KR100563060B1 - Flat panel display with TFT - Google Patents

Abstract

The present invention is to prevent the leakage current increase due to sunlight and to facilitate the implementation of gradation, a substrate, an active layer provided on the substrate to implement a predetermined image, at least a channel region, a gate electrode and And a pixel region having at least one pixel portion thin film transistor having a source / drain electrode, and a shielding member provided to be insulated from the active layer of the pixel portion thin film transistor, and shielding at least a channel region of the active layer. A flat panel display device is provided.

Description

Flat panel display with TFT

1 is a plan view of an active matrix organic electroluminescent display device according to an exemplary embodiment of the present invention;

2 is a cross-sectional view showing an example of a circuit part thin film transistor;

3 is a cross-sectional view illustrating an example of a pixel portion thin film transistor;

4 is a partial plan view for showing the area of the shielding member;

5 is a graph showing the relationship between energy density and grain size in the ELA crystallization method;

6 is a graph showing the relationship between grain size and current mobility;

7 and 8 are graphs showing output characteristics of a pixel region and a circuit region, respectively.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flat panel display, and more particularly, to an active matrix flat panel display having a thin film transistor.

Thin Film Transistors (TFTs) used in flat panel displays, such as liquid crystal display devices, organic electroluminescent display devices, or inorganic electroluminescent display devices, are used as driving devices for driving pixels and switching devices for controlling the operation of each pixel. do.

The thin film transistor has an active layer having a drain region and a source region doped with a high concentration of impurities on a substrate, and a channel region formed between the drain region and the source region, and a gate insulating layer and a channel region of the active layer formed on the active layer. The active layer is divided into amorphous silicon and polycrystalline silicon according to a crystal state of silicon.

Thin film transistors using amorphous silicon have the advantage of being capable of low temperature deposition. However, recently, polycrystalline silicon has been used a lot since electrical properties and reliability are deteriorated, and the large area of the display device is difficult. Polycrystalline silicon has high mobility of tens to hundreds of cm 2 /V.s, and has high frequency operation characteristics and low leakage current value, which is very suitable for use in high-definition and large-area flat panel display devices.

Meanwhile, as described above, the thin film transistor is used as a thin film transistor of a pixel portion such as a switching element or a driving element of a pixel and a circuit portion thin film transistor of a circuit region for driving the same in a flat panel display device.

On the other hand, the organic EL device of the organic EL device using an organic EL device (hereinafter referred to as an "organic EL device") as a light emitting device of the flat panel display is made of an organic material between the anode electrode and the cathode electrode. It has a light emitting layer. In this organic EL device, as the anode and cathode voltages are applied to these electrodes, holes injected from the anode electrode are moved to the light emitting layer via the hole transport layer, and electrons are transferred from the cathode electrode through the electron transport layer. Is injected into the light emitting layer, and electrons and holes recombine in the light emitting layer to generate excitons, and as the excitons change from the excited state to the ground state, the fluorescent molecules in the light emitting layer emit light to form an image. In the case of a full color organic light emitting display device, full color is realized by including pixels emitting three colors of red (R), green (G), and blue (B) as the organic EL element.

In such an active matrix type organic light emitting display (AMOLED), a high resolution panel is increasingly required. In this case, a thin film transistor formed of high-performance polycrystalline silicon as described above causes problems.

That is, in a conventional active matrix flat panel display device such as an active matrix type organic light emitting display device, a circuit part thin film transistor and a pixel part thin film transistor, in particular, a driving thin film transistor are manufactured of the same polycrystalline silicon, Since the circuit thin film transistors have the same current mobility, the switching characteristics of the circuit thin film transistors and the low current driving characteristics of the driving thin film transistors cannot be satisfied at the same time. That is, when the driving thin film transistor and the circuit thin film transistor of the high resolution display device are manufactured using a polycrystalline silicon film having a large current mobility, the high switching characteristics of the circuit thin film transistor can be obtained, but the driving thin film transistor is used as an EL element through the driving thin film transistor. As the amount of current flowing increases, the luminance becomes excessively high, and as a result, the current density per unit area becomes high, thereby reducing the lifetime of the EL element.

