Inkjet printing system and driving method thereof

An inkjet printing system is provided, which comprises: a stage on which a substrate including at least two alignment keys is mounted; an inkjet head device disposed above the stage; and an alignment key sensing device disposed above the stage, wherein the inkjet head device comprises a head unit including an inkjet head, and a supporting unit which supports the head unit and scanning the substrate in a first direction, and wherein the alignment key sensing device comprises: at least two alignment key sensors for sensing positions of the alignment keys; a sensor supporting unit for supporting the at least two alignment key sensors; and a sensor position adjustment device for adjusting positions of the alignment key sensors with respect to the alignment key sensing device.

BACKGROUND OF THE INVENTION

(a) Field of the Invention

The present invention relates to an inkjet printing system and a driving method of the inkjet printing system. More particularly, the present invention relates to an inkjet printing system for precisely forming color filters or light emitting members on a substrate and a driving method of the inkjet printing system.

(b) Description of the Related Art

Inkjet printing systems are used for forming organic light emitting members of organic light emitting displays (“OLED”s), color filters and alignment layers for liquid crystal displays (“LCD”s), and so on.

The inkjet printing systems for forming the color filters, alignment layers, or organic light emitting members include a head unit and an inkjet head attached to the head unit. The inkjet head has a plurality of nozzles. Thereby, the inkjet printing systems deposit ink or other material through the nozzles into desired areas on an insulating substrate to form the colors filters, alignment layers, or organic light emitting members.

At this time, for accurately depositing the inks or other material, alignment of the inkjet head is required.

As a size of a mother glass which is divided into a plurality of cells respectively used as substrates for panels of display devices becomes larger, the number of cells is increased and thereby the time for aligning the head unit and the inkjet head increases.

BRIEF SUMMARY OF THE INVENTION

According to an exemplary embodiment of the present invention, an inkjet printing system comprises: a stage on which a substrate including at least two alignment keys is mounted; an inkjet head device disposed above the stage; and an alignment key sensing device disposed above the stage, wherein the inkjet head device comprises a head unit including an inkjet head, and a supporting unit which supports the head unit and scanning the substrate in a first direction, and wherein the alignment key sensing device comprises: at least two alignment key sensors for sensing positions of the alignment keys; a sensor supporting unit for supporting the at least two alignment key sensors; and a sensor position adjustment device for adjusting positions of the alignment key sensors with respect to the alignment key sensing device.

The sensor position adjustment device may move the alignment key sensors so that a straight line connecting the at least two alignment key sensors may be substantially vertical to the first direction.

The sensor position adjustment device may move the alignment key sensors in two directions which are substantially parallel to a surface of the stage and are substantially vertical to each other with respect to the alignment key sensing device.

The inkjet head device may further comprise a horizontal transporting portion that moves the head unit in a second direction which is substantially perpendicular to the first direction.

The alignment key sensing device may further comprise at least two sensor transporting portions moving the at least two alignment key sensors in a second direction which is substantially perpendicular to the first direction.

According to another exemplary embodiment of the present invention, an inkjet printing system comprises: a stage on which a substrate is mounted; a head unit disposed above the stage; a supporting unit supporting the head unit and scanning the substrate in a first direction; and a horizontal transporting portion moving the head unit according to the supporting unit, wherein the head unit comprises at least one inkjet head, and a head position adjustment device adjusting a position of the inkjet head with respect to the head unit.

The head position adjustment device may move the inkjet head in two directions which are substantially parallel to a surface of the stage and are substantially vertical to each other with respect to the head unit.

The head position adjustment device may adjust the position of the inkjet head while the supporting unit scanning the substrate.

According to another exemplary embodiment of the present invention, an inkjet printing system comprises: a stage on which a substrate is mounted; a head unit which is disposed above the stage and comprises at least one inkjet head; an upper sensor disposed above the stage; a supporting unit supporting the head unit and the upper sensor and scanning the substrate in a first direction; a horizontal transporting portion moving the head unit according to the supporting unit; a sensor transporting portion moving the upper sensor according to the supporting unit; and a lower sensor disposed outside of the stage.

The inkjet head may comprise a plurality of nozzles, and the lower sensor may sense at least one of a position of the nozzles, a distance between the nozzles, and an inclination angle of the inkjet head.

According to an exemplary embodiment of the present invention, an aligning method of an inkjet printing system comprising: a stage; an inkjet head device including a head unit and a supporting unit supporting the head unit; and an alignment key sensing device including at least two alignment key sensors, a sensor supporting unit supporting the at least two alignment key sensors, and a sensor position adjustment device, comprises: mounting a substrate including at least two alignment keys on the stage; sensing the alignment keys using the alignment key sensors and aligning the substrate on the stage; examining a first direction in which the supporting unit scans the substrate and ink is printed; adjusting positions of the alignment key sensors with respect to the alignment key sensing device using the sensor position adjustment device; and realigning the substrate.

The adjusting positions of the alignment key sensors may comprise adjusting the sensor position adjustment device so that a straight line connecting the at least two alignment key sensors may be substantially vertical to the first direction.

The adjusting positions of the alignment key sensors may comprise moving the alignment key sensors in two directions which are substantially parallel to a surface of the stage and are substantially vertical to each other with respect to the alignment key sensing device.

The inkjet head device may further comprise a horizontal transporting portion that moves the head unit in a second direction which is perpendicular to the first direction.

The alignment key sensing device may further comprise at least two sensor transporting portions moving the at least two alignment key sensors in a second direction which is substantially perpendicular to the first direction.

According to another exemplary embodiment of the present invention, an aligning method of an inkjet printing system comprising: comprising: a stage; a head unit including at least one inkjet head and a head position adjustment device; and a supporting unit supporting the head unit, comprises: mounting a substrate on the stage; determining a first direction to print on the substrate; printing on the substrate driving the inkjet head and the supporting unit; and reducing an error distance between the first direction and a printed direction by adjusting a position of the inkjet head with respect to the head unit using the head position adjustment device.

The printing on the substrate and the adjusting of the position of the inkjet head with the head position adjustment device may be performed simultaneously.

The adjusting of the position of the inkjet head may comprise moving the inkjet head in two directions which are substantially parallel to a surface of the stage and are substantially vertical to each other with respect to the head unit.

According to another exemplary embodiment of the present invention, an aligning method of an inkjet printing system comprising: a stage; a head unit including at least one inkjet head which includes a plurality of nozzles; an upper sensor; a supporting unit supporting the head unit and the upper sensor; a horizontal transporting portion moving the head unit according to the supporting unit; a sensor transporting portion moving the upper sensor according to the supporting unit; and a lower sensor disposed outside of the stage, comprises: mounting a substrate on the stage; determining a reference position by matching positions of the upper sensor and the lower sensor; sensing at least one of a position of the nozzles, a distance between the nozzles, and an inclination angle of the inkjet head using the lower sensor; sensing a target position to be printed using the upper sensor; and moving the inkjet head above the target position to be printed.

The method may further comprise aligning the substrate on the stage using the upper sensor.

The moving of the inkjet head above the target position to be printed may comprise referring to information about at least one of the target position to be printed, the position of the nozzles, the distance between the nozzles, and the inclination angle of the inkjet head.

At least one of the lower sensor and the upper sensor may be a CCD camera.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. Exemplary embodiments of inkjet printing systems and driving methods of the inkjet printing systems according to the present invention will now be described with reference toFIGS. 1 to 4.

FIG. 1is a perspective view of an exemplary embodiment of an inkjet printing system according to the present invention,FIG. 2is a bottom view of an exemplary head unit of an exemplary embodiment of an inkjet printing system according to the present invention,FIG. 3is a view demonstrating formation of color filters using an exemplary inkjet head of an exemplary embodiment of an inkjet printing system according to the present invention, andFIG. 4illustrates a state of depositing ink for forming color filters using an exemplary inkjet head of an exemplary embodiment of an inkjet printing system according to the present invention.

Referring toFIGS. 1 to 4, an inkjet printing system includes a stage500on which a mother glass201is disposed, a head unit700spaced a predetermined distance from the stage500in a vertical direction, and a transporting unit300for transporting the head unit700to a predetermined position.

