KR20050052183A - Tft and flat panel display therewith - Google Patents

Abstract

The present invention provides a thin film transistor capable of reducing contact resistance between a source / drain electrode and a semiconductor active layer, and a flat panel display device having the same, and is formed on a substrate, and includes a semiconductor active layer and a semiconductor active layer. A thin film transistor having a gate electrode formed in a region corresponding to a channel region, and a source and a drain electrode formed of a conductive material to be in contact with the source and drain regions of the semiconductor active layer, respectively, wherein the source and drain electrodes and the semiconductor active layer A thin film transistor having a non-conductive layer further comprising a non-conductive material, the thin film transistor having a property of reducing contact resistance between the source and drain electrodes and the semiconductor active layer between source and drain regions of To provide.

Description

Thin film transistor and flat panel display device having same {TFT and Flat panel display therewith}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin film transistor and a flat panel display device having the same, and more particularly, to a thin film transistor having a low contact resistance between a source and a drain electrode and a semiconductor active layer, thereby improving characteristics.

Thin film transistors used in flat panel displays such as liquid crystal display devices, organic electroluminescent display devices, or inorganic electroluminescent display devices (hereinafter referred to as TFTs) are used to drive the switching elements and the pixels that control the operation of each pixel. Used as a drive element.

The TFT has a semiconductor active layer having a source / drain region doped with a high concentration of impurities and a channel region formed between the source / drain regions, the semiconductor active layer being insulated from the semiconductor active layer and corresponding to the channel region. And a source electrode and a drain electrode in contact with the source / drain region, respectively.

However, the source / drain electrodes are usually made of a metal having a low work function so that the flow of charge is smoothly performed. Such a metal causes contact resistance when it comes into contact with the semiconductor active layer, thereby degrading the characteristics of the device. Causes an increase.

Various methods are used to lower the contact resistance between the metal and the semiconductor. When amorphous silicon is used as the semiconductor active layer, an n + silicon layer is provided between the amorphous silicon and the metal source / drain electrode to facilitate the movement of electrons or holes, and when polysilicon is used as the semiconductor active layer, the metal Doping is to improve contact resistance with.

However, the above method has to be used at a high temperature of 300 ° C. or higher, so if the substrate is a plastic substrate vulnerable to heat, there is a problem that cannot be used.

On the other hand, recent flat panel display devices are required to be thin and flexible.

In order to achieve such a flexible property, many attempts have been made to use a plastic substrate as a substrate of a display device unlike a conventional glass substrate. In the case of using the plastic substrate, as described above, the source / drain electrode and the semiconductor active layer There is a problem that can not use the conventional technology for improving the contact resistance.

Disclosure of Invention The present invention has been made to solve the above problems, and it is an object of the present invention to provide a thin film transistor and a flat panel display device having the same, which can reduce contact resistance between a source / drain electrode and a semiconductor active layer.

Another object of the present invention is to provide a thin film transistor which can be manufactured at a low temperature and a flat panel display having the same.

In order to achieve the above object, the present invention is formed on a substrate, the semiconductor active layer, the gate electrode formed in the region corresponding to the channel region of the semiconductor active layer, and the source and drain regions of the semiconductor active layer, respectively In the thin film transistor having a source and a drain electrode provided with a conductive material,

The source and drain electrodes have a characteristic of reducing contact resistance between the source and drain electrodes and the semiconductor active layer between the source and drain regions of the semiconductor active layer. Provides a thin film transistor.

According to another feature of the invention, the semiconductor active layer may be selected from an inorganic semiconductor or an organic semiconductor.

The inorganic semiconductor may include CdS, GaS, ZnS, CdSe, CaSe, ZnSe, CdTe, SiC, and Si.

The organic semiconductor may be provided with a semiconducting organic material having a band gap of 1 eV to 4 eV.

The semiconducting organic material is polythiophene and its derivatives, polyparaphenylenevinylene and its derivatives, polyparaphenylene and its derivatives, polyfluorene and its derivatives, polythiophenevinylene and its derivatives, polythiophene The group consisting of a heterocyclic aromatic copolymer and derivatives thereof, and oligoacenes of pentacene, tetracene, naphthalene and derivatives thereof, oligothiophenes of alpha-6-thiophene and alpha-5-thiophene and derivatives thereof Phthalocyanine and derivatives thereof, pyromellitic dianhydrides or pyromellitic diimides and derivatives thereof, perylenetetracarboxylic acid dianhydrides or perylenetetracarboxylic diimides It may be provided with at least one selected from the group consisting of derivatives thereof.

According to another feature of the invention, the non-conductive layer may be a compound containing an element selected from Group 6 or 7 and an element selected from Group 1 or Group 2.

