Pixel structure of liquid crystal device and driving method thereof

A driving method for activating an optical self-compensated birefringence mode liquid crystal device is provided. The optical self-compensated birefringence mode liquid crystal device has plural pixel structures, plural substrates and a liquid crystal layer sandwiched between the plural substrates. Each of said plural pixel structures comprises a first electrode, a second electrode, a pixel electrode and a common electrode. The driving method comprising steps of: providing a space between said first electrode and said second electrode on one of plural substrate; providing a first potential difference between said first electrode and said second electrode to generate a first electric field; and performing an initialization process from a bend of said second electrode to transitioning an alignment state of said liquid crystal layer from a non-display alignment state to a display alignment state by said first electric field. Further, generate a second electric field by a second potential difference between said pixel electrode and said common electrode.

FIELD OF THE INVENTION

The present application relates to a pixel structure and a driving method for a liquid crystal device, and more particularly to the pixel structure and the driving method for the optically compensated birefringence (OCB) mode liquid crystal device.

BACKGROUND OF THE INVENTION

In recent years, studies on the optically compensated birefringence (OCB) cell that is to be used as a liquid crystal cell instead of a twisted nematic (TN) cell have been quickly increased. In the OCB mode liquid crystal device, the liquid crystal molecules therein are in splay state at the initial state. However, when a voltage is applied to the OCB mode liquid crystal device, the liquid crystal molecules therein will transit from the splay state to the bend state, and it is required to spend some time for the transition from the splay state to the bend state. In the bend state, the top and bottom liquid crystal molecules are always oriented symmetrically, and thus to compensate the birefringence of liquid crystal molecules so as to obtain the uniform viewing angle characteristic at all directions is more easily than that obtained with the orientation division method, and a high-speed response characteristic that is one order faster than that for the conventional TN cells may also be obtained accordingly.

FIGS. 1A and 1Brespectively illustrate the liquid crystal molecules in splay state and bend state in the OCB mode liquid crystal display device. As shown inFIG. 1A, in splay state, the liquid crystal molecules104are uniformly splayed between the glass substrates100and102. However, when a voltage is applied to the glass substrates100and102, the liquid crystal molecules104will be in bend state, as shown inFIG. 1B. In which, the transition time of the liquid crystal molecules104from the splay state to the bend state is one of the determinants for the OCB mode liquid crystal display device due to the fact that all the electro-optical properties of the OCB mode liquid crystal display device are operated when the liquid crystal molecules therein are in bend state.

However, some pixel structures have been disclosed, such as those disclosed in U.S. Pat. Nos. 6,115,087, 6,226,058, 6,661,491 and U.S. Pat. No. 6,597,424, but, some of them are not suitable for OCB mode liquid crystal display devices and there still exist some demerits in the disclosed pixel structures. In addition, the conventional pixel structures usually have the demerits, for example, a space exists between the pixel electrode and the gate electrode, and the common electrode must be introduced and overlapped with the pixel electrode for a certain area so as to form a storage capacitor. However, the above two demerits will result in a small aperture and cause the conventional pixel structures incompatible with the three-level gate driving.

In addition, although some driving methods for a liquid crystal device have been disclosed, such as that Takayuki Konno et al., (U.S. Pat. No. 6,873,377) and Katsuji Hattori et al., (U.S. Pat. No. 6,671,009) have disclosed a driving method for an OCB mode liquid crystal display and Hajime Nakamura et al., (U.S. Pat. No. 6,005,646) have disclosed another driving method for a thin film transistor liquid crystal display (TFT/LCD), there still exist some defects in the disclosed driving methods. For example, the driving method proposed by Katsuji Hattori et al. has a complicated signal input procedure and the applied system design always needs an alignment transition driving circuit, a switching control circuit and a switching circuit. In other words, the cost for the driving method of Katsuji Hattori et al. is always high and the relevant driving method is not so practical, especially for the trend of compactness. In addition, since the potential difference between the signal electrode and the common electrode is morn than 10 volts and that between the gate electrode and the signal electrode is also more than 10 volts in the driving method proposed by Hajime Nakamura, there might exist some problems about the poor uniformity and the slow transition time in driving method of the prior arts.

