JP2006195030A - Aging method, manufacturing method and aging apparatus of spontaneous light emitting apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an aging apparatus effectively and efficiently detecting degradation characteristics of an organic electroluminescence element and defects of a pixel, when compared with a conventional apparatus. <P>SOLUTION: When aging processing of the spontaneous light emitting apparatus in which light emitting is controlled by an active matrix driving system is performed, (a) in parallel with applying a data signal and a line selection signal for active matrix driving to the spontaneous light emitting apparatus, and (b) by applying a control signal for alternate current driving to a transistor connected in series between each light emitting element and a power supply voltage line, (c) each light emitting element is turned on and off within a field period. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

One embodiment of the present invention relates to an aging method for a self-luminous device. Another aspect of the invention relates to a manufacturing method having an aging process of a self-luminous device. Another aspect of the invention relates to an aging device used for aging processing of a self-luminous device.
The self-luminous device here refers to, for example, an organic EL (Electro Luminescence) panel or other current-driven light-emitting device.

One driving method of the organic EL panel is an active matrix driving method.
An organic EL panel employing this driving method is configured by arranging a plurality of pixel circuits each including a plurality of thin film transistors operating as switching elements, capacitive elements, and organic EL elements in a matrix.
The organic EL panel having this structure is formed by the following process, for example. First, a plurality of thin film transistors corresponding to each pixel are formed on one panel. An organic EL layer is formed on one main electrode of each thin film transistor. A scanning line is connected to the gate electrode of each thin film transistor. A signal line is connected to one main electrode of each thin film transistor.
A common counter electrode is provided so as to face the panel having this structure and to be in contact with the upper surface of each organic EL layer.
Through these processes, an active matrix type organic EL panel is manufactured. The organic EL element includes an organic EL layer and electrodes that sandwich the upper and lower surfaces thereof.

By the way, in the organic EL element which is a light emitting element using an organic material, the fall of the emitted light amount by aged deterioration becomes a problem.
In recent years, however, the half-life of the amount of light emission has been dramatically increased, and the organic EL element is in a sufficiently practical range.
However, an aging process under an appropriate condition is important for realizing stable light emission characteristics for a longer time. This is because the deterioration of the organic EL element (light emission luminance reduction characteristic) does not have a simple proportional relationship with the total charge injection amount. For example, as shown in FIG. 1, the deterioration of the organic EL element has a characteristic that the total charge injection amount greatly decreases at the beginning of light emission. For this reason, it is important to effectively execute initial deterioration before product shipment and to stabilize the light emission characteristics after shipment.

In addition, other problems have been pointed out in the organic EL panel. That is, it is a problem of a dark spot pixel generated in the process of forming a large number of pixels. There are dark dot pixels that are confirmed at the manufacturing stage and those that are confirmed during use.
In the former dark pixel, a pinhole or the like occurs in a thin organic EL layer (less than 100 [nm]) due to minute particles attached in the process of forming a large number of pixels and other causes, and the organic EL element forming the pixel is It is generated by short-circuiting.
On the other hand, the latter dark spot pixel is caused by a hidden defect. In this case, the defective pixel does not suddenly emit light during long-time use.
Therefore, it is necessary to detect pixels having defective elements by aging processing before product shipment.
JP 2003-282253 A JP 2002-203672 A JP 2003-297560 A JP 2003-323979 A JP 2003-264073 A JP 2003-332063 A

By the way, long-time aging treatment in the panel manufacturing process is a major factor that deteriorates productivity. For this reason, an aging apparatus capable of effectively and efficiently carrying out deterioration characteristics of organic EL elements and pixel defect detection is required.
The aging process and the inspection process are performed at the end of the panel manufacturing process. For this reason, the aging device here needs to have the same driving ability as the system that drives the organic EL panel as a finished product.

The inventors pay attention to the above technical problems and propose the following technical methods.
That is, when executing the aging process of the self-light-emitting device controlled to emit light by the active matrix driving method,
(A) In parallel with the application of the active matrix driving data signal and line selection signal to the self-luminous device,
(B) applying a control signal for AC driving to a transistor connected in series between each light emitting element and a power supply voltage line;
(C) A method is proposed in which each light emitting element is driven to blink within a field period.

  By adopting this technique, the aging effect can be accelerated compared to the aging process by always lighting. As a result, the initial characteristics can be stabilized in a shorter time than in the prior art. Therefore, the light emission characteristics after product shipment can be stabilized. Further, by accelerating the aging effect, the presence of a pixel having a hidden defect can be detected before product shipment.

