Electric lamp and discharge devices: systems – Plural power supplies – Plural cathode and/or anode load device
Reexamination Certificate
2001-07-03
2003-10-14
Wong, Don (Department: 2821)
Electric lamp and discharge devices: systems
Plural power supplies
Plural cathode and/or anode load device
C315S169100, C315S169200, C345S904000
Reexamination Certificate
active
06633135
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus and method for evaluating an organic electroluminescence display (hereinafter referred to as an “organic EL display”) that makes use of an organic substance for its light-emitting substance, and more particularly relates to an apparatus and method for evaluating an organic EL display used in any of various types of display devices, such as the display panels of cellular telephones, the display panels of car audio systems, display panels for still or moving pictures, and the image displays of digital cameras.
2. Description of the Related Art
Organic electroluminescence elements (hereinafter referred to as “organic EL elements”) have been the subject of considerable research and practical application in recent years.
FIG. 5
is an enlarged cross section of the main components of a conventional type of organic EL element
1
. This organic EL element
1
comprises a glass substrate
2
, an anode
3
, a hole transport layer
4
, an electron transport light-emitting layer
5
and a cathode
6
. Direct current is supplied by applying a specific voltage between the anode
3
and the cathode
6
from a DC power supply
7
.
A transparent electrode made of ITO (Indium Tin Oxide) or the like is employed for the anode
3
, a diamine dielectric (TPAC) is employed for the hole transport layer
4
, an aluminum complex (Alq) is employed for the electron transport light-emitting layer
5
, and the carrier rebonding rate is raised by laminating materials with different carrier transport capabilities. Magnesium (Mg), aluminum (Al), or the like is employed for the cathode
6
.
With an organic EL element
1
structured such as this, the carriers (hole and electron charges) injected from the anode
3
and the cathode
6
are confined in the organic layer of the electron transport light-emitting layer
5
, the carrier rebonding efficiency rises sharply, and a high level of brightness (over 1000 cd/m
2
) can be obtained at a voltage of 10 volts or less.
Such elements are therefore expected to find use in cellular telephones, car audio systems, household electronics, and so forth.
FIG. 6
is a circuit diagram illustrating one pixel
11
in an active matrix type of organic EL display
10
. The organic EL display
10
comprises a plurality of selection lines VG (scanning lines) and signal lines
9
VD) arrange din a matrix, with the pixel
11
connected at the intersection of these lines.
The pixel
11
comprises a switching circuit
12
, a constant current circuit
13
, and an organic EL pixel
14
constituted by the above-mentioned organic EL element
1
. The organic EL pixel
14
emits light when supplied with a constant current by the application of a fairly constant specific voltage from a voltage supply line VLC to the constant current circuit
13
.
The pixel
11
has been disclosed in Japanese Laid-Open Patent Application H5-107561 and elsewhere: for example as shown in
FIG. 7
, a first transistor
15
consisting of a thin film transistor (TFT) or the like is employed as the switching circuit
12
, and a second transistor
16
, similarly made of TFT or the like, and a capacitor
17
are employed as the constant current circuit
13
.
The first transistor
15
is switched in order to supply a constant current to the organic EL pixel
14
.
The second transistor
16
is switched by the first transistor and is connected to the organic EL pixel
14
.
The capacitor
17
is selected to help supply a constant current to the organic EL pixel
14
according to the specific discharge time thereof.
With a pixel
11
structured such as this, the selection of the pixel
11
is made by the first transistor
15
, the result of the selection is transmitted to the second transistor
16
, the voltage applied to the pixel
11
is controlled by the second transistor
16
and by the capacitor
17
, which is able to hold a specific electrical charge for a specific length of time, and a fairly constant specific voltage from the voltage supply line VLC is maintained, thereby reducing the difference in voltage between the various pixels
11
.
In order to evaluate an organic EL display
10
structured such as this, in the past the organic EL display
10
was actually driven only after a drive circuit (not shown) was attached to the organic EL display
10
and everything put together in a form similar to that of an actual finished product, and the work of detecting line defects or dot defects was performed by separate image evaluation devices.
Therefore, a problem was that discrepancies occurred between the various evaluation devices or in the evaluation standards, and this led to lower detection accuracy.
Another method is for the drive or luminescence state of the organic EL display
10
to be visually evaluated by a human, but a problem was that there was variance in the evaluation results depending on the experience of the evaluator and how well he or she was performing on a given day.
Furthermore, if an element is decided to be defective as a result of evaluation, the organic EL display
10
ends up being discarded along with the above-mentioned drive circuit parts attached to it, which is a problem in that it is wasteful. This also results in a waste of the time spent in evaluation.
Organic EL elements have been disclosed in the above-mentioned Japanese Laid-Open Patent Application H5-107561, as well as in Japanese Laid-Open Patent Applications H9-260061 and H10-321367 and elsewhere.
SUMMARY OF THE INVENTION
The present invention was conceived in light of the above problems, and it is an object thereof to provide an apparatus and method for evaluating an organic EL display, with which the drive circuit used for testing the organic EL display has a simple circuit configuration, and which yields evaluation results of high reliability.
It is another object of the present invention to provide an apparatus and method for evaluating an organic EL display, with which the detection accuracy is high and it is possible to evaluate the organic EL display itself, before the finished product drive circuits have been incorporated into the organic EL display.
It is another object of the present invention to provide an apparatus and method for evaluating an organic EL display, with which pixel defects of organic EL display elements can be detected by efficiently detecting, with a simple circuit configuration, the micro-current flowing to the organic EL elements.
It is another object of the present invention to provide an apparatus and method for evaluating an organic EL display, with which the micro-current can be efficiently detected so that the drive current supplied to the organic EL elements for the purpose of detection does not become superposed between a number of organic EL elements.
It is yet another object of the present invention to provide an apparatus and method for evaluating an organic EL display, with which it is possible to suppress the decrease in yield caused by dealing with defective products due to the evaluation results.
Specifically, according to the present invention it is possible to test an active-matrix type organic EL display after assembly of the pixels, the signal lines, the selection lines, and the voltage supply lines by energizing each pixel in turn, measuring a first steady-state current flowing to the EL element after the associated capacitor has been charged through the first transistor, and the second transistor is switched on, by measuring a second steady-state current after the capacitor has been discharged and the second transistor is switched off, by comparing the two measured currents, and by identifying a pixel as defective or defect-free based on the difference between the two currents.
The first aspect of the invention is an apparatus for evaluating an organic EL display having organic EL elements as pixels, wherein the the first and second currents as defined above are measured for each pixel constituted by an organic EL element and pixel defects are identified by detecting a difference in t
Innami Tomoharu
Itoh Masatoshi
Nara Shouji
Ookuma Makoto
Alemu Ephrem
Ostrolenk Faber Gerb & Soffen, LLP
Wintest Corporation
Wong Don
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