As above, since all the electro-optical properties of the OCB mode liquid crystal display device are operated only when the liquid crystal molecules therein are in bend state, the liquid crystal molecules in the OCB mode liquid crystal display devices need to be transformed from the splay state (non-display state) into the bend state (display state) before being used and there still exist some demerits in the conventional pixel structures and driving methods, new driving methods with shorter transition time and new pixel structures contributive to shorten the transition time for activating OCB mode liquid crystal display device are desired.

SUMMARY OF THE INVENTION

In accordance with one aspect of the present application, a driving method for activating an optical self-compensated birefringence mode liquid crystal device is provided. The optical self-compensated birefringence mode liquid crystal device has plural pixel structures, plural substrates and a liquid crystal layer sandwiched between the plural substrates. Each of said plural pixel structures comprises a first electrode, a second electrode, a pixel electrode. The driving method comprising steps of: providing a space between said first electrode and said second electrode on one of plural substrate; providing a first potential difference between said first electrode and said second electrode to generate a first electric field; and performing an initialization process from a bend of said second electrode to transitioning an alignment state of said liquid crystal layer from a non-display alignment state to a display alignment state by said first electric field. Further, generate a second electric field by a second potential difference between said pixel electrode and a common electrode.

In accordance with another aspect of the present application, a liquid crystal display device is provided. The liquid crystal display device has a first substrate, a second substrate opposite to the first substrate, a pixel electrode formed on the first substrate, and a liquid crystal layer sandwiched between the first substrate and the second substrate. The liquid crystal display device includes a first electrode provided on the first substrate, a second electrode located on the first substrate and having a bend portion, and a driving means generating a potential difference between the first electrode and the second electrode. There is a space between the first electrode and the second electrode.

The foregoing and other features and advantages of the present invention will be more clearly understood through the following descriptions with reference to the drawings, wherein:

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present application will now be described more specifically with reference to the following embodiments. It is to be noted that the following descriptions of preferred embodiments of this application are presented herein for purpose of illustration and description only; it is not intended to be exhaustive or to be limited to the precise form disclosed.

Please refer toFIGS. 2A and 2B, which respectively show the pixel structure according to a first preferred embodiment of the present application and the cross-sectional view along the AA′ line inFIG. 2A.

As shown inFIGS. 2A and 2B, the pixel electrode202is partially overlapped with the bias electrode201, the data line203has an extension portion2031with a meander shape extending to the middle of the pixel region. In addition, as shown inFIG. 2B, a common electrode208is located on the upper glass substrate205, the pixel electrode202is located between the bias electrode201and the common electrode208, and the crystal liquid molecules.206are sandwiched between the upper glass substrate205and the lower glass substrate207. In addition, the bias electrode201and the gate line204are in the same layer. Furthermore, as shown inFIG. 2A, there exists a space209between the bias electrode201and the extension portion2031. And the bias electrode201includes an opening for containing the extension portion2031of the data line203and the space209. Wherein the edges of the opening of the bias electrode201and the extension portion2031are complementary to each other; and the shape of the space209between the bias electrode201and the extension portion2031is the same as that of the extension portion2031. It should be noted that the extension portion2031could also be in the serpentine shape, zigzag shape, crank-like shape, wave shape, frame-like shape, and cross-like shape. In general, the applied space209is ranged from 1 μm to 15 μm, preferably from 3 μm to 6 μm. Besides, it should be noted that the space209and the opening of the bias electrode201are in one shape selected from a group consisting of the serpentine shape, zigzag shape, crank-like shape, wave shape, frame-like shape, and cross-like shape, L-shape, stair-shape, bend shape, meander-shape and so on.

