Patent Application
20070236645
These and other objects and advantages and further description of the invention will be more apparent to those skilled in the art by reference to the description, taken in connection with the accompanying drawings, in which:
To enhance the display quality of the LCD panel, it is important to control the gap between the active matrix substrate and the counter substrate. To achieve the controlling, spacers are disposed between the substrates. However, there are the problems that the non-uniformity of the gap tends to occur due to a volumetric change of liquid crystal material or the like when the spacers are subjected to a temperature change and/or that non-uniformity in display tends to occur due to strains generated by stresses.
Therefore, although it is necessary to form liquid crystal cells with spacers compressed within the range of elastic deformation so that the spacers are capable of following during the increase in temperature, when excessively increasing the density of the spacers, there occur problems that a desired gap cannot be formed and/or that air bubbles and the like are generated. On the other hand, when a supporting force becomes too small since the density of the spacers is too small, there occurs a problem that, when the substrate is put in upright position, liquid crystal material move downward by self-weight to stay at a low level thus causing non-uniformity in display or that, when a load is locally applied, spacers undergo plastic deformation thus causing non-uniformity in display.
To control such non-uniformity of the gap, it is necessary to set the density of the spacers to be in an adequate range. In the present invention, recessed parts are formed on at least one of a pair of substrates facing each other. Further, on these recessed parts, multiple kinds of spherical spacers each having a different diameter are disposed, or multiple kinds of recessed parts each having a different depth are formed. Hence, there can be formed parts which constantly support the substrates and parts which normally do not support the substrates so much, but do support the same when a load is locally applied. Therefore, it is possible to provide a product which has a large margin for the non-uniformity of the gap generated by a temperature change and which is highly resistant to the locally applied load. A detailed description is given below with reference to the accompanying drawings.
First, an LCD panel of a first exemplary embodiment of the present invention and a method of manufacturing the LCD panel are described with reference to
An LCD device of the present embodiment includes an LCD panel, a backlight unit illuminating the LCD panel and the like. As shown in
As shown in
As shown in
There is no particular limitation on the film thicknesses and sizes of respective members constituting the above-described LCD panel. However, for example, it is assumed that the thickness of the flattened film 111 is 1.0 μm; the diameter of the spherical spacer 103a is 4.2 μm; and the diameter of the spherical spacer 103b is 3.8 μm. Here, the spacing between a main surface of the flattened film 111 and the counter electrodes 115 is defined as the cell gap. When setting this cell gap to 3.0 μm and when forming the cell in a state where the spherical spacers 103a are being compressed by 0.2 μm, the spherical spacers 103b are put in a state where the same are free to move by 0.2 μm.
Incidentally, as to the disposition densities of the spherical spacers 103a and the spherical spacers 103b, since the both substrates facing each other are mainly supported with the spherical spacers 103a and since the same are supported with the spherical spacers 103b when the gap is changed, the disposition density of the spherical spacers 103b which are disposed secondarily is desired to be approximately several times greater than the disposition density of the spherical spacers 103a with which the both substrates are mainly supported. It is possible to adjust this disposition density by the number of disposing points and/or by the number of spacers disposed at one place. Furthermore, when adjusting the disposition place, plural lines of ink-jet nozzles are prepared, and then, inks in which the spherical spacers having respective diameters are dispersed are discharged through the respective ink-jet nozzles, whereby it is possible to dispose desired spherical spacers on arbitrary recessed parts 101.
