Thin film transistor

A thin film transistor is provided. The thin film transistor includes a gate, at least one inorganic material layer, at least one dielectric layer, a source, a drain and an active layer. The gate is disposed on the substrate. The inorganic material layer covers the gate. The dielectric layer including at least one organic material covers the substrate and has an opening exposing the inorganic material layer on the gate. The source and the drain are disposed on the dielectric layer and a part of the inorganic layer exposed by the opening respectively. A channel region exists between the source and the drain. The active layer is disposed on the channel region.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority benefit of Taiwan application serial no. 97145335, filed on Nov. 24, 2008. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of specification.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to a transistor and a method for fabricating the same, in particular, to a thin film transistor and the method for fabricating the same.

2. Description of Related Art

With growth of the technologies, lighter, thinner, portable and flexible displays have drawn attention of many people, and many big companies have joined the development of such displays. Currently, most of the flexible displays use organic materials to fabricate the insulating layers. For example, the technology has been disclosed in US Patent Application No. 2005/0001210 and US Patent Application No. 2005/0026083. The insulating layer made of an organic material is highly flexible, but often has a low dielectric constant. Further, the quality of the insulating layer is difficult to control, and defects in a thin film cannot be controlled effectively. Therefore, a leakage current easily occurs in a transistor, resulting in unstable characteristics of the transistor.

To improve the dielectric characteristics of the organic material, particles having a high dielectric constant can be added into the organic material by means of hybrid, which, however, increases the roughness of the surface of the organic insulating layer, and increases the retardation effect.

SUMMARY OF THE INVENTION

Accordingly, the present invention is related to a thin film transistor. The thin film transistor includes a gate, at least an inorganic material layer, at least a dielectric layer, a source, a drain, and an active layer. The gate is disposed on a substrate. The inorganic material layer covers the gate. The dielectric layer at least including an organic material covers the substrate, and has an opening exposing the inorganic material layer on the gate. The source and the drain are disposed on the dielectric layer and a part of the inorganic layer exposed by the opening. A channel region exists between the source and the drain. The active layer is disposed on the channel region.

The present invention is also related to a thin film transistor. The thin film transistor includes a gate, at least an inorganic material layer, at least one dielectric layer, a source, a drain, and an active layer. The active layer is located on the substrate. The source and the drain cover a part of the active layer and a part of the substrate. A channel region exists between the source and the drain. The inorganic material layer is filled into the channel region. The dielectric layer at least including an organic material covers the inorganic material, the source and the drain. The gate is disposed on the dielectric layer.

The present invention is further related to a thin film transistor. The thin film transistor includes a gate, an insulating layer, a source, a drain, and an active layer. The source and the drain are disposed above the substrate. A channel region exists between the gate and the drain. The gate is disposed opposite to the channel region. The active layer is disposed opposite to the gate, and is disposed in an active region of the substrate. The insulating layer isolates the gate from the source and the drain. The insulating layer includes an inorganic material layer and a dielectric layer. The inorganic material is at least disposed between the gate and the active layer. The dielectric layer at least including an organic material is at least disposed on the substrate outside the active region.

DESCRIPTION OF THE EMBODIMENTS

An insulating layer of the present invention includes an inorganic material layer and a dielectric layer. The inorganic layer is disposed between a gate and an active layer. The dielectric layer is at least disposed at a position requiring insulation outside an active region. The bottom-contact thin film transistor with the bottom gate and the top-contact thin film transistor with the top gate are taken for example in the following illustration. However, the present invention is not limited to be so, and the present invention is also applicable to a top-contact thin film transistor with a bottom gate, a bottom-contact thin film transistor with a top gate, and other thin film transistors.

FIGS. 1 to 4are schematic cross-sectional views of the method for fabricating a bottom-contact thin film transistor with a bottom gate according to embodiments of the present invention.

Referring toFIG. 1, the method for fabricating a thin film transistor according to this embodiment includes forming a gate12in the active region11of the substrate10. The substrate10can be a rigid substrate or a flexible substrate. The material of the rigid substrate can be glass, quartz, or silicon wafer for example. The material of the flexible of the substrate can be plastic such as acrylic, metal foil, or paper. The active region11is a region preset to form the active layer. The method for forming the gate12includes forming a gate material layer, and then patterning the gate material layer through a lithographic and etching process for example. The material of the gate material layer includes metal, doped polysilicon, or transparent conductive oxide. For example, the metal is gold, silver, aluminum, copper, chromium or alloy thereof, and the transparent conductive oxide is indium tin oxide. For example, the method for forming the gate material layer is a physical vapor deposition process or chemical vapor deposition process. For example, the physical vapor deposition is a sputtering process or an evaporation process. In another embodiment, the method for forming the gate12can be forming a patterned conductive layer directly, for example, through an ink jet process.

