|Publication number||USRE41927 E1|
|Application number||US 11/433,903|
|Publication date||Nov 16, 2010|
|Priority date||Feb 12, 2001|
|Also published as||US6836299, US20020109797|
|Publication number||11433903, 433903, US RE41927 E1, US RE41927E1, US-E1-RE41927, USRE41927 E1, USRE41927E1|
|Inventors||Woo-Suk Chung, Chang-Won Hwang|
|Original Assignee||Samsung Electronics Co., Ltd.|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (33), Referenced by (1), Classifications (24), Legal Events (3)|
|External Links: USPTO, USPTO Assignment, Espacenet|
This application is a reissue application from U.S. patent application Ser. No. 09/911,613 filed on Jul. 25, 2001 and issued as U.S. Pat. No. 6,836,299, which claims priority to and the benefit of Korean Patent Application No. 2001 - 06820 filed on Feb. 12, 2001, which are all hereby incorporated by reference for all purposes as if fully set forth herein.
The present invention relates to a thin film transistor liquid crystal display (TFT LCD) device, and more particularly to a reflective or transflective TFT LCD device having multi-layered pixel electrodes connected to drain electrodes with interposing an insulating layer therebetween.
TFT LCD devices are generally classified into a reflective TFT LCD device using a reflective layer as pixel electrodes, a transmissive TFT LCD device using transparent pixel electrodes, and a transflective TFT LCD device using a reflective layer having a transmissive region in a portion of a reflective region as pixel electrodes, according to reflectance or permeability of pixel electrodes. In the TFT LCD devices, to supply voltage for controlling arrangement of liquid crystal to the pixel electrodes, drain electrodes of thin film transistors formed in each pixel are connected to the corresponding pixel electrodes. The pixel electrodes are generally connected to the drain electrodes through via holes formed in an interlayer insulating layer.
In a transmissive TFT LCD device, pixel electrodes use indium oxides to form transparent electrodes. However, this material may cause a problem that oxidizes wires of aluminum (Al) to form insulating oxides and thereby hinders in supplying voltage to the pixel electrodes. Therefore, in the transmissive TFT LCD device, drain electrodes are formed of a single layer of metal such as chromium (Cr), or a two-layered conductive layer having an Al-contained metal layer and a molybdenum tungsten (MoW) or Cr layer formed on the Al-contained metal layer.
In a reflective TFT LCD device, pixel electrodes usually use aluminum neodymium (AlNd). In this case, materials forming drain electrodes are also limited. Referring to
To solve the problem, an upper layer 212′ of the drain electrode 21′ can be formed of metal such as MoW that is resistant against oxidation, as shown in FIG. 2. However, in this case, battery effect, like inside a chemical battery, can be occurred due to difference of electro-negativity between the upper layer 212′ of the drain electrode 21′ and an Al-containing reflective layer forming the pixel electrodes 27. For example, due to corroding by the battery effect, gaps 29 similar to spike phenomenon generating at the interface between a silicon layer and an Al layer can be formed at the interface between the upper layer 212′ and the Al-containing reflective layer. Also, as a portion of the Al-containing reflective layer around the gaps 29 falls, the Al-containing reflective layer can generate cracks 31 around the via holes. These gaps 29 or cracks 31 cause a problem increasing contact resistance between the pixel electrodes 27 and the drain electrodes 21′.
Generally, the battery effect increases in proportion to the difference of surface area and electronegativity between two metal layers. Accordingly, the drain electrodes 21′ that usually has relatively very small surface area compared to the pixel electrodes 27 enforces the battery effect more, thereby increasing the contact resistance between the pixel electrodes 27 and the drain electrodes 21′ more.
To solve the battery effect, it can be considered to use a MoW or Cr layer as reflective plates or pixel electrodes 27. However, such a choice deteriorates reflectance and conductivity of the pixel electrodes.
Accordingly, a new TFT LCD device, which can prevent increase of contact resistance due to the battery effect or surface oxidation at the interface between the pixel electrodes and the drain electrodes with maintaining highly reflectance and conductivity, is required.
It is an object of the present invention to provide an improved TFT LCD device that can prevent battery effect at the interface between pixel electrodes and drain electrodes, while maintaining high reflectance and conductivity.
It is another object of the present invention to provide an improved TFT LCD device that can prevent insulating oxides at the interface between pixel electrodes and drain electrodes, while maintaining high reflectance and conductivity.
It is other object of the present invention to provide an improved TFT LCD device that can prevent contact resistance increase at the interface between pixel electrodes and drain electrodes, while maintaining high reflectance and conductivity.
These and other objects are provided, according to the present invention, by a TFT LCD device having pixel electrodes formed of a multi-layered conductive layer. Preferably, drain electrodes are composed of multiple layers, and the most upper layer of the multiple layers is composed of a metal layer that is strongly resistant against oxidation. Also, the multi-layered conductive layer is composed of two-layered conductive layer having a lower layer of metal that has small electro-negativity difference between itself and the most upper layer of the drain electrodes and an upper layer of Al-containing metal.
In the present invention, the lower layer of the two-layered conductive layer is preferably composed of the same material as that of the most upper layer of the drain electrodes, for example one selected from a Cr layer and a MoW layer. The Al-containing metal usually uses pure Al or AlNd. Accordingly, the two-layered conductive layer is formed by depositing the lower layer of one selected from a Cr layer and a MoW layer and the upper layer of Al-containing metal and then patterning them.
