Abstract:
Embodiments relate to a quantum rod composition, a quantum rod film, a display device with a quantum rod film, and a method of forming a quantum rod film. The quantum rod film includes a plurality of quantum rods and a polymer with a dipole side chain. Responsive to an external electric field, the major axis of the quantum rods and an axis of the dipole side chain arranges in the same direction. The display device includes a plurality of pixel and common electrodes for generating an electric field, and a backlight unit positioned under a first substrate. Responsive to receiving light from the backlight unit, the quantum rod film emits light polarized in a direction parallel to the major axis of the quantum rods.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to and the benefit of Republic of Korea Patent Application No. 10-2014-0158166 filed in Republic of Korea on Nov. 13, 2014, which is hereby incorporated by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    Embodiments of the invention relate to a quantum rod, and more particularly, to a quantum rod film having a low driving voltage and an improved polarization property, and a quantum rod composition and a display device including the same. 
         [0004]    2. Discussion of the Related Art 
         [0005]    Recently, as the society has entered in earnest upon an information age, a field of display devices that represent all sorts of electrical signals as visual images has developed rapidly. Flat panel display device, such as a liquid crystal display (LCD) device, a plasma display panel (PDP) device, a field emission display (FED) device, and an organic light emitting diode (OLED) device, has been introduced. 
         [0006]    On the other hand, use of a quantum rod (QR) to the display device has been researched or studied. Since the QR has high emitting efficiency and excellent reproducibility, the QR can be applied to various uses. For example, applications of the QR to an emitting diode for lightings and a light source or other elements for the LCD device have been researched. 
         [0007]    The QR includes a nano-sized core particle of II-VI, III-V, I-III-VI, or IV-VI semiconductor particle and a shell covering the core particle. 
         [0008]    Since extinction coefficient and quantum yield of the QR is very large in comparison to general dyes, the QR emits strong fluorescent light. In addition, by controlling a diameter of the QR, a wavelength of light emitted from the QR can be controlled. 
         [0009]    The QR emits linearly-polarized light. Namely, the light from the QR has a linearly-polarized property along a length direction of the QR. 
         [0010]    In addition, the QR has an optical property that is capable of controlling emission by an electric field applied from the outside. This may be referred to as stark effect. 
         [0011]    On the other hand, to simplify a fabricating process of the display device including the QR, a solution process for the QR film is introduced. Namely, by fabricating the QR film by the solution process, e.g., an ink jet method, a dispensing method, a roll-to-roll method, or a spin-coating method, the fabricating process of the display device including the QR is simplified and a thickness uniformity of the QR film is improved. 
         [0012]    For example, the ink jet process is adequate to form a fine pattern and can use a low viscosity solution, and a material loss is minimized. 
         [0013]    To coat the QRs by the ink jet method, an ink formulation of the QRs is required. Namely, the QR ink should have viscosity of about 8 to about 30 cP and surface tension of about 20 to about 40 dyne/cm and low volatility, e.g., a boiling point above 280° C., for the ink jet process. 
         [0014]    However, the polarization property is decreased in the QR film formed by the solution process. In addition, there is a problem of high driving voltage in the QR film formed by the solution process. 
       SUMMARY OF THE INVENTION 
       [0015]    Accordingly, embodiments of the invention are directed to a QR composition, a QR film, and a display device including the same that substantially obviate one or more of the problems due to limitations and disadvantages of the related art, and have other advantages. 
         [0016]    An objective of the invention is to provide a QR film having advantages in driving voltage and polarization property. 
         [0017]    Another objective of the invention is to provide a QR solution for fabricating a QR film. 
         [0018]    Another objective of the invention is to provide a display device having advantages in the production costs. 
         [0019]    Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings. 
         [0020]    Embodiments relate to a quantum rod (QR) composition including a plurality of quantum rods, a polymer including a main chain and a plurality of dipole side chains attached to the main chain, and a solvent. 
         [0021]    Embodiments also relate to a quantum rod film including a plurality of quantum rods, and a polymer including a main chain and a plurality of dipole side chains attached to the main chain, in which the a major axis of the plurality of quantum rods and an axis of the plurality of dipole side chains are arranged along the same direction. 
         [0022]    Embodiments also relate to a display device including a first substrate, a second substrate facing the first substrate, a plurality of pixel electrodes and a plurality of common electrodes on the first substrate, a quantum rod film positioned between the first substrate and the second substrate. The quantum rod film includes a plurality of quantum rods, and a polymer including a main chain and a plurality of dipole side chains attached to the main chain, in which a major axis of the plurality of quantum rods and an axis of the plurality of dipole side chains are arranged along a first direction. The display device further includes a backlight unit under the first substrate, in which responsive to receiving light from the backlight unit, the quantum rod film emits light polarized along the first direction. 
         [0023]    Embodiments also relate to a method of forming a quantum rod film. A plurality of pixel electrodes and a plurality of common electrodes are formed on a substrate. A quantum rod composition is coated on the substrate. The quantum rod composition includes a plurality of quantum rods, a polymer including a main chain and a plurality of dipole side chains attached to the main chain, and a solvent. An electric field between the plurality of pixel electrodes and the plurality of common electrodes is generated, and the quantum rod composition is cured to form a quantum rod film on the substrate, in which a major axis of the plurality of quantum rods and an axis of the plurality of dipole side chains are arranged along a direction substantially parallel to the electric field. 
         [0024]    It is to be understood that both the foregoing general description and the following detailed description are examples and are explanatory and are intended to provide further explanation of the invention as claimed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0025]    The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention. 