Hereinafter, an embodiment of an aging process that employs the technical technique according to the invention will be described.
In addition, the well-known or well-known technique of the said technical field is applied to the part which is not illustrated or described in particular in this specification.
The embodiment described below is one embodiment of the present invention and is not limited thereto.

(A) Acceleration conditions for initial deterioration First, conditions for accelerating initial deterioration will be described.
FIG. 2 shows an example of experimental results when the organic EL element is always driven with a constant current and when driven with a pulsed current. FIG. 2 shows the experimental results under the condition that the average current value is the same between the constant lighting and the intermittent lighting (flashing driving). Incidentally, the vertical axis represents the relative value of the light emission luminance with the light emission amount at the start of the experiment expressed as “1”. The horizontal axis is the experiment time.
As shown in FIG. 2, the characteristic curve of pulse current drive (duty ratio 50%) is always lower than the characteristic curve of constant current drive (duty ratio 100%). That is, the deterioration of the organic EL element is progressing quickly. It can also be seen that even with a duty ratio of 50%, the deterioration progresses faster when the number of blinking cycles in one field is eight compared to one.

Therefore, in the case of an active matrix type organic EL panel, it is understood that the data signal that gives the drive current value of each organic EL element may be controlled in a pulse manner.
However, when considering from the viewpoint of driving the organic EL panel, such driving is not practical.
This is because, in the case of the active matrix driving method, a method is adopted in which a data signal written in line sequential order is taken into a pixel circuit of a selected horizontal line and a corresponding organic EL element emits light.

This will be described with reference to FIG. In the case of the pixel circuit 1, the data signal of the data line is selectively input through the transistor T1 and held in the capacitor C1 for one field period. Then, a drive current having a current value corresponding to the data signal is supplied to the organic EL element 3 through the transistor T2.
For this reason, if the organic EL panel is driven at 1 field = 60 Hz, the drive current cannot be turned on / off at a higher speed.
Therefore, a method of setting the field frequency itself higher than that during normal operation is also conceivable. However, if the field frequency is set to be twice or more that in normal operation, the capacitance parasitic on the transistor T1 cannot be ignored, and a correct data value cannot be held in the capacitive element C1.
Thus, in the case of a pixel circuit having a two-transistor configuration, the aging process cannot be accelerated.

(B) Configuration Example of Pixel Circuit Here, an example of a pixel circuit having a transistor that can control supply and stop of driving current independently of active matrix driving will be described.
FIG. 4 shows an example of a pixel circuit having a three-transistor configuration. The figure also shows the panel drive circuit. That is, the data signal selection circuit 5, the line selection circuit 7, and the lighting / light-off control circuit 13 are also shown.
All or part of these drive circuits are mounted on the panel as drive ICs. However, all or part of these drive circuits may be formed on the panel together with the pixel circuits.

The pixel circuit 11 includes three transistors T1, T2, and T3, a capacitive element C1, and an organic EL element 3. These three transistors T1, T2, and T3 are all constituted by thin film transistors (TFTs). In this circuit example, an N-channel transistor is used as the transistor T1, and a P-channel transistor is used as the transistors T2 and T3.
Among these, the transistor T1 is for taking in a data signal. The control terminal of the transistor T1 is connected to the scanning line, and its opening / closing operation is controlled by the line selection circuit 7. When the transistor T1 is in the closed state, the data signal supplied from the data signal selection circuit 5 through the data line is written and held in the capacitor C1.
The transistor T2 is for supplying a drive current to the organic EL element 3. The control terminal of the transistor T2 is connected to one electrode of the capacitive element C1, and controls the drive current value supplied to the organic EL element 3. That is, the current density is controlled.

The transistor T3 is for controlling the supply and stop (on and off) of the drive current. The transistor T3 is located on the drive current supply path. The control terminal of the transistor T3 is connected to the lighting / extinguishing control circuit 13, and controls the opening / closing operation of the supply path. In conjunction with this opening / closing operation, the organic EL element 3 is turned on or off.
During normal operation, the transistor T3 is used for suppressing the lighting time (light emission time). For example, it is used for suppressing power consumption.
On the other hand, during the aging process, the transistor T3 is used for supply control of the drive current that satisfies the acceleration condition. At this time, the organic EL element 3 is driven to blink at least once within the field period. Note that a transistor having a large current driving capability is used as the transistor T3 so that it can follow even when the frequency of the control signal is high.

