Source: http://2ya.red-faced.us/patent/US-2007096111-A1
Timestamp: 2018-08-17 02:02:41
Document Index: 121467337

Matched Legal Cases: ['art. 10', 'art. 14', '§ 119', 'Application No. 2005', 'art 144', 'art 144', 'art 244', 'art 244', 'art 344', 'art 344', 'art 344', 'art 344', 'art 444', 'art 444', 'art 444', 'art 444']

US-2007096111-A1: Light emitting display
Inventors: OH KWANG S.
Assignees: Lg Philips Lcd Co., Ltd.
Publication Number: US-2007096111-A1
The present disclosure provides a light emitting display device including a first substrate and a second substrate and a light emitting part disposed therebetween. The first substrate includes an active layer, source and drain electrodes, an insulating layer, and a gate electrode. The active layer is doped with first dopant ions and second dopant ions. The light emitting display may have a fast response characteristic due to a reduced resistance of the active layer and an improved characteristic of current drift.
1 . A light emitting display comprising: a first substrate having a gate electrode disposed thereon, a gate insulating layer disposed on the gate electrode, an active layer disposed on the gate insulating layer and doped with first dopant ions, a source electrode disposed at a first side of the active layer and a drain electrode disposed at a second side thereof, and a doping region comprising a predetermined region of the active layer exposed between the source and drain electrodes, the predetermined region being doped with second dopant ions; a second substrate having a first electrode disposed thereon, a light emitting part disposed on the first electrode, and a second electrode disposed on the light emitting part; and a connection electrode for electrically connecting the drain electrode of the first substrate with the second electrode of the second substrate. 2 . The display of claim 1 , wherein the first dopant ions are N type dopants, and the second dopant ions are P type dopants. 3 . The display of claim 1 , wherein the first dopant ions are P type dopants, and the second dopant ions are N type dopants. 4 . The display of claim 1 , wherein the light emitting part comprises an organic light emitting layer. 5 . A light emitting display comprising: a first substrate having an active layer disposed thereon, the active layer being doped at a center thereof with first dopant ions and doped at both sides with second dopant ions, source and drain electrodes disposed at respective sides of the active layer, an insulating layer disposed on the active layer and having contact holes for exposing predetermined regions of the source and drain electrodes, and a gate electrode disposed on the insulating layer to correspond with the active layer; a second substrate having a first electrode disposed thereon, a light emitting part disposed on the first electrode, and a second electrode disposed on the light emitting part; and a connection electrode for electrically connecting the drain electrode of the first substrate with the second electrode of the second substrate. 6 . The display of claim 5 , wherein the first dopant ions are N type dopants, and the second dopant ions are P type dopants. 7 . The display of claim 5 , wherein the first dopant ions are P type dopants, and the second dopant ions are N type dopants. 8 . The display of claim 5 , wherein the light emitting part comprises an organic light emitting layer. 9 . A light emitting display comprising: a driver having a gate electrode disposed on a substrate, a gate insulating layer disposed to cover the gate electrode, an active layer disposed on the gate insulating layer and doped with first dopant ions, a source electrode disposed at a first side of the active layer and a drain electrode disposed at a second side thereof, and a doping region comprising a predetermined portion of the active layer exposed between the source and drain electrodes, the predetermined portion being doped with second dopant ions; a first electrode electrically connected with the drain electrode of the driver; a light emitting part disposed on the first electrode; and a second electrode disposed on the light emitting part. 10 . The display of claim 9 , wherein the first dopant ions are N type dopants, and the second dopant ions are P type dopants. 11 . The display of claim 9 , wherein the first dopant ions are P type dopants, and the second dopant ions are N type dopants. 12 . The display of claim 9 , wherein the light emitting part comprises an organic light emitting layer. 13 . A light emitting display comprising: a driver having an active layer disposed on a substrate, the active layer being doped at a center thereof with first dopant ions and doped at both sides with second dopant ions, source and drain electrodes disposed at both sides of the active layer, an insulating layer disposed on the active layer and having contact holes to expose predetermined regions of the source and drain electrodes, and a gate electrode disposed on the insulating layer to correspond with the active layer; a first electrode electrically connected with the drain electrode of the driver; a light emitting part disposed on the first electrode; and a second electrode disposed on the light emitting part. 14 . The display of claim 13 , wherein the first dopant ions are N type dopants, and the second dopant ions are P type dopants. 15 . The display of claim 13 , wherein the first dopant ions are P type dopants, and the second dopant ions are N type dopants. 16 . The display of claim 13 , wherein the light emitting part comprises an organic light emitting layer.