Then, an inorganic material layer14is formed on the substrate10to cover the gate12. The method for forming the inorganic material layer14is, for example, forming a blanket inorganic material layer first, and then patterning the inorganic material layer through a lithographic and etching process. The inorganic material layer14can be a monolayer or multilayer structure. Each layer in the inorganic material layer14with the multilayer structure can be formed by a single material or multiple materials. The material of the inorganic material layer14includes a low dielectric constant material having a dielectric constant lower than 4 or a high dielectric constant material having a dielectric constant higher than 4, such as a silicon oxide (SiOx), a silicon oxynitride (SiONx), a silicon nitride (SiNx), an aluminum oxide (AlOx), an aluminum nitride (AlNx), a hafnium oxide (HfOx), a hafnium silicon oxide (HfSiOx), a hafnium lanthanum oxide (HfLaOx), or a silicon carbide (SiCx), where x represents various possible values. A thickness of the inorganic material layer14is for example, 100 to 5000 angstroms.

Then, referring toFIG. 2, the dielectric layer16is formed on the substrate10, and has an opening18exposing the inorganic material layer14on the gate12. The insulating layer17is formed by the dielectric layer16and the inorganic material layer14. The dielectric layer16can be a monolayer or multilayer structure. The dielectric layer16can be made of an organic material, such as an organic material having a dielectric constant lower than 4. Furthermore, the material of each layer in the dielectric layer16can be formed of a single organic material, multiple organic materials, or include both organic and inorganic materials. The material of the dielectric layer16can be a photosensitive or non-photosensitive material, such as polyimide (PI), polyvinyl phenol, polystyrene (PS), acrylic or epoxy resin.

In an embodiment, the material of the dielectric layer16is a photosensitive material. The method for forming the dielectric layer16is for example, forming a blanket photosensitive material layer through the physical vapor deposition such as evaporation or through a coating process, then performing a lithographic process to pattern the photosensitive material layer. In another embodiment, the material of the dielectric layer16can be a non-photosensitive material. The method for forming the dielectric layer16is for example, forming a blanket non-photosensitive material layer through the physical vapor deposition such as evaporation or through a coating process, then performing a lithographic and etching process to pattern the non-photosensitive material layer. A thickness of the dielectric layer16can be adjusted as desired. In an embodiment, a thickness of the dielectric layer16is for example, 200 to 20000 angstroms.

Then referring toFIG. 3, a source20and a drain22are formed on the dielectric layer16and the part of the inorganic material layer14exposed by the opening18. A channel region24is between the source20and the drain22. The method for forming the source20and the drain22is e.g., forming a conductive material layer first, and then patterning the conductive material layer. The material of the conductive material layer is for example, metal such as gold, silver, aluminum, copper, chromium or an alloy thereof. The method for forming the conductive material layer includes performing a physical vapor deposition process, which is for example, a sputtering process or an evaporation process. In another embodiment, the method for forming the source20and the drain22can also be forming the patterned conductive layer directly, for example, through an ink jet process.

Then, referringFIG. 4, an active layer26is formed in the channel region24. The active layer26is electrically coupled to the source20and the drain22. The material of the active layer26is for example, semiconductor or organic semiconductor. The semiconductor is for example, amorphous silicon, polysilicon or oxide semiconductor series. The organic semiconductors include N-type or P-type organic small molecular semiconductors, organic polymer semiconductors, or a mixture of the organic small molecular and organic polymer semiconductors. The material of the organic small molecular semiconductors is for example, pentacene or tetracene. The organic polymer semiconductor is for example, poly-(3-hexylthiophene) (P3HT). Thus, the fabrication of the thin film transistor with the bottom gate100A is completed.