The shapes of the spherical spacers 103a and 103b are not necessarily precisely spherical and may be of slightly deformed ellipsoid-like shape. In addition, the materials of the spacers 103a and 103b are not limited to polymer beads or silica beads. Although it is only expected herein that the size of the spherical spacer 103a is larger than that of the spherical spacer 103b, it has been confirmed that, when setting the difference in diameter of the spherical spacer 103a and the spherical spacer 103b to be in the range of approximately 2% to 20% of the diameter of the spherical spacer 103a, the performance of the following of the spacers to a gap change is enhanced so that the non-uniformity of the gap can be effectively controlled. Furthermore, although there are herein used two kinds of spacers including the spherical spacer 103a having a relatively large diameter and the spherical spacer 103b having a relatively small diameter, it is possible to use more than two kinds of spacers each having a different size. In
In
In
Next, a method of manufacturing such LCD panels is described with reference to a flowchart shown in
First, in step S1, the CFT substrate 121 is prepared. The CF substrate 121 is formed in a way that a black matrix 113 is formed by a photolithographic method in an area between pixels on the glass substrate 112; thereafter, the color layers 114 of respective colors, RGB, are formed by a photolithographic method in the areas of respective pixels; and the counter electrode 115 made of a transparent conductive film such as indium tin oxide (ITO) is formed by a sputtering method or the like. The materials, the methods of forming, the forming areas, the thicknesses and the like of the black matrix 113, the color layers 114, and the counter electrode 115 are not limited to the constitution in the drawings.
Next, in step S2, the TFT substrate 120 is prepared. The TFT substrate 120 is formed in a way that the gate wirings 104 and the gate electrodes are formed on another piece of the glass substrate 112 by a sputtering method or the like; and at the same time, the gate light-shielding parts 118 for shielding light leaked from the peripherals of pixels are formed. Subsequently, the gate insulating film 107 made of a silicon dioxide film, a silicon nitride film or the like is formed by a vacuum evaporation method, plasma chemical vapor deposition (CVD) method or the like; on the gate insulating film 107, semiconductor layers made of amorphous silicon, polycrystalline silicon or the like are formed; and thereafter, the drain wirings 105, drain electrodes and source electrodes are formed by a sputtering method or the like. The TFT 117 constituted of the gate electrode, the gate insulating film 107, the semiconductor layers, the drain electrode and the source electrode is formed. The passivation film 108 is formed by a vacuum evaporation method or the like. Subsequently, the flattened film 111 made of photosensitive organic layers, a silicon dioxide film, a silicon nitride film or the like is formed by a coating method, a vacuum evaporation method, a plasma CVD or the like; and the recessed part 101 is formed in a light-shielding area by a photolithographic method. Here, the light-shielding area designates an area where the gate wirings 104 and the drain wirings 105 of the TFT substrate 120 are disposed, or an area where the black matrix 113 of the CF substrate 121 is disposed. Thereafter, the pixel electrodes 109 made of transparent conductive films such as ITO are formed by a sputtering method or the like. There is no particular limitation on the materials, the methods of forming, the forming areas, the thicknesses and the like of the gate wirings 104, the gate light-shielding parts 118, the gate insulating film 107, the semiconductor layers, the drain wirings 105 and the pixel electrodes 109.
Next, in Step S3, the TFT substrate 120 and the CF substrate 121 are respectively cleaned; and solution of polyimide being a material of an alignment film is applied thereto by using a printer or the like to be thereafter baked, thus forming an alignment film. Thereafter, a rubbing process is performed, in which a surface of the alignment film is rubbed in one direction using a buff wrapped around a rotating metallic roller. Next, to remove residue produced after the rubbing process such as fabric scrap of the buff and scrape resulting from the rubbing of the alignment film, the cleaning of the substrates and the drying thereof are performed.
Next, in Step S4, the spherical spacers 103a and the spherical spacers 103b are disposed on the recessed parts 101 of the TFT substrate 120. When using an ink jet method as a method of disposing the spherical spacers on fixed places, inks in which spherical spacers having different diameters are dispersed are discharged over the recessed parts 101 through plural ink jet nozzles, and heat treatment is performed on the substrate on which the spherical spacers are disposed, whereby the spherical spacers are firmly fixed on the substrate.