The mother glass201may be substantially planar to be supported by a substantially planar stage500, and is divided to produce insulating substrates210used for panels of display devices, such as color filter panels of liquid crystal display (“LCD”) devices, as will be further described below. Alternatively, the stage500may be provided with a panel for forming display panels of organic light emitting displays (“OLED”s), as will also be further described below.

A light blocking member220, having a plurality of openings225, is formed on each of the insulating substrates210.

A plurality of alignment keys240and240′, respectively comprising alignment keys241to248and241′ to248′, are formed on opposite sides of each of the respective insulating substrates210, that is, at areas outside of the light blocking member220.

By example only, the insulating substrates210and corresponding light blocking members220may each have a substantially rectangular shape with first and second parallel opposite sides. The alignment keys240are formed on the first side of each substrate210in a line at a predetermined interval, and the alignment keys240′ are formed on the second side opposite to the first side of each substrate210, and the alignment keys240′ face the corresponding alignment keys240. The line of alignment keys240and the line of alignment keys240′ may extend substantially parallel to the first and second sides of each insulating substrate210. Alternatively, the lines of alignment keys240and240′ may extend adjacent third and fourth sides of each insulating substrate210and each light blocking member220.

When the light blocking member220is made of an organic high molecular compound, the alignment keys240and240′ are formed by exposing and developing the organic material as a positive or negative type. However, if the light blocking member220is made of inorganic materials, and after depositing a separate photoresist film, then the alignment keys240and240′ are formed on the material of the light blocking member220by exposing, developing, and etching the inorganic material. The alignment keys240and240′ may be of a circular shape, a cross shape, or other various shapes.

The head unit700includes an inkjet head400and an alignment key position sensor600.

The inkjet head400has a long bar-like shape, however it is not limited to such shape. The inkjet head400includes a plurality of nozzles410provided on substantially an entire lower surface thereof. Ink5for forming color filters for a color filter panel is deposited through the nozzles410on the substrate210. In the event the inkjet printing system is used for providing an alignment layer or organic light emitting members to a substrate, the nozzles410may provide materials, other than ink5, to the substrate on the stage500.

The inkjet head400is inclined to a predetermined angle θ with respect to the Y direction. For example, since a nozzle pitch D (a distance between adjacent nozzles410) is different from a pixel pitch P (a distance between adjacent pixels to be printed), by rotating the inkjet head400to the predetermined angle θ, an interval between adjacent ink deposits through the nozzles410and the pixel pitch P may coincide. Thus, substrates used for a display having a particular pixel pitch P may be accommodated by rotating the inkjet head400to the appropriate angle θ for proper ink deposition regardless of the difference between the nozzle pitch D and the pixel pitch P.

InFIG. 2, one head unit700is shown, however there may be a plurality of head units700. Also, while the illustrated head unit700includes only one inkjet head400, a plurality of inkjet heads400for forming color filters for colors such as, but not limited to, red, green, and blue colors may be provided.

The alignment key position sensor600senses positions of the alignment keys240and240′ and outputs sensing signals corresponding to the sensed positions to a transporting unit controller (not shown). The alignment key position sensor600may be, for example, a charged coupled device (“CCD”) camera.

The transporting unit300includes a supporting unit310to space the head unit700from the substrates210by a predetermined distance, a transporting portion330for transporting the head unit700in X and Y directions, and an elevating unit340for elevating the head unit700.

The number of alignment keys240and240′ may be defined based on screen resolutions of the display devices manufactured or the number of nozzles410.

For example, when an LCD having a screen resolution of 1024×768 is manufactured on the substrate210and the number of nozzles410of the inkjet head400is 128, then a color filter group having 128×768 color filters is formed through the nozzles410of the inkjet head400by one scan of the head unit700in the X direction by the transporting portion330of the transporting unit300. That is, the color filters of 128×768 are formed into openings225of the light blocking member220formed in a pixel block of 128×768 pixels, respectively. As a result, since one scan of the head unit700does not form all color filters on all pixels of the LCD, a plurality of scans of the head unit700are required. In the LCD, the total scanning number is eight (128×8=1024).

Before every scanning procedure of the head unit700in the X direction for forming the color filters, an alignment procedure of the head unit700is performed using the alignment keys240and240′. Therefore, for example, when the LCD having a screen resolution of 1024×768 is manufactured, the alignment procedure is repeated eight times, and thus the number of alignment keys240and240′ for each respective insulating substrate210is required to be eight. In other words, the total number of alignment keys240and240′ formed on opposite sides of each respective substrate210is sixteen. Referring toFIG. 1, since the total number of substrates210formed on the mother glass201is nine, the total number of the alignment keys240and240′ formed on the mother glass201is 144 (16×9=144). The total number of alignment keys240and240′ formed on the mother glass201would thus depend on the total number of substrates210formed on the mother glass201, as well as on the screen resolution of the LCD and the number of nozzles410.

Next, an exemplary method for forming the color filters on the substrate210using an exemplary embodiment of an inkjet printing system according to the present invention will be further described.

The head unit700is arranged over the corresponding substrate210by the transporting portion330and elevating portion340of the transporting unit300.

The head unit700is transported in the X direction by the transporting portion330of the transporting unit300, and the alignment key position sensor600is operated. The sensor600generates alignment key position sensing signals corresponding to the alignment keys241and241′, respectively, and outputs the alignment key position sensing signals to the transporting unit controller (not shown).

The transporting unit controller compares the sensing signals from the alignment key position sensor600with the current position of the head unit700, generates control signals for transporting the head unit700to the scanning start position, and outputs the control signals to the transporting unit300.

Thereby, the transporting portion330of the transporting unit300arranges the head unit700to the scanning start position based on the control signals from the transporting unit controller. Next, by operating the transporting portion330of the transporting unit300and the nozzles410of the inkjet head400, the inkjet printing system transfers the head unit700in the X direction, and thereby, as shown inFIG. 4, the color filters are formed on pixels of one pixel block by ink5deposited into the openings225of the light blocking member220within the one pixel block, where a pixel block includes a matrix of pixels, such as a subset of the total number of pixels for the display.

When the scanning of the head unit700for forming the color filters is finished, the transporting portion330of the transporting unit300repeats the aligning procedure of the head unit700for the next scan, to form color filters on the next pixel block.

In the same way as described above, the sensor600senses positions of the alignment keys242and242′ adjacent to the alignment keys241and241′, respectively, and generates alignment key position sensing signals to output to the transporting unit controller. The transporting unit controller compares positions of the alignment keys242and242′, determined by the sensing signals from the sensor600, with the current position of the head unit700, and generates control signals for transporting the head unit700to the scanning start position and outputs the control signals to the transporting unit300. Thereby, the head unit700at the transporting unit300is moved in the X or Y direction to be positioned at the next scanning start position.

Then, another scan of the head unit700is performed to form color filters in pixels of the next pixel block.

Whenever forming the color filters in a corresponding pixel block, the position sensing operation of the alignment key position sensor600and the position alignment and ink deposition operations of the head unit700are repeated, to form all the color filters.

When all the color filters are formed on the corresponding substrate210, the head unit700is arranged over the next substrate210by the transporting unit300and the color filter forming operation is repeated on the next substrate210. As a result, the color filters are formed on all the substrates210of the mother glass201.

By the aligning operation of the head unit700using the alignment keys240and240′ and the sensor600, the color filters are formed on the desired positions of the substrates210. Accordingly, the reliability of forming the color filters at appropriate locations on the substrates210is increased and the manufacturing cost is decreased.

Next, referring toFIGS. 5 to 7, another exemplary embodiment of an inkjet printing system according to the present invention will be described.

The structures and operations of the inkjet printing system are substantially the same as those of the inkjet printing system shown inFIGS. 1 to 4.

As compared withFIGS. 1 to 4, the elements performing the same operations are indicated by the same reference numerals, and detailed descriptions thereof are omitted.

FIG. 5is a perspective view of another exemplary embodiment of an inkjet printing system according to the present invention,FIG. 6is a bottom view of an exemplary head unit of another exemplary embodiment of an inkjet printing system according to the present invention, andFIG. 7is a block diagram of an exemplary alignment key sensing unit of another exemplary embodiment of an inkjet printing system according to the present invention.

As compared withFIG. 1, an inkjet printing system shown inFIG. 5further includes an alignment key sensing unit1000. In addition, as shown inFIG. 5, a head unit700′ does not include the alignment key position sensor600as compared toFIG. 1.