The compound containing an element selected from Group 6 and an element selected from Group 1 is lithium oxide, sodium oxide, potassium oxide, rubidium oxide, or It may be to include cesium oxide (cesium oxide).

Compounds containing an element selected from Group 7 and an element selected from Group 1 are lithium fluoride, sodium fluoride, potassium fluoride, rubidium fluoride fluoride), or cesium fluoride.

Compounds containing an element selected from Group 6 and an element selected from Group 2 include magnesium oxide, calcium oxide, strontium oxide, or barium oxide. It may be to include.

Compounds containing an element selected from Group 7 and an element selected from Group 2 are magnesium fluoride, calcium fluoride, strontium fluoride, or barium fluoride. barium fluoride).

According to another feature of the invention, the thickness of the non-conductive layer may be 1 kPa to 50 kPa.

According to another feature of the invention, the thin film transistor may be provided on a plastic substrate.

The thin film transistor of the present invention can be applied to a flat panel display having a plurality of subpixels.

In this case, the thin film transistor may be provided on a plastic substrate.

Hereinafter, with reference to the accompanying drawings will be described in detail a preferred embodiment of the present invention.

1 is a cross-sectional view showing a TFT according to a preferred embodiment of the present invention.

Referring to FIG. 1, the TFT 10 is provided on the substrate 11. The substrate 11 may be a glass substrate or a plastic substrate. As described below, when the TFT of the present invention is used in a flexible flat panel display, it is preferable to use a plastic substrate.

The semiconductor active layer 12 is provided on the substrate 11, and the gate insulating layer 13 is formed to cover the semiconductor active layer 12. A gate electrode 14 is formed on the gate insulating film 13, an interlayer insulating film 15 is formed to cover the gate electrode 14, and a source / drain electrode 16 is formed on the interlayer insulating film 15. ) Is formed. The source / drain electrodes 16 are in contact with the semiconductor active layer 12 by contact holes formed in the gate insulating film 13 and the interlayer insulating film 15. The non-conductive layer 17 is further provided between the source / drain electrode 16 and the portion of the semiconductor active layer 12 in contact with each other.

First, the semiconductor active layer 12 provided on the substrate 11 may be selected from an inorganic semiconductor or an organic semiconductor, and n-type or p-type impurities are doped in a source / drain region, and the source / drain A channel region connecting the drain region is provided.

The inorganic semiconductor forming the semiconductor active layer 12 may include CdS, GaS, ZnS, CdSe, CaSe, ZnSe, CdTe, SiC, and Si.

In addition, the organic semiconductor may be provided with a semiconducting organic material having a band gap of 1 eV to 4 eV. As a polymer, polythiophene and its derivatives, polyparaphenylenevinylene and its derivatives, polyparaphenylene and its Derivatives, polyfluorene and derivatives thereof, polythiophenevinylene and derivatives thereof, polythiophene-heterocyclic aromatic copolymers and derivatives thereof, and as small molecules, oligoacenes of pentacene, tetracene, naphthalene and Derivatives thereof, alpha-6-thiophene, oligothiophenes of alpha-5-thiophene and derivatives thereof, phthalocyanine with and without metals and derivatives thereof, pyromellitic dianhydrides or pyromelli Tic diimides and derivatives thereof, perylenetetracarboxylic acid dianhydride or perylenetetracarboxylic diimides and derivatives thereof.

The gate insulating film 13 is made of SiO 2 or the like, and the gate electrode 14 is formed of a conductive metal film of MoW, Al, Cr, Al / Cu, or the like in a predetermined region above the gate insulating film 13. The material forming the gate electrode 14 is not limited thereto, and various conductive materials such as a conductive polymer may be used as the gate electrode 14.

An interlayer insulating layer 15 is provided on the gate electrode 14, and the source / drain electrode 16 is formed in a state where the contact hole 16a is drilled in the interlayer insulating layer 15 and the gate insulating layer 13. It is formed on the interlayer insulating film 15. As the source / drain electrode 16, a conductive metal film such as MoW, Al, Cr, Al / Cu, a conductive polymer, or the like may be used.

Meanwhile, a non-conducting layer 17 may be provided between the source / drain electrode 16 and the interlayer insulating layer 15, and the nonconductive layer 17 may include the source / drain 17. The electrode 16 may be provided between the source / drain electrode 16 and the semiconductor active layer 12 in an area in contact with the semiconductor active layer 12, that is, in a source / drain area of the semiconductor active layer 12. .

The non-conductive layer 17 may be formed after the interlayer insulating layer 15 is formed and the contact hole 16a is drilled. The non-conductive layer 17 is in contact with the semiconductor active layer 12 and the source / drain electrode 16. It is used to improve the resistance.