(C) Aging Process Example Next, a driving example during the aging process will be described.
(A) Driving example 1
Here, an example of driving in the case where the average light emission amount (average driving current amount) is set to be the same as that during normal operation is shown.
FIG. 5 shows an example of a drive signal when the number of blinks in one field cycle is one. FIG. 5 shows a case where the duty ratio of the drive signal given to the transistor T3 is 50% and the data signal giving the drive current value is double that in the normal operation.

Here, FIG. 5A shows the data signal level. In this case, the capacitive element C1 constituting the pixel circuit holds a data signal having a signal level twice that of normal driving for one field (60 Hz).
FIG. 5B shows the control signal level of the transistor T3. In this case, the transistor T3 is turned on in the first half of one field period. That is, as shown in FIG. 5C, the organic EL element 3 is lit in the first half of one field period. Further, the transistor T3 is turned off in the latter half of one field period. That is, as shown in FIG. 5C, the organic EL element 3 is turned off in the second half of one field period.

As a result, the organic EL element 3 blinks at 60 Hz during the aging process period. In this driving condition, the number of blinks in one field cycle is one, but the deterioration rate can be accelerated as compared to the case of constant light emission as shown in FIG.
In the case of this driving condition, the instantaneous driving current value flowing through the organic EL element 3 is twice that in the normal operation. Therefore, it is possible to increase the load for hidden defects. As a result, it is possible to promote the destruction of the hidden defective portion and increase the possibility that the existence of the corresponding pixel is discovered before the product is shipped.

On the other hand, twice the drive current during normal operation also acts on the normal organic EL element 3. Therefore, this drive current gives an overload (thermal load) to the normal organic EL element 3 as well. However, in this example, the average current flowing through the organic EL element 3 is the same as that during normal operation. That is, the average current during the aging process is the same as the average current during normal operation. As a result, the deterioration effect on the normal organic EL element 3 can be made the same as in normal operation.
The normal organic EL element 3 refers to an element that can satisfy a general service life in consideration of manufacturing variations.
As a result, the aging process time can be shortened to 1/2 to 1/4.

(B) Driving example 2
Next, an example of driving when the number of blinks in one field period is set to a plurality of times is shown.
FIG. 6 shows an example of a drive signal when the number of blinks in one field cycle is eight. FIG. 6 shows a case where the duty ratio in one cycle of the drive signal applied to the transistor T3 is 50% and the data signal providing the drive current value is four times that in the normal operation. The aging time is 4 hours.
Here, FIG. 6A shows the data signal level. In this case, a data signal having a signal level four times that of normal driving is held in the capacitive element C1 constituting the pixel circuit for one field (60 Hz).

FIG. 6B shows the control signal level of the transistor T3. In this case, the transistor T3 is turned on / off in eight cycles in one field period. That is, as shown in FIG. 6C, the organic EL element 3 is repeatedly turned on and off eight times in one field cycle.
As a result, the organic EL element 3 blinks at 480 Hz during the aging process period. In this driving condition, the number of blinks in one field period is eight, and the deterioration rate can be accelerated as compared with the case of constant light emission as shown in FIG.
In the case of this drive condition, the instantaneous drive current value flowing through the organic EL element 3 is four times that during normal operation. Therefore, the load on the hidden defect is further increased compared to the previous example. As a result, the destruction of the hidden defective part can be further promoted, and the possibility that the existence of the corresponding pixel is found before the product shipment can be increased.

By the way, in the case of this example, a drive current four times that in normal operation flows through the organic EL element 3. The duty ratio is 50%. For this reason, the average current flowing through the organic EL element 3 is twice that during normal operation. That is, the average current of the driving example 2 is twice the average current of the driving example 1.
As a result, the panel temperature of the driving example 2 becomes higher than the panel temperature of the driving example 1, and the initial deterioration can be further accelerated. Of course, the time required for the aging process can be further shortened.
This effect is shown in FIG. FIG. 7 is a diagram illustrating the number of defective pixels that appear later in the organic EL panel that is aged under the driving conditions of the driving example 2.
When the driving example 2 is applied, it can be seen that only about one dark dot pixel appears even after 4000 hours. On the other hand, in the case of always lighting, about 5 defective pixels may appear in the same time.