As shown inFIGS. 5 to 7, the alignment key sensing unit1000includes a stage1100, an alignment key position sensor1200attached to the stage1100, a memory1300connected to the alignment key position sensor1200, and a transporting unit controller1400connected to the memory1300.

As illustrated, the stage1100may have a similar size and shape to those of the mother glass201, but the size and shape are not limited thereto.

The alignment position sensor1200is a CCD camera movable in X and Y directions of the stage1100by a separate controller (not shown). For movement of the alignment position sensor1200, moving members (not shown) may be provided on the stage1100.

Alternatively, the alignment key position sensor1200may be fixed on the stage1100and the position of the sensor1200may be varied by movement of the stage1100. In this case, the size and shape of the stage1100may be dissimilar to those of the mother glass201, and, for example, the size of the stage1100may be smaller than that of the mother glass201.

The alignment key position sensor1200transfers in the X or Y direction and, at the same time, senses positions of all alignment keys240and240′ formed on the mother glass201to generate a plurality of alignment key position sensing signals corresponding to the position of the respective alignment keys240and240′. For example, each sensing signal may have X and Y coordinate values. InFIG. 5, one alignment key position sensor1200is shown, but more than one alignment key position sensors1200may be provided in alternative embodiments.

As illustrated, the alignment key sensing unit1000is positioned over the head unit700′, however, it may be positioned between the head unit700′ and the mother glass201for sensing purposes, and movable there between so as not to interfere with the printing process.

The memory1300stores the respective alignment key position sensing signals from the sensor1200. The memory1300may be a random access memory (“RAM”).

By using current position signals of the head unit700′ and the sensed position sensing signals of the corresponding alignment keys240and240′ from the memory1300, the transporting unit controller1400generates control signals for controlling the position of the head unit700′, and outputs the control signals to the transporting unit300.

An exemplary forming method of the color filters using another exemplary embodiment of the inkjet printing system according to the present invention will now be described.

The inkjet printing system transfers the alignment key position sensor1200of the alignment key sensing unit1000in the X or Y direction, to sense positions of all the alignment keys240and240′ formed on the mother glass201for generating the alignment key position sensing signals corresponding to the alignment keys240and240′. The alignment key position sensing signals are stored into the memory1300.

For a first scan of the head unit700′ for forming the color filters on a corresponding substrate210, the transporting unit controller1400reads the current position signals of the head unit700′ and the stored alignment key position sensing signals of corresponding alignment keys241and241′, and compares the current position of the head unit700′ with the positions of the alignment keys241and241′. The transporting unit controller1400generates a control signal for transferring the head unit700′ to a scanning start position based on a comparison result between the current position of the head unit700′ and the positions of the alignment keys241and241′ and outputs the control signal to the transporting unit300.

The transporting portion330of the transporting unit300transfers the head unit700′ to the scanning start position in accordance with the control signal from the controller1400, and moves the head unit700′ in the X direction to form the color filters in pixels of a first pixel block by depositing ink5into openings225of a light blocking member220.

By repeating the above-described operations, the color filters are formed in a second pixel block adjacent to the first pixel block.

That is, the transporting unit controller1400reads the current position signals of the head unit700′ and the stored alignment key position sensing signals of corresponding alignment keys242and242′ adjacent to the alignment keys241and241′, respectively, and compares the current position of the head unit700′ with the positions of the alignment keys242and242′. The transporting unit controller1400generates a control signal to move the head unit700′ to a scanning start position based on a comparison result and outputs the control signal to the transporting unit300.

The transporting portion330of the transporting unit300transfers the head unit700′ to the scanning start position in accordance with the control signal from the controller1400, and moves the head unit700′ in the X or Y direction to form the color filters in pixels of the second pixel block by depositing ink5into openings225of a light blocking member220.

The forming operations of the color filters are repeated several times, and thereby the color filters are formed in all the pixels on the corresponding substrate210. For example, when manufacturing the LCD having a screen resolution of 1024×768, the forming operation of the color filters as described above is repeated eight times. When the formation of color filters is finished with respect to one substrate210, the inkjet printing system transfers the head unit700to another substrate adjacent to the substrate210using the transporting unit300, and repeats the forming operations of the color filters. Thereby, the color filters are successively formed on all the substrates210formed on the mother glass201.

Since the inkjet printing system ofFIGS. 5 to 7aligns the position of the head unit700using the alignment key sensing unit1000and the alignment keys240and240′, the color filters are precisely formed on the desired positions of the substrates210. Accordingly, reliability is increased and the manufacturing cost is decreased.

In addition, in the above embodiment of the inkjet printing system ofFIGS. 5 to 7, since the alignment key position sensor1200attached to the alignment key sensing unit1000separately from the head unit700senses the positions of all the alignment keys240and240′ to generate the sensing signals and stores the sensing signals into the memory1300, and the inkjet printing system uses the stored sensing signals for aligning the position of the head unit700, the position sensing operation of the alignment keys240and240′ is not necessary whenever the position of the head unit700is aligned. Therefore, the time for forming the color filters is reduced.

In the exemplary embodiments described above, the head unit700or700′ moves as a result of the sensing operation of the alignment key position sensor600or1200to align the inkjet head400, however, the inkjet head400along with the head unit700or700′ or the inkjet head400may move in response to a separate controller.

In addition, in the exemplary embodiments described herein, the head unit700or700′ moves as a result of the sensing operation of the alignment key position sensor600or1200to align the head unit700or700,′ however, in alternative embodiments, the stage500may move in response to a separate transporting unit.

In the exemplary embodiments of the inkjet printing system, the head units700and700′ may be further aligned concerning position information of the mother glass201with respect to the stage500using separate alignment keys.

Then, an inkjet printing system according to another exemplary embodiment of the present invention in which aligning process are precise and speedy using the above various aligning methods will be described with reference toFIG. 17toFIG. 22sequentially. As compared withFIG. 1toFIG. 4, elements performing the same operations are indicated by the same reference numerals, and detailed descriptions thereof are omitted.

First, an inkjet printing system and an aligning method thereof according to an exemplary embodiment of the present invention will be described with reference toFIG. 17andFIG. 18.

FIG. 17is a perspective view of an inkjet printing system according to an exemplary embodiment of the present invention, andFIG. 18is a plane view of the inkjet printing system shown inFIG. 17.

An inkjet printing system according to an exemplary embodiment of the present invention includes a stage500on which a substrate202is mounted, an inkjet head device1600including a head unit700and a transporting unit300, and an alignment key sensing device1500.

At least two substrate alignment keys2400aand2400bfor aligning the substrate202with respect to the stage500are formed at both side regions of the substrate202.

The head unit700includes at least one inkjet head (not shown), and the transporting unit300includes a supporting unit310, a horizontal transporting portion330, and an elevating unit340. In the present embodiment, the supporting unit310extends in the X direction so that the horizontal transporting portion330may move in the X direction. The supporting unit310may move while scanning the substrate202in the Y direction. Alternatively, the stage500may move in the Y direction with the supporting unit310fixed.

The alignment key sensing device1500includes a first alignment key sensor1200a, a second alignment key sensor1200b, a first sensor transporting portion1030a, a second sensor transporting portion1030b, a sensor supporting unit1010, and a sensor position adjustment device (not shown).

The sensor supporting unit1010locates the first and second sensor transporting portions1030aand1030bat a predetermined distance above the substrate202, and the sensor supporting unit101may move in the Y direction while scanning the substrate202. Alternatively, the stage500may move in the Y direction with the sensor supporting unit1010fixed.

The first and second sensor transporting portions1030aand1030bmove the first and second alignment key sensors1200aand1200bin the X direction.

The first and second alignment key sensors1200aand1200bgenerate sensing signals by sensing the positions of the substrate alignment keys2400aand2400b.

The sensor position adjustment device (not shown) moves the first and second alignment key sensors1200aand1200bin the X and Y directions with respect to the first and second sensor transporting portions1030aand1030b. The sensor position adjustment device (not shown) may be attached to the first and second alignment key sensors1200aand1200b.

Then, a method of adjusting positions of the first and second alignment key sensors1200aand1200bwhen aligning a substrate202on the stage500in the inkjet printing system described above will be described with reference toFIG. 17andFIG. 18.