When the metal and the semiconductor are connected, there is a potential barrier resulting from the difference between the metal and the semiconductor, that is, the difference between the work function of the metal and the electron affinity of the semiconductor. As the potential barrier increases, the flow of electrons can be disturbed and the current flow becomes undesired.

In the present invention, in order to reduce the potential barrier, a nonconductive layer 17 is formed between the semiconductor active layer 12 and the source / drain electrode 16. The nonconductive layer 17 is a source / drain electrode 16 ) And the semiconductor active layer 12 are brought into contact with a small potential barrier. The nonconductive layer 17 has a strong dipole property, and forms a space charge near the contact surface of the source / drain electrode 16 and the semiconductor active layer 12 to lower the potential barrier. Therefore, electrons or holes flow well between the semiconductor active layer 12 and the source / drain electrodes 16.

It is preferable to use a material having a small work function as the material of the nonconductive layer for contact with the semiconductor active layer 12. To this end, the nonconductive layer 17 may be a compound including an element selected from Group 6 or 7 and an element selected from Group 1 or Group 2.

The compound containing an element selected from Group 6 and an element selected from Group 1 is lithium oxide, sodium oxide, potassium oxide, rubidium oxide, or Compounds containing cesium oxide and containing an element selected from Group 7 and an element selected from Group 1 are lithium fluoride, sodium fluoride, and potassium fluoride. (potassium fluoride), rubidium fluoride, or cesium fluoride (cesium fluoride), the compound containing an element selected from Group 6 and an element selected from Group 2 is magnesium oxide (magnesium oxide, calcium oxide, strontium oxide, or barium oxide, and selected from the group 7 above. Compounds containing a losing element and an element selected from Group 2 include magnesium fluoride, calcium fluoride, strontium fluoride, or barium fluoride. .

In addition, the non-conductive layer 17 may be formed to a thickness of 1 Å to 50 Å. If the thickness of the non-conductive layer 17 is less than 1 kV, it is difficult to obtain the effect of lowering the potential barrier. If the thickness of the non-conductive layer 17 is greater than 50 kW, the effect of lowering the potential barrier is reduced and the insulating property is enhanced. The contact resistance between the semiconductor active layers 12 can be increased.

FIG. 2 shows a case in which about 10 microseconds of LiF is formed as the nonconductive layer 17 between the source / drain electrode 16 and the semiconductor active layer 12 (I), and when the nonconductive layer 17 is not used. (II) shows the change of the current density with respect to the operating voltage. As in the present invention, a current of about five times as compared with the case of using the nonconductive layer (I) without using the nonconductive layer (II) Density improvement results can be obtained. This indicates that the contact resistance between the semiconductor active layer 12 and the source / drain electrodes 16 is reduced to improve the flow of current.

The non-conductive layer as described above may not be employed only in the TFT as shown in FIG. 1, but may be employed in all TFTs of various structures.

3 shows a TFT 20 according to another embodiment of the present invention, in which a gate electrode 24 is formed on a substrate 21, and the gate insulating film 23 covers the gate electrode 24. Is formed. The semiconductor active layer 22 is formed on the gate insulating film 23, and the nonconductive layer 27 and the source / drain electrodes 26 are sequentially formed on the gate insulating film 23. In this case, the source / drain electrode 26 is formed to contact a region corresponding to the source / drain region of the semiconductor active layer 22.

As shown in FIG. 3, the nonconductive layer 27 may be formed in a pattern corresponding to the source / drain electrode 26, and although not illustrated in the drawing, to cover the entire semiconductor active layer 22. Of course, it may be formed.

4 illustrates a TFT 30 according to another exemplary embodiment of the present invention, in which a gate electrode 34 is formed on a substrate 31, and the gate insulating layer 34 covers the gate electrode 34. 33) is formed. A source / drain electrode 36 is formed on the gate insulating film 33, and a nonconductive layer 37 and a semiconductor active layer 32 are sequentially formed thereon. At this time, the source / drain electrodes 36 and the source / drain regions of the semiconductor active layer 32 are in contact with each other.

As shown in FIG. 4, the nonconductive layer 37 may be formed on the upper surface of the source / drain electrode 36 and the upper portion of the gate insulating layer 33. Although not illustrated, the semiconductor active layer 32 may be formed. ) And the source / drain electrode 36 may be formed only in the contact area with each other.

The TFT having the above structure may be provided in a subpixel of a flat panel display such as an LCD or an organic electroluminescent display.

5 illustrates that the TFT is applied to an organic light emitting display device, which is one example.

