Patent Grant
8698791
1. Field of the Invention
The present method relates to a display apparatus, and more particularly, to a display apparatus configured to display a color image by driving light emitting elements of different colors to emit light in a time division manner and a method of driving such a display apparatus.
2. Description of the Related Art
One method of displaying a color image is to prepare an array of three types of light emitting elements each configured to emit light of one of R (red), G (green), and B (blue) colors and drive these light emitting elements at the same time to obtain an image with a mixture of colors. This method is widely used to display a color image.
U.S. Pat. No. 7,403,177 discloses another method in which three colors are sequentially emitted in each pixel repeatedly in a short time such that colors are mixed temporally. This method is known as a time-division driving method.
In the time-division driving method, R, G, and B colors are sequentially emitted in each pixel and thus it is possible to share a driving circuit. An organic electroluminescent element may be used as light emitting element. Organic electroluminescent elements of three colors of R, G, and B may be formed one on another into a multilayer structure, and electrodes may be disposed on the top and bottom of the multilayer structure and in an intermediate layer thereof such that the organic electroluminescent elements can be independently driven. This structure allows light of each color to be emitted over the entire area of each pixel.
In the time-division driving method disclosed in U.S. Pat. No. 7,403,177, R, G, and B light emitting elements are driven while temporally switching these light emitting elements. To this end, a switch is disposed between a driving circuit and electrodes of the light emitting elements. U.S. Pat. No. 5,748,160 discloses a technique in which the above-described switch is removed, and, instead, a driving circuit is connected in common to electrodes of R, G, and B light emitting elements and a voltage is applied to opposite electrodes that are separately provided for the respective R, G, and B light emitting elements such that timing of applying the voltage is sequentially shifted to emit light sequentially by the R, G, and B light emitting elements. That is, the voltage is applied to the opposite electrodes of the R, G, and B light emitting elements at different times. To represent a halftone image, a frame may be divided into sub-frames and the applied voltage may be changed stepwise. If R, G, and B images are displayed sequentially in time, an edge of an object in a moving picture is colored when seen by human eyes. This phenomenon is known as color break-up. Because the color break-up is caused by displaying R, G, and B images at different times, the color break-up also occurs when each period of displaying one of R, G, and B images is divided into sub-frames to represent halftone.
In an aspect, the present invention provides an apparatus includes a plurality of light emitting elements configured to emit light of colors assigned to respective light emitting elements by providing currents flowing between first and second electrodes, a plurality of driving circuits connected to the first electrodes of the light emitting elements to supply currents thereto, and a plurality of power supply lines connected to the second electrodes of the light emitting elements to supply voltages to the second electrodes. A set of the light emitting elements that emit light of colors different from each other are connected such that the first electrodes are connected in common to one of the driving circuits, and the second electrodes are separately connected to the plurality of the power supply lines, and the light emitting elements whose second electrodes are connected to one of the power supply lines include light emitting elements configured to emit light of different colors.
In an aspect, the present invention provides a method of driving the display apparatus, including applying a voltage, that causes light emitting elements to turn on to emit light, to one of the power supply lines and applying a voltage, that causes light emitting elements to turn off to emit no light, to the other power supply lines, wherein applying the voltages is performed sequentially for the plurality of power supply lines.
The invention may be applied to an emissive display such as an organic electroluminescent element. The display apparatus may be a stand-alone display such as a television receiver capable of receiving a television broadcast wave and displaying an image thereof, or the display apparatus may be embedded in another apparatus such as a digital camera.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
A light emitting element such as an organic electroluminescent element has a diode characteristic in which a current flows only in one direction to emit light. If one of two electrodes i.e., an anode or a cathode is connected to a current source (hereinafter this electrode is referred to as a first electrode) and the other electrode (hereinafter referred to as a second electrode) is applied with a voltage sufficiently lower than the voltage of the current source, a current flows through the light emitting element. When the voltage applied to the second electrode is higher than the current source voltage applied to the first electrode, no current flows. This means that it is possible to turn on and off the current by controlling the voltage applied to the second electrode.
