JP2010218903A - Light emitting apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light emitting apparatus having a simple construction using laminated organic EL elements for accurately controlling currents. <P>SOLUTION: The light emitting apparatus includes a plurality of organic EL elements EL1-EL3 laminated with their currents in the same direction, a constant voltage source connected to one outsidemost layer electrode 9 of the laminated organic EL elements EL1-EL3, a unidirectional current source 1 connected to the other outsidemost layer electrode 6, and bidirectional current sources 2-5 connected to intermediate electrodes 7, 8. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a light emitting device, and more specifically, an organic electroluminescence (EL) element that emits each color of R (red), G (green), and B (blue) is stacked, and a desired constant current is applied to each organic EL element. The present invention relates to a light-emitting device that applies voltage.

  In recent years, light-emitting elements (hereinafter referred to as organic EL elements) using electroluminescence of organic compounds have been actively developed. A full color matrix display device in which organic EL elements of three colors of red (R), green (G), and blue (B) are formed on a substrate is known.

  In order to perform color display, a method in which three RGB sub-pixels constituting a pixel are adjacently arranged in a plane is known. In this case, the RGB light emitting layers are applied or deposited at different positions. In the case of vapor deposition, a light emitting layer material flying from a vapor deposition source is vapor-deposited only on the metal mask opening using a metal mask having an opening at a desired position.

  Assuming that the display device is used for a mobile phone or the like, a required specification may be a matrix display device having a size of 3 inches facing and a QVGA (320 columns × 240 rows). When this display device is composed of RGB pixels arranged in a plane, the size of each RGB sub-pixel is 63.5 μm × 190.5 μm, which is arranged at a 190.5 μm pitch in the row and column directions.

  It is very difficult to align such a small opening and narrow pitch metal mask so as not to cause a shift, considering that distortion occurs due to heat applied to the mask during vapor deposition.

  In addition, an operation for cleaning and removing the above-described metal mask on which an unnecessary vapor deposition layer is stacked is separately generated, and the number of times the metal mask is reused is limited, thereby increasing the manufacturing cost of the mask.

  Thus, when used in a 3-inch QVGA class display device, it can be said that it is not suitable from the technical and manufacturing viewpoints to separately coat the RGB organic EL layers with a metal mask.

  As an alternative method, Patent Documents 1 and 2 propose a method in which RGB layers are alternately stacked with electrodes sandwiched therebetween, and each layer emits light. The organic layer is deposited on the entire surface without using a deposition mask. The electrodes are provided separately for each pixel, and a drive circuit is connected so that each layer of organic EL elements in the pixel emits light independently.

  In the method of Patent Document 1, RGB light emitting layers are arranged between the lowermost electrode at the reference potential and the three upper electrodes thereon. A voltage is supplied to the upper three layers of electrodes via switching transistors.

  On the other hand, in the method of Patent Document 2, RGB organic EL elements are stacked, and the drive circuit is made independent by sandwiching an insulating layer between the electrodes of each layer. A drive circuit is connected to each organic EL element in the same manner as in the planar arrangement, and a current corresponding to the luminance is supplied.

Republished patent WO2004 / 051614 JP 2007-012359 A

  In the conventional laminated organic EL element, when the electrodes between the layers are used in common for the upper and lower organic EL elements as in Patent Document 1, each organic EL element has a current depending on the voltage applied to the electrodes on both sides. Flows and emits light. Since the organic EL element has voltage-current characteristics like a diode element, the current varies greatly even with slight variations in voltage. For this reason, it is difficult to precisely control the current by the voltage, and it is at best to control the two states of lighting and extinguishing. The halftone had to be displayed by controlling the light emission time.

  In order to control the current and emit light at intermediate luminance, there is a method of insulating each layer and providing a current control drive circuit independently as in Patent Document 2, but the structure of the element and the wiring to each electrode are complicated become.

  The present invention relates to a plurality of organic EL elements stacked with the same current direction, a constant voltage source connected to one outermost layer electrode of the stacked light emitting elements, and the other outermost layer electrode. The light emitting device includes a unidirectional current source and a bidirectional current source connected to the intermediate electrode.

