2 can be easily maintained. For example, when the refresh frequency is changed from 3 Hz to 4 Hz, the rewrite frequency such as 6 Hz, 15 Hz, 30 Hz, and 45 Hz can be changed to the rewrite frequency such as 8 Hz, 20 Hz, 40 Hz, and 60 Hz. Furthermore, if the lowest rewriting frequency is set to an integer of 2 or more such as 6 Hz in the state where the above conditions are satisfied, the refresh frequency becomes 1 Hz or more and the display content on the screen can be updated once or more per second. Therefore, when the clock is displayed on the screen of the liquid crystal panel 2, the second display can be performed accurately at intervals of one second.

  As described above, according to the liquid crystal display device 1 of the present embodiment, low power consumption can be achieved while maintaining good display quality in a configuration having switching elements. Further, by using a liquid crystal display device capable of performing display in the reflection mode as the liquid crystal display device 1, the ratio of low power consumption by driving at 45 Hz or less increases.

  The circuit configuration for low frequency driving used in the liquid crystal display device of the present invention is not limited to the above example, and can be realized by providing a frame memory in the controller or source driver and lowering the clock frequency.

  As described above, according to the first embodiment of the present invention, a liquid crystal display device capable of displaying high quality with low power consumption in which flicker is not visually recognized even when driving at a low frequency of 45 Hz or less is provided. Further, the dual-use liquid crystal display device according to the present invention can perform high-quality display at least with no jaggedness in the transmissive electrode region in a configuration employing a staggered arrangement of switching elements.

(Embodiment 2)
The liquid crystal display device according to Embodiment 2 of the present invention is a dual-use liquid crystal display device in which the electrode potential difference of the reflection portion and the electrode potential difference of the transmission portion are substantially equal. Here, the electrode potential difference refers to a DC voltage applied to the liquid crystal layer in a state where no forcible voltage for display is applied (hereinafter the same). In the dual-use liquid crystal display device according to the second embodiment, since the electrode potential difference between the reflection portion and the transmission portion is substantially equal, the occurrence of flicker due to the electrode potential difference peculiar to the dual-use liquid crystal display device is suppressed.

  First, with reference to FIG. 14 and FIG. 15, the problem of flicker caused by electrode potential difference in a known dual-use liquid crystal display device will be described.

  A dual-use liquid crystal display device 500 shown in FIG. 14 includes a counter-side substrate 510 having a transparent common electrode 512 formed of a columnar crystalline oxide (hereinafter referred to as “ITO”) mainly composed of indium oxide and tin oxide. And an element side substrate 520 having a plurality of pixel electrodes 525 arranged in a matrix each defining a pixel P ′, and a liquid crystal layer 530 sandwiched between the two substrates. Each pixel electrode 525 includes a reflective electrode (reflective electrode region) 524 that defines the reflective portion R ′ of the pixel P ′ and a transparent electrode (transmissive electrode region) 522 that defines the transmissive portion T ′ of the pixel P ′. ing. The reflective electrode 524 is formed from an Al layer, and the transparent electrode 522 is formed from an ITO layer. That is, the liquid crystal layer of the reflective portion R ′ is sandwiched between the Al layer and the ITO layer, and the liquid crystal layer of the transmissive portion T ′ is sandwiched between the ITO layers. In the reflection part R ′, a voltage is applied between the transparent common electrode 512 of the counter-side substrate 510 and the reflection electrode 524 of the element-side substrate 520, and external light incident from the counter-side substrate 510 is reflected on the element-side substrate 520. Display is performed by reflecting the light at 524 and exiting from the opposite substrate 510. On the other hand, in the transmissive portion T ′, a voltage is applied between the transparent common electrode 522 of the counter substrate 510 and the transparent electrode 522 of the element substrate 520, and auxiliary light from the backlight source disposed behind the liquid crystal panel is received. Display is performed by transmitting through and exiting from the opposite substrate 510. Note that the reflective electrode 524 is formed so as to cover the surface of the interlayer insulating film 523 having fine unevenness on the surface, and as a result, the surface of the reflective electrode 524 also has fine unevenness, thereby reflecting the reflected light. The direction of travel is controlled. That is, the reflective electrode 524 reflects with appropriate directivity.

  As described above, the pixel electrode 525 of the dual-use liquid crystal display device 500 is formed of different electrode materials (materials having different work functions) in the reflective electrode 524 of the reflective portion R ′ and the transparent electrode 522 of the transmissive portion T ′. ing. As a result, as shown in FIG. 15, since each electrode potential is different, an electrode potential difference generated in each of the reflection portion R ′ and the transmission portion T ′ (applied to the liquid crystal layer without applying a compulsory voltage for display) (DC voltage difference A and B in the figure).

  Therefore, even when the same voltage is applied to each electrode, the voltage applied to each liquid crystal layer is different between the reflective portion R ′ and the transmissive portion T ′ in the pixel P ′, so that one pixel A uniform voltage is not applied within P ′. That is, even if the offset voltage is set so as to cancel the pull-in voltage and the electrode potential difference A in the transmission part T ′, the reflection part R ′ has an “opposing deviation” corresponding to the electrode potential difference B−the electrode potential difference A, As a result, flicker may be observed.

  Note that the electrode potential difference B in the reflection portion R ′ is greatly influenced by the electrode potential (or work function) of the material constituting the electrodes facing each other through the liquid crystal layer, but even if the same material is used, If the material of the alignment film formed on the liquid crystal layer side surface of the electrode is different, an electrode potential difference may occur. Therefore, although the electrode potential difference A of the transmission part T ′ having a configuration in which the liquid crystal layer is sandwiched between the ITO layers is smaller than the electrode potential difference B, it is generally not zero.

