Organic light emitting transistor and display device having the same

An organic light emitting transistor includes a substrate, a first insulating layer on the substrate, an auxiliary gate electrode between the substrate and the first insulating layer, the auxiliary gate electrode corresponding to a first area, a switching gate electrode between the substrate and the first insulating layer, the switching gate electrode corresponding to a second area defined adjacent to at least one side of the first area, the switching gate electrode being insulated from the auxiliary gate electrode, a source electrode on the first insulating layer, the source electrode corresponding to the second area, a semiconductor layer on the first insulating layer, the semiconductor layer corresponding to at least the first area and the semiconductor layer being connected to the source electrode, a drain electrode corresponding to at least the first area, and a light emitting layer interposed between the drain electrode and the semiconductor layer.

CROSS-REFERENCE TO RELATED APPLICATION

Korean Patent Application No. 10-2014-0170690, filed on Dec. 2, 2014, in the Korean Intellectual Property Office, and entitled: “Organic Light Emitting Transistor and Display Device Having the Same,” is incorporated by reference herein in its entirety.

BACKGROUND

Embodiments relate to an organic light emitting transistor and a display device having the organic light emitting transistor.

2. Description of the Related Art

A flat panel display device is classified into a light-emitting type and a light-receiving type. As the light-emitting type flat panel display device, a flat cathode ray tube, a plasma display panel, and an organic light emitting display are widely used. The organic light emitting display is a self-emissive type display and has various advantages, such as a wide viewing angle, a superior contrast, a fast response time, etc.

The organic light emitting display may be applied to various displays for mobile devices, e.g., a digital camera, a video camera, a camcorder, a mobile information terminal, a smart phone, an ultra slim notebook, a tablet personal computer, a flexible display device, etc., or large-size electronic/electric products. e.g., an ultra-thin TV set.

In the organic light emitting display, holes and electrons are injected into an organic light emitting layer and recombined in the organic light emitting layer to generate excitons. The organic light emitting display emits light when the excitons return to a ground state from an excited state.

SUMMARY

Embodiments are directed to an organic light emitting transistor including a substrate, a first insulating layer on the substrate, an auxiliary gate electrode between the substrate and the first insulating layer, the auxiliary gate electrode corresponding to a first area, a switching gate electrode between the substrate and the first insulating layer, the switching gate electrode corresponding to a second area defined adjacent to at least one side of the first area, the switching gate electrode being insulated from the auxiliary gate electrode, a source electrode on the first insulating layer, the source electrode corresponding to the second area, a semiconductor layer on the first insulating layer, the semiconductor layer corresponding to at least the first area and the semiconductor layer being connected to the source electrode, a drain electrode corresponding to at least the first area, and a light emitting layer interposed between the drain electrode and the semiconductor layer.

The organic light emitting transistor may further include a second insulating layer. The light emitting layer may include a first portion corresponding to the first area and a second portion extending from the first portion and corresponding to the second area. The second insulating layer may be between the second portion and the source electrode, the second insulating layer corresponding to the second area and insulating the first portion from the source electrode.

The second area may surround the first area. The switching gate electrode may surround the auxiliary gate electrode.

The second area may include a first sub-area and a second sub-area that are spaced apart from each other in a direction substantially vertical to a thickness direction of the substrate. The switching gate electrode may include a first sub-switching gate electrode provided in the first sub-area and a second sub-switching gate electrode provided in the second sub-area. The first area may be between the first and second sub-areas. The auxiliary gate electrode may be between the first and second sub-switching gate electrodes.

The source electrode may be spaced apart from the first area by a distance along a direction substantially vertical to a thickness direction of the substrate. The distance may be in a range from about 0.5 micrometers to about 10 micrometers.

The semiconductor layer may include an n-type semiconductor material. An electron transport area may be between the semiconductor layer and the light emitting layer. A hole transport area may be between the semiconductor layer and the drain electrode.

The semiconductor layer may include a p-type semiconductor material. A hole transport area may be between the semiconductor layer and the light emitting layer. An electron transport area may be between the semiconductor layer and the drain electrode.

Embodiments are also directed to a display device including an organic light emitting transistor and a driver controlling the organic light emitting transistor. The organic light emitting transistor includes a substrate, a first insulating layer on the substrate, an auxiliary gate electrode between the substrate and the first insulating layer, the auxiliary gate corresponding to a first area, a switching gate electrode between the substrate and the first insulating layer, the switching gate corresponding to a second area defined adjacent to at least one side of the first area and the switching gate electrode being insulated from the auxiliary gate electrode, a source electrode on the first insulating layer, the source electrode corresponding to the second area, a semiconductor layer on the first insulating layer, the semiconductor layer corresponding to at least the first area and the semiconductor layer being connected to the source electrode, a drain electrode corresponding to at least the first area, and a light emitting layer between the drain electrode and the semiconductor layer. The driver applies an auxiliary voltage to the auxiliary gate electrode and applies a switching voltage different from the auxiliary voltage to the switching gate electrode to minimize a difference in brightness between a first light generated in a center portion of the first area and a second light generated in an edge portion of the first area.