           [0026]      FIG. 1  illustrates a driving principle of a QR film. 
           [0027]      FIG. 2  is a schematic view of a QR for a QR composition according to a first embodiment of the present invention. 
           [0028]      FIGS. 3A and 3B  are views illustrating a driving principle of a QR. 
           [0029]      FIG. 4  is a schematic view of a polymer for a QR composition according to the first embodiment of the present invention. 
           [0030]      FIG. 5  is a schematic view illustrating a change with the On/Off states in the QR composition according to the first embodiment of the present invention. 
           [0031]      FIGS. 6A to 6C  are schematic cross-sectional views illustrating a fabricating process of a QR film according to a second embodiment of the present invention. 
           [0032]      FIG. 7  is a schematic cross-sectional view of a display device including a QR film according to a third embodiment of the present invention. 
           [0033]      FIGS. 8A to 8E  are schematic cross-sectional views illustrating a fabricating process of a QR film according to the third embodiment of the present invention. 
           [0034]      FIG. 9  is a schematic cross-sectional view of a display device including a QR film according to the third embodiment of the present invention. 
           [0035]      FIG. 10  is a graph showing an On/Off property in a display device including the QR film. 
           [0036]      FIG. 11  is a graph showing a polarization property in a display device including the QR film. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0037]    Reference will now be made in detail to embodiments of the invention, examples of which are illustrated in the accompanying drawings. 
         [0038]    The On/Off control and the polarization property of a QR are determined by an arrangement degree of the QRs. 
         [0039]    Namely, the holes and the electrons in the QR is separated by an electric field such that the Off state is provided. In this instance, when the QRs are arranged along the same direction, the driving voltage for the QRs is reduced. In addition, when the QRs are arranged along the same direction, the linearly-polarization property of the light emitted from the QRs is improved. 
         [0040]    However, in the QR film fabricated by the solution process, the polymer used for the solution process of the QRs is randomly arranged such that the arrangement degree of the QRs is decreased. Accordingly, in the QR film fabricated by the solution process, the polarization property is decreased and the driving voltage is increased. In addition, the driving voltage is further increased by a shielding effect of the electric field by the polymer. 
         [0041]    Namely, referring to  FIG. 1  illustrating a driving principle of a QR film, even when the voltage is applied to the QR film to generate an electric field “E”, the QR  10  is trapped by the polymer  20  such that the arrangement degree of the QR  10  is reduced. 
         [0042]    In the present invention, a QR composition, a QR film, and a display device including the QR film being capable of increasing the arrangement degrees of the QRs and being adequate for fabrication in a solution process is disclosed. 
       First Embodiment 
       [0043]    A QR composition of the present invention includes a QR, a polymer having a dipole side chain, and a solvent. 
         [0044]    In the QR composition, the QR has approximately 1 to about 5 weight (wt) %, and the polymer has approximately 10 to 20 wt %. The QR composition includes the solvent in a residual amount. Accordingly, the QR composition has properties, i.e., viscosity, surface tension, volatility, being adequate to the solution process. 
         [0045]    Referring to  FIG. 2 , which is a schematic view of a QR for a QR composition according to a first embodiment of the present invention, the QR  110  for the QR composition of the present invention may include a core  112  and a shell  114  surrounding the core  112 . 
         [0046]    The core  112  may have a sphere shape, an elliptical sphere shape, a polyhedral shape, or a rod shape. The shell  114 , which surrounds the core  112 , may have a rod shape having major and minor axes. The major axis of the QR  110  may refer to an axis along a longer length of the shell  114  or core  112  of the QR  110 . The minor axis of the QR  110  may refer to an axis perpendicular to the major axis of the QR  110 . Accordingly, in a cross-sectional view along the minor axis of the QR  110 , the QR  110  may have a circular shape, an elliptical shape or a polygonal shape. In  FIG. 2 , the QR  110  has the circular shape in the cross-sectional view along the minor axis. 
         [0047]    Alternatively, the QR  110  may have the core  112  without the shell  114 . In this instance, the core  112  may have an elliptical shape or a rod shape. 
         [0048]    In addition, the shell  114  may have a single-layered structure or a multi-layered structure and may be formed of one or more of alloys, an oxide compound and a doped material. The shell  114  may have a ratio of the minor axis to the major axis with a range of 1:1.1 to 1:30. 
         [0049]    The core  112  of the QR  110  is formed of the II-VI, III-V, I-III-VI, or IV-VI semiconductor material. For example, when the core  112  is formed of the II-VI semiconductor material, the core  112  may be formed from one or more of CdSe, CdS, CdTe, ZnO, ZnSe, ZnS, ZnTe, HgSe, HgTe, and CdZnSe. 
         [0050]    To emit red light, the QR  110  may have the core  112  of CdSe and the shell  114  of CdS, or may have the core  112  of CdSeS and the shell  114  of CdS. The QR  110  may include the core  112  of CdZnS without the shell to emit blue light. 
         [0051]    Referring to  FIGS. 3A and 3B , which are views illustrating a driving principle of a QR, without the electric field to the QR  110 , including the core  112  and the shell  114 , the hole “h+” and the electron “e−” are combined in the core  112 . ( FIG. 3A ) On the other hand, when the electric field “E” along the major axis is applied to the QR  110 , the hole “h+” and the electron “e−” are spatially separated such that the emission of the QR  110  is controlled. ( FIG. 3B ) 
         [0052]    Referring to  FIG. 4 , which is a schematic view of a polymer for a QR composition according to the first embodiment of the present invention, the polymer  120  for the QR composition of the present invention has a dipole side chain  124  linked or combined to a main chain  122 . For example, the polymer  120  may be polyoxetane, polysiloxane, or polyester, each of which has the dipole side chain  124 . Namely, the main chain  122  of the polymer  120  may be selected from polyoxetane, polysiloxane, and polyester. 
         [0053]    The dipole side chain  124  is a compound that includes one or more selected from materials in Formulas 1-1 to 1-4. In Formulas 1-1 to 1-4, R is selected from F, CF 3 , and CN. The dipole side chain  124  may have an axis along a length of the compound. For example, in Formulas 1-1 through 1-4, the axis of the dipole side chain  124  may be substantially parallel to a direction from the R group to the oxygen (O) bond of the compound. 
         [0000]    
       