  Hereinafter, the configuration and operation of the dual-use liquid crystal display device 400 according to Embodiment 2 of the present invention will be described with reference to FIGS. 11 and 12. 11 and 12 are diagrams schematically showing a configuration facing one pixel P of the liquid crystal display device 400, and FIG. 11 corresponds to a cross-sectional view taken along line XI-XI in FIG.

  The liquid crystal display device 400 includes a counter substrate (the other substrate) 410 and an element side substrate (one substrate) 420 facing each other, and a liquid crystal layer 430 sandwiched between them.

  The counter substrate 410 is a glass substrate and a counter substrate body 411 is formed. On the outside of the substrate, a retardation plate for controlling the state of incident light, a polarizing plate, and an antireflection film (both shown in the figure). (Not shown) are provided in order. On the other hand, an RGB color filter (not shown) for color display, a transparent common electrode 412 made of ITO or the like, and a rubbing-treated alignment film (not shown) are sequentially provided on the inner side of the substrate.

  The element side substrate 420 is formed of a glass substrate, and an element side substrate body 421 is formed. Inside the substrate, a plurality of gate bus lines (scanning lines) 427 are provided so as to extend in parallel with each other. . In addition, an insulating layer (gate insulating layer; not shown) is provided so as to cover it. On the insulating layer, a plurality of source bus lines (signal lines) 428 are provided so as to extend in parallel with each other in a direction orthogonal to a direction in which the gate bus line 427 extends. At each intersection of the gate bus line 427 and the source bus line 428, a TFT element 429 which is a three-terminal nonlinear switching element is provided. The gate electrode 429 a of the TFT element 429 is connected to the gate bus line 427, and the source electrode 429 b is connected to the source bus line 428. The drain electrode 429c of the TFT element 429 is connected to a substantially rectangular transparent electrode 422 made of, for example, ITO (work function is about 4.9 eV) provided on the insulating layer.

  On the transparent electrode 422, an interlayer insulating film 423 having fine irregularities formed on the surface is provided, and the reflective electrode 424 made of, for example, Al (work function is about 4.3 eV) so as to cover the surface. Is provided. The reflective electrode 424 has a rectangular opening and a portion where the transparent electrode 422 is exposed, and the periphery of the opening serves as a contact portion 424a to electrically connect the transparent electrode 422 and the reflective electrode 424.

  The exposed transparent electrode (transmission electrode region) 422 defines the transmission portion T, and the reflection electrode (reflection electrode region) 424 disposed so as to surround the transparent electrode 422 defines the reflection portion R. That is, one pixel electrode 425 is configured by the transparent electrode 422 and the reflective electrode 424, and one pixel P is configured by the reflective portion R and the transmissive portion T.

In the liquid crystal display device 400 according to the present embodiment, the surface of the reflective electrode 424 has InZnOx (indium oxide (In ₂ O ₃ ) and zinc oxide (ZnO) as main components, the work function is about 4.8 eV). In the reflective portion R, the liquid crystal layer 430 is formed between the transparent common electrode 412 of the opposite substrate 410 and the amorphous transparent conductive film 426 of the element side substrate 420. An electrode potential difference, which is a voltage applied, and an electrode potential difference, which is a voltage applied to the liquid crystal layer 430, between the transparent common electrode 412 of the opposing substrate 410 and the transparent electrode 422 of the element side substrate 420 in the transmission part T are approximately Are equal. Specifically, the difference between the work function of the amorphous transparent conductive film 426 that covers the reflective electrode 424 and the work function of the transparent electrode 422 is set to be within 0.3 eV. If the Al reflective electrode 424 is coated with InZnOx, both of them can be simultaneously formed by etching with a weak acid etchant for Al etching.

  On the pixel electrode 425 which is the uppermost layer of the element side substrate 420, an alignment film (not shown) subjected to a rubbing process is provided.

  The liquid crystal layer 430 is made of nematic liquid crystal having electro-optical characteristics.

  In the liquid crystal display device 400 having the above configuration, external light incident from the counter substrate 410 is reflected by the reflective electrode 424 of the reflecting portion R and emitted from the counter substrate 410, and the back provided on the back of the element substrate 420 is provided. Auxiliary light of light (not shown) is incident from the element-side substrate 420, is transmitted through the transparent electrode 422 of the transmission part T, and is emitted from the counter-side substrate 410. For each pixel P, electrodes on both substrates By controlling the voltage applied between them, the alignment state of the liquid crystal of the liquid crystal layer 430 is changed, thereby adjusting the amount of light emitted from the opposite substrate 410 to perform display.

  According to the dual-use liquid crystal display device 400 having the above-described configuration, the reflective electrode 424 is covered with the amorphous transparent conductive film 426, so that the electrode potential difference of the reflective portion R and the electrode potential difference of the transmissive portion T are substantially equal. In other words, since the DC voltage applied between the portion of the liquid crystal layer 430 corresponding to the reflective portion R and the portion of the liquid crystal layer 430 corresponding to the transmissive portion T is substantially equal, Even when a voltage is applied to these electrodes, a substantially uniform voltage is applied within one pixel P, whereby a good display quality can be obtained.

  As described above, in the dual-use liquid crystal display device 500 having the conventional structure shown in FIG. 14, the work function of the electrode material of the reflective electrode 524 and the work function of the electrode material of the transparent electrode 522 in the pixel electrode 525 are greatly different ( For example, in the case of Al and ITO, the difference in work function is 0.6 eV or more), and the electrode potential difference is greatly different between the reflection portion R ′ and the transmission portion T ′. On the other hand, only one offset voltage can be provided for all the pixels P '. Therefore, for either one of the transmission part T ′ and the reflection part R ′, the optimum offset amount can be set so that the electrode potential difference and the pull-in voltage are canceled and the DC voltage component is not applied to the liquid crystal layer 530 as an effective value. However, with respect to the other of the transmission part T and the reflection part R, a DC voltage component is applied to the liquid crystal layer 530 as an effective value. That is, the waveform of the AC voltage applied to the liquid crystal layer 530 becomes asymmetric at that portion. When the display in this state is visually confirmed, flicker occurs and the display quality becomes extremely low. In addition, when the DC voltage component is applied for a long time, the reliability of the liquid crystal material is also adversely affected.

