Pixel structure and fabrication method thereof

A pixel structure includes a first patterned transparent conductive layer, an active layer, an insulating layer and a second patterned transparent conductive layer. The first patterned transparent conductive layer is disposed on a substrate and includes a source, a drain and a pixel electrode connected to the drain. The active layer connects the source and the drain. The insulating layer covers the source, the drain and the active layer. The second patterned transparent conductive layer is disposed on the insulating layer and includes a gate disposed above the active layer and a common electrode disposed above the pixel electrode. A fabrication method of a pixel structure is also provided.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority benefit of Taiwan application serial no. 101125547, filed on Jul. 16, 2012. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification.

BACKGROUND

Field of the Invention

The invention is directed to an electronic structure and a fabrication method thereof and more particularly, to a pixel structure and a fabrication method thereof.

Description of Related Art

Recently, the advancement of semiconductor devices and display devices flourishingly spreads the development of the multi-media technology. In respect of displays, liquid crystal displays (LCDs) having superior features, such as high definition, compressed space occupation, low power consumption, and free of radiation gradually becomes the mainstream product in the market. To provide better display quality to the liquid crystal display, all kinds of wide viewing angle liquid crystal displays have been developed. The most common ones include, for example, the in-plane switching liquid crystal display (IPS-LCD), the multi-domain vertical alignment liquid crystal display (MVA-LCD), the fringe field switching liquid crystal display (FFS-LCD) and so on.

As for the FFS-LCD, grayscale is produced by an electric field parallel to a substrate and by liquid crystal molecules rotating in a direction parallel to the substrate. The difference between the FFS-LCD and the IPS-LCD lies in different arrangement manners of the electrodes. A pixel electrode and a common electrode in the IPS-LCD are arranged on the same plane, while a pixel electrode and a common electrode in the FFS-LCD are arranged on different planes, wherein one of the pixel electrode and the common electrode has sub-electrodes disposed at intervals, so that the electric field penetrates through the intervals.

However, in the pixel structure of the current FFS-LCD, a bottom-gate type thin film transistor is commonly disposed, which needs six patterning processes to complete the fabrication of the pixel structure.

SUMMARY

The invention is directed to a pixel structure that can effectively achieve cost down.

The invention is directed to a fabrication method of a pixel structure for simultaneously fabricating a gate and a common electrode by using a transparent conductive layer so as to simplify the fabricating process.

According to an embodiment of the invention, a pixel structure including a first patterned transparent conductive layer, an active layer, an insulating layer and a second patterned transparent conductive layer is provided. The first patterned transparent conductive layer is disposed on a substrate and includes a source, a drain and a pixel electrode connected with the drain. The active layer connects the source and the drain. The insulating layer covers the source, the drain and the active layer. The second patterned transparent conductive layer is disposed on the insulating layer and includes a gate disposed above the active layer and a common electrode disposed above the pixel electrode.

According to an embodiment of the invention, a fabrication method of a pixel structure is provided. A first transparent conductive layer is formed on the substrate. The first transparent conductive layer is patterned to form a source, a drain and a pixel electrode connected with the drain. An active layer is formed to connect the source and the drain. An insulating layer is formed to cover the active layer and the pixel electrode. A second transparent conductive layer is formed on the insulating layer. The second transparent conductive layer is patterned to form a gate located above the active layer and a common electrode located above the pixel electrode.

In view of the foregoing, in the pixel structure according to the embodiment of the invention, both the gate and the common electrode are formed by a transparent conductive layer, such that the fabricating process can be simplified, and cost can be reduced. In addition, in the fabrication method of the pixel structure according the embodiment of the invention, the gate and the common electrode can be fabricated by a same patterning process so that an amount of patterning processes used by the pixel structure can be reduced for fabrication cost reduction.

DESCRIPTION OF EMBODIMENTS

FIG. 1is a schematic structural view illustrating a liquid crystal display (LCD) according to an embodiment of the invention. Referring toFIG. 1, an LCD1of the present embodiment includes an active array substrate10, an opposite substrate20, a liquid crystal layer30and a backlight module40. The opposite substrate20is disposed opposite to the active array substrate10. The liquid crystal layer30is located between the active array substrate10and the opposite substrate20. The backlight module40and the liquid crystal layer30are respectively disposed at two opposite sides of the active array substrate10.

FIG. 2is a schematic top view illustrating an active array substrate according to an embodiment of the invention. Referring toFIG. 2, the active array substrate10includes a substrate102, a plurality of data lines118and a plurality of scan lines146. A plurality of pixel structures100is defined between the data line118, the scan line146, the adjacent data line118and the adjacent scan line146. The substrate has an active area102aand a circuit area102b. The circuit area102bis located at the periphery of the active area102a. Typically, the pixel structures100are disposed in the active area102a, and wires connected with the pixel structures100(the data lines and the scan lines) extend from the active area to the circuit area102b.