As an example of the ink jet method, a discharging method using a piezo ink jet head 202 is described with reference to
Thereafter, a photocuring sealant or a thermal curing sealant is formed on any one of the substrates and, further, liquid crystal material is dropped on the other substrate. For example, in
Furthermore, when using an offset printing method instead of the ink jet method, the spherical spacers 103a and 103b are offset-printed on predetermined recessed parts 101 and heated to be thereby firmly fixed. Thereafter, a sequence of processes up to an alignment process is performed on each of the TFT substrate and CF substrate, the sequence thereof being the cleaning of the substrates, the printing of the alignment film, the baking of the alignment film, the rubbing process, the cleaning of the substrates after the rubbing process, and the drying of the substrates. Thereafter, a photocuring sealant or a thermal curing sealant is formed on one of the substrates and, further, liquid crystal material is dropped on the other substrate. In an overlapping process, the both substrates facing each other are overlapped, and then, UV curing of a sealant and thermal curing of the same are performed and, thus, an LCD panel is completed.
As in the manner described above, the flattened film 111 of the TFT substrate is removed to form the recessed parts 101, and the spherical spacers 103a and the spherical spacers 103b each having a different diameter are disposed on the flattened parts 101, whereby the performance of following of the spacers to a gap change due to a temperature change is enhanced so that the non-uniformity of the gap can be effectively controlled. Furthermore, by setting the diameters of the spherical spacers to be larger than the cell gap, a margin to a gap change can be made large. Because of the presence of the recessed parts 101, the moving of the spherical spacers 103a and 103b due to the overlapping of the substrates, vibration, and/or impact is restrained and, consequently, it becomes hard for light leakage and the non-uniformity of the gap to occur, so that reliability can be enhanced. Furthermore, it is possible to collect the spherical spacers 103a and 103b on the recessed parts 101, which do not dry till the last, and to cause the spherical spacers to define their positions in a self-aligned manner, so that the accuracy of the positions of the spherical spacers can be enhanced.
Next, an LCD panel of a second exemplary embodiment of the present invention and a method of manufacturing the LCD panel are described with reference to
Although the recessed parts 101 are formed on the TFT substrate only in the above-described first exemplary embodiment, a feature of the present embodiment is that recessed parts 101 and 102 are respectively formed on both of a TFT substrate and a CF substrate. That is, the recessed parts 101 are formed on the TFT substrate 120 and the recessed parts 102 are formed on the CF substrate 121. In the case where plural aforementioned recessed, parts 101 are disposed on the TFT substrate 120, they are formed to have the same depth, and in the case where plural aforementioned recessed parts 102 are disposed on the CF substrate 121, they are also formed to have the same depth.
Although the LCD panel of the present embodiment has a constitution which is roughly the same as that of the first exemplary embodiment, the LCD panel of the present embodiment is different in that, on the areas where the spherical spacers 103a and 103b are disposed, the recessed parts 102 are also provided on the CF substrate 121. These recessed parts 102 are formed by removing parts of color layers 114 facing the recessed parts 101 when forming the color layers 114 by a photolithographic method. Furthermore, the recessed parts 102 can be easily formed by not forming the color layers 114 on part facing the recessed parts 101.
That is, in Step S1 of the flowchart of
Using the above-described CF substrate 121 and proceeding Steps S1 through S9, the LCD panel of the second exemplary embodiment is completed as in the first exemplary embodiment.
In the present embodiment too, the shapes of the recessed parts 101 and 102 may be of any shape as long as the spherical spacers 103a and 103b engage with the recessed parts 101 and 102. For example, the recessed parts 101 and 102 may be of arbitrary shape being rectangular, triangular, polygonal, circular, elliptical or the like. Furthermore, the shape of the recessed parts 102 may be the same as or different from that of the recessed parts 101 of the TFT substrate 120. In addition, the spherical spacers 103a and the spherical spacers 103b may be put in a manner that these spacers 103a and 103b are in contact only with the bottom surfaces of the recessed parts 101 and 102, in contact with the bottom surfaces and the sidewall surfaces of the recessed parts 101 and 102, or in contact only with the sidewall surfaces of the recessed parts 101 and 102. Moreover, in
By forming the constitution as described above, the diameter of the spherical spacers can be increased, thus enabling further increase of a margin to a gap change. Furthermore, the moving of the spherical spacers due to the overlapping of the substrates, vibration, and/or impact is restrained and, consequently, it becomes hard for light leakage and the non-uniformity of the gap to occur, so that reliability can be further enhanced.