(C) Driving example 3
In the case of driving example 1 and driving example 2, the duty ratio was set to 50%. However, the duty ratio can be set to other values. Here, the variable range of the duty ratio is set in consideration of other driving conditions (data signal level, blinking cycle (frequency), panel material, circuit configuration, etc.). For example, it is set within a range of 40% to 80% within one cycle.
FIG. 8 shows an example of a drive signal in the case where the number of blinks within one field period is one and the duty ratio for one field period of the lighting period is 80%. The data signal is four times that during normal operation.
In this case, the current load applied instantaneously is the same as in driving example 2, but the average driving current flowing in the organic EL element 3 is 3.2 times that in normal operation. For this reason, panel temperature becomes higher and the aging effect becomes higher.

However, if the temperature of the panel rises too much, there is a possibility that a normal organic EL element is seriously damaged. Therefore, it is desirable that the duty ratio can be arbitrarily adjusted within a range where the panel temperature falls within an appropriate range. For example, if the duty ratio is adjusted to 40%, the instantaneous current value flowing through the organic El element 3 remains four times that of normal time, and only the average current can be halved. That is, the average current value can be reduced to 1.6 times the normal value.
By such a method, an appropriate condition may be selected according to the panel to be aged.
The duty ratio may be changed during the aging process. Of course, after an appropriate duty ratio is determined in advance, it may be fixed to the same value during the aging process.
In any case, if the duty ratio can be varied arbitrarily, the acceleration effect of the aging effect can be optimized.

(D) Driving example 4
In the drive example 1, the case where the organic EL element 3 is driven to blink at 60 Hz has been described. In the drive example 2, the case where the organic EL element 3 is driven to blink at 480 Hz has been described. However, the frequency of the control signal giving the blinking cycle is not limited to these. The frequency variable range here may be set in consideration of other driving conditions (data signal level, duty ratio, panel material, circuit configuration, etc.). For example, it may be set in the range of 60H to 700Hz, preferably 300Hz to 700Hz.

FIG. 9 shows the aging effect due to the difference in driving frequency. Note that the peak current value of the drive current is twice that during normal operation. In addition, the vertical axis of FIG. 9 represents the relative value of the light emission luminance with the light emission amount at the start of the experiment represented as “1”, and the horizontal axis represents the experiment time.
As shown in FIG. 9, it can be seen that the deterioration rate when the organic EL element 3 blinks at 700 Hz is higher than when the organic EL element 3 blinks at 300 Hz. In general, the deterioration rate tends to increase as the frequency increases.
Therefore, when the peak current value of the drive current and the duty ratio are fixed, the deterioration rate can be adjusted by changing the frequency.

This effect is shown in FIG. FIG. 10 is a diagram illustrating the number of defective pixels that appear later in the organic EL panel that is aged under the driving conditions of driving example 4.
For example, when AC driving is performed at a driving current of 300 Hz, it can be seen that only about two dark spot pixels appear even after 4000 hours. In addition, for example, when the drive current is AC driven at 700 Hz, it can be seen that only about one dark spot pixel appears after 4000 hours.
On the other hand, in the case of the existing drive condition by always lighting, about 5 defective pixels may appear in the same time.

Note that this frequency change may be performed during the aging process. For example, the frequency may be switched and controlled in units of one field period. Of course, two frequencies may be switched and controlled within one field period.
Of course, after an appropriate frequency is determined in advance, the same frequency value may be fixed during the aging process.
In any case, if the frequency can be arbitrarily changed, the acceleration effect of the aging effect can be optimized.

(D) Aging Device FIG. 11 shows a configuration example of an aging device used for aging processing. The aging device 21 is connected to the organic EL panel 23 through the connection cable 25 and supplies drive signals and various power supply voltages necessary for light emission control of the organic EL panel 23.
The power supply voltage here includes a power supply voltage required for driving the drive circuit in addition to a power supply voltage Vcc (15 V) and a cathode power supply (0 V) required for driving the pixel circuit.
The drive signal here includes a data signal for aging in addition to a clock signal and a start pulse signal of a shift register constituting the drive circuit.
In the figure, a circuit for generating a signal and a power supply voltage necessary for active matrix driving is indicated as a driving signal generating circuit 21A.