First, a substrate202is mounted and aligned on the stage500according to a sensing signal obtained by the first and second alignment key sensors1200aand1200bwhich sense the positions of the substrate alignment keys2400aand2400b. At this stage, the straight line connecting the centers of the first and second alignment key sensors1200aand1200bis parallel to the first alignment line10cshownFIG. 18, and the straight line connecting the two substrate alignment keys2400aand2400bis also substantially parallel to the first alignment line10c.

Next, ink is discharged onto the substrate202by driving the head unit700and the nozzles (not shown) while moving the transporting unit300of the inkjet head device1600in the Y direction or moving the stage500in the Y direction. At this stage, the direction in which the ink is printed may not be the predetermined direction even though the stage202has been aligned on the stage500using the first and second alignment key sensors1200aand1200b. This case may be caused when the alignment keys2400aand2400bof the substrate202are not properly positioned or when the second alignment line10h, which is the direction the supporting unit310of the inkjet head device1600extends and coincides with the X direction, is not parallel to the first alignment line10cof the first and second alignment key sensors1200aand1200bas shown inFIG. 18. In this case, the direction determined to print ink on the substrate202is not the same as the moving direction of the head unit700.

By adjusting the sensor position adjustment device (not shown), the positions of the first and second alignment key sensors1200aand1200bare moved in the X and Y directions, and accordingly, the moving direction of the head unit700in the Y direction may coincide with the direction to print. The straight line connecting the first and second alignment key sensors1200aand1200bmay coincide with the third alignment line10c′ which is parallel to the second alignment line10hof the supporting unit310as shown inFIG. 18.

Next, the substrate202is realigned on the stage500while sensing the position of the substrate alignment keys2400aand2400busing the first and second alignment key sensors1200aand1200bwhich have been realigned.

In this way, the substrate202may be aligned and mounted on the stage500and an ink may be printed on the substrate202exactly in a desired direction only with a simple adjustment of positions of the first and second alignment key sensors1200aand1200bwithout changing arrangements of the inkjet printing system.

According to another embodiment of the present invention, besides the first and second alignment key sensors1200aand1200b, other alignment key sensors attached to the sensor supporting unit1010may be further comprised.

Then, an inkjet printing system and an aligning method thereof according to another embodiment of the present invention will be described with reference toFIG. 17andFIG. 19described above.

FIG. 19is a plane view of an inkjet printing system according to an exemplary embodiment of the present invention.

An inkjet printing system according to the present embodiment has the similar structure to the inkjet printing system shown inFIG. 17with the alignment key sensing device.

The head unit700further comprises a head position adjustment device (not shown) that may move the inkjet head in the X and Y directions with respect to the head unit700.

When a mother substrate201is mounted on the stage500and performing inkjet printing by driving the head unit700and the nozzles (now shown), the moving direction of the head unit700in the Y direction may not coincide with the desired printed direction. For example, as shown inFIG. 19, the mother substrate201or the stage500may not be parallel to the printing direction10aof the head unit700. The position of the inkjet head (not shown) may be adjusted while printing by using the head position adjustment device (not shown) such that the moving direction of the inkjet head (not shown) may coincide with the desired printing direction10a′. Accordingly, the trace50of the dropped ink is formed in the desired printing direction10a′.

Besides, even in the case where errors are generated in the route of the head unit700during a printing process, ink may be dropped onto the exact position of the mother substrate201by adjusting the position of the head unit700in the X and Y directions.

Next, an inkjet printing system and an adjusting method thereof according to another embodiment of the present invention will be described with reference toFIG. 20toFIG. 22

FIG. 20is a perspective view of an inkjet printing system according to an exemplary embodiment of the present invention, andFIG. 21is a bottom view of a head unit of the inkjet printing system shown inFIG. 20, andFIG. 22is an algorithm showing a method of aligning an inkjet head using upper and lower sensors of the inkjet printing system shown inFIG. 20.

An inkjet printing system according to the present embodiment also has the similar structure to the inkjet printing system shown inFIG. 17.

Referring toFIG. 20, an inkjet printing system according to an exemplary embodiment of the present invention includes a stage500on which a mother substrate201is mounted, a supporting unit310, a horizontal transporting portion330and a sensor transporting portion1030cwhich are attached to the supporting unit310, an elevating unit340and a head unit700attached to the horizontal transporting portion330, an upper sensor attached to the bottom of the sensor transporting portion1030c, and a lower sensor1200dprovided outside of the stage500.

Referring toFIG. 21, the head unit700includes at least one inkjet head300, which includes a plurality of nozzles410disposed on the bottom surface of the inkjet head400. The inkjet head400may be inclined at a predetermined angle θ with respect to the Y direction.

The sensor transporting portion1030cis attached to the supporting unit310and may move in the X direction, and the lower sensor1200dmay move in the X and Y directions.

The description of the stage500, the supporting unit310, the horizontal transporting portion330, the elevating unit340, and the head unit700is the same as the description of the same elements of the previous embodiment.

Then, an exemplary method of aligning the nozzles410of the inkjet head400exactly to a position where ink is to be dropped will be described with reference toFIG. 20toFIG. 22.

First, the upper and lower sensors1200cand1200dare moved so that the positions of the upper and lower sensors1200cand1200dmay be coincident, which is the S1step ofFIG. 22. The coincident position of the lower and upper sensors1200cand1200dis stored as a reference position.

Next, the position of the nozzles410of the inkjet head400, the distances between the nozzles410, and the inclination angle θ of the inkjet head400with respect to the Y direction are measured using the lower sensor1200d, which corresponds to S2step ofFIG. 22.

Next, the upper sensor1200cchecks the alignment sate of the mother substrate201with respect to the head unit700and the supporting unit310and senses coordinates of the target position Pt where ink is to be dropped or an alignment key240thereof with respect to the reference position, which corresponds to the S3step ofFIG. 22.

Next, the supporting unit310and the horizontal transporting portion330are moved so that the nozzles410of the inkjet head400are positioned above the target position Pt where ink is to be dropped, which corresponds to the S4step ofFIG. 22. At this stage, information about the coordinates of the target position Pt obtained by the upper sensor1200c, information about the positions, distances, and inclination angles of the inkjet head400and the nozzles410obtained by the lower sensor1200dmay be used.

The second and third steps S2and S3may be changed.

In this way, the nozzles410of the inkjet head700may be located on the exact position to be printed by using the lower and upper sensors1200cand1200dwithout performing printing.

According to another exemplary embodiment, the head unit700of the inkjet printing system shown inFIG. 20may comprise a plurality of inkjet heads400. The lower sensor1200dmay be used to sense the positions of the plurality of inkjet heads400and determine the error distances in the X or Y direction between the inkjet heads400. The error distance in the X direction between the plurality of inkjet heads400may be compensated by adjusting the distances between the inkjet heads400, and the error distance in the Y direction may be compensated by adjusting the dropping time of ink. In this way, by detecting the position of the inkjet heads400using the lower sensor1200dthat may move in the X and Y directions, it is possible to compensate error distances between the inkjet heads400without practicing inkjet printing.

The first and second alignment key sensors1200aand1200b, and the upper and lower sensors1200cand1200dof the inkjet printing system shown inFIG. 17toFIG. 21may be, for example, CCD cameras.

Substrates manufactured by using an inkjet printing system according to embodiments as such described above may be a display panel of an LCD or an OLED. When a display panel for an OLED or an LCD is produced, the inkjet printing system forms color filters for an LCD or organic light emitting members for an OLED.

Next, an LCD using an exemplary panel manufactured by the exemplary embodiments of the inkjet printing system according to the present invention will be described with reference toFIGS. 8 to 13. The exemplary panel may be manufactured by either of the inkjet printing systems described with respect toFIGS. 1 to 4andFIGS. 5 to 7.

FIG. 8is a layout view of an exemplary TFT array panel of exemplary embodiments of an LCD according to the present invention, andFIG. 9is a layout view of an exemplary color filter panel of exemplary embodiments of an LCD according to the present invention.FIG. 10is a layout view of exemplary embodiments of the LCD having the exemplary TFT array panel and the exemplary color filter panel shown inFIGS. 8 and 9according to the present invention,FIG. 11is a sectional view of the exemplary LCD shown inFIG. 10taken along line XI-XI′, andFIG. 12shows sectional views of the exemplary LCD shown inFIG. 10taken along line XII-XII′.