[0001] This nonprovisional patent application claims priority under 35 U.S.C. § 119(a) to Patent Application No. 2005-0082418 filed in Korea on Sep. 05, 2005, the entire contents of which are hereby incorporated by reference. TECHNICAL FIELD [0002] The present disclosure relates to a light emitting display associated with a response characteristic. RELATED ART [0003] An active light emitting device used for a light emitting display may have a light emitting layer formed between two electrodes. The light emitting device can be classified as an inorganic light emitting device or an organic light emitting device depending on material. The light emitting device may further be classified as a passive matrix type or an active matrix type, depending on a driving mode of the light emitting layer. [0004] FIG. 1 is a conventional light emitting device including a driver 10 formed on a first transparent substrate 12 , and a first electrode 16 , a light emitting layer 18 , and a second electrode 20 provided on the driver 10 . In order to protect the device against moisture and oxygen, a getter unit 22 is formed on the second substrate 28 , and the first and second substrates 12 and 28 are sealed by a sealant 26 . [0005] In the driver 10 , the gate electrode 31 is formed on the first substrate 12 , and a gate insulating film 32 is formed on the first substrate 12 to cover the gate electrode 31 . An active layer 35 is formed of amorphous silicon (a-Si) or polycrystalline (poly) silicon (P—Si) on the gate insulating film 32 , and an ohmic contact layer 34 is formed on the active layer 35 . A source electrode 36 and a drain electrode 37 are formed on the active layer 35 . [0006] A protective film 38 can be selectively formed on the first substrate 12 comprising the source and drain electrodes 36 and 37 . In detail, the drain electrode 37 electrically connects with the first electrode 16 through a contact hole which exposes a predetermined region of the drain electrode 37 . The first electrode 16 electrically connects with a light emitting layer 18 as a pixel electrode. [0007] Electrical current caused by driving will be described below with reference to FIG. 2 . [0008] When voltage is applied to the gate electrode 31 , a channel is formed in the active layer 35 by the voltage of the gate electrode 31 . Current (I) applied to the source electrode 36 flows to the drain electrode 37 along a low resistance layer forned in the channel. Since the active layer 35 is formed of amorphous silicon or poly silicon, the driver 10 has a characteristic in which a channel region formed by the gate electrode 31 has a relatively high resistance. [0009] For description of resistance characteristic, it is assumed that resistance of the channel formed by the voltage of the gate electrode 31 is denoted by “R 1 .” Also, it can be appreciated that the following resistance characteristic is provided on the assumption that a resistance fonned at a lower surface of the source electrode 36 is denoted by “R 2 ,” and a resistance formed in the active layer 35 is denoted by “R 3 .” [0010] When a voltage is applied to the gate electrode 31 , the current density (I) between a source and a drain through the channel decreases due to the series resistance of R 1 +R 2 +R 3 . This means that the mobility between the source and the drain through the channel decreases. As a result, a response characteristic of an active current-driven organic light emitting device deteriorates. [0011] Such a deterioration of the response of a current-driven display that uses a light emitting device such as an organic light emitting device or an inorganic light emitting device may impair the performance of the display. SUMMARY [0012] Accordingly, the light emitting display of the present disclosure may solve some of the problems and disadvantages of the related art. [0013] In one aspect, there is provided a light emitting display comprising a first substrate, a second substrate, and a connection electrode. The first substrate has a gate electrode, a gate insulating layer, an active layer, a source electrode, a drain electrode, and a doping region. The gate electrode is disposed on the first substrate. The gate insulating layer is disposed on the gate electrode. The active layer is disposed on the gate insulating layer and is doped with first dopant ions. The source electrode is formed at a first side of the active layer, and the drain electrode is formed at a second side thereof. The doping region comprises a predetermined portion of the active layer exposed between the source and drain electrodes. The predetermined portion is doped with second dopant ions. The second substrate has a first electrode, a light emitting part, and a second electrode. The first electrode is formed on the second substrate. The light emitting part is formed on the first electrode. The second electrode is formed on the light emitting part. The connection electrode electrically connects the drain electrode of the first substrate with the second electrode of the second substrate. [0014] In another aspect, there is provided a light emitting display comprising a first substrate, a second substrate, and a connection