  According to the present invention, there is no need to sandwich an insulating layer between the layers, and the current of each layer can be controlled. Therefore, an organic EL element having a simple structure and capable of halftone control, and a matrix using the same A light emitting device such as a display device can be realized. There is no need to sandwich an insulating layer such as an oxide film between the organic EL elements, and the manufacturing cost can be reduced.

It is sectional drawing of the laminated organic EL element used for the light-emitting device of this invention. 1 is a circuit diagram of a stacked organic EL element and a current source according to a first embodiment of the present invention. It is a specific circuit diagram of the current source of the first embodiment. It is a modification of the current source of 1st Embodiment. It is a circuit diagram of the laminated organic EL element and current source of the 2nd Embodiment of this invention. It is a specific circuit diagram of the current source of the second embodiment. It is a block diagram of the signal generation circuit of a 2nd embodiment.

  FIG. 1 shows a light-emitting device in which three layers of organic EL elements are stacked on a glass substrate 101.

  One organic EL element has a structure in which an organic layer including a light emitting layer is sandwiched between an anode and a cathode. In the lowermost organic EL element EL1, an anode 102, a hole transport layer 103, a light emitting layer 104, and an electron transport layer 105 are sequentially laminated, and a cathode 106 is disposed thereon.

  The cathode 106 also serves as the anode 102 'of the second organic EL element EL2 above it. The second organic EL element EL2 has the same configuration, in which organic layers such as a hole transport layer 103 ', a light emitting layer 104', and an electron transport layer 105 'are stacked, and a cathode 106' covers the organic layer.

  Further, the cathode 106 ′ is also used as the anode 102 ″ of the third organic EL element EL3, and the hole transport layer 103 ″, the light emitting layer 104 ″, and the electron transport layer 105 ″ are stacked, and the outermost cathode 106 ″ is stacked. Is completed.

  All the organic EL elements emit light when a current flows in the direction from the bottom to the top of the substrate.

  One organic EL element is composed of upper and lower electrodes and an organic layer therebetween. The anode of the organic EL element closest to the substrate and the cathode of the uppermost organic EL element constitute the outermost layer, and the other electrodes serve as the cathode of the lower organic EL element and the anode of the upper organic EL element. ing.

  In addition to the above, the configuration of one organic EL element may include an electron injection layer, a hole injection layer, and other functional layers. In addition, a structure in which the light emitting layer 104 also serves as the hole transport layer 103, the electron transport layer 105, or both has been proposed.

  When a current is passed through the organic EL element, electrons and holes flowing from the respective electrodes are combined in the light emitting layer 104 to emit light. The light emission luminance increases in proportion to the current. The organic EL element 301 may be referred to as a current control type light emitting element.

(First embodiment)
FIG. 2 is a diagram showing a first embodiment of a light emitting device of the present invention.

  The light emitting device 10 includes organic EL elements EL1 to EL3 stacked in three layers and a current source 1-5 that is a driving circuit thereof. Each organic EL element has diode characteristics and emits light by forward current. The organic EL elements EL1-EL3 in FIG. 2 correspond to the organic EL elements EL1-EL3 shown in FIG. 1, respectively, and are drawn upside down from FIG.

  The RGB three-color organic EL elements EL1, EL2, and EL3 are stacked so that forward currents for emitting light have the same direction (both away from the substrate). One outermost layer electrode 9 (uppermost layer cathode 106 "in FIG. 1) is connected to the ground potential, and the current source 1 is connected to the other outermost layer electrode 6 (lowermost layer anode 102 in FIG. 1). 7 (cathode 106 = anode 102 ′ in FIG. 1) are connected to current sources 2 and 3, and current sources 4 and 5 are connected to another intermediate electrode 8 (cathode 106 ′ = anode 102 ″ in FIG. 1).

  Although the detailed circuit structure will be described later, the current source 1-5 is configured by a current source circuit in which an output current value is determined by a voltage signal input thereto. In the current source circuits 1, 2, and 4, current flows in the direction of flowing out from the output end, and in the current sources 3 and 5, current flows in the direction of flowing into the output end from the outside. In general, a current source circuit is either a current source from which a current flows from a constant voltage source toward an output terminal or a current sink from which current is sucked from an output terminal toward a constant voltage source, Is the source. A bidirectional current source that doubles as a source and a sink can be considered as two unidirectional current sources connected in parallel.