FIG. 5 shows one subpixel of an organic electroluminescent display, each subpixel having an organic electroluminescent element (hereinafter referred to as an "EL element") as a self-luminous element, and having at least one TFT. It is provided above. Although not shown in the drawings, a separate capacitor is further provided.

Such an organic light emitting display device has various pixel patterns according to the color of light emitted by the EL element OLED, and preferably includes red, green, and blue pixels.

Each of the sub-pixels of red (R), green (G), and blue (B) colors has a TFT structure as shown in FIG. 5 and an EL element (OLED) which is a self-luminous element. And, a TFT is provided, which has a TFT having the same structure as that of FIG. However, the present invention is not necessarily limited thereto, and may be viewed in FIGS. 3 and 4, or other TFTs having various structures.

As can be seen in FIG. 5, a buffer layer 41a is formed on the insulating substrate 41 by SiO2 or the like, and the above-described TFT is provided on the buffer layer 41a.

As shown in FIG. 5, the TFT includes a semiconductor active layer 42 formed on the buffer layer 41a, a gate insulating film 43 formed on the semiconductor active layer 42, and a gate electrode on the gate insulating film 43. Has 44.

As described above, the semiconductor active layer 42 may be formed of an organic semiconductor or an inorganic semiconductor. This semiconductor active layer 42 has a source and a drain region doped with N-type or P-type impurities at a high concentration.

A gate insulating film 43 is provided on the semiconductor active layer 42 by SiO 2 or the like, and a gate electrode 44 is formed of a conductive material on a predetermined region of the gate insulating film 43. The gate electrode 44 is connected to a gate line for applying a TFT on / off signal. The region where the gate electrode 44 is formed corresponds to the channel region of the semiconductor active layer 42.

An inter-insulator 45 is formed on the gate electrode 44, and the source / drain electrodes 46 contact the source / drain regions of the semiconductor active layer 44 through contact holes. do.

At this time, a non-conductive layer 47 as described above is disposed between the source / drain electrode 46 and the semiconductor active layer 44. The non-conductive layer 47 is formed as shown in FIG. It may be formed over the entirety of the upper portion of 45, and may be formed only on the lower surface of the source / drain electrode 46, although not shown in the drawings.

A passivation film 48 made of SiO 2 or the like is formed on the source / drain electrode 46, and a pixel definition film 49 made of acryl, polyimide, or the like is formed on the passivation film 48.

An EL element OLED is connected to the drain electrode 46 of the TFT, and is connected to an anode electrode 50 which becomes one of the EL elements OLED. The anode electrode 50 is formed on the passivation film 48, and a pixel definition film 49 is formed thereon, and a predetermined opening 53 is formed in the pixel definition film 49. After formation, an EL element OLED is formed.

The EL element OLED emits red, green, and blue light according to the flow of current to display predetermined image information. The EL element OLED is connected to the drain electrode of the TFT and receives positive power therefrom. ) And a cathode electrode 52 provided to cover all the pixels and supplying negative power, and an organic light emitting film 51 disposed between the anode electrode 50 and the cathode electrode 52 to emit light. It consists of.

The anode electrode 50 may be formed of a transparent electrode such as ITO, and the cathode electrode 52 is formed by depositing the entire surface with Al / Ca or the like in the case of the bottom emission type emitting light toward the substrate 41, and sealing glass In the case of a top emission type emitting light toward the substrate, a thin semi-permeable thin film may be formed of a metal such as Mg-Ag, and then transparent ITO may be formed thereon. The cathode electrode 52 does not necessarily have to be entirely deposited, and of course, may be formed in various patterns. Of course, the anode electrode 50 and the cathode electrode 52 may be stacked opposite to each other.

The organic film 51 may be a low molecular or polymer organic film. When the low molecular organic film is used, a hole injection layer (HIL), a hole transport layer (HTL), and an organic emission layer (EML) may be used. , Electron Transport Layer (ETL), Electron Injection Layer (EIL), etc. may be formed by stacking in a single or complex structure, and the usable organic materials may be copper phthalocyanine (CuPc), N, N-di (naphthalen-1-yl) -N, N'-diphenyl-benzidine (N, N'-Di (naphthalene-1-yl) -N, N'-diphenyl-benzidine: NPB), Tris Various applications include, for example, tris-8-hydroxyquinoline aluminum (Alq3). These low molecular weight organic films are formed by the vacuum deposition method.

In the case of the polymer organic film, the structure may include a hole transporting layer (HTL) and a light emitting layer (EML). In this case, PEDOT is used as the hole transporting layer, and polyvinylvinylene (PPV) and polyfluorene are used as the light emitting layer. Polymer organic materials such as (Polyfluorene) are used and can be formed by screen printing or inkjet printing.