A screen of a display apparatus includes a plurality of pixels. Each pixel includes light emitting elements of different colors, which may be three colors of R (red), G (green), and B (blue) or may be a combination of other and/or additional colors. First electrodes of these light emitting elements are connected together to a driving circuit serving as a current source, while the second electrode of each light emitting element is separately formed and is individually applied with a voltage. The second electrode formed separately for each light emitting element is connected to second electrodes of light emitting elements of the same color or different colors in other pixels such that the same voltage can be applied at the same time to the second electrode of all pixels. By controlling the voltage of the second electrode, it is possible to emit light from one light emitting element of each pixel while turning off the other light emitting elements. By switching the active light emitting element sequentially, it is possible to switch the color of the image being displayed. If the switching is performed repeatedly at a high speed, the resultant image can be seen by human eyes as an image including a mixture of colors.
The present invention is described in further detail below with reference to specific embodiments in conjunction with the accompanying drawings. In embodiments described below, by way of example, an organic electroluminescent element is used as a light emitting element, although the light emitting element is not limited to the organic electroluminescent element. It is also assumed that an anode is a first electrode connected to a driving circuit and a cathode is a second electrode. Note that a cathode of an organic electroluminescent element may be a first electrode and an anode thereof may be a second electrode, and a current may be supplied in an opposite direction.
First Embodiment
Cathodes of the three organic electroluminescent elements 103 to 105 are separately connected to respective cathode wirings 203 to 205 described below.
Although in the example shown in
The driving circuit 10 for driving the organic electroluminescent elements is not limited to that shown in
A display apparatus is configured such that pixels similar to that shown in
The number of light emitting elements forming one pixel and the combination of colors are not limited to those employed in the example described above in which each pixel includes one R light emitting element, one G light emitting element, and B light emitting element. Each pixel may include two or more light emitting elements. The number of light emitting elements disposed in each pixel is the same for all pixels. Each pixel is configured to include a plurality of light emitting elements to emit at least different colors. In the display apparatus, two or more light emitting elements disposed in one pixel may emit light of the same color. If the same current or the same voltage is applied to a plurality of light emitting elements and they emit light simultaneously, then they can be regarded as one light emitting element. However, when a plurality of light emitting elements of the same color are formed such that electrodes are separately provided therefor and they are driven individually by different signals, then these light emitting elements are regarded as different light emitting elements.
The cathodes of the three RGB organic electroluminescent elements 103 to 105 in each pixel 100 are isolated and extend in a direction perpendicular to a direction in which different colors are arranged, i.e., the cathodes extend in a vertical direction in
The cathode wirings 203 to 205 are connected such that cathodes of organic electroluminescent elements of the same color in pixels 100 at adjacent upper and lower locations are connected together. In
The cathode wirings 203 to 205 extends into an area outside a display area in which the pixels 100 are arranged in the form of a matrix, and the cathode wirings 203 to 205 are respectively connected to corresponding one of three power supply lines 206 to 208. In the outside of the pixel array area, the power supply lines 206 to 208 are selectively connected to one of the cathode wirings 203 to 205 of the pixels. Thus three systems of wirings are formed such that each wiring system includes one of the cathode wirings 203 to 205 and one of the power supply lines 206 to 208 whereby the cathode of each of the organic electroluminescent elements in each pixel is connected to the cathode of one of the organic electroluminescent elements in another pixel for all pixels. That is, the cathodes of the respective organic electroluminescent elements 103 to 105 in one pixel 100 are separately connected to respective three cathodes in another pixel for all pixels.
In the present embodiment, the power supply line 206 is connected to the R cathode wiring 203 in the first column, the G cathode wiring 204 in the second column, and the B cathode wiring 205 in the third column. The power supply line 207 is connected to the G cathode wiring 204 in the first column, the B cathode wiring 205 in the second column, and the R cathode wiring 203 in the third column. The power supply line 208 is connected to the B cathode wiring 205 in the first column, the R cathode wiring 203 in the second column, and the G cathode wiring 204 in the third column. In columns following the third column, connections are made in a similar manner every three columns.