  The output impedance of the current source is sufficiently high, and the voltage at the output end can be arbitrarily changed depending on the load. However, the upper limit or lower limit of the voltage at the output terminal is determined by the power supply voltage of the current source itself (a voltage higher than the load when the output current flows out from the output terminal and a voltage lower than the load when the output current flows into the output terminal).

  Hereinafter, when simply referred to as a current source in this specification, it means a one-way current source. A bidirectional current source is a parallel connection of two unidirectional current sources that output currents in opposite directions. The current sources 2 and 3 in FIG. 2 are combined into one bidirectional current source. The same applies to the current sources 4 and 5.

  In the light emitting device 10 of FIG. 2, the current source 1 is connected to the outermost layer electrode 6, the current sources 2 and 3 are connected to the intermediate electrode 7, and the current sources 4 and 5 are connected to the intermediate electrode 8. The other outermost layer electrode 9 is at a constant voltage, here the ground potential.

  The luminance signal L1 of the first organic EL element EL1 is input to the current source 1 connected to the outermost layer electrode 6, and the output current value I1 is set accordingly. The output direction of the current source 1 is a direction in which a forward current of the first organic EL element EL1, that is, a current accompanied by light emission flows.

  A current source 2 in the direction of flowing current into the intermediate electrode 7 and a current source 3 in a direction of drawing current from the intermediate electrode 7 are connected in parallel to the intermediate electrode 7 below. The current source 2 receives a signal L2 that gives the luminance of the second organic EL element EL2, and outputs an output current I2. The current source 3 receives the signal L1 that gives the luminance of the first organic EL element EL1. Output current I1 is output. As a result, the difference current between the current sources 2 and 3 flows into the intermediate electrode 7 (if I1 is greater than I2, the difference current flows out from the intermediate electrode 7, which is considered to be a negative current in this specification. In the following, only one expression is used.) Therefore, the current I2 flows through the second organic EL element.

  Furthermore, a current source 4 in the direction of flowing current into the intermediate electrode 8 and a current source 5 in a direction of drawing current from the intermediate electrode 8 are connected in parallel to the second intermediate electrode 8 below the second intermediate electrode 8. The luminance signal L3 is input to the current source 4, and the luminance signal L2 is input to the current source 5, and outputs currents I3 and I2, respectively. As a result, the current of I3 is supplied to the third organic EL element.

  In this way, two opposite-direction current sources are connected in parallel to the intermediate electrode, and the luminance signals of two organic EL elements that are on both sides of the intermediate electrode and have the intermediate electrode as a common electrode, Input to the source. Of the two organic EL light emitting elements, the luminance signal of the organic EL element whose intermediate electrode is the anode is input to a current source that is a source from which current flows, and an output current that flows toward the intermediate electrode is created. The luminance signal of the organic EL element whose intermediate electrode is the cathode is input to a current source serving as a sink into which current flows, and an output current is generated in a direction in which current is drawn from the intermediate electrode. The difference is output as the bidirectional current source.

  When viewed from the organic EL element, a current source in the reverse direction of the same output current is connected to a pair of upper and lower electrodes constituting one organic EL element. This current only flows through the organic EL element, and does not flow through other organic EL elements. The upper and lower electrodes of the organic EL element are connected to a current source to which the luminance signal of another organic EL element is input, but the current does not flow to the organic EL element. In this way, the current flowing through the organic EL element in each layer is correctly controlled.

(Second Embodiment)
FIG. 5 is a diagram illustrating a stacked organic EL element and a drive circuit thereof according to the second embodiment of the present invention. The laminated structure of the organic EL element is the same as that of the first embodiment, except that the current source connected to the intermediate electrodes 7 and 8 is a current source that generates a difference current.

  The difference current source 2a connected to the intermediate electrode 7 outputs the difference I2-I1 between the current I1 of EL1 and the current I2 of EL2 with the direction toward the intermediate electrode 7 being positive. When I2 is larger than I1, a positive current flows into the intermediate electrode 7, and when I2 is smaller than I1, a negative current flows out from the intermediate electrode 7. In either case, the differential current source 2a is a bidirectional current source that can generate current in either direction.