                 
         
             
             
         
       
     
         [0054]    The polymer  120  is synthesized by the following. 
         [0055]    1. Synthesis of Monomer 
         [0000]    
       
                 
         
             
             
         
       
     
         [0056]    NaOH solution (1M, 200 ml) was put into a three-neck round flask (500 ml), and 3-methyl-3-oxetanemethanol (2 g, 19.3 mmol) and tetrabutylamonium chloride (0.05 g) were put into the flask. 
         [0057]    After stirring for about 10 minutes, hexane (100 ml) and dibromodecane (12 g, 60.5 mmol) were added, and the mixture was stirred and reacted under room temperature for approximately 8 hours. The mixture was refluxed under a temperature of 60° C. for about 3 hours. The reaction tube was cooled in room temperature, and a hexane layer was separated. Water was removed by MgSO 4 , and the solvent was distilled under a reduced pressure. The resultants of brown color was separated by column chromatography using a developing solvent (ethylacetate:hexane=1:15) and silica. (yield: 78%) 
         [0000]    
       
                 
         
             
             
         
       
     
         [0058]    Acetone (150 ml) was put into the three-neck round flask, and potassium carbonate (6.15 g, 153.6 mmol), tetra-butyl ammonium bromide (1.5 g, 5.1 mmol), 3-[(10-bromohexoxy)methyl]-3-methyloxetane (21.4 g, 66.7 mmol), and compound A (10 g, 51.2 mmol) were put into the flask. The mixture were refluxed for 24 hours under a temperature of 60˜70° C. to react. After completion of the reaction, the resultant was cooled in room temperature. The floating matters were removed by the filter paper, and the solvent were removed under the reduced pressure. The yellow mixture, which was obtained by distillation, was separated by a column-chromatography using a developing solvent of ethylacetate and hexane (1:4) such that compound B was obtained. (yield: 75%) 
         [0059]    2. Synthesis of Polymer 
         [0000]    
       
                 
         
             
             
         
       
     
         [0060]    Boron trifluoride etherate (0.016 g, 0.l4 mmol) was diluted by dichloromethane (1 ml), and the diluted boron trifluoride etherate was slowly dropped into a solution, where compound B (3 g, 6.88 mmol) was dissolved in anhydride dichloromethane (15 ml) for 1 hour under a condition of argon and a temperature of −10° C. The mixture was reacted for 24 hours under room temperature. After completion of the reaction, the solvent was removed by distillation under reduced pressure and a temperature of 60° C., and the resultant was dissolved in dichloromethane and put into the dialysis tube. The dialysis tube was dipped into methanol (250 ml) of high-performance liquid chromatography (HPLC) grade. The matter in the dialysis tube was slowly stirred using the stirrer, and it is verified that monomers were extracted into the solution by the UV lamp. The monomers were removed using refreshed clean solvent once every two hours (for a total of six times) such that polymer in Formula 2-1 was obtained. 
         [0061]    By changing the compound A into compound A′, which has different R, polymers in Formulas 2-2 and 2-3 can also be obtained. Similarly, polymers with different dipole side chain structures may also be obtained by changing the compound A into any one of the compounds in Formulas 1-2 through 1-4. 
         [0000]    
       
                 
         
             
             
         
       
