Patent Publication Number: US-2009230383-A1

Title: Passive matrix organic light emitting diode display device

Description:
BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention relates to passive matrix organic light emitting diode (PMOLED) display devices. More particularly, the present invention relates a PMOLED display device constructed of a matrix of vertical organic light emitting transistors. 
     2. Description of Related Art 
     As one of the most promising flat panel display devices of nowadays, the organic light emitting diode (OLED) display device adopts a light emitting principle different from that of the prior liquid crystal display device, which uses liquid crystals as an optical switching medium. That is because of that liquid crystals do not naturally emit light and thus need a backlight source and an external electric voltage applied thereon to rotate the liquid crystals and manage the light transmission rate of the backlight source. Differently, the organic light emitting diodes emit light when receiving an electric current and need no additional backlight source, thereby bringing advantages of a light weight and a compact size to a display device using the same. 
       FIG. 1  is a diagram of an equivalent circuit of a circuit of a conventional PMOLED (Passive Matrix Organic Light Emitting Diode) display device and  FIG. 2  is a diagram of the circuit of the conventional PMOLED display device. 
     As shown in  FIG. 1 , the equivalent circuit of the circuit of the conventional PMOLED display device comprises a plurality of first transistors (T S11 ˜T S1m , T S21 ˜T S2m , . . . , T Sn1 ˜T Snm ), a plurality of second transistors (T D11 ˜T D1m , T D21 ˜T D2m , . . . , T Dn1 ˜T Dnm ) and a plurality of organic light emitting diodes  11 . 
     Conventionally, the PMOLED display device implements a circuit wiring manner similar to that used in an LCD device, wherein data signal lines (D 1 , D 2 , . . . , Dm) and scan signal lines (S 1 , S 2 , . . . , Sn) are perpendicularly crossed and each set of a said data signal line and a said scan signal line that are crossed controls a pixel unit  12  that comprises one said first transistor T S11 , one said second transistor T D11 , and one said organic light emitting diode  11 . 
     For example, the first transistor T S11 , having a gate that is electrically connected to the scan signal line S 1  and a source that is electrically connected to the data signal line D 1 , acts as a storage switch for addressably storing input image data. The second transistor T D11  has a gate that is electrically connected to a drain of the first transistor T S11  and a source that is electrically connected to a power supply voltage V DD . The organic light emitting diode  11  has an anode that is electrically connected to a drain of the second transistor T D11  and a cathode electrically connected to a ground potential GND. Thereby, each said pixel unit  12  can be turned on/off by using a data driver  13  and a gate driver  14  to control the data signal lines (D 1 , D 2 , . . . , Dm) and the scan signal lines (S 1 , S 2 , . . . , Sn), respectively. 
     However, as can be seen in  FIG. 2 , the first transistors (T S11 ˜T S1m , T S21 ˜T S2m , . . . , T Sn1 ˜T Snm ) and the second transistors (T D11 ˜T D1m , T D21 ˜T D2m , . . . , T Dn1 ˜T Dnm ) take a substantial area on the OLED display device, and consequently decrease an aperture ratio of each said pixel unit  12  that in turn reduce an active area of the pixel unit  12 . To state briefly, the conventional organic light emitting diode display device suffers a limitation in image definition thereof due to the presence of the first transistors (T S11 ˜T S1m , T S21 ˜T S2m , . . . , T Sn1 ˜T Snm ) and the second transistors (T D11 ˜T D1m , T D21 ˜T D2m , . . . , T Dn1 ˜T Dnm ). 
     SUMMARY OF THE INVENTION 
     The present invention provides a passive matrix organic light emitting diode display device, which is composed of a plurality of vertical organic light emitting transistors. Since the vertical organic light emitting transistor is constructed by vertically integrating a transistor with an organic light emitting diode, it takes a reduced area on the organic light emitting diode display device, so as to improve an aperture ratio of each pixel unit and in turn enhance an overall active area as well as a luminance of the organic light emitting diode display device. 