electrode. The first substrate has an active layer, source and drain electrodes, an insulating layer, and a gate electrode. The active layer is disposed on the first substrate and is doped at its center with first dopant ions and at its sides with second dopant ions. The source and drain electrodes are disposed at respective sides of the active layer. The insulating layer is disposed on the active layer and has contact holes for exposing predetermined regions of the source and drain electrodes. The gate electrode is disposed on the insulating layer to correspond with the active layer. The second substrate has a first electrode disposed thereon, a light emitting part disposed on the first electrode, and a second electrode disposed on the light emitting part. The connection electrode electrically connects the drain electrode of the first substrate with the second electrode of the second substrate. [0015] In a further aspect there is provided a light emitting display comprising a driver, a first electrode, a light emitting part, and a second electrode. The driver has a gate electrode, a gate insulating layer, an active layer, a source electrode, a drain electrode, and a doping region. The gate electrode is disposed on a substrate. The gate insulating layer is disposed on the gate electrode. The active layer is disposed on the gate insulating layer and is doped with first dopant ions. The source electrode is dispose at a first side of the active layer and the drain electrode is formed at a second side thereof. The doping region comprises a predetermined portion of the active layer exposed between the source and drain electrodes. The predetermined portion is doped with second dopant ions. The first electrode electrically connects with the drain electrode of the driver. The light emitting part is disposed on the first electrode. The second electrode is disposed on the light emitting part [0016] In a further aspect there is provided a light emitting display comprising a driver, a first electrode, a light emitting part, and a second electrode. The driver has an active layer, source and drain electrodes, an insulating layer, and a gate electrode. The active layer is formed on a substrate and is doped at its center with first dopant ions and at its sides with second dopant ions. The source and drain electrodes are formed at respective sides of the active layer. The insulating layer is disposed on the active layer and has contact holes for exposing predetermined regions of the source and drain electrodes. The gate electrode is formed on the insulating layer to correspond with the active layer. The first electrode electrically connects the drain electrode of the first substrate with the second electrode of the second substrate. The light emitting part is formed on the first electrode. The second electrode is formed on the light emitting part. BRIEF DESCRIPTION OF THE DRAWINGS [0017] FIG. 1 is a view illustrating a conventional light emitting display and an exploded view illustrating a driver. [0018] FIG. 2 illustrates current drift of the driver of FIG. 1 . [0019] FIG. 3 is a view illustrating a light emitting display and an exploded view illustrating a driver according to a first exemplary embodiment. [0020] FIG. 4 illustrates current drift of the driver of FIG. 3 . [0021] FIG. 5 is a view illustrating a light emitting display and an exploded view illustrating a driver according to a second exemplary embodiment. [0022] FIG. 6 is a view illustrating a light emitting display and an exploded view illustrating a driver according to a third exemplary embodiment [0023] FIG. 7 is a view illustrating a light emitting display and an exploded view illustrating a driver according to a fourth exemplary embodiment. DETAILED DESCRIPTION [0024] Various embodiments will be described in a more detailed manner with reference to the drawings. FIRST EMBODIMENT [0025] FIG. 3 is a view illustrating a light emitting display and an exploded view illustrating a driver according to a first exemplary embodiment [0026] Referring to FIG. 3 , the light emitting display according to the first embodiment has an upper substrate and a lower substrate. A gate electrode 131 may be formed under a source electrode 136 and a drain electrode 137 . [0027] The gate electrode 131 may be formed on a first substrate 150 , and an insulating layer 132 may be formed to cover the gate electrode 131 . [0028] An active layer 135 doped with first dopant ions may be formed on the insulating layer 132 to cover the insulating layer 132 . An ohmic contact layer 134 maybe formed on the active layer 135 . A source electrode 136 may be formed on one side of the active layer 135 , and a drain electrode 137 may be formed on the other side thereof. [0029] The active layer 135 is exposed between the source electrode 136 and the drain electrode 137 . The exposed region of the active layer 135 may be doped with second dopant ions. This region is called a doping region 138 . [0030] A protective film 156 may be formed on the source electrode 136 and the drain electrode 137 such that a predetermined portion of the drain electrode 137 is exposed to the outside. The drain electrode 137 may