Alternative thin film transistors for liquid crystal displays

Alternative thin film transistors for liquid crystal displays are disclosed. The alternative transistors can be used for panels of displays such as liquid crystal displays (LCDs), especially those having alternative pixel arrangements. These transistors can be oriented on a panel of an LCD using different, non-traditional configurations, while addressing misalignment and parasitic capacitance.

BACKGROUND

Thin-film transistor (TFT) misalignment and parasitic capacitance can degrade the quality and performance of electronic devices such as liquid crystal displays (LCDs). One known attempt to correct for TFT misalignments and any associated increase in parasitic capacitance is found in U.S. Pat. No. 5,191,451 to Katayama et al (“the '451 patent”).FIG. 1depicts the “double TFT” arrangement100of the '451 patent. Source line104connects to the TFT via source electrode106. Two gate electrodes108are connected to gate line102. Two drain electrodes110connect to the pixel and are formed such that the two gate electrodes108affect conduction from the source electrode to the drain electrodes when activated. It is noted that there are two crossover regions112that are connected to TFT may produce additional parasitic capacitance between the gate and the source. As discussed in the '451 patent, any vertical misalignment of the TFT placement is somewhat corrected by this double TFT arrangement as is discussed therein.

Another manner of reducing the ill effects of TFT misalignment is shown in U.S. Pat. No. 5,097,297 to Nakazawa (“the '297 patent”).FIG. 4depicts a TFT400made in the manner taught in the '297 patent. As may be seen inFIG. 2, gate line402delivers the gate signal to gate electrode408. Source line404sends image data to source electrodes406. When the gate electrode is activated, the image data is transferred to the pixel via the drain electrode410. It is noted that this TFT embodiment contains only one gate crossover412which aids in reducing parasitic capacitance.

Furthermore, prior LCDs use the same orientation to align transistor in the pixel area of the display. However, for alternative pixel arrangements, transistors may need to be located in unconventional locations of a pixel area, while addressing misalignment and parasitic capacitance.

DETAILED DESCRIPTION

Reference will now be made in detail to implementations and embodiments, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.

The following implementations and embodiments disclose alternative thin film transistors for liquid crystal displays are disclosed. The alternative transistors can be used for panels of displays such as liquid crystal displays (LCDs), especially those having alternative pixel arrangements. These transistors can be oriented on a panel of an LCD using different, non-traditional configurations, while addressing misalignment and parasitic capacitance.

FIGS. 2 and 3provide different alternative embodiments to the prior art double TFT structure shown inFIG. 1. These structures can provide reduced source to gate capacitance, which can cause crosstalk in certain images. However, the gate to drain crossover can lessen the damage to image quality. One advantage of the embodiment ofFIG. 3is that there is only one crossover132that may reduce parasitic capacitance.

Another set of TFT redesigns are shown inFIGS. 5 through 10to handle the unevenness of parasitic capacitance that might be introduced by the above described TFT remapping. As TFTs are remapped on the panel, it is possible for some TFTs on the panel to be implemented in different corners or quadrants of a pixel area. For example, some TFTs may be constructed in the upper left hand corner of the pixel area, some in the upper right hand corner of the pixel area and so on. If all such TFTs were constructed the same way, then it would be likely that the source-drain orientation would be reversed for left hand corner and right hand corner implementation. Such non-uniformity of construction might introduce uneven parasitic capacitance in the case of a given TFT misalignment.

FIG. 5is one embodiment of a TFT built with a reverse orientation502as compared with a TFT built with a typical orientation1904. For exemplary purposes, TFT504is constructed within the upper left hand corner of its associated pixel in the usual manner—i.e. without any crossovers to avoid any introduced parasitic capacitance. It is noted that the source (S) and drain (D) electrodes are placed in a left-to-right fashion. TFT502is shown constructed in the upper right hand corner of a pixel area in a reverse orientation—i.e. a crossover514from source line1906is constructed so that the source electrode1910and drain electrode512are also in left-to-right fashion. Thus, if there is a TFT misalignment in the horizontal direction, then TFTs502and504will receive the same amount of added parasitic capacitance—thus, keeping the panel's defects uniform. It will be appreciated that although TFT502and TFT504are depicted side-by-side and connected to the same column, this is primarily for explanatory purposes. It is unlikely that two adjoining subpixels would share the same column/data line—thus, TFT504and its associated pixel is provided to show the distinction between a normal TFT orientation and TFT502in a reverse orientation.

FIG. 6shows another embodiment of TFTs602and604. As can be seen, a new crossover606is added to TFT604so as to balance the added parasitic capacitance via crossover604.FIG. 7is yet another embodiment of TFTs702and704. As may be seen here, the gate electrode crossover606inFIG. 6has been removed in favor of a gate line crossover706which may have a lesser impact on individual pixel elements.

FIGS. 8 and 9are embodiments of pixel elements with corners810and910removed to match the one corner removed containing the TFT structure. These pixel elements as designed here may balance the parasitic capacitances than a normal pixel structure.

FIG. 10is another embodiment of a pixel structure that employs at least one extra metal line1010that may help to shield the pixel element from the parasitic capacitances between the gate lines and the pixel element. Additionally, if a dot inversion scheme is employed, then the opposing polarities on both lines1010will also help to balance any parasitic capacitance between the source lines and the pixel elements.

Regarding the alternative TFT structures and pixel elements disclosed herein, standard LCD fabrication techniques can be implemented to form such structures. Moreover, the column, gate, and electrode lines can be formed of transparent material such as transparent conductive oxide so as not to degrade the optical qualities of the LCD.