That is, each of the power supply lines 206 to 208 is connected such that one color is selected from each column and such that selected colors are different for successive three columns.
The power supply line 206 is connected to a pair of voltage sources 212 and 213 via two switches 214a and 214b. The switch 214a is controlled by a signal 209, while the switch 214b is controlled by an inverted signal 209i produced by inverting the signal 209 by an inverter 217 such that the switches 214a and 214b operate in a complementary manner, i.e., in such a manner that when one of them is in an ON state, the other one is in an OFF state.
Similarly, the power supply lines 207 and 208 are connected to the same pair of voltage sources 212 and 213 via two switches 215a and 215b or 216a and 216b. The switch 215a is controlled by a signal 210, while the switch 215b is controlled by an inverted signal 210i produced by inverting the signal 210 by an inverter 218 such that the switches 215a and 215b operate in a complementary manner. The switch 216a is controlled by a signal 211, while the switch 216b is controlled by an inverted signal 211i produced by inverting the signal 211 by an inverter 219 such that the switches 216a and 216b operate in a complementary manner.
The first cathode power supply 212 outputs a first voltage V1 sufficiently lower than a potential Vcc of the current supply line 40 of the driving circuit 10. The second cathode power supply 213 outputs a second voltage V2 sufficiently higher than the potential Vcc of the current supply line 40. As described below, when the first voltage V1 is supplied to the cathodes of the organic electroluminescent elements 103 to 105, a forward bias voltage is applied between the two electrodes of each organic electroluminescent element and the organic electroluminescent element emits light. On the other hand, when the second voltage V2 is supplied to the pixel, a reverse bias voltage is applied between the two electrodes of each organic electroluminescent element and thus no light is emitted by the organic electroluminescent element. Hereinafter, V1 is referred to a light emission level and V2 is referred to as a no-light emission level.
In the first field from time t1 to time t4, data writing is first performed in a period from t1 to ta. The first, second, third, and following rows are sequentially selected at t1, t2, t3, . . . and so on, and control signals Scan1, Scan2, Scan3, . . . and so on are applied to the selection line 20. In synchronization with the control signals, data signals Data1, Data2, Data3 and so on are applied to data lines 30 in the respective columns. The control signal Scan1 is set to the selection potential in a period from t1 to t2 and data signals Data1=R11, Data2=G12 and Data3=B13 (following this, data signals are related to colors in the same order) are captured by pixels in the first row. These data signals are held as voltages in parasitic capacitance existing between the gate and the source of the driving transistor 102.
The control signal Scan2 is set to the selection potential in a period from t2 to t3 and data signals Data1=R21, Data2=G22, and Data3=B23 are held in the pixel circuits in the second row. Data signals are written in a similar manner for the following rows, and writing is complete for all rows at time ta. In the first field, data signals are written in pixels such that an R data signal is written in the first column, a G data signals is written in the second column, and a B data signal is written in the third column. In the following columns, data signals are written in a similar manner.
After the writing is completed for all rows, in a remaining period from ta to t4 of the first filed, the control signal 209 goes to the selection level (low level), the switch 214a turns on, and the switch 214b turns off. The control signals 210 and 211 are in the non-selection level (high level), the switches 215a and 216a are in the OFF state, and the switches 215b and 216b are in the ON state.
As a result, the power supply line 206 is switched to the light emission level V1, and thus the cathode wirings 203, connected therewith, of organic electroluminescent elements of each pixel column are switched to the light emission level V1. Because the power supply lines 207 and 208 are maintained in the state of being connected with the power supply 213, the potential of the cathode wiring 204 of G organic electroluminescent elements and the potential of the cathode wiring 205 of B organic electroluminescent elements in each column are at the no-light emission level V2. Therefore, in the first column, the forward bias voltage is applied only to R (red) organic electroluminescent elements 103 and light is emitted thereby depending on the held signal voltages. However, no light is emitted by the G (green) organic electroluminescent elements 104 and the B (blue) organic electroluminescent elements 105 in the first column because they are reversely biased. In the second column, light is emitted by G (green) organic electroluminescent elements. In the third column, light is emitted by B (blue) organic electroluminescent elements.