  On the other hand, in the liquid crystal display device 400 of the second embodiment, the electrode potential of the amorphous transparent conductive film (here InZnOx) 426 covering the reflective electrode 424 and the electrode potential of the transparent electrode (here ITO) 422 are different. Since the electrode potential difference of the reflection portion R and the electrode potential difference of the transmission portion T are made substantially equal, the electrode potential difference and the pull-in voltage are offset by one offset voltage, and the liquid crystal layer 430 is effectively It is possible to prevent the DC voltage component from being applied, and it is possible to obtain a good display quality in which flicker is not observed in both the reflection part R and the transmission part T. In addition, since no DC voltage is applied to the liquid crystal layer 430, it is possible to prevent a decrease in the reliability of the liquid crystal material.

  In the liquid crystal display device 400 of the present embodiment, the difference between the work function of the amorphous transparent conductive film 426 that covers the reflective electrode 424 and the work function of the transparent electrode 422 is within 0.3 eV. A sufficient effect can be obtained because the potential of the amorphous transparent conductive film 426 covering the electrode 424 and the potential of the transparent electrode 422 are substantially equal.

  Below, the test done about the liquid crystal display device which changed the work function difference of an amorphous transparent conductive film and a transparent electrode is demonstrated. The work function difference between the amorphous transparent conductive film and the transparent electrode is changed by changing the film forming conditions of the transparent electrode to InZnOx and the transparent electrode to ITO as the amorphous transparent conductive film covering the Al reflective electrode. Four liquid crystal display devices having the same configuration as that of the present embodiment, which are 0.1 eV, 0.2 eV, 0.3 eV, and 0.4 eV, are prepared, respectively, so that no DC voltage component is applied to the liquid crystal layer of the reflective portion. The display quality when the offset voltage was set to was visually evaluated. The driving frequency was set to a general 60 Hz. The results are shown in Table 3.

  In this test result, when the work function difference between the amorphous transparent conductive film and the transparent electrode was 0.3 eV or less, there was no change in luminance in both the reflective part and the transmissive part, whereas the display quality was good. When the work function difference was 0.4 eV, some flicker was generated in the transmission part. This is because if the work function difference is 0.3 eV or less, the electrode potential difference between the reflection part and the transmission part is almost equal to the extent that the offset of the electrode potential can be offset by the application of one offset voltage. On the other hand, when the work function difference is 0.4 eV, the difference between the electrode potentials of the reflection part and the transmission part is slightly large, so that it becomes difficult to cancel the electrode potential difference by applying one offset voltage. It is thought that. Therefore, the work function difference between the amorphous transparent conductive film and the transparent electrode is preferably smaller than 0.4 eV, and more preferably 0.3 eV or less.

  Furthermore, in the liquid crystal display device 400 of this embodiment, the film thickness of the amorphous transparent conductive film 426 that covers the reflective electrode 424 is set to 1 nm or more and 20 nm or less. By setting the film thickness of the amorphous transparent conductive film 426 within the above range, a uniform film thickness can be formed and a good display quality can be obtained. By coating the reflective electrode 424 with the amorphous transparent conductive film 426, the electrode potential difference between the reflective portion R and the transmissive portion T can be made substantially equal, but the amorphous transparent conductive film with a film thickness of several hundred nm is used. When the film 426 is formed, light reflected by the reflective electrode 424 becomes weak due to light absorption by the amorphous transparent conductive film 426, and light reflected by the surface of the amorphous transparent conductive film 426 and reflected by the surface of the reflective electrode 424. The outgoing light is colored by interference with the light to be displayed, and the display quality is low.

  Below, the test done about the liquid crystal display device which changed the film thickness of the amorphous transparent conductive film is demonstrated. In this embodiment, the amorphous transparent conductive film covering the Al reflective electrode is InZnOx, the transparent electrode is ITO, and the film thickness of the amorphous transparent conductive film is 5 nm, 10 nm, 15 nm, 20 nm, and 30 nm, respectively. Five liquid crystal display devices having the same configuration were prepared, and the relationship between each wavelength and reflectance was examined. The result is shown in FIG. For reference, data of an amorphous transparent conductive film not provided, that is, a film thickness of 0 nm is also shown.

  As can be seen from FIG. 13, the reflectance decreases as the film thickness of the amorphous transparent conductive film increases, and the reflectance decreases as the wavelength of light decreases.

  In the dual-use liquid crystal display device, since the color of the reflective electrode directly affects the display quality, it is important to control the film thickness of the amorphous transparent conductive film on the reflective electrode. About said five liquid crystal display devices, each display quality was confirmed visually. The results are shown in Table 4.

  In this test result, when the film thickness of the amorphous transparent conductive film is 20 nm or less, the thinner the film thickness, the less the coloring and the better the display quality, whereas the display film thickness is 30 nm. Was markedly colored. This is considered to be because the influence of light interference is small when the film thickness is 20 nm or less, whereas the influence is large when the film thickness is 30 nm. Therefore, the film thickness of the amorphous transparent conductive film is preferably less than 30 nm, and more preferably 20 nm or less. In addition, even if the film thickness of the amorphous transparent conductive film is 1 nm, it has been confirmed that the effect of making the electrode potential difference substantially equal between the reflective part and the transmissive part is achieved. If the thickness is reduced, it becomes difficult to control the film thickness by sputtering. Therefore, the film thickness of the amorphous transparent conductive film is preferably 1 nm or more.

