BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will become more fully understood from the detailed description given herein below and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein:
FIG. 1 shows a schematic cross-section of a conventional liquid crystal display that includes a circular polarizer.
FIG. 2 shows a schematic cross-section illustrating an embodiment of a conventional domain-forming structure.
FIG. 3 shows a schematic cross-section illustrating another embodiment of a conventional domain-forming structure.
FIGS. 4A and 5A show schematic diagrams illustrating two different optical arrangements for the reflective regions of a multi-domain transflective liquid crystal display according to the invention, and FIGS. 4B and 5B show curve diagrams illustrating the V-R characteristics of the optical arrangements as in FIGS. 4A and 5A, respectively.
FIGS. 6A and 7A show schematic diagrams illustrating two different optical arrangements for the transmissive regions of a multi-domain transflective liquid crystal display according to the invention, and FIGS. 6B and 7B show curve diagrams illustrating the V-T characteristics of the optical arrangements as in FIGS. 6A and 7A, respectively.
FIG. 8 shows a schematic diagram illustrating a picture element including both a transmissive region and a reflective region according to the invention.
DETAILED DESCRIPTION OF THE INVENTION
In a multi-domain transflective liquid crystal display, the reflective region and the transmissive region have their respective optical characteristics when light travel therethrough. Hence, the invention provides two different domain-regulation arrangements respectively for the reflective region and the transmissive region to obtain optimum light transmission and light reflection, under the circumstance where a transflective liquid crystal (LC) cell is combined with a circular polarizer. FIGS. 4A, 5A, 6A and 7A schematically show different arrangements of the optical matching of a transflective LC cell and a circular polarizer, where the arrows indicate the orientation direction of LC molecules (the long axis direction or the orientation of an LC director) in individual domain and the orientation of the axes of retarders and linear polarizers. Besides, FIGS. 4B, 5B, 6B and 7B depict the optical responses (the transmittance or reflectance versus voltage) related to the above arrangements of optical matching.
According to the invention, the domain-forming structure provided on each picture element, such as the protrusions shown in FIG. 2 or the pattern of slits shown in FIG. 3, have different stretches in the reflective region and in the transmissive region, and the angles between the orientation of the LC director and the axes of the retarders and linear polarizers are particularly defined to obtain a maximum light transmittance and light reflectance. Since the structure of a transflective LC cell, the domain-forming structure such as protrusions or a pattern of slits, and the structure of a circular polarizer according to the invention are similar to the conventional design as shown in FIGS. 1 to 3, they are not described in detail here. The different optical arrangements and their respective optical responses for the reflective region and for the transmissive region according to the invention are explained in detail as follows.
1. Reflective Region
FIGS. 4A and 5A show schematic diagrams illustrating two different optical arrangements for the reflective regions of a multi-domain transflective liquid crystal display, in which a linear polarizer and a retarder are used to produce circularly polarized light. FIGS. 4B and 5B show curve diagrams illustrating the V-R characteristics (voltage versus light reflectance) of the optical arrangements as in FIGS. 4A and 5A, respectively.
As shown in FIG. 4A, by adjusting the stretch of a domain-forming structure, in each domain the orientation of a LC director in the reflective region of each picture element makes an angle of substantial 0 degree or 90 degrees with the slow axis of a quarter wave plate 12. Further, the angle between the slow axis of the quarter wave plate 12 and the absorption axis of a linear polarizer 14 is substantially 45 degrees. The V-R characteristics of the above optical arrangement are depicted in FIG. 4B. FIG. 4B shows two curves that depict the reflectance values observed from two separate viewing angles and an average of them represents the actual reflected light intensity sensed by the human eye and provided for the comparison of different optical arrangements. Also, the V-R characteristics shown in FIG. 5B are depicted in two curves with respect to two separate viewing angles.
FIG. 5A shows another optical arrangement for the reflective regions of a multi-domain transflective liquid crystal display. By adjusting the stretch of a domain-forming structure, in each domain the orientation of a LC director in the reflective region of each picture element makes an angle of substantial 45 degrees or 135 degrees with the slow axis of a quarter wave plate 12. The V-R characteristics of the above optical arrangement are depicted in FIG. 5B.
Comparing the respective V-R characteristics shown in FIG. 4B and FIG. 5B, it can be seen the average light reflectance is higher and a smoother curve is obtained when the LC director in the reflective region makes an angle of substantial 45 degrees or 135 degrees with the slow axis of the quarter wave plate 12. This is because, when light passes through a liquid crystal layer in which the LC director makes an angle of substantial 45 degrees or 135 degrees with the slow axis of the retarder, its two mutually orthogonal components X and Y of electric field vector have the same amplitude.
