Patent Grant
9236010
This application claims priority to and the benefit of Korean Patent Application No. 10-2011-0053955 filed in the Korean Intellectual Property Office on Jun. 3, 2011, the entire content of which is incorporated herein by reference.
1. Field
Aspects of embodiments of the present invention are directed toward a test device of a display device, a test method, and a manufacturing method of a display device.
2. Description of Related Art
An organic light emitting diode (OLED) display is a flat display device that has a self emissive characteristic and does not require a separate light source. The OLED display has characteristics such as low power consumption, high luminance, and high response speed. In addition, the OLED display has excellent carrier mobility so that it can be applied to a high-speed operation circuit.
In the OLED display, transmission of a driving current to an OLED may be controlled by a transistor (for example, a driving transistor) formed in each pixel circuit. In such an OLED display, a predetermined driving current cannot be applied to the OLED when the transistor of the pixel circuit malfunctions or wires are disconnected or short-circuited.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.
Aspects of embodiments of the present invention are directed toward a test device of a pixel circuit array of an organic light emitting diode (OLED) display, and a manufacturing method of an OLED display. Embodiments of the present invention provide for a pixel circuit array test device of an OLED display and a test method thereof for accurate determination of normal operation of a driving transistor. Further embodiments of the present invention provide for a method for manufacturing an OLED display having excellent quality and reliability using the pixel circuit array test device and method according to an exemplary embodiment of the present invention.
According to aspects of embodiments of the present invention, a driving transistor is tested to determine an operation failure. In case of failure, a pixel circuit array can be repaired prior to a panel (cell) process so that a manufacturing yield can be improved. In particular, gate node voltages of a plurality of driving transistors in the array are commonly initialized and then measured so that whether the driving transistors are capable of performing normal operations can be accurately tested within a short period of time.
According to an exemplary embodiment of the present invention, an array test method of an organic light emitting diode (OLED) display substrate is provided. The OLED display substrate includes a plurality of pixel circuits. Each of the pixel circuits includes an anode; a first transistor for transmitting a data signal that controls an amount of light emission of an OLED according to a scan signal; a driving transistor for receiving the data signal, generating a driving current corresponding to the data signal, and transmitting the driving current to the OLED; and a second transistor for diode-connecting a gate electrode and a drain electrode of the driving transistor. The array test method includes: injecting electrons or holes that generate an initialization voltage into the anode by turning on the second transistor; radiating electron beams at the anode; and determining whether or not the driving transistor performs normal operation from an amount of secondary electrons emitted from the anode.
While the second transistor is turned on, the initialization voltage may be applied to a gate node of the driving transistor.
The initialization voltage may be higher than a threshold voltage of the driving transistor.
The injection of electrons or holes may be performed through radiation of electron beams for initialization.
The array test method of the OLED display substrate may be performed prior to completion of the OLED by forming an organic light emission layer and a cathode on the anode.
The first transistor may include a gate electrode coupled to a scan line for transmitting the scan signal, a first electrode coupled to a data line for transmitting the data signal, and a second electrode coupled to the gate electrode of the driving transistor.
The driving transistor may include the gate electrode coupled to the first transistor for transmitting the data signal, a first electrode coupled to a driving power source for supplying a first power voltage, and a second electrode coupled to the anode.
The second transistor may include a gate electrode coupled to a gate line for transmitting a gate signal, a first electrode coupled to a node where the driving transistor and the anode are commonly coupled, and a second electrode coupled to the gate electrode of the driving transistor.
The gate signal may be a signal that controls switching of the second transistor to compensate a threshold voltage of the driving transistor or to apply an initialization voltage to the gate electrode of the driving transistor.
Each of the pixel circuits may further include: a first capacitor including a first terminal coupled to the first transistor and a second terminal coupled to a driving power source for supplying a first power voltage for transmission of the driving current; and a second capacitor comprising a first terminal coupled to the first transistor and a second terminal coupled to the driving transistor.