The auxiliary voltage may have an electric potential higher than an electric potential of the switching voltage. The semiconductor layer may include an n-type semiconductor material. An electron transport area may be between the semiconductor layer and the light emitting layer. A hole transport area is between the semiconductor layer and the drain electrode.

The auxiliary voltage may have an electric potential lower than an electric potential of the switching voltage. The semiconductor layer includes an p-type semiconductor material. A hole transport area may be between the semiconductor layer and the light emitting layer. An electron transport area may be between the semiconductor layer and the drain electrode.

DETAILED DESCRIPTION

FIG. 1illustrates a cross-sectional view showing an organic light emitting transistor1000according to an exemplary embodiment.

Referring toFIG. 1, the organic light emitting transistor1000may include a substrate SB, a gate electrode100, a first insulating layer200, a source electrode300, a semiconductor layer400, a second insulating layer500, a first transport area600, a light emitting layer700, a second transport area800, and a drain electrode900.

The gate electrode100may be disposed on the substrate SB. The gate electrode100may include a switching gate electrode110and an auxiliary gate electrode120. The switching gate electrode110and the auxiliary gate electrode120may be insulated from each other. The switching gate electrode110and the auxiliary gate electrode120may be applied with different voltages from each other.

The gate electrode100may include a conductive material. The gate electrode100may be a reflective electrode, a transflective electrode, or a transmissive electrode.

A first area A1and a second area A2are defined on the substrate SB. The first area A1may be a light emitting area through which a light generated by the organic light emitting transistor1000is emitted. The second area A2may be a non-light emitting area. As an example, the second area A2may include a left side second area and a right side second area. The first area A1may be interposed between the left side second area and the right side second area.

The auxiliary gate electrode120may be disposed on the substrate SB to correspond to the first area A1. The switching gate electrode110is disposed on the substrate SB to correspond to the second area A2. Herein, unless otherwise indicated, the terms “correspond to” as in “correspond to the first area A1” or “correspond to the second area A2” may have the same meaning as “located within” or “located entirely within.” For example, the switching gate electrode110and the auxiliary gate electrode120may be spaced apart from each other in a second direction D2by a gate distance SD. Herein, a thickness direction of the substrate SB is referred to as a first direction D1, and the second direction D2is substantially perpendicular to the first direction D1. The gate distance GD may be in a range from about 0.1 micrometers to about 10 micrometers. As an example, the gate distance GD may have a minimum value in a limited resolution range of a process of forming the gate electrode100.

The first insulating layer200may be disposed over an entire surface of the substrate SB. The first insulating layer200may cover the substrate SB and the gate electrode100. The first insulating layer200may insulate the gate electrode100from the source electrode300. The first insulating layer200may insulate the gate electrode100from the semiconductor layer400. The first insulating layer200may serve as a planarization layer.

The first insulating layer200may include an inorganic material. As examples, the first insulating layer200may include at least one of silicon nitride (SiNx), silicon oxide (SiOx), and aluminum oxide (AlxOy). In some implementations, the first insulating layer200may include an organic material, e.g., polystyrene, polymethyl methacrylate, etc.

The source electrode300may be disposed on the first insulating layer200to correspond to the second area A2. The source electrode300may be insulated from the gate electrode100by the first insulating layer200. In addition, the source electrode300may be spaced apart from the first area A1in the second direction D2by a distance in a range from about 0.5 micrometers to about 10 micrometers.

The source electrode300may be a negative electrode. The source electrode300may be a transmission electrode, a transflective electrode, or a reflective electrode. When the source electrode300is the transmission electrode, the source electrode300may include Li, Ca, LiF/Ca, LiF/Al, Al, Mg, BaF, Ba, Ag, or a compound or a mixture thereof, e.g., a mixture of Ag and Mg.

The source electrode300may include an auxiliary electrode. The auxiliary electrode may include a layer formed by depositing a material at a portion of the source electrode300facing the light emitting layer and a transparent metal oxide disposed on the layer, e.g., indium tin oxide (ITO), indium zinc oxide (IZO), zinc oxide (ZnO), indium tin zinc oxide (ITZO), Mo, Ti, etc.

When the source electrode300is a transflective electrode or a reflective electrode, the source electrode300may include Ag, Mg, Al, Pt, Pd, Au, Ni, Nd, Ir, Cr, Li, Ca, LiF/Ca, LiF/Al, Mo, Ti, or a compound or mixture thereof, e.g., a mixture of Ag and Mg. The source electrode300may have a multi-layer structure including a reflective or transflective layer of the above-described material and a transparent conductive layer of ITO, IZO, ZnO, ITZO, etc.