On the other hand, when the driving thin film transistor and the circuit thin film transistor of the display device are manufactured using an amorphous silicon film having a low current mobility, the driving thin film transistor is in the direction of decreasing current, and the circuit thin film transistor is in the direction of increasing current. The thin film transistor should be manufactured.

In order to solve this problem, a method of limiting the amount of current flowing through the driving transistor has been proposed. As a method, the resistance of the channel region is increased by reducing the ratio of the width to the width of the driving transistor (W / L), or the resistance is increased by forming a low-doped region in the source / drain region of the driving transistor. There was a back.

However, the method of increasing the length to reduce the W / L has a length of the channel region, and when the crystallization is performed using the Excimer Laser Annealing (ELA) method, streaks are formed in the channel region, and the opening area is reduced. There was a declining issue. The method of reducing the width by reducing the width is limited by the design rules of the photolithography process, and it is difficult to secure the reliability of the transistor.

In addition, the method of increasing the resistance by forming a low doping region has a problem that an additional doping process should be performed.

On the other hand, in the case of an active matrix flat panel display device, an active layer of the thin film transistor is provided on the upper surface of the substrate. In the case of a bottom emission type organic light emitting display device in which an image is realized in the direction of the substrate, the active layer of the driving thin film transistor is There is a problem that leakage current is generated by exposure to sunlight. In particular, this leakage current is greatest at the boundary between the channel region and the source / drain region of the active layer. The leakage current in the driving thin film transistor causes poor image quality.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a flat panel display device which prevents an increase in leakage current due to sunlight and easily implements gradation.

In order to achieve the object as described above, the present invention,

Board;

A pixel region provided on the substrate, the pixel region including at least one pixel portion thin film transistor having an active layer including at least a channel region, a gate electrode, and a source / drain electrode; And

And a shielding member provided to be insulated from the active layer of the pixel portion thin film transistor and shielding at least a channel region of the active layer.

According to another feature of the invention, the shielding member may be provided with a thermally conductive material.

According to another feature of the invention, the shielding member may be provided with a material that reflects sunlight.

According to another feature of the invention, the shielding member may be provided with a material having an energy band gap of less than 1 eV with sunlight.

According to another feature of the invention, the shielding member may be provided with a metal material.

According to another feature of the invention, the upper surface of the substrate is further provided with a buffer layer, the shielding member may be interposed between the substrate and the buffer layer. In this case, the gate electrode and the shielding member of the pixel portion thin film transistor may be positioned in opposite directions with respect to the active layer.

According to another feature of the invention, the pixel region has a plurality of sub-pixels for implementing a predetermined image, the pixel portion thin film transistor is provided at least one in each sub-pixel, the shielding member is each sub-pixel It may be divided into each.

According to another feature of the invention, the pixel region has a plurality of sub-pixels for implementing a predetermined image, each sub-pixel is provided with an organic electroluminescent element, the pixel portion thin film transistor of each of the sub-pixel And a driving thin film transistor connected to the organic electroluminescent element, and the shielding member may be insulated from the active layer of each of the driving thin film transistors to shield at least a channel region of the active layer.

According to still another aspect of the present invention, a signal region applied to the pixel region is controlled. The circuit region includes at least one circuit portion thin film transistor having at least an active layer including a channel region, a gate electrode, and a source / drain electrode. Further, wherein the size of the crystal grains of at least the channel region of the active layer of the pixel portion thin film transistor may be smaller than the size of the crystal grains of the at least channel region of the active layer of the circuit portion thin film transistor.

In the present invention, the active layer is provided with polycrystalline silicon, the polycrystalline silicon may be formed by a crystallization method by a laser.

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

1 is a plan view illustrating an active matrix organic light emitting display device according to a preferred embodiment of the flat panel display device according to the present invention. Referring to FIG. 1, the organic light emitting display device includes a pixel region 20 and a circuit region 10 at an edge of the pixel region 20.