According to another exemplary embodiment of the present invention, an array test device of an organic light emitting diode (OLED) display substrate is provided. The array test device includes a first electron beam injection means, a second electron beam injection means, an electron detecting means, and a driver for controlling driving of the first electron beam injection means, the second electron beam injection means, and the electron detecting means. The first electron beam injection means is for radiating a first electron beam at an anode of each of a plurality of pixel circuits included in a pixel circuit array. Each of the pixel circuits includes: an anode; a first transistor for transmitting a data signal that controls an amount of light emission of an OLED according to a scan signal; a driving transistor for receiving the data signal, generating a driving current corresponding to the data signal, and transmitting the driving current to the OLED; and a second transistor for diode-connecting a gate electrode and a drain electrode of the driving transistor. The second electron beam injection means is for radiating a second electron beam at the anode after a gate node voltage of the driving transistor is initialized to a reference voltage by the radiation of the first electron beam. The electron detecting means is for detecting an amount of secondary electrons emitted from the anode due to radiation from the second electron beam.
A radiation amount of the first electron beam may be different from that of the second electron beam.
The reference voltage may be higher than a threshold voltage of the driving transistor.
The first electron beam injection means and the second electron beam injection means include one electron beam device.
The one electron beam device may include an e-beam generator or an ionizer.
The first electron beam injection means, the second electron beam injection means, and the electron detecting means may be provided in each of a plurality of micro columns corresponding to ones of the plurality of pixel circuits included in at least one pixel line or pixel column. The micro columns may be configured to be fixed to a loading unit for testing the pixel circuit array, or be configured to be moved relative to the loading unit.
According to yet another exemplary embodiment of the present invention, a manufacturing method of an organic light emitting diode (OLED) display is provided. The method includes forming a pixel circuit array formed of a plurality of pixel circuits. Each of the pixel circuits includes: an anode; a first transistor for transmitting a data signal that controls an amount of light emission of an OLED according to a scan signal; a driving transistor for receiving the data signal, generating a driving current corresponding to the data signal, and transmitting the driving current to the OLED; and a second transistor for diode-connecting a gate electrode and a drain electrode of the driving transistor. The method further includes: radiating a first electron beam at the anode while the second transistor is turned on; determining whether or not the driving transistor performs normal operation by radiating a second electron beam at the anode and detecting an amount of secondary electrons emitted from the anode due to radiation from the second electron beam, after a gate node voltage of the driving transistor is initialized to a reference voltage by the radiation of the first electron beam; determining whether the pixel circuit array is a good product or a bad product based on the determination of whether the driving transistor performs normal operation; repairing the pixel circuit array determined to be a bad product; and completing an OLED of the pixel circuit included in the repaired pixel circuit array or in the pixel circuit array determined to be a good product.
The completing of the OLED may include forming an organic emission layer and a cathode on the anode.
The first electron beam and the second electron beam may be radiated through an e-beam generator or an ionizer.
The reference voltage may be higher than a threshold voltage of the driving transistor.
A radiation amount of the first electron beam may be different from that of the second electron beam.
Since whether the driving transistor performs normal operation can be tested using a relatively simple test device, the time and cost for a test process can be saved or reduced. Further, a panel (cell) process and a module process are not performed on a pixel circuit array determined to be a bad product so that manufacturing time and production cost can be saved or reduced.
The present invention will be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention.
Further, in the exemplary embodiments, like reference numerals designate like elements throughout the specification and are representatively described in a first exemplary embodiment. In later embodiments, only elements other than those of the first exemplary embodiment will be described. Further, the drawings and description are to be regarded as illustrative in nature and not restrictive.
Throughout this specification and the claims that follow, when it is described that an element is “coupled” to another element, the element may be “directly coupled” (for example, connected) to the other element or “electrically coupled” (for example, indirectly coupled or connected) to the other element through one or more third elements. In addition, unless explicitly described to the contrary, the word “comprise” and variations such as “comprises” or “comprising” will be understood to imply the inclusion of stated elements but not the exclusion of any other elements.
In exemplary embodiments, before forming an organic light emitting diode (OLED) display, the transistors of the pixel driving circuits may be tested to determine whether they perform normal operations or not. In addition, bad transistors may be repaired. If the bad transistors cannot be repaired, the next processes, such as a panel (cell) process and a module process, may be canceled to save or reduce manufacturing time and production cost.
However, in some OLED displays, a gate node of the driving transistor (for transmitting a driving current that corresponds to a data signal to the OLED) may be floated after completion of a thin film transistor (TFT) process. Thus, whether or not the driving transistor performs normal operation may not be accurately tested using conventional test equipment.
Accordingly, embodiments of the present invention provide for an array test device of an OLED display and an array test method for accurate determination of normal operation of a floated driving transistor by initializing a gate node of the floated driving transistor in the test of performance of transistors in a pixel circuit array.