When the organic light emitting transistor is a front surface light emitting type, the gate electrode100may be a reflective electrode, and the source electrode300may be a transmission electrode or a transflective electrode. When the organic light emitting transistor is a rear surface light emitting type, the gate electrode100is a transmission electrode or a transflective electrode, and the source electrode300is the reflective electrode.

The semiconductor layer400may be disposed over an entire surface of the first insulating layer200. The semiconductor layer400may cover the source electrode300and the first insulating layer200. The semiconductor layer400may contact and be electrically connected to the source electrode300. In addition, the semiconductor layer400may contact and be electrically connected to the first transport area600.

The semiconductor layer400may include amorphous silicon, crystalline silicon, or metal oxide semiconductor. The semiconductor layer400may include an organic semiconductor material. The semiconductor layer400may include one of an n-type semiconductor material and a p-type semiconductor material. Hereinafter, the semiconductor layer400including the n-type semiconductor material will be described in detail as a representative example.

The first transport area600may be disposed on the semiconductor layer400to correspond to at least the first area A1. Herein, unless otherwise indicated, the term “correspond at least to” indicates that the layer or element referred to may also at least partially overlap an adjoining area. As an example, the first transport area600may include a first portion610provided in the first area A1and a second portion620extending from the first portion610and provided in the second area A2.

The first transport area600may be, for example, an electron transport area. The electron transport area may include one of a hole block layer, an electron transport layer ETL, and an electron injection layer, as examples.

For instance, the electron transport area may have a structure of the electron injection layer/the electron transport layer or the electron injection layer/the electron transport layer/the hole block layer, which are sequentially stacked on the semiconductor layer400. In some implementations, the electron transport area may have a single-layer structure configured to include two or more layers of the above-mentioned layers.

The electron transport area may be formed by a suitable method, such as a vacuum deposition method, a spin coating method, a casting method, a Langmuir-Blodgett (LB), an inkjet printing method, a laser printing method, a laser induced thermal imaging (LITI), etc.

When the electron transport area includes the electron transport layer, the electron transport area may include Alq3 (Tris(8-hydroxyquinolinato)aluminum), TPBi (1,3,5-Tri(1-phenyl-1H-benzo[d]imidazol-2-yl)phenyl), BCP (2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline), Bphen (4,7-diphenyl-1,10-phenanthroline), TAZ (3-(4-biphenylyl)-4-phenyl-5-tert-butylphenyl-1,2,4-triazole), NTAZ (4-(naphthalen-1-yl)-3,5-diphenyl-4H-1,2,4-triazole), tBu-PBD (2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole), BAlq (bis(2-methyl-8-quinolinolato-N1,O8)-(1,1′-biphenyl-4-olato)aluminum), Bebq2 (beryllium bis(benzoquinolin-10-olate)), ADN (9,10-di(naphthalene-2-yl)anthracene), or a mixture thereof. The electron transport layer may have a thickness of about 100 angstroms to about 1000 angstroms, or, for example, about 150 angstroms to about 500 angstroms. When the thickness of the electron transport layer is in the above-mentioned range, superior electron transport characteristics may be obtained without increasing a driving voltage.

When the electron transport area includes the electron injection layer, the electron transport area may include a lanthanum-group metal, e.g., LiF, LiQ (lithium quinolate), Li2O, BaO, NaCl, CsF, Yb, etc., or a halide metal, e.g., RbCl, Rbl, etc. The electron injection layer may include a material obtained by mixing an electron transport material with an organo metal salt having insulating property. The organo metal salt may have an energy band gap of about 4 ev. For example, the organo metal salt may include metal acetate, metal benzoate, metal acetoacetate, metal acetylacetonate, or metal stearate. The electron injection layer may have a thickness of about 1 angstroms to about 100 angstroms, or, for example, about 3 angstroms to about 90 angstroms. When the thickness of the electron injection layer is in the above-mentioned range, superior electron injection characteristics may be obtained without increasing the driving voltage.

As described above, the electron transport area may includes the hole block layer. The hole block layer may include at least one of BCP (2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline) and Bphen (4,7-diphenyl-1,10-phenanthroline), as examples. The hole block layer may have a thickness of about 20 angstroms to about 1000 angstroms, or, for example, about 30 angstroms to about 300 angstroms. When the thickness of the hole block layer is in the above-mentioned range, superior hole block characteristics may be obtained without increasing the driving voltage.

The light emitting layer700may be disposed on the first transport area600to correspond to at least the first area A1. As an example, the light emitting layer700may include a first portion710of the light emitting layer700provided in the first area A1and a second portion720of the light emitting layer700extending from the first portion710and provided in the second area A2.

The light emitting layer700may have a single-layer structure of a single material, a single-layer structure including different materials from each other, or a multi-layer structure of different materials from each other.