In the first exemplary embodiment, the recessed parts 101 are formed on the TFT substrate 120. In the present embodiment, although the recessed parts 101 are formed on the TFT substrate 120 and the recessed parts 102 are formed on the CF substrate 121, only the recessed parts 102 may be formed on the CF substrate 121 as shown in
Next, an LCD panel according to a third exemplary embodiment of the present invention and a method of manufacturing the LCD panel are described with reference to
In the above-described first and second exemplary embodiments, the descriptions are given of the case where the recessed parts 101 and 102 are formed so that they have the same depths. A feature of the present embodiment is that recessed parts having different depths are formed on one substrate. In the above-described first and second exemplary embodiments, the descriptions are given of the case where multiple kinds of spherical spacers each having a different diameter are used. In the present embodiment, a description is given of the case where one kind of spherical spacers is used.
As shown in
The gap adjusting films 106 can be formed on light-shielding areas placed over the gate wirings 104, at the same time when forming the drain wirings 105. That is, by changing the process of preparing the TFT substrate 120 in Step S2 of the flowchart of
There is no particular limitation on the film thicknesses and sizes of respective members constituting the above-described LCD panel. However, for example, it is assumed that the thickness of the flattened film 111 is 1.0 μm; the diameter of the spherical spacer 103 is 3.8 μm; and the film thicknesses of the drain wiring 105 and the gap adjusting film 106 is 0.4 μm. Here, the spacing between a main surface of the flattened film 111 and the counter electrodes 115 is also defined as the cell gap. When setting this cell gap to 3.0 μm and when forming the cell in a state in which the spherical spacers 103 are being compressed by 0.2 μm on the recessed parts 101a where the gap adjusting films 106 are present, the spherical spacers 103b are put in a state where the same are free to move by 0.2 μm on the recessed parts 101b where the gap adjusting films 106 are absent.
For the LCD panel of the present embodiment, the both substrates facing each other are supported mainly with the spherical spacers 103 on the recessed parts 101a where the gap adjusting films 106 are present; and when the magnitude of the gap is changed, the both substrates facing each other are supported with the spherical spacers 103 on the recessed parts 101b where the gap adjusting films 106 are absent. The disposition density of the spherical spacers 103, which are secondarily formed and which are disposed on the recessed parts 101b where the gap adjusting films 106 are absent, is desired to be set to several times greater than that of the spherical spacers 103 with which the both substrates facing each other are mainly supported and which are disposed on the recessed parts 101a where the gap adjusting films 106 are present. This disposition density may be adjusted by changing the disposition densities of the recessed parts 101a and the recessed parts 101b. For example, the adjusting of the disposition density may be achieved by forming the recessed parts 101a and 101b in such a manner that the number of the recessed parts 101b where the gap adjusting films 106 are absent is several times greater than that of the recessed parts 101a where the gap adjusting films 106 are present. Furthermore, it is possible to adjust these deposition densities by the number of deposition points and/or by the number of spacers disposed at one place.
Although it is only expected herein that the recessed parts 101b are deeper than the recessed parts 101a, when setting the difference in depth between these recessed parts to be in the range of approximately 2% to 20% of the diameter of the spherical spacer 103, the performance of following of the spacers to a gap change is enhanced so that the non-uniformity of the gap can be effectively controlled. Furthermore, although there are herein shown two kinds of recessed parts, one being the recessed part 101a having a relatively small depth and the other being the recessed part 101b having a relatively large depth, it is possible to use more than two kinds of recessed parts each having a different depth.