     
         [0062]    The viscosity of the QR composition is controlled by the main chain  122  of the polymer  120 , and the arrangement degree of the QR  110  is improved due to the dipole side chain  124  of the polymer  120 . 
         [0063]    Namely, since the dipole side chain  124  of the polymer  120  has a dipole property, the axis of the dipole side chain  124  is arranged along a direction of the electric field due to the dipole property with the electric field. Accordingly, the arrangement degree of the QR  110  is improved. 
         [0064]    Referring to  FIG. 5 , which is a schematic view illustrating a change with the On/Off states in the QR composition according to the first embodiment of the present invention, without the electric field, the QR  110  and the polymer  120  in the QR composition  100 , which includes the QR  110 , the polymer  120  including the main chain  122  and the dipole side chain  124 , and the solvent (not shown), are randomly arranged. 
         [0065]    However, when the electric field “E” is generated in the QR composition  100 , the dipole is induced in the dipole side chain  124  of the polymer  120  such that the axis of the dipole side chain  124  is arranged along the direction of the electric field “E”. As a result, the arrangement degree of the QR  110  is improved. 
         [0066]    Namely, in the related art QR composition, the arrangement degree of the QR is reduced by the randomly-arranged polymer. However, in the present invention, since the polymer  120  has the dipole side chain  124  being capable of generating an induced dipole, the arrangement degree of the QR  110  with the electric field is improved. 
         [0067]    Accordingly, in the QR film fabricated by the above QR composition, the polarization property is improved, and the driving voltage is reduced. 
       Second Embodiment 
       [0068]      FIGS. 6A to 6C  are schematic cross-sectional views illustrating a fabricating process of a QR film according to a second embodiment of the present invention. 
         [0069]    As shown in  FIG. 6A , the QR composition  100  (of  FIG. 5 ) is coated to form a QR solution layer  230  on a base substrate  200 . 
         [0070]    Namely, the QR composition  100  including the QR  210 , the polymer  220 , which includes the main chain  222  and the dipole side chain  224 , and the solvent (not shown) is coated on the base substrate  200  to form the QR solution layer  230 . For example, the QR composition  100  may be coated by an ink jet method. 
         [0071]    Next, as shown in  FIG. 6B , an electric field “E” ( FIG. 5 ) along a first direction is generated in the QR solution layer  230 , and the QR solution layer  230  is cured. 
         [0072]    For example, first and second electrodes  242  and  244  are positioned at opposite sides of the QR solution layer  230 , and voltages are applied to the first and second electrodes  242  and  244  to form the electric field “E”. The QR solution layer  230  may be cured by heat generated by applying the voltages. Alternatively, a heating process may be performed to the QR solution layer after the electric field is generated or may be simultaneously performed with the electric field generation process. 
         [0073]    By the electric field “E”, as shown in  FIG. 6C , the QRs  210  are arranged along the first direction such that a QR film  250  is formed. The solvent is evaporated by the curing process, which is simultaneously or separately performed with the electric field generation process, such that the QR film  250  may include the QR  210  and the polymer  220  without the solvent. Alternatively, the QR film  250  may further include the cured solvent material. For example, the solvent may be one or more of tetralin and diethylbenzene. 
         [0074]    As mentioned above, in the QR composition, the viscosity of the QR composition is controlled by the main chain  222  of the polymer  220  such that the QR film  250  can be formed by a solution process. In addition, the induced dipole is generated by the dipole side chain  224  of the polymer  220  with the electric field “E” such that the arrangement degree of the QRs  210  is improved. 
         [0075]    Accordingly, in the QR film  250  of the present invention, the polarization property of the light emitted from QR film  250  is improved, and the driving voltage of the QR film  250  is reduced. 
       Third Embodiment 
       [0076]      FIG. 7  is a schematic cross-sectional view of a display device including a QR layer according to a third embodiment of the present invention. 
         [0077]    As shown in  FIG. 7 , a QR display device  300  of the present invention includes a display panel  305 , which includes pixels and common electrodes  350  and  352  for generating an electric field and a QR film  370 , and a backlight unit  307  including a UV light source (not shown). 
         [0078]    The display panel  305  includes a first substrate  330 , which is adjacent to the backlight unit  307 , the pixel and common electrodes  350  and  352 , which is positioned over the first substrate  330 , a second substrate  360 , which faces the first substrate  330 , and the QR film  370  positioned between the first and second substrates  330  and  360 . The QR film  370  includes the QR  310  and the polymer  320 . 
         [0079]    The pixel electrode  350  and the common electrode  352  are positioned between the first substrate  330  and the QR film  370  and generate a horizontal electric field for driving the QR  310  of the QR film  370 . 
         [0080]    Each of the pixel and common electrodes  350  and  352  may have a bar shape. For example, each of the pixel and common electrodes  350  and  352  may have a bar shape extending across the first substrate  330 . 
         [0081]    Alternatively, one of the pixel and common electrodes  350  and  352  may have a plate shape, and the other one of the pixel and common electrodes  350  and  352  may include at least one opening. In this instance, the pixel and common electrodes  350  and  352  are positioned in different layers and overlap each other in a pixel region. Namely, the display panel  305  may have a fringe field switching (FFS) mode electrode structure. 
         [0082]    A thin film transistor (TFT) Tr as a switching element is formed on the first substrate  330 , and the pixel electrode  350  may be connected to the TFT Tr. 
         [0083]    For example, the TFT Tr may include a gate electrode  332  on the first substrate  330 , a gate insulating layer  334  on the gate electrode  332 , a semiconductor layer  336 , which is disposed on the gate insulating layer  334  and overlaps the gate electrode  332 , a source electrode  340  on the semiconductor layer  336 , and a drain electrode  342  on the semiconductor layer  336 , and spaced apart from the source electrode  340 . 
         [0084]    The semiconductor layer  336  may include an active layer  336 a of intrinsic amorphous silicon and an ohmic contact layer  336   b  of impurity-doped amorphous silicon. Alternatively, the semiconductor layer  336  may have a single-layered structure of an oxide semiconductor material. 