     To achieve the aforementioned objective, the disclosed passive matrix organic light emitting diode display device comprises a plurality of vertical organic light emitting transistors, each having a first collector, a first grid/base, and a first emitter, wherein the first collectors are electrically connected and arranged parallelly to form a plurality of first scan units, and the first grids/bases are electrically connected and arranged parallelly to form a plurality of second scan units while the first emitters are electrically connected and arranged parallelly to form a plurality of third scan units, in which the first scan units and the second scan units are crisscrossed while the second scan units and the third scan units are crisscrossed. 
     By implementing the present invention, at least the following progressive effects can be achieved:
     1. By using vertical organic light emitting transistors to construct a passive matrix organic light emitting diode display device, an aperture ratio at each pixel unit is increased.   2. An overall active area and a luminance of a passive matrix organic light emitting diode display device are enhanced.   3. An image definition of a passive matrix organic light emitting diode display device is advanced.   

    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention as well as a preferred mode of use, further objectives and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings, wherein: 
         FIG. 1  is a diagram of an equivalent circuit of a circuit of a conventional passive matrix organic light emitting diode display device; 
         FIG. 2  is a diagram of the circuit of the conventional passive matrix organic light emitting diode display device; 
         FIG. 3  is a perspective view of a passive matrix organic light emitting diode display device according to a first embodiment of the present invention; 
         FIG. 4  is a top view of the passive matrix organic light emitting diode display device according to the first embodiment of the present invention; 
         FIG. 5  is a perspective view of a passive matrix organic light emitting diode display device according to a second embodiment of the present invention; 
         FIG. 6  is a sectional view taken in row A-A of  FIG. 3  according to a first aspect of the present invention; 
         FIG. 7  is a sectional view taken in row A-A of  FIG. 3  according to a second aspect of the present invention; 
         FIG. 8  is a sectional view taken in row A-A of  FIG. 3  according to a third aspect of the present invention; 
         FIG. 9  is a sectional view taken in row A-A of  FIG. 3  according to a fourth aspect of the present invention; and 
         FIG. 10  is a sectional view taken in row A-A of  FIG. 3  according to a fifth aspect of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     As illustrated in  FIG. 3 , a passive matrix organic light emitting diode display device according to a first embodiment of the present invention comprises a plurality of vertical organic light emitting transistors  20 , each having a first collector  21 , a first grid/base  22 , and a first emitter  23 . Therein, the plural vertical organic light emitting transistors  20  are crisscrossed into a matrix. As shown in  FIG. 3 , the display device comprises a matrix constructed from 3×3 vertical organic light emitting transistors  20 . 
     The first collectors  21  of the vertical organic light emitting transistors  20  placed in a same column are electrically connected to form a plurality of first scan units  30  that are mutually parallel. The first grids  22  or the first bases  22  of the vertical organic light emitting transistors  20  placed in a same row are electrically connected to form a plurality of second scan units  40  that are mutually parallel. Similarly, the first emitters  23  of the vertical organic light emitting transistors  20  placed in a same column are electrically connected to form a plurality of third scan units  50  that are mutually parallel. 
     With reference to  FIG. 4 , the first scan units  30  are mutually parallel while being crisscrossed with the second scan units  40 . Similarly, the third scan units  50  are crisscrossed with the second scan units  40 . That is to say, the third scan units  50  and the first scan units  30  are mutually parallel so as to construct the passive matrix organic light emitting diode display device. In addition, an external circuit may be implemented to control the first scan units  30 , the second scan units  40  and the third scan units  50 , thereby driving each said vertical organic light emitting transistor  20 . 
     For example, by conducting the first scan units  30  and the third scan units  50  of the first column plus the second scan units  40  of a second row, the vertical organic light emitting transistor  20  located at an intersection of the second row and the first column can be driven. Or, by conducting the first scan units  30  and the third scan units  50  of the second and third columns plus the second scan units  40  of the first row, the vertical organic light emitting transistor  20  located at an intersection of the second row and the second column and another said vertical organic light emitting transistor  20  located at an intersection of the first row and the third column can be driven at the same time. Consequently, each said vertical organic light emitting transistor  20  can be controlled respectively through the external circuit. 