be electrically connected with a connection electrode 155 . [0031] In a structure having the upper and the lower substrates, a first electrode 140 may be formed over a second substrate 160 , and a light emitting part 144 may be formed on the first electrode 140 , and a second electrode 142 may be formed on the light emitting part 144 . [0032] The first and the second substrates 150 and 160 are electrically connected by the connection electrode 155 , which electrically connects the drain electrode 137 of the first substrate 150 with the second electrode 142 of the second substrate 160 , and are sealed by a sealant 126 , thereby constructing the light emitting display. [0033] In the above structure, a planarization layer 147 rnay be formed on the first electrode 140 , and each color filter 146 may be additionally formed as well. [0034] Therefore, a thin film transistor of the first embodiment may have a characteristic of N-P-N by doping with the first dopant ions of an N type and the second dopant ions of a P type. [0035] In other words, amorphous silicon or poly silicon for forming the active layer 135 may be doped with the N type dopants and may thus be N type region. P type dopants may dope the doping region 138 between the source and the drain electrodes 136 and 137 and thus the doping region 138 may be a P type region. As a result, an N-MOS thin film transistor may be constructed. [0036] Referring to FIG. 3 , the first substrate 150 may be defined as the lower substrate, and the second substrate 160 may be defined as the upper substrate. [0037] Referring to FIGS. 3 and 4 showing a driver current, driving of the light emitting display according to the present embodiment will be described below. [0038] If a voltage is applied to the gate electrode 131 formed on the first substrate 150 , a channel may be formed in the P-type doping region 138 that is positioned over the gate electrode 131 . Electric current may flow from the source electrode 136 to the drain electrode 137 through the channel. [0039] Meanwhile, since the active layer 135 may be formed as N type under the source and the drain electrodes 136 and 137 , an amount of current flowing through the channel may be increased. Further, since the doping region 138 may be formed as a P type region, electrons of the source electrode 136 may be quickly led due to holes of the doping region 138 . [0040] Accordingly, due to a characteristic of moving surface charges from the N type active layer 135 to a depletion layer of the doping region 138 having the holes, mobility between the source and the drain through the channel may be greatly improved. [0041] Due to a significant introduction of electrons from the doping region 138 having P type dopants into the drain electrode 137 having N type dopants, there is an increase in current density through the channel provided in the active layer 135 . [0042] Since the channel formed in the doping region 138 is proportional to the voltage applied to the gate electrode 131 , as the voltage applied to the gate electrode 131 increases, the depletion layer formed in the channel and electron introduction may be increased in proportion to the applied voltage. [0043] It may be assumed that “R 1 ” denotes a resistance formed in the doping region 138 doped with the P type dopants when the voltage is applied to the gate electrode 131 . Also, it may be assumed that “R 2 ” denotes a resistance formed at a lower end of the source electrode 136 , and “R 3 ” denotes a resistance formed in the active layer 135 . [0044] It should be noted that the respective resistances are based on a theoretical analysis not shown in the drawings. [0045] When R 1 +R 1 +R 3 =Rs, a series resistance (Rs) of the active layer 135 formed of amorphous silicon may be reduced. [0046] Accordingly, it can be appreciated that the active layer 135 may be doped with the N type and P type dopants, respectively, thereby reducing the series resistance (Rs) and improving a characteristic of current Also, owing to the improvement of the characteristic of the current, a charge accumulation time may be reduced and at the same time, a high current density may be maintained, thereby increasing a response speed of the current-driven light emitting display. SECOND EMBODIMENT [0047] FIG. 5 is a view illustrating a light emitting display and an exploded view illustrating a driver according to a second exemplary embodiment. [0048] As shown in FIG. 5 , the light emitting display according to the second exemplary embodiment may be formed to have an upper substrate and a lower substrate. A schematic structure in which a gate electrode 231 is disposed higher than a source electrode 236 and a drain electrode 237 is provided as follows. [0049] An active layer 235 doped at its center with first dopant ions and doped at both sides with second dopant ions may be formed on a first substrate 250 . A source electrode 236 may be formed on either side of the active layer 235 , and a drain electrode 237 may be formed on the other side thereof. [0050] An ohmic contact layer 234 may be formed to cover the active layer 235 , the source electrode 236 , and the drain electrode 237 . The gate electrode 