  By the way, an impurity (ionic impurity) may be mixed into the liquid crystal layer 430 during the step of injecting the liquid crystal material between the two substrates or outflow from the sealing resin material. In the case of an AC drive liquid crystal display device, if the electrode materials of the electrodes of the two substrates are different, an electrode potential difference is generated between them, and the impurities are adsorbed on one of the substrates by electrostatic attraction, and the impurities are absorbed in the display region. A non-adsorbed portion and an adsorbed portion are generated, and in the former, a predetermined voltage is applied to the liquid crystal layer, whereas in the latter, a predetermined voltage is not applied to the liquid crystal layer. In this case, it is necessary to set a different offset voltage for each part, but since only one offset voltage can be provided, flicker occurs in the display of the part where the impurities are adsorbed. This flicker is noticeably observed at the peripheral portion of the display area because it is greatly affected by the outflow of impurities from the sealing resin material.

  However, in the liquid crystal display device 400 of the present embodiment, for example, the amorphous transparent conductive film 426 covering the reflective electrode is InZnOx, the transparent electrode 422 is ITO, and the transparent common electrode 412 is ITO, so that the pixel electrode 425 is obtained. If the electrode potential of the transparent common electrode 412 and the electrode potential of the transparent common electrode 412 are substantially equal, the adsorption of impurities to the substrate can be suppressed, thereby suppressing flicker caused by the adsorption of impurities to the substrate and high display quality. Can be obtained.

  The present invention is not limited to this embodiment, and may have other configurations.

  For example, in the present embodiment, an example in which the reflective electrode 424 is formed using Al is shown, but Ag may be used, or a laminated structure of Al / Mo or the like may be used. Further, ITO and InZnOx shown as materials of the transparent common electrode 412, the transparent electrode 422, and the amorphous transparent conductive film 426 are merely examples, and other materials may be used.

  In this embodiment, the reflective electrode 424 is covered with the amorphous transparent conductive film 426. However, the present invention is not particularly limited to this, and the reflective electrode 424 is covered with a crystalline transparent conductive film such as ITO. Also good.

  In this embodiment, the switching element is the TFT element 129. However, the switching element is not particularly limited to this, and an MIM element (Metal Insulator Metal) that is a two-terminal nonlinear element may be used. . When MIM is used, positive and negative pull-in voltages are generated and cancel each other. Therefore, in the MIM type liquid crystal display device, the set value of the offset voltage is changed by that amount from the TFT type.

  In the present embodiment, the reflective electrode 424 is covered with the amorphous transparent conductive film 426 so that the electrode potential difference of the reflective portion R and the electrode potential difference of the transmissive portion T are substantially equal. For example, by performing surface treatment (for example, surface treatment with oxygen plasma, UV ozone, etc.) on the reflective electrode, the work function of the reflective electrode is made close to that of the transparent electrode, thereby transmitting the reflective electrode to the reflective portion. The electrode potential difference of the part may be made substantially equal. Further, by covering both surfaces of the reflective electrode and the transparent electrode with a thin gold film having a thickness of about 0.4 nm, the work functions of the reflective electrode and the transparent electrode are made the same, thereby the electrodes of the reflective part and the transparent part The potential differences may be made substantially equal (note that a thin gold film of about 0.4 nm does not affect the transmittance of the transparent electrode). In addition, by forming a predetermined insulating film or the like on the reflective electrode or applying a predetermined organic material such as an alignment film, the work function (apparent work function) of the reflective electrode is changed to that of the transparent electrode. You may make it the electrode potential difference of a reflection part and a permeation | transmission part substantially equal by it, and thereby.

(Embodiment 3)
Next, the configuration and operation of the liquid crystal display device 600 according to Embodiment 3 of the present invention will be described with reference to FIGS. A liquid crystal display device 600 exemplified below is a dual-use display device in which each pixel has a reflective portion and a transmissive portion, and has a configuration that can electrically compensate for the difference in electrode potential between the reflective portion and the transmissive portion. This is different from the liquid crystal display device 400 described above.

  FIG. 16 shows a schematic equivalent circuit diagram of the liquid crystal display device 600, and FIGS. 17A and 17B show the configuration of one pixel of the liquid crystal display device 600. FIG. 17A is a plan view, and FIG. 17B is a cross-sectional view taken along line 17B-17B 'in FIG. 17A.

  As shown in FIG. 16, the liquid crystal display device 600 has the same circuit configuration as a general active matrix drive type liquid crystal display device.

  A gate bus line 604 as a scanning line extending in the row direction is connected to each of the plurality of scanning terminals 602, and a source bus line 608 is connected to each of the plurality of signal terminals 606 as a signal line. Yes. A TFT 614 serving as a switching element is provided in the vicinity of the intersection between the bus lines 604 and 608. A gate electrode (not shown) of the TFT 614 is connected to the scanning line 604, and a source electrode (not shown) is connected to the signal line 608. Further, a liquid crystal capacitor (pixel electrode) 612 and an auxiliary capacitor (auxiliary capacitor electrode) 616 are connected to the drain side of the TFT 614, and these constitute a pixel capacitor 610. The auxiliary capacitor counter electrode of the auxiliary capacitor 616 is connected in common to the auxiliary capacitor bus line (auxiliary capacitor counter electrode line) 620. The liquid crystal capacitor 612 includes a pixel electrode 612, a counter electrode (628 or 629), and a liquid crystal layer 664 provided therebetween (see FIGS. 17A and 17B).

  The configuration of one pixel of the liquid crystal display device 600 will be described in more detail with reference to FIGS. 17 (a) and 17 (b).