During the process of driving an OCB mode liquid crystal display device with the pixel structure shown inFIGS. 2A and 2B, a lateral electric field is first formed by modulating the potential difference between the bias electrode201and the extension portion2031of the data line203so as to result in the bend nuclei of the liquid crystal molecules therein (not shown), and then a vertical electric field is formed by modulating the potential difference between the pixel electrode202and the common electrode208so as to result in the bend transition of the liquid crystal molecules therein. When the applied voltages on the bias electrode201, the pixel electrode202and common electrode208are respective ±20 Volt, ±6 Volt and −30 Volt, it is found that the transition time for the liquid crystal molecules (not shown) is less than 0.5 second. In addition, when the applied voltages on the bias electrode201, the pixel electrode202and common electrode208are respective 25 Volt, ±6 Volt and 30 Volt, it is found the transition time for the liquid crystal molecules is similarly less than 0.5 second. However, in order to simply illustrate the applied voltages of the driving method according to the present application could be provided by an alternating voltage or a direct voltage,FIGS. 2C and 2D, which respectively show the diagrams of the driving method activated by an alternating voltage and a direct voltage, are provided. InFIGS. 2C, and2D, the voltages of the bias electrode, the data line and the common electrode are respectively indicated by Vbias, Vd and Vcom.

As above, however, since the given period for transforming the alignment state of the liquid crystal molecule from the splay state into the bend state at the start of LCDs operation could be substantially reduced according to the driving method and the pixel structure of the present application, the LCDs using one of the pixel structure and driving method or both of the present invention has a high-speed response as well as a high display quality.

Please refer toFIGS. 2E and 2F, which respectively show the voltage relationships among the pixel electrode, the gate electrode, the bias electrode, the data line and the common electrode under the positive polarity and the negative polarity when an alternating voltage is applied to the OCB mode liquid crystal display device. InFIGS. 2E and 2F, the voltages of the pixel electrode, the gate electrode, the bias electrode, the data line and the common electrode are respectively indicated by Vp, Vg, Vb, Vd and Vcom. After the relevant pixel structure is configured, Vp thereof will be easily coupled to a higher voltage (or a lower voltage) due to the Vb coupling effect and the potential difference ΔVpc among Vp and Vc will be increased accordingly. However, when the thin film transistor (TFT) (not shown) is turned on again, the potential difference ΔVpc will become small again.

Please refer toFIGS. 3A and 3B, which respectively show a pixel structure of an optical self-compensated birefringence mode liquid crystal device according to a second and a third preferred embodiments of the present application.

As shown inFIG. 3A, in the pixel structure according to the present application, the bias electrode301is partially overlapped with the pixel electrode302via the saw-toothed protrusions3011and3021respectively belong to the bias electrode301and pixel electrode302. The driving transistor305is electrically connected to the data line303and the gate line304and the pixel electrode302for controlling the potential differences there-among. Therefore, by scanning the gate line304in accordance with the gate signals, the driving transistors305in the same given gate line304are turned on. At the same time, signals in the data line303are transferred to the pixel electrode302through the driving transistor305to show a picture on the liquid crystal display device. When the applied voltages for the data line303, the gate line304and the bias electrode301are respectively ±6 Volt, 10 Volt and ±20 Volt, it is found that the seed propagations of the liquid crystal molecules are not only easily formed at the bottom of the pixel electrode302, where the pixel electrode302is not overlapped with the gate line304, but also at the top of the pixel electrode302, where the pixel electrode302is overlapped with the bias electrode301(the relevant result is not shown here). Furthermore, as inFIG. 3A, a storage capacitor (not shown) is inherently formed between the pixel electrode302and the gate line304. Therefore, the aperture ratio of the new pixel structure inFIG. 3Ais increased when it is compared to the conventional ones. Furthermore, it should be noted that, in a similar embodiment, it is possible that the data line303is partially overlapped with the pixel electrode302, as shown inFIG. 3B.

Please refer toFIGS. 4A to 4D, which respectively show the pixel structures of an optical self-compensated birefringence mode liquid crystal device according to the forth, fifth, sixth and seventh preferred embodiments of the present application.

As shown inFIGS. 4A to 4D, all the pixel electrodes402according to the forth, fifth, sixth and seventh preferred embodiments of the present application are partially overlapped with the bias electrodes401. In which, the protrusions of the pixel electrode402and the bias electrode401could be taper-shape, rectangular, or saw-toothed and so on.

In addition, please also refer toFIGS. 5A to 5E, which respectively show the pixel structures of the optical self-compensated birefringence mode liquid crystal devices according to eighth, ninth, tenth, eleventh, twelfth and thirteenth preferred embodiments of the present application. These embodiments introduce an initialization process activated by an lateral electric field provided from any two selected from the group consisting of the gate line, bias electrode and data line.