         [0085]    Although not shown, a gate line along one direction is formed on the first substrate  330 , and a data line, which crosses the gate line to a pixel region, is formed on the gate insulating layer  334 . In addition, a common line, which is parallel to and spaced apart from the gate line, is formed on the first substrate  330 . 
         [0086]    A passivation layer  344 , which includes a drain contact hole  346  exposing the drain electrode  342 , is formed to cover the TFT Tr. 
         [0087]    The pixel electrode  350  is formed on the passivation layer  344  and connected to the drain electrode  342  through the drain contact hole  346 . The pixel electrode  350  may have a bar shape. 
         [0088]    The common electrode  352  is formed on the passivation layer  344  and may have a bar shape. The common electrode  352  may be connected to the common line (not shown) through a common contact hole (not shown). The common contact hole is formed through the passivation layer  344  and the gate insulating layer  334  and exposes the common line. 
         [0089]    The common electrode  352  and the pixel electrode  350  are alternately arranged with each other such that an electric field, which is substantially parallel to a surface of the first substrate  330 , is generated between the pixel and common electrodes  350  and  352 . Each common electrode  352  may be positioned in between two pixel electrodes  350 , so that a horizontal electric field is generated between each pair of adjacent pixel and common electrodes  350  and  352 . Namely, a horizontal electric field is generated between the pixel and common electrodes  350  and  352 . In one embodiment, the pixel and common electrodes  350  and  352  may be formed on the same layer. 
         [0090]    The QR film  370  is positioned between the first and second substrates  330  and  360  and includes the QR  310  and the polymer  320 . The polymer  320  includes the main chain  322  and the dipole side chain  324 . The QR  310  and the dipole side chain  324  may be arranged in a direction being substantially parallel to the horizontal electric field between the pixel and common electrodes  350  and  352 . 
         [0091]    Namely, referring to  FIG. 2 , the QR  310  has a rod shape that has a major axis and a minor axis. The QR  310  is arranged such that the major axis of the QR  310  is parallel to the direction of the electric field between the pixel and common electrodes  350  and  352 . In other words, the major axis of the QR  310  is arranged along a direction being perpendicular to an extension direction of the pixel and common electrodes  350  and  352 . 
         [0092]    For example, the QR composition, which includes the QR  310 , the polymer  320 , and the solvent (not shown), are coated over the first substrate  330  including the pixel and common electrodes  350  and  352 . In this instance, the QRs  310  are randomly dispersed in the solvent. When the voltages are applied into the pixel electrode  350  and the common electrode  352 , the QRs  310  are arranged such that the major axis of the QRs  310  is parallel to the direction of the electric field between the pixel and common electrodes  350  and  352 . In this step, the QR composition is cured to form the QR film  370 . As a result, in the QR film  370 , the major axis of the QRs  310  is parallel to the direction of the electric field between the pixel and common electrodes  350  and  352 . 
         [0093]    As mentioned above, since an induced dipole is generated in the dipole side chain  324  of the polymer  320 , the axis of the dipole side chains  324  are arranged along the direction of the electric field between the pixel and common electrodes  350  and  352 . Namely, the polymer  320  serves as a guide for arrangement of the QRs  310 . As a result, the arrangement degree of the QRs  310  is improved. 
         [0094]    In the related art LCD device, an alignment layer should be formed, and the aligning process should be performed. On the other hand, in the related art QR display device, where the QR film is formed by a solution process, the arrangement degree of the QRs is decreased. However, in the display device including the QR film  370  of the present invention, the processes of forming the alignment layer and aligning the alignment layer are not required, and the QR film  370  having the improved QR arrangement degree is formed by a solution process. 
         [0095]    In addition, since the QRs  310  can emit red, green, and blue lights, a color filter, which is required in the LCD device, can be omitted. 
         [0096]    In the QR display device  300  of the present invention, a lower surface of the QR film  370  may contact the pixel and common electrodes  350  and  352  without the alignment layer, and an upper surface of the QR film  370  may contact the second substrate  360 . When other elements are formed on the pixel and common electrodes  350  and  352 , and a bottom side of the second substrate  360 , the QR film  370  may contact these elements. 
         [0097]    On the other hand, when the pixel electrode  350  and the common electrode  352  are configured to have a fringe field switching mode structure, the QR film  370  may contact one of the pixel and common electrodes  350  and  352 . 
         [0098]    In addition, when the pixel electrode  350  and the common electrode  352  are configured to have the fringe field switching mode structure, the length direction, i.e., the major axis, of the QRs  310  are arranged to be parallel to an extension direction, i.e., a major axis, of the opening in one of the pixel electrodes  350  and the common electrodes  352 . 
         [0099]    As mentioned above, the QR  310  is arranged along the direction of the electric field between the pixel and common electrodes  350  and  352 , and the arrangement degree may depend on an aspect ratio of the QR  310 . Namely, as the aspect ratio of the QR  310  is increased, the arrangement degree is increased. However, when the aspect ratio of the QR  310  is increased, the quantum efficiency of the QR  310  is decreased. Namely, the arrangement degree and the quantum efficiency by the aspect ratio have a trade-off 
         [0100]    In addition, in the related art QR film, since the arrangement degree of the QR  310  is further decreased by the polymer in a solution process, the aspect ratio of the QRs should be further increased to have high QR arrangement degree. In this instance, the quantum efficiency of the QR is further decreased. 
         [0101]    However, in the present invention, since the QR film  370  includes the polymer  320  including the dipole side chain  324 , the arrangement degree of the QRs  310  is improved. Namely, the dipole side chain  324  of the polymer  320  serves as a guide for the QRs  310 . Accordingly, without decrease of the quantum efficiency, the QR arrangement degree is increased, and the driving property and the polarization property of the QR display device  300  are improved. 