A pixel circuit array test device (hereinafter, referred to as an array test device) and a pixel circuit array test method (hereinafter, referred to as an array test method) of an organic light emitting diode (OLED) display according to an exemplary embodiment of the present invention may be applied to a step prior to a panel (cell) process for completion of an OLED during a manufacturing process of the OLED display according to an exemplary embodiment of the present invention. The array test method may be performed through a process of initializing a gate node voltage of a driving transistor of a pixel driving circuit using the array test device and then determining whether or not the driving transistor connected to an anode of an exposed OLED (that is, an OLED before forming an organic light emission layer and a cathode) is operating normally by measuring the amount of secondary electrons emitted from the radiation of electron beams (E-beams) at the anode.
Referring to
Returning to the manufacturing method of
For a pixel circuit array determined to be a good product or successfully repaired (S21) after the array test (S2), an organic emission layer and a cathode are formed as part of a panel (cell) process (S3) to complete the corresponding OLEDs. A panel test (S4) is then performed.
A panel determined to be a bad product in the panel test (S4) may be repaired through a repairing process (S31), assuming the panel can be repaired. If the panel cannot be repaired, further production steps or processes on the panel are terminated and no further processes are performed.
For a panel determined to be a good product or successfully repaired (S31) after the panel test (S4), a module process (S5) is performed to produce a finished product. After the module process (S5), a final test (S6) is performed to determine if the module is a finished product or a bad product.
A module determined to be a bad product in the final test (S6) may be repaired through a repairing process (S61), assuming the module can be repaired. If the module cannot be repaired, the module may be terminated or discarded (for example, recycled, destroyed).
As shown in
In further detail, the three transistors of the pixel driving circuit 20 include a driving transistor Md, a first transistor Ms, and a second transistor Mgc. The driving transistor Md is coupled between the OLED and a first power voltage source (ELVDD). The driving transistor Md transmits a driving current, corresponding to a data signal, to the OLED. Further, the first transistor Ms is for switching the data signal and transmitting the switched data signal to a gate electrode of the driving transistor Md. Finally, the second transistor Mgc is disposed between the gate electrode and a drain electrode of the driving transistor Md to diode-connect the driving transistor Md.
In addition, the two capacitors of the pixel driving circuit 20 include a first capacitor C1 for storing the data signal applied to the gate electrode of the driving transistor Md, and a second capacitor C2 for controlling a threshold voltage of the driving transistor Md.
In further detail, the gate electrode of the driving transistor Md is coupled to the second capacitor C2 at a second node N2. A first electrode of the driving transistor Md is coupled to the first power voltage source ELVDD, that is, a driving voltage (e.g., the first power voltage ELVDD) at a fourth node N4. A second electrode of the driving transistor Md is coupled to an anode of the OLED and a first electrode of the second transistor Mgc at a third node N3.
A gate electrode of the first transistor Ms is coupled to a scan line for transmitting a scan signal Scan(n) corresponding to the pixel 10. A first electrode of the first transistor Ms is coupled to a data line for transmitting a corresponding data signal Data(t). A second electrode of the first transistor Ms is coupled to the first capacitor C1 at a first node N1.
The first transistor Ms is a switching transistor that transmits a currently applied data signal Data(t) from the data line to the first node N1 in response to the scan signal Scan(n) corresponding to the pixel 10. Then, the first capacitor C1 coupled to the first node N1 stores a data voltage corresponding to the data signal Data(t) for a time period (for example, a predetermined time period). The driving transistor Md supplies a driving current—according to the data voltage corresponding to the data signal Data(t)—to the OLED.
A gate electrode of the second transistor Mgc is coupled to a gate line for transmitting a gate signal GC(t) for compensation of the threshold voltage of the driving transistor Md. The first electrode of the second transistor Mgc is coupled to the second electrode of the driving transistor Md at the third node N3. A second electrode of the second transistor Mgc is coupled to the gate electrode of the driving transistor Md and the second capacitor C2 at the second node N2.
The second transistor Mgc is a threshold voltage compensation transistor for compensating the threshold voltage of the driving transistor Md in response to the gate signal GC(t). In the array test method according to an exemplary embodiment of the present invention, the second transistor Mgc is turned on while a gate node of the driving transistor Md is initialized to a voltage (for example, a predetermined reference voltage, such as a voltage higher than the threshold voltage of the driving transistor Md) to diode-connect the driving transistor Md.