FIG. 3AthroughFIG. 3Gare schematic top views illustrating a fabricating process of a pixel structure according to an embodiment of the invention.FIG. 4AthroughFIG. 4Gare schematic sectional views ofFIG. 3AthroughFIG. 3Galong line A-A′.FIG. 4AthroughFIG. 4Gare schematic sectional views further illustrating a portion M and a portion N in the circuit area102bdepicted inFIG. 2.

Referring to3A andFIG. 4A, in the present embodiment, an ultraviolet (UV) blocking layer104may be formed on the substrate102. A material of the ultraviolet blocking layer104is, for example, a resin layer, and a material of the resin layer is, for example, silicone resin, acrylic resin or a combination thereof. A method of forming the ultraviolet blocking layer104is, for example, coating the unsolidified resin material on the substrate102first and then solidifying the resin material to form the ultraviolet blocking layer104. A method of solidifying the resin material is, for example, a UV-radiation process or a heating process.

Then, a first transparent conductive layer110ais formed on the substrate102. In the present embodiment, the first transparent conductive layer110ais formed on the ultraviolet blocking layer104.

Referring toFIG. 3BandFIG. 4B, a first patterning process is performed on the first transparent conductive layer110ato form a source112, a drain114and a pixel electrode116. The pixel electrode116is connected with the drain114. The first patterning process is, for example, a photolithography and etching process (PEP).

In addition, while forming the source112, the drain114and the pixel electrode116, the data line118are also formed. The data line118is connected with the source112. The data line118extends to the circuit area102b. It should be mentioned that the source112, the drain114and the pixel electrode116are made of a transparent conductive material, so that transmittance of the pixel structure100can be further improved.

Referring toFIG. 3CandFIG. 4C, an active layer120is formed, and the active layer120connects the source112and the drain114. In the present embodiment, the active layer120, for example, covers at least a portion of the source112and at least a portion of the drain114. A material of the active layer includes a metal oxide semiconductor, such as indium-gallium-zinc oxide (IGZO), tin oxide, aluminum oxide (e.g. Al2O3) or a combination thereof. A second patterning process is, for example, a photolithography and etching process (PEP). For example, the step of forming the active layer120is, for example, forming a metal oxide semiconductor material on the substrate102first and then, performing an annealing process. Next, processes such as photoresist coating, exposing, developing, etching and photoresist stripping are performed so as to form the active layer120. It is to be mentioned that the annealing process contributes to improve ion mobility for the active layer120, and the structure of the active layer120becomes robust. Besides, the annealing process can reduce impedance for the first patterned transparent conductive layer110and increase transmittance for the first patterned transparent conductive layer110. Further, the annealing process may be performed after the active layer120is formed.

Referring toFIG. 1andFIG. 4C, when the material of the active layer120is, for example, the metal oxide semiconductor, a problem of current leakage may be resulted in the active layer120due to a conductivity change of the metal oxide semiconductor when being exposed to UV light. Besides, the ultraviolet blocking layer104formed on the substrate102is located between the backlight module40and the active layer120, absorbs the UV light and allows the visible light to pass through. Thus, when incident light emitted from the backlight module40is transmitted to the ultraviolet blocking layer104, the ultraviolet blocking layer104absorbs the UV light included in the incident light and allows the visible light included in the incident light to penetrate so as to protect the active layer120from damage for being illuminated by the UV light and reduce probability of current leakage of the active layer120.

Referring toFIG. 3DandFIG. 4D, an insulating layer130is omitted inFIG. 3D. An insulating layer130is formed on the substrate102. The insulating layer130covers the active layer120and the pixel electrode116. The insulating layer130provides a function of electrical insulation so as to facilitate a fabricating process of a subsequent conductive layer. Next, a third patterning process is performed to form a contact window130S in the insulating layer130of a periphery area120b. The data line118is exposed from the contact window130S.

Referring toFIG. 3EandFIG. 4E, a second transparent conductive layer140is formed on the insulating layer130.

Referring toFIG. 3FandFIG. 4F, a fourth patterning process is performed on the second transparent conductive layer140ato form a gate142and a common electrode144. The gate142is located above the active layer120, and the common electrode144is located above the pixel electrode116. In the present embodiment, a method of forming the common electrode144is, for example, patterning the second transparent conductive layer140ato form a connection portion144aand a plurality of strip electrodes144bthat are disposed at intervals. The strip electrodes144bare connected with the connection portion144a.