The light emitting layer700may be formed by a suitable method, such as a vacuum deposition method, a spin coating method, a casting method, a Langmuir-Blodgett (LB), an inkjet printing method, a laser printing method, a laser induced thermal imaging (LITI), etc.

The light emitting layer700may include materials emitting red, green, and blue color light. The light emitting layer700may include a fluorescent material or a phosphorescent material. The light emitting layer700includes a host and a dopant.

When the light emitting layer700emits the red color light, the light emitting layer700may include a fluorescent material containing PBD:Eu(DBM)3(Phen) (tris(dibenzoylmethanato)phenanthroline europium) or perylene. When the light emitting layer700emits the red color light, the dopant included in the light emitting layer700may be selected from a metal complex, such as PIQIr(acac) (bis(1-phenylisoquinoline)acetylacetonate iridium), PQIr(acac) (bis(1-phenylquinoline) acetylacetonate iridium), PQIr (tris(1-phenylquinoline)iridium). PtOEP (octaethylporphyrin platinum), etc., or another suitable organometallic complex.

When the light emitting layer700emits a green color light, the light emitting layer700may include a fluorescent material containing Alq3 (tris(8-hydroxyquinolino)aluminum). When the light emitting layer700emits the green color light, the dopant included in the light emitting layer700may be selected from a metal complex such as Ir(ppy)3(fac-tris(2-phenylpyridine)iridium) or another suitable organometallic complex.

When the light emitting layer700emits a blue color light, the light emitting layer700may include a fluorescent material containing one selected from spiro-DPVBi, spiro-6P, distyryl-benzene (DSB), distyryl-arylene (DSA), a polyfluorene-based polymer, and a poly(p-phenylene vinylene)-based polymer. When the light emitting layer700emits the blue color light, the dopant included in the light emitting layer700may be selected from an metal complex such as (4,6-F2ppy)2Irpic or another suitable organometallic complex.

The second transport area800may be disposed on the light emitting layer700to correspond to at least the first area A1. The second transport area800may be, for example, a hole transport area.

The hole transport area may include at least one of a hole injection layer, a hole transport layer, a buffer layer, and an electron block layer.

The hole transport area may have a single-layer structure of a single material, a single-layer structure including different materials from each other, or a multi-layer structure of different materials from each other.

For instance, the hole transport area may have the single-layer structure of different materials from each other. In other implementations, the hole transport area may have a structure of the hole transport layer/the hole injection layer, the buffer layer/the hole transport layer/the hole injection layer, the buffer layer/the hole injection layer, the buffer layer/the hole transport layer, or the electron block layer/the hole transport layer/the hole injection layer.

The hole transport area may be formed by a suitable method, such as a vacuum deposition method, a spin coating method, a casting method, a Langmuir-Blodgett (LB), an inkjet printing method, a laser printing method, a laser induced thermal imaging (LITI), etc.

When the hole transport area includes the hole transport layer, the hole transport area may include a carbazole-based derivative, such as N-phenyl carbazole, polyvinyl carbazole, etc., a fluorine-based derivative, a triphenylamine-based derivative, such as TPD (N,N′-bis(3-methylphenyl)-N,N′-diphenyl-[1,1-biphenyl]-4,4′-diamine), TCTA (4,4′,4″-tris(N-carbazolyl)triphenylamine), etc., NPB (N,N′-di(1-naphthyl)-N,N′-diphenylbenzidine), or TAPC (4,4′-Cyclohexylidene bis[N,N-bis(4-methylphenyl)benzenamine]), as examples.

The hole transport area may have a thickness of about 100 angstroms to about 10,000 angstroms, or, for example, about 100 angstroms to about 1,000 angstroms. When the hole transport area includes the hole injection layer and the hole transport layer, the hole injection layer has a thickness of about 100 angstroms to about 10,000 angstroms, or, for example, about 100 angstroms to about 1,000 angstroms, and the hole transport layer may have a thickness of about 50 angstroms to about 2,000 angstroms, or, for example, about 100 angstroms to about 1,500 angstroms. When the thicknesses of the hole transport area, the hole injection layer, and the hole transport layer are in the above-mentioned ranges, superior hole transport characteristics may be obtained without increasing the driving voltage.

The hole transport area may further include an electric charge generating material to improve the conductivity thereof. The electric charge generating material may be regularly or irregularly dispersed in the hole transport area. For instance, the electric charge generating material may be a p-dopant. The p-dopant may be a quinone derivative, a metal oxide, or a cyano group-containing compound, as examples. For example, the p-dopant may include a quinone derivative such as TCNQ (tetracyanoquinodimethane), F4-TCNQ (2,3,5,6-tetrafluoro-tetracyanoquinodimethane), etc., or a metal oxide such as tungsten oxide, molybdenum oxide, etc.