     As shown in  FIG. 5 , the third scan units  50  may be integrated as a common electrode so that when the third scan units  50  are conducted, the vertical organic light emitting transistor  20  can be selectively driven by controlling the first scan units  30  and the second scan units  40 . For example, the first scan units  30  of the first column and the second scan units  40  of the second row can be conducted to drive the vertical organic light emitting transistor  20  located at an intersection of the second row and the first column. Or, by conducting the first scan units  30  of the second column and the third column plus the second scan units  40  of the first row, the vertical organic light emitting transistors  20  located at an intersection of the second row and the second column as well as another said vertical organic light emitting transistors  20  located at an intersection of the first row and the third column can be driven. 
       FIG. 6  provides a sectional view of the passive matrix organic light emitting diode display device according to a first aspect of the present invention. Therein, each said vertical organic light emitting transistor  20  further comprises a first vertical transistor  60  and a first organic light emitting diode  70 . 
     The first vertical transistor  60  comprises a first electrode  61 , a first organic layer  62 , and a second electrode  63 . The first organic layer  62  is stacked on the first electrode  61  and the second electrode  63  is located in the first organic layer  62 . The second electrode  63  may be located in any portion of the first organic layer  62 , including being settled on the first organic layer  62 . The second electrode  63  controls an amount of electrons/electron holes pass therethrough so as to modulate the luminance of the first organic light emitting diode  70 . 
     The first organic layer  62  may be selected from a group consisting of an HIL (Hole Injection Layer), an HTL (Hole Transport Layer), an HBL (Hole Blocking Layer), an EBL (Electron Blocking Layer), an ETL (Electron Transport Layer) and an EIL (Electron Injection Layer). 
     The first organic light emitting diode  70  comprises a second organic layer  71  and a third electrode  72 . The second organic layer  71  comprises an EML (EMission Layer), or further comprises one layer selected from a group consisting of an HIL, an HTL, an HBL, an EBL, an ETL and an EIL so as to reduce energy barrier difference between the layers and in turn enhance luminescence efficiency of the first organic light emitting diode  70 . The second organic layer  71  is perpendicularly stacked on the first vertical transistor  60 , for example, on the first organic layer  62  or the second electrode  63  while the third electrode  72  is stacked on the second organic layer  71 . 
     The first electrode  61  of the first vertical transistor  60  may be an anode, and may act as the first emitter  23  of the vertical organic light emitting transistor  20 . The first electrode  61  may be a transparent electrode such as ITO (Indium Tin Oxide), or may be made of gold, platinum, molybdenum oxide/aluminum, PEDOT/molybdenum oxide/aluminum, or a combination thereof. The first organic layer  62  may comprises an HIL and an HTL, wherein the HIL may be stacked on the first electrode  61  and the HTL may be then stacked on the HIL. 
     The second electrode  63  of the first vertical transistor  60  may be a grid and may act as the first grid  22  of the vertical organic light emitting transistor  20 . The second electrode  63  may be located in any portion of the HTL, including being settled on the HTL. The third electrode  72  of the first organic light emitting diode  70  may be a cathode for acting as the first collector  21  of the vertical organic light emitting transistor  20 . The third electrode  72  may be made of calcium/aluminum, lithium fluoride/aluminum, cesium fluoride/aluminum, barium/aluminum, or a combination thereof. 
     The second electrode  63  of the first vertical transistor  60  serves to control an amount of the electron holes entering the first organic light emitting diode  70 . The electron holes are allowed to pass the second electrode  63  and enter the first organic light emitting diode  70  by properly modulating voltages of the second electrode  63  and the third electrode  72 . After entering the first organic light emitting diode  70 , the electron holes are recombined with the electrons injected from the third electrode  72  at the second organic layer  71  and thereby the EML of the second organic layer  71  emits light. 
