JP2006210213A - Aging method, manufacturing method and aging device of self-luminous device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an aging device capable of effectively and efficiently implementing detection of a deterioration characteristic of an organic EL element and a defect of a pixel. <P>SOLUTION: When an aging process of a self-luminous device of which the light emission is controlled by an active matrix drive method is executed, a pulse-like A.C. forward voltage which is so controlled that the average luminance in aging is set equal to that in normal use is generated, and each luminescent element is blinked and driven in a field period by applying it to a cathode power line. Thereby, an aging effect is accelerated as compared with that in an aging process by constant lighting; and an initial characteristic can be stabilized in a short time as compared with a conventional technique. <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.
In other words, when executing the aging process of a self-luminous device controlled to emit light by the active matrix driving method, a pulsed AC forward voltage controlled so that the average luminance during aging is the same as that during normal use is applied to the cathode power supply line. Then, a method of blinking each light emitting element within the field period is proposed.

  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.
The data signal is supplied from the data signal selection circuit 5 to each data line. Each scanning line is selected by the line selection circuit 7 at a rate of once per field. That is, each pixel circuit takes in a data signal at a rate of once per field.

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, the aging process cannot be accelerated by controlling the field frequency.

(B) Aging processing example Therefore, a method is proposed in which the cathode power supply voltage is changed in an alternating manner in a pulsed manner so that the drive current is turned on / off faster than one field period. FIG. 4 shows an image of AC drive of the cathode power supply.

(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 the case where the duty ratio of the voltage level applied to the cathode power supply 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 voltage level applied to the cathode power supply. The cathode voltage in this example is given as a binary value of 0V or 15V. Here, 0V corresponds to the cathode voltage during normal driving, and 15V corresponds to the power supply voltage VCC. Therefore, the amplitude of the voltage level is given by 15V (= 15V-0V).

In the figure, the cathode voltage is controlled to 0 V in the first half of one field period. At this time, the transistor T2 is turned on, and the organic EL element 3 is lit in the first half of one field period as shown in FIG.
On the other hand, in the figure, the cathode voltage is controlled to 15 V in the second half of one field period. At this time, 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 within one field period is one, but the deterioration rate can be accelerated as compared with 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. In other words, the average brightness during the aging process is the same as 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. 7 shows an example of a drive signal when the number of blinks in one field period is eight. That is, the case where the cathode power supply is AC driven at 480 Hz will be described.
FIG. 7 shows a case where the duty ratio in one cycle of the voltage level applied to the cathode power supply is 50% and the data signal giving the drive current value is four times that in the normal operation. The aging time is 4 hours.
Here, FIG. 7A 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. 7B shows the voltage level applied to the cathode power supply. Also in this case, the cathode voltage is given as a binary value of 0V or 15V. Therefore, as shown in FIG. 7C, the organic EL element 3 is repeatedly turned on and off eight times in one field period.
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. 8 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 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 cathode voltage that gives 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 the driving frequency of the cathode voltage. It is assumed that the peak current value of the drive current is double that in normal operation, and the cathode voltage is AC driven with a duty ratio of 50%. 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 in the case of AC operation at 700 Hz is higher than that in the case where the organic EL element 3 is AC driven 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 3.
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. However, the drive frequency of the cathode voltage may be switched between two frequencies 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) Driving example 4
In the case of driving example 1 and driving example 2, the duty ratio of the cathode voltage applied to the cathode power supply was fixed, the signal level of the data signal was varied, and the average current value flowing through the organic EL element 3 was adjusted.
However, the average current value flowing through the organic EL element 3 can be adjusted by changing the duty ratio. That is, the acceleration effect of the aging effect can be optimized.
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. 11 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.

(E) Driving example 5
In the driving examples 1 to 4, the driving examples based on the pixel circuit (FIG. 4) having a two-transistor configuration have been described.
However, in the case of an organic EL panel having a pixel circuit configuration that can control the supply and stop of the drive current independently of the active matrix drive, the following drive is also possible.
FIG. 12 shows an example of a pixel circuit having a three-transistor structure capable of this kind of driving.
The pixel circuit 11 includes three transistors T1, T2, and T3, a capacitive element C1, and an organic EL element 3. All of these three transistors T1, T2, and T3 are thin film transistors (TFTs). In the case of FIG. 12, the transistor T1 is an N-channel transistor, and the transistors T2 and T3 are P-channel transistors.

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.
When the transistor T3 is in the “closed state”, a driving current flows and the organic EL element 3 is lit. Further, when the transistor T3 is in the “open state”, the driving current does not flow and the organic EL element 3 is turned off.
By controlling the opening and closing of the transistor T3, the lighting period (duty ratio) within one field cycle can be controlled.

FIG. 13 shows an example of adjusting the average current using the transistor T3. The driving example 2 is the same as the driving example 2 except for the presence of the transistor T3.
That is, the case where the cathode power supply is AC driven at 480 Hz will be described. Further, the case where the duty ratio in one cycle of the voltage level applied to the cathode power supply is 50% and the data signal giving the drive current value is four times that in the normal operation is shown.
The conditions in FIGS. 13A and 13B are the same as those in Driving Example 2.