As described above, the changing of the depth of the recessed parts formed on the TFT substrate 120 is also capable of enhancing the performance of following of the spacers to a gap change due to a temperature change, as in the first exemplary embodiment, so that the non-uniformity of the gap can be controlled. Moreover, because of the presence of the recessed parts 101a and 101b, the moving of the spherical spacers 103 due to the overlapping of the substrates, vibration, and/or impact is restrained and, consequently, it becomes hard for light leakage and the non-uniformity of the gap to occur. Thus, reliability can be enhanced. Furthermore, it is possible to collect the spherical spacers 103 on the recessed parts 101a and 101b which do not dry till the last, and to cause the spherical spacers to define their positions in a self-aligned manner, so that the accuracy of the positions of the spherical spacers can be enhanced.
In
Furthermore, in
Next, an LCD panel of a fourth exemplary embodiment of the present invention and a method of manufacturing the LCD panel are described with reference to
As in the first to third exemplary embodiments, by disposing the spacers on the recessed parts, it is possible to collect the spherical spacers on the recessed parts, which do not dry till the last, and to cause the spherical spacers to define their own positions in a self-aligned manner. A feature of the present embodiment, however, is that further enhancement of the accuracy of the positions of the spherical spacers is achieved.
As shown in
The present embodiment is different from the aforementioned third exemplary embodiment in that, on the near areas surrounding the recessed parts 101a and 101b, the high contact angle films 110, the contact angles of which are larger than those of the recessed parts 101a and 101b, are disposed. It is expected that each of the high contact angle films 110 is formed by a member having a contact angle, which is larger than that of an exposed part of an inner surface of the recessed part. For example, each of the high contact angle films 110 may be formed by a transparent conductive film, which is the same as a pixel electrode 109. Specifically, when a transparent conductive film is patterned to form the pixel electrode 109, a transparent conductive film is simultaneously patterned to form the high contact angle film 110 on a light-shielding area. Alternatively, when the recessed parts 101a and 101b are formed of SiN films and when the near areas surrounding the recessed parts 101a and 101b are formed by photosensitive organic films, since the photosensitive organic film has a larger contact angle as compared with that of the SiN film, an area having the high contact angle can be obtained at the same time when the recessed parts 101a and 101b are formed.
It should be noted that although there is no particular limitation on the area and film thickness of the high contact angle film 110, it is preferred that they be designed by considering the accuracy of printing position. For example, in
The LCD panel of the present embodiment can be manufactured by changing the process of preparing the TFT substrate 120 in Step S2 of the flowchart of
Next, in Step S4, the spherical spacers 103 are disposed on the recessed parts 101a and the recessed parts 101b. Ink 116 in which the spherical spacers 103 are dispersed is discharged to the recessed parts 101a and 101b through inkjet nozzles, and heat treatment is performed on the substrate.
Because of the presence of the high contact angle films 110 disposed on the near areas surrounding the recessed parts 101a and 101b, the ink 116 is collected on the recessed parts 101a and 101b having small contact angles at the time when the ink 116 has dried. This allows the spherical spacers 103 to correct their own positions in a self-aligned manner, so that further enhancement of the accuracy of the positions of the spherical spacers 103 can be achieved. Thereafter, proceeding Steps S5 thorough S9 as in the first exemplary embodiment, the LCD panel of the fourth exemplary embodiment is completed.
In general, it is hard for the spherical spacers to be disposed within predetermined light-shielding areas with high accuracy, when relying only on printing accuracy dependent on the ink jet method or the offset printing method. In the present embodiment, while drying of the ink 116 is progressing in an isotropic manner, the ink 116 remains fresh on the recessed parts 101a and 101b till the last. The spherical spacers 103 can be collected on the recessed parts 101a and 101b which have not dried till the last. Furthermore, the positions of the spherical spacers 103 being disposed can be corrected in a self-aligned manner using the effect in which, by setting the contact angles of the near areas surrounding the recessed parts 101a and 101b to be large compared to the contact angles of the inner surfaces of the recessed parts 101a and 101b, the ink 116 is collected to the areas having small contact angles when the ink has dried.
Moreover, in the present embodiment, there is shown the case where the high contact angle films 110 is formed in the LCD panel of the third exemplary embodiment. The same advantage can be also obtained by forming the high contact angle films 110 in the LCD panel of one of the first and second exemplary embodiments.