As shown inFIGS. 8 to 13, an LCD includes a TFT array panel100, a color filter panel200opposite the TFT array panel100, and an LC layer3having LC molecules disposed between the TFT array panel100and the color filter panel200.

First, the TFT array panel100will be described with reference toFIGS. 8 and 10to12.

A plurality of gate lines121and a plurality of storage electrode lines131are formed on an insulating substrate110of a material such as, but not limited to, transparent glass or plastic.

The gate lines121transmit gate signals and extend substantially in a transverse direction, a first direction. Each of the gate lines121includes a plurality of gate electrodes124projecting downward, in a second direction, and an end portion129having a large area for contact with another layer or an external driving circuit. A gate driving circuit (not shown) for generating the gate signals may be mounted on a flexible printed circuit (“FPC”) film (not shown), which may be attached to the insulating substrate110, directly mounted on the insulating substrate110, or integrated onto the insulating substrate110. Alternatively, the gate lines121may extend to be connected to a driving circuit that may be directly integrated on the insulating substrate110.

The storage electrode lines131are supplied with a predetermined voltage, and each of the storage electrode lines131includes a stem extending substantially parallel to the gate lines121in the first direction and a plurality of pairs of storage electrodes133aand133bbranched from the stems and extending in a second direction, substantially perpendicular to the first direction. Each of the storage electrode lines131is disposed between two adjacent gate lines121, and a stem for each pixel area is positioned closer to one of the two adjacent gate lines121. Each of the storage electrodes133aand133bhas a fixed end portion connected to the stem and a free end portion disposed opposite thereto on an opposite side of the pixel area. The fixed end portion of the storage electrode133ahas a large area, and the free end portion thereof is bifurcated into a linear branch and a curved branch. However, the storage electrode lines131may have various shapes and arrangements and are not limited to the illustrated exemplary embodiments.

The gate lines121and the storage electrode lines131are preferably made of an aluminum Al-containing metal such as Al and an Al alloy, a silver Ag-containing metal such as Ag and an Ag alloy, a copper Cu-containing metal such as Cu and a Cu alloy, a molybdenum Mo-containing metal such as Mo and a Mo alloy, chromium Cr, tantalum Ta, or titanium Ti. The gate lines121and the storage electrode lines131may alternatively have a multi-layered structure including two conductive films (not shown) having different physical characteristics. If a multi-layered structure is employed, one of the two films is preferably made of a low resistivity metal such as an Al-containing metal, an Ag-containing metal, and a Cu-containing metal for reducing signal delay or voltage drop and the other film is preferably made of a material such as a Mo-containing metal, Cr, Ta, or Ti, which have good physical, chemical, and electrical contact characteristics with other materials such as indium tin oxide (“ITO”) or indium zinc oxide (“IZO”). Examples of the combination of the two films in a multi-layered structure include a lower Cr film and an upper Al (alloy) film and a lower Al (alloy) film and an upper Mo (alloy) film. However, the gate lines121and the storage electrode lines131may be made of various metals or conductors.

The lateral sides of the gate lines121and the storage electrode lines131are inclined relative to a surface of the insulating substrate110, and the inclination angle thereof ranges about 30 to about 80 degrees.

A gate insulating layer140preferably made of, but not limited to, silicon nitride (SiNx) or silicon oxide (SiOx) is formed on the gate lines121and the storage electrode lines131. The gate insulating layer140may further be formed over exposed portions of the insulating substrate110.

A plurality of semiconductor stripes151preferably made of hydrogenated amorphous silicon (“a-Si”) or polysilicon are formed on the gate insulating layer140. The semiconductor stripes151extend substantially in the longitudinal direction, the second direction parallel with the storage electrodes133aand133b, and become wide near the gate lines121and the storage electrode lines131such that the semiconductor stripes151cover large areas of the gate lines121and the storage electrode lines131. Each of the semiconductor stripes151includes a plurality of projections154branched out toward the gate electrodes124.

A plurality of ohmic contacts, including ohmic contact stripes and islands161and165, are formed on the semiconductor stripes151. The ohmic contact stripes and islands161and165are preferably made of n+ hydrogenated a-Si heavily doped with an N-type impurity such as phosphorous, or they may be made of silicide. Each ohmic contact stripe161includes a plurality of projections163, and the projections163and the ohmic contact islands165are located in pairs on the projections154of the semiconductor stripes151and spaced apart from each other to form a channel on the projections154.

The lateral sides of the semiconductor stripes151and the ohmic contacts161and165are inclined relative to the surface of the insulating substrate110, and the inclination angles thereof are preferably in a range of about 30 to about 80 degrees.

A plurality of data lines171and a plurality of drain electrodes175are formed on the ohmic contacts161and165and the gate insulating layer140.

The data lines171transmit data signals and extend substantially in the longitudinal direction, the second direction, to intersect the gate lines121. The data lines171are insulated from the gate lines121by the gate insulating layer140disposed between the gate lines121and the data lines171. Each data line171also intersects the storage electrode lines131and runs parallel between adjacent pairs of storage electrodes133aand133b. Each data line171includes a plurality of source electrodes173projecting toward the gate electrodes124and being curved like a crescent, and an end portion179having a large area for contact with another layer or an external driving circuit. A data driving circuit (not shown) for generating the data signals may be mounted on an FPC film (not shown), which may be attached to the insulating substrate110, directly mounted on the insulating substrate110, or integrated onto the insulating substrate110. Alternatively, the data lines171may extend to be connected to a driving circuit that may be directly integrated on the insulating substrate110.

The drain electrodes175are separated from the data lines171and disposed opposite the source electrodes173with respect to the gate electrodes124, thus maintaining the channel over the projection154. Each of the drain electrodes175includes a wide end portion and a narrow end portion. The wide end portion overlaps a storage electrode line131and the narrow end portion is partly enclosed by a source electrode173.

A gate electrode124, a source electrode173, and a drain electrode175along with a projection154of a semiconductor stripe151form a TFT having a channel formed in the projection154disposed between the source electrode173and the drain electrode175and between the ohmic contact island165and the projection163of the ohmic contact stripe161.

The data lines171and the drain electrodes175are preferably made of a refractory metal such as Cr, Mo, Ta, Ti, or alloys thereof. However, the data lines171and the drain electrodes175may alternatively have a multilayered structure including a refractory metal film (not shown) and a low resistivity film (not shown). Examples of the multi-layered structure include, but are not limited to, a double-layered structure including a lower Cr/Mo (alloy) film and an upper Al (alloy) film, and a triple-layered structure of a lower Mo (alloy) film, an intermediate Al (alloy) film, and an upper Mo (alloy) film. However, the data lines171and the drain electrodes175may be made of various metals or conductors.

The data lines171and the drain electrodes175have inclined edge profiles with respect to a surface of the insulating substrate110, and the inclination angles thereof range about 30 to about 80 degrees.

The ohmic contacts161and165are interposed only between the underlying semiconductor stripes151and the overlying conductors171and175thereon, and reduce the contact resistance therebetween. Although the semiconductor stripes151are narrower than the data lines171at most places, the width of the semiconductor stripes151becomes large near the gate lines121and the storage electrode lines131as described above, to smooth the profile of the surface, thereby preventing disconnection of the data lines171. The semiconductor stripes151have almost the same planar shapes as the data lines171and the drain electrodes175as well as the underlying ohmic contacts161and165. However, the semiconductor stripes151include some exposed portions, which are not covered with the data lines171and the drain electrodes175, such as portions located over the projections154between the source electrodes173and the drain electrodes175, thus the exposed portions form a channel.

A passivation layer180is formed on the data lines171, the drain electrodes175, and the exposed portions of the semiconductor stripes151. The passivation layer180may be further formed on exposed portions of the gate insulating layer140as shown. The passivation layer180is preferably made of an inorganic or organic insulator and it may have a flat top surface. Examples of the inorganic insulator include, but are not limited to, silicon nitride and silicon oxide. The organic insulator may have photosensitivity and a dielectric constant of less than about 4.0. Alternatively, the passivation layer180may include a lower film of an inorganic insulator and an upper film of an organic insulator such that it possesses the excellent insulating characteristics of the organic insulator while preventing the exposed portions of the semiconductor stripes151from being damaged with the organic insulator.