231 may be formed to correspond with the active layer 235 on the ohmic contact layer 234 . [0051] An insulating layer 232 may be formed to cover the ohmic contact layer 234 and expose predetermined regions of the source and drain electrodes 236 and 237 . [0052] A first protective film 249 having a contact hole for exposing a predetermined portion of the drain electrode 237 may be formed on the source and drain electrodes 236 and 237 . The drain electrode 237 may be electrically connected with a metal electrode 253 through the contact hole. The metal electrode 253 may be formed to electrically connect with a connection electrode 255 . The connection electrode 255 may be formed on a second protective film 256 , or the connection electrode 255 may also be constructed using a spacer. [0053] A first electrode 240 may be formed over a second substrate 260 , and a light emitting part 244 may be formed on the first electrode 240 , and a second electrode 242 may be formed on the light emitting part 244 . [0054] The drain electrode 237 of the first substrate 250 may be electrically connected with the second electrode of the second substrate 260 through the connection electrode 255 , and the first and second substrates 250 and 260 may be sealed by a sealant 226 , thereby constructing the light emitting display. [0055] In the above structure, a planarization layer 247 may be formed on the first electrode 240 , and each color filter 246 may be additionally formed as well. [0056] A selective constituent element of the light emitting display according to the second exemplary embodiment, a thin film transistor, may have a characteristic of P-N-P by doping with the first dopant ions of a P type and the second dopant ions of an N type. [0057] In other words, amorphous silicon or poly silicon for forming the active layer 235 may be doped with the P type dopants and be a P type region. N type dopants may dope a region between the source and drain electrodes 236 and 237 , and the region may be an N type region. As a result, a P-MOS thin film transistor may be constructed. [0058] Referring to FIG. 5 , the first substrate 250 may be defined as the lower substrate, and the second substrate 260 may be defined as the upper substrate. [0059] Driving of the light emitting display according to the second exemplary embodiment will be described below. [0060] If a voltage is applied to the gate electrode 231 , a channel maybe formed in the P-type active layer 235 that is positioned under the gate electrode 231 . Electric current may flow from the source electrode 236 to the drain electrode 237 through the channel. [0061] Since the active layer 235 has the P type at both sides between the source and drain electrodes 236 and 237 , holes formed in the P type active layer 235 may push electrons toward a center of the N type active layer 235 . [0062] Accordingly, the electrons formed in the center of the N type active layer 235 may quickly move to the P type active layer 235 having the holes. This is due to a characteristic in which high-mobility holes of surface charges move from the P type active layer 235 to the N type active layer 235 and accordingly, current mobility may be greatly improved. [0063] Due to a significant introduction of electrons from the doping region 238 having N type dopants into the drain electrode 237 having P type dopants, there is an increase in current density through the channel provided in the active layer 235 . [0064] Since the channel formed in the active layer 235 is proportional to the voltage applied to the gate electrode 231 , as the voltage applied to the gate electrode 231 increases, the depletion layer formed in the channel and electron introduction may be increased in proportion to the applied voltage. [0065] It may be assumed that “R 1 ” denotes resistance formed in the center of the active layer 235 doped with the N type ions when the voltage is applied to the gate electrode 231 . Also, it may be assumed that “R 2 ” denotes resistance formed in the N type active layer 235 formed adjacent to the source electrode 236 , and “R 3 ” denotes resistance formed in the N type active layer 235 formed adjacent to the drain electrode 237 . [0066] It should be noted that the respective resistances are based on theoretical analysis not shown in the drawings. [0067] When R 1 +R 2 +R 3 =Rs, the series resistance (Rs) of the active layer 235 formed of amorphous silicon may be reduced. [0068] Accordingly, it can be appreciated that the active layer 235 may be doped with the N type and P type ions, respectively, thereby reducing the resistance (Rs) and improving a characteristic of current drift. Also, owing to improvement of the characteristic of the current drift, a charge accumulation time may be reduced and at the same time, high current density may be maintained, thereby increasing a response speed of the current-driven light emitting display. THIRD EMBODIMENT [0069] FIG. 6 is a view illustrating a light emitting display and an exploded view illustrating a driver according to a third exemplary embodiment. [0070] As shown in FIG. 6 , the light emitting display according to the third exemplary embodiment of is structured to