At time t4, the power supply line 206 is switched to the no-light emission level V2, and thus all organic electroluminescent elements are brought into the no-light emission state and the first field period is ended.
At time t4, the second field period starts, and the control signals Scan1, Scan2, . . . are sequentially switched to the selection potential at times t4, t5, t6, . . . in a similar manner to the first field. In synchronization with the control signals, data signals Data1=G11, G21, G31, . . . are captured from the data line in the first column, data signals Data2=B12, B22, B32, . . . are captured from the data line in the second column, and data signals Data3=R13, R23, R33, . . . are captured from the data line in the third column. These data signals are transferred to the pixels as signals that define the light emission luminance of the G (green) organic electroluminescent elements 104.
In a period from t4 to tb, the green data signals are written in all pixels. In a remaining period from tb to t7 in the second field period, the control signal 210 is switched to the selection potential. As a result, the power supply line 207 and the cathode wiring 204 are switched to the light emission level V1. The control signals 209 and 211 are maintained at the non-selection potential, and thus the power supply lines 206 and 208 and the cathode wirings 203 and 205 are set to the no-light emission level V2. As a result, the forward bias voltage is applied to G (green) organic electroluminescent elements in the first column, B (blue) organic electroluminescent elements in the second column, and R (red) organic electroluminescent elements in the third column, whereby light is emitted by these organic electroluminescent elements.
In the third field from time t7 to t10, the operation is performed in a similar manner such that data is written at times t7, t8, t9, . . . and light is emitted in a period from time tc to t10 such that blue light is emitted in the first column, red light in the second column, and green light in the third column.
In each field, light is emitted at the same time for all columns such that R, G, and B colors repeatedly appear every three columns. R, G, and B colors in three columns are cyclically exchanged from one filed to another in three fields. Note that in each field, colors are different between pixels that are adjacent in the row direction. In a case where displaying an image is controlled such that all pixels have the same color over a whole screen, color break-up can occur, i.e., edges of moving objects are colored when viewed by human eyes. However, in the present embodiment, an image includes all three colors in any field, and thus color break-up does not occur except for a special case in which white appears every three columns.
Second Embodiment
Data signals are supplied in the same manner in terms of the columns and the order as in the first embodiment.
As a result, respective pixels emit light of colors in each field as shown in
Third Embodiment
Each of the power supply lines 206 to 208 is connected to one of the three cathode wirings 203 to 205 in each row such that one color is selected from each row and such that selected colors are different for successive three rows. The cathode wirings 203 to 205 are connected to the power supply lines 206 to 208 in a similar manner to the first and second embodiments except that rows and columns are exchanged.
In the present embodiment, organic electroluminescent elements are arranged in the form of stripes in the row direction such that organic electroluminescent elements in each stripe have the same color. Thus, as with the arrangement shown in
The organic electroluminescent elements 103 to 105 respectively include anodes 103a to 105a, organic light emitting layers 7R, 7G, and 7B, and cathodes 103c to 105c such that light is emitted by a current flowing from an anode to a cathode. The selection transistor 101 and the driving transistor 102 are formed on a substrate 1, and each transistor has a semiconductor layer 3 connected to a source/drain electrode via a contact hole 5a formed in an insulating layer 2a. The source electrode of the selection transistor 101 is connected to the data line 30. The drain electrode 5 of the selection transistor 101 is connected to the gate electrode 4 of the driving transistor 102 via a wiring that is not shown in the figure. The current supply line 40 functions as the source electrode of the driving transistor 102. The drain electrode 5 of the driving transistor 102 is connected to the anode 6 of the organic electroluminescent element via the contact hole 5a formed in a second insulating layer 2b. In
The cathodes 103c to 105c are formed by a transparent electrode made of ITO (indium tin oxide) or the like. The separate cathodes 103c to 105c may be formed by forming an ITO film on the whole surface by using evaporation or sputtering and then cutting the ITO film into a plurality of pieces by irradiation of laser light. Alternatively, a metal mask may be used to achieve patterning. Still alternatively, patterning may be performed using an inverse-tapered pixel isolation film, or other similar processes may be used. In the example shown in
The organic electroluminescent element 103 has a structure in which the organic light emitting layer 7R is disposed between the anode 103a and the cathode 103c. In
The organic electroluminescent elements 104 and 105 also have a similar structure although there are differences in materials of the organic light emitting layers and thicknesses of respective layers.