The passivation layer180has a plurality of contact holes182and185exposing the end portions179of the data lines171and the drain electrodes175, respectively. The passivation layer180and the gate insulating layer140have a plurality of contact holes181exposing end portions129of the gate lines121, a plurality of contact holes183aexposing portions of the storage electrode lines131near the fixed end portions of the storage electrodes133a, and a plurality of contact holes183bexposing the linear branches of the free end portions of the storage electrodes133a.

A plurality of pixel electrodes191, a plurality of overpasses83, and a plurality of contact assistants81and82are formed on the passivation layer180. They are preferably made of a transparent conductor such as ITO or IZO, or a reflective conductor such as Ag, Al, Cr, or alloys thereof, such as for use in a reflective LCD.

The pixel electrodes191are physically and electrically connected to the drain electrodes175through the contact holes185such that the pixel electrodes191receive data voltages from the drain electrodes175. The pixel electrodes191supplied with the data voltages generate electric fields in cooperation with a common electrode270of the opposing color filter panel200supplied with a common voltage, which determine the orientations of liquid crystal molecules (not shown) of a liquid crystal layer3disposed between the two panels100and200. A pixel electrode191and the common electrode270form a capacitor referred to as a “liquid crystal capacitor,” which stores applied voltages after the TFT turns off.

A pixel electrode191overlaps a storage electrode line131including storage electrodes133aand133bfor improving an aperture ratio of each pixel. The pixel electrode191and a drain electrode175connected thereto and the storage electrode line131form an additional capacitor referred to as a “storage capacitor,” which enhances the voltage storing capacity of the liquid crystal capacitor.

The contact assistants81and82are connected to the end portions129of the gate lines121and the end portions179of the data lines171through the contact holes181and182, respectively. The contact assistants81and82protect the end portions129and179and enhance the adhesion between the end portions129and179and external devices, such as a gate driving circuit and a data driving circuit as previously described.

The overpasses83cross over the gate lines121and are connected to the exposed portions of the storage electrode lines131and the exposed linear branches of the free end portions of the storage electrodes133athrough the contact holes183aand183b, respectively, which are disposed opposite each other with respect to the gate lines121. That is, each overpass83spans between two adjacent pixels. Thus, each pixel includes a portion of a first overpass83at a lower portion of the pixel area and a portion of a second overpass83at an upper portion of the pixel area. The storage electrode lines131including the storage electrodes133aand133balong with the overpasses83can be used for repairing defects in the gate lines121, the data lines171, or the TFTs.

A description of the color filter panel200follows with reference toFIGS. 9 to 11.

A light blocking member220, also termed a black matrix, for preventing light leakage is formed on an insulating substrate210made of a material such as transparent glass or plastic.

The light blocking member220has a plurality of openings225that face the pixel electrodes191, and it may have substantially the same planar shape as the pixel electrodes191. Otherwise, the light blocking member220may include a plurality of portions facing the gate lines121and data lines171on the TFT array panel100and a plurality of widened portions facing the TFTs on the TFT array panel100. The light blocking member220functions as side walls for sealing ink5for color filters230therein when manufacturing the color filter panel200using the exemplary embodiments of the inkjet printing system.

A plurality of color filters230are also formed on the substrate210. The color filters230are formed using any of the exemplary embodiments of the inkjet printing system according to the present invention. The color filters230are formed substantially in openings225enclosed by the light blocking member220. Alternatively, the color filters230may extend substantially in the longitudinal direction along the pixel electrodes191. The color filters230may each represent one of the colors such as red, green, and blue colors, although other colors are within the scope of these embodiments.

An overcoat250is formed on the color filters230and the light blocking member220. The overcoat250is preferably made of an (organic) insulator for preventing the color filters230from being exposed and for providing a flat surface. Alternatively, the overcoat250may be omitted.

A common electrode270is formed on the overcoat250. The common electrode270is preferably made of a transparent conductive material such as, but not limited to, ITO and IZO.

Alignment layers11and21that may be horizontal or vertical alignment layers are coated on inner surfaces of the panels100and200, and polarizers12and22are provided on outer surfaces of the panels100and200so that their polarization axes may cross perpendicularly with respect to each other and one of the polarization axes may be parallel to the gate lines121. Alternatively, one of the polarizers12and22may be omitted when the LCD is a reflective LCD.

The LCD may further include at least one retardation film (not shown) for compensating the retardation of the LC layer3.

The LCD may further include a backlight unit (not shown) for supplying light to the LC layer3through the polarizers12and22, the retardation film, and the panels100and200.

Now, an exemplary method of manufacturing the exemplary TFT array panel shown inFIGS. 8 to 12will be described.

A metal film is sputtered on an insulating substrate110made of a material such as transparent glass or plastic, and is patterned by wet etching or dry etching with a photoresist pattern to form a plurality of gate lines121including a plurality of gate electrodes124and an end portion129and a plurality of storage electrode lines131having a pair of storage electrodes133aand133b.

After sequential deposition of a gate insulating layer140, an intrinsic a-Si layer, and an extrinsic a-Si layer, the extrinsic a-Si layer and the intrinsic a-Si layer are photo-etched to form a plurality of extrinsic semiconductor stripes and a plurality of intrinsic semiconductor stripes151including a plurality of projections154on the gate insulating layer140. The gate insulating layer140has a thickness of about 1,500 Å to about 5,500 Å, the intrinsic a-Si layer has a thickness of about 500 Å to about 2,000 Å, and the extrinsic a-Si layer thickness is about 300 Å to about 600 Å.

A conductive layer is sputtered with a thickness of about 1,500 Å to about 3,000 Å, and is patterned by etching with a photoresist pattern to form a plurality of data lines171, each including a plurality of source electrodes173and end portion179, and a plurality of drain electrodes175.

Portions of the extrinsic a-Si layer which are not covered with the data lines171and the drain electrodes175are removed by etching to complete a plurality of ohmic contact stripes161including a plurality of projections163and a plurality of ohmic contact islands165, and to expose portions of the intrinsic semiconductor stripes151. Oxygen plasma treatment may follow thereafter in order to stabilize the exposed surfaces of the semiconductor stripes151.

A passivation layer180preferably made of positive photosensitive organic materials is deposited on the data lines171, the drain electrodes175, and the exposed semiconductor stripes151, as well as exposed portions of the gate insulating layer140.

The passivation layer180is exposed to light through a photo mask. The photo mask includes a transparent substrate and an opaque light blocking film, and it is divided into light transmitting areas, light blocking areas, and translucent areas. The light blocking film is not disposed on the light transmitting areas, but it is disposed on the light blocking areas and the translucent areas. The light blocking film exists as a wide area having a width larger than a predetermined value on the light blocking areas, and it exists as a plurality of areas having width or distance smaller than a predetermined value to form slits.

The passivation layer180is developed to form a plurality of contact holes182and185exposing the end portions179of the data lines171and the drain electrodes175. The passivation layer180is also developed along with the gate insulating layer140to form the contact holes181,183a, and183bexposing the end portions129of the gate lines121, and the storage electrodes133aand133bof the storage electrode lines131, respectively.

When the passivation layer180is made of negative photosensitive materials, the positions of the light transmitting areas and the light blocking areas of the photo mask are changed with each other.

Finally, IZO or ITO with a thickness of about 400 Å to about 500 Å is sputtered and etched to form a plurality of pixel electrodes191, a plurality of contact assistants81and82, and overpasses83on the passivation layer180, the exposed drain electrodes175, the end portions179of the data lines171, the end portions129of the gate lines121, and the exposed storage electrode lines131. The alignment layer11may be provided on the TFT array panel100using an inkjet printing system or other method.

While exemplary embodiments of an LCD, and an exemplary TFT array panel100and an exemplary color filter panel200for an LCD, have been described, it should be understood that the exemplary embodiments of the inkjet printing system according to the present invention may be utilized to form color filters230on other embodiments of LCDs not described herein.

Next, an OLED display using a panel manufactured by the exemplary embodiments of the inkjet printing system according to the present invention will be described with reference to the accompanying drawings.

First, an exemplary OLED display according to the present invention is described with reference toFIG. 13.

FIG. 13is an equivalent circuit diagram of an exemplary pixel of an exemplary embodiment of an OLED display according to the present invention.