As shown inFIG. 5A, the pixel electrode502is partially overlapped with the bias electrode501, and there is a space509between the bias electrode501and the gate line504. The bias electrode501is located in the same layer of the gate line504. In the other hand, the bias electrode501and the gate line504could be formed and defined simultaneously. Furthermore, as shown inFIG. 5A, the edges of the bias electrode501and the gate line504are complementary to each other. And the shape of the space509between the bias electrode501and the gate line504is dependent on that of extension portion5031,such as meander-shaped.

However, during the driving process, since there is a space509between the bias electrode501and the gate line504, a lateral electric field could be formed by modulating the potential difference between the bias electrode501and the gate line504. In addition, the pixel electrode502is overlapped with the common electrode located on the upper glass substrate (not shown), and thus a vertical electric field might be formed by modulating the potential difference therebetween.

As shown inFIGS. 5B and 5C, the pixel electrode502is partially overlapped with the bias electrode501, and the data line503has a bend5031. Furthermore, although the data line503is partially overlapped with the bias electrode501, there still exists a space509between the bias electrode501and the bend5031. The bias electrode501includes an opening for containing the bend5031of the data line503and the space509. The bias electrode501is located in the same layer of the gate line504. In the other hand, the bias electrode501and the gate line504could be defined simultaneously. In addition, it should be noted that the bias electrode501could be within the pixel region, as shown inFIG. 5B, or could be an extension portion of the gate line804, as shown inFIG. 5C. And, the bias electrode501is partially overlapped with pixel electrode802inFIGS. 5B and 5C. Furthermore, as shown inFigs. 5B and 5C, the edges of the opening of the bias electrode501and the bend5031are complementary to each other, and the shape of the spaces509between the bias electrode501and the bend5031are dependent on that of extension portion5031, such as meander shaped.

However, during the driving process, since there is a space509between the bias electrode501and the data line503, a lateral electric field could be formed by modulating the potential difference therebetween. In addition, since the pixel electrode502is overlapped with the common electrode located on the upper glass substrate (not shown), a vertical electric field could be formed by modulating the potential difference therebetween.

As shown inFIGS. 5D and 5E, the pixel electrode502is partially overlapped with the gate line504, and the data line503has an extension portion5031. Furthermore, there exists a space509between the gate line504and the extension portion5031. And, the gate line504includes an opening for containing the extension portion5031of the data line503and the space509. Besides, it should be noted that the extension portion5031could be a triangle-shaped protrusion or a meander shape including the serpentine shape, zigzag shape, crank-like shape, wave shape, frame-like shape, and cross-like shape. Furthermore, as shown inFIGS. 5D and 5E, the edges of the opening of the gate line504and the extension portion5031are complementary to each other, and the shape of the space509between the gate line804and the extension portion5031is dependent on that of extension portion5031,such as triangle-shaped or meander-shaped.

However, during the driving process, since there is a space509between the gate line504and the extension portion5031of the data line503, a lateral electric field could be formed by modulating the potential difference therebetween. In addition, the pixel electrode502is overlapped with the common electrode located on the upper glass substrate (not shown), and thus a vertical electric field might be formed by modulating the potential difference therebetween.

As shown inFIG. 5F, the bias electrode501is partially overlapped with the pixel electrode502, and the data line503has the bend5031with a meander shape. The bias electrode501located in the same layer of the data line503has the protrusion5011. In the other hand, the bias electrode501and the date line503could be defined simultaneously. In addition, there exists a space509between the protrusion5011and the meander-shaped bend5031. Furthermore, the edges of the protrusion5011and the meander-shaped bend5031are complementary to each other. As shown inFIG. 5F, the shape of space509between the protrusion5011and the meander-shaped bend5031is dependent on that of the meander-shaped bend5031.

However, during the driving process, since there is a space509between the bias electrode501and the data line503, a lateral electric field could be formed by modulating the potential difference therebetween. In addition, the pixel electrode502is overlapped with the common electrode located on the upper glass substrate (not shown), and thus a vertical electric field might be formed by modulating the potential difference therebetween.