The pixel area 20 includes a plurality of pixels, and each pixel includes a plurality of sub-pixels each having an organic EL device. In the case of a full color organic light emitting display, subpixels of red (R), green (G), and blue (B) are arranged in various patterns such as lines, mosaics, and lattices to form pixels. It may be a mono color flat panel display instead of a display.

The circuit region 10 controls an image signal and the like input to the pixel region 20.

In the organic light emitting display device, at least one thin film transistor may be provided in the pixel region 20 and the circuit region 10, respectively.

The thin film transistor provided in the pixel region 20 includes a switching thin film transistor which transmits a data signal to a light emitting element according to a signal of a gate line and controls its operation; There is a pixel portion thin film transistor such as a driving thin film transistor for driving a current to flow. In addition, the thin film transistor provided in the circuit region 10 includes a circuit part thin film transistor provided to implement a predetermined circuit.

Of course, the number and arrangement of the thin film transistors may vary depending on the characteristics of the display, the driving method, and the like, and the arrangement may also exist in various ways.

These thin film transistors each have an active layer made of amorphous or polycrystalline silicon, which has a predetermined channel region. The channel region is located at the center of the source region and the drain region.

Reference numeral 40 denotes a shielding member provided in each subpixel, and a detailed description thereof will be described later.

2 and 3 show the circuit part thin film transistor 11 and the pixel part thin film transistor 21, respectively.

First, as shown in FIGS. 2 and 3, a buffer layer 2 is formed on an insulating substrate 1, and a circuit portion thin film transistor 11 and a pixel portion thin film transistor ( 21) is formed. The substrate 1 may be formed of a transparent glass material or a plastic material. In addition, the buffer layer 2 may be formed of SiO ₂ , and may be deposited by PECVD, APCVD, LPCVD, ECR, or the like. The buffer layer 2 can be deposited to about 3000 mW.

As shown in FIG. 2, the circuit part thin film transistor 11 includes a semiconductor active layer 12 formed on the buffer layer 2, a gate insulating film 3 formed on the active layer 12, and a gate insulating film ( 3) has an upper gate electrode 13. And a source electrode 14 and a drain electrode 15 in contact with the active layer 12.

The active layer 12 may be formed of an inorganic semiconductor or an organic semiconductor, and may be formed to about 500 GPa. When the active layer 12 is formed of polysilicon in the inorganic semiconductor, after the amorphous silicon is formed, it can be polycrystalline by various crystallization methods. This active layer has a source region S1 and a drain region D1 doped with N-type or P-type impurities at a high concentration, and has a channel region C1 therebetween.

The inorganic semiconductor may include CdS, GaS, ZnS, CdSe, CaSe, ZnSe, CdTe, SiC, and silicon materials such as a-Si (amorphous silicon) or poly-Si (poly silicon).

The organic semiconductor may be provided with a semiconducting organic material having an energy band gap of 1 eV to 4 eV. As a polymer, polythiophene and its derivatives, polyparaphenylenevinylene and its derivatives, polyparaphenylene and And derivatives thereof, 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, oligothiophene of alpha-5-thiophene and derivatives thereof, phthalocyanine and derivatives thereof with or without metal, pyromellitic dianhydride or pyro Melittic diimides and derivatives thereof, perylenetetracarboxylic acid dianhydride or perylenetetracarboxylic diimides and derivatives thereof.

A gate insulating film 3 is provided on the active layer 12 by SiO _{2 or the} like, and a predetermined region on the gate insulating film 3 is formed by a conductive metal film such as MoW, Al, Cr, Al / Cu, or the like. ) Is formed. The material forming the gate electrode 13 is not limited thereto, and various conductive materials such as a conductive polymer may be used. The region where the gate electrode 13 is formed corresponds to the channel region C1 of the active layer 12.