  A similar bidirectional current source 4a is also connected to the intermediate electrode 8.

  In order to generate a difference current, a voltage signal corresponding to the difference current I2-I1 is input to the difference current source 2a. This voltage signal is generated from the luminance signals of EL1 and EL2. A voltage signal corresponding to the difference current I3-I2 is input to the difference current source 4a. This voltage signal is generated from the luminance signals of EL2 and EL3.

  By generating the difference current, the power consumption of the current source can be suppressed smaller than that in the first embodiment. In the first embodiment, the same current as the current flowing in the organic EL element flows through the current source connected to the intermediate electrode. In this embodiment, even if a large current flows through the organic EL element, only the difference current flows through the current source, so that power consumption can be reduced.

  Hereinafter, a specific current source circuit will be described in an embodiment.

  FIGS. 3A to 3C are circuit diagrams of the current source circuit according to the first embodiment of the present invention. The current source is composed of a PMOS or NMOS transistor whose gate-source voltage is controlled. Reference numeral 1-5 corresponds to the current source 1-5 in FIG.

  FIG. 3A is a specific example of the circuits of the current sources 1 and 5 in FIG. This current source circuit includes a pair of PMOS transistors Q1 and Q3 whose gates are commonly connected, and a pair of NMOS transistors Q2 and Q4 whose gates are also commonly connected. The two transistors in each set are chosen so that the characteristics are approximately the same.

  The gate and drain of Q2 are short-circuited, and the gate potential is determined by the current flowing through Q2.

  VGS1 is an input voltage signal generated from the luminance signal of the first organic EL element EL1. A digital luminance signal L1 input from a circuit outside the light emitting device is converted into a digital signal of a current to be passed through the organic EL element via a gamma correction circuit (not shown), and further a voltage signal generation circuit (not shown). Is converted into an analog voltage signal VGS1.

  When the voltage signal VGS1 is applied as a gate-source voltage of the PMOS transistor Q1, a current determined by the following equation is applied to Q1 and Q2 connected in series between the power supply Vcc and GND.

Give rise to Here, Vd is the drain potential of Q1 and is determined by solving the second equation of the above equation. β1 and β2 are current multiplication factors of the transistors Q1 and Q2, and Vth1 and Vth2 are threshold voltages. The voltage signal generation circuit determines VGS1 so that I1 matches the current data provided from the luminance signal L1.

  Since Q3 and Q4 have gates commonly connected to Q1 and Q2, respectively, they constitute a current mirror circuit for a current path formed by Q1 and Q2. That is, when a load is connected to the drain of Q3 or Q4, the same current I1 that flows through Q1 and Q2 flows through the load. This current flows out from the PMOS transistor Q3 and into the NMOS transistor Q4, and plays the role of the current sources 1 and 3 in FIG. 2, respectively.

  FIG. 3B is a specific example of the circuits of the current sources 2 and 5 in FIG. The same operation as in FIG. The voltage signal VGS2 input to the gate of Q5 is a signal that gives the luminance of the second organic EL element EL2. A reverse current I2 is generated from the PMOS transistor Q7 and the NMOS transistor Q6.

  FIG. 3C shows a circuit of the current source 4 of FIG. Since the input voltage signal VGS3 corresponding to the luminance of the third organic EL element EL3 is input to the gate of the PMOS transistor Q9, a current I3 corresponding to the emission luminance of EL3 flows out from Q9.

  The current sources 1-5 shown in FIG. 2 are configured by the circuits shown in FIGS. Since the current sources 1 and 3 are formed by the current mirror circuit from the current flowing through one path (Q1 and Q2), equal voltage values are guaranteed. The same applies to the current sources 2 and 5. As a result, predetermined currents of I1 flow through EL1, I2 flow through EL2, and I3 flow through EL3.

  In the circuit example of FIG. 3, the luminance signal voltage VGS is input between the gate and source of the PMOS transistor to obtain a desired current. Even if the value of the signal voltage VGS set to the NMOS level is input between the gate and source of the NMOS transistor, a desired current is obtained in the same manner.