When a voltage (a forward bias voltage) is applied across the organic electroluminescent element 103 such that its anode has a higher potential than the cathode, holes are injected from the hole injection layer into the light emitting layer and electrodes are injected from the electron injection layer into the light emitting layer. When the injected holes and electrons recombine in the light emitting layer, light is emitted. In a case where a voltage (a reverse bias voltage) is applied reversely such that the anode has a lower potential than the cathode, no carries are injected and no light is emitted. As described above, the organic electroluminescent element has a rectifying characteristic similar to that of a diode.
Fourth Embodiment
A pixel 100 includes four organic electroluminescent elements, i.e., an R (red) organic electroluminescent element 103, a first G (green) organic electroluminescent element 104, a B (blue) organic electroluminescent element 105, and a second G (green) organic electroluminescent element 106, which are arranged in this order in a row direction. These four organic electroluminescent elements 103 to 106 are arranged periodically in the row direction. In each column, organic electroluminescent elements of the same color are arranged although not shown in the figure.
Each pixel has two G (green) organic electroluminescent elements. In human eyes, among all colors, the greatest number of sense organs is provided for green color. By providing twice as many organic electroluminescent elements for green color as organic electroluminescent elements for red and blue, it is possible to increase the resolution compared with the structure in which organic electroluminescent elements of three colors are equally disposed. Hereinafter, the first green is denoted simply as G-I and the second green as G-II. A driving circuit 10 is configured in the same manner for all pixels, and each driving circuit 10 includes a selection transistor 101, a transfer transistor 107, a driving transistor 102, and two storage capacitors CH1 and CH2.
The driving transistor 102 in each driving circuit 10 is connected to a current supply line 40 that supplies a driving current to the organic electroluminescent element and also connected to anode electrodes of the organic electroluminescent elements 103 to 106 such that the current is supplied to these organic electroluminescent elements 103 to 106. The R organic electroluminescent element 103 and the G-I organic electroluminescent element 104 are driven in common by one driving circuit 10, while the B organic electroluminescent element 105 and the G-II organic electroluminescent element 106 are driven in common by another driving circuit 10. In the present embodiment, the R organic electroluminescent element and the G-I organic electroluminescent element form one sub-pixel 100a, while the B organic electroluminescent element and the G-II organic electroluminescent element form another sub-pixel 100b.
The cathodes of the organic electroluminescent elements 103 and 104 in the sub-pixel 100a are separately connected to the respective cathodes of the organic electroluminescent elements 105 and 106 in the adjacent sub-pixel 100b. More specifically, the cathode of the R organic electroluminescent element 103 in the sub-pixel 100a is connected to the cathode of the G-II organic electroluminescent element 106 in the adjacent sub-pixel 100b, and the cathode of the G-I organic electroluminescent element 104 in the sub-pixel 100a is connected to the cathode of the B organic electroluminescent element 105 in the adjacent sub-pixel 100b.
A display unit of a display apparatus is formed in the form of a pixel matrix including 1280 (=640×2) sub-pixels 100a and sub-pixels 100b arranged in the row direction and 480 sub-pixels 100a and sub-pixels arranged in the column direction.