In the present embodiment, the pixel structure100includes, for example, a top-gate type thin film transistor, and the gate142is, for example, made of a transparent conductive material. Thus, the gate142and the common electrode144may be fabricated by a same patterning process to simplify the fabricating process and reduce fabrication cost. In addition, the gate142and the common electrode144are made of the transparent conductive material. Thus, transmittance of the pixel structure100can be further improved. Accordingly, the pixel structure100may be applied in a transparent display since electrodes and wires in the pixel structure100use the transparent conductive material.

Moreover, while forming the gate142and the common electrode144, the scan line146and a contact pad148are further formed. The scan line146is connected with the gate142, and the scan line146extends to the circuit area102b. The scan line146may be further connected with a scan line driving circuit (not shown) to transmit signals to the pixel structure100. The contact pad148is located in the circuit area102and on the insulating layer130, and a portion of the contact pad148is filled in the contact window130S so as to connect the data line118. The contact pad148is, for example, used to connect the data line118with a data line driving circuit (not shown) to transmit signals to the pixel structure100.

Thus, fabrication of the pixel structure100is initially completed. In the present embodiment, the pixel structure100may be fabricated by four patterning processes. Accordingly, the fabrication method of the pixel structure100of the present embodiment can indeed simplify the fabricating process and reduce the fabrication cost.

Moreover, referring toFIG. 3GandFIG. 4G, the insulating layer130and the protection layer150are omitted inFIG. 3G. In order to reduce impact from the environment on components of the pixel structure100, a protection layer150may be further formed on the second patterned transparent conductive layer140. The step of forming the protection layer150is, for example, forming an oxide layer150aon the gate142, the common electrode144and the insulating layer130first and then, forming a nitride layer150bon the oxide layer150b. Next, a fifth patterning process is performed to expose the scan line146and the contact pad148from the circuit area102bso as to electrically connect the scan line146with a scan line driving electrode and electrically connect the data line118with the data line driving circuit. Accordingly, the pixel structure100may be driven by the scan line146and the data line118connected with the contact pad148. However, in another embodiment, the protection layer150and the fifth patterning process may be omitted to decrease the number of patterning processes, so that the number of photomasks used in the patterning processes can be further decreased.

In the present embodiment, the nitride layer150bhas good density and thus, can effectively block the water and oxygen. However, during forming the nitride layer150b, ammonia gas (NH3) may be used in the fabricating process, and nature change of the metal oxide semiconductor used as the active layer120may occur due to being interfered by hydrogen ion. Thus, before forming the nitride layer150b, the oxide layer150amay be formed to cover the second patterned transparent conductive layer140, such that the probability of the hydrogen ion infiltrating the active layer120during forming the nitride layer150bmay be reduced. Therefore, reliability of the pixel structure100can be improved by the protection layer150, and image sticking occurring in display frames using the pixel structure100can be reduced.

Moreover, referringFIG. 3EwithFIG. 4E, the pixel structure100of the present embodiment is described. The pixel structure100includes the first patterned transparent conductive layer110, the active layer120, the insulating layer130and the second patterned transparent conductive layer120. The first patterned transparent conductive layer110is disposed on the substrate102and includes the source112, the drain114and the pixel electrode116connected with the drain114. The active layer120is connected with the source112and the drain114. The insulating layer130covers the source112, the drain114and the active layer120. The second patterned transparent conductive layer140is disposed on the insulating layer130and includes the gate142disposed above the active layer120and the common electrode144disposed above the pixel electrode116.

It to be mentioned that the common electrode144includes the connection portion144aand the plurality of strip electrodes144b. The strip electrodes144bare disposed at intervals and connected with the connection portion144a. The strip electrodes144bare located above the pixel electrode116, and electric field is formed between the strip electrodes144band the pixel electrode116. For example, when the pixel structure100is driven, electric field E is generated between the pixel electrode116and the strip electrodes144b. A portion of the electric field E penetrates through a gap between two adjacent strip electrodes144b. The electric field E penetrating the gap may be used to drive liquid crystal molecules, so that the liquid crystal molecules are rotated in a direction substantially parallel to the substrate102to control grayscale for the display screen. Thus, a pixel structure for a fringe field switching liquid crystal display (FFS-LCD) is formed. Additionally, referring toFIG. 4DwithFIG. 1, the common electrode144of the present embodiment is disposed on the active array substrate10, and thus, the opposite substrate20may not have to be disposed with an electrode.

In light of the foregoing, both the gate and the common electrode of the embodiments of the invention are formed by a transparent conductive layer, and thus, the fabricating process can be simplified for cost down. In addition, in the fabrication method of the pixel structure of the embodiments of the invention, the gate and the common electrode may be fabricated by a same patterning process, so that the number of patterning processes for the pixel structure may be decreased to reduce the fabrication cost.