2. Transmissive Region
FIGS. 6A and 7A show schematic diagrams illustrating two different domain arrangements for the transmissive regions of a multi-domain transflective liquid crystal display, in which a linear polarizer and a retarder are used to produce circularly polarized light. FIGS. 6B and 7B show curve diagrams illustrating the V-T characteristics (voltage versus light transmittance) of the optical arrangements as in FIGS. 6A and 7A, respectively.
As shown in FIG. 6A, by adjusting the stretch of a domain-forming structure, in each domain the orientation of a LC director in the transmissive region of each picture element makes an angle of substantial 0 degree or 90 degrees with the slow axis of both a top quarter wave plate 12a and a bottom quarter wave plate 12b. Further, the angle between the slow axis of the top quarter wave plate 12a and the absorption axis of an upper polarizer 14a is substantially 45 degrees, and the angle between the slow axis of the bottom quarter wave plate 12b and the absorption axis of a lower polarizer 14b is substantially 135 degrees. Besides, the slow axis of the top quarter wave plate 12a is perpendicular to that of the bottom quarter wave plate 12b. The V-T characteristics of the above optical arrangement are depicted in FIG. 6B. FIG. 6B shows two curves that depict the transmittance values observed from two separate viewing angles, and an average of them represents the actual transmitted light intensity sensed by the human eye and provided for the comparison of different optical arrangements. Also, the V-T characteristics shown in FIG. 7B are depicted in two curves with respect to two separate viewing angles.
FIG. 7A shows another domain arrangement for the transmissive regions of a multi-domain transflective liquid crystal display. As shown in FIG. 7A, by adjusting the stretch of a domain-forming structure, in each domain the orientation of a LC director in the transmissive region of each picture element makes an angle of substantial 45 degrees or 135 degrees with the slow axis of both a top quarter wave plate 12a and a bottom quarter wave plate 12b. Further, the angle between the slow axis of the top quarter wave plate 12a and the absorption axis of an upper polarizer 14a is substantially 45 degrees, and the angle between the slow axis of the bottom quarter wave plate 12b and the absorption axis of a lower polarizer 14b is substantially 135 degrees. Besides, the slow axis of the top quarter wave plate 12a is perpendicular to that of the bottom quarter wave plate 12b. The V-T characteristics of the above optical arrangement are depicted in FIG. 7B.
Comparing the respective V-T characteristics shown in FIG. 6B and FIG. 7B, it can be seen the average light transmittance is higher when the liquid crystal director in the transmissive region makes an angle of substantial 0 degree or 90 degrees with the slow axis of the retarder. In that case, because the two quarter wave plates respectively provided on both sides of an LC cell have mutually perpendicular slow axes, the phase retardation effects brought by the two quarter wave plates will cancel each other out, and thus the angular relationship between an LC director and the absorption axis of a polarizer is the dominant factor for deciding the magnitude of the light transmittance. Under the circumstance, an included angle of 0 degree or 90 degrees between the LC director and the retarder results in an included angle of 45 degrees or 135 degrees between the LC director and the absorption axis of the polarizer to obtain an maximum light transmittance.
FIG. 8 shows a schematic diagram illustrating a picture element 20 including both a transmissive region Tr and a reflective region Re. A first domain-forming structure 24 and a second domain-forming structure 26 are respectively formed on the transmission region Tr and the reflective region Re. The domain-forming structure, which may be the protrusions shown in FIG. 2 or a pattern of slits shown in FIG. 3, may be line-shaped to define a specific stretch. Further, the arrows shown in FIG. 8 indicate the orientation direction (the long axis direction) of LC molecules that are tilted as a result of the domain-forming structure.
According to the invention, the stretches of the domain-forming structures in the transmissive region Tr and in the reflective region Re are individually adjusted according to the orientation of the axes of the retarder and the linear polarizer to obtain a maximum light transmittance and light reflectance. For instance, as shown in FIG. 8, an azimuth difference of 45 degrees is provided between the stretch of the domain-forming structure 24 in the transmissive region Tr with respect to that in the reflective region Re, so that an azimuth difference of substantial 45 degrees exists between the distribution of orientation directions of LC molecules in the reflective region Re and that in the transmissive region Tr. More specifically, a maximum light transmittance and light reflectance is obtained in case the included angle between the LC director in the reflective region Re and the slow axis of the retarder is selected as substantial 45 degrees or 135 degrees, and the included angle between the LC director in the transmissive region Tr and the slow axis of the retarder is selected as substantial 0 degree or 90 degrees. As a result, the light utilization efficiency is also improved.
While the invention has been described by way of examples and in terms of the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. On the contrary, it is intended to cover various modifications and similar arrangements as would be apparent to those skilled in the art. Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.
Patent Application
20080088775