In general, as shown inFIGS. 5A to 5F, the applied space509is ranged from 1 μm to 15 μm, preferably from 3 μm to 6 μm. The pixel electrode502is made from a transparent conductor, such as ITO, IZO, ITZO or AZO, and so on. Besides, the space509and the opening of the bias electrode501and gate line504are in a shape selected from the group consisting of the serpentine shape, zigzag shape, crank-like shape, wave shape, frame-like shape, cross-like shape, L-shape, stair-shape, bend shape, meander-shape and so on.

However, it also should be noted that, according to the present application, a lateral electric field is formed by modulating the potential differences between any two selected from the group consisting of the gate line, bias electrode and data line. Furthermore, the above-applied voltages need not be limited to the disclosed embodiments. In addition, as above, it is also found that no matter an alternating voltage or a direct voltage is supplied to the bias electrode, the transition time for the liquid crystal molecules according to the driving method of the present application is less than 0.5 sec, which is much less than the transition time of the conventional driving method.

In addition, please also refer toFIGS. 6A to 6C, which respectively show the pixel structures of the optical self-compensated birefringence mode liquid crystal devices according to fourteenth, fifteenth, and sixteenth preferred embodiments of the present application.

As shown inFIGS. 6A to 6C, the gate line604has an extension portion6041close to the cross point of the gate line604. Besides those illustrated inFIGS. 6A to 6C, the extension portion6041be also able in other shapes, such as the triangle, rectangle, L shape, stair shape, bend shape, meander shape and so on. Moreover, a first bending electrode6031of the data line603and a second bending electrode6061are over the extension portion6041. And the second bending electrode6061is connected to the pixel electrode602. Furthermore, there exists a space609between the first bending electrode6031and the second bending electrode6061. And the shapes of the first bending electrode6031and the second bending electrode6061are complementary to each other. In other words, the first bending electrode6031and the second bending electrode6061have the similar pattern to that of the extension portion6041of the gate line604.

As shown inFIGS. 6A-6C, the shape of the space609between the first bending electrode6031and the second bending electrode6061is the same as that of the first bending electrode6031and the second bending electrode6061. It should be noted that, besides those disclosed inFIGS. 6A-6C, the space609could be in other shapes, such as the triangle, rectangle, L shape, stair shape, bend shape, meander-shape and so on. In addition, the bending points of the first bending electrode6031and the second bending electrode6061are toward the same direction to that of the data line603or the gate line604.

The second bending electrode6061, as the drain electrode of the transistor606, is connected to the pixel electrode602. Therefore, the signal in the data line603is ably transferred to the pixel electrode602via the first bending electrode6031, as the source electrode of the transistor606. However, by scanning the gate line604in accordance with the gate signals, the transistors606in the same given gate line604are turned on. At the same time, signals in the data line603are ably transferred to the pixel electrode602through the transistor606to show a picture on the relevant liquid crystal display device (not shown).

In general, the applied space609is ranged from 1 μm to 15 μm, preferably from 3 μm to 6 μm. The pixel electrode602is made from a transparent conductor, such as ITO, IZO, ITZO or AZO, and so on. Besides the above, the space609and the first bending electrode6031and the second bending electrode6061are also in other shapes, such as the serpentine shape, zigzag shape, crank-like shape, wave shape, frame-like shape, and cross-like shape, L shape, stair shape, bend shape, meander shape and so on.

As above, according to the pixel structure and the driving method of the present application, the period for transforming the liquid crystal molecule from the splay state into the bend state at the start-up of LCDs operation could be substantially reduced, and the LCDs using the pixel structure of the present application will have a high-speed response as well as a high display quality.

Furthermore, since the pixel structures of the present application are more compact than the conventional ones and have a high-speed response as well as a high display quality, and the driving methods thereof can significantly reduce the transition time of the liquid crystal molecules therein, the present application does have the progressiveness, novelty and industrial utility.

While the application has been described in terms of what are presently considered to be the most practical and preferred embodiments, it is to be understood that the application need not be limited to the disclosed embodiment. On the contrary, it is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims, which are to be accorded with the broadest interpretation so as to encompass all such modifications and similar structures. Therefore, the above description and illustration should not be taken as limiting the scope of the present application which is defined by the appended claims.