Referring toFIG. 13, an OLED display includes a plurality of signal lines121,171, and172and a plurality of pixels PX connected thereto and arranged substantially in a matrix.

The signal lines121,171, and172include a plurality of gate lines121, a plurality of data lines171, and a plurality of voltage transmission lines172.

The gate lines121transmit gate signals (or scanning signals), extend substantially in a row direction, first direction, and are substantially parallel to each other. The data lines171transmit data signals, extend substantially in a column direction, second direction, and are substantially parallel to each other and substantially perpendicular to the gate lines121. The voltage transmission lines172transmit driving voltages, extend substantially in the column direction, and are substantially parallel to each other and substantially parallel to the data lines171.

Each pixel PX includes a switching transistor Qs, a driving transistor Qd, a storage capacitor Cst, and an organic light emitting element LD.

The switching transistor Qs has a control terminal corresponding to a gate connected to the gate line121, an input terminal corresponding to a source connected to the data line171, and an output terminal corresponding to a drain connected to the driving transistor Qd. The switching transistor Qs transmits the data signal applied to the data line171to the driving transistor Qd in response to the scanning signal, otherwise termed gate signal, applied to the gate line121.

The driving transistor Qd has a control terminal connected to the switching transistor Qs, an input terminal connected to the voltage transmission line172, and an output terminal connected to the light emitting element LD. The driving transistor Qd flows a current having a magnitude depending on a voltage applied between the control terminal and the output terminal thereof.

The storage capacitor Cst is connected between the control terminal and the output terminal of the driving transistor Qd. The storage capacitor Cst charges and maintains the data signal applied to the control terminal of the driving transistor Qd from the switching transistor Qs.

The light emitting element LD has an anode connected to the output terminal of the driving transistor Qd and a cathode connected to a common voltage Vcom. The light emitting element LD emits light having an intensity depending on an output current ILDof the driving transistor Qd.

The switching transistor Qs and the driving transistor Qd are N-channel field effect transistors (“FETs”). Alternatively, at least one of the transistors Qs and Qd may be a P-channel FET. While a particular configuration has been shown, the connections between the transistors Qs and Qd, the capacitor Cst, and the light emitting element LD may be modified, and such modifications are within the scope of these embodiments.

Now, a structure of an exemplary display panel for an exemplary embodiment of the OLED according to the present invention will be described with reference toFIGS. 14 to 16.

FIG. 14is a schematic plan view of an exemplary display panel for an exemplary embodiment of an OLED according to the present invention,FIG. 15is a sectional view of the exemplary display panel shown inFIG. 14taken along line XV-XV′, andFIG. 16is a sectional view of the exemplary display panel shown inFIG. 14taken along line XVI-XVI′.

A plurality of gate conductors that include a plurality of gate lines121including first gate electrodes124aand second gate electrodes124bare formed on an insulating substrate110. The insulating substrate110may be formed from a material such as, but not limited to, transparent glass or plastic. The first and second gate electrodes124aand124bmay also be termed control electrodes.

The gate lines121transmit gate signals and extend substantially in a transverse direction, a first direction. Each of the gate lines121includes an end portion129having a large area for contact with another layer or an external driving circuit. The first gate electrodes124aproject upward from the gate lines121. A gate driving circuit (not shown) for generating the gate signals may be mounted on a flexible printed circuit (“FPC”) film (not shown), which may be attached to the insulating substrate110, directly mounted on the insulating substrate110, or integrated onto the insulating substrate110. Alternatively, the gate lines121may extend to be connected to a driving circuit that may be directly integrated on the insulating substrate110.

Each of the second gate electrodes124bis separated from the gate lines121and disposed between two adjacent gate lines121. Each second gate electrode124bincludes a storage electrode127that extends downwardly from the second gate electrode124bin a second direction, turns to the right towards a side of a pixel, and then extends lengthwise back upwardly in the second direction. The storage electrode127may extend substantially a full length of a pixel.

The gate conductors121and124b, that include the gate lines121and the first and second gate electrodes124aand124b, are preferably made of an Al containing metal such as Al and Al alloy, a Ag containing metal such as Ag and Ag alloy, a Cu containing metal such as Cu and Cu alloy, a Mo containing metal such as Mo and Mo alloy, Cr, Ti or Ta. The gate conductors121and124bmay have a multi-layered structure including two films having different physical characteristics. In such a multi-layered structure, one of the two films is preferably made of low resistivity metal including an Al containing metal, an Ag containing metal, or a Cu containing metal for reducing signal delay or voltage drop in the gate conductors121and124b, and the other film is preferably made of material such as Cr, Mo, Mo alloy, Ta, or Ti, which has good physical, chemical, and electrical contact characteristics with other materials such as ITO or IZO. Examples of the combination of the two films include a lower Cr film and an upper Al (alloy) film and a lower Al (alloy) film and an upper Mo (alloy) film. However, the gate conductors121and124bmay be made of various metals or conductors.

The lateral sides of the gate conductors121and124bare inclined relative to a surface of the insulating substrate110, and the inclination angle thereof ranges about 30 to about 80 degrees.

A gate insulating layer140preferably made of silicon nitride (SiNx) or silicon oxide (SiOx) is formed on the gate conductors121and124b. The gate insulating layer140may be further formed on exposed portions of the insulating substrate110.

A plurality of semiconductor islands154aand154bpreferably made of hydrogenated a-Si or polysilicon are formed on the gate insulating layer140. The semiconductor islands154aand154bare disposed on the first and second gate electrodes124aand124b, respectively.

A plurality of pairs of first and second ohmic contact islands163aand163band a plurality of pairs of third and fourth ohmic contact islands165aand165bare formed on the semiconductor islands154aand154b, respectively. The ohmic contact islands163a,163b,165a, and165bare preferably made of n+ hydrogenated a-Si heavily doped with an N-type impurity such as phosphorous, or they may be made of silicide.

The first ohmic contact islands163aand165aare disposed on the first semiconductor island154aand separated from each other in pair and the second ohmic contact islands163band165bare disposed on the first semiconductor island154aand separated from each other in pair.

The lateral sides of the semiconductor islands154aand154band the ohmic contacts163a,163b,165a, and165bare inclined relative to the surface of the insulating substrate110, and the inclination angles thereof are preferably in a range of about 30 to about 80 degrees.

A plurality of data conductors including a plurality of data lines171, a plurality of voltage transmission lines172, and a plurality of output electrodes175aand175bare formed on the ohmic contacts163a,163b,165a, and165aand the gate insulating layer140.

The data lines171for transmitting data signals extend substantially in the longitudinal direction, the second direction, and intersect the gate lines121substantially perpendicularly. The data lines171may be insulated from the gate lines121by the gate insulating layer140. Each data line171may include a plurality of first input electrodes173aprojecting toward the first gate electrode124aand an end portion179having a large area for contact with another layer or an external driving circuit. A data driving circuit (not shown) for generating the data signals may be mounted on a FPC film (not shown), which may be attached to the insulating substrate110, directly mounted on the insulating substrate110, or integrated into the insulating substrate110. Alternatively, the data lines171may extend to be connected to a driving circuit that may be directly integrated in the insulating substrate110.

The voltage transmission lines172for transmitting driving voltages for the driving transistor Qd extend substantially in the longitudinal direction, second direction, and intersect the gate lines121and extend parallel to the data lines171. Each voltage transmission line172includes a plurality of second source electrodes173bprojecting toward the second gate electrode124b. The voltage transmission lines172may overlap the storage electrodes127and be connected to each other.

The first and second drain electrodes175aand175bare separated from each other and separated from the data lines171and the voltage transmission lines172. The first and second drain electrodes175aand175bmay also be termed output electrodes.

The first source electrodes173a, which are input electrodes, are disposed opposite the first drain electrodes175awith respect to the first gate electrodes124aand the second source electrodes173b, which are input electrodes, are disposed opposite the second drain electrodes175bwith respect to the second gate electrodes124b.

The data conductors171,172,175a, and175bare preferably made of a refractory metal such as Cr, Mo, Ta, Ti, or alloys thereof. However, they may have a multilayered structure including a refractory metal film (not shown) and a low resistivity film (not shown). Examples of the multi-layered structure include a double-layered structure including a lower Cr/Mo (alloy) film and an upper Al (alloy) film and a triple-layered structure of a lower Mo (alloy) film, an intermediate Al (alloy) film, and an upper Mo (alloy) film. However, data conductors171,172,175a, and175bmay be made of various metals or conductors.