  FIG. 4 shows a modified example of the circuit of FIG. 3A, in which the signal voltage VGS is input to the NMOS transistor. The same reference numerals are assigned to the transistors corresponding to FIG. The difference from FIG. 3A is that the gate and drain of Q1 are short-circuited, and the voltage signal VGS1 is input between the gate and source of the NMOS transistor Q2.

  The second embodiment of the present invention will be described in detail with a specific example of a current source circuit for driving the organic EL element of FIG.

  6A to 6C are specific examples of the circuits of the current sources 1, 2a, and 4a in FIG.

  In the second embodiment, the current sources 2a and 4a each generate a difference current.

  FIG. 7 is a block diagram of a circuit for generating a difference current luminance signal. Here, EL1 is a red organic EL element, EL2 is a green organic EL element, and EL3 is a blue organic EL element.

  The luminance signals L1 to L3 of the respective colors are input to the respective current data conversion circuits 81r, 81g, and 81b, and converted into digital current data I1data to I3data. The current data conversion circuit 81 is a conversion circuit including gamma correction, and calculates and outputs current data corresponding to the RGB organic EL elements from the luminance signal.

  The red current data I1data and the green current data I2data are input to the negative and positive input terminals of the subtraction circuit 82a, respectively. The subtraction circuit 82a is a circuit that calculates a difference between positive input data and negative input data. The digital data of the difference I2data-I1data is output from the subtraction circuit 82a. Similarly, the green current data I2data and the blue current data I3data are input to the negative and positive input terminals of the subtraction circuit 82b, respectively, and digital data of the difference I3data-I2data is output.

The difference current data is input to the next absolute value conversion circuits 83a and 83b. The absolute value conversion circuits 83a and 83b determine the sign of the input digital data and output code data P2SEL and N1SEL, and P3SEL and N2SEL, respectively.
That is, in the absolute value conversion circuit 83a, if I2data> I1data, the plus (+) terminal output P2SEL is “1” and the minus (−) terminal output N1SEL is “0”. Conversely, when I2data <I1data, the plus (+) terminal P2SEL outputs “0” and the minus (−) terminal N1SEL outputs “1”. At the same time, the absolute value of the input data is output.
Similarly, the absolute value conversion circuit 83b also outputs code data P3SEL and N2SEL and absolute value data according to the magnitude of I3data and I2data.

  The current absolute value data and the sign data are input to circuits 85a and 85b that generate voltage signals, and the voltage signal generation circuits 85a and 85b convert the current absolute value data into analog voltage signals VGS21 and VGS32 and output them. To do.

  The voltage signal generation circuit 85a is also set with reference to the code data, and is set to an analog voltage signal level so as to be the gate potential of the PMOS transistor and output when P2SEL is “1” (N1SEL is “0”). At this time, VGS21 is a potential at a level lower than the threshold voltage from the power supply voltage Vcc of the current source circuit, and the potential decreases as the absolute value output of the difference current increases.

  Conversely, when P2SEL is “0” (N1SEL is “1”), the output voltage is set to an analog voltage signal level that is the gate-source voltage of the NMOS transistor. VGS21 is a voltage at a level higher than the threshold value from the ground voltage GND of the current source circuit, and increases as the absolute value output of the difference current increases.

  The operation of the voltage signal generation circuit 85b is exactly the same.

Separately, the red current data I1data generated by the current data conversion circuit 81r is input to a circuit 84 that generates a voltage signal. The voltage signal generation circuit 84 outputs VGS1 at the gate-source voltage level of the PMOS transistor regardless of the sign of the input I1data.
In addition to the voltage signals VGS1, VGS21, and VGS32 output from the voltage signal generation circuits 84, 85a, and b, and the code data P2SEL, N1SEL, P3SEL, and N2SEL output from the absolute value conversion circuits 83a and 83b, the current source circuit shown in FIG. Entered.

  FIG. 6A is a specific example of the circuit of the current source 1 of FIG. When the voltage signal VGS1 generated from the red luminance signal L1 is input to the gate of the PMOS transistor Q21, a current I1 is generated and flows through the red organic EL element EL1 to emit light with luminance L1.