Referring toFIG. 4, in short, the thin film transistor100A of this embodiment includes a gate12, at least an inorganic material layer14, at least a dielectric layer16, a source20, a drain22, and an active layer26. The gate12is disposed in the active region11on the substrate10. The inorganic material layer14covers the gate12and exposes the substrate10. The dielectric layer16covers the substrate10, and has an opening18exposing the inorganic material layer14on the gate12. The inorganic material layer14and the dielectric layer16form the insulating layer17which isolates the gate12from the active layer26. The source20and the drain22are disposed on the dielectric layer16and the part of the inorganic material layer14exposed by the opening18respectively. The channel region24is between the source20and the drain22. The active layer26is disposed in the channel region24.

Referring toFIG. 4, in this embodiment, the inorganic material layer14is disposed in the active region11and extends to the edge of the active region11to conformally cover the top surface and the sidewalls of the gate12. In another embodiment, referring toFIG. 4A, as such, the inorganic material layer14is also disposed in the active region11and extends to the edge of the active region11to cover the top surface and the sidewalls of the gate12. The sides of the inorganic material layer14are in a trapezoid shape to reduce the stress. In another embodiment, referring toFIG. 4B, the inorganic material layer14may also be disposed in only the active region11, cover the top surface of the gate12, but do not cover the sides of the gate12.

Furthermore, the profile of the top surface of the inorganic material layer14can be any shape, such as square, rectangle, or polygon.FIGS. 4C,4D, and4E are top views of the thin film transistor respectively. Alternatively, to reduce the stress generated by bending, the profile of the top surface of the inorganic material layer14can be designed to be curve, such as a square having arc angles, a rectangle having arc angles, a polygon having arc angles, a circle, or an ellipse.FIGS. 4F,4G, and4H are top views of the profile of a rectangle having four arc angles, a circle, and an ellipse of the top surface of the inorganic material layer14of the thin film transistor respectively. However, the profile of the inorganic material layer14is not limited to be so in the present invention, but can be designed to any shape that reduces the stress generated by bending. For the clarity of the figures, the dielectric layer16and the active layer26are not shown inFIGS. 4C to 4H.

Referring toFIGS. 4I,4J,4K, to further absorb the stress, at least an elastomer is formed in the dielectric layer16outside the source20and the drain22. The material of the elastomer28can be a polymer having a Flexural modulus, Young's modulus or tensile modulus lower than that of the dielectric layer16. In an embodiment, the polymer functioning as the elastomer28can be a polymer having a tensile modulus greater than that of the dielectric layer16but smaller than 5000 MPa, for example, from 1300 MPa to 3790 MPa. In another embodiment, the polymer functioning as the elastomer28can be a polymer having a Young's modulus smaller than that of the dielectric layer16. The material of the elastomer is for example, poly(amide imide), poly(benzimidazole), poly(bis maleimide), poly(benzobisthiazole), poly(butylene terephthalate), polycarbonate, polychloral, poly(2,6-dimethyl-1,4-phenylene oxide), poly(ether ether ketone), poly(ether imide), poly(ether sulfone), poly(ethylene-2,6-naphthalate), poly(ethylene sulfide), poly(ethylene terephthalate), poly(lactic acid), poly(methylene oxide), poly(methyl methacrylate), or poly(4-methyl pentene-1).

Referring toFIG. 4I, in an embodiment, the elastomer28extends from the bottom surface of the dielectric layer16to the top surface of the dielectric layer16. The method for forming the elastomer28is for example, forming another opening30aat the same time as forming the opening18in the dielectric layer16. The opening30aexposes the substrate10, and then the polymer is backfilled in the opening30a.Referring toFIG. 4J, in another embodiment, the elastomer28extends from the top surface of the dielectric layer into the dielectric layer. The method for forming the elastomer28inFIG. 4Jis for example, forming another opening30bat the same time as forming the opening18in the dielectric layer16. The opening30bdoes not expose the substrate10, and then the polymer is backfilled in the opening30b.Referring toFIG. 4K, in another embodiment, the elastomer28extends from the bottom surface of the dielectric layer16into the dielectric layer16, but not to the top surface of the dielectric layer16. The method for forming the elastomer28ofFIG. 4Kis for example, forming the polymer layer on the substrate10before forming the dielectric layer16, then patterning the polymer layer.

FIGS. 5 to 8are schematic cross-sectional views of the method for fabricating a top-contact thin film transistor with the top gate according to another embodiment of the present invention. The material of the components of the thin film transistor and the method for forming the same in the following may use the material and the method for the components having the same reference numbers disclosed above, which will not be described in detail again.