         [0102]    In other words, in the display device using the QRs, the display device provides an Off state by separating the hole and electron by the electric field between the pixel and common electrode. The Off property of the display device depends on the QR arrangement degree. Accordingly, with low QR arrangement degree, the driving voltage is increased. 
         [0103]    However, in the QR display device  300  of the present invention, since the QR arrangement degree is increased by the dipole side chain  324  of the polymer  320 , the driving voltage of the QR display device  300  is reduced without decrease of the quantum efficiency of the QR  310 . In addition, due to the increase of the QR arrangement degree, the polarization property of the light emitted from the QR film  370  is increased. 
         [0104]    Moreover, since the polarized light is emitted from the QR film  370  in the QR display device  300 , the polarization plate, which is required in the LCD device, can be omitted. Furthermore, since the red, green, and blue lights are emitted from the QRs  310 , the color filter, which is required in the LCD device, can be omitted. Accordingly, the QR display device  300  of the present invention has advantages in production costs, weight, and thickness. 
         [0105]    In  FIG. 7 , the QR film  370  is disposed between two substrates  330  and  360  of the display device  300 . The QR film  370  is used for various semiconductor devices. Since the QR film  370  has the polarization property, the QR film  370  may be used instead of a polarization plate of a display device. 
         [0106]      FIGS. 8A to 8E  are schematic cross-sectional views illustrating a fabricating process of a QR film according to the third embodiment of the present invention. 
         [0107]    As shown in  FIG. 8A , a first metal layer (not shown) is formed on the first substrate  330  and is patterned to form the gate electrode  332 . The gate line (not shown), which extends from the gate electrode  332 , along a direction is also formed on the substrate  330 . In addition, the common line (not shown), which may be parallel to the gate line, is formed on the substrate  330 . 
         [0108]    Next, an inorganic material, such as silicon oxide or silicon nitride, is deposited to form the gate insulating layer  334  on the gate electrode  332 , the gate line, and the common line. 
         [0109]    Next, an intrinsic amorphous silicon layer (not shown) and an impurity-doped amorphous silicon layer (not shown) are sequentially formed on the gate insulating layer  334  and are patterned to form the semiconductor layer  336 , which includes the active layer  336   a  and the ohmic contact layer  336   b,  in correspondence to the gate electrode  332 . 
         [0110]    Next, a second metal layer (not shown) is formed and patterned to form the source electrode  340  and the drain electrode  342 . The source and drain electrodes  340  and  342  are disposed on the semiconductor layer  336  and spaced apart from each other. In addition, the data line (not shown), which crosses the gate line to define a pixel region and extends from the source electrode  340 , is formed. 
         [0111]    The gate electrode  332 , the gate insulating layer  334 , the semiconductor layer  336 , the source electrode  340 , and the drain electrode  342  constitute the TFT Tr. 
         [0112]    Next, as shown in  FIG. 8B , the passivation layer  344  covering the TFT Tr is formed and is patterned to form the drain contact hole  346 . In addition, the passivation layer  344  and the gate insulating layer  334  are patterned to form the common contact hole (not shown) exposing a portion of the common line. 
         [0113]    Next, a transparent conductive material layer (not shown) is formed on the passivation layer  344  by depositing a transparent conductive material such as indium-tin-oxide (ITO) or indium-zinc-oxide (IZO). The transparent conductive material layer is patterned to form the pixel electrode  350  and the common electrode  352 . 
         [0114]    The pixel electrode  350  is connected to the drain electrode  342  through the drain contact hole  346 , and the common electrode  352  is connected to the common line through the common contact hole. The pixel and common electrodes  350  and  352  are alternately arranged. 
         [0115]    Next, as shown in  FIG. 8C , the QR composition, which includes the QR  310 , the polymer  320 , and the solvent (not shown), is coated over the substrate  330  including the pixel and common electrodes  350  and  352  such that a QR solution layer  354  is formed. For example, the QR composition may be coated by an ink jet process. 
         [0116]    The polymer  320  may include the main chain  322  of polyoxetane, polysiloxane, or polyester and the dipole side chain  324  for generating the induced dipole. The solvent may include at least one of tetraline and diethylbenzene. In the QR solution layer  354 , the QRs  310  are randomly arranged. 
         [0117]    Next, as shown in  FIG. 8D , with generating an electric field between the pixel and common electrodes  350  and  352 , the QR solution layer  354  (of  FIG. 8C ) is cured to form the QR film  370 . When the electric field is generated between the pixel and common electrodes  350  and  352 , the QRs  310  and the axis of the dipole side chains  324  of the polymer  320  are arranged along the direction of the electric field. In addition, after the curing process for forming the QR film  370 , the QRs  310  and the dipole side chains  324  maintain their arrangement without the electric field. The curing process may be performed by heat generated in a step of forming the electric field. Alternatively, an additional curing step including UV irradiation or heating may be performed to the QR solution layer  354  including a UV curing agent or a thermal curing agent. 
         [0118]    Namely, in the present invention, without a process of forming an alignment layer and a process of aligning or rubbing the alignment layer, the QRs  310  can be aligned or arranged to be parallel to the electric field. Since the QR solution layer  354  is cured with the electric field, the curing process for forming the QR film  370  and the aligning process of the QRs  310  are performed in one process. Accordingly, a fabricating process is simplified. 
         [0119]    As mentioned above, since the arrangement degree of the QR  310  is increased by the dipole side chain  324  of the polymer  320  being capable of generating the induced dipole, the QR film  370  has advantages in the driving voltage and the polarization property without loss of quantum efficiency. 
         [0120]    Next, as shown in  FIG. 8E , the second substrate  360  is disposed over the QR film  370 , and the first and second substrates  330  and  360  are attached. As a result, the display panel  305  is fabricated. The backlight unit  307  including the UV light source is disposed under the display panel  305  such that the display device  300  of the present invention is provided. 
       Fourth Embodiment 