  FIG. 6B is a circuit diagram of the current source 2a. The voltage signal VGS21 is commonly input to the gate of the PMOS transistor Q22 and the gate of the NMOS transistor Q23, and this voltage level controls the current flowing through one of the transistors Q22 and Q23 depending on whether the difference current I2data-I1data is positive or negative. .

  When the difference current I2data-I1data is positive, that is, when the current flowing through the green organic EL element EL2 is larger than the current flowing through the red EL element EL1, the VGS21 is at the PMOS control level, so the PMOS transistor Q22 is connected to the output terminal. A current I2-I1 is generated in the direction of flowing out.

  As for the sign output, since the plus (+) output P2SEL is “1” and the minus (−) output N1SEL is “0”, the gate Q4 is turned on and the gate Q5 is closed. For this reason, the current of the NMOS transistor Q23 is cut off, and the current I2-I1 from the PMOS transistor Q22 is output as an output current. Since this current flows in the intermediate electrode 7, it merges with the current I1 flowing through EL1 at the intermediate electrode 7 to supply the current I2 to the green organic EL element EL2.

  When the difference current I2data-I1data is negative, that is, the red organic EL element current is larger, the current I1-I2 flowing into the NMOS transistor Q23 is output as the output current. This flows in the direction in which the current is sucked from the intermediate electrode 7, and is subtracted from the current I1 flowing through EL1, and the remaining current I2 flows into the green organic EL element EL2.

  In either case, a current I2 corresponding to a predetermined luminance L2 flows through green.

  FIG. 6C shows a circuit of the current source 4a of FIG. 5 and signals supplied thereto. The operation is exactly the same as in the circuit of FIG. 6B, and a predetermined current flows through the blue organic EL element EL3 regardless of the magnitude of the current flowing through the green EL element EL2.

  Since the current source circuits 2a and 4a can have bidirectional current outputs, the current source circuits shown in FIGS. 6B and 6C each include output transistors having both PMOS and NMOS polarities. However, since only one of the currents is actually generated and output, the gate potential of either PMOS or NMOS is applied accordingly, and the current is output from either the PMOS or NMOS transistor according to the code data given at the same time. It is taken out.

  In the above embodiment, an organic EL element in which three layers of RGB are stacked has been described. However, the present invention can be applied if the number of stacked organic EL elements is plural. The direction of the current may be upward or downward with respect to the substrate as long as all the layers are aligned. It is possible to arbitrarily select either the order of lamination or the outermost layer electrode to be grounded. The combination of colors is also arbitrary, and a configuration such as adding white to RGB may be used.

1-5 Current source 2a, 4a Differential current source 6-9 Electrode 10 Light emitting device EL1, EL2, EL3 Organic EL element 102, 102 ′, 102 ″ Anode 106, 106 ′, 106 ″ Cathode

Claims (5)

  A plurality of organic EL elements stacked with the same current direction, a constant voltage source connected to one outermost layer electrode of the stacked light emitting elements, and a one-way current connected to the other outermost layer electrode A light emitting device comprising: a source; and a bidirectional current source connected to the intermediate electrode.   The unidirectional current source has an output current controlled by a luminance signal of an organic EL element having the other outermost layer electrode as an electrode, and the bidirectional current source is stacked up and down with the intermediate electrode as a common electrode The light emitting device according to claim 1, wherein the magnitude and direction of the output current are determined from the luminance signals of the two organic EL elements.   The bidirectional current source is a bidirectional current source in which two unidirectional current sources are connected so as to output a current in a reverse direction with respect to the intermediate electrode, and the two unidirectional current sources include: 3. The light emitting device according to claim 2, wherein respective output currents are controlled by luminance signals of the two organic EL elements stacked one above the other using the intermediate electrode as a common electrode.   Two unidirectional currents of equal magnitude and opposite directions generated by a current mirror circuit are respectively supplied to two electrodes constituting one of the plurality of stacked organic EL elements. The light emitting device according to claim 3.   The bidirectional current source is a bidirectional current source in which two unidirectional current sources are connected so as to output a current in a reverse direction with respect to the intermediate electrode. 3. The light emitting device according to claim 2, wherein one of the two outputs a difference current between currents flowing through two organic EL elements stacked vertically using the intermediate electrode as a common electrode, and the other outputs no current. apparatus.