As described above, the hole transport area may further include at least one of the buffer layer and the electron block layer in addition to the hole injection layer and the hole transport layer. The buffer layer may compensate for a resonance distance according to a wavelength of the light exiting from the light emitting layer to enhance the light emission efficiency of the light emitting layer. The material included in the hole transport area may be included in the buffer layer. The electron block layer may prevent electrons from being injected to the hole transport area from the electron transport area.

The drain electrode900may be disposed on the second transport area800to correspond to the first area A1. The drain electrode900may be a pixel electrode or a positive electrode. The drain electrode900may be a transmissive electrode, the transflective electrode, or the reflective electrode.

The drain electrode900may have a single-layer structure of the transparent metal oxide or metal or a multi-layer structure of plural layers. For instance, the drain electrode900may have a single-layer structure of ITO, Ag, or a metal mixture, e.g., a mixture of Ag and Mg), a double-layer structure of ITO/Mg or ITO/MgF, or a triple-layer structure of ITO/Ag/ITO.

InFIG. 1, the first transport area600, the light emitting layer700, the second transport area800, and the drain electrode900are formed in the first area A1and the second area A2adjacent to the first area A1. In other implementations, the first transport area600, the light emitting layer700, the second transport area800, and the drain electrode900may be provided on the entire surface of the substrate SB. In this case, the first transport area600, the light emitting layer700, the second transport area800, and the drain electrode900may cover the second insulating layer500and the semiconductor layer400.

The second insulating layer500may be provided to correspond to the second area A2. The second insulating layer500may insulate portions of the first transport area600, the light emitting layer700, the second transport area800, and the drain electrode900, which are provided in the second area A2, from the source electrode300.

For example, the second insulating layer500may be interposed between the light emitting layer700and the source electrode300to insulate the first portion710of the light emitting layer700from the source electrode300. Similarly, the second insulating layer500may be interposed between the first transport area600and the source electrode300to insulate the second portion620of the first transport area600from the source electrode300.

The second insulating layer500may include at least one of silicon nitride (SiNx), silicon oxide (SiOx), and aluminum oxide (AlxOy), as examples. In some implementations, the first insulating layer200may include an organic material, e.g., polystyrene, polymethyl methacrylate, etc.

In the present exemplary embodiment, the semiconductor layer400may include an n-type semiconductor material. In this case, the source electrode300may be a negative electrode and the drain electrode900may be a positive electrode. Electrons injected from the source electrode300may reach the light emitting layer700through the first transport area600. Holes injected from the drain electrode900may reach the light emitting layer700through the second transport area800. The electrons and holes injected respectively through the first and second transport areas600and800may recombine in the light emitting layer700to generate light.

FIG. 2illustrates a cross-sectional view showing an operation of an inactivation mode according to an exemplary embodiment.

Referring toFIG. 2, a switching voltage V1may be applied to the switching gate electrode110and an auxiliary voltage V2is applied to the auxiliary gate electrode120. In the inactivation mode, the switching voltage V1is smaller than a threshold voltage Vth that forms an n-channel in the semiconductor layer400.

Accordingly, the channel is not formed in the semiconductor layer400disposed in the second area A2, and thus, the electrons provided from the source electrode300may not move to the first transport area600through the semiconductor layer400even though the driving voltage is applied to the source electrode300and the drain electrode900. As a result, the organic light emitting transistor1000does not emit light regardless of an electric potential of the auxiliary voltage V2.

FIG. 3Aillustrates a cross-sectional view showing an operation of a non-uniform mode according to an exemplary embodiment, andFIG. 3Billustrates a cross-sectional view showing a simulated result of the non-uniform mode.

Referring toFIGS. 3A and 3B, in the non-uniform mode, the electric potential of the switching voltage V1is higher than that of the threshold voltage Vth and the electric potential of the auxiliary voltage V2is lower than that of the switching voltage V1.

Therefore, the channel is formed in the semiconductor layer400disposed in the second area A2, and thus the electrons from the source electrode300may reach the first transport area600when the driving voltage is applied to the source electrode300and the drain electrode900.

However, since electrons, which are influenced by an electric field formed by an electric potential difference between the source electrode300and the drain electrode900, may have a tendency to move through a shortest path among paths between the source electrode300and the drain electrode900. The electrons may reach only a portion of the light emitting layer700corresponding to an edge area EA of the first area A1and form a first electron current E1. The electrons from the source electrode300may not reach the light emitting layer700corresponding to a center area CA of the first area A1. The holes from the drain electrode900may be provided to the light emitting layer700corresponding to the edge area EA and may form a hole current HC. Thus, the electrons may recombine with the holes only in the portion of the light emitting layer700corresponding to the edge area EA. As a result, the light emission may occur only in portions of the light emitting layer700corresponding to the edge area EA and may not occur in the light emitting layer700corresponding to the center area CA.