  The pixel electrode 612 of the liquid crystal display device 600 includes a reflective electrode region 651 and a transmissive electrode region 652. In the peripheral portion of the pixel electrode 612, the reflective electrode region 651 overlaps with part of the scanning line 604 and the signal line 608, and contributes to improvement of the pixel aperture ratio. The counter electrode that faces the pixel electrode 612 via the liquid crystal layer 664 includes a first counter electrode 628 that faces the reflective electrode region 651 and a second counter electrode 629 that faces the transmissive electrode region 652. As described above, the two systems of counter electrodes 628 and 629 are provided corresponding to the reflective portion and the transmissive portion, respectively, so that the difference in electrode potential between the reflective portion and the transmissive portion can be electrically compensated. This operation will be described in detail later.

  A cross-sectional structure of the liquid crystal display device 600 will be described with reference to FIG. In FIG. 17B, a polarizing plate, a lighting device, a retardation plate, and the like provided on the outer surfaces of the substrates 622 and 624 are omitted.

The substrate 622 is a transparent insulating substrate (for example, a glass substrate), and a gate electrode 636 of the TFT 614 is formed thereon. A gate insulating film 638 is provided over the gate electrode 636, and a semiconductor layer 640 is provided over the gate insulating film 638 so as to overlap with the gate electrode 636. N ⁺ Si layers 642 and 644 are provided so as to cover both ends of the semiconductor layer 640, a source electrode 646 is provided on the left n ⁺ Si layer 642, and a drain electrode 648 is provided on the right n ⁺ Si layer 644. Is provided. The drain electrode extends to the pixel portion and also functions as the transmissive electrode region 652 of the pixel electrode 612. Further, the auxiliary capacitance bus line 620 forms an auxiliary capacitance 616 (see FIG. 16) between the auxiliary capacitance bus line 620 and the drain electrode 648 through the gate insulating film 638.

  An interlayer insulating film 650 is provided on these including the scanning line 604 and the signal line 608. On the interlayer insulating film 650, a laminated film of Al, an alloy layer containing Al, or Al / Mo is provided as the pixel electrode 612, and this portion serves as a reflective electrode region 651. Further, an opening is formed by removing a part of the interlayer insulating film 650, and the drain electrode 648 of the TFT 614 is connected to the pixel electrode (alloy layer constituting the reflective electrode region 651) 612 by using this part as a contact hole. ing. An extended portion of the drain electrode 648 exposed in the opening of the interlayer insulating film 650 becomes a transmissive electrode region 652. Further, an alignment film 654 is formed on the pixel electrode 612 as necessary. These are collectively referred to as an active matrix substrate 622S.

  On the other hand, the substrate 624 is a transparent insulating substrate (for example, a glass substrate), and a color filter layer (not shown), counter electrodes 628 and 629 made of a transparent conductive film, and an alignment film 660 are provided on the surface. ing. These are collectively referred to as a counter substrate 624S.

  The substrate 624 </ b> S and the substrate 622 </ b> S are held at a distance from each other by a spacer 662, and are bonded to each other at a peripheral portion with a seal member.

  The counter electrode of the conventional liquid crystal display device is formed by a single transparent conductive layer (for example, an ITO layer) over the entire display region. However, as described above, the liquid crystal display device 600 includes the first counter electrode 628. And two counter electrodes of the second counter electrode 629. The first counter electrode 628 and the second counter electrode 629 are each patterned in a comb shape in a direction parallel to the scanning line 604 as schematically shown in FIG. The two groups are electrically separated so that different common signals (also referred to as “common voltages”) can be input to the two groups. In addition, as shown in FIG. 17A, the first counter electrode 628 and the second counter electrode 629 are grouped into the reflective electrode region 651 and the transmissive electrode region 652 when bonded to the active matrix substrate 622S. Are arranged to face each other.

  After the counter substrate 624S and the active matrix substrate 622S are bonded together, the counter electrodes 628 and 629 are connected to the active matrix substrate 622 via the common transition (transfer) 631 in order to input a common signal to the counter electrodes 628 and 629, respectively. Are connected to common signal input wiring (not shown), and corresponding common signals are input from input terminals 632 and 633 of the common signal input wiring. Note that the same signal may be input without providing the common transition.

  Next, the operation of the liquid crystal display device 600 will be described with reference to FIGS. 19A and 19B and FIG. 19A and 19B show an equivalent circuit of one pixel of the liquid crystal display device 600. FIG. 19A shows a state where the TFT 614 is on, and FIG. 19B shows a state where the TFT 614 is off. . FIG. 20 shows signal waveforms (a) to (e) used for driving the pixels.

  The signal waveform (a) indicates a gate signal (scanning signal) Vg input to the scanning line, and the signal waveform (b) indicates a source signal (display signal or data signal) Vs. The signal waveform (c) shows common signals (common signals) Vcom (Vcom1 and Vcom2) input to the counter electrode. Vcom has the same cycle as Vs and the opposite polarity. This is because the absolute value (amplitude) of Vs is reduced and the driving circuit (IC) having a low withstand voltage is used while ensuring the magnitude of the voltage (| Vs−Vcom |) applied to the liquid crystal layer. .

  During the period in which the TFT 614 is in the on state, the voltage Vp (= Vs) is applied to the pixel electrode, and | Vs−Vcom | is applied to the pixel (liquid crystal capacitor Clc and auxiliary capacitor Cs), whereby the liquid crystal capacitor Clc. Further, as shown in FIG. 19A, the auxiliary capacitor Cs is charged with charges of Qlc and Qs, respectively. At this time, the charge Qgd is charged in the gate-drain capacitance Cgd of the TFT 614 to which the gate voltage Vgh (ON voltage) is applied.

  When the TFT 614 is turned off, the state transitions to the state shown in FIG. That is, the charge charged in the gate-drain capacitance Cgd of the TFT 614 to which the gate voltage Vgl is applied is changed to Qgd ′, and as a result, the charges in the liquid crystal capacitance Clc and the auxiliary capacitance Cs are changed to Qlc ′. And Qs ′, and the potential of the pixel electrode changes from Vp to Vp ′. Therefore, when the TFT 614 is switched from on to off, the voltage Vlc applied to the pixel decreases as shown in the signal waveform (d) and signal waveform (e) of FIG.