Like the gate conductors121and124b, the lateral sides of the data conductors171,172,175a, and175bare inclined relative to a surface of the insulating substrate110, and the inclination angle thereof ranges about 30 to about 80 degrees.

The ohmic contacts163a,163b,165a,165bare interposed only between the underlying semiconductor islands154aand154band the overlying data conductors171,172,175a, and175bthereon and reduce the contact resistance there between. The semiconductor islands154aand154binclude some exposed portions, which are not covered with the data conductors171,172,175a, and175b, such as portions located between the source electrodes173aand173band the drain electrodes175aand175b, and between the ohmic contact islands163aand163band the ohmic contact islands165aand165b, thus forming channels there between on the semiconductor islands154aand154b.

A passivation layer180is formed on the data conductors171,172,175a, and175band the exposed portions of semiconductor islands154aand154b. The passivation layer180may further be formed on the exposed portions of the gate insulating layer140. The passivation layer180is preferably made of inorganic or organic insulator and it may have a flat top surface. Examples of the inorganic insulator include silicon nitride and silicon oxide. The organic insulator may have photosensitivity and dielectric constant less than about 4.0. The passivation layer180may include a lower film of inorganic insulator and an upper film of organic insulator, such that it possesses the excellent insulating characteristics of the organic insulator while preventing the exposed portions of the semiconductor islands154and154bfrom being damaged by the organic insulator.

The passivation layer180has a plurality of contact holes182,185a, and185bexposing the end portions179of the data lines171and the first and second drain electrodes175aand175b, respectively. The passivation layer180and the gate insulating layer140have a plurality of contact holes181and184exposing the end portions129of the gate lines121and the second gate electrodes124b, respectively.

A plurality of pixel electrodes191, a plurality of connecting members85, and a plurality of contact assistants81and82are formed on the passivation layer180. They are preferably made of a transparent conductor such as ITO or IZO or a reflective conductor such as Ag, Al, Cr, or alloys thereof.

The pixel electrodes191are physically and electrically connected to the second drain electrodes175bthrough the contact holes185b. The connecting members85are physically and electrically connected to the second gate electrodes124band the first drain electrodes175athrough the contact holes184and185a, respectively.

The contact assistants81and82are physically and electrically connected to the end portions129of the gate lines121and the end portions179of the data lines171through the contact holes181and182, respectively. The contact assistants81and82protect the end portions129and179and enhance the adhesion between the end portions129and179and external devices, such as a gate driving circuit and a data driving circuit.

A partition361is formed on the passivation layer180and may overlap peripheral portions of the pixel electrode191.

The partition361surrounds the pixel electrodes191like a bank, to define openings365to be filled with organic light emitting material. The partition361is preferably made of organic or inorganic insulating material. The partition361may be also formed of photoresist including a black pigment to function as a light blocking member, such that a manufacturing procedure is simplified.

A plurality of light emitting members370are formed on the pixel electrodes191and disposed in the openings365defined by the partition361. The organic light emitting members370are formed using an exemplary embodiment of the inkjet printing system according to the present invention. That is, instead of the insulating substrates210with light blocking members220provided on the stage500, the panel prepared as shown inFIGS. 14 to 16is provided on the stage500for receipt of material for forming the light emitting members370within the openings365. The light emitting members370are preferably made of organic material emitting primary-color lights such as red, green, and blue lights. Thus, the ink5is replaced by material for forming the light emitting members370. The light emitting members370, such as red, green, and blue light emitting members370, are periodically arranged. The OLED represents a desired color by summing the colors from the light emitting members370in space.

Each organic light emitting member370may have a multilayered structure. For example, the organic light emitting member370includes an emitting layer (not shown) emitting light and auxiliary layers (not shown) for improving the efficiency of light emission of the emitting layer. The auxiliary layers may include an electron transport layer (not shown) and a hole transport layer (not shown) for improving the balance of the electrons and holes, and an electron injecting layer (not shown) and a hole injecting layer (not shown) for improving the injection of the electrons and holes.

A common electrode270is formed on the light emitting members370. The common electrode270may further be formed on the partition361. The common electrode270is supplied with the common voltage Vcom. The common electrode270may be preferably made of reflective conductors such as Al, calcium Ca, barium Ba, and magnesium Mg or alloys thereof or transparent conductors such as ITO or IZO.

In the above-described OLED, a first gate electrode124aconnected to the gate line121, a first source electrode173aconnected to the data line171, and a first drain electrode175aalong with a first semiconductor island154aform a switching TFT Qs having a channel formed in the semiconductor island154adisposed between the first source electrode173aand the first drain electrode175a. A second gate electrode124bconnected to the first drain electrode175a, a second source electrode173bconnected to the voltage transmission line172, and a second drain electrode175balong with a second semiconductor island154bform a driving TFT Qd having a channel formed in the semiconductor island154bdisposed between the second source electrode173band the second drain electrode175b. In the switching TFT Qs and the driving TFT Qd, the gate electrodes124aand124bform control electrodes, the source electrodes173aand173bform input electrodes, and the drain electrodes175aand175bform output electrodes. The pixel electrodes191, the organic light emitting members370, and the common electrode270form organic light emitting elements LD. The pixel electrode191may be an anode terminal and the common electrode270may be a cathode terminal. Alternatively, the pixel electrode191may be a cathode terminal and the common electrode270may be an anode terminal. Furthermore, a storage electrode127and a voltage transmission line172overlapped with each other form a storage capacitor Cst.

The OLED emits light upwardly or downwardly with respect to the insulating substrate110to represent the images.

An opaque pixel electrode191and a transparent common electrode270are used in OLEDs of a top emission type representing the images upwardly with respect to the insulating substrate110. A transparent pixel electrode191and a transparent common electrode270are used in OLEDs of a bottom emission type representing the images downwardly with respect to the insulating substrate110.

Meanwhile, when the semiconductor islands154aand154bare made of polysilicon, the OLED includes intrinsic regions (not shown) disposed opposite with respect to the gate electrodes124aand124b, respectively and extrinsic regions (not shown) disposed on the intrinsic regions. The extrinsic regions are electrically connected to the input electrodes173aand173band the output electrodes175aand175b, and the ohmic contacts163a,163b,165a, and165bmay be omitted.

While the illustrated embodiment shows the gate electrodes124aand124bdisposed between the semiconductors154a,154band the insulating substrate110, in an alternative embodiment, the gate electrodes124aand124bmay be disposed on the semiconductors154a,154b, such that the semiconductors154a,154bare disposed between the gate electrodes124a,124band the insulating substrate110. In this case, the gate insulating layer140is disposed between the semiconductors154a,154band the control electrodes124aand124b. Also in such an embodiment, the data conductors171,172,175a, and175bare disposed on the gate insulating layer140and electrically connected to the semiconductors154aand154bthrough contact holes (not shown) formed on the gate insulating layer140. In yet another embodiment, the data conductors171,172,175a, and175bare disposed under the semiconductor islands154aand154band may be connected to the overlaying semiconductor islands154aand154b.

While semiconductors made of a-Si have been described for use in the OLED, the present invention may also be adopted to OLEDs including semiconductors made of polysilicon.

Thus, an inkjet printing system is provided for forming color filters on a color filter layer of an LCD and for forming light emitting members on an OLED. Alignment keys are provided on a panel arranged to receive material for forming the color filters or the light emitting members. The alignment keys are sensed by an alignment key position sensor, and the sensed signals are converted into control signals for proper positioning of a head unit supporting an inkjet head. The alignment key position sensor may be provided on the head unit or on an alignment key sensing unit separate from the head unit.

A driving method of the inkjet printing system includes sensing positions of the alignment keys using the alignment key position sensor to generate sensing signals and using the sensing signals to align a position of the head unit. The sensing signals may be stored in a memory for comparison with a current position of the head unit to generate control signals for aligning the head unit.

By the aligning operation of the head unit using the alignment keys and the alignment key position sensor, the color filters or light emitting members are accurately formed on desired positions of the substrates, thus increasing reliability and decreasing manufacturing cost.

While the present invention has been described in detail with reference to the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.