     Besides, the first electrode  61  of the first vertical transistor  60  may be also a cathode for acting as the first emitter  23  of the vertical organic light emitting transistor  20 . The first electrode  61  may be made of calcium/aluminum, lithium fluoride/aluminum, cesium fluoride/aluminum, barium/aluminum, or a combination thereof. The first organic layer  62  may comprise an ETL that is stacked on the first electrode  61 . The second electrode  63  of the first vertical transistor  60  may be a grid for acting as the first grid  22  of the vertical organic light emitting transistor  20  and may be located in any portion of the ETL, including being settled on the ETL. The third electrode  72  of the first organic light emitting diode  70  may be an anode and may act as the first collector  21  of the vertical organic light emitting transistor  20 . The third electrode  72  may be a transparent electrode such as ITO (Indium Tin Oxide) so that the light emitted from the first organic light emitting diode  70  is allowed to pass through the third electrode  72  and emit upward. Alternatively, the third electrode  72  may be made of gold, platinum, molybdenum oxide/aluminum, PEDOT/molybdenum oxide/aluminum, or a combination thereof. 
     The second electrode  63  serves to control an amount of the electrons entering the first organic light emitting diode  70 . The electrons are allowed to pass the second electrode  63  and enter the first organic light emitting diode  70  by properly modulating voltages of the second electrode  63  and the third electrode  72 . After entering the first organic light emitting diode  70 , the electrons are recombined with the electron holes injected from the third electrode  72  at the second organic layer  71  and thereby the EML of the second organic layer  71  emits light. 
       FIG. 7  provides a sectional view of the passive matrix organic light emitting diode display device according to a second aspect of the present invention. In this aspect, a fourth electrode  73  is additionally provided between the first organic layer  62  of the first vertical transistor  60  and the second organic layer  71  of the first organic light emitting diode  70  of  FIG. 6 . The fourth electrode  73  may be made of a metal, such as aluminum or silver, or the fourth electrode  73  may be formed as a multi-layer structure comprising a highly conductive macromolecular material such as PEDOT or a metal and other materials. Such multi-layer structure may be made of aluminum/molybdenum oxide, aluminum/molybdenum oxide/PEDOT, gold/PEDOT and so on. 
     As mentioned previously, when the first electrode  61  of the first vertical transistor  60  is the anode acting as the first emitter  23  of the vertical organic light emitting transistor  20 , and the second electrode  63  of the first vertical transistor  60  is the grid acting as the first grid  22  of the vertical organic light emitting transistor  20  while the third electrode  72  of the first organic light emitting diode  70  is the cathode acting as the first collector  21  of the vertical organic light emitting transistor  20 , the fourth electrode  73  is properly an anode. 
     Otherwise, when the first electrode  61  of the first vertical transistor  60  is the cathode acting as the first emitter  23  of the vertical organic light emitting transistor  20 , and the second electrode  63  of the first vertical transistor  60  is the grid acting as the first grid  22  of the vertical organic light emitting transistor  20  while the third electrode  72  of the first organic light emitting diode  70  is the anode acting as the first collector  21  of the vertical organic light emitting transistor  20 , the fourth electrode  73  is properly a cathode. 
     In  FIG. 8 , a sectional view of the passive matrix organic light emitting diode display device according to a third aspect of the present invention is provided. Therein, each said vertical organic light emitting transistor  20  comprises a second vertical transistor  80  and a second organic light emitting diode  90 . 
     The second vertical transistor  80  comprises a fifth electrode  81 , a third organic layer  82 , an insulation layer  83 , and a sixth electrode  84 . The third organic layer  82  is stacked on the fifth electrode  81  while the insulation layer  83  is sandwiched between the third organic layer  82  and the sixth electrode  84 . The third organic layer  82  may be selected from a group consisting of an HIL (Hole Injection Layer), an HTL (Hole Transport Layer), an HBL (Hole Blocking Layer), an EBL (Electron Blocking Layer), an ETL (Electron Transport Layer) and an EIL (Electron Injection Layer). 