  This decreasing voltage is called a pull-in voltage (dV), which occurs every time the display signal voltage Vs is switched between positive and negative, and causes flicker. As described above, the offset voltage is set so as to cancel the pull-in voltage, and the common signal Vcom is lowered from the center level of the display signal voltage by the pull-in voltage as described above.

  In the dual-use liquid crystal display device, flicker occurs due to a difference in electrode potential between the reflection portion and the transmission portion in addition to the pull-in voltage. For example, the liquid crystal layer in the reflective part sandwiched between the ITO layer and the Al layer is subjected to an extra DC voltage of about 200 to 300 mV compared to the liquid crystal layer in the transmissive part sandwiched between the ITO layers. Therefore, the optimum offset voltage (counter voltage) is different between the reflection portion and the transmission portion.

  As described with reference to FIGS. 17 and 18, the liquid crystal display device 600 according to Embodiment 3 of the present invention corresponds to the reflective electrode region 651 and the transmissive electrode region 652. 628 and 629, common signal having different center values can be supplied to the respective counter electrodes 628 and 629 as shown as Vcom1 and Vcom2 in the signal waveform (c) of FIG. it can.

  Therefore, as shown in the signal waveform (d) and the signal waveform (e) of FIG. 20, the effective voltages Vrms applied to the liquid crystal layer of the transmissive part and the liquid crystal layer of the reflective part are equal to each other, and are made positive and negative and symmetrical. Therefore, the occurrence of flicker can be prevented. It also suppresses the decrease in voltage holding ratio caused by the deterioration of the liquid crystal material caused by the continuous application of the DC voltage component to the liquid crystal layer, and the display near the seal area around the panel and near the injection port It becomes possible to prevent the occurrence of unevenness and spots.

  Next, the configuration and operation of another liquid crystal display device 700 according to Embodiment 3 will be described with reference to FIGS.

  Similar to the liquid crystal display device 600 described above, the liquid crystal display device 700 includes two counter electrodes (for example, comb shapes) corresponding to the reflection portion and the transmission portion. Similarly to the liquid crystal display device 600, the counter electrode corresponding to the reflective portion is the first counter electrode 628, and the counter electrode corresponding to the transmissive portion is the second counter electrode 629 (see, for example, FIGS. 17 and 18).

  The liquid crystal display device 700 further includes a TFT corresponding to each of the reflective electrode region and the transmissive electrode region, and two auxiliary capacitors corresponding to the reflective portion and the transmissive portion. Also in the liquid crystal display device 700, it is possible to set an offset voltage corresponding to each of the reflective portion and the transmissive portion, the effective voltage Vrms applied to the liquid crystal layer within one pixel can be made uniform, and flicker Can be suppressed.

  FIG. 21 schematically shows the structure of one pixel of the liquid crystal display device 700. The pixel 710 includes a reflective portion 710a and a transmissive portion 710b. The reflective electrode (reflective electrode region) 718a and the transparent electrode (transmissive electrode region) 718b include a TFT 716a, a TFT 716b, and an auxiliary capacitor (CS) 722a, respectively. 722b is connected. The gate electrodes of the TFTs 716a and 716b are both connected to the scanning line 712, and the source electrodes are connected to a common (identical) signal line 714.

  The auxiliary capacitors 722a and 722b are connected to the auxiliary capacitor line 724a and the auxiliary capacitor line 724b, respectively. The auxiliary capacitors 722a and 722b include an auxiliary capacitor electrode electrically connected to the reflective electrode 718a and the transparent electrode 718b, an auxiliary capacitor counter electrode electrically connected to the auxiliary capacitor wires 724a and 724b, respectively, The insulating layer (not shown) provided is formed. The storage capacitor counter electrodes of the storage capacitors 722a and 722b are independent from each other, and have a structure in which different storage capacitor counter voltages can be supplied from the storage capacitor lines 724a and 724b, respectively. The same common signal as that of the first counter electrode 628 is applied to the auxiliary capacitance line 724a corresponding to the reflection portion 710a, and the same common signal as that of the second counter electrode 629 is applied to the auxiliary capacitance line 724b corresponding to the transmission portion 710b. Is done.

  FIG. 22 schematically shows an equivalent circuit for one pixel of the liquid crystal display device 700. In the electrical equivalent circuit, the liquid crystal layers of the reflective portion 710a and the transmissive portion 710b are represented as liquid crystal layers 713a and 713b, respectively. The liquid crystal capacitors formed by the reflective electrode 718a and the transparent electrode 718b, the liquid crystal layers 713a and 713b, and the first and second counter electrodes corresponding to the reflective electrode 718a and the transparent electrode 718b are Clca and Clcb, respectively. Also, auxiliary capacitors 722a and 722b that are independently connected to the liquid crystal capacitors Clca and Clcb of the reflective portion 710a and the transmissive portion 710b are referred to as Ccsa and Ccsb, respectively.

  One electrode of the liquid crystal capacitance Clca and the auxiliary capacitance Ccsa of the reflection portion 710a is connected to the drain electrode of the TFT 716a provided for driving the reflection portion 710a, and the other electrode of the liquid crystal capacitance Clca and the auxiliary capacitance Ccsa is auxiliary. It is connected to the capacitor wiring 724a. One electrode of the liquid crystal capacitor Clcb and the auxiliary capacitor Ccsb of the transmissive portion 710b is connected to the drain electrode of the TFT 716b provided for driving the transmissive portion 710b, and the other electrode of the liquid crystal capacitor Clcb and the auxiliary capacitor Ccsb is auxiliary. It is connected to the capacitor wiring 724b. The gate electrodes of the TFTs 716 a and 716 b are both connected to the scanning line 712, and the source electrodes are both connected to the signal line 714.