       [0121]      FIG. 9  is a schematic cross-sectional view of a display device including a QR layer according to a fourth embodiment of the present invention. 
         [0122]    As shown in  FIG. 9 , a QR display device  400  of the present invention includes a display panel  405 , which includes pixel and common electrodes  450  and  452  for generating an electric field, a QR film  470 , and a polarization plate  480 , and a backlight unit  407  including a UV light source (not shown). 
         [0123]    The display panel  405  includes a first substrate  430 , which is adjacent to the backlight unit  407 , the pixel and common electrodes  450  and  452 , which is positioned over the first substrate  430 , a second substrate  460 , which faces the first substrate  430 , the QR film  470 , which is positioned between the first and second substrates  430  and  460 , and the polarization plate  480  at an outer side of the second substrate  460 . The QR film  470  includes the QR  410  and the polymer  420 . 
         [0124]    The pixel electrode  450  and the common electrode  452  are positioned between the first substrate  430  and the QR film  470  and generate a horizontal electric field for driving the QR  410  of the QR film  470 . As mentioned above, each common electrode  352  may be positioned in between two pixel electrodes  350 , so that a horizontal electric field is generated between each pair of adjacent pixel and common electrodes  350  and  352 . 
         [0125]    Alternatively, as mentioned above, one of the pixel and common electrodes  450  and  452  may have a plate shape, and the other one of the pixel and common electrodes  450  and  452  may include at least one opening. In this instance, the pixel and common electrodes  450  and  452  are positioned in different layers and overlap each other in a pixel region. Namely, the display panel  405  may have a fringe field switching (FFS) mode electrode structure. 
         [0126]    A thin film transistor (TFT) Tr as a switching element is formed on the first substrate  430 , and the pixel electrode  450  may be connected to the TFT Tr. 
         [0127]    The QR film  470  is positioned between the first and second substrates  430  and  460  and includes the QR  410  and the polymer  420 . The polymer  420  includes the main chain  422  and the dipole side chain  424 . The QR  410  and the dipole side chain  424  may be arranged in a direction being substantially parallel to the horizontal electric field between the pixel and common electrodes  450  and  452 . 
         [0128]    Namely, referring to  FIG. 2 , the QR  410  has a rod shape that has a major axis and a minor axis. The QR  410  is arranged such that the major axis of the QR  410  is parallel to the direction of the electric field between the pixel and common electrodes  450  and  452 . In other words, the major axis of the QR  410  is arranged along a direction being perpendicular to an extension direction of the pixel and common electrodes  450  and  452 . 
         [0129]    For example, the QR composition, which includes the QR  410 , the polymer  420 , and the solvent (not shown), are coated over the first substrate  430  including the pixel and common electrodes  450  and  452 . In this instance, the QRs  410  are randomly dispersed in the solvent. When the voltages are applied to the pixel electrode  450  and the common electrode  452 , the QRs  410  are arranged such that the major axis of the QRs  410  is parallel to the direction of the electric field between the pixel and common electrodes  450  and  452 . In this step, the QR composition is cured to form the QR film  470 . As a result, in the QR film  470 , the major axis of the QRs  410  is parallel to the direction of the electric field between the pixel and common electrodes  450  and  452 . 
         [0130]    As mentioned above, since an induced dipole is generated in the dipole side chain  424  of the polymer  420 , the axis of the dipole side chains  424  are arranged along the direction of the electric field between the pixel and common electrodes  450  and  452 . Namely, the polymer  420  serves as a guide for arrangement of the QRs  410 . As a result, the arrangement degree of the QRs  410  is improved. 
         [0131]    In the display device including the QR film  470  of the present invention, the processes of forming the alignment layer and aligning the alignment layer are not required, and the QR film  470  having the improved QR arrangement degree is formed by a solution process. In addition, since the QRs  410  can emit red, green, and blue lights, a color filter, which is required in the LCD device, can be omitted. 
         [0132]    In the QR display device  400  of the present invention, a lower surface of the QR film  470  may contact the pixel and common electrodes  450  and  452  without the alignment layer, and an upper surface of the QR film  470  may contact the second substrate  460 . When the other elements are formed on the pixel and common electrodes  450  and  452  and a bottom side of the second substrate  460 , the QR film  470  may contact these elements. 
         [0133]    On the other hand, when the pixel electrode  450  and the common electrode  452  are configured to have a fringe field switching mode structure, the QR film  470  may contact one of the pixel and common electrodes  450  and  452 . 
         [0134]    In addition, when the pixel electrode  450  and the common electrode  452  are configured to have the fringe field switching mode structure, the length direction, i.e., the major axis, of the QRs  410  are arranged to be parallel to an extension direction, i.e., a major axis, of the opening in one of the pixel electrode  450  and the common electrode  452 . 
         [0135]    The polarization plate  480  of the QR display device  400  is disposed at the outer side of the second substrate  460  and has an optical transmissive axis being parallel to a horizontal length direction, i.e., a major axis direction, of the QR  410 . As a result, the polarization plate  480  transmits the linearly-polarized light emitted from the QR  410  such that images are displayed. 
         [0136]    In addition, since the polarization plate  480  is disposed at an outer position of the QR display device  400 , an ambient light reflection is prevented or minimized. Accordingly, the decrease of the visibility by the ambient light reflection is prevented. 
         [0137]      FIG. 10  is a graph showing an On/Off property in a display device including the QR film, and  FIG. 11  is a graph showing a polarization property in a display device including the QR film. (“OFF ratio (%)” is a ratio of a brightness in On state with voltages to a brightness in OFF state without voltages) 
         [0138]    A QR film is formed using QR composition listed in Table 1 (polymer molecular weight: 20,000, solution viscosity: 10 cP), and the driving property and the polarization property are measured. The “Polymer1” is the compound in the Formula 2-1, the “Polymer2” is the compound in the Formula 2-2, and “Polymer3” is the compound in the Formula 2-3. 
         [0000]    
       