In
B organic electroluminescent elements 105 are located in even-numbered columns and denoted by symbols B12, B14, . . . and so on, while G-II organic electroluminescent elements 106 are also located in even-numbered columns and denoted by symbols G12, G14, . . . and so on. The cathode of each organic electroluminescent element extends in the column direction such that it forms a single electrode together with cathodes of organic electroluminescent elements at upper and lower locations. This electrode is common for all cathodes of organic electroluminescent elements located in each column, and thus cathode wirings 233 and 234 are formed thereby.
In the present embodiment, not only in the column direction, but also in the row direction, cathodes of two adjacent organic electroluminescent elements in the same row are connected together into a single electrode, and thus the cathode wirings of organic electroluminescent elements in adjacent two columns are connected together into a single wiring. More specifically, a cathode wiring 234 is formed by the cathode shared by the G-I organic electroluminescent element G11 in the sub-pixel 100a and the B organic electroluminescent element B12 in the sub-pixel 100b to the right of the sub-pixel 100a. A cathode wiring 233 is formed by the cathode shared by the R organic electroluminescent element R13 in the sub-pixel 100a and the G-II organic electroluminescent element G12 in the sub-pixel 100b to the left of the sub-pixel 100a. In an outermost column, exceptionally, a cathode wiring is formed in a different manner such that a cathode wiring 233 is formed only by cathodes of organic electroluminescent elements R11, R21, R31, . . . and so on in one column.
The cathode wirings 233 and 234 extend into the outside of the display area and are connected alternately to the power supply lines 216 or 217 via contact holes 209. In the present embodiment, two power supply lines are provided and a light emission level voltage V1 and a no-light emission level voltage V2 are supplied to the two power supply lines from two cathode power supplies 212 and 213 such that the supplied voltages are switched periodically between V1 and V2.
One frame is divided into a first half part (a first field) and a second half part (a second field). In the first field, the signals Scan1, Scan2, . . . and so on are applied to the selection lines 20 in the respective rows such that the selection potential (high level) is sequentially supplied to the gates of the selection transistors 101 on a row-by-row basis. The selection line Scan1 in the first row has the selection potential in a period t1 and data signals supplied via data lines (Data1 to Data4) are transferred to first-stage storage capacitors CH1 of the pixel circuits 10. The operation is repeated such that the second row is selected in a period t2, the third row is selected in a period t3, and so on whereby data signals are written in pixel circuits in all rows.
Subsequently, the signals Transfer of the transfer signal lines 21 are switched to the high level in a period t11 at the same time for all rows thereby to turn on the transfer transistors 107 in the pixel circuits 10. As a result, the voltage stored in each first-stage storage capacitor CH1 is transferred to a corresponding second-stage storage capacitor CH2. After the transfer signal lines return to the low level, the voltage stored in each second-stage storage capacitor CH2 is still applied to the gate of a corresponding driving transistor 102.
After the end of the period t11, the light emission level voltage V1 is applied to the first power supply line 206 (Cathode1) and the no-light emission level voltage V2 is applied to the second power supply line 207 (Cathode2). As a result, organic electroluminescent elements on cathode wirings 233 connected to the first power supply line 206 (Cathode1) are forward biased and thus currents flow therethrough and light is emitted. On the other hand, organic electroluminescent elements on cathode wirings 234 connected to the second power supply line 207 (Cathode2) are reverse biases and thus no current flows therethrough and light is not emitted. Thus, in the light emission period in the first field, only one of the two organic electroluminescent elements in each of the sub-pixels 100a and 100b is turned on to emit light, and the other one is turned off to emit no light. In the second field, the Scan1 has the selection potential in a period t4, and the Scan2 has the selection potential in a period t5. Subsequently, the following rows are sequentially switched to the selection potential and the writing operation is performed in a similar manner. Thereafter, the transfer signal line is switched to the selection potential (high level) in a period t12 and thus data signals are transferred to the gates of the driving transistors 102.