  Next, the operation of the liquid crystal display device 700 will be described with reference to FIG. FIG. 23 schematically shows the waveform and timing of each voltage used to drive the liquid crystal display device 700.

  (A) is the signal waveform Vs of the signal line 714, (b) is the signal waveform Vcsa of the auxiliary capacitance wiring 724a, (c) is the signal waveform Vcsb of the auxiliary capacitance wiring 724b, and (d) is the signal waveform Vg of the scanning line 12. (E) shows the signal waveform Vlca of the reflective electrode 718a, and (f) shows the signal waveform Vlcb of the transparent electrode 718b. In addition, the first counter electrode 628 corresponding to the reflection part 710a and the second counter electrode 629 corresponding to the transmission part 710b have signal waveforms of the storage capacitor line 724a of (b) and the storage capacitor line 724b of (c), respectively. The same input signals as Vcsa and Vcsb are applied.

  First, when the voltage of Vg changes from VgL to VgH at time T1, the TFTs 716a and 716b are simultaneously turned on (on state), and the voltage Vs of the signal line 714 is supplied to the reflective electrode 718a and the transparent electrode 718b. The liquid crystal capacitors Clca and Clcb of the reflection part 710a and the transmission part 710b are charged. Similarly, the auxiliary capacitors Ccsa and Ccsb are also charged.

  Next, when the voltage Vg of the scanning line 712 changes from VgH to VgL at time T2, the TFTs 716a and 716b are simultaneously turned off (off state), and the liquid crystal capacitors Clca and Clcb and the auxiliary capacitors Ccsa and Ccsb are all turned on. It is electrically insulated from the signal line 714. Immediately after this, the voltage Vlca and Vlcb of the reflective electrode 718a and the transparent electrode 718b drop by substantially the same voltage Vd due to a pull-in phenomenon due to the influence of the parasitic capacitances and the like of the TFTs 716a and 716b.

  At times T3, T4, and T5, the voltages of the reflective electrode 718a and the transparent electrode 718b follow the voltages Vcsa and Vcsb applied to the storage capacitor counter electrode, and become voltages Vlca and Vlcb.

  Here, the voltages Vlca and Vlcb of the reflective electrode 718a and the transparent electrode 718b will be described.

  (B) When a signal having the same voltage and the same amplitude is applied as Vcsa and (c) Vcsb, when the reflective electrode 718a is made of Al, the electrode potential of the transparent electrode 718b and the counter electrodes 628 and 629 is different from that of ITO. Potential difference (DC voltage) is further applied, and the voltage applied to the reflective electrode 718a becomes a signal waveform shifted to the positive voltage side (before applying the offset voltage) as shown in (e) Vlca, and flicker occurs. To do. Therefore, by applying an offset voltage (after applying the offset voltage) so that the voltage applied to the reflective electrode 718a matches the center value of the voltage Vcsa applied to the counter electrode 628, the DC voltage due to the electrode potential difference is canceled, thereby flickering. A display without any can be obtained.

  As described above, the occurrence of flicker can be suppressed by optimally setting the counter voltage (auxiliary capacitor counter voltage) so as to cancel out the direct current component with respect to each of the reflection unit 710a and the transmission unit 710b. .

  As described above, the liquid crystal display devices 600 and 700 according to the third embodiment of the present invention have two counter electrodes that are opposed to the reflective electrode region and the transmissive electrode region, respectively, and are electrically independent. By inputting a common signal having the same polarity, period, and amplitude as the common electrode supplied to the counter electrode facing the transmissive electrode region and having an offset DC voltage at the center value to the counter electrode facing the reflection electrode, The offset DC voltage resulting from the difference in electrode potential difference between the transmission part and the transmission part can be canceled.

  In the liquid crystal display device 400 according to the second embodiment, the electrode configuration of the reflective electrode region is devised to reduce the electrode potential difference between the reflective portion and the transmissive portion, whereas the liquid crystal display device 600 according to the third embodiment and 700 has a configuration in which a voltage that cancels the difference in electrode potential difference can be applied to a liquid crystal layer (reflection region and transmissive portion) including electrode regions having different electrode potentials. Therefore, by using these configurations in combination, it is possible to make the flicker less visible.

  As described above, according to the second and third embodiments, in the dual display device, the “opposite deviation” caused by the reflection part and the transmission part having different electrode potential differences is eliminated or compensated. be able to. However, as described in the first embodiment, it is difficult to precisely control the offset voltage so as to completely eliminate the opposing deviation. In particular, in the dual-purpose display device, the opposing deviation amounts in the reflective region and the transmissive portion are the same. It is difficult to let Therefore, it is preferable to combine Embodiment 1 with Embodiment 2 and / or Embodiment 3. In particular, as described in the first embodiment, when the liquid crystal display device is driven at a low frequency, it is easy to visually recognize even a slight misalignment. Therefore, by combining the second and third embodiments with the first embodiment, Flicker can be made difficult to see.

  According to the present invention, there is provided a liquid crystal display device capable of displaying high quality with low power consumption, in which flicker is not visually recognized even when driving at a low frequency of 45 Hz or less. Further, the dual-use liquid crystal display device according to the present invention can perform high-quality display at least with no jaggedness in the transmissive electrode region in a configuration employing a staggered arrangement of switching elements.

  In addition, according to the present invention, it is possible to suppress the occurrence of flicker due to the difference in electrode potential between the reflective portion and the transmissive portion in a liquid crystal display device having a reflective portion and a transmissive portion for each pixel, thereby improving display quality. can do.