As shown inFIG. 3B, the semiconductor layer400may include a plurality of areas. A contrast in each area indicates a current density of a corresponding area. A darker contrast in areas indicates a larger current density. As shown inFIG. 3, the current density may be concentrated in the semiconductor layer400corresponding to a first current path area CPA1.

Accordingly, the first electron current E1may flow only through the first transport area600corresponding to the edge area EA and may not flow through the center area CA. For example, the first electron current E1may flow intensively through the edge area EA adjacent to the second insulating layer500.

FIG. 4Aillustrates a cross-sectional view showing an operation of a uniform mode according to an exemplary embodiment andFIG. 4Billustrates a cross-sectional view showing a simulated result of the uniform mode.

Referring toFIGS. 4A and 4B, in the uniform mode, the electric potential of the switching voltage V1is higher than that of the threshold voltage Vth and the electric potential of the auxiliary voltage V2is higher than that of the switching voltage V1.

Therefore, the channel may be formed in the semiconductor layer400disposed in the second area A2, and electrons from the source electrode300may reach to the first transport area600when the driving voltage is applied to the source electrode300and the drain electrode900.

A portion of the electrons from the source electrode300may reach the portion of the light emitting layer700corresponding to the edge area EA to form the first electron current E1. In addition, since the auxiliary voltage V2is higher than the switching voltage V1, the other portion of the electrons from the source electrode300may reach the portion of the light emitting layer700corresponding to a center area CA through the first transport area600corresponding to the center area CA by the switching voltage V1to form a second electron current E2. The holes from the drain electrode900may be provided to the light emitting layer700corresponding to the edge area EA and the center area CA to form the hole current HC.

Thus, the electrons may recombine with the holes in the portions of the light emitting layer700corresponding to the edge area EA and corresponding to the center area CA. Accordingly, light emission may occur on the entire surface of the light emitting layer700corresponding to the first area A1.

As shown inFIG. 4B, the large current density may be formed in the semiconductor layer400corresponding to the first current path area CPA1and corresponding to a second current path area CPA2defined in the center area CA.

For example, the current formed by the electrons from the source electrode300may flow not only through the portion of the first transport area600corresponding to the edge area EA (the first electron current E1) but also through the portion of first transport area600corresponding to the center area CA (the second electron current E2). As a result, the organic light emitting transistor1000may generate the light having uniform brightness over the first area A1.

FIG. 5is a graph showing an I-V curve of the organic light emitting transistor according to an exemplary embodiment.

InFIG. 5, an X-axis indicates the electric potential of the auxiliary voltage V2and a Y-axis indicates the amount of the driving current flowing through the organic light emitting transistor1000. The Y-axis is log scale. Referring toFIG. 5, as the electric potential of the auxiliary voltage V2increases, the amount of the driving current increases. Accordingly, the driving current may be controlled in accordance with the electric potential of the auxiliary voltage V2. The brightness of the light generated by the organic light emitting transistor1000may be controlled by controlling the auxiliary voltage V2.

FIG. 6illustrates a plan view showing a source electrode and a gate electrode according to an exemplary embodiment.

Referring toFIG. 6, the first area A1may have a substantially quadrangular shape and the second area A2may surround the first area A1. The auxiliary gate electrode120may have a substantially quadrangular shape in the first area A1.

The switching gate electrode110may be provided in the second area A2and may have a substantially rectangular ring shape. The switching gate electrode110may surround the auxiliary gate electrode120.

The source electrode300may be provided in the second area A2. For example, the source electrode300may be disposed on the switching gate electrode110to overlap with the switching gate electrode110.

When the driving voltage is applied to the organic light emitting transistor1000in the uniform mode (refer toFIG. 4A), the current from the source electrode flows to the first area A1. For example, a current E11from a first edge310of the source electrode300may flow to the center area CA of the first area A1after passing through a first boundary A11of the first area A1.

Similarly, current from second to fourth edges320to340of the source electrode300may flow to the center area CA of the first area A1after respectively passing through second to fourth boundaries A13to A14. Accordingly, the currents E12to E14may be uniformly provided to the first area A1As a result, the brightness of the light generated by the organic light emitting transistor1000may be uniform in the first area A1.

FIG. 7is a plan view showing a source electrode and a gate electrode according to another exemplary embodiment.

Referring toFIG. 7, the first area A1has a substantially quadrangular shape and the auxiliary gate electrode120may be provided in the first area A1and may have a substantially quadrangular shape.

The second area A2may include a first sub-area SA1and a second sub-area SA2. The first and second sub-areas SA1and SA2may have a substantially quadrangular shape and may be spaced apart from each other in the second direction D2such that the first area A1is disposed between the first and second sub-areas SA1and SA2.

The switching gate electrode110may include a first sub-switching gate electrode111and a second sub-switching gate electrode112. The first and second sub-switching gate electrodes111and112may be provided to respectively correspond to the first and second sub-areas SA1and SA2.