have a driver 300 and a light emitting part 344 formed at a substrate 350 . A schematic structure in which a gate electrode 331 may be formed under a source electrode 336 and a drain electrode 337 is provided as follows. [0071] The gate electrode 331 may be formed on the substrate 350 , and a gate insulating layer 332 may be formed on the substrate 350 to cover the gate electrode 331 . [0072] An active layer 335 doped with first dopant ions may be formed to cover the gate insulating layer 332 . An ohmic contact layer 334 may be formed on the active layer 335 . The source electrode 336 may be formed on one side of the active layer 335 , and the drain electrode 337 may be formed on the other side thereof. [0073] A region of the active layer 335 exposed between the source electrode 336 and the drain electrode 337 may be doped with second dopant ions. This region is called an doping region 338 . A protective film 356 may be formed on the drain electrode 337 such that a predetermined portion of the drain electrode 337 is exposed to the outside. [0074] Here, the driver 300 in which the drain electrode 337 is electrically connected with a first electrode 340 may be formed. [0075] Accordingly, the first electrode 340 may be electrically connected with the drain electrode 337 of the driver 300 , the light emitting part 344 may be formed on the first electrode 340 , and a second electrode 342 may be formed on the light emitting part 344 , thereby providing the light emitting display in which sealing is implemented by a sealant 326 . [0076] The light emitting part 344 may express red (R), green (G), and blue (B) colors 319 . In a general method, separate organic material for emitting red, green, and blue lights may be patterned and used at each pixel. [0077] A selective constituent element of the light emitting display according to the third exemplary embodiment, a thin film transistor, may have a characteristic of N-P-N by doping with the first dopant ions of an N type and the second dopant ions of a P type. [0078] In other words, amorphous silicon or poly silicon for forming the active layer 335 may be doped with N type ions and may be an N type region. P type ions may dope the doping region 338 between the source and drain electrodes 336 and 337 , and the region may be a P type region. As a result, a N-MOS thin film transistor may be constructed. [0079] Driving of the light emitting display according to the third exemplary embodiment will be described below. [0080] If a voltage is applied to the gate electrode 331 formed on the substrate 350 , a channel may be formed in the P-type doping region 338 that is positioned over the gate electrode 331 . At this time, electric current may flow from the source electrode 336 to the drain electrode 337 through the channel. [0081] Since the active layer 335 may be formed as an N type region under the source and drain electrodes 336 and 337 , an amount of current applied to and flowing in the source electrode 336 may be increased. [0082] Accordingly, since the doping region 338 may be formed as a P type region, electrons of the source electrode 336 is quickly led due to holes of the doping region 338 . [0083] This may be due to a characteristic in which holes of surface charges move from the N type active layer 335 to the doping region 338 and accordingly, current mobility may be greatly improved. [0084] Due to a significant introduction of electrons from the doping region 338 having P type dopants into the drain electrode 337 having N type dopants, there is an increase in current density through the channel provided in the active layer 335 . [0085] Since the channel formed in the doping region 338 is be proportional to the voltage applied to the gate electrode 331 , as the voltage applied to the gate electrode 331 increases, the depletion layer formed in the channel and electron introduction may be increased in proportion to the applied voltage. [0086] It may be assumed that “R 1 ” denotes resistance formed in the doping region 338 doped with the P type ions when the voltage is applied to the gate electrode 331 . Also, it may be assumed that “R 2 ” denotes resistance formed at a lower end of the source electrode 336 , and “R 3 ” denotes resistance formed in the active layer 335 . [0087] It should be noted that the respective resistances are based on theoretical analysis not shown in the drawings. [0088] When R 1 +R 2 +R 3 =Rs, the series resistance (Rs) of the active layer 335 formed of amorphous silicon may be reduced. [0089] Accordingly, it can be appreciated that the active layer 335 may be doped with the N t type and P type ions, respectively, thereby reducing the resistance (Rs) and improving a characteristic of current drift. Also, owing to improvement of the characteristic of the current drift, a charge accumulation time may be reduced and at the same time, high current density may be maintained, thereby increasing a response speed of the current-driven light emitting display. FOURTH EMBODIMENT [0090] FIG. 7 is a view illustrating a light emitting display and an exploded view illustrating a driver according to a fourth exemplary embodiment. [0091] As shown in FIG. 7 , the