  The liquid crystal display device according to the present invention is applied to various electronic devices such as mobile devices such as mobile phones, pocket game machines, PDAs (Personal Digital Assistants), mobile TVs, remote controls, notebook personal computers, and other mobile terminals. Preferably used. In particular, when mounted on a battery-driven electronic device, low power consumption can be achieved while maintaining good display quality, and long-time driving is possible.

It is a top view which shows typically the structure of the reflection type liquid crystal display device 100 by Embodiment 1 of this invention. It is a top view which shows typically the structure of the other reflective liquid crystal display device 200 by Embodiment 1 of this invention. It is a top view which shows the arrangement | sequence of the pixel electrode of a transflective liquid crystal display device, (a) shows the Example of the arrangement | sequence by this invention, (b) shows the arrangement | sequence of a comparative example. 1 is a schematic cross-sectional view of a dual-use liquid crystal display device 300 according to Embodiment 1 of the present invention. 1 is a schematic top view of a dual-use liquid crystal display device 300 according to Embodiment 1 of the present invention. It is a top view which shows other arrangement | positioning of the pixel electrode of the dual use type liquid crystal display device by Embodiment 1 of this invention. 1 is a system block diagram of a liquid crystal display device 1 according to Embodiment 1 of the present invention. (A) And (b) is a figure which shows the equivalent circuit about 1 pixel in a liquid crystal panel of the structure provided with auxiliary capacitance CCS. (A) to (e) are diagrams respectively showing a scanning signal waveform, a display signal waveform, a potential of a pixel electrode, and reflected light intensity when the liquid crystal display device according to the first embodiment is driven at a low frequency. It is a graph which shows the drive frequency (rewriting frequency) dependence of liquid crystal voltage holding ratio Hr. It is a figure which shows typically the structure of the dual-use type liquid crystal display device 400 by Embodiment 2 of this invention, and is sectional drawing along the XI-XI line in FIG. It is a top view which shows typically the structure of 1 pixel of the dual use type liquid crystal display device 400 by Embodiment 2 of this invention. It is a graph which shows the relationship between the wavelength of the light for every film thickness of an amorphous transparent conductive film, and a reflectance. It is sectional drawing which shows the structure for one pixel of the dual-use type liquid crystal display device of a conventional structure. It is explanatory drawing shown about the electrode potential difference of a permeation | transmission part, and the electrode potential difference of a reflection part. It is a figure which shows typically the structure of the liquid crystal display device 600 by Embodiment 3 of this invention. (A) And (b) is a figure which shows typically the structure of 1 pixel part of the liquid crystal display device 600 by Embodiment 3 of this invention, (a) is a top view, (b) is in (a). It is sectional drawing along the XVIIb-XVIIb line | wire. It is a top view which shows typically the structure of the counter electrode of the liquid crystal display device 600 by Embodiment 3 of this invention. 4A and 4B are diagrams showing an equivalent circuit of one pixel of a liquid crystal display device 600 according to Embodiment 3 of the present invention, where FIG. 5A shows a state in which a TFT is on and FIG. 5B shows a state in which the TFT is off. It is a figure which shows the signal waveform (a)-signal waveform (e) used for the drive of the liquid crystal display device 600 by Embodiment 3 of this invention. It is a figure which shows typically the structure of 1 pixel of the other liquid crystal display device 700 by Embodiment 3 of this invention. It is a figure which shows typically the equivalent circuit for 1 pixel of the liquid crystal display device 700 by Embodiment 3 of this invention. It is a figure which shows typically the waveform and timing of each voltage used in order to drive the liquid crystal display device 700 by Embodiment 3 of this invention.

Explanation of symbols

10 Pixel electrode 20 TFT
32 Scanning line 34 Signal line 100, 400 Liquid crystal display device 110, 410 Opposite side substrate 111 Opposite side substrate body 112, 412 Transparent common electrode 120, 420 Element side substrate 121 Element side substrate body 122, 422 Transparent electrode 123, 423 Interlayer insulation Films 124 and 424 Reflective electrodes 124a Contact portions 125 and 425 Pixel electrodes 126 Amorphous transparent conductive films 127 Scan lines 128 Source bus lines 129 TFT elements 129a Gate electrodes 129b Source electrodes 129c Drain electrodes 130 and 430 Liquid crystal layers P and P ′ Pixels R, R 'reflection part T, T' transmission part

Claims (5)

A substrate, a plurality of pixel electrodes provided on the substrate, each having a reflective electrode region and a transmissive electrode region, a liquid crystal layer, and at least one opposing surface facing the plurality of pixel electrodes via the liquid crystal layer Each of the plurality of pixel electrodes defines a plurality of pixels, and each of the plurality of pixels includes a reflective portion defined by the reflective electrode region and a transmission defined by the transmissive electrode region. And
In each of the plurality of pixels, the reflective electrode region and the transmissive electrode region are opposed to a common counter electrode,
The reflective electrode region has a reflective conductive layer and a transparent conductive layer provided on the liquid crystal layer side of the reflective conductive layer,
An interlayer insulating film having an opening is formed on the substrate, the reflective electrode region is formed on the interlayer insulating film, and the transmissive electrode region is formed by a transparent electrode exposed in the opening. And the difference between the work function of the transparent conductive layer and the work function of the transparent electrode is within 0.3 eV .   The liquid crystal display device according to claim 1, wherein the transparent conductive layer is amorphous. The transparent electrode is formed of an ITO layer, the reflective conductive layer includes an Al layer, and the transparent conductive layer is formed of an oxide layer mainly composed of indium oxide and zinc oxide. Item 3. A liquid crystal display device according to item 1 or 2 . The transparent thickness of the conductive layer is 1nm or more 20nm or less, the liquid crystal display device according to any one of claims 1 to 3. 5. The liquid crystal display device according to claim 1, wherein an electrode potential difference of the reflection portion and an electrode potential difference of the transmission portion are substantially equal.

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