The first sub-switching gate electrode111may have a substantially rectangular shape. A first side S1of the first sub-switching gate electrode111may be substantially parallel to a second side S2of the auxiliary gate electrode120. The first side S1may correspond in length and placement to one side of the four sides of the first sub-switching gate electrode111that is adjacent to the auxiliary gate electrode120. The second side S2may correspond to the side of the auxiliary gate electrode120that is adjacent to the first sub-switching gate electrode111.

The second sub-switching gate electrode112may have a substantially rectangular shape. A third side S3of the second sub-switching gate electrode112is substantially parallel to a fourth side S4of the auxiliary gate electrode120. The third side S3may correspond in length and placement to one side of the four sides of the second sub-switching gate electrode112that is adjacent to the auxiliary gate electrode120. The fourth side S4may correspond to a the side of the auxiliary gate electrode120that is adjacent to the second sub-switching gate electrode112.

The source electrode300may include a first sub-source electrode301and a second sub-source electrode302. The first sub-source electrode301may be provided in the first sub-area SA1. For example, the first sub-source electrode301may have a shape corresponding to that of the first sub-switching gate electrode111and may be in an overlapping relationship with the first sub-switching gate electrode111.

The second sub-source electrode302may be disposed in the second sub-area SA2. For example, the second sub-source electrode302may have a shape corresponding to that of the second sub-switching gate electrode112and may be in an overlapping relationship with the second sub-switching gate electrode112.

When the driving voltage is applied to the organic light emitting transistor1000in the uniform mode (refer toFIG. 4A), the current from the first sub-source electrode301may flow to the first area A1. For example, the current E5provided from the first edge310of the first sub-source electrode301may flow to the center area CA of the first area A1after passing through the first boundary A11of the first area A1.

Similarly, the current E6provided from the second edge320of the second sub-source electrode302may flow to the center area CA of the first area A1after passing through the second boundary A12of the first area A1. The current may be uniformly provided to the entire surface of the first area A1. The brightness of the organic light emitting transistor1000is uniform in the first area A1.

FIG. 8illustrates a block diagram showing a display device DA according to an exemplary embodiment.

Referring toFIG. 8, the display device DA may include a display panel DP to display an image, a gate electrode driver GD and a data driver DD to drive the display panel DP, and a controller CT to control the gate electrode driver GD and the data driver DD.

The controller CT may receive input image information RGBi and a plurality of control signals CS from the outside of the display device DA. The controller CT may convert a data format of the input image information RGBi to a data format appropriate to an interface between the data driver DD and the controller to generate output image data IDATA and may apply the output image data IDATA to the data driver DD.

The controller CT may generate a data control signal DCS, e.g., an output start signal, a horizontal start signal, etc., on the basis of the control signals CS and a gate electrode control signal GCS, e.g., a vertical start signal, a vertical clock signal, a vertical clock bar signal, etc. The data control signal DCS may be applied to the data driver DD, and the gate electrode control signal GCS may be applied to the gate electrode driver GD.

The gate electrode driver GD may sequentially output gate electrode signals and auxiliary signals in response to the gate electrode control signal GCS provided from the controller CT.

The data driver DD may convert the output image data IDATA into data voltages in response to the data control signal DCS provided from the controller CT and may apply the data voltages to the display panel DP.

The display panel DP may include a plurality of gate electrode line GL1to GLn, a plurality of auxiliary lines AL1to ALn, a plurality of data lines DL1to DLm, and a plurality of pixels PX.

The display panel DP may have a resolution determined by the number of the pixels PX arranged on the display panel DP. For the convenience of explanation,FIG. 8shows only one pixel PX.

Each pixel may display one of primary colors of red, green, blue, and white colors, as examples. In other implementations, the primary colors may further include various colors, e.g., yellow, cyan, magenta, etc.

The gate electrode lines GL1to GLn may extend in a second direction D2and may be arranged to be parallel to each other in a third direction D3substantially perpendicular to the second direction D2. The gate electrode lines GL1to GLn may be connected to the gate electrode driver GD to sequentially receive the gate electrode signals from the gate electrode driver GD.

In addition, the auxiliary lines AL1to ALn may extend in the second direction D2and may be arranged in the third direction D3to be substantially parallel to each other. The auxiliary lines AL1to ALn may be connected to the gate electrode driver GD to sequentially receive the auxiliary signals from the gate electrode driver GD.

The data lines DL1to DLm may extend in the third direction D3and may be arranged in the second direction D2to be substantially parallel to each other. The data lines DL1to DLm may be connected to the data driver DD to receive the data voltages from the data driver DD.

Each of the pixels PX may be connected to a corresponding gate electrode line of the gate electrode lines GL1to GLn, a corresponding auxiliary line of the auxiliary lines AL1to ALn, and a corresponding data line of the data lines DL1to DLm.