In this case, the transistor T3 is closed for 80% of time within one field period. That is, the organic EL element 3 is turned on by 80% within one field period, and the remaining 20% is turned off.
FIG. 13C shows an example of the control signal level in this case. As a result, the blinking operation of the organic EL element 3 is executed only in the period of 80% of the first half of one field cycle as shown in FIG.

This means that the average current of driving example 5 is reduced to 80% of driving example 2. That is, the average current of the driving example 5 is 1.6 times (2 times × 0.8) the average current of the driving example 1.
Accordingly, the instantaneous drive current value flowing through the organic EL element 3 remains four times that during normal operation, and only a reduction in the average current can be realized.
For this reason, while promoting destruction of hidden defects, an excessive increase in panel temperature can be suppressed and damage to the normal organic EL element 3 can be reduced.
If the panel temperature is to be adjusted, the period during which the transistor T3 is closed (duty ratio) may be controlled to increase or decrease.

(C) Aging Device FIG. 14 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 signals 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 the cathode voltage applied to the cathode power source. A circuit for alternatingly driving the cathode voltage is referred to as a cathode voltage generating circuit 21B.
The aging process described above is realized by mounting these drive signal generation circuit 21A and cathode voltage generation circuit 21B.
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 the case of a three-transistor pixel circuit, the drive signal generating circuit 21A directly applies a control signal for driving the transistor T3 to open and close.

(D) Other Embodiments (a) The driving examples 1 to 4 described above are based on the pixel circuit 1 (FIG. 4) having a two-transistor configuration.
However, the driving examples 1 to 4 can be similarly applied to a three-transistor pixel circuit (FIG. 12).
(B) In the driving example 5 described above, the pixel circuit shown in FIG. 12 is assumed. 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. 15 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.
(C) In the driving example described above, 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 normal operation has been described.
However, the peak current value need not be limited to these, and can be set to any value.

(D) In the driving example described above, the amplitude of the cathode voltage that is AC-driven has been described as 15 V (0 V / 15 V).
However, the upper limit value and the lower limit value of the cathode voltage can be determined between the cathode voltage during normal driving (ie, 0 V) and the power supply voltage Vcc (ie, 15 V) supplied to the panel.
For example, the cathode voltage may be AC driven with a binary value of 0V and 13V.
In this case, the amplitude of the cathode voltage is 13V. Thus, the amplitude of the cathode voltage can be varied arbitrarily.
By adjusting the amplitude of the cathode voltage, the peak value of the drive current flowing through the organic EL element 3 can be reduced. That is, the increase in panel temperature can be adjusted by adjusting the average current.
(E) 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 alternating current drive image of a cathode power supply. It is a figure explaining the aging drive example made to blink once within one field period. It is a figure explaining the difference in the initial stage deterioration characteristic in the case of carrying out alternating current drive of a cathode power supply, and making a cathode power supply voltage into direct current drive. 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 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 explaining the example of an aging drive in case a lighting period is set to 80% in 1 field period. It is a figure which shows the other pixel circuit example (3 transistor type) of an active matrix drive system. It is a figure which shows the example of an aging drive in case the pixel circuit shown in FIG. 12 is mounted in the organic electroluminescent panel. 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 Cathode voltage generation circuit 23 Organic EL panel

Claims (8)

A self-light emitting device aging method in which light emission is controlled by an active matrix driving method,
A process of generating a pulsed AC forward voltage controlled so that the average brightness during aging is the same as during normal use;
A method of aging a self-light-emitting device, comprising: applying the AC forward voltage to a cathode power supply line and driving each light-emitting element to blink within a field period. The aging method according to claim 1, wherein
The frequency of the AC forward voltage can be varied arbitrarily. The aging method according to claim 1, wherein
A duty ratio of the AC forward voltage can be arbitrarily varied. The aging method according to claim 1, wherein
When a transistor is connected in series between each light emitting element and the power supply voltage line,
A self-luminous device aging method characterized in that the period during which the transistor is closed within one field is arbitrarily varied. The aging method according to claim 1, wherein
The self-luminous device aging method, wherein the amplitude of the AC forward voltage can be arbitrarily varied. The aging method according to claim 1, wherein
A self-luminous device aging method, wherein a peak value of a data signal for driving an active matrix can be arbitrarily changed. 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,
While applying a data signal and a line selection signal for active matrix driving to the self-luminous device,
A self-luminous device characterized in that a pulsed AC forward voltage controlled so that the average luminance during aging is the same as that during normal use is applied to the cathode power supply line, and each light emitting element is driven to blink within a field period. Manufacturing method. An aging device whose target is a self-light-emitting device whose emission is controlled by an active matrix driving method,
A 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 cathode voltage generator that generates a pulsed AC forward voltage controlled so that the average luminance during aging is the same as during normal use;
The AC forward voltage is applied to a cathode power supply line, and each light emitting element is driven to blink within a field period.

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