         
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Ref 
                 Ex1 
                 Ex2 
                 Ex3 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 Polymer (15 wt %) 
                 Polyester 
                 Polymer1 
                 Polymer2 
                 Polymer3 
               
               
                 QR (3 wt %) 
                 CdSe/CdS 
                 CdSe/CdS 
                 CdSe/CdS 
                 CdSe/CdS 
               
               
                 Solvent (82 wt %) 
                 Tetralin 
                 Tetralin 
                 Tetralin 
                 Tetralin 
               
               
                   
               
             
          
         
       
     
         [0139]    As shown in Table 1 and  FIGS. 10 and 11 , in the QR film including the polymer having the dipole side chain, the driving property and the polarization property are improved. 
         [0140]    Namely, as mentioned above, when the QR film is formed by the QR composition including the polymer having the dipole side chain, there are advantages in the driving voltage and the polarization property without loss of the quantum efficiency. 
         [0141]    In the present invention, since the QR composition includes the polymer having the polymer having the dipole side chain, the QR film can be formed by the solution process and the problem of increase of the driving voltage or decrease of the polarization property are prevented or minimized. 
         [0142]    In addition, in the display panel including the QR film, since the arrangement degree of the QRs is increased without the alignment layer, the fabricating process of the display device is simplified. 
         [0143]    Moreover, since the QR display device does not require the polarization plate and the color filter layer, the thickness of the display device and the production cost are reduced. 
         [0144]    It will be apparent to those skilled in the art that various modifications and variations can be made in the embodiments of the invention without departing from the spirit or scope of the invention. Thus, it is intended that the modifications and variations cover this invention provided they come within the scope of the appended claims and their equivalents.