As an example, each pixel may include the organic light emitting transistor1000shown inFIG. 1. The switching gate electrode110of each pixel PX is connected to the corresponding gate electrode line to receive the gate electrode signal from the gate electrode line connected thereto.

The auxiliary gate electrode120of each pixel PX may be connected to the corresponding auxiliary line to receive the auxiliary signal from the auxiliary line connected thereto. The auxiliary signal may include the above-mentioned auxiliary voltage V2(refer toFIGS. 2 to 4).

The pixels PX may be turned on or turned off in response to the gate electrode signal applied thereto. The turned-on pixel PX may display a grayscale level corresponding to the data voltage applied thereto.

The organic light emitting transistor1000of the pixels PX may be operated in the non-uniform mode or the uniform mode in response to the auxiliary signal applied thereto. The brightness of the image displayed in the organic light emitting transistor1000of the pixels PX may be controlled by the auxiliary signal as described with reference toFIG. 5.

The controller CT may be mounted on the printed circuit board in an integrated circuit chip form and connected to the gate electrode driver GD and the data driver DD. The gate electrode driver GD and the data driver DD may be mounted on a flexible printed circuit board after being formed as plural driving chips, and then connected to the display panel DP in a tape carrier package (TCP) scheme.

In some implementations, the gate electrode driver GD and the data driver DD may be mounted on the display panel DP in a chip on glass (COG) arrangement after being formed as plural driving chips. In addition, the gate electrode driver GD may be substantially simultaneously formed with the transistors of the pixels PX and mounted on the display panel DP in ASG (amorphous silicon TFT gate driver circuit) form.

FIG. 9illustrates a cross-sectional view showing an organic light emitting transistor2000according to another exemplary embodiment.

A semiconductor layer450of the organic light emitting transistor2000shown inFIG. 9may include a p-type semiconductor material. Features of the organic light emitting transistor2000may have similar structure and function as those of the organic light emitting transistor1000shown inFIG. 1, except that a first transport area650may be the hole transport area, a second transport area850may be the electron transport area, and the source and drain electrodes350and950may be positive and negative electrodes, respectively. Accordingly, different features of the organic light emitting transistor2000from the organic light emitting transistor1000shown inFIG. 1will be described in detail.

FIG. 10illustrates a cross-sectional view showing a non-uniform mode of the organic light emitting transistor2000shown inFIG. 9.

Referring toFIG. 10, in the non-uniform mode, the electric potential of the switching voltage V1is lower than the electric potential of the threshold voltage Vth of the semiconductor layer450and the electric potential of the auxiliary voltage V2is higher than the electric potential of the switching voltage V1.

The channel is formed in the semiconductor layer450disposed in the second area A2. Accordingly the holes from the source electrode350reach the first transport area650when the driving voltage is applied to the source electrode350and the drain electrode950. The holes drifted by the electric field may move through the shortest path. Accordingly, the holes may reach only the portion of the light emitting layer700corresponding to the edge area EA of the first area A1and form a first hole current H1. In addition, the holes from the source electrode350may not reach the portion of the light emitting layer700corresponding to the center area CA of the first area A1. The electrons from the drain electrode950may be provided to the portion of the light emitting layer700corresponding to the edge area EA to form the electron current EC. Thus, the electrons may be recombined with the holes only in the portion of the light emitting layer700corresponding to the edge area EA. As a result, light emission may occur only in the portion of the light emitting layer700corresponding to the edge area EA and may not occur in the portion of the light emitting layer700corresponding to the center area CA.

FIG. 11illustrates a cross-sectional view showing an operation of a uniform mode of the organic light emitting transistor2000shown inFIG. 9.

Referring toFIG. 11, in the uniform mode, the electric potential of the switching voltage V1is lower than the electric potential of the threshold voltage Vth and the electric potential of the auxiliary voltage V2is higher than the electric potential of the switching voltage V1.

The channel may be formed in the semiconductor layer450disposed in the second area A2. Accordingly, the holes from the source electrode350may reach the first transport area650when the driving voltage is applied to the source electrode350and the drain electrode950.

A portion of the holes from the source electrode350may reach the portion of the light emitting layer700corresponding to the edge area EA and may form the first hole current H1. Since the auxiliary voltage V2is lower than the switching voltage V1, the other portion of the holes from the source electrode350may reach to the portion of the light emitting layer700corresponding to the center area CA through the portion of the first transport area650corresponding to the center area CA by the switching voltage V1to form a second hole current H2. The electrons from the drain electrode950may be provided to the portion of the light emitting layer700corresponding to the edge area EA and the center area CA to form the electron current EC.

The electrons may recombine with the holes in the light emitting layer700corresponding to the edge area EA and the center area CA, and light emission may occur on the entire surface of the light emitting layer700corresponding to the first area A1.

By way of summation and review, the organic light emitting transistor includes an auxiliary gate electrode and a switching gate electrode. Thus the organic light emitting transistor emits the light having uniform brightness.