It is noted that the multi-layered conductive layer is not limited to the two-layered conductive layer. To reduce the battery effect efficiently, if necessary, an intermediate metal layer can be interposed between the lower and upper layers of the two-layered conductive layer.
The multiple layers of the drain electrodes usually use metal having a high conductivity to prevent a signal voltage drop due to the data line resistance. Also, the drain electrodes are formed of the same conductive material as that of the data lines connected to source electrodes. Accordingly, the multiple layers forming the drain electrodes are preferably composed of a two-layered layer having an Al layer for increasing conductivity and a Cr or MoW layer strongly resistant to oxidation formed on the Al layer, or a three-layered layer having an intermediate Al layer and an upper and a lower Cr or MoW layers formed on and under the intermediate Al-contained layer to prevent spike phenomenon due to silicon layers over an active area. When the drain electrodes formed along with the data lines are of the three-layered layer, the MoW layer as the lower and upper layer preferably is better than the Cr layer since it is easy to be patterned along with the intermediate Al-containing layer.
According to the present invention, since the upper layer of the drain electrodes and the lower layer of the pixel electrodes are formed of same material or metals having small differences in electro-negativity, the battery effect therebetween can be ignored. Also, in the two-layered conductive layer of the pixel electrodes, the upper layer and the lower layer are concurrently formed to have the same surface area by means of same patterning process. This may result in difference in electro-negativity, but battery effect can be prevented. Thus, at the interface between the pixel electrodes and the drain electrodes, the battery effect is considerably reduced and the spike phenomenon or cracks is prevented.
Also, since the upper layer of the drain electrodes is composed of a metal layer strongly resistant to oxidation, insulating oxides are not formed on the upper surface thereof even though it is exposed to oxidizing material such as developer or detergent, and thereby preventing contact resistance increase.
FIG. 1 and
The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which a preferred embodiment of the invention is shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiment set forth herein. Like numbers refer to like elements throughout.
The gate electrodes which form a portion of the gate lines 17 formed in a transverse direction are covered by an interlayer insulating layer (19 of
On the source and drain electrodes 121, 121′ and the data line 210, a protecting layer (23 of
It is natural that the structure of the pixel portions of the TFT LCD device of the present invention described above is the same as that of a conventional TFT LCD device, since the present invention is characterized that pixel electrodes are not formed of a single layer, but of a multi-layered conductive layer.
A method for manufacturing a TFT LCD device in accordance with the present invention will now be described. FIG. 5 through
An ion implantation is performed to the active region pattern 13 by using the gate electrodes as an ion implantation mask. Thus, a line shaped portion of the active region pattern 13 is divided into an source and an drain regions. The ion implantation process is performed twice to each of n-type and p-type impurities since in the polysilicon LCD device, n-type transistors along with p-type transistors are generally disposed at a peripheral portion. In each ion implantation process, an ion implantation mask is formed.
The embodiment of the present invention described above shows an example of a low temperature polysilicon TFT LCD device having an active region formed of polysilicon, but the present invention can be also applied to an amorphous silicon TFT LCD device having an active region formed of amorphous silicon, which a laser annealing process is not performed after a amorphous silicon layer is formed. Also, the present invention can be applied to a bottom gate type TFT LCD devices as well as a top gate type TFT LCD device.
The embodiment of the present invention described above shows a reflective TFT LCD device using a reflective layer as pixel electrodes, but the present invention is not limited to the embodiment. The present invention can be also applied to a transflective TFT LCD as well as the reflective TFT LCD. For example, After a protecting layer exposing a portion of each drain electrode is formed, a pixel electrode pattern is formed in a pixel area. The pixel electrode pattern is composed of transparent electrodes. Then, a Cr and an Al layers are continuously formed over the whole surface of a substrate over which the transparent electrode are formed, and patterned to form a reflective layer pixel electrode pattern having windows in a portion of the pixel area. The drain electrodes are composed of three-layered metal layer having a lower MoW layer, an intermediate Al layer, and an upper MoW layer. In this example, the upper layer of the drain electrodes and the lower layer of the pixel electrodes are not formed of same materials, but a problem due to direct contact between the lower Al layer of the pixel electrodes and the upper layer of the drain electrodes can be considerably reduced.
As apparent from the foregoing description, it can be appreciated that the present invention provides a TFT LCD device which can prevent electrochemical effect such as battery effect having bad influence on the fabrication process, thereby preventing damage of reflective electrodes and increasing reflectance thereof to obtain more high definition.
In the drawings and specification, there have been disclosed typical preferred embodiments of the invention and, although specific terms are employed, they are used in a generic and descriptive sense only and not for purpose of limitation, the scope of the invention being set forth in the following claims.
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|U.S. Classification||349/42, 349/147, 257/72, 257/59, 257/E29.282, 257/E29.278|
|International Classification||G02F1/136, H01L21/3205, H01L21/28, H01L23/52, H01L29/786, H01L21/336, G02F1/1343, G02F1/1362, G02F1/1333, G02F1/1368|
|Cooperative Classification||G02F1/13439, G02F2203/02, H01L29/458, G02F1/136227, H01L27/124, G02F1/1368|
|European Classification||G02F1/1343B, H01L27/12T|
|May 9, 2012||FPAY||Fee payment|
Year of fee payment: 8
|Sep 23, 2012||AS||Assignment|
Owner name: SAMSUNG DISPLAY CO., LTD., KOREA, REPUBLIC OF
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:SAMSUNG ELECTRONICS CO., LTD.;REEL/FRAME:029008/0798
Effective date: 20120904
|Jun 15, 2016||FPAY||Fee payment|
Year of fee payment: 12