In the light emission period in the second field, the no-light emission level voltage V2 is applied to the first power supply line 206, while the light emission level voltage V1 is applied to the second power supply line 207. As a result, the organic electroluminescent element, which is located in each of the sub-pixels 100a and 100b and which were in the OFF state in the light emission period in the first field, is turned on to emit light, while the organic electroluminescent elements which were turned on to emit light in the first field are turned off and no light is emitted thereby.
As shown in
In the first to third embodiments described above, a mixture of RGB colors is emitted in each field. In contrast, in the present embodiment, an image displayed in each filed does not include all colors but the image includes part of colors. However, the image in each filed includes at least different two colors, and thus an occurrence of color break-up is suppressed. Next, a structure of an organic electroluminescent element and a method of producing the organic electroluminescent element according to the present embodiment are described below.
In a region on the left-hand side surrounded by a partition wall 9, an R organic electroluminescent element 103 and a G-I organic electroluminescent element 104 are formed. In a region on the right-hand side, another sub-pixel including two organic electroluminescent elements, i.e., a B organic electroluminescent element 105 and a G-II organic electroluminescent element 106 is formed. As described above, one sub-pixel is formed in one region surrounded by a partition wall 9.
Two organic electroluminescent elements in each region share an anode electrode 61 or 62 and these two organic electroluminescent elements are driven by a single driving transistor 102. R, G, and B organic layers 7R, 7G, and 7B including a light emitting material are formed such that each region includes organic layers of two colors, respectively. Cathodes of two organic electroluminescent elements in each region are formed separately, but cathodes 104C and 105C of the G-I and B organic electroluminescent elements are formed so as to extend over the partition wall 9. The cathodes are connected together via the partition wall 9. Although not shown in the figure, a cathode of the G-II organic electroluminescent element and a cathode of the R organic electroluminescent element are also connected together via a partition wall 9.
A method of forming two organic electroluminescent elements in a region surrounded by a partition wall is described below. A cathode electrode divided into two pieces may be formed as follows. First, a film of an electrode material such as Ag, ITO, IZO, or the like is formed across a whole area by using an evaporation process or a sputtering process, and then the film is divided by irradiation of laser light. Alternatively, patterning may be performed using a metal mask. Still alternatively, patterning may be performed using an inverse-tapered pixel isolation film, or other similar processes may be used.
Two separate organic layers of different colors may be formed by one of the following methods. A first method is to combine white organic electroluminescent elements with color filters. A second method is to form three types of organic electroluminescent layers of R, G, and B colors by using a laser transfer process. A third method is to perform evaporation using a metal mask.
Referring to
A photoresist material is coated on the substrate 1 and patterned to form partition walls 9 for partitioning pixels.
After the partition walls 9 are formed on the substrate 1, R, G, and B organic electroluminescent materials are obliquely evaporated as shown in
Next, a cathode electrode material is obliquely evaporation on the organic layer 7G and the multilayer of organic layers 7R/7B from the left and from the right. As a result, the cathode electrode material is deposited separately on the two organic layers between the partition walls 9. Thus, cathodes are formed as shown in
Finally, red color filters CFR and blue color filters CFB are placed alternately above the multilayer organic electroluminescent elements. Note that no color filter is formed on the green organic electroluminescent elements. As a result, color organic electroluminescent elements 103 to 106 are obtained as shown in
In this structure, R light and B light emit from the organic electroluminescent elements via the respective color filters. The color filters are formed by planarizing the upper part of each cathode by using an inorganic film such as a silicon nitride film and then directly forming the patterned color filters. Alternatively, patterned color filters may be formed on another glass substrate and this substrate may be bonded to the substrate on which organic electroluminescent elements are formed such that these two substrates are precisely positioned to each other.
The display apparatus produced via the process described above has low light absorption loss by the filters compared with the combination of white organic luminescent elements and color filters.