Further, the drive signal necessary for the light emission control of the organic EL panel 23 includes a timing signal necessary for AC driving of the drive current. The lighting / extinguishing control circuit 13 generates a control signal for controlling opening / closing of the transistor T3 based on this timing signal. That is, the timing signal (the duty ratio of the drive current, the number of cycles) of the transistor T3 is controlled by this timing signal.
In the figure, a circuit that generates a timing signal that realizes one or more blinking operations within one field period is referred to as a drive signal generation circuit 21B.
By mounting these two drive signal generation circuits 21A and 21B, the aging process described above is realized.
When the panel is aged before mounting the drive circuit, the drive signal generation circuit 21A directly applies a data signal or a line selection signal. In this case, the drive signal generation circuit 21B directly applies a control signal for AC driving the transistor T3.

(E) Other Embodiments (a) The above embodiments have been described based on the pixel circuit shown in FIG. However, the present invention can be applied not only to an equivalent pixel circuit but also to a pixel circuit as shown in FIG. The pixel circuit shown in FIG. 12 is different in that the transistor T3 is connected between the transistor T2 and the organic EL element 3. Even when this configuration is adopted, acceleration of the aging effect can be realized.
(B) In the above-described embodiment, the case where the peak current value of the data signal applied during the aging process is set to 2 times or 4 times that during the normal operation has been described.
However, the peak current value need not be limited to these, and can be set to any value.
(C) Various modifications can be considered for the above-described embodiments within the scope of the gist of the invention. In particular, numerical values relating to aging processing conditions (for example, frequency, peak value of driving current, power supply voltage, aging time) may be selected as optimum values according to the structure (including materials) and circuit configuration of the pixel circuit. Various modifications and application examples created based on the description of the present specification are also conceivable.

It is a figure explaining an initial stage deterioration characteristic. It is a figure explaining the difference of the initial stage deterioration characteristic in the case where a drive current drives by constant current, and the case where alternating current drive. It is a figure which shows the pixel circuit example (2 transistor type) of an active matrix drive system. It is a figure which shows the pixel circuit example (3 transistor type) of an active matrix drive system. It is a figure explaining the aging drive example made to blink once within one field period. It is a figure explaining the aging drive example made to blink 8 times within 1 field period. It is a figure which shows the appearance characteristic of the defective pixel after an aging process. It is a figure explaining the example of an aging drive in case a lighting period is set to 80% in 1 field period. It is a figure explaining the difference in the initial stage deterioration characteristic according to a drive frequency. It is a figure which shows the appearance characteristic of the defective pixel after an aging process. It is a figure which shows the structural example of an aging apparatus. It is a figure which shows the other pixel circuit example (3 transistor type) of an active matrix drive system.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 11 Pixel circuit 3 Organic EL element 5 Data signal selection circuit 7 Line selection circuit 13 Lighting / extinguishing control circuit 21 Aging device 21A Drive signal generation circuit 21B Drive signal generation circuit 23 Organic EL panel

Claims (7)

A self-light emitting device aging method in which light emission is controlled by an active matrix driving method,
In parallel with the application of the active matrix drive data signal and line selection signal to the self-luminous device,
Apply a control signal for AC driving to a transistor connected in series between each light emitting element and a power supply voltage line,
An aging method for a self-light-emitting device, wherein each light-emitting element is driven to blink within a field period. The aging method according to claim 1, wherein
The self-luminous device aging method, wherein the frequency of the AC drive control signal can be arbitrarily varied. The aging method according to claim 1, wherein
The self-light emitting device aging method, wherein a duty ratio of the control signal for AC driving can be arbitrarily changed. The aging method according to claim 1, wherein
The peak value of the data signal can be arbitrarily changed. The aging method according to claim 1, wherein
The duty ratio of the control signal for AC driving and the peak value of the data signal are set so that the average driving current flowing through each light emitting element is the same as that during normal driving. Method. A method of manufacturing a self-luminous device that is controlled to emit light by an active matrix driving method
When executing the aging process,
A process of applying a data signal and a line selection signal for driving an active matrix to the light emitting device;
A control signal for AC driving is applied to a transistor connected in series between each light emitting element and a power supply voltage line, and a process of driving each light emitting element to blink within a field period is executed. Manufacturing method of light-emitting device. An aging device whose target is a self-light-emitting device whose emission is controlled by an active matrix driving method,
A first drive signal generator for generating a drive signal necessary for applying a data signal and a line selection signal for active matrix drive to the pixel circuit;
A second drive signal generator for generating a drive signal necessary for applying a control signal for AC drive to a transistor connected in series between each light emitting element and a power supply voltage line; An aging device for a self-light-emitting device, wherein the element is driven to blink within a field period.

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