Referring toFIG. 5, the active layer26is formed in the active region11on the substrate10. Then, the source20and the drain22are formed on a part of the active layer26and a part of the substrate10. The channel region24exists between the source20and the drain22, as shown inFIG. 6.

Then, referring toFIG. 7, the inorganic material layer14is formed in the active region11. The inorganic material layer14and the dielectric layer16form the insulating layer17isolating the gate12from the active layer26. Then, the dielectric layer16is formed on the inorganic material layer14, the source20, and the drain22.

After that, referring toFIG. 8, the gate12is formed on the dielectric layer16above the channel region24. Thus, the fabrication of the thin film transistor100B with the top gate is completed.

Referring toFIG. 8, in short, the thin film transistor100B of this embodiment includes the gate12, at least an inorganic material layer14, at least a dielectric layer16, the source20, the drain22, and the active layer26. The active layer26is disposed in the active region11on the substrate10. The source20and the drain22cover a part of the active layer26and a part of the substrate10. The channel region24exists between the source20and the drain22. The inorganic material layer14is filled in the channel region24between the source20and the drain22, and is coupled to the source20and the drain22. The dielectric layer16covers the inorganic material layer14, the source20and the drain22. The inorganic material layer14and the dielectric layer16form the insulating layer17isolating the gate12from the active layer26. The gate12is disposed on the dielectric layer16.

Referring toFIG. 8, in this embodiment, the inorganic material layer14is not only disposed in the channel region24, but also extends to the surface of the source20and the drain22, such that a side of the inorganic material layer14is T-shaped. In another embodiment, referring toFIG. 8A, the inorganic material layer14is only located in the channel region24. Furthermore, the profile of the top surface of the inorganic material layer14can be square, rectangle, or polygon as shown inFIGS. 8B,8C, and8D respectively. Alternatively, to reduce the stress generated by bending, the profile of the top surface of the inorganic material layer14can be designed to be curve, such as a square having arc angles, a rectangle having arc angles, a polygon having arc angles, a circle, or an ellipse.FIGS. 8E,8F, and8G are top views of the profile of a rectangle having four arc angles, a circle, and an ellipse of the top surface of the inorganic material layer14of the thin film transistor respectively. However, the profile of the inorganic material layer14is not limited to be so in the present invention, and the profile can be designed to any shape that reduces the stress generated by bending. For the clarity of the figures, the dielectric layer16and the active layer26are not shown inFIGS. 8B to 8G.

Referring toFIGS. 8H,8I, and8J, as such, to further absorb the stress, at least an elastomer28can be formed in the dielectric layer16outside the source20and the drain22. Referring toFIG. 8H, in an embodiment, the elastomer28extends from the bottom surface of the dielectric layer16to the top surface of the dielectric layer16. The method for forming the elastomer28ofFIG. 8His for example, forming an opening30ain the dielectric layer16. The opening30aexposing the substrate10, and then a polymer is refilled in the opening30a.Referring toFIG. 8I, in another embodiment, the elastomer28extends from the top surface of the dielectric layer into the dielectric layer. The method for forming the elastomer28ofFIG. 8Iis for example, forming the opening30bin the dielectric layer16. The opening30bdoes not expose the substrate10, and a polymer is refilled in the opening30b.Referring toFIG. 8J, in another embodiment, the elastomer28extends from the bottom surface of the dielectric layer16into the dielectric layer16, but not to the top surface of the dielectric layer16. The method for forming the elastomer28ofFIG. 8Jis for example, forming a polymer layer on the substrate10before forming the dielectric layer16, then patterning the polymer layer.

The insulating layer of the present invention includes the inorganic material layer and the dielectric layer. The inorganic material layer is disposed between the gate and the active layer. The inorganic material has a dielectric constant greater than that of the organic material, a controllable quality, and fewer defects. Therefore, the formed transistor has less current leakage, and better device characteristics. The dielectric layer is located outside the active region where isolation is needed. Because the dielectric layer contains the organic material having good flexibility, the stress generated by bending of the device can be absorbed by the organic material, so as to reduce the stress on the inorganic material substantially. The dielectric layer may use a material having a low dielectric constant, so the better transistor characteristics and flexibility of the insulating layer are provided. Furthermore, the inorganic material can be patterned as desired to have edges in a curve pattern, and the elastomer can also be disposed in the dielectric layer, so as to further reduce the stress generated by bending.