     The second organic light emitting diode  90  comprises a fourth organic layer  91  and a seventh electrode  92 . The fourth organic layer  91  comprises an EML (EMission Layer), or further comprises one layer selected from a group consisting of an HIL, an HTL, an HBL, an EBL, an ETL and an EIL so as to reduce energy barrier difference between the layers by different combinations and in turn enhance luminescence efficiency of the second organic light emitting diode  90 . The fourth organic layer  91  is perpendicularly stacked on the second vertical transistor  80 , for example, perpendicularly stacked on the sixth electrode  84  while the seventh electrode  92  is stacked on the fourth organic layer  91 . 
     The fifth electrode  81  of the second vertical transistor  80  may be an anode, and may act as the first emitter  23  of the vertical organic light emitting transistor  20 . The fifth electrode  81  may be a transparent electrode such as ITO (Indium Tin Oxide), or may be made of gold, platinum, molybdenum oxide/aluminum, PEDOT/molybdenum oxide/aluminum, or a combination thereof. The third organic layer  82  may comprise an HIL and an HTL, wherein the HIL may be stacked on the fifth electrode  81  and the HTL may be then stacked on the HIL. The insulation layer  83  may be first stacked on the HTL, and then the sixth electrode  84  may be stacked on the insulation layer  83 . The sixth electrode  84  may be a base for acting as the first base  22  of the vertical organic light emitting transistor  20 . The fourth organic layer  91  of the second organic light emitting diode  90  may comprise an EML (EMission Layer), and the seventh electrode  92  may be a cathode for acting as the first collector  21  of the vertical organic light emitting transistor  20 , wherein the seventh electrode  92  may be made of calcium/aluminum, lithium fluoride/aluminum, cesium fluoride/aluminum, barium/aluminum, or a combination thereof. 
     When the insulation layer  83  and the sixth electrode  84  are in proper thicknesses, the electron holes injected from the fifth electrode  81  are allowed to tunnel through the insulation layer  83  and then pass through the sixth electrode  84  ballistically. By controlling the current of the sixth electrode  84 , the electron holes can pass the sixth electrode  84  and get into the fourth organic layer  91  without collision and contribute to the base current. After passing through the sixth electrode  84  and reaching the fourth organic layer  91 , the electron holes are recombined with the electrons injected from the seventh electrode  92  at the fourth organic layer  91  and thereby the light emits from the EML of the fourth organic layer  91 . Consequently, a light-emitting intensity of the second organic light emitting diode  90  can be controlled by using a current of the sixth electrode  84  to modulate the amount the electron holes entering the second organic light emitting diode  90 . 
     Besides, the fifth electrode  81  of the second vertical transistor  80  may be a cathode for acting as the first emitter  23  of the vertical organic light emitting transistor  20 . The fifth electrode  81  may be made of calcium/aluminum, lithium fluoride/aluminum, cesium fluoride/aluminum, barium/aluminum, or a combination thereof. The third organic layer  82  may comprise an ETL that is stacked on the fifth electrode  81 . The insulation layer  83  may be first stacked on the ETL, and then the sixth electrode  84  may be stacked on the insulation layer  83 . The sixth electrode  84  may be a base for acting as the first base  22  of the vertical organic light emitting transistor  20 . The fourth organic layer  91  of the second organic light emitting diode  90  may comprise an EML (EMission Layer), and the seventh electrode  92  may be an anode for acting as the first collector  21  of the vertical organic light emitting transistor  20 , wherein the seventh electrode  92  may be a transparent electrode such as ITO (Indium Tin Oxide) so that the light emitted from the second organic light emitting diode  90  is allowed to emit upward through the seventh electrode  92 . Alternatively, the seventh electrode  92  may be made of gold, platinum, molybdenum oxide/aluminum, PEDOT/molybdenum oxide/aluminum, or a combination thereof. 