An inter-insulator 4 is formed on the gate electrode 13 by SiO ₂ and / or SiN _x , and contact holes are formed in the inter-layer insulating film 4 and the gate insulating film 3. In the state, the source electrode 14 and the drain electrode 15 are formed on the interlayer insulating film 5. As the source / drain electrodes 14 and 15, a conductive metal film such as MoW, Al, Cr, Al / Cu, or a conductive polymer may be used.

The structure of the thin film transistor as described above is not necessarily limited thereto, and all of the structures of the conventional general thin film transistor may be used as it is.

The pixel portion thin film transistor 21 may be provided as a driving thin film transistor and a switching thin film transistor, and FIG. 3 illustrates the driving thin film transistor.

As shown in FIG. 3, the pixel portion thin film transistor 21, particularly the driving thin film transistor, as described above, has an active layer 22 formed on the buffer layer 2, and a gate insulating film formed on the active layer 22. 3), the gate electrode 23 is formed.

An interlayer insulating film 4 is formed on the gate electrode 23, and a source electrode 24 and a drain electrode 25 are formed thereon.

The passivation film 5 is formed on the source / drain electrodes 24 and 25, and the via hole 5a is drilled through the passivation film 5.

The first electrode layer 31 of the organic EL device 30 is connected to the drain electrode 25 through the via hole 5a on the passivation film 5. The pixel defining layer 6 is formed on the first electrode layer 31 by organic materials such as acrylic, BCB, and polyimide, and a predetermined opening 6a is formed in the pixel defining layer 6. After the formation, the organic light emitting layer 32 and the second electrode layer 33 of the organic electroluminescent element 30 are formed. Before the pixel definition layer 6 is formed, a planarization layer may be further formed between the first electrode layer 31 and the passivation layer 5.

The organic electroluminescent element 30 emits red, green, and blue light according to the flow of current to display predetermined image information. The organic electroluminescent element 30 is connected to the drain electrode 25 of the TFT and receives positive power therefrom. The first electrode layer 31 and the second electrode layer 33 provided to cover all the pixels to supply negative power, and the organic light emitting diodes disposed between the first electrode layer 31 and the second electrode layer 33 to emit light. It consists of a light emitting layer 32.

The first electrode layer 31 and the second electrode layer 33 are insulated from each other by the organic light emitting layer 32, and light is emitted from the organic light emitting layer 32 by applying voltages having different polarities to the organic light emitting layer 32. To do that.

The organic light emitting layer 32 may be a low molecular or polymer organic layer. When the low molecular organic layer is used, a hole injection layer (HIL), a hole transport layer (HTL), and an 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 layers are formed by the vacuum deposition method.

In the case of the polymer organic layer, 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 organic light emitting layer as described above is not necessarily limited thereto, and various embodiments may be applied.

The first electrode layer 31 functions as an anode electrode, and the second electrode layer 33 functions as a cathode electrode. Of course, the first electrode layer 31 and the second electrode layer 33 The polarity may be reversed. Hereinafter, an embodiment in which the first electrode layer 31 is an anode electrode will be described.

The first electrode layer 31 may be provided as a transparent electrode or a reflective electrode. When used as a transparent electrode, the first electrode layer 31 may be provided as ITO, IZO, ZnO, or In ₂ O ₃ . , Mg, Al, Pt, Pd, Au, Ni, Nd, Ir, Cr, and a reflective film may be formed, and then ITO, IZO, ZnO, or In ₂ O ₃ may be formed thereon.

Meanwhile, the second electrode layer 33 may also be provided as a transparent electrode or a reflective electrode. When the second electrode layer 33 is used as a transparent electrode, since the second electrode layer 33 is used as a cathode, a metal having a small work function, namely, Li, Ca, LiF / Ca, LiF / Al, Al, Ag, Mg, and compounds thereof are deposited to face the organic layer 62, and thereafter, ITO, IZO, ZnO, or In ₂ O ₃ or the like. The auxiliary electrode layer and the bus electrode line can be formed of the transparent electrode forming material. When used as a reflective electrode, Li, Ca, LiF / Ca, LiF / Al, Al, Ag, Mg, and compounds thereof are formed by depositing the entire surface.