light emitting display according to the fourth exemplary embodiment may be structured to have a driver 400 and a light emitting part 444 formed at a substrate 450 . A schematic structure in which a gate electrode 431 may be formed under a source electrode 436 and a drain electrode 437 is provided as follows. [0092] An active layer 435 doped at its center with first dopant ions, and doped at both sides with second dopant ions may be formed on the substrate 450 . [0093] The source electrode 436 may be formed on any one side of the active layer 435 , and the drain electrode 437 may be formed on the other side thereof An ohmic contact layer 434 may be formed on the active layer 435 . [0094] The gate electrode 431 may be formed to correspond with the active layer 435 , and the insulating layer 432 may be formed to cover the ohmic contact layer 434 and the gate electrode 431 on the ohmic contact layer 434 . A contact hole may be provided to expose a predetermined region of the drain electrode 437 , and a protective film 449 may be formed. A metal electrode 456 may be formed on the drain electrode 437 , thereby providing the driver 400 electrically connected with the first electrode 440 . [0095] Accordingly, the first electrode 440 may be electrically connected with the drain electrode 437 of the driver 400 , the light emitting part 444 may be formed on the first electrode 440 , and a second electrode 442 may be formed on the light emitting part 444 , thereby providing the light emitting display in which sealing is implemented by a sealant 426 . [0096] The light emitting part 444 may express red (R), green (G), and blue (B) colors 419 . In a general method, separate organic material for emitting red, green, and blue light may be patterned and used at each pixel. [0097] A selective constituent element of the light emitting display according to the fourth exemplary embodiment, a thin film transistor, may have a characteristic of P-N-P by doping with the first dopant ions of a P type and the second dopant ions of an N type. [0098] In other words, amorphous silicon or poly silicon for forming the active layer 435 may be doped with the P type ions and may be a P type region. N type ions may dope a region between the source and drain electrodes 436 and 437 , and it may be an N type region. As a result, a P-MOS thin film transistor may be constructed. [0099] Driving of the light emitting display according to the fourth exemplary embodiment may be described below. [0100] If a voltage is applied to the gate electrode 431 , a channel may be formed in the P-type active layer 435 formed at a center of the active layer 435 that is positioned under the gate electrode 431 . At this time, electric current may flow from the source electrode 436 to the drain electrode 437 through the channel. [0101] Since the active layer 435 may be a P type region at both sides between the source and drain electrodes 436 and 437 , holes formed in the P type active layer 435 may push electrons toward a center of the N type active layer 435 . [0102] The N type electrons formed at a center of the active layer 435 may migrate quickly to the P type active layer 435 having the holes. This is caused by a characteristic in which high-mobility holes of surface charges move from the P type active layer 435 to the N type active layer 435 and accordingly, current mobility may be greatly improved. [0103] Due to a significant introduction of electrons from the doping region 438 having N type dopants into the drain electrode 437 having P type dopants, there is an increase in current density through the channel provided in the active layer 435 . [0104] Since the channel formed in the active layer 435 is proportional to the voltage applied to the gate electrode 431 , as the voltage applied to the gate electrode 431 increases, the depletion layer formed in the channel and electron introduction may be increased in proportion to the applied voltage. [0105] It may be assumed that “R 1 ” denotes resistance formed in the center of the active layer 435 doped with the P type ions when the voltage is applied to the gate electrode 431 . Also, it may be assumed that “R 2 ” denotes resistance formed adjacent to the source electrode 436 , and “R 3 ” denotes resistance formed in the active layer 435 . [0106] It should be noted that the respective resistances are based on theoretical analysis not shown in the drawings. [0107] When R 1 +R 2 +R 3 =Rs, the series resistance (Rs) of the active layer 435 formed of amorphous silicon may be reduced. [0108] Accordingly, it can be appreciated that the active layer 435 may be doped with the N type and P type ions, respectively, thereby reducing the resistance (Rs) and improving a characteristic of current drift. Also, owing to improvement of the characteristic of the current drift, a charge accumulation time may be reduced and at the same time, a high current density may be maintained, thereby increasing a response speed of the current-driven light emitting display. [0109] The present disclosure has described various embodiments, which may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.
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