     Similarly, when the insulation layer  83  and the sixth electrode  84  are in proper thicknesses, the electrons injected from the fifth electrode  81  are allowed to tunnel through the insulation layer  83  and then pass through the sixth electrode  84  ballistically. By controlling the current of the sixth electrode  84 , the electron can pass the sixth electrode  84  and get into the fourth organic layer  91  without collision and contribute to the base current. After passing through the sixth electrode  84  and reaching the fourth organic layer  91 , the electrons are recombined with the electron holes injected from the seventh electrode  92  at the fourth organic layer  91  and thereby the light emits from the EML of the fourth organic layer  91 . Consequently, the light-emitting intensity of the second organic light emitting diode  90  can be controlled by using a current of the sixth electrode  84  to modulate an amount the electrons entering the second organic light emitting diode  90 . 
       FIG. 9  is a sectional view of the passive matrix organic light emitting diode display device according to a third aspect of the present invention. Therein, a fifth organic layer  85  is additionally provided between the sixth electrode  84  of the second vertical transistor  80  and the fourth organic layer  91  of the second organic light emitting diode  90  of the second aspect as shown in  FIG. 8 . The fifth organic layer  85  may be an ETL, an EBL, and HTL or an HBL so as to reduce energy barrier difference between the layers and in turn enhance luminescence efficiency of the second organic light emitting diode  90 . 
       FIG. 10  provides a sectional view of the passive matrix organic light emitting diode display device according to a fourth aspect of the present invention wherein an eighth electrode  86  is further added to the third aspect of the present invention as shown in  FIG. 9 . The fifth organic layer  85  is stacked on the sixth electrode  84  and then the eighth electrode  86  is stacked on the fifth organic layer  85  so that the eighth electrode  86  is sandwiched between the fourth organic layer  91  and the fifth organic layer  85 . The eighth electrode  86  may be made of a metal, such as aluminum or silver, or the eighth electrode  86  may be formed as a multi-layer structure comprising a highly conductive macromolecular material such as PEDOT or a metal and other materials. Such multi-layer structure may be made of aluminum/molybdenum oxide, aluminum/molybdenum oxide/PEDOT, gold/PEDOT and so on. 
     As mentioned previously, when the fifth electrode  81  of the second vertical transistor  80  is the anode acting as the first emitter  23  of the vertical organic light emitting transistor  20 , and the sixth electrode  84  is the base acting as the first base  22  of the vertical organic light emitting transistor  20  while the seventh electrode  92  is the cathode acting as the first collector  21  of the vertical organic light emitting transistor  20 , the eighth electrode  86  is properly an anode. Otherwise, when the fifth electrode  81  of the second vertical transistor  80  is the cathode acting as the first emitter  23  of the vertical organic light emitting transistor  20 , and the sixth electrode  84  is the base acting as the first base  22  of the vertical organic light emitting transistor  20  while the seventh electrode  92  is the anode acting as the first collector  21  of the vertical organic light emitting transistor  20 , the eighth electrode  86  is properly a cathode. 
     For meeting various needs in design, the vertical organic light emitting transistor  20  may be uprighted on either end so that the vertical organic light emitting transistor  20  can emit light upward or downward. Alternatively, a proper material may be used to produce the vertical organic light emitting transistor  20  so that the electrodes at the both ends thereof can be light-previous so that the vertical organic light emitting transistor  20  can emit light at its both ends simultaneously. Furthermore, by constructing the vertical organic light emitting transistors  20  into a passive matrix organic light emitting diode display device, an aperture ratio of each pixel unit in the display device can be increased and consequently an active area as well as a luminance of the display device can be enhanced. Meanwhile, an area of each said pixel unit can be downsized and an image definition of the passive matrix organic light emitting diode display device can be ameliorated. 
     Although the particular embodiments of the invention have been described in detail for purposes of illustration, it will be understood by one of ordinary skill in the art that numerous variations will be possible to the disclosed embodiments without going outside the scope of the invention as disclosed in the claims.