In the present invention, in the pixel portion thin film transistor 21, the shielding member 40 that shields at least the channel region C2 of the active layer 22 is further formed to be insulated from the active layer 22, thereby forming the pixel portion thin film. In the transistor 21, generation of leakage current due to sunlight in the active layer 22 is prevented.

In the case of the preferred embodiment of the present invention according to FIG. 3, an embodiment in which an image is implemented in the direction of the substrate 1 is illustrated. Accordingly, sunlight is incident from the direction of the substrate 1.

Therefore, the shielding member 40 is interposed between the buffer layer 2 and the substrate 1 to protect the channel region C2 of the active layer 22 from sunlight.

The shielding member 40 is thus used to protect at least the channel region C2 of the active layer 22 from sunlight. As shown in FIG. 4, the area of the shielding member 40 is the channel region C2 of the active layer 22. It is preferable to form larger than). Accordingly, it is preferable that the shield member 40 can cover the boundary between the channel region C2 and the source / drain regions S2 and D2.

In addition, since the shielding member 40 may be formed in the pixel portion thin film transistors of all subpixels, as shown in FIG. 1, the shielding member 40 may be patterned to correspond to each subpixel and formed in an island type.

The shield member 40 is preferably formed of a material capable of reflecting sunlight, it may be formed of a metal material. In addition, any material can be applied as long as the energy band gap with sunlight is smaller than 1 eV. In this case, the energy of solar light is not transferred to the active layer, but is absorbed by itself to protect the channel region C2 of the active layer 22.

On the other hand, the shielding member 40 as described above is formed of a material having excellent thermal conductivity, so that the grain size of the active layer in the case of the circuit portion thin film transistor 11 and the pixel portion thin film transistor 21 at the time of crystallization of the active layer. Can be adjusted.

That is, in the case of the circuit part thin film transistor 11, as shown in FIG. 2, the active layer 12 is formed on the buffer layer 2 without the shielding member, and in the case of the pixel part thin film transistor 21, as shown in FIG. 3. When the shielding member 40 is formed on the substrate 1, the buffer layer 2 is formed thereon, and the active layer 22 is formed thereon, the active layers 12 and 22 are crystallized by a laser. In the pixel portion thin film transistor 21, heat loss is generated by the shielding member 40. This heat loss affects the grain size of the polycrystalline silicon, as can be seen in FIG.

5 shows the size of crystal grains according to the energy density of a laser when amorphous silicon is formed into polycrystalline silicon by a crystallization method by a laser. As can be seen in FIG. 5, when the heat loss is caused by the shielding member 40 in the pixel portion thin film transistor 21, the grain size is smaller than that of the circuit portion thin film transistor 11 without the shielding member 40. You lose. However, as can be seen in FIG. 5, when the amorphous silicon thin film receives a laser of too high energy density, the amorphous silicon thin film may be completely melted, and the grain size thereof may be rather reduced. Therefore, it is preferable to irradiate a laser at an energy density such that large crystal grains are formed in the active layer 12 of the circuit part thin film transistor which requires larger crystal grains.

If the grain size is changed in this way, the current mobility is also changed, as shown in FIG. In other words, the larger the grain size, the higher the current mobility, and accordingly, better TFT characteristics can be obtained. Therefore, the active layer of the circuit portion thin film transistor, which usually requires a higher current mobility value, is formed larger than the active layer size of the pixel portion thin film transistor, as described above, so as to have excellent TFT characteristics, and the active layer of the pixel portion thin film transistor Due to the shielding member, the S-factor is increased, and the surface roughness is improved, thereby increasing the dielectric breakdown voltage characteristic.

7 and 8 show the output characteristics of the pixel region and the circuit region, respectively, where I is Vgs, i.e., when the voltage difference between the gate and source is 3V, II is Vgs is 4V, and III is Vgs. 5V is shown.