A first terminal of the first capacitor C1 is coupled to a first terminal of the second capacitor C2 and the second electrode of the first transistor Ms at the first node N1. A second terminal of the first capacitor C1 is coupled to the first power voltage source ELVDD (i.e., the first power voltage), which is a driving voltage to supply a current to the OLED at the fourth node N4.
The first terminal of the second capacitor C2 is coupled to the second electrode of the first transistor Ms and the first terminal of the first capacitor C1 at the first node N1. A second terminal is coupled to the gate electrode of the driving transistor Md and the second electrode of the second transistor Mgc at the second node N2.
The anode (i.e., pixel electrode) of the OLED is coupled to the second electrode of the driving transistor Md and the first electrode of the second transistor Mgc at the third node N3. A cathode (i.e., common electrode) of the OLED is coupled to a second power voltage source ELVSS, that is, a second power voltage ELVSS (i.e., common voltage).
The three transistors of the pixel driving circuit 20 may be PMOS transistors. A thin film transistor (TFT) may be exemplarily used as a field effect transistor. In other embodiments, the transistors may be realized as NMOS transistors. In this case, waveforms of signals driving the transistors may be inverted compared to when the corresponding transistors are realized as PMOS transistors.
After realizing an array formed of a unit pixel such as the unit pixel shown in
Therefore, as shown in the exemplary embodiment of
While the initialization electron beam 1 is being radiated, the gate signal GC(t) transmitted to the gate electrode of the second transistor Mgc is transmitted as a gate-on voltage level, and the second transistor Mgc is turned on in response to the gate signal GC(t). Then, the second transistor Mgc diode-connects the driving transistor Md, and the electrons injected through the electron beam radiation are transmitted to the gate node of the driving transistor Md, that is, the second node N2, through the second transistor Mgc. A gate electrode of each driving transistor of each pixel driving circuit included in the pixel circuit array is thus initialized with a voltage (for example, a predetermined reference voltage) through radiation from the initialization electron beam 1. In this case, the reference voltage for initialization through the electron beam radiation is not particularly restrictive. For example, the initialization voltage may be higher than the threshold voltage of the driving transistor.
After the gate node voltage of the driving transistor Md is initialized to a given voltage, a test electron beam 2 is radiated at the anode 111 to test whether or not the driving transistor is operating normally. The radiation amount of the initialization electron beam 1 may be different from that of the test electron beam 2. It can be tested whether the driving transistor Md coupled to the anode 111 is operating normally or not by radiating the test electron beam 2 at the anode 111 and detecting secondary electrons emitted from the anode 111.
That is, electrons are equally injected into an anode of each pixel included in the pixel circuit array. Thus, when a driving transistor Md of a given pixel driving circuit in the pixel circuit array performs abnormally, an output voltage of the secondary electrons emitted from the anode of the corresponding pixel circuit becomes different from that of other pixel circuits that perform normally. In this case, the gate electrode of the driving transistor of each pixel driving circuit in the pixel circuit array has already been initialized with the initialization voltage. Therefore, it can be easily determined whether or not the driving transistor Md performs normal operation through radiation of the test electron beams and the detection of the corresponding secondary electrons.
As illustrated in
With reference to
After such a pixel circuit array is loaded on, for example, a loading unit (to which the array test device may also be attached), the initialization array beam is radiated at an anode of each pixel circuit (S201). In this case, an input value of electrons injected into the anode of each pixel is equivalent to each other. An e-beam generator or an ionizer may be used as a device for electron beam injection, but it is not restrictive. That is, a known device that can emit electrons or holes may be used.
During this process, the second transistor is turned on. Thus, the gate node voltage of the driving transistor is initialized to a voltage (for example, a predetermined reference voltage) by the electrons injected from the initialization electron beam (S202). In some embodiments, this voltage is larger than the threshold voltage of the driving transistor.
A gate node voltage of each driving transistor of each pixel driving circuit in the pixel circuit array is set by initialization. Then, the test electron beam is applied to an anode of each pixel circuit (S203).
Next, secondary electrons emitted from the anode of each pixel circuit are detected (S204). The gate electrode voltage of the driving transistor of each pixel is set to the reference voltage. Accordingly, it can be determined whether the driving transistor operates normally or not based on the amount of secondary electrons (S205).