In the first and second exemplary embodiments, the descriptions are given of the cases where plural aforementioned recessed parts 101 and 102 are formed on the TFT substrate 120, or the CF substrate 121 or on both of them, and plural spherical spacers having different diameters are distributed. That is, for the plural spherical spacers having different diameters, there are used the spherical spacers 103a having a relatively large diameter and the spherical spacers 103b having a relatively small diameter. In the third exemplary embodiment, the description is given of the case where the multiple of recessed parts having different depths are formed on one of the TFT substrate 120 and the CF substrate 121, or the recessed parts are formed on the TFT substrate 120 and the CF substrate 121 in a way that some of the recessed parts face each other; and the spherical spacers 103 having the same size are disposed. That is, for the plural recessed parts having different depths, there are used the recessed part 101a having a relatively small depth and the recessed part 101b having a relatively large depth. In the fourth exemplary embodiment, the high contact angle films are formed on the near areas surrounding the recessed parts. In the present invention, an LCD panel may be constituted by arbitrarily combining the features of the first to fourth exemplary embodiments.
Although the descriptions described above have been given using the preferred exemplary embodiments, the present invention is not limited to these embodiments, and various changes can be made therein without departing form the spirit of the present invention. For example, in the above-described embodiments, although the ink jet head is described with reference to the piezo type, it is not limited to this, and another type is also applicable. For example, an ink jet head of bubblejet® type can be adopted. In this ink jet head, a heater is placed next to a tank in which ink is stored. The ink in the tank is heated by power supplied to the heater, whereby expansion and bubbles occurs in the ink so that the ink is discharged through the nozzles of the ink jet head. To such an ink jet head, ink in which spherical spacers are dispersed is supplied to be thereby discharged to recessed parts in light-shielding areas, thus enabling the spherical spacers to be disposed on the recessed parts.
Furthermore, using an ink jet head in which plural nozzles are disposed on plural lines, ink in which spherical spacers are dispersed is simultaneously discharged to plural lines of light-shielding areas so that the spherical spacers can be disposed on the recessed parts. Moreover, ink jet heads are prepared for inks in which spherical spacers having different diameters are dispersed, and the inks are respectively discharged with these heads so that the spherical spacers having different diameters can be disposed on the recessed parts. It is conceivable that the discharging of ink in which spherical spacers are dispersed may be performed while moving the ink jet head over a substrate in the direction in which gate wirings are extended, or while moving the ink jet head over a substrate in the direction in which drain wirings are extended.
In the above-described embodiments, although the descriptions are given of the case where the TFTs are used as switching elements, the present invention is also applicable to an LCD panel in which a switching element such a thin-film diode (TFD) or a metal insulator metal (MIM) is used. Furthermore, in the above-described embodiments, although the descriptions are given of the case where the color layers are formed on the counter substrate, the present invention is also applicable to an LCD panel of color-filter-on TFT type in which color filters are formed on a TFT substrate. For a monochrome display LCD panel, the color layers are not necessary.
Moreover, in the above-described embodiments, although the descriptions are given by applying the present invention to a transmissive LCD panel which is formed by the pixel electrodes 109 and counter electrodes 105, the present invention is also applicable to a reflective LCD panel or a semi-transmissive LCD panel. In the case of the reflective LCD panel, a reflective plate is placed inside or outside of an LCD panel; and a pixel electrode itself is formed by a light reflective pixel electrode. In the case of the semi-transmissive LCD panel having a reflective area and a transmissive area, a reflective plate is disposed on a reflective area inside or outside of an LCD panel, and part of a pixel electrode is formed of a light reflective material. In such a reflective LCD panel or such a semi-transmissive LCD panel too, the present invention in which recessed parts are disposed on light-shielding areas and spherical spacers are disposed on the recessed parts is applicable.
Although preferred embodiments of the invention has been described with reference to the drawings, it will be obvious to those skilled in the art that various changes or modifications may be made without departing from the true scope of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006-104520 | Apr 2006 | JP | national |