As can be seen in FIGS. 7 and 8, it can be seen that the pixel region is smoother than the circuit region in which the drain current increases with the increase in Vgs. This means that the S-factor is increased in the pixel area, thereby facilitating gray scale implementation.

As described above, the case where the image is implemented in the direction of the substrate 1 is taken as an example, but the present invention is not necessarily limited thereto, and the same may also be applied when the image is implemented in the direction of the second electrode layer 33. Can be. However, at this time, in order to shield the sunlight, the position of the shielding member 40 should be disposed above the active layer 22. However, in this case, in order to adjust only the size of the crystal grains of the active layer, it may be arranged as it is.

On the other hand, when the image is implemented in the direction of the second electrode layer 33, in order to adjust the grain size of the active layer, as shown in FIG. 1, it may be formed over the entire pixel region without employing a patterned structure. have.

The present invention has shown a driving thin film transistor and a circuit thin film transistor of the pixel thin film transistor, which is not necessarily limited thereto, and may be applied to the switching thin film transistor of the pixel thin film transistor instead of the circuit thin film transistor. .

In addition, the above description is to be made when the present invention is applied to an organic light emitting display device, but the present invention is not limited thereto, and the present invention can be applied to any structure that can use a TFT such as a liquid crystal display device or an inorganic electroluminescent display device. Of course.

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

First, when emitting light in the direction of the substrate, it is possible to control the leakage current due to sunlight, it is possible to prevent poor image quality.

Second, it is possible to have a TFT characteristic that can satisfy both the pixel element and the circuit element.

Third, an active layer having a smaller grain size and improved surface roughness can be provided in the pixel thin film transistor.

Fourth, the S-factor of the pixel thin-film transistor increases, so that the amount of current change due to the increase in Vgs decreases, thereby facilitating gray scale implementation.

Although the above has been described with reference to the preferred embodiment of the present invention, those skilled in the art will be variously modified and modified within the scope of the present invention without departing from the spirit and scope of the present invention described in the claims below. It will be appreciated that it can be changed.

Claims (11)

Board; A pixel region provided on the substrate, the pixel region including a pixel portion thin film transistor having an active layer including at least a channel region, a gate electrode, and a source / drain electrode; And And a shielding member provided to be insulated from the active layer of the pixel portion thin film transistor, and shielding a channel region of the active layer. Controlling a signal applied to the pixel region, the circuit region further comprising a circuit region including at least one active layer including a channel region, a gate electrode, and a circuit part thin film transistor having a source / drain electrode, The size of the crystal grains of the channel region of the active layer of the pixel portion thin film transistor is smaller than the size of the crystal grains of the channel region of the active layer of the circuit portion thin film transistor. The method of claim 1, And the shielding member is formed of a thermally conductive material. The method of claim 1, And the shielding member is formed of a material that reflects sunlight. The method of claim 1, The shielding member is a flat panel display, characterized in that the energy bandgap with sunlight is less than 1eV material. The method of claim 1, And the shielding member is formed of a metal material. The method of claim 1, A buffer layer is further provided on an upper surface of the substrate, and the shielding member is interposed between the substrate and the buffer layer. The method of claim 6, And a gate electrode and the shielding member of the pixel portion thin film transistor are located in opposite directions with respect to the active layer. The method according to any one of claims 1 to 7, The pixel area may include a plurality of subpixels for implementing a predetermined image, the pixel portion thin film transistors are provided in each of the subpixels, and the shielding member is divided into the subpixels. Display. The method according to any one of claims 1 to 7, The pixel region includes a plurality of subpixels for implementing a predetermined image, each subpixel includes an organic electroluminescent element, and the pixel portion thin film transistor is a driving thin film transistor connected to the organic electroluminescent element of each subpixel. And the shielding member is insulated from an active layer of each of the driving thin film transistors to shield a channel region of the active layer. delete The method of claim 1, And the active layer is made of polycrystalline silicon, and the polycrystalline silicon is formed by a laser crystallization method.

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