Fifth Embodiment
As shown in
In even-numbered sub-pixel 100b, a driving circuit 10 is connected to a B organic electroluminescent element 105 and a G-II organic electroluminescent element 106i n the same sub-pixel as that in which the driving circuit 10 is located.
In the present embodiment, unlike the fourth embodiment described above with reference to
To the four organic electroluminescent elements adjacent in the row direction, the light emission level voltage and the no-light emission level voltage are alternately supplied to the cathodes thereof to turn them on and off at the same time. Therefore, these four organic electroluminescent elements are individually driven by different driving circuits.
In the configuration associated with the connection of cathode wirings according to the present embodiment, in the first field, turning-on to emit light is performed at the same time for R organic electroluminescent elements R11, R21, R31, . . . and so on in the first column, G-I organic electroluminescent elements G11, G21, G31, . . . and so on in the first column, B organic electroluminescent elements B12, B22, B32, . . . and so on in the second column, G-II organic electroluminescent elements G14, G24, G34, . . . and so on in the fourth column, R organic electroluminescent elements R15, R25, R35, . . . and so on in the fifth column, G-I organic electroluminescent elements G15, G25, G35, . . . and so on in the fifth column, and B organic electroluminescent elements B16, B26, B36, . . . and so on in the sixth column.
In the second field, turning-on to emit light is performed at the same time for G-II organic electroluminescent elements G12, G22, G32, . . . and so on in the second column, R organic electroluminescent elements R13, R23, R33, . . . and so on in the third column, G-I organic electroluminescent elements G13, G23, G33, . . . and so on in the third column, B organic electroluminescent elements B14, B24, B34, . . . and so on in the fourth column, B-II organic electroluminescent elements G16, G26, G36, . . . and so on in the sixth column, R organic electroluminescent elements R17, R27, R37, . . . and so on the seventh column, G-I organic electroluminescent elements G17, G27, G37, . . . and so on in the seventh column, and B organic electroluminescent elements B18, B28, B38, . . . and so on in the eight column.
That is, four organic electroluminescent elements 103 to 106 forming a pixel are turned on at the same time to emit light in one field. Organic electroluminescent elements are turned on in a similar manner also in the other field. In each field, a mixture of red, green, and blue colors is emitted, and thus color break-up does not occur in usual moving images such as natural images.
In the present embodiment, driving circuits 10 in each odd-numbered column drive organic electroluminescent elements in different two pixels. As described above, a set of organic electroluminescent elements that receive a current supplied from one driving circuit is not necessarily included in one pixel.
In the first to third embodiments described above, three organic electroluminescent elements of R, G, and B colors in each pixel are connected to different power supply lines, and thus it is possible to drive these three organic electroluminescent elements by one driving circuit. That is, a set of organic electroluminescent elements that are driven by the same driving circuit is a set of organic electroluminescent elements that form one pixel.
In the fourth embodiment, not all but part of organic electroluminescent elements in each pixel (for example, GI and B of R, G-I, B, and G-II) share one cathode, and thus at least two these organic electroluminescent elements are driven by different driving circuits. Therefore, two driving circuits are provided in each pixel.
In the fifth embodiment, four adjacent organic electroluminescent elements located over two pixels, i.e., R, G-I, and B organic electroluminescent elements located in one pixel and a G-II organic electroluminescent element located in an adjacent pixel are activated at the same time to emit light such that an image displayed in one field includes all colors. To drive four organic electroluminescent elements by different driving circuits, a driving circuit located in one pixel drives an organic electroluminescent element located in that pixel and also an organic electroluminescent element located in a pixel adjacent thereto via one another pixel.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2010-131248 filed Jun. 8, 2010 and No. 2011-089375, filed Apr. 13, 2011, which are hereby incorporated by reference herein in their entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2010-131248 | Jun 2010 | JP | national |
| 2011-089375 | Apr 2011 | JP | national |
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| Number | Date | Country | |
|---|---|---|---|
| 20110298775 A1 | Dec 2011 | US |