When the driving transistor performs normal operation, the driving transistor undergoes the panel (cell) process (S3) as a good product. Otherwise, the driving transistor is operating abnormally as a bad product. If the driving transistor is repairable, the repairing process (S21) is performed. If the driving transistor is unrepairable, the further processes are canceled.
Referring to
In the exemplary embodiment of
Referring to
During an injection period of the initialization electron beam 515, the second transistor of the corresponding pixel is turned on and transmits electrons injected from the initialization electron beam to the gate node of the driving transistor. Thus, the gate node of the driving transistor is initialized to a voltage (for example, a predetermined reference voltage). A test electron beam 525 is injected through the second electron beam injector 520 into the anode of each pixel circuit of the pixel circuit array moved toward the first direction 540.
The second electron beam injector 520 may be coupled to the electron detecting device 530. The electron detecting device 530 detects an output value of secondary electrons 535, that is, the electrons injected through the test electron beam 525 and then emitted again through the anode.
The output value of the secondary electrons is substantially constant for each pixel for which a corresponding driving transistor is operating normally. However, when the driving transistor is operating abnormally, for example, when a leakage current occurs, the output value changes. Accordingly, a failure of the driving transistor cannot be easily and accurately tested with conventional test equipment.
However, according to the exemplary embodiment shown in
Referring to
In further detail, the fixed axis 620 moves in the first direction 640 (relative to the pixel circuit array substrate 100) by the driver 630. Thus, each anode of the pixel circuit included in each pixel line or pixel column is irradiated by the electron beam to thereby produce the gate node voltage of the driving transistor of each pixel driving circuit. The pixel circuit array substrate 100 may be attached to a loading unit for use in testing the pixel circuit array substrate 100. The array test device may also be fixed to this loading unit.
Then, the fixed axis 620 moves again with respect to the pixel circuit array substrate 100, this time in a second direction 650. Further, the electron beam is radiated again at the anode of the pixel circuit included in each pixel line or each pixel column, for which the gate node of the corresponding driving transistors are initialized. In this case, the secondary electrons emitted from the anode are detected by the electron detecting device included in the micro column 610. Accordingly, a failure of each of the plurality of pixel circuits can be simultaneously tested.
In further embodiments, more than one fixed axis 620 (where the plurality of micro columns 610 are arranged in a line) may be provided in the same array test device so that the test speed can be further improved. Further, according to an exemplary embodiment, a micro column 610 that can emit an electron beam and detect emitted electrons in a fixed manner (that is, without moving the fixed axis 620 relative to the pixel circuit array substrate 100 separately for initializing as well as for testing) corresponding to the entire pixel circuit lines or pixel circuit columns of the pixel circuit array can also be provided.
The movement of the fixed axis 620 relative to the pixel circuit array substrate 100 can take place at the fixed axis 620, the pixel circuit array substrate 100, or a combination of both. For example, instead of moving the fixed axis 620, the gate electrode of the driving transistor of each pixel may be initialized, and a failure of the transistor may be tested, while moving the pixel circuit array substrate 100—that has been completed with the array process (S1)—in the first direction 640 and the second direction 650.
According to the embodiment of
According to the embodiment of
While this invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. On the contrary, the invention is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.
Further, the materials of the components described in the specification may be selectively substituted by various known materials by those skilled in the art. In addition, some of the components described in the specification may be omitted without deterioration of the performance, or added in order to improve the performance by those skilled in the art.
Moreover, the sequence of the steps of the method described in the specification may be changed depending on a process environment or equipment by those skilled in the art. Accordingly, the scope of the present invention should be determined not by the above-mentioned exemplary embodiments but by the appended claims and equivalents thereto.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2011-0053955 | Jun 2011 | KR | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 20060028217 | Liao et al. | Feb 2006 | A1 |
| 20070063935 | Yoshida | Mar 2007 | A1 |
| 20120206145 | Kim et al. | Aug 2012 | A1 |
| 20130257437 | Jin et al. | Oct 2013 | A1 |
| Number | Date | Country |
|---|---|---|
| 10-2006-0017586 | Feb 2006 | KR |
| 10-2007-0027877 | Mar 2007 | KR |
| 10-2010-0057067 | May 2010 | KR |
| Number | Date | Country | |
|---|---|---|---|
| 20120306939 A1 | Dec 2012 | US |