The structure of the organic electroluminescent device according to the preferred embodiment of the present invention as described above is not necessarily limited to the above-described, it is a matter of course that the present invention can be applied to any other structure.

Thus, the organic light emitting display device employing the TFT according to the present invention is suitable for using a flexible plastic substrate as the substrate 41.

According to the present invention as described above, the following effects can be obtained.

First, the TFT resistance can be improved by reducing the contact resistance between the semiconductor active layer of the TFT and the source / drain electrodes.

Second, the low contact resistance between the semiconductor active layer of the TFT and the source / drain electrodes can reduce power consumption when applied to a flat panel display.

Third, since a plastic substrate can be used, it can be applied to a flexible flat panel display.

Although described above with reference to a preferred embodiment of the present invention, those skilled in the art will be variously modified and changed within the scope of the invention without departing from the spirit and scope of the invention described in the claims below I can understand that you can.

1 is a cross-sectional view showing the structure of a thin film transistor according to an embodiment of the present invention;

Graph comparing the current density with respect to the operating voltage of the embodiment and the comparative example according to Figure 2,

3 is a cross-sectional view illustrating a structure of a thin film transistor according to another exemplary embodiment of the present invention;

4 is a cross-sectional view showing the structure of a thin film transistor according to another preferred embodiment of the present invention;

5 is a cross-sectional view when the thin film transistor of FIG. 1 is applied to an organic light emitting display device.

Claims (14)

A semiconductor active layer, a gate electrode formed in a region corresponding to a channel region of the semiconductor active layer, and a source and drain electrode formed of a conductive material to be in contact with the source and drain regions of the semiconductor active layer, respectively. In a thin film transistor, The source and drain electrodes have a characteristic of reducing contact resistance between the source and drain electrodes and the semiconductor active layer between the source and drain regions of the semiconductor active layer. A thin film transistor, characterized in that. The method of claim 1, The semiconductor active layer is a thin film transistor, characterized in that selected from an inorganic semiconductor or an organic semiconductor. The method of claim 2, The inorganic semiconductor thin film transistor comprising CdS, GaS, ZnS, CdSe, CaSe, ZnSe, CdTe, SiC, and Si. The method of claim 2, The organic semiconductor is a thin film transistor, characterized in that provided with a semiconducting organic material having a band gap of 1eV to 4eV. The method of claim 4, wherein The semiconducting organic material is polythiophene and its derivatives, polyparaphenylenevinylene and its derivatives, polyparaphenylene and its derivatives, polyfluorene and its derivatives, polythiophenevinylene and its derivatives, polythiophene The group consisting of a heterocyclic aromatic copolymer and derivatives thereof, and oligoacenes of pentacene, tetracene, naphthalene and derivatives thereof, oligothiophenes of alpha-6-thiophene and alpha-5-thiophene and derivatives thereof Phthalocyanine and derivatives thereof, pyromellitic dianhydrides or pyromellitic diimides and derivatives thereof, perylenetetracarboxylic acid dianhydrides or perylenetetracarboxylic diimides A thin film transistor comprising at least one selected from the group consisting of derivatives thereof. The method of claim 1, The nonconductive layer is a thin film transistor comprising an element selected from Group 6 or 7 and an element selected from Group 1 or Group 2. The method of claim 6, The compound containing an element selected from Group 6 and an element selected from Group 1 is lithium oxide, sodium oxide, potassium oxide, rubidium oxide, or A thin film transistor comprising cesium oxide. The method of claim 6, Compounds containing an element selected from Group 7 and an element selected from Group 1 are lithium fluoride, sodium fluoride, potassium fluoride, rubidium fluoride A thin film transistor comprising fluoride) or cesium fluoride. The method of claim 6, Compounds containing an element selected from Group 6 and an element selected from Group 2 include magnesium oxide, calcium oxide, strontium oxide, or barium oxide. Thin film transistor comprising a. The method of claim 6, Compounds containing an element selected from Group 7 and an element selected from Group 2 are magnesium fluoride, calcium fluoride, strontium fluoride, or barium fluoride. a thin film transistor comprising barium fluoride). The method according to any one of claims 1 to 10, The thickness of the non-conductive layer is a thin film transistor, characterized in that 1 to 50 kHz. The method according to any one of claims 1 to 10, The thin film transistor is provided on a plastic substrate. A plurality of subpixels, each subpixel having at least one thin film transistor, wherein at least one of the thin film transistors is the thin film transistor according to any one of claims 1 to 10. . The method of claim 13, And the subpixel is provided on a plastic substrate.